Epoxidation with Ti(OSiMe3)4: a homogeneous model mimicking titania–silica mixed oxides?

Abstract

Ti(OSiMe₃)₄ is an active homogeneous catalyst for the epoxidation of allylic alcohols under mild conditions using tert-butyl hydroperoxide as oxidant in an apolar solvent. It affords an average turnover frequency of up to 1470 h⁻¹ and 100% regioselectivity (geraniol) or 100% cis-selectivity (cyclohexenol). UV-Vis measurements indicate that the ability of substrates to coordinate to the catalyst determines the reaction rate and stereoselectivity. This is the likely explanation for the poor or completely missing reactivity of substrates possessing no OH function (cyclohexene, methoxycyclohexene) and also for the substrate-dependent effect of water in the system. Ti(OSiMe₃)₄ is suggested to be a good soluble homogeneous model catalyst mimicking the highly active isolated tetrahedral Ti sites in (silylated) titania–silica mixed oxides.