Solvent and Anion Effects on the Electrochemistry of Manganese Dipyrrin-Bisphenols

A series of “N2O2-type” manganese dipyrrin-bisphenols (DPP), formulated as (Ar)­DPPMn, where Ar = pentafluorophenyl (F5Ph), phenyl (Ph), or mesityl (Mes), were electrochemically and spectroscopically characterized in nonaqueous media with and without added anions in the form of tetrabutylammonium salts (TBAX where X = ClO4 –, PF6 –, BF4 –, F–, Cl–, OH–, or CN–). Two major one-electron reductions are observed under most solution conditions, the first of which is assigned as a MnIII/II process and the second as electron addition to the π-ring system as confirmed by spectroelectrochemistry. Each MnIII complex also exhibits one or two one-electron oxidations, the exact number depending upon the positive potential limit of the electrochemical solvent. The two oxidations are separated by 580–590 mV in CH3CN containing 0.1 M TBAPF6 and are assigned as π-ring-centered electron transfers to stepwise form a (Ar)­DPPMnIII π-cation radical and dication under these solution conditions. Comparisons are made between redox properties of (Ar)­DPPMn and manganese­(III) porphyrins, corroles, and corrolazines each of which contains an innocent trianionic complexing ligand. The redox behavior and spectroscopic properties of [(Ar)­DPPMn] n where n = 0, −1, or +1 are also compared to that of other structurally related [(Ar)­DPPM] n complexes under similar solution conditions where M = CoII, CuII, BIII, or AuIII.