Trifluoromethyltrimethylsilane

Trifluoromethyltrimethylsilane (known as Ruppert-Prakash reagent, TMSCF3) is an organosilicon compound with the formula CF3Si(CH3)3. 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(III) reagent that serves as a halogen acceptor.

Use in organic synthesis
In the presence of a metal salt (M+ X−), 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 such as KOtBu are also effective. The mechanism begins by generation of Si(CH3)3X and a highly reactive [CF3]− (trifluoromethide) intermediate. The [CF3]− attacks the carbonyl to generate an alkoxide anion. The alkoxide is silylated by the reagent to give the overall addition product, plus [CF3]−, thus propagating an anionic chain reaction. The reagent competes with the carbonyl for the reactive intermediate, rapidly sequestering [CF3]− in a reversibly-generated -ate complex [(CF3)2Si(CH3)3]−. 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 (M+) 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.