A C-H activation-based multicomponent reaction approach towards benzimidazole-linked covalent organic frameworks for proton conduction.

We report here a robust multicomponent reaction (MCR) strategy for the synthesis of benzimidazole-linked covalent organic frameworks (COFs), overcoming the long-standing requirement for specialized ortho-functionalized precursors. By employing a copper-catalyzed C-H bond amination protocol with readily available non-ortho-functionalized amines, aldehydes, and azidotrimethylsilane (TMSN3), we successfully introduce the necessary nitrogen atom to construct the benzimidazole heterocycle in situ. This methodology not only circumvents synthetic constraints but also significantly expands the structural diversity of benzimidazole-linked COFs, as demonstrated by the successful synthesis of two highly crystalline frameworks, GBU-261 and GBU-262. When impregnated with phosphoric acid (PA), these COFs exhibit exceptional proton conductivity, reaching up to 4.41 × 10-2 S cm-1 at 95% relative humidity and 95 °C. The observed low activation energies indicate a Grotthuss-type proton transport mechanism, facilitated by the synergistic stabilization between the framework and the confined PA networks. This versatile approach paves the way for the rational design and exploration of heterocycle-linked functional materials.