NSF Award
9312533
9312533 Augustine This effort examines an approach to the design of enantioselective heterogeneous catalysts that combines fundamental principles of catalyst systems and surface chemistry with synthetic organic chemistry. It uses a working hypothesis developed from previous work on chiral hydrogenation of pyruvate esters catalyzed by platinum modified with cinchona alkaloids. In this hypothesis, the substrate must be adsorbed on a corner site with the modifier adsorbed on adjacent sites; the distance of the chiral center from the surface is a key factor in determining the enantiomeric selectivity. Chiral modifiers with various spacing between the chiral center and the electron-rich site (which can adsorb to a metal surface) are synthesized and tested in the platinum-catalyzed hydrogenation of pyruvate. Cinchona-induced chirality in the palladium-catalyzed allylation of malates is also studied. Chiral selectivity or enantioselectivity (the production of on "optical " isomer to the exclusion to its mirror image) is of critical importance when producing chemicals intended to produce a biological response such as drugs, pesticides, and perfumes. It is of thus of great value to the pharmaceutical, agrichemical, and fine chemical industries. Although biocatalysts (enzymes) are more often enantioselective that not, they are so substrate-discriminating as to be of limited value in the production of chemicals not occurring naturally. Homogeneous chiral catalysts, on the other hand, are less selective chemically (but more selective chirally) and harder (read more expensive) to use than heterogeneous catalysts. This work will elaborate principles that can be used to improve enantioselectivity in heterogeneous catalysts.
