Catalysis and CO2 Capture by Palladium-Incorporated Covalent Organic Frameworks

Abstract

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 PdII/TAT-DHBD (3) and PdII/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 13C NMR spectroscopy, X-ray photoelectron spectroscopy (XPS), SEM, TEM, and Brunauer–Emmett–Teller (BET) surface area measurements. TEM studies corroborated the uniform distribution of PdII 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.