Therefore, we undertook a detailed mechanistic study of the system described in Fig. , finding that the photo-reduction of Ni(II) to Ni(I) by the Ir(ppy)3 excited state can be directly observed. Further, we have characterized the nickel-bipyridine complexes formed in this system, studied their reactivity with excited state Ir(ppy)3, found evidence to support oxidative Figure . Schemes describing an energy transfer (A), reductive quenching (B), or oxidative quenching (C) initiated catalytic cycle with examples given that include detailed experimental support for the proposed quenching events. PC = photocatalyst. Sac = sacrificial reductant. TOF = turnover frequency. addition of aryl halides at Ni(I) as well as the existence of a 'dark' Ni(I)/Ni(III) cycle, and discovered that bromide and iodide anions are oxidized by Ir(IV) to aid in photocatalyst turnover. Intriguingly, the observed kinetics following the photo-reduction event were best fit with a model invoking a persistent heteronuclear Ni(I)/Ir(IV) ion pair. These findings have enabled us to advance this system and achieve improved reactivity and scope with aryl chloride coupling partners.