Control of Stereoselectivity in Heterogeneous Catalysis by Functionalization of Pt Nanoparticles with alpha-Amino Acids

The asymmetric hydrogenation of ß-keto esters over amino acid-functionalized Pt nanoparticles (NPs) was explored. The investigated catalysts are chemoselective and stereoselective due to specific ligand-reactant interactions between ligands and reactants. Based on structure-selectivity relationships, the previously for L-proline-functionalized Pt NPs suggested ligand-reactant interaction model could be validated, extended to other amino acid ligands, and further refined. Nonlinear effect analysis revealed that in most cases the stereoselectivity is determined mainly by a 1:1 ligand-reactant interaction. Adjusting the interactions between ligands and reactants allowed to improve the stereoselectivity up to an enantiomeric excess over 80%. Most amino acid ligands not only induce selectivity but also enhance the reaction rate. The results of a systematic kinetic study provided an important contribution to the understanding of the reaction mechanism.