PREPARATION OF 5-MEMBERED NICKELACYCLES OF N-DONOR LIGANDS BY ACTIVATION OF C-X BONDS (X=F,CL,OR BR) - X-RAY CRYSTAL-STRUCTURE OF [NIBR(2-(CH=NCH(2)PH)C6H4)(2,4,6-ME(3)C(5)H(2)N)]

The five-membered metallacycles [Ni(C-N)XL] (L = 2-picoline, 2,4-lutidine, or 2,4,6-collidine, X = Cl or Br) have been prepared by reaction of [Ni(cod)(2)] with ortho halo-substituted imines or N,N-dimethylbenzylamines in toluene or tetrahydrofuran, in the presence of an aromatic amine as stabilizing ligand. The molecular structure of [NiBr{2(CH=NCH(2)Ph)C6H4}{2,4,6-Me(3)(C5H2N)}] has been determined by a single-crystal X-ray crystallographic study. The reaction of [Ni(cod)(2)] with ortho halo-substituted imines or with C(6)Cl(5)CH(2)NMe(2), in toluene or THF, in the presence of dimethylphenylphosphine, gave the metalated compounds [NiX(C-N)(PMe(2)Ph)(2)], 8 or 9, through oxidative addition of one of the ortho C-X bonds (X = Br or Cl) of the N-donor ligand. All the spectroscopic evidence indicates a square-planar geometry for these compounds, with the phosphine molecules in a trans arrangement and the iminic nitrogen atom in an axial position around the metal, giving a pseudopentacoordinated compound. Surprisingly, when the oxidative addition reaction was performed in a 1/1 molar ratio of nickel/phosphine, the formation of the metallacycles [NiX(C-N)(PMe(2)Ph)] was not observed, but 8 or 9, containing two phosphine molecules by the metal atom, were formed. The oxidative addition of one of the ortho C-F bonds of the imine C6F5CH=NCH(2)Ph to [Ni(cod)(2)] was also observed under very mild conditions, and compound [NiBr(C6F4CH=NCH(2)Ph)(PMe(2)Ph)(2)] was obtained when the reaction was performed in the presence of LiBr and PMe(2)Ph.