Pseudohalogen Chemistry in Ionic Liquids with Non-innocent Cations and Anions

Within the second funding period of the SPP 1708 “Material Synthesis near Room Temperature”,which started in 2017, we were able to synthesize novel anionic species utilizing Ionic Liquids (ILs) both, as reaction media and reactant. ILs, bearing the decomposable and non-innocent methyl carbonate anion [CO₃Me]⁻, served as starting material and enabled facile access to pseudohalide salts by reaction with Me₃Si−X (X=CN, N₃, OCN, SCN). Starting with the synthesized Room temperature Ionic Liquid (RT-IL) [nBu₃MeN][B(OMe)₃(CN)], we were able to crystallize the double salt [nBu₃MeN]₂[B(OMe)₃(CN)](CN). Furthermore, we studied the reaction of [WCC]SCN and [WCC]CN (WCC=weakly coordinating cation) with their corresponding protic acids HX (X=SCN, CN), which resulted in formation of [H(NCS)₂]⁻ and the temperature labile solvate anions [CN(HCN)_n]⁻ (n=2, 3). In addition, the highly labile anionic HCN solvates were obtained from [PPN]X ([PPN]=μ-nitridobis(triphenylphosphonium), X=N₃, OCN, SCN and OCP) and HCN. Crystals of [PPN][X(HCN)₃] (X=N₃, OCN) and [PPN][SCN(HCN)₂] were obtained when the crystallization was carried out at low temperatures. Interestingly, reaction of [PPN]OCP with HCN was noticed, which led to the formation of [P(CN)₂]⁻, crystallizing as HCN disolvate [PPN][P(CN⋅HCN)₂]. Furthermore, we were able to isolate the novel cyanido(halido) silicate dianions of the type [SiCl_0.78(CN)_5.22]²⁻ and [SiF(CN)₅]²⁻ and the hexa-substituted [Si(CN)₆]²⁻ by temperature controlled halide/cyanide exchange reactions. By facile neutralization reactions with the non-innocent cation of [Et₃HN]₂[Si(CN)₆] with MOH (M=Li, K), Li₂[Si(CN)₆] ⋅ 2 H₂O and K₂[Si(CN)₆] were obtained, which form three dimensional coordination polymers. From salt metathesis processes of M₂[Si(CN)₆] with different imidazolium bromides, we were able to isolate new imidazolium salts and the ionic liquid [BMIm]₂[Si(CN)₆]. When reacting [Mes(nBu)Im]₂[Si(CN)₆] with an excess of the strong Lewis acid B(C₆F₅)₃, the voluminous adduct anion {Si[CN⋅B(C₆F₅)₃]₆}²⁻ was obtained.     

Coexistence of Tellurium Cations and Anions in Phosphonium-Based Ionic Liquids

Elemental tellurium readily dissolves in ionic liquids (ILs) based on tetraalkylphosphonium cations even at temperatures below 100 °C. In the case of ILs with acetate, decanoate, or dicyanamide anions, dark red to purple colored solutions form. A study combining NMR, UV-Vis and Raman spectroscopy revealed the formation of tellurium anions (Te_n)²⁻ with chain lengths up to at least n=5, which are in dynamic equilibrium with each other. Since external influences could be excluded and no evidence of an ionic liquid reaction was found, disproportionation of the tellurium is the only possible dissolution mechanism. Although the spectroscopic detection of tellurium cations in these solutions is difficult, the coexistence of tellurium cations, such as (Te₄)²⁺ and (Te₆)⁴⁺, and tellurium anions could be proven by cyclic voltammetry and electrodeposition experiments. DFT calculations indicate that electrostatic interactions with the ions of the ILs are sufficient to stabilize both types of tellurium ions in solution.     

Lewis Superacidic Ionic Liquids with Tricoordinate Borenium Cations

The first examples of ionic liquids based on borenium cations, [BCl₂L]⁺, are reported. These compounds form highly Lewis acidic liquids under solvent‐free conditions. Their acidity was quantified by determining the Gutmann acceptor number (AN). Extremely high ANs were recorded (up to AN=182, δ_31P=120 ppm), demonstrating that these borenium ionic liquids are the strongest Lewis superacids reported to date, with the acidity enhanced by the ionic liquid environment.     

On the Nature of Interactions between Ionic Liquids and Small Amino‐Acid‐Based Biomolecules

During the last decade, ionic liquids (ILs) have revealed promising properties and applications in many research fields, including biotechnology and biological sciences. The focus of this contribution is to give a critical review of the phenomena observed and current knowledge of the interactions occurring on a molecular basis. As opposed to the huge advances made in understanding the properties of proteins in ILs, complementary investigations dealing with interactions between ILs and peptides or oligopeptides are underrepresented and are mostly only of phenomenological nature. However, the field has received more attention in the last few years. This Review features a meta‐analysis of the available data and findings and should, therefore, provide a basis for a scientifically profound understanding of the nature and mechanisms of interactions between ILs and structured or nonstructured peptides. Fundamental aspects of the interactions between different peptides/oligopeptides and ILs are complemented by sections on the experimental (spectroscopy, structural biology) and theoretical (computational chemistry) possibilities to explain the phenomena reported so far in the literature. In effect, this should lead to the development of novel applications and support the understanding of IL–solute interactions in general.     

Ionic Liquids Based on Azolate Anions

Compartmentalized molecular level design of new energetic materials based on energetic azolate anions allows for the examination of the effects of both cation and anion on the physiochemical properties of ionic liquids. Thirty one novel salts were synthesized by pairing diverse cations (tetraphenylphosphonium, ethyltriphenylphosphonium, N‐phenyl pyridinium, 1‐butyl‐3‐methylimidazolium, tetramethyl‐, tetraethyl‐, and tetrabutylammonium) with azolate anions (5‐nitrobenzimidazolate, 5‐nitrobenzotriazolate, 3,5‐dinitro‐1,2,4‐triazolate, 2,4‐dinitroimidazolate, 4‐nitro‐1,2,3‐triazolate, 4,5‐dinitroimidazolate, 4,5‐dicyanoimidazolate, 4‐nitroimidazolate, and tetrazolate). These salts have been characterized by DSC, TGA, and single crystal X‐ray crystallography. The azolates in general are surprisingly stable in the systems explored. Ionic liquids were obtained with all combinations of the 1‐butyl‐3‐methylimidazolium cation and the heterocyclic azolate anions studied, and with several combinations of tetraethyl‐ or tetrabutylammonium cations and the azolate anions. Favorable structure–property relationships were most often achieved when changing from 4‐ and 4,5‐disubstituted anions to 3,5‐ and 2,4‐disubstituted anions. The most promising anion for use in energetic ionic liquids of those studied here, was 3,5‐dinitro‐1,2,4‐triazolate, based on its contributions to the entire set of target properties.     

离子交换色谱法检测离子液体中阴离子

建立了用阴离子交换分离柱、化学抑制模式、电导检测测定系列离子液体中BF4^-阴离子及其他杂阴离子（F^-、Cl^-、Br^-）含量的方法，并用于在线监控离子液体合成工艺中阴离子杂质含量。确定淋洗液组成为1．6mmol／L Na2CO3＋3．9mmol／L NaHCO3，流速为0．6mL／min。本方法对所测阴离子检出限分别为50μg／L（F^-、Br^-）和80μg／L（BF4^-）；线性范围在3个数量级以上；r〉0．999；回收率在98％～102％之间。方法用于对离子液体小试工艺样品分析及过程监控时，结果满意，样品的RSD小于2．6％（n=6）。     

离子色谱法在离子液体阴阳离子分析中的应用

离子液体作为一种新型绿色环保有机化合物,因具有饱和蒸气压低、溶解性良好以及电导率高等优异性质,而在化学化工领域中得到了较为广泛的应用,并越来越受到人们的关注。该文综述了近年来离子色谱在离子液体阴阳离子分析中的应用,对离子色谱法分析离子液体阳离子、离子液体阴离子以及同时分析离子液体阴阳离子三方面进行讨论,并对离子色谱法分析离子液体的发展趋势进行了展望。     

Bifunctional Acid–Base Ionic Liquid Organocatalysts with a Controlled Distance Between Acid and Base Sites

Bifunctional acid–base ionic liquid organocatalysts with different distances between the two sites have been synthesised, and their activity for the Knoevenagel condensation has been tested. As has been found to be the case with enzymes, the distance between the acidic and basic sites determines the activity of the bifunctional organocatalyst, and at the optimal distance the reaction rate increases by two orders of magnitude with respect to the purely acidic or basic counterpart organocatalysts. The experimental results have been rationalised through the study of the reaction mechanism of the Knoevenagel condensation between malononitrile and benzaldehyde by means of DFT calculations. It has been found that it consists of two consecutive steps. First, deprotonation of malononitrile on the basic site to obtain a methylene carbanion intermediate takes place, and second, co‐adsorption and activation of benzaldehyde on the acid centre of this intermediate followed by the C? C bond‐formation reaction. The calculations and the kinetic study indicate that there is an inversion of the rate‐controlling step when the distance between the acidic and the basic sites is modified, with a direct implication on the reaction rate.     

Cyanohydridoborate Anions: Synthesis,Salts, and Low-Viscosity Ionic Liquids

High-yield syntheses up to molar scales for salts of [BH(CN)₃]⁻ ( 2 ) and [BH₂(CN)₂]⁻ ( 3 ) starting from commercially available Na[BH₄] (Na 5 ), Na[BH₃(CN)] (Na 4 ), BCl₃, (CH₃)₃SiCN, and KCN were developed. Direct conversion of Na 5 into K 2 was accomplished with (CH₃)₃SiCN and (CH₃)₃SiCl as a catalyst in an autoclave. Alternatively, Na 5 is converted into Na[BH{OC(O)R}₃] (R=alkyl) that is more reactive towards (CH₃)₃SiCN and thus provides an easy access to salts of 2 . Some reaction intermediates were identified, for example, Na[BH(CN){OC(O)Et}₂] (Na 7 b ) and Na[BH(CN)₂{OC(O)Et}] (Na 8 b ). A third entry to 2 and 3 uses ether adducts of BHCl₂ or BH₂Cl such as the commercial 1,4-dioxane adducts that react with KCN and (CH₃)₃SiCN. Alkali metal salts of 2 and 3 are convenient starting materials for organic salts, especially for low viscosity ionic liquids (ILs). [EMIm] 3 has the lowest viscosity and highest conductivity with 10.2 mPa s and 32.6 mS cm⁻¹ at 20 °C known for non-protic ILs. The ILs are thermally, chemically, and electrochemically robust. These properties are crucial for applications in electrochemical devices, for example, dye-sensitized solar cells (Grätzel cells).     

Schiff Base Structured Acid–Base Cooperative Dual Sites in an Ionic Solid Catalyst Lead to Efficient Heterogeneous Knoevenagel Condensations

An acid–base bifunctional ionic solid catalyst [PySaIm]₃PW was synthesized by the anion exchange of the ionic‐liquid (IL) precursor 1‐(2‐salicylaldimine)pyridinium bromide ([PySaIm]Br) with the Keggin‐structured sodium phosphotungstate (Na₃PW). The catalyst was characterized by FTIR, UV/Vis, XRD, SEM, Brunauer–Emmett–Teller (BET) theory, thermogravimetric analysis, ¹H NMR spectroscopy, ESI‐MS, elemental analysis, and melting points. Together with various counterparts, [PySaIm]₃PW was evaluated in Knoevenagel condensation under solvent and solvent‐free conditions. The Schiff base structure attached to the IL cation of [PySaIm]₃PW involves acidic salicyl hydroxyl and basic imine, and provides a controlled nearby position for the acid–base dual sites. The high melting and insoluble properties of [PySaIm]₃PW are relative to the large volume and high valence of PW anions, as well as the intermolecular hydrogen‐bonding networks among inorganic anions and IL cations. The ionic solid catalyst [PySaIm]₃PW leads to heterogeneous Knoevenagel condensations. In solvent‐free condensation of benzaldehyde with ethyl cyanoacetate, it exhibits a conversion of 95.8 % and a selectivity of 100 %; the conversion is even much higher than that (78.2 %) with ethanol as a solvent. The solid catalyst has a convenient recoverability with only a slight decrease in conversion following subsequent recyclings. Furthermore, the new catalyst is highly applicable to many substrates of aromatic aldehydes with activated methylene compounds. On the basis of the characterization and reaction results, a unique acid–base cooperative mechanism within a Schiff base structure is proposed and discussed, which thoroughly explains not only the highly efficient catalytic performance of [PySaIm]₃PW, but also the lower activities of various control catalysts.     

Azolate Anions in Ionic Liquids: Promising and Under-Utilized Components of the Ionic Liquid Toolbox

Owing to their ease of synthesis, diffuse positive charge, and chemical stability, 1-alkyl-3-methylimidazolium cations (i.e., [C_nmim]⁺) are one of the most routinely utilized and historically important components in ionic liquid (IL) chemistry. However, while this is a routinely encountered member of the IL family as cations, relatively few workers have explored the versatile chemistry of azoles to allow their use as an anionic component in ILs, as azolates. Azolate anions possess many of the desired properties for IL formation, including a diffuse ionic charge, tailorable asymmetry, and synthetic flexibility, with the added advantages of not relying on halogen atoms for electron-withdrawing effects, as is commonly encountered with IL anions such as hexafluorophosphate. This review explores the 122 azolate-containing ILs known in the literature (prepared from only 39 disparate azolate anions), with a view to highlighting not only their demonstrated utility as an IL component, but the ways in which the larger scientific community may utilize their advantageous properties for new tailored materials.     

Substitution Reactions by Azide and Thiocyanide Anions in Room Temperature Ionic Liquids

Conducted in the ionic liquids,activated and inactivated halides,acyl chlorides,tosylate and bezotriazolyl acylates were converted to corresponding azide and thiocyanide compounds in high yields under mild conditions.     

功能化离子液体的制备及其在合成中的应用

功能化离子液体;手性离子液体;酸性离子液体     

A Specific Interaction between Ionic Liquids’ Cations and Reichardt’s Dye

Solvatochromic probes are often used to understand solvation environments at the molecular scale. In the case of ionic liquids constituted by an anion and a cation, which are designed and paired in order to obtain a low melting point and other desirable physicochemical properties, these two indivisible components can interact in a very different way with the probe. This is the case with one of the most common probes: Reichardt’s Dye. In the cases where the positive charge of the cation is delocalized on an aromatic ring such as imidazolium, the antibonding orbitals of the positively charged aromatic system are very similar in nature and energy to the LUMO of Reichardt’s Dye. This leads to an interesting, specific cation-probe interaction that can be used to elucidate the nature of the ionic liquids’ cations. Parallel computational and experimental investigations have been conducted to elucidate the nature of this interaction with respect to the molecular structure of the cation.     

Dipolarity versus Polarizability and Acidity versus Basicity of Ionic Liquids as a Function of Their Molecular Structures

The four empirical solvent polarity parameters according to the Catalán scale—solvent acidity (SA), solvent basicity (SB), solvent polarizability (SP), and solvent dipolarity (SdP)—of 64 ionic liquids (ILs) were determined by the solvatochromic method. The SA parameter was determined solely by using [Fe^II(1,10‐phenanthroline)₂(CN)₂] ( Fe ), the SB parameter by using the pair of structurally comparable dyes 3‐(4‐amino‐3‐methylphenyl)‐7‐phenylbenzo[1,2‐b:4,5‐b′]difuran‐2,6‐dione ( ABF ) and 3‐(4‐N,N‐dimethylaminophenyl)‐7‐phenylbenzo[1,2‐b:4,5‐b′]‐difuran‐2,6‐dione ( DMe‐ABF ), and the SP and SdP parameters by using the homomorphic pair of 4‐tert‐butyl‐2‐(dicyanomethylene)‐5‐[4‐(diethylamino)benzylidene]‐Δ³‐thiazoline ( Th ) and 2‐[4‐(N,N‐dimethylamino)benzylidene]malononitrile ( BMN ). The separation of SP and SdP for a set of 64 various ILs was performed for the first time. Correlation analyses of SP with physicochemical data related to ionization potentials of anions of ILs as well as with theoretical data show the correctness of the applied method. The found correlations of the Catalán parameters with each other and with the alkyl‐chain length of 1‐alkyl‐3‐methylimidazolium‐type ILs gives new information about interactions within ILs. An analytical comparison of the determined Catalán parameters with the established Kamlet–Taft parameters and the Gutmann acceptor and donor numbers is also presented.     

Elucidating Interactions between DMSO and Chelate‐Based Ionic Liquids

The C?D bond stretching vibrations of deuterated dimethyl sulfoxide ([D₆]DMSO) and the C₂?H bond stretching vibrations of 1,1,1,5,5,5‐hexafluoropentane‐2,4‐dione (hfac) ligand in anion are chosen as probes to elucidate the solvent–solute interaction between chelate‐based ionic liquids (ILs) and DMSO by vibrational spectroscopic studies. The indirect effect from the interaction of the adjacent S=O functional group of DMSO with the cation [C₁₀mim]⁺ and anion [Mn(hfac)₃]^? of the ILs leads to the blue‐shift of the C?D stretching vibrations of DMSO. The C₂?H bond stretching vibrations in hfac ligand is closely related to the ionic hydrogen bond strength between the cation and anion of chelate‐based ILs. EPR studies reveal that the crystal field of the central metal is kept when the chelate‐based ILs are in different microstructure environment in the solution.     

Evaluation of Ionic Liquids and Ionic Liquids Active Pharmaceutical Ingredients Inhibition in Elastase Enzyme Activity

Human neutrophil elastase (HNE) is used as diagnostic biomarker for inflammation/infection. In this work, 10 ionic liquids (ILs) and 11 ionic liquids active pharmaceutical ingredients (ILs-APIs) were tested to evaluate the inhibition effect on the activity of porcine pancreatic elastase enzyme, frequently employed as a model for HNE. The insertion of ionic liquids in some drugs is useful, as the insertion of ILs with inhibitory capacity will also slow down all processes in which this enzyme is involved. Therefore, a spectrophotometric method was performed to the determination of EC₅₀ values of the compounds tested. EC₅₀ values of 124 ± 4 mM to 289 ± 11 mM were obtained, with the most toxic IL for elastase being tetrabutylammonium acetate and the least toxic 1-butyl-3-methylimidazolium acetate. Moreover, sodium salicylate (raw material) presented the lower and benzethonium bistriflimide the higher EC₅₀ when compared with all the IL-APIs tested. This work provides significant information about the effect of the studied IL and IL-APIs in elastase enzyme activity.     

Physico-Chemical Properties of Magnetic Dicationic Ionic Liquids with Tetrahaloferrate Anions

A series of imidazolium-based symmetrical and asymmetrical dicationic ionic liquids (DcILs) with alkyl spacers of different length and with [FeCl₃Br]⁻ as counter ion have been synthesized. The synthesized DcILs are characterized by using FTIR and Raman spectroscopy as well as mass spectrometry, along with single-crystal XRD analysis. Physicochemical properties such as solubility, thermal stability and magnetic susceptibility are also measured. These compounds show low melting points, good solubility in water and organic solvents, thermal stability, and paramagnetism. The products of molar susceptibility and temperature (χ_mol⋅T) for the synthesized DcILs have been found between 4.05 to 4.79 emu mol⁻¹ K Oe⁻¹ and effective magnetic moment values have also been determined to be compared to that expected from the spin-only approximation.