Relevance of the reaction of a manganese(III) chelate with hydroxide ion to photosynthesis: Reaction of hydroxide ion with 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)porphinatomanganese(III) in ligating and nonligating solvents

The reaction of HO^- with 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)porphinatomanganese(III) chloride [(TMP)Mn^III(Cl)] in ligating solvents (CH₃CN, dimethyl sulfoxide, pyridine) results in formation of (TMP)Mn^II (≈10⁶ M^-1·s^-r), which in a slower reaction is converted to a product whose structure is suggested to be that of a porphyrin manganese(III) peroxo dimer. Admittance of O₂ at any time during these reactions leads to formation of the manganese(III) peroxide (TMP)Mn^III(O₂)^-. In nonligating solvents [CH₂Cl₂, (CH₃)₂CO], the reaction of HO^- with (TMP)Mn^III(Cl) yields (TMP)Mn^IV(OH)₂.