Electro-driven Dioxygenation of Indole by Iron Porphyrin with Faradaic Efficiency Exceeding 10 ⁴ %

The selective dioxygenation of indoles by heme enzymes is a significant biochemical process. Synthetic FeII porphyrins were used to catalyze indole dioxygenation, but the formation of μ-oxo-bridged FeIII–O–FeIII caused catalyst deactivation. Herein, we report a homogeneous electro-driven strategy to realize catalytic indole dioxygenation by Fe tetra(pentafluorophenyl)porphyrin with a turnover number up to 8825 and Faradaic efficiency exceeding 104%. In homogeneous catalysis, inert FeIII–O–FeIII, which is generated upon the oxidation of FeII porphyrin by FeIII-superoxo and/or FeIV═O, can be electrochemically reduced to FeII porphyrin to reinitiate catalysis. Moreover, we identified an intermediate formed between FeIII-superoxo and dimethylindole by in situ electrochemical mass spectrometry.