Catalyst-free dynamic covalent Knoevenagel/amine condensation for the synthesis and optimization of Imine-linked covalent organic frameworks

Abstract

With the rapid recent advances in constitutional dynamic chemistry (CDC), covalent organic frameworks (COFs), and dynamic polymers, the discovery and development of new dynamic covalent bonds have become a central priority, providing routes to novel architectures, controllable dynamic transformations, and emergent adaptive functions. Here, we report a facile, catalyst-free dynamic covalent condensation reaction between Knoevenagel derivatives (Kn) and amines that generate imines. Electron-withdrawing barbituric motifs intrinsically activate the carbon electrophile and lower the activation barrier relative to conventional aldehyde-amine condensations. The equilibrium constant (K_eq) can be effectively tuned across three orders of magnitude by modulating the push-pull conjugation within the Kn reactants. We demonstrate that this reaction enables gram-scale COF synthesis under mild, catalyst-free, non-sealed conditions. Introducing electron-donating substituents on the Kn monomers effectively improves framework crystallinity and porosity. This Knoevenagel/amine condensation approach provides a clean, efficient, and tunable dynamic covalent platform for the development of COFs and constitutional dynamic libraries/materials.