Interaction of tris(2,2′-bipyrazine)ruthenium(2+) ion with radiolytically-generated radicals in aqueous solution. Reactivity of Ru(bpz) +3 toward electron relays

Abstract

The one-electron reduction of Ru(bpz) 2+ 3 by (CH 3) 2ḢOH is rapid ( k = 3.5 × 10 9 M -1 s -1) and quantitative. The product of the reaction, which possesses a ligand-radical coordinated to a Ru(II) center, can be written generically as Ru(bpz) + 3, and represented as Ru(bpz) 2( .bpz -) + in alkaline solution and its conjugate acid [Ru(bpz) 2( .bpzH) 2+; p K a = 7.1] in acidic solution. The reaction of Ru(bpz) 2+ 3 with .OH ( k = 5.5 × 10 9 M -1 s -1) yields the OH-adduct to the ring system of the ligands; Ru(bpz) 2( .bpzOH) 2+ is unstable toward bimolecular decay ( k ∼4× 10 8 M -1 s -1). Reaction with H . ( k = 3 × 10 9 M -1 s -1) results in hydrogenation at a ring-carbon; this product is unstable in the time frame of seconds. No reaction is observed between Ru(bpz) 2+ 3 and Cl -. 2. Ru(bpz) 2( .bpz -) + reduces Co(sep) 3+ ( k = 3.3 × 10 5 M -1 s -1) at pH 10, but there is no reaction at pH 4. However, Ru(bpz) 2( .bpzH) 2+ establishes an electron-transfer equilibrium ( K eq = 7) with Cr(bpy) 3+ 3 at pH 3.