Singly Reduced Iridium Chromophores: Synthesis, Characterization, and Photochemistry

Abstract

One-electron reduced photosensitizers have been invokedas crucialintermediates in photoredox catalysis, including multiphoton excitationand electrophotocatalytic processes. However, such reduced chromophoreshave been less investigated, limiting mechanistic studies of theirassociated electron transfer processes. Here, we report a total of11 different examples of isolable singly reduced iridium chromophores.Chemical reduction of a cyclometalated iridium complex with potassiumgraphite affords a 19-electron species. Structural and spectroscopiccharacterizations reveal a ligand-centered reduction product. Thereduced chromophore absorbs a wide range of light from ultravioletto near-infrared and exhibits photoinduced bimolecular electron transferreactivity. These studies shed light on elusive reduced iridium chromophoresin both ground and excited states, providing opportunities to investigatea commonly invoked intermediate in photoredox catalysis.