Nickel organometallic compounds containing optically active Schiff bases. A chiral carbon atom as a sensor of structural features†

Abstract

The reaction of [Ni(cod)₂] with optically active ortho-halogeno-substituted imines, (R)-C₆H_nR_5 – nCHNCH(Me)Ph (C–N), in the presence of an aromatic amine (L = 2,4,6-trimethylpyridine or 2,4-dimethylpyridine or dimethylphenylphosphine as stabilizing ligand, gave either five-membered metallacycles [Ni(C–N)XL] or the metallated compounds [NiX(C–N)(PMe₂Ph)₂] through oxidative addition of one of the ortho C–X bonds (X = Br or Cl) of the imine. When the reaction was performed with the imines (R)-2,3,6-Cl₃C₆H₂CHNCH(Me)Ph and 2,3,6-Cl₃C₆H₂CHNCH₂Ph, in the presence of dimethylphenylphosphine, a mixture of compounds coming from nucleophilic attack at C–Cl in 2 or 6 position was obtained, but when the stabilizing ligand was an aromatic amine only attack at C–Cl in position 2 occurred. The oxidative addition of one of the ortho C–F bonds of the imine (R)-C₆F₅CHNCH(Me)Ph to [Ni(cod)₂] was also observed under mild conditions and compounds (R)-[NiBr{C₆F₄CHNCH(Me)Ph}{2,4,6-Me₃(C₅H₂N)}] and (R)-[NiBr{C₆F₄CH NCH(Me)Ph}(PMe₂Ph)₂] were obtained when the reaction was performed in the presence of LiBr and 2,4,6-trimethylpyridine or PMe₂Ph respectively. The presence of a chiral carbon atom provides information about the structural features of the compounds here described.