Relative Abundances of Surface Diastereomeric Complexes Formed by Two Chiral Modifiers that Differ by a Methyl Group

Enantioselectivity in heterogeneous catalysis can be induced through the adsorption of optically active compounds known as chiral modifiers. The modifiers typically stereodirect prochiral reactants on the metal surface through the formation of diastereomeric complexes. Surface science measurements on model systems show several examples where such complexes display multiple abundant binding configurations. Insight into the factors determining the relative populations of complexation states can be potentially gained from comparing slightly variant chiral modifiers. Here, we compare STM data for chirality transfer complexes formed by (R)-1-(1-naphthyl)ethylamine and (R)-1-(8-methyl-1-naphthyl)ethylamine coadsorbed with the prochiral substrate 2,2,2-trifluoroaceto¬phenone in order to probe for changes induced by the methyl substituent. The comparison shows changes in relative abundances beyond those predicted by only direct steric interaction. DFT methods are used to calculated complexation complexation energ...