Sigma-Bond Activation and Catalysis Facilitated by Metal-Phosphorus Ligand Cooperativity

Ohio State University, The, Columbus OH

Investigators

Abstract

This project is funded by the Catalysis Program of the Chemistry Division. Dr. Christine Thomas of The Ohio State University is developing metal catalysts using inexpensive Earth-abundant metals. The approach involves cooperation between the metal and a phosphorus atom bound to the metal. Implementing more efficient, economical and environmentally friendly catalyst technologies is the key to developing more sustainable processes for the production of fuels, commodity chemicals, and consumer products. Large scale industrial catalysts are most commonly derived from metals such as palladium, platinum, rhodium, or iridium. These are often referred to as "precious metals" owing to their high cost and low Earth-abundance. A better solution is to replace the precious metals in these catalysts with more economically viable Earth-abundant metals such as manganese, iron, cobalt, nickel, and copper. However, the development of catalysts featuring these metals has been challenging because such metals are often reluctant to undergo the complex chemical processes required to make and break chemical bonds. By actively involving both the metal and the phosphorus atom in the cleavage and formation of chemical bonds, these obstacles may be overcome, allowing more sustainable, economical, and environmentally friendly catalytic processes to be developed. Through this project Dr. Thomas is providing rigorous training in scientific research for both undergraduate and graduate students. Dr. Thomas is also actively involved in outreach activities geared towards K-12 programs, public forums on the importance of catalysis and sustainability, and efforts to encourage and support women in careers in STEM. Dr. Thomas is developing a new strategy for promoting sigma-bond activation processes with ultimate catalytic applications using metal-ligand cooperativity. Cooperative approaches of this type have proven particularly effective for facilitating reactions using Earth-abundant transition metals, which are often limited in the range of reactions they can perform on their own. This limitation stems from the reluctance of Earth-abundant transition metals such as manganese, iron, cobalt, nickel, and copper to undergo multi-electron redox changes. Participation of a ligand in sigma-bond activation processes, either via ligand-based redox activity or by ligand involvement in heterolytic sigma-bond cleavage events, alleviates at least some of the redox requirements on the transition metal. Dr. Thomas is investigating N-heterocyclic phosphenium (NHP+) and phosphido (NHP-) ligands and their transition metal complexes using a chelating diphosphine pincer ligand framework to enforce metal coordination and impart stability upon the resulting complexes. When incorporated into a rigid chelating framework, NHP+ phosphenium cations can be reduced to their anionic NHP- form, allowing for further ligand-based redox processes to occur. The unique properties of NHP+/- ligands allows them to participate directly in bifunctional sigma-bond activation processes. A complete series of first row transition metal complexes is under investigation and studies of their reactivity and catalytic applications are ongoing. In support of the broader impacts of this project, Dr. Thomas is actively involved in outreach activities geared towards K-12 programs, public forums on the importance of catalysis and sustainability, and efforts to encourage and support women in careers in STEM. 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.