Electrochemical reduction of a bridging imide: generation of ammonia at a dimolybdenum tris(mu-thiolate) site

The electrochemical reduction of the imide complex Mo2(cp)2(mu-SMe)3(mu-NH)]+ (1+) has been investigated in THF and MeCN electrolytes by cyclic voltammetry, controlled-potential electrolysis and coulometry. In the absence of free protons, the electrochemical reduction produces the amide derivative Mo2(cp)2(mu-SMe)3(mu-NH2)] (2) after consumption of 1 Fmol(-1) of 1+. In THF in the presence of acid, the reduction of 1+ occurs through a two-electron process. The presence of acid also results in the shift of the equilibrium between 1+ and amide dication 2(2+) (MeCN electrolyte) or induces an isomerisation of the imide ligand (THF electrolyte). This allows the electrolysis to be conducted at a potential 600 mV less negative than the reduction potential of 1+. Controlled-potential electrolyses in the presence of acid (2 equiv HTsO) produce the ammine derivative. Ammonia is released from these compounds either by coordination of the solvent (MeCN electrolyte) or by the binding of chloride to the ammine-tosylate complex (electrolyses in THF in the presence of acid and chloride). The final products, isolated almost quantitatively (>95%), are Mo2(cp)2(mu-SMe)3(MeCN)2]+ and Mo2(cp)2(mu-SMe)3(mu-Cl)], respectively.