Crowded Diphosphinomethane Ligands in Catalysis: [(R2PCH2PR鈥?sub>2-魏2P)NiR鈥砞+ Cations for Ethylene Polymerization without Activators

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• 作者：Madeleine Schultz ; Frank Eisentr盲ger ; Christian Regius ; Frank Rominger ; Patrick Hanno-Igels ; Paul Jakob ; Irene Gruber ; Peter Hofmann
• 刊名：Organometallics
• 出版年：2012
• 出版时间：January 9, 2012
• 年：2012
• 卷：31
• 期：1
• 页码：207-224
• 全文大小：625K
• 年卷期：v.31,no.1(January 9, 2012)
• ISSN：1520-6041

文摘

The preparation of a series of nickel dichloride complexes with bulky diphosphinomethane chelate ligands R₂PCH₂PR鈥?sub>2 is reported. Reaction with the appropriate Grignardreagent leads to the corresponding dimethyl and dibenzyl complexes. Cationic monomethyl and mono-畏³-benzyl complexes are generated from these dialkyl complexes by protonation with [H(OEt₂)₂]⁺[B(3,5-(CF₃)₂C₆H₃)₄]^{鈭?/sup>, while the complex [(dtbpm-魏2P)Ni(畏3-CH(CH₂Ph)Ph]+[B(3,5-(CF₃)₂C₆H₃)₄]鈭?/sup> is obtained from protonation of the Ni(0) olefin complex (dtbpm-魏2P)Ni(畏2-trans-stilbene). Crystal structures of examples of dichlorides, dimethyl, dibenzyl, cationic methyl, and cationic 畏3-benzyl complexes are reported. Solutions of the cations polymerize ethylene under mild conditions and without the necessity of an activating agent, to form polyethylene having high molecular weights and low degrees of chain branching. In comparison to the Ni methyl cations, the 畏3-benzyl cation complexes are more stable and somewhat less active but still very efficient in C₂H₄ polymerization. The effect on the resulting polyethylene of varying the substituents R, R鈥?on the phosphine ligand has been examined, and a clear trend for longer chain PE with less branching in the presence of more bulky substituents on the diphosphine has been found. Density functional calculations have been used to examine the rapid suprafacial 畏3 to 畏3 haptotropic shift processes of the [(R₂PCH₂PR鈥?sub>2)Ni] fragment and the 畏3鈥撐?sup>1 change of the coordination mode of the benzyl group required for polymerization in those cations.}