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)](PF(6)) (1, L1 = N-methyl-N-(2-pyrimidinyl)imidazolylidene), [CoCl(L2)(2)](PF(6))(2) (, L2 = N-picolyl-(2-pyrimidinyl)imidazolylidene), [Co(L3)(2)](PF(6))(3) (3, L3 = bis(N-2-pyrimidylimidazolylidenyl)methane) and [CoCl(2)(L3)](PF(6)) (4) have been prepared from the corresponding pyrimidine functionalized imidazolium salts [HL1](PF(6)), [HL2](PF(6)), and [H(2)L3](PF(6))(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.