ELECTROCHEMICAL REDUCTION OF (2,2'-BIPYRIDINE) AND BIS((2-PYRIDYL)PYRAZINE)RUTHENIUM(II) COMPLEXES USED AS BUILDING-BLOCKS FOR SUPRAMOLECULAR SPECIES - REDOX SERIES MADE OF 8, 10, AND 12 REDOX STEPS

The electrochemical reduction of the [Ru(2,3-dpp)n(bpy)3-n]2+ complexes (n = 1-3), which are extensively used as building blocks for the synthesis of polynuclear compounds, has been investigated at -54-degrees-C in DMF solution up to a limit of -3.1 V vs SCE (dpp is the potential bridging ligand bis(2-pyridyl)pyrazine and bpy is 2,2'-bipyridine). For comparison purposes, the electrochemical behavior of the free 2,3-dpp ligand has also been investigated. The results obtained have been discussed and compared with those previously reported for bpy and Ru(bpy)3(2+). Convolutive analysis and simulation of the cyclic voltammetric curves have been performed to obtain the redox potentials in the case of overlapping waves. [Ru(2,3-dpp)3]2+, [Ru(2,3-dpp)2(bpy)]2+, and [Ru(2,3-dpp)(bpy)2]2+ display 12, 10, and 8 reduction steps, respectively, in the potential window examined. The corresponding redox series are thus noticeably more extended than those exhibited by [Ru(bpy)3]2+ and related complexes not containing bridging-type ligands. The analysis of the genetic diagram which relates the redox potentials observed for 2,3-dpp, [Ru(2,3-dpp)3]2+, [Ru(2,3-dpp)2(bpy)]2+, [Ru(2,3-dpp)(bpy)2]2+, [Ru(bpy)3]2+, and bpy shows that each redox step in the metal complexes is essentially localized on a specific ligand. A satisfactory assignment of the redox sites has been proposed, and their mutual interactions have been discussed. The results obtained show that in order to arrive at a satisfactory assignment of the redox series for a complex containing redox-active ligands a comparison with the behavior of complexes of the same family is as much instructive as a comparison with the behavior of the free ligands.