Effect of Axial Ligands on the Spectroscopic and Electrochemical Properties of Diruthenium Compounds

Abstract

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 Ru2(dpb)4Cl, Ru2(dpb)4(CO), and Ru2(dpb)4(NO) in the solid state, where dpb = diphenylbenzamidinate anion. Different forms of Ru2(dpb)4Cl are observed in solution depending on the utilized solvent and the counteranion added to solution. Each Ru2(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 Ru2(5+/4+) and Ru2(5+/6+) processes of Ru2(dpb)4Cl were monitored by UV-vis spectroscopy in both CH2Cl2 and PhCN. A conversion of Ru2(dpb)4Cl to [Ru2(dpb)4(CO)](+) was also carried out by simply bubbling CO gas through a CH2Cl2 solution of Ru2(dpb)4Cl at room temperature. The chemically generated [Ru2(dpb)4(CO)](+) complex undergoes several electron transfer processes in CH2Cl2 containing 0.1 M TBAClO4 under a CO atmosphere, and the same reactions were seen for a chemically synthesized sample of Ru2(dpf)4(CO) in CH2Cl2, 0.1 M TBAClO4 under a N2 atmosphere, where dpf = N,N'-diphenylformamidinate anion. Ru2(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 Ru2(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 Ru2(dpf)4(CO) and Ru2(dpf)4(NO) derivatives under similar solution conditions.

Structural, spectroscopic and theoretical studies of a diruthenium(II,II) tetraformamidinate that reversibly binds dioxygen

“…The reversible reaction with dioxygen suggests that it is axially binding to the complex, rather than generating mono-or di-nuclear oxo products. This is similar to the observed reactivity of diruthenium tetraformamidinate with CO previously by reported by Bear and Kadish [10,15].…”

“…However, diruthenium paddlewheel compounds supported by N,N donor ligands are more resistant to decomposition. For example, Ru 2 (dpf) 4 Cl and Ru 2 (dpf) 3 (O 2 CMe)Cl (dpf = N,N'-diphenyformamidinate) react with one or two equivalents of NO (g) CO (dpb = N,N'-diphenylbenzamidinate) have been obtained [10,15]. They display long Ru-Ru bond distances (2.5544(8) Å and 2.4789(8) Å respectively) indicating that the σ 2 π 4 δ 2 π *4 electronic configuration has been retained by the diruthenium core.…”

Drastic Tuning of the Electronic Structures of Diruthenium Aryl Complexes by Isoelectronic Axial Ligands

“…This is particularly remarkable in a Ru 2 (II,III) complex because all other known examples of Ru 2 (II,III) and Ru 2 (II,II) species bearing axial CO adducts respectively exhibit ν CO values of ca. 2016 and 1926 cm –1 (averages). − Accordingly, the C–O bond in 4 [1.146(2) Å] is slightly longer than that of free CO (1.128 Å) due to dπ–π back-donation and is the same as that determined for Ru 2 (DPhF) 4 (CO) [1.148(11) Å]. Electrochemical and IR spectroscopic data for known Ru 2 n + ( n = 3–5) complexes with axial CO ligands are given in Table S6.…”

Ultrasound-assisted synthesis of water-soluble monosubstituted diruthenium compounds

“…All the complexes show only one-electron redox couple within the cathodic limit of water. This is assigned to the Ru 2 5+ /Ru 2 4+ redox couple according to other diruthenium complexes with similar ligands in aqueous and nonaqueous solvents [48] , [49] , [58] , [66] , [67] , [68] , [69] , [70] , [71] , [72] . The redox properties of these compounds vary depending on the nature of the ligand.…”