Sodium bis(trimethylsilyl)amide


Sodium bis(trimethylsilyl)amide
Sodium bis(trimethylsilyl)amide
Identifiers
Abbreviations NaHMDS
CAS number 1070-89-9
PubChem 2724254 YesY
ChemSpider 21169873 YesY
EC number 213-983-8
UN number UN 3263
Beilstein Reference 3629917
Jmol-3D images Image 1
Properties
Molecular formula C6H18NNaSi2
Molar mass 183.37 g/mol
Appearance off-white solid
Density 0.9 g/cm3, solid
Melting point

171-175 °C, 444-448 K, 340-347 °F

Boiling point

170 °C, 443 K, 338 °F (2 mmHg)

Solubility in water reacts with water
Solubility in other solvents THF, benzene
toluene
Structure
Molecular shape Triangular pyramidal
Hazards
R-phrases R11 R15 R34
S-phrases S16 S24/25
Main hazards Highly flammable, corrosive
Related compounds
Other cations Lithium
bis(trimethylsilyl)amide

(LiHMDS)
Potassium
bis(trimethylsilyl)amide
Related compounds Lithium diisopropylamide (LDA)
KH
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Sodium bis(trimethylsilyl)amide is the chemical compound with the formula ((CH3)3Si)2NNa. This species, usually called NaHMDS (sodium hexamethyldisilazide), is a strong base used for deprotonation reactions or base catalyzed reaction. Its advantages are that it is available as a solid and it is soluble in a wide range of nonpolar solvents such as THF, diethyl ether, benzene, and toluene by virtue of the lipophilic TMS groups.[1]

NaHMDS is quickly destroyed by water to form sodium hydroxide and bis(trimethylsilyl)amine.

Contents

Structure

It is common that polar organometallic reagents are depicted as ions, when in fact such species are rarely ionic. The structure shown in the figure is a better representation - the sodium atom is attached to the nitrogen atom via a polar covalent bond. When unsolvated, this compound is trimeric in the solid state.[2]

Applications in synthesis

NaHMDS is widely used as a base for C-H acids. Typical reactions:

  • To deprotonate ketones and esters to generate enolate derivatives.
  • Generate halocarbenes such as CHBr and CHI by dehydrohalogenation of the CH2X2 (X = Br, I). These carbene reagents add to alkenes to give substituted cyclopropanes.
  • To generate Wittig reagents via deprotonation of phosphonium salts.
  • Deprotonate cyanohydrins.

NaHMDS is also used as a base for N-H acids.

NaHMDS reacts with alkyl halides to give amine derivatives:

(CH3)3Si)2NNa + RBr → (CH3)3Si)2NR + NaBr
(CH3)3Si)2NR + H2O → (CH3)3Si)2O + RNH2

This method has been extended to aminomethylation via the reagent (CH3)3Si)2NCH2OMe, which contains a displaceable methoxy group.

  • To deprotonate precursors to give stable carbenes.

See also

References

  1. ^ Watson, B. T.; Lebel, H. "Sodium bis(trimethylsilyl)amide" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. doi:10.1002/047084289X.rs071m.pub2
  2. ^ Driess, Matthias; Pritzkow, Hans; Skipinski, Markus; Winkler, Uwe (1997). "Synthesis and Solid State Structures of Sterically Congested Sodium and Cesium Silyl(fluorosilyl)phosphanide Aggregates and Structural Characterization of the Trimeric Sodium Bis(trimethylsilyl)amide". Organometallics 16 (23): 5108–5112. doi:10.1021/om970444c. 

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