Novel and efficient multifunctional periodic mesoporous organosilica supported benzotriazolium ionic liquids for reusable synthesis of 2,4,5-trisubstituted imidazoles

A series of periodic mesoporous organosilica supported benzotriazolium ionic liquids were synthesized and tested as effective and practical heterogeneous catalysts in the condensation reaction of diphenylethanedione, aromatic aldehydes and ammonium acetate. The catalyst PMO@ILBF4(1.0) showed brilliant catalytic activity for the synthesis of 2,4,5-trisubstituted imidazoles with good to high yields. We also found that the catalytic activity could be significantly influenced by the loading levels and functional anions of the benzotriazolium-cation ionic liquid, probably due to an intensification of intramolecular synergistic effect. Furthermore, the multifunctional catalyst PMO@ILBF4(1.0) could be easily recovered by filtration and recycled for six times with no significant loss in activity, indicating its excellent stability and reusability. This method provides an efficient and environmentally-friendly procedure for the production of 2,4,5-trisubstituted imidazoles.     

Functionalized Periodic Mesoporous Organosilica: A Highly Enantioselective Catalyst for the Michael Addition of 1,3‐Dicarbonyl Compounds to Nitroalkenes

A functionalized periodic mesoporous organosilica with incorporated chiral bis(cyclohexyldiamine)‐based Ni^II complexes within the silica framework was developed by the co‐condensation of (1R,2R)‐cyclohexyldiamine‐derived silane and ethylene‐bridge silane, followed by the complexation of NiBr₂ in the presence of (1R,2R)‐N,N′‐dibenzylcyclohexyldiamine. Structural characterization by XRD, nitrogen sorption, and TEM disclosed its orderly mesostructure, and FTIR and solid‐state NMR spectroscopy demonstrated the incorporation of well‐defined single‐site bis(cyclohexyldiamine)‐based Ni^II active centers within periodic mesoporous organosilica. As a chiral heterogeneous catalyst, this functionalized periodic mesoporous organosilica showed high catalytic activity and excellent enantioselectivity in the asymmetric Michael addition of 1,3‐dicarbonyl compounds to nitroalkenes, comparable to those with homogeneous catalysts. In particular, this heterogeneous catalyst could be recovered easily and reused repeatedly up to nine times without obviously affecting its enantioselectivity, thus showing good potential for industrial applications.     

Sustainable and efficient 2,3-dihydroquinazolin-4(1H)-ones production over heterogeneous and recyclable Al-MCM-41 supported dual imidazolium ionic liquids nanocomposites

A type of Al-MCM-41 supported dual imidazolium ionic liquids nanocomposites have been synthesized and efficiently used as catalysts in the one-pot synthesis of 2,3-dihydroquinazolin-4(1H)-ones. It was shown that the highest efficiency was achieved in the condensation of a range of aldehydes and anthranilamide in the presence of the (2)Al-MCM-41@ILCeCl₄(0.5) solid catalyst under mild conditions. Hot filtration test confirmed that the reaction follows a heterogeneous pathway. Moreover, the catalyst was stable, very active, robust, and displayed good recyclability without significant loss of catalytic activity after five consecutive cycles during the process. Green reaction conditions, operational simplicity, feasibility, high to excellent yields, sustainability of the functionalized catalyst are the main highlights of the present protocol.     

Organorhodium‐Functionalized Periodic Mesoporous Organosilica: High Hydrophobicity Promotes Asymmetric Transfer Hydrogenation in Aqueous Medium

Three organosilica‐bridged periodic mesoporous organosilicas were prepared by the immobilization of a chiral N‐sulfonylated diamine‐based organorhodium complex within their silicate network. Structural analysis and characterization confirmed their well‐defined single‐site active rhodium centers, whilst electron microscopy revealed their highly ordered hexagonal mesostructures. Among these three different organosilica‐bridged periodic mesoporous organosilicas, the ethylene‐bridged periodic mesoporous organosilica catalyst exhibited excellent heterogeneous catalytic activity and high enantioselectivity in the aqueous asymmetric transfer hydrogenation of aromatic ketones. This superior catalytic performance was attributed to its salient hydrophobicity, whilst its comparable enantioselectivity relative to the homogeneous catalyst was derived from the confined nature of the chiral organorhodium catalytic sites. Furthermore, this ethylene‐bridged periodic mesoporous organosilica could be conveniently recovered and reused at least 12 times without the loss of its catalytic activity. This feature makes this catalyst attractive for practical organic synthesis in an environmentally friendly manner. This study offers a general way of optimizing the bridged organosilica moiety in periodic mesoporous organosilicas, thereby enhancing its catalytic activity in heterogeneous catalysis.     

Periodic Mesoporous Organosilicas as Efficient Nanoreactors in Cascade Reactions Preparing Cyclopropanic Derivatives

In this work, three organosilica precursors functionalized with carbamate moieties were synthesized by condensing of 3‐isocyanatopropyltriethoxysilane and coupling regents of either hydroquinone (HQ), bisphenol A (BPA), or 1,1′‐bi‐2‐naphthol (BN). These organosilica precursors were covalently bonded in the framework of periodic mesoporous organosilicas by co‐condensation and hydrolysis with tetraethyl orthosilicate (TEOS) under hydrothermal treatment. The compositions and physical properties were characterized with FTIR, XRD, thermogravimetric/differential thermal analysis (TG/DTA), ²⁹Si NMR, ¹³C NMR spectroscopies, SEM, TEM, and BET technologies. These characterizations suggest that three different structures were formed as the result of different sizes and compositions of the organosilica precursors. The three mesoporous organosilicas were applied as heterogeneous catalysts in the one‐pot cascade Knoevenagel and Michael cyclopropanic reactions for the synthesis of cyclopropanic derivatives and showed excellent activity and selectivity. The highest conversion was obtained with mesoporous catalyst (MC)‐HQ owing to its ordered mesostructure, highest surface area, and weakest stereo effect of the organic linking groups compared with MC‐BAP and MC‐BN. This methodology employed cheaper and more easily obtainable raw materials as reagents over the traditional alkene additive system and these heterogeneous catalysts exhibit superior performance and recyclability than typical homogeneous organic catalysts.     

Surfactant‐directed one‐pot preparation of novel Ti‐containing mesomaterial with improved catalytic activity and reusability

Titanium was incorporated in ionic liquid based periodic mesoporous organosilica to prepare a nanostructured catalyst (Ti@PMO‐IL) with high activity. Procedure for the synthesis of Ti@PMO‐IL was followed according the simultaneous hydrolysis and condensation of alkylimidazolium ionic liquid, tetramethoxysilane (TMOS) and tetrabutylorthotitanate (TBOT) where a surfactant template was used together with a simple acid‐based catalytic aproach. N₂ adsorption isotherm of the Ti@PMO‐IL was studied to measure its mean pore volume, pore size distribution and specific surface area. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was applied to identify the chemical bonds present in Ti@PMO‐IL. The morphology of this nanomaterial was investigated by scanning electron microscopy (SEM). Transmission electron microscopy (TEM) image was used to study mesoporosity and structure order of the catalyst. The catalytic activity of Ti@PMO‐IL was then studied and found to be efficient and reusable to catalyze Hantzsch reaction.     

Aminated Ordered Mesoporous Carbons: Preparation and Catalytic Performance for Knoevenagel Condensation Reactions

The amine‐ and diamine‐functionalized mesoporous carbons with hexagonal mesostructure have been prepared by a rationally two‐step modification procedure under mild reaction conditions, respectively. The physicochemical properties of the obtained solid basic mesoporous catalysts were characterized by XRD, TEM, N₂ adsorption‐desorption, FT‐IR, EDX and elemental analysis techniques. The results indicated the organic amine groups were successfully introduced inside the channels of mesoporous carbons without destroying the well‐ordered 2D hexagonal mesostructure. A series of Knoevenagel condensation of aldehyde/ketone with active methylene compounds have been carried out over the diamine‐function‐ alized mesoporous carbons, which proved to be efficient heterogeneous basic catalysts and exhibited a similar catalytic activity after sixth cycles. This can be attributed to its hydrophobic framework and hydrophilic diamine groups, which led to amphiphilic properties and offered some advantages for the Knoevenagel condensation reactions.     

Bifunctional Catalysts Containing Zn(II) and Imidazolium Salt Ionic Liquids for Chemical Fixation of Carbon Dioxide

Zn(II) can efficiently promote the catalytic performance of imidazolium salt ionic liquids (imi-ILs) for the chemical fixation of CO₂ into epoxides. To obtain sustainability, immobilized bifunctional catalysts containing both imi-ILs and Zn(II) were prepared using bimodal mesoporous silica (BMMs) as carrier, through grafting of Zn(OAc)₂ and 1-(trimethoxysilyl)propyl-3-methylimidazolium chloride (Si-imi) separately in the nanopores. The catalysts, named as BMMs−Zn&ILs, were identified as efficient catalysts for cycloaddition reaction of CO₂ into epoxides under solvent-free conditions. BMMs−Zn&ILs showed good catalytic activity, which increased with the increase of the molar ratio of Zn(II) to Si-imi. As a comparison, different catalytic systems including homogeneous imi-IL, BMMs-ILs and BMMs−Zn were studied to demonstrate different cooperation behaviors. Furthermore, the kinetics studies of homogeneous and heterogeneous bifunctional catalysts were employed to confirm the differences, as well as to support the proposed cooperative catalysis mechanism in the nanopores.     

Novel Basic Ionic Liquid Based on Alkylammonium as Efficient Catalyst for Knoevenagel Reaction

The typical Knoevenagel condensation was carried out smoothly in the presence of a basic ionic liquid of N,N,N′,N′-tetramethyl-N′-hexyl-ethylenediammonium tetrafluoroborate ([TMHEDA]BF₄), and 99% of yield was obtained using ethyl cyanoacetate and benzaldehyde as substrates at 60 °C for 1 h. Four reuses of the ionic liquid without dramatic decrease in catalytic activity for Knoevenagel condensation demonstrated the good stability and operability of the ionic liquid. Moreover, the typical nucleophilic addition reactions were also accomplished by the same ionic liquid to check its feasibility. The dual function of the basic ionic liquid both as solvent and catalyst, combined with simple product separation and recycling, is expected to contribute to the development of a green and environmentally friendly strategy.     

Organic Reactions in Ionic Liquids: Ionic Liquid Promoted Knoevenagel Condensation of Aromatic Aldehydes with (2‐Thio)Barbituric Acid

Abstract

The Knoevenagel condensation of aromatic aldehydes with (2‐thio)barbituric acid proceeded efficiently in reusable ionic liquids, EAN, BmimBF₄, and BmimPF₆ at room temperature in the absence of any catalyst with high yields.     

Imidazolium-Based Phosphinite Ionic Liquid (IL-OPPh2) as Reusable Catalyst and Solvent for the Knoevenagel Condensation Reaction

A task-specific ionic liquid (IL, OPPh₂) that bears a phosphinite weak Lewis base group in an imidazolium cation was found to efficiently catalyze the Knoevenagel condensation of arylaldehydes with malononitrile, dimethyl(diethyl)malonate, and ethyl cyanoacetate. This IL plays a dual role as both the reaction media and also catalyst, and it can be easily recovered and reused in several runs. Satisfactory results were obtained with good yields, short reaction time, and simplicity in the experimental procedure. A variety of coumarin derivatives were synthesized in this procedure.     

Selective oxidation of alcohols with hydrogen peroxide catalyzed by tungstate ions (WO4) supported on periodic mesoporous organosilica with imidazolium frameworks (PMO-IL)

Tungstate ions supported on the periodic mesoporous organosilica with ionic liquid frameworks (WO₄⁼@PMO-IL) were found to be a recoverable catalyst system for the highly selective oxidation of various primary or secondary alcohols to the corresponding aldehydes or ketones by 30% H₂O₂ as green oxidant under neutral aqueous reaction conditions. The catalyst can be also recovered and efficiently reused in seven subsequent reaction cycles without any remarkable decreasing in the catalyst activity and selectivity. Moreover, N₂ sorption analysis, transmission electron microscopy (TEM) images, and thermal gravimetric analysis (TGA) showed that the structure regularity and functional groups loaded of the catalyst were not affected during the reaction process.     

Imidazolium ionic liquids with short polyoxyethylene chains

It has been observed by us earlier that imidazolium ionic liquids ([bmim][BF₄] react with paraformaldehyde giving in nearly quantitative yield imidazolium ionic liquids substituted at 2‐position with hydroxymethyl group ([bhmim][BF₄]). In this article, we describe the application of those ionic liquids (after converting hydroxyl group into alkoxide anion by reaction with sodium hydride) as initiators for anionic polymerization of ethylene oxide (EO). Up to DP_n ～ 30 polymerization proceeds without side reactions, and the product is exclusively low‐molecular‐weight polyoxyethylene containing imidazolium head group (POE‐IL) with DP_n equal to [EO]/[bhmim] ratio. By increasing [EO]/[bhmim] ratio further, side reaction start to interfere, and macromolecules that does not contain imidazolium head groups are also formed, as evidenced by analysis of MALDI TOF spectra. Blending of POE‐IL with high‐molecular‐weight POE leads to significant reduction of crystallinity of POE. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6961–6968, 2008     

Basic ionic liquids. A short review

Basic ionic liquids as environmental-friendly solvents and catalysts with high activity and selectivity and easily recovered materials were used to replace traditional bases such as KOH, NaOH, K₂CO₃, NaHCO₃, NaOAc, triethylamine, or tetrabutylammonium acetate. Using the traditional bases generally suffered from disadvantages such as waste production, corrosion and environmental problems. Basic ionic liquids offering a new possibility for developing environmentally friendly basic catalysts due to the combination of the advantages of inorganic bases and ionic liquids. They are flexible, nonvolatile,noncorrosive, and immiscible with many organic solvents. Basic ionic liquids (BILs) have been used in base-catalyzed processes such as Michael addition, Markovnikov addition, Knoevenagel condensation, Henry reaction, Mannich reaction, oximation, Feist-Benary reaction and etc. In this short review, we wish to present an overview of the types, properties, synthesis and applications of basic ionic liquids.     

室温离子液体促进的5-亚芳基巴比妥酸衍生物的合成

在室温离子液体1-丁基-3-甲基咪唑四氟硼酸盐([bmim]BF₄)存在下, 采用室温研磨和微波辐射的方法, 由芳香醛和巴比妥酸或硫代巴比妥酸经Knoevenagel缩合反应, 制备了相应的5-亚芳基巴比妥酸或5-亚芳烃基硫代巴比妥酸衍生物. 在室温研磨条件下反应2 h, 产率为78%～96%, 在微波辐射功率为160 W时反应20 s, 产率为82%～98%, 产物结构经¹H NMR确证.     

离子液体功能化二氧化硅催化Knoevenagel反应

在100 ℃, 无外加溶剂条件下, 离子液体功能化二氧化硅催化一系列芳醛和活泼亚甲基化合物进行Knoevenagel 缩合反应, 以高产率生成相应产物. 当反应底物为水杨醛与氰基乙酸乙酯的时候, 产物为3-乙氧基羰基香豆素, 这是水杨醛和氰基乙酸乙酯缩合关环, 再发生氰基醇解的产物. 采用离子液体功能化二氧化硅作为反应催化剂, 反应后催化剂可回收再利用.     

Studies on –SO3H functionalized Brønsted acidic imidazolium ionic liquids (ILs) for one-pot,two-step synthesis of 2-styrylquinolines

Four task-specific –SO₃H functionalized imidazolium ionic liquids (ILs) were investigated for Brønsted acidities by Hammett functions. After knowing their thermal stabilities, the catalytic activity was observed for the preparation of 2-styrylquinolines by following consecutive Friedländer and Knoevenagel reactions in solvent-free thermal energy. The acidity order ([Dsim][OOCCF₃] > [Dsim][OTs] > [Dsim][OOCCl₃] > [Msim][OOCCF₃]) of three ILs was consistent with their activity order observed in the acid-catalyzed synthesis of 2-styrylquinolines under solvent-free conditions at 90° C, with the exception of [Dsim][OTs]. The best catalytic activity was shown by 25 mol% of [Dsim][OOCCF₃] IL. The less acidic IL required 50 mol% to give good yield of 2-styrylquinolines under the optimized condition.     

Alkylation of phenol with isopropanol over MCM-49 zeolites

Four novel Br?nsted acidic ionic liquids with two different acid sites on the imidazolium cations were synthesized and employed as catalysts and media in the esterification of acetonitrile with alcohols. The results showed that [HSO₃-pHim]HSO4 was the most efficient catalyst and medium which could be recycled easily without obvious decline in the catalytic activity.     

离子液体催化吲哚羟烷基化反应

报道了咪唑类离子液体催化吲哚和环状碳酸酯反应合成羟烷基吲哚,系统考察了反应时间、催化剂用量、反应温度和反应物比例对离子液体催化反应性能的影响.在优化的反应条件下,吲哚与碳酸乙烯酯或碳酸丙烯酯反应可高效地生成1-(2-羟乙基)吲哚、1-(2-羟丙基)吲哚及其相应的衍生物.离子液体的催化活性与离子液体中的阴离子有关,其催化活性顺序为BF₄^-﹤Br^-﹤Cl^-﹤OAc^-,与阴离子的碱度顺序一致.     

New basic mesoporous silica catalyst obtained by ammonia grafting

NH3-treated mesoporous silica (FSM-16) contains SiNH2 sites which exhibit basic catalytic activity for Knoevenagel condensation; SiNH2 and SiOH pair sites formed at lower NH3-treatment temperatures exhibit higher turnover frequencies (TFs) in comparison with SiNH2 single sites.