Covalent-Frameworked 2D Crown Ether with Chemical Multifunctionality

Here, we present the synthesis and characterization of a novel 2D crystalline framework, named CO, which mainly consists of carbon and oxygen in a 2:1 molar ratio and features crown ether holes in its skeletal structure. The covalent-frameworked 2D crown ether can be synthesized on a gram-scale and exhibits fine chemical stability in various environments, including acid, base, and different organic solvents. The CO efficiently activates KI through the strong coordination of K⁺ with crown ether holes in a rigid framework, which enhances the nucleophilicity of I^- and significantly improves its catalytic activity for CO₂ fixation with epoxides. The presence of CO with KI results in remarkable increases in CO₂ conversion from 5.7% to 99.9% and from 2.9% to 74.2% for epichlorohydrin and allyl glycidyl ether, respectively. Moreover, CO possesses both electrophilic and nucleophilic sites at the edge of its framework, allowing for the customization of physicochemical properties by a diverse range of chemical modifications. Specifically, incorporating allyl glycidyl ether (AGE) as an electrophile or ethoxyethylamine (EEA) as a nucleophile into CO enables the synthesis of CO-AGE or CO-EEA, respectively. These modified frameworks exhibit improved conversions of 97.2% and 99.9% for CO₂ fixation with allyl glycidyl ether, outperforming unmodified CO showing a conversion of 74.2%. This newly developed scalable, durable, and customizable covalent framework holds tremendous potential for the design and preparation of outstanding materials with versatile functionalities, rendering them highly attractive for a wide range of applications.