Synthesis and Electrochemical Properties of Half-Sandwich Rhodium and Iridium Methyl Complexes

A series of complexes of the form [Cp(*)M(bpy)(CH3)]I was accessed by treatment of CpM(bpy) or Cp*M(bpy) with methyl iodide (M = Rh, Ir; Cp = cyclopentadienyl; Cp* = pentamethylcyclopentadienyl; bpy = 2,2'-bipyridyl). Solid state structures (X-ray diffraction) reveal the expected distorted octahedral geometry, with Cp or Cp* bound in the eta(5) mode and bpy bound in the typical kappa(2) mode. Electrochemical studies demonstrate that the Cp* complexes undergo a single, quasi-reversible one-electron reduction, whereas the Cp complexes undergo both a quasi-reversible one-electron reduction and a second, more negative, irreversible reduction. Electron paramagnetic resonance studies and comparisons between complexes of different metals suggest that the formulation of the singly reduced species is formally M(III) complexes with a bound bpy anion radical. The second reduction observed in the Cp complexes, on the other hand, results in cleavage of the M-C bond. Taken together, the results suggest that the compounds have strong metal methyl interactions, but these can be labilized upon reduction.