Synthesis, characterization and ethylene oligomerization of nickel complexes bearing N-(2-(1H-benzo[d]imidazol-2-yl)quinolin-8-yl)benzamide derivatives

Abstract

A series of N-(2-(1-R-1H-benzo[d]imidazol-2-yl)quinolin-8-yl)-2-R¹-4-R²-benzamide derivatives (5–12) was synthesized and characterized. These compounds 5–11 (5: R = H, R¹ = H, R² = H; 6: R = H, R¹ = Cl, R² = H; 7:R = H, R¹ = H, R² = Cl; 8: R = H, R¹ = H, R² = Br; 9: R = Me, R¹ = H, R² = H; 10: R = Et, R¹ = H, R² = H; 11: R = ⁱPr, R¹ = H, R² = H.) were treated with KOH, and then reacted with Ni(Ac)₂·4H₂O to form their nickel complexes (5a-11a), however, the dimethylated compound 12 reacted with NiCl₂·6H₂O to give complex 14a. Further investigation confirmed that compound 12 hydrolysized into a new compound N-methyl-2-(1-methyl-1H-benzo[d]imidazol-2-yl)quinolin-8-amine 14, and alternative synthesis confirmed the formation mechanism of 14a. All nickel complexes were characterized by elemental and spectroscopic analyses, and molecular structures of the representative compounds (12, 5a and 14a) were determined by the single-crystal X-ray diffraction. These Ni(II) complexes exhibited good to high activities up to 7.6 × 10⁶g mol⁻¹(Ni) h⁻¹ in ethylene oligomerization upon activation with Et₂AlCl. The reaction conditions and the nature of ligands affected on the catalytic performances of nickel complexes.