Electrochemical Oxidation and Reduction of Methylene-Bridged Complexes of Manganese, Cobalt, and Rhodium

The oxidation and reduction of a series of alkylidene-bridged dimetallic compounds containing Mn, Co, or Rh have been studied by electrochemical and spectroscopic techniques. Oxidation results in production of a cation radical whose stability depends on the identity of the metal in the complex and the nature of the bridge substituent. Among the dirhodium complexes, the one having bridging carbonyl groups gives the most stable cation. The cobalt and rhodium compounds are susceptible to attack by nucleophiles, and all cations decompose to give mononuclear products. One-electron reduction gives detectable anions in the case of Co and Rh compounds, but these anion radicals rapidly decompose. It is concluded that both oxidation and reduction weaken the M-C-M triangle, consistent with the description of these compounds as dimetallacyclopropanes.