Fluoride abstraction

A.I. Agulyansky, E.L. Tichomirova, V.T. Kalinnikov, Tes. Dokladov VIII Vses. Symposium po khim. Neorg. Ftoridov (VIII Rus. Symposium on chem.. of inorg. Fluorides. Abstracts), Nauka, Polevskoy, 1987, p. 27. 

Korobeinikov, VIII Symposium on chemistry of inorganic fluorides -Abstracts, Polevskoy, Nauka, Moscow, 1987, p. 25. 

A derived Ru(II) CF3 complex, Ru(CF3)Cl(CO)(MeCN)(PPh3)2, is a good substrate for generation of a CF2 complex using either anhydrous HC1 gas (22) or Me3SiCI as fluoride-abstracting reagents,... 

Attempted syntheses of trifluoromethyl derivatives of germanium, tin, and lead by thermal decarboxylation either resulted in decomposition of the trifluoroacetate without forming carbon dioxide (22,39,40) or gave carbon dioxide but no trifluoromethyl organometallic (22). In the latter case, the metal fluoride was detected. This suggests that the trifluoromethyl compound is thermally unstable and decomposes by fluoride abstraction. 

Reactions of organoxenonium salts [RXe][EFn+)] with Lewis acids do not result in transformation of the organo group of the cation [RXe]+ (6), but rather give rise to fluoride abstraction from the counteranion [EFn+i]. For example, organoxenonium fluoroborates were converted into [EF6]" salts by using arsenic or antimony pentafluoride or their adducts, EFj L (eqs 9, 10) (22, 30). 

Finally, the metal-perfluoroalkyl linkage also appears to be less susceptible to facile decomposition by the a- or -elimination pathways that dominate much of the chemistry of hydrocarbon alkyls and lead to metal hydrides. The absence of these reaction pathways, at least for the later transition metals, may reflect the relative strength of the C—F bond versus the M—F bond compared to C—H/M—H analogues (32). However, a-fluoride abstraction reactions can be accomplished with exogenous fluoride acceptors to give fluorinated carbene complexes (see Section III,B,1). One example of an apparent -fluorine elimination reaction is shown in Eq. (2) (33) and presumably is driven by the stronger bond to fluorine formed by early transition... 

In contrast to the results obtained in reactions of M—CF3 complexes with BF3 (see Section III,B,1), the reaction of the perfluoronickelacyclopentane complex 49 appears to proceed via fluoride abstraction, followed by phosphine migration to the electron-deficient carbon to afford the a-fluorophos-phonium ylid complex 50 and related derivatives (117). 

Bromoethynes, in iron cluster compounds, 6, 296 4-Bromothiazoles, synthesis, 9, 38-39 Br0nsted acids, in fluoride abstraction, 1, 735 Buckyferrocenes, synthesis, 6, 187 Butadienes... 

This suggests that the formation of the CF3+ cation and fluoride abstraction from SbF6- leads to the product CF4. 

In fact, this tendency is so great that it can result in the generation of unusual cations by fluoride abstraction. For example, the C1F2+ cation can be generated by the reaction... 

Kawashima et al. have devised a new method for the synthesis of monocyclic phosphoranes by the reaction of the thiophosphinate (33) with triethyloxonium tetrafluoroborate to form the phosphonium salt (34) which, on exchange of the CH2CI2 solvent for Et20, was converted quantitatively to (35) by fluoride abstraction from the counterion. 

The arsenie(V) fluoroanion [AsF6] whieh is a regular oetahedron in the salt, is well known, and often considered a noneoordinating anion. In fact, like other related speeies, it is better viewed as weakly eoordinating and is known to bind to metals in the absence of other ligands.In many cases where it is found as a product of fluoride abstraction from nonmetal... 

Fluoride abstraction requires a tertiary C-F bond which has been termed the Achilles heel of saturated fluorocarbons [68]. The reasons for this puzzling difference in reactivity are not yet clear but this observation is important to consider given the widespread use of these reagents to abstract halides in organic and organometallic synthesis. 

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