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)MnIII (Cl)] in ligating solvents (CH3 CN, dimethyl sulfoxide, pyridine) results in formation of (TMP)MnII (≈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)MnIII (O2 )- . In nonligating solvents [CH2 Cl2 , (CH3 )2 CO], the reaction of HO- with (TMP)MnIII (Cl) yields (TMP)MnIV (OH)2 .