Different Bonding Modes of the C₇ Ring on Iridium\nClusters. Synthesis, Electrochemistry, and Solid State\nStructure of [Ir₆(CO)₁₃(μ₃-η²:η²:η²-C₇H₈)],\n[Ir₆(CO)₁₂(μ₃-η²:η³:η²-C₇H₇)]^-, and\n[Ir₆(CO)₁₂(μ₃-η²:η²:η²-C₇H₈)]^2-

Abstract

The cluster [Ir₆(CO)₁₃(C₇H₈)] (<b>1</b>) was synthesized from [Ir₆(CO)₁₆] and excess cycloheptatriene in refluxing toluene. In the solid state, the six iridium atoms define an octahedral\nmetal cage, and one face is capped by the μ₃-η²:η²:η²-C₇H₈ ligand, which is a six-electrondonor,\nthrough the three CC double bonds. Reaction of <b>1</b> with Na₂CO₃ in THF yields\n[Ir₆(CO)₁₂(C₇H₇)]^- (<b>2</b>). In this octahedral anion, the cycloheptatrienyl ring is almost planar\nand is coordinated to a triangular face in the μ₃-η²:η³:η²-fashion. Reaction of <b>1</b> or <b>2</b> with\nNaOH in THF yields [Ir₆(CO)₁₂(C₇H₈)]^2- (<b>3</b>), in which a μ₃-η²:η²:η²-C₇H₈ is also present. The\n¹H NMR spectra of <b>1</b> and <b>3</b> show five signals, which were assigned to the nonequivalent\nhydrogen atoms by bidimensional experiments. The spectrum of <b>2</b> shows a singlet, even at\nlow temperature, in agreement with a highly fluxional ligand. The interconversions of <b>1</b> to\nthe anions <b>2</b> and <b>3</b>, respectively, have been followed by electrochemical investigations. The\nneutral [Ir₆(CO)₁₃(C₇H₈)] proves to undergo a two-electron reduction, which, being accompanied by decarbonylation, affords the dianion [Ir₆(CO)₁₂(C₇H₈)]^2-. In turn, the latter\nundergoes a two-electron oxidation, which followed by deprotonation affords the monoanion\n[Ir₆(CO)₁₂(C₇H₇)]^-.