Electrochemistry in liquid sulfur dioxide. 3. Electrochemical production of new highly oxidized 2,2'-bipyridine complexes of ruthenium and iron

The electrochemical oxidation of R ~ ( b p y ) ~ ~ + and Fe(bpy)32+ in liquid sulfur dioxide was investigated. Ru(bpy),2+ shows two oxidation waves corresponding to the 3+ (1.01 V) and 4+ (2.76 V) forms while Fe(bpy),*+ undergoes three oxidations to the 3+ (0 .70 V), 4+ (2.92 V), and 5+ ( -3 .09 V) forms. While the 3+ form is stable. for both compounds on a coulometric time scale, the higher oxidation states react with solvent to regenerate the 3+ form. The kinetics of this reaction was studied as a function of temperature by cyclic voltammetry, chronocoulometry, and chronoamperometry. Introduction Liquid sulfur dioxide containing a suitable electrolyte (e.g., tetra-n-butylammonium perchlorate, TBAP) has been shown to be a useful solvent for electrochemical studies, especially in the region of very positive potentials where strongly oxidizing species can exist.',* Thus the limit for background oxidation with 0.1 0002-7863/82/ 1504-6373$01.25/0