CLAY-SUPPORTED NONCHIRAL AND CHIRAL MN(SALEN) COMPLEXES AS CATALYSTS FOR OLEFIN EPOXIDATION

Clay-supported non-chiral Mn(salen) catalysts have been prepared by tw o methods, direct exchange of the complex or treatment of the Mn-excha nged 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 r eactions with iodosylbenzene, reaching turnover numbers similar or hig her than those obtained in solution with related catalysts. However, t he supported chiral catalyst leads to a slightly lower enantioselectiv ity. The recovery of the catalysts leads to a reduction of activity an d mainly of enantioselectivity, as in the case of the chiral catalyst, which cannot be related with leaching of complex. Spectroscopic studi es indicate that the decomposition of the ligand is the main reason fo r this behaviour. (C) 1998 Elsevier Science B.V. All rights reserved.