Immobilization of titanium chiral alkoxides on SBA-15 and modelling the active sites of heterogeneous catalyst using titanium silsesquioxane complexes

A molecular precursor approach involving simple grafting procedures was used to produce site isolated titanium-supported epoxidation catalysts. The complexes [{Ti(OiPr)2(OMent)}2] (1) and [Ti(OMent)4] (2) (MentO = 1R,2S,5R-(−)-menthoxo) react with the remaining hydroxyl groups of SBA-15 after silanization with Me3SiCl, via loss of iPrOH and/or menthol and introduction of titanium species onto the silica surface. Grafting 1 and 2 onto SBA-15 yields mostly isolated Ti(IV) sites, as evidenced by DRUV–vis. In addition, the silsesquioxane derivatives [Ti(OiPr)2(OMent){(c-C5H9)7Si8O13}] (3) and [Ti(OMent)3{(c-C5H9)7Si8O13}] (4) have been synthesized in order to compare the different homogeneous and heterogenous systems mentioned above in the asymmetric epoxidation of cinnamyl alcohol to evaluate their catalytic activity and enantioselectivity.

Graphical abstractA molecular precursor approach involving simple grafting procedures was used to produce site isolated titanium-supported epoxidation catalysts. Organotitanium complexes bearing chiral groups react with the remaining hydroxyl groups of SBA-15 after silanization with Me3SiCl yielding mostly isolated Ti(IV) sites, as evidenced by DRUV–vis. In addition, silsesquioxane derivatives have been synthesized in order to compare the different homogeneous and heterogenous systems mentioned above in the asymmetric epoxidation of cinnamyl alcohol to evaluate their catalytic activity and enantioselectivity.Figure optionsDownload full-size imageDownload as PowerPoint slide