Abstract: The chemistry of N-heterocyclic carbenes (NHCs) has grown rapidly in the past decade. NHCs are now important ligands in homogeneous catalysis that show better catalytic activities than the typical phosphines in a number of transition metal catalyzed organic transformations, especially in C-C/heteroatom bond formation reactions. Ni is a much cheaper metal and the most promising alternative to Pd, and is receiving increasing attention. In this article we summarize new developments in the catalytic applications of nickel-NHC complexes in coupling reactions that include typical cross couplings of organic halides with various organometallic reagents and reductive coupling reactions.

Key words: nickel;N-heterocyclic carbene, cross-coupling reaction, reductive coupling, homogeneous catalysis