3D Microporous Base‐Functionalized Covalent Organic Frameworks for Size‐Selective Catalysis

The design and synthesis of 3D covalent organic frameworks (COFs) have been considered a challenge, and the demonstrated applications of 3D COFs have so far been limited to gas adsorption. Herein we describe the design and synthesis of two new 3D microporous base‐functionalized COFs, termed BF‐COF‐1 and BF‐COF‐2, by the use of a tetrahedral alkyl amine, 1,3,5,7‐tetraaminoadamantane (TAA), combined with 1,3,5‐triformylbenzene (TFB) or triformylphloroglucinol (TFP). As catalysts, both BF‐COFs showed remarkable conversion (96 % for BF‐COF‐1 and 98 % for BF‐COF‐2), high size selectivity, and good recyclability in base‐catalyzed Knoevenagel condensation reactions. This study suggests that porous functionalized 3D COFs could be a promising new class of shape‐selective catalysts.     

共价有机框架材料催化剂

共价有机框架材料（covalent organic frameworks, COF）是功能材料领域研究的热点之一。COF具有孔道结构高度有序、孔径可调、比表面积较大、合成方法多样和易于功能化修饰等优点,是一类新兴的多相催化剂。目前,COF催化剂主要设计思路是：基于“自下而上”策略将非金属催化活性中心嵌入材料骨架来构筑本征型COF催化剂,或者以COF为载体,通过后修饰方式负载金属颗粒或离子构建多相催化剂。鉴于COF以上优势,预计COF催化剂在多相催化和手性催化领域中的应用也将取得更大的进展。本文综述了COF催化剂的合成和功能化策略,并展望了COF在多相催化领域中的应用前景。     

Homochiral Covalent Organic Frameworks for Asymmetric Catalysis

Owing to their permanent porosity, highly ordered and extended structure, good chemical stability, and tunability, covalent organic frameworks (COFs) have emerged as a new type of organic materials that can offer various applications in different fields. Benefiting from the huge database of organic reactions, the required functionality of COFs can be readily achieved by modification of the corresponding organic functional groups on either polymerizable monomers or established COF frameworks. This striking feature allows homochiral covalent organic frameworks (HCCOFs) to be reasonably designed and synthesized, as well as their use as a unique platform to fabricate asymmetric catalysts. This contribution provides an overview of new progress in HCCOF-based asymmetric catalysis, including design, synthesis, and their application in asymmetric organic synthesis. Moreover, major challenges and developing trends in this field are also discussed. It is anticipated that this review article will provide some new insights into HCCOFs for heterogeneous asymmetric catalysis and help to encourage further contributions in this young but promising field.     

Synthesis of Two-Dimensional Covalent Organic Frameworks in Ionic Liquids

Two-dimensional covalent organic frameworks were synthesized in high yields by polycondensation in nonvolatile ionic liquids. The resulting crystallites are highly porous and exhibit exceptional capability of removing bisphenol A from water. The one reported is a general method to synthesize microporous and mesoporous frameworks, it allows to achieve regular macroscopic shapes, and it is effective in a wide range of reaction temperatures.     

Metal–Covalent Organic Frameworks (MCOFs): A Bridge Between Metal–Organic Frameworks and Covalent Organic Frameworks

Many sophisticated chemical and physical properties of porous materials strongly rely on the presence of the metal ions within the structures. Whereas homogeneous distribution of metals is conveniently realized in metal–organic frameworks (MOFs), the limited stability potentially restricts their practical implementation. From that perspective, the development of metal–covalent organic frameworks (MCOFs) may address these shortcomings by incorporating active metal species atop highly stable COF backbones. This Minireview highlights examples of MCOFs that tackle important issues from their design, synthesis, characterization to cutting‐edge applications.     

Bromine-Functionalized Covalent Organic Frameworks for Efficient Triboelectric Nanogenerator

Covalent organic frameworks (COFs) enable precise integration of various organic building blocks into porous skeletons through topology predesign. Here, we report the first example of COFs by integrating electron withdrawing bromine group onto the skeletons for triboelectric nanogenerators (TENG). The resulting framework exhibits high surface area and good crystallinity. Thus, the bromine functionalized COF has more regular aligned π columns and arrays over the skeleton than bare COFs, which in turn significantly enhances charge transport ability. As a result, bromine functionalized COFs showed higher electrical output performance at 5 Hz with a peak value of short circuit current density of 43.6 μA and output voltage of 416 V, which is 2 and 1.3 times higher than those of bare COFs (21.6 μA and 318 V), respectively. These results demonstrated that this strategy for engineering electron withdrawing groups on the skeleton could open a new aspect of COFs for developing TENG devices.     

Enzyme-Decorated Covalent Organic Frameworks as Nanoporous Platforms for Heterogeneous Biocatalysis

Sustainability in chemistry heavily relies on heterogeneous catalysis. Enzymes, the main catalyst for biochemical reactions in nature, are an elegant choice to catalyze reactions due to their high activity and selectivity, although they usually suffer from lack of robustness. To overcome this drawback, enzyme-decorated nanoporous heterogeneous catalysts were developed. Three different approaches for Candida antarctica lipase B (CAL-B) immobilization on a covalent organic framework (PPF-2) were employed: physical adsorption on the surface, covalent attachment of the enzyme in functional groups on the surface and covalent attachment into a linker added post-synthesis. The influence of the immobilization strategy on the enzyme uptake, specific activity, thermal stability, and the possibility of its use through multiple cycles was explored. High specific activities were observed for PPF-2-supported CAL-B in the esterification of oleic acid with ethanol, ranging from 58 to 283 U mg⁻¹, which was 2.6 to 12.7 times greater than the observed for the commercial Novozyme 435.     

Effect of Building Block Transformation in Covalent Triazine-Based Frameworks for Enhanced CO2 Uptake and Metal-Free Heterogeneous Catalysis

Covalent triazine frameworks (CTFs) have provided a unique platform in functional material design for a wide range of applications. This work reports a series of new CTFs with two new heteroaromatic building blocks (pyrazole and isoxazole groups) through a building-block transformation approach aiming for carbon capture and storage (CCS) and metal-free catalysis. The CTFs were synthesized from their respective building blocks [(4,4′-(1H-pyrazole-3,5-diyl)dibenzonitrile (pyz) and 4,4′-(isoxazole-3,5-diyl)dibenzonitrile (isox))] under ionothermal conditions using ZnCl₂. Both of the building blocks were designed by an organic transformation of an acetylacetone containing dinitrile linker to pyrazole and isoxazole groups, respectively. Due to this organic transformation, (i) linker aromatization, (ii) higher surface areas and nitrogen contents, (iii) higher aromaticity, and (iv) higher surface basicity was achieved. Due to these enhanced properties, CTFs were explored for CO₂ uptake and metal-free heterogeneous catalysis. Among all, the isox-CTF, synthesized at 400 °C, showed the highest CO₂ uptake (4.92 mmol g⁻¹ at 273 K and 2.98 mmol g⁻¹ at 298 K at 1 bar). Remarkably, these CTFs showed excellent metal-free catalytic activity for the aerobic oxidation of benzylamine at mild reaction conditions. On studying the properties of the CTFs, it was observed that organic transformations and ligand aromatization of the materials are crucial factor to tune the important parameters that influence the CO₂ uptake and the catalytic activity. Overall, this work highlights the substantial effect of designing new CTF materials by building-block organic transformations resulting in better properties for CCS applications and heterogeneous catalysis.     

Research Progress in Covalent Organic Frameworks for Photoluminescent Materials

Covalent organic frameworks (COFs) are an emerging kind of crystalline porous polymers that present the precise integration of organic building blocks into extensible structures with regular pores and periodic skeletons. The diversity of organic units and covalent linkages makes COFs a rising materials platform for the design of structure and functionality. Herein, recent research progress in developing COFs for photoluminescent materials is summarised. Structural and functional design strategies are highlighted and fundamental problems that need to be solved are identified, in conjunction with potential applications from perspectives of photoluminescent materials.     

Tailoring Covalent Organic Frameworks To Capture Water Contaminants

Covalent organic frameworks (COFs) are attractive materials receiving increasing interest in the literature due to their crystallinity, large surface area, and pore uniformity. Their properties can be tailored towards specific applications by judicious design of COF building blocks, giving access to tailor-made pore sizes and surfaces. In this Concept article, developments in the field of COFs that have allowed these materials to be explored for contaminant adsorption are discussed. Strategies to obtain water-stable materials with highly ordered structures and large surface areas are reviewed. Post-synthetic modification approaches, by which pore surfaces can be tuned to target specific contaminants, are described. Recent advances in COF formulations, crucial for future implementation in adsorption devices, are highlighted. At the end, future challenges which need to be addressed to allow for the deployment of COFs for the capture of water contaminants will be discussed.     

Covalent Organic Frameworks and Cage Compounds: Design and Applications of Polymeric and Discrete Organic Scaffolds

Porous organic materials are an emerging class of functional nanostructures with unprecedented properties. Dynamic covalent assembly of small organic building blocks under thermodynamic control is utilized for the intriguingly simple formation of complex molecular architectures in one‐pot procedures. In this Review, we aim to analyze the basic design principles that govern the formation of either covalent organic frameworks as crystalline porous polymers or covalent organic cage compounds as shape‐persistent molecular objects. Common synthetic procedures and characterization techniques will be discussed as well as more advanced strategies such as postsynthetic modification or self‐sorting. When appropriate, comparisons are drawn between polymeric frameworks and discrete organic cages in terms of their underlying properties. Furthermore, we highlight the potential of these materials for applications ranging from gas storage to catalysis and organic electronics.     

共价有机框架材料催化研究进展

共价有机框架材料(COFs)是一类具有高比表面积、高孔隙率、高结晶度的结构多样性多孔材料.由于COFs具有可设计性、易功能化的特点,可通过"自上而下"或者后修饰策略将具有催化活性的官能团或金属颗粒嵌入到材料骨架当中,从而设计出高效催化剂. COFs已逐渐在多相催化及其它催化领域展现出非常大的应用价值.本文综述了COFs作为催化剂载体在多种催化反应中的合成策略与应用,对COFs催化剂的现状进行了总结与展望,同时指出该领域面临的问题与挑战.     

金属有机骨架材料在催化中的应用

金属有机骨架(MOFs)材料是一种相对新型的多孔材料,由于其结构的多样性、可设计性、可剪裁性以及超高的比表面积,近年来吸引了广泛的研究兴趣,并在很多领域展现了潜在的应用前景.特别是在催化方面的应用更受到了强烈的关注.本文的前两部分主要以催化活性位点的来源进行分类,包括配位不饱和金属中心、功能性有机配体、化学修饰接入功能位点以及嵌入在MOFs孔内的金属配合物或金属纳米颗粒等,总结了近几年来MOFs及其复合材料在多相催化方向取得的一些进展.同时在后面两部分也简要地介绍了MOFs在光催化及以MOFs为模板构筑的多孔纳米材料在催化(特别是电催化)方面的一些应用.最后,对MOFs在催化方面的应用前景做了展望.     

Triphenylphosphine-Based Covalent Organic Frameworks and Heterogeneous Rh-P-COFs Catalysts

The synthesis of phosphine-based functional covalent organic frameworks (COFs) has attracted great attention recently. Herein, we present two examples of triphenylphosphine-based COFs (termed P-COFs) with well-defined crystalline structures, high specific surface areas, and good thermal stability. Furthermore, rhodium catalysts with these P-COFs as support material show high turnover frequency for the hydroformylation of olefins, as well as excellent recycling performance. This work not only extends the phosphine-based COF family, but also demonstrates their application in immobilizing homogeneous metal-based (e.g., Rh-phosphine) catalysts for application in heterogeneous catalysis.     

共价有机框架材料固定化酶的研究进展

共价有机框架（Covalent Organic Frameworks, COFs）是一种新型的多孔材料,具有结构规整、骨架稳定、孔径结构可调等特点,被视为固定化酶的理想载体。我们主要总结了近10年来COFs材料作为载体,通过物理吸附、共价连接、包埋的固定化策略制备固定化酶的研究进展与应用,并讨论了COFs材料在酶固定化领域所面临的机遇和挑战。     

Unveiling the Local Structure of Palladium Loaded into Imine-Linked Layered Covalent Organic Frameworks for Cross-Coupling Catalysis

Layered covalent organic frameworks (2D-COFs), composed of reversible imine linkages and accessible pores, offer versatility for chemical modifications towards the development of catalytic materials. Nitrogen-enriched COFs are good candidates for binding Pd species. Understanding the local structure of reacting Pd sites bonded to the COF pores is key to rationalize interactions between active sites and porous surfaces. By combining advanced synchrotron characterization methods with periodic computational DFT modeling, the precise atomic structure of catalytic Pd sites attached to local defects is resolved within an archetypical imine-linked 2D-COF. This material was synthesized using an in situ method as a gel, under which imine hydrolysis and metalation reactions are coupled. Local defects formed in situ within imine-linked 2D-COF materials are highly reactive towards Pd metalation, resulting in active materials for Suzuki–Miyaura cross-coupling reactions.     

Sophisticated Design of Covalent Organic Frameworks with Controllable Bimetallic Docking for a Cascade Reaction

Precise control of the number and position of the catalytic metal ions in heterogeneous catalysts remains a big challenge. Here we synthesized a series of two‐dimensional (2D) covalent organic frameworks (COFs) containing two different types of nitrogen ligands, namely imine and bipyridine, with controllable contents. For the first time, the selective coordination of the two nitrogen ligands of the 2D COFs to two different metal complexes, chloro(1,5‐cyclooctadiene)rhodium(I) (Rh(COD)Cl) and palladium(II) acetate (Pd(OAc)₂), has been realized using a programmed synthetic procedure. The bimetallically docked COFs showed excellent catalytic activity in a one‐pot addition–oxidation cascade reaction. The high surface area, controllable metal‐loading content, and predesigned active sites make them ideal candidates for their use as heterogeneous catalysts in a wide range of chemical reactions.     

Design of Photoactive Covalent Organic Frameworks as Heterogeneous Catalyst for Preparation of Thiophosphinates from Phosphine Oxides and Thiols

Two new covalent organic frameworks (COFs) were synthesized from 4,4′,4′′,4′′′-(pyrene-1,3,6,8-tetrayl)tetraaniline and 2,5-dimethoxyterephthalaldehyde (Py-DMTA-COF) or 2′,5′-dimethoxy-[1,1′:4′,1′′-terphenyl]-4,4′′-dicarbaldehyde (Py-DMTPDA-COF) under solvothermal conditions. These two COFs were further facilely developed as efficient photocatalytic platforms for the synthesis of thiophosphinates. Py-DMTA-COF exhibited better photocatalytic activity, broad substrate applicability, and excellent recycling capacity for the preparation of thiophosphinates from P(O)H compounds and thiols compared to Py-DMTPDA-COF. This methodology was further extended to the seamless gram-scale production of target phosphorothioate derivatives. The results demonstrate that COFs can provide a robust platform for developing metal-free, base-free, highly efficient, and reusable heterogeneous photocatalysts for organic transformations.     

Postsynthetic Functionalization of Three‐Dimensional Covalent Organic Frameworks for Selective Extraction of Lanthanide Ions

Chemical functionalization of covalent organic frameworks (COFs) is critical for tuning their properties and broadening their potential applications. However, the introduction of functional groups, especially to three‐dimensional (3D) COFs, still remains largely unexplored. Reported here is a general strategy for generating a 3D carboxy‐functionalized COF through postsynthetic modification of a hydroxy‐functionalized COF, and for the first time exploration of the 3D carboxy‐functionalized COF in the selective extraction of lanthanide ions. The obtained COF shows high crystallinity, good chemical stability, and large specific surface area. Furthermore, the carboxy‐functionalized COF displays high metal loading capacities together with excellent adsorption selectivity for Nd³⁺ over Sr²⁺ and Fe³⁺ as confirmed by the Langmuir adsorption isotherms and ideal adsorbed solution theory (IAST) calculations. This study not only provides a strategy for versatile functionalization of 3D COFs, but also opens a way to their use in environmentally related applications.     

Urea‐Based Porous Organic Frameworks: Effective Supports for Catalysis in Neat Water

Two urea‐based porous organic frameworks, UOF‐1 and UOF‐2, were synthesized through a urea‐forming condensation of 1,3,5‐benzenetriisocyanate with 1,4‐diaminobenzene and benzidine, respectively. UOF‐1 and UOF‐2 possess good hydrophilic properties and high scavenging ability for palladium. Their palladium polymers, Pd^II/UOF‐1 and Pd^II/UOF‐2, exhibit high catalytic activity and selectivity for Suzuki–Miyaura cross‐coupling reactions and selective reduction of nitroarenes in water. The catalytic reactions can be efficiently performed at room temperature. Palladium nanoparticles with narrow size distribution were formed after the catalytic reaction and were well dispersed in UOF‐1 and UOF‐2. XPS analysis confirmed the coordination of the urea oxygen atom with palladium. SEM and TEM images showed that the original network morphology of UOF‐1 and UOF‐2 was maintained after palladium loading and catalytic reactions.