Download Hi-Res ImageDownload to MS-PowerPointCite This:ACS Macro Lett. 2018, 7, 3, 305-311

Methylene-Bridged Bisphosphine Monoxide Ligands for Palladium-Catalyzed Copolymerization of Ethylene and Polar Monomers

Yusuke Mitsushige
Yusuke Mitsushige
Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
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Hina Yasuda
Hina Yasuda
Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
More by Hina Yasuda
http://orcid.org/0000-0002-8770-0039

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

Shingo Ito
Shingo Ito
Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
More by Shingo Ito
http://orcid.org/0000-0003-1776-4608

Minoru Kobayashi
Minoru Kobayashi
Japan Polychem Corporation, 1 Toho-cho, Yokkaichi, Mie 510-0848, Japan
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Takao Tayano
Takao Tayano
Japan Polychem Corporation, 1 Toho-cho, Yokkaichi, Mie 510-0848, Japan
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Yumiko Watanabe
Yumiko Watanabe
Computational Science and Technology Information Center, Showa Denko K.K., 1-1-1 Ohnodai, Midori-ku, Chiba, Chiba 267-0056, Japan
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Yoshishige Okuno
Yoshishige Okuno
Computational Science and Technology Information Center, Showa Denko K.K., 1-1-1 Ohnodai, Midori-ku, Chiba, Chiba 267-0056, Japan
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Shinya Hayashi
Shinya Hayashi
Institute for Advanced and Core Technology, Showa Denko K.K., 2 Nakanosu, Oita, Oita 870-1809, Japan
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Junichi Kuroda
Junichi Kuroda
Institute for Advanced and Core Technology, Showa Denko K.K., 2 Nakanosu, Oita, Oita 870-1809, Japan
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Yoshikuni Okumura
Yoshikuni Okumura
Institute for Advanced and Core Technology, Showa Denko K.K., 2 Nakanosu, Oita, Oita 870-1809, Japan
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, and

Kyoko Nozaki*
Kyoko Nozaki
Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
*E-mail: [email protected]
More by Kyoko Nozaki
http://orcid.org/0000-0002-0321-5299

Cite this: ACS Macro Lett. 2018, 7, 3, 305–311

Publication Date (Web):February 16, 2018

https://doi.org/10.1021/acsmacrolett.8b00034

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Abstract

A series of palladium complexes bearing a bisphosphine monoxide with a methylene linker, that is, [κ²-P,O-(R¹₂P)CH₂P(O)R²₂]PdMe(2,6-lutidine)][BAr^F₄] (Pd/BPMO), were synthesized and evaluated as catalysts for the homopolymerization of ethylene and the copolymerization of ethylene and polar monomers. X-ray crystallographic 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 constant 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 copolymerization in terms of molecular weight and polymerization activity. Meanwhile, complex 3e (R¹ = t-Bu; R² = Me) exhibited a markedly higher incorporation of comonomers in the copolymerization of ethylene and allyl acetate (≤12.0 mol %) or methyl 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-molecular-weight copolymers from the copolymerization of ethylene and polar monomers.

Given that the reactivity of homogeneous transition-metal catalysts depends not only on the metal center, but also largely on the nature of the ligands, the development of bespoke ligands is a central pillar of research in this area. In order to develop new ligands, the stereoelectronic effects of the ligands can be optimized by changing the type of coordination site, as well as substituents on or around the coordination site. In the case of bidentate ligands, the backbone structure of the ligand is also an important factor to modulate the distance between two coordination sites and the bite angle, which may influence the reactivity and selectivity of the catalysts.(1) The backbone structure of the ligand may also affect the electron-donating ability of bidentate ligands.(2) Thus, acquiring in-depth knowledge on the effect of the backbone structure on the catalytic performance is essential to the design of novel bidentate ligands for active and selective homogeneous transition-metal-based catalysts.

Intensive efforts have been devoted to the development of late-transition-metal-catalyzed copolymerizations of ethylene and polar monomers for synthesizing functional polyolefin materials; seminal discoveries in this area include palladium/α-diimine,(3,4) palladium/phosphine–sulfonate,(5−7) and palladium/IzQO catalysts.(8) Given that the latter two systems are able to copolymerize a wider range of comonomers, various bidentate ligands have been designed and synthesized in an attempt to mimic their unique structural features,(9) that is, electronically unsymmetric coordination sites consisting of a strong σ-donating group with bulky substituents and a weak σ-donating group. This unsymmetric structure is responsible for suppressing β-hydride elimination and subsequent chain-transfer, which leads to an increase in molecular weight of the resulting polymers.(10) In comparison, less attention has been focused on the backbone structure of the bidentate ligands. While almost all of the group-10-metal-based copolymerization catalysts bear an unsymmetric bidentate ligand with an arylene linker between the two coordination sites,(9,11) fewer examples of group-10-metal-based catalysts with an alkylene-bridged bidentate ligand that catalyzed (co)oligo- and polymerizations of ethylene are known:(9a,12) Notable examples include nickel/2-(di-tert-butylphosphino)-1-phenylethan-1-one catalysts for ethylene/methyl 10-undecenoate copolymerization,(13) and palladium/cyclopentane-1,2-diyl-bridged phosphine–sulfonate complexes for ethylene/methyl acrylate and ethylene/vinyl fluoride copolymerization.(14)

Our group has previously developed phenylene-bridged bisphosphine monoxide (BPMO) ligands of the type R¹₂PC₆H₄PR²₂═O (R¹ = i-Pr, Ph, 2-MeOC₆H₄, 2-CF₃C₆H₄; R² = t-Bu, i-Pr, Me), which can promote the palladium-catalyzed coordination–insertion copolymerization of ethylene with various polar monomers.(15) Further investigations on this ligand platform revealed that changing the ligand backbone significantly influences the catalytic performance. Herein we describe the synthesis of novel palladium/BPMO complexes that bear a methylene linker (Figure 1)(16) and their catalytic performance in the homopolymerization of ethylene and the copolymerization of ethylene and polar monomers. The introduction of bulky R¹ groups, such as tert-butyl and menthyl, on the phosphine moiety is thereby essential to obtain high-molecular-weight (co)polymers.

Figure 1. Palladium complexes bearing phenylene- and methylene-bridged BPMO ligands.

Methylene-bridged BPMO ligands 1a–f were synthesized according to Scheme 1. Ligands 1a–c and 1e–f were obtained from reactions of the corresponding chlorophosphines (ClPR¹₂) with the respective (phosphorylmethyl)lithium (LiCH₂P(═O)R²₂) compounds that were prepared via the deprotonation of the corresponding methylphosphine oxides with alkyllithium (Scheme 1a). Ligand 1d was prepared by the monoxidation of bis(di-tert-butylphosphanyl)methane (Scheme 1b). A subsequent reaction between ligands 1a–f and PdMeCl(cod) afforded complexes 2a–f, which were purified by recrystallization (Scheme 1c). Finally, complexes 2a–f were converted to complexes 3a–f with sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaBAr^F₄) in the presence of 2,6-lutidine.

Scheme 1. Synthesis of Methylene-Bridged BPMO Ligands and Their Palladium Complexes

The structures of all these palladium complexes were characterized by multinuclear NMR spectroscopy, as well as mass spectrometry and/or elemental analysis. The molecular structures of 2c and 2f were moreover characterized by single-crystal X-ray diffraction analysis (Figure 2). For comparison, the corresponding palladium complex 4,(15a) which bears a phenylene-bridged BPMO ligand (R¹ = i-Pr, R² = t-Bu), is also shown in Figure 2c. The bite angles of complexes 2c (85.05(8)°) and 2f (88.41 (10)°) are narrower than that of complex 4 (91.19(6)°), which is consistent with the bite angles of well-known diphosphine ligands that form five-membered rings or six-membered rings (1,2-bis(diphenylphosphino)ethane: 85°; and 1,2-bis(diphenylphosphino)propane: 91°) upon chelation.(1b) The narrower bite angles of complexes 2c and 2f relative to complex 4 induces an elongation of the Pd1–O1 bond by about 0.11 Å. As a result, electron donation from the phosphine oxide moiety seems to be slightly weakened, which results in a contraction of the Pd1–C1 bond in 2c and 2f compared to that in 4. It is notable that the Pd1–P1 bond length and P1–Pd1–C1 angle are comparable in 2c, 2f, and 4. These results suggest that changing the backbone from phenylene to methylene modulates the environment around the phosphine oxide moiety electronically and sterically without changing the environment around the phosphine moiety.

Figure 2. X-ray structures of palladium/BPMO complexes (a) 2c, (b) 2f, and (c) 4 with 50% thermal ellipsoids. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (°): (a) 2c: Pd1–P1 2.2054(13), Pd1–O1 2.236(3), Pd1–C1 2.033(5), P1–Pd1–O1 85.05(8), P1–Pd1–C1 92.33(14). (b) 2f: Pd1–P1 2.2188(16), Pd1–O1 2.224(5), Pd1–C1 2.027(7), P1–Pd1–O1 88.45(12), P1–Pd1–C1 91.55(18). (c) 4: Pd1–P1 2.2285(10), Pd1–O1 2.120(2), Pd1–C1 2.068(3), P1–Pd1–O1 91.19(6), P1–Pd1–C1 92.51(11).

Palladium complexes 3a–f were examined in the homopolymerization of ethylene (Table 1). Complexes 3a and 3b, which bear aryl groups on the phosphine moiety, exclusively afforded oligoethylenes, indicating inferior performance relative to the corresponding palladium complexes bearing a phenylene-bridged BPMO ligand (5a and 5b) (compare entries 1 and 2 with entries 7 and 8). Alkyl-substituted complex 3c also exhibited a poorer performance than the corresponding phenylene-bridged complex (5c; compare entries 3 and 9). Considering the X-ray structures of 2c and 4, this difference could arise from the change in the steric environment around the palladium center caused by the smaller bite angle of the methylene-bridged ligands. The decrease of “steric protection” is known to cause relatively faster β-hydride elimination followed by chain transfer leading ultimately in lower catalytic activity.(6b,c) It is noteworthy that 3a–3c afforded highly linear polyethylenes with less than 1–4 methyl branches per 10³ carbon atoms (entries 1–3), while complexes 5a–5c afforded moderately branched polyethylenes (5–17 methyl branches per 10³ carbon atoms, see entries 7–9). These results could be rationalized in terms of a fast chain transfer after the β-hydride elimination, as the formation of methyl-branched structures requires reinsertion of the formed alkene in the opposite direction after the β-hydride elimination. We therefore decided to increase the steric bulk around the phosphine moiety in order to suppress the chain transfer. When the R¹ group was changed from isopropyl to tert-butyl, the molecular weight of the resulting polyethylene dramatically increased to M_n = 24 × 10³ (entry 4). These results suggest that substituents on the phosphine moiety should be bulky to compensate for the decreased steric hindrance caused by the small bite angle in the case of methylene-bridged ligands. Further modification of the ligands revealed that changing the R² group to methyl (3e) improved the catalytic activity and linearity compared to 3d, while maintaining the molecular weight (entry 5). This behavior stands in stark contrast to that discussed in our previous report, in which a decrease of molecular weight was observed upon changing the substituents on the phosphine oxide moiety from tert-butyl to methyl.(15b) Finally, complex 3f, which has menthyl groups on the phosphine moiety and methyl groups on the phosphine oxide moiety, exhibited the highest catalytic activity and linearity among complexes synthesized in this study (2,000 kg mol^–1 h^–1, < 1 methyl branch per 10³ carbon atoms; entry 6).

Table 1. Homopolymerization of Ethylene by Palladium/BPMO Complexesa

entry	catalyst	yield (g)	activity (kg mol^–1 h^–1)	M_nb (10³)	M_w/M_nb	Me br.c (10³ C)
1	3a	0.70	930	2.9	2.1	2
2	3b	0.59	790	2.3	2.1	1
3	3c	0.10	130	1.5	1.8	4
4	3d	0.12	160	24	2.2	9
5	3e	0.67	890	24	2.0	2
6	3f	1.50	2000	29	2.1	<1
7d	5a	1.74	2300	12	4.2	14
8d	5b	0.79	1100	21	2.8	17
9d	5c	2.00	2700	31	3.1	5

^{^a}

Conditions: ethylene (3.0 MPa) and catalyst (0.75 μmol) in toluene (15 mL) were stirred for 1 h at 100 °C in a 50 mL stainless autoclave.

^{^b}

Molecular weight determined by size-exclusion chromatography (SEC) analysis using polystyrene as an internal standard and calibrated by universal calibration.

^{^c}

Number of branched carbon atoms per 1000 carbon atoms determined by quantitative ¹³C NMR analysis.

^{^d}

Data from ref (15b).

With the best catalyst 3f in hand, the copolymerization of ethylene with various polar monomers was investigated (entries 1–10; Table 2). Copolymerization of ethylene (3.0 MPa) and allyl acetate (AAc; 20 vol % in toluene) at 80 °C afforded an ethylene/AAc copolymer with an AAc incorporation of 0.4 mol % (entry 1). When the concentration of AAc was increased to 80 vol % and the temperature was raised to 100 °C, the incorporation ratio of AAc increased almost 5-fold (2.1 mol %) as compared to that in entry 1 (entry 2). We subsequently explored the copolymerization of ethylene and polar monomers of the type CH₂═CHOR, such as vinyl acetate (VAc) and butyl vinyl ether (BVE) (entries 3–8). Copolymers of ethylene and VAc or BVE were successfully obtained with incorporation ratios of 0.7–1.6 mol % of the polar monomer (entries 3–6). It should be noted that the incorporation ratio of BVE could be doubled under high-concentration conditions (compare entries 5 and 6). The catalyst system was also applied to acrylic monomers such as acrylonitrile (AN) and methyl acrylate (MA). The use of 20 vol % of AN at 80 °C resulted in the formation of polyethylene without any functional groups (entry 7); however, under high-concentration conditions, AN was successfully incorporated (1.0 mol %; entry 8). MA was also incorporated into the linear polyethylene, and the incorporation ratio could be increased 3-fold under high-concentration conditions (0.5 to 1.6 mol %; entries 9 and 10).

Table 2. Copolymerization of Ethylene and Polar Monomers by Palladium Complexes 3f and 3ea

entry	catalyst	polar monomer (mL)	toluene (mL)	ethylene (MPa)	temp (°C)	yield (g)	activity (kg mol^–1 h^–1)	M_nb (10³)	M_w/M_nb	incorp.c (mol %)
1	3f	AAc (3.0)	12	3.0	80	0.79	5.3	36	2.2	0.4
2	3f	AAc (12)	3.0	3.0	100	0.39	2.6	9.5	2.0	2.1
3	3f	VAc (12)	3.0	3.0	80	0.38	2.6	4.4	2.9	0.7
4	3f	VAc (12)	3.0	3.0	100	0.47	3.1	3.1	2.3	0.7
5	3f	BVE (3.0)	12	3.0	80	0.97d	6.4	8.0	3.4	0.8
6	3f	BVE (12)	3.0	3.0	100	0.37d	2.5	9.0	1.9	1.6
7	3f	AN (3.0)	12	3.0	80	0.96	6.4	3.7	2.2	0
8	3f	AN (12)	3.0	3.0	100	0.10	0.7	1.0	1.6	1.0
9	3f	MA (3.0)	12	3.0	80	3.1	20	12	2.1	0.5
10e	3f	MA (12)	3.0	3.0	100	0.47	3.1	15	2.6	1.6
11	3e	AAc (1.0)	14	3.0	80	0.09	0.6	10	2.1	1.4
12	3e	AAc (2.0)	13	3.0	80	0.06	0.4	7.4	2.1	2.7
13	3e	AAc (3.0)	12	3.0	80	0.06	0.4	6.3	2.0	3.2
14	3e	AAc (5.0)	10	3.0	80	0.04	0.3	2.4	2.7	5.7
15f	3e	AAc (7.5)	7.5	3.0	80	0.05	0.2	1.5	2.8	8.6
16f,g	3e	AAc (12)	3.0	3.0	80	0.07	0.1	0.5	5.2	12.0
17	3e	VAc (12)	3.0	3.0	80	0.12	0.8	1.2	1.9	2.7
18	3e	AN (3.0)	12	3.0	80	0.27	1.8	3.1	2.3	0.3
19h	3e	MA (3.0)	12	3.0	80	0.03	0.2	0.9	1.9	7.2
20h	3e	MMA (3.0)	12	2.0	100	0.88	5.9	10	2.7	0.1
21h	3e	MMA (12)	3.0	2.0	100	0.41	2.7	7.3	3.0	0.2
22h	3e	MMA (15)	0	1.0	100	0.09	0.6	2.2	4.0	0.6

^{^a}

Conditions: ethylene (1.0–3.0 MPa), 3f or 3e (10 μmol), and comonomer (x mL) in toluene (15–x mL) were stirred for 15 h at the indicated temperature in a 50 mL stainless steel autoclave. AAc: allyl acetate; VAc: vinyl acetate; BVE: butyl vinyl ether; AN: acrylonitrile; MA: methyl acrylate; MMA: methyl methacrylate.

^{^b}

Determined by SEC analysis using polystyrene as an internal standard and calibrated by universal calibration.

^{^c}

Incorporation ratio of polar monomer determined by ¹H NMR or quantitative ¹³C NMR analysis.

^{^d}

Yield after Soxhlet extraction with chloroform in order to remove the BVE homopolymer.

^{^e}

50 μmol of galvinoxyl was added.

^{^f}

20 μmol of 3e was used.

^{^g}

Stirred for 36 h.

^{^h}

90 μmol of BHT was added.

During the investigation of the copolymerization, we serendipitously discovered a significant increase of comonomer incorporation efficiency when complex 3e was used as a catalyst (entries 11–22 in Table 2). First, we examined the copolymerization of ethylene and AAc using 3e (entries 11–16). As the concentration of AAc was increased from 6.7 to 80 vol %, the incorporation ratios also increased from 1.4 to 12.0 mol %. In order to compare the efficiency of the incorporation of AAc, we plotted the AAc incorporation ratios (mol %) as a function of the concentration of AAc (mol·L^–1) divided by the pressure of ethylene (MPa), under the postulation that the amount of ethylene dissolved in the reaction mixture is linearly proportional to the pressure of ethylene and does not depend on the AAc:toluene ratio (Figure 3).(17) Solid blue and red lines represent the copolymerization results of 3e and 3f, respectively, while dotted green, orange, and purple lines represent those obtained from palladium/phosphine–sulfonate catalysts(7e,18) and palladium/phosphine-phosphinic amide catalyst.(9i) This comparison clearly shows that 3e can incorporate AAc more efficiently at 80 °C than any other of these palladium complexes with a [P–O]-type bidentate ligand. Notably, an incorporation ratio of 12.0 mol % AAc in the coordination–insertion copolymerization of ethylene is the highest value reported so far (entry 16). Subsequently, we carried out the copolymerization of ethylene with VAc, which resulted in the formation of a copolymer with an incorporation ratio of 2.7 mol % (entry 17), which represents the highest value among any other late-transition-metal-catalyzed ethylene/VAc copolymerizations reported to date. This catalytic system was also applied to the copolymerization of other polar monomers (entries 18–22). Complex 3e could incorporate 0.3 mol % of AN under low-concentration conditions (20 vol %); in contrast, no copolymer was obtained under the conditions when 3f was used as a catalyst (compare entries 7 and 18). Complex 3e moreover afforded a copolymer of ethylene and MA with a high incorporation ratio (7.2 mol %), albeit at the expense of low activity and molecular weight (entry 19). NMR analyses revealed that MA was incorporated mainly into the polymer main chain (78%) and into the polymer chain ends (22%).(19) Finally, the copolymerization of ethylene and MMA was examined (entries 20–22). Although many late-transition-metal complexes catalyze the copolymerization of ethylene and MMA,(20) very few catalysts produce statistical copolymers of ethylene and MMA.(8c) Complex 3e efficiently incorporated MMA into the main chain of polyethylenes with moderately high-molecular-weight (0.1 mol %, M_n = 10 × 10³; entry 20). Under high-concentration conditions (80 vol %), incorporation ratio of MMA was doubled (0.2 mol %; entry 21), while reducing the ethylene pressure and increasing the MMA concentration (1.0 MPa, 100 vol %) resulted in the increase of the incorporation ratio of MMA to up to 0.6 mol % (entry 22). In our previous reports on successful formation of the statistical copolymer of ethylene and MMA,(8c) the unique capabilities of the palladium/IzQO catalyst allowed us to bridge the difference in the reactivities of ethylene and MMA (arising from differences in their steric demands). These differences prove to be detrimental in conventional systems. Along the same lines, the catalytic system in this work would also be expected to be insensitive toward different steric demands of different olefinic monomers.

Figure 3. Comparison of AAc incorporation ratios (mol %) as a function of the concentration of AAc (mol·L^–1) divided by the pressure of ethylene (MPa) obtained from 3e, 3f, and other previously reported catalyst systems at 80 °C. Solid lines represent the results of this study, while dotted lines represent the results reported in ref (7e), (9i), and (18).

In conclusion, we have developed novel palladium/methylene-bridged BPMO catalysts, which successfully catalyze the copolymerization of ethylene and various polar monomers such as AAc, VAc, BVE, AN, MA, and MMA. The catalytic system represents one of the first examples of late-transition-metal complexes bearing a bidentate ligand bridged by an alkylene linker that are able to copolymerize ethylene with polar monomers. Catalyst 3f produces high-molecular-weight (co)polymers. Meanwhile, catalyst 3e exhibited higher incorporation efficiency than 3f, affording ethylene/AAc copolymers with AAc incorporations ratios of up to 12.0 mol %. Furthermore, complex 3e successfully incorporated MMA with an incorporation ratio of 0.6 mol %, thus representing the second example for the successful formation of a statistical ethylene/MMA copolymer. We are convinced that these insights into the effect of the ligand backbone structures on the ethylene homopolymerization and the ethylene/polar monomer copolymerization will benefit the future design of new functional polymeric materials.

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsmacrolett.8b00034.

Experimental procedure, NMR spectra of complexes and (co)polymers, and X-ray crystallographic data (PDF).

mz8b00034_si_001.pdf (2.28 MB)

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Corresponding Author
- Kyoko Nozaki - Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan; http://orcid.org/0000-0002-0321-5299; Email: [email protected]
Authors
- Yusuke Mitsushige - Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
- Hina Yasuda - Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan; http://orcid.org/0000-0002-8770-0039
- Brad P. Carrow - Department of Chemistry, Princeton University, Princeton, New Jersey, United States; http://orcid.org/0000-0003-4929-8074
- Shingo Ito - Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan; http://orcid.org/0000-0003-1776-4608
- Minoru Kobayashi - Japan Polychem Corporation, 1 Toho-cho, Yokkaichi, Mie 510-0848, Japan
- Takao Tayano - Japan Polychem Corporation, 1 Toho-cho, Yokkaichi, Mie 510-0848, Japan
- Yumiko Watanabe - Computational Science and Technology Information Center, Showa Denko K.K., 1-1-1 Ohnodai, Midori-ku, Chiba, Chiba 267-0056, Japan
- Yoshishige Okuno - Computational Science and Technology Information Center, Showa Denko K.K., 1-1-1 Ohnodai, Midori-ku, Chiba, Chiba 267-0056, Japan
- Shinya Hayashi - Institute for Advanced and Core Technology, Showa Denko K.K., 2 Nakanosu, Oita, Oita 870-1809, Japan
- Junichi Kuroda - Institute for Advanced and Core Technology, Showa Denko K.K., 2 Nakanosu, Oita, Oita 870-1809, Japan
- Yoshikuni Okumura - Institute for Advanced and Core Technology, Showa Denko K.K., 2 Nakanosu, Oita, Oita 870-1809, Japan
Notes
The authors declare no competing financial interest.

Acknowledgments

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This work was supported by JST, CREST, and “Nanotechnology Platform” (Project No.12024046) of MEXT, Japan. Y.M. is grateful to Program for Leading Graduate Schools (MERIT) from JSPS. S.I. is grateful for the financial support from Tonen General Sekiyu Foundation.

References

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This article references 20 other publications.

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Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry (1999), (10), 1519-1530CODEN: JCDTBI; ISSN:0300-9246. (Royal Society of Chemistry)
A review with 72 refs.; over the past twenty years, a correlation between the P-M-P bite angle in diphosphine complexes and selectivity has been obsd. in various catalytic reactions such as hydroformylation, hydrocyanation and cross coupling. The large no. of examples indicates that this correlation is not fortuitous. In order better to understand the underlying principles of the bite angle effect, we have first analyzed crystal structures available in the Cambridge Crystallog. Database. Systematic searches indicate that for many bidentate diphosphine ligands the P-M-P angles conc. in surprisingly small ranges, even if complexes of different metals in various oxidn. states are considered. Several examples in the literature show that continuous electronic changes assocd. with changing bite angles cannot only be verified by different spectroscopic techniques, but also explained on a theor. level (Walsh diagrams). The ligand bite angle is a useful parameter for the explanation of obsd. rates and selectivities and likewise for the design of ligands for new catalytic reactions.
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(c) Kamer, P. C. J.; van Leeuwen, P. W. N. M.; Reek, J. N. H. Wide Bite Angle Diphosphines: Xantphos Ligands in Transition Metal Complexes and Catalysis. Acc. Chem. Res. 2001, 34, 895– 904, DOI: 10.1021/ar000060+
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1c
Wide Bite Angle Diphosphines: Xantphos Ligands in Transition Metal Complexes and Catalysis
Kamer, Paul C. J.; van Leeuwen, Piet W. N. M.; Reek, Joost N. H.
Accounts of Chemical Research (2001), 34 (11), 895-904CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
A review is presented in which is described the development and application of new diphosphine ligands, designed to induce large P-M-P angles in transition metal complexes. The reactivity of organotransition metal complexes is dependent on the ligand environment of the metal. Aided by computational chem., a homologous range of diphosphines based on rigid heterocyclic arom. backbones of the xanthene-type with natural bite angles of ∼100-134° were developed. The special structure of the ligands has an enormous impact on stability and reactivity of various transition metal complexes. Highly active and selective catalysts were obtained by influencing this reactivity.
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Teng, Q.; Huynh, H. V. Determining the Electron-Donating Properties of Bidentate Ligands by ¹³C NMR Spectroscopy. Inorg. Chem. 2014, 53, 10964– 10973, DOI: 10.1021/ic501325j
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2
Determining the Electron-Donating Properties of Bidentate Ligands by 13C NMR Spectroscopy
Teng, Qiaoqiao; Huynh, Han Vinh
Inorganic Chemistry (2014), 53 (20), 10964-10973CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
A series of 15 mononuclear complexes [PdBr(iPr2-bimy)(L2)]PF6 (1-15) (iPr2-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene, L2 = arom. 1,2-diimines, diazabutadienes, or methylene-, ethylene- and propylene-bridged di-N-heterocyclic carbenes) and two dicarbene-bridged, dinuclear complexes [Pd2Br4(iPr2-bimy)2(diNHC)] (16 and 17) were synthesized and characterized by multinuclear NMR spectroscopy, electrospray ionization mass spectrometry, and in some cases x-ray diffraction anal. The influence of the 15 bidentate ligands L2 on the 13Ccarbene signals of the iPr2-bimy reporter ligand in the chelate complexes was studied, on the basis of which a facile methodol. for the donor strength detn. of bidentate ligands was developed.
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(a) Johnson, L. K.; Killian, C. M.; Brookhart, M. New Pd(II)- and Ni(II)-Based Catalysts for Polymerization of Ethylene and α-Olefins. J. Am. Chem. Soc. 1995, 117, 6414– 6415, DOI: 10.1021/ja00128a054
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3a
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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(b) Killian, C. M.; Tempel, D. J.; Johnson, L. K.; Brookhart, M. Living Polymerization of α-Olefins Using Ni^II–α-Diimine Catalysts. Synthesis of New Block Polymers Based on α-Olefins. J. Am. Chem. Soc. 1996, 118, 11664– 11665, DOI: 10.1021/ja962516h
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3b
Living polymerization of α-olefins using NiII-α-diimine catalysts. Synthesis of new block polymers based on α-olefins
Killian, Christopher M.; Tempel, Daniel J.; Johnson, Lynda K.; Brookhart, Maurice
Journal of the American Chemical Society (1996), 118 (46), 11664-11665CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Procedures for carrying out the living polymn. of α-olefins have been developed using nickel(II) complexes stabilized by sterically bulky α-diimine ligands. At 10° and low monomer concns., near monodisperse elastomeric poly(α-olefin) homo- and block copolymers have been prepd. The structure and properties of these polymers can be systematically varied as a function of catalyst structure and α-olefin chain length.
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(c) 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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3c
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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For review, see:
(d) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Late-Metal Catalysts for Ethylene Homo- and Copolymerization. Chem. Rev. 2000, 100, 1169– 1204, DOI: 10.1021/cr9804644
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3d
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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For recent examples, see:
(a) Takano, S.; Takeuchi, D.; Osakada, K.; Akamatsu, N.; Shishido, A. Dipalladium Catalyst for Olefin Polymerization: Introduction of Acrylate Units into the Main Chain of Branched Polyethylene. Angew. Chem., Int. Ed. 2014, 53, 9246– 9250, DOI: 10.1002/anie.201404339
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4a
Dipalladium Catalyst for Olefin Polymerization: Introduction of Acrylate Units into the Main Chain of Branched Polyethylene
Takano, Shigenaga; Takeuchi, Daisuke; Osakada, Kohtaro; Akamatsu, Norihisa; Shishido, Atsushi
Angewandte Chemie, International Edition (2014), 53 (35), 9246-9250CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
A dipalladium complex with a double-decker structure catalyzes ethylene-acrylate copolymn. to produce the branched polymer contg. the acrylate units in the polymer chain, not at the branch terminus. The cooperation of the two palladium centers, which are fixed in a rigid framework of the macrocyclic ligand, is proposed to have a significant dinuclear effect on the copolymn.
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(b) Allen, K. E.; Campos, J.; Daugulis, O.; Brookhart, M. Living Polymerization of Ethylene and Copolymerization of Ethylene/Methyl Acrylate Using “Sandwich” Diimine Palladium Catalysts. ACS Catal. 2015, 5, 456– 464, DOI: 10.1021/cs5016029
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4b
Living Polymerization of Ethylene and Copolymerization of Ethylene/Methyl Acrylate Using "Sandwich" Diimine Palladium Catalysts
Allen, Kate E.; Campos, Jesus; Daugulis, Olafs; Brookhart, Maurice
ACS Catalysis (2015), 5 (1), 456-464CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
Cationic Pd(II) catalysts incorporating bulky 8-p-tolylnaphthyl substituted diimine ligands have been synthesized and investigated for ethylene polymn. and ethylene/methyl acrylate copolymn. Homopolymn. of ethylene at room temp. resulted in branched polyethylene with narrow Mw/Mn values (ca. 1.1), indicative of a living polymn. A mechanistic study revealed that the catalyst resting state was an alkyl olefin complex and that the turnover-limiting step was migratory insertion, thus the turnover frequency is independent of ethylene concn. Copolymn. of ethylene and Me acrylate (MA) was also achieved. MA incorporation was found to increase linearly with MA concn., and copolymers with up to 14 mol % MA were prepd. Mechanistic studies revealed that acrylate insertion into a Pd-CH3 bond occurs at -70 °C to yield a four-membered chelate, which isomerizes first to a five-membered chelate and then to a six-membered chelate. Barriers to migratory insertion of both the (diimine)PdCH3(C2H4)+ (19.2 kcal/mol) and (diimine)PdCH3(η2-C2H3CO2Me)+ (15.2 kcal/mol) were measured by low-temp. NMR kinetics.
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(c) Dai, S.; Sui, X.; Chen, C. Highly Robust Palladium(II) α-Diimine Catalysts for Slow-Chain-Walking Polymerization of Ethylene and Copolymerization with Methyl Acrylate. Angew. Chem., Int. Ed. 2015, 54, 9948– 9953, DOI: 10.1002/anie.201503708
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4c
Highly Robust Palladium(II) α-Diimine Catalysts for Slow-Chain-Walking Polymerization of Ethylene and Copolymerization with Methyl Acrylate
Dai, Shengyu; Sui, Xuelin; Chen, Changle
Angewandte Chemie, International Edition (2015), 54 (34), 9948-9953CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
A series of sterically demanding α-diimine ligands bearing electron-donating and electron-withdrawing substituents were synthesized by an improved synthetic procedure in high yield. Subsequently, the corresponding Pd complexes were prepd. and isolated by column chromatog. These Pd complexes demonstrated unique properties in ethylene polymn., including high thermal stability and high activity, thus generating polyethylene with a high mol. wt. and very low branching d. Similar properties were obsd. for ethylene/methyl acrylate copolymn. Because of the high mol. wt. and low branching d., the generated polyethylene and ethylene/methyl acrylate copolymer were semicryst. solids. The (co)polymers had unique microstructures originating from the unique slow-chain-walking activity of these Pd complexes.
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(d) 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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4d
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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(e) Dai, S.; Zhou, S.; Zhang, W.; Chen, C. Systematic Investigations of Ligand Steric Effects on α-Diimine Palladium Catalyzed Olefin Polymerization and Copolymerization. Macromolecules 2016, 49, 8855– 8862, DOI: 10.1021/acs.macromol.6b02104
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4e
Systematic Investigations of Ligand Steric Effects on α-Diimine Palladium Catalyzed Olefin Polymerization and Copolymerization
Dai, Shengyu; Zhou, Shixin; Zhang, Wen; Chen, Changle
Macromolecules (Washington, DC, United States) (2016), 49 (23), 8855-8862CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
In the Brookhart type α-diimine palladium catalyst system, it is highly challenging to tune the polymer branching densities through ligand modifications or polymn. conditions. In this contribution, the authors describe the synthesis and characterization of α-diimine ligands and the corresponding palladium catalysts bearing both the dibenzhydryl moiety and with systematically varied ligand sterics. In ethylene polymn., it is possible to tune the catalytic activities ((0.77-8.85) × 105 g/(mol Pd·h)), polymer mol. wts. (Mn: (0.2-164.7) × 104), branching densities (25-116/1000C), and polymer melting temps. (amorphous to 98°) over a very wide range. In ethylene-Me acrylate (E-MA) copolymn., it is possible to tune the catalytic activities ((0.3-8.8) × 103 g/(mol Pd·h)), copolymer mol. wts. (1.1 × 103-79.8 × 103), branching densities (30-119/1000C), and MA incorporation ratio (0.4-13.8%) over a very wide range. The mol. wts. and branching densities could also be tuned in α-olefin polymn. The tuning in polymer microstructures leads to significant tuning in polyethylene mech. properties and the surface properties of the E-MA copolymer.
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(f) Dai, S.; Chen, C. Direct Synthesis of Functionalized High-Molecular-Weight Polyethylene by Copolymerization of Ethylene with Polar Monomers. Angew. Chem., Int. Ed. 2016, 55, 13281– 13285, DOI: 10.1002/anie.201607152
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4f
Direct Synthesis of Functionalized High-Molecular-Weight Polyethylene by Copolymerization of Ethylene with Polar Monomers
Dai, Shengyu; Chen, Changle
Angewandte Chemie, International Edition (2016), 55 (42), 13281-13285CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
The introduction of even a small amt. of polar functional groups into polyolefins could excise great control over important material properties. As the most direct and economic strategy, the transition-metal-catalyzed copolymn. of olefins with polar, functionalized monomers represents one of the biggest challenges in this field. The presence of polar monomers usually dramatically reduces the catalytic activity and copolymer mol. wt. (to the level of thousands or even hundreds Da), rendering the copolymn. process and the copolymer materials far from ideal for industrial applications. In this contribution, we demonstrate that these obstacles can be addressed through rational catalyst design. Copolymers with highly linear microstructures, high melting temps., and very high mol. wts. (close to or above 1 000 000 Da) were generated. The direct synthesis of polar functionalized high-mol.-wt. polyethylene was thus achieved.
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(g) Chen, Z.; Liu, W.; Daugulis, O.; Brookhart, M. Mechanistic Studies of Pd(II)-Catalyzed Copolymerization of Ethylene and Vinylalkoxysilanes: Evidence for a β-Silyl Elimination Chain Transfer Mechanism. J. Am. Chem. Soc. 2016, 138, 16120– 16129, DOI: 10.1021/jacs.6b10462
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4g
Mechanistic studies of Pd(II)-catalyzed copolymerization of ethylene and vinylalkoxysilanes: evidence for a β-silyl elimination chain transfer mechanism
Chen, Zhou; Liu, Weijun; Daugulis, Olafs; Brookhart, Maurice
Journal of the American Chemical Society (2016), 138 (49), 16120-16129CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Copolymns. of ethylene with vinyltrialkoxysilanes are reported using both a "traditional" cationic Pd(II) aryldiimine catalyst, [[acen(NAr)2]PdMe(L)][BArF4] (t-1, acen = acenaphthene-1,2-diylidene; Ar = 2,6-diisopropylphenyl; L = MeCN, OEt2, C2H4), and a "sandwich-type" aryldiimine catalyst, [[acen(NAr1)2]PdMe(OEt2)][BArF4] (s-2, Ar1 = 8-p-tolyl-1-naphthyl; L = MeCN, OEt2, C2H4). Incorporation levels of vinyltrialkoxysilanes between 0.25 and 2.0 mol% were achieved with remarkably little rate retardation relative to ethylene homopolymns. In the case of the traditional catalyst system, mol. wts. decrease as the level of comonomer increases and only one trialkoxysilyl group is incorporated per chain. Mol. wt. distributions of ca. 2 are obsd. For the sandwich catalyst, higher mol. wts. are obsd. with many more trialkoxysilyl groups incorporated per chain. Polymers with mol. wt. distributions of ca. 1.2-1.4 are obtained. Detailed NMR mechanistic studies have revealed the formation of intermediate π-complexes of the type [[acen(NAr)]PdR[CH2:CHSi(OR1)3]]+. 1,2-Migratory insertions of these complexes occur with rates similar to ethylene insertion and result in formation of observable five-membered chelate intermediates. These chelates are rapidly opened with ethylene forming alkyl ethylene complexes, a requirement for chain growth. An unusual β-silyl elimination mechanism was shown to be responsible for chain transfer and formation of low mol. wt. copolymers in the traditional catalyst system, t-1. This chain transfer process is retarded in the sandwich system 2. Relative binding affinities of ethylene and vinyltrialkoxysilanes to the cationic palladium center have been detd. The quant. mechanistic studies reported fully explain the features of the bulk polymn. results.
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(h) Zhao, M.; Chen, C. Accessing Multiple Catalytically Active States in Redox-Controlled Olefin Polymerization. ACS Catal. 2017, 7, 7490– 7494, DOI: 10.1021/acscatal.7b02564
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4h
Accessing Multiple Catalytically Active States in Redox-Controlled Olefin Polymerization
Zhao, Minhui; Chen, Changle
ACS Catalysis (2017), 7 (11), 7490-7494CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
The majority of work in the field of olefin polymn. catalysis has been focused on ligand modifications. In this work, authors describe an alternative strategy for the modulation of olefin polymn. and copolymn. processes. The two ferrocenyl units in an α-diimine palladium catalyst can be oxidized in a stepwise fashion. This stepwise redox control can be used to modulate the catalyst properties during the homopolymn. of ethylene and 1-hexene, as well as the copolymns. of ethylene with norbornene, Me acrylate, and 5-norbornene-2-yl acetate. Moreover, polymer microstructure and polydispersity can be controlled during these stepwise oxidn. processes.
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(i) Li, M.; Wang, X.; Luo, Y.; Chen, C. A Second-Coordination-Sphere Strategy to Modulate Nickel- and Palladium-Catalyzed Olefin Polymerization and Copolymerization. Angew. Chem., Int. Ed. 2017, 56, 11604– 11609, DOI: 10.1002/anie.201706249
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4i
A Second-Coordination-Sphere Strategy to Modulate Nickel- and Palladium-Catalyzed Olefin Polymerization and Copolymerization
Li, Min; Wang, Xingbao; Luo, Yi; Chen, Changle
Angewandte Chemie, International Edition (2017), 56 (38), 11604-11609CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
Transition-metal-catalyzed copolymn. reactions of olefins with polar-functionalized comonomers are highly important and also highly challenging. A second-coordination-sphere strategy was developed to address some of the difficulties encountered in these copolymn. reactions. A series of α-diimine ligands bearing nitrogen-contg. second coordination spheres were prepd. and characterized. The properties of the corresponding nickel and palladium catalysts in ethylene polymns. and copolymns. were investigated. In the nickel system, significant redn. in polymer branching d. was obsd., while lower polymer branching densities, as well as a wider range of polar monomer substrates, were achieved in the palladium system. Control expts. and computational results reveal the crit. role of the metal-nitrogen interaction in these polymn. and copolymn. reactions.
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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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For review, see:
(a) Berkefeld, A.; Mecking, S. Coordination Copolymerization of Polar Vinyl Monomers H₂C═CHX. Angew. Chem., Int. Ed. 2008, 47, 2538– 2542, DOI: 10.1002/anie.200704642
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6a
Coordination copolymerization of polar vinyl monomers H2C=CHX
Berkefeld, Andreas; Mecking, Stefan
Angewandte Chemie, International Edition (2008), 47 (14), 2538-2542CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
Risina review on neutral phosphinosulfonate PdII complexes as versatile catalysts even for the challenging insertion copolymn. of polar functionalized vinyl comonomers H2C=CHX, such as acrylonitrile, vinyl acetate, and alkyl vinyl ethers.
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(b) Nakamura, A.; Ito, S.; Nozaki, K. Coordination–Insertion Copolymerization of Fundamental Polar Monomers. Chem. Rev. 2009, 109, 5215– 5244, DOI: 10.1021/cr900079r
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6b
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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(c) Ito, S.; Nozaki, K. Coordination–Insertion Copolymerization of Polar Vinyl Monomers by Palladium Catalysts. Chem. Rec. 2010, 10, 315– 325, DOI: 10.1002/tcr.201000032
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6c
Coordination-insertion copolymerization of polar vinyl monomers by palladium catalysts
Ito, Shingo; Nozaki, Kyoko
Chemical Record (2010), 10 (5), 315-325CODEN: CRHEAK; ISSN:1527-8999. (John Wiley & Sons, Inc.)
A review. Random incorporation of polar functional groups into polyolefins and polyketones along with the precise control of incorporation ratios and polymer microstructures is one of the most significant challenges in polymer chem. For such a purpose, late-transition-metal complexes are often employed as a catalyst for the copolymn. of polar vinyl monomers, because of their high functional group compatibility. This account describes our contribution to the development of coordination-insertion copolymn. of polar vinyl monomers by palladium catalysts. In particular, the use of palladium/phosphine-sulfonate catalysts enables to incorporate various polar vinyl monomers into polyolefins and polyketones. © 2010 The Japan Chem. Journal Forum and Wiley Periodicals, Inc. Chem Rec 10: 315-325; 2010: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.201000032.
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(d) Nakamura, A.; Anselment, T. M. J.; Claverie, J. P.; 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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6d
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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(e) Carrow, B. P.; Nozaki, K. Transition-Metal-Catalyzed Functional Polyolefin Synthesis: Effecting Control through Chelating Ancillary Ligand Design and Mechanistic Insights. Macromolecules 2014, 47, 2541– 2555, DOI: 10.1021/ma500034g
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6e
Transition-Metal-Catalyzed Functional Polyolefin Synthesis: Effecting Control through Chelating Ancillary Ligand Design and Mechanistic Insights
Carrow, Brad P.; Nozaki, Kyoko
Macromolecules (Washington, DC, United States) (2014), 47 (8), 2541-2555CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
A review. The incorporation of polar functional groups into polyolefins can significantly alter the adhesion, barrier and surface properties, dyeability, printability, and compatibility of the resulting "functional polyolefin". Thus, the development of methods for the controlled synthesis of functional polyolefins from industrially relevant monomers holds the potential to expand the range of applications available to this already ubiquitous class of materials. In this Perspective, recent advances in transition-metal-catalyzed functional polyolefin synthesis will be reviewed. A common thread among the innovations discussed here is the perturbation of catalyst function by tailored design of the chelating ancillary ligand, aided in many cases by improved mechanistic understanding. Specific topics discussed here include rare examples of catalyst control over the regio- and stereochem. of polar monomer insertion by phosphine-sulfonato palladium complexes (Drent-type), rate acceleration of insertion polymn. by binuclear cooperativity using salicylaldiminato nickel complexes (Grubbs-type), and formation of linear copolymers of ethylene and polar vinyl monomers using a cationic palladium catalyst ligated by a bisphosphine monoxide (BPMO) that contrasts the typical polymer microstructures formed by other cationic group 10 catalysts ligated by an α-diimine (Brookhart-type).
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(f) Guo, L.; Dai, S.; Sui, X.; Chen, C. Palladium and Nickel Catalyzed Chain Walking Olefin Polymerization and Copolymerization. ACS Catal. 2016, 6, 428– 441, DOI: 10.1021/acscatal.5b02426
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6f
Palladium and Nickel Catalyzed Chain Walking Olefin Polymerization and Copolymerization
Guo, Lihua; Dai, Shengyu; Sui, Xuelin; Chen, Changle
ACS Catalysis (2016), 6 (1), 428-441CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
A review. In this perspective, recent developments on palladium and nickel mediated chain walking olefin polymn. and copolymn. with polar functionalized comonomers are described. First, the chain walking polymn. mechanism is discussed followed by its implications in olefin polymn. and copolymn. Then, recent advances in catalyst design are provided. Special attention is paid to the influence of ligand structures on the catalytic properties. Subsequently, the applications of these chain walking polymn. catalysts in the synthesis of functionalized hyperbranched polymers and copolymers are summarized. Finally, some recent developments and perspectives on very fast and very slow chain walking polymn. catalysts are discussed.
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7
For recent examples not included in ref (6d), see:
(a) Leicht, H.; Göttker-Schnetmann, I.; Mecking, S. Incorporation of Vinyl Chloride in Insertion Polymerization. Angew. Chem., Int. Ed. 2013, 52, 3963– 3966, DOI: 10.1002/anie.201209724
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7a
Incorporation of Vinyl Chloride in Insertion Polymerization
Leicht, Hannes; Goettker-Schnetmann, Inigo; Mecking, Stefan
Angewandte Chemie, International Edition (2013), 52 (14), 3963-3966CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
Palladium complexes made it possible for the first time an insertion copolymn. of VC (vinyl chloride) with ethylene to form chlorine-contg. copolymers. NMR anal. of the polymers, labeling, and stoichiometric insertion studies reveal that incorporation of CHCl units proceeds by 2,1-insertion of VC into palladium hydride species. After this 2,1-insertion of VC, ethylene insertion resulting in monochlorinated polyethylene is competitive to chain walking (which through the net 1,2-insertion of VC would result in a detrimental β-chloride elimination). Regardless of the limited incorporation of vinyl chloride, this first isolation of chlorine-contg. polymers in combination with a mechanistic understanding represents a significant impetus to a long-standing challenge. Future studies will focus on further suppression of chain walking, which results in the problematic net 1,2-insertion of VC, and on facilitating in chain incorporation of VC into polymers.
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(b) 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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7b
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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(c) Lanzinger, D.; Giuman, M. M.; Anselment, T. M. J.; Rieger, B. Copolymerization of Ethylene and 3,3,3-Trifluoropropene Using (Phosphine-sulfonate)Pd(Me)(DMSO) as Catalyst. ACS Macro Lett. 2014, 3, 931– 934, DOI: 10.1021/mz5004344
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7c
Copolymerization of Ethylene and 3,3,3-Trifluoropropene Using (Phosphine-sulfonate)Pd(Me)(DMSO) as Catalyst
Lanzinger, Dominik; Giuman, Marco M.; Anselment, Timo M. J.; Rieger, Bernhard
ACS Macro Letters (2014), 3 (9), 931-934CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
(Phosphine-sulfonate)Pd(Me)(DMSO) catalyzed copolymn. of ethylene and 3,3,3-trifluoropropene (TFP) allows the synthesis of linear copolymers with high fluorine contents of up to 15 wt % (8.9 mol % TFP). 13C and 19F NMR analyses of the copolymers were performed, showing that most of the incorporated TFP is located in the polymer backbone. Copolymn. of ethylene-d4 with TFP revealed that TFP is inserted into Pd-D bonds in 1,2- as well as in 2,1-mode, although 1,2-insertion is slightly preferred. Chain transfer after TFP insertion is exclusively obsd. following 2,1-insertion. With higher TFP incorporation, an increase in the ratio of internal to terminal double bonds was detected in the 1H NMR spectra. This indicates that, in the case of 2,1-insertion of TFP, chain walking is facilitated relative to direct chain release after β-H transfer to the palladium center.
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(d) Jian, Z.; Wucher, P.; Mecking, S. Heterocycle-Substituted Phosphinesulfonato Palladium(II) Complexes for Insertion Copolymerization of Methyl Acrylate. Organometallics 2014, 33, 2879– 2888, DOI: 10.1021/om500400a
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7d
Heterocycle-Substituted Phosphinesulfonato Palladium(II) Complexes for Insertion Copolymerization of Methyl Acrylate
Jian, Zhongbao; Wucher, Philipp; Mecking, Stefan
Organometallics (2014), 33 (11), 2879-2888CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
A family of heterocycle-substituted binuclear phosphinesulfonato Pd(II) complexes {[R2P(C6H4SO2O)]PdMeClLi(DMSO)}2 (1a-d-LiCl-DMSO: 1a-LiCl-DMSO, R = 2-furyl; 1b-LiCl-DMSO, R = 2-thienyl; 1c-LiCl-DMSO, R = 2-(N-methyl)pyrrolyl; 1d-LiCl-DMSO, R = 2-benzofuryl) was synthesized, and the solid-state structures of 1a-c-LiCl-DMSO were detd., which revealed various modes of bridging between the two metal fragments. 1A-d-LiCl-DMSO further generated either the mononuclear Pd(II) complexes {[κ2P,O-R2P(C6H4SO2O)]PdMe(pyr)} (1a-d-pyr) by addn. of pyridine or the more labile mononuclear Pd(II) complex {[κ2P,O-(2-thienyl)2P(C6H4SO2O)]PdMe(DMSO)} (1b-DMSO) by chloride abstraction with AgBF4. Stoichiometric Me acrylate (MA) insertion expts. indicated that, in comparison with the other three substituents, the thienyl-substituted Pd(II) complexes undergo faster insertion of MA in a primary 2,1-fashion, and 1b-DMSO possesses the fastest insertion rate due to the relative weakly coordinating DMSO mol. All Pd complexes were employed in ethylene polymn., affording highly linear polyethylene with relatively low mol. wts. (Mn = (0.5-7.4) × 103). Under these pressure reactor conditions, the thienyl motif displays the highest activity (order: 1b-DMSO > 1b-pyr > 1a-pyr > 1d-pyr > 1c-pyr » 1a-d-LiCl-DMSO). Copolymn. reactions of ethylene and MA further revealed that MA incorporation in the obtained linear copolymers depends moderately on the heterocyclic substituents.
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(e) Ota, Y.; Ito, S.; Kuroda, J.; 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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7e
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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(f) Jian, Z.; Baier, M. C.; Mecking, S. Suppression of Chain Transfer in Catalytic Acrylate Polymerization via Rapid and Selective Secondary Insertion. J. Am. Chem. Soc. 2015, 137, 2836– 2839, DOI: 10.1021/jacs.5b00179
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7f
Suppression of Chain Transfer in Catalytic Acrylate Polymerization via Rapid and Selective Secondary Insertion
Jian, Zhongbao; Baier, Moritz C.; Mecking, Stefan
Journal of the American Chemical Society (2015), 137 (8), 2836-2839CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
In catalytic copolymn., undesired chain transfer after incorporation of a polar vinyl monomer is a fundamental problem. Authors show an approach to overcome this problem by a fast consecutive insertion. The second double bond of acrylic anhydride rapidly inserts intramolecularly to regio- and stereoselectively form a cyclic repeat unit and a primary alkyl favorable for chain growth (>96%). This results in significantly enhanced copolymer mol. wts. vs monofunctional acrylate monomers.
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(g) Chen, M.; Yang, B.; Chen, C. Redox-Controlled Olefin (Co)Polymerization Catalyzed by Ferrocene-Bridged Phosphine-Sulfonate Palladium Complexes. Angew. Chem., Int. Ed. 2015, 54, 15520– 15524, DOI: 10.1002/anie.201507274
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7g
Redox-Controlled Olefin (Co)Polymerization Catalyzed by Ferrocene-Bridged Phosphine-Sulfonate Palladium Complexes
Chen, Min; Yang, Bangpei; Chen, Changle
Angewandte Chemie, International Edition (2015), 54 (51), 15520-15524CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
The facile and reversible interconversion between neutral and oxidized forms of Pd complexes contg. ferrocene-bridged phosphine sulfonate ligands was demonstrated. The activity of these Pd complexes could be controlled using redox reagents during ethylene homopolymn., ethylene/methyl acrylate copolymn., and norbornene oligomerization. Specifically in norbornene oligomerization, the neutral complexes were not active at all whereas the oxidized counterparts showed appreciable activity. In situ switching between the neutral and oxidized forms resulted in an interesting off and on behavior in norbornene oligomerization. This work provides a new strategy to control the olefin polymn. process.
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(h) Jian, Z.; Mecking, S. Insertion Homo- and Copolymerization of Diallyl Ether. Angew. Chem., Int. Ed. 2015, 54, 15845– 15849, DOI: 10.1002/anie.201508930
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7h
Insertion Homo- and Copolymerization of Diallyl Ether
Jian, Zhongbao; Mecking, Stefan
Angewandte Chemie, International Edition (2015), 54 (52), 15845-15849CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
The previously unresolved issue of polymn. of allyl monomers CH2=CHCH2X is overcome by a palladium-catalyzed insertion polymn. of diallyl ether as a monomer. An enhanced 2,1-insertion of diallyl ether as compared to mono-allyl ether retards the formation of an unreactive five-membered cyclic O-chelate (after 1,2-insertion) that otherwise hinders further polymn., and also enhances incorporation in ethylene polymers (20.4 mol %). Cyclic ether repeat units are formed selectively (96 %-99 %) by an intramol. insertion of the second allyl moiety of the monomer. These features even enable a homopolymn. to yield polymers (poly-diallyl ether) with ds.p. of DPn≈44.
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(i) Jian, Z.; Leicht, H.; Mecking, S. Direct Synthesis of Imidazolium-Functional Polyethylene by Insertion Copolymerization. Macromol. Rapid Commun. 2016, 37, 934– 938, DOI: 10.1002/marc.201600073
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7i
Direct Synthesis of Imidazolium-Functional Polyethylene by Insertion Copolymerization
Jian, Zhongbao; Leicht, Hannes; Mecking, Stefan
Macromolecular Rapid Communications (2016), 37 (11), 934-938CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
Cationic imidazolium-functionalized polyethylene is accessible by insertion copolymn. of ethylene and allyl imidazolium tetrafluoroborate (AIm-BF4) with phosphinesulfonato palladium(II) catalyst precursors. Imidazolium-substituted repeat units are incorporated into the main chain and the initiating satd. chain end of the linear polymers, rather than the terminating unsatd. chain end. The counterion of the allyl imidazolium monomer is decisive, with the chloride analog (AIm-Cl) no polymn. is obsd. Stoichiometric studies reveal the formation of an inactive chloride complex from the catalyst precursor. An effect of moderate densities (0.5 mol%) of ionic groups on the copolymers' phys. properties is exemplified by an enhanced wetting by water.
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(j) Jian, Z.; Mecking, S. Short-Chain Branched Polar-Functionalized Linear Polyethylene via “Tandem Catalysis”. Macromolecules 2016, 49, 4057– 4066, DOI: 10.1021/acs.macromol.6b00581
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7j
Short-Chain Branched Polar-Functionalized Linear Polyethylene via "Tandem Catalysis"
Jian, Zhongbao; Mecking, Stefan
Macromolecules (Washington, DC, United States) (2016), 49 (11), 4057-4066CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
Cationic PdII complex 1 chelated by an N-fixed phosphine sultam has been synthesized and structurally characterized. Exposure of 1 to ethylene resulted in the formation of short-chain olefins (1-butene: 2-butene: 1-hexene: 1-octene = 86:7:6:1) with a high catalytic activity of 105 molE molPd-1 h-1. By combination of 1 and one of the well-known phosphinesulfonato PdII catalyst precursors 2-5, linear polyethylenes contg. Me, Et, and Bu branches of up to 100 per 1000 C were generated from the polymn. of ethylene alone in a "tandem catalysis" one-pot approach. In further exploitation of this concept, linear polyethylenes with both various short-chain branches and a choice of different polar functional groups incorporated into the main chain were obtained for the first time from the copolymn. of ethylene and polar vinyl monomers (Me acrylate, N-isopropylacrylamide, Me vinyl sulfone, acrylonitrile, Et vinyl ether, vinyl acetate, and allyl bromide). All these apolar and polar branches are incorporated into the linear polyethylene backbones to varying degrees, while the type of initiating and terminating chain ends of the resulting polyethylenes depends significantly on the nature of polar vinyl monomer.
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(k) Jian, Z.; Mecking, S. Insertion Polymerization of Divinyl Formal. Macromolecules 2016, 49, 4395– 4403, DOI: 10.1021/acs.macromol.6b00983
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7k
Insertion Polymerization of Divinyl Formal
Jian, Zhongbao; Mecking, Stefan
Macromolecules (Washington, DC, United States) (2016), 49 (12), 4395-4403CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
Copolymn. of ethylene and divinyl formal by [{κ2-P,O-(2-MeOC6H4)2PC6H4SO3}PdMe(dmso)] (1) by a coordination-insertion mechanism affords highly linear polyethylenes with a high (12.5 mol %) incorporation of divinyl formal. This significantly exceeds the thus far relatively low incorporation (6.9 mol %) and activity with Bu vinyl ether monomer in insertion polymn. The resulting ethylene-divinyl formal copolymers exclusively (>98%) contain five-membered (trans-1,3-dioxolane) and six-membered (cis-/trans-1,3-dioxane) cyclic acetal units in the main chain, and also in the initiating ends of this functionalized polyethylene. Comprehensive NMR anal. of the microstructure of these copolymers revealed that under pressure reactor conditions consecutive 2,1-1,2-insertion of divinyl formal into a Pd-H bond is preferred, but consecutive 1,2-1,2-insertion of divinyl formal into more bulky Pd-alkyls (growing polymer chain) is favored. Moreover, homopolymn. of divinyl formal yielded a non-crosslinking poly(divinyl formal) with ds. p. of DPn ≈ 26.
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(l) Ota, Y.; Ito, S.; Kobayashi, M.; Kitade, S.; Sakata, K.; Tayano, T.; Nozaki, K. Crystalline Isotactic Polar Polypropylene from the Palladium-Catalyzed Copolymerization of Propylene and Polar Monomers. Angew. Chem., Int. Ed. 2016, 55, 7505– 7509, DOI: 10.1002/anie.201600819
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7l
Crystalline Isotactic Polar Polypropylene from the Palladium-Catalyzed Copolymerization of Propylene and Polar Monomers
Ota, Yusuke; Ito, Shingo; Kobayashi, Minoru; Kitade, Shinichi; Sakata, Kazuya; Tayano, Takao; Nozaki, Kyoko
Angewandte Chemie, International Edition (2016), 55 (26), 7505-7509CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
Moderately isospecific homopolymn. of propylene and the copolymn. of propylene and polar monomers have been achieved with palladium complexes bearing a phosphine-sulfonate ligand. Optimization of substituents on the phosphorus atom of the ligand revealed that the presence of bulky alkyl groups (e.g. menthyl) is crucial for the generation of high-mol.-wt. polypropylenes (Mw≈104), and the substituent at the ortho-position relative to the sulfonate group influences the mol. wt. and isotactic regularity of the obtained polypropylenes. Statistical anal. suggested that the introduction of substituents at the ortho-position relative to the sulfonate group favors enantiomorphic site control over chain end control in the chain propagation step. The triad isotacticity could be increased to mm=0.55-0.59, with formation of cryst. polar polypropylenes, as supported by the presence of m.ps. and sharp peaks in the corresponding X-ray diffraction patterns.
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(m) Wada, S.; Jordan, R., F. Olefin Insertion into a Pd–F Bond: Catalyst Reactivation Following β-F Elimination in Ethylene/Vinyl Fluoride Copolymerization. Angew. Chem., Int. Ed. 2017, 56, 1820– 1824, DOI: 10.1002/anie.201611198
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7m
Olefin Insertion into a Pd-F Bond: Catalyst Reactivation Following β-F Elimination in Ethylene/Vinyl Fluoride Copolymerization
Wada, Shinji; Jordan, Richard F.
Angewandte Chemie, International Edition (2017), 56 (7), 1820-1824CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
The discrete (phosphinoarenesulfonate)Pd fluoride complex (POBp,OMe)PdF(lutidine), where POBp,OMe=(2-MeOC6H4)(2-{2,6-(MeO)2C6H3}C6H4)(2-SO3-5-MeC6H3)P, inserts vinyl fluoride (VF) to form (POBp,OMe)PdCH2CHF2(lutidine) and inserts multiple ethylene (E) units to generate polyethylene that contains -CH2F chain ends. These results provide strong evidence that the -CHF2 and -CH2F chain ends in E/VF copolymer generated by (phosphinoarenesulfonate)PdR catalysts form by β-F elimination of Pd(β-F-alkyl) species, VF or E insertion of the resulting (PO)PdF species, and subsequent chain growth. These results also imply that β-F elimination is not an important catalyst deactivation reaction in this system.
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(n) Zhang, D.; Chen, C. Influence of Polyethylene Glycol Unit on Palladium- and Nickel-Catalyzed Ethylene Polymerization and Copolymerization. Angew. Chem., Int. Ed. 2017, 56, 14672– 14676, DOI: 10.1002/anie.201708212
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7n
Influence of Polyethylene Glycol Unit on Palladium- and Nickel-Catalyzed Ethylene Polymerization and Copolymerization
Zhang, Dan; Chen, Changle
Angewandte Chemie, International Edition (2017), 56 (46), 14672-14676CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
The transition-metal-catalyzed copolymn. of olefins with polar functionalized co-monomers represents a major challenge in the field of olefin polymn. It is extremely difficult to simultaneously achieve improvements in catalytic activity, polar monomer incorporation, and copolymer mol. wt. through ligand modifications. Herein we introduce a polyethylene glycol unit to some phosphine-sulfonate palladium and nickel catalysts, and its influence on ethylene polymn. and copolymn. is investigated. In ethylene polymn., this strategy leads to enhanced activity, catalyst stability, and increased polyethylene mol. wt. In ethylene copolymn. with polar monomers, improvements in all copolymn. parameters are realized. This effect is most significant for polar monomers with hydrogen-bond-donating abilities.
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(a) Nakano, R.; Nozaki, K. Copolymerization of Propylene and Polar Monomers Using Pd/IzQO Catalysts. J. Am. Chem. Soc. 2015, 137, 10934– 10937, DOI: 10.1021/jacs.5b06948
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8a
Copolymerization of Propylene and Polar Monomers Using Pd/IzQO Catalysts
Nakano, Ryo; Nozaki, Kyoko
Journal of the American Chemical Society (2015), 137 (34), 10934-10937CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Palladium catalysts bearing imidazo[1,5-a]quinolin-9-olate-1-ylidene (IzQO) ligands polymerize α-olefins while incorporating polar monomers. The steric environment provided by N-heterocyclic-carbene (NHC) enables regioselective insertion of α-olefins and polar monomers, yielding polypropylene, propylene/allyl carboxylate copolymers, and propylene/methyl acrylate copolymer. Known polymn. catalysts bearing NHC-based ligands decomp. rapidly, whereas the present catalyst is durable because of structural confinement, wherein the NHC-plane is coplanar to the metal square plane. The present catalyst system enables facile access to a new class of functionalized polyolefins and helps conceive a new fundamental principle for designing NHC-based ligands.
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(b) Tao, W.; Nakano, R.; Ito, S.; Nozaki, K. Copolymerization of Ethylene and Polar Monomers by Using Ni/IzQO Catalysts. Angew. Chem., Int. Ed. 2016, 55, 2835– 2839, DOI: 10.1002/anie.201510077
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8b
Copolymerization of Ethylene and Polar Monomers by Using Ni/IzQO Catalysts
Tao, Wen-jie; Nakano, Ryo; Ito, Shingo; Nozaki, Kyoko
Angewandte Chemie, International Edition (2016), 55 (8), 2835-2839CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
The replacement of precious metals in catalysis by earth-abundant metals is currently one of the urgent challenges for chemists. Whereas Pd-catalyzed copolymn. of ethylene and polar monomers is a valuable method for the straightforward synthesis of functionalized polyolefins, the corresponding Ni-based catalysts have suffered from poor thermal tolerance and low mol. wt. of the polymers formed. Herein, the authors report neutral Ni complexes bearing imidazo[1,5-a]quinolin-9-olate-1-ylidene (IzQO) ligands. The Ni/IzQO system can catalyze ethylene polymn. at 50-100° with reasonable activity in the absence of any cocatalyst, whereas most known Ni-based catalysts are deactivated at this temp. range. The Ni/IzQO catalyst was successfully applied to the copolymn. of ethylene with allyl monomers to obtain the corresponding copolymers with the highest mol. wt. reported for a Ni-catalyzed system.
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(c) Yasuda, H.; Nakano, R.; Ito, S.; Nozaki, K. Palladium/IzQO-Catalyzed Coordination–Insertion Copolymerization of Ethylene and 1,1-Disubstituted Ethylenes Bearing a Polar Functional Group. J. Am. Chem. Soc. 2018, 140, 1876– 1883, DOI: 10.1021/jacs.7b12593
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8c
Palladium/IzQO-Catalyzed Coordination-Insertion Copolymerization of Ethylene and 1,1-Disubstituted Ethylenes Bearing a Polar Functional Group
Yasuda, Hina; Nakano, Ryo; Ito, Shingo; Nozaki, Kyoko
Journal of the American Chemical Society (2018), 140 (5), 1876-1883CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Coordination-insertion copolymn. of ethylene with 1,1-disubstituted ethylenes bearing a polar functional group, such as Me methacrylate (MMA), is a long-standing challenge in catalytic polymn. The major obstacle for this process is the huge difference in reactivity of ethylene vs. 1,1-disubstituted ethylenes towards both coordination and insertion. Herein we report the copolymn. of ethylene and 1,1-disubstituted ethylenes by using an imidazo[1,5-a]quinolin-9-olate-1-ylidene (IzQO)-supported palladium catalyst. Various types of 1,1-disubstituted ethylenes were successfully incorporated into the polyethylene chain. In-depth characterization of the obtained copolymers and mechanistic inferences drawn from stoichiometric reactions of alkylpalladium complexes with Me methacrylate and ethylene indicate that the copolymn. proceeds by the same coordination-insertion mechanism that has been postulated for ethylene.
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(a) Nagai, Y.; Kochi, T.; Nozaki, K. Synthesis of N-Heterocyclic Carbene-Sulfonate Palladium Complexes. Organometallics 2009, 28, 6131– 6134, DOI: 10.1021/om9004252
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9a
Synthesis of N-Heterocyclic Carbene-Sulfonate Palladium Complexes
Nagai, Yusuke; Kochi, Takuya; Nozaki, Kyoko
Organometallics (2009), 28 (20), 6131-6134CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
The syntheses of sulfomethylimidazolium ligand precursors I (R = 2,4-di-iPrC6H3, 2,4,6-tri-MeC6H2) are reported. Upon reaction with silver oxide, an oligomeric silver complex is formed in which the N-heterocyclic carbene (NHC) ligands coordinate to the silver atoms in a monodentate fashion. Treatment of the silver complex with appropriate palladium sources results in the formation of monomeric NHC-sulfonate palladium complexes II (L = PPh3, 2,6-lutidine). The structures of complexes II were detd. by single-crystal x-ray anal. as the first examples of bidentate coordination of imidazolium-sulfonates to a metal center.
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(b) Zhou, X.; Jordan, R. F. Synthesis, cis/trans Isomerization, and Reactivity of Palladium Alkyl Complexes That Contain a Chelating N-Heterocyclic-Carbene Sulfonate Ligand. Organometallics 2011, 30, 4632– 4642, DOI: 10.1021/om200482a
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9b
Synthesis, cis/trans Isomerization, and Reactivity of Palladium Alkyl Complexes That Contain a Chelating N-Heterocyclic-Carbene Sulfonate Ligand
Zhou, Xiaoyuan; Jordan, Richard F.
Organometallics (2011), 30 (17), 4632-4642CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
The chem. of Pd alkyl complexes that incorporate the NHC-sulfonate ligand N-(2,6-iPr2-Ph)-N'-2-benzenesulfonate-NHC ([C-O]-, NHC = cyclo-CNCH2CH2N) is described. The reaction of {C-O}Ag (2) with Pd2(μ-Cl)2Me2(PPh3)2 affords cis-C,C-{C-O}PdMe(PPh3) (3, 79%). The reaction of 2 with Pd2(μ-Cl)2Me2(2,6-lutidine)2 at 25° in CH2Cl2 gives a 4/1 mixt. of trans-C,C-{C-O}PdMe(2,6-lutidine) (4a) and cis-C,C-{C-O}PdMe(2,6-lutidine) (4b), which were isolated in 62% and 18% yield, resp., by recrystn. The NHC-sulfonate ligands bind in a κ2-C,O fashion in 3 and 4a,b. 4A isomerizes to 4b by dissocn. of the Ar-SO3- unit to form a configurationally labile three-coordinate intermediate. This process is accelerated by H bond donors (CD3OD, lutidinium) and Lewis acids (B(C6F5)3) that can labilize the sulfonate group. 4A and 4b react with 1 equiv of B(C6F5)3 to yield the O-bound adduct cis-C,C-{C-O-B(C6F5)3}PdMe(2,6-lutidine) (5). 5 Decomps. at 40° by C-C reductive elimination to afford (in the presence of pyridine to trap the B(C6F5)3) N-(2,6-iPr2-Ph)-N'-2-benzenesulfonate-imidazolium Me (6). Trans-C,C-4a reacts with CO and tBuNC to yield the insertion products {C-O}Pd{C(O)Me}(2,6-lutidine) (7) and {C-O}Pd{C(:NtBu)Me}(tBuNC) (9), in which the acyl and iminoacyl ligands are cis to the NHC ligand, via stereospecific displacement of Ar-SO3- by the substrate followed by migratory insertion. The bis-isocyanide adduct {κ1-C-C-O}PdMe(tBuNC)2, in which the tBuNC ligands are trans, is an intermediate in the formation of 9. tBuNC reversibly displaces the Ar-SO3- ligand of 9 to form {κ1-C-C-O}Pd{C(:NtBu)Me}(tBuNC)2 (10). In contract, cis-C,C-4a does not undergo net reaction with CO and reacts with tBuNC via reductive elimination to yield 6. Displacement of the ArSO3- ligand of cis-C,C-4b by potential substrates yields adducts in which the substrate and Me group are trans and insertion is not possible.
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(c) Gott, A. L.; Piers, W. E.; Dutton, J. L.; McDonald, R.; Parvez, M. Dimerization of Ethylene by Palladium Complexes Containing Bidentate Trifluoroborate-Functionalized Phosphine Ligands. Organometallics 2011, 30, 4236– 4249, DOI: 10.1021/om2004095
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9c
Dimerization of Ethylene by Palladium Complexes Containing Bidentate Trifluoroborate-Functionalized Phosphine Ligands
Gott, Andrew L.; Piers, Warren E.; Dutton, Jason L.; McDonald, Robert; Parvez, Masood
Organometallics (2011), 30 (16), 4236-4249CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
As an alternative to the widely reported phosphine-sulfonate ligand system, a series of potassium aryltrifluoroborate-functionalized phosphine ligands and zwitterionic phosphonium salts were prepd. and structurally characterized. The phosphine ligands formed complexes of the general formula [κ2-(P,F)RPdClMe] (where R = Ph, 2-OMe-Ph) when reacted with PdClMe(COD); however, cleavage of the chloride ligand proved problematic. Reaction of the phosphonium salts with PdMe2(tmeda) yield complexes of the general type [κ-(P)RPdMe(tmeda)], which react with pyridine derivs. to displace tmeda. Manipulation of the steric bulk of the pyridine ligands affords some control over the coordination mode of the fluoroborate phosphine, yielding facile access to complexes of the general type [κ2-(P,F)RPdMe(lutidine)]. Investigations into the insertion chem. of the palladium Me moiety with simple small mols. revealed that the release of the lutidine ligand is slow and that insertion of ethylene occurs in a very slow manner; this is attributed to the relative electron deficiency of the aryltrifluoroborate moiety as compared to sulfonate. The palladium lutidine complexes slowly dimerize ethylene to a mixt. of propene and butenes.
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(d) Kim, Y.; Jordan, R. F. Synthesis, Structures, and Ethylene Dimerization Reactivity of Palladium Alkyl Complexes That Contain a Chelating Phosphine–Trifluoroborate Ligand. Organometallics 2011, 30, 4250– 4256, DOI: 10.1021/om200472x
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9d
Synthesis, Structures, and Ethylene Dimerization Reactivity of Palladium Alkyl Complexes That Contain a Chelating Phosphine-Trifluoroborate Ligand
Kim, Young-Min; Jordan, Richard F.
Organometallics (2011), 30 (16), 4250-4256CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
The chem. of palladium alkyl complexes that incorporate the phosphine-trifluoroborate ligand ortho-(Ph2P)C6H4(BF3-)(PF-) is described. The reaction of the pinacol borane ortho-(Ph2P)C6H4(Bpin) with K[HF2] yields ortho-(Ph2P)C6H4(BF3K) (K[PF], 1). Crystn. of 1 from Et2O/THF in the presence of 18-crown-6 yields [K-(18-crown-6)][PF]·0.5THF (2·0.5THF). In the solid state, the phosphine-borate anion of 2 is ion-paired with the [K-(18-crown-6)] cation through weak contacts with the phosphorus and two fluorine atoms. 1 Reacts with (COD)PdMeCl in the presence of 18-crown-6 to form [K-(18-crown-6)][(PF)PdMeCl] (3) and with (COD)PdMeCl and 2,4,6-collidine (col) to yield (PF)PdMe(col) (4). The PF- ligands in 3 and 4 are bound to Pd in a κ2 mode through the phosphine and one fluorine of the -ArBF3- unit. The other two fluorines are weakly bound to the K(18-crown-6)+ cation in 3. NMR studies show that the Pd-F interactions in 3 and 4 are maintained in soln. and that, for 4, the three fluorine atoms undergo fast site exchange on the NMR time scale. 4 Reacts with excess pyridine to yield (κ1-P-PF)PdMe(py)2 (6), in which the -ArBF3- unit has been completely displaced by pyridine. 4 Slowly dimerizes ethylene to 1-butene (36 t.o./h, 23°, CH2Cl2, 400 psi ethylene). The catalyst resting state is (PF)PdEt(col) (7). Addn. of [H(OEt2)2][B(3,5-(CF3)2-C6H3)4] traps the collidine as [collidinium][B(3,5-(CF3)2-C6H3)4] and results in a 10-fold increase in the ethylene dimerization rate (385 t.o./h, 23°C, CD2Cl2, 150 psi ethylene).
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(e) Wucher, P.; Roesle, P.; Falivene, L.; Cavallo, L.; Caporaso, L.; Göttker-Schnetmann, I.; Mecking, S. Controlled Acrylate Insertion Regioselectivity in Diazaphospholidine-Sulfonato Palladium(II) Complexes. Organometallics 2012, 31, 8505– 8515, DOI: 10.1021/om300755j
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9e
Controlled acrylate insertion regioselectivity in diazaphospholidine-sulfonato palladium(II) complexes
Wucher, Philipp; Roesle, Philipp; Falivene, Laura; Cavallo, Luigi; Caporaso, Lucia; Goettker-Schnetmann, Inigo; Mecking, Stefan
Organometallics (2012), 31 (24), 8505-8515CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
Diazaphospholidine-sulfonato Pd(II) complexes I [1a·L-1f·L; X = Me, L = dmso, pyridine, lutidine, μ-ClLi(solvent); 1a: Ar = Ph, 1b: Ar = 2-MeC6H4, 1c: Ar = 2-MeOC6H4, 1d: Ar = 2,4,6-Me3C6H2, 1e: Ar = 2,6-iPr2C6H3, 1f: Ar = 2,6-(p-tolyl)2C6H3] were prepd. and structurally characterized. The complexes 1·L undergo insertion of Me acrylate (MA) into palladium-carbon bond, the regioselectivity of the insertion reaction being dependent on the steric bulk of the N-aryl substituents Ar. The regioselectivity of MA insertion into the Pd-Me bond is entirely inverted from >93% 1,2-insertion for bulky substituents in the complexes 1d-f, yielding the insertion products II (12, Z = CH2, R = Me) to the usual electronically controlled 2,1-insertion (>95%) for the less bulky Ar = Ph in the complex 1a, yielding the insertion product (11, shown as II, Z = bond, R = Et), and β-H elimination product Me crotonate. DFT studies underline that this is due to a more favorable insertion transition state (2,1- favored by 12 kJ mol-1 over 1,2- for 1a) vs. destabilization of the 2,1-insertion transition state in 1d,e. By contrast, MA insertion into the novel isolated and structurally characterized hydride and deuteride complexes (9e, 10e, shown as I, X = H, D; L = lutidine, Ar = 2,6-iPr2C6H3) occurs 2,1-selectively. This is due to the insertion occurring from the isomer with the P-donor and the olefin in trans arrangement, rather than the insertion into the alkyl from the cis isomer in which the olefin is in proximity to the bulky diazaphospholidine. The complexes 1a-f are precursors to active catalysts for ethylene polymn. to highly linear polyethylene with Mn up to 35 000 g mol-1. In copolymn. expts., norbornene was incorporated in up to 6.1 mol % into the polyethylene backbone.
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(f) 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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9f
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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(g) Zhang, Y.; Cao, Y.; Leng, X.; Chen, C.; Huang, Z. Cationic Palladium(II) Complexes of Phosphine–Sulfonamide Ligands: Synthesis, Characterization, and Catalytic Ethylene Oligomerization. Organometallics 2014, 33, 3738– 3745, DOI: 10.1021/om5004094
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(h) Jian, Z.; Falivene, L.; Wucher, P.; Roesle, P.; Caporaso, L.; Cavallo, L.; Göttker-Schnetmann, I.; Mecking, S. Insights into Functional-Group-Tolerant Polymerization Catalysis with Phosphine–Sulfonamide Palladium(II) Complexes. Chem. - Eur. J. 2015, 21, 2062– 2075, DOI: 10.1002/chem.201404856
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9h
Insights into Functional-Group-Tolerant Polymerization Catalysis with Phosphine-Sulfonamide Palladium(II) Complexes
Jian, Zhongbao; Falivene, Laura; Wucher, Philipp; Roesle, Philipp; Caporaso, Lucia; Cavallo, Luigi; Goettker-Schnetmann, Inigo; Mecking, Stefan
Chemistry - A European Journal (2015), 21 (5), 2062-2075CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
Two series of cationic Pd(II) Me complexes {[(2-MeOC6H4)2PC6H4SO2NHC6H3(2,6-R1,R2)]PdMe}2[A]2 (X1+-A: R1 = R2 = H: H1+-A; R1 = R2 = CHMe2: DIPP1+-A; R1 = H, R2 = CF3: CF31+-A; A = BF4 or SbF6) and neutral Pd(II) Me complexes {[(2-MeOC6H4)2PC6H4SO2NC6H3(2,6-R1,R2)]PdMe(L)} (X1-acetone: L = acetone; X1-DMSO: L = DMSO; X1-pyr: L = pyridine) chelated by a phosphine-sulfonamide were synthesized and fully characterized. Stoichiometric insertion of Me acrylate (MA) into all complexes revealed that a 2,1 regiochem. dominates in the 1st insertion of MA. Subsequently, for the cationic complexes X1+-A, β-H elimination from the 2,1-insertion product X2+-AMA-2,1 is overwhelmingly favored over a 2nd MA insertion to yield two major products X4+-AMA-1,2 and X5+-AMA. By contrast, for the weakly coordinated neutral complexes X1-acetone and X1-DMSO, a 2nd MA insertion of the 2,1-insertion product X2MA-2,1 is faster than β-H elimination and gives X3MA as major products. For the strongly coordinated neutral complexes X1-pyr, no 2nd MA insertion and no β-H elimination (except for DIPP2-pyrMA-2,1) were obsd. for the 2,1-insertion product X2-pyrMA-2,1. The cationic complexes X1+-A exhibited high catalytic activities for ethylene dimerization, affording butenes (C4) with a high selectivity of up to 97.7% (1-butene: 99.3 %). Differences in activities and selectivities suggest that the phosphine-sulfonamide ligands remain coordinated to the metal center in a bidentate fashion in the catalytically active species. By comparison, the neutral complexes X1-acetone, X1-DMSO, and X1-pyr showed very low activity towards ethylene to give traces of oligomers. DFT analyses taking into account the two possible coordination modes (O or N) of the sulfonamide ligand for the cationic system CF31+ suggested that the exptl. obsd. high activity in ethylene dimerization is the result of a facile 1st ethylene insertion into the O-coordinated PdMe isomer and a subsequent favored β-H elimination from the N-coordinated isomer formed by isomerization of the insertion product. Steric hindrance by the N-aryl substituent in the neutral systems CF31 and H1 appears to contribute significantly to a higher barrier of insertion, which accounts for the exptl. obsd. low activity towards ethylene oligomerization.
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(i) 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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9i
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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(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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10a
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) 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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10b
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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Wu, Z.; Chen, M.; Chen, C. Ethylene Polymerization and Copolymerization by Palladium and Nickel Catalysts Containing Naphthalene-Bridged Phosphine–Sulfonate Ligands. Organometallics 2016, 35, 1472– 1479, DOI: 10.1021/acs.organomet.6b00076
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11
Ethylene Polymerization and Copolymerization by Palladium and Nickel Catalysts Containing Naphthalene-Bridged Phosphine-Sulfonate Ligands
Wu, Zixia; Chen, Min; Chen, Changle
Organometallics (2016), 35 (10), 1472-1479CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
Naphthalene-bridged phosphine-sulfonate ligands and the corresponding Pd(II) complexes [κ2(P,O)-2-(R2P)-1-naphthalenesulfonato]Pd(Me)(DMSO) (1, R = Ph; 2, R = o-MeO-C6H4; 3, R = Cy) and Ni(II) complexes [κ2(P,O)-2-(R2P)-1-naphthalenesulfonato]Ni(η3-C3H5) (Ni-1, R = o-MeO-C6H4; Ni-2, R = Cy) were prepd. and characterized. The analogous benzo-bridged phosphine-sulfonate Pd(II) complex [κ2(P,O)-(R2P)-benzenesulfonato]Pd(Me)(DMSO) (2', R = o-MeO-C6H4) and Ni(II) complex [κ2(P,O)-(R2P)-benzenesulfonato]Ni(η3-C3H5) (Ni-1', R = o-MeO-C6H4) were prepd. for comparison. In ethylene polymn., complex 2 showed activity of up to 7.5 × 106 g mol-1 h-1, which is among the most active Pd catalysts for ethylene homopolymn. Under the same conditions, complex 2 showed up to 1 order of magnitude higher catalytic activity than complex 2', generating polyethylene with slightly smaller mol. wt. and similar branching d. The Ni(II) complex Ni-1 was also more active than complex Ni-1', generating polyethylene with up to 1 order of magnitude higher mol. wt. In ethylene-Me acrylate copolymn., complex 2 showed lower activity, affording a copolymer with higher Me acrylate incorporation and higher copolymer mol. wt. in comparison to complex 2'.
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(a) Murry, R. E. U.S. Patent 4,689,437. Aug 25, 1987.
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(b) van Doorn, J. A.; Drent, E.; van Leeuwen, P. W. M. N.; Meijboon, N.; van Oort, A. B.; Wife, R. L. Eur. Pat. Appl. 0,280,380, Aug 31, 1988.
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(c) Keim, W.; Maas, H.; Mecking, S. Palladium Catalyzed Alternating Cooligomerization of Ethylene and Carbon Monoxide to Unsaturated Ketones. Z. Naturforsch., B: J. Chem. Sci. 1995, 50, 430– 438, DOI: 10.1515/znb-1995-0318
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12c
Palladium catalyzed alternating cooligomerization of ethylene and carbon monoxide to unsaturated ketones
Keim, Wilhelm; Maas, Heiko; Mecking, Stefan
Zeitschrift fuer Naturforschung, B: Chemical Sciences (1995), 50 (3), 430-8CODEN: ZNBSEN; ISSN:0932-0776. (Verlag der Zeitschrift fuer Naturforschung)
Cationic palladium catalysts were used to cooligomerize ethylene and carbon monoxide. At high ethylene/CO ratios (m/m = 10:1) in CH2Cl2 as a solvent, unsatd. alternating cooligomers were obtained. I, II, III, and IV (n = 1-3, R = Me, Et) were used as catalysts. With PnBu3 as a ligand, selectivities for Et vinyl ketone of 40% based on the CO converted were obtained. The hemilabile phosphino-ester and phosphino-thiophene ligands behave like monodentate phosphine under catalytic conditions.
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(d) Bennett, J. L.; Brookhart, M.; Johnson, L. K.; PCT Int. Appl. WO199830610, July 16, 1998.
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(e) Brassat, I.; Keim, W.; Killat, S.; Möthrath, M.; Mastrorilli, P.; Nobile, C. F.; Suranna, G. P. Synthesis and Catalytic Activity of Allyl, Methallyl and Methyl Complexes of Nickel(II) and Palladium(II) with Biphosphine Monoxide Ligands: Oligomerization of Ethylene and Copolymerization of Ethylene and Carbon Monoxide. J. Mol. Catal. A: Chem. 2000, 157, 41– 58, DOI: 10.1016/S1381-1169(99)00449-5
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12e
Synthesis and catalytic activity of allyl, methallyl and methyl complexes of nickel(II) and palladium(II) with biphosphine monoxide ligands: oligomerization of ethylene and copolymerization of ethylene and carbon monoxide
Brassat, I.; Keim, W.; Killat, S.; Mothrath, M.; Mastrorilli, P.; Nobile, C. F.; Suranna, G. P.
Journal of Molecular Catalysis A: Chemical (2000), 157 (1-2), 41-58CODEN: JMCCF2; ISSN:1381-1169. (Elsevier Science B.V.)
The syntheses of new cationic Ni complexes {[η3-methallyl]Ni[κ2P,O-Ph2P(X)P(O)Ph2]}SbF6, [X = (o-C6H4), (NH)] were accomplished. The complexes oligomerize ethylene to linear α-olefins with selectivities ≤89%. A dependence of oligomerization grade and activity on backbone geometry was shown. New cationic allyl and Me complexes of Pd(II) [(MeCN)(Me)Pd(κ2P,O-Ar2P(CH2)nP(O)Ar2)]X [n = 1-3, X = BF4, Ar = Ph] [n = 1, X = SbF6, Ar = p-tolyl; n = 1 or 2, X = SbF6, Ar = Ph]; [(η3-C3H5)Pd(κ2P,O-Ph2P(CH2)nP(O)Ph2)]X, [n = 2, X = triflate, tosylate; n = 3, X = triflate, tosylate], [(η3-C3H5)Pd(κ2P,O-Ar2P(CH2)nP(O)Ar2)]X, [n = 1, X = SbF6, Ar = p-tolyl; n = 2, X = SbF6 Ar = Ph] were synthesized in good yields. These complexes were used in the catalytic oligomerization of ethylene, and in the catalytic alternating copolymn. of ethylene and CO, to yield polyketones.
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(f) Malinoski, J. M.; Brookhart, M. Polymerization and Oligomerization of Ethylene by Cationic Nickel(II) and Palladium(II) Complexes Containing Bidentate Phenacyldiarylphosphine Ligands. Organometallics 2003, 22, 5324– 5335, DOI: 10.1021/om030388h
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12f
Polymerization and Oligomerization of Ethylene by Cationic Nickel(II) and Palladium(II) Complexes Containing Bidentate Phenacyldiarylphosphine Ligands
Malinoski, Jon M.; Brookhart, Maurice
Organometallics (2003), 22 (25), 5324-5335CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
A series of Ni(II) and Pd(II) catalysts have been synthesized from the P,O chelating ligands phenacyl(aryl)2phosphine. The (P,O)Ni-allyl+B(Arf)-4 [Arf = 3,5-(CF3)2C6H3] complexes 6a-c are active for polymn. of ethylene in the case of 6b (aryl = 2,4,6-(CH3)3C6H2) and for dimerization of ethylene to butenes in the case of 6a (aryl = C6H5) and 6c (aryl = C6H5, 2,4,6-(C6H5)3C6H2). These catalysts are characterized by their high initial activity but relatively short catalytic lifetime and poor thermal stability. The palladium analogs (P,O)PdMe(NCMe)+B(Arf)-4 are approx. an order of magnitude less active than the Ni analogs and generate butenes and hexenes. The barriers for migratory insertion in a series of Me ethylene complexes [(p-XC6H4)2PCH2C(O)(p-YC6H4)]Pd(CH3)(C2H4)+B(Arf)-4 (X,Y = H, H; -OCH3, H; -CF3, H; H, -OCH3; H, -CF3) were measured. Values of ΔG⧧ ranged from 18.2 to 20.3 kcal/mol and, relative to the unsubstituted system, decreased for X,Y = -CF3 and increased for X,Y = -OCH3.
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(g) Bettucci, L.; Bianchini, C.; Claver, C.; Suarez, E. J. G.; Ruiz, A.; Meli, A.; Oberhauser, W. Ligand Effects in the Non-alternating CO–Ethylene Copolymerization by Palladium(II) Catalysis. Dalton Trans. 2007, 5590– 5602, DOI: 10.1039/b711280g
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12g
Ligand effects in the non-alternating CO-ethylene copolymerization by palladium(II) catalysis
Bettucci, Lorenzo; Bianchini, Claudio; Claver, Carmen; Suarez, Eduardo J. Garcia; Ruiz, Aurora; Meli, Andrea; Oberhauser, Werner
Dalton Transactions (2007), (47), 5590-5602CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
In this paper we report on a comparative study of the non-alternating CO-C2H4 copolymn. catalyzed by neutral PdII complexes with the phosphine-sulfonate ligands bis(o-methoxyphenyl)phosphinophenylenesulfonate and bis(o-methoxyphenyl)phosphino-ethylenesulfonate. The former ligand, featuring a lower skeletal flexibility, was found to form more active catalysts and produce polyketones with higher mol. wt. and higher extra-ethylene incorporation. Operando high-pressure NMR studies have allowed us to intercept, for the first time, PdII(phosphine-sulfonate) β-chelates in the non-alternating copolymn. cycle, while model organometallic reactions have contributed to demonstrate that PdII (phosphine-sulfonate) fragments do not form stable carbonyl complexes. The opening of the β-chelates was a viable process by either comonomer, which contrasts with the behavior of PdII (chelating diphosphine) catalysts for the perfectly alternating copolymn.
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Liu, W.; Malinoski, J. M.; Brookhart, M. Ethylene Polymerization and Ethylene/Methyl 10-Undecenoate Copolymerization Using Nickel(II) and Palladium(II) Complexes Derived from a Bulky P,O Chelating Ligand. Organometallics 2002, 21, 2836– 2838, DOI: 10.1021/om0201516
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13
Ethylene Polymerization and Ethylene/Methyl 10-Undecenoate Copolymerization Using Nickel(II) and Palladium(II) Complexes Derived from a Bulky P,O Chelating Ligand
Liu, Weijun; Malinoski, Jon M.; Brookhart, Maurice
Organometallics (2002), 21 (14), 2836-2838CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
Cationic Ni(II) and Pd(II) complexes ([LNi(η3-allyl)]BAr'4 (L = tBu2PCH2C(O)Ph) and [Me(L)PdL1]BAr'4 (L1 = Et2O, NCMe)) based on the bulky P,O ligand phenacyldi-tert-butylphosphine are active for the polymn. of ethylene and copolymn. of ethylene and Me 10-undecenoate, a functionalized monomer.
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Black, R. E.; Jordan, R. F. Synthesis and Reactivity of Palladium(II) Alkyl Complexes that Contain Phosphine-cyclopentanesulfonate Ligands. Organometallics 2017, 36, 3415– 3428, DOI: 10.1021/acs.organomet.7b00572
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Synthesis and reactivity of palladium(II) alkyl complexes that contain phosphine-cyclopentanesulfonate ligands
Black, Rebecca E.; Jordan, Richard F.
Organometallics (2017), 36 (17), 3415-3428CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
Palladium cyclopentane-based monophosphine-sulfonate Me complexes [[(CH2)3CHPAr2CHSO3]PdMe(L)] were prepd. and examd. for catalytic activity in ethylene-acrylate copolymn. The synthesis of the phosphine-cyclopentanesulfonate pro-ligands Li/K[2-PPh2-cyclopentanesulfonate] (Li/K[2a]), Li/K[2-P(2-OMe-Ph)2-cyclopentanesulfonate] (Li/K[2b]), and H[2b], and the corresponding Pd(II) alkyl complexes (κ2-P,O-2a)PdMe(py) (3a) and (κ2-P,O-2b)PdMe(py) (3b) is described. The sulfonate-bridged base-free dimer {(2b)PdMe}2 (4b) was synthesized by abstraction of pyridine from 3b using B(C6F5)3. The borane-coordinated base-free dimer [{2b·B(C6F5)3}PdMe]2 (5b), in which B(C6F5)3 binds to a sulfonate oxygen, was prepd. by addn. of 1 equiv of B(C6F5)3 per Pd to 4b or addn. of 2 equiv of B(C6F5)3 to 3b. Compds. 3b, 4b, and 5b polymerize ethylene with low activity (up to 210 kg mol-1 h-1 at 250 psi and 80°) to linear polyethylene (Mn = 1950-5250 Da) with predominantly internal olefin placements. Complexes 3b and 4b copolymerize ethylene with Me acrylate to linear copolymers that contain up to 11.7 mol % Me acrylate, which is incorporated as -CH2CH(CO2Me)CH2- (80%) in-chain units and -CH2CH(CO2Me)Me (8%) and -CH2CH:CH(CO2Me) (12%) chain-end units. The complexes 3b and 4b also copolymerize ethylene with vinyl fluoride to linear copolymers that contain up to 0.41 mol % vinyl fluoride, which is incorporated as -CH2CHFCH2- (∼80%) in-chain units and -CH2CF2H (7%), -CH2CHFCH3 (5%), and -CH2CH2F (8%) chain-end units. Complexes 3b and 4b are more stable and active in ethylene polymn. than analogous (PAr2CH2CH2SO3)PdR catalysts, but are less active than analogous (PAr2-arenesulfonate)PdR catalysts. Low-temp. NMR studies show that 4b reacts with ethylene below -10° to form the ethylene adduct cis-P,R-(2b)PdMe(ethylene) (7b), which undergoes ethylene insertion at 5°. DFT calcns. for a model (PMe2-cyclopentanesulfonate)Pd(Pr)(ethylene) species show that ethylene insertion proceeds by cis-P,R/trans-P,R isomerization followed by migratory insertion, and that the lower activity of 3b and 4b vis-a-vis analogous (PAr2-arenesulfonate)PdR catalysts results from a higher barrier for migratory insertion of the trans-P,R isomer.
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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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15a
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) 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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15b
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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16
A part of the present work has already been disclosed in a patent, see:Nozaki, K.; Carrow, B. P.; Okumura, Y.; Kuroda, J. WO2013168626, 2013.
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17
The amount of ethylene dissolved in toluene does not linearly correlate with the pressure of ethylene, especially when the pressure of ethylene is <0.5 MPa; see:Schuster, N.; Rünzi, T.; Mecking, S. Reactivity of Functionalized Vinyl Monomers in Insertion Copolymerization. Macromolecules 2016, 49, 1172– 1179, DOI: 10.1021/acs.macromol.5b02749
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17
Reactivity of Functionalized Vinyl Monomers in Insertion Copolymerization
Schuster, Nicole; Ruenzi, Thomas; Mecking, Stefan
Macromolecules (Washington, DC, United States) (2016), 49 (4), 1172-1179CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
We report the reactivities of a comprehensive range of polar vinyl comonomers and 1-olefins in the copolymn. with ethylene by [{(o-MeOC6H4)2PC6H4SO3}PdMe(L)] from pressure reactor studies (95 °C, 3-20 bar), as defined by rE = kethylene/kcomonomer from Markov statistics. 13C NMR chem. shifts of the monomers' β vinyl carbon atom and Charton and Sterimol parameters were found to be appropriate descriptors for the monomers' electronic nature and steric demand, resp. A comprehensive picture of their impact on monomer reactivity and also regioselectivity of insertion arises. This shall also allow for predictions of the reactivity of other monomers.
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18
Ito, S.; Kanazawa, M.; Munakata, K.; Kuroda, J.; 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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18
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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19
For details, see Figure S63 in the Supporting Information.
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20
There are several types of ethylene/MMA copolymers formed via late transition metal catalysis: (1) ethylene/MMA copolymers featuring chain-end incorporation of MMA formed via coordination–insertion mechanism (for the recent example, see:Chen, M.; Chen, C. A Versatile Ligand Platform for Palladium- and Nickel-catalyzed Ethylene Copolymerizations with Polar Monomers. Angew. Chem., Int. Ed. 2018, in press. DOI: DOI: 10.1002/anie.201711753 ); (2) multiblock ethylene/MMA copolymers by a combination of coordination–insertion and radical mechanisms; (3) ethylene/MMA copolymers which might include consecutive polyMMA units formed by the intermediacy of radical-related processes. For the details, see ref (8c) and references cited therein.
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Abstract
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Figure 1
Figure 1. Palladium complexes bearing phenylene- and methylene-bridged BPMO ligands.
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Scheme 1
Scheme 1. Synthesis of Methylene-Bridged BPMO Ligands and Their Palladium Complexes
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Figure 2
Figure 2. X-ray structures of palladium/BPMO complexes (a) 2c, (b) 2f, and (c) 4 with 50% thermal ellipsoids. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (°): (a) 2c: Pd1–P1 2.2054(13), Pd1–O1 2.236(3), Pd1–C1 2.033(5), P1–Pd1–O1 85.05(8), P1–Pd1–C1 92.33(14). (b) 2f: Pd1–P1 2.2188(16), Pd1–O1 2.224(5), Pd1–C1 2.027(7), P1–Pd1–O1 88.45(12), P1–Pd1–C1 91.55(18). (c) 4: Pd1–P1 2.2285(10), Pd1–O1 2.120(2), Pd1–C1 2.068(3), P1–Pd1–O1 91.19(6), P1–Pd1–C1 92.51(11).
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Figure 3
Figure 3. Comparison of AAc incorporation ratios (mol %) as a function of the concentration of AAc (mol·L^–1) divided by the pressure of ethylene (MPa) obtained from 3e, 3f, and other previously reported catalyst systems at 80 °C. Solid lines represent the results of this study, while dotted lines represent the results reported in ref (7e), (9i), and (18).
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  Wide Bite Angle Diphosphines: Xantphos Ligands in Transition Metal Complexes and Catalysis
  Kamer, Paul C. J.; van Leeuwen, Piet W. N. M.; Reek, Joost N. H.
  Accounts of Chemical Research (2001), 34 (11), 895-904CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
  A review is presented in which is described the development and application of new diphosphine ligands, designed to induce large P-M-P angles in transition metal complexes. The reactivity of organotransition metal complexes is dependent on the ligand environment of the metal. Aided by computational chem., a homologous range of diphosphines based on rigid heterocyclic arom. backbones of the xanthene-type with natural bite angles of ∼100-134° were developed. The special structure of the ligands has an enormous impact on stability and reactivity of various transition metal complexes. Highly active and selective catalysts were obtained by influencing this reactivity.
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2. 2
  Teng, Q.; Huynh, H. V. Determining the Electron-Donating Properties of Bidentate Ligands by ¹³C NMR Spectroscopy. Inorg. Chem. 2014, 53, 10964– 10973, DOI: 10.1021/ic501325j
  [ACS Full Text ], [CAS], Google Scholar
  2
  Determining the Electron-Donating Properties of Bidentate Ligands by 13C NMR Spectroscopy
  Teng, Qiaoqiao; Huynh, Han Vinh
  Inorganic Chemistry (2014), 53 (20), 10964-10973CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
  A series of 15 mononuclear complexes [PdBr(iPr2-bimy)(L2)]PF6 (1-15) (iPr2-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene, L2 = arom. 1,2-diimines, diazabutadienes, or methylene-, ethylene- and propylene-bridged di-N-heterocyclic carbenes) and two dicarbene-bridged, dinuclear complexes [Pd2Br4(iPr2-bimy)2(diNHC)] (16 and 17) were synthesized and characterized by multinuclear NMR spectroscopy, electrospray ionization mass spectrometry, and in some cases x-ray diffraction anal. The influence of the 15 bidentate ligands L2 on the 13Ccarbene signals of the iPr2-bimy reporter ligand in the chelate complexes was studied, on the basis of which a facile methodol. for the donor strength detn. of bidentate ligands was developed.
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3. 3
  (a) Johnson, L. K.; Killian, C. M.; Brookhart, M. New Pd(II)- and Ni(II)-Based Catalysts for Polymerization of Ethylene and α-Olefins. J. Am. Chem. Soc. 1995, 117, 6414– 6415, DOI: 10.1021/ja00128a054
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  3a
  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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  .
  (b) Killian, C. M.; Tempel, D. J.; Johnson, L. K.; Brookhart, M. Living Polymerization of α-Olefins Using Ni^II–α-Diimine Catalysts. Synthesis of New Block Polymers Based on α-Olefins. J. Am. Chem. Soc. 1996, 118, 11664– 11665, DOI: 10.1021/ja962516h
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  3b
  Living polymerization of α-olefins using NiII-α-diimine catalysts. Synthesis of new block polymers based on α-olefins
  Killian, Christopher M.; Tempel, Daniel J.; Johnson, Lynda K.; Brookhart, Maurice
  Journal of the American Chemical Society (1996), 118 (46), 11664-11665CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Procedures for carrying out the living polymn. of α-olefins have been developed using nickel(II) complexes stabilized by sterically bulky α-diimine ligands. At 10° and low monomer concns., near monodisperse elastomeric poly(α-olefin) homo- and block copolymers have been prepd. The structure and properties of these polymers can be systematically varied as a function of catalyst structure and α-olefin chain length.
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  .
  (c) 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
  [ACS Full Text ], [CAS], Google Scholar
  3c
  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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  .
  For review, see:
  (d) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Late-Metal Catalysts for Ethylene Homo- and Copolymerization. Chem. Rev. 2000, 100, 1169– 1204, DOI: 10.1021/cr9804644
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  3d
  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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4. 4
  For recent examples, see:
  (a) Takano, S.; Takeuchi, D.; Osakada, K.; Akamatsu, N.; Shishido, A. Dipalladium Catalyst for Olefin Polymerization: Introduction of Acrylate Units into the Main Chain of Branched Polyethylene. Angew. Chem., Int. Ed. 2014, 53, 9246– 9250, DOI: 10.1002/anie.201404339
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  4a
  Dipalladium Catalyst for Olefin Polymerization: Introduction of Acrylate Units into the Main Chain of Branched Polyethylene
  Takano, Shigenaga; Takeuchi, Daisuke; Osakada, Kohtaro; Akamatsu, Norihisa; Shishido, Atsushi
  Angewandte Chemie, International Edition (2014), 53 (35), 9246-9250CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  A dipalladium complex with a double-decker structure catalyzes ethylene-acrylate copolymn. to produce the branched polymer contg. the acrylate units in the polymer chain, not at the branch terminus. The cooperation of the two palladium centers, which are fixed in a rigid framework of the macrocyclic ligand, is proposed to have a significant dinuclear effect on the copolymn.
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  .
  (b) Allen, K. E.; Campos, J.; Daugulis, O.; Brookhart, M. Living Polymerization of Ethylene and Copolymerization of Ethylene/Methyl Acrylate Using “Sandwich” Diimine Palladium Catalysts. ACS Catal. 2015, 5, 456– 464, DOI: 10.1021/cs5016029
  [ACS Full Text ], [CAS], Google Scholar
  4b
  Living Polymerization of Ethylene and Copolymerization of Ethylene/Methyl Acrylate Using "Sandwich" Diimine Palladium Catalysts
  Allen, Kate E.; Campos, Jesus; Daugulis, Olafs; Brookhart, Maurice
  ACS Catalysis (2015), 5 (1), 456-464CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  Cationic Pd(II) catalysts incorporating bulky 8-p-tolylnaphthyl substituted diimine ligands have been synthesized and investigated for ethylene polymn. and ethylene/methyl acrylate copolymn. Homopolymn. of ethylene at room temp. resulted in branched polyethylene with narrow Mw/Mn values (ca. 1.1), indicative of a living polymn. A mechanistic study revealed that the catalyst resting state was an alkyl olefin complex and that the turnover-limiting step was migratory insertion, thus the turnover frequency is independent of ethylene concn. Copolymn. of ethylene and Me acrylate (MA) was also achieved. MA incorporation was found to increase linearly with MA concn., and copolymers with up to 14 mol % MA were prepd. Mechanistic studies revealed that acrylate insertion into a Pd-CH3 bond occurs at -70 °C to yield a four-membered chelate, which isomerizes first to a five-membered chelate and then to a six-membered chelate. Barriers to migratory insertion of both the (diimine)PdCH3(C2H4)+ (19.2 kcal/mol) and (diimine)PdCH3(η2-C2H3CO2Me)+ (15.2 kcal/mol) were measured by low-temp. NMR kinetics.
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  .
  (c) Dai, S.; Sui, X.; Chen, C. Highly Robust Palladium(II) α-Diimine Catalysts for Slow-Chain-Walking Polymerization of Ethylene and Copolymerization with Methyl Acrylate. Angew. Chem., Int. Ed. 2015, 54, 9948– 9953, DOI: 10.1002/anie.201503708
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  4c
  Highly Robust Palladium(II) α-Diimine Catalysts for Slow-Chain-Walking Polymerization of Ethylene and Copolymerization with Methyl Acrylate
  Dai, Shengyu; Sui, Xuelin; Chen, Changle
  Angewandte Chemie, International Edition (2015), 54 (34), 9948-9953CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  A series of sterically demanding α-diimine ligands bearing electron-donating and electron-withdrawing substituents were synthesized by an improved synthetic procedure in high yield. Subsequently, the corresponding Pd complexes were prepd. and isolated by column chromatog. These Pd complexes demonstrated unique properties in ethylene polymn., including high thermal stability and high activity, thus generating polyethylene with a high mol. wt. and very low branching d. Similar properties were obsd. for ethylene/methyl acrylate copolymn. Because of the high mol. wt. and low branching d., the generated polyethylene and ethylene/methyl acrylate copolymer were semicryst. solids. The (co)polymers had unique microstructures originating from the unique slow-chain-walking activity of these Pd complexes.
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  .
  (d) 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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  4d
  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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  .
  (e) Dai, S.; Zhou, S.; Zhang, W.; Chen, C. Systematic Investigations of Ligand Steric Effects on α-Diimine Palladium Catalyzed Olefin Polymerization and Copolymerization. Macromolecules 2016, 49, 8855– 8862, DOI: 10.1021/acs.macromol.6b02104
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  4e
  Systematic Investigations of Ligand Steric Effects on α-Diimine Palladium Catalyzed Olefin Polymerization and Copolymerization
  Dai, Shengyu; Zhou, Shixin; Zhang, Wen; Chen, Changle
  Macromolecules (Washington, DC, United States) (2016), 49 (23), 8855-8862CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
  In the Brookhart type α-diimine palladium catalyst system, it is highly challenging to tune the polymer branching densities through ligand modifications or polymn. conditions. In this contribution, the authors describe the synthesis and characterization of α-diimine ligands and the corresponding palladium catalysts bearing both the dibenzhydryl moiety and with systematically varied ligand sterics. In ethylene polymn., it is possible to tune the catalytic activities ((0.77-8.85) × 105 g/(mol Pd·h)), polymer mol. wts. (Mn: (0.2-164.7) × 104), branching densities (25-116/1000C), and polymer melting temps. (amorphous to 98°) over a very wide range. In ethylene-Me acrylate (E-MA) copolymn., it is possible to tune the catalytic activities ((0.3-8.8) × 103 g/(mol Pd·h)), copolymer mol. wts. (1.1 × 103-79.8 × 103), branching densities (30-119/1000C), and MA incorporation ratio (0.4-13.8%) over a very wide range. The mol. wts. and branching densities could also be tuned in α-olefin polymn. The tuning in polymer microstructures leads to significant tuning in polyethylene mech. properties and the surface properties of the E-MA copolymer.
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  .
  (f) Dai, S.; Chen, C. Direct Synthesis of Functionalized High-Molecular-Weight Polyethylene by Copolymerization of Ethylene with Polar Monomers. Angew. Chem., Int. Ed. 2016, 55, 13281– 13285, DOI: 10.1002/anie.201607152
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  4f
  Direct Synthesis of Functionalized High-Molecular-Weight Polyethylene by Copolymerization of Ethylene with Polar Monomers
  Dai, Shengyu; Chen, Changle
  Angewandte Chemie, International Edition (2016), 55 (42), 13281-13285CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  The introduction of even a small amt. of polar functional groups into polyolefins could excise great control over important material properties. As the most direct and economic strategy, the transition-metal-catalyzed copolymn. of olefins with polar, functionalized monomers represents one of the biggest challenges in this field. The presence of polar monomers usually dramatically reduces the catalytic activity and copolymer mol. wt. (to the level of thousands or even hundreds Da), rendering the copolymn. process and the copolymer materials far from ideal for industrial applications. In this contribution, we demonstrate that these obstacles can be addressed through rational catalyst design. Copolymers with highly linear microstructures, high melting temps., and very high mol. wts. (close to or above 1 000 000 Da) were generated. The direct synthesis of polar functionalized high-mol.-wt. polyethylene was thus achieved.
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  .
  (g) Chen, Z.; Liu, W.; Daugulis, O.; Brookhart, M. Mechanistic Studies of Pd(II)-Catalyzed Copolymerization of Ethylene and Vinylalkoxysilanes: Evidence for a β-Silyl Elimination Chain Transfer Mechanism. J. Am. Chem. Soc. 2016, 138, 16120– 16129, DOI: 10.1021/jacs.6b10462
  [ACS Full Text ], [CAS], Google Scholar
  4g
  Mechanistic studies of Pd(II)-catalyzed copolymerization of ethylene and vinylalkoxysilanes: evidence for a β-silyl elimination chain transfer mechanism
  Chen, Zhou; Liu, Weijun; Daugulis, Olafs; Brookhart, Maurice
  Journal of the American Chemical Society (2016), 138 (49), 16120-16129CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Copolymns. of ethylene with vinyltrialkoxysilanes are reported using both a "traditional" cationic Pd(II) aryldiimine catalyst, [[acen(NAr)2]PdMe(L)][BArF4] (t-1, acen = acenaphthene-1,2-diylidene; Ar = 2,6-diisopropylphenyl; L = MeCN, OEt2, C2H4), and a "sandwich-type" aryldiimine catalyst, [[acen(NAr1)2]PdMe(OEt2)][BArF4] (s-2, Ar1 = 8-p-tolyl-1-naphthyl; L = MeCN, OEt2, C2H4). Incorporation levels of vinyltrialkoxysilanes between 0.25 and 2.0 mol% were achieved with remarkably little rate retardation relative to ethylene homopolymns. In the case of the traditional catalyst system, mol. wts. decrease as the level of comonomer increases and only one trialkoxysilyl group is incorporated per chain. Mol. wt. distributions of ca. 2 are obsd. For the sandwich catalyst, higher mol. wts. are obsd. with many more trialkoxysilyl groups incorporated per chain. Polymers with mol. wt. distributions of ca. 1.2-1.4 are obtained. Detailed NMR mechanistic studies have revealed the formation of intermediate π-complexes of the type [[acen(NAr)]PdR[CH2:CHSi(OR1)3]]+. 1,2-Migratory insertions of these complexes occur with rates similar to ethylene insertion and result in formation of observable five-membered chelate intermediates. These chelates are rapidly opened with ethylene forming alkyl ethylene complexes, a requirement for chain growth. An unusual β-silyl elimination mechanism was shown to be responsible for chain transfer and formation of low mol. wt. copolymers in the traditional catalyst system, t-1. This chain transfer process is retarded in the sandwich system 2. Relative binding affinities of ethylene and vinyltrialkoxysilanes to the cationic palladium center have been detd. The quant. mechanistic studies reported fully explain the features of the bulk polymn. results.
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  .
  (h) Zhao, M.; Chen, C. Accessing Multiple Catalytically Active States in Redox-Controlled Olefin Polymerization. ACS Catal. 2017, 7, 7490– 7494, DOI: 10.1021/acscatal.7b02564
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  4h
  Accessing Multiple Catalytically Active States in Redox-Controlled Olefin Polymerization
  Zhao, Minhui; Chen, Changle
  ACS Catalysis (2017), 7 (11), 7490-7494CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  The majority of work in the field of olefin polymn. catalysis has been focused on ligand modifications. In this work, authors describe an alternative strategy for the modulation of olefin polymn. and copolymn. processes. The two ferrocenyl units in an α-diimine palladium catalyst can be oxidized in a stepwise fashion. This stepwise redox control can be used to modulate the catalyst properties during the homopolymn. of ethylene and 1-hexene, as well as the copolymns. of ethylene with norbornene, Me acrylate, and 5-norbornene-2-yl acetate. Moreover, polymer microstructure and polydispersity can be controlled during these stepwise oxidn. processes.
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  .
  (i) Li, M.; Wang, X.; Luo, Y.; Chen, C. A Second-Coordination-Sphere Strategy to Modulate Nickel- and Palladium-Catalyzed Olefin Polymerization and Copolymerization. Angew. Chem., Int. Ed. 2017, 56, 11604– 11609, DOI: 10.1002/anie.201706249
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  4i
  A Second-Coordination-Sphere Strategy to Modulate Nickel- and Palladium-Catalyzed Olefin Polymerization and Copolymerization
  Li, Min; Wang, Xingbao; Luo, Yi; Chen, Changle
  Angewandte Chemie, International Edition (2017), 56 (38), 11604-11609CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Transition-metal-catalyzed copolymn. reactions of olefins with polar-functionalized comonomers are highly important and also highly challenging. A second-coordination-sphere strategy was developed to address some of the difficulties encountered in these copolymn. reactions. A series of α-diimine ligands bearing nitrogen-contg. second coordination spheres were prepd. and characterized. The properties of the corresponding nickel and palladium catalysts in ethylene polymns. and copolymns. were investigated. In the nickel system, significant redn. in polymer branching d. was obsd., while lower polymer branching densities, as well as a wider range of polar monomer substrates, were achieved in the palladium system. Control expts. and computational results reveal the crit. role of the metal-nitrogen interaction in these polymn. and copolymn. reactions.
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5. 5
  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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  5
  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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6. 6
  For review, see:
  (a) Berkefeld, A.; Mecking, S. Coordination Copolymerization of Polar Vinyl Monomers H₂C═CHX. Angew. Chem., Int. Ed. 2008, 47, 2538– 2542, DOI: 10.1002/anie.200704642
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  6a
  Coordination copolymerization of polar vinyl monomers H2C=CHX
  Berkefeld, Andreas; Mecking, Stefan
  Angewandte Chemie, International Edition (2008), 47 (14), 2538-2542CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Risina review on neutral phosphinosulfonate PdII complexes as versatile catalysts even for the challenging insertion copolymn. of polar functionalized vinyl comonomers H2C=CHX, such as acrylonitrile, vinyl acetate, and alkyl vinyl ethers.
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  (b) Nakamura, A.; Ito, S.; Nozaki, K. Coordination–Insertion Copolymerization of Fundamental Polar Monomers. Chem. Rev. 2009, 109, 5215– 5244, DOI: 10.1021/cr900079r
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  6b
  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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  (c) Ito, S.; Nozaki, K. Coordination–Insertion Copolymerization of Polar Vinyl Monomers by Palladium Catalysts. Chem. Rec. 2010, 10, 315– 325, DOI: 10.1002/tcr.201000032
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  6c
  Coordination-insertion copolymerization of polar vinyl monomers by palladium catalysts
  Ito, Shingo; Nozaki, Kyoko
  Chemical Record (2010), 10 (5), 315-325CODEN: CRHEAK; ISSN:1527-8999. (John Wiley & Sons, Inc.)
  A review. Random incorporation of polar functional groups into polyolefins and polyketones along with the precise control of incorporation ratios and polymer microstructures is one of the most significant challenges in polymer chem. For such a purpose, late-transition-metal complexes are often employed as a catalyst for the copolymn. of polar vinyl monomers, because of their high functional group compatibility. This account describes our contribution to the development of coordination-insertion copolymn. of polar vinyl monomers by palladium catalysts. In particular, the use of palladium/phosphine-sulfonate catalysts enables to incorporate various polar vinyl monomers into polyolefins and polyketones. © 2010 The Japan Chem. Journal Forum and Wiley Periodicals, Inc. Chem Rec 10: 315-325; 2010: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.201000032.
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  (d) Nakamura, A.; Anselment, T. M. J.; Claverie, J. P.; 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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  6d
  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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  (e) Carrow, B. P.; Nozaki, K. Transition-Metal-Catalyzed Functional Polyolefin Synthesis: Effecting Control through Chelating Ancillary Ligand Design and Mechanistic Insights. Macromolecules 2014, 47, 2541– 2555, DOI: 10.1021/ma500034g
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  6e
  Transition-Metal-Catalyzed Functional Polyolefin Synthesis: Effecting Control through Chelating Ancillary Ligand Design and Mechanistic Insights
  Carrow, Brad P.; Nozaki, Kyoko
  Macromolecules (Washington, DC, United States) (2014), 47 (8), 2541-2555CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
  A review. The incorporation of polar functional groups into polyolefins can significantly alter the adhesion, barrier and surface properties, dyeability, printability, and compatibility of the resulting "functional polyolefin". Thus, the development of methods for the controlled synthesis of functional polyolefins from industrially relevant monomers holds the potential to expand the range of applications available to this already ubiquitous class of materials. In this Perspective, recent advances in transition-metal-catalyzed functional polyolefin synthesis will be reviewed. A common thread among the innovations discussed here is the perturbation of catalyst function by tailored design of the chelating ancillary ligand, aided in many cases by improved mechanistic understanding. Specific topics discussed here include rare examples of catalyst control over the regio- and stereochem. of polar monomer insertion by phosphine-sulfonato palladium complexes (Drent-type), rate acceleration of insertion polymn. by binuclear cooperativity using salicylaldiminato nickel complexes (Grubbs-type), and formation of linear copolymers of ethylene and polar vinyl monomers using a cationic palladium catalyst ligated by a bisphosphine monoxide (BPMO) that contrasts the typical polymer microstructures formed by other cationic group 10 catalysts ligated by an α-diimine (Brookhart-type).
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  (f) Guo, L.; Dai, S.; Sui, X.; Chen, C. Palladium and Nickel Catalyzed Chain Walking Olefin Polymerization and Copolymerization. ACS Catal. 2016, 6, 428– 441, DOI: 10.1021/acscatal.5b02426
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  6f
  Palladium and Nickel Catalyzed Chain Walking Olefin Polymerization and Copolymerization
  Guo, Lihua; Dai, Shengyu; Sui, Xuelin; Chen, Changle
  ACS Catalysis (2016), 6 (1), 428-441CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  A review. In this perspective, recent developments on palladium and nickel mediated chain walking olefin polymn. and copolymn. with polar functionalized comonomers are described. First, the chain walking polymn. mechanism is discussed followed by its implications in olefin polymn. and copolymn. Then, recent advances in catalyst design are provided. Special attention is paid to the influence of ligand structures on the catalytic properties. Subsequently, the applications of these chain walking polymn. catalysts in the synthesis of functionalized hyperbranched polymers and copolymers are summarized. Finally, some recent developments and perspectives on very fast and very slow chain walking polymn. catalysts are discussed.
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7. 7
  For recent examples not included in ref (6d), see:
  (a) Leicht, H.; Göttker-Schnetmann, I.; Mecking, S. Incorporation of Vinyl Chloride in Insertion Polymerization. Angew. Chem., Int. Ed. 2013, 52, 3963– 3966, DOI: 10.1002/anie.201209724
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  7a
  Incorporation of Vinyl Chloride in Insertion Polymerization
  Leicht, Hannes; Goettker-Schnetmann, Inigo; Mecking, Stefan
  Angewandte Chemie, International Edition (2013), 52 (14), 3963-3966CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Palladium complexes made it possible for the first time an insertion copolymn. of VC (vinyl chloride) with ethylene to form chlorine-contg. copolymers. NMR anal. of the polymers, labeling, and stoichiometric insertion studies reveal that incorporation of CHCl units proceeds by 2,1-insertion of VC into palladium hydride species. After this 2,1-insertion of VC, ethylene insertion resulting in monochlorinated polyethylene is competitive to chain walking (which through the net 1,2-insertion of VC would result in a detrimental β-chloride elimination). Regardless of the limited incorporation of vinyl chloride, this first isolation of chlorine-contg. polymers in combination with a mechanistic understanding represents a significant impetus to a long-standing challenge. Future studies will focus on further suppression of chain walking, which results in the problematic net 1,2-insertion of VC, and on facilitating in chain incorporation of VC into polymers.
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  (b) 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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  7b
  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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  (c) Lanzinger, D.; Giuman, M. M.; Anselment, T. M. J.; Rieger, B. Copolymerization of Ethylene and 3,3,3-Trifluoropropene Using (Phosphine-sulfonate)Pd(Me)(DMSO) as Catalyst. ACS Macro Lett. 2014, 3, 931– 934, DOI: 10.1021/mz5004344
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  7c
  Copolymerization of Ethylene and 3,3,3-Trifluoropropene Using (Phosphine-sulfonate)Pd(Me)(DMSO) as Catalyst
  Lanzinger, Dominik; Giuman, Marco M.; Anselment, Timo M. J.; Rieger, Bernhard
  ACS Macro Letters (2014), 3 (9), 931-934CODEN: AMLCCD; ISSN:2161-1653. (American Chemical Society)
  (Phosphine-sulfonate)Pd(Me)(DMSO) catalyzed copolymn. of ethylene and 3,3,3-trifluoropropene (TFP) allows the synthesis of linear copolymers with high fluorine contents of up to 15 wt % (8.9 mol % TFP). 13C and 19F NMR analyses of the copolymers were performed, showing that most of the incorporated TFP is located in the polymer backbone. Copolymn. of ethylene-d4 with TFP revealed that TFP is inserted into Pd-D bonds in 1,2- as well as in 2,1-mode, although 1,2-insertion is slightly preferred. Chain transfer after TFP insertion is exclusively obsd. following 2,1-insertion. With higher TFP incorporation, an increase in the ratio of internal to terminal double bonds was detected in the 1H NMR spectra. This indicates that, in the case of 2,1-insertion of TFP, chain walking is facilitated relative to direct chain release after β-H transfer to the palladium center.
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  (d) Jian, Z.; Wucher, P.; Mecking, S. Heterocycle-Substituted Phosphinesulfonato Palladium(II) Complexes for Insertion Copolymerization of Methyl Acrylate. Organometallics 2014, 33, 2879– 2888, DOI: 10.1021/om500400a
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  7d
  Heterocycle-Substituted Phosphinesulfonato Palladium(II) Complexes for Insertion Copolymerization of Methyl Acrylate
  Jian, Zhongbao; Wucher, Philipp; Mecking, Stefan
  Organometallics (2014), 33 (11), 2879-2888CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  A family of heterocycle-substituted binuclear phosphinesulfonato Pd(II) complexes {[R2P(C6H4SO2O)]PdMeClLi(DMSO)}2 (1a-d-LiCl-DMSO: 1a-LiCl-DMSO, R = 2-furyl; 1b-LiCl-DMSO, R = 2-thienyl; 1c-LiCl-DMSO, R = 2-(N-methyl)pyrrolyl; 1d-LiCl-DMSO, R = 2-benzofuryl) was synthesized, and the solid-state structures of 1a-c-LiCl-DMSO were detd., which revealed various modes of bridging between the two metal fragments. 1A-d-LiCl-DMSO further generated either the mononuclear Pd(II) complexes {[κ2P,O-R2P(C6H4SO2O)]PdMe(pyr)} (1a-d-pyr) by addn. of pyridine or the more labile mononuclear Pd(II) complex {[κ2P,O-(2-thienyl)2P(C6H4SO2O)]PdMe(DMSO)} (1b-DMSO) by chloride abstraction with AgBF4. Stoichiometric Me acrylate (MA) insertion expts. indicated that, in comparison with the other three substituents, the thienyl-substituted Pd(II) complexes undergo faster insertion of MA in a primary 2,1-fashion, and 1b-DMSO possesses the fastest insertion rate due to the relative weakly coordinating DMSO mol. All Pd complexes were employed in ethylene polymn., affording highly linear polyethylene with relatively low mol. wts. (Mn = (0.5-7.4) × 103). Under these pressure reactor conditions, the thienyl motif displays the highest activity (order: 1b-DMSO > 1b-pyr > 1a-pyr > 1d-pyr > 1c-pyr » 1a-d-LiCl-DMSO). Copolymn. reactions of ethylene and MA further revealed that MA incorporation in the obtained linear copolymers depends moderately on the heterocyclic substituents.
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  (e) Ota, Y.; Ito, S.; Kuroda, J.; 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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  7e
  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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  (f) Jian, Z.; Baier, M. C.; Mecking, S. Suppression of Chain Transfer in Catalytic Acrylate Polymerization via Rapid and Selective Secondary Insertion. J. Am. Chem. Soc. 2015, 137, 2836– 2839, DOI: 10.1021/jacs.5b00179
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  7f
  Suppression of Chain Transfer in Catalytic Acrylate Polymerization via Rapid and Selective Secondary Insertion
  Jian, Zhongbao; Baier, Moritz C.; Mecking, Stefan
  Journal of the American Chemical Society (2015), 137 (8), 2836-2839CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  In catalytic copolymn., undesired chain transfer after incorporation of a polar vinyl monomer is a fundamental problem. Authors show an approach to overcome this problem by a fast consecutive insertion. The second double bond of acrylic anhydride rapidly inserts intramolecularly to regio- and stereoselectively form a cyclic repeat unit and a primary alkyl favorable for chain growth (>96%). This results in significantly enhanced copolymer mol. wts. vs monofunctional acrylate monomers.
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  (g) Chen, M.; Yang, B.; Chen, C. Redox-Controlled Olefin (Co)Polymerization Catalyzed by Ferrocene-Bridged Phosphine-Sulfonate Palladium Complexes. Angew. Chem., Int. Ed. 2015, 54, 15520– 15524, DOI: 10.1002/anie.201507274
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  7g
  Redox-Controlled Olefin (Co)Polymerization Catalyzed by Ferrocene-Bridged Phosphine-Sulfonate Palladium Complexes
  Chen, Min; Yang, Bangpei; Chen, Changle
  Angewandte Chemie, International Edition (2015), 54 (51), 15520-15524CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  The facile and reversible interconversion between neutral and oxidized forms of Pd complexes contg. ferrocene-bridged phosphine sulfonate ligands was demonstrated. The activity of these Pd complexes could be controlled using redox reagents during ethylene homopolymn., ethylene/methyl acrylate copolymn., and norbornene oligomerization. Specifically in norbornene oligomerization, the neutral complexes were not active at all whereas the oxidized counterparts showed appreciable activity. In situ switching between the neutral and oxidized forms resulted in an interesting off and on behavior in norbornene oligomerization. This work provides a new strategy to control the olefin polymn. process.
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  (h) Jian, Z.; Mecking, S. Insertion Homo- and Copolymerization of Diallyl Ether. Angew. Chem., Int. Ed. 2015, 54, 15845– 15849, DOI: 10.1002/anie.201508930
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  7h
  Insertion Homo- and Copolymerization of Diallyl Ether
  Jian, Zhongbao; Mecking, Stefan
  Angewandte Chemie, International Edition (2015), 54 (52), 15845-15849CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  The previously unresolved issue of polymn. of allyl monomers CH2=CHCH2X is overcome by a palladium-catalyzed insertion polymn. of diallyl ether as a monomer. An enhanced 2,1-insertion of diallyl ether as compared to mono-allyl ether retards the formation of an unreactive five-membered cyclic O-chelate (after 1,2-insertion) that otherwise hinders further polymn., and also enhances incorporation in ethylene polymers (20.4 mol %). Cyclic ether repeat units are formed selectively (96 %-99 %) by an intramol. insertion of the second allyl moiety of the monomer. These features even enable a homopolymn. to yield polymers (poly-diallyl ether) with ds.p. of DPn≈44.
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  (i) Jian, Z.; Leicht, H.; Mecking, S. Direct Synthesis of Imidazolium-Functional Polyethylene by Insertion Copolymerization. Macromol. Rapid Commun. 2016, 37, 934– 938, DOI: 10.1002/marc.201600073
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  7i
  Direct Synthesis of Imidazolium-Functional Polyethylene by Insertion Copolymerization
  Jian, Zhongbao; Leicht, Hannes; Mecking, Stefan
  Macromolecular Rapid Communications (2016), 37 (11), 934-938CODEN: MRCOE3; ISSN:1022-1336. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Cationic imidazolium-functionalized polyethylene is accessible by insertion copolymn. of ethylene and allyl imidazolium tetrafluoroborate (AIm-BF4) with phosphinesulfonato palladium(II) catalyst precursors. Imidazolium-substituted repeat units are incorporated into the main chain and the initiating satd. chain end of the linear polymers, rather than the terminating unsatd. chain end. The counterion of the allyl imidazolium monomer is decisive, with the chloride analog (AIm-Cl) no polymn. is obsd. Stoichiometric studies reveal the formation of an inactive chloride complex from the catalyst precursor. An effect of moderate densities (0.5 mol%) of ionic groups on the copolymers' phys. properties is exemplified by an enhanced wetting by water.
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  (j) Jian, Z.; Mecking, S. Short-Chain Branched Polar-Functionalized Linear Polyethylene via “Tandem Catalysis”. Macromolecules 2016, 49, 4057– 4066, DOI: 10.1021/acs.macromol.6b00581
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  7j
  Short-Chain Branched Polar-Functionalized Linear Polyethylene via "Tandem Catalysis"
  Jian, Zhongbao; Mecking, Stefan
  Macromolecules (Washington, DC, United States) (2016), 49 (11), 4057-4066CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
  Cationic PdII complex 1 chelated by an N-fixed phosphine sultam has been synthesized and structurally characterized. Exposure of 1 to ethylene resulted in the formation of short-chain olefins (1-butene: 2-butene: 1-hexene: 1-octene = 86:7:6:1) with a high catalytic activity of 105 molE molPd-1 h-1. By combination of 1 and one of the well-known phosphinesulfonato PdII catalyst precursors 2-5, linear polyethylenes contg. Me, Et, and Bu branches of up to 100 per 1000 C were generated from the polymn. of ethylene alone in a "tandem catalysis" one-pot approach. In further exploitation of this concept, linear polyethylenes with both various short-chain branches and a choice of different polar functional groups incorporated into the main chain were obtained for the first time from the copolymn. of ethylene and polar vinyl monomers (Me acrylate, N-isopropylacrylamide, Me vinyl sulfone, acrylonitrile, Et vinyl ether, vinyl acetate, and allyl bromide). All these apolar and polar branches are incorporated into the linear polyethylene backbones to varying degrees, while the type of initiating and terminating chain ends of the resulting polyethylenes depends significantly on the nature of polar vinyl monomer.
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  (k) Jian, Z.; Mecking, S. Insertion Polymerization of Divinyl Formal. Macromolecules 2016, 49, 4395– 4403, DOI: 10.1021/acs.macromol.6b00983
  [ACS Full Text ], [CAS], Google Scholar
  7k
  Insertion Polymerization of Divinyl Formal
  Jian, Zhongbao; Mecking, Stefan
  Macromolecules (Washington, DC, United States) (2016), 49 (12), 4395-4403CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
  Copolymn. of ethylene and divinyl formal by [{κ2-P,O-(2-MeOC6H4)2PC6H4SO3}PdMe(dmso)] (1) by a coordination-insertion mechanism affords highly linear polyethylenes with a high (12.5 mol %) incorporation of divinyl formal. This significantly exceeds the thus far relatively low incorporation (6.9 mol %) and activity with Bu vinyl ether monomer in insertion polymn. The resulting ethylene-divinyl formal copolymers exclusively (>98%) contain five-membered (trans-1,3-dioxolane) and six-membered (cis-/trans-1,3-dioxane) cyclic acetal units in the main chain, and also in the initiating ends of this functionalized polyethylene. Comprehensive NMR anal. of the microstructure of these copolymers revealed that under pressure reactor conditions consecutive 2,1-1,2-insertion of divinyl formal into a Pd-H bond is preferred, but consecutive 1,2-1,2-insertion of divinyl formal into more bulky Pd-alkyls (growing polymer chain) is favored. Moreover, homopolymn. of divinyl formal yielded a non-crosslinking poly(divinyl formal) with ds. p. of DPn ≈ 26.
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  (l) Ota, Y.; Ito, S.; Kobayashi, M.; Kitade, S.; Sakata, K.; Tayano, T.; Nozaki, K. Crystalline Isotactic Polar Polypropylene from the Palladium-Catalyzed Copolymerization of Propylene and Polar Monomers. Angew. Chem., Int. Ed. 2016, 55, 7505– 7509, DOI: 10.1002/anie.201600819
  [Crossref], [CAS], Google Scholar
  7l
  Crystalline Isotactic Polar Polypropylene from the Palladium-Catalyzed Copolymerization of Propylene and Polar Monomers
  Ota, Yusuke; Ito, Shingo; Kobayashi, Minoru; Kitade, Shinichi; Sakata, Kazuya; Tayano, Takao; Nozaki, Kyoko
  Angewandte Chemie, International Edition (2016), 55 (26), 7505-7509CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Moderately isospecific homopolymn. of propylene and the copolymn. of propylene and polar monomers have been achieved with palladium complexes bearing a phosphine-sulfonate ligand. Optimization of substituents on the phosphorus atom of the ligand revealed that the presence of bulky alkyl groups (e.g. menthyl) is crucial for the generation of high-mol.-wt. polypropylenes (Mw≈104), and the substituent at the ortho-position relative to the sulfonate group influences the mol. wt. and isotactic regularity of the obtained polypropylenes. Statistical anal. suggested that the introduction of substituents at the ortho-position relative to the sulfonate group favors enantiomorphic site control over chain end control in the chain propagation step. The triad isotacticity could be increased to mm=0.55-0.59, with formation of cryst. polar polypropylenes, as supported by the presence of m.ps. and sharp peaks in the corresponding X-ray diffraction patterns.
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  (m) Wada, S.; Jordan, R., F. Olefin Insertion into a Pd–F Bond: Catalyst Reactivation Following β-F Elimination in Ethylene/Vinyl Fluoride Copolymerization. Angew. Chem., Int. Ed. 2017, 56, 1820– 1824, DOI: 10.1002/anie.201611198
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  7m
  Olefin Insertion into a Pd-F Bond: Catalyst Reactivation Following β-F Elimination in Ethylene/Vinyl Fluoride Copolymerization
  Wada, Shinji; Jordan, Richard F.
  Angewandte Chemie, International Edition (2017), 56 (7), 1820-1824CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  The discrete (phosphinoarenesulfonate)Pd fluoride complex (POBp,OMe)PdF(lutidine), where POBp,OMe=(2-MeOC6H4)(2-{2,6-(MeO)2C6H3}C6H4)(2-SO3-5-MeC6H3)P, inserts vinyl fluoride (VF) to form (POBp,OMe)PdCH2CHF2(lutidine) and inserts multiple ethylene (E) units to generate polyethylene that contains -CH2F chain ends. These results provide strong evidence that the -CHF2 and -CH2F chain ends in E/VF copolymer generated by (phosphinoarenesulfonate)PdR catalysts form by β-F elimination of Pd(β-F-alkyl) species, VF or E insertion of the resulting (PO)PdF species, and subsequent chain growth. These results also imply that β-F elimination is not an important catalyst deactivation reaction in this system.
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  (n) Zhang, D.; Chen, C. Influence of Polyethylene Glycol Unit on Palladium- and Nickel-Catalyzed Ethylene Polymerization and Copolymerization. Angew. Chem., Int. Ed. 2017, 56, 14672– 14676, DOI: 10.1002/anie.201708212
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  7n
  Influence of Polyethylene Glycol Unit on Palladium- and Nickel-Catalyzed Ethylene Polymerization and Copolymerization
  Zhang, Dan; Chen, Changle
  Angewandte Chemie, International Edition (2017), 56 (46), 14672-14676CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  The transition-metal-catalyzed copolymn. of olefins with polar functionalized co-monomers represents a major challenge in the field of olefin polymn. It is extremely difficult to simultaneously achieve improvements in catalytic activity, polar monomer incorporation, and copolymer mol. wt. through ligand modifications. Herein we introduce a polyethylene glycol unit to some phosphine-sulfonate palladium and nickel catalysts, and its influence on ethylene polymn. and copolymn. is investigated. In ethylene polymn., this strategy leads to enhanced activity, catalyst stability, and increased polyethylene mol. wt. In ethylene copolymn. with polar monomers, improvements in all copolymn. parameters are realized. This effect is most significant for polar monomers with hydrogen-bond-donating abilities.
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8. 8
  (a) Nakano, R.; Nozaki, K. Copolymerization of Propylene and Polar Monomers Using Pd/IzQO Catalysts. J. Am. Chem. Soc. 2015, 137, 10934– 10937, DOI: 10.1021/jacs.5b06948
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  8a
  Copolymerization of Propylene and Polar Monomers Using Pd/IzQO Catalysts
  Nakano, Ryo; Nozaki, Kyoko
  Journal of the American Chemical Society (2015), 137 (34), 10934-10937CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Palladium catalysts bearing imidazo[1,5-a]quinolin-9-olate-1-ylidene (IzQO) ligands polymerize α-olefins while incorporating polar monomers. The steric environment provided by N-heterocyclic-carbene (NHC) enables regioselective insertion of α-olefins and polar monomers, yielding polypropylene, propylene/allyl carboxylate copolymers, and propylene/methyl acrylate copolymer. Known polymn. catalysts bearing NHC-based ligands decomp. rapidly, whereas the present catalyst is durable because of structural confinement, wherein the NHC-plane is coplanar to the metal square plane. The present catalyst system enables facile access to a new class of functionalized polyolefins and helps conceive a new fundamental principle for designing NHC-based ligands.
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  (b) Tao, W.; Nakano, R.; Ito, S.; Nozaki, K. Copolymerization of Ethylene and Polar Monomers by Using Ni/IzQO Catalysts. Angew. Chem., Int. Ed. 2016, 55, 2835– 2839, DOI: 10.1002/anie.201510077
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  8b
  Copolymerization of Ethylene and Polar Monomers by Using Ni/IzQO Catalysts
  Tao, Wen-jie; Nakano, Ryo; Ito, Shingo; Nozaki, Kyoko
  Angewandte Chemie, International Edition (2016), 55 (8), 2835-2839CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  The replacement of precious metals in catalysis by earth-abundant metals is currently one of the urgent challenges for chemists. Whereas Pd-catalyzed copolymn. of ethylene and polar monomers is a valuable method for the straightforward synthesis of functionalized polyolefins, the corresponding Ni-based catalysts have suffered from poor thermal tolerance and low mol. wt. of the polymers formed. Herein, the authors report neutral Ni complexes bearing imidazo[1,5-a]quinolin-9-olate-1-ylidene (IzQO) ligands. The Ni/IzQO system can catalyze ethylene polymn. at 50-100° with reasonable activity in the absence of any cocatalyst, whereas most known Ni-based catalysts are deactivated at this temp. range. The Ni/IzQO catalyst was successfully applied to the copolymn. of ethylene with allyl monomers to obtain the corresponding copolymers with the highest mol. wt. reported for a Ni-catalyzed system.
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  (c) Yasuda, H.; Nakano, R.; Ito, S.; Nozaki, K. Palladium/IzQO-Catalyzed Coordination–Insertion Copolymerization of Ethylene and 1,1-Disubstituted Ethylenes Bearing a Polar Functional Group. J. Am. Chem. Soc. 2018, 140, 1876– 1883, DOI: 10.1021/jacs.7b12593
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  8c
  Palladium/IzQO-Catalyzed Coordination-Insertion Copolymerization of Ethylene and 1,1-Disubstituted Ethylenes Bearing a Polar Functional Group
  Yasuda, Hina; Nakano, Ryo; Ito, Shingo; Nozaki, Kyoko
  Journal of the American Chemical Society (2018), 140 (5), 1876-1883CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Coordination-insertion copolymn. of ethylene with 1,1-disubstituted ethylenes bearing a polar functional group, such as Me methacrylate (MMA), is a long-standing challenge in catalytic polymn. The major obstacle for this process is the huge difference in reactivity of ethylene vs. 1,1-disubstituted ethylenes towards both coordination and insertion. Herein we report the copolymn. of ethylene and 1,1-disubstituted ethylenes by using an imidazo[1,5-a]quinolin-9-olate-1-ylidene (IzQO)-supported palladium catalyst. Various types of 1,1-disubstituted ethylenes were successfully incorporated into the polyethylene chain. In-depth characterization of the obtained copolymers and mechanistic inferences drawn from stoichiometric reactions of alkylpalladium complexes with Me methacrylate and ethylene indicate that the copolymn. proceeds by the same coordination-insertion mechanism that has been postulated for ethylene.
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9. 9
  (a) Nagai, Y.; Kochi, T.; Nozaki, K. Synthesis of N-Heterocyclic Carbene-Sulfonate Palladium Complexes. Organometallics 2009, 28, 6131– 6134, DOI: 10.1021/om9004252
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  9a
  Synthesis of N-Heterocyclic Carbene-Sulfonate Palladium Complexes
  Nagai, Yusuke; Kochi, Takuya; Nozaki, Kyoko
  Organometallics (2009), 28 (20), 6131-6134CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  The syntheses of sulfomethylimidazolium ligand precursors I (R = 2,4-di-iPrC6H3, 2,4,6-tri-MeC6H2) are reported. Upon reaction with silver oxide, an oligomeric silver complex is formed in which the N-heterocyclic carbene (NHC) ligands coordinate to the silver atoms in a monodentate fashion. Treatment of the silver complex with appropriate palladium sources results in the formation of monomeric NHC-sulfonate palladium complexes II (L = PPh3, 2,6-lutidine). The structures of complexes II were detd. by single-crystal x-ray anal. as the first examples of bidentate coordination of imidazolium-sulfonates to a metal center.
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  (b) Zhou, X.; Jordan, R. F. Synthesis, cis/trans Isomerization, and Reactivity of Palladium Alkyl Complexes That Contain a Chelating N-Heterocyclic-Carbene Sulfonate Ligand. Organometallics 2011, 30, 4632– 4642, DOI: 10.1021/om200482a
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  9b
  Synthesis, cis/trans Isomerization, and Reactivity of Palladium Alkyl Complexes That Contain a Chelating N-Heterocyclic-Carbene Sulfonate Ligand
  Zhou, Xiaoyuan; Jordan, Richard F.
  Organometallics (2011), 30 (17), 4632-4642CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  The chem. of Pd alkyl complexes that incorporate the NHC-sulfonate ligand N-(2,6-iPr2-Ph)-N'-2-benzenesulfonate-NHC ([C-O]-, NHC = cyclo-CNCH2CH2N) is described. The reaction of {C-O}Ag (2) with Pd2(μ-Cl)2Me2(PPh3)2 affords cis-C,C-{C-O}PdMe(PPh3) (3, 79%). The reaction of 2 with Pd2(μ-Cl)2Me2(2,6-lutidine)2 at 25° in CH2Cl2 gives a 4/1 mixt. of trans-C,C-{C-O}PdMe(2,6-lutidine) (4a) and cis-C,C-{C-O}PdMe(2,6-lutidine) (4b), which were isolated in 62% and 18% yield, resp., by recrystn. The NHC-sulfonate ligands bind in a κ2-C,O fashion in 3 and 4a,b. 4A isomerizes to 4b by dissocn. of the Ar-SO3- unit to form a configurationally labile three-coordinate intermediate. This process is accelerated by H bond donors (CD3OD, lutidinium) and Lewis acids (B(C6F5)3) that can labilize the sulfonate group. 4A and 4b react with 1 equiv of B(C6F5)3 to yield the O-bound adduct cis-C,C-{C-O-B(C6F5)3}PdMe(2,6-lutidine) (5). 5 Decomps. at 40° by C-C reductive elimination to afford (in the presence of pyridine to trap the B(C6F5)3) N-(2,6-iPr2-Ph)-N'-2-benzenesulfonate-imidazolium Me (6). Trans-C,C-4a reacts with CO and tBuNC to yield the insertion products {C-O}Pd{C(O)Me}(2,6-lutidine) (7) and {C-O}Pd{C(:NtBu)Me}(tBuNC) (9), in which the acyl and iminoacyl ligands are cis to the NHC ligand, via stereospecific displacement of Ar-SO3- by the substrate followed by migratory insertion. The bis-isocyanide adduct {κ1-C-C-O}PdMe(tBuNC)2, in which the tBuNC ligands are trans, is an intermediate in the formation of 9. tBuNC reversibly displaces the Ar-SO3- ligand of 9 to form {κ1-C-C-O}Pd{C(:NtBu)Me}(tBuNC)2 (10). In contract, cis-C,C-4a does not undergo net reaction with CO and reacts with tBuNC via reductive elimination to yield 6. Displacement of the ArSO3- ligand of cis-C,C-4b by potential substrates yields adducts in which the substrate and Me group are trans and insertion is not possible.
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  (c) Gott, A. L.; Piers, W. E.; Dutton, J. L.; McDonald, R.; Parvez, M. Dimerization of Ethylene by Palladium Complexes Containing Bidentate Trifluoroborate-Functionalized Phosphine Ligands. Organometallics 2011, 30, 4236– 4249, DOI: 10.1021/om2004095
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  9c
  Dimerization of Ethylene by Palladium Complexes Containing Bidentate Trifluoroborate-Functionalized Phosphine Ligands
  Gott, Andrew L.; Piers, Warren E.; Dutton, Jason L.; McDonald, Robert; Parvez, Masood
  Organometallics (2011), 30 (16), 4236-4249CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  As an alternative to the widely reported phosphine-sulfonate ligand system, a series of potassium aryltrifluoroborate-functionalized phosphine ligands and zwitterionic phosphonium salts were prepd. and structurally characterized. The phosphine ligands formed complexes of the general formula [κ2-(P,F)RPdClMe] (where R = Ph, 2-OMe-Ph) when reacted with PdClMe(COD); however, cleavage of the chloride ligand proved problematic. Reaction of the phosphonium salts with PdMe2(tmeda) yield complexes of the general type [κ-(P)RPdMe(tmeda)], which react with pyridine derivs. to displace tmeda. Manipulation of the steric bulk of the pyridine ligands affords some control over the coordination mode of the fluoroborate phosphine, yielding facile access to complexes of the general type [κ2-(P,F)RPdMe(lutidine)]. Investigations into the insertion chem. of the palladium Me moiety with simple small mols. revealed that the release of the lutidine ligand is slow and that insertion of ethylene occurs in a very slow manner; this is attributed to the relative electron deficiency of the aryltrifluoroborate moiety as compared to sulfonate. The palladium lutidine complexes slowly dimerize ethylene to a mixt. of propene and butenes.
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  (d) Kim, Y.; Jordan, R. F. Synthesis, Structures, and Ethylene Dimerization Reactivity of Palladium Alkyl Complexes That Contain a Chelating Phosphine–Trifluoroborate Ligand. Organometallics 2011, 30, 4250– 4256, DOI: 10.1021/om200472x
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  9d
  Synthesis, Structures, and Ethylene Dimerization Reactivity of Palladium Alkyl Complexes That Contain a Chelating Phosphine-Trifluoroborate Ligand
  Kim, Young-Min; Jordan, Richard F.
  Organometallics (2011), 30 (16), 4250-4256CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  The chem. of palladium alkyl complexes that incorporate the phosphine-trifluoroborate ligand ortho-(Ph2P)C6H4(BF3-)(PF-) is described. The reaction of the pinacol borane ortho-(Ph2P)C6H4(Bpin) with K[HF2] yields ortho-(Ph2P)C6H4(BF3K) (K[PF], 1). Crystn. of 1 from Et2O/THF in the presence of 18-crown-6 yields [K-(18-crown-6)][PF]·0.5THF (2·0.5THF). In the solid state, the phosphine-borate anion of 2 is ion-paired with the [K-(18-crown-6)] cation through weak contacts with the phosphorus and two fluorine atoms. 1 Reacts with (COD)PdMeCl in the presence of 18-crown-6 to form [K-(18-crown-6)][(PF)PdMeCl] (3) and with (COD)PdMeCl and 2,4,6-collidine (col) to yield (PF)PdMe(col) (4). The PF- ligands in 3 and 4 are bound to Pd in a κ2 mode through the phosphine and one fluorine of the -ArBF3- unit. The other two fluorines are weakly bound to the K(18-crown-6)+ cation in 3. NMR studies show that the Pd-F interactions in 3 and 4 are maintained in soln. and that, for 4, the three fluorine atoms undergo fast site exchange on the NMR time scale. 4 Reacts with excess pyridine to yield (κ1-P-PF)PdMe(py)2 (6), in which the -ArBF3- unit has been completely displaced by pyridine. 4 Slowly dimerizes ethylene to 1-butene (36 t.o./h, 23°, CH2Cl2, 400 psi ethylene). The catalyst resting state is (PF)PdEt(col) (7). Addn. of [H(OEt2)2][B(3,5-(CF3)2-C6H3)4] traps the collidine as [collidinium][B(3,5-(CF3)2-C6H3)4] and results in a 10-fold increase in the ethylene dimerization rate (385 t.o./h, 23°C, CD2Cl2, 150 psi ethylene).
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  (e) Wucher, P.; Roesle, P.; Falivene, L.; Cavallo, L.; Caporaso, L.; Göttker-Schnetmann, I.; Mecking, S. Controlled Acrylate Insertion Regioselectivity in Diazaphospholidine-Sulfonato Palladium(II) Complexes. Organometallics 2012, 31, 8505– 8515, DOI: 10.1021/om300755j
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  9e
  Controlled acrylate insertion regioselectivity in diazaphospholidine-sulfonato palladium(II) complexes
  Wucher, Philipp; Roesle, Philipp; Falivene, Laura; Cavallo, Luigi; Caporaso, Lucia; Goettker-Schnetmann, Inigo; Mecking, Stefan
  Organometallics (2012), 31 (24), 8505-8515CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  Diazaphospholidine-sulfonato Pd(II) complexes I [1a·L-1f·L; X = Me, L = dmso, pyridine, lutidine, μ-ClLi(solvent); 1a: Ar = Ph, 1b: Ar = 2-MeC6H4, 1c: Ar = 2-MeOC6H4, 1d: Ar = 2,4,6-Me3C6H2, 1e: Ar = 2,6-iPr2C6H3, 1f: Ar = 2,6-(p-tolyl)2C6H3] were prepd. and structurally characterized. The complexes 1·L undergo insertion of Me acrylate (MA) into palladium-carbon bond, the regioselectivity of the insertion reaction being dependent on the steric bulk of the N-aryl substituents Ar. The regioselectivity of MA insertion into the Pd-Me bond is entirely inverted from >93% 1,2-insertion for bulky substituents in the complexes 1d-f, yielding the insertion products II (12, Z = CH2, R = Me) to the usual electronically controlled 2,1-insertion (>95%) for the less bulky Ar = Ph in the complex 1a, yielding the insertion product (11, shown as II, Z = bond, R = Et), and β-H elimination product Me crotonate. DFT studies underline that this is due to a more favorable insertion transition state (2,1- favored by 12 kJ mol-1 over 1,2- for 1a) vs. destabilization of the 2,1-insertion transition state in 1d,e. By contrast, MA insertion into the novel isolated and structurally characterized hydride and deuteride complexes (9e, 10e, shown as I, X = H, D; L = lutidine, Ar = 2,6-iPr2C6H3) occurs 2,1-selectively. This is due to the insertion occurring from the isomer with the P-donor and the olefin in trans arrangement, rather than the insertion into the alkyl from the cis isomer in which the olefin is in proximity to the bulky diazaphospholidine. The complexes 1a-f are precursors to active catalysts for ethylene polymn. to highly linear polyethylene with Mn up to 35 000 g mol-1. In copolymn. expts., norbornene was incorporated in up to 6.1 mol % into the polyethylene backbone.
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  (f) 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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  9f
  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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  (g) Zhang, Y.; Cao, Y.; Leng, X.; Chen, C.; Huang, Z. Cationic Palladium(II) Complexes of Phosphine–Sulfonamide Ligands: Synthesis, Characterization, and Catalytic Ethylene Oligomerization. Organometallics 2014, 33, 3738– 3745, DOI: 10.1021/om5004094
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  There is no corresponding record for this reference.
  .
  (h) Jian, Z.; Falivene, L.; Wucher, P.; Roesle, P.; Caporaso, L.; Cavallo, L.; Göttker-Schnetmann, I.; Mecking, S. Insights into Functional-Group-Tolerant Polymerization Catalysis with Phosphine–Sulfonamide Palladium(II) Complexes. Chem. - Eur. J. 2015, 21, 2062– 2075, DOI: 10.1002/chem.201404856
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  9h
  Insights into Functional-Group-Tolerant Polymerization Catalysis with Phosphine-Sulfonamide Palladium(II) Complexes
  Jian, Zhongbao; Falivene, Laura; Wucher, Philipp; Roesle, Philipp; Caporaso, Lucia; Cavallo, Luigi; Goettker-Schnetmann, Inigo; Mecking, Stefan
  Chemistry - A European Journal (2015), 21 (5), 2062-2075CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Two series of cationic Pd(II) Me complexes {[(2-MeOC6H4)2PC6H4SO2NHC6H3(2,6-R1,R2)]PdMe}2[A]2 (X1+-A: R1 = R2 = H: H1+-A; R1 = R2 = CHMe2: DIPP1+-A; R1 = H, R2 = CF3: CF31+-A; A = BF4 or SbF6) and neutral Pd(II) Me complexes {[(2-MeOC6H4)2PC6H4SO2NC6H3(2,6-R1,R2)]PdMe(L)} (X1-acetone: L = acetone; X1-DMSO: L = DMSO; X1-pyr: L = pyridine) chelated by a phosphine-sulfonamide were synthesized and fully characterized. Stoichiometric insertion of Me acrylate (MA) into all complexes revealed that a 2,1 regiochem. dominates in the 1st insertion of MA. Subsequently, for the cationic complexes X1+-A, β-H elimination from the 2,1-insertion product X2+-AMA-2,1 is overwhelmingly favored over a 2nd MA insertion to yield two major products X4+-AMA-1,2 and X5+-AMA. By contrast, for the weakly coordinated neutral complexes X1-acetone and X1-DMSO, a 2nd MA insertion of the 2,1-insertion product X2MA-2,1 is faster than β-H elimination and gives X3MA as major products. For the strongly coordinated neutral complexes X1-pyr, no 2nd MA insertion and no β-H elimination (except for DIPP2-pyrMA-2,1) were obsd. for the 2,1-insertion product X2-pyrMA-2,1. The cationic complexes X1+-A exhibited high catalytic activities for ethylene dimerization, affording butenes (C4) with a high selectivity of up to 97.7% (1-butene: 99.3 %). Differences in activities and selectivities suggest that the phosphine-sulfonamide ligands remain coordinated to the metal center in a bidentate fashion in the catalytically active species. By comparison, the neutral complexes X1-acetone, X1-DMSO, and X1-pyr showed very low activity towards ethylene to give traces of oligomers. DFT analyses taking into account the two possible coordination modes (O or N) of the sulfonamide ligand for the cationic system CF31+ suggested that the exptl. obsd. high activity in ethylene dimerization is the result of a facile 1st ethylene insertion into the O-coordinated PdMe isomer and a subsequent favored β-H elimination from the N-coordinated isomer formed by isomerization of the insertion product. Steric hindrance by the N-aryl substituent in the neutral systems CF31 and H1 appears to contribute significantly to a higher barrier of insertion, which accounts for the exptl. obsd. low activity towards ethylene oligomerization.
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  .
  (i) 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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  9i
  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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10. 10
  (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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  10a
  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) 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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  10b
  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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11. 11
  Wu, Z.; Chen, M.; Chen, C. Ethylene Polymerization and Copolymerization by Palladium and Nickel Catalysts Containing Naphthalene-Bridged Phosphine–Sulfonate Ligands. Organometallics 2016, 35, 1472– 1479, DOI: 10.1021/acs.organomet.6b00076
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  11
  Ethylene Polymerization and Copolymerization by Palladium and Nickel Catalysts Containing Naphthalene-Bridged Phosphine-Sulfonate Ligands
  Wu, Zixia; Chen, Min; Chen, Changle
  Organometallics (2016), 35 (10), 1472-1479CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  Naphthalene-bridged phosphine-sulfonate ligands and the corresponding Pd(II) complexes [κ2(P,O)-2-(R2P)-1-naphthalenesulfonato]Pd(Me)(DMSO) (1, R = Ph; 2, R = o-MeO-C6H4; 3, R = Cy) and Ni(II) complexes [κ2(P,O)-2-(R2P)-1-naphthalenesulfonato]Ni(η3-C3H5) (Ni-1, R = o-MeO-C6H4; Ni-2, R = Cy) were prepd. and characterized. The analogous benzo-bridged phosphine-sulfonate Pd(II) complex [κ2(P,O)-(R2P)-benzenesulfonato]Pd(Me)(DMSO) (2', R = o-MeO-C6H4) and Ni(II) complex [κ2(P,O)-(R2P)-benzenesulfonato]Ni(η3-C3H5) (Ni-1', R = o-MeO-C6H4) were prepd. for comparison. In ethylene polymn., complex 2 showed activity of up to 7.5 × 106 g mol-1 h-1, which is among the most active Pd catalysts for ethylene homopolymn. Under the same conditions, complex 2 showed up to 1 order of magnitude higher catalytic activity than complex 2', generating polyethylene with slightly smaller mol. wt. and similar branching d. The Ni(II) complex Ni-1 was also more active than complex Ni-1', generating polyethylene with up to 1 order of magnitude higher mol. wt. In ethylene-Me acrylate copolymn., complex 2 showed lower activity, affording a copolymer with higher Me acrylate incorporation and higher copolymer mol. wt. in comparison to complex 2'.
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12. 12
  (a) Murry, R. E. U.S. Patent 4,689,437. Aug 25, 1987.
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  There is no corresponding record for this reference.
  (b) van Doorn, J. A.; Drent, E.; van Leeuwen, P. W. M. N.; Meijboon, N.; van Oort, A. B.; Wife, R. L. Eur. Pat. Appl. 0,280,380, Aug 31, 1988.
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  (c) Keim, W.; Maas, H.; Mecking, S. Palladium Catalyzed Alternating Cooligomerization of Ethylene and Carbon Monoxide to Unsaturated Ketones. Z. Naturforsch., B: J. Chem. Sci. 1995, 50, 430– 438, DOI: 10.1515/znb-1995-0318
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  12c
  Palladium catalyzed alternating cooligomerization of ethylene and carbon monoxide to unsaturated ketones
  Keim, Wilhelm; Maas, Heiko; Mecking, Stefan
  Zeitschrift fuer Naturforschung, B: Chemical Sciences (1995), 50 (3), 430-8CODEN: ZNBSEN; ISSN:0932-0776. (Verlag der Zeitschrift fuer Naturforschung)
  Cationic palladium catalysts were used to cooligomerize ethylene and carbon monoxide. At high ethylene/CO ratios (m/m = 10:1) in CH2Cl2 as a solvent, unsatd. alternating cooligomers were obtained. I, II, III, and IV (n = 1-3, R = Me, Et) were used as catalysts. With PnBu3 as a ligand, selectivities for Et vinyl ketone of 40% based on the CO converted were obtained. The hemilabile phosphino-ester and phosphino-thiophene ligands behave like monodentate phosphine under catalytic conditions.
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  (d) Bennett, J. L.; Brookhart, M.; Johnson, L. K.; PCT Int. Appl. WO199830610, July 16, 1998.
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  (e) Brassat, I.; Keim, W.; Killat, S.; Möthrath, M.; Mastrorilli, P.; Nobile, C. F.; Suranna, G. P. Synthesis and Catalytic Activity of Allyl, Methallyl and Methyl Complexes of Nickel(II) and Palladium(II) with Biphosphine Monoxide Ligands: Oligomerization of Ethylene and Copolymerization of Ethylene and Carbon Monoxide. J. Mol. Catal. A: Chem. 2000, 157, 41– 58, DOI: 10.1016/S1381-1169(99)00449-5
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  12e
  Synthesis and catalytic activity of allyl, methallyl and methyl complexes of nickel(II) and palladium(II) with biphosphine monoxide ligands: oligomerization of ethylene and copolymerization of ethylene and carbon monoxide
  Brassat, I.; Keim, W.; Killat, S.; Mothrath, M.; Mastrorilli, P.; Nobile, C. F.; Suranna, G. P.
  Journal of Molecular Catalysis A: Chemical (2000), 157 (1-2), 41-58CODEN: JMCCF2; ISSN:1381-1169. (Elsevier Science B.V.)
  The syntheses of new cationic Ni complexes {[η3-methallyl]Ni[κ2P,O-Ph2P(X)P(O)Ph2]}SbF6, [X = (o-C6H4), (NH)] were accomplished. The complexes oligomerize ethylene to linear α-olefins with selectivities ≤89%. A dependence of oligomerization grade and activity on backbone geometry was shown. New cationic allyl and Me complexes of Pd(II) [(MeCN)(Me)Pd(κ2P,O-Ar2P(CH2)nP(O)Ar2)]X [n = 1-3, X = BF4, Ar = Ph] [n = 1, X = SbF6, Ar = p-tolyl; n = 1 or 2, X = SbF6, Ar = Ph]; [(η3-C3H5)Pd(κ2P,O-Ph2P(CH2)nP(O)Ph2)]X, [n = 2, X = triflate, tosylate; n = 3, X = triflate, tosylate], [(η3-C3H5)Pd(κ2P,O-Ar2P(CH2)nP(O)Ar2)]X, [n = 1, X = SbF6, Ar = p-tolyl; n = 2, X = SbF6 Ar = Ph] were synthesized in good yields. These complexes were used in the catalytic oligomerization of ethylene, and in the catalytic alternating copolymn. of ethylene and CO, to yield polyketones.
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  (f) Malinoski, J. M.; Brookhart, M. Polymerization and Oligomerization of Ethylene by Cationic Nickel(II) and Palladium(II) Complexes Containing Bidentate Phenacyldiarylphosphine Ligands. Organometallics 2003, 22, 5324– 5335, DOI: 10.1021/om030388h
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  12f
  Polymerization and Oligomerization of Ethylene by Cationic Nickel(II) and Palladium(II) Complexes Containing Bidentate Phenacyldiarylphosphine Ligands
  Malinoski, Jon M.; Brookhart, Maurice
  Organometallics (2003), 22 (25), 5324-5335CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  A series of Ni(II) and Pd(II) catalysts have been synthesized from the P,O chelating ligands phenacyl(aryl)2phosphine. The (P,O)Ni-allyl+B(Arf)-4 [Arf = 3,5-(CF3)2C6H3] complexes 6a-c are active for polymn. of ethylene in the case of 6b (aryl = 2,4,6-(CH3)3C6H2) and for dimerization of ethylene to butenes in the case of 6a (aryl = C6H5) and 6c (aryl = C6H5, 2,4,6-(C6H5)3C6H2). These catalysts are characterized by their high initial activity but relatively short catalytic lifetime and poor thermal stability. The palladium analogs (P,O)PdMe(NCMe)+B(Arf)-4 are approx. an order of magnitude less active than the Ni analogs and generate butenes and hexenes. The barriers for migratory insertion in a series of Me ethylene complexes [(p-XC6H4)2PCH2C(O)(p-YC6H4)]Pd(CH3)(C2H4)+B(Arf)-4 (X,Y = H, H; -OCH3, H; -CF3, H; H, -OCH3; H, -CF3) were measured. Values of ΔG⧧ ranged from 18.2 to 20.3 kcal/mol and, relative to the unsubstituted system, decreased for X,Y = -CF3 and increased for X,Y = -OCH3.
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  .
  (g) Bettucci, L.; Bianchini, C.; Claver, C.; Suarez, E. J. G.; Ruiz, A.; Meli, A.; Oberhauser, W. Ligand Effects in the Non-alternating CO–Ethylene Copolymerization by Palladium(II) Catalysis. Dalton Trans. 2007, 5590– 5602, DOI: 10.1039/b711280g
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  12g
  Ligand effects in the non-alternating CO-ethylene copolymerization by palladium(II) catalysis
  Bettucci, Lorenzo; Bianchini, Claudio; Claver, Carmen; Suarez, Eduardo J. Garcia; Ruiz, Aurora; Meli, Andrea; Oberhauser, Werner
  Dalton Transactions (2007), (47), 5590-5602CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
  In this paper we report on a comparative study of the non-alternating CO-C2H4 copolymn. catalyzed by neutral PdII complexes with the phosphine-sulfonate ligands bis(o-methoxyphenyl)phosphinophenylenesulfonate and bis(o-methoxyphenyl)phosphino-ethylenesulfonate. The former ligand, featuring a lower skeletal flexibility, was found to form more active catalysts and produce polyketones with higher mol. wt. and higher extra-ethylene incorporation. Operando high-pressure NMR studies have allowed us to intercept, for the first time, PdII(phosphine-sulfonate) β-chelates in the non-alternating copolymn. cycle, while model organometallic reactions have contributed to demonstrate that PdII (phosphine-sulfonate) fragments do not form stable carbonyl complexes. The opening of the β-chelates was a viable process by either comonomer, which contrasts with the behavior of PdII (chelating diphosphine) catalysts for the perfectly alternating copolymn.
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13. 13
  Liu, W.; Malinoski, J. M.; Brookhart, M. Ethylene Polymerization and Ethylene/Methyl 10-Undecenoate Copolymerization Using Nickel(II) and Palladium(II) Complexes Derived from a Bulky P,O Chelating Ligand. Organometallics 2002, 21, 2836– 2838, DOI: 10.1021/om0201516
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  13
  Ethylene Polymerization and Ethylene/Methyl 10-Undecenoate Copolymerization Using Nickel(II) and Palladium(II) Complexes Derived from a Bulky P,O Chelating Ligand
  Liu, Weijun; Malinoski, Jon M.; Brookhart, Maurice
  Organometallics (2002), 21 (14), 2836-2838CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  Cationic Ni(II) and Pd(II) complexes ([LNi(η3-allyl)]BAr'4 (L = tBu2PCH2C(O)Ph) and [Me(L)PdL1]BAr'4 (L1 = Et2O, NCMe)) based on the bulky P,O ligand phenacyldi-tert-butylphosphine are active for the polymn. of ethylene and copolymn. of ethylene and Me 10-undecenoate, a functionalized monomer.
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14. 14
  Black, R. E.; Jordan, R. F. Synthesis and Reactivity of Palladium(II) Alkyl Complexes that Contain Phosphine-cyclopentanesulfonate Ligands. Organometallics 2017, 36, 3415– 3428, DOI: 10.1021/acs.organomet.7b00572
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  14
  Synthesis and reactivity of palladium(II) alkyl complexes that contain phosphine-cyclopentanesulfonate ligands
  Black, Rebecca E.; Jordan, Richard F.
  Organometallics (2017), 36 (17), 3415-3428CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  Palladium cyclopentane-based monophosphine-sulfonate Me complexes [[(CH2)3CHPAr2CHSO3]PdMe(L)] were prepd. and examd. for catalytic activity in ethylene-acrylate copolymn. The synthesis of the phosphine-cyclopentanesulfonate pro-ligands Li/K[2-PPh2-cyclopentanesulfonate] (Li/K[2a]), Li/K[2-P(2-OMe-Ph)2-cyclopentanesulfonate] (Li/K[2b]), and H[2b], and the corresponding Pd(II) alkyl complexes (κ2-P,O-2a)PdMe(py) (3a) and (κ2-P,O-2b)PdMe(py) (3b) is described. The sulfonate-bridged base-free dimer {(2b)PdMe}2 (4b) was synthesized by abstraction of pyridine from 3b using B(C6F5)3. The borane-coordinated base-free dimer [{2b·B(C6F5)3}PdMe]2 (5b), in which B(C6F5)3 binds to a sulfonate oxygen, was prepd. by addn. of 1 equiv of B(C6F5)3 per Pd to 4b or addn. of 2 equiv of B(C6F5)3 to 3b. Compds. 3b, 4b, and 5b polymerize ethylene with low activity (up to 210 kg mol-1 h-1 at 250 psi and 80°) to linear polyethylene (Mn = 1950-5250 Da) with predominantly internal olefin placements. Complexes 3b and 4b copolymerize ethylene with Me acrylate to linear copolymers that contain up to 11.7 mol % Me acrylate, which is incorporated as -CH2CH(CO2Me)CH2- (80%) in-chain units and -CH2CH(CO2Me)Me (8%) and -CH2CH:CH(CO2Me) (12%) chain-end units. The complexes 3b and 4b also copolymerize ethylene with vinyl fluoride to linear copolymers that contain up to 0.41 mol % vinyl fluoride, which is incorporated as -CH2CHFCH2- (∼80%) in-chain units and -CH2CF2H (7%), -CH2CHFCH3 (5%), and -CH2CH2F (8%) chain-end units. Complexes 3b and 4b are more stable and active in ethylene polymn. than analogous (PAr2CH2CH2SO3)PdR catalysts, but are less active than analogous (PAr2-arenesulfonate)PdR catalysts. Low-temp. NMR studies show that 4b reacts with ethylene below -10° to form the ethylene adduct cis-P,R-(2b)PdMe(ethylene) (7b), which undergoes ethylene insertion at 5°. DFT calcns. for a model (PMe2-cyclopentanesulfonate)Pd(Pr)(ethylene) species show that ethylene insertion proceeds by cis-P,R/trans-P,R isomerization followed by migratory insertion, and that the lower activity of 3b and 4b vis-a-vis analogous (PAr2-arenesulfonate)PdR catalysts results from a higher barrier for migratory insertion of the trans-P,R isomer.
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15. 15
  (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
  [ACS Full Text ], [CAS], Google Scholar
  15a
  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) 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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  15b
  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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16. 16
  A part of the present work has already been disclosed in a patent, see:Nozaki, K.; Carrow, B. P.; Okumura, Y.; Kuroda, J. WO2013168626, 2013.
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17. 17
  The amount of ethylene dissolved in toluene does not linearly correlate with the pressure of ethylene, especially when the pressure of ethylene is <0.5 MPa; see:Schuster, N.; Rünzi, T.; Mecking, S. Reactivity of Functionalized Vinyl Monomers in Insertion Copolymerization. Macromolecules 2016, 49, 1172– 1179, DOI: 10.1021/acs.macromol.5b02749
  [ACS Full Text ], [CAS], Google Scholar
  17
  Reactivity of Functionalized Vinyl Monomers in Insertion Copolymerization
  Schuster, Nicole; Ruenzi, Thomas; Mecking, Stefan
  Macromolecules (Washington, DC, United States) (2016), 49 (4), 1172-1179CODEN: MAMOBX; ISSN:0024-9297. (American Chemical Society)
  We report the reactivities of a comprehensive range of polar vinyl comonomers and 1-olefins in the copolymn. with ethylene by [{(o-MeOC6H4)2PC6H4SO3}PdMe(L)] from pressure reactor studies (95 °C, 3-20 bar), as defined by rE = kethylene/kcomonomer from Markov statistics. 13C NMR chem. shifts of the monomers' β vinyl carbon atom and Charton and Sterimol parameters were found to be appropriate descriptors for the monomers' electronic nature and steric demand, resp. A comprehensive picture of their impact on monomer reactivity and also regioselectivity of insertion arises. This shall also allow for predictions of the reactivity of other monomers.
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18. 18
  Ito, S.; Kanazawa, M.; Munakata, K.; Kuroda, J.; 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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  18
  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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19. 19
  For details, see Figure S63 in the Supporting Information.
  There is no corresponding record for this reference.
20. 20
  There are several types of ethylene/MMA copolymers formed via late transition metal catalysis: (1) ethylene/MMA copolymers featuring chain-end incorporation of MMA formed via coordination–insertion mechanism (for the recent example, see:Chen, M.; Chen, C. A Versatile Ligand Platform for Palladium- and Nickel-catalyzed Ethylene Copolymerizations with Polar Monomers. Angew. Chem., Int. Ed. 2018, in press. DOI: DOI: 10.1002/anie.201711753 ); (2) multiblock ethylene/MMA copolymers by a combination of coordination–insertion and radical mechanisms; (3) ethylene/MMA copolymers which might include consecutive polyMMA units formed by the intermediacy of radical-related processes. For the details, see ref (8c) and references cited therein.
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Methylene-Bridged Bisphosphine Monoxide Ligands for Palladium-Catalyzed Copolymerization of Ethylene and Polar Monomers

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Methylene-Bridged Bisphosphine Monoxide Ligands for Palladium-Catalyzed Copolymerization of Ethylene and Polar Monomers

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