Chemistry of ruthenium. Part 8. new tris complexes of ruthenium(_III). Synthesis, spectra, and redox activity

Abstract

A group of new low-spin tris complexes of ruthenium(III) has been synthesized using triazene 1-oxides, RN(O)=N–NH–C₆H₄X-p(HL; R = Et or Ph, X = Me, H, Cl, CO₂Et, or NO₂) as ligands. The green to yellow-green complexes [RuL₃] are believed to have a meridional RuN₃O₃ co-ordination sphere. They display ligand, metal charge-transfer transitions in the region 550–750 nm. In acetonitrile solution the [RuL₃] complexes exhibit a quasi-reversible Ru^III–Ru^II couple (E₂₉₈°, –0.6 to –1.2 V vs. s.c.e.) and a nearly reversible Ru^IV–Ru^III couple (E₂₉₈°, 0.2–0.7 V vs. s.c.e.) at a platinum working electrode. The E₂₉₈° values of both couples correlate linearly with the Hammett constant of substituent X. The reaction constants lie in the range 0.1–0.2 V. The electronic spectra of [RuL₃]^– and [RuL₃]⁺ are briefly reported. The former complex is unstable.