Nickel(II) N-Heterocyclic Carbene Complexes: Versatile Catalysts for C-C, C-S and C-N Coupling Reactions

A variety of Ni-II complexes with a wide range of electronic and steric properties, bearing picolylimidazolidene ligands (a-g) and Cp (Cp = eta 5-C5H5; 2a-f) or Cp* (Cp* = eta(5)-C5Me5; 3a, c, g) groups, have been synthesised and characterised by using NMR spectroscopy and single-crystal X-ray crystallography. The complexes have been used as precatalysts for a wide range of catalytic transformations, which most likely involve a Ni-0/Ni-II catalytic cycle. In particular, the new welldefined 2a, 2c, 3a and 3c complexes have demonstrated great efficiency and versatility towards Suzuki-Miyaura coupling reactions, hydroamination of activated olefins and C-S cross-coupling reactions of aryl halides and thiols under mild conditions.