Electrochemistry and Spectroscopy of Sulfate Complexes of (Tetraphenylporphyrinato)manganese

The electrochemical and spectroscopic properties of [Mn2(tpp)2(SO4)] (H2tpp=tetraphenylporphyrin=5,10,15,20-tetraphenyl-21H,23H-porphine) were studied to characterize the stability of this compound as a function of solvent, redox state, and sulfate concentration. In non-coordinating solvents such as 1,2-dichloroethane, the dimer was stable, and two cyclic voltammetric waves were observed in the region for MnIII reduction. These waves correspond to reduction of the dimer to [MnII(tpp)] and [MnIII(tpp)(OSO3)]−, and reduction of [MnIII(tpp)(OSO3)]− to [MnII(tpp)(OSO3)]2−, respectively. In the coordinating solvent DMSO, [Mn2(tpp)2(SO4)] was unstable and dissociated to form [MnIII(tpp)(DMSO)2]+. A single voltammetric wave was observed for MnIII reduction in this solvent, corresponding to formation of [MnII(tpp)(DMSO)]. In non-coordinating solvent systems, addition of sulfate (as the bis(triphenylphosphoranylidene)ammonium (PPN+) salt) resulted in dimer dissociation, yielding [MnIII(tpp)(OSO3)]−. Reduction of this monomer produced [MnII(tpp)(OSO3)]2−. In DMSO, addition of SO led to displacement of solvent molecules forming [MnIII(tpp)(OSO3)]−. Reduction of this species in DMSO led to [MnII(tpp)(DMSO)].