Fully Conjugated Donor–Acceptor Covalent Organic Frameworks for Photocatalytic Oxidative Amine Coupling and Thioamide Cyclization

Abstract

Covalent organic frameworks (COFs) are promising candidates as heterogeneous photocatalysts because of their porosity and tunable light absorption. The photostability and charge separation of COFs are highly important to improve the efficiency of photocatalytic transformation. In this work, a fully conjugated donor–acceptor COF is constructed with a benzothiadiazole unit, which exhibits high stability and enhanced charge separation. The prepared COF can efficaciously produce superoxide radical anions under air and visible light, which mediate the photocatalytic oxidative amine coupling and cyclization of thioamide to 1,2,4-thiadiazole in moderate to high yield and high recyclability (18 examples). This study demonstrates the great capacity of fully conjugated COFs with a D–A structure for light-driven organic synthesis.

Strongly Reducing (Diarylamino)benzene-Based Covalent Organic Framework for Metal-Free Visible Light Photocatalytic H2O2 Generation

“…Functionalities such as triazine, porphyrin, and benzothiadiazole have been incorporated into COFs to improve charge transfer kinetics and charge carrier separation. 2 , 6 By incorporating alternating donor–acceptor moieties into an extended framework, several COFs have been rendered suitable for photocatalysis. 7 , 8 There remains, however, extensive potential to design COFs optimized for photocatalysis by tweaking their structures at a molecular level.…”

All sp2 carbon covalent organic frameworks

“…By contrast, the [C 2 + C 2 ] scheme with a C 2 -symmetric knot and C 2 -symmetric linker allows the design of two different polygonal structures. One is a rhombic backbone (Figure 1C) and the other is the kagome structure (Figure 1D) [12,[14][15][16][17]23,25]. Kagome COFs usually comprise two different types of pores, hexagonal mesopores and trigonal mesopores or micropores [17].…”

“…Por-sp 2 c-COF bearing a porphyrin knot (Figure 5J) has been shown to serve as a photocatalyst promoting photoinduced aerobic oxidation of secondary amines to imines ( [20,36] and the supplemental information online). The donor-acceptor Py-BSZ-COF (Figure 6A) facilitates the oxidative amine coupling reaction with air at room temperature to form various benzylamines at 84-99% yield and 98-99% selectivity ( [25] and the supplemental information online). The COF-701 (Figure 3O) with BF 3 •OEt 2 in pores acts as a catalyst to promote the Diels-Alder cycloaddition reaction [31].…”

“…Interestingly, Jiang and colleagues observed that 2D sp 2 carbon COFs are distinct from 1D sp 2 carbon polymers and graphene in terms of their π conjugation and polaron behavior [14]. This finding inspired the synthesis of a diversity of sp 2 carbon COFs with different building blocks and topologies, shaping a molecular platform for the exploration of sp 2 carbon materials [15][16][17][18][19][20][21][22][23][24][25].…”

Covalent organic frameworks in Lieb lattice for tunable photocatalytic water splitting under visible light

“…These findings offer immense opportunities for chemists to fabricate COFs with desired photocatalytic activity, and will tremendously boost their applications in overall water splitting, 6 metal-free catalysis, 34 and other photocatalytic chemical transformations. [35][36]…”