Encapsulation of a chiral Mn-III(salen) compkx in ordered mesoporous silicas: an approach towards heterogenizing asymmetric epoxidation catalysts for non-functionalized alkenes

摘要

Two immobilized chiral Mnlu(salen) complexes covalently anchored on modified MCM-41 (50 angstrom) and SBA-15 (75 angstrom) were prepared using 3-aminopropyltriethoxysilane as a reactive surface modifier to afford comparable or even higher enantioselectivity than homogeneous catalysts for the enantioselective epoxidation of a series of smaller to bulkier alkenes. The catalyst immobilized in silica with larger pore diameters was found to be more active. Compared to homogeneous catalysts, the heterogenized catalysts are more stable and can be recycled four times with retention of enantioselectivity. (c) 2005 Elsevier Ltd. All rights reserved.