The tetra-n-butylammonium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TBA+TFPB-) electrolyte/methylene chloride solvent system improves the electrochemical reversibility of pentamethylcyclopentadienyl (Cp*) ruthenocenes, Cp*RuCp' (Cp' = fluorenyl, indenyl, cyclopentadienyl (Cp), acetylcyclopentadienyl, pentachlorocyclopentadienyl), as indicated by ipc/ip,a ratios of 0.79-1.0 as determined by cyclic voltammetry. The quasi-reversible potentials (E°') of the Cp*RuCp' complexes and the complete series of group 9 Cp2M and Cp*2M complexes (M = Fe, Ru, Os) are also reported in TBA+TFPB_/CH2Cl2. In addition, a study of the E°' values of group 9 complexes containing the (trifluoromethyl)tetramethylcyclopentadienyl (Cp‡) ligand indicate that the Cp‡ complexes are slightly (0.06-0.08 V per Cp‡) more difficult to oxidize than the cyclopentadienyl (Cp) derivatives. The structure of [C5(CF3)(CH3)4]Fe(C5H5) was determined at -101 °C by a single-crystal X-ray diffraction study. The structure shows eclipsed Cp‡ and Cp rings, and the iron to Cp‡ centroid distance (1.643 Å) is slightly shorter than the iron to Cp centroid distance (1.651 Å); otherwise, no extreme differences in the coordination of the Cp‡ and Cp rings are noted. An infrared spectroelectrochemistry study of trans-[Cp‡Fe(CO)2]2 shows that it is electrochemically oxidized to trans-[Cp‡Fe(CO)2]2+ in TBA+TFPB-/CH2C12.