Heck reactions of aryl halides in phosphonium salt ionic liquids: library screening and applications

The Heck cross-coupling of aryl iodides and bromides with olefins proceeds in the phosphonium salt ionic liquid trihexyl(tetradecyl)phosphonium chloride (THP-Cl) in excellent yields. Furthermore, it is shown that the counter anion matched to the phosphonium cation exerts a measurable effect on the overall yield.     

Diels-Alder reaction in protic ionic liquids

Protic imidazolium ionic liquids have been tested as reaction media in the Diels-Alder reaction between cyclopentadiene and two dienophiles (dimethyl maleate and methyl acrylate). Good conversions and endo/exo selectivities were achieved. The activation of the dienophile by hydrogen bonding with protic imidazolium ILs was demonstrated.     

Mechanistic studies on the formation of Pt(II) hydroformylation catalysts in imidazolium-based ionic liquids

The kinetics of the formation of the active species cis-[Pt^II(PPh₃)₂Cl(SnCl₃)] and cis-[Pt^II(PPh₃)₂(SnCl₃)₂] from the hydroformylation catalyst precursor cis-[Pt^II(PPh₃)₂Cl₂] in the presence of SnCl₂, was studied in two different imidazolium-based ionic liquids. A large range of different chlorostannate melts consisting of 1-butyl-3-methyl-imidazolium cations and [Sn_xCl_y]^{(−y + 2x)} anions with varying molar fraction of SnCl₂, were prepared and characterized by ¹H and ¹¹⁹Sn NMR. The observed chemical shifts point to major changes in the composition of the anionic species within the melt. The second ionic liquid employed, viz., 1-butyl-3-methyl-imidazolium-bis(trifluormethylsulfonyl)amide was prepared in a colorless quality that enabled its application in kinetic studies. The concentration and temperature dependence of the substitution of Cl⁻ by [SnCl₃]⁻ to yield cis-[Pt^II(PPh₃)₂Cl(SnCl₃)], could be studied in detail. Theoretical (DFT) calculations were employed to model the reaction progress and to resolve the role of the ionic liquid in the activation of the catalyst. The available results are presented and a plausible mechanism for the formation of the catalytically active species is suggested.     

Microwave-promoted synthesis of polyhydroxydeoxybenzoins in ionic liquids

A microwave-promoted synthesis of polyhydroxydeoxybenzoins and -phenylpropanones has been developed, using bis{(trifluoromethyl)sulfonyl}amine (HNTf₂) or BF₃·OEt₂ in an ionic liquid solvent.     

Mononuclear rearrangement of heterocycles in ionic liquids catalyzed by copper(II) salts

The reactivity of E- and Z-phenylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole in the presence of CuCl₂ and Cu(ClO₄)₂·6H₂O has been studied in four imidazolium ionic liquids [bmim][X] (X=BF₄⁻, PF₆⁻, SbF₆⁻ and CF₃SO₃⁻). The reaction may follow different mechanistic patterns, depending on the nature of the ionic liquid anion, accounting for both qualitative and kinetic data. In the presence of CuCl₂, two processes take place at the same time, i.e., the E?Z isomerization and the rearrangement of Z-isomer into the relevant 4-benzoylamino-2,5-diphenyl-1,2,3-triazole. In contrast, in the presence of Cu(ClO₄)₂·6H₂O, the rearrangement occurs only in solution of [bmim][BF₄] and [bmim][CF₃SO₃]. Collected data show that the effect of the ionic liquid on the isomerization and the rearrangement is different. In particular, a higher cross-linking degree seems to favour the triazole, but disfavour the E?Z isomerization.     

Promoting effect of ionic liquids on ligand substitution reactions

Ionic liquid solvents N-hexylpyridinium bistrifylimide ([C₆pyr][Tf₂N]] and 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄mim][PF₆]) promoted the displacement of anionic ligands by pyridine derivatives in trans-(Ph₃P)₂Rh(CO)NO₃ to a much greater extent than did dichloromethane. Thus, addition of a slight excess of 2-fluoropyridine to trans-(Ph₃P)₂Rh(CO)NO₃ in [C₄mim][PF₆] gave a 29:71 product mixture of trans-(Ph₃P)₂Rh(CO)NO₃:[trans-(Ph₃P)₂Rh(CO)(2-fluoropyridine)][NO₃], while the ratio was 91:9 in dichloromethane.     

Hydrogen transfer reduction of different ketones in ionic liquids

Ionic liquids were tested as the reaction media for hydrogen transfer reduction of substituted acetophenones and some other ketones with the [RuCl(TsDPEN)]₂ complex as the catalyst. Reactions were going well and faster than in common solvents. Corresponding alcohols had high ees in the case of aryl alkyl ketones, but just medium ees were reached in the case of dialkyl or unsaturated ketones. An interesting phenomenon was observed, namely that rise of the reaction temperature did not have negative influence on the ee of the reaction product. Correspondence: Štefan Toma, Faculty of Natural Science, Comenius University Bratislava, SK-84215 Bratislava, Slovakia.     

Alanine-supported protic ionic liquids as efficient catalysts for aldol condensation reactions

A series of novel protic ionic liquids were immobilized on alanine, a cheap readily available amino acid. These short aliphatic chain ionic liquids have a low cost of preparation, a low toxicity, and need simple synthesis/purification processes. Their catalytic activity was tested for citral–acetone and benzaldehyde–acetone condensations, two reactions with an interest for pharmacological as well as flavor and fragrance industry. Good results were obtained in terms of conversion and selectivity; moreover, the catalysts can be recycled and reused for several consecutive cycles without significant loss of activity.     

First application of chiral ionic liquids in asymmetric Baylis-Hillman reaction

The first example of the use of chiral ionic liquids as reaction media in the asymmetric Baylis-Hillman reaction was described using N-alkyl-N-methylephedrinium salts. Good yields and significant enantiomeric excesses were obtained.     

Diels-Alder reactions in pyridinium based ionic liquids

Diels-Alder reactions have been investigated in pyridinium based ionic liquids. These solvents are found to be more effective compared to the organic solvent studied, in enhancing the reaction rate and product yields. Recycled ionic liquids also gave excellent results.     

The Baeyer-Villiger oxidation of ketones with Oxone in the presence of ionic liquids as solvents

Cyclic and linear ketones were readily oxidised with Oxone^® at 40 °C in ionic liquids as solvents and short times (2.5-20 h), affording their corresponding lactones and esters in high yields (65-95%). Both, aprotic and protic ionic liquids were used. The best conversion of ketones and the highest yields of products were obtained with 1-buty-3-methylimidazolium tetrafluoroborate and 1-methylimidazolium acetate as solvents. These ionic liquids were also efficiently recycled in the Baeyer-Villiger reaction without significant loss of activity. Several factors, such as the partial solubility of KHSO₅ in the ionic liquid, its viscosity and the presence of a proton in protic ionic liquids, have an influence on the course of the reaction.     

Chloride based ionic liquids as promoting agents for Meerwein reaction in solventless conditions

Chloride based ionic liquids were used as chloride source in Meerwein reaction either in [bmim]X (bmim = 1-butyl-3-methylimidazolium, X = BF₄, PF₆) as solvents or in solventless conditions. Satisfactory yields (49-71%) with diversely substituted diazonium salts were achieved by using 1,3-dibutylimidazolium chloride in the presence of a bimetallic Zn/Cu catalyst.     

Asymmetric Mannich-type reactions catalyzed by indium(III) complexes in ionic liquids

In(III) complexes efficiently catalyse asymmetric Mannich-type reactions in ionic liquids with high diastereoselectivity and good yield.     

Tin mediated Barbier type allylation in ionic liquids

The Barbier type allylation of carbonyl compounds is a useful organic transformation as the resultant homoallylic alcohols are important building blocks for many biologically active molecules. Tin mediated Barbier allylation of different carbonyl compounds in room temperature ionic liquid, [BMIM][BF₄] afforded the corresponding homoallylic alcohols in good to excellent yields. The ionic liquid was successfully recycled and reused in allylation reactions.     

Three-component coupling reactions in ionic liquids: One-pot synthesis of isoxazolidines

1-Butyl-3-methylimidazolium based ionic liquids are found to accelerate significantly the intermolecular 1,3-dipolar cycloaddition of nitrones derived in situ from aldehydes and phenyl hydroxylamine, with electron deficient olefins to afford enhanced rates and improved yields of isoxazolidines with high regio- and diastereoselectivity.     

Wetting study of imidazolium ionic liquids

In this work, we present a systematic contact angles study of a series of 1-alkyl, 3-methyl-imidazolium ionic liquids (ILs) on well-defined polar and nonpolar monolayer surfaces supported on Si wafers. The advancing and receding contact angles of ILs were used to determine the surface energy of the monolayer surfaces using Neumann's equation-of-state and Zisman's critical surface tension approaches. In parallel, the contact angles of conventional probe fluids (molecular liquids) including water, formamide, methylene iodide, ethylene glycol, and hexadecane were determined on the same surfaces. The results obtained showed a great deal of similarity in wetting behavior of ionic vs molecular probe fluids: the contact angles of both sets of liquids followed the same patterns in accord with the surface tension of the fluid. A good agreement was found between the surface energy determined by different sets of liquids.     

Heteronuclear NOE spectroscopy of ionic liquids

(19)F,(1)H HOESY experiments with three ionic liquids ([bmim]BF(4), [bmim]PF(6) and [emim]BF(4)) were run in two different solvents and neat. The results give preferred probabilities of presence and enable us to systematically study interactions between the cations and the anions in the ionic liquid phase by NMR spectroscopy. The influence of different solvents and of the presence or absence of air (i.e. oxygen) is discussed. This enabled us to substantially speed up the NMR experiments and to develop a more precise method for the investigation of liquid-phase structures in ionic liquids.     

Highly efficient synthesis of amides via Ritter chemistry with ionic liquids

The utility of Brønsted-acidic imidazolium ionic liquid [BMIM(SO₃H)][OTf] as catalyst for the high yield synthesis of a wide variety of amides under mild conditions via the Ritter reaction of alcohols with nitriles has been demonstrated. As alternative methods for the carbocation generation step, NOPF₆ immobilized in [BMIM][PF₆] ionic liquid was used in the Ritter reaction of bromides with nitriles and for the synthesis of adamantyl amides from adamantane and nitriles.     

A SEM–EDX study of highly stable supported liquid membranes based on ionic liquids

This work evaluates the operational stability of six different supported liquid membranes (SLMs) based on ionic liquids (ILs). [bmim⁺][PF₆⁻]_, [bmim⁺][BF₄⁻] and [bmim⁺][NTf₂⁻] were used as supporting phase in Nylon^® and Mitex^® membranes. Scanning electron microscopy (SEM) combined with energy dispersive X-ray (EDX) analysis was used to characterize the membrane surface morphologically and examine the global chemical composition of the membranes and the distribution of the ILs within them.

Study of the freshly impregnated membranes showed that, in all cases, the ILs were homogeneously distributed, mostly filling the pores of the membranes although, in some cases, a small amount of excess of IL was located on the external membrane surface. Stability tests were performed by keeping the respective impregnated membranes immersed for a week in a diffusion cell including two independent compartments and using n-hexane/n-hexane as the respective feed and receiving phases. The SEM–EDX study of membranes after continuous operation showed that the ILs were still retained within the membrane pores and only small losses of the IL initially located on the external surface were observed. These observations are in complete agreement with the ionic losses determined by mass balance.     

Microwave-assisted separation of ionic liquids from aqueous solution of ionic liquids

Microwave-assisted separation has been applied to recover ionic liquid (IL) from its aqueous solution as an efficient method with respect to time and energy compared to the conventional vacuum distillation. Hydrophilic ILs such as 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF(4)]), 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([Bmim][TfO]) and 1-ethyl-3-methylimidazolium methylsulfate ([Emim][MS]) could be recovered in 6 min from the mixture of ILs and water (1:1, w/w) under microwave irradiation at constant power of 10 W while it took at least 240 min to obtain ILs containing same water content (less than 0.5 wt%) by conventional vacuum oven at 363.15 K with 90 kPa of vacuum pressure. Energy consumptions per gram of evaporated water from the homogeneous mixture of hydrophilic ILs and water (1:1, w/w) by microwave-assisted separation were at least 52 times more efficient than those in conventional vacuum oven. It demonstrated that microwave-assisted separation could be used for complete recovery of ILs in sense of time and energy as well as relevant purity.