Cinchona-Modified Pt as a Catalyst for Enantioselective Hydrogenation: Criticism of the "Template Model"-A Reply

Abstract

Research and development towards catalysts that can induce high enantiomeric excess (ee) under mild reaction conditions is important from both academic and applications perspectives. In particular, a heterogeneous system capable of inducing high ee under mild conditions without additional external forces (i.e. sonication) would be of interest. A novel preparation of Pt nanoclusters (3 nm) deposited on a non-porous alumina support and modified with cinchonidine was found to be very efficient for hydrogenation of ethyl pyruvate at low pressures. The catalyst demonstrated 80–88% of enantiomeric excess in ethyl pyruvate hydrogenation under mild reaction conditions (2.5–10 bar of hydrogen pressure) in acetic acid. Further, the catalyst was found to be very stable and could be recycled at least four times without an observable decrease of activity or enantioselectivity. The influence of the nature of the catalyst and modifier on the obtained enantiomeric excess was investigated via DRIFTS (diffuse reflectance infra-red fourier transform spectroscopy) measurements.