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Activation and Deactivation of Neutral Palladium(II) Phosphinesulfonato Polymerization Catalysts
13C-Labeled ethylene polymerization (pre)catalysts [κ2-(anisyl)2 P,O]Pd(13CH3)(L) (1- 13 CH 3 -L) (L = pyridine, dmso) based on di(2-anisyl)phosphine benzenesulfonate were used to assess the degree of incorporation of 13CH3 groups into the formed polyethylenes. Polymerizations of variable reac...
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| Published in: | Organometallics 2012-12, Vol.31 (23), p.8388-8406 |
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| Main Authors: | , , , , , , , , |
| Format: | Article |
| Language: | English |
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| Online Access: | Get full text |
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| Summary: | 13C-Labeled ethylene polymerization (pre)catalysts [κ2-(anisyl)2 P,O]Pd(13CH3)(L) (1- 13 CH 3 -L) (L = pyridine, dmso) based on di(2-anisyl)phosphine benzenesulfonate were used to assess the degree of incorporation of 13CH3 groups into the formed polyethylenes. Polymerizations of variable reaction time reveal that ca. 60–85% of the 13C-label is found in the polymer after already 1 min polymerization time, which provides evidence that the pre-equilibration between the catalyst precursor 1- 13 CH 3 -L and the active species 1- 13 CH 3 -(ethylene) is fast with respect to chain growth. The fraction of 1- 13 CH 3 -L that initiates chain growth is likely higher than the 60–85% determined from the 13C-labeled polymer chain ends since (a) chain walking results in in-chain incorporation of the 13C-label, (b) irreversible catalyst deactivation by formation of saturated (and partially volatile) alkanes diminishes the amount of 13CH3 groups incorporated into the polymer, and (c) palladium-bound 13CH3 groups, and more general palladium-bound alkyl(polymeryl) chains, partially transfer to phosphorus by reductive elimination. NMR and ESI-MS analyses of thermolysis reactions of 1- 13 CH 3 -L provide evidence that a mixture of phosphonium salts (13CH3) x P+(aryl)4–x (2–7) is formed in the absence of ethylene. In addition, isolation and characterization of the mixed bis(chelate) palladium complex [κ2-(anisyl)2 P,O]Pd[κ2-(anisyl)( 13 CH3)P,O] (11) by NMR and X-ray diffraction analyses from these mixtures indicate that oxidative addition of phosphonium salts to palladium(0) species is also operative. The scrambling of palladium-bound carbyls and phosphorus-bound aryls is also relevant under NMR, as well as preparative reactor polymerization conditions exemplified by the X-ray diffraction analysis of [κ2-(anisyl)2 P,O]Pd[κ2 -(anisyl)(CH2CH3)P,O] (12) and [κ2-(anisyl)2 P,O]Pd[κ2-(anisyl)((CH2)3CH3)P,O] (13) isolated from pressure reactor polymerization experiments. In addition, ESI-MS analyses of reactor polymerization filtrates indicate the presence of (odd- and even-numbered alkyl)(anisyl)phosphine sulfonates (14) and their respective phosphine oxides (15). Furthermore, 2-(vinyl)anisole was detected in NMR tube and reactor polymerizations, which results from ethylene insertion into a palladium–anisyl bond and concomitant β-hydride elimination. In addition to these scrambling reactions, formation of alkanes or fully saturated polymer chains, bis(chelate)pa |
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| ISSN: | 0276-7333 1520-6041 |
| DOI: | 10.1021/om300969d |