Triflate ionic liquid

Scheme 4.4 Synthesis of imidazolium triflate ionic liquids from alkylimidazoles (where R is an alkyl group)...

Many ionic liquids with other anions are produced in related one-pot methylation reactions that do not give rise to by-products [13]. For example, methyl triflate, CF3S03Me, can be used to methylate alkylimidazoles to give 1,3-alkyl-methylimidazolium triflate ionic liquids as shown in Scheme 4.4. 

Leclercq L, Suisse I, Nowogrocki G et al (2007) Hahde-free highly-puie imidazohum triflate ionic liquids preparation and use in palladium-catalysed aUyUc alkylation. Green Chem 9 1097-1103... 

Coman SM, Elorea M, Parvulescu VI et al (2007) Metril-triflate ionic liquid systems immobilized onto mesoporous MS41 materials as new and efficient catrilysts for 7V-acylation. J Catal 249 359-369... 

Rencurosi A, Lay L, Russo G, Caneva E, Poletti L (2006) NMR evidence for the participation of triflated ionic liquids in glycosylation reaction mechanisms. Carbohydr Res 341 903-908... 

Scheme 5.2-44 The nitration of aromatic compounds in triflate ionic liquids [96,97].

In order to eliminate the possibility for in situ carbene formation Raubenheimer et al. synthesized l-alkyl-2,3-dimethylimidazolium triflate ionic liquids and applied these as solvents in the rhodium catalyzed hydroformylation of l-hejEne and 1-dodecene [178]. Both, the classical Wilkinson type complex [RhCl(TPP)3] and the chiral, stereochemically pure complex (—)-(j7 -cycloocta-l,5-diene)-(2-menthyl-4,7-dimethylindenyl)rhodium(i) were applied. The Wilkinson catalyst showed low selectivity towards n-aldehydes whereas the chiral catalyst formed branched aldehydes predominantly. Hydrogenation was significant with up to 44% alkanes being formed and also a significant activity for olefin isomerization was observed. Additionally, hydroformylation was found to be slower in the ionic liquid than in toluene. Some of the findings were attributed by the authors to the lower gas solubility in the ionic liquid and the slower diffusion of the reactive gases H2 and CO into the ionic medium. 

Dzudza, A. and Marks, T.J., Efficient intramolecular hydroalkoxylation of unactivated alkenols mediated by recyclable lanthanide triflate ionic liquids scope and mechanism, Chem. Eur. J. 16, 3403-3422 (2010). 

Leclercq, L., Suisse, L, Nowogrocki, G. and Agbossou-Niedercorn, F., Halide-free highly-pure imidazolium triflate ionic liquids Preparation and use in palladium-catalysed allylic alkylation, Green Chem. 9 (10), 1097-1103 (2007). 

Dzudza A, Marks TJ (2009) Efficient intramolecular hydroalkoxylation/cyclization of unactivated alkenols mediated by lanthanide triflate ionic liquids. Org Lett 11 1523-1526... 

The second element of general importance in the synthesis of a task-specific ionic liquid is the source of the functional group that is to be incorporated. Key to success here is the identification of a substrate containing two functional groups with different reactivities, one of which allows the attachment of the substrate to the core, and the other of which either is the functional group of interest or is modifiable to the group of interest. Functionalized alkyl halides are commonly used in this capacity, although the triflate esters of functionalized alcohols work as well. 

Scheme 5.1-27 The zinc triflate-catalyzed coupling of alkynes with aldehydes to give propargyl alcohols in an ionic liquid.

Scheme 5.1-43 Three-component reaction of benzaldehyde, aniline, and diethyl phosphonate in ionic liquids, catalyzed by lanthanide triflates and indium(lll) chloride.

In order to overcome these problems, attention was focused on the use of heterogeneous catalysis. We have found that functionalized solid materials, e.g., ionic liquids or tin triflates immobilized into mesoporous materials, can be used in N-acylation reactions as environmentally friendly replacements for traditional homogeneous acids which are useful but environmentally unacceptable catalysts [17, 18]. They had comparable activity to homogeneous reagents but can offer greater stability, safer and easier handling and can be... 

The advantages of using ionic liquids as solvents for Diels-Alder reactions are exemplified by the scandium triflate catalysed reactions [14] in [bmim][PFg], [bmim][SbF6] and [bmim][OTf] for the reaction shown in Scheme 7.6. Whilst the nature of the anion seems to have little effect, all these solvents give rate enhancements for a range of Diels-Alder reactions compared to when the reactions are carried out in dichloromethane (DCM). Also, the selectivity towards the endo product is higher than in conventional solvents. As well as the enhanced rates and selectivities, the products can also be removed by extraction with diethyl ether and the ionic liquid and catalyst can immediately be reused. Experiments... 

Figure 5.8 The reactions between toluene and nitric acid in (a) a halide-based ionic liquid, (b) a triflate-based ionic liquid, and (c) a mesylate-based ionic liquid.

The solubility of a Lewis acidic salt in an ionic liquid is dependent on the nature of both the salt and the ionic liquid. Hydrophobic ionic liquids have lower solubilities for such salts. For example, metal triflates such as Sc(TfO)3 readily dissolve... 

Changing the ionic liquid anion to triflate leads to a further increase in the activity with no loss of selectivity (Scheme 3). The reaction product could be removed by extraction with diethyl ether. 

Metal triflate Lewis acids can also be dispersed in ionic liquids for catalytic applications. Acetylation of alcohols with acetic anhydride and acetic acid has been reported with Cu(OTf)2, Yb(OTf)3, Sc(OTf)3, In(OTf)3, HfClq. (THF)2, and InCl3 in ionic liquids that consist of [BMIM] and the anions BF4, PF, or SbF 166). With lmol% acid, all the catalysts in [BMIMJPF showed >99% acetylation products in acetyl anhydride acetylation of benzyl alcohol. Sc(OTf)3 showed the best yield with recycling, with a 25% drop in yield after two cycles. A relatively long reaction period was needed to obtain a high yield (95-98%) for the acetylation of benzyl alcohol with acetic acid, indicating that the activities of the catalysts were... 

Non-chlorinated Lewis acids, such as scandium triflate, were found to be good catalysts for Friedel-Crafts alkylation reactions (167). Although no aromatic hydrocarbon alkylation occurred in CH2CI2, [BMIMJPFg, Sc(OTf)3 catalyzed the alkylation of benzene with high yields of the monoalkylated product. The lower acidity of the ionic liquid led to fewer byproducts and therefore higher yields. The products were separated by simple decantation and the catalyst was reused. 

In another example, a catalytic amount of cerium triflate hydrate was dispersed and isolated in [BMIMJPFg for the direct formation of tetrahydropyranol derivatives. The reaction involves a simple homoallyl alcohol and an aldehyde. When an organic solvent such as chloroform was employed, an undesired ether derivative formed as the major product. In the ionic liquid, however, the desired tetrahydropyranol was exclusive. Although the yield was moderate, this example constitutes the first relatively facile and direct formation of the synthetically useful pyranol derivative the only effective catalyst reported is the ionic liquid (168). 

OTf)3 (5 mol%). The use of bismuth triflate/[bmim]BF4 is the ideal catalytic system for these condensations because the recovery and reuse of bismuth triflate is especially easy in ionic liquids compared to toluene. 

In subsequent studies, methyl vinyl ketone (2.0 mmole) was chosen as the dienophile so as to determine the combined effect of the ionic liquid (2 mL) and the Lewis acids (0.2 and 0.5 wt%) upon the yield and selectivity. Without the Lewis acid catalyst, this system demonstrated a 52% conversion of the cyclopentadiene (2.2 mmol) in 1 h with the endojexo selectivity being 85/15. The cerium triflate-catalyzed reaction was quantitative in 5 min and the endo. exo selectivity was very good for this experiment as well (94 6, endo. exo). Also with the scandium or yttrium salts tested, reactions came to completion in a short time with high stereo-selection. Cerium, scandium and yttrium triflates are strong Lewis acids known to be quite effective catalysts in the cycloadditions of cyclopentadiene with acyclic aldehydes, ketones, quinones and cycloalkenones. These compounds are expected to act as strong Lewis acids because of their hard character and the electron-withdrawing triflate group. On the other hand, reaction times of 1 hour were required for... 

The Heck reaction is a C-C coupling reaction where an unsaturated hydrocarbon or arene halide/triflate/sulfonate reacts with an alkene in presence of a base and Pd(0) catalyst so as to form a substituted alkene. Kaufmann et al. showed that the Heck reaction carried out in presence of ILs such as tetra-alkyl ammonium and phosphonium salts without the phosphine ligands, resulted in high yields of product. They attributed the activity to the stabilizing effect of ammonium and phosphonium salts on Pd(0) species. Carmichael et al. used ionic liquids containing either A,A -dialkylimidazolium and A-alkylpyridinium cations with anions such as halide, hexafluorophosphate or tetrafiuoroborate to carry out reactions of aryl halide and benzoic anhydride with ethyl and butyl acrylates in presence of Pd catalyst. An example of iodobenzene reacting with ethyl acrylate to give trans-et vy cinnamate is shown in Scheme 14. 

Scheme 5.1-55 The alkylation of benzene with hex-1 -ene, catalyzed by scandium(lll) triflate in ionic liquids.

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