A polyhedral oligomeric silsesquioxane (POSS)-bridged oxo-molybdenum Schiff base complex with enhanced heterogeneous catalytic activity in epoxidation

摘要

We have generated a new heterogeneous catalyst by bridging an oxo-molybdenum Schiff base on a polyhedral oligomeric silsesquioxane (POSS) via covalent attachment. The resulting POSS-bridged oxo-molybdenum Schiff base complex catalyst was fully characterized by ~1H NMR, XRD, FT-IR, SEM, TGA, and contact angle analysis, and its catalytic potential was studied for the epoxidation of alkenes using aqueous tert-butyl hydroperoxide (TBHP) as the oxidant. The catalyst was found to be highly efficient and showed higher catalytic reactivity than the corresponding homogeneous analogues with added benefits of facile recovery and recycling of the heterogeneous catalyst. The POSS-bridged oxo-molybdenum Schiff base complex was successfully reused for four runs without significant loss in activity. The unique three dimensional network catalyst structure and the hydrophobic properties of the POSS units in the catalyst are revealed to be responsible for the catalyst's excellent performance in epoxidation reactions.