Structural Changes Induced by Electron-Transfer Reactions. Isomerization of an Alkylidene Moiety by Reversible Metal−Carbon Bond Cleavage in an Alkylidene-Bridged Cobaltadithiolene Complex

Electrochemical investigations concerning the reduction of an alkylidene adduct of a cobaltadithiolene complex are described. [(Cp)Co{S2C2(COOMe)2}{C(COOMe)2}] (Cp = η5-C5H5) exists as an equilibrium mixture of alkylidene-bridged (2) and ylide forms (3) in solution. Both isomers are reducible by one electron, but the radical anion of the bridged form (2 - ) undergoes rapid and irreversible isomerization to the ylide form anion (3 - ). Conventional cyclic voltammetry (CV), thin-layer CV, optically transparent thin-layer electrode (OTTLE), and differential pulse polarography (DPP) have been used to establish these mechanisms. In the reaction with trimethyl phosphite, an X-ray structure analysis and CV have also been used to prove the existence of the ylide structure.