CAREER: N-heterocyclic Phosphenium Cation-Containing Pincer Ligands: A Chelating Analogue of the Nitrosyl Ligand and its Non-Innocent Behavior

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With this award from the Chemical Catalysis Program, Professor Christine M. Thomas from Brandeis University will focus on developing a new series of redox non-innocent pincer ligands for use in catalysis. She and her students have developed a new class of tridentate pincer ligand incorporating a central N-heterocyclic phosphenium (NHP) unit. While catalytic applications of N-heterocyclic carbene (NHC) ligands have been explored extensively, their phosphorus analogues NHPs have not been evaluated in transition metal catalysis, and far less is known about their coordination chemistry. Professor Thomas and coworkers have designed an NHP-containing diphosphine pincer ligand as a method to allow more extensive studies into the transition metal chemistry of NHP ligands. Preliminary results from the Thomas' group strongly support an analogy to nitrosyl ligands, and thus the ability of NHPs to function as redox active ligands to support two-electron transformations is a promising avenue. Professor Thomas and her group will be investigating the coordination chemistry of the new NHP-diphosphine ligands with a wide variety of transition metals and exploring two-electron transformations facilitated by the NHP unit. Computational and electrochemical methods will be used to evaluate the redox-induced transformations in NHP complexes and new NHP-containing multidentate ligands will be investigated. Owing to the importance of multi-electron redox transformations in catalysis, the ultimate goal of the proposed research project is to utilize these analogues of both nitrosyls and NHCs to facilitate catalytic transformations such as C-C or C-X bond forming or breaking reactions, transfer hydrogenation, cross-coupling and other sigma-bond activation processes. The designed ligands have the potential to support two-electron redox chemistry at metals that are less prone to undergo two-electron transformations. This includes first row transition metals and early transition metals, both of which are cheaper and more naturally abundant than the traditional noble metals used in catalysis such as platinum, palladium and, rhodium. In addition to specific contributions to catalysis, the PI will use the funds to fostering the development of undergraduates interested in chemistry, and to cultivate and interest in science among K-8 students by working closely with local science museums, schools, and after-school clubs.