Homogeneous and heterogeneous asymmetric reactions. Part 13*. Clay-supported noble metal catalysts in enantioselective hydrogenations

The preparation, characterization and application of new clay-supported Pt and Pd catalysts containing cinchonidine as chiral modifier are described. The preparation was carried out by deposition of the metal by impregnation followed by the immobilization of the modifier. The catalysts were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The samples were tested in enantioselective hydrogenation of ethyl pyruvate and 2-methyl-2-pentenoic acid. The catalysts were found to be active in the hydrogenations producing moderate to good enantioselectivities (up to 56% ee for the (R)-ethyl lactate). Moreover, the Pt catalysts were found to be recyclable. The immobilization of modifier on clay-supported catalysts led us to draw important conclusions concerning the existing mechanistic explanations.