离子液体介导CO2化学转化研究进展

The efficient utilization of carbon dioxide (CO₂) as a C1 feedstock is of great significance for green and sustainable development. Therefore, the efficient chemical conversion of CO₂ into value-added products has recently attracted a lot of research attention in recent years. The transformation of CO₂ generally requires high-energy substrates, specific catalysts, and harsh reaction conditions due to its high thermodynamic stability and kinetic inertness. Consequently, several efforts have been dedicated toward the development of high-performance catalysts and new reaction routes for CO₂ conversion over the last few decades. To date, many routes of convert CO₂ into value-added chemicals have been proposed, together with the development of heterogeneous and homogeneous catalysts. Among the advanced catalysts reported to date, ionic liquids (ILs) have been widely investigated and show great potential for the efficient, selective, and economical conversion of CO₂ into highly valuable products under mild conditions, even under ambient conditions. Some task-specific ILs have been designed with unique functional groups (e.g., —OH, —SO₃H, —NH₂, —COOH, and —C≡N), which can act as the solvent, absorbent, activating agent, catalyst, or cocatalyst to realize the transformation of CO₂ under metal-free and mild conditions. In addition, a variety of catalytic systems composed of ILs and metal catalysts have also been reported for the transformation of CO₂, in which the combination of the IL and metal catalyst is responsible for CO₂ conversion with high efficiency. In this review article, we summarize the recent advances in IL-mediated CO₂ transformation into chemicals prepared via C—O, C—N, C—S, C—H, and C—C bond forming processes. ILs that can chemically capture CO₂ with high capacity are first introduced, which can activate CO₂ via the formation of IL-based carbonates or carbamates, thus realizing the transformation of CO₂ under metal-free and mild conditions. Recent progress in IL-mediated CO₂ transformations to form carbonates and various kinds of N- and S-containing compounds (e.g., oxazolidinones, ureas, benzimidazolones, formamides, methylamines, benzothiazoles, and other chemicals) as well as CO₂ hydrogenation to give formic acid, methane, acetic acid, low-carbon alcohols, and hydrocarbons has been summarized in this review with a focus on the reaction routes, catalytic systems, and reaction mechanism. In these reactions, ILs can simultaneously activate the substrate via strong H-bonding in addition to activating CO₂, and the cooperative effects among the ionic and molecular species and metal catalysts accomplish the reactions of CO₂ with various kinds of substrates to afford a wide range of value-added chemicals. Finally, the shortcomings and perspectives of ILs are discussed. In short, IL-mediated CO₂ transformations provide green and effective routes for the synthesis of high-value chemicals, which may have great potential for a wide range of applications.     

Basic ionic liquids promoted chemical transformation of CO<Subscript>2</Subscript> to organic carbonates

Ionic liquids (ILs), especially basic ILs with unique physicochemical properties, have wide application in catalysis. Using basic ILs as catalysts for the conversion of cheap, abundant, nontoxic, and renewable CO₂ into value-added organic carbonates is highly significant in view of environmental and economic issues. This review aims at giving a detailed overview on the recent advances on basic ILs promoted chemical transformation of CO₂ to cyclic and linear carbonates. The structures of various basic ILs, as well as the basic ILs promoted reactions for the transformation of CO₂ to organic carbonates are discussed in detail, including the reaction conditions, the yields of target products, the catalytic activities of basic ILs and the reaction mechanism.     

Basic ionic liquids promoted chemical transformation of CO_2 to organic carbonates

Ionic liquids(ILs), especially basic ILs with unique physicochemical properties, have wide application in catalysis. Using basic ILs as catalysts for the conversion of cheap, abundant, nontoxic, and renewable CO_2 into value-added organic carbonates is highly significant in view of environmental and economic issues. This review aims at giving a detailed overview on the recent advances on basic ILs promoted chemical transformation of CO_2 to cyclic and linear carbonates. The structures of various basic ILs, as well as the basic ILs promoted reactions for the transformation of CO_2 to organic carbonates are discussed in detail,including the reaction conditions, the yields of target products, the catalytic activities of basic ILs and the reaction mechanism.     

Electrochemical Quantification of Hygroscopicity of Ionic Liquids with Solution‐Dissolved Potassium Ferricyanide as the Redox Probe

Quantification of hygroscopicity of ionic liquids (ILs) is of great importance in both fundamental studies and practical applications of ILs. This study demonstrates an electrochemical method for effectively quantifying the hygroscopicity of ILs through electrochemically monitoring water contents absorbed into ILs. The measurements of water content absorbed into the ILs are performed with square wave voltammetry (SWV) based on the water‐induced enhancement of diffusion of solution‐dissolved potassium ferricyanide (K₃Fe(CN)₆) redox probe. For demonstration, two kinds of ILs with different hygroscopicity (i.e., hydrophilic Bmim⁺Gly^? and hydrophobic Bmim⁺PF₆^?) are employed in this study. The dissolution of K₃Fe(CN)₆ redox probe into ILs is found to have little effect on the hygroscopicity of ILs. The hygroscopicity of ILs is thus able to be quantified by monitoring water content absorbed into ILs as a function of time when ILs are stored at room temperature and standard atmospheric pressure under 55 % relative humidity (RH). Under the conditions employed in this study, the hygroscopicity of Bmim⁺Gly^? and Bmim⁺PF₆^? is determined to be 1.33 M per hour and 0.05 M per hour, respectively, which are almost consistent with those measured with Karl Fischer titration under the same conditions. The electrochemical method demonstrated in this study is experimentally simply and environmentally benign and may be potentially extended for general quantification of hygroscopicity of ILs.     

Ruthenium-Catalyzed Regioselective 1,2-Hydrosilylation of N-Heteroarenes

An efficient method for the regioselective 1,2-hydrosilylation of N-heteroarenes is reported utilizing silanes as the hydride donor. The ruthenium complex [RuCl(PPh₃)₂(η⁵-(3-phenylindenylidene))], a versatile catalyst is, for the first time, employed in this catalytic reaction. The catalyst displays high catalytic efficiency at low loading and operates under mild conditions. This catalytic approach showcases high compatibility and regioselectivity with quinolines bearing different substituents and related N- heterocyclic compounds. The mechanism of this transformation was probed by performing stoichiometric reactions and examined using DFT calculations.     

An epoxide ring-opening reaction by using sol–gel-synthesized palladium supported on a strontium hydroxyl fluoride catalyst

Palladium supported on a strontium hydroxyl fluoride catalyst was synthesized by a one-pot fluorolytic sol–gel method. The prepared catalyst was characterized by various physicochemical techniques. The sol–gel method has led to the formation of a high surface area (57 m²g⁻¹), mesoporous (pore diameter = 13.0 nm) catalyst with uniform dispersion of Pd nanoparticles of size ∼7 nm on the surface of strontium hydroxyl fluoride. The catalyst was used for epoxide alcoholysis, and 100% conversion was obtained with 96% selectivity for β-alkoxy alcohols under mild conditions. The catalyst could be recycled for up to three catalytic cycles without any appreciable decrease in conversion and selectivity, indicating the stability of the catalyst under the reaction conditions. Further, the mechanism of alcoholysis was proposed on the basis of the physicochemical characteristics of the catalyst and on the basis of the products formed during the catalytic reaction.     

Glaser oxidative coupling in ionic liquids: an improved synthesis of conjugated 1,3-diynes

Terminal alkynes undergo oxidative-coupling smoothly in the presence of the CuCl-TMEDA catalytic system in hydrophobic [bmim]PF₆ ionic liquid under aerobic conditions to produce 1,3-diynes in excellent yields under mild conditions. The substrates, alkynes, show enhanced reactivity and selectivity in ionic liquids (ILs). The recovery of the catalyst is facilitated by the hydrophobic nature of the [bmim]PF₆ ionic liquid.     

Catalytic studies of 2-benzthiazolethiol (BzTa)-linked manganese(III) and cobalt(II) porphyrin complexes

Four 2-benzthiazolethiol (BzTa)-linked porphyrins (1)–(4), and their complexes with Co^II and Mn^III, (5)–(12), were prepared and characterized by elemental analysis, ¹H-n.m.r., i.r., u.v.–vis. and mass spectra. The hydroxylation of cyclohexane in the presence of these complexes and PhIO under mild conditions was investigated. The catalytic activities of these complexes were higher than that of corresponding TPPMn^IIICl and TPPCo^II species respectively, which indicated that the terminal group, BzTa, played an important role in the catalysis. A possible mechanism is proposed.     

Heterocyclic Carbene‐Catalyzed Hydride Transfer in the Hydroboration of Carbonyl Compounds

N‐Heterocyclic carbene (NHC) enabled the highly efficient catalytic hydroboration of a wide range of ketones and aldehydes under mild conditions, and a new mechanism of catalytic hydroboration reaction which involves direct hydride transfer is proposed.     

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.     

Highly Efficient Carbon Monoxide Capture by Carbanion-Functionalized Ionic Liquids through C-Site Interactions

A novel method for the highly efficient and reversible capture of CO in carbanion-functionalized ionic liquids (ILs) by a C-site interaction is reported. Because of its supernucleophilicity, the carbanion in ILs could absorb CO efficiently. As a result, a relatively high absorption capacity for CO (up to 0.046 mol mol⁻¹) was achieved under ambient conditions, compared with CO solubility in a commonly used IL [Bmim][Tf₂N] (2×10⁻³ mol mol⁻¹). The results of quantum mechanical calculations and spectroscopic investigation confirmed that the chemical interaction between the C-site in the carbanion and CO resulted in the superior CO absorption capacities. Furthermore, the subsequent conversion of captured CO into valuable chemicals with good reactivity was also realized through the alkoxycarbonylation reaction under mild conditions. Highly efficient CO absorption by carbanion-functionalized ILs provides a new way of separating and converting CO.     

Copper mediated oxidation of amides to imides by Selectfluor

The combination of Selectfluor and copper(I) bromide has shown a strong oxidation ability, readily oxidizing amides into the corresponding imides in acetonitrile at room temperature in less than 1 h. This transformation under mild conditions gives good to excellent chemical yields. A possible reaction mechanism is proposed.     

Nitration of Simple Aromatics with NO2 under Air Atmosphere in the Presence of Novel Brønsted Acidic Ionic Liquids

Abstract

Aromatics nitrate with NO₂/air catalyzed by novel Brønsted acidic ionic liquids (ILs) without any volatile chlorinated organic solvent under mild conditions. The ILs employed were caprolactam based, [Caprolactam]X (X^?=pTSO^?, BSO^?, BF₄ ^?, NO₃ ^?), which are of relatively lower cost and lower toxicity than traditional imidazolium‐based ILs. The nitration reactions were carried out at ?15 to ?0°C first, then at room temperature for a longer time with a little excessive NO₂ (ca. 1.4 eqv.) for moderate yield (for toluene). The IL could be reused four times.     

Gold(I)‐ and Yb(OTf)3‐Cocatalyzed Rearrangements of Epoxy Alkynes: Transfer of a Carbonyl Group in a Five‐Membered Carbocycle

We report here the intramolecular reactions between α,β‐epoxy ketones and alkynes cocatalyzed by gold(I) and Yb(OTf)₃. This new catalytic system based on a combination of gold(I) and Yb(OTf)₃ allows facile transformation of epoxy alkynes to give novel indene derivatives in moderate to good yields under mild conditions. Moreover, we describe here the first observation of a transfer of a carbonyl group in a five‐membered carbocycle during gold‐catalyzed reactions. This proposed mechanism is corroborated by isotope‐labeling experiments (D and ¹³C). Furthermore, the probable role of each catalyst in this interesting domino reaction has been examined by ³¹P NMR experiments. The utilization of gold catalysts combined with rare‐earth metal salts offers a new concept for the design of catalyst combinations for domino or cascade reactions.     

Highly Efficient Carbon Monoxide Capture by Carbanion‐Functionalized Ionic Liquids through C‐Site Interactions

A novel method for the highly efficient and reversible capture of CO in carbanion‐functionalized ionic liquids (ILs) by a C‐site interaction is reported. Because of its supernucleophilicity, the carbanion in ILs could absorb CO efficiently. As a result, a relatively high absorption capacity for CO (up to 0.046 mol mol⁻¹) was achieved under ambient conditions, compared with CO solubility in a commonly used IL [Bmim][Tf₂N] (2×10⁻³ mol mol⁻¹). The results of quantum mechanical calculations and spectroscopic investigation confirmed that the chemical interaction between the C‐site in the carbanion and CO resulted in the superior CO absorption capacities. Furthermore, the subsequent conversion of captured CO into valuable chemicals with good reactivity was also realized through the alkoxycarbonylation reaction under mild conditions. Highly efficient CO absorption by carbanion‐functionalized ILs provides a new way of separating and converting CO.     

Reaktionen mit Blei(IV)-acetat,XVI. Eine neuartige Umwandlung von 2-Acetoxy-3-oxo-4,5-epoxy-steroiden

Treatment of 3-oxo-4, 5-oxido steroids with lead tetraacetate results in acetoxylation in the 2α-position as could be shown by independent synthesis of the acetoxylated compounds. The products of this reaction rearrange even under very mild conditions (chromatography on silicagel or alumina) to the corresponding 2,3-dioxo-Δ⁴ compounds. The influence of structure and conformation of the various intermediates on their NMR.-spectra is discussed. A mechanism for this new transformation is proposed.     

Glucose transformation to 5‐hydroxymethylfurfural in acidic ionic liquid: A quantum mechanical study

Isomerization and transformation of glucose and fructose to 5‐hydroxymethylfurfural (HMF) in both ionic liquids (ILs) and water has been studied by the reference interaction site model self‐consistent field spatial electron density distribution (RISM‐SCF‐SEDD) method coupled with ab initio electronic structure theory, namely coupled cluster single, double, and perturbative triple excitation (CCSD(T)). Glucose isomerization to fructose has been investigated via cyclic and open chain mechanisms. In water, the calculations support the cyclic mechanism of glucose isomerization; with the predicted activation free energy is 23.8 kcal mol^?1 at experimental condition. Conversely, open ring mechanism is more favorable in ILs with the energy barrier is 32.4 kcal mol^?1. Moreover, the transformation of fructose into HMF via cyclic mechanism is reasonable; the calculated activation barriers are 16.0 and 21.5 kcal mol^?1 in aqueous and ILs solutions, respectively. The solvent effects of ILs could be explained by the decomposition of free energies and radial distribution functions of solute‐solvent that are produced by RISM‐SCF‐SEDD. © 2015 Wiley Periodicals, Inc.     

Indium(III)trifluoromethanesulfonate as a mild, efficient catalyst for the formation of acetals and ketals in the presence of acid sensitive functional groups

Aldehydes and ketones, including acetophenone and benzophenone, are readily protected under mild, neutral conditions in the presence of various alcohols or orthoformates and catalytic amounts of indium(III) trifluoromethanesulfonate (<0.8 mol %) under either room temperature or mild heating conditions to give the corresponding cyclic and acyclic acetals and ketals in good to excellent yields. Acid sensitive functional groups, N-Boc, THP, and TBDMS do not undergo competitive deprotection under the reported conditions.     

Dehydrogenative Silylation of Alkenes for the Synthesis of Substituted Allylsilanes by Photoredox,Hydrogen‐Atom Transfer,and Cobalt Catalysis

A synergistic catalytic method combining photoredox catalysis, hydrogen‐atom transfer, and proton‐reduction catalysis for the dehydrogenative silylation of alkenes was developed. With this approach, a highly concise route to substituted allylsilanes has been achieved under very mild reaction conditions without using oxidants. This transformation features good to excellent yields, operational simplicity, and high atom economy. Based on control experiments, a possible reaction mechanism is proposed.     

Dehydrogenative Silylation of Alkenes for the Synthesis of Substituted Allylsilanes by Photoredox,Hydrogen‐Atom Transfer,and Cobalt Catalysis

A synergistic catalytic method combining photoredox catalysis, hydrogen‐atom transfer, and proton‐reduction catalysis for the dehydrogenative silylation of alkenes was developed. With this approach, a highly concise route to substituted allylsilanes has been achieved under very mild reaction conditions without using oxidants. This transformation features good to excellent yields, operational simplicity, and high atom economy. Based on control experiments, a possible reaction mechanism is proposed.