Versatile relay and cooperative palladium(0) N-heterocyclic carbene/copper(I) N-heterocyclic carbene catalysis for the synthesis of tri- and tetrasubstituted alkenes

Two new and efficient dual catalytic procedures for the synthesis of tri- and tetra-substituted alkenes using aryl bromides and chlorides are reported. The formation of these vinyl arenes occurs independently in a one-pot relay and a one-pot cooperative procedure using well-defined Pd-NHC and Cu-NHC complexes. Mechanistic studies were performed to elucidate the key role of the solvent in each procedure as well as the formation of the key intermediate, [Cu(alkenylboron)(NHC)], allowing the transmetallation with the Pd-NHC co-catalyst in the cooperative catalysis.