Turning Reactive Organic Intermediates into Versatile Metal Ligands: Organometallic Complexes and Catalysts from Alkylidene Dihydropyridines

With the support of the Chemical Catalysis Program in the Division of Chemistry, Professor Christopher Pigge of the University of Iowa is developing new transition metal catalysts (catalysts are chemical additives that help a reaction occur or proceed more rapidly) for use in organic synthesis. Broadly applicable and highly active catalysts are essential tools in chemistry for the efficient construction of small molecules, including molecules that are used in pharmaceuticals, materials and polymers, and a host of other applications. The reactivity and scope of metal catalysts is often influenced by supporting ligands; this project is developing enhanced and tunable catalysts by incorporating novel and readily available ligands into catalytically relevant metal complexes. In addition to the wide-ranging impact of the new catalysts, the broader impacts of this work are allowing students at the undergraduate and graduate level to be involved in state-of-the-art training in organic and organometallic chemistry, Over the course of this training, the students are developing expertise in catalyst design and evaluation. Outreach efforts to middle and high school students are further broadening participation in STEM-related activities. Carbon-donor (C-donor) ligands show promise as key components of highly active yet stable transition metal catalysts, but the chemistry of C-donor metal complexes is underdeveloped. This project is investigating the catalytic activity of metal complexes that feature novel C-donor ligands prepared from N-alkylpyridinium salts. These molecular frameworks are readily accessible and are easily modified to accommodate monodentate and polydentate ligand scaffolds, including chiral non-racemic ligands for use in asymmetric catalysis. The electron-donating properties of the ligands are systematically tuned through the incorporation of different activating groups along the pyridine periphery, allowing access to ylide-type, yldiide-type, and carbone-type C-donor groups from a common molecular core. Organometallic complexes prepared from catalytically active metal centers (such as Pd, Rh, and Au) are easily obtained and are being developed for use in important synthetic transformations that engage an array of common organic functional groups. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.