Synthetic Tuning of Bio-Inspired Aminopyridine Complexes for CO2 Reduction

With support of the Chemical Mechanism, Function, and Properties Program and Chemical Catalysis Programs of the Division of Chemistry, Professor Smaranda C. Marinescu of the Department of Chemistry at the University of Southern California will study the development of biologically inspired catalytic systems for the electrochemical conversion of carbon dioxide into chemical fuels. The goal of the project is to develop a series of cobalt complexes with pendent amines and explore their electrochemical activity to understand the effect of proton relays on multi-electron, multi-proton reactions. The ligand framework allows for excellent control of electronic and positioning effects, as well as the number of proton relays incorporated in the second coordination sphere of the metal complex, which facilitate structure-activity studies. The project lies at the interface of synthetic inorganic and organic chemistry, as well as electrochemistry and catalysis, and is therefore well suited to provide the highest level of education and training for scientists at all levels. Previous studies in the Marinescu group have shown that a series of cobalt complexes with zero to four pendent secondary amines (NH) displays a linear correlation between the rate of CO2 reduction and the number of pendent NH moieties. Experiment and theory suggest that the pendent NH groups do not directly transfer protons to CO2, but instead bind acid molecules from solution, leading to the formation of a catalyst-acid adduct, held together through a hydrogen-bonding network, that enables direct proton transfer from acid to the activated CO2 substrate. The research goals of this proposal are to understand the factors that govern the catalytic properties of these complexes, in terms of activity and selectivity for CO2 reduction, by characterizing and changing the electronic environment (the primary and secondary coordination spheres) of these metal aminopyridine macrocycles. This project focuses on the synthesis and characterization of a variety of aminopyridine complexes with pendent hydrogen bond donors or cationic groups, to understand the effects of these moieties on the catalyst activity and selectivity. 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.