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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Metallocene-catalyzed alkene polymerization and the observation of Zr-allyls
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Metallocene-catalyzed alkene polymerization and the observation of Zr-allyls

机译：茂金属催化的烯烃聚合及Zr-烯丙基的观察

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Single-site polymerization catalysts enable exquisite control over alkene polymerization reactions to produce new materials with unique properties. Knowledge of catalyst speciation and fundamental kinetics are essential for full mechanistic understanding of zirconocene-catalyzed alkene polymerization. Currently the effect of activators on fundamental polymerization steps is not understood. Progress in understanding activator effects requires determination of fundamental kinetics for zirconocene catalysts with noncoordinating anions such as [B(C6F5)(4)](-). Kinetic NMR studies at low temperature demonstrate a very fast propagation rate for 1-hexene polymerization catalyzed by [(SBI)Zr(CH2SiMe3)][B(C6F5)(4)] [where SBI is rac-Me2Si(indenyl)(2)] with complete consumption of 1-hexene before the first NIMR spectrum. Surprisingly, the first NMR spectrum reveals, aside from uninitiated catalyst, Zr-allyls as the sole catalyst-containing species. These Zr-allyls, which exist in two diastereomeric forms, have been characterized by physical and chemical methods. The mechanism of Zr-allyl formation was probed with a trapping experiment, leading us to favor a mechanism in which Zr-polymeryl undergoes beta-H transfer to metal without dissociation of coordinated alkene followed by sigma-bond metathesis to form H-2 and Zr-allyl. Zr-allyl species undergo slow reactions with alkene but react rapidly with H-2 to form hydrogenation products.
机译：单中心聚合催化剂可实现对烯烃聚合反应的精确控制，从而生产出具有独特性能的新材料。催化剂形态和基本动力学的知识对于全面理解锆茂催化的烯烃聚合至关重要。目前尚不了解活化剂对基本聚合步骤的影响。要了解活化剂的作用，需要确定具有非配位阴离子如[B（C6F5）（4）]（-）的锆茂催化剂的基本动力学。低温动力学NMR研究表明[[SBI] Zr（CH2SiMe3）] [B（C6F5）（4）] [其中SBI为rac-Me2Si（茚基）（2） ]在第一个NIMR谱图之前完全消耗1-己烯。出乎意料的是，除了未引发的催化剂外，第一NMR光谱还显示出Zr-烯丙基是唯一的含催化剂的物质。这些Zr-烯丙基以两种非对映异构形式存在，已通过物理和化学方法进行了表征。 Zr-烯丙基形成的机理已通过诱捕实验进行了探索，这使我们偏向于Zr-聚合基经历β-H转移至金属而没有配位烯烃解离，然后由sigma键易位形成H-2和Zr的机理。 -烯丙基。 Zr-烯丙基物质与烯烃的反应缓慢，但与H-2的反应迅速，形成氢化产物。

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