Peroxo-Zr/Hf-Containing Wells-Dawson Polyoxometalates for H2O2-based Homogeneous, Heterogeneous, and Biphasic Oxidation Catalysis

Abstract

Four peroxo-Zr and Hf containing polyanions, [M2(O2)2(X2W17O61)2]16􀀀 (X=P, M=ZrIV (ZrP), HfIV (HfP); X=As, M=ZrIV (ZrAs), HfIV (HfAs) were synthesized and structurally characterized. The structures consist of two monolacunary Wells-Dawson ions which are connected head-on via two sideon peroxo bridges. The four new polyanions are solution-stable as shown by 31P NMR, Raman and FT-IR spectroscopic studies. Comparative studies on alcohol oxidation with a solvent- and phase-transfer catalyst-free biphasic oxidative system with homogeneous and supported-catalyst were performed and several noteworthy observations in reactivity and selectivity were observed, such as the highly selective ring-opening oxidation of cyclohexanol to adipic acid. Tetra-n-butylammonium salts of ZrP and HfP were also synthesized to study the catalytic activity of the compounds in the homogenous H2O2-based oxidation of olefins, α,β-unsaturated carbonyl compounds,and thioethers in organic solvent.