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, N-2 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.