Synthesis, physicochemical and electrochemical properties of metal–metal bonded ruthenium corrole homodimers

Two diruthenium(III,III) corrole dimers, [(Et6Me2Cor)Ru]2 and [(Me6Et2Cor)Ru]2, where Et6Me2Cor and Me6Et2Cor are the 2,3,8,12,17,18-hexaethyl-7,13-dimethylcorrole and 8,12-diethyl-2,3,7,13,17,18-hexamethylcorrole trianions, respectively, were synthesized and characterized as to their spectroscopic and electrochemical properties. They exhibit up to three oxidations and two reductions by cyclic voltammetry in CH2Cl2 or pyridine containing 0.1 M TBAP, almost all of which are electrochemically reversible on the voltammetric and/or thin-layer spectroelectrochemical timescale. The two reductions and the first two oxidations involve one-electron transfer processes which are separated from each other by 770–880 mV upon reduction and by 350–420 mV upon oxidation. The UV–vis spectroelectrochemical data suggest that the first two one-electron oxidations occur at the diruthenium metal centers while the third oxidation (seen only in CH2Cl2) is proposed to be macrocycle-based, leading to the formation of a Ru2(IV,IV) corrole species. The formation of a Ru(III,IV) complex after abstraction of one electron is also suggested by the rhombic ESR spectrum of singly oxidized [(Me6Et2Cor)Ru]2 at 77 K. The first one-electron reduction is also assigned as metal-centered and leads to the formation of a Ru2(III,II) complex. Finally, a comparison of electrochemical properties between the investigated diruthenium(III,III) corroles and an earlier characterized diruthenium(II,II) octaethylporphyrin, [(OEP)Ru]2, is presented.