Effect Of Axial Ligands On The Spectroscopic And Electrochemical Properties Of Diruthenium Compounds

Three related diruthenium complexes containing four symmetrical anionic bridging ligands were synthesized and characterized as to their electrochemical and spectroscopic properties. The examined compounds are represented as Ru-2(dpb)(4)Cl, Ru-2(dpb)(4)(CO), and Ru-2(dpb)(4)(NO) in the solid state, where dpb = diphenylbenzamidinate anion. Different forms of Ru-2(dpb)(4)Cl are observed in solution depending on the utilized solvent and the counteranion added to solution. Each Ru-2(5+) form of the compound undergoes multiple redox processes involving the dimetal unit. The reversibility as well as potentials of these diruthenium-centered electrode reactions depends upon the solvent and the bound axial ligand. The Ru-2(5+/4+) and Ru-2(5+/6+) processes of Ru-2(dpb)(4)Cl were monitored by UV-vis spectroscopy in both CH2Cl2 and PhCN. A conversion of Ru-2(dpb)(4)Cl to [Ru-2(dpb)(4)(CO)](+) was also carried out by simply bubbling CO gas through a CH2Cl2 solution of Ru-2(dpb)(4)Cl at room temperature. The chemically generated [Ru-2(dpb)(4)(CO)](+) complex undergoes several electron transfer processes in CH2Cl2 containing 0.1 M TBAClO(4) under a CO atmosphere, and the same reactions were seen for a chemically synthesized sample of Ru-2(dpf)(4)(CO) in CH2Cl2, 0.1 M TBAClO(4) under a N-2 atmosphere, where dpf = N,N'-diphenylformamidinate anion. Ru-2(dpb)(4)(NO) undergoes two successive one-electron reductions and a single one-electron oxidation, all of which involve the diruthenium unit. The CO and NO adducts of Ru-2(dpb)(4) were further characterized by FTIR spectroelectrochemistry, and the IR spectral data of these compounds are discussed in light of results for previously characterized Ru-2(dpf)(4)(CO) and Ru-2(dpf)(4)(NO) derivatives under similar solution conditions.