The strong influence of structures around titanium centers in dimeric mono-, di-, and tri-titanium(IV)-substituted Keggin polyoxotungstates on the catalytic epoxidation of alkenes with H2O2

Dimeric mono-, di-, and tri-titanium(IV)-substituted Keggin polyoxotungstates [(α-PTiW11O39)2O]8− (1), [(α-1,2-PW10Ti2O38)2O2]10− (2), and [(α-1,2,3-PTi3W9O37)2O3]12− (3) catalyzed the epoxidation of cyclooctene, cyclohexene, and 1-octene with aqueous H2O2 at 25 °C in a homogeneous system. Structures around the titanium centers had a strong influence on the catalytic activities. Complex 3, in particular, was the most active because it exhibited the fastest rate of formation of the active hydroperoxotitanium(IV) intermediate. The bond valence sum calculation of the oxygen atoms using the observed bond lengths revealed that protons in the countercations were bound to the surface edge-sharing oxygen atoms of each A-Ti3 site in complex 3, which accelerated the formation of the hydroperoxotitanium(IV) intermediate.