Download Hi-Res ImageDownload to MS-PowerPointCite This:J. Am. Chem. Soc. 2018, 140, 28, 8841-8850

Electron-Rich Metal Cations Enable Synthesis of High Molecular Weight, Linear Functional Polyethylenes

Wei Zhang
Wei Zhang
Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
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Peter M. Waddell
Peter M. Waddell
Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
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Margaret A. Tiedemann
Margaret A. Tiedemann
Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
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Christian E. Padilla
Christian E. Padilla
Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
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Jiajun Mei
Jiajun Mei
Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
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Liye Chen
Liye Chen
Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
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, and

Brad P. Carrow*
Brad P. Carrow
Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
*[email protected]
More by Brad P. Carrow
http://orcid.org/0000-0003-4929-8074

Cite this: J. Am. Chem. Soc. 2018, 140, 28, 8841–8850

Publication Date (Web):June 26, 2018

https://doi.org/10.1021/jacs.8b04712

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Abstract

Group 10 metal catalysts have shown much promise for the copolymerization of nonpolar with polar alkenes to directly generate functional materials, but access to high copolymer molecular weights nevertheless remains a key challenge toward practical applications in this field. In the context of identifying new strategies for molecular weight control, we report a series of highly polarized P(V)–P(III) chelating ligands that manifest unique space filling and electrostatic effects within the coordination sphere of single component Pd polymerization catalysts and exert important influences on (co)polymer molecular weights. Single component, cationic phosphonic diamide-phosphine (PDAP) Pd catalysts are competent to generate linear, functional polyethylenes with M_w up to ca. 2 × 10⁵ g mol^–1, significantly higher than prototypical catalysts in this field, and with polar content up to ca. 9 mol %. Functional groups are positioned by these catalysts almost exclusively along the main chain, not at chain ends or ends of branches, which mimics the microstructures of commercial linear low-density polyethylenes. Spectroscopic, X-ray crystallographic, and computational data indicate PDAP coordination to Pd manifests cationic yet electron-rich active species, which may correlate to their complementary catalytic properties versus privileged catalysts such as electrophilic α-diimine (Brookhart-type) or neutral phosphine-sulfonato (Drent-type) complexes. Though steric blocking within the catalyst coordination sphere has long been a reliable strategy for catalyst molecular weight control, data from this study suggest electronic control should be considered as a complementary concept less prone to suppression of comonomer enchainment that can occur with highly sterically congested catalysts.

Introduction

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Tailored applications of polymeric materials demand access to a continuum of material properties, which in turn requires flexible polymerization methods with precise control over macromolecular structure. Polyolefin materials, polyethylene (PE), and polypropylene (PP), being the most common examples, are thus attractive targets for new methods development because they comprise the large majority of all polymer production by weight.(1) Though the semicrystalline nature of PE and isotactic PP engender strength and toughness, the associated hydrophobicity of these polymers also restricts their potential applications by limiting surface properties, compatibility and rheology. The incorporation of polar functional groups into the parent polyolefin structure, even in relatively minor amounts, can significantly alter the material properties of the resulting “functional” polyolefins and has long been the focus of synthetic efforts.

High molecular weight, linear functional polyethylenes (f-PE) represent a particularly attractive target for insertion polymerization because of their structural analogy to linear low-density polyethylene (LLDPE). Even though the $40 billion global market volume (2013) for LLDPE is forecast to continue expanding,(2) established polyolefin markets such as this are still insufficient to fully capture the massive volume of light olefins that have resulted from shale gas production.(3) The potential applications of polar analogues of LLDPE are manifold because of enhanced surface properties, compatibility in polymer blends, printability, dye retention, and degradability. New polyolefin classes therefore have added value both in their fundamental material properties but also for their potential to capture carbon that would otherwise be burned as fuel. A fundamental challenge to this end, however, is that few methods for functional polyolefin synthesis selectively generate linear polymer microstructures with high molecular weight.

Common synthetic approaches to incorporate polar functional groups into the hydrocarbon backbone of polyolefins are summarized in Scheme 1. High energy intensity methods, such as free radical copolymerizations of ethylene with polar alkenes, have been commercialized (Scheme 1a).(4) Copolymers formed by such methods are mechanistically biased toward microstructures with long chain branching and low crystallinity. On the other hand, the direct metal-catalyzed insertion copolymerization of olefins and industrial polar monomers represents a potentially ideal and tunable route to functional polyolefin materials. Significant progress has been made in this area over the last two decades using group 10 metal catalysts.(5) Brookhart’s cationic Pd and Ni complexes coordinated by an α-diimine ligand have been very successful in this regard, which tolerate acrylates or several other polar vinyl monomers to generate branched copolymers (Scheme 1b).(6) Mechanistic studies on these systems have established that branch formation occurs through a characteristic “chain walking” mechanism due to facile β-hydrogen elimination and reinsertion allowing monomer enchainment to occur at internal positions along the polymer chain. As a consequence of this mechanistic behavior, polar functional groups are positioned at the ends of branches.

Scheme 1. Common Functional Polyolefin Synthesis Methods

Strictly linear functional polyolefins can be generated by ring opening metathesis polymerization (ROMP) or acyclic diene metathesis polymerization (ADMET).(7) Both of these methods provide highly controlled and tunable routes to well-defined copolymers, but the requisite postpolymerization hydrogenation and specialty monomers nevertheless impose major barriers to large-scale applications. Alternatively, Drent and Pugh discovered that phosphine-sulfonato Pd catalysts generate linear (co)polymers by insertion polymerization (Scheme 1c).(8) The contrasting catalyst behavior of Brookhart-type versus Drent-type polymerization catalysts has been established through theoretical studies to originate from the electronic (a)symmetry of the respective chelating ligands.(9) A variety of group 10 metal catalysts with other (P^O)-type ligands have since been shown to conserve the linear polymer selectivity of Drent-type catalysts and can make high molecular weight PE in some cases,(10) but very few can access high f-PE molecular weights (i.e., ≥10⁵ g mol^–1) needed for many applications.(11) Even Drent-type complexes, arguably the most successful catalyst class,(12) rarely achieve (co)polymer M_w exceeding 10⁴ g mol^–1.(13) The direct synthesis of f-PE with high molecular weight therefore remains a significant ongoing challenge that could benefit from new catalysts and rational design strategies.

A typical design strategy to increase polymer molecular weight using Drent-type and related catalysts is based on a steric blocking model (Scheme 2a) to inhibit the rate of chain transfer at these square planar metals that occurs through associative ligand substitution by monomer.(9a) Increased steric bulk at the ancillary ligand, which must emanate from phosphorus(III) substituents in Drent-type catalysts, therefore tends to increase polymer molecular weight by blocking monomer coordination at the apical sites. The liability of this common approach during insertion copolymerizations is that bulkier P(III) substituents exacerbate the relative energy barrier of enchaining any comonomer relative to ethylene, the smallest alkene (Scheme 2b). Drent-type catalysts therefore tend to exhibit an antagonistic relationship between polymer molecular weight and comonomer enchainment, and it is not clear a priori how catalysts could be designed to avoid this mechanistic paradox by variation of the P(III) substituents alone.

Scheme 2. General Considerations of Catalyst Steric Effects on Insertion Copolymerizations

Computational studies on Drent-type phosphine-sulfonato Pd catalysts have also suggested that isomerization of the reacting ligands occurs prior to each monomer enchainment and that the most reactive intermediate has mutually cis π-alkene and tertiary phosphine ligands.(9) On the basis of this characteristic feature of (P^O)-coordinated polymerization catalysts, we hypothesized that steric bulk emanating from the O ligand rather than from the P ligand should still enhance polymer molecular weight but also lessen the impact of ligand size on ΔΔG^‡ for competing monomer enchainment because coordinated monomer is positioned trans to the O ligand (Scheme 2c). The substituents of P(V) oxides seem well-suited as a platform to test this hypothesis.(10,14) In particular, a phosphonic diamide group was attractive to us because it is derived from abundant secondary amines that could facilitate a high degree of structural tunability. An initial challenge to this end was the lack of any precedent for metal catalysis involving a phosphonic diamide in a chelating (P^O)-type ligand scaffold. We report here the first examples of single component Pd catalysts featuring a chelating P(V)–P(III) ligand based on a phosphonic diamide-phosphine (PDAP) motif. We have found these types of ligands do indeed provide a tunable platform for generating highly active Pd catalysts for synthesis of linear f-PE from industrial polar monomers, including high molecular weight examples that few other catalysts can match.

Results and Discussion

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PDAP-Pd Catalyst Synthesis and Steric Benchmarking

The highly polarized P–O bond in phenylphosphonic diamides functions as a good directing group for ortho-metalation, which provided a straightforward synthesis of PDAP ligands 1a–1i by a one-pot sequence of directed ortho-lithiation followed by nucleophilic substitution at a chlorophosphine reagent (Table 1).(15) The PDAP ligands possessing a diarylphosphino moiety are air-stable and were purified by simple flash chromatography.(16) Air sensitive alkylphosphines were carried forward without purification. Ligand exchange of the PDAP for cyclooctadiene in (COD)Pd(CH₃)Cl occurred within minutes at rt and gave the neutral complexes 2a–2i. Exchange of the chloride ligand for 2,6-lutidine generated the final air and moisture-stable single component precatalysts (3a–3i) in 15%–76% isolated yield over three steps. We next pursued a quantitative assessment of the space filling properties of PDAP ligands to test our initial hypothesis that the phosphonic diamide provides suitable steric properties.

Table 1. Synthesis of Phosphine–Phosphonic Diamide (PDAP) Ligands and Single Component Precatalystsa

complex	R¹	R²	R³	yieldb (%)
3a	Me	H	i-Pr	51
3b	i-Pr	H	i-Pr	43
3c	i-Pr	H	i-C₅H₁₁	55
3d	i-Pr	H	Ph	76
3e	Me	H	2-(MeO)-C₆H₄	54
3f	Et	H	2-(MeO)-C₆H₄	48
3g	i-Pr	H	2-(MeO)-C₆H₄	43
3h	i-Pr	H	2,6-F₂C₆H₃	28
3i	Me	NMe₂	2,4-(MeO)₂C₆H₃	15

^{^a}

Reagents and conditions: (a) tert-butyl lithium (1.2 equiv), THF at 0 °C for 1 h the ClP(R³)₂ (1.2 equiv), THF at 0 °C then warming to rt for 0.5 h; (b) (COD)PdCl(Me) (1.0 equiv), CH₂Cl₂ at rt for 0.5 h; (c) NaBAr^F₄ (1.0 equiv), 2,6-lutidine (1.1 equiv), CH₂Cl₂ at −78 °C warming to rt for 0.5 h.

^{^b}

Yield over three steps. Ar^F = 3,5-(CF₃)₂C₆H_3.

To quantitate how the coordination chemistry of the aforementioned phosphonic diamide group differs from other common types of neutral and anionic oxygen ligands, we conducted a systematic steric analysis of a PDAP versus other common (P^O)-type ligands. To do so, we prepared and crystallographically characterized six (P^O)Pd(CH₃)Cl coordination compounds relevant to olefin polymerization and oligomerization. The structures of these complexes differ only by the identity of the O group and should thus provide a clear indication of how the new PDAP ancillary ligand fills the primary coordination sphere relative to existing catalysts and, by corollary, could affect chain transfer during alkene polymerization.

Solid-state data for complexes 2g and 4–8 were analyzed by Cavallo’s SambVca 2.0 program to generate topographical steric maps (Figure 1).(17) Complexes possessing small ester (4), sulfonate (7), or carboxylate (8) groups expectedly display significant open space in the western hemisphere (O side) of their coordination sphere. On the other hand, the complex with a diisopropyl phosphonic diamide group (2g) fills significantly more space. Percent buried volume data for these complexes also indicate the diispropyl phosphonic diamide group in 2g fills more space than do other O ligands based on P(V) moieties, such as diethyl phosphonate in 5 or di-tert-butyl phosphine oxide in 6. Variation of the amine substituents in the PDAP ligand subsequently provided a straightforward means for catalyst tuning (vide infra).

Figure 1. Topographical steric maps of (P^O)Pd(CH₃)Cl complexes 2g and 4–8 in which the Pd atom defines the center of the *xyz* coordinate system, the metal square plane defines the xz-plane and the z-axis bisects the O–Pd–P angle. Pd(CH₃)Cl fragment omitted from each plot. Colors indicate occupied space in the +z direction toward the covalent ligands (red) or −z direction toward the dative ligands (blue).

Ligand-Dependent Catalyst Activity and Stability

The single component PDAP-Pd complexes 3a–3i were next benchmarked as catalysts for ethylene polymerization (Table 2) to identify promising candidates for f-PE synthesis. Catalysts 3a–3c possessing only alkyl substituents on both the P(V) and P(III) groups formed PE with decreasing activity as the size of the alkyl substituents increased (entries 1–3). In contrast, PDAP-Pd complexes were much more reactive with more hindered arene P(III) substituents. Complex 3d that contains a simple diphenylphosphino group formed only trace PE after 30 min (entry 4), but complexes possessing ortho-arene substituents were highly reactive (entries 5–11). The highest average turnover frequency (TOF) of 3.6 × 10⁵ h^–1 (100 s^–1) was observed using 3h (entry 12) with electron-poor 2,6-difluorophenyl P(III) substituents, which ranks among the highest activities reported for any Pd polymerization catalyst(13a,14c) and even compares favorably to values first reported for cationic α-diimine nickel complexes (TOF up to 3.9 × 10⁵ h^–1) or classic homogeneous metallocene complexes such as [Cp₂ZrMe]⁺[MeB(C₆F₅)₃]⁻ (TOF up to 1.6 × 10⁵ h^–1).(6a,18)

Table 2. Ligand-Dependent Catalyst Activity and Polymer Structure Effects During Ethylene Polymerizationa

entry	catalyst	[C₂H₄] (bar)	time (min)	yield (g)	activity (kg mol_Pd^–1 h^–1)	M_wb (×10^–3 g/mol)	D̵b	Me br.c	T_md (°C)
1	3a	30	60	7.14	2900	5.2	1.8	0.5	130
2	3b	30	15	1.08	1700	39	1.6	2.5	131
3e	3c	23	30	2.60	1000	81	1.4	16f	124
4	3d	30	30	trace
5	3e	30	15	3.60	5800	120	1.6	1.4	137
6		15	30	3.56	2800	130	1.6	2.9f	134
7		7	30	2.48	2000	100	1.5	2.7f	131
8		3.5	30	1.19	950	21	2.5	7.0f	126
9	3f	30	15	1.56	2500	120	1.4	3.4f	136
10	3g	30	15	1.35	2200	240	1.4	13	127
11		3.5	120	1.35	270	16	1.6	21	105
12	3h	30	15	6.30	10000	80	1.8	3.0f	130
13g	3i	30	15	2.12	6800	120	1.4	3.0f	133

^{^a}

Conditions: catalyst (2.5 μmol) and toluene (0.1 L) were added to a 450 mL stainless steel autoclave at rt under N₂, equilibrated to 90 °C, then charged with ethylene.

^{^b}

Determined by GPC with multidetection.

^{^c}

Methyl branches per 1000 C as determined by quantitative ¹³C NMR.

^{^d}

Peak T_m determined by DSC, second heating cycle.

^{^e}

5 μmol catalyst.

^{^f}

Determined by ¹H NMR.

^{^g}

[Pd] = 12.5 μM.

Importantly, PE molecular weight also increased significantly upon variation of the amino substituents in 3e–3g from Me or Et to i-Pr (e.g., entries 5, 9, and 10). Complex 3g formed PE with the highest molecular weight (M_w = 2.4 × 10⁵ g mol^–1), and this molecular weight is substantially higher than the PE formed by any other (P^O)Pd catalyst reported to date that possesses the same P(III) moiety. For instance, a phosphine-sulfonato palladium catalyst with identical ligand backbone and bis-o-anisylphosphino group generated PE with 6× lower M_w under similar reaction conditions.(19) Additionally, the dependence of PE molecular weight on pC₂H₄ saturates above ca. 7 bar using catalyst 3e (entries 5–8), but the catalyst activity increased proportionally with pC₂H₄ from 3.5 to 30 bar.

Methyl branching increases with increasing amino substituent size in 3e–3g, from 1 to 13 per 1000 methylene carbons, leading to a corresponding depression of peak PE melting temperature (T_m) by 10 °C, respectively. Monomer pressure also affects branch density, which is most pronounced for catalyst 3g for which depression of T_m by 22 °C was observed upon decreasing pC₂H₄ from 30 to 3.5 bar (entries 10 and 11). This modulation of short chain branching contrasts the uniformly linear PE produced by Drent-type catalysts and highlights an advantage of the modular oxygen ligand in the PDAP scaffold.(20)

Another important catalyst property for practical applications in olefin polymerization is high thermal stability to allow for high turnover numbers and frequencies at reaction temperatures required for industrial reactors (ca. 80–140 °C).(21) Though group 10 α-diimine complexes developed by Brookhart and co-workers (e.g., 9, eq 1) are very reactive at mild temperatures, they can suffer from facile decomposition at reaction temperatures above ca. 60 °C.(6a,b,21,22) Many subsequent modifications to the classic α-diimine ligands have since been made with the goal of improved thermal stability,(23,13a) but the absolute activities reported for these are diminished compared to Brookhart’s original room temperature reactions. Salicylaldiminato nickel complexes developed by Grubbs (e.g., 10, eq 1) are similarly thermally sensitive, displaying excellent low temperature reactivity but deactivation occurs upon heating.(24) It is therefore instructive to benchmark the lifetime of PDAP-Pd catalysts during polymerizations at high temperature.

Thermal stability was assessed from the relationship between production of PE versus time during batch polymerizations. It was necessary to decrease the catalyst concentration (4.2 μM) and ethylene pressure (3.5 bar) to avoid fast saturation of the autoclave with PE during polymerizations at 90 °C. Under these conditions, steady production of PE was observed using catalyst 3i over a period of 24 h before a deviation in linearity was apparent (Figure 2). In contrast, a representative Brookhart (9) catalyst exhibited an initial burst of PE formation followed by rapid deactivation, consistent with literature observations. The prototypical Drent-type catalyst (e.g., 11, eq 1) displayed a slightly lower activity than did the PDAP-Pd catalyst 3i. The PDAP catalyst 3g was also tested, which gave a more measured accumulation of PE over time. Using this catalyst, linear PE productivity (R² > 0.99) was observed over an even longer period (48 h) at 90 °C, which is indicative of excellent thermal stability at this temperature. The yield of PE (13.7 g) formed by 3g corresponds to 1.2 × 10⁶ catalyst turnovers. A deviation from linearity was evident between 48 and 72 h, but the similar mass yields at 48 h using 3g, 3i, or 11 suggest to us that the autoclave may be saturated with polymer at this point. In any case, these data are consistent with the PDAP ligand engendering excellent catalyst thermal stability.

Figure 2. Batch ethylene (3.5 bar) polymerization catalyzed by 3g, 3i, or 9–11 (1.25 μmol) in toluene (300 mL) at 90 °C. Methylaluminoxane (1.25 mmol) added to the reaction with 9; Ni(cod)₂ (1.25 mmol) added to reaction with 10.

Copolymerizations with Polar Alkenes

A preliminary series of small-scale reactions (i.e., 15 mL total volume) using PDAP-Pd complexes for copolymerizations of ethylene with a polar alkene (Table S6) was conducted to identify promising candidates for further study. During this initial screening, the most active catalyst for ethylene homopolymerization (3h) was found to generate poly(ethylene-co-methyl acrylate) with quite low molecular weight (M_w 9 × 10³ g mol^–1, Table S6, entry 2), similar to the copolymers formed using prototypical Drent catalysts (e.g., 11).(8c) On the other hand, copolymerization of ethylene with methyl acrylate (MA) catalyzed by the more electron-rich 3e generated the highest M_w (2.1 × 10⁴ g mol^–1) in the initial survey (Table 3, entry 1). The analogue 3i, which is more electron-rich yet isosteric to 3e, also generated promising polymer molecular weight (Table S6, entry 4). Catalysts 3e and 3i were selected for subsequent reactions.

Table 3. Copolymerization of Ethylene and Polar Alkenes Catalyzed by Cationic PDAP-Pd Complexesa

entry	catalyst	comonomer (M)	yield (g)	productivity (kg mol_Pd^–1)	M_wb (×10^–3 g/mol)	D̵b	Me brc	inc. ratioc (mol %)	FG distr. (main/chain ends)c^,d	T_me (°C)	ΔHe (J g^–1)
1f	3e	MA (2.2)	0.26	26	21	1.4	10	2.3	94:6	107	–
2		BA (1.1)	2.8	570	47	1.4	3.4	4.6	>98:2	116	116
3	3i	MA (1.0)	11.1	740	85	1.3	1.7	1.7	n.d.i	113	107
4		MA (2.0)	4.5	300	49	1.1	2.9	4.1	n.d.i	106	95
5		MA (3.0)	2.3	150	28	1.2	2.7	5.4	>97:3	100	100
6		BA (1.0)	7.0	470	84	1.2	1.3	2.7	n.d.i	113	108
7g		BA (1.0)	15.4	1000	220	1.6	0.5	0.7	n.d.i	125	140
8h		BA (1.0)	15.2	1000	190	1.8	1.6	0.3	n.d.i	135	160
9g		BA (0.5)	26.5	1800	190	2.0	2.0	0.3	n.d.i	135	169
10		BA (2.0)	3.9	260	53	1.5	1.3	8.2	n.d.i	104	82
11		BA (3.0)	2.9	190	62	1.5	0.8	9.6	n.d.i	97	72
12		ⁱBorA (1.0)	5.9	390	92	1.2	n.d.	1.5	n.d.i	116	108
13		ⁱBorA (2.0)	3.0	200	37	1.2	n.d.	2.4	n.d.i	107	88
14		ⁱBorA (3.0)	2.7	180	18	1.5	n.d.	4.3	n.d.i	100	65
15		AA (1.0)	1.7	110	31	1.6	3.1	1.5	n.d.i	121	125
16		AA (2.0)	0.91	61	12	1.4	6.1	3.1	n.d.i	116	120
17		AA (3.0)	0.63	42	3.0	1.3	6.6	4.0	85:15	111	83
18		BVE (1.0)	0.74	49	21	1.7	1.3	0.5j	90:10	128	186
19		BVE (2.0)	0.70	47	39	1.6	1.3	0.2j	n.d.i	130	165
20		BVE (3.0)	0.50	33	19	2.4	1.5	0.4j	87:13	128	165

^{^a}

Conditions: catalyst (15 μmol), comonomer, and toluene (300 mL) were added to a 450 mL autoclave at rt under N₂, charged with ethylene (30 bar), then heated to 90 °C.

^{^b}

Determined by GPC with multidetection.

^{^c}

Methyl branches per 1000 C, comonomer incorporation, and functional group distributions determined by quantitative ¹³C NMR or ¹H NMR.

^{^d}

Ratio of functional groups in the polymer main chain versus the chain ends.

^{^e}

Peak melting temperature determined by DSC, second heating cycle.

^{^f}

10 μmol [Pd], 15 mL total volume, 95 °C for 12 h.

^{^g}

pC₂H₄ = 40 bar, 70 °C.

^{^h}

pC₂H₄ = 40 bar, 60 °C.

^ⁱ

Chain-ends were not detectible by ¹H NMR; see SI for limit of detection estimation for each sample. n.d. = not detected.

^{^j}

Determination of BVE incorporation was complicated by overlapping ¹H NMR resonances.

A series of copolymerizations (300 mL total volume) was next conducted using 3e or 3i (Table 3). The typical conditions for these reactions involved 50 μM [Pd], 30 bar of ethylene, and 1–3 M concentrations of comonomer in toluene at 90 °C.(25) Under these conditions, complex 3i generated poly(ethylene-co-butyl acrylate) with nearly double the molecular weight (M_w 8.4 vs 4.7 × 10⁴ g mol^–1, respectively) than did 3e (entries 2 and 6), which contrasts the weak poly(ethylene-co-methyl acrylate) molecular weight dependence on remote P(III) substituent electronic effects reported for Drent-type catalysts.(26) The magnitude of this difference was surprising because it is unlikely to originate from a classic steric blocking effect given that 3e and 3i are approximately isosteric. A rationalization for these polymer molecular weight differences based on ligand electronic effects is therefore favored (vide infra). A considerable difference in f-PE M_w is also observed between a prototypical Drent catalyst (11) and PDAP-Pd catalyst 3i with P(III) substituents of comparable size, the latter 10× larger under identical reaction conditions (see Table S8 versus Table 3, entry 3). Increasing pC₂H₄ to 40 bar and/or lowering the reaction temperature from 90 °C to 60–70 °C (Table 3, entries 6–8) generated poly(ethylene-co-butyl acrylate) with even higher molecular weights (M_w ∼ 2 × 10⁵ g mol^–1), which is highly desirable yet rare among linear functional polyolefins formed by insertion polymerization.(11b,13) The incorporation ratio (e.g., 2.7–9.6 mol %; Table 3, entries 6, 10, and 11) increased concomitantly with butyl acrylate (BA) concentration (1–3 M). This trend also occurred using methyl acrylate or isobornyl acrylate (ⁱBorA) that possess smaller and larger ester substituents, respectively. All poly(ethylene-co-acrylate) copolymers generated by 3i are highly linear with few methyl branches (≤6 CH₃ per 1000 C).

Catalyst 3i is also compatible with other more challenging polar monomers. The copolymerization of ethylene with acrylic acid (AA) or butyl vinyl ether (BVE) to generate statistical copolymers demonstrates the tolerance of PDAP-Pd catalysts to both acidic and nucleophilic reagents, albeit with reduction in catalyst activity and copolymer molecular weights (Table 3, entries 15–20). Contact angle (θ) measurements for the poly(ethylene-co-acrylic acid) with 1.5 mol % AA incorporation (78(3)°) or 3.1 mol % AA incorporation (65(3)°) reflect a significantly more hydrophilic polymer surface than commercial low density PE (102°).(27) This reinforces the substantial effects polar functional groups can exert on polyolefin material properties even at relatively low incorporation ratios (i.e., <10 mol %).

Structure analysis of the poly(ethylene-co-methyl acrylate) formed in Table 3, entry 1 by quantitative ¹³C NMR spectroscopy revealed a statistical distribution of methyl ester groups almost exclusively along the main chain (94 mol %) (Figure 3). Only 6 mol % of incorporated acrylate was positioned at the saturated chain-end, which corresponds to initiation of a new polymer chain via acrylate insertion into a Pd–H species. More importantly, no alkenyl ester groups were detectable at the unsaturated chain ends. This observation suggests chain transfer does not occur from the presumed catalyst resting state, a Pd-ester enolate complex, formed by enchainment of methyl acrylate.(12o) Analyses of ¹³C and ¹H NMR data for other poly(ethylene-co-acrylate) samples in entries 3–14 indicate the sequence distribution of functional groups, heavily concentrated in the main chain versus chain ends in the copolymer formed by 3e, is conserved when using catalyst 3i. This microstructure formed by a PDAP-Pd catalyst compliments the f-PE typically formed by Drent-type catalysts, which generally have a significant fraction of unsaturated chain ends with functional groups. A potential connection between Pd-ester enolate stability and polymer molecular weight control is therefore conceivable but has received little attention to date. The frequent correlation between decreasing copolymer molecular weight and increasing polar monomer content in f-PE synthesis may suggest this effect deserves further consideration.

Figure 3. Assignment of characteristic ¹³C NMR resonances in poly(ethylene-co-methyl acrylate) in Table 3, entry 1. See SI for full spectrum (* = galvinoxyl).

The range of accessible molecular weights and comonomer content in the f-PE formed by 3i, which in the best cases are comparable to single site LLDPE samples, could provide a useful platform for comparative material property studies. An initial indication that unanticipated properties could be manifested in these functional analogues is apparent from their melting behavior, as determined by differential scanning calorimetry (DSC). The relative depression in peak melting temperature (T_m) of poly(ethylene-co-acrylate) samples with increasing comonomer content (Figure 4) track closely with literature values for LLDPE reported by Kim at lower comonomer content (ca. 0–5 mol %).(28a) At higher comonomer content (ca. 5–10 mol %), however, T_m decreases to a larger extent for the nonpolar poly(ethylene-co-octene) samples than for the functional analogues. The inclusion of methyl branching in this analysis maintains the same general trend (see Figure S1). The origin of these differences requires further study, but one potential cause could be statistical differences in the spacing between functional groups (i.e., ester versus hexyl) in the nominally random copolymer structures that arise from the catalytic behaviors of the respective metallocene or PDAP-Pd catalysts.

Figure 4. Relationship between melt temperature and comonomer content in f-PE generated by 3i (Table 3, entries 3–8 and 10–17). Literature values for hydrophobic analogues shown in open circles.(28)

Differentiating O Ligand Electronic Properties

In addition to the beneficial space filling characteristics of this new ligand class, our copolymerization data (e.g., Table 3, entries 1 vs 4 or 2 vs 6) suggested there could be an electronic component to the polymer molecular weight control because 3e and 3i are nearly isosteric and a steric blocking model (Scheme 2a) does not adequately account for the near doubling of M_w using the latter catalyst with either MA or BA. On the other hand, assessment of any significant ligand electronic differences is hindered by the general lack of systematic and quantitative data benchmarking the electronic properties of oxygen-based ligands to late transition metals,(29) particularly moieties commonly used in (P^O)-type ligands for alkene polymerization catalysts. We thus conducted additional experiments to build some understanding of how the coordination chemistry of the aforementioned phosphonic diamide group differs from other common neutral and anionic oxygen ligands. To do so, we returned to the structures of (P^O)Pd(CH₃)Cl compounds 2g, 4–8, which differ only by the identity of the O group.

A systematic change in trans influence is evident in complexes 2g and 4–8 as measured by the change in Pd–C bond length (Figure 5) for the methyl ligand situated trans to the O ligand. Elongation of the Pd–C bond reflects a more strongly σ-donating oxygen atom in these complexes. The L-type oxygen ligands in 4 (ester) and 5 (phosphonate) are poor donors and exhibit expectedly weak trans influence. On the other hand, the X-type anionic donors in 7 (sulfonate) and 8 (carboxylate) displayed higher trans influence. A surprising observation was that the formally L-type phosphonic diamide group in 2g actually falls within the strongly donating X-type region. This suggests the phosphonic diamide σ-donicity is unusually strong for a neutral ligand and beyond what other P(V) ligands (i.e., phosphonate and phosphine oxide) exhibit.

Figure 5. Systematic variation in O ligand *trans* influence in (P^O)Pd(CH₃)Cl complexes 2g and 4–8 determined from solid state data, and atomic charge in analogous (P^O)Rh(CO)Cl complexes 12–17, determined by NBO analysis. Error bars indicate ±3σ.

The solid-state structure of 2g (Figure 6) provides some indication as to why the phosphonic diamide is such a strong donor among L-type oxygen ligands. The sum of the C–N–C and C–N–P bond angles was 355.5(3)° for N1 and 359.5(3)° for N2.(30) This trigonal planar geometry at each nitrogen atom is consistent with strong N–P multiple bond character through negative hyperconjugation. A more polarized P–O bond is then expected for the phosphonic diamide versus other P(V) oxides, such as phosphonates or phosphine oxides. A more polarized P–O bond has previously been correlated to stronger coordination of monodentate P(V) donors to lanthanide metals with the trend: phosphonate < phosphine oxide < phosphoramide.(31)

Figure 6. ORTEP diagram of 2g. Thermal ellipsoids are shown at 50% probability. Hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): Pd–P2 2.2181(4), Pd–O1 2.163(1), Pd–C1 2.034(2), Pd–Cl1 2.3824(4), P1–O1 1.490(1), P2–Pd–O1 89.02(3), C23–N2–C26 114.8(1), C23–N2–P1 120.8(1), C26–N2–P1 123.9(1), C29–N1–C32 113.2(1), C29–N1–P1 113.3(1), C32–N1–P1 129.0(1).

A departure in the bonding trends between hard lanthanide and soft late transition metals is suggested from a natural bond order (NBO) analysis conducted on a related series of (P^O)Rh(CO)Cl complexes (12–17) that possess the same ligands as 2g and 4–8. These complexes, which are geometrically similar to Pd(II), were initially targeted for their CO reporter ligand that reflects the net metal electron density (vide infra). The atomic charge (q) on the metal is plotted in Figure 5, which indicates that (i) higher trans influence generally correlates to decreasing metal charge in this series of complexes, and (ii) the PDAP ligand is a significant outlier in this trend.

The atomic charge (q) on oxygen in (1g)Rh(CO)Cl (16) was also the most negative versus any other complex in the series (Table 4), which suggests the PDAP exhibits the weakest ligand-to-metal charge transfer (LMCT) even though the phosphonic diamide is the strongest σ-donating L-type ligand. This contrasts the bonding trend of P(V) oxides to lanthanides for which phosphoramides show the highest LMCT.(31)

Table 4. Systematic Effects of O Ligand Identity on the Electronic Properties of 2g, 4–8, and 12–17

					atomic chargec
entry	X	δ_C Pd–CH₃ (ppm)	ν CO_exptl (cm^–1)a	ν CO_theor (cm^–1)b	q(Rh)	q(O)
1	–CO₂Me	–1.2	1990	2083	–0.3502	–0.5950
2	–P(O)(OEt)₂	–1.3d	1982	2079	–0.3475	–1.029
3	–P(O)^tBu₂	–2.3	1975	2075	–0.3704	–1.048
4	–SO₃^–	–2.1e^,f	1980f	2077	–0.3719	–0.9528
4	–SO₃^–	–3.5g	1971g	2077	–0.3719	–0.9528
5	–P(O)(NⁱPr₂)₂	–2.5	1973	2076	–0.3251	–1.055
6	–CO₂^–	–4.2f	1971f	2060	–0.3764	–0.7041
6	–CO₂^–	–5.3g	1960g	2060	–0.3764	–0.7041

^{^a}

Determined by ¹³C NMR in CD₂Cl₂ for 2g and 4–8.

^{^b}

Calculated for 12–17 at ωB97XD/6-31G(d)/LANL2DZ (Rh) level; CPCM solvent model (CH₂Cl₂).

^{^c}

Determined by NBO analysis for for 12–17.

^{^d}

From ref (14b).

^{^e}

From ref (12c).

^{^f}

(Et₃NH)⁺ cation.

^{^g}

[Ph₃P=N=PPh₃]⁺ cation.

Additional spectroscopic data for complexes 2g, 4–8, and 12–17 further support the general trend in O ligand σ-donicity and also the disconnection between donicity and metal electron density for PDAP-coordinated complexes (Table 4). A consistent increase in shielding of the Pd–CH₃ resonances in 2g and 4–8 is observed by ¹³C NMR spectroscopy as the oxygen ligand fluctuates from the weakest L-type ester group (δ_C −1.2 ppm) to the strongest X-type carboxylate anion (δ_C −4.2 to −5.3 ppm),(32) corroborating the general trend in σ-donicity suggested by the trans influence data. Note that complex 2g exhibited a Pd–CH₃ chemical shift of δ_C −2.5 ppm that is similar to the complex with a sulfonate (δ_C −2.1 to −3.5), which again suggests the donicity of this neutral phosphonic diamide group rivals oxygen anions.

The (P^O)Rh(CO)Cl complexes (12–17) used for NBO analysis were also synthesized to determine the experimental carbonyl stretching frequency as a reporter of net metal electron density (Table 4). A general red shift in these stretching frequencies, measured in CH₂Cl₂ solution, was observed for (P^O) ligands that exhibit higher trans influence. The complex (1g)Rh(CO)Cl (16) with a phosphonic diamide group exhibited a CO stretch (1973 cm^–1) that was blue-shifted compared to either the phosphine-sulfonato (1971 cm^–1) or phosphine-carboxylate rhodium complexes (1960 cm^–1) that possess a noncoordinating cation (PPN⁺).(27) The theoretical stretching frequencies determined for 12–17 using DFT calculations generally agree with the experimental trend. The PDAP ligand thus appears to again be an outlier because the electron density at Rh is less than would be expected based on the high σ-donicity of the phosphonic diamide donor alone, which suggests that localization of positive charge at the metal by the PDAP exerts a significant competing electrostatic effect.

In total, these experimental and computational data establish a spectrum of electronic properties for common oxygen ligands used for the design of alkene polymerization and oligomerization catalysts. These data are also consistent with the conclusion that complexes with a phosphonic diamide group are less electron-rich than would be expected based purely on this O ligand’s high σ-donicity. Considering also that PDAP ligand 1g is still substantially more electron-releasing than is a prototypical Brookhart-type α-diimine ligand, such as Dipp-BIAN (Δν_CO = 25 cm^–1),(6a,33,34) we propose that the PDAP-Pd polymerization catalysts 3a–3i are best described as electron-rich metal cations. Consequently, these catalysts are electronically differentiated from both the very electrophilic, cationic Brookhart-type catalysts and the electron-rich, neutral SHOP-type(35) or Drent-type catalysts.

Finally, a potential electronic contribution to the polymer molecular weight control by PDAP-Pd catalysts can be inferred from the above data. Mechanisms of chain transfer (Scheme 3, middle) and chain-walking (Scheme 3, bottom) during group 10 metal-catalyzed insertion polymerization both generally proceed through initial formation of a metal hydride by β-H elimination from the propagating organometallic intermediate. The most stable isomer of this metal hydride in a P^O-coordinated Pd complex is the one with hydride and oxygen ligands mutually trans. Higher trans influence in the oxygen ligand, such as for the phosphonic diamide group, should then destabilize this intermediate and thereby disfavor chain transfer. This effect could contribute to the higher polymer molecular weight of 3i versus 3e because the dimethylamino group in the former should make the O ligand a stronger donor. Such an electronic effect may work synergistically with the higher steric shielding by the phosphonic diamide as compared to small sulfonate or carboxylate groups, thereby slowing chain transfer during ethylene propagation and also potentially from the catalyst resting state (Scheme 3, top) generated immediately after polar alkene enchainment. Future studies will attempt to scrutinize this hypothesis.

Scheme 3. Mechanistic Pathways Controlling Polar Group Distribution in Functional Polyolefins

Conclusion

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A series of cationic palladium complexes ligated by a chelating phosphonic diamide-phosphine (PDAP) have been developed. Several of these PDAP-Pd complexes (e.g., 3e and 3i) are potent catalysts for insertion copolymerization with polar vinyl monomers. Importantly, poly(ethylene-co-acrylate) materials with M_w up to 2 × 10⁵ g mol^–1 were formed, which is a molecular weight threshold far higher than functional polyethylenes (f-PE) formed by the important Drent-type catalysts that possess analogous P(III) substituents (e.g., o-anisyl). This increase in molecular weight control highlights the utility of tunability in the O hemisphere of the coordination sphere of P^O-coordinated late transition metal catalysts, which is enabled by the modular amino groups in the PDAP structure.

Analysis of the f-PE structures formed by PDAP-Pd catalysts showed that the polar comonomer was incorporated almost exclusively into the polymer main chain, which complements copolymers formed by existing catalysts that tend to have significant functional group content at chain ends or at the ends of branches. Furthermore, the linear production of polymer over 24–48 h at 90 °C by PDAP-Pd catalysts 3g and 3i established the excellent thermal stability engendered by PDAP coordination, which is an important property needed for practical applications.

Quantitative analysis of the steric properties of a prototypical PDAP ligand (1g) versus other common chelating (P^O)-type ligands confirmed that the former fills more space than typical ester, sulfonate, phosphonate, phosphine oxide or carboxylate groups, which helps to inhibit coordinative chain transfer. Spectroscopic, solid-state structural and computational data are consistent with the phosphonic diamide being a more potent σ-donor to late metals, such as Pd or Rh, than any other neutral oxygen donor that was tested. We therefore conclude that PDAP-Pd catalysts can be described as electron-rich metal cations, which is distinct from existing catalyst types such as electrophilic, cationic Brookhart-type α-diimine Pd catalysts and electron-rich, neutral Drent-type catalysts. The potential of these ligands to access new and complementary catalytic behaviors in alkene polymerization when coordinated to Pd, and potentially other transition metals, should provide opportunities to explore material properties of high molecular weight polar-functionalized polyethylenes.

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/jacs.8b04712.

Experimental procedures, crystallographic data, characterization data for ligands, metal compounds, and polymers (PDF)
Crystallographic structures (CIF)

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Corresponding Author
- Brad P. Carrow - Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States; http://orcid.org/0000-0003-4929-8074; Email: [email protected]ceton.edu
Authors
- Wei Zhang - Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
- Peter M. Waddell - Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
- Margaret A. Tiedemann - Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
- Christian E. Padilla - Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
- Jiajun Mei - Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
- Liye Chen - Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
Notes
The authors declare the following competing financial interest(s): A patent was filed by Princeton University: Carrow, B. P.; Zhang, W. WO 2015/200849 A2, December 30, 2015.

Acknowledgments

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We thank Richard Register for helpful suggestions and access to analytical instrumentation, Adam Burns for assistance with DSC measurements, and Jason Brandt for assistance with manuscript revisions. C.E.P. thanks the NSF for a graduate fellowship. Bruker is thanked for sample analysis on a 10 mm cryoprobe 500 MHz NMR spectrometer. We thank the NSF (CHE-1654664), the Princeton Center for Complex Materials, a MRSEC supported by NSF Grant DMR 1420541, and Princeton University for financial support.

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Ethylene and propylene were copolymd. with acrylates to give high molar mass polymers using Pd diimine complexes as initiators. The copolymers are highly branched, the acrylate comonomer being incorporated predominantly at the ends of branches. Low-temp. NMR was used to study the mechanism of initiation.
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(c) Guan, Z.; Popeney, C. S. Recent Progress in Late Transition Metal α-Diimine Catalysts for Olefin Polymerization. Top. Organomet. Chem. 2009, 26, 179– 220, DOI: 10.1007/978-3-540-87751-6_6
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6c
Recent progress in late transition metal α-diimine catalysts for olefin polymerization
Guan, Zhibin; Popeney, Chris S.
Topics in Organometallic Chemistry (2009), 26 (Metal Catalysts in Olefin Polymerization), 179-220CODEN: TORCFV; ISSN:1436-6002. (Springer GmbH)
A review. This chapter reviews recent development of cationic α-diimine nickel(II) and palladium(II) complexes for olefin polymn. The contributions of ligand structure to the catalytic polymn. properties of late metal complexes are particularly emphasized in this review. Unique among transition metal polymn. systems, these late metal complexes also catalyze the formation of branched polymers. The mechanisms of elemental reaction steps for these catalytic systems are discussed. The Pd(II) system also permits the copolymn. of ethylene and α-olefins with various polar comonomers, esp. acrylates. Finally, a discussion of new research in ligand design is provided. A new class of cyclophane-based ligands has exhibited high thermal stability. The mechanism of copolymns. is significantly altered, leading to elevated incorporations of polar monomers. An axial-donation hemilabile cyclic ligand is also discussed, the Ni(II) and Pd(II) complexes of which afford high mol. wt. polyethylene despite their reduced steric bulk.
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(d) Camacho, D. H.; Guan, Z. Designing late-transition metal catalysts for olefin insertion polymerization and copolymerization. Chem. Commun. 2010, 46, 7879– 7893, DOI: 10.1039/c0cc01535k
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6d
Designing late-transition metal catalysts for olefin insertion polymerization and copolymerization
Camacho, Drexel H.; Guan, Zhibin
Chemical Communications (Cambridge, United Kingdom) (2010), 46 (42), 7879-7893CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
A review. The innovation of polyolefin with unique architecture, compn. and topol. continues to inspire polymer chemists. An exciting recent direction in the polyolefin field is the design of new catalysts based on late-transition metals. In this review, we highlight recent developments in rationally designing late-transition metal catalysts for olefin polymn. The examples described in this review showcase the power of the design of well-defined late-metal catalysts for tailored polyolefin synthesis, which may usher in a new era in the polymer industry.
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7
(a) Watson, M. D.; Wagener, K. B. Tandem Homogeneous Metathesis/Heterogeneous Hydrogenation: Preparing Model Ethylene/CO2 and Ethylene/CO Copolymers. Macromolecules 2000, 33, 3196– 3201, DOI: 10.1021/ma991595p
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(b) Watson, M. D.; Wagener, K. B. Ethylene/Vinyl Acetate Copolymers via Acyclic Diene Metathesis Polymerization. Examining the Effect of “Long” Precise Ethylene Run Lengths. Macromolecules 2000, 33, 5411– 5417, DOI: 10.1021/ma9920689
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7b
Ethylene/Vinyl Acetate Copolymers via Acyclic Diene Metathesis Polymerization. Examining the Effect of "Long" Precise Ethylene Run Lengths
Watson, Mark D.; Wagener, Kenneth B.
Macromolecules (2000), 33 (15), 5411-5417CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
Tandem acyclic diene metathesis (ADMET) polymn./catalytic hydrogenation was used to synthesize copolymers modeling ethylene/vinyl acetate (EVA) materials. A series of four sequence-ordered ethylene-co-vinyl acetate copolymers were prepd. possessing precisely defined ethylene run lengths from 18 to 26 carbons. Use of the well-defined ADMET reaction in combination with a quant. olefin-hydrogen technique generates well-defined EVA's, all of which are semicryst. with a linear relationship between ethylene run length and melting temp. All polymers except that with the lowest ethylene run length are film and fiber forming.
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(c) Watson, M. D.; Wagener, K. B. Functionalized Polyethylene via Acyclic Diene Metathesis Polymerization: Effect of Precise Placement of Functional Groups. Macromolecules 2000, 33, 8963– 8970, DOI: 10.1021/ma0010332
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(d) Schwendeman, J. E.; Church, A. C.; Wagener, K. B. Synthesis and Catalyst Issues Associated with ADMET Polymerization. Adv. Synth. Catal. 2002, 344, 597– 613, DOI: 10.1002/1615-4169(200208)344:6/7<597::AID-ADSC597>3.0.CO;2-P
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7d
Synthesis and catalyst issues associated with ADMET polymerization
Schwendeman, John E.; Church, A. Cameron; Wagener, Kenneth B.
Advanced Synthesis & Catalysis (2002), 344 (6+7), 597-613CODEN: ASCAF7; ISSN:1615-4150. (Wiley-VCH Verlag GmbH)
A review on acyclic diene metathesis (ADMET) which is a flexible approach for the prodn. of diverse polymeric materials. The advent of well defined catalysts and the simplification of lab. techniques has made the ADMET reaction useful for many applications, such as polyolefin model studies and the synthesis of org./inorg. hybrid polymers, telechelics, copolymers, conjugated polymers, liq. cryst. polymers, and amino acid-based chiral polymers. Many of the polymer architectures that have been produced using ADMET cannot be made by other means.
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(e) Hillmyer, M. A.; Laredo, W. R.; Grubbs, R. H. Ring-Opening Metathesis Polymerization of Functionalized Cyclooctenes by a Ruthenium-Based Metathesis Catalyst. Macromolecules 1995, 28, 6311– 6316, DOI: 10.1021/ma00122a043
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7e
Ring-Opening Metathesis Polymerization of Functionalized Cyclooctenes by a Ruthenium-Based Metathesis Catalyst
Hillmyer, Marc A.; Laredo, Walter R.; Grubbs, Robert H.
Macromolecules (1995), 28 (18), 6311-16CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
The ring-opening metathesis polymn. (ROMP) of a variety of 5-substituted cyclooctenes by the well-defined metathesis catalyst (PCy3)2Cl2RuCHCHCPh2 (I) was accomplished. Direct polymn. of functionalized monomers allowed the incorporation of alc., ketone, ester, or bromine functionality along the polymer backbone. The polymers were obtained in moderate-to-good yields. The attempted polymn. of epoxy- and cyano-substituted cyclooctenes by I failed. Structures of the polymers were confirmed by IR, 1H NMR, and 13C NMR spectroscopies. The mol. wt. of acetate-contg. polymer was controlled by varying the monomer-to-catalyst ratio and by the addn. of a chain-transfer agent to the polymn. soln. Hydrogenation of the acetate deriv. gave the corresponding ethylene/vinyl copolymer. The thermal properties of the polymers are reported.
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(f) Lehman, S. E.; Wagener, K. B.; Baugh, L. S.; Rucker, S. P.; Schulz, D. N.; Varma-Nair, M.; Berluche, E. Linear Copolymers of Ethylene and Polar Vinyl Monomers via Olefin Metathesis–Hydrogenation: Synthesis, Characterization, and Comparison to Branched Analogues. Macromolecules 2007, 40, 2643– 2656, DOI: 10.1021/ma070085p
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(g) Scherman, O. A.; Walker, R.; Grubbs, R. H. Synthesis and Characterization of Stereoregular Ethylene-Vinyl Alcohol Copolymers Made by Ring-Opening Metathesis Polymerization. Macromolecules 2005, 38, 9009– 9014, DOI: 10.1021/ma050686l
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7g
Synthesis and characterization of stereoregular ethylene-vinyl alcohol copolymers made by ring-opening metathesis polymerization
Scherman, Oren A.; Walker, Ron; Grubbs, Robert H.
Macromolecules (2005), 38 (22), 9009-9014CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
Regioregular as well as stereoregular ethylene-vinyl alc. (EVOH) copolymers are prepd. by ring-opening metathesis polymn. (ROMP) with ruthenium catalysts. Sym. cyclooctenediol monomers were protected as acetates, carbonates, or acetonides to temporarily increase ring strain as well as impart soly. to the monomer. Polymer mol. wts. could be easily controlled by either varying the monomer-to-catalyst ratio or by the addn. of a chain transfer agent. Hydrogenation and subsequent deprotection of the ROMP polymers afforded the EVOH materials in high yields, and the structures were confirmed by 1H NMR and 13C NMR spectroscopies. Thermal properties of the corresponding EVOH copolymers were detd. and suggest that differences in diol stereochem. significantly affect the polymer morphol.
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8
(a) Murray, R. E. U.S. Patent 4,689,437 August 25, 1987.
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(b) Drent, E. P., Pellp, D. H.; Jager, W. W. EP Application 0,589,527 March 30, 1994.
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(c) Drent, E.; van Dijk, R.; van Ginkel, R.; van Oort, B.; Pugh, R. I. Palladium catalysed copolymerisation of ethene with alkylacrylates: polar comonomer built into the linear polymer chain. Chem. Commun. 2002, 744– 745, DOI: 10.1039/b111252j
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8c
Palladium catalysed copolymerisation of ethene with alkylacrylates: polar comonomer built into the linear polymer chain
Drent, Eite; van Dijk, Rudmer; van Ginkel, Roel; van Oort, Bart; Pugh, Robert. I.
Chemical Communications (Cambridge, United Kingdom) (2002), (7), 744-745CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
Copolymn. of ethene and alkyl acrylates is catalyzed by palladium modified with di(2-methoxyphenyl)phosphinobenzene-2-sulfonic acid (DOPPBS); a linear polymer is produced in which acrylate units are incorporated into the polyethylene backbone.
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9
(a) Noda, S.; Nakamura, A.; Kochi, T.; Chung, L. W.; Morokuma, K.; Nozaki, K. Mechanistic Studies on the Formation of Linear Polyethylene Chain Catalyzed by Palladium Phosphine–Sulfonate Complexes: Experiment and Theoretical Studies. J. Am. Chem. Soc. 2009, 131, 14088– 14100, DOI: 10.1021/ja9047398
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9a
Mechanistic Studies on the Formation of Linear Polyethylene Chain Catalyzed by Palladium Phosphine-Sulfonate Complexes: Experiment and Theoretical Studies
Noda, Shusuke; Nakamura, Akifumi; Kochi, Takuya; Chung, Lung Wa; Morokuma, Keiji; Nozaki, Kyoko
Journal of the American Chemical Society (2009), 131 (39), 14088-14100CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Linear polyethylene propagation starting from Pd phosphine-sulfonate complexes, Pd(CH3)(L)(Ar2PC6H4SO3) (L = 2,6-lutidine, Ar = o-MeOC6H4 (2a) and L = pyridine, Ar = Ph (2b)), was studied both exptl. and theor. Exptl., highly linear polyethylene was obtained with Pd(CH3)(L)(Ar2PC6H4SO3) complexes 2a and 2b. Formation of a long alkyl-substituted palladium complex (3) was detected as a result of ethylene oligomerization on a palladium center starting from methylpalladium complex. Addnl., well-defined Et and Pr complexes (6Et and 6Pr) were synthesized as stable n-alkyl palladium complexes. In spite of the existence of β-hydrogens, the β-hydride elimination to give 1-alkenes was very slow or negligible in all cases. On the other hand, isomerization of 1-hexene in the presence of a methylpalladium/phosphine-sulfonate complex 2a indicated that this catalyst system actually undergoes β-hydride elimination and reinsertion to release internal alkenes. On the theor. side, the relative energies were calcd. for intermediates and transition states for chain-growth, chain-walking, and chain-transfer on the basis of the starting model complex Pd(n-C3H7)(pyridine)(o-Me2PC6H4SO3) (8). First, cis/trans isomerization process via the Berry's pseudorotation was proposed for the Pd/phosphine-sulfonate system. The second oxygen atom of sulfonate group is involved in the isomerization process as the associative ligand, which is one of the most unique natures of the sulfonate group. Chain propagation was suggested to take place from the less stable alkylPd(ethylene) complex 10' with the TS of 27.4/27.7 ((E+ZPC)/G) kcal/mol. Possible β-hydride elimination was suggested to occur under low concn. of ethylene: the highest-energy transition state to override for β-hydride elimination was either >37.4/25.3 kcal/mol (TS(9-12)) or 29.1/27.4 kcal/mol (TS(8'-9') to reach 12'). The ethylene insertion to the iso-alkylpalladium species (14') is allowed via a TS of 28.6/29.1 kcal/mol (TS(14'-15')), slightly higher in energy than that for the normal-alkylpalladium species (TS(10'-11')). Easy chain transfer was suggested to proceed from the more stable PdH(olefin) complex 12' if β-hydride elimination to 12' does take place. Thus, the prodn. of linear polyethylene with high mol. wt. under ethylene pressure suggests that the cis and trans PdH(alkene)(phosphine-sulfonate) complexes (12 and 12') are merely accessible in the presence of excess amt. of ethylene.
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(b) Hasanayn, F.; Achord, P.; Braunstein, P.; Magnier, H. J.; Krogh-Jespersen, K.; Goldman, A. S. Theoretical Structure–Reactivity Study of Ethylene Insertion into Nickel–Alkyl Bonds. A Kinetically Significant and Unanticipated Role of trans Influence in Determining Agostic Bond Strengths. Organometallics 2012, 31, 4680– 4692, DOI: 10.1021/om300001n
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(c) Nakano, R.; Chung, L. W.; Watanabe, Y.; Okuno, Y.; Okumura, Y.; Ito, S.; Morokuma, K.; Nozaki, K. Elucidating the Key Role of Phosphine–Sulfonate Ligands in Palladium-Catalyzed Ethylene Polymerization: Effect of Ligand Structure on the Molecular Weight and Linearity of Polyethylene. ACS Catal. 2016, 6, 6101– 6113, DOI: 10.1021/acscatal.6b00911
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9c
Elucidating the key role of phosphine-sulfonate ligands in palladium-catalyzed ethylene polymerization: effect of ligand structure on the molecular weight and linearity of polyethylene
Nakano, Ryo; Chung, Lung Wa; Watanabe, Yumiko; Okuno, Yoshishige; Okumura, Yoshikuni; Ito, Shingo; Morokuma, Keiji; Nozaki, Kyoko
ACS Catalysis (2016), 6 (9), 6101-6113CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
The mechanism of linear polyethylene formation catalyzed by palladium/phosphine-o-sulfonate hemilabile complex and the effect of the ligand structure on the catalytic performance, such as linearity and mol. wt. of the polyethylene, were reinvestigated theor. and exptl. We used dispersion-cor. d. functional theory (DFT-D3) to study the entire mechanism of polyethylene formation from (R2PC6H4SO3)PdMe(2,6-lutidine) (R = Me, t-Bu) and elucidated the key steps that det. the mol. wt. and linearity of the polyethylene. The alkylpalladium ethylene complex is the key intermediate for both linear propagation and β-hydride elimination from the growing polymer chain. On the basis of the key species, the effects of substituents on the phosphorus atom (R = t-Bu, i-Pr, Cy, Men, Ph, 2-MeOC6H4, biAr) were further investigated theor. to explain the exptl. results in a comprehensive manner. Thus, the exptl. trend of mol. wts. of polyethylene could be correlated to the ΔΔG⧺ value between (i) the transition state of linear propagation and (ii) the transition state of the path for ethylene dissocn. leading to β-hydride elimination. Moreover, the exptl. behavior of the catalysts under varied ethylene pressure was well explained by our computation on the small set of key species elucidated from the entire mechanism. In our addnl. exptl. investigations, [(o-Ani2PC6H4SO3)PdH(PtBu3)] catalyzed a hydrogen/deuterium exchange reaction between ethylene and MeOD. The deuterium incorporation from MeOD into the main chain of polyethylene, therefore, can be explained by the incorporation of deuterated ethylene formed by a small amt. of Pd-H species. These insights into the palladium/phosphine-sulfonate system provide a comprehensive understanding of how the phosphine-sulfonate ligands function to produce linear polyethylene.
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(d) Szabo, M. J.; Jordan, R. F.; Michalak, A.; Piers, W. E.; Weiss, T.; Yang, S.-Y.; Ziegler, T. Polar Copolymerization by a Palladium–Diimine-Based Catalyst. Influence of the Catalyst Charge and Polar Substituent on Catalyst Poisoning and Polymerization Activity. A Density Functional Theory Study. Organometallics 2004, 23, 5565– 5572, DOI: 10.1021/om049485g
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9d
Polar Copolymerization by a Palladium-Diimine-Based Catalyst. Influence of the Catalyst Charge and Polar Substituent on Catalyst Poisoning and Polymerization Activity. A Density Functional Theory Study
Szabo, Miklos J.; Jordan, Richard F.; Michalak, Artur; Piers, Warren E.; Weiss, Thomas; Yang, Sheng-Yong; Ziegler, Tom
Organometallics (2004), 23 (23), 5565-5572CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
Copolymn. of ethylene with electroneg. alkenes catalyzed by palladium diimine complex was explored by DFT calcns. Combined gradient-cor. d. functional theory and mol. mechanics (QM/MM) was used to investigate the copolymn. of ethylene with the CH2:CHX (2a-f; X = H, Me, CN, COOMe, OCOMe, Cl). The cationic complex [(ArN:CR2CR3:NAr-κN,κN')PdMe]+ (Ar = 2,6-iPr2C6H3, 1, R2 = H) and its neutral and anionic analogs (R2 = BH3-, R3 = H and R2 = R3 = BH3-, resp.) were used as catalysts. The consecutive insertion steps of CH2:CHX into the Pd-Me bond and of ethylene into the Pd-C(X)HCH2CH3 bond were investigated. Focus was put on the role of the X functional groups and the effect of the cationic, neutral, and anionic environments on the Pd(II)-diimine system. Calcns. were performed on the CH2:CHX monomers, model catalysts, precursor π-complexes, and σ-complexes of the monomers, as well as the chelate and H-agostic insertion products. The transition state of the insertion reaction and the corresponding activation energy was detd. for both investigated insertion steps. The results show that the X group has only a minor effect on the insertion of the CH2:CHX monomers into the Pd-CH3 bond. On the other hand, the barrier for insertion of ethylene into the Pd-CHXR bond revealed an increase with the electron-withdrawing ability of X. The application of neutral and anionic catalysts leads to a preference for π-complexation over σ-complexation of the polar monomers. Unfortunately, for an anionic model system the barriers for the first and second insertion are significantly increased for ethylene, whereas the first insertion barrier for the polar monomers only is moderately increased. Thus, while anionic catalysts are highly tolerant toward polar monomers, they are nearly inactive toward ethylene insertion.
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10
Johnson, A. M.; Contrella, N. D.; Sampson, J. R.; Zheng, M.; Jordan, R. F. Allosteric Effects in Ethylene Polymerization Catalysis. Enhancement of Performance of Phosphine-Phosphinate and Phosphine-Phosphonate Palladium Alkyl Catalysts by Remote Binding of B(C6F5)3. Organometallics 2017, 36, 4990– 5002, DOI: 10.1021/acs.organomet.7b00815
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10
Allosteric Effects in Ethylene Polymerization Catalysis. Enhancement of Performance of Phosphine-Phosphinate and Phosphine-Phosphonate Palladium Alkyl Catalysts by Remote Binding of B(C6F5)3
Wilders, Alison M.; Contrella, Nathan D.; Sampson, Jessica R.; Zheng, Mingfang; Jordan, Richard F.
Organometallics (2017), 36 (24), 4990-5002CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
Remote binding of B(C6F5)3 to (PPO)PdMeL (L = pyridine or lutidine) or {(PPO)PdMe}2 ethylene polymn. catalysts that contain phosphine-arenephosphinate or phosphine-arenephosphonate ligands (PPO- = [1-PAr2-2-PR'O2-C6H4]-: Ar = R' = Ph (1a); Ar = Ph, R' = OEt (1b); Ar = Ph, R' = OiPr (1c); Ar = 2-OMe-C6H4, R' = OiPr (1d)) significantly increases the catalyst activity and the mol. wt. of the polyethylene (PE) product. In the most favorable case, in situ conversion of (1d)PdMe(py) to the base-free adduct {1d·B(C6F5)3}PdMe increases the ethylene polymn. activity from 9.8 to 5700 kg mol-1 h-1 and the Mn of the PE product from 9030 to 99,200 Da (80°, 410 psi). X-ray structural data, trends in ligand lability, and comparative studies of BF3 activation suggest that these allosteric effects are primarily electronic in origin. The B(C6F5)3 binding enhances the chain growth rate (Rgrowth) by increasing the degree of pos. charge on the Pd center. This effect does not result in the large increase in the chain transfer rate (Rtransfer) and concomitant redn. in PE mol. wt. seen in previous studies of analogous (PO)PdRL catalysts that contain phosphine-arenesulfonate ligands, because of the operation of a dissociative chain transfer process, which is inhibited by the increased charge at Pd.
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11
(a) Long, B. K.; Eagan, J. M.; Mulzer, M.; Coates, G. W. Semi-Crystalline Polar Polyethylene: Ester-Functionalized Linear Polyolefins Enabled by a Functional-Group-Tolerant, Cationic Nickel Catalyst. Angew. Chem., Int. Ed. 2016, 55, 7106– 7110, DOI: 10.1002/anie.201601703
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11a
Semi-Crystalline Polar Polyethylene: Ester-Functionalized Linear Polyolefins Enabled by a Functional-Group-Tolerant, Cationic Nickel Catalyst
Long, Brian K.; Eagan, James M.; Mulzer, Michael; Coates, Geoffrey W.
Angewandte Chemie, International Edition (2016), 55 (25), 7106-7110CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
A dibenzobarrelene-bridged, α-diimine NiII catalyst (rac-3) was synthesized and shown to have exceptional behavior for the polymn. of ethylene. The catalyst afforded high mol. wt. polyethylenes with narrow dispersities and degrees of branching much lower than those made by related α-diimine nickel catalysts. Catalyst rac-3 demonstrated living behavior at room temp., produced linear polyethylene (Tm=135 °C) at -20 °C, and, most importantly, was able to copolymerize ethylene with the biorenewable polar monomer Me 10-undecenoate to yield highly linear ester-functionalized polyethylene.
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(b) Xin, B. S.; Sato, N.; Tanna, A.; Oishi, Y.; Konishi, Y.; Shimizu, F. Nickel Catalyzed Copolymerization of Ethylene and Alkyl Acrylates. J. Am. Chem. Soc. 2017, 139, 3611– 3614, DOI: 10.1021/jacs.6b13051
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11b
Nickel Catalyzed Copolymerization of Ethylene and Alkyl Acrylates
Xin, Bruce S.; Sato, Naomasa; Tanna, Akio; Oishi, Yasuo; Konishi, Yohei; Shimizu, Fumihiko
Journal of the American Chemical Society (2017), 139 (10), 3611-3614CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Ni(II) complexes bearing an o-bis(aryl)phosphinophenolate ligand were synthesized as catalysts for copolymn. of ethylene and alkyl acrylates. When the P-bound aryl group was 2,6-dimethoxyphenyl group, one of the oxygen atoms in the methoxy groups coordinated to the nickel center on its apical position. This complex was a highly active catalyst without any activators to give highly linear and high mol. wt. copolymers. The structures of the copolymers were detd. by 1H and 13C NMR to clarify that the alkyl acrylate comonomers were incorporated in the main chain and that the structures of the copolymers were significantly influenced by the structure of the aryl group in the ligand.
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(c) Connor, E. F.; Younkin, T. R.; Henderson, J. I.; Hwang, S.; Grubbs, R. H.; Roberts, W. P.; Litzau, J. J. Linear functionalized polyethylene prepared with highly active neutral Ni(II) complexes. J. Polym. Sci., Part A: Polym. Chem. 2002, 40, 2842– 2854, DOI: 10.1002/pola.10370
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11c
Linear functionalized polyethylene prepared with highly active neutral Ni(II) complexes
Connor, Eric F.; Younkin, Todd R.; Henderson, Jason I.; Hwang, Sonjong; Grubbs, Robert H.; Roberts, William P.; Litzau, Johnathan J.
Journal of Polymer Science, Part A: Polymer Chemistry (2002), 40 (16), 2842-2854CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)
Neutral Ni(II) salicylaldimine catalysts (pendant ligand = NCMe or PPh3) were used to copolymerize ethylene with monomers contg. esters, alcs., anhydrides, and amides and yielded linear functionalized polyethylene in a single step. α-Olefins and polycyclic olefin comonomers carrying functionality were directly incorporated into the polyethylene backbone by the catalysts without any cocatalyst, catalyst initiator, or other disturber compds. The degree of comonomer incorporation was related to the monomer structure: tricyclononenes > norbornenes > α-olefins. A wide range of comonomer incorporation, up to 30 mol %, was achieved while a linear polyethylene structure was maintained under mild conditions (40°C, 100 psi ethylene). Results from the characterization of the copolymers by soln. and solid-state NMR techniques, thermal anal., and mol. wt. demonstrated that the materials contained a relatively pure microstructure for a functionalized polyethylene that was prepd. in one step with no catalyst additive.
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(a) Kacker, S.; Jiang, Z.; Sen, A. Alternating Copolymers of Functional Alkenes with Carbon Monoxide. Macromolecules 1996, 29, 5852– 5858, DOI: 10.1021/ma960255q
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(b) Mecking, S.; Johnson, L. K.; Wang, L.; Brookhart, M. Mechanistic Studies of the Palladium-Catalyzed Copolymerization of Ethylene and α-Olefins with Methyl Acrylate. J. Am. Chem. Soc. 1998, 120, 888– 899, DOI: 10.1021/ja964144i
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12b
Mechanistic Studies of the Palladium-Catalyzed Copolymerization of Ethylene and α-Olefins with Methyl Acrylate
Mecking, Stefan; Johnson, Lynda K.; Wang, Lin; Brookhart, Maurice
Journal of the American Chemical Society (1998), 120 (5), 888-899CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Mechanistic aspects of palladium-catalyzed insertion copolymn s. of ethylene (I) and α-olefins with Me acrylate to give high molar-mass polymers are described. Complexes [(N N)Pd(CH2)3C(O)OMe]BAr'4 or [(N N)Pd(CH3)(L)]BAr'4 (L = OEt2, NCMe,NCAr'') (N N ≡ ArN:C(R)-C(R):NAr, e.g., Ar ≡ 2,6-C6H3(i-Pr)2, R ≡ H, Me; Ar' ≡ 3,5-C6H3(CF3)2) with bulky substituted α-diimine ligands were used as catalyst precursors. The copolymers are highly branched, the acrylate comonomer being incorporated predominantly at the ends of branches as -CH2CH2C(O)OMe groups. The effects of reaction conditions and catalyst structure on the copolymn. reaction are rationalized. Low-temp. NMR studies show that migratory insertion in the η2-Me acrylate (MA) complex [(N N)PdMe{H2C:CHC(O)OMe}]+ occurs to give initially the 2,1-insertion product [(N N)PdCH(CH2CH3)C(O)OMe]+, which rearranges stepwise to yield the final product upon warming to -20°. Activation parameters (ΔH⧧ = 12.1 ± 1.4 kcal/mol and ΔS⧧ = -14.1 ± 7.0 eu) were detd. for the conversion of 5a to 6a. Rates of I homopolymn. obsd. in preparative-scale polymns. (1.2 s-1 at 25°, ΔG⧧ = 17.4 kcal/mol for 2b) correspond well with low-temp. NMR kinetic data for migratory insertion of I in [(N N)Pd{(CH2)2nMe}(H2C:CH2)]+. Relative binding affinities of olefins to the metal center were also studied. For [(N N)PdMe(H2C:CH2)]+ + MA .dblharw. 5a + H2C:CH2, Keq(-95 °C) = (1.0 ± 0.3) × 10-6 was detd. Combination of the above studies provides a mechanistic model that agrees well with acrylate incorporations obsd. in copolymn. expts. Data obtained for equil. 2 + H2C:CHR'' .dblharw. [(N N)Pd{(CH2)3C(O)OMe}(H2C:CHR'')]+ (R' ≡ H, Me, nC4H9) shows that chelating coordination of the carbonyl group is favored over olefin coordination at room temp. Formation of chelates analogous to 2 during the copolymn. is assumed to render the subsequent monomer insertion a turnover-limiting step.
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(c) Kochi, T.; Yoshimura, K.; Nozaki, K. Synthesis of anionic methylpalladium complexes with phosphine-sulfonate ligands and their activities for olefin polymerization. Dalton Trans. 2006, 25– 27, DOI: 10.1039/B512452M
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(d) Luo, S.; Vela, J.; Lief, G. R.; Jordan, R. F. Copolymerization of Ethylene and Alkyl Vinyl Ethers by a (Phosphine- sulfonate)PdMe Catalyst. J. Am. Chem. Soc. 2007, 129, 8946– 8947, DOI: 10.1021/ja072562p
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12d
Copolymerization of Ethylene and Alkyl Vinyl Ethers by a (Phosphine- sulfonate)PdMe Catalyst
Luo, Shuji; Vela, Javier; Lief, Graham R.; Jordan, Richard F.
Journal of the American Chemical Society (2007), 129 (29), 8946-8947CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
The neutral complex (PO-OMe)PdMe(py) (1, PO-OMe = 2-[bis(2-OMe-Ph)phosphino]-4-methylbenzenesulfonate) polymerizes ethylene to a linear polymer with 1-10 branches/103 carbons (mostly methyl) and vinyl and 2-olefin unsatd. end groups. Complex 1 copolymerizes ethylene and alkyl vinyl ethers (CH2:CHOR, 2a-c: R = tBu (a), Et (b), Bu (c)) in toluene at 60-100 °C to linear copolymers contg. up to 7 mol % of vinyl ether. Addn. of CH2:CHOR lowers the polymn. rate and the polymer mol. wt. The copolymer structures are similar to that of homopolyethylene generated under the same conditions. The major comonomer units are -CH2CH(OR)CH2- (I) and CH3CH(OR)CH2- (II). The ethylene/CH2:CHOR copolymers can be converted to hydroxy- and bromo-polyethylene. The results of control expts. argue against cationic and radical mechanisms for the copolymn., and an insertion mechanism is proposed. The reaction of base-free (PO-OMe)PdMe with CH2:CHOEt yields the adduct (PO-OMe)PdMe(CH2:CHOEt), which undergoes 1,2-insertion to generate (PO-OMe)PdCH2CH(OEt)Me.
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(e) Weng, W.; Shen, Z.; Jordan, R. F. Copolymerization of Ethylene and Vinyl Fluoride by (Phosphine-Sulfonate)Pd(Me)(py) Catalysts. J. Am. Chem. Soc. 2007, 129, 15450– 15451, DOI: 10.1021/ja0774717
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12e
Copolymerization of Ethylene and Vinyl Fluoride by (Phosphine-Sulfonate)Pd(Me)(py) Catalysts
Weng, Wei; Shen, Zhongliang; Jordan, Richard F.
Journal of the American Chemical Society (2007), 129 (50), 15450-15451CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
The PdII complexes [PO]Pd(Me)(py) (1a-c; [PO] = 2-PAr2-4-Me-benzenesulfonate; Ar = 2-Et-Ph (a), 2-OMe-Ph (b), Ph (c)) catalyze the copolymn. of ethylene and vinyl fluoride in toluene at 80° to produce fluorinated polyethylene. Low levels (0.1-0.5 mol%) of vinyl fluoride incorporation are obsd. At 80 psi vinyl fluoride and 220 psi ethylene, 1a produces a linear copolymer with Mw = 35,000, Mw/Mn = 3.0, and 0.17 mol% vinyl fluoride incorporation. At a total pressure of 300 psi, increasing the proportion of vinyl fluoride in the feed results in an increase in the level of vinyl fluoride incorporation (to 0.45 mol %) and a decrease in polymer yield and mol. wt. 1A is more reactive and produces higher mol. wt. copolymer than 1b, c, but all three catalysts incorporate similar levels of vinyl fluoride. Control expts. rule out a radical copolymn. mechanism, and an insertion mechanism is proposed.
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(f) Kochi, T.; Noda, S.; Yoshimura, K.; Nozaki, K. Formation of Linear Copolymers of Ethylene and Acrylonitrile Catalyzed by Phosphine Sulfonate Palladium Complexes. J. Am. Chem. Soc. 2007, 129, 8948– 8949, DOI: 10.1021/ja0725504
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12f
Formation of Linear Copolymers of Ethylene and Acrylonitrile Catalyzed by Phosphine Sulfonate Palladium Complexes
Kochi, Takuya; Noda, Shusuke; Yoshimura, Kenji; Nozaki, Kyoko
Journal of the American Chemical Society (2007), 129 (29), 8948-8949CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Linear copolymers of ethylene and acrylonitrile were prepd. using palladium complexes bearing phosphine-sulfonate bidentate ligands. Acrylonitrile units located in the linear polyethylene backbones were detected for the first time by 13C NMR spectroscopy. Catalyst systems employing isolated palladium complexes such as 3 showed much higher activity for the copolymn. than the in situ generation procedures, and mol. wt. of the copolymers and acrylonitrile incorporation were dependent on the palladium complexes. Obtained linear copolymers of ethylene and acrylonitrile melt at higher temp. than branched copolymers.
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(g) Guironnet, D.; Roesle, P.; Rünzi, T.; Göttker-Schnetmann, I.; Mecking, S. Insertion Polymerization of Acrylate. J. Am. Chem. Soc. 2009, 131, 422– 423, DOI: 10.1021/ja808017n
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12g
Insertion Polymerization of Acrylate
Guironnet, Damien; Roesle, Philipp; Ruenzi, Thomas; Goettker-Schnetmann, Inigo; Mecking, Stefan
Journal of the American Chemical Society (2009), 131 (2), 422-423CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Multiple insertions of acrylate in copolymn. with ethylene, and an insertion homo-oligomerization of Me acrylate were obsd. for the first time. Key to these findings, and to mechanistic insights reported, are labile-substituted complexes as catalyst precursors.
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(h) Borkar, S.; Newsham, D. K.; Sen, A. Copolymerization of Ethene with Styrene Derivatives, Vinyl Ketone, and Vinylcyclohexane Using a (Phosphine–sulfonate)palladium(II) System: Unusual Functionality and Solvent Tolerance. Organometallics 2008, 27, 3331– 3334, DOI: 10.1021/om800237r
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12h
Copolymerization of Ethene with Styrene Derivatives, Vinyl Ketone, and Vinylcyclohexane Using a (Phosphine-sulfonate)palladium(II) System: Unusual Functionality and Solvent Tolerance
Borkar, Sachin; Newsham, David K.; Sen, Ayusman
Organometallics (2008), 27 (14), 3331-3334CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
A (phosphine-sulfonate)palladium(II) system [Me(pyridine)Pd(O3SC6H4(P(C6H4OMe-2)2)-2)] catalyzes the copolymn. of ethene with a variety of styrene derivs., including those with O functionalities. The copolymns. also proceed in protic solvents, including H2O, allowing metal-mediated emulsion copolymn. of ethene and styrene.
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(i) Ito, S.; Munakata, K.; Nakamura, A.; Nozaki, K. Copolymerization of Vinyl Acetate with Ethylene by Palladium/Alkylphosphine–Sulfonate Catalysts. J. Am. Chem. Soc. 2009, 131, 14606– 14607, DOI: 10.1021/ja9050839
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12i
Copolymerization of Vinyl Acetate with Ethylene by Palladium/Alkylphosphine-Sulfonate Catalysts
Ito, Shingo; Munakata, Kagehiro; Nakamura, Akifumi; Nozaki, Kyoko
Journal of the American Chemical Society (2009), 131 (41), 14606-14607CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Coordination copolymn. of vinyl acetate (VAc) with ethylene, leading to linear copolymers that possess in-chain -CH2CH(OAc)- units, has been accomplished using novel palladium complexes bearing alkylphosphine-sulfonate ligands.
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(j) Guironnet, D.; Caporaso, L.; Neuwald, B.; Göttker-Schnetmann, I.; Cavallo, L.; Mecking, S. Mechanistic Insights on Acrylate Insertion Polymerization. J. Am. Chem. Soc. 2010, 132, 4418– 4426, DOI: 10.1021/ja910760n
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12j
Mechanistic Insights on Acrylate Insertion Polymerization
Guironnet, Damien; Caporaso, Lucia; Neuwald, Boris; Goetker-Schnetmann, Inigo; Cavallo, Luigi; Mecking, Stefan
Journal of the American Chemical Society (2010), 132 (12), 4418-4426CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Complexes [{(P and O)PdMe}n] (1n; P and O = κ2-P,O-Ar2PC6H4SO2O with Ar = 2-MeOC6H4) are a single-component precursor of the (P and O)PdMe fragment devoid of addnl. coordinating ligands, which also promotes the catalytic oligomerization of acrylates. Exposure of 1n to Me acrylate afforded the two diastereomeric chelate complexes [(P and O)Pd{κ2-C,O-CH(C(O)OMe)CH2CH(C(O)OMe)CH2CH3}] (3-meso and 3-rac) resulting from two consecutive 2,1-insertions of Me acrylate into the Pd-Me bond with the same or opposite stereochem., resp., in a 3:2 ratio as demonstrated by comprehensive NMR spectroscopic studies and single crystal X-ray diffraction. These six-membered chelate complexes are direct key models for intermediates of acrylate insertion polymn., and also ethylene-acrylate copolymn. to high acrylate content copolymers. Studies of the binding of various substrates (pyridine, dmso, ethylene and Me acrylate) to 3-meso and 3-rac show that hindered displacement of the chelating carbonyl moiety by π-coordination of incoming monomer significantly retards, but does not prohibit, polymn. For 3-meso,3-rac + C2H4 ↹ 3-meso-C2H4,3-rac-C2H4 an equil. const. K(353 K) ≈ 2 × 10-3 L mol-1 was estd. Reaction of 3-meso, 3-rac with Me acrylate afforded higher insertion products [(P and O)Pd(C4H6O2)nMe] (n = 3, 4) as obsd. by electrospray ionization mass spectrometry (ESI-MS). Theor. studies by DFT methods of consecutive acrylate insertion provide relative energies of intermediates and transition states, which are consistent with the aforementioned exptl. observations, and give detailed insights to the pathways of multiple consecutive acrylate insertions. Acrylate insertion into 3-meso,3-rac is assocd. with an overall energy barrier of ca. 100 kJ mol-1.
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(k) Rünzi, T.; Fröhlich, D.; Mecking, S. Direct Synthesis of Ethylene–Acrylic Acid Copolymers by Insertion Polymerization. J. Am. Chem. Soc. 2010, 132, 17690– 17691, DOI: 10.1021/ja109194r
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12k
Direct Synthesis of Ethylene-Acrylic Acid Copolymers by Insertion Polymerization
Ruenzi, Thomas; Froehlich, Dominik; Mecking, Stefan
Journal of the American Chemical Society (2010), 132 (50), 17690-17691CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Neutral palladium(II) phosphinesulfonato polymn. catalysts were found to be stable toward carboxylic acid moieties and to enable direct linear copolymn. of ethylene with acrylic acid.
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(l) Kryuchkov, V. A.; Daigle, J.-C.; Skupov, K. M.; Claverie, J. P.; Winnik, F. M. Amphiphilic Polyethylenes Leading to Surfactant-Free Thermoresponsive Nanoparticles. J. Am. Chem. Soc. 2010, 132, 15573– 15579, DOI: 10.1021/ja104182w
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12l
Amphiphilic Polyethylenes Leading to Surfactant-Free Thermoresponsive Nanoparticles
Kryuchkov, Vladimir A.; Daigle, Jean-Christophe; Skupov, Kirill M.; Claverie, Jerome P.; Winnik, Francoise M.
Journal of the American Chemical Society (2010), 132 (44), 15573-15579CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Linear copolymers of ethylene and acrylic acid (PEAA) were prepd. by catalytic polymn. of ethylene and tert-Bu acrylate followed by hydrolysis of the ester groups. The copolymers contained COOH groups inserted into the cryst. unit cell with formation of intramol. hydrogen-bonds, as established on the basis of differential scanning calorimetry (DSC), Fourier-transform IR spectroscopy (FTIR), and X-ray diffraction (XRD) studies. A solvent-exchange protocol, with no added surfactant, converted a soln. in THF of a PEAA sample contg. 12 mol % of acrylic acid (AA) into a colloidally stable aq. suspension of nanoparticles. Transmission electron microscopy (TEM), dynamic light scattering (DLS), and high sensitivity differential scanning calorimetry (HS-DSC) were used to characterize the nanoparticles. They are single crystals of elongated shape with a polar radius of 49 nm (σ = 15 nm) and an equatorial radius of 9 nm (σ = 3 nm) stabilized in aq. media via carboxylate groups located preferentially on the particle/water interface. The PEAA (AA: 12 mol %) nanoparticles dispersed in aq. media exhibited a remarkable reversible thermoresponsive behavior upon heating/cooling from 25 to 80 °C.
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(m) Friedberger, T.; Wucher, P.; Mecking, S. Mechanistic Insights into Polar Monomer Insertion Polymerization from Acrylamides. J. Am. Chem. Soc. 2012, 134, 1010– 1018, DOI: 10.1021/ja207110u
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12m
Mechanistic Insights into Polar Monomer Insertion Polymerization from Acrylamides
Friedberger, Tobias; Wucher, Philipp; Mecking, Stefan
Journal of the American Chemical Society (2012), 134 (2), 1010-1018CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
N-Iso-Pr acrylamide (NIPAM), N,N-di-Me acrylamide (DMAA), and 2-acetamidoethyl acrylate (AcAMEA) were copolymd. with ethylene employing [(P%O)PdMe(DMSO)] (1-DMSO; P%O = κ2-P,O-Ar2PC6H4SO2O with Ar = 2-MeOC6H4) as a catalyst precursor. Inhibition studies with nonpolymerizable polar additives show that reversible κ-O-coordination of free amide retards polymn. significantly. Retardation of polymn. increases in the order Et acetate « Me Et sulfone < acetonitrile < N,N-dimethylacetamide ≈ N-methylacetamide ≈ propionic acid < dimethylsulfoxide. Pseudo-first-order rate consts. for the insertion into 1-DMSO were detd. to increase in the order DMAA < AcAMEA < NIPAM < Me acrylate. Exposure of 1-DMSO to NIPAM resulted in the formation of consecutive insertion products [(P%O)Pd(C6H11NO2)nMe] (n ≤ 3), as detd. by electrospray ionization mass spectrometry. The solid-state structure of the methanol adduct of the 2,1-insertion product of NIPAM into 1-DMSO, [(P%O)Pd{η1-CH(CONHiPr)CH2CH3}(κ1-O-MeOD)] (2-MeOD), was detd. by single crystal x-ray diffraction. Both 2,1- and 1,2-insertions of DMAA into the Pd-Me bond of a [(P%O)PdMe] fragment occur to afford a ca. 4:1 mixt. of chelates [(P%O)Pd{κ2-C,O-C(CH2CH3)C(O)NMe2}] (3) and [(P%O)Pd{κ2-C,O-CH2C(CH3)C(O)NMe2}] (4). The four-membered chelate of 3 is opened by coordination of 2,6-lutidine (3 + 2,6-lutidine .dblharw. 3-LUT) with ΔH° = -41.8(10.5) kJ and ΔS° = -115(37) J mol-1 K-1.
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(n) Ito, S.; Kanazawa, M.; Munakata, K.; Kuroda, J.-i.; Okumura, Y.; Nozaki, K. Coordination–Insertion Copolymerization of Allyl Monomers with Ethylene. J. Am. Chem. Soc. 2011, 133, 1232– 1235, DOI: 10.1021/ja1092216
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12n
Coordination-Insertion Copolymerization of Allyl Monomers with Ethylene
Ito, Shingo; Kanazawa, Masafumi; Munakata, Kagehiro; Kuroda, Jun-Ichi; Okumura, Yoshikuni; Nozaki, Kyoko
Journal of the American Chemical Society (2011), 133 (5), 1232-1235CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Coordination-insertion copolymn. of allyl monomers with ethylene was developed by using a palladium/phosphine-sulfonate catalyst. A variety of allyl monomers, including allyl acetate, allyl alc., protected allylamines, and allyl halides, were copolymd. with ethylene to form highly linear copolymers that possess in-chain -CH2CH(CH2FG)- units.
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(o) Neuwald, B.; Falivene, L.; Caporaso, L.; Cavallo, L.; Mecking, S. Exploring Electronic and Steric Effects on the Insertion and Polymerization Reactivity of Phosphinesulfonato PdII Catalysts. Chem. - Eur. J. 2013, 19, 17773– 17788, DOI: 10.1002/chem.201301365
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12o
Exploring Electronic and Steric Effects on the Insertion and Polymerization Reactivity of Phosphinesulfonato PdII Catalysts
Neuwald, Boris; Falivene, Laura; Caporaso, Lucia; Cavallo, Luigi; Mecking, Stefan
Chemistry - A European Journal (2013), 19 (52), 17773-17788CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
Thirteen different sym. and asym. phosphinesulfonato palladium complexes ([{(X1-Cl)-μ-M}n], M=Na, Li, 1=X(P%O)PdMe) were prepd. (see Figure 1). The solid-state structures of the corresponding pyridine or lutidine complexes were detd. for (MeO)21-py, (iPrO)21-lut, (MeO,Me2)1-lut, (MeO)31-lut, CF31-lut, and Ph1-lut. The reactivities of the catalysts X1, obtained after chloride abstraction with AgBF4, toward Me acrylate (MA) were quantified through detn. of the rate consts. for the first and the consecutive MA insertion and the anal. of β-H and other decompn. products through NMR spectroscopy. Differences in the homo- and copolymn. of ethylene and MA regarding catalyst activity and stability over time, polymer mol. wt., and polar co-monomer incorporation were investigated. DFT calcns. were performed on the main insertion steps for both monomers to rationalize the effect of the ligand substitution patterns on the polymn. behaviors of the complexes. Full anal. of the data revealed that: 1) electron-deficient catalysts polymerize with higher activity, but fast deactivation is also obsd.; 2) the double ortho-substituted catalysts (MeO)21 and (MeO)31 allow very high degrees of MA incorporation at low MA concns. in the copolymn.; and 3) steric shielding leads to a pronounced increase in polymer mol. wt. in the copolymn. The catalyst properties induced by a given P-aryl (alkyl) moiety were combined effectively in catalysts with two different non-chelating aryl moieties, such as cHexO/(MeO)21, which led to copolymers with significantly increased mol. wts. compared to the prototypical MeO1.
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(a) Skupov, K. M.; Marella, P. R.; Simard, M.; Yap, G. P. A.; Allen, N.; Conner, D.; Goodall, B. L.; Claverie, J. P. Palladium Aryl Sulfonate Phosphine Catalysts for the Copolymerization of Acrylates with Ethene. Macromol. Rapid Commun. 2007, 28, 2033– 2038, DOI: 10.1002/marc.200700370
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13a
Palladium aryl sulfonate phosphine catalysts for the copolymerization of acrylates with ethene
Skupov, Kirill M.; Marella, Pooja R.; Simard, Michel; Yap, Glenn P. A.; Allen, Nathan; Conner, David; Goodall, Brian L.; Claverie, Jerome P.
Macromolecular Rapid Communications (2007), 28 (20), 2033-2038CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
The reaction of 2-[bis(2-methoxy-phenyl)phosphanyl]-4-methyl-benzenesulfonic acid (a) and 2-[bis(2',6'-dimethoxybiphenyl-2-yl)phosphanyl]benzenesulfonic acid (b) with dimethyl(N,N,N',N'-tetramethylethylenediamine)-palladium(II) (PdMe2(TMEDA)) leads to the formation of TMEDA bridged palladium based polymn. catalysts (1a and 1b). Upon reaction with pyridine, two mononuclear catalysts are formed (2a and 2b). These catalysts are able to homopolymerize ethylene and also copolymerize ethylene with acrylates or with norbornenes. With ligand b, high mol. wt. polymers are formed in high yields, but higher comonomer incorporations are obtained with ligand a.
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(b) Ota, Y.; Ito, S.; Kuroda, J.-i.; Okumura, Y.; Nozaki, K. Quantification of the Steric Influence of Alkylphosphine–Sulfonate Ligands on Polymerization, Leading to High-Molecular-Weight Copolymers of Ethylene and Polar Monomers. J. Am. Chem. Soc. 2014, 136, 11898– 11901, DOI: 10.1021/ja505558e
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13b
Quantification of the Steric Influence of Alkylphosphine-Sulfonate Ligands on Polymerization, Leading to High-Molecular-Weight Copolymers of Ethylene and Polar Monomers
Ota, Yusuke; Ito, Shingo; Kuroda, Jun-ichi; Okumura, Yoshikuni; Nozaki, Kyoko
Journal of the American Chemical Society (2014), 136 (34), 11898-11901CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
A series of palladium/ alkylphosphine- sulfonate catalysts were synthesized and examd. in the homopolymn. of ethylene and the copolymn. of ethylene and polar monomers. Catalysts with alkylphosphine- sulfonate ligands contg. sterically demanding alkyl substituents afforded (co)polymers whose mol. wt. was increased by up to 2 orders of magnitude relative to polymers obtained from previously reported catalyst systems. The polymer mol. wt. was found to be closely correlated to the Sterimol B5 parameter of the alkyl substituents in the alkylphosphine- sulfonate ligands. Thus, the use of bulky alkylphosphine- sulfonate ligands represents an effective and versatile method to prep. high-mol.-wt. copolymers of ethylene and various polar monomers, which are difficult to obtain by previously reported methods.
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(a) Carrow, B. P.; Nozaki, K. Synthesis of Functional Polyolefins Using Cationic Bisphosphine Monoxide–Palladium Complexes. J. Am. Chem. Soc. 2012, 134, 8802– 8805, DOI: 10.1021/ja303507t
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14a
Synthesis of Functional Polyolefins Using Cationic Bisphosphine Monoxide-Palladium Complexes
Carrow, Brad P.; Nozaki, Kyoko
Journal of the American Chemical Society (2012), 134 (21), 8802-8805CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
The copolymn. of ethylene with polar vinyl monomers, such as vinyl acetate, acrylonitrile, vinyl ethers, and allyl monomers, was accomplished using cationic palladium complexes ligated by a bisphosphine monoxide (BPMO). The copolymers formed by these catalysts have highly linear microstructures and a random distribution of polar functional groups throughout the polymer chain. Our data demonstrate that cationic palladium complexes can exhibit good activity for polymns. of polar monomers, in contrast to cationic α-diimine palladium complexes (Brookhart-type) that are not applicable to industrially relevant polar monomers beyond acrylates. Addnl., the studies reported here point out that phosphine-sulfonate ligated palladium complexes are no longer the singular family of catalysts that can promote the reaction of ethylene with many polar vinyl monomers to form linear functional polyolefins.
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(b) Contrella, N. D.; Sampson, J. R.; Jordan, R. F. Copolymerization of Ethylene and Methyl Acrylate by Cationic Palladium Catalysts That Contain Phosphine-Diethyl Phosphonate Ancillary Ligands. Organometallics 2014, 33, 3546– 3555, DOI: 10.1021/om5004489
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14b
Copolymerization of Ethylene and Methyl Acrylate by Cationic Palladium Catalysts That Contain Phosphine-Diethyl Phosphonate Ancillary Ligands
Contrella, Nathan D.; Sampson, Jessica R.; Jordan, Richard F.
Organometallics (2014), 33 (13), 3546-3555CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
A series of benzo-linked phosphine-diethyl phosphonate (P-PO) and phosphine-bis(di-Et phosphonate) (P-(PO)2) ligands and the corresponding (P-PO)PdMe(2,6-lutidine)+ and (P-(PO)2)PdMe(2,6-lutidine)+ complexes were synthesized. Cationic (P-PO)PdMe(2,6-lutidine)+ complexes are active for ethylene oligomerization/polymn., with activities of 2 kg mol-1 h-1 for {κ2-1-PiPr2-2-P(O)(OEt)2-5-Me-Ph}PdMe(2,6-lutidine)+ (3c), 125 kg mol-1 h-1 for {κ2-1-PPh2-2-P(O)(OEt)2-5-Me-Ph}PdMe(2,6-lutidine)+ (3a), and 1470 kg mol-1 h-1 for {κ2-1-P(2-OMe-Ph)2-2-P(O)(OEt)2-Ph}PdMe(2,6-lutidine)+ (3b). The polyethylene is highly linear, with over 80% terminal unsatn. and low (230-1890 Da) mol. wt. in all cases. 3B copolymerizes ethylene with Me acrylate, exhibiting highly selective (95%) in-chain (rather than chain-end) acrylate incorporation. The P-(PO)2 catalyst {κ2-1-P(4-tBu-Ph)(2-P(O)(OEt)2-5-Me-Ph)-2-P(O)(OEt)2-5-Me-Ph}PdMe(2,6-lutidine)+ (3d) is more active for ethylene homopolymn. (2640 kg mol-1 h-1), yielding linear, low-mol.-wt. polymer (1280-1430 Da) with predominantly internal olefin placement. In ethylene/methyl acrylate copolymn., 3d incorporates 2.6 mol % Me acrylate, 60% of which is in-chain. Both 3b and 3d catalyze ethylene/acrylic acid copolymn., albeit with low (<10 kg mol-1 h-1) activities and acrylic acid incorporation up to 1.1 mol %.
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(c) Sui, X.; Dai, S.; Chen, C. Ethylene Polymerization and Copolymerization with Polar Monomers by Cationic Phosphine Phosphonic Amide Palladium Complexes. ACS Catal. 2015, 5, 5932– 5937, DOI: 10.1021/acscatal.5b01490
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14c
Ethylene Polymerization and Copolymerization with Polar Monomers by Cationic Phosphine Phosphonic Amide Palladium Complexes
Sui, Xuelin; Dai, Shengyu; Chen, Changle
ACS Catalysis (2015), 5 (10), 5932-5937CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
The synthesis, characterization, and olefin (co)polymn. studies of a series of palladium complexes bearing phosphine phosphonic amide ligands were investigated. In this ligand framework, substituents on three positions could be modulated independently, which distinguishes this class of ligand and provides a great deal of flexibilities and opportunities to tune the catalytic properties. The palladium complex with an o-MeO-Ph substituent on phosphine is one of the most active palladium catalysts in ethylene polymn., with 1 order of magnitude higher activity than the corresponding classic phosphine-sulfonate palladium complex. Meanwhile, the polyethylene generated by this new palladium complex showed ca. 6 times higher mol. wt. in comparison to that by the classic phosphine-sulfonate palladium complex. In ethylene/methyl acrylate copolymn., the new palladium complex showed lower activity, generating copolymer with similar Me acrylate incorporation and much higher mol. wt. The new palladium complex was also able to copolymerize ethylene with other polar monomers, including Bu vinyl ether and allyl acetate, making it one of the very few catalyst systems that can copolymerize ethylene with multiple industrially relevant polar monomers.
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(d) Mitsushige, Y.; Carrow, B. P.; Ito, S.; Nozaki, K. Ligand-controlled insertion regioselectivity accelerates copolymerisation of ethylene with methyl acrylate by cationic bisphosphine monoxide-palladium catalysts. Chem. Sci. 2016, 7, 737– 744, DOI: 10.1039/C5SC03361F
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14d
Ligand-controlled insertion regioselectivity accelerates copolymerisation of ethylene with methyl acrylate by cationic bisphosphine monoxide-palladium catalysts
Mitsushige, Yusuke; Carrow, Brad P.; Ito, Shingo; Nozaki, Kyoko
Chemical Science (2016), 7 (1), 737-744CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
A new series of palladium catalysts ligated by a chelating bisphosphine monoxide bearing diarylphosphino groups (aryl-BPMO) exhibits markedly higher reactivity for ethylene/methyl acrylate copolymn. when compared to the first generation of alkyl-BPMO-palladium catalysts that contain a dialkylphosphino moiety. Mechanistic studies suggest that the origin of this disparate catalyst behavior is a change in regioselectivity of migratory insertion of the acrylate comonomer as a function of the phosphine substituents. The best aryl-BPMO-palladium catalysts for these copolymns. were shown to undergo exclusively 2,1-insertion, and this high regioselectivity avoids formation of a poorly reactive palladacycle intermediate. Furthermore, the aryl-BPMO-palladium catalysts can copolymerize ethylene with other industrially important polar monomers.
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(e) Mitsushige, Y.; Yasuda, H.; Carrow, B. P.; Ito, S.; Kobayashi, M.; Tayano, T.; Watanabe, Y.; Okuno, Y.; Hayashi, S.; Kuroda, J.; Okumura, Y.; Nozaki, K. Methylene-Bridged Bisphosphine Monoxide Ligands for Palladium-Catalyzed Copolymerization of Ethylene and Polar Monomers. ACS Macro Lett. 2018, 7, 305– 311, DOI: 10.1021/acsmacrolett.8b00034
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14e
Methylene-Bridged Bisphosphine Monoxide Ligands for Palladium-Catalyzed Copolymerization of Ethylene and Polar Monomers
Mitsushige, Yusuke; Yasuda, Hina; Carrow, Brad P.; Ito, Shingo; Kobayashi, Minoru; Tayano, Takao; Watanabe, Yumiko; Okuno, Yoshishige; Hayashi, Shinya; Kuroda, Junichi; Okumura, Yoshikuni; Nozaki, Kyoko
ACS Macro Letters (2018), 7 (3), 305-311CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
A series of palladium complexes bearing a bisphosphine monoxide with a methylene linker, i.e., [κ2-P,O-(R12P)CH2P(O)R22]PdMe[(2,6-lutidine)][BArF4] (Pd/BPMO), were synthesized and evaluated as catalysts for the homopolymn. of ethylene and the copolymn. of ethylene and polar monomers. X-ray crystallog. analyses revealed that these Pd/BPMO complexes exhibit significantly narrower bite angles and longer Pd-O bonds than Pd/BPMO complexes bearing a phenylene linker, while maintaining almost const. Pd-P bond lengths. Among the complexes synthesized, menthyl-substituted complex 3f (R1 = (1R,2S,5R)-2-isopropyl-5-methylcyclohexan-1-yl; R2 = Me) showed the best catalytic performance in the homo- and copolymn. in terms of mol. wt. and polymn. activity. Meanwhile, complex 3e (R1 = t-Bu; R2 = Me) exhibited a markedly higher incorporation of comonomers in the copolymn. of ethylene and allyl acetate (≤12.0 mol %) or Me methacrylate (≤0.6 mol %). The catalytic system represents one of the first examples of late-transition-metal complexes bearing an alkylene-bridged bidentate ligand that afford high-mol.-wt. copolymers from the copolymn. of ethylene and polar monomers.
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Dashan, L.; Trippett, S. The ortho-lithiation of N, N,N′,N′-tetramethylphenylphosphonic diamide. Tetrahedron Lett. 1983, 24, 2039– 2040, DOI: 10.1016/S0040-4039(00)81838-9
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PPDA ligands with dialkylphosphino groups (i.e., 1a–1c) must be handled under an inert atmosphere.
There is no corresponding record for this reference.
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Falivene, L.; Credendino, R.; Poater, A.; Petta, A.; Serra, L.; Oliva, R.; Scarano, V.; Cavallo, L. SambVca 2. A Web Tool for Analyzing Catalytic Pockets with Topographic Steric Maps. Organometallics 2016, 35, 2286– 2293, DOI: 10.1021/acs.organomet.6b00371
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SambVca 2. A Web Tool for Analyzing Catalytic Pockets with Topographic Steric Maps
Falivene, Laura; Credendino, Raffaele; Poater, Albert; Petta, Andrea; Serra, Luigi; Oliva, Romina; Scarano, Vittorio; Cavallo, Luigi
Organometallics (2016), 35 (13), 2286-2293CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
Developing more efficient catalysts remains one of the primary targets of organometallic chemists. To accelerate reaching this goal, effective mol. descriptors and visualization tools can represent a remarkable aid. Here, we present a Web application for analyzing the catalytic pocket of metal complexes using topog. steric maps as a general and unbiased descriptor that is suitable for every class of catalysts. To show the broad applicability of our approach, we first compared the steric map of a series of transition metal complexes presenting popular mono-, di-, and tetracoordinated ligands and three classic zirconocenes. This comparative anal. highlighted similarities and differences between totally unrelated ligands. Then, we focused on a recently developed Fe(II) catalyst that is active in the asym. transfer hydrogenation of ketones and imines. Finally, we expand the scope of these tools to rationalize the inversion of enantioselectivity in enzymic catalysis, achieved by point mutation of three amino acids of mononuclear p-hydroxymandelate synthase.
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Yang, X.; Stern, C. L.; Marks, T. J. Cation-like homogeneous olefin polymerization catalysts based upon zirconocene alkyls and tris(pentafluorophenyl)borane. J. Am. Chem. Soc. 1991, 113, 3623– 3625, DOI: 10.1021/ja00009a076
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Cation-like homogeneous olefin polymerization catalysts based upon zirconocene alkyls and tris(pentafluorophenyl)borane
Yang, Xinmin; Stern, Charlotte L.; Marks, Tobin J.
Journal of the American Chemical Society (1991), 113 (9), 3623-5CODEN: JACSAT; ISSN:0002-7863.
The reaction of zirconocene dialkyls L2ZrMe2 (L = η5-C5H5, η5-1,2-Me2C5H3, η5-C5Me5) with B(C6F5)3 yields "cation-like" zirconocene complexes L2ZrMe+MeB(C6F5)3-. (1,2-Me2C5H3)2ZrMe+MeB(C6F5)3- was characterized crystallog. With the exception of a shortened Zr-Me distance [2.252(4) Å], the metrical parameters within the "bent sandwich" L2ZrMe+ cation are unexceptional. The cation interacts weakly via a highly unsym. Zr-(μ-Me)B bridge with the essentially tetrahedral MeB(C6F5)3- anion. The L2ZrMe+MeB(C6F5)3- complexes are active catalysts for olefin polymn. For ethylene polymn., Nt(1) ≈ 45 s-1 at 25°, 1 atm (∼4.5 × 106 g polyethylene/mol Zr h atm) to yield linear polyethylene. For propylene polymn at 25°, 1-5 atm, atactic polypropylene is produced with Nt(1) ≈ 4.2 s-1.
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Vela, J.; Lief, G. R.; Shen, Z.; Jordan, R. F. Ethylene Polymerization by Palladium Alkyl Complexes Containing Bis(aryl)phosphino-toluenesulfonate Ligands. Organometallics 2007, 26, 6624– 6635, DOI: 10.1021/om700869c
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Ethylene Polymerization by Palladium Alkyl Complexes Containing Bis(aryl)phosphino-toluenesulfonate Ligands
Vela, Javier; Lief, Graham R.; Shen, Zhongliang; Jordan, Richard F.
Organometallics (2007), 26 (26), 6624-6635CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
The reaction of L'2PdR2 (L' = pyridine (py), pyridazine; L'2 = cyclooctadiene, TMEDA) with 2-{(2-MeOC6H4)2P}-4-Me-benzenesulfonic acid ([PO-OMe]H, [1a]H) or 2-{(2-EtC6H4)2P}-4-Me-benzenesulfonic acid ([PO-Et]H, [1b]H) yields [PO-OMe]Pd(R)(L) (L = py, R = CH2SiMe3 (2a), CH2tBu (3a), CH2Ph (4a); R = Me, L = pyridazine (5a), py (6a), PPh3 (7a)) or [PO-Et]Pd(Me)(py) (6b). 2A and 6b have square-planar structures in which the alkyl group is cis to the phosphine and the [PO]Pd chelate rings are puckered. The reaction of 2a and 3a with B(C6F5)3 yields {[PO-OMe]Pd(R)}2 (R = CH2SiMe3 (8a), CH2tBu (9a)). 8A is a sulfonate-bridged dimer in the solid state. 2A, 6a, and 6b polymerize ethylene to linear polyethylene that contains low levels of Me branches, one C:C unit per chain (mostly 1- or 2-olefins), and Mn in the range 6000 to 19,000. 6A is slightly more active but produces polymers with similar mol. wt. and structure compared to 6b. 6A copolymerizes ethylene and hexene at low ethylene pressure (5 atm), but no α-olefin incorporation is obsd. at high pressure (30 atm). An ethylene polymn. mechanism is proposed, which involves insertion and chain transfer of [PO]Pd(R)(ethylene) species (I) and ethylene trapping and much slower chain-walking of the [PO]Pd(CH2CH2R) species formed by insertion of I. The crystal and mol. structures of 2a·1.5CH2Cl2, 6b and 8a·CH2Cl2 were detd. by x-ray crystallog.
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Cai, Z.; Shen, Z.; Zhou, X.; Jordan, R. F. Enhancement of Chain Growth and Chain Transfer Rates in Ethylene Polymerization by (Phosphine-sulfonate)PdMe Catalysts by Binding of B(C6F5)3 to the Sulfonate Group. ACS Catal. 2012, 2, 1187– 1195, DOI: 10.1021/cs300147c
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Enhancement of Chain Growth and Chain Transfer Rates in Ethylene Polymerization by (Phosphine-sulfonate)PdMe Catalysts by Binding of B(C6F5)3 to the Sulfonate Group
Cai, Zhengguo; Shen, Zhongliang; Zhou, Xiaoyuan; Jordan, Richard F.
ACS Catalysis (2012), 2 (6), 1187-1195CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
Binding of B(C6F5)3 to a sulfonate oxygen of (ortho-phosphino-arenesulfonate)PdR catalysts results in a 3-4 fold increase in the rate of chain growth and a larger increase in the rate of chain transfer. The reaction of (PO-Et)PdMe(py) (1a, [PO-Et]- = ortho-{(2-Et-Ph)2P}-para-toluenesulfonate) with 1 equiv of B(C6F5)3 yields the base-free dimer {(PO-Et)PdMe}2 (2a), in which the (PO-Et)PdMe units are linked through an eight-membered [PdSO2]2 ring. The reaction of {(PO-3,5-tBu2)PdMe}2(TMEDA) (4b; [PO-3,5-tBu2]- = ortho-{(3,5-tBu2-Ph)2P}-para-toluenesulfonate, TMEDA = N,N,N',N'-tetramethylethylenediamine) with BF3·Et2O yields the sol. base-free dimer {(PO-3,5-tBu2)PdMe}2 (2b), in which the (PO-3,5-tBu2)PdMe units are linked through a four-membered Pd2O2 ring. 2b reacts with 2 equiv of B(C6F5)3 to yield {[PO·B(C6F5)3-3,5-tBu2]PdMe}2 (5b, [PO·B(C6F5)3-3,5-tBu2]- = [2-{(3,5-tBu2-Ph)2P}-4-Me-C6H3SO2OB(C6F5)3]-), which crystallizes from Et2O as the monomeric complex [PO·B(C6F5)3-3,5-tBu2]PdMe(Et2O) (6b). In both 5b and 6b, the B(C6F5)3 binds to a sulfonate oxygen. In toluene soln. at 60 °C, 2b polymerizes ethylene (80 psi) to linear polyethylene with Mn = 3000, while the B(C6F5)3 adducts 5b and 6b yield ethylene oligomers (Mn = 160-170). 5b and 6b are 3-4 times more active than 2b. Similarly, 1a polymerizes ethylene to linear polyethylene with Mn = 29,300 (toluene, 80 °C, 435 psi), while 1a-4 B(C6F5)3 yields polymer with Mn = 2520 with a 4 fold increase in activity. 2b reacts with ethylene at 7 °C to form the ethylene adduct (PO-3,5-tBu2)PdMe(CH2=CH2) (7b) followed by multiple insertions to generate (PO-3,5-tBu2)Pd(CH2CH2)nCH3 species. In contrast, 5b reacts with ethylene to form [PO·B(C6F5)3-3,5-tBu2]PdMe(CH2=CH2) (8b) followed by insertion and β-H transfer to yield propene with subsequent catalytic formation of 1-butene and higher olefins. The rate of ethylene insertion of 8b is 3 times greater than that of 7b, consistent with the batch polymn. results. The polymer yield and mol. wt. data show that binding of B(C6F5)3 to 2b and 1a increases the chain transfer rates by a factor of 80 and 42, resp.
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Xie, T.; McAuley, K. B.; Hsu, J. C. C.; Bacon, D. W. Gas Phase Ethylene Polymerization: Production Processes, Polymer Properties, and Reactor Modeling. Ind. Eng. Chem. Res. 1994, 33, 449– 479, DOI: 10.1021/ie00027a001
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Gas Phase Ethylene Polymerization: Production Processes, Polymer Properties, and Reactor Modeling
Xie, Tuyu; McAuley, Kim B.; Hsu, James C. C.; Bacon, David W.
Industrial & Engineering Chemistry Research (1994), 33 (3), 449-79CODEN: IECRED; ISSN:0888-5885.
A review, with many refs., of relevant macroscopic and microscopic processes of gas-phase ethylene polymn., both chem. and phys., is given. The com. technol. development of gas-phase ethylene polymn. processes is illustrated through a selective survey of the patent literature. Both advantages and disadvantages of gas phase polymn. processes are addressed, and the challenges of lab. studies of gas-phase polymn. are also outlined. Physicochem. phenomena of ethylene polymn. using heterogeneous catalysts are discussed, including examn. of catalyst prepn., polymer morphol. development, and elementary chem. reactions. Metallocene-based catalysts and their kinetic performance for olefin polymns. are also discussed. The current state of the art for reactor modeling of polymn. rate, mol. wt. development, reactor dynamics, and resin-grade transition strategies is illustrated on the basis of the most recent academic studies. Finally, relationships between resin properties and polymer microstructures as well as characterization methods are described briefly. In particular, temp.-rising elution fractionation technol. is emphasized for characterization of ethylene copolymers. The fundamental issues involved in gas-phase ethylene polymn. and their interrelationships are also discussed in some detail.
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(a) Gates, D. P.; Svejda, S. A.; Oñate, E.; Killian, C. M.; Johnson, L. K.; White, P. S.; Brookhart, M. Synthesis of Branched Polyethylene Using (α-Diimine)nickel(II) Catalysts: Influence of Temperature, Ethylene Pressure, and Ligand Structure on Polymer Properties. Macromolecules 2000, 33, 2320– 2334, DOI: 10.1021/ma991234+
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22a
Synthesis of Branched Polyethylene Using (α-Diimine)nickel(II) Catalysts: Influence of Temperature, Ethylene Pressure, and Ligand Structure on Polymer Properties
Gates, Derek P.; Svejda, Steven A.; Onate, Enrique; Killian, Christopher M.; Johnson, Lynda K.; White, Peter S.; Brookhart, Maurice
Macromolecules (2000), 33 (7), 2320-2334CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
Detailed investigations of the polymn. of ethylene by (α-diimine)nickel(II) catalysts are reported. Effects of structural variations of the diimine ligand on catalyst activities, polymer mol. wts., and polymer microstructure are described. The pre-catalysts employed were [{(2,6-RR'C6H3)-N:C(Nap)-C(Nap):N-(2,6-RR'C6H3)}NiBr2] (Nap = 1,8-naphthdiyl) (4a, R = CF3, R' = H; 4b, R = CF3, R' = CH3; 4c, R = C6F5, R' = H; 4d, R = C6F5, R' = CH3; 4e, R = CH3, R' = H; 4f, R = R' = CH3; 4g, R = R' = CH(CH3)2), [{(2,6-C6H3(i-Pr)2)-N:C(CH2CH2CH2CH2)C:N-(2,6-C6H3(i-Pr)2)}NiBr2] (5), and [{(2,6-C6H3(i-Pr)2)-N:C(Et)C(Me):N-(2,6-C6H3(i-Pr)2)}NiBr2] (6). Active polymn. catalysts were formed in situ by combination of 4-6 with modified methylaluminoxane. In general, as the bulk and no. of ortho substituents increase, polymer mol. wts., turnover frequencies and extent of branching in the polyethylenes all increase. Effects of varying ethylene pressure and temp. on polymns. are also reported. The degree of branching in the polymers rapidly decreases with increasing ethylene pressure but mol. wts. are not markedly affected. Temp. increases result in more extensive branching and moderate redns. in mol. wts. Catalyst productivity decreases above 60° due to catalyst deactivation.
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(b) Tempel, D. J.; Johnson, L. K.; Huff, R. L.; White, P. S.; Brookhart, M. Mechanistic Studies of Pd(II)−α-Diimine-Catalyzed Olefin Polymerizations1. J. Am. Chem. Soc. 2000, 122, 6686– 6700, DOI: 10.1021/ja000893v
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22b
Mechanistic studies of Pd(II)-α-diimine-catalyzed olefin polymerizations
Tempel, Daniel J.; Johnson, Lynda K.; Huff, R. Leigh; White, Peter S.; Brookhart, Maurice
Journal of the American Chemical Society (2000), 122 (28), 6686-6700CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Mechanistic studies of olefin polymns. catalyzed by aryl-substituted α-diimine-Pd(II) complexes are presented. Syntheses of several cationic catalyst precursors, [(N N)Pd(CH3)(OEt2)]BAr'4 (N N = aryl-substituted α-diimine, Ar' = 3,5-(CF3)2C6H3), are described. X-ray structural analyses of [ArN:C(H)C(H):NAr]Pd(CH3)(Cl) and [ArN:C(Me)C(Me):NAr]Pd(CH3)2 (Ar = 2,6-(iPr)2C6H3) illustrate that o-aryl substituents crowd axial sites in these square planar complexes. Low-temp. NMR studies show that the alkyl olefin complexes, (N N)Pd(R)(olefin)+, are the catalyst resting states and that the barriers to migratory insertions lie in the range 17-19 kcal/mol. Following migratory insertion, the cationic palladium alkyl complexes (N N)Pd(alkyl)+ formed are β-agostic species which exhibit facile metal migration along the chain ("chain walking") via β-hydride elimination/readdn. reactions. Model studies using palladium- Pr and -iso-Pr systems provide mechanistic details of this process, which is responsible for introducing branching in the polyethylenes made by these systems. Decompn. of the cationic Me complexes (ArN NAr)Pd(CH3)(OEt2)+ (Ar = 2,6-(iPr)2C6H3, 2-tBuC6H4) occurs by C-H activation of β-C-H bonds of the ortho iso-Pr and tert-Bu substituents and loss of methane. The rate of associative exchange of free ethylene with bound ethylene in (N N)Pd(CH3)(C2H4)+ is retarded by bulky substituents. The relationship of these exchange expts. to chain transfer is discussed.
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23
(a) Camacho, D. H.; Salo, E. V.; Ziller, J. W.; Guan, Z. Cyclophane-Based Highly Active Late-Transition-Metal Catalysts for Ethylene Polymerization. Angew. Chem., Int. Ed. 2004, 43, 1821– 1825, DOI: 10.1002/anie.200353226
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23a
Cyclophane-based highly active late-transition-metal catalysts for ethylene polymerization
Camacho, Drexel H.; Salo, Eric V.; Ziller, Joseph W.; Guan, Zhibin
Angewandte Chemie, International Edition (2004), 43 (14), 1821-1825CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
Exploitation of the macrocyclic architecture of a cyclophane-based ligand provides new highly active catalysts with improved thermal stability for ethylene polymn. The strategic positioning of the metal center at the core of the cyclophane-based ligand is the key to the obsd. high activity and thermal stability, and to the high mol. wt. of the polyethylene.
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(b) Schmid, M.; Eberhardt, R.; Klinga, M.; Leskelä, M.; Rieger, B. New C2v- and Chiral C2-Symmetric Olefin Polymerization Catalysts Based on Nickel(II) and Palladium(II) Diimine Complexes Bearing 2,6-Diphenyl Aniline Moieties: Synthesis, Structural Characterization, and First Insight into Polymerization Properties. Organometallics 2001, 20, 2321– 2330, DOI: 10.1021/om010001f
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(c) Meinhard, D.; Wegner, M.; Kipiani, G.; Hearley, A.; Reuter, P.; Fischer, S.; Marti, O.; Rieger, B. New Nickel(II) Diimine Complexes and the Control of Polyethylene Microstructure by Catalyst Design. J. Am. Chem. Soc. 2007, 129, 9182– 9191, DOI: 10.1021/ja070224i
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23c
New Nickel(II) Diimine Complexes and the Control of Polyethylene Microstructure by Catalyst Design
Meinhard, Dieter; Wegner, Marcus; Kipiani, Georgy; Hearley, Andrew; Reuter, Peter; Fischer, Stefan; Marti, Othmar; Rieger, Bernhard
Journal of the American Chemical Society (2007), 129 (29), 9182-9191CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Starting from differently substituted boronic acids as versatile building block, new "ortho-aryl" α-diimine ligands a-h were synthesized in an easy, high-yielding route. Reaction of the complex precursor diacetylacetonato-nickel(II) with a trityl salt, like [CPh3][B(C6F5)4] or [CPh3][SbCl6], in the presence of the diimine ligands afford the monocationic, square planar complexes 2a-g in almost quant. yields. Suitable crystals (2d',e,f,g) were submitted for x-ray diffraction anal. A geometry model was developed to describe the orientation of ligand fragments around the nickel(II) center that influence the polymer microstructure. At elevated reaction temp. and pressure, and in the presence of hydrogen, 2a-e catalyze the homopolymn. of ethylene to give branched PE products ranging from HD- to LLD-PE grades. The polymn. results indicate the possibility of precise microstructure control depending on the particular complex substitution. Preliminary studies on material d. and mech. behavior by uniaxial stretching until failure point toward new material properties that can result from the simple ethylene monomer by catalyst design.
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(d) Moody, L. S.; Mackenzie, P. B.; Killian, C. M.; Lavoie, G. G.; Ponasik, J. A.; Barrett, A. G. M.; Smith, T. W.; Pearson, J. C. WO 0050470 August 31, 2000.
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(e) Rhinehart, J. L.; Brown, L. A.; Long, B. K. A Robust Ni(II) α-Diimine Catalyst for High Temperature Ethylene Polymerization. J. Am. Chem. Soc. 2013, 135, 16316– 16319, DOI: 10.1021/ja408905t
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23e
A Robust Ni(II) α Diimine Catalyst for High Temperature Ethylene Polymerization
Rhinehart, Jennifer L.; Brown, Lauren A.; Long, Brian K.
Journal of the American Chemical Society (2013), 135 (44), 16316-16319CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Sterically demanding NiII α-diimine precatalysts were synthesized utilizing 2,6-bis-(diphenyl-methyl)-4-Me aniline. When activated with methylaluminoxane, the catalyst NiBr2(ArNC-(Me)-C-(Me)NAr) (Ar = 2,6 bis-(diphenyl-methyl)-4-methylbenzene) was highly active, produced well-defined polyethylene at temps. up to 100° (Mw/Mn = 1.09-1.46), and demonstrated remarkable thermal stability at temps. appropriate for industrially used gas-phase polymns. (80-100°).
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(f) Liu, F.-S.; Hu, H.-B.; Xu, Y.; Guo, L.-H.; Zai, S.-B.; Song, K.-M.; Gao, H.-Y.; Zhang, L.; Zhu, F.-M.; Wu, Q. Thermostable α-Diimine Nickel(II) Catalyst for Ethylene Polymerization: Effects of the Substituted Backbone Structure on Catalytic Properties and Branching Structure of Polyethylene. Macromolecules 2009, 42, 7789– 7796, DOI: 10.1021/ma9013466
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23f
Thermostable α-Diimine Nickel(II) Catalyst for Ethylene Polymerization: Effects of the Substituted Backbone Structure on Catalytic Properties and Branching Structure of Polyethylene
Liu, Feng-Shou; Hu, Hai-Bin; Xu, Ying; Guo, Li-Hua; Zai, Shao-Bo; Song, Ke-Ming; Gao, Hai-Yang; Zhang, Ling; Zhu, Fang-Ming; Wu, Qing
Macromolecules (Washington, DC, United States) (2009), 42 (20), 7789-7796CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
On the basis of the strategy of promoting thermostability of α-diimine nickel catalyst by ligand backbone framework, a series of α-diimine nickel(II) complexes with bulky camphyl or diaryl-substituted backbones, [2,6-(R2)2C6H3-N=C(R1)-C(R1)=N-2,6-(R2)2C6H3]NiBr2 (1a, R1 = Ph, R2 = CH3; 2a, R1 = 4-methylphenyl, R2 = CH3; 3a, R1 = 4-fluorophenyl, R2 = CH3; 4a, R1 = camphyl, R2 = CH3; 4b, R1 = camphyl, R2 = i-Pr), were synthesized and used as catalyst precursors for ethylene polymn. Crystallog. anal. revealed that the bulky camphyl backbone has a valid steric-effect on the nickel center by blocking the axial site for the metal center and suppressing the potential rotation of the CAr-N bond. Ethylene polymns. catalyzed by these nickel α-diimine complexes activated by MAO were systematically investigated and the influences of the substituted backbones as well as reaction temp. on the catalytic activity, mol. wt. and branching structure of the polymers were evaluated. It was found that the catalysts contg. a camphyl backbone have excellent thermal stability and polymer structure control for ethylene polymns. Even at 80 °C, the 4b/MAO system still kept high activity and relatively stable kinetics and produced high mol. wt. polyethylene. Moreover, the branching degrees and branched chain distribution of the polyethylenes obtained by the complex could also be controlled by tuning the reaction temp.
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(g) Rhinehart, J. L.; Mitchell, N. E.; Long, B. K. Enhancing α-Diimine Catalysts for High-Temperature Ethylene Polymerization. ACS Catal. 2014, 4, 2501– 2504, DOI: 10.1021/cs500694m
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23g
Enhancing α-Diimine Catalysts for High-Temperature Ethylene Polymerization
Rhinehart, Jennifer L.; Mitchell, Nolan E.; Long, Brian K.
ACS Catalysis (2014), 4 (8), 2501-2504CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
Sterically demanding 2,6-bis(diphenylmethyl)-4-methylaniline was condensed onto acenaphthenequinone via an aminoalane intermediate and metalated using nickel(II) dibromide dimethoxyethane adduct to yield bis[(2,6-dibenzhydryl-4-methylimino) acenaphthene]dibromo nickel(II). This α-diimine precatalyst was examd. for high-temp. ethylene polymn. and is thermally robust at temps. as high as 90°, demonstrating enhanced activity as compared with related catalysts. Furthermore, the resultant polymers displayed increased melting transitions as compared with those produced using catalysts with identical N-aryl moieties appended to nonacenaphthenequinone-derived ligand backbones.
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(a) Younkin, T. R.; Connor, E. F.; Henderson, J. I.; Friedrich, S. K.; Grubbs, R. H.; Bansleben, D. A. Neutral, Single-Component Nickel(II) Polyolefin Catalysts That Tolerate Heteroatoms. Science 2000, 287, 460– 462, DOI: 10.1126/science.287.5452.460
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24a
Neutral, single-component nickel(II) polyolefin catalysts that tolerate heteroatoms
Younkin, Todd R.; Connor, Eric F.; Henderson, Jason I.; Friedrich, Stefan K.; Grubbs, Robert H.; Bansleben, Donald A.
Science (Washington, D. C.) (2000), 287 (5452), 460-462CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
A family of catalysts has been developed whose members are tolerant of both heteroatoms and less pure starting materials. These heteroatom-tolerant neutral late transition metal complexes are in fact highly active systems that produce high-mol.-wt. polyethylene, polymerize functionalized olefins, and require no cocatalyst.
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(b) Wang, C.; Friedrich, S.; Younkin, T. R.; Li, R. T.; Grubbs, R. H.; Bansleben, D. A.; Day, M. W. Neutral Nickel(II)-Based Catalysts for Ethylene Polymerization. Organometallics 1998, 17, 3149– 3151, DOI: 10.1021/om980176y
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24b
Neutral Nickel(II)-Based Catalysts for Ethylene Polymerization
Wang, Chunming; Friedrich, Stefan; Younkin, Todd R.; Li, Robert T.; Grubbs, Robert H.; Bansleben, Donald A.; Day, Michael W.
Organometallics (1998), 17 (15), 3149-3151CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
Neutral salicylaldiminato Ni(II) complexes having the structure I, where R = H, tert-Bu, Ph, 9-phenanthrenyl, or 9-anthracenyl and R1 = H, MeO, or NO2, were synthesized, and their structure was confirmed by an x-ray anal. of I (R = 9-anthracenyl and R1 = H). These compds. are active catalysts for the polymn. of ethylene under mild conditions in the presence of a phosphine scavenger such as Ni(COD)2 or BPh3.
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25
The reaction time was arbitrarily long and held constant for all larger scale reactions.
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26
Wucher, P.; Goldbach, V.; Mecking, S. Electronic Influences in Phosphinesulfonato Palladium(II) Polymerization Catalysts. Organometallics 2013, 32, 4516– 4522, DOI: 10.1021/om400297x
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26
Electronic Influences in Phosphinesulfonato Palladium(II) Polymerization Catalysts
Wucher, Philipp; Goldbach, Verena; Mecking, Stefan
Organometallics (2013), 32 (16), 4516-4522CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
To study the influence of electronics on catalytic polymn. properties independent from sterics, phosphinesulfonato Pd(II) complexes bearing remotely located substituents on the nonchelating P-bound aryls [κ2-(P,O)-(4-R-2-anisyl)2PC6H4SO2O]Pd(Me)(dmso) (1a-e-dmso: 1a, R = CF3; 1b, R = Cl; 1c, R = H; 1d, R = CH3; 1e, R = OCH3) were prepd. The electron-poor complex 1a-dmso (4-CF3) undergoes the fastest insertion of Me acrylate (MA) and is the most active for ethylene polymn. The polyethylene mol. wt. increases by a factor of 2 for the more electron rich complex 1e-dmso (4-OCH3) (Mn = 17 × 103 vs 8 × 103 for 1a-dmso (4-CF3)). MA/ethylene copolymn. expts. revealed that the MA incorporation ratio and copolymer mol. wts. are largely independent of the electronic nature of the remote substituents. These trends were further confirmed by studies of two mixed P-aryl/-alkyl complexes 1f-dmso ([κ2-(2,4,6-(OMe)3C6H2)(tBu)PC6H4SO2O]Pd(Me)(dmso)) and 1g-dmso ([κ2-(C6H5)(tBu)PC6H4SO2O]Pd(Me)(dmso)). In ethylene/MA copolymn., 1f-dmso affords a significantly higher mol. wt. polymer with reasonable MA incorporation (Mn = 12 × 103 and 7.7 mol % MA) and activities similar to those obsd. for complexes 1a-e-dmso.
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Inagaki, N.; Tasaka, S.; Hibi, K. In Plasma Surface Modification of Polymers: Relevance to Adhesion; Strobel, M., Lyons, C. S., Mittal, K. L., Eds.; VSP: Utrecht, The Netherlands, 1994; p 280.
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28
(a) Kim, M.-H.; Phillips, P. J. Nonisothermal melting and crystallization studies of homogeneous ethylene/α-olefin random copolymers. J. Appl. Polym. Sci. 1998, 70, 1893– 1905, DOI: 10.1002/(SICI)1097-4628(19981205)70:10<1893::AID-APP4>3.0.CO;2-6
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28a
Nonisothermal melting and crystallization studies of homogeneous ethylene/α-olefin random copolymers
Kim, Man-Ho; Phillips, Paul J.
Journal of Applied Polymer Science (1998), 70 (10), 1893-1905CODEN: JAPNAB; ISSN:0021-8995. (John Wiley & Sons, Inc.)
A study of nonequil. melting, nonisothermal, and isothermal crystn. behavior of ethylene-1-octene random copolymers (EO), produced using metallocene catalysts has carried out. As branch (or defect) content increases, the nonisothermal and isothermal crystn. rates, melting temps., and heats of fusion decrease. There is also a branch length effect on melting temp. depression, the melting temp. depression of EO random copolymers with hexyl branches were significantly larger than those of ethylene-1-butene (EB) and ethylene-1-propene (EP) copolymers having Et and Me branches, resp. The melting temps. of homogeneous random copolymers, have been found to be always lower than those of fractions of heterogeneous copolymers, having approx. the same branch content and mol. wt. Hence, defect distribution in copolymer systems is at least as important a parameter as the defect content.
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(b) Bensason, S.; Minick, J.; Moet, A.; Chum, S.; Hiltner, A.; Baer, E. Classification of homogeneous ethylene-octene copolymers based on comonomer content. J. Polym. Sci., Part B: Polym. Phys. 1996, 34, 1301– 1315, DOI: 10.1002/(SICI)1099-0488(199605)34:7<1301::AID-POLB12>3.0.CO;2-E
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28b
Classification of homogeneous ethylene-octene copolymers based on comonomer content
Bensason, S.; Minick, J.; Moet, A.; Chum, S.; Hiltner, A.; Baer, E.
Journal of Polymer Science, Part B: Polymer Physics (1996), 34 (7), 1301-15CODEN: JPBPEM; ISSN:0887-6266. (Wiley)
Ethylene-octene copolymers prepd. by INSITE constrained geometry catalyst technol. present a broad range of solid-state structures from highly cryst., lamellar morphologies to the granular morphol. of low-crystallinity copolymers. As the comonomer content increases, the accompanying tensile behavior changes from necking and cold drawing typical of a semicryst. thermoplastic to uniform drawing and high recovery characteristic of an elastomer. Although changes in morphol. features and tensile properties occur gradually with increasing comonomer content, the combined body of observations from melting behavior, morphol., dynamic mech. response, yielding, and large-scale deformation suggest a classification scheme with four distinct categories. Materials with densities >0.93 g/mL, type IV, exhibit a lamellar morphol. with a well developed spherulitic superstructure. Type III polymers with densities 0.91-0.93 g/mL have thinner lamellae and smaller spherulites. Type II materials with densities 0.89-0.91 g/mL have a mixed morphol. of small lamellae and bundled crystals. These materials can form very small spherulites. Type I copolymers with densities <0.89 g/mL have no lamellae or spherulites. Fringed micellar or bundled crystals are inferred from the low degree of crystallinity, the low melting temp., and the granular, nonlamellar morphol.
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(c) Chen, H. Y.; Chum, S. P.; Hiltner, A.; Baer, E. Comparison of semicrystalline ethylene–styrene and ethylene–octene copolymers based on comonomer content. J. Polym. Sci., Part B: Polym. Phys. 2001, 39, 1578– 1593, DOI: 10.1002/polb.1130
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28c
Comparison of semicrystalline ethylene-styrene and ethylene-octene copolymers based on comonomer content
Chen, H. Y.; Chum, S. P.; Hiltner, A.; Baer, E.
Journal of Polymer Science, Part B: Polymer Physics (2001), 39 (14), 1578-1593CODEN: JPBPEM; ISSN:0887-6266. (John Wiley & Sons, Inc.)
The structure and properties of homogeneous copolymers of ethylene and styrene (ES) and ethylene and octene (EO) were compared. Semicryst. copolymers presented a broad spectrum of solid-state structures from highly cryst., lamellar morphologies to the granular, fringed micellar morphol. of low-crystallinity copolymers. The combined observations from d., thermal behavior, and morphol. with primarily at. force microscopy revealed that the cryst. phase depended on the amt. of comonomer but was not strongly affected by whether the comonomer was styrene or octene. This was consistent with the exclusion of both comonomers from the crystal. However, ES and EO showed strong differences in the amorphous phase. ES had a much higher β-relaxation temp. than EO, which was attributed to restrictions on chain mobility imposed by the bulky Ph side group. The deformation behavior of ES and EO exhibited the same trends with comonomer content, from necking and cold drawing typical of a semicryst. thermoplastic to uniform drawing and high recovery characteristic of an elastomer. Aspects of deformation behavior that depended on crystallinity, such as yielding and cold drawing, were detd. primarily by comonomer content. However, the difference in the β-relaxation temp. resulted in much higher strain hardening of ES than EO. This was particularly evident with low-crystallinity, elastomeric copolymers. A classification scheme for semicryst. copolymers based on comonomer content, previously developed for EO, was remarkably applicable to ES.
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29
Billow, B. S.; McDaniel, T. J.; Odom, A. L. Quantifying ligand effects in high-oxidation-state metal catalysis. Nat. Chem. 2017, 9, 837, DOI: 10.1038/nchem.2843
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29
Quantifying ligand effects in high-oxidation-state metal catalysis
Billow, Brennan S.; McDaniel, Tanner J.; Odom, Aaron L.
Nature Chemistry (2017), 9 (9), 837-842CODEN: NCAHBB; ISSN:1755-4330. (Nature Publishing Group)
Catalysis by high-valent metals such as titanium(IV) impacts our lives daily through reactions like olefin polymn. In any catalysis, optimization involves a careful choice of not just the metal but also the ancillary ligands. Because these choices dramatically impact the electronic structure of the system and, in turn, catalyst performance, new tools for catalyst development are needed. Understanding ancillary ligand effects is arguably one of the most crit. aspects of catalyst optimization and, while parameters for phosphines have been used for decades with low-valent systems, a comparable system does not exist for high-valent metals. A new electronic parameter for ligand donation, derived from expts. on a high-valent chromium species, is now available. Here, we show that the new parameters enable quant. detn. of ancillary ligand effects on catalysis rate and, in some cases, even provide mechanistic information. Analyzing reactions in this way can be used to design better catalyst architectures and paves the way for the use of such parameters in a host of high-valent processes.
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30
Hartmann, F.; Dahlems, T.; Mootz, D. Crystal structure of hexamethylphosphoric triamide,(C₂H₆N)₃PO. Z. Kristallogr. - New Cryst. Struct. 1998, 213, 667– 668, DOI: 10.1524/ncrs.1998.213.14.667
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31
Gholivand, K.; Mahzouni, H. R.; Esrafili, M. D. How do phosphoramides compete with phosphine oxides in lanthanide complexation? Structural, electronic and energy aspects at ab initio and DFT levels. Theor. Chem. Acc. 2010, 127, 539– 550, DOI: 10.1007/s00214-010-0743-5
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31
How do phosphoramides compete with phosphine oxides in lanthanide complexation? Structural, electronic and energy aspects at ab initio and DFT levels
Gholivand, Khodayar; Mahzouni, Hamid Reza; Esrafili, Mehdi D.
Theoretical Chemistry Accounts (2010), 127 (5-6), 539-550CODEN: TCACFW; ISSN:1432-2234. (Springer)
Novel comparison of the structural, electronic and energy aspects of lanthanide complexes of model phosphoramides (PAs) with those of phosphine oxides (POs), phosphate esters (PEs) and phosphoryl trihalides (PHs) has been carried out by ab initio and DFT calcns. Atoms in Mols. (AIM) and Natural Bonding Orbital (NBO) analyses were performed to understand the electronic structure of ligands L and related complexes, L-Ln3+. NBO anal. indicates that the neg. charge on phosphoryl oxygen (OP) and the p character of the phosphoryl lone pair, Lp(OP), increase in the order PH < PE < PO < PA. Pos. charge of the lanthanide cation in PA complexes is less than those of PH, PE and PO complexes, due to the more intense ligand to metal charge transfer (LMCT). The metal-ligand distance decreases in the order PH > PE > PO > PA, which is confirmed by the results of AIM anal. Charge d. at the bond crit. point of L-Ln3+ follows the sequence PH < PE < PO < PA. The results of the Energy Decompn. Anal. (EDA) indicate that the donative interaction and LMCT increases in order PH < PO < PE < PA. The effect of basis set superposition error (BSSE) on the L···Ln3+ interaction energies was also studied in detail at DFT, MP2 and CCSD(T) levels using the counterpoise (CP) method. Trends in the CP-cor. L-Ln3+ bond energies are in good accordance with the optimized OP···Ln3+ distances. The results show that the difference between CP-cor. and uncorrected interaction energies in PA complexes is larger than those in the others, because PAs are more deformable. It is depicted that PAs are comparable with POs in lanthanide complexation.
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32
The spectroscopic data of the anionic Pd complexes were sensitive to the identity of the countercation. This effect complicates quantitative comparison of charged and neutral Pd complexes.
There is no corresponding record for this reference.
33
Dipp = 2,6-diisopropylphenyl; BIAN = bisaryliminoacenaphthene.
There is no corresponding record for this reference.
34
Mahabiersing, T.; Luyten, H.; Nieuwendam, R. C.; Hartl, F. Synthesis, Spectroscopy and Spectroelectrochemistry of Chlorocarbonyl {1,2-Bis[(2,6-diisopropylphenyl)imino]acenaphthene-κ2-N,N’}rhodium(I). Collect. Czech. Chem. Commun. 2003, 68, 1687– 1709, DOI: 10.1135/cccc20031687
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Synthesis, spectroscopy and spectroelectrochemistry of chlorocarbonyl{1,2-bis[(2,6-diisopropylphenyl)imino]-acenaphthene-κ2-N,N'}rhodium(I)
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Collection of Czechoslovak Chemical Communications (2003), 68 (9), 1687-1709CODEN: CCCCAK; ISSN:0010-0765. (Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic)
Reaction of dinuclear [{Rh(CO)2}2(μ-Cl)2] with an α-diimine ligand, 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (iPr2Ph-bian), produces square-planar [RhCl(CO)(iPr2Ph-bian)]. For the 1st time, 2:1 and 1:1 α-diimine/dimer reactions yielded the same product. The rigidity of iPr2Ph-bian together with its flexible electronic properties and steric requirements of the 2,6-diisopropyl substituents on the benzene rings allow rapid closure of a chelate bond and replacement of a CO ligand instead of chloride. A resonance Raman study of [RhCl(CO)(iPr2Ph-bian)] revealed a predominant Rh-to-bian charge transfer (MLCT) character of electronic transitions in the visible spectral region. The stabilization of [RhCl(CO)(iPr2Ph-bian)] in lower oxidn. states by the π-acceptor iPr2Ph-bian ligand was studied in situ by UV-visible, IR and EPR spectroelectrochem. at variable temps. The construction of the novel UV-visible-NIR-IR low-temp. OTTLE cell used in these studies is described in the last part of the paper.
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35
Nickel oligomerization catalysts used for the Shell Higher Olefin Process typically possess chelating phosphine-carboxylate or phosphine-O-enolate ligands.
There is no corresponding record for this reference.

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Abstract
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Scheme 1
Scheme 1. Common Functional Polyolefin Synthesis Methods
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Scheme 2
Scheme 2. General Considerations of Catalyst Steric Effects on Insertion Copolymerizations
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Figure 1
Figure 1. Topographical steric maps of (P^O)Pd(CH₃)Cl complexes 2g and 4–8 in which the Pd atom defines the center of the xyz coordinate system, the metal square plane defines the xz-plane and the z-axis bisects the O–Pd–P angle. Pd(CH₃)Cl fragment omitted from each plot. Colors indicate occupied space in the +z direction toward the covalent ligands (red) or −z direction toward the dative ligands (blue).
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Figure 2
Figure 2. Batch ethylene (3.5 bar) polymerization catalyzed by 3g, 3i, or 9–11 (1.25 μmol) in toluene (300 mL) at 90 °C. Methylaluminoxane (1.25 mmol) added to the reaction with 9; Ni(cod)₂ (1.25 mmol) added to reaction with 10.
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Figure 3
Figure 3. Assignment of characteristic ¹³C NMR resonances in poly(ethylene-co-methyl acrylate) in Table 3, entry 1. See SI for full spectrum (* = galvinoxyl).
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Figure 4
Figure 4. Relationship between melt temperature and comonomer content in f-PE generated by 3i (Table 3, entries 3–8 and 10–17). Literature values for hydrophobic analogues shown in open circles.(28)
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Figure 5
Figure 5. Systematic variation in O ligand trans influence in (P^O)Pd(CH₃)Cl complexes 2g and 4–8 determined from solid state data, and atomic charge in analogous (P^O)Rh(CO)Cl complexes 12–17, determined by NBO analysis. Error bars indicate ±3σ.
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Figure 6
Figure 6. ORTEP diagram of 2g. Thermal ellipsoids are shown at 50% probability. Hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): Pd–P2 2.2181(4), Pd–O1 2.163(1), Pd–C1 2.034(2), Pd–Cl1 2.3824(4), P1–O1 1.490(1), P2–Pd–O1 89.02(3), C23–N2–C26 114.8(1), C23–N2–P1 120.8(1), C26–N2–P1 123.9(1), C29–N1–C32 113.2(1), C29–N1–P1 113.3(1), C32–N1–P1 129.0(1).
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Scheme 3
Scheme 3. Mechanistic Pathways Controlling Polar Group Distribution in Functional Polyolefins
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  A review with 110 refs. on copolymn. using Group IV catalysts, protecting group chem., and late transition metal catalysts.
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  Late-Metal Catalysts for Ethylene Homo- and Copolymerization
  Ittel, Steven D.; Johnson, Lynda K.; Brookhart, Maurice
  Chemical Reviews (Washington, D. C.) (2000), 100 (4), 1169-1203CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
  A review with 427 refs. on the use of late transition metal complexes as catalysts for ethylene polymn.
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  Coordination-Insertion Copolymerization of Fundamental Polar Monomers
  Nakamura, Akifumi; Ito, Shingo; Nozaki, Kyoko
  Chemical Reviews (Washington, DC, United States) (2009), 109 (11), 5215-5244CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
  A review. In this review, two topics regarding the transition-metal-catalyzed coordination-insertion copolymn. of fundamental polar monomers have been comprehensively reviewed: one is copolymn. of polar vinyl monomers with nonpolar olefins and the other is copolymn. of olefins and imines with carbon monoxide. The products thus obtained by the copolymns. possess unique structures that have never been achieved by the conventional methods or required multi step synthesis.
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  Late transition metal catalysts for the copolymerization of olefins and polar monomers
  Goodall, Brian L.
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  A review. The evolution of olefin polymn. catalysis since Karl Ziegler's and Giulio Natta's Nobel Prize-winning discoveries in the mid-1950s has involved a prolific interplay of polymer science and organometallic chem. and led to the development and com. deployment of catalysts that rival the activities of enzymes and systems, yielding polyolefins possessing structures and phys. properties that allow them to be applied in countless applications worldwide. In contrast, com. processes for the copolymn. of ethylene with polar monomers such as acrylate and vinyl acetate still exclusively employ free radical processes. This chapter reviews recent developments in the catalytic copolymn. of ethylene and these polar comonomers, including well-defined, single-component catalysts capable of copolymg. (for example) acrylates and vinyl ethers to high mol. wt., linear, random copolymers.
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  5e
  Coordination Polymerization of Polar Vinyl Monomers by Single-Site Metal Catalysts
  Chen, Eugene Y.-X.
  Chemical Reviews (Washington, DC, United States) (2009), 109 (11), 5157-5214CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
  A review on significant advances in the coordination polymn. of polar vinyl monomers by discrete lanthanide and early and later metal catalysts for the past 16 years, esp. in the area of stereochem. control of polymn., producing a large body of publications. Addnl., major advances in the coordination copolymn. of vinyl monomers with nonpolar olefins by late metal catalysts were also reviewed.
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  (f) Nakamura, A.; Anselment, T. M. J.; Claverie, J.; Goodall, B.; Jordan, R. F.; Mecking, S.; Rieger, B.; Sen, A.; van Leeuwen, P. W. N. M.; Nozaki, K. Ortho-Phosphinobenzenesulfonate: A Superb Ligand for Palladium-Catalyzed Coordination–Insertion Copolymerization of Polar Vinyl Monomers. Acc. Chem. Res. 2013, 46, 1438– 1449, DOI: 10.1021/ar300256h
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  5f
  Ortho-Phosphonebenzenesulfonate: A Superb Ligand for Palladium-Catalyzed Coordination-Insertion Copolymerization of Polar Vinyl Monomers
  Nakamura, Akifumi; Anselment, Timo M. J.; Claverie, Jerome; Goodall, Brian; Jordan, Richard F.; Mecking, Stefan; Rieger, Bernhard; Sen, Ayusman; van Leeuwen, Piet W. N. M.; Nozaki, Kyoko
  Accounts of Chemical Research (2013), 46 (7), 1438-1449CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
  A review. Ligands, Lewis bases that coordinate to the metal center in a complex, can completely change the catalytic behavior of the metal center. In this Account, we summarize new reactions enabled by a single class of ligands, phosphine-sulfonates (ortho-phosphinobenzenesulfonates). Using their palladium complexes, we have developed four unusual reactions, and three of these have produced novel types of polymers. In one case, we have produced linear high-mol. wt. polyethylene, a type of polymer that group 10 metal catalysts do not typically produce. Secondly, complexes using these ligands catalyzed the formation of linear poly(ethylene-co-polar vinyl monomers). Before the use of phosphine-sulfonate catalysts, researchers could only produce ethylene/polar monomer copolymers that have different branched structures rather than linear ones, depending on whether the polymers were produced by a radical polymn. or a group 10 metal catalyzed coordination polymn. Thirdly, these phosphine-sulfonate catalysts produced nonalternating linear poly(ethylene-co-carbon monoxide). Radical polymn. gives ethylene-rich branched ethylene/CO copolymers. Prior to the use of phosphine-sulfonates, all of the metal catalyzed processes gave completely alternating ethylene/carbon monoxide copolymers. Finally, we produced poly(polar vinyl monomer-alt-carbon monoxide), a copolymn. of common polar monomers with carbon monoxide that had not been previously reported. Although researchers have often used sym. bidentate ligands such as diimines for the polymn. catalysis, phosphine-sulfonates are unsym., contg. two nonequivalent donor units, a neutral phosphine, and an anionic sulfonate. We discuss the features that make this ligand unique. In order to understand all of the new reactions facilitated by this special ligand, we discuss both the steric effect of the bulky phosphines and electronic effects. We provide a unified interpretation of the unique reactivity by considering of the net charge and the enhanced back donation in the phosphine-sulfonate complexes.
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6. 6
  (a) Johnson, L. K.; Killian, C. M.; Brookhart, M. New Pd(II)- and Ni(II)-Based Catalysts for Polymerization of Ethylene and.alpha.-Olefins. J. Am. Chem. Soc. 1995, 117, 6414– 6415, DOI: 10.1021/ja00128a054
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  6a
  New Pd(II)- and Ni(II)-Based Catalysts for Polymerization of Ethylene and α-Olefins
  Johnson, Lynda K.; Killian, Christopher M.; Brookhart, Maurice
  Journal of the American Chemical Society (1995), 117 (23), 6414-15CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Palladium(II) and nickel(II) complexes [(ArN:C(R)C(R):NAr)M(CH3)(OEt2)]+BAr4'- (M = Pd, Ni; Ar' = 3,5-C6H3(CF3)2) stabilized by sterically bulky diimine ligands are active catalysts for the polymn. of ethylene and α-olefins to high molar mass polymers. The microstructure of these polymers can be varied through systematic variations of temp., pressure, and ligand substituents to give, for example, ethylene homopolymers that range from linear semicryst. materials to highly branched, amorphous oils. These observations and low-temp. NMR studies, including the spectroscopic detection of an alkyl olefin complex as the catalyst resting state, provide the basis for a mechanistic understanding of these late metal polymn. catalysts.
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  6b
  Copolymerization of Ethylene and Propylene with Functionalized Vinyl Monomers by Palladium(II) Catalysts
  Johnson, Lynda K.; Mecking, Stefan; Brookhart, Maurice
  Journal of the American Chemical Society (1996), 118 (1), 267-8CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Ethylene and propylene were copolymd. with acrylates to give high molar mass polymers using Pd diimine complexes as initiators. The copolymers are highly branched, the acrylate comonomer being incorporated predominantly at the ends of branches. Low-temp. NMR was used to study the mechanism of initiation.
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  (c) Guan, Z.; Popeney, C. S. Recent Progress in Late Transition Metal α-Diimine Catalysts for Olefin Polymerization. Top. Organomet. Chem. 2009, 26, 179– 220, DOI: 10.1007/978-3-540-87751-6_6
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  Recent progress in late transition metal α-diimine catalysts for olefin polymerization
  Guan, Zhibin; Popeney, Chris S.
  Topics in Organometallic Chemistry (2009), 26 (Metal Catalysts in Olefin Polymerization), 179-220CODEN: TORCFV; ISSN:1436-6002. (Springer GmbH)
  A review. This chapter reviews recent development of cationic α-diimine nickel(II) and palladium(II) complexes for olefin polymn. The contributions of ligand structure to the catalytic polymn. properties of late metal complexes are particularly emphasized in this review. Unique among transition metal polymn. systems, these late metal complexes also catalyze the formation of branched polymers. The mechanisms of elemental reaction steps for these catalytic systems are discussed. The Pd(II) system also permits the copolymn. of ethylene and α-olefins with various polar comonomers, esp. acrylates. Finally, a discussion of new research in ligand design is provided. A new class of cyclophane-based ligands has exhibited high thermal stability. The mechanism of copolymns. is significantly altered, leading to elevated incorporations of polar monomers. An axial-donation hemilabile cyclic ligand is also discussed, the Ni(II) and Pd(II) complexes of which afford high mol. wt. polyethylene despite their reduced steric bulk.
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  Designing late-transition metal catalysts for olefin insertion polymerization and copolymerization
  Camacho, Drexel H.; Guan, Zhibin
  Chemical Communications (Cambridge, United Kingdom) (2010), 46 (42), 7879-7893CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
  A review. The innovation of polyolefin with unique architecture, compn. and topol. continues to inspire polymer chemists. An exciting recent direction in the polyolefin field is the design of new catalysts based on late-transition metals. In this review, we highlight recent developments in rationally designing late-transition metal catalysts for olefin polymn. The examples described in this review showcase the power of the design of well-defined late-metal catalysts for tailored polyolefin synthesis, which may usher in a new era in the polymer industry.
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7. 7
  (a) Watson, M. D.; Wagener, K. B. Tandem Homogeneous Metathesis/Heterogeneous Hydrogenation: Preparing Model Ethylene/CO2 and Ethylene/CO Copolymers. Macromolecules 2000, 33, 3196– 3201, DOI: 10.1021/ma991595p
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  7b
  Ethylene/Vinyl Acetate Copolymers via Acyclic Diene Metathesis Polymerization. Examining the Effect of "Long" Precise Ethylene Run Lengths
  Watson, Mark D.; Wagener, Kenneth B.
  Macromolecules (2000), 33 (15), 5411-5417CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
  Tandem acyclic diene metathesis (ADMET) polymn./catalytic hydrogenation was used to synthesize copolymers modeling ethylene/vinyl acetate (EVA) materials. A series of four sequence-ordered ethylene-co-vinyl acetate copolymers were prepd. possessing precisely defined ethylene run lengths from 18 to 26 carbons. Use of the well-defined ADMET reaction in combination with a quant. olefin-hydrogen technique generates well-defined EVA's, all of which are semicryst. with a linear relationship between ethylene run length and melting temp. All polymers except that with the lowest ethylene run length are film and fiber forming.
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  (c) Watson, M. D.; Wagener, K. B. Functionalized Polyethylene via Acyclic Diene Metathesis Polymerization: Effect of Precise Placement of Functional Groups. Macromolecules 2000, 33, 8963– 8970, DOI: 10.1021/ma0010332
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  Synthesis and catalyst issues associated with ADMET polymerization
  Schwendeman, John E.; Church, A. Cameron; Wagener, Kenneth B.
  Advanced Synthesis & Catalysis (2002), 344 (6+7), 597-613CODEN: ASCAF7; ISSN:1615-4150. (Wiley-VCH Verlag GmbH)
  A review on acyclic diene metathesis (ADMET) which is a flexible approach for the prodn. of diverse polymeric materials. The advent of well defined catalysts and the simplification of lab. techniques has made the ADMET reaction useful for many applications, such as polyolefin model studies and the synthesis of org./inorg. hybrid polymers, telechelics, copolymers, conjugated polymers, liq. cryst. polymers, and amino acid-based chiral polymers. Many of the polymer architectures that have been produced using ADMET cannot be made by other means.
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  7e
  Ring-Opening Metathesis Polymerization of Functionalized Cyclooctenes by a Ruthenium-Based Metathesis Catalyst
  Hillmyer, Marc A.; Laredo, Walter R.; Grubbs, Robert H.
  Macromolecules (1995), 28 (18), 6311-16CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
  The ring-opening metathesis polymn. (ROMP) of a variety of 5-substituted cyclooctenes by the well-defined metathesis catalyst (PCy3)2Cl2RuCHCHCPh2 (I) was accomplished. Direct polymn. of functionalized monomers allowed the incorporation of alc., ketone, ester, or bromine functionality along the polymer backbone. The polymers were obtained in moderate-to-good yields. The attempted polymn. of epoxy- and cyano-substituted cyclooctenes by I failed. Structures of the polymers were confirmed by IR, 1H NMR, and 13C NMR spectroscopies. The mol. wt. of acetate-contg. polymer was controlled by varying the monomer-to-catalyst ratio and by the addn. of a chain-transfer agent to the polymn. soln. Hydrogenation of the acetate deriv. gave the corresponding ethylene/vinyl copolymer. The thermal properties of the polymers are reported.
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  7g
  Synthesis and characterization of stereoregular ethylene-vinyl alcohol copolymers made by ring-opening metathesis polymerization
  Scherman, Oren A.; Walker, Ron; Grubbs, Robert H.
  Macromolecules (2005), 38 (22), 9009-9014CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
  Regioregular as well as stereoregular ethylene-vinyl alc. (EVOH) copolymers are prepd. by ring-opening metathesis polymn. (ROMP) with ruthenium catalysts. Sym. cyclooctenediol monomers were protected as acetates, carbonates, or acetonides to temporarily increase ring strain as well as impart soly. to the monomer. Polymer mol. wts. could be easily controlled by either varying the monomer-to-catalyst ratio or by the addn. of a chain transfer agent. Hydrogenation and subsequent deprotection of the ROMP polymers afforded the EVOH materials in high yields, and the structures were confirmed by 1H NMR and 13C NMR spectroscopies. Thermal properties of the corresponding EVOH copolymers were detd. and suggest that differences in diol stereochem. significantly affect the polymer morphol.
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8. 8
  (a) Murray, R. E. U.S. Patent 4,689,437 August 25, 1987.
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  (c) Drent, E.; van Dijk, R.; van Ginkel, R.; van Oort, B.; Pugh, R. I. Palladium catalysed copolymerisation of ethene with alkylacrylates: polar comonomer built into the linear polymer chain. Chem. Commun. 2002, 744– 745, DOI: 10.1039/b111252j
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  Palladium catalysed copolymerisation of ethene with alkylacrylates: polar comonomer built into the linear polymer chain
  Drent, Eite; van Dijk, Rudmer; van Ginkel, Roel; van Oort, Bart; Pugh, Robert. I.
  Chemical Communications (Cambridge, United Kingdom) (2002), (7), 744-745CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
  Copolymn. of ethene and alkyl acrylates is catalyzed by palladium modified with di(2-methoxyphenyl)phosphinobenzene-2-sulfonic acid (DOPPBS); a linear polymer is produced in which acrylate units are incorporated into the polyethylene backbone.
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9. 9
  (a) Noda, S.; Nakamura, A.; Kochi, T.; Chung, L. W.; Morokuma, K.; Nozaki, K. Mechanistic Studies on the Formation of Linear Polyethylene Chain Catalyzed by Palladium Phosphine–Sulfonate Complexes: Experiment and Theoretical Studies. J. Am. Chem. Soc. 2009, 131, 14088– 14100, DOI: 10.1021/ja9047398
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  9a
  Mechanistic Studies on the Formation of Linear Polyethylene Chain Catalyzed by Palladium Phosphine-Sulfonate Complexes: Experiment and Theoretical Studies
  Noda, Shusuke; Nakamura, Akifumi; Kochi, Takuya; Chung, Lung Wa; Morokuma, Keiji; Nozaki, Kyoko
  Journal of the American Chemical Society (2009), 131 (39), 14088-14100CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Linear polyethylene propagation starting from Pd phosphine-sulfonate complexes, Pd(CH3)(L)(Ar2PC6H4SO3) (L = 2,6-lutidine, Ar = o-MeOC6H4 (2a) and L = pyridine, Ar = Ph (2b)), was studied both exptl. and theor. Exptl., highly linear polyethylene was obtained with Pd(CH3)(L)(Ar2PC6H4SO3) complexes 2a and 2b. Formation of a long alkyl-substituted palladium complex (3) was detected as a result of ethylene oligomerization on a palladium center starting from methylpalladium complex. Addnl., well-defined Et and Pr complexes (6Et and 6Pr) were synthesized as stable n-alkyl palladium complexes. In spite of the existence of β-hydrogens, the β-hydride elimination to give 1-alkenes was very slow or negligible in all cases. On the other hand, isomerization of 1-hexene in the presence of a methylpalladium/phosphine-sulfonate complex 2a indicated that this catalyst system actually undergoes β-hydride elimination and reinsertion to release internal alkenes. On the theor. side, the relative energies were calcd. for intermediates and transition states for chain-growth, chain-walking, and chain-transfer on the basis of the starting model complex Pd(n-C3H7)(pyridine)(o-Me2PC6H4SO3) (8). First, cis/trans isomerization process via the Berry's pseudorotation was proposed for the Pd/phosphine-sulfonate system. The second oxygen atom of sulfonate group is involved in the isomerization process as the associative ligand, which is one of the most unique natures of the sulfonate group. Chain propagation was suggested to take place from the less stable alkylPd(ethylene) complex 10' with the TS of 27.4/27.7 ((E+ZPC)/G) kcal/mol. Possible β-hydride elimination was suggested to occur under low concn. of ethylene: the highest-energy transition state to override for β-hydride elimination was either >37.4/25.3 kcal/mol (TS(9-12)) or 29.1/27.4 kcal/mol (TS(8'-9') to reach 12'). The ethylene insertion to the iso-alkylpalladium species (14') is allowed via a TS of 28.6/29.1 kcal/mol (TS(14'-15')), slightly higher in energy than that for the normal-alkylpalladium species (TS(10'-11')). Easy chain transfer was suggested to proceed from the more stable PdH(olefin) complex 12' if β-hydride elimination to 12' does take place. Thus, the prodn. of linear polyethylene with high mol. wt. under ethylene pressure suggests that the cis and trans PdH(alkene)(phosphine-sulfonate) complexes (12 and 12') are merely accessible in the presence of excess amt. of ethylene.
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  9c
  Elucidating the key role of phosphine-sulfonate ligands in palladium-catalyzed ethylene polymerization: effect of ligand structure on the molecular weight and linearity of polyethylene
  Nakano, Ryo; Chung, Lung Wa; Watanabe, Yumiko; Okuno, Yoshishige; Okumura, Yoshikuni; Ito, Shingo; Morokuma, Keiji; Nozaki, Kyoko
  ACS Catalysis (2016), 6 (9), 6101-6113CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  The mechanism of linear polyethylene formation catalyzed by palladium/phosphine-o-sulfonate hemilabile complex and the effect of the ligand structure on the catalytic performance, such as linearity and mol. wt. of the polyethylene, were reinvestigated theor. and exptl. We used dispersion-cor. d. functional theory (DFT-D3) to study the entire mechanism of polyethylene formation from (R2PC6H4SO3)PdMe(2,6-lutidine) (R = Me, t-Bu) and elucidated the key steps that det. the mol. wt. and linearity of the polyethylene. The alkylpalladium ethylene complex is the key intermediate for both linear propagation and β-hydride elimination from the growing polymer chain. On the basis of the key species, the effects of substituents on the phosphorus atom (R = t-Bu, i-Pr, Cy, Men, Ph, 2-MeOC6H4, biAr) were further investigated theor. to explain the exptl. results in a comprehensive manner. Thus, the exptl. trend of mol. wts. of polyethylene could be correlated to the ΔΔG⧺ value between (i) the transition state of linear propagation and (ii) the transition state of the path for ethylene dissocn. leading to β-hydride elimination. Moreover, the exptl. behavior of the catalysts under varied ethylene pressure was well explained by our computation on the small set of key species elucidated from the entire mechanism. In our addnl. exptl. investigations, [(o-Ani2PC6H4SO3)PdH(PtBu3)] catalyzed a hydrogen/deuterium exchange reaction between ethylene and MeOD. The deuterium incorporation from MeOD into the main chain of polyethylene, therefore, can be explained by the incorporation of deuterated ethylene formed by a small amt. of Pd-H species. These insights into the palladium/phosphine-sulfonate system provide a comprehensive understanding of how the phosphine-sulfonate ligands function to produce linear polyethylene.
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  .
  (d) Szabo, M. J.; Jordan, R. F.; Michalak, A.; Piers, W. E.; Weiss, T.; Yang, S.-Y.; Ziegler, T. Polar Copolymerization by a Palladium–Diimine-Based Catalyst. Influence of the Catalyst Charge and Polar Substituent on Catalyst Poisoning and Polymerization Activity. A Density Functional Theory Study. Organometallics 2004, 23, 5565– 5572, DOI: 10.1021/om049485g
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  9d
  Polar Copolymerization by a Palladium-Diimine-Based Catalyst. Influence of the Catalyst Charge and Polar Substituent on Catalyst Poisoning and Polymerization Activity. A Density Functional Theory Study
  Szabo, Miklos J.; Jordan, Richard F.; Michalak, Artur; Piers, Warren E.; Weiss, Thomas; Yang, Sheng-Yong; Ziegler, Tom
  Organometallics (2004), 23 (23), 5565-5572CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  Copolymn. of ethylene with electroneg. alkenes catalyzed by palladium diimine complex was explored by DFT calcns. Combined gradient-cor. d. functional theory and mol. mechanics (QM/MM) was used to investigate the copolymn. of ethylene with the CH2:CHX (2a-f; X = H, Me, CN, COOMe, OCOMe, Cl). The cationic complex [(ArN:CR2CR3:NAr-κN,κN')PdMe]+ (Ar = 2,6-iPr2C6H3, 1, R2 = H) and its neutral and anionic analogs (R2 = BH3-, R3 = H and R2 = R3 = BH3-, resp.) were used as catalysts. The consecutive insertion steps of CH2:CHX into the Pd-Me bond and of ethylene into the Pd-C(X)HCH2CH3 bond were investigated. Focus was put on the role of the X functional groups and the effect of the cationic, neutral, and anionic environments on the Pd(II)-diimine system. Calcns. were performed on the CH2:CHX monomers, model catalysts, precursor π-complexes, and σ-complexes of the monomers, as well as the chelate and H-agostic insertion products. The transition state of the insertion reaction and the corresponding activation energy was detd. for both investigated insertion steps. The results show that the X group has only a minor effect on the insertion of the CH2:CHX monomers into the Pd-CH3 bond. On the other hand, the barrier for insertion of ethylene into the Pd-CHXR bond revealed an increase with the electron-withdrawing ability of X. The application of neutral and anionic catalysts leads to a preference for π-complexation over σ-complexation of the polar monomers. Unfortunately, for an anionic model system the barriers for the first and second insertion are significantly increased for ethylene, whereas the first insertion barrier for the polar monomers only is moderately increased. Thus, while anionic catalysts are highly tolerant toward polar monomers, they are nearly inactive toward ethylene insertion.
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10. 10
  Johnson, A. M.; Contrella, N. D.; Sampson, J. R.; Zheng, M.; Jordan, R. F. Allosteric Effects in Ethylene Polymerization Catalysis. Enhancement of Performance of Phosphine-Phosphinate and Phosphine-Phosphonate Palladium Alkyl Catalysts by Remote Binding of B(C6F5)3. Organometallics 2017, 36, 4990– 5002, DOI: 10.1021/acs.organomet.7b00815
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  10
  Allosteric Effects in Ethylene Polymerization Catalysis. Enhancement of Performance of Phosphine-Phosphinate and Phosphine-Phosphonate Palladium Alkyl Catalysts by Remote Binding of B(C6F5)3
  Wilders, Alison M.; Contrella, Nathan D.; Sampson, Jessica R.; Zheng, Mingfang; Jordan, Richard F.
  Organometallics (2017), 36 (24), 4990-5002CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  Remote binding of B(C6F5)3 to (PPO)PdMeL (L = pyridine or lutidine) or {(PPO)PdMe}2 ethylene polymn. catalysts that contain phosphine-arenephosphinate or phosphine-arenephosphonate ligands (PPO- = [1-PAr2-2-PR'O2-C6H4]-: Ar = R' = Ph (1a); Ar = Ph, R' = OEt (1b); Ar = Ph, R' = OiPr (1c); Ar = 2-OMe-C6H4, R' = OiPr (1d)) significantly increases the catalyst activity and the mol. wt. of the polyethylene (PE) product. In the most favorable case, in situ conversion of (1d)PdMe(py) to the base-free adduct {1d·B(C6F5)3}PdMe increases the ethylene polymn. activity from 9.8 to 5700 kg mol-1 h-1 and the Mn of the PE product from 9030 to 99,200 Da (80°, 410 psi). X-ray structural data, trends in ligand lability, and comparative studies of BF3 activation suggest that these allosteric effects are primarily electronic in origin. The B(C6F5)3 binding enhances the chain growth rate (Rgrowth) by increasing the degree of pos. charge on the Pd center. This effect does not result in the large increase in the chain transfer rate (Rtransfer) and concomitant redn. in PE mol. wt. seen in previous studies of analogous (PO)PdRL catalysts that contain phosphine-arenesulfonate ligands, because of the operation of a dissociative chain transfer process, which is inhibited by the increased charge at Pd.
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11. 11
  (a) Long, B. K.; Eagan, J. M.; Mulzer, M.; Coates, G. W. Semi-Crystalline Polar Polyethylene: Ester-Functionalized Linear Polyolefins Enabled by a Functional-Group-Tolerant, Cationic Nickel Catalyst. Angew. Chem., Int. Ed. 2016, 55, 7106– 7110, DOI: 10.1002/anie.201601703
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  11a
  Semi-Crystalline Polar Polyethylene: Ester-Functionalized Linear Polyolefins Enabled by a Functional-Group-Tolerant, Cationic Nickel Catalyst
  Long, Brian K.; Eagan, James M.; Mulzer, Michael; Coates, Geoffrey W.
  Angewandte Chemie, International Edition (2016), 55 (25), 7106-7110CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  A dibenzobarrelene-bridged, α-diimine NiII catalyst (rac-3) was synthesized and shown to have exceptional behavior for the polymn. of ethylene. The catalyst afforded high mol. wt. polyethylenes with narrow dispersities and degrees of branching much lower than those made by related α-diimine nickel catalysts. Catalyst rac-3 demonstrated living behavior at room temp., produced linear polyethylene (Tm=135 °C) at -20 °C, and, most importantly, was able to copolymerize ethylene with the biorenewable polar monomer Me 10-undecenoate to yield highly linear ester-functionalized polyethylene.
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  (b) Xin, B. S.; Sato, N.; Tanna, A.; Oishi, Y.; Konishi, Y.; Shimizu, F. Nickel Catalyzed Copolymerization of Ethylene and Alkyl Acrylates. J. Am. Chem. Soc. 2017, 139, 3611– 3614, DOI: 10.1021/jacs.6b13051
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  11b
  Nickel Catalyzed Copolymerization of Ethylene and Alkyl Acrylates
  Xin, Bruce S.; Sato, Naomasa; Tanna, Akio; Oishi, Yasuo; Konishi, Yohei; Shimizu, Fumihiko
  Journal of the American Chemical Society (2017), 139 (10), 3611-3614CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Ni(II) complexes bearing an o-bis(aryl)phosphinophenolate ligand were synthesized as catalysts for copolymn. of ethylene and alkyl acrylates. When the P-bound aryl group was 2,6-dimethoxyphenyl group, one of the oxygen atoms in the methoxy groups coordinated to the nickel center on its apical position. This complex was a highly active catalyst without any activators to give highly linear and high mol. wt. copolymers. The structures of the copolymers were detd. by 1H and 13C NMR to clarify that the alkyl acrylate comonomers were incorporated in the main chain and that the structures of the copolymers were significantly influenced by the structure of the aryl group in the ligand.
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  .
  (c) Connor, E. F.; Younkin, T. R.; Henderson, J. I.; Hwang, S.; Grubbs, R. H.; Roberts, W. P.; Litzau, J. J. Linear functionalized polyethylene prepared with highly active neutral Ni(II) complexes. J. Polym. Sci., Part A: Polym. Chem. 2002, 40, 2842– 2854, DOI: 10.1002/pola.10370
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  11c
  Linear functionalized polyethylene prepared with highly active neutral Ni(II) complexes
  Connor, Eric F.; Younkin, Todd R.; Henderson, Jason I.; Hwang, Sonjong; Grubbs, Robert H.; Roberts, William P.; Litzau, Johnathan J.
  Journal of Polymer Science, Part A: Polymer Chemistry (2002), 40 (16), 2842-2854CODEN: JPACEC; ISSN:0887-624X. (John Wiley & Sons, Inc.)
  Neutral Ni(II) salicylaldimine catalysts (pendant ligand = NCMe or PPh3) were used to copolymerize ethylene with monomers contg. esters, alcs., anhydrides, and amides and yielded linear functionalized polyethylene in a single step. α-Olefins and polycyclic olefin comonomers carrying functionality were directly incorporated into the polyethylene backbone by the catalysts without any cocatalyst, catalyst initiator, or other disturber compds. The degree of comonomer incorporation was related to the monomer structure: tricyclononenes > norbornenes > α-olefins. A wide range of comonomer incorporation, up to 30 mol %, was achieved while a linear polyethylene structure was maintained under mild conditions (40°C, 100 psi ethylene). Results from the characterization of the copolymers by soln. and solid-state NMR techniques, thermal anal., and mol. wt. demonstrated that the materials contained a relatively pure microstructure for a functionalized polyethylene that was prepd. in one step with no catalyst additive.
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12. 12
  (a) Kacker, S.; Jiang, Z.; Sen, A. Alternating Copolymers of Functional Alkenes with Carbon Monoxide. Macromolecules 1996, 29, 5852– 5858, DOI: 10.1021/ma960255q
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  There is no corresponding record for this reference.
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  (b) Mecking, S.; Johnson, L. K.; Wang, L.; Brookhart, M. Mechanistic Studies of the Palladium-Catalyzed Copolymerization of Ethylene and α-Olefins with Methyl Acrylate. J. Am. Chem. Soc. 1998, 120, 888– 899, DOI: 10.1021/ja964144i
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  12b
  Mechanistic Studies of the Palladium-Catalyzed Copolymerization of Ethylene and α-Olefins with Methyl Acrylate
  Mecking, Stefan; Johnson, Lynda K.; Wang, Lin; Brookhart, Maurice
  Journal of the American Chemical Society (1998), 120 (5), 888-899CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Mechanistic aspects of palladium-catalyzed insertion copolymn s. of ethylene (I) and α-olefins with Me acrylate to give high molar-mass polymers are described. Complexes [(N N)Pd(CH2)3C(O)OMe]BAr'4 or [(N N)Pd(CH3)(L)]BAr'4 (L = OEt2, NCMe,NCAr'') (N N ≡ ArN:C(R)-C(R):NAr, e.g., Ar ≡ 2,6-C6H3(i-Pr)2, R ≡ H, Me; Ar' ≡ 3,5-C6H3(CF3)2) with bulky substituted α-diimine ligands were used as catalyst precursors. The copolymers are highly branched, the acrylate comonomer being incorporated predominantly at the ends of branches as -CH2CH2C(O)OMe groups. The effects of reaction conditions and catalyst structure on the copolymn. reaction are rationalized. Low-temp. NMR studies show that migratory insertion in the η2-Me acrylate (MA) complex [(N N)PdMe{H2C:CHC(O)OMe}]+ occurs to give initially the 2,1-insertion product [(N N)PdCH(CH2CH3)C(O)OMe]+, which rearranges stepwise to yield the final product upon warming to -20°. Activation parameters (ΔH⧧ = 12.1 ± 1.4 kcal/mol and ΔS⧧ = -14.1 ± 7.0 eu) were detd. for the conversion of 5a to 6a. Rates of I homopolymn. obsd. in preparative-scale polymns. (1.2 s-1 at 25°, ΔG⧧ = 17.4 kcal/mol for 2b) correspond well with low-temp. NMR kinetic data for migratory insertion of I in [(N N)Pd{(CH2)2nMe}(H2C:CH2)]+. Relative binding affinities of olefins to the metal center were also studied. For [(N N)PdMe(H2C:CH2)]+ + MA .dblharw. 5a + H2C:CH2, Keq(-95 °C) = (1.0 ± 0.3) × 10-6 was detd. Combination of the above studies provides a mechanistic model that agrees well with acrylate incorporations obsd. in copolymn. expts. Data obtained for equil. 2 + H2C:CHR'' .dblharw. [(N N)Pd{(CH2)3C(O)OMe}(H2C:CHR'')]+ (R' ≡ H, Me, nC4H9) shows that chelating coordination of the carbonyl group is favored over olefin coordination at room temp. Formation of chelates analogous to 2 during the copolymn. is assumed to render the subsequent monomer insertion a turnover-limiting step.
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  (c) Kochi, T.; Yoshimura, K.; Nozaki, K. Synthesis of anionic methylpalladium complexes with phosphine-sulfonate ligands and their activities for olefin polymerization. Dalton Trans. 2006, 25– 27, DOI: 10.1039/B512452M
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  (d) Luo, S.; Vela, J.; Lief, G. R.; Jordan, R. F. Copolymerization of Ethylene and Alkyl Vinyl Ethers by a (Phosphine- sulfonate)PdMe Catalyst. J. Am. Chem. Soc. 2007, 129, 8946– 8947, DOI: 10.1021/ja072562p
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  12d
  Copolymerization of Ethylene and Alkyl Vinyl Ethers by a (Phosphine- sulfonate)PdMe Catalyst
  Luo, Shuji; Vela, Javier; Lief, Graham R.; Jordan, Richard F.
  Journal of the American Chemical Society (2007), 129 (29), 8946-8947CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  The neutral complex (PO-OMe)PdMe(py) (1, PO-OMe = 2-[bis(2-OMe-Ph)phosphino]-4-methylbenzenesulfonate) polymerizes ethylene to a linear polymer with 1-10 branches/103 carbons (mostly methyl) and vinyl and 2-olefin unsatd. end groups. Complex 1 copolymerizes ethylene and alkyl vinyl ethers (CH2:CHOR, 2a-c: R = tBu (a), Et (b), Bu (c)) in toluene at 60-100 °C to linear copolymers contg. up to 7 mol % of vinyl ether. Addn. of CH2:CHOR lowers the polymn. rate and the polymer mol. wt. The copolymer structures are similar to that of homopolyethylene generated under the same conditions. The major comonomer units are -CH2CH(OR)CH2- (I) and CH3CH(OR)CH2- (II). The ethylene/CH2:CHOR copolymers can be converted to hydroxy- and bromo-polyethylene. The results of control expts. argue against cationic and radical mechanisms for the copolymn., and an insertion mechanism is proposed. The reaction of base-free (PO-OMe)PdMe with CH2:CHOEt yields the adduct (PO-OMe)PdMe(CH2:CHOEt), which undergoes 1,2-insertion to generate (PO-OMe)PdCH2CH(OEt)Me.
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  (e) Weng, W.; Shen, Z.; Jordan, R. F. Copolymerization of Ethylene and Vinyl Fluoride by (Phosphine-Sulfonate)Pd(Me)(py) Catalysts. J. Am. Chem. Soc. 2007, 129, 15450– 15451, DOI: 10.1021/ja0774717
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  12e
  Copolymerization of Ethylene and Vinyl Fluoride by (Phosphine-Sulfonate)Pd(Me)(py) Catalysts
  Weng, Wei; Shen, Zhongliang; Jordan, Richard F.
  Journal of the American Chemical Society (2007), 129 (50), 15450-15451CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  The PdII complexes [PO]Pd(Me)(py) (1a-c; [PO] = 2-PAr2-4-Me-benzenesulfonate; Ar = 2-Et-Ph (a), 2-OMe-Ph (b), Ph (c)) catalyze the copolymn. of ethylene and vinyl fluoride in toluene at 80° to produce fluorinated polyethylene. Low levels (0.1-0.5 mol%) of vinyl fluoride incorporation are obsd. At 80 psi vinyl fluoride and 220 psi ethylene, 1a produces a linear copolymer with Mw = 35,000, Mw/Mn = 3.0, and 0.17 mol% vinyl fluoride incorporation. At a total pressure of 300 psi, increasing the proportion of vinyl fluoride in the feed results in an increase in the level of vinyl fluoride incorporation (to 0.45 mol %) and a decrease in polymer yield and mol. wt. 1A is more reactive and produces higher mol. wt. copolymer than 1b, c, but all three catalysts incorporate similar levels of vinyl fluoride. Control expts. rule out a radical copolymn. mechanism, and an insertion mechanism is proposed.
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  (f) Kochi, T.; Noda, S.; Yoshimura, K.; Nozaki, K. Formation of Linear Copolymers of Ethylene and Acrylonitrile Catalyzed by Phosphine Sulfonate Palladium Complexes. J. Am. Chem. Soc. 2007, 129, 8948– 8949, DOI: 10.1021/ja0725504
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  12f
  Formation of Linear Copolymers of Ethylene and Acrylonitrile Catalyzed by Phosphine Sulfonate Palladium Complexes
  Kochi, Takuya; Noda, Shusuke; Yoshimura, Kenji; Nozaki, Kyoko
  Journal of the American Chemical Society (2007), 129 (29), 8948-8949CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Linear copolymers of ethylene and acrylonitrile were prepd. using palladium complexes bearing phosphine-sulfonate bidentate ligands. Acrylonitrile units located in the linear polyethylene backbones were detected for the first time by 13C NMR spectroscopy. Catalyst systems employing isolated palladium complexes such as 3 showed much higher activity for the copolymn. than the in situ generation procedures, and mol. wt. of the copolymers and acrylonitrile incorporation were dependent on the palladium complexes. Obtained linear copolymers of ethylene and acrylonitrile melt at higher temp. than branched copolymers.
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  (g) Guironnet, D.; Roesle, P.; Rünzi, T.; Göttker-Schnetmann, I.; Mecking, S. Insertion Polymerization of Acrylate. J. Am. Chem. Soc. 2009, 131, 422– 423, DOI: 10.1021/ja808017n
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  12g
  Insertion Polymerization of Acrylate
  Guironnet, Damien; Roesle, Philipp; Ruenzi, Thomas; Goettker-Schnetmann, Inigo; Mecking, Stefan
  Journal of the American Chemical Society (2009), 131 (2), 422-423CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Multiple insertions of acrylate in copolymn. with ethylene, and an insertion homo-oligomerization of Me acrylate were obsd. for the first time. Key to these findings, and to mechanistic insights reported, are labile-substituted complexes as catalyst precursors.
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  (h) Borkar, S.; Newsham, D. K.; Sen, A. Copolymerization of Ethene with Styrene Derivatives, Vinyl Ketone, and Vinylcyclohexane Using a (Phosphine–sulfonate)palladium(II) System: Unusual Functionality and Solvent Tolerance. Organometallics 2008, 27, 3331– 3334, DOI: 10.1021/om800237r
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  12h
  Copolymerization of Ethene with Styrene Derivatives, Vinyl Ketone, and Vinylcyclohexane Using a (Phosphine-sulfonate)palladium(II) System: Unusual Functionality and Solvent Tolerance
  Borkar, Sachin; Newsham, David K.; Sen, Ayusman
  Organometallics (2008), 27 (14), 3331-3334CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  A (phosphine-sulfonate)palladium(II) system [Me(pyridine)Pd(O3SC6H4(P(C6H4OMe-2)2)-2)] catalyzes the copolymn. of ethene with a variety of styrene derivs., including those with O functionalities. The copolymns. also proceed in protic solvents, including H2O, allowing metal-mediated emulsion copolymn. of ethene and styrene.
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  (i) Ito, S.; Munakata, K.; Nakamura, A.; Nozaki, K. Copolymerization of Vinyl Acetate with Ethylene by Palladium/Alkylphosphine–Sulfonate Catalysts. J. Am. Chem. Soc. 2009, 131, 14606– 14607, DOI: 10.1021/ja9050839
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  12i
  Copolymerization of Vinyl Acetate with Ethylene by Palladium/Alkylphosphine-Sulfonate Catalysts
  Ito, Shingo; Munakata, Kagehiro; Nakamura, Akifumi; Nozaki, Kyoko
  Journal of the American Chemical Society (2009), 131 (41), 14606-14607CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Coordination copolymn. of vinyl acetate (VAc) with ethylene, leading to linear copolymers that possess in-chain -CH2CH(OAc)- units, has been accomplished using novel palladium complexes bearing alkylphosphine-sulfonate ligands.
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  (j) Guironnet, D.; Caporaso, L.; Neuwald, B.; Göttker-Schnetmann, I.; Cavallo, L.; Mecking, S. Mechanistic Insights on Acrylate Insertion Polymerization. J. Am. Chem. Soc. 2010, 132, 4418– 4426, DOI: 10.1021/ja910760n
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  12j
  Mechanistic Insights on Acrylate Insertion Polymerization
  Guironnet, Damien; Caporaso, Lucia; Neuwald, Boris; Goetker-Schnetmann, Inigo; Cavallo, Luigi; Mecking, Stefan
  Journal of the American Chemical Society (2010), 132 (12), 4418-4426CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Complexes [{(P and O)PdMe}n] (1n; P and O = κ2-P,O-Ar2PC6H4SO2O with Ar = 2-MeOC6H4) are a single-component precursor of the (P and O)PdMe fragment devoid of addnl. coordinating ligands, which also promotes the catalytic oligomerization of acrylates. Exposure of 1n to Me acrylate afforded the two diastereomeric chelate complexes [(P and O)Pd{κ2-C,O-CH(C(O)OMe)CH2CH(C(O)OMe)CH2CH3}] (3-meso and 3-rac) resulting from two consecutive 2,1-insertions of Me acrylate into the Pd-Me bond with the same or opposite stereochem., resp., in a 3:2 ratio as demonstrated by comprehensive NMR spectroscopic studies and single crystal X-ray diffraction. These six-membered chelate complexes are direct key models for intermediates of acrylate insertion polymn., and also ethylene-acrylate copolymn. to high acrylate content copolymers. Studies of the binding of various substrates (pyridine, dmso, ethylene and Me acrylate) to 3-meso and 3-rac show that hindered displacement of the chelating carbonyl moiety by π-coordination of incoming monomer significantly retards, but does not prohibit, polymn. For 3-meso,3-rac + C2H4 ↹ 3-meso-C2H4,3-rac-C2H4 an equil. const. K(353 K) ≈ 2 × 10-3 L mol-1 was estd. Reaction of 3-meso, 3-rac with Me acrylate afforded higher insertion products [(P and O)Pd(C4H6O2)nMe] (n = 3, 4) as obsd. by electrospray ionization mass spectrometry (ESI-MS). Theor. studies by DFT methods of consecutive acrylate insertion provide relative energies of intermediates and transition states, which are consistent with the aforementioned exptl. observations, and give detailed insights to the pathways of multiple consecutive acrylate insertions. Acrylate insertion into 3-meso,3-rac is assocd. with an overall energy barrier of ca. 100 kJ mol-1.
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  (k) Rünzi, T.; Fröhlich, D.; Mecking, S. Direct Synthesis of Ethylene–Acrylic Acid Copolymers by Insertion Polymerization. J. Am. Chem. Soc. 2010, 132, 17690– 17691, DOI: 10.1021/ja109194r
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  12k
  Direct Synthesis of Ethylene-Acrylic Acid Copolymers by Insertion Polymerization
  Ruenzi, Thomas; Froehlich, Dominik; Mecking, Stefan
  Journal of the American Chemical Society (2010), 132 (50), 17690-17691CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Neutral palladium(II) phosphinesulfonato polymn. catalysts were found to be stable toward carboxylic acid moieties and to enable direct linear copolymn. of ethylene with acrylic acid.
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  (l) Kryuchkov, V. A.; Daigle, J.-C.; Skupov, K. M.; Claverie, J. P.; Winnik, F. M. Amphiphilic Polyethylenes Leading to Surfactant-Free Thermoresponsive Nanoparticles. J. Am. Chem. Soc. 2010, 132, 15573– 15579, DOI: 10.1021/ja104182w
  [ACS Full Text ], [CAS], Google Scholar
  12l
  Amphiphilic Polyethylenes Leading to Surfactant-Free Thermoresponsive Nanoparticles
  Kryuchkov, Vladimir A.; Daigle, Jean-Christophe; Skupov, Kirill M.; Claverie, Jerome P.; Winnik, Francoise M.
  Journal of the American Chemical Society (2010), 132 (44), 15573-15579CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Linear copolymers of ethylene and acrylic acid (PEAA) were prepd. by catalytic polymn. of ethylene and tert-Bu acrylate followed by hydrolysis of the ester groups. The copolymers contained COOH groups inserted into the cryst. unit cell with formation of intramol. hydrogen-bonds, as established on the basis of differential scanning calorimetry (DSC), Fourier-transform IR spectroscopy (FTIR), and X-ray diffraction (XRD) studies. A solvent-exchange protocol, with no added surfactant, converted a soln. in THF of a PEAA sample contg. 12 mol % of acrylic acid (AA) into a colloidally stable aq. suspension of nanoparticles. Transmission electron microscopy (TEM), dynamic light scattering (DLS), and high sensitivity differential scanning calorimetry (HS-DSC) were used to characterize the nanoparticles. They are single crystals of elongated shape with a polar radius of 49 nm (σ = 15 nm) and an equatorial radius of 9 nm (σ = 3 nm) stabilized in aq. media via carboxylate groups located preferentially on the particle/water interface. The PEAA (AA: 12 mol %) nanoparticles dispersed in aq. media exhibited a remarkable reversible thermoresponsive behavior upon heating/cooling from 25 to 80 °C.
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  (m) Friedberger, T.; Wucher, P.; Mecking, S. Mechanistic Insights into Polar Monomer Insertion Polymerization from Acrylamides. J. Am. Chem. Soc. 2012, 134, 1010– 1018, DOI: 10.1021/ja207110u
  [ACS Full Text ], [CAS], Google Scholar
  12m
  Mechanistic Insights into Polar Monomer Insertion Polymerization from Acrylamides
  Friedberger, Tobias; Wucher, Philipp; Mecking, Stefan
  Journal of the American Chemical Society (2012), 134 (2), 1010-1018CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  N-Iso-Pr acrylamide (NIPAM), N,N-di-Me acrylamide (DMAA), and 2-acetamidoethyl acrylate (AcAMEA) were copolymd. with ethylene employing [(P%O)PdMe(DMSO)] (1-DMSO; P%O = κ2-P,O-Ar2PC6H4SO2O with Ar = 2-MeOC6H4) as a catalyst precursor. Inhibition studies with nonpolymerizable polar additives show that reversible κ-O-coordination of free amide retards polymn. significantly. Retardation of polymn. increases in the order Et acetate « Me Et sulfone < acetonitrile < N,N-dimethylacetamide ≈ N-methylacetamide ≈ propionic acid < dimethylsulfoxide. Pseudo-first-order rate consts. for the insertion into 1-DMSO were detd. to increase in the order DMAA < AcAMEA < NIPAM < Me acrylate. Exposure of 1-DMSO to NIPAM resulted in the formation of consecutive insertion products [(P%O)Pd(C6H11NO2)nMe] (n ≤ 3), as detd. by electrospray ionization mass spectrometry. The solid-state structure of the methanol adduct of the 2,1-insertion product of NIPAM into 1-DMSO, [(P%O)Pd{η1-CH(CONHiPr)CH2CH3}(κ1-O-MeOD)] (2-MeOD), was detd. by single crystal x-ray diffraction. Both 2,1- and 1,2-insertions of DMAA into the Pd-Me bond of a [(P%O)PdMe] fragment occur to afford a ca. 4:1 mixt. of chelates [(P%O)Pd{κ2-C,O-C(CH2CH3)C(O)NMe2}] (3) and [(P%O)Pd{κ2-C,O-CH2C(CH3)C(O)NMe2}] (4). The four-membered chelate of 3 is opened by coordination of 2,6-lutidine (3 + 2,6-lutidine .dblharw. 3-LUT) with ΔH° = -41.8(10.5) kJ and ΔS° = -115(37) J mol-1 K-1.
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  (n) Ito, S.; Kanazawa, M.; Munakata, K.; Kuroda, J.-i.; Okumura, Y.; Nozaki, K. Coordination–Insertion Copolymerization of Allyl Monomers with Ethylene. J. Am. Chem. Soc. 2011, 133, 1232– 1235, DOI: 10.1021/ja1092216
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  12n
  Coordination-Insertion Copolymerization of Allyl Monomers with Ethylene
  Ito, Shingo; Kanazawa, Masafumi; Munakata, Kagehiro; Kuroda, Jun-Ichi; Okumura, Yoshikuni; Nozaki, Kyoko
  Journal of the American Chemical Society (2011), 133 (5), 1232-1235CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Coordination-insertion copolymn. of allyl monomers with ethylene was developed by using a palladium/phosphine-sulfonate catalyst. A variety of allyl monomers, including allyl acetate, allyl alc., protected allylamines, and allyl halides, were copolymd. with ethylene to form highly linear copolymers that possess in-chain -CH2CH(CH2FG)- units.
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  (o) Neuwald, B.; Falivene, L.; Caporaso, L.; Cavallo, L.; Mecking, S. Exploring Electronic and Steric Effects on the Insertion and Polymerization Reactivity of Phosphinesulfonato PdII Catalysts. Chem. - Eur. J. 2013, 19, 17773– 17788, DOI: 10.1002/chem.201301365
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  12o
  Exploring Electronic and Steric Effects on the Insertion and Polymerization Reactivity of Phosphinesulfonato PdII Catalysts
  Neuwald, Boris; Falivene, Laura; Caporaso, Lucia; Cavallo, Luigi; Mecking, Stefan
  Chemistry - A European Journal (2013), 19 (52), 17773-17788CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Thirteen different sym. and asym. phosphinesulfonato palladium complexes ([{(X1-Cl)-μ-M}n], M=Na, Li, 1=X(P%O)PdMe) were prepd. (see Figure 1). The solid-state structures of the corresponding pyridine or lutidine complexes were detd. for (MeO)21-py, (iPrO)21-lut, (MeO,Me2)1-lut, (MeO)31-lut, CF31-lut, and Ph1-lut. The reactivities of the catalysts X1, obtained after chloride abstraction with AgBF4, toward Me acrylate (MA) were quantified through detn. of the rate consts. for the first and the consecutive MA insertion and the anal. of β-H and other decompn. products through NMR spectroscopy. Differences in the homo- and copolymn. of ethylene and MA regarding catalyst activity and stability over time, polymer mol. wt., and polar co-monomer incorporation were investigated. DFT calcns. were performed on the main insertion steps for both monomers to rationalize the effect of the ligand substitution patterns on the polymn. behaviors of the complexes. Full anal. of the data revealed that: 1) electron-deficient catalysts polymerize with higher activity, but fast deactivation is also obsd.; 2) the double ortho-substituted catalysts (MeO)21 and (MeO)31 allow very high degrees of MA incorporation at low MA concns. in the copolymn.; and 3) steric shielding leads to a pronounced increase in polymer mol. wt. in the copolymn. The catalyst properties induced by a given P-aryl (alkyl) moiety were combined effectively in catalysts with two different non-chelating aryl moieties, such as cHexO/(MeO)21, which led to copolymers with significantly increased mol. wts. compared to the prototypical MeO1.
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13. 13
  (a) Skupov, K. M.; Marella, P. R.; Simard, M.; Yap, G. P. A.; Allen, N.; Conner, D.; Goodall, B. L.; Claverie, J. P. Palladium Aryl Sulfonate Phosphine Catalysts for the Copolymerization of Acrylates with Ethene. Macromol. Rapid Commun. 2007, 28, 2033– 2038, DOI: 10.1002/marc.200700370
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  13a
  Palladium aryl sulfonate phosphine catalysts for the copolymerization of acrylates with ethene
  Skupov, Kirill M.; Marella, Pooja R.; Simard, Michel; Yap, Glenn P. A.; Allen, Nathan; Conner, David; Goodall, Brian L.; Claverie, Jerome P.
  Macromolecular Rapid Communications (2007), 28 (20), 2033-2038CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
  The reaction of 2-[bis(2-methoxy-phenyl)phosphanyl]-4-methyl-benzenesulfonic acid (a) and 2-[bis(2',6'-dimethoxybiphenyl-2-yl)phosphanyl]benzenesulfonic acid (b) with dimethyl(N,N,N',N'-tetramethylethylenediamine)-palladium(II) (PdMe2(TMEDA)) leads to the formation of TMEDA bridged palladium based polymn. catalysts (1a and 1b). Upon reaction with pyridine, two mononuclear catalysts are formed (2a and 2b). These catalysts are able to homopolymerize ethylene and also copolymerize ethylene with acrylates or with norbornenes. With ligand b, high mol. wt. polymers are formed in high yields, but higher comonomer incorporations are obtained with ligand a.
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  .
  (b) Ota, Y.; Ito, S.; Kuroda, J.-i.; Okumura, Y.; Nozaki, K. Quantification of the Steric Influence of Alkylphosphine–Sulfonate Ligands on Polymerization, Leading to High-Molecular-Weight Copolymers of Ethylene and Polar Monomers. J. Am. Chem. Soc. 2014, 136, 11898– 11901, DOI: 10.1021/ja505558e
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  13b
  Quantification of the Steric Influence of Alkylphosphine-Sulfonate Ligands on Polymerization, Leading to High-Molecular-Weight Copolymers of Ethylene and Polar Monomers
  Ota, Yusuke; Ito, Shingo; Kuroda, Jun-ichi; Okumura, Yoshikuni; Nozaki, Kyoko
  Journal of the American Chemical Society (2014), 136 (34), 11898-11901CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  A series of palladium/ alkylphosphine- sulfonate catalysts were synthesized and examd. in the homopolymn. of ethylene and the copolymn. of ethylene and polar monomers. Catalysts with alkylphosphine- sulfonate ligands contg. sterically demanding alkyl substituents afforded (co)polymers whose mol. wt. was increased by up to 2 orders of magnitude relative to polymers obtained from previously reported catalyst systems. The polymer mol. wt. was found to be closely correlated to the Sterimol B5 parameter of the alkyl substituents in the alkylphosphine- sulfonate ligands. Thus, the use of bulky alkylphosphine- sulfonate ligands represents an effective and versatile method to prep. high-mol.-wt. copolymers of ethylene and various polar monomers, which are difficult to obtain by previously reported methods.
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14. 14
  (a) Carrow, B. P.; Nozaki, K. Synthesis of Functional Polyolefins Using Cationic Bisphosphine Monoxide–Palladium Complexes. J. Am. Chem. Soc. 2012, 134, 8802– 8805, DOI: 10.1021/ja303507t
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  14a
  Synthesis of Functional Polyolefins Using Cationic Bisphosphine Monoxide-Palladium Complexes
  Carrow, Brad P.; Nozaki, Kyoko
  Journal of the American Chemical Society (2012), 134 (21), 8802-8805CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  The copolymn. of ethylene with polar vinyl monomers, such as vinyl acetate, acrylonitrile, vinyl ethers, and allyl monomers, was accomplished using cationic palladium complexes ligated by a bisphosphine monoxide (BPMO). The copolymers formed by these catalysts have highly linear microstructures and a random distribution of polar functional groups throughout the polymer chain. Our data demonstrate that cationic palladium complexes can exhibit good activity for polymns. of polar monomers, in contrast to cationic α-diimine palladium complexes (Brookhart-type) that are not applicable to industrially relevant polar monomers beyond acrylates. Addnl., the studies reported here point out that phosphine-sulfonate ligated palladium complexes are no longer the singular family of catalysts that can promote the reaction of ethylene with many polar vinyl monomers to form linear functional polyolefins.
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  (b) Contrella, N. D.; Sampson, J. R.; Jordan, R. F. Copolymerization of Ethylene and Methyl Acrylate by Cationic Palladium Catalysts That Contain Phosphine-Diethyl Phosphonate Ancillary Ligands. Organometallics 2014, 33, 3546– 3555, DOI: 10.1021/om5004489
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  14b
  Copolymerization of Ethylene and Methyl Acrylate by Cationic Palladium Catalysts That Contain Phosphine-Diethyl Phosphonate Ancillary Ligands
  Contrella, Nathan D.; Sampson, Jessica R.; Jordan, Richard F.
  Organometallics (2014), 33 (13), 3546-3555CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  A series of benzo-linked phosphine-diethyl phosphonate (P-PO) and phosphine-bis(di-Et phosphonate) (P-(PO)2) ligands and the corresponding (P-PO)PdMe(2,6-lutidine)+ and (P-(PO)2)PdMe(2,6-lutidine)+ complexes were synthesized. Cationic (P-PO)PdMe(2,6-lutidine)+ complexes are active for ethylene oligomerization/polymn., with activities of 2 kg mol-1 h-1 for {κ2-1-PiPr2-2-P(O)(OEt)2-5-Me-Ph}PdMe(2,6-lutidine)+ (3c), 125 kg mol-1 h-1 for {κ2-1-PPh2-2-P(O)(OEt)2-5-Me-Ph}PdMe(2,6-lutidine)+ (3a), and 1470 kg mol-1 h-1 for {κ2-1-P(2-OMe-Ph)2-2-P(O)(OEt)2-Ph}PdMe(2,6-lutidine)+ (3b). The polyethylene is highly linear, with over 80% terminal unsatn. and low (230-1890 Da) mol. wt. in all cases. 3B copolymerizes ethylene with Me acrylate, exhibiting highly selective (95%) in-chain (rather than chain-end) acrylate incorporation. The P-(PO)2 catalyst {κ2-1-P(4-tBu-Ph)(2-P(O)(OEt)2-5-Me-Ph)-2-P(O)(OEt)2-5-Me-Ph}PdMe(2,6-lutidine)+ (3d) is more active for ethylene homopolymn. (2640 kg mol-1 h-1), yielding linear, low-mol.-wt. polymer (1280-1430 Da) with predominantly internal olefin placement. In ethylene/methyl acrylate copolymn., 3d incorporates 2.6 mol % Me acrylate, 60% of which is in-chain. Both 3b and 3d catalyze ethylene/acrylic acid copolymn., albeit with low (<10 kg mol-1 h-1) activities and acrylic acid incorporation up to 1.1 mol %.
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  (c) Sui, X.; Dai, S.; Chen, C. Ethylene Polymerization and Copolymerization with Polar Monomers by Cationic Phosphine Phosphonic Amide Palladium Complexes. ACS Catal. 2015, 5, 5932– 5937, DOI: 10.1021/acscatal.5b01490
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  14c
  Ethylene Polymerization and Copolymerization with Polar Monomers by Cationic Phosphine Phosphonic Amide Palladium Complexes
  Sui, Xuelin; Dai, Shengyu; Chen, Changle
  ACS Catalysis (2015), 5 (10), 5932-5937CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  The synthesis, characterization, and olefin (co)polymn. studies of a series of palladium complexes bearing phosphine phosphonic amide ligands were investigated. In this ligand framework, substituents on three positions could be modulated independently, which distinguishes this class of ligand and provides a great deal of flexibilities and opportunities to tune the catalytic properties. The palladium complex with an o-MeO-Ph substituent on phosphine is one of the most active palladium catalysts in ethylene polymn., with 1 order of magnitude higher activity than the corresponding classic phosphine-sulfonate palladium complex. Meanwhile, the polyethylene generated by this new palladium complex showed ca. 6 times higher mol. wt. in comparison to that by the classic phosphine-sulfonate palladium complex. In ethylene/methyl acrylate copolymn., the new palladium complex showed lower activity, generating copolymer with similar Me acrylate incorporation and much higher mol. wt. The new palladium complex was also able to copolymerize ethylene with other polar monomers, including Bu vinyl ether and allyl acetate, making it one of the very few catalyst systems that can copolymerize ethylene with multiple industrially relevant polar monomers.
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  (d) Mitsushige, Y.; Carrow, B. P.; Ito, S.; Nozaki, K. Ligand-controlled insertion regioselectivity accelerates copolymerisation of ethylene with methyl acrylate by cationic bisphosphine monoxide-palladium catalysts. Chem. Sci. 2016, 7, 737– 744, DOI: 10.1039/C5SC03361F
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  14d
  Ligand-controlled insertion regioselectivity accelerates copolymerisation of ethylene with methyl acrylate by cationic bisphosphine monoxide-palladium catalysts
  Mitsushige, Yusuke; Carrow, Brad P.; Ito, Shingo; Nozaki, Kyoko
  Chemical Science (2016), 7 (1), 737-744CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
  A new series of palladium catalysts ligated by a chelating bisphosphine monoxide bearing diarylphosphino groups (aryl-BPMO) exhibits markedly higher reactivity for ethylene/methyl acrylate copolymn. when compared to the first generation of alkyl-BPMO-palladium catalysts that contain a dialkylphosphino moiety. Mechanistic studies suggest that the origin of this disparate catalyst behavior is a change in regioselectivity of migratory insertion of the acrylate comonomer as a function of the phosphine substituents. The best aryl-BPMO-palladium catalysts for these copolymns. were shown to undergo exclusively 2,1-insertion, and this high regioselectivity avoids formation of a poorly reactive palladacycle intermediate. Furthermore, the aryl-BPMO-palladium catalysts can copolymerize ethylene with other industrially important polar monomers.
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  (e) Mitsushige, Y.; Yasuda, H.; Carrow, B. P.; Ito, S.; Kobayashi, M.; Tayano, T.; Watanabe, Y.; Okuno, Y.; Hayashi, S.; Kuroda, J.; Okumura, Y.; Nozaki, K. Methylene-Bridged Bisphosphine Monoxide Ligands for Palladium-Catalyzed Copolymerization of Ethylene and Polar Monomers. ACS Macro Lett. 2018, 7, 305– 311, DOI: 10.1021/acsmacrolett.8b00034
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  14e
  Methylene-Bridged Bisphosphine Monoxide Ligands for Palladium-Catalyzed Copolymerization of Ethylene and Polar Monomers
  Mitsushige, Yusuke; Yasuda, Hina; Carrow, Brad P.; Ito, Shingo; Kobayashi, Minoru; Tayano, Takao; Watanabe, Yumiko; Okuno, Yoshishige; Hayashi, Shinya; Kuroda, Junichi; Okumura, Yoshikuni; Nozaki, Kyoko
  ACS Macro Letters (2018), 7 (3), 305-311CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
  A series of palladium complexes bearing a bisphosphine monoxide with a methylene linker, i.e., [κ2-P,O-(R12P)CH2P(O)R22]PdMe[(2,6-lutidine)][BArF4] (Pd/BPMO), were synthesized and evaluated as catalysts for the homopolymn. of ethylene and the copolymn. of ethylene and polar monomers. X-ray crystallog. analyses revealed that these Pd/BPMO complexes exhibit significantly narrower bite angles and longer Pd-O bonds than Pd/BPMO complexes bearing a phenylene linker, while maintaining almost const. Pd-P bond lengths. Among the complexes synthesized, menthyl-substituted complex 3f (R1 = (1R,2S,5R)-2-isopropyl-5-methylcyclohexan-1-yl; R2 = Me) showed the best catalytic performance in the homo- and copolymn. in terms of mol. wt. and polymn. activity. Meanwhile, complex 3e (R1 = t-Bu; R2 = Me) exhibited a markedly higher incorporation of comonomers in the copolymn. of ethylene and allyl acetate (≤12.0 mol %) or Me methacrylate (≤0.6 mol %). The catalytic system represents one of the first examples of late-transition-metal complexes bearing an alkylene-bridged bidentate ligand that afford high-mol.-wt. copolymers from the copolymn. of ethylene and polar monomers.
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15. 15
  Dashan, L.; Trippett, S. The ortho-lithiation of N, N,N′,N′-tetramethylphenylphosphonic diamide. Tetrahedron Lett. 1983, 24, 2039– 2040, DOI: 10.1016/S0040-4039(00)81838-9
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16. 16
  PPDA ligands with dialkylphosphino groups (i.e., 1a–1c) must be handled under an inert atmosphere.
  There is no corresponding record for this reference.
17. 17
  Falivene, L.; Credendino, R.; Poater, A.; Petta, A.; Serra, L.; Oliva, R.; Scarano, V.; Cavallo, L. SambVca 2. A Web Tool for Analyzing Catalytic Pockets with Topographic Steric Maps. Organometallics 2016, 35, 2286– 2293, DOI: 10.1021/acs.organomet.6b00371
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  17
  SambVca 2. A Web Tool for Analyzing Catalytic Pockets with Topographic Steric Maps
  Falivene, Laura; Credendino, Raffaele; Poater, Albert; Petta, Andrea; Serra, Luigi; Oliva, Romina; Scarano, Vittorio; Cavallo, Luigi
  Organometallics (2016), 35 (13), 2286-2293CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  Developing more efficient catalysts remains one of the primary targets of organometallic chemists. To accelerate reaching this goal, effective mol. descriptors and visualization tools can represent a remarkable aid. Here, we present a Web application for analyzing the catalytic pocket of metal complexes using topog. steric maps as a general and unbiased descriptor that is suitable for every class of catalysts. To show the broad applicability of our approach, we first compared the steric map of a series of transition metal complexes presenting popular mono-, di-, and tetracoordinated ligands and three classic zirconocenes. This comparative anal. highlighted similarities and differences between totally unrelated ligands. Then, we focused on a recently developed Fe(II) catalyst that is active in the asym. transfer hydrogenation of ketones and imines. Finally, we expand the scope of these tools to rationalize the inversion of enantioselectivity in enzymic catalysis, achieved by point mutation of three amino acids of mononuclear p-hydroxymandelate synthase.
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18. 18
  Yang, X.; Stern, C. L.; Marks, T. J. Cation-like homogeneous olefin polymerization catalysts based upon zirconocene alkyls and tris(pentafluorophenyl)borane. J. Am. Chem. Soc. 1991, 113, 3623– 3625, DOI: 10.1021/ja00009a076
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  18
  Cation-like homogeneous olefin polymerization catalysts based upon zirconocene alkyls and tris(pentafluorophenyl)borane
  Yang, Xinmin; Stern, Charlotte L.; Marks, Tobin J.
  Journal of the American Chemical Society (1991), 113 (9), 3623-5CODEN: JACSAT; ISSN:0002-7863.
  The reaction of zirconocene dialkyls L2ZrMe2 (L = η5-C5H5, η5-1,2-Me2C5H3, η5-C5Me5) with B(C6F5)3 yields "cation-like" zirconocene complexes L2ZrMe+MeB(C6F5)3-. (1,2-Me2C5H3)2ZrMe+MeB(C6F5)3- was characterized crystallog. With the exception of a shortened Zr-Me distance [2.252(4) Å], the metrical parameters within the "bent sandwich" L2ZrMe+ cation are unexceptional. The cation interacts weakly via a highly unsym. Zr-(μ-Me)B bridge with the essentially tetrahedral MeB(C6F5)3- anion. The L2ZrMe+MeB(C6F5)3- complexes are active catalysts for olefin polymn. For ethylene polymn., Nt(1) ≈ 45 s-1 at 25°, 1 atm (∼4.5 × 106 g polyethylene/mol Zr h atm) to yield linear polyethylene. For propylene polymn at 25°, 1-5 atm, atactic polypropylene is produced with Nt(1) ≈ 4.2 s-1.
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19. 19
  Vela, J.; Lief, G. R.; Shen, Z.; Jordan, R. F. Ethylene Polymerization by Palladium Alkyl Complexes Containing Bis(aryl)phosphino-toluenesulfonate Ligands. Organometallics 2007, 26, 6624– 6635, DOI: 10.1021/om700869c
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  19
  Ethylene Polymerization by Palladium Alkyl Complexes Containing Bis(aryl)phosphino-toluenesulfonate Ligands
  Vela, Javier; Lief, Graham R.; Shen, Zhongliang; Jordan, Richard F.
  Organometallics (2007), 26 (26), 6624-6635CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  The reaction of L'2PdR2 (L' = pyridine (py), pyridazine; L'2 = cyclooctadiene, TMEDA) with 2-{(2-MeOC6H4)2P}-4-Me-benzenesulfonic acid ([PO-OMe]H, [1a]H) or 2-{(2-EtC6H4)2P}-4-Me-benzenesulfonic acid ([PO-Et]H, [1b]H) yields [PO-OMe]Pd(R)(L) (L = py, R = CH2SiMe3 (2a), CH2tBu (3a), CH2Ph (4a); R = Me, L = pyridazine (5a), py (6a), PPh3 (7a)) or [PO-Et]Pd(Me)(py) (6b). 2A and 6b have square-planar structures in which the alkyl group is cis to the phosphine and the [PO]Pd chelate rings are puckered. The reaction of 2a and 3a with B(C6F5)3 yields {[PO-OMe]Pd(R)}2 (R = CH2SiMe3 (8a), CH2tBu (9a)). 8A is a sulfonate-bridged dimer in the solid state. 2A, 6a, and 6b polymerize ethylene to linear polyethylene that contains low levels of Me branches, one C:C unit per chain (mostly 1- or 2-olefins), and Mn in the range 6000 to 19,000. 6A is slightly more active but produces polymers with similar mol. wt. and structure compared to 6b. 6A copolymerizes ethylene and hexene at low ethylene pressure (5 atm), but no α-olefin incorporation is obsd. at high pressure (30 atm). An ethylene polymn. mechanism is proposed, which involves insertion and chain transfer of [PO]Pd(R)(ethylene) species (I) and ethylene trapping and much slower chain-walking of the [PO]Pd(CH2CH2R) species formed by insertion of I. The crystal and mol. structures of 2a·1.5CH2Cl2, 6b and 8a·CH2Cl2 were detd. by x-ray crystallog.
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20. 20
  Cai, Z.; Shen, Z.; Zhou, X.; Jordan, R. F. Enhancement of Chain Growth and Chain Transfer Rates in Ethylene Polymerization by (Phosphine-sulfonate)PdMe Catalysts by Binding of B(C6F5)3 to the Sulfonate Group. ACS Catal. 2012, 2, 1187– 1195, DOI: 10.1021/cs300147c
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  20
  Enhancement of Chain Growth and Chain Transfer Rates in Ethylene Polymerization by (Phosphine-sulfonate)PdMe Catalysts by Binding of B(C6F5)3 to the Sulfonate Group
  Cai, Zhengguo; Shen, Zhongliang; Zhou, Xiaoyuan; Jordan, Richard F.
  ACS Catalysis (2012), 2 (6), 1187-1195CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  Binding of B(C6F5)3 to a sulfonate oxygen of (ortho-phosphino-arenesulfonate)PdR catalysts results in a 3-4 fold increase in the rate of chain growth and a larger increase in the rate of chain transfer. The reaction of (PO-Et)PdMe(py) (1a, [PO-Et]- = ortho-{(2-Et-Ph)2P}-para-toluenesulfonate) with 1 equiv of B(C6F5)3 yields the base-free dimer {(PO-Et)PdMe}2 (2a), in which the (PO-Et)PdMe units are linked through an eight-membered [PdSO2]2 ring. The reaction of {(PO-3,5-tBu2)PdMe}2(TMEDA) (4b; [PO-3,5-tBu2]- = ortho-{(3,5-tBu2-Ph)2P}-para-toluenesulfonate, TMEDA = N,N,N',N'-tetramethylethylenediamine) with BF3·Et2O yields the sol. base-free dimer {(PO-3,5-tBu2)PdMe}2 (2b), in which the (PO-3,5-tBu2)PdMe units are linked through a four-membered Pd2O2 ring. 2b reacts with 2 equiv of B(C6F5)3 to yield {[PO·B(C6F5)3-3,5-tBu2]PdMe}2 (5b, [PO·B(C6F5)3-3,5-tBu2]- = [2-{(3,5-tBu2-Ph)2P}-4-Me-C6H3SO2OB(C6F5)3]-), which crystallizes from Et2O as the monomeric complex [PO·B(C6F5)3-3,5-tBu2]PdMe(Et2O) (6b). In both 5b and 6b, the B(C6F5)3 binds to a sulfonate oxygen. In toluene soln. at 60 °C, 2b polymerizes ethylene (80 psi) to linear polyethylene with Mn = 3000, while the B(C6F5)3 adducts 5b and 6b yield ethylene oligomers (Mn = 160-170). 5b and 6b are 3-4 times more active than 2b. Similarly, 1a polymerizes ethylene to linear polyethylene with Mn = 29,300 (toluene, 80 °C, 435 psi), while 1a-4 B(C6F5)3 yields polymer with Mn = 2520 with a 4 fold increase in activity. 2b reacts with ethylene at 7 °C to form the ethylene adduct (PO-3,5-tBu2)PdMe(CH2=CH2) (7b) followed by multiple insertions to generate (PO-3,5-tBu2)Pd(CH2CH2)nCH3 species. In contrast, 5b reacts with ethylene to form [PO·B(C6F5)3-3,5-tBu2]PdMe(CH2=CH2) (8b) followed by insertion and β-H transfer to yield propene with subsequent catalytic formation of 1-butene and higher olefins. The rate of ethylene insertion of 8b is 3 times greater than that of 7b, consistent with the batch polymn. results. The polymer yield and mol. wt. data show that binding of B(C6F5)3 to 2b and 1a increases the chain transfer rates by a factor of 80 and 42, resp.
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21. 21
  Xie, T.; McAuley, K. B.; Hsu, J. C. C.; Bacon, D. W. Gas Phase Ethylene Polymerization: Production Processes, Polymer Properties, and Reactor Modeling. Ind. Eng. Chem. Res. 1994, 33, 449– 479, DOI: 10.1021/ie00027a001
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  21
  Gas Phase Ethylene Polymerization: Production Processes, Polymer Properties, and Reactor Modeling
  Xie, Tuyu; McAuley, Kim B.; Hsu, James C. C.; Bacon, David W.
  Industrial & Engineering Chemistry Research (1994), 33 (3), 449-79CODEN: IECRED; ISSN:0888-5885.
  A review, with many refs., of relevant macroscopic and microscopic processes of gas-phase ethylene polymn., both chem. and phys., is given. The com. technol. development of gas-phase ethylene polymn. processes is illustrated through a selective survey of the patent literature. Both advantages and disadvantages of gas phase polymn. processes are addressed, and the challenges of lab. studies of gas-phase polymn. are also outlined. Physicochem. phenomena of ethylene polymn. using heterogeneous catalysts are discussed, including examn. of catalyst prepn., polymer morphol. development, and elementary chem. reactions. Metallocene-based catalysts and their kinetic performance for olefin polymns. are also discussed. The current state of the art for reactor modeling of polymn. rate, mol. wt. development, reactor dynamics, and resin-grade transition strategies is illustrated on the basis of the most recent academic studies. Finally, relationships between resin properties and polymer microstructures as well as characterization methods are described briefly. In particular, temp.-rising elution fractionation technol. is emphasized for characterization of ethylene copolymers. The fundamental issues involved in gas-phase ethylene polymn. and their interrelationships are also discussed in some detail.
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22. 22
  (a) Gates, D. P.; Svejda, S. A.; Oñate, E.; Killian, C. M.; Johnson, L. K.; White, P. S.; Brookhart, M. Synthesis of Branched Polyethylene Using (α-Diimine)nickel(II) Catalysts: Influence of Temperature, Ethylene Pressure, and Ligand Structure on Polymer Properties. Macromolecules 2000, 33, 2320– 2334, DOI: 10.1021/ma991234+
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  22a
  Synthesis of Branched Polyethylene Using (α-Diimine)nickel(II) Catalysts: Influence of Temperature, Ethylene Pressure, and Ligand Structure on Polymer Properties
  Gates, Derek P.; Svejda, Steven A.; Onate, Enrique; Killian, Christopher M.; Johnson, Lynda K.; White, Peter S.; Brookhart, Maurice
  Macromolecules (2000), 33 (7), 2320-2334CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
  Detailed investigations of the polymn. of ethylene by (α-diimine)nickel(II) catalysts are reported. Effects of structural variations of the diimine ligand on catalyst activities, polymer mol. wts., and polymer microstructure are described. The pre-catalysts employed were [{(2,6-RR'C6H3)-N:C(Nap)-C(Nap):N-(2,6-RR'C6H3)}NiBr2] (Nap = 1,8-naphthdiyl) (4a, R = CF3, R' = H; 4b, R = CF3, R' = CH3; 4c, R = C6F5, R' = H; 4d, R = C6F5, R' = CH3; 4e, R = CH3, R' = H; 4f, R = R' = CH3; 4g, R = R' = CH(CH3)2), [{(2,6-C6H3(i-Pr)2)-N:C(CH2CH2CH2CH2)C:N-(2,6-C6H3(i-Pr)2)}NiBr2] (5), and [{(2,6-C6H3(i-Pr)2)-N:C(Et)C(Me):N-(2,6-C6H3(i-Pr)2)}NiBr2] (6). Active polymn. catalysts were formed in situ by combination of 4-6 with modified methylaluminoxane. In general, as the bulk and no. of ortho substituents increase, polymer mol. wts., turnover frequencies and extent of branching in the polyethylenes all increase. Effects of varying ethylene pressure and temp. on polymns. are also reported. The degree of branching in the polymers rapidly decreases with increasing ethylene pressure but mol. wts. are not markedly affected. Temp. increases result in more extensive branching and moderate redns. in mol. wts. Catalyst productivity decreases above 60° due to catalyst deactivation.
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  .
  (b) Tempel, D. J.; Johnson, L. K.; Huff, R. L.; White, P. S.; Brookhart, M. Mechanistic Studies of Pd(II)−α-Diimine-Catalyzed Olefin Polymerizations1. J. Am. Chem. Soc. 2000, 122, 6686– 6700, DOI: 10.1021/ja000893v
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  22b
  Mechanistic studies of Pd(II)-α-diimine-catalyzed olefin polymerizations
  Tempel, Daniel J.; Johnson, Lynda K.; Huff, R. Leigh; White, Peter S.; Brookhart, Maurice
  Journal of the American Chemical Society (2000), 122 (28), 6686-6700CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Mechanistic studies of olefin polymns. catalyzed by aryl-substituted α-diimine-Pd(II) complexes are presented. Syntheses of several cationic catalyst precursors, [(N N)Pd(CH3)(OEt2)]BAr'4 (N N = aryl-substituted α-diimine, Ar' = 3,5-(CF3)2C6H3), are described. X-ray structural analyses of [ArN:C(H)C(H):NAr]Pd(CH3)(Cl) and [ArN:C(Me)C(Me):NAr]Pd(CH3)2 (Ar = 2,6-(iPr)2C6H3) illustrate that o-aryl substituents crowd axial sites in these square planar complexes. Low-temp. NMR studies show that the alkyl olefin complexes, (N N)Pd(R)(olefin)+, are the catalyst resting states and that the barriers to migratory insertions lie in the range 17-19 kcal/mol. Following migratory insertion, the cationic palladium alkyl complexes (N N)Pd(alkyl)+ formed are β-agostic species which exhibit facile metal migration along the chain ("chain walking") via β-hydride elimination/readdn. reactions. Model studies using palladium- Pr and -iso-Pr systems provide mechanistic details of this process, which is responsible for introducing branching in the polyethylenes made by these systems. Decompn. of the cationic Me complexes (ArN NAr)Pd(CH3)(OEt2)+ (Ar = 2,6-(iPr)2C6H3, 2-tBuC6H4) occurs by C-H activation of β-C-H bonds of the ortho iso-Pr and tert-Bu substituents and loss of methane. The rate of associative exchange of free ethylene with bound ethylene in (N N)Pd(CH3)(C2H4)+ is retarded by bulky substituents. The relationship of these exchange expts. to chain transfer is discussed.
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23. 23
  (a) Camacho, D. H.; Salo, E. V.; Ziller, J. W.; Guan, Z. Cyclophane-Based Highly Active Late-Transition-Metal Catalysts for Ethylene Polymerization. Angew. Chem., Int. Ed. 2004, 43, 1821– 1825, DOI: 10.1002/anie.200353226
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  23a
  Cyclophane-based highly active late-transition-metal catalysts for ethylene polymerization
  Camacho, Drexel H.; Salo, Eric V.; Ziller, Joseph W.; Guan, Zhibin
  Angewandte Chemie, International Edition (2004), 43 (14), 1821-1825CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Exploitation of the macrocyclic architecture of a cyclophane-based ligand provides new highly active catalysts with improved thermal stability for ethylene polymn. The strategic positioning of the metal center at the core of the cyclophane-based ligand is the key to the obsd. high activity and thermal stability, and to the high mol. wt. of the polyethylene.
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  .
  (b) Schmid, M.; Eberhardt, R.; Klinga, M.; Leskelä, M.; Rieger, B. New C2v- and Chiral C2-Symmetric Olefin Polymerization Catalysts Based on Nickel(II) and Palladium(II) Diimine Complexes Bearing 2,6-Diphenyl Aniline Moieties: Synthesis, Structural Characterization, and First Insight into Polymerization Properties. Organometallics 2001, 20, 2321– 2330, DOI: 10.1021/om010001f
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  There is no corresponding record for this reference.
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  (c) Meinhard, D.; Wegner, M.; Kipiani, G.; Hearley, A.; Reuter, P.; Fischer, S.; Marti, O.; Rieger, B. New Nickel(II) Diimine Complexes and the Control of Polyethylene Microstructure by Catalyst Design. J. Am. Chem. Soc. 2007, 129, 9182– 9191, DOI: 10.1021/ja070224i
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  23c
  New Nickel(II) Diimine Complexes and the Control of Polyethylene Microstructure by Catalyst Design
  Meinhard, Dieter; Wegner, Marcus; Kipiani, Georgy; Hearley, Andrew; Reuter, Peter; Fischer, Stefan; Marti, Othmar; Rieger, Bernhard
  Journal of the American Chemical Society (2007), 129 (29), 9182-9191CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Starting from differently substituted boronic acids as versatile building block, new "ortho-aryl" α-diimine ligands a-h were synthesized in an easy, high-yielding route. Reaction of the complex precursor diacetylacetonato-nickel(II) with a trityl salt, like [CPh3][B(C6F5)4] or [CPh3][SbCl6], in the presence of the diimine ligands afford the monocationic, square planar complexes 2a-g in almost quant. yields. Suitable crystals (2d',e,f,g) were submitted for x-ray diffraction anal. A geometry model was developed to describe the orientation of ligand fragments around the nickel(II) center that influence the polymer microstructure. At elevated reaction temp. and pressure, and in the presence of hydrogen, 2a-e catalyze the homopolymn. of ethylene to give branched PE products ranging from HD- to LLD-PE grades. The polymn. results indicate the possibility of precise microstructure control depending on the particular complex substitution. Preliminary studies on material d. and mech. behavior by uniaxial stretching until failure point toward new material properties that can result from the simple ethylene monomer by catalyst design.
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  (d) Moody, L. S.; Mackenzie, P. B.; Killian, C. M.; Lavoie, G. G.; Ponasik, J. A.; Barrett, A. G. M.; Smith, T. W.; Pearson, J. C. WO 0050470 August 31, 2000.
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  (e) Rhinehart, J. L.; Brown, L. A.; Long, B. K. A Robust Ni(II) α-Diimine Catalyst for High Temperature Ethylene Polymerization. J. Am. Chem. Soc. 2013, 135, 16316– 16319, DOI: 10.1021/ja408905t
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  23e
  A Robust Ni(II) α Diimine Catalyst for High Temperature Ethylene Polymerization
  Rhinehart, Jennifer L.; Brown, Lauren A.; Long, Brian K.
  Journal of the American Chemical Society (2013), 135 (44), 16316-16319CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Sterically demanding NiII α-diimine precatalysts were synthesized utilizing 2,6-bis-(diphenyl-methyl)-4-Me aniline. When activated with methylaluminoxane, the catalyst NiBr2(ArNC-(Me)-C-(Me)NAr) (Ar = 2,6 bis-(diphenyl-methyl)-4-methylbenzene) was highly active, produced well-defined polyethylene at temps. up to 100° (Mw/Mn = 1.09-1.46), and demonstrated remarkable thermal stability at temps. appropriate for industrially used gas-phase polymns. (80-100°).
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  .
  (f) Liu, F.-S.; Hu, H.-B.; Xu, Y.; Guo, L.-H.; Zai, S.-B.; Song, K.-M.; Gao, H.-Y.; Zhang, L.; Zhu, F.-M.; Wu, Q. Thermostable α-Diimine Nickel(II) Catalyst for Ethylene Polymerization: Effects of the Substituted Backbone Structure on Catalytic Properties and Branching Structure of Polyethylene. Macromolecules 2009, 42, 7789– 7796, DOI: 10.1021/ma9013466
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  23f
  Thermostable α-Diimine Nickel(II) Catalyst for Ethylene Polymerization: Effects of the Substituted Backbone Structure on Catalytic Properties and Branching Structure of Polyethylene
  Liu, Feng-Shou; Hu, Hai-Bin; Xu, Ying; Guo, Li-Hua; Zai, Shao-Bo; Song, Ke-Ming; Gao, Hai-Yang; Zhang, Ling; Zhu, Fang-Ming; Wu, Qing
  Macromolecules (Washington, DC, United States) (2009), 42 (20), 7789-7796CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
  On the basis of the strategy of promoting thermostability of α-diimine nickel catalyst by ligand backbone framework, a series of α-diimine nickel(II) complexes with bulky camphyl or diaryl-substituted backbones, [2,6-(R2)2C6H3-N=C(R1)-C(R1)=N-2,6-(R2)2C6H3]NiBr2 (1a, R1 = Ph, R2 = CH3; 2a, R1 = 4-methylphenyl, R2 = CH3; 3a, R1 = 4-fluorophenyl, R2 = CH3; 4a, R1 = camphyl, R2 = CH3; 4b, R1 = camphyl, R2 = i-Pr), were synthesized and used as catalyst precursors for ethylene polymn. Crystallog. anal. revealed that the bulky camphyl backbone has a valid steric-effect on the nickel center by blocking the axial site for the metal center and suppressing the potential rotation of the CAr-N bond. Ethylene polymns. catalyzed by these nickel α-diimine complexes activated by MAO were systematically investigated and the influences of the substituted backbones as well as reaction temp. on the catalytic activity, mol. wt. and branching structure of the polymers were evaluated. It was found that the catalysts contg. a camphyl backbone have excellent thermal stability and polymer structure control for ethylene polymns. Even at 80 °C, the 4b/MAO system still kept high activity and relatively stable kinetics and produced high mol. wt. polyethylene. Moreover, the branching degrees and branched chain distribution of the polyethylenes obtained by the complex could also be controlled by tuning the reaction temp.
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  (g) Rhinehart, J. L.; Mitchell, N. E.; Long, B. K. Enhancing α-Diimine Catalysts for High-Temperature Ethylene Polymerization. ACS Catal. 2014, 4, 2501– 2504, DOI: 10.1021/cs500694m
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  23g
  Enhancing α-Diimine Catalysts for High-Temperature Ethylene Polymerization
  Rhinehart, Jennifer L.; Mitchell, Nolan E.; Long, Brian K.
  ACS Catalysis (2014), 4 (8), 2501-2504CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  Sterically demanding 2,6-bis(diphenylmethyl)-4-methylaniline was condensed onto acenaphthenequinone via an aminoalane intermediate and metalated using nickel(II) dibromide dimethoxyethane adduct to yield bis[(2,6-dibenzhydryl-4-methylimino) acenaphthene]dibromo nickel(II). This α-diimine precatalyst was examd. for high-temp. ethylene polymn. and is thermally robust at temps. as high as 90°, demonstrating enhanced activity as compared with related catalysts. Furthermore, the resultant polymers displayed increased melting transitions as compared with those produced using catalysts with identical N-aryl moieties appended to nonacenaphthenequinone-derived ligand backbones.
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24. 24
  (a) Younkin, T. R.; Connor, E. F.; Henderson, J. I.; Friedrich, S. K.; Grubbs, R. H.; Bansleben, D. A. Neutral, Single-Component Nickel(II) Polyolefin Catalysts That Tolerate Heteroatoms. Science 2000, 287, 460– 462, DOI: 10.1126/science.287.5452.460
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  24a
  Neutral, single-component nickel(II) polyolefin catalysts that tolerate heteroatoms
  Younkin, Todd R.; Connor, Eric F.; Henderson, Jason I.; Friedrich, Stefan K.; Grubbs, Robert H.; Bansleben, Donald A.
  Science (Washington, D. C.) (2000), 287 (5452), 460-462CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
  A family of catalysts has been developed whose members are tolerant of both heteroatoms and less pure starting materials. These heteroatom-tolerant neutral late transition metal complexes are in fact highly active systems that produce high-mol.-wt. polyethylene, polymerize functionalized olefins, and require no cocatalyst.
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  Organometallics (1998), 17 (15), 3149-3151CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  Neutral salicylaldiminato Ni(II) complexes having the structure I, where R = H, tert-Bu, Ph, 9-phenanthrenyl, or 9-anthracenyl and R1 = H, MeO, or NO2, were synthesized, and their structure was confirmed by an x-ray anal. of I (R = 9-anthracenyl and R1 = H). These compds. are active catalysts for the polymn. of ethylene under mild conditions in the presence of a phosphine scavenger such as Ni(COD)2 or BPh3.
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  Wucher, P.; Goldbach, V.; Mecking, S. Electronic Influences in Phosphinesulfonato Palladium(II) Polymerization Catalysts. Organometallics 2013, 32, 4516– 4522, DOI: 10.1021/om400297x
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  Electronic Influences in Phosphinesulfonato Palladium(II) Polymerization Catalysts
  Wucher, Philipp; Goldbach, Verena; Mecking, Stefan
  Organometallics (2013), 32 (16), 4516-4522CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  To study the influence of electronics on catalytic polymn. properties independent from sterics, phosphinesulfonato Pd(II) complexes bearing remotely located substituents on the nonchelating P-bound aryls [κ2-(P,O)-(4-R-2-anisyl)2PC6H4SO2O]Pd(Me)(dmso) (1a-e-dmso: 1a, R = CF3; 1b, R = Cl; 1c, R = H; 1d, R = CH3; 1e, R = OCH3) were prepd. The electron-poor complex 1a-dmso (4-CF3) undergoes the fastest insertion of Me acrylate (MA) and is the most active for ethylene polymn. The polyethylene mol. wt. increases by a factor of 2 for the more electron rich complex 1e-dmso (4-OCH3) (Mn = 17 × 103 vs 8 × 103 for 1a-dmso (4-CF3)). MA/ethylene copolymn. expts. revealed that the MA incorporation ratio and copolymer mol. wts. are largely independent of the electronic nature of the remote substituents. These trends were further confirmed by studies of two mixed P-aryl/-alkyl complexes 1f-dmso ([κ2-(2,4,6-(OMe)3C6H2)(tBu)PC6H4SO2O]Pd(Me)(dmso)) and 1g-dmso ([κ2-(C6H5)(tBu)PC6H4SO2O]Pd(Me)(dmso)). In ethylene/MA copolymn., 1f-dmso affords a significantly higher mol. wt. polymer with reasonable MA incorporation (Mn = 12 × 103 and 7.7 mol % MA) and activities similar to those obsd. for complexes 1a-e-dmso.
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  Inagaki, N.; Tasaka, S.; Hibi, K. In Plasma Surface Modification of Polymers: Relevance to Adhesion; Strobel, M., Lyons, C. S., Mittal, K. L., Eds.; VSP: Utrecht, The Netherlands, 1994; p 280.
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  A study of nonequil. melting, nonisothermal, and isothermal crystn. behavior of ethylene-1-octene random copolymers (EO), produced using metallocene catalysts has carried out. As branch (or defect) content increases, the nonisothermal and isothermal crystn. rates, melting temps., and heats of fusion decrease. There is also a branch length effect on melting temp. depression, the melting temp. depression of EO random copolymers with hexyl branches were significantly larger than those of ethylene-1-butene (EB) and ethylene-1-propene (EP) copolymers having Et and Me branches, resp. The melting temps. of homogeneous random copolymers, have been found to be always lower than those of fractions of heterogeneous copolymers, having approx. the same branch content and mol. wt. Hence, defect distribution in copolymer systems is at least as important a parameter as the defect content.
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  Ethylene-octene copolymers prepd. by INSITE constrained geometry catalyst technol. present a broad range of solid-state structures from highly cryst., lamellar morphologies to the granular morphol. of low-crystallinity copolymers. As the comonomer content increases, the accompanying tensile behavior changes from necking and cold drawing typical of a semicryst. thermoplastic to uniform drawing and high recovery characteristic of an elastomer. Although changes in morphol. features and tensile properties occur gradually with increasing comonomer content, the combined body of observations from melting behavior, morphol., dynamic mech. response, yielding, and large-scale deformation suggest a classification scheme with four distinct categories. Materials with densities >0.93 g/mL, type IV, exhibit a lamellar morphol. with a well developed spherulitic superstructure. Type III polymers with densities 0.91-0.93 g/mL have thinner lamellae and smaller spherulites. Type II materials with densities 0.89-0.91 g/mL have a mixed morphol. of small lamellae and bundled crystals. These materials can form very small spherulites. Type I copolymers with densities <0.89 g/mL have no lamellae or spherulites. Fringed micellar or bundled crystals are inferred from the low degree of crystallinity, the low melting temp., and the granular, nonlamellar morphol.
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  The structure and properties of homogeneous copolymers of ethylene and styrene (ES) and ethylene and octene (EO) were compared. Semicryst. copolymers presented a broad spectrum of solid-state structures from highly cryst., lamellar morphologies to the granular, fringed micellar morphol. of low-crystallinity copolymers. The combined observations from d., thermal behavior, and morphol. with primarily at. force microscopy revealed that the cryst. phase depended on the amt. of comonomer but was not strongly affected by whether the comonomer was styrene or octene. This was consistent with the exclusion of both comonomers from the crystal. However, ES and EO showed strong differences in the amorphous phase. ES had a much higher β-relaxation temp. than EO, which was attributed to restrictions on chain mobility imposed by the bulky Ph side group. The deformation behavior of ES and EO exhibited the same trends with comonomer content, from necking and cold drawing typical of a semicryst. thermoplastic to uniform drawing and high recovery characteristic of an elastomer. Aspects of deformation behavior that depended on crystallinity, such as yielding and cold drawing, were detd. primarily by comonomer content. However, the difference in the β-relaxation temp. resulted in much higher strain hardening of ES than EO. This was particularly evident with low-crystallinity, elastomeric copolymers. A classification scheme for semicryst. copolymers based on comonomer content, previously developed for EO, was remarkably applicable to ES.
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  Billow, B. S.; McDaniel, T. J.; Odom, A. L. Quantifying ligand effects in high-oxidation-state metal catalysis. Nat. Chem. 2017, 9, 837, DOI: 10.1038/nchem.2843
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Electron-Rich Metal Cations Enable Synthesis of High Molecular Weight, Linear Functional Polyethylenes

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Abstract

Introduction

Scheme 1

Scheme 2

Results and Discussion

PDAP-Pd Catalyst Synthesis and Steric Benchmarking

Figure 1

Ligand-Dependent Catalyst Activity and Stability

Figure 2

Copolymerizations with Polar Alkenes

Figure 3

Figure 4

Differentiating O Ligand Electronic Properties

Figure 5

Figure 6

Scheme 3

Conclusion

Supporting Information

Terms & Conditions

Author Information

Acknowledgments

References

Cited By

Abstract

Scheme 1

Scheme 2

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Scheme 3

References