Nickel(0)-induced geminal bond cleavages leading to carbon-carbon double bonds: Intermediacy of nickel(0)-carbene complexes as a unifying hypothesis

Article abstract of DOI:10.1016/0022-328X(95)05948-O

The possibility of effecting geminal bond cleavages of organic monomers with nickel(0) complexes to achieve olefinic dimers has been investigated both in stoichiometric reactions between monomers of the type R₂CE₂ and R₂C=E and the complexes (Cod)₂Ni, (Et₃P)₄Ni and (Bpy)(Cod)Ni and in nickel(0)-catalytic α-elimination reactions of α-lithioorganic sulfones, RR′C(Li)(SO₂R″). Substrates for the stoichiometric geminal bond cleavages comprised geminal dihalides, aminomethyl sulfides, cyclopropenes, thioketones and ketones. Reductive dimerization to the olefin or its hydroxy derivatives was found to occur to a varying degree in most cases, including the catalytic decomposition of the α-lithioorganic sulfones. Accordingly, this method offers considerable promise in organic synthesis. A gamut of known nickel(0) chemistry, results of chemical-trapping and spectroscopic evidence are marshaled in support of the proposal that such geminal bond cleavages and reductive coupling processes most likely proceed via nickel(0)-carbene intermediates of the type R₂C=Ni · L_n.