Titanium–Germoxy Precursor Route to Germanium-Modified Epoxidation Catalysts with Enhanced Activity

Abstract

The complex Ti[OGeiPr3]4 (1), prepared via the reaction of Ti(OiPr)4 with iPr3GeOH, represents a useful structural and spectroscopic model for titanium–germanium species dispersed onto silica. This precursor was used to introduce site-isolated Ti(IV) centers onto the surface of a mesoporous SBA15 support via the thermolytic molecular precursor method. The local environments of the supported materials (TiGe3SBA15 and calcined TiGe3SBA15-O2) were studied by various spectroscopic methods, including X-ray absorption spectroscopy. These materials are active catalysts for the epoxidation of cyclic and terminal olefins with alkyl hydroperoxides under anhydrous conditions. Compared to catalysts synthesized from siloxide-only precursors, the new catalysts produce 2–3 times more product after 9 h under identical reaction conditions for the epoxidations of cyclohexene and 1-octene. The new materials did not significantly leach under reaction conditions.