An Electrochemically Promoted, Nickel-Catalyzed Mizoroki-Heck Reaction

Despite significant efforts to replace Pd-based catalysts with those of Ni, the Ni-catalyzed Mizoroki-Heck coupling of aryl halides and alkenes remains challenging. This work details the development of a Mizoroki-Heck reaction of aryl halides and a broad range of alkenes that utilizes electrochemistry as a means to promote Ni-catalyzed coupling under mild conditions. Stoichiometric studies implicate low-valent Ni complexes as key intermediates in route to rapid reactions with even unactivated alkenes. As such, electrochemistry is employed to readily provide the reducing potentials necessary to access these reactive intermediates and render the transformation catalytic. Cyclohexenone was found to be an unreactive substrate but a crucial additive that promotes facile electroreduction of the Ni catalyst and functionalization of other alkenes in high yields. Finally, preliminary mechanistic studies suggest that reactions proceed via an electron-chain transfer process that rapidly terminates but is reinitiated upon electroreduction.