Oxidative Addition of Allylammonium BPh4- to Nickel(0): Synthesis, Crystal Structure, Fluxional Behavior, and Catalytic Activity of Chiral [(η3-allyl)(NH3)(PCy3)Ni]BPh4

Abstract

The synthesis, crystal structure, fluxional behavior, and reactivity of [(η3-C3H5)Ni(PCy3)(NH3)]BPh4 (1) are described. Complex 1 was obtained by oxidative addition of allylammonium tetraphenylborate, (CH2CHCH2NH3)BPh4, to Ni(0) [(Cy3P)2Ni(η2-CO2) or (Cy3P)2NiNNNi(PCy3)2], under mild conditions, through selective activation of the N−C-allyl bond. Complex 1 is a unique example of an allyl−Ni cationic complex with three different ligands and donor atoms. It has been fully characterized both in the solid state and in solution. The X-ray study shows that the cation [(η3-C3H5)Ni(PCy3)(NH3)]+ (1+) is chiral as a result of the two possible orientations of the allyl group and the different ancillary ligands bound to the (η3-C3H5)Ni+ moiety. In the solid state, cation 1+ exists as a racemic mixture of the two enantiomers 1a+ and 1b+. In solution, complex 1+ is involved in a slow fluxional process that causes the left-to-right exchange of syn and anti protons of the allyl group and leads to the interconversion of t...