Sodium bis(trimethylsilyl)amide

Sodium bis(trimethylsilyl)amide is the organosilicon 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 reactions. Its advantages are that it is commercially available as a solid and it is soluble not only in ethers, such as THF or diethyl ether, but also in aromatic solvents, like benzene and toluene by virtue of the lipophilic TMS groups.[1]

Sodium bis(trimethylsilyl)amide
Names
Preferred IUPAC name
Sodium 1,1,1-trimethyl-N-(trimethylsilyl)silanaminide
Other names
Sodium hexamethyldisilazide
Sodium hexamethyldisilazane
Identifiers
3D model (JSmol)
Abbreviations NaHMDS
3629917
ChemSpider
ECHA InfoCard 100.012.713
EC Number
  • 213-983-8
UN number UN 3263
Properties
C6H18NNaSi2
Molar mass 183.37 g/mol
Appearance off-white solid
Density 0.9 g/cm3, solid
Melting point 171 to 175 °C (340 to 347 °F; 444 to 448 K)
Boiling point 170 °C (338 °F; 443 K) 2 mmHg
reacts with water
Solubility in other solvents THF, benzene
toluene
Structure
Triangular pyramidal
Hazards
Main hazards Highly flammable, corrosive
R-phrases (outdated) R11 R15 R34
S-phrases (outdated) S16 S24/25
Related compounds
Other cations
 Lithium
bis(trimethylsilyl)amide
(LiHMDS)
Potassium
bis(trimethylsilyl)amide
Related compounds
 Lithium diisopropylamide (LDA)
KH
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

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

Structure

Although the N-Na bond is polar covalent as a solid, when dissolved in nonpolar solvents this compound is trimeric, consisting of a central Na3N3 ring.[2]

Applications in synthesis

NaHMDS is used as a base in organic synthesis. Typical reactions:

NaHMDS is also used as a base to deprotonate other compounds containing weakly acidic O-H, S-H, and N-H bonds. These include cyanohydrins and thiols.[5]

NaHMDS is reagent to convert alkyl halides to amines in a two step process that begins with N-alkylation followed by hydrolysis of the N-Si bonds.

((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.

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.
  3. Sergey A. Kozmin, Shuwen He, and Viresh H. Rawal. "Preparation of (E)-1-Dimethylamino-3-tert-Butyldimethylsiloxy-1,3-Butadiene". Organic Syntheses.CS1 maint: multiple names: authors list (link); Collective Volume, 10, p. 301
  4. Paul Binger, Petra Wedemann, and Udo H. Brinker. "Cyclopropene: A New Simple Synthesis and its Diels-Alder Reaction with Cyclopentadiene". Organic Syntheses.CS1 maint: multiple names: authors list (link); Collective Volume, 10, p. 231
  5. J. Christopher McWilliams, Fred J. Fleitz, Nan Zheng, and Joseph D. Armstrong, III. "Preparation of n-Butyl 4-Chlorophenyl Sulfide". Organic Syntheses.CS1 maint: multiple names: authors list (link); Collective Volume, 10, p. 147
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