Heterogeneous Organocatalyst Research Articles

Design and Characterization of l-Prolinate-Amberlite as a Novel Heterogeneous Organocatalyst and Its Catalytic Application in the Synthesis of Pyrazol-Derivates

The [Amb]l-prolinate obtained from the immobilization of l-prolinate anion onto amberlite IRA900OH, was used as a new organocatalyst for the efficient synthesis of 4,4′-(arylmethylene)-bis-(1H-pyrazol-5-ol) derivatives. The prepared heterogeneous organocatalyst was well characterized by using of FTIR, TGA, DTG, XRD and elemental analysis techniques. Short reaction times (5–18 min), excellent yields (82–98 %) and simple experimental procedure with an easy work-up are some of the advantages of the procedure.

Efficient Synthesis of 3,3‐diaryloxindoles Catalyzed by L‐prolinate Anion Immobilized onto Amberlite as a Novel Heterogeneous Organocatalyst

AbstractL‐prolinate anion immobilized onto amberlite IRA900OH ([Amb]L‐Prolinate) is reported as a new, reusable and cheap organocatalyst for the condensation of indoles with isatins to afford the corresponding 3,3′‐diaryloxindol derivatives in ethanol under reflux condition. [Amb]L‐Prolinate was achieved by the treatment of a MeOH/H2O solution of L‐proline with amberlite IRA900OH at 60 °C. The procedure for heterogenization of L‐proline organocatalyst is based on non‐covalent ion‐pair immobilization of L‐proline on the surface of anion‐exchange resin amberlite IRA900OH (AmbIRA900OH) as a commercially accessible cationic polymer support. The prepared heterogeneous organocatalyst was well characterized by using of FTIR, TGA, DTG, XRD and elemental analysis techniques. The catalytic activity of the catalyst was also examined in the reaction of indole and isatin. The catalyst has been recovered and its reusability confirmed in 8 runs

Ion-pair immobilization of l-prolinate anion onto cationic polymer support and a study of its catalytic activity for one-pot synthesis of spiroindolones

A novel clean and simple technique for the heterogenization of l-proline organocatalyst has been introduced. This procedure is based on non-covalent immobilization of l-proline on the surface of anion-exchange resin amberlite IRA900OH (AmbIRA900OH) as an efficient, cheap and commercially accessible cationic polymer support. The ion-pair immobilization of l-proline on the surface of amberlite IRA900OH was achieved by the treatment of a MeOH/H2O solution of l-proline with amberlite IRA900OH at 60 °C. l-Proline anion was exchanged with hydroxyl anion and immobilized via ionic interaction between carboxylate group of l-prolinate and quaternary ammonium cation of the cationic amberlite support. The prepared heterogeneous organocatalyst was well characterized using FTIR, TGA, DTG, XRD and elemental analysis techniques. This heterogeneous catalyst was used as an efficient recoverable catalyst for the synthesis of spiroindolone derivatives and good-to-excellent yields were obtained. The efficiency of the catalyst was almost completely maintained after 5 runs and very low leaching amount of organocatalyst into the reaction mixture occurred.

Synthesis and characterization of ionic liquid immobilized on magnetic nanoparticles: A recyclable heterogeneous organocatalyst for the acetylation of alcohols

Herein, we describe a simple and efficient procedure for the preparation of 3-((3-(trisilyloxy)propyl)propionamide)-1-methylimidazolium chloride ionic liquid supported on magnetic nanoparticle (TPPA–IL–Fe3O4). The structure of this magnetic ionic liquid is fully characterized by FT-IR, TGA, XRD, VSM, SEM, EDX and DLS techniques. TPPA–IL–Fe3O4 is employed as a catalyst for the acetylation of alcohols with acetic anhydride under mild and heterogeneous conditions at room temperature with good to excellent yields. The magnetic catalyst could be readily separate from the reaction media by simple magnetic decantation, and reused several times without significant loss of its catalytic activity.

Solid poly-N-heterocyclic carbene catalyzed CO2 reduction with hydrosilanes

The utility of solid poly-N-heterocyclic carbene (poly-NHC) materials as organocatalysts for carbon dioxide reduction was studied. These poly-NHC particles were demonstrated to be useful as heterogeneous organocatalysts for the reduction of carbon dioxide to methanol and for the formylation of N–H bonds with hydrosilanes as a hydride donor. These solid catalysts could potentially be useful in large-scale syntheses due to the ease of catalyst recycle and reuse, providing cost savings and environmental sustainability in the long run.

Ion-pair immobilization of l-prolinate anion onto cationic polymer support and a study of its catalytic activity as an efficient heterogeneous catalyst for the synthesis of 2-amino-4H-chromene derivatives

A novel clean and simple technique for the heterogenization of l-proline organocatalyst has been introduced. This procedure is based on non-covalent immobilization of l-proline on the surface of an anion-exchange resin amberlite IRA900OH (AmbIRA900OH) as an efficient, cheap, and commercially accessible cationic polymer support. The ion-pair immobilization of l-proline on the surface of AmbIRA900OH was achieved by the treatment of a MeOH/H2O solution of l-proline with AmbIRA900OH at 60 °C. l-Proline anions were exchanged with hydroxyl anions and immobilized via ionic interaction between a carboxylate group of l-prolinate and quaternary ammonium cations of the cationic amberlite support. The prepared heterogeneous organocatalyst was well characterized by using FTIR, TGA, DTG, XRD, and elemental analysis techniques. The prepared heterogeneous organocatalyst was used as a catalyst for the one-pot, three-component synthesis of 2-amino-4H-chromene derivatives in EtOH at 80 °C. The reactions were efficiently performed in the presence of the title catalyst with short reaction times and gave the desired products at high yields. This catalyst can be straightforwardly recovered by simple filtration and recycled up to eight consecutive runs. Very low leaching of then organocatalyst into the reaction mixture occurred.

Urea–pyridine bridged periodic mesoporous organosilica: An efficient hydrogen-bond donating heterogeneous organocatalyst for Henry reaction

Hydrogen-bond donating (HBD) organocatalysts have been employed as an important class of catalysts for the activation of small molecules. However, the use of these catalysts was restricted on account of the self-aggregation of HBD-active species. In this work, a successful approach was developed to construct novel urea–pyridine bridged periodic mesoporous organosilica (PMO) to prevent the unwanted self-recognition and aggregation of urea-based catalytic center by spatial isolation, unleashing its HBD organocatalytic activity along with cooperative effect from the pyridine unit for efficient Henry reaction. The urea–pyridine bridged PMO catalyst presents high structural stability and high catalytic recyclability.

A magnetically recyclable heterogeneous BINOL organocatalyst for the asymmetric aldol reaction

A chiral organocatalyst derived from (R)-1,1′-bi-2-naphthol (BINOL) was developed for immobilisation onto magnetic iron oxide particle (MIOP). This heterogeneous organocatalyst was characterised using infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA) and scanning electron microscope (SEM). The performance of BINOL-grafted MIOP (BINOL–MIOP) was then evaluated using aldol reaction between benzaldehydes and cyclic ketones. Comparative studies between homogeneous versus heterogeneous aldol reaction revealed the similar reactivity for both reaction systems. The reaction system mediated by BINOL–MIOP was versatile to produce aldol adducts in moderate-to-good yields (45–99%) from different benzaldehydes and cyclic ketones. In addition, more syn adducts were produced in most cases. Up to 35% ee was observed in anti adducts, despite that a higher 50% ee of anti adduct was observed in the homogeneous reaction system. This observation was supported by the results obtained from the molecular modelling, which revealed the reduced selectivity in the heterogeneous system that was possibly caused by the torsional angle distortion of BINOL after immobilisation. In contrast to the free-BINOL, the distorted-BINOL exhibited lower tendency to form a complex with aldehyde, thereby reducing the selectivity that the free-BINOL could deliver. In addition, the reaction system mediated by BINOL–MIOP was exhibiting an excellent reusability for up to 10 cycles of reactions.

Dimethylaminopyridine-supported graft polymer catalyst and its flow system.

A new heterogeneous organocatalyst, graft polymer supported dimethylaminopyridine (g-DMAP), is developed. This catalyst has a flexible structure and comprises DMAP anchored to the polyethylene-graft-polyacrylic acid (PE-g-PAA). It exhibits higher activity than DMAP supported on polystyrene cross-linked with divinylbenzene and can be recovered in batch mode acetylation. The activity and stability of this catalyst allow its application in continuous flow systems. Continuous acetylation proceeds with excellent conversion, and a turnover number of 560 can be achieved using g-DMAP. Parallel fixed bed reactors were used to scale up the synthesis of this continuous flow system. Eight parallel fixed bed reactors displayed excellent conversion.

Urea-containing metal-organic frameworks as heterogeneous organocatalysts

Two novel pillared MOFs containing a urea-functional group are introduced and their efficiency as organocatalysts is evaluated in methanolysis of epoxides.

Efficient magnetic and recyclable SBILC (supported basic ionic liquid catalyst)-based heterogeneous organocatalysts for the asymmetric epoxidation of trans-methylcinnamate

A green heterogeneous catalytic alternative was developed for the asymmetric epoxidation of trans-methylcinnamate to (2R,3S)-phenyl glycidate.

Nanostructured oxytyramine catalyst for the facile one-pot synthesis of cyclohexanecarbonitrile derivatives

A magnetic, recyclable heterogeneous organocatalyst, OT@Si@SPIONs, has been developed for the facile synthesis of cyclohexanecarbonitriles.

Green and Sustainable Heterogeneous Organo-Catalyst for Asymmetric Aldol Reactions

Linear amino acids covalently supported on graphene sheet were employed as catalysts for asymmetric aldol reactions between cyclohexanone and aldehydes (aliphatic and/or aromatic) in a batch type reactor in the presence of water. The reactions were found to exhibit high yield as well as excellent ee value. Additionally, the catalysts were found to be truly heterogeneous and eco-friendly.

N-Heterocyclic Carbenes Supported on Vinylic Addition Polynorbornene: A Recyclable and Recoverable Organocatalyst

A bromoalkyl functionalized vinylic addition polynorbornene has been used as an inert new scaffold to support imidazolium salts by straightforward nucleophilic substitution using different imidazoles ImR (R=Me, mesityl, 2,6-iPr2C6H3). These polymers, VA-PNB-(CH2)4ImRBr, are precursors of N-heterocyclic carbenes which are useful as heterogeneous organocatalysts. The polymeric carbenes have been tested in two model reactions: The synthesis of saturated esters from α,β-unsaturated aldehydes and the conjugate umpolung reaction of α,β-unsaturated aldehydes for the synthesis of γ-butyrolactones. The supported catalyst (R=mesityl) is fully recyclable and can be recovered as an imidazolium salt and stored for further use.

Mesoporous Poly(melamine–formaldehyde): A Green and Recyclable Heterogeneous Organocatalyst for the Synthesis of Benzoxazoles and Benzothiazoles Using Dioxygen as Oxidant

AbstractA simple, highly efficient, and sustainable strategy for the synthesis of benzoxazole and benzothiazole derivatives was developed by using inexpensive, green, readily available, and recyclable mesoporous poly(melamine–formaldehyde) as a green, heterogeneous organocatalyst. The corresponding substituted benzoxazoles and benzothiazoles were obtained in good to excellent yields by aerobic oxidation of o‐substituted aminobenzenes with various aldehydes under dioxygen atmosphere. The catalyst can be completely recovered through simple filtration to be reused more than six times without significant loss of catalytic activity.

Catalytic Performance of Silica Supported Cinchona Alkaloids as Heterogeneous Catalysts for Asymmetric Michael Reaction

Silica supported cinchona alkaloids were prepared by thio-ene coupled reaction so as to develop novel highly efficient heterogeneous organocatalysts for asymmetric Michael reaction. As-prepared supported cinchona alkaloids were used as heterogeneous catalysts to catalyze the asymmetric Michael reaction between 1,3-dicarbonyl compounds and N-benzylmaleimide, and their catalytic performance was evaluated. It was found that, when toluene is employed as the solvent, silica supported cinchona alkaloid catalysts can catalyze the aforementioned Michael reaction with medium enantiomeric excess (ee) values (up to 87 %) and significant diastereo ratio (dr) values (up to 96:4). In the meantime, they can be recovered and reused for at least five cycles while their stereo-selectivity remains almost unchanged. This means that the title catalysts could be highly efficient organocatalysts for the investigated Michael reaction.

Heterogeneous organocatalysts composed of microporous polymer networks assembled by Tröger's base formation

Microporous polymer networks are assembled from triamino-triptycene monomers using a polymerisation reaction based on the formation of Troger's base (TB). The highly rigid triptycene units ensure that the polymer networks demonstrate significant intrinsic microporosity as demonstrated by apparent surface areas of up to 1000 m2 g−1. These networks act as heterogeneous basic catalysts which enhance greatly the rate of a model Knovenagel reaction between malonontrile and benzaldehyde. Indeed, the microporous networks, which possess a high concentration of basic sites, enhance the rate of the Knovenagel reaction even more efficiently than using Troger's base as a homogeneous catalyst.

Acid functionalized mesoporous PAN monolith as reusable heterogeneous organocatalyst

A polyacrylonitrile (PAN) monolith has been functionalized by hydrolysis of the surface nitrile into carboxylic acid groups. This mesoporous acid functionalized polyacrylonitrile monolith (AFPM) has been characterized by Fourier transform infrared spectroscopy (FT IR), chemical analysis, solid state MAS NMR spectroscopy, elemental mapping, field-emission scanning electron microscopy and N2 adsorption–desorption study. N2 sorption analysis revealed high surface areas (130–138m2g−1) and narrow pore size distributions (1.6–5.3nm) along with macropore for different samples. FT IR, elemental mapping and MAS NMR results revealed the presence of both nitrile and acid group in the same monolith which supports the hydrolysis of surface nitrile groups during the hydrolysis. The acid functionalized monolith can serve as a reusable heterogeneous organocatalyst as demonstrated in its successful application to the synthesis of xanthene in room temperature.

Synthesis and characterization of mesoporous poly(N-vinyl-2-pyrrolidone) containing palladium nanoparticles as a novel heterogeneous organocatalyst for Heck reaction

Mesoporous poly(N-vinyl-2-pyrrolidone) (MPVP) was prepared through a nanocasting technique based on mesoporous silica KIT-6 as sacrificial templates, and served as an efficient scaffold for supporting Pd nanoparticles. The physical and chemical properties of Pd-MPVP were characterized using FT-IR, XRD, BET, DRS UV–Vis, SEM, TEM and TGA techniques. The application of this novel purely organic heterogeneous catalyst, which combine the advantage of organic polymers and mesoporous materials, was investigated for CC bond formation through the Heck coupling reaction of aryl iodides, bromides and chlorides with styrene. It was observed that the activity of this catalyst decreased just 5% after nine regeneration processes were performed. This unique result opens new perspectives for application of purely organic mesoporous polymers as structurally defined hydrophobic catalyst in catalytic reactions.

L-Proline-modified magnetic nanoparticles (LPMNP): a novel magnetically separable organocatalyst

This study offers a new and efficient method for the stabilization of L-proline moieties on magnetic nanoparticles in order to prepare a novel magnetic recyclable organocatalyst for application in organic transformations. The catalytic activity of this heterogeneous organocatalyst was evaluated in the condensation reaction of indoles and aldehydes for the synthesis of bis(indolyl)methanes in water.