Construction of Pyridine-Based Chiral Ionic Covalent Organic Frameworks as a Heterogeneous Catalyst for Promoting Asymmetric Henry Reactions

Asymmetric heterogeneous catalysis using crystalline porous materials

Asymmetric catalysis has emerged as a pivotal strategy in the synthesis of chiral compounds, offering significant advantages in selectivity and efficiency. In recent years, heterogeneous catalysis has become a focal point in the fields of organic synthesis and materials science due to continuous advancements in science and technology, especially the use of crystalline porous materials (CPMs) as catalysts. This review summarizes recent advances in using CPMs, such as metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and zeolites, as promising supports for asymmetric catalysts. These materials provide high surface areas, tunable porosity, and the ability to host active catalytic sites, which enhance reaction rates and selectivity. In this review, we summarize the stereostructural properties of chiral CPMs to guide the future design of asymmetric heterogeneous catalysts and the study of catalytic mechanisms. Moreover, we discuss various strategies for incorporating catalytic moieties into these frameworks, including direct synthesis, post-synthesis modification and induced synthesis methods. Additionally, we highlight recent examples where CPMs have been successfully applied in asymmetric transformations, examining their mechanistic insights and the role of substrate diffusion in achieving high enantioselectivity. This review concludes with a perspective on the challenges and future directions in this rapidly evolving field, emphasizing the need for further integration of advanced artificial intelligence techniques and design principles to optimize the synthesis and catalytic performance of chiral CPMs.

A critical review of COFs-based photocatalysis for environmental remediation

Covalent organic frameworks (COFs) are highly porous crystalline polymers formed through covalent bonding of molecular building blocks. Numerous fabrication strategies have been developed, including solvothermal, ionothermal, microwave, mechanochemical, and sonochemical methods, alongside ligand substitution and post-modification techniques, which allow for precise control over the structures and properties of COFs. The exceptional physicochemical stability, large specific surface area, broad visible light absorption, and extended π-conjugated systems have sparked significant interest in photocatalytic applications. Recently, COFs have shown remarkable efficacy in environmental remediation, demonstrating the ability to degrade a wide range of organic pollutants, including dyes, antibiotics, and drugs, as well as to reduce/oxidize heavy metals such as Cr(VI), U(VI), and As(III), in addition to targeting biological pollutants. This review comprehensively explores recent advancements in COFs-based photocatalysis, covering synthetic methods, COF types, modification method, theoretical calculations, environmental applications, and underlying mechanisms. Additionally, the challenges and opportunities for COFs as a robust, cost-effective technology in practical applications was discussed, and offering valuable insights for researchers in environmental remediation, materials science, and photocatalysis.

Ultrathin zwitterionic COF membranes from colloidal 2D-COF towards precise molecular sieving

Membrane technology is an important component of resource recovery. Covalent organic frameworks (COFs) with inherent long-range ordered structure and permanent porosity are ideal materials for fabricating advanced membrane. Zwitterionic COFs have unique features beyond single ionic COFs containing anions or cations. Here, a zwitterionic colloidal 2D-COF (TpPa-Py) is synthesized via a single-phase method. ultrathin zwitterionic COF membranes are fabricated via a facile blade-coating method. Experimental and molecular dynamics simulation results showed that due to the unique amphiphilic nature of the TpPa-Py, the TpPa1-Py1 membrane exhibits high level permeance and rejection of both positively and negatively charged dyes. Moreover, the TpPa1-Py1 membrane exhibits excellent dye/dye and dye/salt separation performance. The selectivity factors were 89 for the separation of acid blue and rhodamine B, and 47.8 for the separation of methyl blue and NaCl. This work provides a promising solution for the development of high-performance membranes tailored for resource recovery of dye wastewater, addressing a critical need in water treatment.

Ionic porous materials: from synthetic strategies to applications in gas separation and catalysis

Ionic porous materials possess a unique combination of tunable pore sizes and task-specific interactions between guest molecules and the charged frameworks, which endow them with versatility across diverse domains in chemistry and materials science. Significant advancements in their applications for gas separation and catalysis have been achieved in recent years due to the incorporation of ionic functionalities and ultra-microporous structures that enable molecular-scale recognition of guest molecules. This review summarizes recent advancements in the synthetic strategies of ionic porous materials, establishing design guidelines for the incorporation of ionic moieties into the backbone to fine-tune pore sizes and chemistry. It highlights the synergistic interplay of task-specific interactions with custom-designed pore structures in key applications, including adsorption separation, membrane separation, and gas conversion. Additionally, it examines structure-property relationships, offering deeper insights into enhancing performance. The report also addresses the current challenges in the practical application of these materials. Finally, the review provides future perspectives on ionic porous materials from both scientific and industrial viewpoints. Overall, this review aims to provide insights into pore structure and chemistry, supporting the precise placement of ionic functionalities.

Covalent Organic Frameworks for Green Energy: Synthesis, Properties, and Applications

Covalent organic frameworks (COFs) are a new type of porous organic crystalline material, which have become an emerging platform for promoting the development of green energy technology due to their high surface area, adjustable pores, low skeleton density, and easy functionalization. In recent years, with the continuous advancement of synthesis technology, the synthesis efficiency and sustainability of COFs have been significantly improved, from traditional solvothermal methods to the emergence of various green synthesis strategies such as ion thermal, mechanochemical, and ultrasound assisted methods. This article reviews the main synthesis methods of COFs and explores their applications in the field of green energy, such as photocatalysis, gas adsorption and separation, electrocatalysis, battery, supercapacitor and Proton exchange membrane fuel cell. By analyzing the performance and mechanism of COFs in these applications in detail, this article further looks forward to the challenges and future development trends faced by COFs in green energy technology, aiming to provide valuable reference and inspiration for researchers in related fields.

Recent Advance in the Synthesis and Applications of Chiral Covalent Organic Frameworks: A Mini-Review

Chiral covalent organic frameworks (CCOFs) are emerging porous materials with tunable chiral structures, abundant pores, and high surface areas, gaining significant attentions in separation, sensing, and asymmetric catalysis. This review summarizes the synthesis methods of CCOFs and their applications in chiral recognition. It discusses the advantages and limitations of three synthesis strategies, including chiral post-modification, direct synthesis, and chiral-induced synthesis. The review also highlights the potential of CCOFs in chiral separation, sensing, and asymmetric catalysis for efficient purification, detection, and synthesis of chiral molecules. Challenges and future directions for the preparation and application of CCOFs are also addressed, aiming to guide further research and practical applications.

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.

Thiophene-Based Covalent Triazine Frameworks as Visible-Light-Driven Heterogeneous Photocatalysts for the Oxidative Coupling of Amines

This study reports on a metal-free Covalent Triazine Framework (CTF) incorporating bithiophene structural units (TP-CTF) with a semicrystalline structure as an efficient heterogeneous photocatalyst under visible light irradiation. The physico-chemical properties and composition of this material was confirmed via different characterization solid-state techniques, such as XRD, TGA, CO2 adsorption and FT-IR, NMR and UV-Vis spectroscopies. The compound was synthesized through a solvothermal process and was explored as a heterogeneous photocatalyst for the oxidative coupling of amines to imines under visible light irradiation. TP-CTF demonstrated outstanding photocatalytic activity, with high conversion rates and selectivity. Importantly, the material exhibited exceptional stability and recyclability, making it a strong candidate for sustainable and efficient imine synthesis. The low bandgap of TP-CTF enabled the efficient absorption of visible light, which is a notable advantage for visible-light-driven photocatalysis.

Raising the Asymmetric Catalytic Efficiency of Chiral Covalent Organic Frameworks by Tuning the Pore Environment

Chiral covalent organic frameworks (COFs) hold considerable promise in the realm of heterogeneous asymmetric catalysis. However, fine-tuning the pore environment to enhance both the activity and stereoselectivity of chiral COFs in such applications remains a formidable challenge. In this study, we have successfully designed and synthesized a series of clover-shaped, hydrazone-linked chiral COFs, each with a varying number of accessible chiral pyrrolidine catalytic sites. Remarkably, the catalytic efficiencies of these COFs in the asymmetric aldol reaction between cyclohexanone and 4-nitrobenzaldehyde correlate well with the number of accessible pyrrolidine sites within the frameworks. The COF featuring nearly one pyrrolidine moiety at each nodal point demonstrated excellent reaction yields and enantiomeric excess (ee) values, reaching up to 97 and 83%, respectively. The findings not only underscore the profound impact of a deliberately controlled chiral pore environment on the catalytic efficiencies of COFs but also offer a new perspective for the design and synthesis of advanced chiral COFs for efficient asymmetric catalysis.

Click nanosponge - A novel amine-rich β-cyclodextrin-based crosslinked polymer for heterogeneous catalysis

Cyclodextrin-based nanosponges are promising materials for heterogeneous catalysis due to their inherent synthetic versatility, tunable porosity and nontoxicity. In this work, a primary amine-rich β-cyclodextrin nanosponge was synthesized via click imine condensation reaction between 1,6-hexamethylamine-functionalized β-cyclodextrin (CDAM) and glutaraldehyde (GLT) to afford CDGLAM, in mild conditions. The crosslinked polymer exhibited a BET surface area of 36.39 m2 g-1, an average pore diameter of 3.09 nm (as assessed by the BJH method), and thermal stability up to 253 °C. CDGLAM was tested as heterogeneous catalyst for the metal-free Henry and Knoevenagel reactions, between aromatic aldehydes and nitromethane or ethyl cyanoacetate, respectively, affording the products in moderate to very high yields. These results show the ease of preparation of β-CD-based nanosponges from a green chemistry perspective, as well as their potential for future use in catalytic systems.

Post-synthetic modifications of covalent organic frameworks (COFs) for diverse applications

Covalent organic frameworks (COFs) are porous and crystalline organic polymers, which have found usage in various fields. These frameworks are tailorable through the introduction of diverse functionalities into the platform. Indeed, functionality plays a key role in their different applications. However, sometimes functional groups are not compatible with reaction conditions or can compete and interfere with other groups of monomers in the direct synthetic method. Also, pre-synthesis of bulky moieties in COFs can negatively affect crystal formation. To avoid these problems a post-synthetic modification (PSM) approach is a helpful tactic. Also, with the assistance of this strategy porous size can be tunable and stability can be improved without considerable effect on the crystallite. In addition, conductivity, hydrophobicity/ hydrophilicity, and chirality are among the features that can be reformed with this method. In this review, different types of PSM strategies based on recent articles have been divided into four categories: (i) post-functionalization, (ii) post-metalation, (iii) chemical locking, and (iv) host-guest post-modifications. Post-functionalization and chemical locking methods are based on covalent bond formation while in post-metalation and host-guest post-modifications, non-covalent bonds are formed. Also, the potential of these post-modified COFs in energy storage and conversion (lithium-sulfur batteries, hydrogen storage, proton-exchange membrane fuel cells, and water splitting), heterogeneous catalysts, food safety evaluation, gas separation, environmental domains (greenhouse gas capture, radioactive element uptake, and water remediation), and biological applications (drug delivery, biosensors, biomarker capture, chiral column chromatography, and solid-state smart nanochannels) have been discussed.

Chiral Materials: Progress, Applications, and Prospects

Chirality is a universal phenomenon in molecular and biological systems, denoting an asymmetric configurational property where an object cannot be superimposed onto its mirror image by any kind of translation or rotation, which is ubiquitous on the scale from neutrinos to spiral galaxies. Chirality plays a very important role in the life system. Many biological molecules in the life body show chirality, such as the "codebook" of the earth's biological diversity-DNA, nucleic acid, etc. Intriguingly, living organisms hierarchically consist of homochiral building blocks, for example, l-amino acids and d-sugars with unknown reason. When molecules with chirality interact with these chiral factors, only one conformation favors the positive development of life, that is, the chiral host environment can only selectively interact with chiral molecules of one of the conformations. The differences in chiral interactions are often manifested by chiral recognition, mutual matching, and interactions with chiral molecules, which means that the stereoselectivity of chiral molecules can produce changes in pharmacodynamics and pathology. Here, the latest investigations are summarized including the construction and applications of chiral materials based on natural small molecules as chiral source, natural biomacromolecules as chiral sources, and the material synthesized by design as a chiral source.

Chiral Ionic Covalent Organic Framework as an Enantioselective Fluorescent Sensor for Phenylalaninol Determination

Phenylalaninol (PAL) is a significant chemical intermediate widely utilized in drug development and chiral synthesis, for instance, as a reactant for bicyclic lactams and oxazoloisoindolinones. Since the absolute stereochemical configuration significantly impacts biological action, it is crucial to evaluate the concentration and enantiomeric content of PAL in a quick and convenient manner. Herein, an effective PAL enantiomer recognition method was reported based on a chiral ionic covalent organic framework (COF) fluorescent sensor, which was fabricated via one-step postquaternization modification of an achiral COF by (1R, 2S, 5R)-2-isopropyl-5-methylcyclohexyl-carbonochloridate (L-MTE). The formed chiral L-TB-COF can be applied as a chiral fluorescent sensor to recognize the stereochemical configuration of PAL, which displayed a turn-on fluorescent response for R-PAL over that of S-PAL with an enantioselectivity factor of 16.96. Nonetheless, the single L-MTE molecule had no chiral recognition ability for PAL. Moreover, the ee value of PAL can be identified by L-TB-COF. Furthermore, density functional theory (DFT) calculations demonstrated that the chiral selectivity came from the stronger binding affinity between L-TB-COF and R-PAL in comparison to that with S-PAL. L-TB-COF is the first chiral ionic COF employed to identify chiral isomers by fluorescence. The current work expands the range of applications for ionic COFs and offers fresh suggestions for creating novel chiral fluorescent sensors.

Construction of Covalent Organic Frameworks via Multicomponent Reactions

Multicomponent reactions (MCRs) combine at least three reactants to afford the desired product in a highly atom-economic way and are therefore viewed as efficient one-pot combinatorial synthesis tools allowing one to significantly boost molecular complexity and diversity. Nowadays, MCRs are no longer confined to organic synthesis and have found applications in materials chemistry. In particular, MCRs can be used to prepare covalent organic frameworks (COFs), which are crystalline porous materials assembled from organic monomers and exhibit a broad range of properties and applications. This synthetic approach retains the advantages of small-molecule MCRs, not only strengthening the skeletal robustness of COFs, but also providing additional driving forces for their crystallization, and has been used to prepare a series of robust COFs with diverse applications. The present perspective article provides the general background for MCRs, discusses the types of MCRs employed for COF synthesis to date, and addresses the related critical challenges and future perspectives to inspire the MCR-based design of new robust COFs and promote further progress in this emerging field.

Fluorinated covalent organic frameworks for efficient drug delivery

In this study, two novel fluorine-functionalized crystalline covalent organic frameworks (COFs), namely DF-TAPB-COF and DF-TATB-COF, were synthesized, and their ordered structure, porosity, suitable pore size, and abundant fluorine groups were expected to serve as effective carriers in drug delivery. The excellent cell viability of DF-TAPB-COF and DF-TATB-COF was verified using MTT assays. Both COFs exhibited very high loading capacities in terms of drug loading performance, in particular the drug loading rate of DF-TAPB-COF for 5-fluorouracil (5-FU) was up to 69%. They also exhibited efficient drug release performance in a simulated body fluid environment. Cell endocytosis experiments demonstrated that DF-TAPB-COF and DF-TATB-COF could be effectively endocytosed by cells. Hence, this study offers new insight into the design and development of COF-based drug carrier systems.

Covalent Organic Frameworks with Ionic Liquid-Moieties (ILCOFs): Structures, Synthesis, and CO2 Conversion

CO₂, an acidic gas, is usually emitted from the combustion of fossil fuels and leads to the formation of acid rain and greenhouse effects. CO₂ can be used to produce kinds of value-added chemicals from a viewpoint based on carbon capture, utilization, and storage (CCUS). With the combination of unique structures and properties of ionic liquids (ILs) and covalent organic frameworks (COFs), covalent organic frameworks with ionic liquid-moieties (ILCOFs) have been developed as a kind of novel and efficient sorbent, catalyst, and electrolyte since 2016. In this critical review, we first focus on the structures and synthesis of different kinds of ILCOFs materials, including ILCOFs with IL moieties located on the main linkers, on the nodes, and on the side chains. We then discuss the ILCOFs for CO₂ capture and conversion, including the reduction and cycloaddition of CO₂. Finally, future directions and prospects for ILCOFs are outlined. This review is beneficial for academic researchers in obtaining an overall understanding of ILCOFs and their application of CO₂ conversion. This work will open a door to develop novel ILCOFs materials for the capture, separation, and utilization of other typical acid, basic, or neutral gases such as SO₂, H₂S, NOx, NH₃, and so on.

Challenges and opportunities for chiral covalent organic frameworks

As highly versatile crystalline porous materials, covalent organic frameworks (COFs) have emerged as an ideal platform for developing novel functional materials, attributed to their precise tunability of structure and functionality. Introducing chiral functional units into frameworks produces chiral COFs (CCOFs) with chiral superiorities through chirality conservation and conversion processes. This review summarises recent research progress in CCOFs, including synthetic methods, chiroptical characterisations, and their applications in asymmetric catalysis, chiral separation, and enantioselective recognition and sensing. Challenges and limitations are discussed to uncover future opportunities in CCOF research.

Designing Sites in Heterogeneous Catalysis: Are We Reaching Selectivities Competitive With Those of Homogeneous Catalysts?

A critical review of different prominent nanotechnologies adapted to catalysis is provided, with focus on how they contribute to the improvement of selectivity in heterogeneous catalysis. Ways to modify catalytic sites range from the use of the reversible or irreversible adsorption of molecular modifiers to the immobilization or tethering of homogeneous catalysts and the development of well-defined catalytic sites on solid surfaces. The latter covers methods for the dispersion of single-atom sites within solid supports as well as the use of complex nanostructures, and it includes the post-modification of materials via processes such as silylation and atomic layer deposition. All these methodologies exhibit both advantages and limitations, but all offer new avenues for the design of catalysts for specific applications. Because of the high cost of most nanotechnologies and the fact that the resulting materials may exhibit limited thermal or chemical stability, they may be best aimed at improving the selective synthesis of high value-added chemicals, to be incorporated in organic synthesis schemes, but other applications are being explored as well to address problems in energy production, for instance, and to design greener chemical processes. The details of each of these approaches are discussed, and representative examples are provided. We conclude with some general remarks on the future of this field.

Porous polyelectrolyte frameworks: synthesis, post-ionization and advanced applications

Porous organic polymers (POPs), which feature high surface areas, robust skeletons, tunable pores, adjustable functionality and versatile applicability, have constituted a designable platform to develop advanced organic materials. Endowing polyelectrolytes with the distinct characteristics of POPs will attract mounting interest as the structural diversity of polyelectrolytes will bring the new hope of intriguing applications and potential benefits. In this review, the striking progress in ionized POPs (i-POPs) has been systematically summarized with regard to their synthetic strategies and applications. In the synthesis of i-POPs, we illustrate the representative ionic building blocks and charged functional groups capable of constructing the polyelectrolyte frameworks. The synthetic methods, including direct synthesis and post-modification, are detailed for the i-POPs with amorphous or crystalline structures, respectively. Subsequently, we outline the distinctive performances of i-POPs in adsorption, separation, catalysis, sensing, ion conduction and biomedical applications. The survey concerns the interplay between the surface chemistry, ionic interaction and pore confinement that cooperatively promote the performance of i-POPs. Finally, we conclude with the remaining challenges and promising opportunities for the on-going development of i-POPs.