Synthesis and Reductive Electropolymerization of Metal Complexes with 5,5′-Divinyl-2,2′-Bipyridine

Eight transition-metal complexes with 5,5′-divinyl-2,2′-bipyridine (5,5′-dvbpy) or 4,4′-divinyl-2,2′-bipyridine (4,4′-dvbpy) have been synthesized and studied. The ruthenium complexes [Ru(5,5′-dvbpy)(bpy)2]2+, [Ru(5,5′-dvbpy)(4,4′-dpbpy)2]2+, and [Ru(5,5′-dvbpy)(5,5′-dpbpy)2]2+ (bpy = 2,2′-bipyridine; dpbpy = diphenyl-2,2′-bipyridine) with one 5,5′-dvbpy ligand have been successfully deposited on electrode surfaces by reductive electropolymerization. The resulting films are stable and adherent and show well-defined redox processes. In contrast, the complex [Ru(4,4′-dvbpy)(bpy)2]2+ does not polymerize under the same conditions. Complexes [Ru(5,5′-dvbpy)2(bpy)]2+ and [Ru(5,5′-dvbpy)3]2+ with two or three 5,5′-dvbpy ligands have been polymerized as well. As a result of increasing degrees of entanglement, the resulting polymeric films show larger charge-trapping currents and smaller apparent diffusion constants than films of [Ru(5,5′-dvbpy)(bpy)2]2+. The electrochemical properties of the iridium complex [Ir(5,5′-dvbpy)(ppy)2]+ (ppy = 2-phenylpyridine) and the rhenium complex [Re(5,5′-dvbpy)(CO)3Cl] have been studied. The former complex can be polymerized, but the films show an irreversible anodic process. The latter complex does not polymerize under the same conditions. Additionally, characterizations of the above polymeric films using FTIR, SEM, and spectroscopic techniques are presented.