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     

Vibrational Dephasing in Ionic Liquids as a Signature of Hydrogen Bonding

Understanding both structure and dynamics is crucial for producing tailor‐made ionic liquids (ILs). We studied the vibrational and structural dynamics of medium versus weakly hydrogen‐bonded C?H groups of the imidazolium ring in ILs of the type [1‐alkyl‐3‐methylimidazolium][bis(trifluoromethanesulfonyl)imide] ([C_nmim][NTf₂]), with n=1, 2, and 8, by time‐resolved coherent anti‐Stokes Raman scattering (CARS) and quantum‐classical hybrid (QCH) simulations. From the time series of the CARS spectra, dephasing times were extracted by modeling the full nonlinear response. From the QCH calculations, pure dephasing times were obtained by analyzing the distribution of transition frequencies. Experiments and calculations reveal larger dephasing rates for the vibrational stretching modes of C(2)?H compared with the more weakly hydrogen‐bonded C(4,5)?H. This finding can be understood in terms of different H‐bonding motifs and the fast interconversion between them. Differences in population relaxation rates are attributed to Fermi resonance interactions.     

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.     

Effects of Ionic Liquids on the Thermodynamics of Hydrogen Activation by Frustrated Lewis Pairs: A Density Functional Theory Study**

Nowadays, hydrogen activation by frustrated Lewis pairs (FLPs) and their applications are one of the emerging research topics in the field of catalysis. Previous studies have shown that the thermodynamics of this reaction is determined by electronic structures of FLPs and solvents. Herein, we investigated systems consisting of typical FLPs and ionic liquids (ILs), which are well known by their large number of types and excellent solvent effects. The density functional theory (DFT) calculations were performed to study the thermodynamics for H₂ activation by both inter- and intra-molecular FLPs, as well as the individual components. The results show that the computed overall Gibbs free energies in ILs are more negative than that computed in toluene. Through the thermodynamics partitioning, we find that ILs favor the H−H cleavage elemental step over the elemental steps of proton attachment, hydride attachment and zwitterionic stabilization. Moreover, the results show that these effects are strongly dependent on the type of FLPs, where intra-molecular FLPs are more affected compared to the inter-molecular FLPs.     

Synthesis,Stabilization, Functionalization and,DFT Calculations of Gold Nanoparticles in Fluorous Phases (PTFE and Ionic Liquids)

Gold nanoparticles (Au‐NPs) were reproducibly obtained by thermal, photolytic, or microwave‐assisted decomposition/reduction under argon from Au(CO)Cl or KAuCl₄ in the presence of n‐butylimidazol dispersed in the ionic liquids (ILs) BMIm⁺BF₄^?, BMIm⁺OTf^?, or BtMA⁺NTf₂^? (BMIm⁺=n‐butylmethylimidazolium, BtMA⁺=n‐butyltrimethylammonium, OTf^?=^?O₃SCF₃, NTf₂^?=^?N(O₂SCF₃)₂). The ultra small and uniform nanoparticles of about 1–2 nm diameter were produced in BMIm⁺BF₄^? and increased in size with the molecular volume of the ionic liquid anion used in BMIm⁺OTf^? and BtMA⁺NTf₂^?. Under argon the Au‐NP/IL dispersion is stable without any additional stabilizers or capping molecules. From the ionic liquids, the gold nanoparticles can be functionalized with organic thiol ligands, transferred, and stabilized in different polar and nonpolar organic solvents. Au‐NPs can also be brought onto and stabilized by interaction with a polytetrafluoroethylene (PTFE, Teflon) surface. Density functional theory (DFT) calculations favor interactions between IL anions instead of IL cations. This suggests a Au???F interaction and anionic Au_n stabilization in fluorine‐containing ILs. The ¹⁹F NMR signal in BMIm⁺BF₄^? shows a small Au‐NP concentration‐dependent shift. Characterization of the dispersed and deposited gold nanoparticles was done by transmission electron microscopy (TEM/HRTEM), transmission electron diffraction (TED), dynamic light scattering (DLS), UV/Vis absorbance spectroscopy, scanning electron microscopy (SEM), electron spin resonance (ESR), and electron probe micro analyses (EPM, SEM/EDX).     

Activation of Hydrogen Peroxide by Ionic Liquids: Mechanistic Studies and Application in the Epoxidation of Olefins

Imidazolium‐based ionic liquids that contain perrhenate anions are very efficient reaction media for the epoxidation of olefins with H₂O₂ as an oxidant, thus affording cyclooctene in almost quantitative yields. The mechanism of this reaction does not follow the usual pathway through peroxo complexes, as is the case with long‐known molecular transition‐metal catalysts. By using in situ Raman, FTIR, and NMR spectroscopy and DFT calculations, we have shown that the formation of hydrogen bonds between the oxidant and perrhenate activates the oxidant, thereby leading to the transfer of an oxygen atom onto the olefin demonstrating the special features of an ionic liquid as a reaction environment. The influence of the imidazolium cation and the oxidant (aqueous H₂O₂, urea hydrogen peroxide, and tert‐butyl hydrogen peroxide) on the efficiency of the epoxidation of cis‐cyclooctene were examined. Other olefinic substrates were also used in this study and they exhibited good yields of the corresponding epoxides. This report shows the potential of using simple complexes or salts for the activation of hydrogen peroxide, owing to the interactions between the solvent medium and the active complex.     

Straightforward Synthesis of the Brønsted Acid hfipOSO3H and its Application for the Synthesis of Protic Ionic Liquids

The easily accessible hexafluoroisopropoxysulfuric acid ( 1 , hfipOSO₃H ; hfip=C(H)(CF₃)₂) was synthesized by the reaction of hexafluoroisopropanol and chlorosulfonic acid on the kilogram scale and isolated in 98 % yield. The calculated gas‐phase acidity (GA) value of 1 is 58 kJ mol^?1 lower in ΔG° than that of sulfuric acid (GA value determined by a CCSD(T)‐MP2 compound method). Considering the gas‐phase dissociation constant as a measure for the intrinsic molecular acid strength, a hfipOSO₃H molecule is more than ten orders of magnitude more acidic than a H₂SO₄ molecule. The acid is a liquid at room temperature, distillable at reduced pressure, stable for more than one year in a closed vessel, reactive towards common solvents, and decomposes above 180 °C. It is a versatile compound for further applications, such as the synthesis of ammonium‐ and imidazolium‐based air‐ and moisture‐stable protic ionic liquids (pILs). Among the six synthesized ionic compounds, five are pILs with melting points below 100 °C and three of them are liquids at nearly room temperature. The conductivities and viscosities of two representative ILs were investigated in terms of Walden plots, and the pILs were found to be little associated ILs, comparable to conventional aprotic ILs.     

Changes in the Structural Dimensionality of Selenidostannates in Ionic Liquids: Formation,Structures, Stability,and Photoconductivity

In situ transformations of selenidostannate frameworks in ionic liquids (ILs) were initiated by treatment of the starting phase K₂[Sn₂Se₅] and the consecutive reaction products by means of temperature increase and/or amine addition. Along the reaction pathway, the framework dimensionalities of the five involved selenidostannate anions develop from 3D to 1D and back, both in top‐down and bottom‐up style. Addition of ethane‐1,2‐diamine (en) led to the reversion of the 2D→1D step from 2D‐{[Sn₂₄Se₅₆]^16?} to 1D‐{[Sn₆Se₁₄]^4?}. As rationalized by DFT investigations, the 2D anion is thermodynamically favored. Photoconductivity measurements reveal that all samples show Schottky contact behavior with absolute thresholds below 10 V. One of the samples exhibits conductive states within the energy range of visible photons.     

Synthesizing 2D and 3D Selenidostannates in Ionic Liquids: The Synergistic Structure‐Directing Effects of Ionic Liquids and Metal–Amine Complexes

Presented are the ionothermal syntheses, characterizations, and properties of a series of two‐ and three‐dimensional selenidostannate compounds synergistically directed by metal–amine complex (MAC) cations and ionic liquids (ILs) of [Bmmim]Cl (Bmmim=1‐butyl‐2,3‐dimethylimidazolium). Four selenidostannates, namely, 2D‐(Bmmim)₃[Ni(en)₃]₂[Sn₉Se₂₁]Cl ( 1 , en=ethylenediamine), 2D‐(Bmmim)₈[Ni₂(teta)₂(μ‐teta)]Sn₁₈Se₄₂ ( 2 , teta=triethylenetetramine), 2D‐(Bmmim)₄[Ni(tepa)Cl]₂[Ni(tepa)Sn₁₂Se₂₈] ( 3 , tepa=tetraethylenepentamine), and 3D‐(Bmmim)₂[Ni(1,2‐pda)₃]Sn₈Se₁₈ ( 4 , 1,2‐pda=1,2‐diaminopropane), were obtained. Single‐crystal X‐ray diffraction analyses revealed that compounds 1 and 2 possess a lamellar anionic [Sn₃Se₇]_n^2n? structure comprising distinct eight‐membered ring units, whereas 3 features a MAC‐decorated anionic [Ni(tepa)Sn₁₂Se₂₈]_n^6n? layered structure. In contrast to 1 – 3 , compound 4 exhibits a 3D open framework of anionic [Sn₄Se₉]_n^2n?. The structural variation from 1 to 4 clearly indicates that on the basis of the synergistic structure‐directing ability of the MACs and ILs, variation of the organic polyamine ligand has a significant impact on the formation of selenidostannates.     

Surface Interaction of Ionic Liquids: Stabilization of Polyethylene Terephthalate-Degrading Enzymes in Solution

The effect of aqueous solutions of selected ionic liquids solutions on Ideonella sakaiensis PETase with bis(2-hydroxyethyl) terephthalate (BHET) substrate were studied by means of molecular dynamics simulations in order to identify the possible effect of ionic liquids on the structure and dynamics of enzymatic Polyethylene terephthalate (PET) hydrolysis. The use of specific ionic liquids can potentially enhance the enzymatic hydrolyses of PET where these ionic liquids are known to partially dissolve PET. The aqueous solution of cholinium phosphate were found to have the smallest effect of the structure of PETase, and its interaction with (BHET) as substrate was comparable to that with the pure water. Thus, the cholinium phosphate was identified as possible candidate as ionic liquid co-solvent to study the enzymatic hydrolyses of PET.     

Theoretical Explanation for How SO3H‐Functionalized Ionic Liquids Promote the Conversion of Cellulose to Glucose

While the catalytic transformation of cellulose to glucose by functionalized ionic liquids (ILs) has been achieved successfully under mild conditions, insight into the fundamental molecular mechanism is still lacking. The present work presents the first attempt to address the fundamental reaction chemistry of the catalytic transformation. An enzyme‐like catalytic mechanism of ILs, in which glycosidic bond hydrolysis proceeds through a retaining mechanism and/or an inverting mechanism, is proposed. DFT calculations show that both mechanisms involve moderate barriers (<30 kcal mol^?1), which is consistent with the catalytic performance of the ILs under mild conditions (<100 °C). The “biomimetic” mechanism model proposed herein is expected to be viable for understanding the unique catalytic activity of ILs under mild conditions.     

The Dissolution of Polyols in Salt Solutions and Ionic Liquids at Molecular Level: Ions,Counter Ions,and Hofmeister Effects

The dissolving process of polyols in salt solutions (TBAF, TBAC, TBAB, TBAI, TMAF) and imidazolium-based ionic liquids ([C₂mim][OAc], [C₂mim][Et₂PO₄], [C₂mim][EtSO₄], [C₂mim][SCN]) is exemplarily studied by IR spectroscopy. Vibrational bands and their shifts in the OH stretch region reveal crucial information for the dissolved polyol interacting with the anions of the salt solutions and ionic liquids. The well-chosen set of ionic solutions confirms the linear relation between the OH-stretch frequencies and the solubility capacity of the salt solutions. Likewise, it also provides an explanation of the dissolving process at molecular level. Notably, the solubility capacities of the anions in the salt solutions follow the well-known Hofmeister series. This phenomenon can be understood on the basis of the disruption power of the anions and the specific size ratio of the anion/cation combinations.     

Controlling the Subtle Energy Balance in Protic Ionic Liquids: Dispersion Forces Compete with Hydrogen Bonds

The properties of ionic liquids are determined by the energy‐balance between Coulomb‐interaction, hydrogen‐bonding, and dispersion forces. Out of a set of protic ionic liquids (PILs), including trialkylammonium cations and methylsulfonate and triflate anions we could detect the transfer from hydrogen‐bonding to dispersion‐dominated interaction between cation and anion in the PIL [(C₆H₁₃)₃NH][CF₃SO₃]. The characteristic vibrational features for both ion‐pair species can be detected and assigned in the far‐infrared spectra. Our approach gives direct access to the relative strength of hydrogen‐bonding and dispersion forces in a Coulomb‐dominated system. Dispersion‐corrected density functional theory (DFT) calculations support the experimental findings. The dispersion forces could be quantified to contribute about 2.3 kJ mol^?1 per additional methylene group in the alkyl chains of the ammonium cation.     

Brønsted Acidity and the Medium: Fundamentals with a Focus on Ionic Liquids

Fundamental aspects of Brønsted acidity in ionic liquid systems, in relation to those of simple protic molecules in the gas phase, pure protic molecules in the condensed phase and solutions of protic molecules in molecular systems, are presented. The variety of acidities possible, beyond those observed in aqueous systems, is emphasised and discussed in terms of differences of solvent levelling, ionisation, dissociation, homo‐/hetero‐conjugate ion speciation and the stabilisation of proton‐transfer products from solvent to solvent. It is argued that data regarding aqueous systems do not necessarily explain acid/base behaviour in other liquids satisfactorily. Methods of measuring acidity are reviewed, particularly by spectrophotometry and electrochemistry and recommendations proffered for estimating speciation and acidity of ionic liquids of various complexities.     

Ionic Liquids for the Chemical Recycling of Polymeric Materials and Control of Their Solubility

Plastics are wonderful materials that have modernized our daily life; however, importance of effective recycling of plastics is gradually recognized widely. In this account, we describe our discovery of new and efficient methods for the chemical recycling of plastics using ionic liquids (ILs). Since the chemical recycling usually requires high temperature conditions to breakdown chemical bonds in polymeric materials, we thought that less-flammability and non-volatility of ionic liquids are the most suitable physical properties for this purpose. Ionic liquids successfully depolymerized polyamides and unsaturated polyesters smoothly and corresponding monomeric materials were obtained in good yields. To the best of our knowledge, this was the first use of Ionic liquids for such reactions. However, we encountered another difficult problem-separation. To solve the problem, we developed solubility-switchable ionic liquids, a new type of ionic liquids in which solubility is readily changed using the chemistry of protective groups. Conversion between hydrophilic and lipophilic forms was readily achieved using a simple chemical treatment under mild conditions, and the complete separation of products was achieved by liquid-liquid-extraction. The robustness of either form unlocks their wide use as reaction solvents.