Solar C(sp)–H Carboxylation: Silver-Embedded Covalent Organic Framework Film as a Highly Efficient Photocatalyst for Carboxylation of C(sp)–H Bonds with CO2 under Solar Light

Abstract Carbon dioxide (CO2) fixation is an innovative approach to address the challenges of climate concerns and sustainable energy systems. The utilization of CO2 as an abundant and renewable carbon source in carboxylation reactions offers an attractive and sustainable strategy to access high-value-added carboxylic acids. In this context, the direct C–H carboxylation of terminal alkynes with CO2 has gained significant attention for the rapid synthesis of propiolic acids. However, achieving efficient C(sp)–H carboxylation of terminal alkynes under mild conditions remains a significant challenge. Herein, we report the carboxylation of the C(sp)–H bond in aromatic terminal alkynes with CO2 at room temperature and atmospheric pressure using a highly efficient silver nanoparticles (Ag)-embedded β-ketoenamine-linked covalent organic framework (Tp-APB@Ag) film as a photocatalyst under solar light irradiation. Remarkably, the as-synthesized Tp-APB@Ag film photocatalyst achieved an impressive aromatic propiolic acid formation as high as 99.9% yield and 100% selectivity. Additionally, the photocatalyst demonstrated outstanding recyclability without significant loss in catalytic activity and structural integrity. Moreover, this sustainable and economic carboxylation strategy exhibited mild reaction conditions, good functional group tolerance, and a broad scope across various reactants. This work not only enables the rational molecular-level engineering of advanced photocatalysts but also provides in-depth insights for efficient CO2 transformation into valuable commodity chemicals at ambient conditions.