Cyclooctene Epoxidation by Hydrogen Peroxide in the Presence of Vanadium‐Substituted Lindqvist‐Type Polyoxotungstate [VW 5 O 19 ] 3 –

The vanadium‐substituted, Lindqvist‐type polyoxotungstate [VW 5 O 19 ] 3– significantly promotes cyclooctene epoxidation using H 2 O 2 in CH 3 CN at 30 °C. The catalytic processes discussed are based on the results of the UV/Vis, ESI–MS, 51 V NMR, and 183 W NMR spectra of [VW 5 O 19 ] 3– in a H 2 O 2 /cyclooctene/CH 3 CN system. ESI–MS spectral analysis revealed that the [VW 5 O 19 ] 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 H 2 O 2 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 H 2 O 2 dependence (–0.63) indicates that a catalytically active species is immediately formed with H 2 O 2 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 51 V 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 H 2 O 2 dependence value also shows that [VW 5 O 19 ] 3– catalyzes H 2 O 2 decomposition considerably, not only epoxidation. The generation of a significant amount of O 2 was observed.