Cobalt(iii) complexes bearing bidentate, tridentate, and tetradentate N-heterocyclic carbenes: synthesis, X-ray structures and catalytic activities.

Cobalt(iii) complexes, CoCl(2)(L1)(2) (1, L1 = N-methyl-N-(2-pyrimidinyl)imidazolylidene), CoCl(L2)(2)(2) (, L2 = N-picolyl-(2-pyrimidinyl)imidazolylidene), Co(L3)(2)(3) (3, L3 = bis(N-2-pyrimidylimidazolylidenyl)methane) and CoCl(2)(L3) (4) have been prepared from the corresponding pyrimidine functionalized imidazolium salts HL1, HL2, and H(2)L3(2)via in situ generated silver carbene complexes under mild conditions. These cobalt complexes were characterized by (1)H and (13)C NMR spectroscopy and X-ray diffraction analysis. The cobalt complexes have been found to be good catalyst precursors for Kumada-Corriu cross-coupling reactions of aryl halides and Grignard reagents at room temperature. Complex 1 is more active under the mild conditions.