Clay-supported non-chiral and chiral Mn(salen) complexes as catalysts for olefin epoxidation

Clay-supported non-chiral Mn(salen) catalysts have been prepared by two methods, direct exchange of the complex or treatment of the Mn-exchanged clay with the salen ligand. The first method, which leads to more homogeneously distributed catalysts, has been also used with a chiral Mn(salen) complex. Depending on the size and the amount of exchanged complex and the structure and surface area of the clays, the catalysts can show expanded basal spacings. AU the solids promote epoxidation reactions with iodosylbenzene, reaching turnover numbers similar or higher than those obtained in solution with related catalysts. However, the supported chiral catalyst leads to a slightly lower enantioselectivity. The recovery of the catalysts leads to a reduction of activity and mainly of enantioselectivity, as in the case of the chiral catalyst, which cannot be related with leaching of complex. Spectroscopic studies indicate that the decomposition of the ligand is the main reason for this behaviour. (C) 1998 Elsevier Science B.V. All rights reserved.