Effect of ligand exchange on the one-electron oxidation process of alkoxo or phenoxo bridged binuclear copper(II) complexes

Abstract

In the present paper, we report on the influence of methanol/methoxide on the structure and the mono-electronic oxidation process of two different dicopper(II,II) complexes: a binuclear µ-alkoxo µ-acetato dicopper(II,II) complex obtained with a tetraamide-containing ligand (1) or a new unsymmetric µ-phenoxo, µ-hydroxo dicopper(II,II) complex based on a ligand bearing one bis(2-pyridylmethyl)aminomethyl arm (BPA) and one thiosemicarbazone (2). Structural data obtained from X-ray diffraction analysis showed that, in the case of complex 2, bridging hydroxide was replaced by a methoxide bound in a bridging mode (2-OMe). Concerning complex 1, redox properties were investigated by electrochemistry and rationalized using theoretical calculations. Our studies indicate that (i) the acetate bridge of 1 is decoordinated from the copper ions after mono-oxidation (ii) in presence of methoxide, acetate is released and a complex with two pendant exogen ligands (one methoxide and one solvent, 1-OMe-DMF) is a plausible structure although bridging methoxide cannot be excluded. In the case of 2 the anodic potentials are not influenced by the nature of the bridge (hydroxo in 2 or methoxo in 2-OMe). Finally, the computed redox potentials using DFT calculations are in good agreement with the experimental ones and indicates that in the case of the complexes derived from 1, oxidation is copper-centered therefore leading to Cu(II)Cu(III) species although oxidation is ligand-centered in the case of 2 and 2-OMe.