Multicomponent Linkage Engineering of Quinoline‐Linked Covalent Organic Frameworks for Atmospheric‐Pressure Metal‐Free CO 2 Cycloaddition

ABSTRACT Developing efficient metal‐free porous catalysts for the cycloaddition of CO 2 with epoxides under atmospheric‐pressure conditions remains challenging because strong CO 2 affinity, efficient epoxide activation, and framework stability are difficult to integrate within a single material. Herein, we report a chemically robust bifunctional quinoline‐linked covalent organic framework, Quinoline‐COF COOH , synthesized via a three‐component Doebner multicomponent reaction. This approach enables the direct incorporation of CO 2 ‐philic triazine units and Brønsted acidic carboxylic acid groups into an ordered porous framework without post‐synthetic modification. Owing to the fused quinoline linkage, Quinoline‐COF COOH exhibits high crystallinity, permanent porosity, excellent chemical stability, and a surface area of 1296 m 2 g −1 . Compared with the imine‐linked analogue, Quinoline‐COF COOH shows significantly enhanced CO 2 uptake and higher isosteric heat of adsorption (Qst = 43.2 kJ mol −1 ), indicating strong framework‐CO 2 interactions. Benefiting from the synergistic effect of triazine units and Brønsted acidic sites, Quinoline‐COF COOH efficiently catalyzes the cycloaddition of epoxides with CO 2 under atmospheric‐pressure and metal/solvent‐free conditions, achieving >99% conversion and selectivity within 6 h. Mechanistic studies and DFT calculations reveal that the carboxylic acid groups promote epoxide activation, while the triazine units facilitate CO 2 adsorption and insertion. This work highlights multicomponent linkage engineering for constructing a bifunctional COF for sustainable CO 2 conversion.