Polyoxometalate oxidation with

Oxidations with the phosphorus-containing polyoxometalate [Ru(HjO) PWjj(0)3, r are considered above (1.9.1). 

Goals and five limitations in conjunction with the development of selective catalytic homogeneous oxidation systems are evaluated. Systems are presented that address several of the problems or goals. One involves oxidation of alkenes by hypochlorite catalyzed by oxidatively resistant d-electron-transition-metal-substituted (TMSP) complexes. A second involves oxidation of alkenes by H2O2 catalyzed by specific TMSP complexes, and a third addresses functionalization of redox active polyoxometalate complexes with organic groups. 

Liquid-Phase Oxidations with Hydrogen Peroxide and Molecular Oxygen Catalyzed by Polyoxometalate-Based Compounds... 

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. 

Other Bleaching Agents Oxidation with Polyoxometalate (POM)... 

Additional features of polyoxometalates impact some of the six limitations. First, polyoxometalates are oxidatively resistant as a great majority of them are composed of d° transition metal ions (most commonly W(VI), Mo(V), and/or V(V)) and oxide ions. Second, the unusually high stability of polyoxometalates coupled with the tunability of their catalytically relevant properties defines a considerable ability to avoid problems associated with intermediate oxidation states, p-oxo dimers, and product inhibition. Illustrations of two representative polyoxometalates, Wio0324 , an isopolyoxometalate (or isopolyanion) and (TM)XWii039 , a transition metal (TM) substituted heteropolyoxometalate (or heteropolyanion) in polyhedral notation are given in Figure 1. 

Shown in Fig. 3 is one of several preliminary results obtained recently in our laboratory addressing the general mechanistic features of reduced polyoxometalate reoxidations. Here, two distinct species of the two electron reduced decatungstate [HxWio032] ", where x = 0 or 2, were oxidized with... 

The use of MIL-lOl-encapsulated polyoxometallate (POM) has also been reported for the a-oxidation of cyclohexene and a-pinene [113]. Both Ti- and Co-POM/MIL-101 catalysts showed fairly good activity and selectivity toward a-pinene oxidation with 40% and 45% conversion, respectively, and an average selectivity of 30% for both verbenol and verbenone compared with unmodified MIL-101 (14-18% conversion). 

An example of a system for photocatalytic water oxidation with a molecular catalyst based on abundant metals is shown in Fig. Id. The Cobalt polyoxometalate catalyst is oxidized with Ru —trisbipyridine that is generated by quenching of the photo-excited Ru —trisbipyridine sensitizer with peroxodisulfate as sacrificial electron acceptor. The system operates at pH 8 and exhibits a high (30 %) photon-to-02 yield while the stability of the catalyst allowed for turnover numbers >220 that were limited by depletion of electron acceptor only [7]. This performance of the abundant-metal-based catalyst is superior to that of an analogue ruthenium polyoxometalate water oxidation catalyst. 

In the present section we have highlighted research that has been carried out using polyoxometalates as catalysts for oxidation with peroxygen compounds. Not all of the synthetic applications have been noted, but those missing have been previously reviewed [2]. It is important to stress that from a synthetic point of view various substrates with varying functional groups can be effectively transformed to desired products. In addition, interesting reaction selectivity can be obtained in certain cases. 

Scheme 9.9 Redox-type mechanism for oxidation with polyoxometalates.

Kuznetsov AE, Geletii YV, fEU CL, Morokuma J, Musaev DG. Dioxygen and water activation processes on mrJti-Ru-subsrituted polyoxometalates comparison with the blue-dimer water oxidation catalyst. J Am Chem Soc. 2009 131 6844-6854. 

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. 

Neumann R (2004) Polyoxometalates as catalysts for oxidation with hydrogen peroxide and molecular oxygen. In Beller M, Bolm C (eds) Transition metals for organic synthesis, 2nd edn., vol 2, WUey, Weinheim, p 415... 

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