Difluorocarbene, direct

Trifluoromethylzinc compounds can be prepared via the direct reaction of dihaloditluoromethane with zinc powder in DMF [J5] (equation 24) In this reaction, the DMF functions both as solvent and reactant Mechanistic experiments support a difluorocarbene reaction intermediate Indeed, a mixture of zinc and difluorodibromomethane in THF has been used for the synthesis of gewi-difluo-ro-cyclopropane derivatives [34 (equaUon 25)... 

CVD processes can also be used to grow polymers from nanocarbons. An important example is the coating of a CNT forest with a thin layer of poly(tetrafluorethlylene) (PTFE) via hot filament CVD to produce a superhydrophobic substrate [245]. Here, a vertically aligned MWCNT forest was prepared and placed in a CVD reaction chamber. Hexafluorpropylene oxide gas was then thermally decomposed to form the reactive radical difluorocarbene (CF2) and flowed over the CNT substrate along with a small amount of initiator where direct polymerization of PTFE onto the CNTs occurred [245]. 

Trifluoromethylzinc reagent can be prepared from the direct reaction of dihalodifluoromethane and zinc in DMF [42] (Scheme 13). In this remarkable reaction, DMF functions both as a solvent and reactant, and difluorocarbene is the reactive intermediate, based on mechanistic experiments. Dolbier et al. have utilized this reaction as a difluoromethylene cyclopropanation reaction [43] (Scheme 14). 

Seyferth concludes that phenyl(lrifluoromethyl)mercury is an excellent precursor for difluorocarbene. In the general procedure, 1 molar eq. of CeHjHgCFj, 2.5-3.0 molar eq. of well-dried sodium iodide, and 3.0 molar eq. of the dried olefin are used (N2). Benzene is distilled into the reaction flask directly from sodium benzophenone ketyl. The reaction mixture is stirred and heated at reflux under Nj for 12 18 hr. Filtration removes phenyl mercuric iodide and Nal and Nab" the gem-difluorocyclo-propanes are isolated by distillation or by gas chromatography, usually in good yield. 

More direct evidence for the formation of difluorocarbene as an intermediate comes from the photolysis of difluorodiazirine in the presence of chlorine, iodine, dinitrogen tetroxide, and nitryl chloride when the corresponding difluoromethane derivatives were formed, and in the presence of isobutene, buta-l,3-diene, and cis- and frans-but-2-ene when the corresponding 1,1-difluorocyclopropane derivatives were formed. Even with considerable excesses of olefins, appreciable tetra-... 

This rearrangement can be conveniently combined with the addition of difluorocarbene to afford 3-fluorofurans directly from a, -unsaturated ketones. Treatment of 17 -benzoyloxy-2-benzylidene-5a-androstan-3-one (23) in refluxing triglyme with 30 equivalents of sodium chloro-difluoroacetate (see Section 1.A.1.2.1.4.) afforded, after column chromatography, the furan 24 in 52% yield. ... 

The major polymerizable products of the plasma can, therefore, be summarized as (CF2)n which, as will be seen later, can be derived either directly from the injected monomer by electron impact or from reactions involving tetrafluoroethylene and difluorocarbene formed as a consequence of the etching process, the latter mechanism being the more favorable. It is interesting to note that these observations... 

However, carbenes react with dienes 6.457 to give vinylcyclopropanes 6.458, avoiding the symmetry-allowed [2 + 4] cycloaddition with a linear approach giving cyclopentenes 6.456. Almost the only exceptions to this pattern are the reaction of difluorocarbene with norbornadiene, where a [2 + 2 + 2] reaction is in competition with the [2 + 2],934 and the [2 + 4] pathway taking place in the opposite direction in the easy loss of carbon monoxide from strained cyclopentenones as in the decarbonylation 6.408 6.409. 

Fluorodiazirines have also been used extensively as carbene photoprecursors for cryogenic matrix isolation " and laser flash photolysis studies. Photolysis of fluorophenoxydiazirine has made observation of the corresponding carbene directly observable in yet another fashion encapsulated in a hemicarcer-and. Diazirines have been used for studies in solution of carbene philicities as well as for synthesis of cyclopropanes and cyclopropenes.Of course, diazo compounds can also serve as carbene photoprecursors, but for carbenes such as difluorocarbene, the diazo precursor is either nonexistent or extremely unstable. 

Vapor deposition is a highly desirable method for modifying surfaces with fluo-ropolymers and has been extensively reviewed [1-6], In chemical vapor deposition (CVD), one or more reactants are metered into a vacuum chamber. Inside the CVD reactor, monomer vapors undergo polymerization and thin film formation in a single step. In the case of vinyl polymerization, monomer vapors are inttoduced directly into the CVD chambers as reactants. Alternatively, less stable monomers, such as difluorocarbene (CFj ), can be generated via in situ reaction (Table 7.1). 

Russian workers have shown that co-pyrolysis of hexafioorobenzene with polytetrafluoioethylene at 550 °C in an autoclave yields perfluorotoluene, niainly, and a mixture of peiftnoioj lenes in which the meta-isomer predominates. This lends support to their proposal that the formation of perfluorotoluene via pyrolysis of hexafluorobenzene and during thermal fluorination of hexachlorobenzcne with potassium fluoride (which also yields chloroheptafluorotoluenes, principally m-Cl CaFi CF, and perfluoro-mesitylene ) involves the generation of difluorocarbene, as does the conclusion that direct expulsion of difluorocarbene occurs from the molecular ion of hexafluorobenzene (CeF," - CsFi -f CFj) (see also p. 256). 

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