Identifying Intermediates in Electrocatalytic Water Oxidation with a Manganese Corrole Complex

Water nucleophilic attack (WNA) on high-valent terminal Mn-oxo species is proposed for O-O bond formation in natural and artificial water oxidation. Herein, we report an electrocatalytic water oxidation reaction with Mn^IIItris(pentafluorophenyl)corrole (1) in propylene carbonate (PC). O₂was generated at the Mn^V/IVpotential with hydroxide, but a more anodic potential was required to evolve O₂with only water. With a synthetic Mn^V(O) complex of 1 , a second-order rate constant,k₂(OH^-), of 7.4 × 10³M^-1s^-1was determined in the reaction of the Mn^V(O) complex of 1 with hydroxide, whereas its reaction with water occurred much more slowly with ak₂(H₂O) value of 4.4 × 10^-3M^-1s^-1. This large reactivity difference of Mn^V(O) with hydroxide and water is consistent with different electrocatalytic behaviors of 1 with these two substrates. Significantly, during the electrolysis of 1 with water, a Mn^IV-peroxo species was identified with various spectroscopic methods, including UV-vis, electron paramagnetic resonance, and infrared spectroscopy. Isotope-labeling experiments confirmed that both O atoms of this peroxo species are derived from water, suggesting the involvement of the WNA mechanism in water oxidation by a Mn complex.