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 (MeN5 and iPrN5) and the tetrakis-imino-bis-pyridine ligand (iPrN6) react with FeCl2 and/or CoX2 (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, 1H 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 FeII and CoII 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 iPrN6Co2Cl4, which is more active than any other known CoII catalyst for the polymerization of ethylene to HDPE.