Reticulating Crystalline Porous Materials for Asymmetric Heterogeneous Catalysis

Asymmetric catalysis is essential for addressing the increasing demand for enantiopure compounds. Recent advances in reticular chemistry have demonstrated that metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) possess highly regular porous architectures, exceptional tunability, and the ability to incorporate chiral functionalities through their open channels or cavities. These characteristics make them highly effective and enantioselective catalysts for a wide range of asymmetric transformations. The chiral microenvironments within these frameworks facilitate precise control over reactant orientation and transition states, enhancing both catalytic activity and enantioselectivity, thereby offering significant advantages over traditional systems. This review overviews recent developments in chiral MOFs (CMOFs) and chiral COFs (CCOFs), focusing on their design strategies, and synthetic methods, and highlights the structure-property relationships that connect key structural features to asymmetric catalytic performance. Additionally, the current challenges and future prospects in this field are addressed, highlighting the pivotal role of reticular chemistry in the creation of chiral porous materials. It is anticipated that this review will inspire further research into the application of crystalline porous materials in asymmetric catalysis and promote the rational design of novel chiral heterogeneous catalysts for industrial use.

Construction of a series of pH stable Ca-based MOFs, their CO2 adsorption and catalytic activity

In this study, three different solvent systems have been employed to investigate the effect of reaction parameters on the synthesis of four alkaline earth metal-based MOFs namely [Ca(0.5 1,4-phenyl diacetic acid)2(H2O)DMF]∞ (Ca-MOF-1), [Ca(1,4-naphthalene dicarboxylate)DMF]∞ (Ca-MOF-2), [Ca2(0.5 1,2,4,5-benzene tetracarboxylate)2(H2O)3DMF]∞ (Ca-MOF-3) and [Ca2(2,6-naphthalene dicarboxylate)2(H2O)6]∞ (Ca-MOF-4). The crystal structures of these four MOFs have been resolved through single crystal X-ray analysis and the bulk phase purity of these MOFs was assessed using PXRD and FT-IR analysis. To check the stability of these MOFs, thermogravimetric analysis (TGA) was carried out. To analyze the robustness of these MOFs, the PXRD of the samples was also collected at different pH levels. These MOFs were further explored as Lewis acid catalysts for the alcoholysis of epoxides and the activity of these catalysts depend on the open metal sites present in the MOFs. The catalytic activity follows the order: Ca-MOF-2 > Ca-MOF-4 > Ca-MOF-1 > Ca-MOF-3. The activity was also checked with various epoxide substrates using Ca-MOF-2. Density functional theory (DFT) calculations also support this trend with the help of the thermodynamic feasibility of epoxide binding, considering model MOF structures. The weak interaction between the epoxide oxygen and the metal centre of the most stable MOF structure has also been clarified by computational studies.

Investigation of the Influence of Functionalization Strategy on Urea 2D MOF Catalytic Performance

Urea-functionalized MOFs with unique properties have recently been used as efficient platforms to conduct organocatalytic reactions. To gain more insight into the key factors which govern an efficient organocatalytic reaction in urea-MOFs, two different urea-containing 2D MOFs TMU-58 ([Zn(L1)(oba)].CH₃CN) and TMU-83 ([Zn(L2)(oba)].DMF), where L1 = (1E,5E)-1,5-bis(1-(pyridine-4-ylethylidene)carbonohydrazide, L2 = (1E,5E)-1,5-bis(1-(pyridine-4-ylmethylene)carbonohydrazide, and oba = 4,4'-oxybisbenzoic acid, with abundant accessible active sites, were selected and examined in the methanolysis of styrene oxide. TMU-58 with the ability to form a two-point H-bond with different substrates revealed a high organocatalytic efficiency in the regioselective ring opening of styrene oxide. The catalytic activation of epoxide oxygen by the urea N-H functional sites, followed by the nucleophilic attack of methanol at the benzylic carbon led to the formation of 2-methoxy-2-phenylethanol as the major product. DFT calculations were also performed to investigate the acidic strength of the urea hydrogens in both TMU-58 and TMU-83 structures as a major factor to conduct an efficient catalytic reaction. The results indicated the more acidic nature of the urea hydrogens in TMU-83; however, its catalytic efficiency was remarkably reduced due to the inappropriate orientation of the active interaction sites within the framework revealing the importance of proper orientation of the urea hydrogens in conducting an efficient organocatalytic reaction. The current study provides a comparative study on the function-property relationship in 2D MOF assemblies which has not been explored so far.

Chiral Metal-Organic Frameworks

In the past two decades, metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) assembled from metal ions or clusters and organic linkers via metal-ligand coordination bonds have captivated significant scientific interest on account of their high crystallinity, exceptional porosity, and tunable pore size, high modularity, and diverse functionality. The opportunity to achieve functional porous materials by design with promising properties, unattainable for solid-state materials in general, distinguishes MOFs from other classes of materials, in particular, traditional porous materials such as activated carbon, silica, and zeolites, thereby leading to complementary properties. Scientists have conducted intense research in the production of chiral MOF (CMOF) materials for specific applications including but not limited to chiral recognition, separation, and catalysis since the discovery of the first functional CMOF (i.e., d- or l-POST-1). At present, CMOFs have become interdisciplinary between chirality chemistry, coordination chemistry, and material chemistry, which involve in many subjects including chemistry, physics, optics, medicine, pharmacology, biology, crystal engineering, environmental science, etc. In this review, we will systematically summarize the recent progress of CMOFs regarding design strategies, synthetic approaches, and cutting-edge applications. In particular, we will highlight the successful implementation of CMOFs in asymmetric catalysis, enantioselective separation, enantioselective recognition, and sensing. We envision that this review will provide readers a good understanding of CMOF chemistry and, more importantly, facilitate research endeavors for the rational design of multifunctional CMOFs and their industrial implementation.

Recent Advances in Photocatalytic CO2 Utilisation Over Multifunctional Metal–Organic Frameworks

The efficient conversion of carbon dioxide (CO2) to high-value chemicals using renewable solar energy is a highly attractive but very challenging process that is used to address ever-growing energy demands and environmental issues. In recent years, metal–organic frameworks (MOFs) have received significant research attention owing to their tuneability in terms of their composition, structure, and multifunctional characteristics. The functionalisation of MOFs by metal nanoparticles (NPs) is a promising approach used to enhance their light absorption and photocatalytic activity. The efficient charge separation and strong CO2 binding affinity of hybrid MOF-based photocatalysts facilitate the CO2 conversion process. This review summarises the latest advancements involving noble metal, non-noble-metal, and miscellaneous species functionalised MOF-based hybrid photocatalysts for the reduction of CO2 to carbon monoxide (CO) and other value-added chemicals. The novel synthetic strategies and their corresponding structure–property relationships have also been discussed for solar-to-chemical energy conversion. Furthermore, the current challenges and prospects in practical applications are also highlighted for sustainable energy production.

Metal-Organic Framework (MOF)/Epoxy Coatings: A Review

Epoxy coatings are developing fast in order to meet the requirements of advanced materials and systems. Progress in nanomaterial science and technology has opened a new era of engineering for tailoring the bulk and surface properties of organic coatings, e.g., adhesion to the substrate, anti-corrosion, mechanical, flame-retardant, and self-healing characteristics. Metal-organic frameworks (MOFs), a subclass of coordinative polymers with porous microstructures, have been widely synthesized in recent years and applied in gas and energy storage, separation, sensing, environmental science and technology, and medicine. Nevertheless, less attention has been paid to their performance in coatings. Well-known as micro- and nanoporous materials, with a tailorable structure consisting of metal ions and organic linkers, MOFs have a huge loading capacity, which is essential for the delivery of corrosion inhibitors. This review paper attempts to highlight the importance of epoxy/MOF composites for coating applications. A particular emphasis was explicitly placed on the anti-corrosion, flame-retardant, mechanical, and dielectric properties of epoxy/MOF coatings.

A novel homochiral metal–organic framework with an expanded open cage based on (R)-3,3′-bis(6-carboxy-2-naphthyl)-2,2′-dihydroxy-1,1′-binaphthyl: synthesis, X-ray structure and efficient HPLC enantiomer separation

A new homochiral MOF with an expanded open cage was synthesized and utilized as a chiral stationary phase for HPLC.

Molecular design of chiral zirconium metal–organic frameworks for asymmetric transfer hydrogenation of imines

Two chiral zirconium metal–organic frameworks are designed with high enantioselectivity for asymmetric transfer hydrogenation of imines.

Selective recognition of Fe3+ and CrO42− ions using a Zn(ii) metallacycle and a Cd(ii) coordination polymer and their heterogeneous catalytic application

A Zn(ii) metallacycle [Zn₂{(L)₂(DMF)₂(NO₃)₂}]·(NO₃)₂ (1) along with a Cd(ii) coordination polymer [{Cd(L)₂(DMF)₂}·(NO₃)₂]_n (2) have been synthesized, structurally characterized and exploited as a multifunctional material.

Homochiral metal–organic frameworks as heterogeneous catalysts

Homochiral metal–organic frameworks (HMOFs) are attractive materials for asymmetric catalysis because they possess high surface area and uniform active sites.

Highly enantioselective Friedel–Crafts alkylation of N,N-dialkylanilines with trans-β-nitrostyrene catalyzed by a homochiral metal–organic framework

The first enantioselective Friedel–Crafts alkylation of N,N-dialkylanilines with trans-β-nitrostyrene catalyzed by a homochiral MOF afforded the addition products in high yields (∼96%) with excellent ee (∼98%).

Development of recyclable chiral macrocyclic metal complexes for asymmetric aminolysis of epoxides: application for the synthesis of an enantiopure oxazolidine ring

Macrocyclic Cr(iii)-salen complexes were synthesized for the ring opening reaction of various epoxides with anilines to furnish the corresponding β-amino-α-hydroxyl esters and β-amino alcohols with excellent ee/yield upto 99/95%.

Asymmetric ring-opening reaction of meso-epoxides with aromatic amines using homochiral metal–organic frameworks as recyclable heterogeneous catalysts

Asymmetric ring-opening reactions of meso-epoxides by aromatic amines were achieved by using some chiral metal–organic frameworks. The corresponding β-amino alcohols were obtained with good yields and enantioselectivities (up to 97% ee).

Sixteen isostructural phosphonate metal-organic frameworks with controlled Lewis acidity and chemical stability for asymmetric catalysis

Heterogeneous catalysts typically lack the specific steric control and rational electronic tuning required for precise asymmetric catalysis. Here we demonstrate that a phosphonate metal–organic framework (MOF) platform that is robust enough to accommodate up to 16 different metal clusters, allowing for systematic tuning of Lewis acidity, catalytic activity and enantioselectivity. A total of 16 chiral porous MOFs, with the framework formula [M₃L₂(solvent)₂] that have the same channel structures but different surface-isolated Lewis acid metal sites, are prepared from a single phosphono-carboxylate ligand of 1,1′-biphenol and 16 different metal ions. The phosphonate MOFs possessing tert-butyl-coated channels exhibited high thermal stability and good tolerances to boiling water, weak acid and base. The MOFs provide a versatile family of heterogeneous catalysts for asymmetric allylboration, propargylation, Friedel–Crafts alkylation and sulfoxidation with good to high enantioselectivity. In contrast, the homogeneous catalyst systems cannot catalyze the test reactions enantioselectively.

Asymmetric synthesis predominantly falls within the realm of homogeneous catalysis. Here, the authors synthesized 16 chiral metal–organic frameworks differing in the nature of the transition metal and demonstrate their excellent stability, catalytic activity and recyclability in a number of enantioselective reactions.

Heterogeneous Catalysis in Zeolites, Mesoporous Silica, and Metal-Organic Frameworks

Crystalline porous materials are important in the development of catalytic systems with high scientific and industrial impact. Zeolites, ordered mesoporous silica, and metal-organic frameworks (MOFs) are three types of porous materials that can be used as heterogeneous catalysts. This review focuses on a comparison of the catalytic activities of zeolites, mesoporous silica, and MOFs. In the first part of the review, the distinctive properties of these porous materials relevant to catalysis are discussed, and the corresponding catalytic reactions are highlighted. In the second part, the catalytic behaviors of zeolites, mesoporous silica, and MOFs in four types of general organic reactions (acid, base, oxidation, and hydrogenation) are compared. The advantages and disadvantages of each porous material for catalytic reactions are summarized. Conclusions and prospects for future development of these porous materials in this field are provided in the last section. This review aims to highlight recent research advancements in zeolites, ordered mesoporous silica, and MOFs for heterogeneous catalysis, and inspire further studies in this rapidly developing field.

The mechanism of an asymmetric ring-opening reaction of epoxide with amine catalyzed by a metal–organic framework: insights from combined quantum mechanics and molecular mechanics calculations

QM/MM computations suggest that the asymmetric ring-opening reaction of epoxide with amine is controlled by CH–π interactions between aniline and a naphthol moiety.

Synthesis and structural diversity of d10 metal coordination polymers constructed from new semi-rigid bis(3-methyl-1H-pyrazole-4-carboxylic acid)alkane ligands

Three isomeric ligands, and four d¹⁰ metal CPs were synthesized, varying from 1D to 2D, together with achirality to chirality variation.

Efficient HPLC enantiomer separation using a pillared homochiral metal–organic framework as a novel chiral stationary phase

HPLC enantioseparation of various racemates using novel pillared homochiral MOF–silica composite as chiral stationary phase has been successfully demonstrated.

Enantioselective Diels–Alder reaction in the confined space of homochiral metal–organic frameworks

A novel homochiral porous MOF synthesized using (R)-2,2′-dihydroxy-1,1′-binaphthyl-4,4′-dibenzoic acid was shown to be an effective heterogeneous catalyst for asymmetric Diels–Alder reaction between isoprene and N-ethyl maleimide.

Chiral Co(iii)–salen complex supported over highly ordered functionalized mesoporous silica for enantioselective aminolysis of racemic epoxides

New mesoporous chiral Co(iii)-catalyst has been synthesed and used in the synthesis of chiral β-amino alcohols with excellent yield and enantioselectivity (ee > 99%) under neat conditions at RT.

A new chiral Fe(iii)–salen grafted mesoporous catalyst for enantioselective asymmetric ring opening of racemic epoxides at room temperature under solvent-free conditions

A new heterogeneous chiral Fe(iii)–salen grafted mesoporous catalyst has been synthesized for the enantioselective (ee > 99%) ARO reaction of racemic epoxides with aromatic amine under solvent-free conditions.

Enantioselective syntheses of β-amino alcohols catalyzed by recyclable chiral Fe(iii) metal complex

An efficient asymmetric desymmetrization of meso-epoxides with anilines catalyzed by a series of simple and environmentally benign in situ generated Fe(iii) complexes based on chiral tridentate ligands L1–L7 was carried out at rt.

Tuning the structure and function of metal-organic frameworks via linker design

Metal-organic frameworks (MOFs) are constructed from metal ions/clusters coordinated by organic linkers (or bridging-ligands). The hallmark of MOFs is their permanent porosity, which is frequently found in MOFs constructed from metal-clusters. These clusters are often formed in situ, whereas the linkers are generally pre-formed. The geometry and connectivity of a linker dictate the structure of the resulting MOF. Adjustments of linker geometry, length, ratio, and functional-group can tune the size, shape, and internal surface property of a MOF for a targeted application. In this critical review, we highlight advances in MOF synthesis focusing on linker design. Examples of building MOFs to reach unique properties, such as unprecedented surface area, pore aperture, molecular recognition, stability, and catalysis, through linker design are described. Further search for application-oriented MOFs through judicious selection of metal clusters and organic linkers is desirable. In this review, linkers are categorized as ditopic (Section 1), tritopic (Section 2), tetratopic (Section 3), hexatopic (Section 4), octatopic (Section 5), mixed (Section 6), desymmetrized (Section 7), metallo (Section 8), and N-heterocyclic linkers (Section 9).

Multicomponent versus domino reactions: One-pot free-radical synthesis of β-amino-ethers and β-amino-alcohols

Following an optimized multicomponent procedure, an aryl amine, a ketone, and a cyclic ether or an alcohol molecule are assembled in a one-pot synthesis by nucleophilic radical addition of ketyl radicals to ketimines generated in situ. The reaction occurs under mild conditions by mediation of the TiCl4/Zn/t-BuOOH system, leading to the formation of quaternary β-amino-ethers and -alcohols. The new reaction conditions guarantee good selectivity by preventing the formation of secondary products. The secondary products are possibly derived from a competitive domino reaction, which involves further oxidation of the ketyl radicals.

Heterometallic coordination polymers: syntheses, structures and heterogeneous catalytic applications

Heterometallic coordination polymers function as heterogeneous catalysts for various organic transformation reactions via preferential interaction with the substrates.

Coordination polymers with free Brønsted acid sites for selective catalysis

The Cu(ii) coordination polymers with free –COOH groups as Brønsted acid sites show high activity and regioselectivity in catalyzing epoxide ring-opening reactions.

Chiral porous metal–organic frameworks containing μ-oxo-bis[Ti(salan)] units for asymmetric cyanation of aldehydes

Two chiral porous metal–organic frameworks containing μ-oxo-bis[Ti(salan)] dimers are constructed and shown to be efficient and recyclable heterogeneous catalysts for asymmetric cyanation reaction of aldehydes.