Professor Richard L. Keiter, Department of Chemistry, Eastern Illinois University, is supported by the Inorganic, Bioinorganic, and Organometallic Chemistry Program of the Chemistry Division for mechanistic studies of intramolecular exchange of bound and unbound phosphorus donor groups in transition metal complexes containing multidentate phosphine ligands. In some Group 6 transition metal carbonyl complexes that also containing both coordinated and dangling phosphino groups the rate of phosphine exchange is much faster than expected. The fact that a large through space carbon-phosphorus spin-spin coupling constant occurs between dangling phosphino and cis-carbonyl groups indicates that an electronic interaction may be an important factor in the acceleration. By using a series of phosphine ligands containing substituents with differing steric and electronic properties, a mechanistic model in which a short dangling phosphine arm accelerates the exchange reaction by interacting with the cis carbonyl groups of the complex will be tested. The study will then be extended to known and new chiral ditertiary phosphines. The usefulness of these in asymmetric hydrogenation will be evaluated.
Substitution reactions have been studied extensively for many years but very few of these investigations have addressed phosphine substitution. The absence of such exploration is surprising given the current interest in phosphine chemistry that centers on ligand design for asymmetric synthesis, site-specific drug delivery, and water-soluble phosphine. In addition, the kinetic stability of the metal-phosphorus bond is highly important in catalysis and catalyst degradation. This study will provide thermodynamic and kinetic insight into the factors that control phosphine substitution in transition metal complexes. An additional, very important aspect of the project is the education of undergraduate chemistry majors and the opportunity it will provide both B.S. and M.S. students to engage in cutting edge research.
