Synthesis, Characterization, and Ethylene Polymerization Studies of Chromium, Iron, and Cobalt Complexes Containing 1,3-Bis(imino)-N-Heterocyclic Carbene Ligands

New chromium­(III), iron­(II), and cobalt­(II) complexes of acyclic 1,3-bis­[(2,6-dimethylphenylimino)­ethyl and benzyl]­imidazol-2-ylidene were prepared from the corresponding silver or copper adduct as transmetalating agent or from in situ deprotonation of the parent imidazolium salt. The catalytic activities of all three complexes were evaluated for ethylene polymerization at atmospheric pressure and room temperature with activation by methylaluminoxane. The Cr­(III) complexes were found to be the most active, with a rate of 35 kg PE mol^–1 Cr h<sup>–1