A novel enantiopure proline-based organickel(III) halide monocation with a pentadentate C, N2, O2-bonded bis(ortho-chelating) aryldiamine ligand

Abstract

An attempt was made to use the enantiopure arylnickel(II) complex [Ni(L*-N, C, N)Br], 1, (L* is the monoanionic ligand, 2, 6-bis[(2-(S)-2-isopropoxycarbonyl-1-pyrrolidinyl)methyl]phenyl) as a catalyst for the Kharasch addition reaction of CCl4 to alkenes which led instead to a new ionic arylnickel(III) complex [Ni(L*Cl]2[NiCl4] (= [2-Cl]2[NiCl4]. An X-ray diffraction study of this complex revealed the presence of two identical monocations [2-Cl]+ that have octahedrally coordinated Ni(III) centres and a single dianionic NiCl2-4 unit. The octahedral ligand sphere of cation [2-Cl]+ is best described as tetragonally compressed, with the meridional coordination comprising N2, O2 donative bonding from the two N atoms of the pyrollidine groups and two carbonyl O atoms of the ester groups of L*, the mutually trans apical sites are occupied by a Cl atom and the C atom of the Ni-Caryl bond; i.e. the monoanionic organic ligand L* binds as a monoanionic C, N2, O2 pentadentate system. Spectroscopic data for [2-Cl]+ are presented and compared with those for the square-planar arylnickel(II) complex 1, in which the oxygen donor atoms of the ester groups of L* are not coordinated and the ligand thus acts as a C, N2 terdentate system.