Synthesis of a New Polydentate Ligand Obtained by Coupling 2,6-Bis(imino)pyridine and (Imino)pyridine Moieties and Its Use in Ethylene Oligomerization in Conjunction with Iron(II) and Cobalt(II) Bis-h

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• 作者：Claudio Bianchini ; Giuliano Giambastiani ; Itzel Guerrero Rios ; Andrea Meli ; Werner Oberhauser ; Lorenzo Sorace ; Alessandro Toti
• 刊名：Organometallics
• 出版年：2007
• 出版时间：September 24, 2007
• 年：2007
• 卷：26
• 期：20
• 页码：5066 - 5078
• 全文大小：239K
• 年卷期：v.26,no.20(September 24, 2007)
• ISSN：1520-6041

文摘

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 and^CyAr2N₅M₂Cl₄. 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 Fe^II and Co^II complexes generate effective catalysts for the oligomerizationof ethylene to -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 Co^IIprecursors, and in particular that of the dinuclear derivative ^CyAr2N₅Co₂Cl₄, which is 4 times higher thanthat of the mononuclear analogue ^CyAr2N₅CoCl₂, a Co^II 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.