The visible light-driven, catalytic aerobic oxidation of benzylic C-H bonds was mediated by a Mn-III corrolazine complex. To achieve catalytic turnovers, a strict selective requirement for the addition of protons was established. The resting state of the catalyst was unambiguously characterized by X-ray diffraction as [Mn-III((HO)-O-2)(TBP(8)Cz(H))](+), in which a single, remote site on the ligand is protonated. If two remote sites are protonated, however, reactivity with O-2 is shut down. Spectroscopic methods revealed that the related Mn-V(O) complex is also protonated at the same remote site at -60 degrees C, but undergoes valence tautomerization upon warming.