Hexamethylenetetramine-based ionic liquid anchored onto the metal–organic framework MIL-101(Cr) as a superior and reusable heterogeneous catalyst for the preparation of hexahydroquinolines

Research on Chemical Intermediates - Regarding the significance of medicinal and pharmacological sciences, we explored one-pot multicomponent reaction of aromatic aldehydes, aryl amines,...     

Solid-state NMR studies of the acidity of functionalized metal–organic framework UiO-66 materials

The acid strength of metal–organic frameworks plays a key role in their catalytic performance such as activity and selectivity during catalytic reactions. Solid-state nuclear magnetic resonance in combination with probe molecules including 2-¹³C-acetone and pyridine-d₅ was employed to characterize the acid strength of UiO-66-X (X = -H, -2COOH, -SO₃H). It was found that after introduction of the functional groups, the acid strength of UiO-66-2COOH and UiO-66-SO₃H is considerably enhanced compared with that of parent UiO-66, with that of the former being similar to that of zeolite H-ZSM-5, and with that of the latter being slightly stronger than that of the former. Even though the acid density can efficiently be modified through changing the relative ratio in multivariate functionalized UiO-66-X, no significant alternation for the acid strength could be discerned in the MTV-UiO-66-X compared with acidic same-link counterpart. Theoretical calculations were employed to further confirm the acid strength of UiO-66-SO₃H and UiO-66-2COOH.     

Synthesis of new α-aminophosphonates using nanoscale nickel-based metal–organic framework as a heterogeneous catalyst and their antibacterial activity

An elegant approach was presented for the synthesis of novel α-aminophosphonates: a three-component one-pot condensation of 3-(trifluoromethyl)aniline, substituted aromatic aldehydes, and diethyl phosphite using a nickel-based metal–organic framework (Ni-MOF). The Ni-MOF was synthesized using 4,4′-biphenyldicarboxylic acid and further characterized using various techniques such as X-ray diffraction, Fourier-transform infrared, thermogravimetry/differential thermal analysis, Brunauer–Emmett–Teller, and field-emission scanning electron microscopy analyses. Ni-MOF seems to be an eco-friendly, an easily recyclable, and heterogeneous catalyst up to the eighth run with minimal reduction in its catalytic activity. The synthesized α-aminophosphonates were also investigated for antibacterial and antioxidant activities. In few cases, compounds 4a–4x show similar as well as higher antibacterial activity. Among the synthesized α-aminophosphonates, 4a–4x had more potent antibacterial activity against pathogenic bacteria while compounds 4h, 4m, 4n, 4q, 4u, 4v, and 4w exhibited significant antioxidant activity.     

Palladium supported on metal–organic framework as a catalyst for the hydrogenation of nitroarenes under mild conditions

Sustainable development demands an environmentally friendly and efficient method for the hydrogenation of organic molecules, including the hydrogenation of functionalized nitroarenes. In this study, a highly active and selective metal–organic framework-supported palladium catalyst was prepared for the catalytic hydrogenation of nitroarenes. High selectivity (>99%) and excellent yield (98%) of aniline were realized after 2 hours in ethanol under hydrogen (1 atm) at room temperature. The reductions were successfully carried out in the presence of a wide range of other reducible functional groups. More importantly, the catalyst was very stable without the loss of its catalytic activity after five cycles.     

Immobilized Pd on a NHC functionalized metal–organic framework MIL-101(Cr): an efficient heterogeneous catalyst in Suzuki−Miyaura coupling reaction in water

A novel Pd−NHC functionalized metal–organic framework (MOF) based on MIL-101(Cr) was synthesized and used as an efficient heterogeneous catalyst in the C-C bond formation reactions. Using this heterogeneous Pd catalyst system, the Suzuki−Miyaura coupling reaction was accomplished well in water, and coupling products were obtained in good to excellent yields in short reaction time. The Pd−NHC−MIL-101(Cr) was characterized using some different techniques, including Fourier transform-infrared, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy, inductively coupled plasma and elemental analysis. The microscopic techniques showed the discrete octahedron structure of MIL-101(Cr), which is also stable after chemical modification process to prepare the catalyst system. The TEM images of the catalyst showed the existence of palladium nanoparticles immobilized in the structure of the catalyst, while no reducing agent was used. It seems that the NHC groups and imidazolium moieties in the structure of the MOF can reduce Pd (II) to Pd (0) species. This modified MOF substrate can also prevent aggregation of Pd nanoparticles, resulting in high stability of them in organic transformation. The Pd−NHC−MIL-101(Cr) catalyst system could be simply extracted from the reaction mixture, providing an efficient synthetic method for the synthesis of biaryls derivatives using the aforementioned coupling reaction. The Pd−NHC−MIL-101(Cr) catalyst could be recycled in this organic reaction with almost consistent catalytic efficiency.     

Choline chloride·2ZnCl2 ionic liquid: an efficient and reusable catalyst for the solvent free Kabachnik–Fields reaction

The choline based Zn containing deep eutectic mixture was applied as an efficient and eco-friendly ionic liquid catalyst for the one pot three-component synthesis of α-aminophosphonates under solvent-free condition at room temperature. The reactions were completed in short times and products were obtained in good to excellent yields.     

Integration of zeolite@metal–organic framework: a composite catalyst for isopropyl alcohol conversion to aromatics

In this study, a Zn-based metal-organic framework (MOF)-zeolite composite ZSM-5@IRMOF-1 was synthesized for the alternative production of BTX from isopropyl alcohol (IPA). Incorporation ensured the capacity to tune the Lewis acidity at a framework level and design accessible pore structures, making composites highly attractive to be used as catalysts. The combination of monodispersed HZSM-5 zeolites on and within acidic IRMOF-1 provided the highly selective production of lower aromatics from IPA. The interaction of IPA with catalysts was investigated at different temperatures in a fixed-bed continuous flow reactor. The obtained product was analyzed using a standard test method ASTM D6730 through gas chromatography-detail hydrocarbon analyser. The results indicated that the reaction between IPA and MOF-supported zeolite occurred without substantial participation of MOFs. The maximum aromatic (BTEX) selectivity of 38.2% was achieved among all hydrocarbons at 92.3% carbon conversion. In addition, the gas yield was <20% for this catalyst system. The appropriate density of Brønsted and Lewis acidic sites and hierarchical pore structures provided the composite catalyst with outstanding aromatic selectivity yield and high stability.     

Low temperature ionic conductor: ionic liquid incorporated within a metal–organic framework

Ionic liquids (ILs) show promise as safe electrolytes for electrochemical devices. However, the conductivity of ILs decreases markedly at low temperatures because of strong interactions arising between the component ions. Metal–organic frameworks (MOFs) are appropriate microporous host materials that can control the dynamics of ILs via the nanosizing of ILs and tunable interactions of MOFs with the guest ILs. Here, for the first time, we report on the ionic conductivity of an IL incorporated within a MOF. The system studied consisted of EMI-TFSA (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide) and ZIF-8 (Zn(MeIM)₂, H(MeIM) = 2-methylimidazole) as the IL and the MOF, respectively. While the ionic conductivity of bulk EMI-TFSA showed a sharp decrease arising from freezing, the EMI-TFSA@ZIF-8 showed no marked decrease because there was no phase transition. The ionic conductivity of EMI-TFSA@ZIF-8 was higher than that of bulk EMI-TFSA below 250 K. This result points towards a novel method by which to design electrolytes for electrochemical devices such as batteries that can operate at low temperatures.     

A sulfonic acid functionalized ionic liquid as a homogeneous and recyclable catalyst for the one-pot synthesis of α-aminophosphonates

A sulfonic acid functionalized ionic liquid is used as a Brønsted acid catalyst for the one-pot, three-component synthesis of α-aminophosphonates from aldehydes and ketones at room temperature in water. This homogeneous catalytic procedure is simple and efficient and the catalyst can be reused at least six times without any noticeable decrease in catalytic activity.     

Iron(III)–salen complex on a polymer scaffold as heterogeneous catalyst for synthesis of benzimidazoles

Research on Chemical Intermediates - Benzimidazoles are important bioactive compounds with diverse applications in the medicinal, industrial, as well as agrochemical fields. In this study, an...     

Nano TiO_2 as a heterogeneous catalyst in an efficient one-pot three-component Mannich synthesis of β-aminocarbonyls

TiO₂ nanoparticles（TiO₂ NPs） worked as an efficient heterogeneous catalyst in a one-pot,three-component,and solvent free Mannich reaction;producing variousβ-aminocarbonyls in good yields,and with good stereoselectivities.The catalyst was easily separated from the reaction mixture and was recycled four times with no significant loss of its catalytic activity.     

Nano-SnCl4·SiO2 – a versatile and efficient catalyst for synthesis of 14-aryl- or 14-alkyl-14H-dibenzo[a,j]xanthenes

2-Naphthol and various aldehydes were used for the synthesis of 14-aryl- or 14-alkyl-14H-di-benzo[a,j]xanthene in the presence of nano-SnCl₄∙SiO₂ under solvent-free condition. Nano-SnCl₄∙SiO₂ is an efficient, readily available, and reusable catalyst for this reaction resulting in good to excellent yields.     

Highly efficient, one-pot, solvent-free synthesis of 2,4,6-triarylpyridines using a Br?nsted-acidic ionic liquid as reusable catalyst

Abstract  

A simple, efficient, and green method for synthesis of 2,4,6-triarylpyridines by one-pot three-component reaction of acetophenones, aryl aldehydes, and ammonium acetate using 3-methyl-1-(4-sulfonylbutyl)imidazolium hydrogen sulfate [HO₃S(CH₂)₄MIM][HSO₄], a Br?nsted-acidic ionic liquid, as an effective and reusable catalyst under solvent-free conditions is described. This method has several advantages, for example simple procedure with an easy work-up, shorter reaction times, and high yields.     

Influence of oxophilic behavior of UiO-66(Ce) metal–organic framework with superior catalytic performance in Friedel-Crafts alkylation reaction

In recent years, one of the analogous metal organic frameworks (MOFs) with UiO-66(Zr) topology receiving wider attention is UiO-66(Ce), which exhibits interesting properties and high thermal and chemical stability. Hence, in the present work, UiO-66(Ce) is synthesized by adopting an earlier procedure and characterized by series of spectroscopic techniques like UV-visible (UV-Vis), Fourier transform infrared (FT-IR), Raman and scanning electron microscope (SEM) to confirm its structural features and crystallinity using powder X-ray diffraction (XRD) and these results are in close agreement with other reports. The catalytic performance of UiO-66(Ce) was evaluated in the Friedel–Crafts alkylation reaction between β-nitrostyrene and indole to obtain heterocyclic compounds with biological activity. A series of control experiments indicate that Ce⁴⁺ located within the framework plays an important role in promoting this reaction and its activity is found to be much superior to that of UiO-66(Zr). This enhanced activity with Ce⁴⁺ compared to Zr⁴⁺ is attributed due to the higher oxophilicity of Ce⁴⁺, which can readily bind with an oxygen-containing substrate such as β-nitrostyrene. The leaching test confirms the heterogeneity of the reaction and the catalyst can be reused three times with identical activity to the fresh solid. UiO-66(Ce) shows wide substrate scope with high yields of the desired product. A proposed mechanism is also discussed.     

Covalently anchored sulfonic acid on silica gel （SiO2-R-SO3H） as an efficient and reusable heterogeneous catalyst for the one-pot synthesis of 1,8-dioxooctahydroxanthenes under solvent-free conditions

A highly efficient one-pot synthesis of 1,8-dioxooctahydroxanthenes under solvent-free conditions catalyzed by sulfonic acid covalently anchored onto the surface of silica gel is reported.All types of aldehydes,including aromatic,unsaturated,and heterocyclic,are used.The silica gel/sulfonic acid catalyst (SiO2-R-SO3H) is completely heterogeneous and can be recycled.     

Fe（HSO4）3： An efficient,heterogeneous and reusable catalyst for the synthesis of 14-aryl- or alkyl- 14H-dibenzo[a,j]xanthenes

Fe（HSO4）3 has been used as an efficient and recyclable catalyst for the one-pot synthesis of 14-aryl- or alkyl-14Hdibenzo[aj]xanthene derivatives by the reaction of 2-naphtol and aldehydes. Different types of aromatic and aliphatic aldehydes are used in the reaction and in all cases the products were obtained in good to excellent yields.     

Effect of structural and thermodynamic factors on the sorption of hydrogen by metal–organic framework compounds

The characteristics of the sorption of hydrogen by metal–organic framework compounds (MOF) were examined, and the structural and thermodynamic factors that favor the sorption of H₂ by such substances were determined. The effect of the structure of the MOF and the size and geometry of the pores on the sorption characteristics was analyzed. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 2, pp. 67-87, March-April, 2009.     

MCM-41 mesoporous silica: a highly efficient and recoverable catalyst for rapid synthesis of α-aminonitriles and imines

In this work, pure MCM-41 mesoporous silica with active mesoporous sites has been successfully applied, as a highly efficient and recoverable catalyst, for the rapid and convenient synthesis of α-aminonitriles and imines. Various imines, as the intermediate of the Strecker reaction, were simply prepared from condensation of a wide range of aldehydes and amines in the presence of low loading of MCM-41 mesoporous silica under solvent-free conditions at room temperature in high to quantitative yields. Furthermore, the corresponding α-aminonitrile derivatives were prepared through the three-component Strecker reaction using trimethylsilylcyanide catalyzed by MCM-41 as a bifunctional heterogeneous mesoporous solid catalyst.