College of Environmental and Chemical Engineering, Dalian University, Dalian 116622, China.
Guizhou Provincial Key Laboratory of Coal Clean Utilization, School of Chemistry and Materials Engineering, Liupanshui Normal University, Liupanshui 553004, China.
Int J Mol Sci. 2022 Sep 17;23(18):10879. doi: 10.3390/ijms231810879.
The development of bifunctional ionic polymers as heterogeneous catalysts for effective, cocatalyst- and metal-free cycloaddition of carbon dioxide into cyclic carbonates has attracted increasing attention. However, facile fabrication of such polymers having high numbers of ionic active sites, suitable types of hydrogen bond donors (HBDs), and controlled spatial positions of dual active sites remains a challenging task. Herein, imidazolium-based ionic polymers with hydroxyl/carboxyl groups and high ionic density were facilely prepared by a one-pot quaternization reaction. Catalytic evaluation demonstrated that the presence of HBDs (hydroxyl or carboxyl) could enhance the catalytic activities of ionic polymers significantly toward the CO cycloaddition reaction. Among the prepared catalysts, carboxyl-functionalized ionic polymer (PIMBr-COOH) displayed the highest catalytic activity (94% yield) in the benchmark cycloaddition reaction of CO and epichlorohydrin, which was higher than hydroxyl-functionalized ionic polymer (PIMBr-OH, 76% yield), and far exceeded ionic polymer without HBDs groups (PIMBr, 54% yield). Furthermore, PIMBr-COOH demonstrated good recyclability and wide substrate tolerance. Under ambient CO pressure, a number of epoxides were smoothly cycloadded into cyclic carbonates. Additionally, density functional theory (DFT) calculation verified the formation of strong hydrogen bonds between epoxide and the HBDs of ionic polymers. Furthermore, a possible mechanism was proposed based on the synergistic effect between carboxyl and Br functionalities. Thus, a facile, one-pot synthetic strategy for the construction of bifunctional ionic polymers was developed for CO fixation.
作为非均相催化剂，双功能离子聚合物在有效、无共催化剂和金属的条件下将二氧化碳环加成生成环状碳酸酯的研究受到了越来越多的关注。然而，制备具有高数量的离子活性位、合适类型氢键供体（HBD）和双活性位的可控空间位置的离子聚合物仍然是一项具有挑战性的任务。在此，通过一锅法季铵化反应，简便地制备了具有羟基/羧基和高离子密度的基于咪唑鎓的离子聚合物。催化评价表明，HBD（羟基或羧基）的存在可以显著提高离子聚合物对 CO 环加成反应的催化活性。在所制备的催化剂中，羧基功能化离子聚合物（PIMBr-COOH）在 CO 和表氯醇的基准环加成反应中表现出最高的催化活性（94%收率），高于羟基功能化离子聚合物（PIMBr-OH，76%收率），远远超过没有 HBD 基团的离子聚合物（PIMBr，54%收率）。此外，PIMBr-COOH 表现出良好的可回收性和广泛的底物耐受性。在环境 CO 压力下，许多环氧化物被顺利地环加成生成环状碳酸酯。此外，密度泛函理论（DFT）计算验证了环氧化物与离子聚合物的 HBD 之间形成了强氢键。此外，基于羧基和 Br 官能团的协同效应，提出了一种可能的反应机制。因此，开发了一种简便的一锅法合成策略，用于构建双功能离子聚合物以固定 CO。
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