Asymmetric hydrogenation of ethyl pyruvate on chirally modified Pt catalysts supported on Al₂O₃@FDU-14 mesoporous composites

A series of Al₂O₃@FDU-14 composites with different alumina loadings were prepared using a solid state grinding method. The 4% Pt catalysts supported on Al₂O₃@FDU-14 were prepared by impregnation using H₂PtCl₆. X-ray diffraction, transmission electron microscopy, and nitrogen adsorption characterization of the Pt/Al₂O₃@FDU-14 catalysts indicated that the mesoporous features of the FDU-14 mesopolymer were retained. The Pt/Al₂O₃@FDU-14 catalysts were used in the asymmetric hydrogenation of ethyl pyruvate after they were chirally modified with cinchonidine. For Al₂O₃ loading from 5% to 15%, Al₂O₃ was uniformly dispersed inside the mesoporous channels of FDU-14 host. Ethyl pyruvate conversion and their ee values increased with increasing alumina loading, with a highest ee value of 80%. It was suggested that the alumina coating inside the mesoporous channels of FDU-14 decreased the surface electronic density of the FDU-14 mesopolymer so that cinchonidine can be easily adsorbed on the surface of Pt/Al₂O₃@FDU-14 catalysts. As compared with chirally modified Pt/FDU-14 catalysts, chirally modified Pt/Al₂O₃@FDU-14 catalysts gave higher ee values.