Trifluoromethyltrimethylsilane (known as Ruppert-Prakash reagent, TMSCF<sub>3</sub>) is an organosilicon compound with the formula CF<sub>3</sub>Si(CH<sub>3</sub>)<sub>3</sub>. 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 It was further developed as a reagent by G. K. Surya Prakash, who reported activation of TMSCF<sub>3</sub> by fluoride to perform nucleophilic trifluoromethylation of carbonyl compounds. In the same year, Stahly described similar reactions for the synthesis of trifluoromethylated phenols and anilines. Since then TMSCF<sub>3</sub> has been widely used as a nucleophilic trifluoromethylating agent. Potassium (trifluoromethyl)trimethoxyborate for this purpose has been synthesised from B(OMe)<sub>3</sub>, CF<sub>3</sub>SiMe<sub>3</sub> and KF. Aryl functionalization by C-H activation has also been reported.
The reagent is prepared from trimethylsilyl chloride and bromotrifluoromethane in the presence of a phosphorus(III) reagent that serves as a halogen acceptor.
In the presence of a metal salt (M<sup>+</sup> X<sup>âÂÂ</sup>), the reagent reacts with aldehydes and ketones to give a trimethylsilyl ether, the net product of insertion of the carbonyl into the Si-CF<sub>3</sub> 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(CH<sub>3</sub>)<sub>3</sub>X and a highly reactive [CF<sub>3</sub>]<sup>âÂÂ</sup> (trifluoromethide) intermediate. The [CF<sub>3</sub>]<sup>âÂÂ</sup> attacks the carbonyl to generate an alkoxide anion. The alkoxide is silylated by the reagent to give the overall addition product, plus [CF<sub>3</sub>]<sup>âÂÂ</sup>, thus propagating an anionic chain reaction. The reagent competes with the carbonyl for the reactive intermediate, rapidly sequestering [CF<sub>3</sub>]<sup>âÂÂ</sup> in a reversibly-generated -ate complex [(CF<sub>3</sub>)<sub>2</sub>Si(CH<sub>3</sub>)<sub>3</sub>]<sup>âÂÂ</sup>. 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<sup>+</sup>) playing a major role in controlling the overall rate.
One of the known uses of TMSCF3 is in the synthesis of Alpelisib.