Ruthenium phenolates: synthesis, characterization and reactivities of a group of salicylaldiminato and 2-(arylazo)phenolato complexes of ruthenium

Abstract

Some ruthenium(II) complexes of type [Ru¹¹ (trpy)(L)Cl] [trey=2,2′:6′,2″-terpyridine ; L = salicylaldiminate and 2-(arylazo)phenolate anion] have been synthesized and characterized. The complexes are diamagnetic (low-spin d⁶, S = 0) and show intense metal-to-ligand charge transfer transitions in the visible region. Cyclic voltammetry of these complexes show a reversible ruthenium (II)-ruthenium(III) oxidation in the range 0.16-0.46 V vs saturated calomel electrode (SCE) and an irreversible ruthenium(III)-ruthenium(IV) oxidation near 1.5-1.6 V vs SCE. The ruthenium (II)-ruthenium (III) oxidation potential is sensitive to the nature of substituents on L. A reduction of coordinated trpy is also observed near -1.45 V vs SCE. Two representative [Ru^III(trpy)(L)Cl]⁺ complexes have been synthesized by chemical and electrochemical oxidation of their ruthenium(II) precursors and isolated as perchlorate salts. These oxidized complexes are paramagnetic (low-spin d⁵, S = ½) and show rhombic ESR spectra at 77 K. They show intense ligand-to-metal charge transfer transitions in the visible region and weak ligand-field transitions at lower energies. Aquo complexes of type [Ru^II(trpy)(L)(H₂O)]⁺ have been prepared by displacing Cl^- from [Ru^II(trpy)(L)CI] by Ag⁺ in aqueous medium.