Octahedral (cyclopentadienyl)rhodium clusters [Rh6Cp6(μ6-C)]2+ and [Rh6Cp6(μ3-CO)2]2+: Synthesis, structures and electrochemistry

The 86-electron dicationic octahedral rhodium clusters containing Cp (Cp = C5H5) ligands and either an interstitial carbon atom, [Rh6Cp6(μ6-C)]2+ ([1]2+), or two carbonyl groups, [Rh6Cp6(μ3-CO)2]2+ ([2]2+), were synthesized in low yields by reactions of Rh3Cp3(μ-CO)3 with RhCp(C2H4)2 or [RuCp∗(MeCN)3]+ (Cp∗ = C5Me5), respectively. The structures of [1]2+ and [2]2+ were determined by X-ray diffraction. Their electrochemical behavior proved that they possess a rather extended electron transfer activity. In accordance with DFT calculations, the nearly octahedral structure of [1]2+ and [2]2+ is retained both upon oxidation (2+/3+) and the first reduction (2+/+); however, the second reduction (+/0) results in the breaking of one (for [1]0) or two (for [2]0) Rh–Rh bonds. In the case of the related Dahl’s nickel cluster Ni6Cp6 the nearly octahedral structure is retained upon all redox steps (3+/2+/+/0/−/2−).