Heterogeneous Organocatalyst Research Articles

Guanidine-Based Covalent Organic Frameworks: Cooperation between Cores and Linkers for Chromic Sensing and Efficient CO2 Conversion.

C(sp)-H carboxylation with CO2 is an attractive route of CO2 utilization and is traditionally promoted by transition metal catalysts, and organocatalysis for the conversion remains rarely explored and challenging. In this article, triaminoguanidine-derived covalent organic frameworks (COFs) were used as platforms to develop heterogeneous organocatalysts for the reaction. We demonstrated that the COFs with guanidine cores and pyrazine linkers show high catalytic performance as a result of the cooperation between cores and linkers. The core is vitally important, which is deprotonated to the guanidinato group that binds and activates CO2. The pyrazine linker collaborates with the core to activate the C(sp)-H bond through hydrogen bonding. In addition, the COFs show acid- and base-responsive chromic behaviors thanks to the amphoteric nature of the core and the auxochromic effect of the pyrazine linker. The work opens up new avenues to organocatalysts for C-H carboxylation and chromic materials for sensing and switching applications.

Sulfamic acid grafted to cross-linked chitosan by dendritic units: a bio-based, highly efficient and heterogeneous organocatalyst for green synthesis of 2,3-dihydroquinazoline derivatives.

In this work, novel cross-linked chitosan by the G1 dendrimer from condensation of melamine and toluene-2,4-diisocyante terminated by sulfamic acid groups (CS-TDI-Me-TDI-NHSO3H), as a bio-based and heterogeneous acidic organocatalyst, was designed and prepared. Also, the structure of the prepared organocatalyst was characterized by Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and thermogravimetric analysis/derivative thermogravimetry (TGA/DTA). Subsequently, the catalytic performance of the biobased and dendritic CS-TDI-Me-TDI-NHSO3H, as a multifunctional solid acid, was evaluated for the preparation of 2,3-dihydroquinazoline derivatives through a three-component reaction by following green chemistry principles. Some of the advantages of this new protocol include high to excellent yields and short reaction times as well as easy preparation and remarkable catalyst stability of the introduced acidic organocatalyst. The CS-TDI-Me-TDI-SO3H catalyst can be used for up to five cycles for the preparation of quinazoline derivatives with a slight decrease in its catalytic activity.

Synthesis of 2,2‐disubstituted‐2H‐1‐benzopyrans using tetraphenylethylene‐based heterogeneous acidic organocatalyst and the evaluation of their binding interaction with human serum albumin

AbstractA facile method for the synthesis of 2,2‐disubstituted‐2H‐1‐benzopyrans from easily accessible tertiary propargylic alcohols and phenolic derivatives is described using a sulfonated tetraphenylethylene‐based hypercrosslinked polymer (THP‐SO3H) as the heterogeneous organocatalyst. The organocatalyst can be easily recovered by filtration and reused up to five consecutive cycles with nominal loss in catalytic efficiency. The binding interaction of the synthesized benzopyrans with human serum albumin was investigated using fluorescence spectroscopy and molecular docking techniques.

Hydroboration of Hollow Microporous Organic Polymers: A Promising Postsynthetic Modification Method for Functional Materials.

This work shows that hydroboration can be efficiently applied to the postsynthetic modification (PSM) of the Sonogashira-Hagihara coupling-based microporous organic polymers (MOPs). Hollow MOPs (H-MOPs) were prepared by template synthesis through the Sonogashira-Hagihara coupling of tetra(4-ethynylphenyl)methane with 1,4-diiodobenzene. The H-MOPs were used as platforms in the PSM-based functionalization. The heat-treatment of H-MOPs in the presence of a neat pinacolborane reagent resulted in the successful addition of pinacolborane groups to the internal alkynes of H-MOPs, generating H-MOPs with pinacolboranes (H-MOP-BPs). The pinacolborane moieties in the H-MOP-BP were further converted to boronic acid groups. The resultant H-MOP-BAs were used as heterogeneous organocatalysts in the CO2 fixation with epoxides to cyclic carbonates at ambient temperature (50 °C). Moreover, H-MOP-BAs could be recycled with retention of the catalytic performance in five successive reactions.

Prolinate-based heterogeneous catalyst for Knoevenagel condensation reaction: Insights into mechanism reaction using solid-state electrochemical studies

The carbon-carbon bond formation is essential to producing relevant organic compounds that exhibit pharmacological and biological properties. In this regard, Knoevenagel and multicondensation reactions have been employed to test the acid-base cooperativity of functionalized mesoporous silica nanoparticles with L-prolinate based groups (Prol-MSN) in comparison with choline hydroxide fragments (Chol-MSN). Thus, Prol-MSN material has shown to be a promising heterogeneous organocatalyst for condensation reactions. The use of electrochemical sensor techniques allowed through cyclic and differential pulse voltammetry studies a better understanding of the catalytic mechanism of Knoevenagel reaction for the Prol-MSN material, including the role of silanol surface groups and protic solvents.

Anticonvulsant activity, molecular modeling and synthesis of spirooxindole-4H-pyran derivatives using a novel reusable organocatalyst.

Fifteen derivatives of spirooxindole-4H-pyran (A1-A15) were subjected to evaluate through intravenous infusion of pentylenetetrazole (PTZ)-induced epilepsy mouse models. Four doses of the compounds (20, 40, 60 and 80mg/kg) were tested in comparison with diazepam as positive control. The resulted revealed that compounds A3 and A12 were the most active compounds and indicated significant anticonvulsant activity in the PTZ test. The tested compounds were prepared via a multicomponent reaction using graphene oxide (GO) based on the 1-(2-aminoethyl) piperazine as a novel heterogeneous organocatalyst. The prepared catalyst (GO-A.P.) was characterized using some diverse microscopic and spectroscopic procedures as well. The results showed high catalytic activity of the catalyst in the synthesis of spirooxindole-4H-pyran derivatives. The GO-A.P. catalyst was reusable at least for 5 times with no significant decrease in its catalytic action. In silico assessment of physicochemical activity of all compounds also were done which represented appropriate properties. Finally, molecular docking study was performed to achieve their binding affinities as γ-aminobutyric acid-A (GABA-A) receptor agonists as a plausible mechanism of their anticonvulsant action. Binding free energy values of the compounds represented strongly matched with biological activity.

Optimisation of PET glycolysis by applying recyclable heterogeneous organocatalysts

Functionalized silica gels were applied as heterogeneous organocatalysts in PET glycolysis, and were recycled by filtration while preserving high monomer yields over five cycles.

Poly(N-vinylimidazole): A biocompatible and biodegradable functional polymer, metal-free, and highly recyclable heterogeneous catalyst for the mechanochemical synthesis of oximes.

The catalytic activity of poly(N-vinylimidazole), a biocompatible and biodegradable synthetic functional polymer, was investigated for the synthesis of oximes as an efficient, halogen-free, and reusable heterogeneous catalyst. The corresponding oximes were afforded in high to excellent yields at room temperature and in short times using the planetary ball mill technique. Some merits, such as the short reaction times and good yields for poorly active carbonyl compounds, and avoiding toxic, expensive, metal-containing catalysts, and hazardous and flammable solvents, can be mentioned for the current catalytic synthesis of the oximes. Furthermore, the heterogeneous organocatalyst could be easily separated after the reaction, and the regenerated catalyst was reused several times with no significant loss of its catalytic activity.

Cross-Linked Porous Polymers as Heterogeneous Organocatalysts for Task-Specific Applications in Biomass Transformations, CO2 Fixation, and Asymmetric Reactions

Cross-Linked Porous Polymers as Heterogeneous Organocatalysts for Task-Specific Applications in Biomass Transformations, CO₂ Fixation, and Asymmetric Reactions

Heterogeneous and Recyclable Organocatalyst for Oxidation of Alcohols

Heterogeneous and Recyclable Organocatalyst for Oxidation of Alcohols

Sodium alginate: Biopolymeric catalyst for the synthesis of 2-amino-4-arylthiazole derivatives in aqueous medium

Regarded as a naturally occurring macromolecule and without any post-modification, sodium alginate which possesses a granular form was found to be an efficient and recoverable bifunctional heterogeneous organocatalyst for the synthesis of 2-amino-4-arylthiazole derivatives was carried out by the reaction of substituted phenyl acetylene and thiourea in an eco-friendly condition in the presence of TBBDA (tetrabromobenzene-1,3-disulfonamide (tetrabromobenzene-1,3-disulfonamide). Mild reaction conditions, simple reaction procedure, easy purification, high yields of products, eco-friendly catalyst usage and convenient reusability are the highlighted points of this protocol.

Catalytic activity of a CuGHK peptide-based porous material

The CuGHK peptide-based porous material acts as a heterogeneous organocatalyst in the Henry reaction due to a periodic distribution of pockets decorated with lysine side chain active sites.

Porous organic polymers as metal free heterogeneous organocatalysts

This review addresses the current literature on porous organic polymers (POPs) as a new class of metal free green heterogeneous catalysts.

Synthetic Strategies for Hydrazinyl Thiazole Derivatives

AbstractHydrazinyl thiazole is frequently encountered in natural as well as in synthetic compounds. It is also an important pharmacophore and has some other useful applications. In this review article, we have compiled different green synthetic procedures for the synthesis of hydrazinyl thiazole derivatives. Also, the critical analysis of different synthetic schemes will help to understand the lacks in developed procedures and to develop new methodologies regarding its synthesis, specially using heterogeneous organocatalyst and photocatalyst.

“Ship‐in‐a‐Bottle” Strategy for Immobilization of 9‐Amino(9‐deoxy)epi‐Cinchona Alkaloid into Molecularly Imprinted Solid Acid: Acetal Hydrolysis/Asymmetric Aldol Tandem Reaction

AbstractDirect immobilization of versatile 9‐amino(9‐deoxy)epi‐cinchona alkaloids without molecule modification to achieve heterogeneous organocatalysis is of interest in the low‐cost production of optically active compounds. In this paper, an exquisite “ship‐in‐a‐bottle” strategy for direct and simple immobilization of 9‐amino‐(9‐deoxy)epi‐quinine (QNNH2) into hollow polystyrene nano‐bowl with imprinted free space around −SO3H was developed via acid‐base reaction and radical polymerization. The heterogeneous organocatalyst with 0.44 mmol g−1 of QNNH2 and 0.48 mmol g−1 of residual −SO3H possessed fast mass transfer due to the characteristic architectural features, such as thin shell thickness, free space around catalytic site, and hollow interior. In heterogeneous acetal hydrolysis/asymmetric aldol tandem reaction, good to excellent catalytic performances (90–95 % yields, anti/syn=88/12–96/4, and 97–99 % ee anti) for acetals bearing electron‐withdrawing substituents (R=o, m, p‐NO2, Cl) were achieved. The “ship‐in‐a‐bottle” QNNH2 displayed good stability and reusability with excellent catalytic performances in the reuses.

Heterogeneous Organocatalysts for the Reduction of Carbon Dioxide with Silanes

The utilization of carbon dioxide (CO2 ) as feedstock for chemical industries is gaining interest as a sustainable alternative to nonrenewable fossil resources. However, CO2 reduction is necessary to increase its energy content. Hydrosilane is a potential reducing agent that exhibits excellent reactivity under ambient conditions. CO2 hydrosilylation yields versatile products such as silylformate and methoxysilane, whereas formamides and N-methylated products are obtained in the presence of amines. In these transformations, organocatalysts are considered as the more sustainable choice of catalyst. In particular, heterogeneous organocatalysts featuring precisely designed active sites offer higher efficiency due to their recyclability. Herein, an overview is presented of the current development of basic organocatalysts immobilized on various supports for application in the chemical reduction of CO2 with hydrosilanes, and the potential active species parameters that might affect the catalytic activity are identified.

Light-driven, heterogeneous organocatalysts for C-C bond formation toward valuable perfluoroalkylated intermediates.

The favorable exploitation of carbon nitride (CN) materials in photocatalysis for organic synthesis requires the appropriate fine-tuning of the CN structure. Here, we present a deep investigation of the structure/activity relationship of CN in the photocatalytic perfluoroalkylation of organic compounds. Four types of CN bearing subtle structural differences were studied via conventional characterization techniques and innovative nuclear magnetic resonance (NMR) experiments, correlating the different structures with the fundamental mechanistic nexus and especially highlighting the importance of the halogen bond strength between the reagent and the catalyst surface. The optimum catalyst exhibited an excellent performance, with a very wide reaction scope, and could prominently trigger the model reaction using natural sunlight. The work lays a platform for establishing a new approach in the development of heterogeneous photocatalysts for organic synthesis related to medical, agricultural, and material chemistry.

Telescoped Continuous Flow Synthesis of Optically Active γ-Nitrobutyric Acids as Key Intermediates of Baclofen, Phenibut, and Fluorophenibut.

The two-step flow asymmetric synthesis of chiral γ-nitrobutyric acids as key intermediates of the GABA analogues baclofen, phenibut, and fluorophenibut is reported on a multigram scale. The telescoped process comprises an enantioselective Michael-type addition facilitated by a polystyrene-supported heterogeneous organocatalyst under neat conditions followed by in situ-generated performic acid-mediated aldehyde oxidation. Simple access to valuable optically active substances is provided with key advances in terms of productivity and sustainability compared to those of previous batch approaches.

Porous organic polymer bearing triazine and pyrene moieties as an efficient organocatalyst

Materials with high specific surface area and bearing abundant basic sites at their pore surface are very demanding as heterogeneous catalyst for the eco-friendly base catalyzed reactions. Here we have developed a new secondary amine linked triazine and pyrene containing microporous organic polymer (TrzPyPOP) through a simple polycondensation reaction between tetramine1,4-bis(4,6-diamino-s-triazin-2-yl)-benzene (SL-1) and monoaldehyde pyrene-1-carboxaldehyde. This new porous organic polymer TrzPyPOP is very rich in N-content with high BET surface area (1016 m2 g−1). High surface area and N-rich surface basic sites have been explored in its potential as heterogeneous organocatalyst for the synthesis of dihydropyrimidones via Biginelli condensation involving three-component coupling reaction. Only a very little amount of catalyst was effective for the synthesis of dihydropyrimidones derivatives (yields = 88–99 %) together with high recycling efficiency under the optimum reaction conditions.

Hierarchically nanoporous copolymer with built-in carbene-CO2 adducts as halogen-free heterogeneous organocatalyst towards cycloaddition of carbon dioxide into carbonates

A serial of porous polymers incorporating N‑heterocyclic carbene-CO2 adducts (designated as NHC-CO2 adducts) were facilely synthesized via radical polymerization of N-vinylimidazolate and ethyleneglycol dimethacrylate plus post-treatment with dimethyl carbonate (DMC). The polymers possessed tunable chemical structure, large surface area along with abundant meso-macropores and enhanced CO2 uptake which functioned as metal-halogen-free heterogeneous organocatalysts for solvent-free cycloaddition of CO2 to styrene oxide under 10 bar CO2 pressure, exhibiting highly catalytic activity and stable recyclability. Further, turnover frequency (TOF) of 7.1 h−1 (94.3% yield, 12 h) was obtainable under ambient condition, much higher than those of reported metal-halogen-free heterogeneous catalysts, even comparable with existing halogen-containing ones. Furthermore, the catalyst could efficiently convert various epoxides including internal epoxides into corresponding cyclic carbonates under mild condition (1 bar, 70–120 °C). The excellent catalytic performance was ascribed to the appropriate proportion of NHC-CO2 adducts in porous skeleton structure triggered by DMC. A plausible reaction mechanism was proposed to understand NHC-catalyzed fixation of CO2. This study highlights porous organic polymer is a versatile platform of NHC-CO2 adducts to construct eco-friendly solid catalyst towards efficient CO2 conversion.