MOF modified with a Cu-complex as a novel MOF-based heterogeneous catalyst for the one-pot one-step synthesis of α-aminophosphonates directly from alcohols by a tandem oxidation process

Abstract

A metal–organic framework functionalized with a copper complex, named Cu-ISA-MIL-Fe, was fabricated through post-synthetic modification of Fe-MIL-101-NH₂ via isatin Schiff-base formation followed by coordination with Cu(OAc)₂. The newly synthesized Cu-ISA-MIL-Fe was characterized by analytical methods, including PXRD, FT-IR, XPS, FESEM, EDS elemental mapping, TEM, and elemental analysis. The similarity of its PXRD pattern with that of Fe-MIL-101-NH₂ indicated that the crystalline structure of the MOF in the post-synthetic modification remained intact. FT-IR analysis endorsed the successful construction and functionalization of the MOF. FESEM and TEM images showed that the octahedral morphology of the MOF with an edge length of ∼500 nm was well preserved. XPS elemental survey and EDS elemental mapping confirmed the existence of C, N, O, Cu and Fe, with a uniform distribution throughout the MOF structure. Cu-ISA-MIL-Fe was used as the first MOF-based catalyst for the one-pot one-step synthesis of dialkyl α-aminophosphonates directly from readily available alcohols via a tandem oxidation process. The catalyst showed an extremely high catalytic performance for the selective oxidation of different benzyl alcohols, followed by the condensation of the in situ-prepared benzaldehyde with anilines and alkyl phosphites (tri-ethyl/methyl/iso-propyl and di-iso-propyl phosphites) to produce a variety of dialkyl α-aminophosphonates. This methodology offers a number of merits, including cost-effective operational conditions, efficient and selective product formation in 75–95% yields, reduced reaction times, use of a green solvent, and facile catalyst separation and recyclability. Besides, conducting a simplified one-pot one-step synthetic procedure contributes to step saving, minimizes the procedural complexity and decreases waste production, further enhancing the overall efficiency of the method.