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

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.