The synthesis and electrochemical behavior of ruthenium(III) bipyridine complexes: [Ru(dcbpy)Cl 4] − (dcbpy = 4,4′-dicarboxylic acid-2,2′-bipyridine) and [Ru(bpy)Cl 3L] (L = CH 3OH, PPh 3, 4,4′-bpy, CH 3CN)

Abstract

The ruthenium(III) complexes [Ru(L 1)Cl 4] − (L 1 = 2,2′-bipyridine (bpy, 1) or 4,4′-dicarboxylic acid-2,2′-bipyridine (dcbpy, 2)) and [Ru(bpy)Cl 3(L 2)] (L 2 = methanol (MeOH, 3), triphenylphosphine (PPh 3, 4), 4,4′-bipyridine (4,4′-bpy, 5) or acetonitrile (CH 3CN, 6)) were synthesized, and structurally characterized by single-crystal X-ray crystallography. Substitution of methanol ligand in complex 3 by other neutral ligands was exploited in the synthesis of complexes 4– 6. The methanol ligand was found to be more labile than the other studied ligands. This feature makes [Ru(bpy)Cl 3(MeOH)] a potential starting compound for the synthesis of series of Ru(III) bipyridine complexes under mild reaction conditions. It was found that in acetonitrile solutions the lability of ligands toward solvent coordination follows the order MeOH = 4,4′-bpy > Cl − > PPh 3. The redox properties of complexes 1– 6 were studied by means of cyclic voltammetry (CV). In acetonitrile solution, the reversible metal-based Ru(III)–Ru(IV) oxidation couples ( E 1/2 = 0.69−1.77 V vs. Ag/Ag +) were observed, and the Ru(III)–Ru(II) reductions were mainly reversible in nature. The CV studies showed the convergence of the voltammograms of 1–3, and of 5 with the voltammogram of acetonitrile complex 6. The methanol ligand in 3, and 4,4′-bipyridine ligand in 5 were rapidly exchanged with acetonitrile. In the case of the complexes 1 and 2, the substitution of chlorides took place more slowly. However, the voltammetric differences of complexes 4 and 6 suggest that a mixture of solvent coordination products was formed. Depending on the choice of the adjacent ligands in the Ru(bpy)Cl 3L moieties, the solvent coordination reactions with ruthenium(III) bipyridines can be directed towards the desired products.