Understanding the Reactions of Carbon Dioxide with Late Transition Metal Complexes

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The conversion of carbon dioxide (CO2) into more valuable compounds is an important goal due to the potential of this waste product as a readily available, sustainable, non-toxic, and inexpensive chemical feedstock. Catalysts based on transition metals, such as nickel or palladium, show promise speeding up the reactions of carbon dioxide so that they are practical, but improvements in efficiency are required for further implementation. In this project, Dr. Hazari of Yale University is developing an understanding of how carbon dioxide interacts with a variety of transition metal complexes using both experimental and computational techniques. This knowledge is crucial for the design of improved systems for carbon dioxide utilization as it will provide information on how to modify the catalyst as well as how to improve the conditions under which reactions are performed (temperature, pressure, etc.). This research has potential to increased selectivity so that only desired products are formed. The research is complemented by Dr. Hazari’s involvement in a series of outreach activities related to carbon dioxide utilization. These activities focus on students from underrepresented minorities in science, technology, engineering and mathematics (STEM) disciplines. The activities include a one week summer program on energy for high school students in the New Haven area and opportunities for undergraduates to perform research in Dr. Hazari’s laboratory. With funding from the Chemical Structure, Dynamics, and Mechanisms B (CSDM-B) Program of the Chemistry Division, Dr. Hazari from Yale University is developing a fundamental understanding of the insertion of carbon dioxide into late-transition metal bonds. This research provides guidance about the design of catalysts and optimization of reaction conditions for processes involving carbon dioxide utilization. Specifically, the rates of carbon dioxide insertion into Group 10 pincer-supported transition metal hydrides, hydroxides, alkyls, and aryls are being measured. Factors that are being probed include the effects of the metal center, ancillary ligand, solvent, and additives, such as Lewis acids, on the kinetics of carbon dioxide insertion. A major focus is the development of scaling relationships that correlate the rate of carbon dioxide insertion into a metal hydride (a kinetic property), with the hydricity of transition metal hydrides, a thermodynamic property. This enables the evaluation of hypotheses relating to whether secondary coordination sphere effects such as hydrogen bonding or electrostatic effects that stabilize the transition state for carbon dioxide insertion. Density Functional Theory calculations are carried out in parallel with the experimental work and probe the structure of the transition states, determine the geometries of unstable intermediates, and measure hydricity.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.