In contrast, at low Ni loadings (e.g. 0.2 mM), the calculated quantum yield suggests that PhenO should exceed the performance of Ir(ppy)3 in the oxidative quenching step as ΦPET values for Ir MLCT and 3 PhenO are 0.26 (all from T1) and 0.90 (all from T1), respectively. Indeed, we observed a modest increase in conversion when PhenO was used as compared with the Ir PC at Ni concentrations of 2 mM, 0.2 mM and 0.02 mM (See SI, Section 6.2). Since the overall reaction performance at this Ni loading is poor, we suspect that another step is limiting reaction progress, most likely oxidative addition.