Aerobic Oxidation of Vicinal Diols Catalyzed by an Anderson-Type Polyoxometalate, [IMo₆O₂₄]^5-

An Anderson-type polyoxometalate, [I^VIIMo₆O₂₄]^5-, has been used as a catalyst for the aerobic oxidation at 80°C of vicinal diols (glycols). This is the first report on the use of such a polyoxometalate as an oxidation catalyst. Reactivity and selectivity were dependent on the substrate. Thus, aryl-substituted diols yielded mostly the carbon-carbon bond cleavage products, while 1,2-cyclohexanediol yielded cyclohexanone-2-ol and 1,2-cyclohexanedione. Aliphatic diols were less reactive but yielded carbon-carbon bond cleavage products in the presence of additional acid. An abbreviated mechanistic study was carried out indicating that the polyoxometalate oxidizes the diol to the various products even under anaerobic conditions. The reduced polyoxometalates (heteropoly blues and heteropoly browns) formed in the oxidation of the diols are re-oxidized by the molecular oxygen.