Trifluoromethyltrimethylsilane


Trifluoromethyltrimethylsilane is an organosilicon compound with the formula CF3Si3. It is a colorless liquid. The compound is a reagent used in organic chemistry for the introduction of the trifluoromethyl group. The compound was first prepared in 1984 by Ingo Ruppert and further developed as a reagent by G. K. Surya Prakash.

Preparation

The reagent is prepared from trimethylsilyl chloride and bromotrifluoromethane in the presence of a phosphorus reagent that serves as a halogen acceptor.

Use in organic synthesis

In the presence of an anionic initiator, the reagent reacts with aldehydes and ketones to give a trimethylsilyl ether, the net product of insertion of the carbonyl into the Si-CF3 bond. Hydrolysis gives trifluoromethyl methanols. The reagent also converts esters to trifluoromethyl ketones. A typical initiator is a soluble fluoride-containing species such as tetrabutylammonium fluoride, however simple alkoxides, e.g. KOtBu, are also effective. The mechanism begins by generation of Si3X and a highly reactive − intermediate. The − attacks the carbonyl to generate an alkoxide anion. The alkoxide is silylated by the reagent to give the overall addition product, plus −, thus propagating an anionic chain reaction. The reagent competes with the carbonyl for the reactive intermediate, rapidly sequestering − in a reversibly-generated -ate complex −. This -ate complex is unable to react directly with the carbonyl, resulting in powerful inhibition of the chain reaction by the reagent. This inhibitory process is common to all anion-initiated reactions of the reagent, with the identity of the counter-cation playing a major role in controlling the overall rate.
The reagent has largely supplanted trifluoromethyllithium, which is not isolable and rapidly decomposes to yield lithium fluoride and difluorocarbene.