Facile Fabrication of Hierarchical MOF-Metal Nanoparticle Tandem Catalysts for the Synthesis of Bioactive Molecules.

Multifunctional metal-organic frameworks (MOFs) that possess permanent porosity are promising catalysts in organic transformation. Herein, we report the construction of a hierarchical MOF functionalized with basic aliphatic amine groups and polyvinylpyrrolidone-capped platinum nanoparticles (Pt NPs). The post-synthetic covalent modification of organic ligands increases basic site density in the MOF, and simultaneously introduce mesopores to create a hierarchically porous structure. The multifunctional MOF is capable of catalyzing a sequential Knoevenagel condensation-hydrogenation-intramolecular cyclization reaction. The unique selective reduction of nitro group to intermediate hydroxylamine by Pt NPs supported on MOF, followed by intramolecular cyclization with cyano group to afford an excellent yield (up to 92%) to the uncommon quinoline N-oxides over quinolines. The hierarchical MOF and polyvinylpyrrolidone capping agent on Pt NPs synergistically facilitate the enrichment of substrates, and thus lead to high activity in the reduction-intramolecular cyclization reaction. The bioactivity assay indicates that the synthesized quinoline N-oxides evidently inhibit the proliferation of lung cancer cells. Our findings demonstrated the feasibility of MOF-catalyzed direct synthesis of bioactive molecules from readily available compounds under mild conditions.