Unprecedented Square-Planar α‑Diimine Dibromonickel Complexes and Their Ethylene Polymerizations Modulated by Ni–Phenyl Interactions

Combined bulky 8-p-tolylnaphthylamine and bulky dibenzo-/dinaphthobarrelene backbones, unprecedented “opening box”-like α-diimine dibromonickel complexes were synthesized. Their square-planar geometries and the Ni–phenyl interactions in both solid and solution were identified by single-crystal X-ray diffraction analysis, NMR analysis, and density functional theory (DFT) simulations. Bulky α-diimine nickel complexes as ethylene polymerization precatalysts exhibited enhanced activity and thermal stability and produced unexpected lightly branched polyethylenes (PEs) (32–42/1000C) with melting temperatures of 81–93 °C. A combined experimental and theoretical study clearly showed how weak attractive Ni–phenyl interactions could decrease PE branching density in ethylene polymerization. The ethylene coordination as a crucial step was promoted by Ni–phenyl interactions, causing acceleration of linear chain growth.