RUTHENIUM(II) COMPLEXES OF N,N'-BRIDGED DERIVATIVES OF 2,2'-BIIMIDAZOLE

Ruthenium(II) complexes of the type RuL3[PF6]2and RuL(bpy)2[PF6]2have been prepared where L is an N,N'-bridged derivative of 2,2'-biimidazole. Molecular mechanics calculations have been employed to compare the geometries of these ligands to those of analogous 2,2'-bipyridine systems. Analysis of 1H NMR spectra indicates that in the coordinated state the bridged biimidazoles show greater conformational mobility than their bipyridine counterparts. For the dimethylene-bridged biimidazole, the bite angle is too unfavorable to allow bidentate coordination and NMR evidence points to monodentate coordination in the mixed-ligand complex. The electronic spectra of the RuL32+complexes show absorption at about 400 nm, which indicates a high-lying π*state. This observation is reinforced by low oxidation potentials and high reduction potentials for these systems. The mixed-ligand complexes show an absorption band at even shorter wavelength, which we assign to the biimidazole MLCT state. The redox chemistry of these systems appears to be governed primarily by the bpy ligands. © 1990, American Chemical Society. All rights reserved.