Electron-transfer properties of a series of bimetallic rhodium(I) and iridium(I) complexes

The electron-transfer properties of [NBu4][M2(dcbmi)(CO)4], [NBu4][M2(dcbmi)(cod)2], (M = Rh or Ir) and [NBu4][Rh2(dcbmi)(CO)2(PPh3) 2] (H3dcbmi = 2-methylimidazole-4,5-dicarboxylic acid, cod = cycloocta-1,5-diene) were determined by electrochemical UV/VIS and infrared spectroelectrochemical, and synthetic investigations. Relatively easy oxidations, but no reduction processes, were observed in acetonitrile, methylene chloride or tetrahydrofuran. The effect of the solvent on the electron-transfer properties of these complexes is discussed and the spectroelectrochemical results establish the site of electron transfer. Surface effects are observed and for [NBu4][Ir2(dcbmi)(CO)4] the growth of a conducting film has been monitored by cyclic voltammetry. Partial oxidation of [Ir2(dcmbi)(CO)4]- results in formation of [NR4]0.5[Ir2(dcbmi)(CO)4] (R = Bu or Pr). Isotropic conductivities, measured on pressed pellets at room temperature, were 8 × 10-5 ohm-1 cm-1 for R = Pr and 2 × 10-5 ohm-1 cm-1 for R = Bu. The synthesis of [ttf][Rh2(dcbmi)(CO)4] (ttf = tetrathiofulvalene) and the mixed-valence species [Rh2(dcbmi)(CO)4] is also reported; the former exhibits solid-state conductive properties, presumably due to the ttf cation.