Reduction of aryl halides at transition metal cathodes. Conditions for aryl-aryl bond formation. The Ullmann's reaction revisited

International audienceThe cathodic reduction of some aryl halides ArX (1-naphthyl halides NpI and NpBr, iodo benzene and bromobenzene PhI and PhBr taken as model substrates) was achieved essentially in propylene carbonate (PC) considered for its high dielectric permittivity. Different electrode materials such as copper, silver, palladium, silver palladium alloy and nickel were used. Such conditions permit the activation of the C-X bond by metal (the step featuring similarity with Ullmann's reaction). Electron transfer to organometallic intermediates generated at the metal interface activates the formation of Ar-Ar linkages often in good yields, especially in the case of aryl iodides