The First Neutral Dinuclear Vanadium Complex Comprising VO and VO2 Cores: Synthesis, Structure, Electrochemical Properties, and Catalytic Activity

A neutral dinuclear vanadium complex containing both oxido and dioxidovanadium cores with hydrazone based ligand, [VO(OCH3)(CH3OH)(HL)VO2] (1) {H4L = bis[(E)-N-(5-bromo-2-hydroxybenzylidene)]-carbohydrazide}, was synthesized and fully characterized by X-ray crystallography and spectroscopic methods (IR, UV/Vis, NMR). The ligand acts as a trinegative hexadentate N3O3 donor ligand to form a dinuclear complex and during the reaction V4+ is oxidized to V5+. The coordination polyhedra are a VO5N distorted octahedron for the mono-oxidovanadium core and a VO3N2 trigonal bipyramid for the dioxidovanadium core. The results of catalytic reactions indicate that 1 is a highly active catalyst in the clean epoxidation reaction of cis-cyclooctene using aqueous hydrogen peroxide in acetonitrile. Cyclic voltammetric experiments of 1 in DMSO reveal two quasi-reversible peaks due to the VO3+-VO2+ and VO2+-VO2 couples.