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.

Highly efficient photosynthesis of hydrogen peroxide by a stable Zr(IV)-based MOF with a diamino-functionalized ligand.

Metal-organic frameworks (MOFs) have emerged as a promising class of materials for solar-driven hydrogen peroxide (H2O2) generation due to their porosity, large surface area and designable molecular building blocks; however, producing H2O2 from oxygen and water without sacrificial agents remains a major challenge. Herein, we have constructed two UiO-67-type MOFs, UiO-67-NH2 and UiO-67-(NH2)2, by a solvothermal method using 2-amino-4,4'-biphenyldicarboxylic acid and 2,2'-diamino-4,4'-biphenyldicarboxylic acid as ligands, respectively. A variety of photochemical measurements have shown that the introduction of diamino groups into UiO-67-(NH2)2 not only enhances its absorption ability for visible light, but also facilitates the separation of photogenerated electron/hole pairs. Consequently, compared to monoamino-functionalized UiO-67-NH2, UiO-67-(NH2)2 exhibits a 5.5 times higher H2O2 production rate in pure water for 1 h. A two-step one-electron oxygen reduction reaction pathway for photocatalytic H2O2 production was suggested based on a series of control experiments and active species trapping tests by electron paramagnetic resonance spectra. This work provides new insights into the regulation of functionalized MOF ligands at the molecular level and a catalytic mechanism towards MOF-based photocatalysts for H2O2 production with high activity.