title: Adsorption states and modifier-substrate interactions on Pt(111) relevant to the enantioselective hydrogenation of alkyl pyruvates in the Orito reaction.
abstract: Reflectance FTIR spectroscopy (RAIRS) was used to study the chemisorption and intermolecular interactions of methyl pyruvate and (+/-)-1-(1-naphthyl)ethylamine (NEA) on Pt(111). NEA serves, in this study, as a tractable model of a chiral modifier in the asymmetric hydrogenation of alpha-dicarbonyls on alkaloid-modified platinum surfaces-the Orito reaction. The results show the presence of a majority enediolate state on the clean surface. A perpendicularly adsorbed trans conformation state is populated at close to full-monolayer coverage on the clean surface. The latter state desorbs at 185 K. The enediolate undergoes dissociation at 230 K. NEA displays hydrogen-bond association at high coverages. Coadsorption studies show that NEA inhibits the formation of the enediolate state. Multilayer methyl pyruvate shows a clear hydrogen-bond interaction with chemisorbed NEA, leading to a reorientation of the ethylamine group. The high-coverage trans-chemisorbed methyl pyruvate state also hydrogen-bonds to chemisorbed NEA. The latter interaction renders the trans state stable to above 300 K. A new schematic mechanism for the Orito reaction is proposed on the basis of these data.
authors.affiliation: Département de Chimie, Université Laval, Québec, Canada G1K 7P4.
authors.forename: S
authors.initials: S
authors.lastname: Lavoie
authors.forename: M-A
authors.initials: MA
authors.lastname: Laliberté
authors.forename: P H
authors.initials: PH
authors.lastname: McBreen