ETA-2-(C,O) KETENE COORDINATION AT NICKEL(0) - SYNTHESIS, BONDING, AND MOLECULAR-STRUCTURE OF (DTBPM)NI[ETA-2-(C,O)-PH2C2O]

Qualitative electronic structure considerations and MO model calculations are presented, which predict eta(2)-(C,O) coordination to be preferred over eta(2)-(C,C) coordination for ketene complexes of P2Ni0 and P2Pt0 (d10) bis(phosphane) metal fragments. The relative energetic preference for an eta(2)-(C,O)-bonding mode of ketenes is shown to increase with a decreasing P-M-P angle. Bis(di-tert-butylphosphino)methane ((t)Bu2PCH2P(t)Bu2, dtbpm) is a tailor-made chelating bis(phosphane) ligand, which allows one to realize P-Ni-P angles below 80-degrees within four-membered NiPCP chelate rings. Starting from the stilbene complex (dtbpm)Ni(eta(2)-trans-PhCH = CHPh) (25), the 14-electron intermediate [(dtbpm)Ni0] could be generated and trapped by diphenylketene to yield the eta(2)-(C,O)-coordinated diphenylketene complex (dtbpm)Ni-[eta(2)-(C,O)-Ph2C2O] (30), which has been characterized spectroscopically and by X-ray diffraction. Crystals of compound 30.C6D6 (C31H48OP2Ni.C6D6) are monoclinic, space group P2(1)/n, with a = 11.957 (2) angstrom, b = 14.911 (2) angstrom, c = 20.111 (2) angstrom, beta = 99.73 (1)-degrees, V = 3534.0 angstrom-3, and Z = 4. The molecular structure of 30 provides the first example of a nickel triad ketene complex, for which ketene to metal bonding has been established unequivocally. Its eta(2)-(C,O) geometry is in accord with EH model calculations for Ni and Pt, but it contrasts ab initio results for analogous platinum systems reported in the literature and may have interesting consequences for understanding reactivity patterns of d10-ML2 ketene complexes (M = Ni(0), Pd(0), Pt(0)).