CAS: Development of Multidentate Ligands that Incorporate Metal-Ligand Cooperativity into Catalytic Hydrofunctionalization Reactions

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With the support of the Chemical Catalysis program in the Division of Chemistry, Professor Christine Thomas at Ohio State University is studying the fundamental design of new, more sustainable, catalysts for hydrofunctionalization reactions. Catalytic hydrofunctionalization reactions provide an environmentally friendly method to convert widely available chemical feedstocks into synthetic intermediates that can easily be converted into value-added products with uses in pharmaceuticals, consumer products, and the commodity chemical industry. The project aims to uncover new catalysts that are easily produced from naturally abundant and inexpensive precursors, particularly taking advantage of Earth-abundant metals such as manganese, iron, and cobalt. This project is directly contributing to the rigorous training of both graduate students and undergraduate researchers in preparation for their careers as scientific researchers. In efforts to increase the participation of underrepresented groups in chemistry, Professor Thomas serves as the faculty advisor to the student organization for women in chemistry at Ohio State (Females of Chemistry Uniting Scientists, FOCUS), is an active member of the NOBCChE (National Organization for the Professional Advancement of Black Chemists and Chemical Engineers) Collaborative, and will be launching a new summer undergraduate program in the Ohio State Department of Chemistry and Biochemistry specifically focused on providing research opportunities for underrepresented minority students (CoNQUER, Collaborative NOBCChE Quintessential Undergraduate Experience in Research). With the support of the Chemical Catalysis program in the Division of Chemistry, Professor Christine Thomas at Ohio State University is studying the design of new multidentate ligand frameworks in an effort to promote metal-ligand cooperativity with Earth-abundant first row transition metals (e.g., iron, cobalt, manganese). The project aims to uncover more sustainable catalytic methods by using metal-ligand cooperative processes as a strategy to make and break chemical bonds without relying on two-electron redox cycles that are often inaccessible to first row metals. Ligand design is at the heart of this project, and the Thomas group is evaluating several different approaches in this regard. A tridentate PPP-based pincer ligand featuring an N-heterocyclic phosphide fragment has been shown to actively participate in metal-ligand cooperative reactions in which sigma bonds are cleaved across the metal-phosphide linkage, and ongoing studies focus on the expansion of established stoichiometric reactions and their incorporation into catalytic cycles for the hydroboration, hydrogenation, and hydrosilylation of unsaturated substrates. In addition, Thomas’s research team is exploring a new tetradentate PNNP-based ligand that contains two amide donors as potential sites for metal-ligand cooperativity. The coordination of this ligand to Fe, Co, and Mn and the stoichiometric reactivity of the resulting (PNNP)M compounds towards the activation of substrates such as hydrogen, silanes, and boranes across the two metal-amide bonds is under investigation, with the ultimate goal of incorporating these fundamental reaction steps into catalytic hydrofunctionalization reactions. Lastly, a newly discovered metal-templated procedure for the elimination and substitution of phosphine substituents will be leveraged to synthesize an expanded family of ligands, including tetradentate ligand derivatives that feature both phosphide and amide donors as potential reactive sites, PPP- and PNNP-based ligands with more electron-rich alkyl substituents, and tridentate and tetradentate ligands with P-chiral functionalities for use in asymmetric catalysis. The new synthetic method will provide researchers in the field with a new economical and straightforward method to synthesize large families of multidentate ligand derivatives including P-chiral variants without the need for expensive precursors.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.