A Strained Ion Pair Permits Carbon Dioxide Fixation at Atmospheric Pressure by C–H H-Bonding Organocatalysis

作者：Jiaxi Xu, Anmei Xian, Zhenjiang Li, Jingjing Liu, Zhihao Zhang, Rui Yan, Luoyu Gao, Bo Liu, Lili Zhao, Kai Guo · 发表于：The Journal of Organic Chemistry · 年份：2021 · DOI：10.1021/acs.joc.0c02790 · 被引用次数：49 · 研究领域：Carbon dioxide utilization in catalysis、CO2 Reduction Techniques and Catalysts、Chemistry and Chemical Engineering

The cycloadditions of carbon dioxide into epoxides to afford cyclic carbonates by H-bond donor (HBD) and onium halide (X) cocatalysis have emerged as a key strategy for CO 2 fixation. However, if the HBD is also a halide receptor, the two will quench each other, decreasing the catalytic activity. Here, we propose a strained ion pair tris(alkylamino)cyclopropenium halide (TAC·X), in which TAC repels X. TAC possesses a positively charged cyclopropenium core that makes the vicinal C–H or N–H a nonclassical HBD. The interionic strain within TAC·X makes TAC a more electrophilic HBD, allowing it to activate the oxygen of the epoxide and making X more nucleophilic and better able to attack the methylene carbon of the epoxide. NMR titration spectra and computational studies were employed to probe the mechanism of the cycloaddition of CO 2 to epoxides reactions under the catalysis of TAC·X. The 1 H and 13 C{ 1 H}NMR titration spectra of the catalyst with the epoxide substrate unambiguously confirmed H-bonding between TAC and the epoxide. DFT computational studies identified the transition states in the ring-opening of the epoxide (TS1) and in the ring-closure of the cyclic carbonate (TS2).