AVS 52nd International Symposium
    Surface Science Monday Sessions
       Session SS1-MoM

Paper SS1-MoM2
Surface Science Insights on the Enantioselective Hydrogenation of Activated Ketones on Chirally-Modified Platinum

Monday, October 31, 2005, 8:40 am, Room 202

Session: Catalytic Chemistry of Hydrocarbons
Presenter: S. Lavoie, Université Laval, Canada
Authors: S. Lavoie, Université Laval, Canada
P.H. McBreen, Université Laval, Canada
Correspondent: Click to Email
The asymmetric hydrogenation of alpha-ketoesters on chirally-modified platinum catalysts, the Orito reaction, involves a complex set of interrelated interactions. These include the chemisorption of the chiral modifier and the ketoester on the metal surface, as well as the modifier-ketoester interactions responsible for enantiodifferentiation. In order to isolate the key modifier-ketoester interactions, RAIRS studies were performed on a range of aromatic-carbonyl co-adsorption systems of progressively increasing complexity. All effective modifiers for the Orito reaction contain both an extended aromatic function and a function capable of conventional H-bonding. It is generally accepted that the aromatic function serves to anchor the chiral modifier to the platinum surface, and that it may also play a steric role in inducing asymmetry. However, evidence will be presented for a key additional role for the aromatic anchor. Using results for the Pt(111) surface, it will be shown that the modifier-ketoester interaction may be described in terms of two distinct H-bonds, one of which is to the chemisorption activated aromatic system. It will be shown that such a two-point H-bonding interaction can account for most observations in the catalysis literature concerning the Orito reaction.