1 Interdisciplinary Nanoscience Center - INANO-Fysik, Ny Munkegade, Interdisciplinary Nanoscience Center, Science and Technology, Aarhus University2 Interdisciplinary Nanoscience Center, Science and Technology, Aarhus University3 Department of Physics and Astronomy, Science and Technology, Aarhus University4 Laval University5 Department of Physics and Astronomy, Science and Technology, Aarhus University6 Interdisciplinary Nanoscience Center, Science and Technology, Aarhus University
Chirally modified Pt catalysts are used in the heterogeneous asymmetric hydrogenation of α-ketoesters. Stereoinduction is believed to occur through the formation of chemisorbed modifier–substrate complexes. In this study, the formation of diastereomeric complexes by coadsorbed methyl 3,3,3-trifluoropyruvate, MTFP, and (R)-(+)-1-(1-naphthyl)ethylamine, (R)-NEA, on Pt(111) was studied using scanning tunneling microscopy and density functional theory methods. Individual complexes were imaged with sub-molecular resolution at 260 K and at room temperature. The calculations find that the most stable complex isolated in room-temperature experiments is formed by the minority rotamer of (R)-NEA and pro-S MTFP. The stereodirecting forces in this complex are identified as a combination of site-specific chemisorption of MTFP and multiple non-covalent attractive interactions between the carbonyl groups of MTFP and the amine and aromatic groups of (R)-NEA.
Journal of the American Chemical Society, 2013, Vol 135, Issue 27, p. 9999-10002