N-heterocyclic carbenes: Reaction to give anilines

The attempted synthesis of bis(NHC)palladium complexes via the direct reaction of an imidazolium salt with palladium acetate results in the formation of a mixed NHC/aniline complex. The route by which the aniline is formed has not been completely elucidated, but it does originally derive from an imidazolium salt.     

Electrostatic and Non‐covalent Interactions in Dicationic Imidazolium–Sulfonium Salts with Mixed Anions

A series of thioether‐functionalised imidazolium salts have been prepared and characterized. Subsequent reaction of the thioether‐functionalised imidazolium salts with iodomethane affords imidazolium–sulfonium salts composed of doubly charged cations and two different anions. Imidazolium–sulfonium salts containing a single anion type are obtained either by a solvent extraction method or by anion exchange. The imidazolium–sulfonium salts undergo a methyl‐transfer reaction on exposure to water, giving rise to a new, singly charged imidazolium salt with iodide introduced at the 2‐position of the imidazolium ring. Crystal structures of some of the imidazolium–sulfonium salts were determined by X‐ray crystallography providing the topology of the interactions between the dications and the anions. Electrospray ionization mass spectrometry and quantum‐chemical calculations were used to rationalise the relative strength of these interactions.     

A highly active ionic liquid catalyst for Morita-Baylis-Hillman reaction

The Morita-Baylis-Hillman reaction is an efficient carbon-carbon bond forming reaction for the preparation of α-methylene-β-hydroxycarbonyl compounds. A new and highly active di-naphthalene imidazolium salt has been synthesized. We have found that 1,3-bis[2-(naphthalene-2-yloxy)propyl]imidazolium bromid promoted the Morita-Baylis-Hillman reaction of various aryl aldehyde compounds in the absence of solvents. Our studies show that the Morita-Baylis-Hillman reaction by the influence of ionic liquid to give a high yield and short reaction time.     

含氟抗菌单体的合成和抗菌口腔粘接材料的构建

将1-氯代十二烷与1-乙烯基咪唑进行季铵化反应制备咪唑盐单体, 用氟置换氯离子, 制得含氟咪唑盐可聚合抗菌单体, 利用氢核磁共振波谱对合成的中间产物及含氟咪唑盐可聚合抗菌单体进行表征. 将氟离子以有机氟的形式引入粘接系统中, 通过释氟试验和接触抗菌实验研究了含氟咪唑盐抗菌单体改性粘接剂的氟离子释放行为和粘接剂的抗菌性能. 同时, 利用粘接强度测试检测含氟咪唑盐可聚合抗菌单体改性对粘接剂粘接性能的影响. 研究结果表明, 所合成的含氟咪唑盐可聚合抗菌单体具有良好的抗菌作用, 能实现靶向防龋能力, 且添加到粘接系统中后不影响粘接剂的粘接性能, 具有潜在的临床价值.     

Photomodulation of ionic interaction and reactivity: reversible photoconversion between imidazolium and imidazolinium

An interconversion system between imidazolium and imidazolinium has been proposed for the first time. Imidazolium and imidazolinium cations exhibit different reactivity due to the difference in the aromaticity and charge localization structure, which is successfully controlled by means of photoirradiation in the present system. A 4,5-dithiazolylimidazolium salt was prepared and studied as a new class of photochromic materials modulating electrostatic interactions and chemical reactivities. The photochromic 4,5-dithiazolylimidazolium showed reversible photoconversions between imidazolium open-form and imidazolinium closed-form upon successive irradiation with UV and visible light. The imidazolinium closed-form exhibited characteristic solvato- and ionochromisms in which the absorption maximum shifted by more than 80 nm depending on the solvent polarity and counteranions, whereas the imidazolium open-form showed no such solvent-dependent property. Because the corresponding nonionic 4,5-dithiazolylimidazole also did not exhibit the solvent-dependent absorption profile both in open- and closed-forms, the appearance of these chromisms in imidazolinium closed-form was attributed to the change in the extent of ionic interaction, which was brought about by the photoconversion of imidazolium to imidazolinium. The photoderived strong ionic interaction of imidazolinium with counteranion was further applied to the photocontrolled nucleophilic reaction system. Whereas the imidazolium open-form was inert to nucleophiles such as sodium methoxide, the imidazolinium closed-form was reactive to the nucleophilic reaction, demonstrating a photogated reaction system.     

Ion‐Responsive Behavior of Ionic‐Liquid Surfactant Aggregates with Applications in Controlled Release and Emulsification

We propose a simple but efficient, rapid, and quantitative ion‐responsive micelle system based on counter‐anion exchange of a surfactant with an imidazolium unit. The ion‐exchange reaction results in the amphiphilic‐to‐hydrophobic transition of the imidazolium salt, leading to the destruction of the micelles, which has been successfully applied to controlled release and emulsification. The proposed design offers a novel alternative stimulus to control these smart physical aggregates besides pH, temperature and light—with extra advantages. Our finding greatly benefits both fundamental research and industry.     

Functionalized Ionic (Poly)Styrenes and their Application as Catalysts in the Cycloaddition of CO2 to Epoxides

Valorization of CO₂, an abundant C(1) synthon, into platform chemicals is of growing interest. In this context, a key reaction is the cycloaddition of CO₂ to epoxides to form carbonates (CCE). A series of organocatalysts for this reaction, based on imidazolium salts modified with a styrene functional group and a second variable functional group, were prepared and characterized. Both the ionic salts and ionic polymers derived from the salts were evaluated in this reaction. In general, the monomers perform slightly better than the polymers; however, the latter are considerably more convenient to use. Of the catalysts studied, the ionic polystyrene imidazolium salt with an ammonium functionality shows highest activity, tolerates a range of epoxides, and can be recycled multiple times without loss of activity.     

Revelation from the Reaction of 1,4‐Diazabutadiene with Perchloric Acid: An Approach to the Synthesis of Imidazolium Perchlorates

The reactions of 1,4‐diazabutadienes 1 with HClO₄ were studied in detail. The final products obtained were not the hydroperchlorates of 1 but imidazolium perchlorates 2 or 3 . A possible reaction process is postulated on the basis of the isolation of the intermediate 2‐iminomethylimidazolium salt 4 . The factors influencing the conversion of 4 to the imidazolium perchlorates 2 and 3 were discussed with regard to the electronic and steric effects of the N‐substituents. This reaction can serve as an approach for the synthesis of imidazolium derivatives.     

An intermediate for the clean synthesis of ionic liquids: isolation and crystal structure of 1,3-dimethylimidazolium hydrogen carbonate monohydrate

1,3-Dimethylimidazolium-2-carboxylate and carbonic acid have been used to prepare a 1,3-dimethylimidazolium hydrogen carbonate salt by means of a Krapcho reaction. The ability to form hydrogen carbonate azolium salts allows for them to be used as precursors for fast, efficient, environmentally benign, and halide-free syntheses of many ionic liquids by a simple, acid-base reaction of virtually any acid (inorganic, organic, and organic noncarboxylic) with a pK(a) less than that of HCO(3) (-). Additionally, the kinetics of this reaction can be accelerated by employing catalytic amounts of DMSO (a traditional Krapcho solvent used in decarboxylation reactions) to catalyze the decarboxylation. The crystal structure of 1,3-dimethylimidazolium hydrogen carbonate monohydrate is the first example of an imidazolium-based hydrogen carbonate salt. There is a strong 2D hydrogen-bonded network with facially pi-stacked imidazolium cations located in the cavities created by this framework.     

Air-stable, convenient to handle Pd based PEPPSI (pyridine enhanced precatalyst preparation, stabilization and initiation) themed precatalysts of N/O-functionalized N-heterocyclic carbenes and its utility in Suzuki-Miyaura cross-coupling reaction

Several new air-stable, convenient to handle and easily synthesized Pd based PEPPSI (Pyridine Enhanced Precatalyst Preparation, Stabilization and Initiation) type precatalysts supported over N/O-functionalized N-heterocyclic carbenes (NHC) namely, trans-[1-(benzyl)-3-(N-t-butylacetamido)imidazol-2-ylidene]Pd(pyridine)Cl2 (), trans-[1-(2-hydroxy-cyclohexyl)-3-(benzyl)imidazol-2-ylidene]Pd(pyridine)Cl2 () and trans-[1-(o-methoxybenzyl)-3-(t-butyl)imidazol-2-ylidene]Pd(pyridine)Br2 (), have been designed. Specifically, the Pd-NHC complexes, , and , were conveniently synthesized from their respective imidazolium halide salts by the reaction with PdCl2 in pyridine in presence of K2CO3 as a base. A new imidazolium chloride salt, 1-(benzyl)-3-(N-t-butylacetamido)imidazolium chloride () was synthesized by the alkylation reaction of benzyl imidazole with N-t-butyl-2-chloroacetamide. The molecular structures of the imidazolium chloride salt, , and the Pd-NHC complexes, , and , have been determined by X-ray diffraction studies. The density functional theory studies of the , and complexes were carried out to in order to gain insight about their structure, bonding and the electronic properties. The nature of the NHC-metal bond in these complexes was examined using Charge Decomposition Analysis (CDA), which revealed that the N-heterocyclic carbene ligands are effective sigma-donors. In addition, the catalysis studies revealed that the Pd-NHC complexes, , and , are effective catalysts for the Suzuki-Miyaura type C-C cross-coupling reactions.     

Ionic solid-state dimers and polymers derived from imidazolium dicarboxylic acids

A series of imidazolium dicarboxylic acids have been prepared from the reaction of the 1,3‐bis(carboxymethyl)imidazolium zwitterion with the Brønsted acids HX (X=F, Br, Cl, ClO₄). The structures of these acids have been established in the solid state by single‐crystal X‐ray diffraction, which revealed that the cations and anions form strong hydrogen bonds through O? H???X interactions, leading to the formation of dimeric and polymeric networks. These acids react with elemental zinc and cobalt to form stable polymeric coordination complexes, some of which have also been characterised by X‐ray diffraction.     

Imidazole‐coordinated monodentate NHC–Pd(II) complex derived from proline and its application to the coupling reaction of arylboronic acids with carboxylic acid anhydrides in water at room temperature

Cleavage of a C N bond of imidazolium salt derived from N‐phenyl‐substituted proline was observed in this laboratory. A novel imidazole‐coordinated monodentate NHC–Pd(II) complex 5 was obtained as the sole product in good yield in the reaction of imidazolium salt 4 with Pd(OAc)₂ in refluxing THF. The structure of complex 5 was determined unambiguously by an X‐ray diffraction. The complex was found to be a good catalyst in the cross‐coupling reaction of arylboronic acids with carboxylic acid anhydrides in water at room temperature. Copyright © 2011 John Wiley & Sons, Ltd.     

Coordination versatility of pyridine-functionalized N-heterocyclic carbenes: a detailed study of the different activation procedures. Characterization of new Rh and Ir compounds and study of their catalytic activity

Three different reaction procedures for the coordination of N-n-butyl-N'-(2-pyridylmethyl)imidazolium salt have produced new N-heterocyclic complexes of Rh and Ir. The direct reaction of the imidazolium salt with [IrCl(cod)](2) provides a NHC-Ir(III)-H complex, while transmetalation from a silver-NHC complex and deprotonation with NEt(3) give new NHC complexes of M(I) and M(III) when reacting with [MCl(cod)](2) or [MCl(coe)(2)](2) (M = Rh, Ir). The crystal structures of the biscarbene Rh(III) and Ir(III) complexes are described. The catalytic properties of the compounds obtained have been tested in the hydrosilylation of acetylenes, the cyclization of acetylenic carboxylic acids, and hydrogen transfer to ketones.     

Total synthesis of 7'-desmethylkealiiquinone

The total synthesis of an analogue of the marine alkaloid kealiiquinone has been completed through application of an intramolecular Diels-Alder reaction of an imidazole-containing enyne. Oxidative aromatization of the lactone adduct and N-methylation facilitates C2-oxidation via the imidazolium salt. Conversion of the lactone to the phthalaldehyde derivative and then to the dihydroxybenzoquinone was achieved via a reaction with glyoxal in the presence of KCN. Esterification of the vinylogous diacid and deprotection provided 7'-desmethylkealiiquinone.     

Lamellar to inverted hexagonal mesophase transition in DNA complexes with calamitic, discotic, and cubic shaped cationic lipids

In this study, we report on the lipid tail molecular shape/size effect on the mesophase self-assembly behaviors of various cationic lipids complexed with double-stranded DNA. The molecular shape of the cationic lipids was tailored from rodlike (a cyanobiphenyl imidazolium salt) to discotic (a triphenylene imidazolium salt), and finally to cubic [a polyhedral oligomeric silsesquioxane (POSS) imidazolium salt]. An increase in the cross-sectional area of the hydrophobic tails with respect to the hydrophilic imidazolium head induced a negative spontaneous curvature of the cationic lipids. As a result, a morphological change from lamello-columnar (L(C)(alpha)) phase for the DNA-cyanobiphenyl imidazolium salt (DNA-rod) and DNA-triphenylene imidazolium salt (DNA-disk) complexes to an inverted hexagonal columnar (H(C)(II)) phase for the DNA-POSS imidazolium salt (DNA-cube) complex was observed. The DNA-rod complex had a typical smectic A (SmA) L(C)(alpha) morphology, whereas the DNA-disk complex had a double lamello-columnar liquid crystalline phase. However, when the lipid tail changed to POSS, an H(C)(II) morphology was achieved. These morphological changes were successfully characterized by X-ray diffraction and transmission electron microscopy. We expect that these liquid crystalline and crystalline DNA hybrid materials may become potential functional materials for various applications such as organic microelectronics and gene transfection.     

Preparation of mononuclear, homodinuclear, and heterotrinuclear complexes by salicylaldiminato-functionalized imidazolium salt: approach to multifunctional catalysts

A salicylaldiminato imidazolium salt that bears both a Schiff base and imidazolium salt moiety was used to synthesize heterometallic compounds that could serve as multifunctional catalysts in certain reactions. The successful preparation of seven mononuclear compounds with a variety of transition metals (Pd, Ir, Ru, Zn, Ni) illustrated the high versatility of this class of ligands, which is crucial for the design of catalysts. Synthesis of homodinuclear compounds and heterotrinuclear compounds provided practical methods to connect multiple metal fragments through these ligands. The heterotrinuclear complex (Ni/Ir) was employed as a catalyst in the reaction of dehalogenation/transfer hydrogenation of halo-acetophenones. The preliminary catalytic study showed that this heterometallic species is more active than a combination of the corresponding monometallic species.     

Glucose-containing imidazolium salt-catalyzed cross-aldol reaction of isatins and unactivated ketones

Research on Chemical Intermediates - Ketone–ketone cross-aldol reaction of isatins and unactivated ketones was catalyzed by glucose-containing imidazolium salt...     

Nickel-catalyzed enantio- and diastereoselective three-component coupling of 1,3-dienes, aldehydes, and silanes using chiral N-heterocyclic carbenes as ligands

Nickel(0)-catalyzed asymmetric three-component coupling of 1,3-dienes, aldehydes, and silanes has been realized utilizing a chiral N-heterocyclic carbene as a ligand. On the basis of the screening of various NHC precursors, an imidazolium salt having 1-(2,4,6-trimethylphenyl)propyl groups on the nitrogen was designed and synthesized. In this reaction, various coupling products were produced in good yields with high regio-, diastereo- (anti selective in the case of the internal 1,3-diene), and enantioselectivities (up to 97% ee).     

Direct Catalytic Addition of Alkylnitriles to Aldehydes by Transition‐Metal/NHC Complexes

Direct catalytic addition of alkylnitriles to aldehydes allows for an atom‐economical access to β‐hydroxynitriles under proton transfer conditions. Direct use of alkylnitriles as pronucleophiles has been hampered due to their low acidity resulting in an inability to generate α‐cyano carbanions in a catalytic manner. A transition metal/N‐heterocyclic carbene (NHC) complex prepared from [{Rh(OMe)(cod)}₂] and an imidazolium‐based carbene was identified as an effective catalyst to promote the reaction with as little as 1.25 mol % of catalyst loading. The corresponding Rh complex, derived from chiral triazolium salt, rendered the reaction enantioselective, albeit with moderate enantioselectivity.     

从四氢叶叶酸辅酶模型合成麝香酮中间体2,1 5-十六二.酮

麝香酮是麝香中重要的具有生理活性的组分.自Ruzicka[1]确定其结构以来,化学家研究和发展了许多合成麝香酮的方法[2].Stoll[3]提出的由2,15-十六二酮经分子内环合后氢化得到麝香酮,其操作简便,但尚需解决2,15-十六二酮的来源问题.5,6,7,8-四氢叶酸辅酶在生物体内的功能和作用及仿生合成已成为仿生化学研究的重要课题[4].四氢叶酸辅酶在生物体内传递不同氧化态的-碳单元,当-碳单元处于甲酸氧化态时,活性部位是形成的咪唑啉环[5,6].因此,本文以咪唑啉盐作为四氢叶酸辅酶模型,与亲核试剂双格利雅试剂作用,仿生合成2,15-十六二酮.