Metal–Organic Framework Surface Functionalization Enhancing the Activity and Stability of Palladium Nanoparticles for Carbon–Halogen Bond Activation

Supported metal nanocatalyst is one of the efficient tools for organic transformations. However, catalyst deactivation caused by the migration, aggregation, and leaching of active metal species in the reaction process remains challenging. Herein, a metal-organic framework (MOF), MIL-101, was employed to covalently graft the PPh3 ligand on its surface and then supported palladium nanoparticles (Pd NPs), affording Pd/MIL-101-PPh3. A variety of spectral characterizations and DFT calculation reveal that there is an electron-donating effect of the MOF surface PPh3 toward Pd NPs, which markedly boosts the activation of the carbon-halogen bond in aryl halides. Consequently, Pd/MIL-101-PPh3 exhibits excellent activity for the three-component reaction of 2-iodoaniline, CO2, and isocyanide, as well as Suzuki-Miyaura and Heck coupling reactions, far exceeding amino-functionalized Pd/MIL-101-NH2, naked Pd/MIL-101, and other commercial-supported Pd catalysts. Furthermore, Pd/MIL-101-PPh3 can also frustrate the migration, aggregation, and leaching of reactive Pd species in the reaction process due to the molecular fence effect generated by MOF surface functionalization.