Enzyme-like Acyl Transfer Catalysis in a Bifunctional Organic Cage

Amide-based organic cage cavities are, in principle, ideal enzyme active site mimics. Yet, cage-promoted organocatalysis has remained elusive, in large part due to synthetic accessibility of robust and functional scaffolds. Herein, we report the acyl transfer catalysis properties of robust, hexaamide cages in organic solvent. Cage structural variation reveals that esterification catalysis with an acyl anhydride acyl carrier occurs only in bifunctional cages featuring internal pyridine motifs and two crucial antipodal carboxylic acid groups. 1H NMR data and X-ray crystallography show that the acyl carrier is rapidly activated inside the cavity as a covalent mixed-anhydride intermediate with an internal hydrogen bond. Michaelis-Menten (saturation) kinetics suggest weak binding (KM = 0.16 M) of the alcohol pronucleophile close to the internal anhydride. Finally, activation and delivery of the alcohol to the internal anhydride by the second carboxylic acid group forms ester product and releases the cage catalyst. Eyring analysis indicates a strong enthalpic stabilization of the transition state (5.5 kcal/mol) corresponding to a rate acceleration of 104 over background acylation, and an ordered, associative rate-determining attack by the alcohol, supported by DFT calculations. We conclude that internal bifunctional organocatalysis specific to the cage structural design is responsible for the enhancement over the background reaction. These results pave the way for organic-phase enzyme mimicry in self-assembled cavities with the potential for cavity elaboration to enact selective acylations.

Platform for the Immobilizing of Ultrasmall Pd Clusters for Carbonylation: In Situ Self-Templating Fabrication of ZIF-8 on ZnO

Incorporating metal clusters into the confined cavities of metal-organic frameworks (MOFs) to form MOF-supported catalysts has attracted considerable research interest with regard to carbonylation reactions. Herein, a self-templating method is used to prepare the zinc oxide (ZnO)-supported core-shell catalyst ZnO@Pd/ZIF-8. This facile strategy controls the growth of metal sources on the ZIF-8 shell layer and avoids the metal diffusion or aggregation problems of the conventional synthesis method. The characteristics of the catalysts show that the palladium (Pd) clusters are highly dispersed with an average particle size of ≈1.2 nm, making them excellent candidates as a catalyst for carbonylation under mild conditions. The optimal catalyst (1.25-ZnO@Pd/ZIF-8) exhibits excellent activity in synthesizing α, β-alkynyl ketones under 1 atm of carbon monooxide (CO), and the conversion rate of 1, 3-diphenylprop-2-yn-1-one is 3.09 and 3.87 times more than those of Pd/ZIF-8 and Pd2+, respectively, for the first 2 h. Moreover, the 1.25-ZnO@Pd/ZIF-8 is recyclable, showing negligible metal leaching, and, under the conditions used in this investigation, can be reused at least five times without considerable loss in its catalytic efficiency. This protocol can also be applied with other nucleophile reagents to synthesize esters, amides, and acid products.

A Chiral [2+3] Covalent Organic Cage Based on 1,1'-Bi-2-naphthol (BINOL) Units

A [2+3] chiral covalent organic cage is produced through a dynamic covalent chemistry approach by mixing two readily available building units, viz. an enantiopure 3,3'-diformyl 2,2'-BINOL compound (A) with a triamino spacer (B). The two enantiomeric (R,R,R) and (S,S,S) forms of the cage C are formed nearly quantitatively thanks to the reversibility of the imine linkage. The X-ray diffraction analysis of cage (S,S,S)-C highlights that the six OH functions of the BINOL fragments are positioned inside the cage cavity. Upon reduction of the imine bonds of cage C, the amine cage D is obtained. The ability of the cage D to host the 1-phenylethylammonium cation (EH+) as a guest is evaluated through UV, CD and DOSY NMR studies. A higher binding constant for (R)-EH+ cation (Ka=1.7 106±10 % M-1) related to (S)-EH+ (Ka=0.9 106±10 % M-1) is determined in the presence of the (R,R,R)-D cage. This enantiopreference is in close agreement with molecular dynamics simulation.

Isomorphous Substitution of Organic Cage Crystal by Pd Nanoclusters for Selective Hydrogenation

For supporting active metal, the cavity confinement and mass transfer facilitation lie not in one sack, a trade-off between high activity and good stability of the catalyst is present. Porous organic cages (POCs) are expected to break the trade-off when metal particles are properly loaded. Herein, three organic cages (CC3, RCC3, and FT-RCC3) are employed to support Pd nanoclusters for catalytic hydrogenation. Subnanometer Pd clusters locate differently in different cage frameworks by using the same reverse double-solvents approach. Compared with those encapsulated in the intrinsic cavity of RCC3 and anchored on the outer surface of CC3, the Pd nanoclusters orderly assembled in FT-RCC3 crystal via isomorphous substitution exhibit superior activity, high selectivity, and good stability for semi-hydrogenation of phenylacetylene. Isomorphous substitution of FT-RCC3 crystal by Pd nanoclusters is originated from high crystallization capacity of FT-RCC3 and specific interaction of each Pd nanocluster with four cage windows. Both confinement function and H2 accumulation capacity of FT-RCC3 are fully utilized to support active Pd nanoclusters for efficient selective hydrogenation. The present results provide a new perspective to the heterogeneous catalysis field in terms of crystalizing metal nanoclusters in POC framework and outside the cage for making the best use of both parts.

Promoting Piezocatalytic H2 O2 Production in Pure Water by Loading Metal-Organic Cage-Modified Gold Nanoparticles on Graphitic Carbon Nitride

Piezocatalytic hydrogen peroxide (H2 O2 ) production is a green synthesis method, but the rapid complexation of charge carriers in piezocatalysts and the difficulty of adsorbing substrates limit its performance. Here, metal-organic cage-coated gold nanoparticles are anchored on graphitic carbon nitride (MOC-AuNP/g-C3 N4 ) via hydrogen bond to serve as the multifunctional sites for efficient H2 O2 production. Experiments and theoretical calculations prove that MOC-AuNP/g-C3 N4 simultaneously optimize three key parts of piezocatalytic H2 O2 production: i) the MOC component enhances substrate (O2 ) and product (H2 O2 ) adsorption via host-guest interaction and hinders the rapid decomposition of H2 O2 on MOC-AuNP/g-C3 N4 , ii) the AuNP component affords a strong interfacial electric field that significantly promotes the migration of electrons from g-C3 N4 for O2 reduction reaction (ORR), iii) holes are used for H2 O oxidation reaction (WOR) to produce O2 and H+ to further promote ORR. Thus, MOC-AuNP/g-C3 N4 can be used as an efficient piezocatalyst to generate H2 O2 at rates up to 120.21 μmol g-1  h-1 in air and pure water without using sacrificial agents. This work proposes a new strategy for efficient piezocatalytic H2 O2 synthesis by constructing multiple active sites in semiconductor catalysts via hydrogen bonding, by enhancing substrate adsorption, rapid separation of electron-hole pairs and preventing rapid decomposition of H2 O2 .

Formation and Growth of Atomic Scale Seeds of Au Nanoparticle in the Nanospace of an Organic Cage Molecule

Seed-mediated growth has been widely used to synthesize noble metal nanoparticles with controlled size and shape. Although it is becoming possible to directly observe the nucleation process of metal atoms at the single atom level by using transmission electron microscopy (TEM), it is challenging to control the formation and growth of seeds with only a few metal atoms in homogeneous solution systems. This work reports site-selective formation and growth of atomic scale seeds of the Au nanoparticle in a nanospace of an organic cage molecule. We synthesized a cage molecule with amines and phenols, which were found to both capture and reduce Au(III) ions to spontaneously form the atomic scale seeds containing Au(0) in the nanospace. The growth reaction of the atomic scale seeds afforded Au nanoparticles with an average diameter of 2.0±0.2 nm, which is in good agreement with the inner diameter of the cage molecule.

Dynamic covalent self-assembly and self-sorting processes in the formation of imine-based macrocycles and macrobicyclic cages

Investigating the self-assembly and self-sorting behaviour of dynamic covalent organic architectures makes possible the parallel generation of multiple discrete products in a single one pot procedure. We here report the self-assembly of covalent organic macrocycles and macrobicyclic cages from dialdehyde and polyamine components via multiple [2 + 2] and [3 + 2] polyimine condensations. Furthermore, component self-sorting processes have been monitored within the dynamic covalent libraries formed by these macrocycles and macrobicyclic cages. The progressive assembly of the final structures involves intermediates which undergo component selection and self-correction to generate the final thermodynamic constituents. The homo-self-sorting observed seems to involve entropic factors, as the homoleptic species present a higher symmetry than the competing heteroleptic ones. This study not only emphasizes the importance of an adequate design of the components of complex self-sorting systems, but also verifies the conjecture that systems of higher complexity may generate simpler outputs through the operation of competitive self-sorting.

Photoinitiated Energy Transfer in Porous-Cage-Stabilised Silver Nanoparticles

We report a new composite material consisting of silver nanoparticles decorated with three-dimensional molecular organic cages based on light absorbing porphyrins. The porphyrin cages serve to both stabilize the particles and allow diffusion and trapping of small molecules close to the metallic surface. Combining these two photoactive components results in a Fano resonant interaction between the porphyrin Soret band and the nanoparticle localised surface plasmon resonance. Time resolved spectroscopy revealed the silver nanoparticles transfer up to 37% of their excited state energy to the stabilising layer of porphyrin cages. These unusual photophysics cause a 2-fold current increase in photoelectrochemical water splitting measurements. The composite structure provides a compelling proof-of-concept for advanced photosensitiser systems with intrinsic porosity for photocatalytic and sensing applications.

Heterogenized Phenanthroline-Pd(2+)-Catalyzed Alkoxycarbonylation of Aryl Iodides in Base-Free Conditions

A phenanthroline-based porous organic polymer-supported heterogeneous Pd catalyst (Pd@Phen-POP) is facilely synthesized by the solvent knitting of a Phen scaffold via the Lewis-acid-catalyzed Friedel-Crafts reaction using dichloromethane as a source for linker in the presence of AlCl₃. The catalyst very effectively catalyzes the alkoxycarbonylation of various substituted aryl iodides with various alcohols to give corresponding products in good to excellent yields. Owing to the heterotic nature of the catalyst, it can be easily separated by simple filtration from the reaction mixture and recycled.

N-heterocyclic carbene-stabilized metal nanoparticles within porous organic cages for catalytic application

Tuning the surface-embellishing ligands of metal nanoparticles (NPs) is a powerful strategy to modulate their morphology and surface electronic and functional features, impacting their catalytic activity and selectivity. In this work, we report the design and synthesis of a polytriazolium organic cage PIC-T, capable of stabilizing PdNPs within its discrete cavity. The obtained material (denoted Pd@PCC-T) is highly durable and monodispersed with narrow particle-size distribution of 2.06 ± 0.02 nm, exhibiting excellent catalytic performance and recyclability in the Sonogashira coupling and tandem reaction to synthesize benzofuran derivatives. Further investigation indicates that the modulation of N-heterocyclic carbene sites embedded in the organic cage has an impact on NPs' catalytic efficiency, thus providing a novel methodology to design superior NP catalysts.

Supramolecular nanocapsules as two-fold stabilizers of outer-cavity sub-nanometric Ru NPs and inner-cavity ultra-small Ru clusters

The synthesis of metallic nanoparticles (MNP) with high surface area and controlled shape is of paramount importance to increase their catalytic performance. The detailed growing process of NP is mostly unknown and understanding the specific steps would pave the way for a rational synthesis of the desired MNP. Here we take advantage of the stabilization properties exerted by the tetragonal prismatic supramolecular nanocapsule 8·(BArF)8 to develop a synthetic methodology for sub-nanometric RuNP (0.6-0.7 nm). The catalytic properties of these sub-nanometric nanoparticles were tested on the hydrogenation of styrene, obtaining excellent selectivity for the hydrogenation of the alkene moiety. In addition, the encapsulation of [Ru5] clusters inside the nanocapsule is strikingly observed in most of the experimental conditions, as ascertained by HR-MS. Moreover, a thorough DFT study enlightens the nature of the [Ru5] clusters as tb-Ru5H2(η6-PhH)2(η6-pyz)3 (2) trapped by two arene moieties of the clip, or as tb-Ru5H2(η1-pyz)6(η6-pyz)3 (3) trapped between the two Zn-porphyrin units of the nanocapsule. Both options fulfill the Wade-Mingos counting rules, i.e. 72 CVEs for the closotb. The trapped [Ru5] metallic clusters are proposed to be the first-grown seeds of subsequent formation of the subnanometric RuNP. Moreover, the double role of the nanocapsule in stabilising ∼0.7 nm NPs and also in hosting ultra-small Ru clusters, is unprecedented and may pave the way towards the synthesis of ultra-small metallic clusters for catalytic purposes.

Molecular Cavity for Catalysis and Formation of Metal Nanoparticles for Use in Catalysis

The employment of weak intermolecular interactions in supramolecular chemistry offers an alternative approach to project artificial chemical environments like the active sites of enzymes. Discrete molecular architectures with defined shapes and geometries have become a revolutionary field of research in recent years because of their intrinsic porosity and ease of synthesis using dynamic non-covalent/covalent interactions. Several porous molecular cages have been constructed from simple building blocks by self-assembly, which undergoes many self-correction processes to form the final architecture. These supramolecular systems have been developed to demonstrate numerous applications, such as guest stabilization, drug delivery, catalysis, smart materials, and many other related fields. In this respect, catalysis in confined nanospaces using such supramolecular cages has seen significant growth over the years. These porous discrete cages contain suitable apertures for easy intake of substrates and smooth release of products to exhibit exceptional catalytic efficacy. This review highlights recent advancements in catalytic activity influenced by the nanocavities of hydrogen-bonded cages, metal-ligand coordination cages, and dynamic or reversible covalently bonded organic cages in different solvent media. Synthetic strategies for these three types of supramolecular systems are discussed briefly and follow similar and simplistic approaches manifested by simple starting materials and benign conditions. These examples demonstrate the progress of various functionalized molecular cages for specific chemical transformations in aqueous and nonaqueous media. Finally, we discuss the enduring challenges related to porous cage compounds that need to be overcome for further developments in this field of work.

Confinement synthesis in porous molecule-based materials: a new opportunity for ultrafine nanostructures

A balance between activity and stability is greatly challenging in designing efficient metal nanoparticles (MNPs) for heterogeneous catalysis. Generally, reducing the size of MNPs to the atomic scale can provide high atom utilization, abundant active sites, and special electronic/band structures, for vastly enhancing their catalytic activity. Nevertheless, due to the dramatically increased surface free energy, such ultrafine nanostructures often suffer from severe aggregation and/or structural degradation during synthesis and catalysis, greatly weakening their reactivities, selectivities and stabilities. Porous molecule-based materials (PMMs), mainly including metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and porous organic polymers (POPs) or cages (POCs), exhibit high specific surface areas, high porosity, and tunable molecular confined space, being promising carriers or precursors to construct ultrafine nanostructures. The confinement effects of their nano/sub-nanopores or specific binding sites can not only effectively limit the agglomeration and growth of MNPs during reduction or pyrolysis processes, but also stabilize the resultant ultrafine nanostructures and modulate their electronic structures and stereochemistry in catalysis. In this review, we highlight the latest advancements in the confinement synthesis in PMMs for constructing atomic-scale nanostructures, such as ultrafine MNPs, nanoclusters, and single atoms. Firstly, we illustrated the typical confinement methods for synthesis. Secondly, we discussed different confinement strategies, including PMM-confinement strategy and PMM-confinement pyrolysis strategy, for synthesizing ultrafine nanostructures. Finally, we put forward the challenges and new opportunities for further applications of confinement synthesis in PMMs.

A coordination cage hosting ultrafine and highly catalytically active gold nanoparticles

Ultrafine metal nanoparticles (MNPs) with size <2 nm are of great interest due to their superior catalytic capabilities. Herein, we report the size-controlled synthesis of gold nanoparticles (Au NPs) by using a thiacalixarene-based coordination cage CIAC-108 as a confined host or stabilizer. The Au NPs encapsulated within the cavity of CIAC-108 (Au@CIAC-108) show smaller size (∼1.3 nm) than the ones (∼4.7 nm) anchored on the surface of CIAC-108 (Au/CIAC-108). The cage-embedded Au NPs can be used as a homogeneous catalyst in a mixture of methanol and dichloromethane while as a heterogeneous catalyst in methanol. The homogeneous catalyst Au@CIAC-108-homo exhibits significantly enhanced catalytic activities toward nitroarene reduction and organic dye decomposition, as compared with its larger counterpart Au/CIAC-108-homo and its heterogeneous counterpart Au@CIAC-108-hetero. More importantly, the as-prepared Au@CIAC-108-homo possesses remarkable stability and durability.

The size-controlled synthesis of Au NPs was achieved by using a coordination cage CIAC-108 as a support. The Au NPs encapsulated within the cavity of CIAC-108 show smaller size (∼1.3 nm) than the ones (∼4.7 nm) anchored on the surface of CIAC-108.

Recent advances in the applications of porous organic cages

Porous organic cages (POCs) have emerged as a new sub-class of porous materials that stand out by virtue of their tunability, modularity, and processibility. Similar to other porous materials such...

Organic transformations in the confined space of porous organic cage CC2; catalysis or inhibition

Porous organic cages have shape persistent cavities which provide a suitable platform for encapsulation of guest molecules with size suitably fitting to the cavity. The interactions of the guest molecule with the porous organic cage significantly alter the properties of the guest molecule. Herein, we report the effect of encapsulation on the kinetics of various organic transformations including 2 + 4 cycloaddition, 1,5-sigmatropic, 6π-electrocyclization, ring expansion, cheletropic, dyotropic, trimerization and tautomerization reactions. Non-bonding interactions are generated between the CC2 cage and encapsulated species. However, the number and nature/strength of interactions are different for reactant and TS with the CC2 cage and this difference detects the reaction to be accelerated or slowed down. A significant drop in the barrier of reactions is observed for reactions involving strong interactions of the transition state within the cage. However, for some reactions such as the Claisen rearrangement, reactants are stabilized more than the transition state and therefore an increase in activation barrier is observed. Furthermore, non-covalent analyses of all transition states (inside the cage) confirm the interaction between the CC2 cage and substrate. The current study will promote further exploration of the potential of other porous structures for similar applications.

Porous organic cages have shape persistent cavities which provide a suitable platform for encapsulation of guest molecules with size suitably fitting to the cavity.

Self-assembly of chiral BINOL cages via imine condensation

Condensation of an (S)- or (R)-BINOL-derived dialdehyde and tris(2-aminoethyl)amine produced chiral [2+3] imine cages, which were further reduced to furnish more stable chiral amine cages and applied in the enantioselective recognition of (1R,2R)- and (1S,2S)-1,2-diaminocyclohexane.

Coordination-driven self-assembly of a series of dinuclear M2L2 mesocates with a bis-bidentate pyridylimine ligand

Four isostructural dinuclear M2L2 mesocates of the general formula [M2(NCS)4(L)2]·4.5MeOH (1M; M = Mn, Fe, Co, Zn) were constructed by using the coordination-driven self-assembly of the [M(NCS)2] precursor and the flexible bis-bidentate pyridylimine Schiff base ligand L (L = 4,4'-(1,4-phenylenebis(oxy))bis(N-(pyridin-2-ylmethylene)aniline). The centrosymmetric M2L2 mesocate forms through the side-by-side coordination of two L ligands to a pair of M(ii) ions. The mesocates exhibit a reversible temperature induced desolvation-solvation behavior without losing their structural integrity. The activated 1Co, as the representative M2L2 mesocate, shows an exceptionally high MeOH vapour uptake capacity of 481.9 cm3 g-1 (68.8 wt%) at STP with good recyclability. Notably, it also exhibits CO2 adsorption with an uptake capacity of 20.2 cm3 g-1 (3.6 wt%) at room temperature and 1 bar.

The Ionic Organic Cage: An Effective and Recyclable Testbed for Catalytic CO2 Transformation

Porous organic cages (POC) are a class of relatively new molecular porous materials, whose concept was raised in 2009 by Cooper’s group and has rarely been directly used in the area of organic catalysis. In this contribution, a novel ionic quasi-porous organic cage (denoted as Iq-POC), a quaternary phosphonium salt, was easily synthesized through dynamic covalent chemistry and a subsequent nucleophilic addition reaction. Iq-POC was applied as an effective nucleophilic catalyst for the cycloaddition reaction of CO2 and epoxides. Owing to the combined effect of the relatively large molecular weight (compared with PPh3+I−) and the strong polarity of Iq-POC, the molecular catalyst Iq-POC displayed favorable heterogeneous nature (i.e., insolubility) in this catalytic system. Therefore, the Iq-POC catalyst could be easily separated and recycled by simple centrifugation method, and the catalyst could be reused five times without obvious loss of activity. The molecular weight augmentation route in this study (from PPh3+I− to Iq-POC) provided us a “cage strategy” of designing separable and recyclable molecular catalysts.

Recent advances in process engineering and upcoming applications of metal-organic frameworks

Progress in metal-organic frameworks (MOFs) has advanced from fundamental chemistry to engineering processes and applications, resulting in new industrial opportunities. The unique features of MOFs, such as their permanent porosity, high surface area, and structural flexibility, continue to draw industrial interest outside the traditional MOF field, both to solve existing challenges and to create new businesses. In this context, diverse research has been directed toward commercializing MOFs, but such studies have been performed according to a variety of individual goals. Therefore, there have been limited opportunities to share the challenges, goals, and findings with most of the MOF field. In this review, we examine the issues and demands for MOF commercialization and investigate recent advances in MOF process engineering and applications. Specifically, we discuss the criteria for MOF commercialization from the views of stability, producibility, regulations, and production cost. This review covers progress in the mass production and formation of MOFs along with future applications that are not currently well known but have high potential for new areas of MOF commercialization.

An imine linked fluorescent covalent organic cage: the sensing of chloroform vapour and metal ions, and the detection of nitroaromatics

Fluorescent covalent organic cage molecule (F-COC) showed enhanced emission intensity in chloroform solution and polymer matrix film form in presence of chloroform vapours.

Phosphine-Built-in Porous Organic Cage for Stabilization and Boosting the Catalytic Performance of Palladium Nanoparticles in Cross-Coupling of Aryl Halides

Herein, we report first a novel phosphine-containing porous organic cage (PPOC) from a [2 + 3] self-assembly of triphenyl phosphine-based trialdehyde and (S,S)-1,2-diaminocyclohexane via dynamic imine chemistry, which was employed as a porous material for the controlled growth of palladium nanoparticles (NPs) due to the strong affinity of Pd to the phosphine ligand based on the principle of hard and soft acids and bases. Comprehensive characterizations including X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, NMR, and X-ray absorption spectroscopy reveal that ultrafine Pd NPs with narrow size distribution (1.7 ± 0.3 nm) and enhanced surface electronic density via a strong interaction between NPs and phosphine were homogeneously dispersed in the PPOC. The resultant catalyst Pd@PPOC exhibits remarkably superior catalytic activities for various cross-coupling reactions of aryl halides, for example, Sonogashira, Suzuki, Heck, and carbonylation. The catalytic activity of Pd@PPOC outperforms the state-of-the-art Pd complexes and other Pd NPs supported on N-containing porous cages under identical conditions, owing to the enhanced surface electronic density of Pd NPs and their high stability and dispersibility in solution. More importantly, Pd@PPOC is highly stable and easily recycled and reused without loss of their catalytic activity. This work provides a new functional POC with extended potentials in catalysis and material science.

Nucleation of Tiny Silver Nanoparticles by Using a Tetrafacial Organic Molecular Barrel: Potential Use in Visible-Light-Triggered Photocatalysis

Coordination-driven self-assembly of discrete molecular architectures of diverse shapes and sizes has been well studied in the last three decades. Use of dynamic imine bonds for designing analogous metal-free architectures has become a growing challenge recently. This article reports an organic molecular barrel (OB4^R ) as a potential template for nucleation and stabilization of very tiny (<1.5 nm) Ag nanoparticles (AgNPs). Imine bond condensation of a rigid tetra-aldehyde with a flexible diamine followed by imine-bond reduction yielded the discrete tetragonal organic barrel (OB4^R ). The presence of a molecular pocket ornamented with eight diamine moieties gives the potential for encapsulation of silver(I). The organic barrel was finally used as a molecular vessel for the controlled nucleation of silver nanoparticles (AgNPs) with fine size tuning through binding of Ag^I ions in the confined space of the barrel followed by reduction. Transmission electron microscopy (TEM) analysis of the Ag⁰ @OB4^R composite revealed that the mean particle size is 1.44±0.16 nm. The composite material has approximately 52 wt % silver loading. The barrel-supported ultrafine AgNPs [Ag⁰ @OB4^R ] are found to be an efficient photocatalyst for facile Ullmann-type aryl-amination coupling of haloarenes at ambient temperature without using any additives. The catalyst was stable for several cycles of reuse without any agglomeration. The new composite Ag⁰ @OB4^R represents the first example of discrete organic barrel-supported AgNPs employed as a photocatalyst in Ullmann-type coupling reactions at room temperature.

Organic cage supported metal nanoparticles for applications

Porous shape-persistent organic cages can anchor metal nanoparticles either inside the cavity or in the external cavity generated through self-assembly. The size of these nanoparticles range from 1-2 nm depending upon the host and can be controlled within a narrow size distribution. The nanoparticles thus formed are quite stable as they are segregated efficiently preventing their association and eventual precipitation. These fine nanoparticles are found to be quite effective in catalyzing a number of organic transformations besides showing interesting emission properties.

Ultrastable and Highly Catalytically Active N-Heterocyclic-Carbene-Stabilized Gold Nanoparticles in Confined Spaces

Controlling the size and surface functionalization of nanoparticles (NPs) can lead to improved properties and applicability. Herein, we demonstrate the efficiency of the metal-carbene template approach (MCTA) to synthesize highly robust and soluble three-dimensional polyimidazolium cages (PICs) of different sizes, each bearing numerous imidazolium groups, and use these as templates to synthesize and stabilize catalytically active, cavity-hosted, dispersed poly-N-heterocyclic carbene (NHC)-anchored gold NPs. Owing to the stabilization of the NHC ligands and the effective confinement of the cage cavities, the as-prepared poly-NHC-shell-encapsulated AuNPs displayed promising stability towards heat, pH, and chemical regents. Most notably, all the Au@PCCs (PCC=polycarbene cage) exhibited excellent catalytic activities in various chemical reactions, together with high stability and durability.

Amphiphilic Organic Cages: Self-Assembly into Nanotubes and Enhanced Anion-π Interactions

An amphiphilic organic cage was synthesized and used as self-assembly synthon for the fabrication of novel functional supramolecular structures in solution. The transmission electron microscopy (TEM) results showed that this amphiphilic cage self-assembled in aqueous solution into unilamellar nanotubes with a diameter of 29±4 nm at a concentration of 0.05 mg mL^-1 . Interestingly, the self-assembly of this cage significantly enhanced the anion-π interactions as indicated by a remarkable increasement of association constant (K_a ) between Cl^- and this amphiphilic cage after self-assembly. In specific, K_a was increased from 223 M^-1 for discrete cages in methanol to 6800 M^-1 for aggregated cages after self-assembly in water at the same concentration of 2.26×10^-5  M. A mechanism based on a synergistic effect was proposed in order to explain this self-assembly process through enhanced anion-π interactions.

Solvent-controlled self-assembly of tetrapodal [4 + 4] phosphate organic molecular cage

Two flexible subcomponents, namely tris(4-formylphenyl)phosphate and tris(2-aminoethyl)amine, are assembled into a tetrapodal [4 + 4] cage depending on the solvent effect. Single-crystal structure analysis reveals that the caivity is surrounded by four phosphate uints. Good selectivity of CO₂ adsorption over CH₄ is demonstrated by the gas adsorption experiment.

Flexibility Induced Encapsulation of Ultrafine Palladium Nanoparticles into Organic Cages for Tsuji-Trost Allylation

A series of three positional isomers of organic cages namely o-OC, m-OC, and p-OC, have been self-assembled using dynamic covalent chemistry. Their room temperature controlled fabrication with palladium gives ultrafine diameter (1-2 nm) of palladium nanoparticles (Pd NPs). We observed that the shape-flexibility of cages have great impact on the formation of Pd NPs. Theoretical calculations reveals that theoretically obtainable size of Pd NPs for each cage which was complementary to the experimental results. Theoretical studies indicate that the driving forces for the specific orientational preference may be ascribed to subtle variations on the level of π-π interactions, which ultimately governs the growth of Pd NPs therein. It is the first example of shape-flexible synthesis of organic cages where flexibility governs the nanoparticle growth. Pd NPs have shown excellent catalysis of Tsuji-Trost allylation at room temperature and pressure in water.

Photochromic organic cage-encapsulated Au nanoparticles: light-regulated cavities for catalytic reduction of 4-nitrophenol

Encapsulated Au nanoparticles in a diarylethene-based photochromic cage with adjustable particle sizes under UV and visible light exhibited different catalytic rates for the reduction of 4-nitrophenol.

Synthesis of a Large, Shape-Flexible, Solvatomorphic Porous Organic Cage

Porous organic cages have emerged over the last 10 years as a subclass of functional microporous materials. However, among all of the organic cages reported, large multicomponent organic cages with 20 components or more are still rare. Here, we present an [8 + 12] porous organic imine cage, CC20, which has an apparent surface area up to 1752 m² g^-1, depending on the crystallization and activation conditions. The cage is solvatomorphic and displays distinct geometrical cage structures, caused by crystal-packing effects, in its crystal structures. This indicates that larger cages can display a certain range of shape flexibility in the solid state, while remaining shape persistent and porous.

Organic Imine Cages: Molecular Marriage and Applications

Imine condensation has been known to chemists for more than a century and is used extensively to synthesize large organic cages of defined shapes and sizes. Surprisingly, in the context of the synthetic methods for organic imine cages (OICs), a self-sorting/self-selection (molecular marriage) process has been overlooked over the years. Such processes are omnipresent in nature, from the creation of galaxies to the formation of the smallest building blocks of life (the cell). Such processes have the incredible ability to guide a system toward the formation of a specific product or products out of a collection of equally probable multiple possibilities. This Minireview sheds light on new opportunities in cage design offered by the self-sorting/self-selection protocol in OICs. Recent efforts to explore organic cages for various exciting new applications are discussed; for example, for detection of harmful small organic molecules, as templates for nucleation of metal nanoparticles (MNPs), and as proton-conducting materials.