AVS 45th International Symposium
    Surface Science Division Monday Sessions
       Session SS2-MoM

Paper SS2-MoM9
Conformation and Orientation of Methyl Pyruvate on Ni(111)

Monday, November 2, 1998, 11:00 am, Room 309

Session: Molecular Adsorbates on Metals
Presenter: P.H. McBreen, Université Laval, Canada
Authors: P.H. McBreen, Université Laval, Canada
M. Castonguay, Université Laval, Canada
J.R. Roy, Université Laval, Canada
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Both the orientation and molecular conformation of adsorbed layers are determining factors in a variety of properties including chemical reactivity. The question of surface orientation and conformation are particularly important for methyl pyruvate since it possesses both a keto and an ester carbonyl and it can undergo cis-trans isomerization. Its hydrogenation to methyl lactate is one of the very few well documented cases of enantioselective heterogeneous catalysis. To the best of our knowledge this is first report of an investigation of the intrinsic adsorption of this prochiral molecule on a metal surface using surface science techniques. RAIRS data shows that methyl pyruvate is chemisorbed on Ni(111) at all coverages with its molecular plane perpendicular to the surface. Two different adsorption conformations are detected. The full monolayer is found to be exclusively in the bidentate cis-conformation.The results, and DFT calculations, indicate that the keto cabonyl metal surface interaction is stronger than the ester carbonyl metal surface interaction. Comment will be made on the fact that the observed molecular orientation and conformation are at odds with the model usually assumed in rationalizations of the enantioselective hydrogenation of methyl pyruvate.