Improved method for immobilization of a chiral complex on PTA/alumina for asymmetric hydrogenation of a beta-ketoester

Abstract

Ru-BINAP was immobilized on alumina using the well-known Augustine method with heteropoly acid (HPA) as the anchoring agent ("Augustine catalyst"). The supported catalyst was tested in a high-pressure reaction such as asymmetric hydrogenation of methyl acetoacetate (MAA). Since the activity of the supported catalyst was significantly lower than that of the homogeneous catalyst, the solvent used in preparing PTA/Al2O3 was changed from ethanol to a solution of HCl. The modified supported catalyst ("modified Augustine catalyst") exhibited higher conversion, better selectivity, and improved enantioselectivity compared with the catalyst prepared by the Augustine method. The modified Augustine catalyst also produced beta-hydroxyesters with good yield and enantioselectivity in asymmetric hydrogenation of various beta-ketoester derivatives. The modified Augustine catalyst was examined by FT-IR, XRD, NH3-TPD, and ICP-AES, which revealed the existence of strong acid sites formed by HPA with a Keggin structure. These results were attributed to the effect of enhanced acidity on the modified Augustine catalyst. (C) 2013 Elsevier B.V. All rights reserved.