Synthesis of titanium–triazine based MCM-41 hybrid materials as catalyst for the asymmetric epoxidation of cinammyl alcohol

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(OPri)4] and [{Ti(OPri)3(OMent)}2] (MentO = 1R,2S,5R-(−)-menthoxo) complexes were heterogenized by reaction with the modified MCM-41. Finally, after [Ti(OPri)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.

Graphical abstractA 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(OPri)4] and [{Ti(OPri)3(OMent)}2] (MentO = 1R,2S,5R-(−)-menthoxo) complexes were heterogenized by reaction with the modified MCM-41. Finally, after [Ti(OPri)4] immobilization on to the organomodified support the reaction with the chiral auxiliar (+)-diethyl-l-tartrate was accomplished. The different systems were tested in the asymmetric epoxidation of cinnamyl alcohol in order to evaluate their catalytic activity and enantioselectivity.Figure optionsDownload full-size imageDownload as PowerPoint slide