Synthesis and Structures of the μ-Vinylidene Binuclear Nickel Complexes [Ni2(μ-CCH2)(dmpm)2Cl2] and [Ni2(μ-CCH2)(dppm)2Br2]: Comparison of the Electronic Structures of Nickel A-Frames

Abstract

The reaction of bis(cyclooctadiene)nickel(0) with bis(dimethylphosphino)methane (dmpm) and 1,1-dichlorovinylidene in THF yields the vinylidene-bridged binuclear nickel A-frame complex [Ni2(μ-CCH2)(dmpm)2Cl2] (1a). The structure of 1a was determined by X-ray crystallography. The Ni−Ni separation is 2.898(2) A, and the vinylidene carbon−carbon bond distance is 1.35(2) A. The structure of the bis(diphenylphosphino)methane (dppm) bridged μ-vinylidene complex [Ni2(μ-CCH2)(dppm)2Br2] (2b) was also determined by X-ray crystallography. The Ni−Ni separation of 2.874(2) A for 2b is comparable to that of 1a. The series of μ-vinylidene nickel A-frames with substituted terminal ligands [Ni2(μ-CCH2)(PR2CH2PR2)2X2] (X = Cl, Br, I, R = Me; X = Cl, Br, I, NCS, OCN; R = Ph) were prepared and characterized. The nickel A-frames with different bridging ligands [Ni2(μ-CE)(dppm)2Cl2] (E = O, NPh) were also examined. Extended Huckel molecular orbital (EHMO) calculations indicate that the HOMO in these nickel A-frame complexes is...