Phenyl mercury Seyferth

The observation that phenyl(trichloromethyl)mercury undergoes dissociation at 150 °C to give phenyl-mercury(II) chloride and dichlorocarbene has led to a wide range of organomercury compounds (PhHgCX3 — Seyferth reagents)15-18 which serve as efficient dihalocarbene transfer reagents (equation... 

Treatment of the title compound with an aqueous base under phase-transfer catalysis conditions generates, by a-elimination, chloro(trifluoromethyl)carbene that can be trapped by cycloaddition to allylsilane and allylstannane derivatives, e.g. formation of 1 and 2. This method represents a fast and mild alternative to the Seyferth method that starts from the same alkyl halide and generates the carbene by thermal decomposition of l-bromo-l,2,2,2-tetra-fluoroethyl(phenyl)mercury (see Section 1.2.1.2.4.1.1). 

Many other examples, in particular reactions of dihalocarbenes obtained by phase-transfer catalyzed a-elimination of the corresponding trihalomethane derivatives, confirm the stereospecificity of these cycloadditions. This is also valid for most cyclopropanations performed with dibromomethylene obtained from phenyl(tribromomethyl)mercury (Seyferth reagent2, see Vol. IV/3, p 179), however, a few exceptions have been reported3. 

Seyferth et al. (//O) have also synthesized N,N-diethyl-trichlorovinyl-amine (128, R CjHj) from the reaction of triethylamine and phenyl-(trichloromethyl)mercury (138). The best yield was 23 %, obtained when a benzene solution of the amine (45 mM) was added to a refluxing solution of phenyl(trichloromethyl)mercury (10 mM) in benzene. Although no mechanistic study was attempted because of the low yields and the intractable nature of the reaction mixture, the authors proposed the following mechanistic sequence ... 

Seyferth (7) discovered that phenyl(trihalomethyl)mercury compounds decompose when heated in a solvent giving dihalocarbenes. When the solvent contains a suitable olefin, carbene addition occurs giving 1,1-dihalocyclopropane derivatives. The reaction has the advantage that strong base is not required in the reaction mixture, and base-... 

The advantages of this method of carbene synthesis are that reaction can be carried out in neutral solution, and that reaction yields are often dramatically improved. Thus, although reactions of dihalocarbenes generally do not give rise to products corresponding to single bond insertion, Seyferth has reported insertion of phenyl (trihalomethyl) mercury-generated carbenes into... 

Examples of carbene insertions into the carbon-silicon bond of SCBs have been known since 1967, when Seyferth studied the behavior of SCBs exposed to dichlorocarbene, which was generated by thermolytic activation of phenyl(bromodichloromethyl)mercury <1967JA1538>. The reaction produces a mixture of products arising from Si-C and C-H bond insertions, with the major products being the ring-expanded silacyclopentanes that result from Si-C bond insertions (Scheme 30). 

As mentioned earlier, the carbene ligand in our complexes shows nucleophilic character with respect to the metal fragment. Therefore, we decided to combine it with an electrophilic carbene. For this purpose we treated pentacarbonyl[methoxy(phenyl)carbene]chromium(0) with phenyl(tri-chloromethyl) mercury (85). Compounds of this kind have been studied intensively by Seyferth et al. (86) and are known as a source of dihalogeno-carbenes. The carbene complex reacted with the carbenoid compound at... 

Seyferth and coworkers504 have also synthesized N,N-diethyltrichlorovinylamine from the reaction of triethylamine and phenyl(trichloromethyl)mercury. 

Seyferth, D. 1972. Phenyl(trihalomethyl)mercury compounds. Exceptionally versatile dihalocarbene precursors. Acc Chem Res 5, 65-74. 

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. 

Review. The chemistry of phenyl(trihalomcthyl)mercury compounds has been reviewed by Seyferth. ... 

Tor a review of the use of phenyl(trihalomethyl)mercury compounds as dihalocarbene or dihalocarbenoid precursors, see Seyferth, D. Acc. Chem. Res. 1972, 5, 65. For a review of the synthesis of cyclopropanes with the use of organomercury reagents, see Larock, R.C. Organomercurcury Compounds in Organic Synthesis, Springer, NY, 1985, pp. 341-380. 

Preparation. Reutov and Lovtsova prepared phenyl(trichloromethyl)mercury (II) by reaction of phenylmercuric chloride with potassium r-butoxide and chloroform in benzene. Use of bromoform affords I. Seyferth and Burlitch, who carried... 

Diisopropylcarbodiimide heated at ca. 80° with 2 moles phenyl (bromodichloro-methyl) mercury in chlorobenzene until phenylmercuric bromide starts to precipitate N-isopropyldichlorazomethine. Y 92%. F. e. s. D. Seyferth and R. Damrauer, Tetrah. Let. 1966, 189. 

The work of Seyferth s group on phenyl(trihalogenomethyl)mercury compounds as dihalogenocarbene precursors has been reviewed. "... 

Triphenylsilane heated 2-4 hrs. with phenyl (bromodichloromethyl) mercury in benzene at ca. 80° until thin layer chromatography shows that all of the mercurial has been consumed triphenyl (dichloromethyl) silane. Y 90%. F. e., also insertion into G-H bonds, s. D. Seyferth and J. M. Burlitch, Am. Soc. 85, 2067 (1963). 

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