The dicationic clusters [(C5Me5)4Ir4S4] 2+ (2+) and [(C5Me5)3Ir3S2] 2+ (2+) were prepared by treatment of [(C5Me5)IrCl2]2 with (Me3Si)2S followed by ion exchange chromatography. Crystallographic characterization of the tetrairidium cluster 2+ reveals a cubane motif consisting of interpenetrated Ir4 and S4 tetrahedra. The Ir4 core is distorted from idealized tetrahedral symmetry by virtue of a single IrIV-IrIV bonding contact of 2.764(1) Å. The four IrIV-IrIII contacts are nearly equivalent at 3.5 Å, while the IrIII⋯IrIII distance is 3.683(1) Å. Variable-temperature 1H NMR studies indicate that [I]2+ is fluxional with a coalescence temperature of 13 °C (400 MHz), corresponding to ΔG‡ = 57 kJ/mol. This dynamic process is attributed to migration of the metal-metal bond arising from internal IrIV/IrIII self-exchange. Cyclic voltammetry studies of 2+ reveal a pair of reversible one-electron reductions at -218 and -487 mV vs Ag/AgCl. Chemical reduction of 2+ was effected with cobaltocene while the neutral cluster could be reoxidized with HC1/O2. In the solid state 2+ features a trigonal-bipyramidal Ir3S2 core with average Ir-Ir contacts of 2.82 Å and Ir-S distances of 2.28 Å. Cyclic voltammetry studies indicate that this closo dication undergoes two single electron reductions at -712 and -993 mV. Cobaltocene reduction of 2+ afforded dark blue crystals of neutral 0. Variable-temperature 1H NMR spectra of 0 reveal dynamic behavior, with coalescence at 60 °C (400 MHz), corresponding to ΔG‡ = 64 kJ/mol. These structural dynamics suggest migration of the nonbonding Ir⋯Ir interaction among the three edges of the Ir3 triangle.
ASJC Scopus subject areas
- Colloid and Surface Chemistry