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 η5 mode and bpy bound in the typical
κ2 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.