Catalyst-Enabled In Situ Linkage Reduction in Imine Covalent Organic Frameworks

New linkages for covalent organic frameworks (COFs) have been continuously pursued by chemists as they serve as the structure and property foundation for the materials. Developing new reaction types or modifying known linkages have been the only two methods to create new COF linkages. Herein, we report a novel strategy that uses H₃PO₃ as a bifunctional catalyst to achieve amine-linked COFs from readily available amine and aldehyde linkers. The acidic proton of H₃PO₃ catalyzes the imine framework formation, which is then in situ reduced to the amine COF by the reductive P–H moiety. The amine-linked COF outperforms its imine analogue in promoting Knoevenagel condensation because of the more basic sites and higher stability.