Nickel N-Heterocyclic Carbene-Catalyzed C–C Bond Formation: Reactions and Mechanistic Aspects

The chemistry of nickel N-heterocyclic carbene complexes is a research area that has blossomed over the last 10 years, and a large number of new complexes with a variety of architectural motifs are now known. The evolution of this chemistry has led to increasing applications of these complexes in catalytic bond formation. The rapid expansion of this field now calls for a review of the kinds of reactions that are catalyzed and a summary of the state of the art at this time. As the breadth of reactions catalyzed by such complexes is vast, this review specifically targets catalytic C–C bond formation, in particular C–C cross-couplings and C–C couplings via C–H bond activation, mediated by nickel–N-heterocyclic carbene complexes. A special emphasis is placed on mechanistic data, because this allows possible new insights into catalyst improvement.