New immobilized chiral Mn(III) salen complexes on pyridine N-oxide-modified MCM-41 as effective catalysts for epoxidation of nonfunctionalized alkenes

We prepared new chiral Mn(III) salen complexes 1'-4' immobilized on pyridine N-oxide-modified MCM-41 through the axial coordination. Epoxidation of styrene and 4-chlorostyrene with the use of these complexes as catalysts in the presence of NaOCl was found to proceed enantioselectively (ee, 62-69%) at 0 degrees C in 8-12 h, which is a significantly higher enantioselectivity than that observed for their homogeneous counterparts (ee, 36-51%). These catalysts were also effective for the relatively bulkier alkenes, such as indene and 2,2-dimethylchromene, and have shown a reactivity (82-98%) and an enantioselectivity (69-92%) similar to those observed for their homogeneous system. The catalysts could be recycled several times without loss of performance. (c) 2004 Published by Elsevier Inc.