Electrochemical Behavior and Electron-Transfer Chain (ETC) Reactions of H₄Ru₄(CO)₁₂

The electrochemical reduction of H₄Ru₄(CO)₁₂ in tetrahydrofuran (THF) is studied by means of dc and ac polarography, cyclic voltammetry, and FT-IR spectroscopy following electrolysis in a optically transparent thin-layer electrochemical (OTTLE) cell. The reduction of the title complex generates a transient radical anion, [H₄Ru₄(CO)₁₂]^-, which produces the stable anion [H₃Ru₄(CO)₁₂]^- on a longer time scale. In the presence of triphenylphosphine, nucleophilic substitutions readily take place by electrochemical initiation and produce mono and bisubstituted derivatives in yields depending on PPh₃ concentration. The termination side chain reaction is the loss of a hydrido ligand, to give the above mentioned anion, which is inert to substitution even in the presence of a large excess of Lewis base.