(513cm) Facile Fabrication of Hierarchically Porous MOF-Metal Nanoparticle Tandem Catalysts for the Synthesis of Bioactive Quinoline N-Oxides

Multifunctional metal-organic frameworks (MOFs) that possess permanent porosity are promising catalysts in organic transformation. Herein, we report the construction of a hierarchically porous MOF with both basic amine groups and polyvinylpyrrolidone-capped platinum nanoparticles (PVP-Pt/UiO-NM). The post-synthetic covalent modification of the organic linkers of MOF increases basic site density, and simultaneously creates mesopores to form hierarchically structure. The resulted material is efficient in catalyzing a sequential Knoevenagel condensation–hydrogenation–intramolecular cyclization reaction. The unique reduction of nitro group to intermediate hydroxylamine by Pt NPs supported on MOF, followed by intramolecular cyclization with cyano group afford an excellent yield to the uncommon quinoline N-oxides (up to 92%) over quinolines. The hierarchical porous MOF and polyvinylpyrrolidone synergistically facilitate the enrichment of substrates and thus lead to high activity in the tandem reaction. The obtained quinoline N-oxides showed promising bioactivity and inhibited the proliferation of lung cancer cells obviously. The catalyst is stable under the reaction conditions and maintains its catalytic activity after reused five times. This work represents the first to use a hierarchically porous MOF-metal nanoparticle catalyst in the tandem reaction to synthesize bioactive quinoline N-oxides under mild reaction conditions directly.