Abstract
A molecular precursor approach involving tethering procedures was used to produce site isolated titanium-supported asymmetric epoxidation catalysts. This was done by first modifying the support in one step with a mixture of silanes: the synthesized triazine propyl triethoxysilane as functional linker and hexamethyldisilizane as capped agent, to increase the hydrophobicity of the support and mask the remaining silanol groups. In addition, [Ti(OPr i) 4] and [{Ti(OPr i) 3(OMent)} 2] (MentO = 1R,2S,5R-(−)-menthoxo) complexes were heterogenized by reaction with the modified MCM-41. Finally, after [Ti(OPr i) 4] immobilization on to the organomodified support the reaction with the chiral auxiliary (+)-diethyl- l-tartrate was accomplished. All the materials were characterized by elemental analysis, X-ray diffraction, nitrogen adsorption techniques, FT-IR, ICP-MS, DR-UV–vis, 29Si and 13C MAS NMR and TGA. The different systems were tested in the asymmetric epoxidation of cinnamyl alcohol in order to evaluate their catalytic activity and enantioselectivity.
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