1,5-Benzodiazepine synthesis via cyclocondensation of 1,2-diamines with ketones using iron-based metal-organic framework MOF-235 as an efficient heterogeneous catalyst

A crystalline iron-based metal-organic framework MOF-235 was synthesized, and characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR), atomic absorption spectrophotometer (AAS), and nitrogen physisorption measurements. The MOF-235 could be used as a heterogeneous catalyst for the synthesis of 1,5-benzodiazepines by the cyclocondensation of 1,2-diamines with ketones. Excellent conversions to 1,5-benzodiazepines were achieved in the presence of 5 mol% MOF-235 catalyst using molecular oxygen in air as the stoichiometric oxidant. The Fe-MOF exhibited higher catalytic activity for the cyclocondensation reaction than those of other MOFs including MOF-5, Mn(BDC), MOF-199, and Ni-2(BDC)(2)(DABCO). The Fe-MOF catalyst could be separated from the reaction mixture by centrifugation, and could be recovered and reused several times without a significant degradation in catalytic activity. To the best of our knowledge, 1,5-benzodiazepines were not previously synthesized using MOFs as heterogeneous catalysts. (C) 2015 Elsevier Inc. All rights reserved.