Post-Synthetic Generation of Amino-Acid-Functionalized UiO-66-NH₂ Metal–Organic Framework Nanostructures as an Amphoteric Catalyst for Organic Reactions

Abstract

Herein, the L-serine-functionalized metal−organic framework nanostructure is obtained via a simple two-step postsynthetic modification strategy. Interesting properties of serine, such as the existence of both acidic and basic groups, provide amphoteric active sites on UiO-66-NH 2 that are not accessible through direct synthesis. In this sense, an excess amount of 1,6 hexamethylene diisocyanate is primarily used as a linker to allow the conversion of nucleophilic groups in UiO-66-NH 2 to isocyanate as a suitable electrophile group. L-serine reacted with isocyanate to generate the corresponding urea derivative. SEM, TEM, and nitrogen adsorption analyses confirm an average particle size of approximately 24 nm and a pore size of 6.68 nm within the framework. Notably, the synthesized amphoteric nanomaterial exhibited high catalytic activity, stability, and durability in the solventfree procedures in synthesizing a diverse range of 4H-pyrano[2,3-b] pyridine-3,6-dicarbonitriles and octahydropyrimido [4,5 b][1,8]naphthyridine-7-carbonitriles. Moreover, the catalyst was easily separated�indicating a substantial decrease of catalytic activity upon five consecutive runs in the reaction.

Postsynthetic Modification of Amine-Functionalized MIL-101(Cr) Metal–Organic Frameworks with an EDTA–Zn(II) Complex as an Effective Heterogeneous Catalyst for Hantzsch Synthesis of Polyhydroquinolines

“…The initial mass loss (12%) below 200 °C is due to the evaporation of moisture absorbed in the pores of MOF from solvents and air. 2 , 46 The next weight loss that occurred in the range of 225–480 °C, which is equal to 45.02%, was caused by the pyrolysis of the organic moieties. 2 , 46 , 47 The DSC curve shows two continuous endothermic pyrolysis processes for this range that confirm the stepwise pyrolysis of 2-aminoterephthalic acid and EDTA in the MOF-supported complex.…”

“…Considering heterogeneous catalysis, metal–organic frameworks (MOFs) have been developed into a popular concept. − They are self-assembled by the coordination of metal cations or clusters acting as nodes and organic ligands acting as linkers. , As a result of the tenability of pore size, chemical tenability, topologies, and a very substantial inner surface area, significant metallic dispersion is to be anticipated for MOFs, which will convert them into a unique class of functional materials with potential applications in catalysis. − Moreover, the thin micropore distribution of MOFs may result in monodisperse nanometric metallic clusters, which are of great importance for catalytic activity and selectivity. − The highly programmable organic and inorganic components of MOFs distinguish them from other porous inorganic materials like zeolites. − In this sense, organic moieties allow them to be customized with various functional groups (i.e., acid, bases and metal complexes), also known as a postsynthetic modification (PSM) process, to improve their characteristics for various applications, especially in the field of catalysis. − MIL-101­(Cr)–NH 2 (MIL stands for Materials of Institute Lavoisier), which was constructed using chromium clusters and a 2-amino terephthalate ligand, is one of the best-known MOFs that have been previously produced. − The functionalization of this MOF can be achieved through the PSM method on its active amine groups, offering a significant technique to enhance its capacity for catalytic applications. , …”

Sustainable carbonaceous nanomaterial supported palladium as an efficient ligand-free heterogeneouscatalyst for Suzuki–Miyaura coupling

“…A broad spectrum of support materials, spanning both inorganic and organic varieties such as mesoporous silica, alumina, zeolites, metal–organic frameworks (MOFs), supramolecular polymers, alongside various carbon-based materials like graphite, carbon black, and activated carbon, find utility in dispersing active components across numerous catalytic processes. 6–12 However carbon, distinguished for its substantial specific surface area, notable porosity, excellent electron conductivity, and relative chemical inertness, has emerged as a prominent support material for chemical transformation reactions. An additional advantage lies in its capacity to be sourced from residual biomass, thus contributing to the overall reduction of the carbon footprint in biomass transformation processes.…”

Construction of a Dual-Functionalized Acid–Base Nanocatalyst via HEPES Buffer Functionalized on Fe3O4 as a Reusable Catalyst for Annulation Reactions

“…Malononitrile, a versatile and readily available building block, has garnered significant attention in organic synthesis due to its unique reactivity and potential for diverse functionalizations. , As a key synthon, malononitrile facilitates the production of a diverse array of compounds, such as medicines, pesticides, and bioactive substances . Moreover, its ability to act as a Michael acceptor, nucleophile, and precursor to various functional groups makes it an essential component in the design and development of new synthetic strategies, especially for tandem Knoevenagel–Michael–Thorpe–Ziegler-type heterocyclization reactions under catalytic conditions. − This unique sequence can be used for condensation reactions of various reactants, leading to the synthesis of diverse heterocycles . Furthermore, malononitrile can readily combine with aldehydes, albeit not very quickly, resulting in corresponding α,β-unsaturated products as excellent Michael acceptors .…”

“…Bifunctional catalysis has recently been applied to the aforementioned class of synthesis using special molecules that possess both acid and base sitesalso known as zwitterionic buffering agents. ,− In this sense, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) is a zwitterionic buffering agent that consists of a piperazine backbone attached to two different ethyl groups containing a sulfonic acid group and a hydroxyl group at their ends, which impart unique properties to HEPES . Meanwhile, the sulfonic acid group is highly acidic and can donate protons.…”