期刊
ORGANOMETALLICS
卷 30, 期 11, 页码 2908-2919出版社
AMER CHEMICAL SOC
DOI: 10.1021/om100998c
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资金
- NSFC [21028001]
- JSPS [21750068, 21225004]
- Fundamental Research Funds for the Central Universities [DUT-1000-893117]
- SEM Scientific Research Funding for the ROCS
- Changjiang Scholar Program for visiting professors
- Grants-in-Aid for Scientific Research [21225004, 21750068] Funding Source: KAKEN
The copolymerization of styrene and ethylene by the cationic half-sandwich scandium alkyl species (eta(5)-C5Me5)Sc(CH2SiMe3) has been computationally investigated by using the quantum mechanics/molecular mechanics (QM/MM) method. It has been found that the initiation of styrene polymerization both kinetically and energetically prefers 2,1-insertion (secondary insertion, free-energy barrier of 12.6 kcal/mol, and exergonic by 19.1 kcal/mol) to 1,2-insertion (primary insertion, free-energy barrier of 19.0 kcal/mol, and exergonic by 8.9 kcal/mol). This is in contrast to a titanocene-based catalyst system, in which the initiation of styrene polymerization was computationally found to prefer 1,2-insertion, while the subsequent styrene insertion (polymerization) proceeds in a 2,1-insertion pattern. In the current Sc-based catalyst system, although the insertion of styrene into the metal-alkyl bond of the active species is kinetically slower than that of ethylene, the formation of a styrene pi-complex is more favorable than that of an ethylene complex. Also, the insertion of styrene into an ethylene-preinserted species is more energetically favorable than continuous ethylene insertion into the ethylene-preinserted species. These thermodynamic factors could add to a better understanding of styrene-ethylene copolymerization. The thermodynamic preference for the insertion of styrene rather than that of ethylene into the active species with an ethylene end group was not reported for group 4 catalyst systems. It is also found that the syndiospecific selectivity is inherently determined by the substituent of the ancillary ligand eta(5)-C5Me5.
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