Direct STM evidence of a surface interaction between chiral modifier and pro-chiral reagent:: Methylacetoacetate on R,R-tartaric acid modified Ni{111}

The asymmetric hydrogenation of methylacetoacetate to R-methyl-3-hydroxybutyrate over R,R-tartaric acid modified Ni catalysts is a well known example of heterogeneous enantioselective catalysis. Using STM, RAIRS and TPD, we investigate the adsorption of methylacetoacetate on Ni{1 1 1} and R,R-TA modified Ni{1 1 1} in order to shed light on the molecular mechanisms underlying the enantioselective catalysis. We show that methylacetoacetate adsorption can only occur in regions of low R,R-tartaric acid coverage. Once adsorption occurs, methylacetoacetate is able to locally rearrange the tartrate modifiers to produce a two-dimensional co-crystal. We consider the implications of our work in explaining the mechanism of enantioselective hydrogenation in this type of system. (C) 2002 Elsevier Science B.V. All rights reserved.