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α‐Diamine Nickel Catalysts with Nonplanar Chelate Rings for Ethylene Polymerization
Author(s) -
Liao Heng,
Zhong Liu,
Xiao Zefan,
Zheng Ting,
Gao Haiyang,
Wu Qing
Publication year - 2016
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201602467
Subject(s) - diamine , nickel , catalysis , steric effects , polymer chemistry , branching (polymer chemistry) , diimine , polymerization , ethylene , isopropyl , chemistry , chelation , materials science , polymer , organic chemistry
A series of novel α‐diamine nickel complexes, (ArNH‐C(Me)‐(Me)C‐NHAr)NiBr 2 , 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 /Et 2 AlCl at 35 °C or 2 /Et 2 AlCl 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.