COMP 111 |
| Palladium dicarboxylate complexes of N-heterocyclic carbenes are known to catalyze the aerobic oxidation of alcohols to ketones. We sought to combine the substrate scope and rate of NHC-based catalysts with the enantioselectivity demonstrated by ((-)-sparteine)PdCl2 by introducing stereocenters into carbene frameworks and computationally screening for enantioselectivity, activity and stability. First, a mechanistic study identified the geometry of the rate-limiting transition state, i.e. transfer of the beta-hydrogen of the metal-bound alkoxide to an acetate ligand. A mechanism potentially able to racemize chiral alcohols was found to lie only slightly higher in energy. Increasing the basicity of the carboxylate ligand simultaneously lowers the barrier to substrate oxidation and inhibits racemization. Finally, the ligand screen identified specific positions at which substitution affects the activation energy of substrate oxidation and the ability of the ligand to discriminate between enantiomers of 1-phenylethanol. |
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Bold Predictions in Theoretical Chemistry: A Poster Session in Honor of One of the Boldest, Bill Goddard, on the Occasion of his 70th Birthday
7:30 PM-9:30 PM, Sunday, August 19, 2007 BCEC -- Exhibit Hall - B2, Poster
Division of Computers in Chemistry |