Synthesis, crystal structures of oxovanadium(V) complexes with hydrazone ligands and their catalytic performance for the styrene oxidation

Abstract

Four new oxovanadium(V) complexes, [VO(aha)L1] (1), [VO(aha)L2] (2), [VO(aha)L3] (3), and [VO(aha)L4]·EtOH (4) (Haha=acetohydroxamic acid, H2L1=4-nitrophenyl 2-(2-hydroxybenzylidene)hydrazinecarboxylate, H2L2=N′-(2-hydroxylbenzylidene)-4-methoxybenzohydrazide, H2L3=N′-(2-hydroxylbenzylidene)-4-methylbenzohydrazide, HL4=N′-(5-bromo-2-hydroxybenzylidene)-3-methyl benzohydrazide), have been prepared and structurally characterized by physico-chemical methods and X-ray diffraction. The V atoms in the complexes are in octahedral coordination, with the three donor atoms of the hydrazone ligand and the deprotonated hydroxyl O atom of the aha ligand defining the equatorial plane, and with the carbonyl O atom of the aha ligand and one oxo O atom occupying the axial positions. Crystal structures of the complexes are stabilized by hydrogen bonds. In addition, the catalytic performances for the peroxidative oxidation (with hydrogen peroxide) of complexes 1–4 and their starting materials VO(acac)2 were studied by the reaction of styrene (St) to benzaldehyde (BzA) (the maximum total turnover number is 667) under the mild conditions.