A dimeric molecular precursor [(tBUO)2Ti{μ-O2Si[OSi(OtBu)3]2}]2 to Ti(IV)/SiO2 catalysts for selective cyclohexene epoxidation

The new dimeric complex [((BUO)-B-t)(2)Ti{mu-O2Si[OSi((OBu)-Bu-t)(3)](2)}]2 (1), prepared via silanolysis of Ti((OBu)-Bu-t)(4) with (HO)(2)Si[OSi((OBu)-Bu-t)(3)](2), is a structural and spectroscopic (NMR, FT-IR, UV-vis, XPS) model for Ti(IV)/SiO2. The molecular complex was used to prepare titanium-containing silica materials through both the thermolytic molecular precursor method (yielding TiO2 center dot 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 degrees C in toluene. (c) 2005 Elsevier B.V. All rights reserved.