Innovative application of high nitrogen magnetic MOF as a catalyst in the aza-Michael reaction

Abstract

The application of nitrogen-rich metal–organic framework (N-rich MOF) and its magnetic composite in the aza-Michael reaction as a catalyst was investigated. The synthesis of anionic N-rich MOF, [CuBT(H₂O)₂]_n (CuBT)) from the 5,5′-bistetrazole ligand (H₂BT) to increase efficiency and reduce energy consumption was optimized using the hydrothermal method within 24 h with a ratio of (ligand 3: metal salt 3: solvent 1). To increase the application and ease of separation, magnetite nanoparticles encapsulated in polyvinylpyrrolidone (Fe₃O₄@PVP) were stabilized on the surface of MOF (Fe₃O₄@PVP@CuBT) by sonication and hydrothermal methods. The materials were characterized using various analyses, including FT-IR, ¹H NMR, ¹³C NMR, XRD, TEM, SEM, EDX & mapping, BET-BJH, Zeta, DLS, VSM, and ICP. The composite exhibited a surface area (S_BET) of 33.727 m²/g and an average pore diameter of 9.34 nm. XRD analysis confirmed the successful synthesis of the MOF and the presence of magnetite peaks. ICP analysis determined that Fe₃O₄@PVP@CuBT contains 21.507% Cu and 6.197% Fe. VSM analysis showed that the composite has magnetic properties, with a saturation magnetization (M_s) of 5.19 emu/g, indicating its superparamagnetic behavior and ease of separation with a strong magnet. The catalytic properties of the MOF and its magnetic composite were evaluated in the aza-Michael reaction with different amines. Fe₃O₄@PVP@CuBT (3% W) demonstrated the highest conversion percentage (94%) as a strong and recyclable Lewis acid catalyst under mild conditions in the reaction of 2-vinyl pyridine with aniline.