Synthesis, crystal structures and catalytic oxidation of aromatic hydrocarbons by oxovanadium(V) complexes of aminebis(phenolate) ligands

Abstract

The coordination chemistry of two aminebis(phenolate) ligands (H 2L 1 and H 2L 2) around vanadium(V) is described. Vanadium(V) oxo complexes ( 1, 2 and 3) of all the ligands were obtained readily by the reaction between the ligand precursors and [VO(acac) 2]. Single crystal X-ray structure analysis showed that all of the complexes are penta-coordinated with trigonal bipyramidal geometry in NO 4 coordination environment. The tripodal nitrogen atom of the respective ligands and monodentate alkoxo group occupy apical positions. These complexes structurally resemble very closely to the active sites of vanadium haloperoxidases (VHPO) and were found to catalyze the oxidation of toluene to benzoic acid and isomers of xylene to the corresponding hydroxy acids with turn over numbers ranging between 134 and 188. Based on mass spectra the mechanism of the catalytic process was proposed to proceed through the formation of hydroxo–hydroperoxo intermediate, which is different from halo peroxidase reactions.