Visible light-induced formation of corrole-manganese(V)-oxo complexes: Observation of multiple oxidation pathways

Abstract

Two manganese(V)-oxo corroles [MnV(Cor)O] that differ in their electronic environments were produced by visible light irradiation of highly photo-labile corrole-manganese(IV) bromates. The corrole ligands under study include 5,10,15-tris(pentafluorophenyl)corrole (TPFC), and 5,10,15-triphenylcorrole (TPC). The kinetics of oxygen transfer atom (OAT) reactions with various organic reductants by these photo-generated MnV(Cor)O were also studied in CH3CN and CH2Cl2 solutions. MnV(Cor)O exhibits remarkable solvent and ligand effect on its reactivity and spectral behavior. In the more electron-deficient TPFC system and in the polar solvent CH3CN, MnV(Cor)O returned MnIII corrole in the end of oxidation reactions. However, in the less polar solvent CH2Cl2 or in the less electron-deficient TPC system, MnIV product was formed instead of MnIII. Furthermore, with the same substrates and in the same solvent, the order of reactivity of MnV(Cor)O was TPC>TPFC, which is inverted from that expected based on the electron-demand of corrole ligands. Our spectral and kinetic results in this study provide compelling evidence in favor of multiple oxidation pathways, where MnV(Cor)O may serve as direct two-electron oxidant or undergo a disproportionation reaction to form a manganese(VI)-oxo corrole as the true oxidant. The choice of pathways is strongly dependent on the nature of the solvent and the corrole ligand.