Structure and properties of tungsten peroxopolyoxo complexes - Promising catalysts for organics oxidation. I. Structure of peroxocomplexes studied during the stepwise synthesis of tetra(diperoxotungsten)phosphate-tetra-n-butyl ammonium

Article abstract of DOI:10.1016/j.molcata.2010.09.007

Catalysis via metal complexes has been studied using EXAFS and Raman spectroscopy. Main polyoxo- and peroxopolyoxocomplexes of tungsten, resulting from the interaction of phosphorus tungsten heteropolyacid with hydrogen peroxide in water solutions, were investigated with regard to their form and structure. Interaction was shown to reduce the nuclearity of forming complexes with respect to their precursor - H₃PW₁₂O₄₀. The symmetry of oxygen environment of tungsten was found to change, distances W-W remaining the same. After complex [Buⁿ₄N] ₃{PO₄[WO(O₂)₂]₄} is isolated, binuclear anion [W₂O₃(O₂) ₄(H₂O)₂]^2- stays in the solution. Raman scattering, EXAFS and IR spectroscopy show that isolated peroxocomplex in its crystal state has four nuclei, and most probably retains this structure being dissolved in acetonitrile. Synthesized catalytic complex [Bu ⁿ₄N]₃{PO₄[WO(O₂) ₂]₄} was tested in oxidation of cyclic alkenes and alcohols with hydrogen peroxide. Complex [Buⁿ₄N] ₃{PO₄[WO(O₂)₂]₄} was proved to provide higher yields of mono- and dicarbonic acids in comparison to in situ synthesized catalyst.