Synthesis and Catalytic Application of Robust Grafted Tripodal (Phenoxy) Ti-POSS Complexes in Crosslinked Hyperbranched Poly(siloxysilane) Matrix

Abstract

We have studied synthesis, activity, epoxide selectivity, H2O2 efficiency, and recyclability of new robust heterogeneous alkene epoxidation catalysts of grafted tripodal (phenoxy) Ti-polyhedral oligomeric silsesquioxane (Ti-POSS) complexes in hyperbranched poly(siloxysilane) matrix. Crosslinked hyperbranched (CHB) poly(siloxysilane)-grafted [Ti(OC6H4CN-p){(HSiMe2(CH2)3)-(i-C4H9)6Si7O12}] (5) and CHB-poly(siloxysilane)-grafted [Ti(OC6H5){(HSiMe2(CH2)3)(i-C4H9)6Si7O12}] (6) have demonstrated high activity, epoxide selectivity (≥99%) and H2O2 efficiency (≥98%) in cyclohexene and 1-octene epoxidation with aqueous H2O2 higher than titanosilicate catalysts such as TS-1 and Ti-β, due to high Lewis acidity of the Ti-center and to the use of CHB-poly(siloxysilane) matrix. The catalysts are readily recyclable with retained activity.