Rational Embedding of DMAP into Covalent Triazine Frameworks for Efficient Heterogeneous Organocatalysis

Abstract

The development of a straightforward strategy to design and synthesize covalent triazine frameworks (CTFs) with high catalytic efficiency is of great importance. Here, we report the construction of a DMAP-embedded CTF (DMAP-CTF) via a mild aldehyde-amidine condensation, using 4-dimethylaminopyridine (DMAP) as the catalytic building block. The resulting DMAP-CTF exhibits a limited crystallinity. Assisted by a NaCl template, the material achieves a high surface area of 675 m² g⁻¹ and a well-developed pore structure. Comprehensive characterization confirms the atomic-level incorporation of DMAP units within the triazine framework. DMAP-CTF acts as a highly effective heterogeneous catalyst for two types of transformations: the Steglich esterification of various alcohols and phenols (84-99% yield) and the green, aqueous-phase synthesis of 1,2,4-triazolidine-3-thiones (86-95% yield). The catalyst demonstrates excellent stability and recyclability over 15 consecutive cycles. Furthermore, it was successfully implemented in a continuous-flow fixed-bed reactor for the scalable synthesis of phenolic esters, maintaining stable activity for at least 30 h. Through combined experimental and computational studies, the structure-activity relationship was elucidated, identifying the nucleophilic pyridinic nitrogen of the DMAP moiety as the key active site. This work highlights the potential of bottom-up constructed DMAP-integrated CTFs, prepared via aldehyde-amidine condensation, for advanced catalytic applications.