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 Cu-2(BDC)(2)(BPY), Cu-3(BTC)(2), Cu-2(BDC)(2)(DABCO), Ni-2(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.