Fabrication of DABCO functionalized poly(ionic liquids): Vital role of ferric oxides in the formation of mesoporous structure and used as highly efficient and recyclable catalysts for multi-component reactions

The preparation of well-defined porous materials as carriers is critically fundamental for the design of heterogeneous catalysts. In this study, 1,4-Diazabicyclo[2.2.2]octane (DABCO) based hypercross-linked ionic copolymers with well-developed mesopores were fabricated, in which the alkene modified ferric oxides nanoparticles play a vital role for the formation of the mesoporous structure. The magnetic copolymers, fully characterized by N-2 adsorption-desorption, scanning electron microscopy (SEM)/transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and vibrating sample magnetometer (VSM), exhibited abundant active ionic centers, rich mesoporosity and moderate surface area. The as-prepared materials were found to be used as efficient catalysts for one-pot synthesis of indole derivatives and 3,4-fused indoles with seven-membered ring and good to excellent products yields were achieved within 10 h. The kinetic study revealed that the meso-porosity increased the catalytic efficiency in terms of reaction rate and yield, albeit with mass transfer resistance produced by mesoporous channels. Finally, the catalyst could be readily recovered using external magnetic force and recycled at least ten times without significant loss in catalytic activities, which makes it attractive for green transformation in chemical industry. (C) 2020 Elsevier Inc. All rights reserved.