Nickel(ii) complexes chelated by 2,6-pyridinedicarboxamide: syntheses, characterization, and ethylene oligomerization

Abstract

N,N′-Bis(2,6-R-phenyl)-2,6-pyridinedicarboxamides (L: R = Cl, L1; R = F, L2; R = H, L3; R = Me, L4; R = Et, L5; R = ⁱPr, L6) were designed as neutral ligands, and the corresponding nickel complexes LNiBr₂ (Ni1–Ni6) were synthesized as precatalysts for ethylene oligomerization. All new ligands were fully characterized by NMR, and FT-IR spectroscopy, and elemental analysis, while the nickel complexes were examined using FT-IR spectroscopy and elemental analysis. The coordination mode of the ligand with nickel in complexes Ni5 and Ni6 was tridentate (O^N^O), as established by single crystal X-ray diffractions. All the nickel complexes Ni1–Ni6 were tested for ethylene oligomerization with different alkylaluminum compounds as cocatalysts, and diethylaluminum chloride (Et₂AlCl) was proved to be the most effective. Upon activation with Et₂AlCl, all nickel complexes showed high catalytic activity (up to 7.55 × 10⁵ g mol⁻¹ (Ni) h⁻¹ atm⁻¹) with good selectivity for α-C₄.