Construction of Flexible Amine‐linked Covalent Organic Frameworks by Catalysis and Reduction of Formic Acid via the Eschweiler–Clarke Reaction. (26th April 2021)

• Record Type: Journal Article
• Authors: Zhang, Meicheng; Li, Yang; Yuan, Wenli; Guo, Xinghua; Bai, Chiyao; Zou, Yingdi; Long, Honghan; Qi, Yue; Li, Shoujian; Tao, Guohong; Xia, Chuanqin; Ma, Lijian
• Is Part Of: Angewandte Chemie. Volume 133:Number 22(2021)
• Page Start: 12504
• Page End: 12513
• Publication Date: 2021-04-26
• Subjects: covalent organic frameworks (COFs) -- Eschweiler–Clarke reaction -- flexible amine-linked -- formic acid -- pore-shrink effect; Chemistry -- Periodicals; 540
• DOI: 10.1002/ange.202102373
• Languages: English
• ISSNs: 0044-8249

Abstract

Abstract: Compared to the current mainstream rigid covalent organic frameworks (COFs) linked by imine bonds, flexible COFs have certain advantages of elasticity and self‐adaptability, but their construction and application are greatly limited by the complexity in synthesis and difficulty in obtaining regular structure. Herein, we reported for the first time a series of flexible amine‐linked COFs with high crystallinity synthesized by formic acid with unique catalytic and reductive bifunctional properties, rather than acetic acid, the most common catalyst for COF synthesis. The reaction mechanism was demonstrated to be a synchronous in situ reduction during the formation of imine bond. The flexibilities of the products endow them with accommodative adaptability to guest molecules, thus increasing the adsorption capacities for nitrogen and iodine by 27 % and 22 %, respectively. Impressively, a novel concept of flexibilization degree was proposed firstly, which provides an effective approach to rationally measure the flexibility of COFs. Abstract : Using the Eschweiler–Clarke reaction, a series of flexible amine‐linked COFs was synthesized by catalysis and reduction of formic acid. The unique bifunctional properties of formic acid can not only catalyze the formation of rigid C=N bond like acetic acid, the most common catalyst in COF synthesis, but also reduce and transform it to flexible C−N bond simultaneously, giving COFs the accommodative adaptability to guest molecules.