Preparation and electrochemical properties of novel cyclic dinuclear acetylacetonato ruthenium complexes doubly bridged with sulfur and/or disulfur

A novel cyclic dinuclear acetylacetonato ruthenium complex doubly bridged with sulfur and/or disulfur at the γ-position of acetylacetonato ligand has been obtained by two different synthetic methods. The molecular structure of the dinuclear complex has been determined by single crystal X-ray diffraction study. Other two cyclic dinuclear β-diketonato ruthenium complexes were also prepared in good yields by the reaction of single bridged dinuclear complexes as starting materials with disulfur dichloride. The cyclic voltammograms of all the dinuclear complexes exhibit two one-electron reduction and oxidation waves in acetonitrile (AN) and dichloromethane (DM). The comproportionation constants (Kc) for mixed-valence state of both RuII/RuIII and RuIII/RuIV were evaluated in both solvents at 25 or −30 °C. The values of both Kc (RuII/RuIII) and log10 Kc (RuIII/RuIV) for double bridged complex are large compared to those of corresponding single bridged complexes. This fact was rationally explained by the double bridging effect caused by the spread of electronic communication and also demonstrated the usefulness of the double bridged dinuclear complexes.