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Zwitterionic Ni(II) complexes bearing pyrazolyl-ether-imidazolium ligands: synthesis, structural characterization and use in ethylene oligomerization

Abstract : A series of new tetracoordinated Ni(II) complexes of general formula NiCl3(L) (Ni1, L = 1-(2-(2-methylimidazole-ethoxy)ethyl)-3,5-dimethylpyrazole; Ni2, L = 1-(2-(1,2-dimethylimizadole-ethoxy)ethyl)-pyrazole; Ni3, L = 1-(2-(1,2-dimethylimizadole-ethoxy)ethyl)-3,5-dimethyllpyrazole; Ni4, L = 1-(2-(2-n-butylimizadole-ethoxy)ethyl)-3,5-dimethylpyrazole) were prepared in high yields. All these complexes were characterized by elemental analysis, and X-ray crystallography was performed for Ni1, Ni2, and Ni3. In the solid state, these nickel complexes are monomeric with the pyrazolyl-ether-imidazolium acting as a monodentate ligand. The positive charge on the imidazolium unit is cancelled out by the negative charge that is provided by the third chloride ion linked to Ni(II), forming a zwitterionic structure. Upon activation with methylaluminoxane (MAO) or ethylaluminum sesquichloride (EASC), these complexes show moderate activity in ethylene oligomerization [TOF = 2100–29300 (mol C2H4)·(mol Ni−1 h−1)] with good selectivities for 1-butene (80.4–89.8 wt% of total products), which vary according to the ligand environment. Under biphasic conditions, the Ni3/[Bmim]·[AlCl4]/toluene catalytic system proved to be active for ethylene oligomerization with a TOF of 10700 (mol C2H4)·(mol Ni−1 h−1) and highly selective towards production of 1-butene (90.9 wt%)
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Submitted on : Wednesday, February 10, 2016 - 12:42:03 PM
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Ana H. D. P. S. Ulbrich, Jorge L. S. Milani, Thierry Roisnel, Jean-François Carpentier, Osvaldo L Casagrande. Zwitterionic Ni(II) complexes bearing pyrazolyl-ether-imidazolium ligands: synthesis, structural characterization and use in ethylene oligomerization. New Journal of Chemistry, Royal Society of Chemistry, 2015, 39 (9), pp.7234--7242. ⟨10.1039/C5NJ01538C⟩. ⟨hal-01208408⟩

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