Fluorocarbon unsaturated

The reaction of OF2 and various unsaturated fluorocarbons has been examined (35,36) and it is claimed that OF2 can be used to chain-extend fluoropolyenes, convert functional perfluorovinyl groups to acyl fluorides and/or epoxide groups, and act as a monomer for an addition-type copolymerization with diolefins. 

Although fluorocarbons are considered very stable compounds, they can be defluonnated to unsaturated denvatives under certain mild conditions. Hexa-decafluorobicyclo[4.4.0]dec-I(6)-ene reacts with activated zinc powder at 80-100 °C to yield partially and fully aromatized products [61] The final product composition depends on the solvent. Dioxane, acetonitrile, and dimethylform-amide, m this order, effect increasing unsaturation (equation 30). 

Unsaturated fluorocarbons are much more reactive toward nucleophiles than then hydrocarbon counterparts owing to fluorme s ability to both stabihze carban ions and mductively increase the electrophihcity of multiple bonds and aromatic nngs Nucleophihc attack dominates the chemistry of unsaturated fluorocarbons, and the role of fluonde ion in fluorocarbon chemistry is analogous to that of the proton in hydrocarbon chemistry [129] Like the related electrophilic reactions for hydrocarbons, there are fluonde-promoted isomenzations and dimenzations (equation 9), oligomenzations (equation 10), additions (equation 11), and amomc Fnedel-Crafts alkylations (equation 12) that all proceed via carbamomc intermediates [729 7 7]... 

As a ligand towards metals, C2F4 and other unsaturated fluorocarbons differ markedly from alkenes (p. 931). 

In contrast to their hydrocarbon analogues, many unsaturated fluorocarbons react with anionic transition metal nucleophiles to yield products arising from net displacement of fluoride ion. This synthetic approach has been successful in producing a host of fluorovinyl and fluoroaryl complexes (95-110). 

It is claimed that addition of catalytic quantities of a quaternary ammonium salt greatly enhances both reactivity and yield [48] in the formation and subsequent reactions of (58). Tertiary fluorinated carbanions, generated from corresponding unsaturated precursors, react with a variety of electrophiles [46, 49,50] (Scheme 25), the most surprising being with fluorocarbon iodides, to give remarkable fluoride-bridged products, e. g. (60) [47],... 

Table 3. Some nucleophilic reactions of unsaturated fluorocarbons ...

Reactions of cyanide with unsaturated fluorocarbons have been reported and an example is shown below [119,120] (Scheme 56). 

Polytetrafluoroethylene (PTFE) was subjected to 3 keV electron bombardment and then heated in vacuum to 300 C. The behavior of the material as a function of radiation dose and temperature was studied by x-ray photoelectron spectroscopy (XPS) of the surface and mass spectroscopy of the species evolved. Lightly damaged material heated to 300 C evolved saturated fluorocarbon species, whereas unsaturated fluorocarbon species were evolved from heavily damaged material. 

Also at these temperatures and doses both saturated and unsaturated fluorocarbon species were evolved from the surface. 

Fluoride-ion-induced reactions A similar polymer to that in Figure 7.87 is obtained upon anionic polymerisation of hexafluoro-2-butyne initiated by fluoride ion in a solvent [311-313] (Figure 7.89). This is a clear example of an anionic polymerisation of an unsaturated fluorocarbon, although the growing anion can be trapped by a sufficiently reactive system [291, 314], such as pentafluoropyridine [315] (Figure 7.90). There is little difference between the ultraviolet spectra of 7.90A and 7.90B, confirming that conjugation in the polyene system is inhibited by steric effects. 

It will become clear that, in some cases, the classical routes to organometallics are not available but, compensating for this, the different chemistry of, for example, unsaturated fluorocarbons has often been exploited to provide quite new synthetic approaches. 

Alkenyl and aryl derivatives of transition metals are generally more stable than the corresponding alkyl derivatives. This has been attributed to the unsaturated groups being able to accept charge from the metal via tt orbitals. This process should be enhanced by the introduction of fluorine or fluorocarbon groups into the alkene or aromatic compound. 

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