Abstract: During last few years, metal-organic frameworks have attracted significant interest as catalysts for acid catalysis due to their unique structure, physicochemical properties and ability to adjustment of their acidity by the variation of the nature of the metals and/or organic ligands. These materials can be attractive for synthesis of oxygen- and nitrogen-containing heterocyclic compounds, which are widely used in different fields of chemistry and medicine. We investigated the catalytic potential of the MOFs (MIL-53(V, Fe, Cr, Al), MIL-100(V, Fe, Al, Cr), porous aluminium trimesates Al-BTCs (MIL-96(Al), MIL-100(Al) and MIL-110(Al)) and the system containing, in the cavities of the NH2-MIL-101(Al) structure, 15 wt % calix[4]arene (Ks) in the cone conformation (Fig. 1) in synthesis of five- and seven-membered heterocycles. The main attention was focused on the reveal the “structure-surface acidity-reactivity” relationships. It was demonstrated that their catalytic efficiency is related to the interaction between active sites and reactants. It was found that in heterocyclization of acetone with glycerine and propylene oxide to five-membered heterocycles (Schema 1) catalytic properties of MOFs were determined by the formation of acid sites due to the interaction of metal ion of MOF and methanol used as solvent. Reaction rate increased with decreasing the value of the zero point of the surface charge (pHPZC) in the following order: MIL-100(V) > MIL-100(Al) > MIL-100(Fe) > MIL-100(Cr). Moreover, the length of the M-O bond in framework of MOF affects the accessibility of active sites and, therefore the reaction selectivity. The decrease in the length of the M-O bond favours the increase in the formation of five-membered solketal. In synthesis of 1,5-benzodiazepine (Schema 2) catalytic behaviour of MOFs depends on the complexing ability of the M3+ ion to NH2-groups in (I), i.e. formation of M:←NH2R bond. The decreasing complexing ability, estimated in terms of ionic potential , leads to the decreasing yield of 1,5-benzodiazepine in the order: MIL-100(V) > MIL-100(Fe) > MIL-100(Cr) > MIL-100(Al). Reaction rate and yield of (II) can be increased by (a) the insertion of –SO3H group into framework of MOF (for example, UiO-66(Zr)) and (b) the insertion of calix[4]arene into framework of NH2-MIL-101(Al) (Table 1). The type of functional groups of calix[4]arene affects the activity of NH2-MIL-101(Al)-Ks system. Activity and yield of (II) increased after insertion of Ks with CN-groups into framework of MOF in contrast of Ks with –SO3H groups. This trend can be related with the decreasing surface acidity of composite due to the strong interaction between –SO3H groups with –NH2 groups of NH2-MIL-101(Al). Noteworthy that efficiency of MOFs was comparable and higher than that of zeolites. Recycling experiments point that MOFs can be used al least during six catalytic cycles without change activity. Noteworthy that efficiency of MOFs was comparable and higher than that of zeolites. Recycling experiments point that MOFs can be used al least during six catalytic cycles without change activity. Noteworthy that efficiency of MOFs was comparable and higher than that of zeolites. Recycling experiments point that MOFs can be used al least during six catalytic cycles without change activity

Cite: Timofeeva M.N. , Panchenko V.N. , Jhung S.H.
Metal-Organic Frameworks as Catalysts for the Cyclization Reactions of Synthesis of Oxygen- and Nitrogen-Containing Heterocyclic Compounds
In compilation Proceeding of International Symposium on Advanced Materials for Energy/Environment. 2018.

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