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

摘要

Phenyl-bis(imino) pyridine ((I2P)-I-Ph) complexes, ((I2P)-I-Ph) ZnCl2 (1), ((I2P-)-I-Ph) ZnCl (2) and ((I2P-)-I-Ph) 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 (I2P)-I-Ph-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, ((I2P-)-I-Ph) AlCl2 (4), that we prepared for comparison. We were unable to obtain (I2P)-I-Ph Mg complexes, and so the more electron rich methyl-substituted bis(imino) pyridine ligand, (I2P)-I-Me, was investigated. Reaction of two-electron reduced (I2P)-I-Me with MgCl2 and Mg(OTf)(2) did afford the two-electron reduced ligand complexes [((Me)I(2)P2-)Mg(THF)]2(mu-MgCl2) (5) and ((Me)I(2)P2-) Mg(THF) 2 (6), respectively ((I2P)-I-Me = 2,6-bis(1-methylethyl)-N-(2-pyridinylmethylene) phenylamine). Complex 5 crystallizes as a trinuclear Mg complex consisting of two ((I2P2-)-I-Me) Mg moieties bridged by MgCl2 and the ((I2P2-)-I-Me) ligand is symmetric across the pyridine ring, but is not planar. In contrast, the ((I2P2-)-I-Me) 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.