Spectroelectrochemical characterization of meso triaryl-substituted Mn(IV), Mn(III) and Mn(II) corroles. Effect of solvent and oxidation state on UV- visible spectra and redox potentials in nonaqueous media

Two series of substituted manganese triarylcorroles were synthesized and characterized as to their electrochemical and spectroelectrochemical properties in CH2Cl2, CH3CN and pyridine. The investigated compounds are represented as (YPh)(3)CorMn(III) and (YPh)(3)CorMn(IV)Cl, where Cor is a trianion of the corrole and Y is a Cl, F, H or CH3 para-substituent on the three phenyl rings of the macrocycle. Each neutral Mn(III) corrole exists as a four-coordinate complex in CH2Cl2 and CH3CN and as a five-coordinate species in pyridine. (YPh)(3)CorMn(III) undergoes two oxidations to stepwise generate a Mn(IV) corrole and a Mn(IV) pi-cation radical. It also undergoes one reduction to generate a Mn(II) corrole in CH2Cl2 or CH3CN. In contrast, the reduction of (YPh)(3)CorMn(III) leads to a Mn(III) corrole pi-anion radical in pyridine. One oxidation is observed for (YPh)(3)CorMn(IV)Cl in CH2Cl2 and CH3CN to generate a Mn(IV) corrole pi-cation radical while Mn(III) and Mn(II) corroles are stepwise formed after reduction of the same compound. The second reduction of (YPh)(3)CorMn(IV)Cl in pyridine gives a Mn(III) pi-anion radical as opposed to a Mn(II) corrole with an unreduced pi-ring system. The neutral, reduced and oxidized forms of each corrole were characterized by electrochemistry and UV-visible spectroelectrochemistry and comparisons are made between the UV-visible spectra and redox potentials of the compounds in different central metal oxidation states. An overall reduction/oxidation mechanism in the three solvents is proposed.