[18903-82-7]  · C8H18Cl4HgSi2  · Bis(dichlorotrimethylsilylmethyl)mercury  · (MW 512.80)

(by thermal treatment formally transfers :CClSiMe3 to alkenes, resulting in cyclopropane formation,2 and to silanes, inserting into Si-H bond2)

Physical Data: mp 143-146 °C.

Solubility: sol hexane, benzene, chlorobenzene.

Preparative Methods: reaction of Me3SiCCl2Li3 with HgBr2 at -135 °C in a solvent mixture containing THF, Et2O, and pentane furnishes the title reagent in 35% yield.2,4 For this class of silicon-containing organomercurials, the above approach has proven superior to the more classical t-BuOK procedure1 (see also Phenyl(trichloromethyl)mercury).

Purification: recrystallization from hexane.

Handling, Storage, and Precautions: flame-dried glassware and an atmosphere of dry nitrogen are used for the reactions. Organomercury 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 synthetic relevance of a-haloorganomercury compounds stems mainly from their utility in preparing cyclopropanes (see also Phenyl(trichloromethyl)mercury) by carbene transfer to simple alkenes. In this respect, bis(dichlorotrimethylsilylmethyl)mercury is quite stable thermally and does not transfer divalent carbon under mild conditions; for example, it was recovered unaltered after heating with cyclohexene at 83 °C for 7 days. However, addition of 1 equiv of Diphenylmercury results in activation of the reagent with respect to the a-haloorganomercurial.2,5 The Hg(CCl2SiMe3)2-HgPh2 system cyclopropanates cyclooctene at 125 °C under nitrogen (eq 1).2

Insertion into Si-H Bond.

Another common feature of the reactivity of a-haloorganomercurials is their easy reaction with Si-H bonds. Thus insertion of the functional carbene :CClSiMe3 into the Si-H bond takes place when a 1:1 mixture of Hg(CCl2SiMe3)2-HgPh2 is reacted with an excess of triethylsilane (eq 2).2 The PhHgCl byproduct was not isolated, but it reacts with the excess of silane under the reaction conditions, furnishing mercury and diphenylmercury.

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.; Hanson, E. M. JACS 1968, 90, 2438.
3. Seyferth, D.; Armbrecht, F. M., Jr.; Hanson, E. M. JOM 1967, 10, 25.
4. Seyferth, D.; Hanson, E. M.; Armbrecht, F. M., Jr. JOM 1970, 23, 361.
5. Seyferth, D.; Hanson, E. M. JOM 1971, 27, 19.

José Barluenga, Miguel Tomás & José M. González

Universidad de Oviedo, Spain

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