Catalysis and CO₂ Capture by Palladium-Incorporated Covalent Organic Frameworks

Triazine-based imine and β-ketoenamine linked covalent organic frameworks (COFs), TAT-DHBD (1) and TAT-TFP (2), have been synthesized from 1,3,5-tris-(4'-aminophenyl)triazine (TAT) and 2,5-dihydroxybenzene-1,4-dicarboxaldehyde (DHBD) or 1,3,5-triformylphloroglucinol (TFP) under solvothermal conditions in dioxane/mesitylene mixture. These COFs exhibit significant surface areas owing to their meso- and micropores. The presence of basic nitrogen sites offers excellent affinity towards Pd nanoparticles and carbon dioxide. Post treatment of COFs 1 and 2 with palladium acetate gives Pd^II /TAT-DHBD (3) and Pd^II /TAT-TFP (4), which on reduction by NaBH₄ yields Pd⁰ /TAT-DHBD (5) and Pd⁰ /TAT-TFP (6), respectively. The new COFs have been characterized by FTIR, solid-state ¹³ C NMR spectroscopy, X-ray photoelectron spectroscopy (XPS), SEM, TEM, and Brunauer-Emmett-Teller (BET) surface area measurements. TEM studies corroborated the uniform distribution of Pd^II and Pd⁰ sites in the COFs. Compounds 3-6 are active towards the Suzuki-Miyaura cross-coupling of arenes with meager catalyst leaching even after five cycles. In addition, 4 exhibits CO₂ uptake of 11 wt % and 7.5 wt % at 273 and 298 K, respectively, at 1 bar.