Synthesis of New Polydentate Nitrogen Ligands and Their Use in Ethylene Polymerization in Conjunction with Iron(II) and Cobalt(II) Bis-halides and Methylaluminoxane

Original synthetic routes to polydentate nitrogen ligands combining in the same molecular structure either 2,6-bis(imino)pyridine and (imino)pyridine moieties or two 2,6-bis(imino)pyridine units are described. The tris-imino-bis-pyridine ligands ( Me N 5 and iPr N 5 ) and the tetrakis-imino-bis-pyridine ligand ( iPr N 6 ) react with FeCl 2 and/or CoX 2 (X = Cl, Br) to give paramagnetic monometallic, homobimetallic, or heterobimetallic complexes. These have been characterized, both in the solid state and in solution, by a variety of techniques, including single-crystal X-ray diffraction analyses, magnetic susceptibility determinations, IR, vis−NIR, 1 H NMR, and X-band EPR spectroscopies. The combination of these analytical tools has allowed us to unravel the geometrical and electronic structure of quite complicated systems. Selected mono- and binuclear Fe II and Co II complexes have been used as catalyst precursors in toluene for the polymerization of ethylene to high-density polyethylene (HDPE) upon activation with MAO. From fairly good to very good catalytic activities (up to 64.5 tons of PE (mol of M) -1 h -1 ) have been observed. Of particular relevance is the dicobalt complex iPr N 6 Co 2 Cl 4, which is more active than any other known Co II catalyst for the polymerization of ethylene to HDPE.