Suppression of 尾-Hydride Chain Transfer in Nickel(II)-Catalyzed Ethylene Polymerization via Weak Fluorocarbon Ligand鈥揚roduct Interactions

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• 作者：Michael P. Weberski ; Jr. ; Changle Chen ; Massimiliano Delferro ; Cristiano Zuccaccia ; Alceo Macchioni ; Tobin J. Marks
• 刊名：Organometallics
• 出版年：2012
• 出版时间：May 14, 2012
• 年：2012
• 卷：31
• 期：9
• 页码：3773-3789
• 全文大小：1004K
• 年卷期：v.31,no.9(May 14, 2012)
• ISSN：1520-6041

文摘

The synthesis and characterization of two neutrally charged Ni(II) ethylene polymerization catalysts, [2-tert-butyl-6-((2,6-(3,5-dimethylphenyl)phenylimino)methyl)phenolato]nickel(II) methyl trimethylphosphine ((CH₃)FI-Ni) and [2-tert-butyl-6-((2,6-(3,5-bis(trifluoromethyl)phenyl)phenylimino)methyl)phenolato]nickel(II) methyl trimethylphosphine ((CF₃)FI-Ni) are reported. In the presence of a Ni(COD)₂ cocatalyst, these catalysts produce markedly different polyethylenes: densely branched oligomers with M_w = 1.4 脳 10³ g mol^鈥? for (CH₃)FI-Ni vs lightly branched polyethylenes with M_w = 92 脳 10³ g mol^鈥? for (CF₃)FI-Ni and with 6.5脳 the polymerization activity and with much greater performance thermal stability. HOESY 2D ¹⁹F,¹H NMR spectra of a model Ni-ethyl compound, [2-tert-butyl-6-((2,6-(3,5-bis(trifluoromethyl)phenyl)phenylimino)methyl)phenolato]nickel(II) ethyl 2,4-lutidine ((CF₃)FI-Ni-Et), indicate non-negligible C_尾鈥揌_尾路路路F₃C through-space dipolar interactions, and molecular modeling reveals that C_尾鈥揌_尾路路路F(C) distances can be as small as 2.61 脜 during the polymerization process. Furthermore, there is no structural or spectroscopic evidence for fluorocarbon inductive effects on the structure, bonding, and reactivity of these complexes, and a catalyst with CF₃ introduced 尾 to the imino N produces only low-M_w oligomers with low activity. These results argue that weak (ligand)C鈥揊路路路H鈥揅(polymer) interactions can significantly influence the chain transfer characteristics of these catalysts.