Unprecedented Square-Planar α-Diimine Dibromonickel Complexes and Their Ethylene Polymerizations Modulated by Ni–Phenyl Interactions
Handou Zheng, Yinwu Li, Wenbo Du, Chi Shing Cheung, Donghui Li, Heng Gao, Heng Gao, Huiyun Deng, Haiyang Gao, Haiyang Gao
Abstract
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.