TASF reagent

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The TASF reagent or tris(dimethylamino)sulfonium difluorotrimethylsilicate is a reagent in organic chemistry with structural formula ((CH3)2N)3S+,F2Si(CH3)3-. It is an anhydrous source of fluoride and is used to cleave silyl ether protective groups. Many other fluoride reagents are known, but few are truly anhydrous, because of the extraordinary basicity of "naked" F-. In TASF, the fluoride is masked as an adduct with the weak Lewis acid FSi(CH3)3. The sulfonium cation ((CH3)2N)3S+ is unusually non-electrophilic due to the electron-donating properties of the three (CH3)2N substituents.

This compound is prepared from sulfur tetrafluoride:

3 (CH3)2NSi(CH3)3 + SF4 → 2 (CH3)3SiF + [((CH3)2N)3S][F2Si(CH3)3]

The colorless salt (melting point: 98–101 °C) precipitates from the reaction solvent (ether).

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