Different bonding modes of the C-7 ring on iridium clusters: Synthesis, electrochemistry, and solid state structure of [Ir-6(CO)(13)(mu(3)-eta(2):eta(2):eta(2)-C7H8)], [Ir-6(CO)(12)(mu(3)-eta(2):eta(3):eta(2)-C7H7)](-), and [Ir-6(CO)(12)(mu(3)-eta(2):eta(2):eta(2)-C7H8)](2-)

The cluster [Ir 6 (CO) 1 3 (C 7 H 8 )] (1) was synthesized from [Ir 6 (CO) 1 6 ] 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 η 3 -η 2 :η 2 :η 2 -C 7 H 8 ligand, which is a six-electrondonor, through the three C=C double bonds. Reaction of 1 with Na 2 CO 3 in THF yields [Ir 6 (CO) 1 2 (C 7 H 7 )] - (2). In this octahedral anion, the cycloheptatrienyl ring is almost planar and is coordinated to a triangular face in the μ 3 -η 2 :η 3 :η 2 -fashion. Reaction of 1 or 2 with NaOH in THF yields [Ir 6 (CO) 1 2 (C 7 H 8 )] 2 - (3), in which a η 3 -η 2 :η 2 :η 2 -C 7 H 8 is also present. The 1 H 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 [Ir 6 (CO) 1 3 (C 7 H 8 )] proves to undergo a two-electron reduction, which, being accompanied by decarbonylation, affords the dianion [Ir 6 (CO) 1 2 (C 7 H 8 )] 2 - . In turn, the latter undergoes a two-electron oxidation, which followed by deprotonation affords the monoanion [Ir 6 (CO) 1 2 (C 7 H 7 )] - .