N-Heterocyclic “Pincer” Dicarbene Complexes of Cobalt(I), Cobalt(II), and Cobalt(III)

The complex Co(C−N−C)Br2 (C−N−C = 2,6-bis(arylimidazol-2-ylidene)pyridine, aryl = 2,6-Pri2C6H3), prepared by aminolysis of CoN(SiMe3)22 with the corresponding imidazolium salt (CH−N−CH)Br2, was methylated to the square-planar Co(C−N−C)(CH3) and oxidized with BrN(SiMe3)2 to give Co(C−N−C)Br3. The Co(I), Co(II), and Co(III) complexes show no ethylene polymerization activity.