Cyclooctene Epoxidation by Hydrogen Peroxide in the Presence of Vanadium‐Substituted Lindqvist‐Type Polyoxotungstate [VW5O19]3–

Abstract

The vanadium‐substituted, Lindqvist‐type polyoxotungstate [VW5O19]3– significantly promotes cyclooctene epoxidation using H2O2 in CH3CN at 30 °C. The catalytic processes discussed are based on the results of the UV/Vis, ESI–MS, 51V NMR, and 183W NMR spectra of [VW5O19]3– in a H2O2/cyclooctene/CH3CN system. ESI–MS spectral analysis revealed that the [VW5O19]3– anion retained a Lindqvist‐type structure and that multiple peroxidation occurred at both the V and W sites during epoxidation. Together with the synergistic effects provided by the W(peroxo) sites, the V(peroxo) site plays a catalytically active role in both epoxidation and H2O2 decomposition. Enhancement between each metal's sites in Lindqvist‐type polyoxometalates is strong, as all metal atoms are directly linked to each other via the central oxygen atom. The small negative H2O2 dependence (–0.63) indicates that a catalytically active species is immediately formed with H2O2 and that the transfer of the O atom from the peroxo ligand to cyclooctene proceeds rapidly, which was supported by the phenomenon wherein ESI–MS and 51V NMR measurements for a sample solution become increasingly difficult to obtain when the epoxidation reaction proceeds favorably. This is because structural changes around the V site are frequentative. This small negative H2O2 dependence value also shows that [VW5O19]3– catalyzes H2O2 decomposition considerably, not only epoxidation. The generation of a significant amount of O2 was observed.