摘要:
The preparation of a series of nickel dichloride complexes with bulky diphosphinomethane chelate ligands R2PCH2PR'(2) is reported. Reaction with the appropriate Grignard reagent leads to the corresponding dimethyl and dibenzyl complexes. Cationic monomethyl and mono-eta(3)-benzyl complexes are generated from these dialkyl complexes by protonation with [H(OEt2)(2)](+)[B(3,5-(CF3)(2)C6H3)(4)](-), while the complex [(dtbpm-K2P)Ni(eta(3)-CH(CH2Ph)Ph](+)[B(3,5-(CF3)(2)C6H3)(4)](-) is obtained from protonation of the Ni(0) olefin complex (dtbpm-kappa P-2)Ni(eta(2)-trans-stilbene). Crystal structures of examples of dichlorides, dimethyl, dibenzyl, cationic methyl, and cationic eta(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 eta(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' on the phosphine ligand has been examined, and a dear 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 eta(3) to eta(3) haptotropic shift processes of the [(R2PCH2PR'(2))Ni] fragment and the eta(3)-eta(1) change of the coordination mode of the benzyl group required for polymerization in those cations.