TASF reagent

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 trimethylsilylfluoride (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.

TASF reagent
Skeletal formulas of the TASF reagent
Names
Preferred IUPAC name
2-(Dimethylamino)-1,1,3,3-tetramethyldiazathian-2-ium difluorotri(methyl)silanuide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.156.426
  • InChI=1S/C6H18N3S.C3H9F2Si/c1-7(2)10(8(3)4)9(5)6;1-6(2,3,4)5/h1-6H3;1-3H3/q+1;-1 checkY
    Key: JMGVTLYEFSBAGJ-UHFFFAOYSA-N checkY
  • InChI=1/C6H18N3S.C3H9F2Si/c1-7(2)10(8(3)4)9(5)6;1-6(2,3,4)5/h1-6H3;1-3H3/q+1;-1
    Key: JMGVTLYEFSBAGJ-UHFFFAOYAE
  • F[Si-](F)(C)(C)C.N([S+](N(C)C)N(C)C)(C)C
Properties
C9H27F2N3SSi
Molar mass 275.48
Appearance Colorless solid
Melting point 98 to 101 °C (208 to 214 °F; 371 to 374 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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 precipitates from the reaction solvent, diethyl ether.[1]

Structure

The cation [((CH3)2N)3S]+ is a sulfonium ion. The S-N distances are 1.612 and 1.675 pm. The N-S-N angles are 99.6°. The anion is [F2Si(CH3)3]−. It is trigonal bipyramidal with mutually trans fluorides. The Si-F distances are 176 picometers. The Si-C distances are 188 pm.[2]

References
  1. W. J. Middleton (1990). "Tris(dimethylamino)sulfonium difluorotrimethylsilicate". Organic Syntheses.; Collective Volume, vol. 7, p. 528
  2. Dixon, David A.; Farnham, William B.; Heilemann, W.; Mews, R.; Noltemeyer, M. (1993). "Structural studies of tris(dialkylamino) sulfonium (TAS) fluorosilicates". Heteroatom Chemistry. 4 (2–3): 287–295. doi:10.1002/hc.520040225.
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