Covalent Organic Frameworks as Heterogeneous Photocatalysts for Cross-Coupling Reactions

Abstract

Cross-coupling reactions, which occur in both homogeneous and heterogeneous catalysis, have emerged as versatile tools in organic transformations and have had a profound impact on medicinal chemistry and drug discovery. However, conventional homogeneous systems have limitations such as small-scale synthesis, poor recyclability, and susceptibility of catalysts to degradation. In contrast, heterogeneous systems with immobilized catalytic active sites offer superior stability and recyclability, making them essential for industrial applications. Recent interest in solar-driven organic transformations, particularly carbon-carbon and carbon-heteroatom cross-coupling reactions, has stimulated extensive research efforts. Among many materials, covalent organic frameworks (COFs) have emerged as leading candidates for heterogeneous photocatalysis due to their high crystallinity, π-conjugated framework, narrow band structure, uniform porosity, and tunable functionality. This review comprehensively examines the advantages of COFs as heterogeneous photocatalysts for carbon-carbon coupling, carbon-heteroatom cross-coupling, and oxidative coupling of amines. It highlights their role in providing a green catalytic route for organic transformations and proposes strategies to enhance their photocatalytic efficiency. Finally, the review discusses the future trajectory of COF-based heterogeneous catalysts for various cross-coupling reactions under visible light irradiation, highlighting the novelty and driving force behind the current progress in this burgeoning field.