Mobile Metal-Metal Bonds: Studies on Mixed Valence Ir3 and Ir4 Clusters

Anne Venturelli, Thomas B. Rauchfuss

Research output: Contribution to journalArticlepeer-review


The dicationic clusters [(C5Me5)4Ir4S4] 2+ ([1]2+) and [(C5Me5)3Ir3S2] 2+ ([2]2+) were prepared by treatment of [(C5Me5)IrCl2]2 with (Me3Si)2S followed by ion exchange chromatography. Crystallographic characterization of the tetrairidium cluster [1]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 [1]2+ reveal a pair of reversible one-electron reductions at -218 and -487 mV vs Ag/AgCl. Chemical reduction of [1]2+ was effected with cobaltocene while the neutral cluster could be reoxidized with HC1/O2. In the solid state [1]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]2+ afforded dark blue crystals of neutral [2]0. Variable-temperature 1H NMR spectra of [2]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.

Original languageEnglish (US)
Pages (from-to)4824-4831
Number of pages8
JournalJournal of the American Chemical Society
Issue number11
StatePublished - Jun 1 1994

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry
  • Biochemistry
  • Colloid and Surface Chemistry


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