Electrochemical investigation of a rotationally flexible bibenzimidazole di-iron complex

Ligand systems used for electrochemical reductions commonly comprise single metal centres. This is opposed to complexes with two or more adjacent metals for which are significantly less studied. In order to fill this gap a Fe dimer embedded into the 1,1’,5,5’,6,6’-hexamethyl-4,4’-bis(picolinimino)-2,2’-bibenzimidazole ( Me bpbbi ) ligand system is studied in the present work with focus on electrochemical properties in acetonitrile solution. A combination of cyclic voltammetry and density functional theory (DFT) reveals that the complex is present at least as an open, non-bridged, and a closed, (µ-Cl) 2 bridged complex. Both forms possess very different redox properties and ligand exchange energetics. The presence of a stable reversible electron transfer couple for the non-bridged complex is promising for electrocatalytic reactions. Surprisingly, our calculations demonstrate that the iron ions essentially maintain their charge while the ligand accommodates the charges involved in the different redox steps.