Electro-organic reactions. Part III. Mechanistic aspects of the cathodic hydrogenation of activated carbon–carbon double bonds

Abstract

Mechanisms have been elucidated for the cathodic reduction of compounds of the type Ph(R)C:C(CN)X (R = H, Me, Bu^t, or Ph; X = CN or CO₂Et), methyl phenanthrene-9-carboxylate, and methyl 10-methylphenanthrene-9-carboxylate. Cyclic voltammetry in aprotic solvents and e.s.r. spectroscopy have been used to show that, except for R = H or Me, reversible one-electron reduction to a radical-anion is followed at more cathodic potentials by further irreversible reduction to a dianion. In the presence of an added proton donor two-electron cathodic hydrogenation of the carbon–carbon double bond is observed in the region of the first reduction peak potential. The relative effectiveness of a variety of proton donors is discussed on the basis of cyclic voltammetric results. For compounds with R = H or Me irreversible one-electron reduction with dimerisation is observed even with an added proton source. Rapid dimersion of the radical-anions is proposed.