Suo Xian, Fu Yuqing, Do-Thanh Chi-Linh, Qiu Li-Qi, Jiang De-En, Mahurin Shannon M, Yang Zhenzhen, Dai Sheng
Department of Chemistry, Institute for Advanced Materials and Manufacturing, University of Tennessee, Knoxville, Tennessee 37996, United States.
ZJU-Hangzhou Global Scientific and Technological Innovation Center, Hangzhou 311215, China.
J Am Chem Soc. 2022 Nov 30;144(47):21658-21663. doi: 10.1021/jacs.2c09189. Epub 2022 Nov 15.
Superbase-derived task-specific ionic liquids (STSILs) represent one of the most attractive and extensively studied systems in carbon capture via chemisorption, in which the obtained CO uptake capacity has a strong relationship with the basicity of the anions. High energy input in desorption and side reactions caused by the strong basicity of the anions are still unsolved issues. The development of other customized STSILs leveraging an alternative driving force to achieve efficient CO chemisorption/desorption is highly desirable yet challenging. In this work, carbanion-derived STSILs were developed for efficient CO chemisorption via a carboxylic acid formation pathway. The STSIL with the deprotonated malononitrile molecule ([MN]) as the anion exhibited much higher CO uptake capacity than the one derived from 2-methylmalononitrile ([MMN]). Notably, this trend was opposite to their basicity ([MN] < [MMN]). Detailed characterization of the products, supported by density functional theory simulations of spectra and calculations of the reaction energetics, demonstrated that carboxylic acid was formed upon reacting with CO via proton transfer in [MN]-derived STSILs but not in the case of [MMN] due to lack of an α-H. The preference of the carboxylic acid product over carboxylate formation was driven by the extended conjugation among the central sp carbon, the as-formed carboxylic acid, and the two nitrile groups. The achievements made in this work provide an alternative design principle of STSILs by leveraging the extended conjugation in the CO-integrated product.
基于超强碱的特定任务离子液体（STSILs）是通过化学吸附进行碳捕获中最具吸引力且研究广泛的体系之一，其中所获得的CO吸收能力与阴离子的碱性密切相关。阴离子的强碱性导致解吸过程中的高能量输入和副反应仍是未解决的问题。利用替代驱动力实现高效CO化学吸附/解吸的其他定制STSILs的开发非常必要，但具有挑战性。在这项工作中，通过羧酸形成途径开发了用于高效CO化学吸附的碳负离子衍生的STSILs。以去质子化的丙二腈分子（[MN]）作为阴离子的STSIL表现出比由2-甲基丙二腈（[MMN]）衍生的STSIL更高的CO吸收能力。值得注意的是，这种趋势与它们的碱性相反（[MN] < [MMN]）。通过光谱的密度泛函理论模拟和反应能量学计算对产物进行的详细表征表明，在[MN]衍生的STSILs中，与CO反应时通过质子转移形成了羧酸，而在[MMN]的情况下由于缺乏α-H则没有形成羧酸。羧酸产物优于羧酸盐形成的原因是中心sp碳、形成的羧酸和两个腈基之间的共轭扩展。这项工作取得的成果通过利用CO整合产物中的共轭扩展提供了STSILs的另一种设计原则。
