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

Abstract

Cobalt(III) complexes, [CoCl₂(L1)₂](PF₆) (1, L1 = N-methyl-N-(2-pyrimidinyl)imidazolylidene), [CoCl(L2)₂](PF₆)₂ (2, L2 = N-picolyl-(2-pyrimidinyl)imidazolylidene), [Co(L3)₂](PF₆)₃ (3, L3 = bis(N-2-pyrimidylimidazolylidenyl)methane) and [CoCl₂(L3)](PF₆) (4) have been prepared from the corresponding pyrimidine functionalized imidazolium salts [HL1](PF₆), [HL2](PF₆), and [H₂L3](PF₆)₂via in situ generated silver carbene complexes under mild conditions. These cobalt complexes were characterized by ¹H and ¹³C 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.