Synthesis of 2D Imine-Linked Covalent Organic Frameworks through Formal Transimination Reactions

Covalent organic frameworks (COFs) are crystalline, permanently porous, two-dimensional or three-dimensional polymers with tunable topology and functionality. COFs linked with imines or β-ketoenamines are more chemically stable than their boron-linked counterparts, making them more promising for a broad range of applications, including energy storage devices, proton-conductive membranes, and catalyst supports. We report a general and scalable method for synthesizing imine- and β-ketoenamine-linked COFs based on the formal transimination of N-aryl benzophenone imines. These substrates are often the synthetic precursors of traditional polyfunctional aryl amine monomers and are more stable, soluble, and easy to handle and purify. The imine- and β-ketoenamine-linked COFs obtained from this approach show excellent materials quality, as characterized by X-ray diffraction and surface area analysis. The most optimized COF exhibited a Brunauer–Emmett–Teller surface area (>2600 m2/g) very close to its theoretical value (2830 m2/g). This method is amenable to both conventional solvothermal conditions and microwave heating, providing similar or even improved materials quality with shorter reaction times. The high materials quality, scalability, and availability of benzophenone imine monomers are all attractive features of this approach.