Two-Dimensional Self-Assembly and Catalytic Function: Conversion of Chiral Alcohols into Self-Assembled Enols on Pt(111)

The chemical transformation and subsequent self-assembly of chiral alcohols on platinum was studied using three different pairs of prochiral ketones and their alcohol products. The ketones were chosen because they represent three different types of substrates in the asymmetric hydrogenation on chirally modified platinum catalysts. Scanning tunneling microscopy and high-resolution electron energy loss vibrational spectroscopy data were combined to show that methyl lactate transforms into the enol tautomer of methyl pyruvate on Pt(111) at room temperature. Specifically, the chiral alcohol undergoes dehydrogenation leading to the same adsorbed enol assemblies that are formed directly through the adsorption of the prochiral alpha-ketoester. Similarly, 1-phenylethanol transforms into assemblies of the enol tautomer of acetophenone. The interrelationship between surface reactivity and self-assembly was further explored by studying the oxidation of 1-pheny1-2,2,2-trifluoroethanol to form CH center dot center dot center dot O bonded 2,2,2-trifluoroacetophenone assemblies. In terms of catalytic function, these self-assembly processes provide insight on the optimization of the asymmetric hydrogenation of activated ketones on chirally modified platinum catalysts.