Preparation of five-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=NCH2Ph)C6H4}(2,4,6-Me 3C5H2N)]

Article abstract of DOI:10.1021/om00012a022

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=NCH₂Ph)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 C₆Cl₅CH₂NMe₂, in toluene or THF, in the presence of dimethylphenylphosphine, gave the metalated compounds [NiX(C-N)(PMe₂Ph)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)(PMe₂Ph)] 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=NCH₂Ph to [Ni(cod)₂] was also observed under very mild conditions, and compound [NiBr(C₆F₄CH=NCH₂Ph)(PMe₂Ph) ₂] was obtained when the reaction was performed in the presence of LiBr and PMe₂Ph.