Dr. Wayne Tikkanen, Chemistry Department, California State University - Los Angeles, is supported by the Inorganic, Bioinorganic, and Organometallic Program of the Chemistry Division for the development of pentaarylcyclopentadienyls as facially directing ligands in chiral metallocenes. Chiral zirconium and niobium complexes that contain a pentaarylcyclopentadienyl ligand and a chiral mono- and bi-dentate alkoxide or amido ligand will be prepared. The chiral alkoxide and amido ligands will bear large groups that will force the aromatic rings on the pentaarylcyclopentadienyl group into a chiral conformation. This should result in chiral amplification and the complexes will be evaluated as catalysts for asymmetric C-C bond forming reactions. Specifically, they will be tested for their efficacy in the catalysis of [4+2] cycloaddition of acrylate dienophiles, silylcyanation of aldehydes and oxo-ene reactions. The mechanism of catalysis will be probed in order to determine the factors underlying selectivity. This information will be used to design more effective catalysts.
The challenge of the stereo-selective formation of carbon-carbon bonds to form single enantiomers from achiral reactants is a problem with both academic and practical importance. This challenge is especially important in the synthesis of bioactive molecules. For example, medications sold as single enantiomers make up half of the top 100 selling drugs. The intellectual merit of this proposal derives from the determination of the relationship between catalyst structure and product distribution applied to the development of useful catalysts. Another impact from this work will be to increase the number of under-represented groups in the scientific workplace. Undergraduates will be involved in all aspects of this work, from bench-work to experimental design to dissemination at meetings and in publications. Since the student body of Cal State Los Angeles is comprised mostly of under-represented minorities, the students participating in this work will be from those groups.
