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首页> 外文期刊>Chemistry: A European journal >A joint experimental/theoretical investigation of the statistical olefin/ conjugated diene copolymerization catalyzed by a hemi-lanthanidocene [(Cp*)(BH_4)LnR]
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A joint experimental/theoretical investigation of the statistical olefin/ conjugated diene copolymerization catalyzed by a hemi-lanthanidocene [(Cp*)(BH_4)LnR]

机译：半-镧系二烯[[Cp *）（BH_4）LnR]催化的统计烯烃/共轭二烯共聚合的联合实验/理论研究

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摘要

Statistical copolymerization of ethylene and isoprene was achieved by using a borohydrido half-lanthani- docene complex. Under copolymeriza- tion conditions, activation of [(Cp*)- (BH_(4)2)Nd(thf) _2](Cp* = η5-C_5Me_5)by an appropriate alkylating agent affords trans-1,4-poly-isoprene-co-ethylene. Analysis of the microstructure of the copolymer revealed the presence of successive short sequences of ethylene/ ethylene, trans-1,4-isoprene/ethylene, and trans-1,4-isoprene/trans-1,4-iso- prene. A small amount of 1,2-insertion of isoprene was observed, and no cyclic structures within the chain were characterized. Test runs showed that these catalysts are unable to copolymerize a- olefins (such as hex-1-ene) with isoprene. The probable initial steps in the copolymerization have been computed at the DFT level of theory. Analysis of the energy profile provides insight into the catalyst's activity and selectivity. Our theoretical results highlight the key role played by the allyl intermediate, in which diene insertion, and to a lesser extent olefin insertion, is the rate-determining step of the process. These results also illustrate the coordination behavior of the allyl ligand during the insertion of an incoming monomer, which directly inserts, after pre-coordination to the metal center, into the η~3-allyl ligand without inducing an η~3 to η~1 haptotropic shift. Finally, the inactivity of this family of catalysts towards the copolymerization of hex-1- ene was rationalized on the basis of the free-energy profile of the copolymeri- zation.
机译：乙烯和异戊二烯的统计共聚是通过使用硼氢化半-镧系-二十二烯配合物实现的。在共聚条件下，通过合适的烷基化剂活化[（Cp *）-（BH_（4）2）Nd（thf）_2]（Cp * =η5-C_5Me_5）可以得到反式1,4-聚异戊二烯-共-乙烯。对该共聚物的微观结构的分析表明，存在乙烯/乙烯，反式-1,4-异戊二烯/乙烯和反式-1,4-异戊二烯/反式-1,4-异戊二烯的连续短序列的存在。观察到少量异戊二烯的1,2-插入，并且未表征链内的环状结构。试验表明，这些催化剂不能使α-烯烃（如己-1-烯）与异戊二烯共聚。共聚中可能的初始步骤已在理论的DFT水平上进行了计算。能量分布图分析提供了对催化剂活性和选择性的深入了解。我们的理论结果突显了烯丙基中间体所起的关键作用，其中，二烯的插入，以及程度较小的烯烃插入，是该方法的速率决定步骤。这些结果还说明了烯丙基配体在引入的单体插入过程中的配位行为，该单体在预先配位至金属中心后直接插入η〜3-烯丙基配体中，而不会引起η〜3至η〜1触觉转变。最后，根据共聚反应的自由能曲线，合理化了该系列催化剂对己烯-1-烯共聚反应的惰性。

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