Rate-Acceleration and Stereoselection in

Heterogeneous Chiral Catalysis

Peter H. McBreen

Département de chimie, Université Laval, Canada

The Orito reaction describes the enantioselective hydrogenation of activated ketones such as alpha-ketoesters on cinchona-modified Pt catalysts. There is a consensus in the literature that the reaction proceeds through the formation of 1:1 chiral modifier-substrate complexes. One of the most interesting facets of the reaction is the observation of rate-enhancement on the chirally-modified surface with respect to the rate of the racemic reaction on the non-modified surface.  For example, ethyl pyruvate displays significant rate-enhancement of the enantioselective reaction. However, several groups have also reported results for substrates that display negligible rate-enhancement. In this presentation, we assume that there is a real rate-enhancement effect for ethyl pyruvate under typical operating conditions. In support of a rate-enhancement effect, STM and RAIRS data show that clustering of methyl pyruvate on Pt(111) arises from enol formation, a reversible process. Studies of a range of substrates on Pt(111) will be presented and the results will be discussed within the context of literature data for rate-acceleration and enantioselection.