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 In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

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 Bromotrifluoromethane, commonly known as Halon 1301, R13B1, Halon 13B1 or BTM, is an organic halide with the chemical formula C Br F3. It is used for gaseous fire suppression as a far less toxic alternative to bromochloromethane. Table of physi ...

in the presence of a phosphorus(III) reagent that serves as a halogen acceptor.

Use in organic synthesis

In the presence of an anionic initiator (M⁺ X⁻), the reagent reacts with aldehydes and

ketones In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double bon ...

to give a trimethylsilyl ether, the net product of insertion of the carbonyl into the Si-CF₃ bond.

Hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

gives trifluoromethyl

methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a ...

s. The reagent also converts esters to trifluoromethyl

. 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 F₃sup>− (trifluoromethide) intermediate. The F₃sup>− attacks the carbonyl to generate an alkoxide anion. The alkoxide is silylated by the reagent to give the overall addition product, plus F₃sup>−, thus propagating an anionic chain reaction. The reagent competes with the carbonyl for the reactive intermediate, rapidly sequestering F₃sup>− in a reversibly-generated

-ate complex In chemistry, an ate complex is a salt formed by the reaction of a Lewis acid with a Lewis base whereby the central atom (from the Lewis acid) increases its valence and gains a negative formal charge. (In this definition, the meaning of valence i ...

CF₃)₂Si(CH₃)₃sup>−. This

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.{{cite journal, title=Anion-Initiated Trifluoromethylation by TMSCF₃: Deconvolution of the Siliconate–Carbanion Dichotomy by Stopped-Flow NMR/IR, author1=Craig P. Johnston, author2=Thomas H. West, author3=Ruth E. Dooley, author4=Marc Reid, author5= Ariana B. Jones, author6= Edward J. King, author7=Andrew G. Leach, author8=Guy C. Lloyd-Jones , journal=Journal of the American Chemical Society, volume=140, issue=35, pages=11112–11124, year=2018, doi=10.1021/jacs.8b06777, pmid=30080973, pmc=6133236, hdl=10023/16552 The reagent has largely supplanted trifluoromethyllithium, which is not isolable and rapidly decomposes to yield lithium fluoride and difluorocarbene.

References

Trifluoromethyl compounds Reagents for organic chemistry Carbosilanes Trimethylsilyl compounds