NICKEL(0)-INDUCED GEMINAL BOND CLEAVAGES LEADING TO CARBON-CARBON DOUBLE-BONDS - INTERMEDIACY OF NICKEL(0)-CARBENE COMPLEXES AS A UNIFYING HYPOTHESIS

The possibility of effecting geminal bond cleavages of organic monomer s with nickel(0) complexes to achieve olefinic dimers has been investi gated both in stoichiometric reactions between monomers of the type R( 2)CE(2) and R(2)C=E and the complexes (Cod)(2)Ni, (Et(3)P)(4)Ni and (B py)(Cod)Ni and in nickel(0)-catalytic alpha-elimination reactions of a lpha-lithioorganic sulfones, RR'C(Li)(SO(2)R ''). Substrates for the s toichiometric geminal bond cleavages comprised geminal dihalides, amin omethyl sulfides, cyclopropenes, thioketones and ketones, Reductive di merization to the olefin or its hydroxy derivatives was found to occur to a varying degree in most cases, including the catalytic decomposit ion of the alpha-lithioorganic sulfones, Accordingly, this method offe rs 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 cleava ges and reductive coupling processes most likely proceed via nickel(0) -carbene intermediates of the type R(2)C=Ni . L(n).