Novel oxovanadium(iv) complexes with 4-acyl pyrazolone ligands: synthesis, crystal structure and catalytic activity towards the oxidation of benzylic alcohols

Abstract

A series of oxovanadium(IV) complexes of 4-acylpyrazolone ligands were synthesized and characterized by elemental analyses, FT-IR, UV-Vis, EPR spectroscopy and single crystal XRD. The single-crystal X-ray analysis of the complex VO(L¹)₂ shows that the ligands were coordinated with the vanadium atom in a twisted form to create a distorted octahedral geometry and two O,O-chelating acylpyrazolonate ligands constitute two six-membered rings with the vanadium atom. The catalytic activity of all the complexes was evaluated for the oxidation of benzylic alcohols with H₂O₂ as an oxidant. The conditions for maximum conversion as well as selectivity for the desired product were optimized by varying different parameters such as the molar ratio of substrate to H₂O₂, the amount of the catalyst, reaction time and solvent. A possible pathway for the oxidation of benzylic alcohols was also proposed on the basis of the spectral evidence.