Supramolecular Catalytic Systems Research Articles

Recent applications of macrocycles in supramolecular catalysis

Numerous supramolecular macrocycles have been utilized for developing catalysts by exploiting their specific molecular recognition and ability to form inclusion complexes through noncovalent interactions. The cyclic structure and modified functional groups of these macrocycles can influence substrate and transition state stability, as well as reaction selectivity. The inner cavities of these macrocycles are particularly beneficial, as they enable substrates to adopt preorganized arrangements and serve as versatile platforms for highly efficient supramolecular catalytic systems. This minireview provides an overview of recent advancements in supramolecular catalysis using various macrocycles, such as crown ethers, cyclodextrins, calixarenes, pillararenes, cucurbiturils, and other novel macrocycles.

Cyclodextrin-based multifunctional supramolecular catalysts for aqueous CuAAC reaction

As an excellent bioorthogonal reaction, CuAAC reaction has been widely used in biological research. In this work, three cyclodextrin derivatives β-CD-3, β-CD-4 and CD-P were synthesized in different ways. Among them, use of trace amounts of the β-CD-3 could efficiently promote the CuAAC reaction under mild conditions. Only using 20 ppm concentration of β-CD-3-Cu(I), the TON of the reaction was up to 45,000, and the catalyst still has high catalytic activity after repeated cycling, which may be attributed to its chelating structure formed by coordination with copper more stable than β-CD-4-Cu(I) and CD-P-Cu(I). In addition, we have also proved that the construction of supramolecular catalytic systems can effectively achieve extracellular click reactions at ultra-low concentrations, and therefore can be applied to the synthesis of various functional compounds such as catalysis, imaging, targeting and medicine.

Immobilized Supramolecular Systems as Efficient Synzymes for CO2 Activation and Conversion

AbstractSupramolecular catalysis can provide distinct advantages for the catalytic conversion of CO2 into carbonates by cycloaddition to epoxides. For example, the absence of metals in the catalytic site, and the easy design for optimization. The incorporation of multiple functionalities in pseudopeptidic macrocycles with a pendant arm allows catalytic systems to be obtained where halide anions (nucleophilic activating agents for epoxides), hydrogen bond acceptor sites (activating agents for epoxides and stabilizing sites for anionic intermediates), and amine groups (Lewis basic sites for activating CO2) are in proximity. This allows a high activity in the cycloaddition of CO2 to styrene oxide under mild conditions (turnover number (TON) = 900, CO2 balloon, 100 °C, 5 h). The primary amino groups in the arm facilitate the immobilization of these macrocyclic structures in cross‐linked polymeric matrices containing ammonium halide fragments. Such multifunctional insoluble polymers afford excellent catalytic results with high TON and turnover frequency values and remarkable productivities (>10 gprod gresin−1 h−1). This activity is maintained for a variety of epoxides and is retained after several catalytic runs. Their performance is significantly higher than those reported for most heterogenous supramolecular catalytic systems for CO2 transformation into carbonates.

Supramolecular Catalyst Functions in Catalytic Amount: Cucurbit[7]uril Accelerates Click Reaction in Water

AbstractMacrocycles have garnered significant interest for their potential utility as supramolecular catalysts in modulating chemical transformations. Here, we report a reusable supramolecular catalytic system to accelerate copper(I) catalyzed Click cycloaddition (CuAAC) reactions in water. Our system comprises of 5 mol % CuI and 0.5 mol % of the supramolecular co‐catalyst, cucurbit[7]uril (CB7), which stabilizes and prevents the oxidation of CuI. This catalysis can be cycled is that the triazole product or alkyne reactant hardly bind in the cavity of CB7 while there is an interaction between azide reactant and CB7 through molecular recognition. The dual catalysts can be facilely separated from the reaction system. As a result, the catalyst system can be recycled and reused for more than 10 consecutive cycles while maintaining high catalytic activity.

Molecular Dynamics Simulations of a Catalytic Multivalent Peptide-Nanoparticle Complex.

Molecular modeling of a supramolecular catalytic system is conducted resulting from the assembling between a small peptide and the surface of cationic self-assembled monolayers on gold nanoparticles, through a multiscale iterative approach including atomistic force field development, flexible docking with Brownian Dynamics and µs-long Molecular Dynamics simulations. Self-assembly is a prerequisite for the catalysis, since the catalytic peptides do not display any activity in the absence of the gold nanocluster. Atomistic simulations reveal details of the association dynamics as regulated by defined conformational changes of the peptide due to peptide length and sequence. Our results show the importance of a rational design of the peptide to enhance the catalytic activity of peptide–nanoparticle conjugates and present a viable computational approach toward the design of enzyme mimics having a complex structure–function relationship, for technological and nanomedical applications.

Dynamic Activation of C1 Molecules Evoked by Zeolite Catalysis.

Direct observation of the activation and transformation of reactant molecules is extremely attractive but very challenging in the study of most chemical processes. Here is reported the first case of dynamic activation of C1 molecules in zeolite-catalyzed chemistry. During the methanol conversion over the HZSM-5 zeolite, a sequence of progressive activation states of dimethyl ether (DME) evoked by the special catalysis from CH3-Zeo, a hybrid supramolecular catalytic system formed by the organic methylic species growing on the inorganic silico-aluminate zeolite framework, has been directly observed by in situ ssNMR spectroscopy at programmed temperatures. Operando simulations visually display the variability of this hybrid supramolecular system of which the C–O bond property goes through a dynamic transition from covalent to ionic with the temperature increase, and thus the gradually enhanced electrophilicity of CH3δ+ and nucleophilicity of Zeoδ− lead to the dynamic activation of DME. This dynamic transition is generally reflected in the alkyl-Zeo system with other alkoxy groups, which linked the alkoxy species and carbocations in zeolite catalysis. Consequently, this work not only sheds light on the key issue of the first carbon–carbon (C–C) bond formation in the methanol to hydrocarbons (MTH) process but also brings a new awareness on the essence of acid catalysis in zeolite mediated chemical processes.

Photo-Controllable Catalysis and Chiral Monosaccharide Recognition Induced by Cyclodextrin Derivatives.

A supramolecular catalytic system was constructed from polycationic α-cyclodextrin (6-Iz-α-CD) and gold nanoparticles (AuNP) using a supramolecular assembly strategy. The cavity of cyclodextrin is the channel by which the substrate molecules come into contact with the catalytic center. Introduction of the azobenzene-modified diphenylalanine (Azo-FF) guest molecule allowed for precise photo-control of the catalytic activity owing to its sensitive response to irradiation. Importantly, as a unique glucose oxidase the AuNP@6-Iz-α-CD realizes unprecedented chiral recognition catalysis for chiral monosaccharides. In combination with a 3,3',5,5'-tetramethylbenzidine (TMB) color reaction, AuNP@6-Iz-α-CD is able to recognize the chirality of various monosaccharides.

Photo‐Controllable Catalysis and Chiral Monosaccharide Recognition Induced by Cyclodextrin Derivatives

AbstractA supramolecular catalytic system was constructed from polycationic α‐cyclodextrin (6‐Iz‐α‐CD) and gold nanoparticles (AuNP) using a supramolecular assembly strategy. The cavity of cyclodextrin is the channel by which the substrate molecules come into contact with the catalytic center. Introduction of the azobenzene‐modified diphenylalanine (Azo‐FF) guest molecule allowed for precise photo‐control of the catalytic activity owing to its sensitive response to irradiation. Importantly, as a unique glucose oxidase the AuNP@6‐Iz‐α‐CD realizes unprecedented chiral recognition catalysis for chiral monosaccharides. In combination with a 3,3′,5,5′‐tetramethylbenzidine (TMB) color reaction, AuNP@6‐Iz‐α‐CD is able to recognize the chirality of various monosaccharides.

Asymmetric Ring-Opening of Epoxides Catalyzed by Metal–Salen Complexes

The asymmetric ring-opening of epoxides is an important reaction in organic synthesis, since it allows for the enantioselective installation of two vicinal functional groups with specific stereochemistry within one step from a highly available starting material. An effective class of catalysts for the asymmetric ring-opening of epoxides is metal–salen complexes. This review summarizes the development of metal–salen catalyzed enantioselective desymmetrization of meso-epoxides and kinetic resolution of epoxides with various nucleophiles, including the design and application of both homogeneous- and heterogeneous epoxide-opening catalysts as well as multi-metallic covalent and supramolecular catalytic systems.

Cu-tethered macrocycle catalysts: Synthesis and size-selective CO2-fixation to propargylamines under ambient conditions

A novel air-stable, Cu-tethered macrocycle catalyst possessing a large inner cavity was successfully synthesized, creating a unique supramolecular catalytic system. The catalyst was utilized in the CO2-fixation reaction to propargylamines. The reaction proceeded more efficiently compared to the conventional CuI catalyst under atmospheric CO2 condition. Notably, owing to its topological effect, the Cu-tethered macrocycle catalyst exhibited unique substrate size selectivity.

A new supramolecular catalytic system: the self-assembly of Rh8 cage host anthracene molecules for [4 + 4] cycloaddition induced by UV irradiation.

The supramolecular assembly, used as a molecular reactor, is of great significance in host-guest chemistry. In this work, we used a tetratopic pyridyl ligand as a building block to hierarchically combine a slightly twisted cuboid with half-sandwich rhodium fragments. The cuboid directionally self-assembled hydrophobic pockets that can encapsulate conjugated molecules like anthracene (ANT) as guests in solutions, by supramolecular interactions including hydrogen bonding and hydrophobic interactions. The array of the ANT molecules in the confined pockets was subjected to a [4 + 4] photocycloaddition reaction under UV light irradiation as an external stimulus in a methanol solution. Furthermore, the mechanism underlying the process was proposed. The cuboid was fully characterized by 1H NMR, single-crystal X-ray diffraction (SCXRD), and mass spectrometry (MS), and its host-guest and cycloaddition processes were monitored by 1H NMR spectroscopy and UV-visible spectrophotometry.

Cover Feature: “Backdoor Induction” of Chirality: Trans‐1,2‐cyclohexanediamine as Key Building Block for Asymmetric Hydrogenation Catalysts (Eur. J. Org. Chem. 11/2019)

The Cover Feature shows a supramolecular catalytic system, envisioned as a factory machine. The worker uses a chiral cyclohexane to control the chirality in the remote rhodium machine head which does the selective hydrogenation reaction. The transfer of chirality is achieved by stacked phenyl-phosphine gears shown in the insides of the machine. The system has enabled distant chirality transfer, named 𠄌backdoor induction”, for hydrogenation of model substrates with very high selectivity (up to 97% ee). The future goal is to apply this system to industrially relevant substrates. More information can be found in the Full Paper by S. I. Kirin et al.

Supramolecular Catalytic Systems Based on a Cationic Amphiphile and Sodium Polystyrene Sulfonate for Decomposition of Organophosphorus Pollutants

A supramolecular catalytic system for hydrolytic decomposition of toxic phosphorus acid esters has been obtained on the basis of a cationic surfactant with a morpholinium head group and sodium polystyrene sulfonate. Self-organization of the new binary catalytic system has been studied by tensiometry, conductometry, pH-metry, spectrophotometry, and dynamic and electrophoretic light scattering, and its aggregation thresholds have been determined. High solubilizing ability of the system with respect to a hydrophobic guest has been revealed. The morpholinium surfactant has been found to accelerate the hydrolysis of phosphonates up to 50 times in comparison to the reaction in water. The apparent hydrolysis rate constant in the presence of the polyelectrolyte decreases threefold due to reduction of the reactant binding constants.

Supramolecular Catalytic Systems for Decomposition of Toxic Esters of Acids of Phosphorus

Supramolecular Catalytic Systems for Decomposition of Toxic Esters of Acids of Phosphorus

Supramolecular Catalytic Systems for Decomposition of Toxic Esters of Acids of Phosphorus

Supramolecular Catalytic Systems for Decomposition of Toxic Esters of Acids of Phosphorus

Pillar[5]arene-based N-heterocyclic carbene ligand for Pd-catalysed Suzuki reaction

A pillar[5]arene-based N-heterocyclic carbene ligand was prepared by reaction of bromoethoxy pillar[5]arene with excess 1-methylimidazole at 130 °C in the absence of solvent and used as a catalyst for the Suzuki coupling reaction. Excellent yields were obtained when the Suzuki reactions were carried out under ambient atmosphere in ethanol, employing 0.2 mol% ligand, 1 mol% PdCl2(CH3CN)2 and 1.5 mmol of K2CO3. The novel pillar[5]arene-based imidazolium salt is a promising material for the construction of highly active supramolecular catalytic systems.

Tandem Catalysis of an Aldol-'Click' Reaction System within a Molecular Hydrogel.

A heterogeneous supramolecular catalytic system for multicomponent aldol-‘click’ reactions is reported. The copper(I) metallohydrogel functionalized with a phenyltriazole fragment was able to catalyze the multicomponent reaction between phenylacetylene, p-nitrobenzaldehyde, and an azide containing a ketone moiety, obtaining the corresponding aldol products in good yields. A possible mechanistic pathway responsible for this unexpected catalytic behavior has been proposed.

Synthesis of Cr(III) Salen Complexes as Supramolecular Catalytic Systems for Ring‐Opening Reactions of Epoxides

AbstractThe synthesis of two conformationally restricted Cr(III) salen complexes, 2 and 3, is described. Together, they constitute a supramolecular hydrogen‐bonding catalytic system for the recently reported asymmetric ring‐opening reactions of epoxides by a dynamic supramolecular catalyst. The synthesis involves state‐of‐the art transformations in frontline synthetic chemistry applied to heterocyclic chemistry. Hence, palladium‐catalyzed reactions were employed, including carbonylative annelation and Suzuki cross‐coupling reactions, for the formation of one of the heterocyclic rings (quinolone) and the functionalization of the formed rings. For the construction of the second heterocyclic ring (isoquinolone), a Curtius rearrangement was employed. The corresponding salen ligands were then prepared by Schiff‐base reactions, yielding the final complexes after metal insertion. For reference purposes the less conformationally restricted Cr(III) complexes 4 and 5 were also synthesized.

Supramolecular catalytic systems based on 1, 4-diazabicyclo[2.2.2]octane, its alkylated quaternary derivatives, and lanthanum nitrate

Spectrophotometry was used to study the catalytic effects of the systems composed of N-monoand N, N-dialkylated 1, 4-diazabicyclo[2.2.2]octanes and lanthanum nitrate on the hydrolysis rate of O-alkyl O-4-nitrophenyl chloromethylphosphonates (Alk = Et, Bun, and n-hexyl). The mechanism of action and efficiency of the catalytic system depend on the structure of the heterocycle, its propensity to aggregation and complexation with the lanthanum cation, and the relative content of the components in solution. The maximum catalytic effect (a ∼115-fold increase in the hydrolysis rate constant) was achieved in micellar solutions of the cationic monoalkylated derivative of 1, 4-diazabicyclo[2.2.2]octane and lanthanum nitrate.

A novel supramolecular catalytic system based on amphiphilic triphenylphosphonium bromide for the hydrolysis of phosphorus acid esters

Abstract The biomimetic nature of micellar catalysis can significantly affect the rate of chemical reactions due to the effects of concentration and the change of microenvironment. Here, a key role is played by the nature of the head group. The catalytic activity of alkyltriphenylphosphonium bromides (TPPB-n; n = 10, 12, 14, 16, 18; n is the number of carbon atoms in alkyl groups) in the nucleophilic substitution of p-nitrophenyl esters of alkylchloromethylphosphonic acid were investigated by the method of spectrophotometry. Using pyrene, prodan and Sudan I as probes the values of critical micelle concentrations and aggregation numbers were determined. A comparison of the results of kinetic dependence processing by Berezin equation obtained for TPPB series with the known ammonium analogues was carried out. It was found that for TPPB-n series, the higher acceleration of reaction has been achieved due to concentration factor compared to ammonium surfactants. This agrees with the fact that alkyltriphenylphosphonium bromides demonstrate higher aggregation activity forming micelles with higher solubilizing capacity.