Preparation and reactivity study of chromium(III), iron(II), and cobalt(II) complexes of 1,3-bis(imino)benzimidazol-2-ylidene and 1,3-bis(imino)pyrimidin- 2-ylidene

Chromium(III), iron(II), and cobalt(II) complexes of bis(imino) benzimidazol-2-ylidene and bis(imino)pyrimidin-2-ylidene were successfully prepared by reaction of either the benzimidazolium or pyrimidinium salts or the corresponding copper complexes with the respective metal halide. X-ray diffraction analysis of the Cr(III) complex of the pyrimidin-2-ylidene ligand demonstrated, for the first time, the ability of bis(imino)carbene-type ligands to coordinate to metal centers in a tridentate fashion. The coordination mode of these ligands was surprisingly highly dependent on the nature of both the metal and the ligand itself. The activity of these complexes in ethylene polymerization was assessed under ambient conditions (room temperature and 1 atm of C ₂H ₄) using methylaluminoxane as cocatalyst. In contrast to the iron and cobalt complexes, both chromium complexes were active in ethylene polymerization.