An Ion‐Pairing Approach to Stereoselective Metal‐Free Ring‐Opening Metathesis Polymerization
An Ion‐Pairing Approach to Stereoselective Metal‐Free Ring‐Opening Metathesis Polymerization
复制标题
立体选择性金属自由环开复分解聚合的离子配对方法
DOI：
10.1002/anie.202016393
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发表时间：
2021
期刊：
影响因子：
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通讯作者：
Boydston, Andrew J.
中科院分区：
文献类型：
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作者：
Yang, Xuejin;Gitter, Sean R.;Roessler, Allison G.;Zimmerman, Paul M.;Boydston, Andrew J.
立体化学可以对聚合物和材料性能产生深远的影响。不幸的是，实现高水平立体控制聚合的简单方法通常难以实现。与传统的金属介导的开环易位聚合（ROMP）不同，我们发现了一种非常简单的方法来控制光氧化还原介导的无金属 ROMP 中的烯烃立体化学。离子对、引发剂空间和溶剂化效应都对聚降冰片烯（PNB）的立体化学产生深远的影响。对反应条件进行简单修改即可产生反式烯烃含量为 25% 至 >98% 的 PNB。高顺式含量是由相对较大的抗衡离子、甲苯作为溶剂、低温（-78°C）和低查顿值引发剂获得的。相反，较小的抗衡离子、二氯甲烷作为溶剂以及具有较高Charton值的烯醇醚能够生产具有高反式含量的PNB。来自组合实验和计算研究的数据与在热力学控制下进行的自由基阳离子机制的立体控制步骤一致。
Stereochemistry can have a profound impact on polymer and materials properties. Unfortunately, straightforward methods for realizing high levels of stereocontrolled polymerizations are often challenging to achieve. In a departure from traditional metal‐mediated ring‐opening metathesis polymerization (ROMP), we discovered a remarkably simple method for controlling alkene stereochemistry in photoredox mediated metal‐free ROMP. Ion‐pairing, initiator sterics, and solvation effects each had profound impact on the stereochemistry of polynorbornene (PNB). Simple modifications to the reaction conditions produced PNB withtransalkene content of 25 to >98 %. Highciscontent was obtained from relatively larger counterions, toluene as solvent, low temperatures (−78 °C), and initiators with low Charton values. Conversely, smaller counterions, dichloromethane as solvent, and enol ethers with higher Charton values enabled production of PNB with hightranscontent. Data from a combined experimental and computational investigation are consistent with the stereocontrolling step of the radical cationic mechanism proceeding under thermodynamic control.