Sodium bis(trimethylsilyl)amide

Sodium bis(trimethylsilyl)amide

Names
Preferred IUPAC name Sodium 1,1,1-trimethyl-N-(trimethylsilyl)silanaminide
Other names Sodium hexamethyldisilazide Sodium hexamethyldisilazane
Identifiers
CAS Number	1070-89-9  N
3D model (JSmol)	Interactive image
Abbreviations	NaHMDS
Beilstein Reference	3629917
ChemSpider	21169873  Y
ECHA InfoCard	100.012.713
EC Number	213-983-8
PubChem CID	2724254
UN number	3263
CompTox Dashboard (EPA)	DTXSID5061451
InChI InChI=1S/C6H18NSi2.Na/c1-8(2,3)7- 9(4,5)6;/h1-6H3;/q-1;+1 N Key: WRIKHQLVHPKCJU-UHFFFAOYSA-N Y 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
SMILES C[Si](C)(C)N([Na])[Si](C)(C)C
Properties
Chemical formula	NaN(Si(CH3)3)2
Molar mass	183.377 g·mol−1
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	202 °C (396 °F; 475 K) 2 mmHg
Solubility in water	Reacts with water
Solubility in other solvents	THF, benzene toluene
Structure
Molecular shape	Triangular pyramidal
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Highly flammable, corrosive
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H302, H312, H314, H332, H412
Precautionary statements	P260, P261, P264, P270, P271, P273, P280, P301+P312, P301+P330+P331, P302+P352, P303+P361+P353, P304+P312, P304+P340, P305+P351+P338, P310, P312, P321, P322, P330, P363, P405, P501
Related compounds
Other cations	Lithium bis(trimethylsilyl)amide (LiHMDS) Potassium bis(trimethylsilyl)amide
Related compounds	Lithium diisopropylamide (LDA) Sodium hydride Potassium hydride
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

Sodium bis(trimethylsilyl)amide is the organosilicon compound with the formula NaN(Si(CH₃)₃)₂. This species, usually called NaHMDS (sodium hexamethyldisilylamide), 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]

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

Structure

Although the Na–N 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 strong base in organic synthesis. Typical reactions:

• To deprotonate ketones and esters to generate enolate derivatives. ^[3]
• Generate carbenes by dehydrohalogenation of halocarbons. These carbene reagents add to alkenes to give substituted cyclopropanes and cyclopropenes. ^[4]
• To deprotonation of phosphonium salts, generating Wittig reagents.

NaHMDS deprotonates compounds containing weakly acidic O–H, S–H, and N–H bonds. These include cyanohydrins and thiols. ^[5]

NaHMDS converts alkyl halides to amines in a two step process that begins with N-alkylation followed by hydrolysis of the N–Si bonds:

NaN(Si(CH₃)₃)₂ + RX → RN(Si(CH₃)₃)₂ + NaX

RN(Si(CH₃)₃)₂ + H₂O → O(Si(CH₃)₃)₂ + RNH₂

where X is a halogen and R is an alkyl.

This method has been extended to aminomethylation via the reagent CH₃OCH₂N(Si(CH₃)₃)₂, which contains a displaceable methoxy group CH₃O–.

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.
3. Sergey A. Kozmin, Shuwen He, and Viresh H. Rawal. "Preparation of (E)-1-Dimethylamino-3-tert-Butyldimethylsiloxy-1,3-Butadiene". Organic Syntheses ; Collected Volumes, vol. 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 ; Collected Volumes, vol. 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 ; Collected Volumes, vol. 10, p. 147.