Iridium(III) complexes comprised of one planar tridentate ligand such as 2,2′:6′,2′′-terpyridine, an ortho-metallated 2-phenyl pyridine ligand (ppy), and a mondentate labile ligand belong to a rare class of photocatalysts that reduce carbon dioxide without the usual requirement of an additional sensitizer. The catalysis is enabled partly by the mild overpotentials observed by cyclic voltammetry. This talk will focus on the derivative [Ir(pyridine-2,6-bis(benzimidazole)(ppy)(CH3CN)]2+ and detailed electrochemical investigation of the mechanisms of CO2 reduction to CO. In CH3CN, the catalyst is versatile and operates by at least five mechanisms depending on the potential, the protonation state of intermediates, and the role of CO2 or protons as the oxide acceptor. Selectivity for CO2 reduction over proton reduction is maintained at water concentrations up to 30%. The catalytic activity is compared to [Ir(pyridine-2,6-bis(benzimidazole)(bpy)(Cl)]2+, which is a poor catalyst but undergoes stoichiometric reactions with CO2.

Multifaced mechanisms of CO2 reduction to CO by iridium(III) phenyl-pyridine photo- and electro-catalysts

256th National Meeting (2018)

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