[42201-75-2]  · C8H5BrF4Hg  · 1-Bromo-1,2,2,2-tetrafluoroethyl(phenyl)mercury  · (MW 457.62)

(excellent source of tetrafluoroethylidene, :CFCF3; cyclopropanates alkenes; inserts into Si-H bonds; reacts with C=S bonds)

Physical Data: mp 121-122 °C.

Solubility: sol THF, benzene, dichloromethane.

Analysis of Reagent Purity: spectroscopic data: IR, NMR (1H and 19F).2

Preparative Method: prepared in 65% yield by reaction of PhHgCl with CF3CHFBr in dry THF in the presence of MeONa-MeOH.2,3

Purification: recrystallization from hexane (colorless prisms).

Handling, Storage, and Precautions: flame-dried glassware and an atmosphere of dry nitrogen are used for the reactions. Organomercury(II) compounds should be carefully handled and skin contact and inhalation should be particularly avoided. All reactions must be conducted in a well-ventilated hood.

Cyclopropanation of Alkenes.

The reagent was introduced3 as an attractive alternative source of divalent :CFCF3 to circumvent problems of volatility and toxicity4 associated with Hg(CFBrCF3)25 and Hg(CFClCF3)2.6 In this context, PhHgCFBrCF3 has proven to be a valuable and synthetically useful reagent for transferring tetrafluoroethylidene to alkenes. Its reaction with several representative alkenes has been studied; for instance, cyclopropanation of cyclooctene occurs with almost quantitative yield (isomer ratio based on 19F NMR data) (eq 1).

As anticipated, thermal treatment of PhHgCFBrCF3 transfers the :CFCF3 species and eliminates PhHgBr with no evidence of competitive PhHgF formation being observed.7,8 Another interesting feature is that the yield of cyclopropane formation and mercury elimination correlates well and, thus, side reactions do not take place.9 Reactions were carried out in sealed tubes and similar results are obtained for acyclic mono- and disubstituted alkenes. Allylsilane is also a good partner for PhHgCFBrCF3, affording the corresponding cyclopropane in 93% yield; however, in the case of vinylsilane the yield is quite low (16%) and does not correlate well with the amount of PhHgBr recovered from the reaction mixture (60%). Finally, PhHgCFBrCF3 is superior to PhHgCFClCF3 as a source of :CFCF3; the latter requires longer reaction times (typically 5 days at 140 °C).10

Insertion into Si-H Bond.

Thermal reaction of Et3SiH with PhHgCFBrCF3 furnishes Et3SiCHFCF3 in 53% yield after 24 h at 155 °C in a sealed tube,2 the result of insertion of divalent carbon into the Si-H bond.1

Reaction with Thiobenzophenone.

The C=S bond of thiobenzophenone reacts with the organomercury reagent at 155 °C for 40 h in a sealed tube, affording Ph2C=CFCF3 and sulfur (eq 2).2 The expected thiirane ring is not isolated, although it is presumably formed; instead it probably undergoes, under the reaction conditions, sulfur extrusion to the observed alkene, as depicted (eq 2).

1. (a) Seyferth, D. PAC 1970, 23, 391. (b) Seyferth, D. ACR 1972, 5, 65. (c) Zeller, K.-P.; Straub, H. MOC 1974, 13/2b, 351. (d) Larock, R. C. Organomercury Compounds in Organic Synthesis; Springer: Berlin, 1985; Chapter X, pp 327-413.
2. Seyferth, D.; Murphy, G. J.; Woodruff, R. A. JOM 1975, 92, 7.
3. Seyferth, D.; Murphy, G. J. JOM 1973, 52, C1.
4. Aldrich, P. E.; Howard, E. G.; Linn, W. J.; Middleton, W. J.; Sharkey, W. H. JOC 1963, 28, 184.
5. Tarrant, P.; O'Connor, D. E. JOC 1964, 29, 2012.
6. Krespan, C. G. JOC 1960, 25, 105.
7. Seyferth, D.; Hopper, S. P.; Darragh, K. V. JACS 1969, 91, 6536.
8. Seyferth, D.; Haas, C. K.; Hopper, S. P. JOM 1971, 33, C1.
9. Seyferth, D.; Woodruff, R. A.; Mueller, D. C.; Lambert, R. L. Jr. JOM 1972, 43, 55.
10. Seyferth, D.; Mueller, D. C. JACS 1971, 93, 3714.

José Barluenga, Miguel Tomás, & José M. González

Universidad de Oviedo, Spain

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