The newly prepared 8-(2-benzhydrylnaphthylimino)-5,6,7-trihydroquinoline derivatives (L1–L3) individually reacted with (DME)NiBr₂ or NiCl₂ to form their corresponding nickel bromide complexes (Ni1–Ni3) and nickel chloride complexes (Ni4–Ni6). These nickel complexes were fully characterized by FT-IR spectroscopy and elemental analysis as well as single crystal X-ray analysis. The representative molecular structures of Ni1 and Ni4, confirmed by single crystal X-ray diffraction, revealed a distorted octahedral geometry around nickel atom as the halo-bridged centro-symmetric dimers with formulae as L₂Ni₂X₄ (X = Br, Ni1–Ni3; X = Cl, Ni4–Ni6). All nickel complexes, activated with either modified methylaluminoxane (MMAO) or diethylaluminiumchloride (Et₂AlCl), exhibited high activities toward ethylene polymerization, producing branched polyethylene with low molecular weights. The obtained polyethylenes showed tail peaks in the high molecular weight portion according to the GPC curves due to the constrained geometry caused by the bulky 2-benzhydrylnaphthyl-substituted 8-arylimino-5,6,7-trihydroquinoline derivatives.