Synthesis, spectral characterization, and theoretical studies of oxo-peroxo tungsten (VI) Schiff base complex with an isonicotinohydrazone ligand and its application in the selective oxidation of benzylic alcohols

A tungsten (VI) complex, [WO(O2)L(CH3OH)], L = (E)-N'-(2-hydroxy-3-methoxybenzylidene)isonicotinohydrazide has been synthesized by the action of WO3 with a ONO donor tridentate Schiff base using H2O2. The tungsten(VI) complex has been characterized by CHN, FT-IR, multinuclear (1H & 13C) NMR, and UV-Vis. spectroscopic methods. Theoretical calculations, using DFT at the B3LYP level of theory at the Def2-TZVP basis set, for the estimation of geometrical parameters like natural bond orbital (NBO), molecular electrostatic potential (MEP), and frontier molecular orbitals (FMOs) analysis of the synthesised compounds showed that the numerical results correspond to the actual findings. The catalytic activity of WO(O2)L(CH3OH) for the selective oxidation of benzylic alcohols to the corresponding aryl aldehydes was studied utilizing various factors, like the nature of the oxidant, the effect of solvent, and the amount of catalyst. The best results were obtained by using 2 mmol of urea hydrogen peroxide (UHP) as an oxidant in the presence of 1 mol% of the catalyst in CH3CN under reflux conditions.