Preparation and Characterization of Metal-Organic Framework Supported Gold Catalysts and Their Catalytic Performance for Three-Component Coupling Reaction

IRMOE-3-SI-Au(PS) and IRMOE-3-SI-Au(OP) catalysts were synthesized by post-synthesis method (PS) and one-pot method (OP), respectively. The catalysts were characterized by X-ray diffraction, infrared spectroscopy, thermogravimetric analysis and differential thermal, transmission electron microscopy, and temperature-programmed reduction. These two catalysts were tested by three-component coupling reaction of aldehydes, alkynes, and amines. The substrate scope, catalyst reusability, and possible mechanism were investigated. Both two catalysts showed higher conversions of benzaldehyde and 100% selectivity for propargylamines. Compared with IRMOE-SI-Au(OP), IRMOE-SI-Au(PS) gave a higher aldehyde consumption rate at 120 degrees C (13.7 vs 2.0 mmol/(g.h)) based on total gold content. Both aromatic and aliphatic aldehydes including those bearing functional groups, such as alkoxy, alkyl, and chloro-group, were able to undergo the corresponding three-component-coupling. It was found that aryl aldehydes possessing electron-drawing group afforded higher conversion than that with an electron-donating group bound to the benzene ring. Among the various amines tested, alicyclic amines, such as piperidine, pyrolidine, and morpholine, gave high conversions of benzaldehyde, whereas the diethylamine afforded lower conversion of benzaldehyde. The catalysts could be reused for three reaction cycles with only slight drop in activity. A tentative mechanism was proposed involving the activation of the C-H bond of alkyne by IRMOF-3 immobilized gold catalysts.