Synthesis and characterization of bis(imino)pyridine complexes of divalent Mg and Zn

Abstract

Phenyl-bis(imino)pyridine (^PhI₂P) complexes, (^PhI₂P)ZnCl₂ (1), (^PhI₂P⁻)ZnCl (2) and (^PhI₂P⁻)Zn(py)Cl (3) were obtained with the I₂P ligand in both the neutral and the one-electron reduced state. In all examples, the metal ion is Zn(II). Metrical parameters obtained from solid state structures of 2 and 3 indicate that the ^PhI₂P⁻ ligand exists as a radical which is supported at the carbon atom of the imino donor, and this electronic state is also apparent in the analogous one-electron reduced ligand Al(III) complex, (^PhI₂P⁻)AlCl₂ (4), that we prepared for comparison. We were unable to obtain ^PhI₂P Mg complexes, and so the more electron rich methyl-substituted bis(imino)pyridine ligand, ^MeI₂P, was investigated. Reaction of two-electron reduced ^MeI₂P with MgCl₂ and Mg(OTf)₂ did afford the two-electron reduced ligand complexes [(^MeI₂P²⁻)Mg(THF)]₂(μ-MgCl₂) (5) and (^MeI₂P²⁻)Mg(THF)₂ (6), respectively (^MeI₂P = 2,6-bis(1-methylethyl)-N-(2-pyridinylmethylene)phenylamine). Complex 5 crystallizes as a trinuclear Mg complex consisting of two (^MeI₂P²⁻)Mg moieties bridged by MgCl₂ and the (^MeI₂P²⁻) ligand is symmetric across the pyridine ring, but is not planar. In contrast, the (^MeI₂P²⁻) ligand in 6 is asymmetric across the pyridine ring and all atoms in the ligand are coplanar. Cyclic voltammetry measurements reveal that in complexes, 1, 4, 5, 6, the I₂P⁰, I₂P⁻, and I₂P²⁻ ligand charge states are accessible electrochemically.