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

The preparation, characterization and application of new K-10 montmorillonite supported noble metal catalysts containing immobilized chiral modifier are described, The active contents of the catalysts were Pt, Pd and Rh, while 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 montmorillonite by direct surface reaction or ion exchange followed by impregnation with metal salts, and finally, reduction. Method II, in contrast, starts with the deposition of the metal by impregnation, and then reduction, which is followed by the immobilization of the modifier. The catalysts thus prepared were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), solid state Si-29 NMR and infrared (FT-IR) spectroscopies. The samples were tested in enantioselective hydrogenation of ethyl pyruvate, as well. Only Pt and Rh catalysts were found to be active in the hydrogenation 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 with cinchona alkaloids. (C) 1999 Elsevier Science B.V. All rights reserved.