Amine-grafted on lanthanide metal-organic frameworks: Three solid base catalysts for Knoevenagel condensation reaction

A facile, rapid procedure for Knoevenagel condensation reaction catalyzed by efficient amino-bifunctional frameworks under mild conditions

A series of bifunctional hexagonal MOFs have been successfully constructed by the introduction of various amine functional groups within the unsaturated Cu-based MOF, HKUST, to access amino-modified frameworks. The prepared compounds are cost-effective and display high chemical and thermal stability. They were effectually exploited as efficacious and superb heterogeneous catalysts in rapid and facile Knoevenagel condensation reactions for a variety of substrates containing different electron-donating and electron-withdrawing substituents with very high conversion, good reusability under mild conditions, and very short reaction time. The contaminant presence of Lewis acid and basic sites resulted in efficient condensation reactions by the prepared catalysts.

Nanoporous {Y2}-Organic Frameworks for Excellent Catalytic Performance on the Cycloaddition Reaction of Epoxides with CO2 and Deacetalization-Knoevenagel Condensation

Stable metal-organic frameworks containing periodically arranged nanosized pores and active Lewis acid-base active sites are considered as ideal candidates for efficient heterogeneous catalysis. Herein, the exquisite combination of [Y₂(CO₂)₇(H₂O)₂] cluster (abbreviated as {Y₂}) and multifunctional linker of 2,4,6-tri(2,4-dicarboxyphenyl)pyridine (H₆TDP) led to a nanoporous framework of {[Y₂(TDP)(H₂O)₂]·5H₂O·4DMF}_n (NUC-53, NUC = North University of China), which is a rarely reported binuclear three-dimensional (3D) framework with hierarchical tetragonal-microporous (0.78 nm) and octagonal-nanoporous (1.75 nm) channels. The inner walls of these channels are aligned by {Y₂} clusters and plentifully coexisted Lewis acid-base sites of Y^III ions and N_pyridine atoms. Furthermore, NUC-53 has a quite large void volume of ∼65.2%, which is significantly higher than most documented 3D rare-earth-based MOFs. The performed catalytic experiments exhibited that activated NUC-53 showed a high catalytic activity on the cycloaddition reactions of CO₂ with styrene oxide under mild conditions with excellent turnover number (TON: 1980) and turnover frequency (TOF: 495 h^-1). Moreover, the deacetalization-Knoevenagel condensation reactions of benzaldehyde dimethyl acetal and malononitrile could be efficiently prompted by the heterogeneous catalyst of NUC-53. These findings not only pave the way for the construction of nanoporous MOF based on rare-earth clusters with a variety of catalytic activities but also provide some new insights into the catalytic mechanism.

An Overview of Metal-free Sustainable Nitrogen-based Catalytic Knoevenagel Condensation Reaction ‎

Knoevenagel condensation reaction counts as a vital condensation in organic chemistry due to the synthesis of valuable intermediates, ‎heterocycles, and fine chemicals from commercially available reactants through forming new C=C...

Recent progress in lanthanide metal–organic frameworks and their derivatives in catalytic applications

Research progress in lanthanide metal–organic frameworks and their derivatives in the field of catalysis has been presented on the basis of different organic reactions.

Rare-earth metal–organic frameworks: from structure to applications

In the past 30 years, rare-earth metal–organic frameworks (MOFs) have been gaining attention owing to their diverse chemical structures, and tunable properties.

Observation of Olefin/Paraffin Selectivity in Azo Compound and Its Application into a Metal-Organic Framework

Olefin/paraffin separation is an important and challenging issue because the two molecules have similar physicochemical properties. Although a couple of olefin adsorbents have been developed by introducing inorganic nanoparticles into metal-organic frameworks (MOFs), there has been no study on the development of an olefin adsorbent by introducing a certain organic functional group into a MOF. In this study, we posited that azo compounds could offer olefin/paraffin selectivity. We have revealed using first-principles calculations that the simplest aromatic azo compound (azobenzene, Azob) has an unusual propylene/propane selectivity due to special electrostatic interactions between Azob and propylene molecules. On the basis of this interesting discovery, we have synthesized a novel propylene adsorbent, MIL-101(Cr)_DAA, by grafting 4,4'-diaminoazobenzene (DAA) into open metal sites in a mesoporous MIL-101(Cr). Remarkably, MIL-101(Cr)_DAA exhibited enhanced propylene/propane selectivity as well as considerably higher propylene heat of adsorption compared to pristine MIL-101(Cr) while maintaining the high working capacity of MIL-101(Cr). This clearly indicates that azo compounds when introduced into MOFs can provide propylene selectivity. Moreover, MIL-101(Cr)_DAA showed good C₃H₆/C₃H₈ separation and easy regeneration performances from packed-bed breakthrough experiments and retained its propylene adsorption capacity even after exposure to air for 12 h. As far as we know, this is the first study that improves the olefin selectivity of MOF by postsynthetically introducing an organic functional group.

Amine-Functionalized Sugarcane Bagasse: A Renewable Catalyst for Efficient Continuous Flow Knoevenagel Condensation Reaction at Room Temperature

A biomass-based catalyst with amine groups (–NH₂), viz., amine-functionalized sugarcane bagasse (SCB-NH₂), was prepared through the amination of sugarcane bagasse (SCB) in a two-step process. The physicochemical properties of the catalyst were characterized through FT-IR, elemental analysis, XRD, TG, and SEM-EDX techniques, which confirmed the –NH₂ group was grafted onto SCB successfully. The catalytic performance of SCB-NH₂ in Knoevenagel condensation reaction was tested in the batch and continuous flow reactions. Significantly, it was found that the catalytic performance of SCB-NH₂ is better in flow system than that in batch system. Moreover, the SCB-NH₂ presented an excellent catalytic activity and stability at the high flow rate. When the flow rate is at the 1.5 mL/min, no obvious deactivation was observed and the product yield and selectivity are more than 97% and 99% after 80 h of continuous reaction time, respectively. After the recovery of solvent from the resulting solution, a white solid was obtained as a target product. As a result, the SCB-NH₂ is a promising catalyst for the synthesis of fine chemicals by Knoevenagel condensation reaction in large scale, and the modification of the renewable SCB with –NH₂ group is a potential avenue for the preparation of amine-functionalized catalytic materials in industry.