Metal-Ligand and Metal-Metal Cooperativities as Design Principles for Base Metal Catalysis

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With funding from the Chemical Catalysis Program of the Chemistry Division, Dr. Hairong Guan of the University of Cincinnati is developing new catalysts for the synthesis of organic molecules. Catalysis reactions play indispensable roles in making new drugs and novel materials, reducing energy consumption, preventing chemical waste, and utilizing renewable feedstocks. Precious metals such as ruthenium, rhodium, palladium, iridium, and platinum are often used in catalytic reactions. However, they are expensive, limited in supply, and difficult to remove from the chemical products. To develop more sustainable syntheses, efforts are being directed at using base metals, which include iron, cobalt, nickel and copper, for catalysis. The difficulty is that catalysts derived from these metals are usually less reactive and more prone to decomposition. In this project, Dr. Guan is developing new catalysts featuring cooperativity between a metal and a ligand, or cooperativity between two metals. With this strategy, catalysts derived from inexpensive and abundant metals are more efficient and robust, mimicking the reactivity of their precious metal analogs. Dr. Guan develops research-based educational materials for an undergraduate laboratory course focusing on catalysis. He also provides research opportunities to students from groups that are underrepresented in the STEM fields, enhancing student professional development through his collaborations with the local chemical industry. This research enhances national welfare, by providing sustainable innovation in advanced chemical manufacturing, renewable energy and chemical industry. Dr. Guan is developing new strategies to design base metal catalysts with reactivity akin to the precious metal catalysts. Iron and copper complexes supported by tridentate ligands capable of transferring protons are synthesized and tested for catalytic hydrogenation of aldehydes, ketones, esters, amides, and carbon dioxide (CO2). Heterobimetallic complexes of Fe-Cu or Fe-Zn are prepared and used to catalyze reduction reactions under water-gas shift reaction conditions. These reactions may be relevant to industry, for example manufacturing of detergent alcohols. The catalysts may also have impact in the areas of carbon dioxide conversion and energy storage. Mechanistic studies are carried out for a better understanding of structure-reactivity relationships, particularly the synergy between ligand and metal or between two metals. In support of the broader impacts of the project, Dr. Guan is actively engaged in programs focusing on providing research opportunities to underrepresented STEM students including those at collaborating primarily undergraduate institutions and community colleges. Through research-based teaching and collaborations with local companies, Dr. Guan is assisting students to develop their creative and critical thinking skills and facilitating their career development.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.