Heterogeneous asymmetric Diels–Alder reactions using a copper–chiral bis(oxazoline) complex immobilized on mesoporous silica

A chiral bis(oxazoline)–copper complex was immobilized onto mesoporous silica and the resulting heterogeneous catalyst was employed in asymmetric Diels–Alder reactions. Reactions using the catalyst exhibited good enantioselectivity of 78% enantiomeric excess and endo/exo-selectivity (17:1) better than the corresponding homogeneous reaction. The catalyst could be easily recovered and reused several times without significant loss of the remarkable reactivity, diastereoselectivity and enantioselectivity.     

Magnetite tethered mesoionic carbene‐palladium (II): An efficient and reusable nanomagnetic catalyst for Suzuki‐Miyaura and Mizoroki‐Heck cross‐coupling reactions in aqueous medium

In this paper, a highly active, air‐ and moisture‐stable and easily recoverable magnetic nanoparticles tethered mesoionic carbene palladium (II) complex (MNPs‐MIC‐Pd) as nanomagnetic catalyst was successfully synthesized by a simplistic multistep synthesis under aerobic conditions using commercially available inexpensive chemicals for the first time. The synthesized MNPs‐MIC‐Pd nanomagnetic catalyst was in‐depth characterized by numerous physicochemical techniques such as FT‐IR, ICP‐AES, FESEM, EDS, TEM, p‐XRD, XPS, TGA and BET surface area analysis. The prepared MNPs‐MIC‐Pd nanomagnetic catalyst was used to catalyze the Suzuki–Miyaura and Mizoroki–Heck cross‐coupling reactions and exhibited excellent catalytic activity for various substrates under mild reaction conditions. Moreover, MNPs‐MIC‐Pd nanomagnetic catalyst could be easily and rapidly recovered by applying an external magnet. The recovered MNPs‐MIC‐Pd nanomagnetic catalyst exhibited very good catalytic activity up to ten times in Suzuki–Miyaura and five times in Mizoroki–Heck cross‐coupling reactions without considerable loss of its catalytic activity. However, MNPs‐MIC‐Pd nanomagnetic catalyst shows notable advantages such as heterogeneous nature, efficient catalytic activity, mild reaction conditions, easy magnetic work up and recyclability.     

Catalytic oxidation of primary aromatic amines with sodium periodate catalyzed by Mn(III)salophen complex supported on polystyrene-bound imidazole

The catalytic activity of Mn(III)salophen complex supported on polystyrene-bound imidazole, [Mn(salophen)Cl-PSI], was studied in the oxidation of primary aromatic amines in acetonitrile/water, using sodium periodate as an oxygen source. Amines were oxidized efficiently to their corresponding azo derivatives in the presence of this catalyst. The heterogeneous catalyst showed high stability and reusability in the oxidation reactions and could be reused several times without loss of its activity. The effect of different solvents was studied in the oxidation of p-toluidine and CH₃CN/H₂O was chosen as the solvent.     

Impregnated copper or palladium–copper on magnetite as catalysts for the domino and stepwise Sonogashira-cyclization processes: a straightforward synthesis of benzo[b]furans and indoles

An impregnated copper on magnetite catalyst is a versatile system for different domino Sonogashira-cyclization processes between 2-iodophenol and different alkynes to give the corresponding substituted benzo[b]furans. The catalyst could be recovered ten times without losing its activity. The related process using 2-iodoaniline was, however, better catalyzed by mixed palladium–copper on magnetite giving exclusively, in this case, the products arising from the Sonogashira coupling. The cyclization to the corresponding substituted indoles could be easily and quantitatively performed by zinc bromide treatment. This catalyst avoids the use of any type of expensive and difficult to handle organic ligand, showing excellent yields, under mild reaction conditions. The catalyst is very easy to remove from the reaction medium, just by using a simple magnet.     

NH insertion reactions catalyzed by reusable water-soluble ruthenium(II)-hm-phenyloxazoline complex

A water-soluble Ru(II)-hm-pheox complex was efficiently catalyzed NH insertion of EDA with a broad class of amine derivatives in water/ether biphasic medium to deliver the biologically active precursors α-aminoester products with excellent yields (up to >99%). The products were separated by decantation and the catalyst was washed and reused several times (at least 8 times) without any specific loss of its catalytic activity. The plausible mechanism of the reaction was explained. Additionally, In case of ethylene diamine, the NH insertion product could be transformed to biological active piperazinone compound in high yield. The asymmetric version of this catalytic reaction is under investigation.     

A novel amino acid functionalized ionic liquid promoted one-pot solvent-free synthesis of 3,4-dihydropyrimidin-2-(1H)-thiones

An environmentally benign, cheap and reusable L-amino acid functionalized ionic liquid [L-AAIL]/AlCl₃ was found to be an effective catalyst for the synthesis of 3,4-dihydropyrimidine-2-(1H)-thione derivatives in good to excellent yield under solvent-free condition. Compared with the classical Biginelli reactions, this method consistently enjoys the advantages of mild reaction conditions, easy work-up, and short reaction time. These one-pot three-component Biginelli products could be separated easily from the catalyst–water system, and the catalyst could be reused at least five times without noticeably reducing catalytic activity.     

Improvement in nanocomposite host (nanocavity of dealuminated zeolite Y)-guest (12-molybdophosphoric acid) catalytic activity and its application to the one-pot three-component synthesis of tetrahydrobenzo[b]pyrans

Zeolite Y was dealuminated by chemical methods (with ethylenediaminetetraacetic acid) to modify the zeolite structure for 12-molybdophosphoric acid (MPA) loading. MPA was encapsulated in the nanocavities of modified dealuminated zeolite Y (MDAZY) and characterized by Fourier transform infrared, X-ray diffraction, and atomic absorption spectroscopy. The new catalyst was applied for an efficient chemoselective synthesis of tetrahydrobenzo[b]pyran derivatives, and the corresponding products were obtained in good to excellent yields in very short reaction times. Furthermore, the catalytic activity of this new catalyst in the synthesis of tetrahydrobenzo[b]pyrans was compared with MPA encapsulated in zeolite Y dealuminated by the hydrothermal method. The catalyst (MPA–MDAZY) was recovered and reused several times without loss of its catalytic activity.     

Xylan-type hemicelluloses supported terpyridine–palladium(II) complex as an efficient and recyclable catalyst for Suzuki–Miyaura reaction

Xylan-type hemicelluloses supported terpyridine–palladium(II) as a novel biomass-supported catalyst was synthesized and characterized in terms of morphology, composition, and thermal stability. The nano-Pd catalyst was further explored for Suzuki–Miyaura reaction between arylboronic acid and aryl halide under aerobic condition, with a yield up to 98 %. In particular, the catalyst exhibited both high catalytic activity and stability for Suzuki–Miyaura reaction. Furthermore, the catalyst could be easily recovered by simple filtration and reused at least six times without significant loss of its catalytic activity. This work provides a novel and effective supported catalyst, and broadens the applications of polysaccharides in green catalysis.     

Ionic CNT-supported Ru–carbene complex for recyclable ring-closing metathesis

The ionic multi-walled carbon nanotubes (IM-f-MWCNTs), which were covalently functionalized with imidazolium salt, have been utilized as support materials for the immobilization of Hoveyda-type Ru–carbene complex. The catalytic activity and recyclability of the ionic CNT-supported Ru–carbene complexes have been investigated for ring-closing metathesis of various dienes, and the recovered catalyst can be reused up to 10 times without any significant loss of catalytic activity.     

A reusable polymer supported copper catalyst for the C–N and C–O bond cross-coupling reaction of aryl halides as well as arylboronic acids

A simple and industrially viable protocol for C–N and C–O coupling was reported here. The polymer supported heterogeneous copper catalyst was prepared from chloromethyl polystyrene using a simple procedure. O-Arylation of substituted phenols with various aryl halides was achieved using this copper catalyst in DMSO medium. This heterogeneous copper catalyst, also efficiently works for the N-arylation of N–H heterocycles with aryboronic acids in methanol. This catalyst was also effective in amination reaction of primary amines with aryl halides as well as arylboronic acids in DMSO medium. The effects of solvent, base and temperature for the O-Arylation and amination reactions were reported. Further, the catalyst can be easily recovered quantitatively by simple filtration and reused up to several times without sufficient loss of its catalytic activity.     

A reusable polymer supported copper catalyst for the C–N and C–O bond cross-coupling reaction of aryl halides as well as arylboronic acids

A simple and industrially viable protocol for C–N and C–O coupling was reported here. The polymer supported heterogeneous copper catalyst was prepared from chloromethyl polystyrene using a simple procedure. O-Arylation of substituted phenols with various aryl halides was achieved using this copper catalyst in DMSO medium. This heterogeneous copper catalyst, also efficiently works for the N-arylation of N–H heterocycles with aryboronic acids in methanol. This catalyst was also effective in amination reaction of primary amines with aryl halides as well as arylboronic acids in DMSO medium. The effects of solvent, base and temperature for the O-Arylation and amination reactions were reported. Further, the catalyst can be easily recovered quantitatively by simple filtration and reused up to several times without sufficient loss of its catalytic activity.     

Copper- and phosphine-free Sonogashira coupling reactions of aryl iodides catalyzed by an N,N-bis(naphthylideneimino)diethylenetriamine-functionalized polystyrene resin supported Pd(II) complex under aerobic conditions

A polymer-supported palladium(II) N,N-bis(naphthylideneimino)diethylenetriamine complex is found to be a highly active catalyst for Sonogashira coupling reactions. The reactions are performed under copper- and phosphine-free conditions in an air atmosphere. The palladium catalyst is easily separated, and can be reused several times without significant loss in catalytic activity.     

Homogeneous and biphasic autoxidation of tetralin catalyzed by transition metal salts and complexes

The biphasic autoxidation of tetralin was carried out using various Co, Ni and Mn complexes as catalysts. Cobalt–N,N′-dimethylethylenediamine complex, which is amphiphilic and surface-active, was found to be most effective; it could be easily recovered in a compact emulsion layer after the reaction and could be reused with no apparent loss of activity. The biphasic reaction differs from the homogeneous counterpart in that (1) little hydroperoxide product is formed, (2) there is lesser sensitivity to product inhibition and a greater degree of conversion and (3) there is an easier catalyst recovery and substrate recycle.     

Highly reusable support‐free copper(II) complex of para‐hydroxy‐substituted salen: Novel,efficient and versatile catalyst for C─N bond forming reactions

An air‐stable, highly active and versatile method for C─N bond forming reactions is reported. Under mild conditions using a highly reusable support‐free Cu(II)–salen complex, structurally diverse N ‐aryl‐substituted compounds were obtained via direct C─N bond forming reaction of HN‐heterocycles with aryl iodides or three‐component C─N bond forming reaction of 2‐bromobenzaldehyde, aniline derivatives and sodium azide in good to excellent yields. C─N bond forming reaction for benzimidazole derivatives was also performed in the presence of the catalyst under ambient conditions. A series of hybrid benzimidazoles bearing morpholine, tetrazole and quinoxaline backbones were produced using this method. All reactions were performed in short times under air. The Cu(II) catalyst could be reused up to eight times in the direct cross‐coupling reaction of 9H –carbazole with iodobenzene without any decrease in its catalytic activity.     

Synthesis of a polymer–ruthenium complex Ru(pbbp)(pydic) and its catalysis in the oxidation of secondary alcohols with TBHP as oxidant

A polymer–ruthenium complex Ru(pbbp)(pydic) was synthesized from the reaction of poly-2,6-bis(benzimidazolyl)pyridine (pbbp) with RuCl₃ and disodium pyridine-2,6-dicarboxylate (pydic). The Ru(pbbp)(pydic) was characterized thoroughly by spectroscopic methods. ICP analysis revealed that the percentage of complexation of 2,6-bis(benzimidazolyl)pyridine unit in pbbp was about 83%. The complex was tested as a heterogeneous catalyst for the oxidation of secondary alcohols to their corresponding carbonyl compounds in solvent-free conditions using aqueous tert-butyl hydroperoxide as oxidant. The developed catalytic system exhibited high activity and broad functional group compatibility, allowing a variety of secondary alcohols, including substituted secondary benzylic alcohols and secondary aliphatic ones, to be oxidized to the corresponding ketones in high yields. This Ru(pbbp)(pydic) could be recycled for several times, but it dissolved in part in the reaction mixture during the catalytic run leading to gradual deactivation of the catalyst with repeated runs.     

Multi-wall carbon nanotube-supported manganese(III) porphyrin: An efficient and reusable catalyst for the oxidation of alkenes with H2O2 under ultrasonic irradiation

A manganese complex of meso-tetrakis(p-hydroxyphenyl)porphyrin immobilized onto functionalized multi-wall carbon nanotubes has been synthesized and characterized. The catalytic activity of this heterogeneous catalyst was investigated in the oxidation of various olefins with hydrogen peroxide under ultrasonic irradiation. The role of the stoichiometric amounts of acetic anhydride/or acetic acid as an activator that introduces in situ peracetic acid is discussed. This heterogeneous catalyst was highly reusable in the oxidation reactions and reused several times without significant loss of its catalytic activity.     

Effect of spacers on the activity of soluble polymer supported catalysts for the asymmetric addition of diethylzinc to aldehydes

A chiral Zn(II)-salen complex tethered with poly(ethylene glycol) (PEG) was synthesized. This soluble polymer-supported complex was found to catalyze the asymmetric addition of diethylzinc to a series of aromatic aldehydes in good yields and with good enantiomeric ratio (er). The PEG-supported catalyst could be recycled and reused up to three times. The reactivity and selectivity of the catalyst was dependent on the nature of the linker between the polymer and the complex.     

Styrene epoxidation over a SBA-15-supported Mn(III) Schiff-base complex

2,4-Di-tert-butyl-6-((E)-(propylimino)methyl)phenol as a Schiff-base ligand was immobilized onto an amino-functionalized SBA-15 through the reaction between di-tert-butyl-salicylaldahyde and the tethered amino group. The Mn(III) metal complex of the immobilized Schiff-base ligand was proven to be an active catalyst for the epoxidation of styrene withtert-butyl hydroperoxide as a terminal oxidant. The catalysts behaved as an oxidation catalyst in the epoxidation and could be used many times without structural degradation, leaching of active manganese species and significant activity loss. It has been concluded that the reversible redox cycles of the metal center play a key role during the epoxidation reaction, as well as in the reusability of the catalysts.     

Polystyrene-supported cu(II)-R-Box as recyclable catalyst in asymmetric Friedel–Crafts reaction

The complex of copper(II) trifluoromethanesulfonate with chiral isopropyl bis(oxazoline) ligand (i-Pr-Box) was immobilized on accessible and inexpensive Merrifield resin according to a “click” procedure. The resulting catalyst showed high efficiency and recyclability in the asymmetric Friedel–Crafts alkylation of indole and its derivatives. The catalyst can be recycled five times without appreciable loss in activity and enantioselectivity.     

Sulfonated palladium(II) N‐heterocyclic carbene complex immobilized on nano–micro size poly(4‐vinylpyridinium chloride) for Suzuki‐Miyaura cross‐coupling reaction

The sulfonated palladium(II) N‐heterocyclic carbene complex Pd^II(NHC)SO₃^?, supported on poly(4‐vinylpyridinium chloride), was used as a heterogeneous, recyclable and active catalyst for the Suzuki–Miyaura reaction. This catalyst was applied for coupling of various aryl halides with phenylboronic acid and the corresponding products were obtained in excellent yields and short reaction times. The catalyst was characterized using Fourier transform infrared and diffuse reflectance UV–visible spectroscopies, scanning electron microscopy and elemental analysis. After each reaction, the catalyst was recovered easily by simple filtration and reused several times without significant loss of its catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.