Metal trifluoromethanesulfonates

Rare Earth Metal Trifluoromethanesulfonates as Water-Tolerated Lewis Acid Catiaysts Organic Synthesis," Kobavashi. Synlett, 1994, 679... 

N-Tfa- and iV-Fmoc-a-amino ketones have been synthesized56 by reaction of some N -heterocycles or benzene with chiral AM Tfa- and Fmoc-a-aminoacyl)benzotriazoles [e.g. (49)] in the presence of aluminium trichloride. Full preservation of chirality was reported. Aromatic side-chains in some of the (a-amineacyl)benzotriazole compounds gave a competitive intramolecular cyclization, again with retention of chirality [e.g. (49) to (50)]. A full report57 on the intramolecular acylation of aromatics with Meldrum s acid derivatives catalysed by metal trifluoromethanesulfonates under mild reaction conditions has appeared [e.g. (51) to (52)]. The method tolerates many functional groups and was extended to the synthesis of 1-tetralones, 1-benzosuberones and donepezil (53). 

Traditionally Lewis acid catalysed reactions often utilise metal halides, however in recent years, metal trifluoromethanesulfonates or triflates having the general formula Mn+(S02CF3)n have been reported as a new and interesting type of Lewis acid4. These... 

C. C. Wang, S. Y. Luo, C. R. Shie, and S.-C. Hung, Metal trifluoromethanesulfonate-catalyzed regioselective borane-reductive ring opening of benzylidene acetals A concise synthesis of 1,4-dideoxy-l,4-imino-L-xylitol, Org. Lett., 4 (2002) 847-849. 

Metal-catalyzed hydroarylation of alkynes catalyzed by electrophilic transition metal complexes has received much attention as a valuable synthetic alternative to the Heck and cross-coupling processes for the synthesis of alkenyl arenes (384). Metal trifluoromethanesulfonates (metal triflates) [M(OTQn M = Sc, Zr, In] catalyze the hydroarylation of alkynes via 71 complexation to give 1,1-diarylalkenes in very good yields (Scheme 32) (385). The reaction likely proceeds by a Friedel-Crafts mechanism via the alkenyl cation intermediate where the aryl starting material also serves as the solvent. 

Kobayashi, S. 1994. Rare earth metal trifluoromethanesulfonates as water-tolerant Lewis acid catalysts in organic synthesis. Synlett 689-701. 

In certain cases, homoleptic solvento-complexes containing halides as counterions have been prepared (see Table 4.2). In general, preparation of such homoleptic solvento-complexes is of limited use due to the difficulties inherent in the preparation of the necessary anhydrous salts. In recent years it has been found that trifluoromethanesulfonate salts are easily prepared in anhydrous form. The CF3S03 ion only rarely fomas isolable complexes in which it is coordinated to a metal ion and is normally a weaker donor than the perchlorate anion. Unlike the common perchlorate salts, metal trifluoromethanesulfonates are not typically explosive under normal laboratory conditions. Thus, anhydrous met trifluoromethanesulfonates are very useful precursors in the preparation of homoleptic solvento-complexes. 

Perchloric acid (HCIO4 Ho —13.0), fluorosulfuric acid (HSO3F Ho — 15.1), and trifluoromethanesulfonic acid (CF3SO3H Ho —14.1) are considered to be superacids, as is truly anhydrous hydrogen fluoride. Complexing with Lewis acidic metal fluorides of higher valence, such as antimony, tantalum, or niobium pentafluoride, greatly enhances the acidity of all these acids. 

The metallic salts of trifluoromethanesulfonic acid can be prepared by reaction of the acid with the corresponding hydroxide or carbonate or by reaction of sulfonyl fluoride with the corresponding hydroxide. The salts are hydroscopic but can be dehydrated at 100°C under vacuum. The sodium salt has a melting point of 248°C and decomposes at 425°C. The lithium salt of trifluoromethanesulfonic acid [33454-82-9] CF SO Li, commonly called lithium triflate, is used as a battery electrolyte in primary lithium batteries because solutions of it exhibit high electrical conductivity, and because of the compound s low toxicity and excellent chemical stabiUty. It melts at 423°C and decomposes at 430°C. It is quite soluble in polar organic solvents and water. Table 2 shows the electrical conductivities of lithium triflate in comparison with other lithium electrolytes which are much more toxic (24). 

High enantioselectivities may be reached using the kinetic controlled Michael addition of achiral tin enolates, prepared in situ, to a,/i-unsaturated carbonyl compounds catalyzed by a chiral amine. The presence of trimethylsilyl trifluoromethanesulfonate as an activator is required in these reactions236. Some typical results, using stoichiometric amounts of chiral amine and various enolates are given below. In the case of the l-(melhylthio)-l-[(trimethylsilyl)thio]ethene it is proposed that metal exchange between the tin(II) trifluoromethanesulfonate and the ketene acetal occurs prior to the 1,4-addition237,395. 

Rare earth metals and scandium trifluoromethanesulfonates (lanthanide and scandium triflates) are strong Lewis acids that are quite effective as catalysts in... 

The addition reactions discussed in Sections 4.1.1 and 4.1.2 are initiated by the interaction of a proton with the alkene. Electron density is drawn toward the proton and this causes nucleophilic attack on the double bond. The role of the electrophile can also be played by metal cations, and the mercuric ion is the electrophile in several synthetically valuable procedures.13 The most commonly used reagent is mercuric acetate, but the trifluoroacetate, trifluoromethanesulfonate, or nitrate salts are more reactive and preferable in some applications. A general mechanism depicts a mercurinium ion as an intermediate.14 Such species can be detected by physical measurements when alkenes react with mercuric ions in nonnucleophilic solvents.15 The cation may be predominantly bridged or open, depending on the structure of the particular alkene. The addition is completed by attack of a nucleophile at the more-substituted carbon. The nucleophilic capture is usually the rate- and product-controlling step.13,16... 

Allylations, allenylations, and propargylations of carbonyl compounds in aqueous media can also be carried out with preformed organic tin reagent, rather than the use of metals.86,87,88 For example, the allylation reaction of a wide variety of carbonyl compounds with tetraal-lyltin was successfully carried out in aqueous media by using scandium trifluoromethanesulfonate (scandium triflate) as a catalyst (Eq. 8.40).89 A phase-transfer catalyst (PTC) was found to help the allylation mediated by tin at room temperature without any other assistance.90... 

Because trifluoromethanesulfonic acid is a stronger acid than perchloric acid, under no circumstances should perchlorate salts be used with the neat acid, because the hot anhydrous perchloric acid so formed represents an extreme explosion hazard, especially in contact with transition metal complexes (or with organic materials). See Perchloric acid Dehydrating agents See other ORGANIC ACIDS... 

Recently, there has been considerable interest in developing molten salts that are less air and moisture sensitive. Melts such as l-methyl-3-butylimidazolium hexa-fluorophosphate [211], l-ethyl-3-methylimidazolium trifluoromethanesulfonate [212], and l-ethyl-3-methylimidazolium tetrafluoroborate [213] are reported to be hydro-phobic and stable under environmental conditions. In some cases, metal deposition from these electrolytes has been explored [214]. They possess a wide potential window and sufficient ionic conductivity to be considered for many electrochemical applications. Of course if one wishes to take advantage of their potential air stability, one loses the opportunity to work with the alkali and reactive metals. Further, since these ionic liquids are neutral and lack the adjustable Lewis acidity common to the chloroaluminates, the solubility of transition metal salts into these electrolytes may be limited. On a positive note, these electrolytes are significantly different from the chloroaluminates in that the supporting electrolyte is not intended to be electroactive. 

Facile C-H bond activation by Pt(II) metal centers seems to require at least one labile ligand in the coordination sphere of platinum. One of the earliest intermolecular examples of this is the activation of C-D bonds in benzene-f/, by 0 an.S -(PAIe .) Pt(neopentyl)(OTf) at 133 °C, where trifluoromethanesulfonate (triflate, OTf) provides the labile group (Scheme 7, A) (26). 

Krypton difluoride, 4313 Potassium hexaoxoxenonate-xenon trioxide, 4674 Tetrafluoroammonium hexafluoroxenate, 4386 Xenon difluoride dioxide, 4322 Xenon difluoride oxide, 4319 Xenon difluoride, 4332 Xenon hexafluoride, 4377 Xenon tetrafluoride, 4353 Xenon tetrafluoride oxide, 4346 Xenon tetraoxide, 4863 Xenon trioxide, 4857 Xenon(II) fluoride methanesulfonate, 0443 Xenon(II) fluoride perchlorate, 3977 Xenon(II) fluoride trifluoroacetate, 0634 Xenon(II) fluoride trifluoromethanesulfonate, 0356 Xenon(IV) hydroxide, 4533 Xenon(II) pentafluoroorthoselenate, 4382 Xenon(II) pentafluoroorthotellurate, 4383 Xenon(II) perchlorate, 4110 See Other NON-METAL HALIDES, NON-METAL OXIDES... 

Silver ions (as silver trifluoroacetate or trifluoromethanesulfonate), Cu", and other transition metal ions in their 1h- oxidation state [99,100] are frequently employed to obtain [M-rmetal] ions from non-functionalized or at least nonpolar hydrocarbons, [101] polyethylene, [102,103] or polystyrene (for an example see Chap. 10.5.1). [99,100,104-106]... 

Interestingly, salts other than tin(ll) bis-(2-ethylhexanoate) such as scandium and tin trifluoromethanesulfonate [41 3], zinc octoate [44, 45], and aluminum acetyl acetonate [45] were reported to mediate the ROP of lactones. As far as scandium trifluoromethanesulfonate is concerned, the main advantage is the increase of its Lewis acidity enabling the polymerization to be carried out at low temperatures with acceptable kinetics. Later, faster kinetics were obtained by extending the process to scandium trifluoromethanesulfonimide [Sc(NTf2)3] and scandium nonafluorobutanesulfonimide [Sc(NNf2)3] and to other rare earth metal catalysts (metal=Tm, Sm, Nd) [46]. 

Substituted 3,6-dialkoxy-2,5-dihydropyrazines are regioselectively metalated by strong alkyl-lithium bases, such as butyllithium, (l-methylpropyl)lithium, fcrf-butyllithium, or lithium diiso-propylamide, at the less substituted carbon atom (C5). Metalation proceeds at low temperatures (in general, below — 70 C) in THF as solvent. Electrophiles suitable for alkylation of the lithiated derivatives include alkyl iodides, bromides and chlorides, as well as alkyl methanesulfonates, 4-methylbenzenesulfonates and trifluoromethanesulfonates. The electrophile adds trans to the substituent at C2 in a highly stereoselective fashion, with typical diastereomeric excesses of greater than 90% (syn addition has been reported in only one case where a-methylphenyl alanine was used as chiral auxiliary and an alkyl trifluoromethanesulfonate as electrophile18). 

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