A nickel catalyst was modeled with ligand L^2, [NH = CH-CH = CH-O]^-, whichshould have potential use as a syndiotactic polyolefin catalyst, and the reaction mechanim wasstudied by theoretical calculations using the de...A nickel catalyst was modeled with ligand L^2, [NH = CH-CH = CH-O]^-, whichshould have potential use as a syndiotactic polyolefin catalyst, and the reaction mechanim wasstudied by theoretical calculations using the density functional method at the B3LYP/LANL2MB level.The mechanism involves the formation of the intermediate [NiL^2Me]^+, in which the metal occupies aT-shaped geometry. This intermediate has two possible structures with the methyl group trans eitherto the oxygen or to the nitrogen atom of L^2. The results show that both structures can lead to thedesired product via similar reaction paths, A and B. Thus, the polymerization could be considered astaking place either with the alkyl group occupying the position trans to the Ni-O or trans to theNi-N bond in the catalyst. The polymerization process thus favors the catalysis of syndiotacticpolyolefins. The syndiotactic synthesis effects could also be enhanced by variations in the ligandsubstituents. From energy considerations, we can conclude that it is more favorable for the methylgroup to occupy the trans-O position to form a complex than to occupy the trans-N position. Frombond length considerations, it is also more favoured for ethene to occupy the trans-O position thanto occupy the trans-N position.展开更多
文摘A nickel catalyst was modeled with ligand L^2, [NH = CH-CH = CH-O]^-, whichshould have potential use as a syndiotactic polyolefin catalyst, and the reaction mechanim wasstudied by theoretical calculations using the density functional method at the B3LYP/LANL2MB level.The mechanism involves the formation of the intermediate [NiL^2Me]^+, in which the metal occupies aT-shaped geometry. This intermediate has two possible structures with the methyl group trans eitherto the oxygen or to the nitrogen atom of L^2. The results show that both structures can lead to thedesired product via similar reaction paths, A and B. Thus, the polymerization could be considered astaking place either with the alkyl group occupying the position trans to the Ni-O or trans to theNi-N bond in the catalyst. The polymerization process thus favors the catalysis of syndiotacticpolyolefins. The syndiotactic synthesis effects could also be enhanced by variations in the ligandsubstituents. From energy considerations, we can conclude that it is more favorable for the methylgroup to occupy the trans-O position to form a complex than to occupy the trans-N position. Frombond length considerations, it is also more favoured for ethene to occupy the trans-O position thanto occupy the trans-N position.
