Synthesis, characterization and reactivity of a ruthenium-quinone complex

Abstract

A mixed ligand ruthenium-quinone complex, Ru(trpy)(DBQ)Cl [trpy = 2,2′: 6′,2″-terpyridine, DBQ = 3,5-di-tert-butylquinone] has been synthesized. The complex is paramagnetic (1 upe) and shows a sharp EPR signal at g ≈ 2. A Ru^II-DBSQ [DBSQ = semiquinonate form of DBQ] charge distribution is therefore assigned to this complex. It shows intense absorption bands in the visible and near-infrared regions which are assigned to allowed charge-transfer transitions. In dichloromethane solution it shows three reversible cyclic voltammetric responses, one ruthenium(II)-ruthenium(III) oxidation and the reductions of DBSQ and trpy ligands. The chloride ligand in Ru(trpy)(DBSQ)Cl can be replaced in aqueous medium by reacting it with Ag⁺to afford the [Ru(trpy)(DBSQ)(H₂O]⁺ ioin, which has been isolated and characterized as the perchlorate salt. This aquo complex is easily converted back to the parent chloro complex by reaction with the chloride ion.