A major challenge for the reduction of CO2 remains the discovery of catalysts with efficient pathways to products beyond formate and CO. We are inspired by biological systems that utilize organic molecules to capture CO2 and affect sequential H+/e− transfers for reduction. Our strategy is to add design motifs into polypyridyl ligands on transition metal centers such that CO2 may bind to the ligand and be reduced through intra-ligand hydride transfers, as opposed to traditional pathways that involve direct interaction of CO2 at a metal center. Although the metal is not involved directly in CO2 reduction, it may still act as a scaffold to lock the ligand into a particular geometry, as a shuttle for rapid electron transfer, or to assist with light absorption to initiate photocatalytic pathways. We recently were able to synthesis and characterize several new Ru-polypyridyl complexes with ligand-centered reactivity for CO2 reduction. These complexes contain two 2,2′-bipyridine ligands and a third bidentate ligand that contains a pyridyl or quinolyl moiety for hydride formation and an amine for capturing CO2 through well-known acid-base interactions. Cyclic voltammetry of these complexes under Ar shows an irreversible reduction event, followed by a series of reversible ligand reductions. Under an atmosphere of CO2, sequential ligand reductions result in an irreversible peak of increased current, indicating a catalytic reaction between the complexes and CO2. In an attempt to gain insight into the mechanism, the amine functionality of the ligand was methylated to prevent reaction with CO2. Interestingly, it appears that CO2 may insert into the N−CH3 bond upon ligand reduction, and these complexes may still act as competent catalysts for the reduction of CO2. Studies are underway to determine the products and better understand the mechanism by which this occurs, as well as investigations into driving these processes photochemically.

New Ru complexes demonstrate ligand-centered reactivity for the reduction of CO2

255th National Meeting (2018)

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