Lanthanoid-based ionic liquids incorporating the dicyanonitrosomethanide anion

A series of low-melting-point salts with hexakisdicyanonitrosomethanidolanthanoidate anions has been synthesised and characterised: (C(2) mim)(3) [Ln(dcnm)(6)] (1?Ln; 1?Ln=1?La, 1?Ce, 1?Pr, 1?Nd), (C(2) C(1) mim)(3) [Pr(dcnm)(6)] (2?Pr), (C(4) C(1) pyr)(3) [Ce(dcnm)(6)] (3?Ce), (N(1114))(3) [Ln(dcnm)(6)] (4?Ln; 4?Ln=4?La, 4?Ce, 4?Pr, 4?Nd, 4?Sm, 4?Gd), and (N(1112OH) )(3) [Ce(dcnm)(6)] (5?Ce) (C(2) mim=1-ethyl-3-methylimidazolium, C(2) C(1) mim=1-ethyl-2,3-dimethylimidazolium, C(4) C(1) py=N-butyl-4-methylpyridinium, N(1114) =butyltrimethylammonium, N(1112OH) =2-(hydroxyethyl)trimethylammonium=choline). X-ray crystallography was used to determine the structures of complexes 1?La, 2?Pr, and 5?Ce, all of which contain [Ln(dcnm)(6)](3-) ions. Complexes 1?Ln and 2?Pr were all ionic liquids (ILs), with complex 3?Ce melting at 38.1?°C, the lowest melting point of any known complex containing the [Ln(dcnm)(6)](3-) trianion. The ammonium-based cations proved to be less suitable for forming ILs, with complexes 4?Sm and 4?Gd being the only salts with the N(1114) cation to have melting points below 100?°C. The choline-containing complex 5?Ce did not melt up to 160?°C, with the increase in melting point possibly being due to extensive hydrogen bonding, which could be inferred from the crystal structure of the complex.     

Synthesis and characterization of boranate ionic liquids (BILs)

Straightforward access to hydridoborate-based ionic liquids (BILs) is provided. They fall into a barely developed area of research and are of interest as, for example, reagents for organic synthesis. A series of pure [BH(4)](-) ILs with 1-butyl-2,3-dimethylimidazolium (BMMIM), 1-ethyl-3-methylimidazolium (EMMIM), 1-propyl-1-methylpiperidinium (PropMPip), and1-butyl-1-methylpyrrolidinium (BMP) cations were prepared. All synthesized ILs are well soluble in CH(2)Cl(2). We developed a procedure that gives clean products with correct elemental analyses. In contrast to earlier reports, which when conducted by us yielded only mixtures of the boranate anion with major halide contamination (maximum [BH(4)](-) content: 77.5?%). These materials can be viewed as the starting material for the (hypothetical) hydrogen-storage redox shuttling sequence between [BH(4)](-) and [B(12)H(12)](2-), in which the triboranate anion [B(3)H(8)](-) is a formal intermediate. Here we also developed a facile route to [B(3)H(8)](-) ILs with [BMMIM](+), [EMMIM](+), [PropMPip](+), and [NBu(4)](+), in which Na[BH(4)] reacts in situ (enhanced by ultrasound) with the solvent CH(2)Cl(2) as the oxidizing agent to give the triboranate IL in high yield and purity according to the equation: 3?[BH(4)](-)+2?CH(2)Cl(2)+[Cat](+)→[B(3)H(8)](-)[Cat](+)+H(2)+2?CH(3)Cl+2?Cl(-). We further investigated this reaction path by additional NMR spectroscopic experiments, powder-XRD analysis, and quantum chemical DFT calculations.     

In search of ionic liquids incorporating azolate anions

Twenty-eight novel salts with tetramethyl-, tetraethyl-, and tetrabutylammonium and 1-butyl-3-methylimidazolium cations paired with 3,5-dinitro-1,2,4-triazolate, 4-nitro-1,2,3-triazolate, 2,4-dinitroimidazolate, 4,5-dinitroimidazolate, 4,5-dicyanoimidazolate, 4-nitroimidazolate, and tetrazolate anions have been prepared and characterized by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and single-crystal X-ray crystallography. The effects of cation and anion type and structure on the physicochemical properties of the resulting salts, including several ionic liquids, have been examined and discussed. Ionic liquids (defined as having m.p.<100 degrees C) were obtained with all combinations of the 1-butyl-3-methylimidazolium cation ([C(4)mim](+)) and the heterocyclic azolate anions studied, and with several combinations of tetraethyl or tetrabutylammonium cations and the azolate anions. The [C(4)mim](+) azolates were liquid at room temperature exhibiting large liquid ranges and forming glasses on cooling with glass-transition temperatures in the range of -53 to -82 degrees C (except for the 3,5-dinitro-1,2,4-triazolate salt with m.p. 33 degrees C). Six crystal structures of the corresponding tetraalkylammonium salts were determined and the effects of changes to the cations and anions on the packing of the structure have been investigated.     

Synthesis and characterization of catalytic iridium nanoparticles in imidazolium ionic liquids

The reduction of [Ir(cod)Cl](2) (cod=1,5-cyclooctadiene) dissolved in 1-n-butyl-3-methyl tetrafluoroborate, hexafluorophosphate and trifluoromethane sulphonate ionic liquids in the presence of 1-decene by molecular hydrogen produces Ir(0) nanoparticles. The formation of these nanoparticles follows the two-step [A-->B, A+B-->2B (k(1),k(2))] autocatalytic mechanism. The same mean diameter values of around 2-3 nm were estimated from in situ TEM and SAXS analyses of the Ir(0) nanoparticles dispersed in the ionic liquids and by XRD of the isolated material. XPS and EXAFS analyses clearly show the interactions of the ionic liquid with the metal surface demonstrating the formation of an ionic liquid protective layer surrounding the iridium nanoparticles. SAXS analysis indicated the formation of an ionic liquid layer surrounding the metal particles with an extended molecular length of around 2.8-4.0 nm depending on the type of the anion.     

Synthesis and characterization of Pt0 nanoparticles in imidazolium ionic liquids

The controlled decomposition of Pt2(dba)3 (dba = dibenzylideneacetone) dispersed in 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMI.BF4) and hexafluorophosphate (BMI.PF6) ionic liquids in the presence of cyclohexene by molecular hydrogen produces Pt0 nanoparticles. The formation of these nanoparticles follows the two-step [A --> B, A + B --> 2B (k1, k2)] autocatalytic mechanism. The catalytic activity in the hydrogenation of cyclohexene is influenced by the nature of the anion rather than the mean-diameter of the nanoparticles. Thus, higher catalytic activity was obtained with Pt0 dispersed in BMI.BF4 containing the less coordinating anion although these nanoparticles possess a larger mean diameter (3.4 nm) than those obtained in BMI.PF6 (2.3 nm). Similar mean diameter values were estimated from in situ XRD and SAXS. XPS analyses clearly show the interactions of the ionic liquid with the metal surface demonstrating the formation of an ionic liquid protective layer surrounding the platinum nanoparticles. SAXS analysis indicated the formation of a semi-organized ionic liquid layer surrounding the metal particles with an extended molecular length of around 2.8 nm in BMI.BF4 and 3.3 nm in BMI.PF6.     

Synthesis and characterization of nickel nanoparticles dispersed in imidazolium ionic liquids

The diameter and size-distribution of Ni nanoparticles prepared by the decomposition of [bis(1,5-cyclooctadiene)nickel(0)] organometallic precursor dissolved in 1-alkyl-3-methylimidazolium N-bis(trifluoromethanesulfonyl) amide ionic liquids depend on the length of the alkyl side-chain of the imidazolium ring. The increase of the organization range order of the ionic liquid that increases with that of the alkyl side-chain (from n-butyl to n-hexadecyl) induces the formation of nanoparticles with a smaller diameter and size-distribution. The cubic fcc Ni nanoparticles with 4.9 +/- 0.9 to 5.9 +/- 1.4 nm in mean diameter and monomodal size-distribution thus prepared are probably composed of a small cap layer of NiO around a core of Ni metal. The contribution of the oxide layer also depends on the medium i.e. the metal oxide ratio increases in salts containing four to eight carbons on their side-chains and then decreases as the number of carbons increases. The Ni nanoparticles dispersed in the ionic liquids are active catalysts for the hydrogenation of olefins under relatively mild reaction conditions.     

Synthesis and characterization of new pyrrolidinium based protic ionic liquids. Good and superionic liquids

New pyrrolidinium-cation-based protic acid ionic liquids (PILs) were prepared through a simple and atom-economic neutralization reactions between pyrrolidine and Br?nsted acids, HX, where X is NO 3 (-), HSO 4 (-), HCOO (-), CH 3COO (-) or CF 3COO (-) and CH 3(CH 2) 6COO (-). The thermal properties, densities, electrochemical windows, temperature dependency of dynamic viscosity and ionic conductivity were measured for these PILs. All protonated pyrrolidinium salts studied here were liquid at room temperature and possess a high ionic conductivity (up to 56 mS cm (-1)) at room temperature. Pyrrolidinium based PILs have a relatively low cost, a low toxicity and exhibit a large electrochemical window as compared to other protic ionic liquids (up 3 V). Obtained results allow us to classify them according to a classical Walden diagram and to determinate their "Fragility". Pyrrolidinium based PILs are good or superionic liquids and shows extremely fragility. They have wide applicable perspectives for fuel cell devices, thermal transfer fluids, and acid-catalyzed reaction media as replacements of conventional inorganic acids.     

Synthesis and ionic conductivity of polymer ionic liquids

Four vinyl monomers containing a covalently bonded cation ethylimidazolium and various anions—Br^?, (CF₃SO₂)₂N^?, (CN)₂N^?, and CF₃SO ₃ ^? —have been synthesized. High-molecular-mass polymers (M _w up to 1.84 × 10⁶) having the structure of ionic liquids have been prepared via the free-radical polymerization of 1-vinyl-3-ethylimidazolium in bulk and molecular and ionic solvents. The thermal stability and heat resistance of the resulting polymer salts have been estimated. It has been demonstrated that the thermal characteristics of these salts significantly depend on the nature of anions. The glass-transition temperatures of the polymers range from 19 to 235°C. The ionic conductivity of the polymer salts and their compositions with individual ionic liquids has been studied in the frequency range 50–10⁶ Hz. The highest conductivity (1.5 × 10^?5 S/cm) is exhibited by the polymer containing the (CN)₂N^? anion.     

The effect of ionic liquids on the outcome of nitrile oxide cycloadditions

Nitrile oxide cycloadditions between benzonitrile oxide and a series of alkenes were investigated in ionic liquids and molecular solvents. The regioselectivity of the process alters on changing solvent type, with the steric requirements of the reaction being increased in ionic liquids. The rate of the cycloaddition process was found to be faster in ionic liquid solvents, and a concomitant increase in the rate of dimerisation of the nitrile oxide starting material was also observed.     

Novel imidazolium chiral ionic liquids that contain a urea functionality

Nine chiral room temperature ionic liquids (RTILs), which contain a chiral moiety and a urea functionality bonded to a imidazolium ring, have been designed and synthesized. The synthesis of these ionic liquids is concise and practical due to the commercial availability of the starting materials. These novel RTILs were readily prepared from 1-(3-aminopropyl)imidazole and amino acid ester derived isocyanates. We envision that these new chiral RTILs can serve as effective reaction media as well as chiral catalysts, which are presently being investigated in our laboratory.     

Synthesis, characterization, and catalytic activity of ionic liquids based on biosources

New room-temperature ionic liquids were synthesized from natural and easily available feedstocks (choline hydroxide and amino acids) following an economical and green route in which the only by-product was water. They were successfully applied as catalysts for the Knoevenagel test reaction between benzaldehyde and different active methylene compounds, at room temperature and under solvent-free conditions, to produce α,β-unsaturated carbonyl compounds, exhibiting good conversions and high selectivities. The catalytic role of cholinium and aminoacetate ions in the Knoevenagel condensation is discussed.     

Synthesis and characterization of protic ionic liquids containing cyclic amine cations and tetrafluoroborate anion

Several ionic liquids containing pyrrolidinium-, oxopyrrolidinium-, piperidinium-, morpholinium- and trialkylammonium-based cation are synthesized and their thermal property, refractive index, polarity, electrochemical property, and temperature dependency of dynamic viscosity, density and ionic conductivity are characterized. All tetrafluoroborate-based room temperature ionic liquids studied here have a high ionic conductivity (up to 31.4 mS cm^?1). These ILs were successfully used as suitable electrolytes for the diffusion coefficient measurement of ferrocene. Absorbance solvatochromic probes Nile red is used to investigate the relative polarity of these ionic liquids and compared them with several organic solvents. The relation of fluidity to conductance is considered in terms of a Walden plot that is shown to provide a useful basis for organizing the applications of solvent media for ??green?? synthetic reactions.     

Synthesis and characterization of dicationic ionic liquids that contain both hydrophilic and hydrophobic anions

A series of dicationic ionic liquids, in which each dication is associated with both a hydrophobic anion and a hydrophilic anion, are synthesized. The thermal properties and solubility in organic solvents of these ILs are characterized. The ionic liquids show interesting properties, which are different from those of dicationic ionic liquids, in which each dication is associated with two identical anions.     

Surface characterization of functionalized imidazolium-based ionic liquids

The surface composition of oligo(ethylene glycol) ether functionalized bis(trifluoromethylsulfonyl)imide ionic liquids has been studied by means of X-ray photoelectron spectroscopy (XPS). For [Me(EG)MIM][Tf 2N], [Et(EG) 2MIM][Tf 2N], and [Me(EG) 3MIM][Tf 2N], which vary by the number of ethylene glycol (EG) units (from 1 to 3), we have shown that the stoichiometry of the surface near region is in excellent agreement with the bulk stoichiometry, which confirms the high purity of the ionic liquid samples investigated and rules out pronounced surface orientation effects. This has been deduced from the experimental observation that the angle-resolved XP spectra of all elements present in the IL anions and cations (C, N, O, F, S) show identical signals in the bulk and surfaces sensitive geometry, i.e., at 0 degrees and 70 degrees emission angle, respectively. The relative intensity ratios of all elements were found to be in nearly perfect agreement with the nominal values for the individual ILs. In contrast to these findings, we identified surface-active impurities in [Me(EG)MIM]I, which is the starting material for the final anion exchange step to synthesize [Me(EG)MIM][Tf 2N]. Sputtering of the surface led to a depletion of this layer, which however recovered with time. The buildup of this contamination is attributed to a surface enrichment of a minor bulk contamination that shows surface activity in the iodide melt.     

Design and synthesis of pyridinium chiral ionic liquids tethered to a urea functionality

Nine chiral room-temperature ionic liquids (RTILs), which contain a chiral moiety and a urea functionality bonded to a pyridinium ring, have been designed and synthesized. The synthesis of these ionic liquids is concise and practical due to the commercial availability of the starting materials. These novel RTILs were readily prepared from 2-(aminomethyl)pyridine and amino acid ester derived isocyanates. We envision that these new chiral RTILs can serve as effective reaction media as well as chiral catalysts for asymmetric reactions, which are presently being investigated in our laboratory.     

Hydrophobic ionic liquids incorporating N-alkylisoquinolinium cations and their utilization in liquid-liquid separations

The first examples of Room Temperature Ionic Liquids (RTIL) containing fused polycyclic N-alkylisoquinolinium cations ([Cnisoq]+) in combination with the bis(perfluoroethylsulfonyl)imide anion ([BETI]-) have been synthesized, characterized, and utilized in liquid-liquid partitioning from water; these salts have unexpectedly low melting points and give high distribution ratios for aromatic solutes, especially chlorobenzenes, between the RTIL and water.     

Bicyclic imidazolium-based ionic liquids: synthesis and characterization

We previously reported the use of imidazole as starting compound for preparing a bicyclic imidazolium ionic liquid, [b-3C-im][NTf₂], with an overall 29% isolated yield in four synthetic steps. This new room temperature ionic liquid was shown to be far more chemically stable than commonly used [bmim][PF₆], [bdmim][PF₆], and [bdmim][NTf₂]. Because of this intriguing chemical stability, it prompted us to develop a more generalized and high yielding synthesis so that molecular diversity of bicyclic ionic liquids may be explored. In this work, we amended the previous synthetic route by employing 4-chlorobutyronitrile or 5-chlorovaleronitrile as starting materials and successfully developed a five-step synthesis of a series of novel bicyclic imidazolium-based ionic liquids in 40-53% overall isolated yields. We investigated intrinsic reactivity of all bicyclic ionic liquids prepared and found that, under strongly basic conditions, among all tested ionic liquids the 5,5-membered [R-3C-im][NTf₂] ionic liquids were most stable to solvent deuterium isotope exchange while the previously reported [bdmim][NTf₂] ionic liquid was 50% deuterium exchanged at its C-2 methyl in 30 min at ambient temperature. Under identical condition, the commonly used [bmim][NTf₂] ionic liquid was deuterium exchanged instantaneously at its C-2 hydrogen. In the absence of bases, only [bmim][PF₆] was deuterium exchanged (50% within 1 h) and all other ionic liquids gave no detectable exchanges even after 25 days at ambient temperature. Moreover, both [bmim][NTf₂] and [bdmim][NTf₂] ionic liquids were readily methylated at C-2 position with methyl iodide under basic condition at room temperature. Under the same condition, [R-3C-im][NTf₂] and [R-4C-im][NTf₂] ionic liquids were completely stable and chemically inert. We envisioned that [R-3C-im][NTf₂] should be well suited as solvents for organic synthesis.     

Synthesis and properties of novel chiral-amine-functionalized ionic liquids

A novel class of chiral-amine-functionalized ionic liquids (CAFILs) has been synthesized efficiently from natural amino acids, and their structures have been determined by spectroscopic analysis and low temperature X-ray diffraction analysis. The CAFILs have been characterized by physical properties such as melting point, glass transition temperature, thermal degradation and specific rotation. NMR measurements indicate that the CAFILs may be promising alternatives in the field of chiral discrimination.     

Synthesis and properties of chiral ammonium-based ionic liquids

New chiral ammonium-based ionic liquids containing the (1R,2S,5R)-(-)-menthyl group can be easily and efficiently prepared under ambient conditions. The preparation and characterization of trialkyl[(1R,2S,5R)-(-)-menthoxymethyl]ammonium salts is reported. The salts have been demonstrated to be air- and moisture-stable under ambient conditions and can be readily used in a variety of standard experimental procedures. The single-crystal X-ray structure of butyldimethyl[(1R,2S,5R)-(-)-menthoxymethyl]ammonium chloride has been determined. The chiral, room-temperature ionic liquids have been characterized by physical properties such as specific rotation, density, viscosity, thermal degradation, and glass transition temperature. Trialkyl[(1R,2S,5R)-(-)-menthoxymethyl]ammonium chloride prototype ionic liquids have also been found to exhibit strong antimicrobial and high antielectrostatic activities.