TAGRA 2025

Metal-organic frameworks (MOFs) are crystalline porous materials formed by coordinating metal ions or clusters with organic ligands, creating highly ordered 3D networks. We describe the synthesis and catalytic application of a copper-based metal-organic framework (MOF), Cu(BDC), for the N-arylation of NH-heterocycles with aryl halides. The metal-organic framework Cu(BDC) was prepared using a previously established method and extensively characterized through XRD, SEM, TGA, FT-IR, AAS, and nitrogen physisorption analyses. Atomic absorption spectroscopy revealed the final copper content to be 2.61 mmol g-1. The material has a specific surface area of 710 m2 g-1, Langmuir surface area of 753 m2 g-1, micropore volume of 0.78 cm3 g-1, and average pore size of 4.4 nm Multiple BJH peaks at 1.22, 10.65, 21.79, 33.24, and 59.76 nm reveal a multimodal pore size distribution.
Cu(BDC) demonstrated efficient catalytic activity in facilitating C-N bond formation between NH-heterocycles and iodo-, bromo-, and chloroarenes. Optimal reaction conditions were established by systematically investigating key parameters, including solvent, temperature, base, and catalyst loading. The MOF was applied as the catalyst in the coupling reaction of NH-heterocycles with chloro-, bromo-, and iodoarenes. Iodo- and bromoarenes exhibited high reactivity, whereas chloroarenes were less reactive. Imidazole and benzimidazole demonstrated superior activity compared to 2-methylbenzimidazole. The efficiency and reusability of the catalyst were assessed over multiple catalytic cycles using the reaction between imidazole and bromobenzene as a model. It was observed that, the efficiency remained nearly constant during the first three cycles, followed by a gradual reduction in later cycles. The stability and heterogeneous characteristics of Cu(BDC) were investigated by quantifying copper leaching during the coupling reaction of bromobenzene (1.0 mmol) with imidazole (1.5 mmol) in the presence of the catalyst (30 mg, Cu 7.8 mol%). The analysis revealed copper leaching of 0.0016 mmol, corresponding to a negligible level of 2.0%.