NICKEL-CATALYZED ELECTROCHEMICAL HOMOCOUPLING OF ALKENYL HALIDES - RATES AND MECHANISMS

We describe the electroanalytical determination of the successive elec tron transfer/chemical steps involved in the nickel-catalyzed electros ynthesis of conjugated dienes from alkenyl halides in DMF. Two catalyt ic sequences are proposed, depending on the potential applied. The fir st mechanism is shown to proceed through oxidative addition of the vin yl halide to electrogenerated Ni-0 and vinyl-Ni-I species. The diene i s obtained by reductive elimination from a Ni-III species. An alternat ive coupling mechanism is proposed which involves both oxidative addit ion of RX on Ni-0 and electron transfer from Ni-0 to RNiX. The influen ce of various parameters on the rates are discussed, such as the natur e of both the halide and the stereoisomer used, as well as the coordin ation environment of the nickel complex.