Catalysis by metal–organic frameworks: proline and gold functionalized MOFs for the aldol and three-component coupling reactions

Translation of homogeneous catalysis into heterogeneous catalysis is a promising solution to green and sustainable development in the chemical industry. Recent research has shown that metal–organic frameworks (MOFs) could bridge the gap between homogeneous and heterogeneous catalysis. We successfully prepared for the first time a novel homochiral Zn-containing MOF referred to as CUP-1 based on the mixed linkers of 2-aminoterephthalic acid and L-lactic acid in a one-pot synthesis. The free NH2 group in the homochiral framework of CUP-1, similar to the well known achiral IRMOF-3, is potentially available for undergoing a variety of organic transformations, as demonstrated by choosing the auxiliary chiral L-proline and nano gold to functionalize MOFs with postsynthetic modification and one-pot synthesis strategies. IRMOF-3, CUP-1 and their functionalized samples were in-depth characterized by X-ray diffraction, N2 adsorption–desorption, optical and transmission electron microscopy, infrared spectroscopy, solid state nuclear magnetic resonance, thermogravimetric and differential thermal analysis, and temperature-programmed reduction. L-Proline functionalized IRMOF-3 shows fair to excellent enantioselectivity (up to 98%) in asymmetrical aldol reactions of aldehydes and acetone with higher turnover numbers and catalytic stabilities than the homogeneous counterpart. The gold functionalized CUP-1 catalysts are found to be highly active, stable and reusable for the three-component coupling reactions of aldehydes, alkynes and amines. This work provides general methods to functionalize MOFs with the active ligand and metal nanoparticles for fabrication of highly efficient MOF-based heterogeneous catalysts.