• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Chemistry: A European journal >New insights into the polymerization of methyl methacrylate initiated by rare-earth borohydride complexes: A combined experimental and computational approach
【24h】

New insights into the polymerization of methyl methacrylate initiated by rare-earth borohydride complexes: A combined experimental and computational approach

机译：稀土硼氢化物络合物引发的甲基丙烯酸甲酯聚合的新见解：实验与计算相结合的方法

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

Polymerization of methyl methacrylate (MMA) initiated by the rare-earth borohydride complexes [Ln(BH4)(3)(thf)(3)] (Ln=Nd, Sm) or [Sm(BH4)(CP*)(2)(thf)] (Cp*=eta-C5Me5) proceeds at ambient temperature to give rather syndiotactic poly(methyl methacrylate) (PMMA) with molar masses M, higher than expected and quite broad molar mass distributions, which is consistent with a poor initiation efficiency. The polymerization of MMA was investigated by performing density functional theory (DFT) calculations on an eta-C2H5 model metallocene and showed that in the reaction of [Eu(BH4)(CP)(2)] with MMA the borate [Eu(CP)(2){OBH3)(OMe)C=C(Me)(2)}] (e-2) complex, which forms via the enolate [EU(CP)(2){O(OMe)C=C(Me)(2)}] (e), is calculated to be exergonic and is the most likely of all of the possible products. This product is favored because the reaction that leads to the formation of carboxylate [Eu(Cp)(2){OOC-C(Me)(=CH2)}] (f) is thermodynamically favorable, but kinetically disfavored, and both of the potential products from a Markovnikov [Eu(Cp)(2){O(OMe)C-CH(Me)-(CH2BH3)}] (g) or anti-Markovnikov [Eu(CP)(2){O(OMe)C-C(Me-2)(BH3)}] (h) hydroboration reaction are also kinetically inaccessible. Similar computational results were obtained for the reaction of [Eu(BH4)(3)] and MMA with all of the products showing extra stabilization. The DFT calculations performed by using [Eu(Cp),(H)] to model the mechanism previously reported for the polymerization of MMA initiated by [Sm(Cp*)(2)(H)](2) confirmed the favorable exergonic formation of the intermediate [Eu(Cp)(2){O(OMe)C=C(Me)2}] (e") as the kinetic product, this enolate species ultimately leads to the formation of PMMA as experimentally observed. Replacing H by BH4 thus prevents the 1,4-addition of the [Eu(BH4(Cp)(2)] borohydride ligand to the first incoming MMA molecule and instead favors the formation of the borate complex e-2. This intermediate is the somewhat active species in the polymerization of MMA initiated by the borohydride precursors [Ln(BH4)1(thf)3] or [Sm(BH4)(CP*)2(thf)].
机译：由稀土硼氢化物络合物[Ln（BH4）（3）（thf）（3）]（Ln = Nd，Sm）或[Sm（BH4）（CP *）（2）引发的甲基丙烯酸甲酯（MMA）聚合[（thf）]（Cp * = eta-C5Me5）在环境温度下进行，得到相当间同的聚甲基丙烯酸甲酯（PMMA），其摩尔质量M高于预期，摩尔质量分布相当宽，这与不良的引发反应是一致的效率。通过对η-C2H5模型茂金属进行密度泛函理论（DFT）计算，研究了MMA的聚合反应，结果表明在[Eu（BH4）（CP）（2）]与MMA的反应中，硼酸盐[Eu（CP） （2）{OBH3）（OMe）C = C（Me）（2）}]（e-2）络合物，它通过烯醇盐[EU（CP）（2）{O（OMe）C = C（Me ）（2）}]（e）被计算为是运动性的，并且是所有可能产品中最有可能的。该产品之所以受欢迎，是因为导致形成羧酸盐[Eu（Cp）（2）{OOC-C（Me）（= CH2）}]（f）的反应在热力学上是有利的，但在动力学上是不利的，并且两者Markovnikov [Eu（Cp）（2）{O（OMe）C-CH（Me）-（CH2BH3）}]（g）或反Markovnikov [Eu（CP）（2）{O（OMe） CC（Me-2）（BH3）}]（h）硼氢化反应在动力学上也是不可及的。 [Eu（BH4）（3）]和MMA与所有产物的反应都显示出相似的计算结果，显示出额外的稳定性。通过使用[Eu（Cp），（H）]建模先前报道的由[Sm（Cp *）（2）（H）]（2）引发的MMA聚合机理的DFT计算证实了良好的能谱形成中间体[Eu（Cp）（2）{O（OMe）C = C（Me）2}]（e“）的动力学产物，该烯醇化物最终导致形成PMMA，如实验观察到的那样。因此，BH4可以防止[Eu（BH4（Cp）（2）]硼氢化物配体向第一个进入的MMA分子的1,4-加成，而有利于硼酸盐复合物e-2的形成。硼氢化物前体[Ln（BH4）1（thf）3]或[Sm（BH4）（CP *）2（thf）]引发的MMA聚合反应中的各种杂化。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号