Sodium bis(trimethylsilyl)amide

Sodium bis(trimethylsilyl)amide

General
Systematic name	Sodium bis(trimethylsilyl)amide
Other names	sodium hexamethyldisilazane, sodium hexamethyldisilazide, NaHMDS
Molecular formula	C₆H₁₈NNaSi₂
Molar mass	183.37 g/mol
Appearance	off-white solid
CAS number	[1070-89-9]
Properties
Density and phase	0.9 g/cm³, solid
Solubility in water	reacts with water
Other solvents	THF, benzene toluene
Melting point	171-175 °C (approx 446 K)
Boiling point	170 °C/2 mmHg
Basicity (pK_a) of conj. acid:	26 (in THF), 30 in DMSO)
Structure
Molecular shape	Bent at nitrogen
Crystal structure	?
Dipole moment	? D
Hazards
MSDS	External MSDS
Main hazards	Highly flammable, corrosive
NFPA 704
Flash point	? °C
R/S statement	R: 11,15,34 S: 16, 24/25
RTECS number	?
Supplementary data page
Structure and properties	n, ε_r, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Related compounds
Other anions	?
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 disclaimer and 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 by virtue of the lipophilic TMS groups.^[1]

Additional recommended knowledge

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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.

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 displacable methoxy group.

To deprotonate precursors to give stable carbenes.

References

^ 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: 10.1002/047084289.

Categories: Organosilicon compounds | Amides

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Sodium_bis(trimethylsilyl)amide". A list of authors is available in Wikipedia.