Synthesis of new polydentate nitrogen ligands and their use in ethylene polymerization in conjunction with iron(II) and cobalt(II) bis-halides and methylaluminoxane

In this paper are described the synthesis, characterization, and coordinating properties of a new potentially pentadentate nitrogen ligand, CyAr2N5, 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 MCl2 (M ) Fe, Co) to give paramagnetic mononuclear or homodinuclear complexes of the formula CyAr2N5MCl2 and CyAr2N5M2Cl4. 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, 1H NMR, and X-band EPR spectroscopies. On activation by methylaluminoxane (MAO) in toluene, the FeII and CoII 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 CoII precursors, and in particular that of the dinuclear derivative CyAr2N5Co2Cl4, which is 4 times higher than that of the mononuclear analogue CyAr2N5CoCl2, a CoII complex has been synthesized where the supporting ligand is sterically similar to CyAr2N5, 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 CyAr2N5 play an active role under catalytic conditions, even when the precursor contains a free (imino)pyridine moiety.