Four asymmetric α‐diimine dibromide nickel(II) complexes bearing both 2,6‐diisopropyl phenyl and substituted triphenyl {[(C3H7)2C6H3NC(C10H6)CN(R2C6H3)2C6H3]NiBr2, R = CH3, Catal.1; CF3, Catal.2; OCH3, Catal.3; C6H5, Catal.4} were synthesized and characterized. In the presence of B(C6F5)3, these newly synthesized nickel complexes showed high activities toward norbornene (NBE) homopolymerization (0.84–4.88 × 105 gpolymer/molNi‧h) under elevated temperatures, yielding high molecular weight polymers (106.5–657.9 kDa). These Ni/B catalytic systems also efficiently promoted the copolymerization of NBE with n‐butyl methacrylate (n‐BMA) and di(n‐butyl) itaconate (n‐DBI) under 70°C, respectively, affording copolymers with high molecular weight (n‐BMA: 95.0–235 kDa; n‐DBI:35.4–52.5 kDa) and moderate polar monomer incorporations (n‐BMA:1.2–6.4 mol%; n‐DBI:0.8–2.8 mol%). The copolymers with polar groups showed improved solubilities. The unimodal molecular weight distribution of the resultant polymers implied the single‐site catalytic behavior of these nickel catalysts toward NBE (co)polymerization. In addition, both the obtained PNB and the copolymers showed high glass transition temperature (289–345°C) and excellent thermal stability.