Carbon dioxide (CO₂) emissions have been connected to climate change, ocean acidification, and severe weather events. Therefore, sequestration of CO₂ from industrial processes and chemical transformation into value-added products remains a desirable goal. In this effort, catalysts are required to overcome the unfavorable thermodynamics of CO₂ reduction. Design of CO₂ reduction catalysts must be multi-dimensional regarding stability, product selectivity, efficiency and cost. An emerging area of interest in catalysis has been the combination of metal-ligand cooperativity (MLC) and redox noninnocence to address challenging small molecules such as CO₂. By binding substrates through both the metal center and attached ligand, MLC complexes offer exceptional tunability and utility for efficient catalysis; furthermore, addition of ligand centered redox activity has the potential to access new synthetic transformations. In this work, we explore the binding properties and redox activity of a series of Ru-based coordination complexes containing multifunctional noninnocent ligands through systematic modification of the ligand structure. Borane (BH₃) serves as a surrogate substrate, enabling fundamental binding and reactivity studies that will be extended and applied to CO₂chemistry. Electrochemically monitored titrations by cyclic voltammetry track BH₃-complex binding as a function of redox-activity. Interpretation of cyclic voltammetry data alongside corroborating density functional theory calculations and crystallographic data yields MLC binding constants for these complexes with BH₃. Ultimately, these results show how various ligand modifications affect MLC binding affinity, which can be valuable for tuning the binding properties of MLC coordination complexes for the application of catalysis. Future directions include applying knowledge from these fundamental studies to design and test MLC coordination complexes as CO₂ electrocatalysts. This work will come in the form of studies to understand the interaction of CO₂ with these complexes as well as bulk electrolysis experiments to perform CO₂ reduction coupled with product analysis.

Jason Keith

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