A dimeric molecular precursor [( tBuO) 2Ti{μ-O 2Si[OSi(O tBu) 3] 2}] 2 to Ti(IV)/SiO 2 catalysts for selective cyclohexene epoxidation

Abstract

The new dimeric complex [( t BuO) 2Ti{μ-O 2Si[OSi(O t Bu) 3] 2}] 2 ( 1), prepared via silanolysis of Ti(O t Bu) 4 with (HO) 2Si[OSi(O t Bu) 3] 2, is a structural and spectroscopic (NMR, FT-IR, UV–vis, XPS) model for Ti(IV)/SiO 2. The molecular complex was used to prepare titanium-containing silica materials through both the thermolytic molecular precursor method (yielding TiO 2·3SiO 2) or by grafting 1 onto mesoporous SBA-15 silica. Grafting 1 onto SBA-15 yields mostly isolated Ti(IV) sites, as evidenced by DRUV–vis and photoluminescence spectroscopies. The resulting materials were found to be active and highly selective in the epoxidation of cyclohexene, yielding up to 71% of cyclohexene oxide based on oxidant (cumene hydroperoxide) after 2 h at 65 °C in toluene.