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

Abstract

The cluster [Ir6(CO)13(C7H8)] (1) was synthesized from [Ir6(CO)16] and excess cycloheptatriene in refluxing toluene. In the solid state, the six iridium atoms define an octahedral metal cage, and one face is capped by the μ3-η2:η2:η2-C7H8 ligand, which is a six-electrondonor, through the three CC double bonds. Reaction of 1 with Na2CO3 in THF yields [Ir6(CO)12(C7H7)]- (2). In this octahedral anion, the cycloheptatrienyl ring is almost planar and is coordinated to a triangular face in the μ3-η2:η3:η2-fashion. Reaction of 1 or 2 with NaOH in THF yields [Ir6(CO)12(C7H8)]2- (3), in which a μ3-η2:η2:η2-C7H8 is also present. The 1H NMR spectra of 1 and 3 show five signals, which were assigned to the nonequivalent hydrogen atoms by bidimensional experiments. The spectrum of 2 shows a singlet, even at low temperature, in agreement with a highly fluxional ligand. The interconversions of 1 to the anions 2 and 3, respectively, have been followed by electrochemical investigations. The neutral [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 undergoes a two-electron oxidation, which followed by deprotonation affords the monoanion [Ir6(CO)12(C7H7)]-.