Ionic moisture-stable

A related study used the air- and moisture-stable ionic liquids [RMIM][PFg] (R = butyl-decyl) as solvents for the oligomerization of ethylene to higher a-olefins [49]. The reaction used the cationic nickel complex 2 (Figure 7.4-1) under biphasic conditions to give oligomers of up to nine repeat units, with better selectivity and reactivity than obtained in conventional solvents. Recycling of the catalyst/ionic liquid solution was possible with little change in selectivity, and only a small drop in activity was observed. 

Ionic liquids, having per definition a melting point below 100 °C, and especially room temperature ionic liquids (RTIL) have attracted much interest in recent years as novel solvents for reactions and electrochemical processes [164], Some of these liquids are considered to be green solvents [165]. The scope of ionic liquids based on various combinations of cations and anions has dramatically increased, and continuously new salts [166-168] and solvent mixtures [169] are discovered. The most commonly used liquids are based on imidazolium cations like l-butyl-3-methylimidazolium [bmim] with an appropriate counter anion like hexafluorophos-phate [PFg]. Salts with the latter anion are moisture stable and are sometimes called third generation ionic liquids. 

Also the use of moisture stable ionic liquids as solvents in the Diels-Alder reaction has been carried out, and in all examples an enhanced reaction rate was observed [182,183]. The application of pyridinium-based ionic liquids allowed the utilization of isoprene as diene [184]. The chiral ionic liquid [bmim][L-lactate] was used as a solvent and accelerated the reaction of cyclopentadiene and ethyl acrylate, however, no enantiomeric excess was observed [183]. In addition several amino acid based ionic liquids have been recently tested in the Diels-Alder reaction. Similar exo. endo ratios were found but the product was obtained as racemate. The ionic liquids were prepared by the addition of equimolar amounts of HNO3 to the amino acids [185]. Furthermore, an enantiopure imidazolium salt incorporating a camphor motive was tested in the Diels-Alder reaction. No enantiomeric excess was found [186]. 

The stereoselective synthesis of c/.v-fused pyrano and furanobenzopyran can be achieved through the one-pot three-component reaction of o-hydroxy benzaldehyde, aromatic amines, and cyclic enolethers in the presence of catalytic amounts of Bi(OTf)3 (10 mol%) in air and the moisture-stable ionic liquid [bmim]PF6 [116]. The reaction of salicilaldehyde, aniline and 2,3-dihydrofuran furnishes the c/.v-fused furanochroman. In a similar fashion, various substituted salicilaldehydes and... 

Ionic liquids in molecular solvents "Second-generation" or "modern" ILs are well defined cation-anion combinations that are liquid at room (or reaction) temperature. They normally consist of exactly one cation and one anion, and they are often air- and moisture-stable. Therefore, investigations on structure and speciation of this class of ILs have a different focus. In addition, the higher stability of these... 

Attempts have also been made to develop biphasic methodologies for the hydrogenation of aromatics. The hydrogenation of benzene derivatives was studied using various Ru complexes.468,469 A trinuclear cluster cationic species was isolated as the tetrafluoroborate salt and showed increased activity in hydrogenation.470 The air/ moisture-stable [bmim][BF4] ionic liquid and water with [Rh r -CgHg).,] [BF4] as the catalyst precursor is an effective system under usual conditions (90°C, 60 atm)471 A system composed of stabilized Rh(0) nanoparticles proved to be an efficient catalyst in the hydrogenation of alkylbenzenes 472... 

Significant developments were achieved with the discovery in the 1970s and 1980s of varied room-temperature ionic liquids.41,42 These were organoaluminate ionic liquids, typically a mixture of quaternary ammonium salts with aluminum chloride. A major breakthrough came in 1992 by the discovery of air- and moisture-stable ionic liquids.43 1,3-Dialkylimidazolium cations (1), specifically,... 

In 1992, Zaworotko used weakly coordinating anions such as hexafluorophosphate and tetrafluo roborate, greatly expanded the range of ionic liquids available.15 Modern ionic liquids that are air- and moisture stable based on non-coordinating anions has meant that the field has attracted tremendous... 

Scheme 2.5 General synthetic route to producing air- and moisture-stable ionic liquids.

Wilkes launched the field of air- and moisture-stable ionic liquids by introducing five new materials, each containing the Tethyl-3-methylimidazolium cation [EMIMJ+ with one of five anions nitrate [NC>3], nitrite [NO2]-, sulfate [SC>4]2, methyl carbonate [CH3CO2]- and tetrafluoroborate [BF [47]. Only the last two materials had melting points lower than room temperature, and the reactive nature of the methyl carbonate would make it unsuitable for many applications. This led to the early adoption of [EMIM][BF4] as a favored ionic liquid, which has since been the subject of over 350 scientific publications. One of the first appeared in 1997 [50], reporting the investigation of [EMIM][BF4] as the electrolyte system for a number of processes, including the electrodeposition of lithium (intended for use in lithium ion batteries). 

Exploration of these concepts began a number of years ago with the use of chloroaluminate ionic liquids and has more recently focused on the use of air and moisture stable species. These are discussed separately in Section 7.3. First we discuss general experimental techniques in Section 7.2. Characterization methods are then surveyed in Section 7.4. 

Shi et al. [70] were the first to demonstrate the use of an air and moisture stable ionic liquid, [C4mim][PF,s], for the electrochemical synthesis of poly(thiophene), grown onto a platinum working electrode by potentiodynamic, constant potential or constant current techniques. The use of growth potentials between 1.7 and 1.9 V (vs. Ag/AgCl) reportedly gave smooth, blue-green electroactive films, whereas potentials above 2 V resulted in film destruction by overoxidation. 

Abbott et al. [98-103] reported the synthesis and characterization of new moisture-stable, Lewis acidic ionic liquids made from metal chlorides and commercially available quaternary ammonium salts (see Chapter 2.3). They showed that mixtures of choline chloride (2-hydroxyethyltrimethylammonium chloride, [Me3NC2H40H]Cl and MCU (M=Zn, Sn) give conducting and viscous liquids at or around room temperature. These deep eutectic solvents/ionic liquids are easy to prepare, are water-and air-stable, and their low cost enables their use in large-scale applications. Furthermore, they reported [104] that a dark green, viscous liquid can be formed by mixing choline chloride with chromium(III) chloride hexahydrate and that the... 

Nevertheless, Mattes s group and Fuchigami s group achieved independently electrooxidative polymerization of pyrrole, thiophene, and aniline in different moisture stable imidazolium ionic liquids [38 0]. Mattes s group used 1-butyl-... 

Because of the extensive amount of waste generated in traditional Friedel-Crafts reactions, it is not surprising that this reaction has been studied in RTIL. Early examples included the use of catalytic chloroaluminate ionic liquids. However, the moisture sensitivity of such systems was a drawback. Therefore, water-stable rare-earth Lewis acids, such as Sc(CF3S03)3, have come to be used for these reactions.The same Lewis acid has also been used to catalyse Diels-Alder reactions in RTILs.Interestingly, in this example, the RTIL not only provided a means for recycling the catalyst but also accelerated the rate and improved selectivity. It has also been demonstrated that a moisture stable, Lewis acidic, catalytic ionic liquid could be prepared from choline chloride and zinc dichloride, and that this was an excellent medium for the Diels-Alder reaction. Yields of 90% or more were achieved in reaction times of between 8 min and 5h for a range of dienes and dienophiles. 

Abbott A P, Capper G, Davies D L, et al. Preparation of novel, moisture-stable, Lewis-acidic ionic liquids containing quaternary ammonium salts with functional side chains. Chem. Commun. 2001. 1, 2010-2011. 

The modem world of chemical synthesis is unthinkable without NMR spectroscopy. Especially in organic synthesis, the information content of a combination of various NMR techniques is tremendeous and unmatched by any other spectroscopic method. Thus, since ionic liquids ( ILs for short) are predominantly used as solvents these days, the application of magnetic resonance spectroscopy to ionic solvents has become very important. None the less, the unique properties of this modem solvent class has put quite some challenge to researchers trying to apply NMR for ILs. In this review, I will describe the development of NMR in modem (i.e. air- and moisture-stable, predominantly imidazolium-based) ILs of the last 8 years historically from an experimental perspective. If you are looking for a more substrate-specific point of view or are interested in the early developments with chloroaluminate ILs, you are kindly asked to refer to the recent literature [1],... 

Ionic liquids (ILs) are a group of organic salts that are liquid at room temperature. They have unique chemical and physical properties, including being air and moisture stable, a high solubility power, and virtually no vapor pressure. " Because of these properties, they can serve as a green recyclable alternative to the volatile organic compounds that are traditionally... 

Catalytic asymmetric Diels-Alder reactions in ionic liquids, using an air- and moisture-stable chiral BlNOL-indium complex prepared from ( S)-BINOL and InClj, have also reported [46]. The reactions of various dienes with 2-methacrolein or 2-bromoacrolein proceeded in an ionic hquid with good yields and excellent enantioselectivities (up to 98% ee). The chiral In(lll) catalyst immobilized in ionic liquid [hmim][PF 5] could be reused seven times without any significant loss in catalytic activity (Scheme 7.13). 

Cu(ll) complexes ofbisoxazohnes 42a, 42b and 43 (Figure 7.12) have been reported to catalyze the asymmetric cyclopropanation of olefins with diazo-compounds in ionic liquids (Table 7.11). The catalytic activities increased in ionic liquids compared with that in organic solvent (compare entry 1 with 9 entry 2 with entries 3 and 6) [63]. One important finding here was that catalytically less-active but cheaper and moisture-stable CuCfi could be activated in ionic liquids, in which the anion of the ionic liquid may exchange with chloride to generate the more reactive... 

Poly-L-leucine and a polymeric BINOL the epoxidation of enones. Poly-L-leucine imni An air- and moisture-stable ionic liquid in. hiral (salen)Mn(III) complexes that are used i Ketone reductions. Corey s oxazaboroh virane reduction. A cheap borane source for tl. ilso modifications, for example, using alunui jerivative 85." ... 

An air- and moisture-stable ionic liquid in the reaction media facilitates recovery of chiral (salen)Mn(III) complexes that are used in asymmetric epoxidation. 

Conducting pol miers, based on pol q)henylenes have intensively been studied due to their interesting electroluminescence property [66, 67]. However, PPP is unstable and also the synthesis is problematic due to the humidity sensitivity of the pol nnerization process. To overcome these problems, ILs can be applied. Endres and coworkers used moisture-stable ionic liquids... 

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