| Abstract
| - In this paper are described the synthesis, characterization, and coordinating properties of a new potentiallypentadentate 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 andCyAr2N5M2Cl4. In the dinuclear complexes, one metal center is five-coordinate, while the other is four-coordinate. 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 susceptibilitydeterminations, 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 oligomerizationof ethylene to α-olefins with productivities and Schulz−Flory parameters depending on the type andnumber of the coordinated metals. In an attempt to rationalize the surprisingly high activity of the CoIIprecursors, and in particular that of the dinuclear derivative CyAr2N5Co2Cl4, which is 4 times higher thanthat of the mononuclear analogue CyAr2N5CoCl2, a CoII complex has been synthesized where the supportingligand 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 anactive role under catalytic conditions, even when the precursor contains a free (imino)pyridine moiety.
- The new tris-imino-bis-pyridines CyAr2N5 react with FeCl2 and CoCl2 to give high-spin paramagnetic mononuclear and homodinuclear complexes that, upon activation with MAO, generate effective catalysts for the oligomerization of ethylene to α-olefins in a Schulz−Flory distribution.
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