Mechanism and Effect of Polar Styrenes on Scandium-Catalyzed Copolymerization with Ethylene
Mechanism and Effect of Polar Styrenes on Scandium-Catalyzed Copolymerization with Ethylene
复制标题
极性苯乙烯钪催化乙烯共聚机理及影响
DOI：
10.1002/anie.201808836
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Cui Dongmei
中科院分区：
文献类型：
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作者：
Liu Bo;Qiao Kening;Fang Jian;Wang Tiantian;Wang Zichuan;Liu Dongtao;Xie Zhigang;Maron Laurent;Cui Dongmei
乙烯（E）和极性乙烯基单体的共聚仍然是一个问题，因为E的传播受到阻碍。在此，我们首次报道了使用亲氧性钪催化剂进行E和极性苯乙烯（SR）的共聚，当R是吸电子基团时，该催化剂表现出比E和SR均聚更高的周转频率。通过计算 DFT (B3PW91) 理论水平上的 E/SF 共聚反应曲线，阐明了这种积极的共聚单体效应。结果表明，最后一个和倒数第二个插入的 SF 单元的 Sc3+ 与苯基之间的二次相互作用导致 E 插入势垒降低，因为吸电子取代基通过二次相互作用介导的诱导效应增强了 Sc3+ 的亲电性。 E 单元连续插入 3 次后，次级相互作用消失，SFinsertion 在动力学上优于 E 插入。该过程与NMR谱分析一致，结果表明所得共聚物主要含有SR(E)xSR序列，其中x≤3。
Copolymerization of ethylene (E) and polar vinyl monomers remains a problem because E propagation is hindered. Herein, for the first time, we report the copolymerization of E and polar styrenes (SR) by using an oxophilic scandium catalyst that exhibits higher turnover frequencies than both E and SRhomopolymerizations when R is an electron‐withdrawing group. This positive comonomer effect was elucidated through computing reaction profiles of E/SFcopolymerization at the DFT (B3PW91) level of theory. It reveals that the secondary interaction between Sc3+and phenyl of the last and penultimate inserted SFunits leads to a decrease of the E insertion barrier, because the electron‐withdrawing substituent enhances the electrophilicity of Sc3+by an inductive effect mediated by the secondary interaction. After three consecutive insertions of the E units, the secondary interaction is lost and the SFinsertion is kinetically preferred over the E insertion. This process is in line with the NMR spectrum analyses which show that the resultant copolymers mainly contain SR(E)xSRsequences where x≤3.