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Design and Theoretical Study of Nickel Catalysts for Syndiotactic Polyolefins
Author(s) -
Ying Liu,
Yue Liu,
JiaWen Liu,
Michael Drew G. B.
Publication year - 2003
Publication title -
chinese journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.28
H-Index - 41
eISSN - 1614-7065
pISSN - 1001-604X
DOI - 10.1002/cjoc.20030210502
Subject(s) - chemistry , tacticity , catalysis , polyolefin , polymerization , nickel , polymer chemistry , ligand (biochemistry) , trans effect , reaction mechanism , crystallography , organic chemistry , crystal structure , polymer , biochemistry , receptor , layer (electronics)
A nickel catalyst was modeled with ligand L 2 , [NH = CH—CH = CH—O] − , which should have potential use as a syndiotactic polyolefin catalyst, and the reaction mechanism was studied by theoretical calculations using the density functional method at the B3LYP/ LANL2MB level. The mechanism involves the formation of the intermediate [NiL 2 Me] + , in which the metal occupies a T‐shaped geometry. This intermediate has two possible structures with the methyl group trans either to the oxygen or to the nitrogen atom of L 2 . The results show that both structures can lead to the desired product via similar reaction paths, A and B. Thus, the polymerization could be considered as taking place either with the alkyl group occupying the position trans to the Ni—O or trans to the Ni—N bond in the catalyst. The polymerization process thus favors the catalysis of syndiotactic polyolefins. The syndiotactic synthesis effects could also be enhanced by variations in the ligand sub‐stituents. From energy considerations, we can conclude that it is more favorable for the methyl group to occupy the trans‐O position to form a complex than to occupy the trans ‐N position. From bond length considerations, it is also more favoured for ethene to occupy the trans‐O position than to occupy the trans ‐N position.