Thiourea and urea catalysts have received much attention in the field of ring‐opening polymerization. In the (thio)urea/alkoxide catalytic system, sidearm groups can influence the catalytic performance of the organocatalyst moiety. In this work, a series of (thio)ureas bearing 2‐, 3‐ and 4‐pyridyl moieties were designed and synthesized. The (thio)ureas bearing a 2‐pyridyl group exhibited much higher catalytic activities than the (thio)ureas bearing 3‐ or 4‐pyridyl groups, suggesting a sidearm effect. Both crystal data and computational studies indicated that 2‐pyridyl can form an intramolecular hydrogen bond with the NH moiety, resulting in a Brønsted base/Lewis acid bifunctional catalytic system. Furthermore, the catalyst was stimuli‐responsive in Lewis acid/base‐modulated ring‐opening polymerization. Coordination between the Lewis acid BEt₃ and the catalyst was found to terminate the polymerization. Subsequently, the coordinated species was cleaved using the Lewis base bicyclo[2.2.2]‐1,4‐diazaoctane, resulting in the reactivation of the catalyst. © 2020 Society of Chemical Industry

中文翻译：

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（硫）脲/醇盐介导的环酯开环聚合中的侧臂效应

硫脲和尿素催化剂在开环聚合领域受到了广泛的关注。在（硫代）脲/醇盐催化体系中，侧臂基团可影响有机催化剂部分的催化性能。在这项工作中，设计并合成了一系列带有2-，3-和4-吡啶基的（硫）脲。带有2-吡啶基的（硫代）脲比带有3-或4-吡啶基的（硫代）脲表现出更高的催化活性，表明具有侧臂效应。晶体数据和计算研究均表明2-吡啶基可与NH部分形成分子内氢键，从而形成布朗斯台德碱/路易斯酸双功能催化体系。此外，该催化剂在路易斯酸/碱调节的开环聚合反应中具有刺激性。Lewis酸BET之间的配位_{如图3所示}，发现催化剂终止了聚合反应。随后，使用路易斯碱双环[2.2.2] -1,4-二氮杂辛烷裂解配位物质，从而使催化剂重新活化。©2020化学工业协会