Journal of the American Chemical Society, Vol.135, No.27, 9999-10002, 2013
Stereodirection of an alpha-Ketoester at Sub-molecular Sites on Chirally Modified Pt(111): Heterogeneous Asymmetric Catalysis
Chirally modified Pt catalysts are used in the heterogeneous asymmetric hydrogenation of alpha-ketoesters. Stereoinduction is believed to occur through the formation of chernisorbed modifier-substrate complexes. In this study, the formation of diastereomeric complexes by coadsorbed methyl 3,3,3-trifluoropyruvate, MTFP, and (R)-(+)-1-(1-naphthyl)ethylarnine, (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 stereo-directing forces in this complex are identified as a combination of site-specific chernisorption of MTFP and multiple non-covalent attractive interactions between the carbonyl groups of MTFP and the amine and aromatic groups of (R)-NEA.