1 Key Laboratory of Engineering Plastics and Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
2 CAS Research/Education Center for Excellence in Molecular Sciences, University of Chinese Academy of Sciences, Beijing 100049, China.
3 Department of Chemical and Materials Engineering, Concordia University, Montreal, Quebec H3G1M8, Canada.
4 State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China.

In the present work, four new mono(imino)pyridine ligands, 2-((2,4-bis(bis(4-R-phenyl)methyl)-6-fluorophenylimino)methyl)pyridine (R = H, L1; R = OCH₃, L2; R = F, L3) and 2-((2-(bis(4-fluorophenyl)methyl)-4-((3-(bis(4-fluorophenyl)methyl)-4-amine-5-fluoro-phenyl)(phenyl)methyl)-6-fluorophenylimino)methyl)pyridine (L4), have been designed in good yields. Additionally, three novel benzhydryl-bridged bis(imino)pyridine ligands, 2-(2-(bis(4-R-phenyl)methyl)-6-fluoro-phenylimino)pyridine (R = H, L5; R = OCH₃, L6; R = F, L7), were also prepared for comparison. All these organic compounds have been characterized by FT-IR analysis, ¹H/¹³C NMR spectroscopy, and elemental analysis. The treatment of L1-L7 with nickel halides afforded the corresponding monometallic (Ni1-Ni4) and bimetallic (Ni5-Ni7) nickel complexes in moderate to good overall yields. Upon activation with methylaluminoxane (MAO), Ni4 _Cl showed the highest activity up to 8.3 × 10⁶ g of polyethylene (PE) (mol of Ni)^-1 h^-1 among Ni1-Ni7 for ethylene polymerization. In all cases, unsaturated PEs with low molecular weights (0.7-13.3 kg mol^-1) were produced effectively. The introduction of remote para-substituents into the benzhydryl groups showed a beneficial effect on catalytic activity with the overall activities following the order of Ni-F > Ni-OCH₃ > Ni-H. In addition, these para-substituents were also found to affect not only the catalytic performance of catalysts but also the branching content of the PE product. Generally, the resultant PE waxes were moderately branched and contained both terminal vinyls (-CH=CH₂) and internal vinylenes (-CH=CH-) while with different ratios of vinyls to vinylenes. Notably, the polymers produced using para-methoxy-substituted Ni2/MAO and Ni6/MAO possessed the least branching content and uniquely high vinyl contributions.