Ionic imidazolium-based

The pyridinium- and the imidazolium-based chloroaluminate ionic liquids share the disadvantage of being reactive with water. In 1990, Mike Zaworotko (Eigure 1.4) took a sabbatical leave at the Air Eorce Academy, where he introduced a new dimension to the growing field of ionic liquid solvents and electrolytes. 

Figure 2.3-5 Imidazolium-based task-specific ionic iiquids with cation-appended fiuorous taiis.

The room temperature conductivity data for a wide variety of ionic liquids are listed in Tables 3.6-3, 3.6-4, and 3.6-5. These tables are organized by the general type of ionic liquid. Table 3.6-3 contains data for imidazolium-based non-haloaluminate alkylimidazolium ionic liquids. Table 3.6-4 data for the haloaluminate ionic liquids, and Table 3.6-5 data for other types of ionic liquids. There are multiple listings for several of the ionic liquids in Tables 3.6-3-3.6-5. These represent measurements by different researchers and have been included to help emphasize the significant vari-... 

The use of imidazolium-based ionic liquids in Pd-catalyzed Heck reactions always carries with it the possibility of in situ formation of Pd-carbene complexes (for more details see Section 5.2.2.3). The formation of these under the conditions of the Heck reaction was confirmed by investigations by Xiao et al. [30], who described a significantly enhanced reactivity of the Heck reaction in [BMIM]Br in relation to the same reaction in [BMIM][Bp4] and explained this difference by the fact that formation of Pd-carbene complexes was observed only in the bromide melt. 

With the enthusiasm currently being generated by the (so-called) stable carbenes (imidazolylidenes) [7], it is surprising that there are few reports of imidazolium-based ionic liquids being used to prepare metal imidazolylidene complexes. Xiao et al. have prepared bis(imida2olylidene)palladium(II) dibromide in [BMIMJBr [8]. All four possible conformers are formed, as shown in Scheme 6.1-3. 

Olefin dimerisation with Ni-NHC complexes became a topic of interest following reports of Ni(II) phosphine complexes being employed in imidazolium-based ionic liquid solvents [23, 24]. It had previonsly been established that aIkyl-Ni(II) complexes containing NHC ligands can rapidly decompose via imidazolium formation (Scheme 4.1) [5], and it was thus of interest to explore the effect that an excess of the imidazolinm cation would have on this reaction. 

Among these in situ protocols are those using ionic liquids as the solvent, or as both the solvent and the ligand. It was shown that the use of PdCOAc) in imidazolium-based ionic liquids forms in situ NHC-Pd(II) species [42], The use of methylene-bridged bis-imidazolium salt ionic liquids to form chelated complexes has also been reported [43], although better results have been obtained when Bu NBr is used as the solvent [44] and imidazolium salts were added together with PdCl in catalytic amounts [45]. Other related catalytic species such as bis-NHC complexes of silica-hybrid materials have been tested as recyclable catalysts [46,47]. 

Banerjee, T., Singh, M. K., Khanna, A. Prediction of binary VLE for imidazolium based ionic liquid systems using COSMO-RS. Ind. Eng. Chem. Res. 2006, 45, 3207-3219. 

Costa C, Hihn JH, Rebetez M et al (2008) Transport-limited current and microsonoreactor characterization at 3 low frequencies in the presence of water, acetonitrile and imidazolium-based ionic liquids ([BuMIm] [(CF3S02)2N]). Phys Chem Chem Phys 10 2149-2158... 

Lee, C.M., Jeong, H.J., Lim, S.T., Sohn, M.H. and Kim, D.W. (2010) Synthesis of iron oxide nanopartides with control over shape using imidazolium-based ionic liquids. ACS Applied Materials S, Interfaces, 2 (3), 756-759. 

Besides the advantage of recyclability, reactions in ionic liquids are generally faster and are run under milder conditions than reactions with conventional solvents. Further activation may come from ultrasonic agitation.520 Since the majority of ionic liquids used are imidazolium salts, the effect of these solvents can be at least partly attributed to the in situ formation of carbene complexes (Section 9.6.3.4.10).521 Cross-coupling of ArB(OH)2 can also be efficiently performed in ionic liquids based on long-chain tetraalkylphosphonium salts, in which case aryl bromides and some aryl chlorides can be processed in the presence of the trivial ligand PPh3.522... 

In a recent study, the group of Buijsman presented a microwave-mediated preparation of a different N-imidazolium-based ionic analogue of the well-known AMEBA solid support (Scheme 7.93). With this soluble support, a set of various sulfonamides and amides was prepared, and furthermore the use of this novel linker in the synthesis of a potent analogue of the antiplatelet drug tirofiban was presented [106]. 

The synthetic routes used to prepare ionic liquids vary depending upon the ionic liquid being made. Ionic liquids with metal halide anions are, at least in principle, very simple to prepare. Scheme 4.1 illustrates the synthesis of imidazolium-based ionic liquids with a chloroaluminate anion, commencing with methylimidazole [6],... 

The physical properties of ionic liquids have been extensively studied and some trends are beginning to emerge. In particular, ionic liquids based on 1,3-dialkylimidazolium cations have been investigated in detail, partly due the their wide use as solvents to conduct synthesis and catalysis. The attraction of the imidazolium cation in synthetic applications is because the two substituent groups can be varied to modify the properties of the solvent. For example, Table 4.1... 

Table 4.1 Effect of the R group on the melting point of some imidazolium-based ionic liquids...

Ionic liquids based on imidazolium cations and either [BF4]- or [PF6] anions have been used to immobilize transition metal based oxidation catalysts developed... 

When Heck reactions and other C-C coupling reactions are carried out in imidazolium-based ionic liquids, the base can react with the acidic proton on the... 

Ott, L. S. Cline, M. L. Deetlefs, M. et al. Nanoclusters in ionic liquids evidence for A-heterocyclic carbene formation from imidazolium-based ionic liquids detected by H-2 NMR, J. Am. Chem. Soc., 2005, 127(16), 5758-5759 Hamill, N. A., Hardacre, C. McMath, S. E. J. In situ XAES investigation of palladium species present during the Heck reaction in room temperature ionic liquids. Green Chem., 2002, 4(2), 139-142. 

Bemot, R. J. Brueseke, M. A. Evans-White, M. A. Lamberti, G. A. Acute and chronic toxicity of imidazolium-based ionic liquids on daphnia magna. Environ. Toxicol. Chem., 2005, 24(1), 87-92. 

Imidazolium-based ionic liquids (ILs) have been used extensively as media for the formation and stabilization of transition-metal nanoparticles [14—17]. These 1,3-dialkylimidazolium salts (Figure 15.3) possess very interesting properhes they have a very low vapor pressure, they are nonflammable, have high thermal and electrochemical stabilities, and display different solubilities in organic solvents [18-20]. 

Figure 15.3 The chemical structures of the general imidazolium-based ionic liquids.

Various solid-supported perruthenate reagents have been designed for the oxidation of alcohols.Solid-supported NMO has also been used. A number of perruthenate systems employing O2 as the terminal oxidant have also been reported. The use of ionic liquids based upon substituted imidazolium cations as alternative solvent media for the selective oxidation of alcohols to aldehydes and ketones has also been investigated. ... 

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. 

The salts were investigated in the Diels-Alder reaction of crotonaldehyde with cyclopentadiene (Scheme 67). The yields obtained were between 35% and 40% with an endo. exo ratio of 90 10. The control reaction without the salt at -25 °C gave no product. The observed ee with the enantiopure salt 66 was less than 5%. Nevertheless, this was the first example which showed, that imidazolium-based ionic liquids can be used in substoichiometric amounts as Lewis acid catalysts. 

The imidazolium-based ionic liquid [bmim][BF ] has been used as a catalyst in the aza-Michael reaction of various aliphatic amines to unsaturated compounds with different electron withdrawing groups in good yields as shown in Scheme 76. Water was used as the solvent in order to obtain up to 98% yield in 7 h. In the presented example, 95% yield in 7 h was achieved [198], The ionic liquid could be recovered and reused five times without loss of activity. 

PREPARATION OF 1-BUTYL-3-METHYL IMIDAZOLIUM-BASED ROOM TEMPERATURE IONIC LIQUIDS... 

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