title: α-Diamine Nickel Catalysts with Nonplanar Chelate Rings for Ethylene Polymerization.
abstract: A series of novel α-diamine nickel complexes, (ArNH-C(Me)-(Me)C-NHAr)NiBr2, 1: Ar=2,6-diisopropylphenyl, 2: Ar=2,6-dimethylphenyl, 3: Ar=phenyl), have been synthesized and characterized. X-ray crystallographic analysis showed that the coordination geometry of the α-diamine nickel complexes is markedly different from conventional α-diimine nickel complexes, and that the chelate ring (N-C-C-N-Ni) of the α-diamine nickel complex is significantly distorted. The α-diamine nickel catalysts also display different steric effects on ethylene polymerization in comparison to the α-diimine nickel catalyst. Increasing the steric hindrance of the α-diamine ligand by substitution of the o-methyl groups with o-isopropyl groups leads to decreased polymerization activity and molecular weight; however, catalyst thermal stability is significantly enhanced. Living polymerizations of ethylene can be successfully achieved using 1/Et2AlCl at 35 °C or 2/Et2AlCl at 0 °C. The bulky α-diamine nickel catalyst 1 with isopropyl substituents can additionally be used to control the branching topology of the obtained polyethylene at the same level of branching density by tuning the reaction temperature and ethylene pressure.
authors: School of Materials Science and Engineering, PCFM Laboratory, Sun Yat-sen University, Guangzhou, 510275, China.|School of Chemistry and Chemical Engineering, GD HPPC Laboratory, Sun Yat-sen University, Guangzhou, 510275, China.
authors: Heng
authors: H
authors: Liao
authors: School of Chemistry and Chemical Engineering, GD HPPC Laboratory, Sun Yat-sen University, Guangzhou, 510275, China.
authors: Liu
authors: L
authors: Zhong
authors: School of Chemistry and Chemical Engineering, GD HPPC Laboratory, Sun Yat-sen University, Guangzhou, 510275, China.
authors: Zefan
authors: Z
authors: Xiao
authors: School of Chemistry and Chemical Engineering, GD HPPC Laboratory, Sun Yat-sen University, Guangzhou, 510275, China.
authors: Ting
authors: T
authors: Zheng
authors: School of Materials Science and Engineering, PCFM Laboratory, Sun Yat-sen University, Guangzhou, 510275, China. gaohy@mail.sysu.edu.cn.
authors: Haiyang
authors: H
authors: Gao
authors: School of Materials Science and Engineering, PCFM Laboratory, Sun Yat-sen University, Guangzhou, 510275, China.
authors: Qing
authors: Q
authors: Wu
keywords: N ligands; branching topology; homogeneous catalysis; living polymerization; nickel