Microwave-assisted preparation of dialkylimidazolium tetrachloroaluminates and their use as catalysts in the solvent-free tetrahydropyranylation of alcohols and phenols

Microwave-assisted preparation of dialkylimidazolium tetrachloroaluminates, [CnMIM][AlCl4] and their application as recyclable catalysts for the efficient and eco-friendly protection of alcohols as tetrahydropyranyl (THP) ethers are described. The same catalyst can also be utilized for the deprotection of THP ethers.     

聚苯胺盐在无溶剂条件下有效催化羰基保护反应

合成了自掺杂聚苯胺盐PABSA,并成功应用于醛和乙酸酐的缩醛化反应,发现此聚苯胺盐催化剂具有高效、可回收等特性。同时,利用二元醇作为保护基团,醛也可以转化成相应的缩醛。考察了反应时间、温度和催化剂用量对反应的影响,并通过IR、1H NMR、13C NMR和元素分析对部分产物进行了结构表征。     

Metal- and Solvent-Free Transesterification and Aldol Condensation Reactions by a Homogenous Recyclable Basic Ionic Liquid Based on the 1,3,5-Triazine Framework

A new recyclable basic ionic liquid was introduced as an efficient catalyst for aldol condensation and transesterification reactions under environmentally friendly conditions. The catalyst was prepared based on methyl imidazolium moieties bearing hydroxide counter anions via the Hofmann elimination on a 1,3,5-triazine framework. The ionic liquid with two functionalities including anion stabilizer and high basicity, was used as an efficient catalyst for aldol condensation as well as transesterification reaction of a variety of alkyl benzoates. All reactions were performed in the absence of any external reagent, co-catalyst, or solvent, in line with environmental protection. The kinetics isotope effect (KIE) was conducted for the transesterification reaction to elucidate the mechanism and rate determining step (RDS). It worth noted that, the homogeneous catalyst could be recycled from the reaction mixture and reused for several consecutive runs with insignificant drop of basicity and conversion.     

Supramolecular synthesis of 3,4-dihydropyrimidine-2(1H)-one/thiones under neat conditions

An efficient solvent free method for the synthesis of various 3,4-dihydropyrimidin-2(1H)-one/thiones in excellent yields using sulfonatedβ-cyclodextrine as recyclable catalyst is described.Sulfonatedβ-cyclodextrine was found to be efficient,recyclable heterogeneous catalyst and showed rate enhancements,high yields and short reaction times in this transformation.     

Recyclable Catalysts for Alkyne Functionalization

In this review, we present an assessment of recent advances in alkyne functionalization reactions, classified according to different classes of recyclable catalysts. In this work, we have incorporated and reviewed the activity and selectivity of recyclable catalytic systems such as polysiloxane-encapsulated novel metal nanoparticle-based catalysts, silica–copper-supported nanocatalysts, graphitic carbon-supported nanocatalysts, metal organic framework (MOF) catalysts, porous organic framework (POP) catalysts, bio-material-supported catalysts, and metal/solvent free recyclable catalysts. In addition, several alkyne functionalization reactions have been elucidated to demonstrate the success and efficiency of recyclable catalysts. In addition, this review also provides the fundamental knowledge required for utilization of green catalysts, which can combine the advantageous features of both homogeneous (catalyst modulation) and heterogeneous (catalyst recycling) catalysis.     

Synthesis and characterization of a novel Fe3O4@SiO2/bipyridinium dichloride nanocomposite and its application as a magnetic and recyclable phase-transfer catalyst in the preparation of β-azidoalcohols, β-cyanohydrins,and β-acetoxy alcohols

β-Azidoalcohols, β-cyanohydrins, and β-acetoxy alcohols have been synthesized in the presence of a Fe₃O₄@SiO₂/bipyridinium nanocomposite (Fe₃O₄@SiO₂/BNC) as a novel magnetic and recyclable phase-transfer catalyst (PTC) in water. The catalyst was characterized with FT–IR, SEM, XRD, VSM, and TGA. This methodology offers several advantages, including easy work-up procedure, excellent regioselectivity, high yields, short reaction times, recyclable catalyst, easy separation of the catalyst through an external magnet and eco-friendly procedure.     

Protic ionic liquid [TMG][Ac] as an efficient,homogeneous and recyclable catalyst for Boc protection of amines

An efficient and practical protocol for the chemoselective N-Boc protection of various structurally different aryl, aliphatic and heterocyclic amines was carried out with (Boc)₂O using protic 1, 1, 3, 3-tetra-methylguanidinium acetate (10 mol%) as recyclable catalyst under solvent free condition at ambient temperature. No competitive side reactions (isocyanate, urea and N, N-di-Boc) were observed. α-Amino alcohols afforded the N-Boc-derivative without oxazolidinone formation.     

Carbon‐Supported Copper Nanomaterials: Recyclable Catalysts for Huisgen [3+2] Cycloaddition Reactions

Highly disperse copper nanoparticles immobilized on carbon nanomaterials (CNMs; graphene/carbon nanotubes) were prepared and used as a recyclable and reusable catalyst to achieve Cu^I‐catalyzed [3+2] cycloaddition click chemistry. Carbon nanomaterials with immobilized N‐heterocyclic carbene (NHC)‐Cu complexes prepared from an imidazolium‐based carbene and Cu^I show excellent stability including high efficiency at low catalyst loading. The catalytic performance evaluated in solution and in bulk shows that both types of Cu‐CNMs can function as an effective recyclable catalysts (more than 10 cycles) for click reactions without decomposition and the use of external additives.     

Synthesis and new application of green and recyclable cyclic poly(L‐lactide)‐clay hybrid

We report on the application of biodegradable cyclic poly(L ‐lactide) (PLLA) as new stabilizer; synthesis and application of a cyclic PLLA‐clay hybrid material as recyclable catalyst support. Cyclic PLLAs were used to stabilize palladium nanoparticles synthesized by a wet chemical method. It was found that the palladium particles were smaller with cyclic PLLA stabilizer (～5–10 nm) than the particles obtained from linear PLLA. The cyclic PLLA‐clay hybrid was prepared by a zwitterionic ring‐opening polymerization catalyzed by in situ‐generated N‐heterocyclic carbene catalyst. Palladium (0) nanoparticles were supported and well dispersed on the cyclic PLLA‐clay hybrid to form a new nanocomposite. The nanocomposite was found to be a highly efficient and recyclable catalyst for the aminocarbonylation reactions of aryl halides with various amines. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4167–4174     

Recyclable Cu nanoparticle catalyzed azide-alkyne click polymerization

The Cu(I)-catalyzed alkyne-azide cycloaddition(CuAAC) has been developed into a powerful polymerization reaction for the synthesis of new polytriazoles with versatile properties. However, research on recyclable and reusable copper catalyst for click polymerization to meet the requirement of green chemistry was rarely reported. Copper nanoparticles were reported to be capable catalysts for CuAAC. Replacing conventional copper catalyst with copper nanoparticles may realize the recycle and reuse of the copper catalyst in click polymerization. In this paper, copper nanoparticles were prepared and used as an effective catalyst for click polymerization, and soluble polytriazoles with high molecular weights were obtained in excellent yields under optimized reaction conditions. Importantly, the copper nanoparticles can be recycled and reused for up to 11 times for the click polymerization. Moreover, introducing aggregation-induced emission(AIE)-active moiety of tetraphenylethylene into the monomers makes the resultant polymers retain the AIE feature. This work not only provides an efficient recyclable catalytic system for the azide-alkyne click polymerization, but also might inspire polymer chemists to use recyclable copper species to catalyze other polymerizations.     

Nanosilica‐anchored Pd(II)‐Schiff base complex as efficient heterogeneous catalyst for activation of aryl halides in Suzuki–Miyaura cross‐coupling reaction in water

A nanosilica (derived from rice husk)‐anchored Pd(II)–Schiff base complex has been synthesized and characterized. This immobilized complex has been found to be a very effective and recyclable heterogeneous catalyst for the Suzuki–Miyaura cross‐coupling reaction of various aryl halides with arylboronic acid in aqueous medium under mild conditions. The products were identified using ¹H NMR and mass spectral studies. This complex can be easily filtered out from the reaction medium and reused up to six times without significant loss of catalytic activity. Since the reaction proceeds under mild conditions in aqueous medium as well as the catalyst being recyclable, it provides an environmentally benign alternative route to the existing protocols for the Suzuki–Miyaura reaction.     

Hydrotalcite catalysis in ionic liquid medium: a recyclable reaction system for heterogeneous Knoevenagel and nitroaldol condensation

Knoevenagel condensation proceeds efficiently in recyclable [bmim]PF₆ and [bmim]BF₄ without any catalyst, and hydrotalcites in ionic liquid serve as a safe and recyclable reaction system for both Knoevenagel as well as nitroaldol condensations.     

A robust hydrophilic pyridine-bridged bis-benzimidazolylidene palladium pincer complex: synthesis and its catalytic application towards Suzuki-Miyaura couplings in aqueous solvents

A novel hydrophilic pyridine-bridged bis-benzimidazolylidene palladium pincer complex (3) acted as a highly efficient robust recyclable molecular catalyst towards Suzuki-Miyaura coupling reactions in aqueous media and tolerated various functional groups (even heterocycles) with extremely low catalyst loading.     

Functionalization of silicon surfaces with catalytically active Pd complexes and application to the aerobic oxidation of benzylic alcohols

A single-crystal silicon surface was modified with a bisoxazoline-Pd molecular layer and utilized as a highly efficient (catalyst turnover number up to 780,000, 110 degrees C, 72 h) and recyclable catalyst in the aerobic oxidation of benzylic alcohols.     

An efficient synthesis of (E)-nitroalkenes catalyzed by recoverable diamino-functionalized mesostructured polymers

A clean, efficient, and simple method has been developed for synthesis of (E)-nitroalkenes using FDU-ED as an efficient catalyst. The reactions proceeded with moderate to high yields (60-96%) under mild conditions. The catalyst FDU-ED is recyclable and can be reused more than seven times without significant loss of activity and selectivity.     

Synthesis of 1,1-diacetates catalysed by silica-supported boron sulfonic acid under solvent-free conditions and ambient temperature

1,1-Diacetates derivatives were prepared using the direct condensation of aldehydes with acetic anhydride in the presence of silica-supported boron sulfonic acid (SiO₂/B(SO₄H)₃) as a tri-functional inorganic Brønsted acid catalyst under solvent-free conditions at ambient temperature. The salient features of this methodology are: (i) cheaper process ready availability of the catalyst; (ii) versatility; (iii) high regio-selectivity of the procedure and recyclable property of the catalyst.     

Mn(III)–pentadentate Schiff base complex supported on multi‐walled carbon nanotubes as a green,mild and heterogeneous catalyst for the synthesis of tetrahydrobenzo[b]pyrans via tandem Knoevenagel–Michael cyclocondensation reaction

Mn(III)–pentadentate Schiff base complex supported on multi‐walled carbon nanotubes as a recyclable and reusable, green and nano‐heterogeneous catalyst was designed and fully characterized using infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy , inductively coupled plasma mass spectrometry, elemental analysis and thermogravimetric analysis. A facile, eco‐friendly, mild and green procedure was developed for the one‐pot three‐component synthesis of tetrahydrobenzo[b ]pyrans via tandem Knoevenagel–Michael cyclocondensation reactions between aromatic aldehydes, 1,3‐diones and malononitrile using a catalytic amount of Mn(III)–pentadentate Schiff base complex supported on MWCNTs as an efficient recyclable heterogeneous catalyst under solvent‐free conditions at room temperature. This process has the advantages of easy availability, stability, recyclability and eco‐friendliness of the catalyst, short reaction times, high to excellent yields and simple work‐up procedure.     

Carbon-Based Solid Acid as An Efficient and Reusable Catalyst for One-Pot Synthesis of Tetrasubstituted Imidazoles under Solvent-Free Conditions

Carbon‐based solid acid catalyst was found to be highly efficient, eco‐friendly and recyclable heterogeneous catalyst for the multicomponent reaction of benzil, aromatic aldehyde, primary amine and ammonium acetate, giving rise to 1,2,4,5‐tetrasubstituted imidazoles in good to excellent yields. The present methodology offers several advantages, such as high yields, short reaction time, mild reaction condition and a recyclable catalyst with a very easy work up.     

Fe-pillared bentonite—an efficient catalyst for sulfonylation of arenes using aryl and alkyl sulfonyl chlorides

Fe-pillared bentonite (Fe-PILC) was shown to be an extremely efficient catalyst for the sulfonylation of activated as well as unactivated carbocyclic aromatic compounds and heterocyclic aromatic compounds. The catalyst was also found to be recyclable.     

Immobilization of a palladium(II) bis(imidazolium) complex onto graphene oxide by noncovalent interactions: an efficient and recyclable catalyst for Suzuki–Miyaura reaction

In this research, the Suzuki–Miyaura coupling reaction catalyzed by a palladium(II) complex containing bis(imidazolium) ligand, Pd^II(BIM), immobilized on graphene oxide (GO) as heterogeneous, recyclable and active catalyst is reported. The catalyst, Pd^II(BIM)@GO, was characterized by FT-IR, diffuse reflectance UV–Vis spectroscopy, ICP, field emission scanning electron microscopy, energy-dispersive X-ray analysis, and elemental analysis. It was demonstrated that the GO-supported palladium(II) complex can act as an efficient catalyst and is reusable several times without a significant loss of their catalytic activity.