Synthesis, Characterization, and Ethylene Polymerization Behavior of 8-(Nitroarylamino)-5,6,7-trihydroquinolylnickel Dichlorides: Influence of the Nitro Group and Impurities on Catalytic Activity

The series of N-(5,6,7-trihydroquinolin-8-ylidene)nitroarylamine ligands (L1–L4) was prepared and used to synthesize the chloro-bridged dinickel complexes (Ni1–Ni4) and the bis-ligated mononickel(II) complex (Ni5) in good yield. Molecular structures of Ni1, Ni2, Ni4, and Ni5 were confirmed by single-crystal X-ray diffraction analysis, revealing a pseudosquare–pyramidal geometry around nickel in the chloro-bridged complexes (Ni1, Ni2, and Ni4) and a distorted octahedral geometry at the nickel atom in the bis-ligated complex (Ni5). Upon treatment with ethylaluminum sesquichloride (EASC, Et3Al2Cl3) or methylaluminoxane (MAO), all nickel complexes exhibited high activities (up to 4.05 × 106 g (PE) mol–1 h–1) for ethylene polymerization. Moreover, heterocyclic impurities such as tetrahydrofuran (THF) and pyridine, often detected in common solvents, were added to the catalytic system of precatalyst Ni2 under controlled conditions and were found to have a negative influence on the catalytic behavior during ethylene polymerization.