Supported Au/MIL-53(Al): a reusable green solid catalyst for the three-component coupling reaction of aldehyde, alkyne, and amine

MIL-53(Al) was synthesized in a mixture of aluminum nitrate, 1,4-benzenedicarboxylic acid, and water using the hydrothermal and reflux methods. A metal-organic-framework-supported Au-based heterogeneous catalyst (Au/MIL-53(Al)) was prepared using the impregnation method under mild conditions with HAuCl4 center dot 4H(2)O as the Au precursors. The physicochemical properties of the samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TG), transmission electron microscopy (TEM), and inductively coupled plasma atomic emission spectroscopy (ICP-AES). MIL-53(Al) indicates excellent chemical stability without structure degradation during the loading and catalysis process. The XPS spectra indicate that the catalyst Au/MIL-53(Al) contains coexisting Au-0 and Au3+ ions. The catalytic performance of the catalyst was examined in one-pot synthesis of structurally divergent propargylamines via three component coupling of aldehyde, alkyne, and amine (A(3)) in 1,4-dioxane. The results showed that the catalyst Au/MIL-53(Al) displayed high activity without any additives or an inert atmosphere (the yield reached 97.9 % for 5 h at 120 A degrees C). Au/MIL-53(Al) has proven to be applicable to a wide range of substrates. Various aromatic/aliphatic aldehydes, aromatic alkynes, and piperidine were able to undergo A(3) coupling on the catalyst Au/MIL-53(Al). In addition, the catalyst could be recovered easily by centrifugation and reused three times.