Oxidovanadium(V) Complexes Containing Hydrazone Based O,N,O-Donor Ligands: Synthesis, Structure, Catalytic Properties and Theoretical Calculations

Abstract

Two new mono oxidovanadium(V) complexes, [VOL1(OEt)] (1) and [VOL2(OMe)] (2), of the tridentate Schiff base hydrazone-type O,N,O-donor ligands H<inf>2</inf>L1 and H<inf>2</inf>L2, obtained by monocondensation of 3-hydroxy-2-naphthohydrazide with 5-bromo-2-hydroxybenzaldehyde and benzoylacetone, respectively, have been synthesized starting from VO(acac)<inf>2</inf> [H<inf>2</inf>L1 = (E)-N′-(5-bromo-2-hydroxybenzylidene)-3-hydroxy-2-naphthohydrazide; H <inf>2</inf>L2 = (E)-3-hydroxy-N′-((Z)-4-hydroxy-4-phenylbut-3- en-2-ylidene)-2-naphthohydrazide]. Single-crystal X-ray structure analysis revealed for both complexes a slightly distorted square-based pyramidal NO <inf>4</inf> coordination environment around the metal centre, with the aroylhydrazone Schiff bases acting as O,N,O-tridentate, dinegative ligands. The complexes were also characterized by spectroscopic methods in the solid state (IR) and in solution (UV-Vis, 1H NMR) and by cyclic voltammetric experiments in DMSO, and their properties were interpreted by means of DFT theoretical calculations. The catalytic potential of these complexes has been tested for the oxidation of thioanisol using H<inf>2</inf>O<inf>2</inf> as the terminal oxidant. The effects of various parameters, including the molar ratio of oxidant to substrate, the temperature and the solvent, have been studied. Both complexes showed superabundant catalytic activity in the oxidation of thioanisol at room temperature with excellent conversions. © 2013 Elsevier Ltd.