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 Mn^III/II process and the second as electron addition to the π-ring system as confirmed by spectroelectrochemistry. Each Mn^III 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)DPPMn^III 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] where n = 0, -1, or +1 are also compared to that of other structurally related [(Ar)DPPM] complexes under similar solution conditions where M = Co^II, Cu^II, B^III, or Au^III.