Combined Experimental and Theoretical Study of the Synthesis of 5,7-Dihydroxy-4-methylcoumarin via a Pechmann Condensation in the Presence of UiO-66-SO3H Catalysts

An efficient synthesis of 5,7-dihydroxy-4-methylcoumarin from phloroglucinol with ethyl acetoacetate in the UiO-66-SO3H metal-organic framework is reported. The potential of UiO-66-SO3H as a solid catalyst was determined through optimized-condition experiments and quantum molecular calculations. The optimal conditions for the synthesis of 5,7-dihydroxy-4-methylcoumarin with UiO-66-SO3H were as follows: phloroglucinol/ethyl acetoacetate molar ratio = 1:1.6, reaction time = 4 h, and temperature = 140 °C, for which the reaction yield reached 66.0%. The reusability of UiO-66-SO3H catalysts for Pechmann condensation was examined. The activation energy of the reaction occurring on a sulfonic group of the UiO-66-SO3H catalyst was 12.6 kcal/mol, which was significantly lower than 22.6 kcal/mol of the same reaction on the UiO-66 catalyst. To comprehend the reaction mechanism, density functional theory with the ONIOM approach was applied for the synthesis of coumarin on the UiO-66-SO3H and UiO-66 clusters. A possible reaction mechanism was proposed involving three steps: a trans-esterification step, an intramolecular hydroxyalkylation step, and a dehydration step. The rate-determining step was suggested to be the first step which acquired an activation energy of 15.7 and 29.5 kcal/mol, respectively. Information from this study can be used as guidelines to develop more efficient catalytic metal-organic frameworks for various organic syntheses.

Two pillared-layer metal-organic frameworks based on the pinwheel trinuclear carboxylate-clusters of Zn(II) and Co(II): synthesis, crystal structures, magnetic study, and Lewis acid catalysis

Using a dicarboxylic acid, [1,1'-biphenyl]-4,4'-dicarboxylic acid (H₂L1) and an exobidentate ligand, (1E,1'E)-N,N'-(1,4-phenylene)bis(1-(pyridin-4-yl)methanimine) (L2), two 3D interpenetrated networks, {[Zn₃(L1)₃(L2)]·9H₂O}_n (Zn-MOF) and {[Co₃(L1)₃(L2)(DMF)]·0.5DMF}_n (Co-MOF), have been prepared in good yields. The crystal structure analysis of Zn-MOF and Co-MOF revealed that both have a 3D pillared-layer structure based on pinwheel trinuclear metal-carboxylate clusters as secondary building units (SBUs). Furthermore, the structures also exhibited three-fold interpenetration. Although the overall networks in Zn-MOF and Co-MOF showed significant resemblances, there are marked differences in their crystal structures, which are associated with the coordination environment of the metal centre and the binding modes of the carboxylates. Gas adsorption studies (N₂ at 77 K and 1 bar) indicated that Co-MOF is more porous than Zn-MOF. Magnetic measurements on Co-MOF indicate a significant antiferromagnetic interaction (45 K to 303 K) between trimeric Co(II) S = 3/2 spins through syn-syn carboxylato bridges. Both MOFs were studied for the Lewis acid catalyzed Knoevenagel condensation reactions between benzaldehydes and malononitrile with an active methylene group, where Zn-MOF was found to be a better catalyst than Co-MOF. This was supported by the Monte Carlo simulations indicating the better substrate binding ability of Zn-MOF than Co-MOF.

Copper-Catalyzed Synthesis of Coumarins. A Mini-Review

Coumarin (2H-chromen-2-one) derivatives have important uses in medicinal and synthetic chemistry, for example, as fluorescent probes. These properties have prompted chemists to develop efficient synthetic methods to synthesize the coumarin core and/or to functionalize it. In this context, many metal-catalyzed syntheses of coumarins have been introduced; among them, copper-catalyzed reactions appear to be very promising owing to the non-toxicity and cheapness of copper complexes. In this mini-review, the results in this field are summarized. We hope to stimulate other applications of these complexes in the preparation of coumarin derivatives.

Preparation of Ni-microsphere and Cu-MOF using aspartic acid as coordinating ligand and study of their catalytic properties in Stille and sulfoxidation reactions

In this study, the thermal and catalytic behavior of Ni-microsphere and Cu-MOF were investigated with aspartic acid as the coordinating ligand with different morphologies. The Ni-microsphere and Cu-MOF with aspartic acid, as the coordinating ligand, were prepared via a solvothermal method. The morphology and porosity of the obtained Ni microsphere and Cu-MOF were characterized by XRD, FTIR, TGA, DSC, BET and SEM techniques. The catalytic activity of the Ni-microsphere and Cu-MOF was examined in Stille and sulfoxidation reactions. The Ni microsphere and Cu-MOF were easily isolated from the reaction mixtures by simple filtration and then recycled four times without any reduction of catalytic efficiency.

Solvent-assisted ligand exchange (SALE) for the enhancement of epoxide ring-opening reaction catalysis based on three amide-functionalized metal-organic frameworks

In recent years, functionalized pillar ligands have gained significant interests due to their important role in MOF structure and performance. The synthesis of MOF compounds with a particular functionalized ligand is not always successful, and sometimes, synthesis cannot be achieved easily or directly, even by employing several methods. However, this limitation can be overcome by applying a post-synthesis step that swaps the functional groups without changing the backbone of the pillar ligand. Solvent-assisted ligand exchange (SALE) is a post-synthesis method that has been used for confronting this challenge by replacing a functional group with an alternative. Through this investigation, we tried to improve the properties of MOF compounds and increase their catalytic efficiency by importing new functional groups into their structures. The N1,N3-di (pyridine-4-yl) malonamide linker (S) is a pillar ligand, which does not easily enter into the structure during the synthesis of MOF compounds. Therefore, to solve this issue, amide-functionalized, benzene-core ligand derivatives were designed as linkers to manufacture the new 3D structures [Co(oba)(bpta)]·(DMF)₂ TMU-50 and [Co₂(oba)₂(bpfn)]·(DMF)_2.5 TMU-51 and the novel 2D structure [Co(oba)(bpfb)]·(DMF)₂ TMU-49. These structures were achieved by layering the compounds via hydrothermal reaction. Moreover, the ability of these structures to act as catalysts was evaluated using the methanolysis reaction of epoxides. To increase the MOF catalytic efficiency, we designed the N1,N3-di (pyridine-4-yl) malonamide linker (S) as a malonamide pillar ligand, which contains an acidic hydrogen that is suitable for catalyzing an epoxide ring-opening reaction and therefore enhancing the catalytic activity. As the synthesis of the MOF structure with this linker was not successful, we designed three new structures by incorporating different percentages of S linkers by exchanging the acylamide functional group with malonamide via the SALE pathway. The acylamide functional group was successfully replaced and produced daughter MOFs TMU-49S, TMU-50S and TMU-51S. PXRD and NMR spectroscopy confirmed that the S linker was incorporated into the acylamide-MOF structure. The obtained materials TMU-49S, TMU-50S and TMU-51S are isostructural with their parent frameworks. The S spacer significantly improved the catalytic properties of the MOF compounds in the ring-opening reaction of epoxides, with TMU-50S showing a 98% catalytic efficiency after incorporating the S linker. The catalysts could be recycled without any significant loss in the catalytic efficiency.

Luminescent metal organic frameworks for sensing and gas adsorption studies

Two three-dimensional metal organic frameworks (LZn and LCd) were synthesized solvothermally for sensing of nitro phenolic explosives and gas adsorption studies. LZn showed selectivity towards N₂ gas at 77 K.

Structure, characterization, and catalytic properties of open-metal sites in metal organic frameworks

This review provides an overview of the current understanding of structure–catalytic properties of open-metal sites in metal organic framework materials.

Coumarin Derivatives Solvent-Free Synthesis under Microwave Irradiation over Heterogeneous Solid Catalysts

A suitable methodology of synthesis of coumarin derivatives by Pechmann reaction over heterogeneous solid acid catalysts in a free solvent media under microwave irradiation is described. Resorcinol, phenol and ethyl acetoacetate were selected as model reactants in the Pechmann condensation. The catalytic activity of several materials—Amberlyst-15, zeolite β and sulfonic acid functionalized hybrid silica—in solvent-free microwave-assisted synthesis of the corresponding coumarin derivatives has been investigated in detail. 7-Hydroxy-4-methylcoumarin and 4-methylcoumarin were obtained in 97% and 43% yields, respectively, over Amberlyst-15. This was the most active catalyst in the Pechmann reaction under studied conditions.

Incorporation of Molecular Catalysts in Metal-Organic Frameworks for Highly Efficient Heterogeneous Catalysis

Porous metal-organic frameworks (MOFs) are built from periodically alternate organic moieties and metal ions/clusters. The unique features of the open framework structures, the high surface areas, the permanent porosity, and the appropriate hydrophilic and hydrophobic pore nature mean that MOF materials are a class of ideal host matrices for immobilization of molecular catalysts. The emerging porous materials can not only retain but are also able to enhance the catalytic functions of the single individuals. MOF catalysts have the following super characters: i) uniformly dispersed catalytic sites on the pore surfaces to improve the utility, ii) appropriate hydrophilic and hydrophobic pore nature to facilitate the recognition and transportation of reactant and product molecules, iii) a collaborative microenvironment to realize synergistic catalysis, and iv) simple separation and recovery for long-term usage. Accompanying the development of the synthetic strategies and the technologies for the characterization of MOF materials, MOF catalysis has undergone an upsurge, which has transcended the stage of opportunism. Here, the rational design and synthesis of MOF catalysts are discussed, along with the key factors of active sites, microenvironments, and transmission channels that lead to the distinct catalytic properties of MOF catalysts.

A porous two-dimensional Zn(ii)-coordination polymer exhibiting SC–SC transmetalation with Cu(ii): efficient heterogeneous catalysis for the Henry reaction and detection of nitro explosives

The 2D Zn(ii)-CP, 1Zn and its Cu-analogue 1Cu exhibit efficient catalytic activity for the Henry reaction. 1Zn can be utilized for detecting trace amounts of nitro explosives in DMSO.

Synthesis of 1,2-Dicarbonyl-3-enes by Hydroacylation of 1-Alkynes with Glyoxal Derivatives Using Metal-Organic Framework Cu/MOF-74 as Heterogeneous Catalyst

A crystalline copper-based metal-organic framework Cu/MOF-74 was synthesized, and used as an efficient heterogeneous catalyst for the synthesis of 1,2-dicarbonyl-3-enes by means of the hydroacylation of 1-alkynes with glyoxal derivatives in the presence of a base. Cu/MOF-74 was found to be more catalytically active for the synthesis of 1,2-dicarbonyl-3-enes than other MOFs including Cu₂ (BDC)₂ (DABCO), Cu₃ (BTC)₂ , Cu(BDC), Cu₂ (NDC)₂ (DABCO), Cu₄ I₄ (DABCO)₂ , Ni-MOF-74, Zn-MOF-74, Fe₃ O(BDC)₃ , In(OH)(BDC), and Zr₆ O₄ (OH)₄ (BDC)₆ . Cu/MOF-74 also exhibited better performance than other homogeneous copper catalysts, including Cu(OAc)₂ , Cu(NO₃ )₂ , CuI, CuBr, CuCl, CuCl₂ , and CuBr₂ . The Cu/MOF catalyst was able to be recovered and reused several times without a significant degradation in catalytic activity. To the best of our knowledge, the formation of 1,2-dicarbonyl-3-enes has not previously been carried out under heterogeneous catalysis conditions.

The UiO-66-SO3H metal–organic framework as a green catalyst for the facile synthesis of dihydro-2-oxypyrrole derivatives

The multicomponent domino reaction synthesis of dihydro-2-oxopyrroles has been performed using the sulfonated metal–organic framework, UiO-66-SO₃H (UiO is the University of Oslo), as a highly efficient acid catalyst.

Adsorption mechanism on metal organic frameworks of Cu-BTC, Fe-BTC and ZIF-8 for CO2 capture investigated by X-ray absorption fine structure

XAFS analysis demonstrates the physical driving force, plus minor chemical transformation for the CO₂ adsorption mechanism by MOFs.

Synthesis of imidazo[1,5-a]pyridines via oxidative amination of the C(sp3)–H bond under air using metal–organic framework Cu-MOF-74 as an efficient heterogeneous catalyst

1,3-Diarylated imidazo[1,5-a]pyridines were synthesized via oxidative amination of the C(sp³)–H bond using Cu-MOF-74 as an efficient heterogeneous catalyst.

Application of iron-based metal–organic frameworks in catalysis: oxidant-promoted formation of coumarins using Fe3O(BPDC)3 as an efficient heterogeneous catalyst

An iron-based metal–organic framework Fe₃O(BPDC)₃ was used as an efficient heterogeneous catalyst for the synthesis of coumarins.

pH dependent synthesis of Zn(ii) and Cd(ii) coordination polymers with dicarboxyl-functionalized arylhydrazone of barbituric acid: photoluminescence properties and catalysts for Knoevenagel condensation

Coordination polymers of Zn(ii) and Cd(ii) act as recyclable heterogeneous catalysts for Knoevenagel condensation reaction of aldehydes with malononitrile.

Metal-organic frameworks: versatile heterogeneous catalysts for efficient catalytic organic transformations

Novel catalytic materials are highly demanded to perform a variety of catalytic organic reactions. MOFs combine the benefits of heterogeneous catalysis like easy post reaction separation, catalyst reusability, high stability and homogeneous catalysis such as high efficiency, selectivity, controllability and mild reaction conditions. The possible organization of active centers like metallic nodes, organic linkers, and their chemical synthetic functionalization on the nanoscale shows potential to build up MOFs particularly modified for catalytic challenges. In this review, we have summarized the recent research progress in heterogeneous catalysis by MOFs and their catalytic behavior in various organic reactions, highlighting the key features of MOFs as catalysts based on the active sites in the framework. Examples of their post functionalization, inclusion of active guest species and metal nanoparticles have been discussed. Finally, the use of MOFs as catalysts for asymmetric heterogeneous catalysis and stability of MOFs has been presented as separate sections.

Benzouracil-coumarin-arene conjugates as inhibiting agents for chikungunya virus

Chikungunya virus (CHIKV) is an arbovirus that was first recognized in an epidemic form in East Africa in 1952-1953. The virus is primarily transmitted through mosquitoes and the resulting disease, chikungunya fever, is found in nearly 40 countries. Neither an effective vaccine nor a specific antiviral drug exists for treatments of chikungunya fever. Thus 22 new conjugated compounds of uracil-coumarin-arene were designed and synthesized as potential inhibiting agents. Their chemical structures were determined unambiguously by spectroscopic methods, including single-crystal X-ray diffraction crystallography. The three units in these conjugates were connected by specially designed -SCH2- and -OSO2- joints. Five of these new conjugates were found to inhibit CHIKV in Vero cells with significant potency (EC50 = 10.2-19.1 μM) and showed low toxicity (CC50 = 75.2-178 μM). The selective index values were 8.8-11.5 for three conjugates. By analysis of the data from the anti-viral assays, the structure-activity relationship is derived on the basis of the nature of the uracil, the functional groups attached to the arene, and the joints between the ring units.

Expanding applications of zeolite imidazolate frameworks in catalysis: synthesis of quinazolines using ZIF-67 as an efficient heterogeneous catalyst

A cobalt zeolite imidazolate framework (ZIF-67) was successfully synthesized and characterized, then used as an efficient catalyst in a reaction to form quinazoline products. ZIF-67 could be recovered and reused several times without significant degradation in its activity.

Enhanced catalytic activity of a hierarchical porous metal–organic framework CuBTC

A hierarchical porous metal–organic framework CuBTC with mesopores of 3.9 nm pore size has been facilely obtained as Lewis acid catalyst.

Preparation and catalytic properties of Pd nanoparticles supported on micro-crystal DUT-67 MOFs

The obtained Pd/DUT-67 composites exhibited high catalytic performance in Suzuki coupling and nitrobenzene hydrogenation reactions.

Ligand-free N-arylation of heterocycles using metal–organic framework [Cu(INA)2] as an efficient heterogeneous catalyst

A metal–organic framework [Cu(INA)₂] was synthesized and used as a heterogeneous catalyst for arylation of a wide range of N–H heterocycles and aryl halides under ligand-free conditions.