2-iminopyridine nickel(II) complexes bearing electron-withdrawing groups in the ligand core: Synthesis, characterization, ethylene oligo- and polymerization behavior

A series of novel 2-[(arylimino)alkyl]pyridine derivatives, containing electron-withdrawing groups (F, Cl, Br, CF3, NO2, CN) in the aryl rings, have been synthesized and characterized by H-1, C-13 and F-19 NMR spectroscopy. The corresponding nickel(II) complexes (24 complexes) have been prepared in good yields. The nature of the Ni complexes has been established by elemental analysis, paramagnetic H-1 NMR and Xray diffraction studies. Those complexes, activated with MAO, have been found to be highly active in the oligomerization and polymerization of ethylene (up to 9600 kg (mol of Ni)(-1) h(-1) bar(-1)), affording highly branched low-MW PE or ethylene oligomers, predominantly butenes and hexenes. The dependence of content and ratio of ethylene oligomers as well as of the polymer characteristics (molecular weight, degree of branching) on the nature of the substituents in the aryl(imino) and pyridine rings has been analyzed systematically. (E)-N-(1-(pyridin-2-yl)ethylidene)-2-(trifluoromethyl)aniline Ni complex supported on silica-alumina affords polyethylene with higher molecular weights, broader molecular weight distribution, and lower level of branching than the homogeneous catalyst. (C) 2016 Elsevier B. V. All rights reserved.