Homogeneous and heterogeneous asymmetric reactions. Part X: Enantioselective hydrogenations over K-10 montmorillonite supported noble metal catalystswith immobilized modifier

The preparation, characterization and application of new K-10 montmorilloni te supported noble metal catalysts containing immobilized chiral modifier a re described, The active contents of the catalysts were Pt, Pd and Rh, whil e cinchonidine was used as chiral modifier. The preparation was carried out by two methods. Method I consists of the modification of the parent K-10 m ontmorillonite by direct surface reaction or ion exchange followed by impre gnation with metal salts, and finally, reduction. Method II, in contrast, s tarts with the deposition of the metal by impregnation, and then reduction, which is followed by the immobilization of the modifier. The catalysts thu s prepared were characterized by X-ray diffraction (XRD), transmission elec tron microscopy (TEM), solid state Si-29 NMR and infrared (FT-IR) spectrosc opies. The samples were tested in enantioselective hydrogenation of ethyl p yruvate, as well. Only Pt and Rh catalysts were found to be active in the h ydrogenation producing moderate to good enantioselectivities (up to 75% ee for the R isomer). To the best of our knowledge, the results described here are the first data concerning the preparation of clays chirally modified w ith cinchona alkaloids. (C) 1999 Elsevier Science B.V. All rights reserved.