Polyoxometalates hydrogen peroxide, activation

The synthetic utility of the [WZnMn"2(H20)2][(ZnW9034)2] polyoxometalate as catalyst for hydrogen peroxide activation, was then extended to additional substrate classes having various functional units [57]. Thus, allylic primary alcohols were oxidized selectively to the corresponding epoxides in high yields and >90% selectivity. Allylic secondary alcohols were oxidized to a mixture of aP-unsaturated ketones (the major product) and epoxides (the minor product). Secondary alcohols were oxidized... 

We report here three studies that address three separate but significant issues in the emerging area of selective catalytic oxidation by TMSP-type complexes. The first study establishes for the first time that some TMSP complexes are compatible with basic oxidants and basic conditions. The second study reports the first oxidation, in this case selective alkene epoxidation, by the economically and environmentally desirable oxidant, aqueous hydrogen peroxide, catalyzed by TMSP complexes. The third study demonstrates that redox active polyoxometalates can be derivatized with alcohols in a manner that should prove useful for fabricating future generations of more sophisticated and selective TMSP catalysts. 

Hydrogen peroxide is an inexpensive oxidant, but it requires a catalyst to effect oxidation of an alcohol to the ketone. Removal of the catalyst then becomes an issue. Ronny Neumann of the Weizmann Institute of Science reports (J. Am. Chem. Soc. 2004,126, 884) the development of a hybrid organic-tungsten polyoxometalate complex that is not soluble in organic solvents, but that nonetheless catalyzes the hydrogen peroxide oxidation of alcohols to ketones. The solid catalyst is removed by filtration after the completion of the reaction. The catalyst retained its activity after five recyles. 

Neumann, R. Mixed Addenda Phosphomolybdovanadates as Catalysts for Oxidations with Dioxygen and Hydrogen Peroxide. In Polyoxometalates from Platonic Solids to Anti-retroviral Activity Pope, M. T., Muller, A., Eds. Kluwer Academic Publishers Dordrecht, 1994 pp 307-313. 

NomiyaK, Nemoto Y, HasegawaT, Matsuoka S (2000) Multicenter active sites of vanadium-substituted polyoxometalate catalysts on benzene hydroxylation with hydrogen peroxide and two reaction types with and without an induction period. J Mol Catal A Chem 152 55-68 Ono Y (1992) Perspectives in catalysis. In Thomas JM, Zamaraev KI (eds). Blackwell scientific publications, Oxford... 

Jahier, C., Coustou, M., Cantuel, M., et al. (2011). Optically Active Tripodal Dendritic Polyoxometalates Synthesis, Characterization and their Use in Asymmetric Sulfide Oxidation with Hydrogen Peroxide, Eur. J. Inorg. Chem., pp. 727-738. 

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