Single-chiral-catalytic-surface-sites: STM and DFT study of stereodirecting complexes formed between (R)-1-(1-naphthyl)ethylamine and ketopantolactone on Pt(111)

Abstract

The formation of bimolecular complexes on metal surfaces through interaction between a single chemisorbed chiral molecule and a single chemisorbed prochiral substrate molecule can be considered as a preorganization step toward chirality transfer. In the case of asymmetric hydrogenation on chirally modified platinum catalysts, the metal surface dissociates H₂ and provides atomic hydrogen for the desymmetrization step. Along the reaction path, the combined chemisorption and intermolecular interactions in the assembly formed between the modifier and the substrate determine which enantiomer is formed in excess. In this study, we use DFT calculations and STM measurements to describe chemisorption and intermolecular interactions in isolable structures formed between single ketopantolactone and single (R)-1-(1-naphthyl)ethylamine molecules on Pt(111). The study reveals several distinct complexation geometries at the sub-molecular level as well as the stereodirecting forces operating in the most abundant bimolecular assemblies. The comparison of theoretical and experimental data strongly suggests that partial hydrogenation of KPL occurs under the experimental conditions and that some of the most abundant complexes are formed by the hydroxy intermediate.