Initiation of Catalysis via Oxidative Quenching. With the possible Ni(II) complexes that may serve as quenchers of the Ir(ppy)3 excited state known, we set out to determine the nature of the reaction between these species. Using nanosecond transient absorption spectroscopy (ns-TA) in combination with electrochemical methods, we engaged in a mechanistic exploration of the quenching step. In the absence of a quencher, the photophysical characteristics of Ir(ppy)3 are well known; Normalized (to highest peak) difference spectra from spectroelectrochemical experiments in which Ir(ppy)3 was oxidized to Ir(IV) or a mixture of NiBr2•glyme and OMebpy (2 eq. relative to Ni) was reduced electrochemically, overlaid with the t = 10 µs ns-TA spectrum from the same experiment in (B). (E) Generalized mechanism for C-O bond formation. We note that when PC = Ir(ppy)3 the observed kinetics are consistent with a persistent ion pairing mechanism as described below (See Fig. and) that differs from this scheme. (F) PCs and structures used in this work. Rate constants measured in this work are reported with lowercase letters indicating the relevant mechanistic steps. Photoinduced electron transfer rates (kPET) were measured via Stern-Volmer quenching studies using ns-TA data, except for the singlet state quenching of PhenO, which used time-correlated single photon counting. a Bimolecular rate constants in M -1 s -1 , pseudo 1st order rate constants in s -1 . b Species being quenched in Stern-Volmer studies. The quencher was a mixture of NiBr2•glyme and OMebpy (2 eq. relative to Ni) unless otherwise indicated. For kOA the aryl halide was 4-iodobenzotrifluoride. The quencher was a mixture of NiBr2•glyme and OMebpy (1 eq. relative to Ni). d Observed pseudo 1st order rate constant from full reaction under standard conditions (See below, Fig. ). e Reoptimized conditions, see Fig. . See supporting information for additional details.