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 C2H4) using methylaluminoxane
as cocatalyst. In contrast to the iron and cobalt complexes, both
chromium complexes were active in ethylene polymerization.