Peroxotungstate complexes

In conclusion, this report introduces a truly heterogeneous catalyst based on the in situ generation of active peroxotungstate complexes. By taking profit of the variability of the anion population, a new class of tailor-made catalysts is available. The hydrophobicity of the surface can be tuned, and heteronuclear anion oligomers can be synthesized at the sohd-liquid interphase. 

In another approach, heterogeneous olefin epoxidation catalysts were prepared by electrostatic attachment of binuclear peroxotungstate complexes onto an imidazolium-grafted silica support by ion-exchange [78]. The catalyst was made by initial grafting of the imidazolium-cations onto a pre-dried silica support by treatment with l-octyl-3-(3-triethoxysilypropyl)-imidazolium hexafluorophosphate. 

Over the years it has been shown that complexes prepared from organophosphorous ligands in combination with peroxotungstic acid or its quaternary ammonium salts exhibit efficient catalytic properties. In order to make an efficient recycling of the catalyst possible and get tungsten-free products and effluents, some of these catalysts were immobilized onto polystyrene, poly benzimidazole and polymethacrylate copolymers modified by the introduction of the phosphorous(V)-containing ligands. 

Chromium compounds are covered above. Most tetraperoxomolybdates(2-) and tetra-peroxotungstates(2-) explode when heated or struck [1], An acetate bridged bis-diperoxomolybdate(VI) exploded when heated [3], Organoperoxoniobium compounds occasionally explode on exposure to air [2], A peroxovanadate complex is reported seriously explosive. 

Gelbard has used peroxotungstates supported on polypyridine polymers in the epoxidation of cyclohexene with hydrogen peroxide.66 Polypyridine polymers were also used to support heteropolyperoxometallates for use in the oxidation of alcohols with hydrogen peroxide.67 The tetranuclear complex [cetylpyridinium chloride][P04 WO(02)2 4] supported on polypyridine was found to be an effective catalyst for the oxidation of cyclohexanol to cyclohexanone, also with hydrogen peroxide. 

N. J. Cambell, A. C. Dengel, C. J. Edwards, W. P. Griffith, Studies on transition metal peroxo complexes. Part 8. The nature of peroxomolybdates and peroxotungstates in aqueous solution. J. Chem. Soc., Dalton Trans. 6 (1989) 1203. 

Catalytic oxidations by in situ generated peroxotungsten complexes immobilized on layered double hydroxides (LDH) Relation between catalytic properties and peroxotungstate micro-environment... 

The Venturello-Ishii chemistry is extraordinarily complex. There may be a multitude of weaker epoxidizing agents that are peroxotungstates of higher nuclearity. 

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