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

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The reaction of HO(-) with 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)porphinatomanganese(III) chloride [(TMP)Mn(III)(Cl)] in ligating solvents (CH(3)CN, dimethyl sulfoxide, pyridine) results in formation of (TMP)Mn(II) ( approximately 10(6) 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 O(2) at any time during these reactions leads to formation of the manganese(III) peroxide (TMP)Mn(III)(O(2))(-). In nonligating solvents [CH(2)Cl(2), (CH(3))(2)CO], the reaction of HO(-) with (TMP)Mn(III)(Cl) yields (TMP)Mn(IV)(OH)(2).