Redox-Control Over Ligand Binding: Consequences for Stoichiometric and Catalytic Reactions

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Dr. Chad A. Mirkin, Department of Chemistry, Northwestern University, is supported by the Inorganic, Bioinorganic, and Organometallic Program of the Chemistry Division to perform studies of redox-active ligands with transition metals. The ligands, known as redox-switchable hemilabile ligands (RHLs), are designed to yield electrochemical control over the steric and electronic environment of the transition metals to which they are bound. The magnitude of these effects will be quantified, and the relative importance of electrostatic and inductive effects in binding affinity changes resulting from the redox chemistry will be assessed. Electrochemical control of chemical transformations that occur at late transition metal centers is the ultimate objective. Potential applications for these complexes include catalytic olefin hydrogenation, asymmetric olefin hydrogenation, hydrosilation, hydrocyanation, and methanol carbonylation. Compounds containing metal ions such as rhodium which are bound to molecules containing phosphorus, oxygen and sulfur atoms have been found to be particularly useful catalysts, and this results from the fact that one part of the molecule binds much more strongly than the other part. The objective of this project is to synthesize new molecules of this sort, known as redox-switchable hemilabile ligands, where the binding of the ligand can be controlled by the addition or abstraction of an electron to or from a redox active substituent on the ligand itself. Because the oxidation state of the ligand can be controlled quite easily using electrochemistry, this could provide an additional element of control to the catalytic reactions, making the catalysts either more or less reactive depending on the oxidation state. The increased level of control is expected to have important implications for industrially important catalytic processes.