Perfluoroalkyl cations

Aryl-A3-iodanes bearing an electron-deficient alkyl ligand such as aryl(sul-fonylmethyl)-A3-iodanes (Section 3.2.7) and aryl(perfluoroalkyl)-A3-iodanes are relatively stable. A series of (perfluoroalkyl)phenyl-A3-iodanes 96 were synthesized in good yields by treating bis(trifluoroacetoxy)-A3-iodanes with benzene in the presence of triflic acid [47]. The AModanes 96 transfer the perfluoroalkyl groups to a variety of nucleophiles with reductive elimination of iodobenzene. The nucleophiles involve Grignard reagents, alkyllithiums, enolate anions, alkenes, alkynes, trimethylsilyl enol ethers, arenes, phenols, and thiols. In these reactions, the AModane 96 serves as a source of the perfluoroalkyl cation and, in... 

Cationic alkylation of phenol takes place by the action of perfluoroalkyl-phenyliodonium trifluoromethanesullonates [161] (equation 138)... 

Cobalt trifluoride fluorination corresponds to the electron-transfer mechanism via a radical cation. RF groups attached to the ring enhance the stability of intermediate dienes and monoenes. Perfluoroalkyl pyridines, pyrazines, and pyrimidines were successfully fluorinated but pyridazines eliminated nitrogen. The lack of certain dienes was attributed to the difference in stability of FC=C and RFC=C and steric effects [81JCS(P1)2059]. 

A cationic complex, formed in situ from 5 and [Rh(COD)2]OTf, was also active in biphasic hydrogenation [14]. No preference for the fluorous phase was found for ligands containing only one perfluoroalkyl tail, but neutral and cationic complexes, containing mono- and bidentate 4a or 5, respectively, were selectively dissolved in the fluorous phase. No leaching and recycling studies were performed. 

Various classes of cationic surfactants, including quats, esterquats, alkyl ethoxy amines, quaternary perfluoroalkyl ammoniums and gemini surfactants have been analysed extensively with LC—MS and LC—MS—MS techniques, and their spectra have been fully characterised. Different ionisation methods have been applied for the detection of such surfactants, including API techniques (APCI and ESI) in negative and positive modes of operation. In addition, detailed examples regarding MS—MS fragmentation of these compounds have been reported and presented in this chapter. 

Aminoenone (87), when heated with phosphoryl chloride, cyclizes to 2-(trif uoro-methyl)quinoline, rather than the expected 4-isomer.126 A series of crossover experiments using different perfluoroalkyl and aniline moieties suggest an amine exchange process. A 1,3-diaminoallyl cation (88), i.e. a vinylogous formidinimn salt, is proposed to act as turntable in the process. 

Perfluoroalkyl compounds have been manufactured since the 1950s.The total production of fluorinated surfactants (anionic, cationic and neutral) was 2001 in 1979, whereas in 2000 the total production of PFOS (perfluorooctane sulfonate) alone was nearly 3000t (Shoeib et al., 2004). Together with PFOA (perfluoroocta-noic acid), PFOS is used in refrigerants, surfactants, fire retardants, stain-resistant coatings for fabrics, carpets and paper and insecticides. Surface treatments, such as protection of clothing and carpets constitute the largest volume of PFOS production (Moriwaki, Takata and Arakawa, 2003). PFOA as well is present in several... 

The synthesis of chlorine (I) and bromine (I) trifluoromethanesulfonates (triflates) was reported by DesMarteau. Stability and reactivity of these materials are similar to those of perfluoroalkyl hypohalites. Both compounds readily react at low temperature with a variety of fluoroolefins. Based on NMR analysis of the products of adding CF3S020X to pure cis- or trans-isomers of 1, 2-difluoroethylene, it was concluded that the reaction proceeds as syn-addition [35]. This statement was later criticized [18], since the assignment of stereoisomers was found to be incorrect. According to [18], addition of CF3S020X to haloolefins, as well as reactions of ClF, BrF and IF proceed as anti-addition via cyclic halonium cationic intermediates. 

Several cationic 7r-cyclopentadienylcobalt derivatives have been prepared. Treichel and Werber (235, 236) have produced a number of perfluoroalkyl complexes [CpCo(CO)LRF]+CI04-, where L = PPh3, CH3CN, py and Rf= C2F5, C3F7. The stability of these cations approximately parallels the... 

Systems with perfluoroalkyl groups directly attached to the double bond are particularly unreactive towards electrophiles but reaction of hexafluoropropene (HFP) with SbFs leads to a perfluoroallyl cation, which then reacts with another molecule of HFP to give a dimer, probably by an electrophilic process [168] (Figure 7.51) that is analogous to that described earlier for 1,1,1-trifluoropropene [169], (Chapter 4, Section VIB). Similar addition and isomerisation reactions, which proceed via carbocationic intermediates, are given in Figure 7.52 [170-172]. 

The first examples of 3,6-(perfluoroalkyl)-l,2-dithiins have been obtained through the oxidative deprotection and cyclisation of (Z,Z)-l,4-6 (t-butylthio)-l,4-6w(perfluoroalkyl)-1,3-butadienes. They adopt a similar twist geometry to the parent dithiin and during electrochemical oxidation appear to form a planar radical cation (Scheme 29) <03JOC8110>. 

Chiral cationic Rh catalysts for the hydrogenation of prochiral C-C double bonds require the use of BARF or related anions even with potentially CO2-S0IU-ble ligands such as Et-DuPHOS (DuPHOS l,2-bis(2,5-dialkylphospholano)-benzene) [70] or a perfluoroalkyl-substituted aryl phosphonite [19]. The ligand... 

FAP]- Tris(perfluoroalkyl)trifluorophosphate For cations, n represents the carbon number of the alkyl chain, i.e.. ethyl = 2, butyl = 4, etc. 

In addition to the arenes, enolates, and other nucleophiles depicted in Scheme 2.142, FITS reagents are also reactive in the perfluoroalkylation of unactivated alkenes, alkadienes [19], and acetylenes [20] (Scheme 2.146). In contrast with olefin perfluoroalkylation by means of perfluoroalkyl bromides or iodides (Section 2.2.1), this reaction does not follow a free radical mechanism but proceeds via cationic intermediates which can be either trapped by addition of nucleophiles or nucleophilic solvents or quenched by -deprotonation with a base (Scheme 2.147). 

In these reactions, the ligand coupling mechanism is not involved. A different mechanism operates the formation of an intermediate cationic species which is likely to result from the initial formation of a Tc-complex (106).212 Such a mechanism has been invoked to explain the perfluoroalkylation of a number of ethylenic and acetylenic compounds.213-215... 

The reaction of enol trimethylsilyl ethers of carbonyl compounds with (a,a-dihydroperfluoroalkyl) phenyliodonium triflates required promotion by potassium fluoride to proceed at room temperature to give the P-perfluoroalkyl carbonyl compounds in good yields.225 in the case of the silyl enol ether of an a,p-unsaturated ketone (119), the 6-perfluoroalkyl-o,p-unsaturated carbonyl compound (120) was the only product formed. The reaction is likely to follow a path similar to the one used in the reaction of silyl enol ethers with (perfluoroalkyl)phenyliodonium salts. In a first step, a ic-complex is formed which evolves into the cationic product of a- or y-addition, followed by desilylation to the carbonyl reaction product. 

Ring-opening cationic polymerization of a perfluoroalkyl-substituted oxetane monomer using a Lewis acid catalyst and a diol initiator leads to an amphiphilic a, co-diol. Sulfation of the terminal hydroxyl groups leads to an anionic bola-amphiphile. 

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