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Synthesis and characterization of monomeric and polymeric pyridinylimine-based Ni(II) complexes and their catalytic activities in ethylene oligomerization



A new polymeric ligand was synthesized through the reaction of 4-(pyridinylimine)phenol and formaldehyde in a basic medium, and its corresponding polymer–nickel complexes were formed in a 1:1 molar ratio. The synthesized compounds were characterized using elemental and spectral analyses. The monomeric and polymeric Ni(II) complexes (C1 and C2, respectively) were evaluated as catalyst precursors for ethylene oligomerization, using methylaluminoxane as an activator at two different ethylene pressures. C2 was found to be a more effective pre-catalyst than C1, with the co-catalyst having a similar effect in both cases. C2 exhibited an activity of 1.282 × 106 g (mol Ni)−1 h−1 bar−1, with an Al:Ni ratio of 2000:1 at room temperature and 1 atm ethylene pressure. Meanwhile C1 exhibited an activity of 1.126 × 106 g (mol Ni)−1 h−1 bar−1 under similar experimental conditions. At 5 atm ethylene pressure, C1 favoured the formation of high-density polyethylene, whereas C2 favoured the formation of branched low-density polyethylene. Copyright © 2012 Society of Chemical Industry