Sodium bis(trimethylsilyl)amide

Sodium bis(trimethylsilyl)amide
Preferred IUPAC name Sodium bis(trimethylsilyl)amide
Systematic name Sodiobis(trimethylsilyl)amine
Other names Sodium hexamethyldisilazane Sodium hexamethyldisilazide
Identifiers
Abbreviations	NaHMDS
CAS number	1070-89-9
PubChem	2724254 Y
ChemSpider	21169873 Y
EC number	213-983-8
UN number	UN 3263
Beilstein Reference	3629917
Jmol-3D images	Image 1
SMILES C[Si](C)(C)N([Na])[Si](C)(C)C
InChI InChI=1S/C6H18NSi2.Na/c1-8(2,3)7- 9(4,5)6;/h1-6H3;/q-1;+1 Key: WRIKHQLVHPKCJU-UHFFFAOYSA-N InChI=1/C6H18NSi2.Na/c1-8(2,3)7-9(4,5)6;/h1-6H3;/q-1;+1/rC6H18NNaSi2/c1-9(2,3)7(8)10(4,5)6/h1-6H3 Key: WRIKHQLVHPKCJU-JSJAVMDOAQ InChI=1S/C6H18NSi2.Na/c1-8(2,3)7-9(4,5)6;/h1-6H3;/q-1;+1 Key: WRIKHQLVHPKCJU-UHFFFAOYSA-N
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.

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

• Metal bis(trimethylsilyl)amides

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.