In this paper are described the synthesis, characterization, and coordinating properties of a new potentially pentadentate nitrogen ligand, CyAr2 N 5 , that combines in the same molecular structure 2,6-bis(imino)-pyridine and (imino)pyridine moieties. This ligand reacts with 1 or 2 equiv of anhydrous MCl 2 (M ) Fe, Co) to give paramagnetic mononuclear or homodinuclear complexes of the formula CyAr2 N 5 MCl 2 and CyAr2 N 5 M 2 Cl 4 . In the dinuclear complexes, one metal center is five-coordinate, while the other is fourcoordinate. Ligand and metal complexes 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. On activation by methylaluminoxane (MAO) in toluene, the Fe II and Co II complexes generate effective catalysts for the oligomerization of ethylene to R-olefins with productivities and Schulz-Flory parameters depending on the type and number of the coordinated metals. In an attempt to rationalize the surprisingly high activity of the Co II precursors, and in particular that of the dinuclear derivative CyAr2 N 5 Co 2 Cl 4 , which is 4 times higher than that of the mononuclear analogue CyAr2 N 5 CoCl 2 , a Co II complex has been synthesized where the supporting ligand is sterically similar to CyAr2 N 5 , yet it contains only the three nitrogen donor atoms of the 2,6-bis-(imino)pyridine moiety. From this study, it is concluded that all five nitrogen atoms of CyAr2 N 5 play an active role under catalytic conditions, even when the precursor contains a free (imino)pyridine moiety.

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 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 iPr N 6 Co 2 Cl 4 , which is more active than any other known CoII catalyst for the polymerization of ethylene to HDPE.

The homogeneous surface coating of multiwalled carbon nanotubes with linear low-density polyethylenes, containing from 3 to 34 branches per 1000 carbon atoms, has been achieved for the first time by combining the polymerization-filling technique (PFT) with tandem copolymerization catalysis. This method, which takes advantage of the use of ethylene as single monomer feed, allows for the breakup of the native nanotube bundles and provides an effective way to control the branching in the PEs produced at the nanotube surface. TEM micrographs of the composite materials have shown an interesting dependence of the PE-coating morphology on the experimental parameters of the tandem system.