Interaction of the Pro-Chiral Molecule, Methylacetoacetate, with (S)-Aspartic Acid Modified Ni{111}

The adsorption of aspartic acid is studied on Ni{111} under ultrahigh vacuum conditions using scanning tunnelling microscopy, reflection absorption infrared spectroscopy, and temperature-programmed desorption. At low coverage, aspartic acid undergoes a self-polymerization process to form oligosuccinimide species at surface defects. As the coverage of aspartic acid is increased, the terraces become filled with aspartate species. The pro-chiral molecule, methylacetoacetate (MAA), is unable to stick to a saturated monolayer of aspartic acid. However, at low aspartic acid coverage, MAA adsorbs in the enol tautomeric form in the vicinity of oligosuccinimide clusters. We discuss the implications of our findings for explaining the behavior of aspartic acid modified Ni catalysts for the enantioselective hydrogenation of β-ketoesters.