Aqueous-Phase Synthesis of Cyclic Trinuclear Cluster-Based Metal–Organic Frameworks

Abstract

The synthesis of metal–organic frameworks (MOFs) often involves high-boiling-point organic solvents, which can have extensive environmental impact and limit their large-scale applications. Here, we present a one-pot aqueous-phase approach for the rapid preparation of 33 trinuclear-copper-cluster-based MOFs (1 to 33) with different pyrazoles under ultrasonic irradiation. To address the water-solubility challenge of organic linkers, we employ aromatic amines/aldehydes and pyrazole aldehydes/amines to in situ generate imine-based pyrazoles. This linker dismantling strategy enables the formation of low-concentration pyrazoles, which are essential for the assembly of trinuclear-copper-cluster-based MOFs in the aqueous phase. The use of preassembled trinuclear gold complexes instead of aromatic amines affords an Au–Cu-based MOF (34) of alternating gold and copper clusters, a rare example of MOFs with mixed yet precise arrangement of metal compositions. Additionally, the direct addition of pyruvic acid to the reaction mixture results in the facile synthesis of a carboxylic-acid-functionalized MOF (35), eliminating the need for preinstallation or postmodification steps in traditional MOF synthesis. Furthermore, we demonstrate 11-AA as an efficient photocatalyst for cross-dehydrogenative coupling (CDC) reactions, exploiting the synergetic effect of substrate activation on the copper sites and subsequent coupling initiated by the photosensitive organic linkers. This work offers a simple solution for making MOFs with minimal environmental impact; it also opens up possibilities for developing multifunctional MOFs for diverse applications.