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Abstract
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Chemical transformations via catalysis are known as key processes in organic synthesis and energy storage/conversion, in which metals usually serve as central roles in catalysts, such as, metal nanoparticles (NPs) and metal complexes [1]. As a type of classical heterogeneous catalysts, metal NPs present significant promise in a wide range of catalytic fields, where the active metal sites are often located at crystal corners, edges, and facets, bearing different catalytic properties. To normalize the catalytic behaviors and maximize the utilization efficiency of metals, downsizing the metal NPs is considered as an effective method to greatly boost the catalytic performances with enhanced activities and selectivity [2]. Metal-organic frameworks (MOFs) (also called porous coordination polymers, PCPs), as constructed by both inorganic nodes (metal ions/clusters) and organic ligands via coordination bonds, have gained considerable attention, achieving overall and breakthrough progress since the 1990s [3]. The structural diversity, ultrahigh surface area, and easy tailorability as well as the crystalline nature allow the MOFs to be widely applied in various fields including the early discovered catalysis [4]. Also, 1,4-dihydropyridine with indole and coumarin structures have significant biological properties such as analgesic, anticoagulant, antibacterial and etc. [5]. On the basis of above-mentioned facts, synthesis of biological structure with indole moieties in the presence of reusable solid acid is our main research interest. With this aim, bimetal-organic frameworks with phosphorous acid tags as a porous-catalyst structure was synthesized, characterized and used in synthesis chromeno[3,4-b]pyrazolo[4,3-e]pyridin with indole moieties under mild and green condition (Scheme 1).
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