(Dibromomethyl)trimethylsilane

Me3SiCHBr2

[2612-42-2]  · C4H10Br2Si  · (Dibromomethyl)trimethylsilane  · (MW 246.03)

(reagent for the preparation of vinylsilanes)

Alternate Name: trimethyl(dibromomethyl)silane.

Physical Data: bp 49.5-51.5 °C/12 mmHg; d 1.519 g cm-3.1b

Solubility: sol most organic solvents.

Preparative Method: to a dry, 1.0 L three-neck flask, equipped with a mechanical stirrer, a pentane thermometer, a nitrogen inlet tube, and a pressure-equalizing addition funnel, was added 62.0 g (0.245 mol) of Bromoform and 300 mL of dry THF. The reaction was cooled to -90 °C and 0.25 mol of isopropylmagnesium chloride in 200 mL of THF was added during 30 min at such a rate that the temperature was kept at -80 °C or below. The reaction was stirred at -90 °C for 15 min and then 0.25 mol of Chlorotrimethylsilane in 100 mL of THF was added at such a rate that the temperature did not exceed -80 °C. After 1 h, the reaction was allowed to warm to rt. The reaction mixture was hydrolyzed with saturated NH4Cl solution until large lumps of salt cake formed. The organic layer was poured off, dried over anhydrous Na2SO4, and distilled at atmospheric pressure to remove most of the THF. A trap-to-trap distillation of the residue at 0.1 mmHg was followed by distillation through an 11 in. Vigreux column. The fraction boiling at 49.5-51.5 °C/12 mmHg was collected, affording 47.9 g (79%) of (dibromomethyl)trimethylsilane.1a

Lithium-Halogen Exchange.

Reaction of (dibromomethyl)trimethylsilane with n-Butyllithium at -110 °C results in the formation of trimethylsilylbromomethyllithium. The silane and the n-BuLi are added simultaneously in order to suppress side reactions. Treatment of the intermediate lithium reagent with Chlorotrimethylsilane (eq 1) or mercury(II) bromide (eq 2) affords bis(trimethylsilyl)bromomethane or bis(trimethylsilylbromomethyl)mercury, respectively. If the lithium reagent is allowed to warm in the presence of cyclohexene, the only reaction observed is an alkylation with the n-butyl bromide formed in the exchange reaction. The alkylated product is formed in 89% yield.1a

In an alternative procedure, the lithium reagent was obtained by reaction with Lithium metal. Subsequent reaction with a trialkylborane (eq 3) followed by oxidation provided access to a-hydroxysilanes. The yields are good for simple trialkylboranes but are diminished as the alkyl groups become more hindered.2

Deprotonation.

(Dibromomethyl)trimethylsilane can be deprotonated with Lithium Diisopropylamide at -78 °C. Reaction of the intermediate anion with n-butyl iodide (eq 4) furnished the alkylated product in 93% yield.3,4 If the anion was allowed to warm to 20 °C in the absence of an electrophile, the bis(trimethylsilyl)ethylene (eq 5) was produced.4

Vinylsilanes.

Two reports have appeared on the formation of the 1,1-di-Grignard reagent using Magnesium Amalgam. In the first report, the di-Grignard, prepared indirectly from the dizinc reagent, was combined with cyclohexanone to produce the vinylsilane in 40% yield.5 In the second, satisfactory results were obtained only with the non-enolizable benzophenone (eq 6). Cyclohexanone afforded only 13% of the vinylsilane. In addition, the di-Grignard was treated with Chlorotrimethylstannane to furnish bis(trimethylstannyl)trimethylsilylmethane in 94% yield.6

The gem-dichromium reagent was prepared by reduction of the dibromide with Chromium(II) Chloride. This reagent will stereoselectively produce (E)-alkenylsilanes in excellent yield. The reagent can chemoselectively react with an aldehyde (eq 7) in the presence of a ketone.7

Esters (eq 8) and thioesters (eq 9) can be silylmethylenated by the action of the dibromide with low-valent titanium prepared from Titanium(IV) Chloride and Zinc. The reaction produces b-hetero-substituted vinylsilanes and was (Z) selective.8

Miscellaneous.

The kinetics of the cleavage of the dibromomethyl group by ammonia buffer have been reported.9


1. (a) Seyferth, D.; Lambert, R. L.; Hanson, E. M. JOM 1970, 24, 647. (b) Villieras, J. BSF(2) 1967, 1520.
2. (a) Rosario, O.; Oliva, A.; Larson, G. L. JOM 1978, 146, C8. (b) Larson, G. L.; Argüelles, R.; Rosario, O.; Sandoval, S. JOM 1980, 198, 15.
3. Villieras, J.; Bacquet, C.; Masure, D.; Normant, J. F. JOM 1973, 50, C7.
4. Villieras, J.; Bacquet, C.; Normant, J. F. BSF(2) 1975, 1797.
5. Martel, B.; Varache, M. JOM 1972, 40, C53.
6. van de Heisteeg, B. J. J.; Schat, G.; Tinga, M. A. G. M.; Akkerman, O. S.; Bickelhaupt, F. TL 1986, 27, 6123.
7. Takai, K.; Kataoka, Y.; Okazoe, T.; Utimoto, K. TL 1987, 28, 1443.
8. Takai, K.; Tezuka, M.; Kataoka, T.; Utimoto, K. SL 1989, 27.
9. (a) Chojnowski, J.; Stanczyk, W. JOM 1974, 73, 41. (b) Chojnowski, J.; Stanczyk, W. JOM 1975, 99, 359.

Michael J. Taschner

The University of Akron, OH, USA



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