Dung T. Le

Application of iron-based metal–organic frameworks in catalysis: oxidant-promoted formation of coumarins using Fe3O(BPDC)3 as an efficient heterogeneous catalyst

An iron-based metal–organic framework, Fe3O(BPDC)3, was synthesized, and was characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, atomic absorption spectrophotometry (AAS), and nitrogen physisorption measurements. The Fe-MOF could be used as an efficient heterogeneous catalyst for the synthesis of coumarins from salicylaldehydes and activated methylene compounds in the presence of tert-butyl hydroperoxide as the oxidant under base-free conditions. The Fe3O(BPDC)3 was more catalytically active for the synthesis of coumarins than other MOFs such as Cu2(BDC)2(BPY), Cu3(BTC)2, Cu2(BDC)2(DABCO), Ni2(BDC)2(DABCO), and Fe3O(BDC)3. This Fe-MOF also offered significantly higher catalytic activity for the transformation than that of common metal salts such as FeCl3, Fe(NO3)3, FeSO4, CuCl2, CuCl, Cu(NO3)2, and Ni(NO3)2. The Fe3O(BPDC)3 catalyst could be recovered and reused several times without significant degradation in catalytic activity. To the best of our knowledge, the oxidant-promoted formation of coumarins under heterogeneous catalysis conditions was not previously mentioned in the literature.

Synthesis of triphenylamines via ligand-free selective ring-opening of benzoxazoles or benzothiazoles under superparamagnetic nanoparticle catalysis

CuFe2O4 superparamagnetic nanoparticles were utilized as an effective recyclable heterogeneous catalyst for the synthesis of triphenylamines via the ligand-free selective ring-opening reaction of benzoxazoles or benzothiazoles with iodoarenes. The nano CuFe2O4 demonstrated noticeably higher catalytic efficiency than a series of homogeneous catalysts and heterogeneous catalysts. It was possible to separate the nano CuFe2O4 by using a magnet, and the recovered catalyst was reused many times while its activity could be maintained. To the best of our knowledge, this is the first example of heterogeneous catalysis for the transformation of benzoxazoles, and the transformation of benzothiazoles to triphenylamines has not been previously reported in the literature.