Iridium(III) complexes supported by a planar tridentate ligand such as 2,2′:6′,2′′-terpyridine (tpy) and an ortho-metallated 2-phenyl pyridine ligand (ppy) represent a rare class of catalysts that reduce carbon dioxide photochemically without the usual requirement of an added photosensitizer. The catalysis is enabled partly by the mild redox potentials observed by cyclic voltammetry. This talk will explore mechanistic aspects of catalysis using [Ir(tpy)(ppy)(CH3CN)]2+ and the derivative [Ir(pyridine-2,6-bis(benzimidazole)(ppy)(CH3CN)]2+ deduced from electrochemical investigations, CO2 binding studies, and infrared spectroelectrochemistry. In CH3CN, the catalysts are versatile and operate with several 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 proposed mechanisms are supported by DFT calculations.

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

2019 Spring National Meeting

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