Lithium bis(trimethylsilyl)amide

Lithium bis(trimethylsilyl)amide
IUPAC name

lithium bis(trimethylsilyl)azanide
Other names

Lithium bis(trimethylsilyl)amide and lithium hexamethyldisilazide
Identifiers
CAS number 4039-32-1 Y
Jmol-3D images Image 1
Properties
Molecular formula C6H18LiNSi2
Molar mass 167.326 g/mol
Appearance White solid
Melting point

71-72 °C
Boiling point

80 - 84 °C (0.001 mm Hg)
Solubility in water decomposes in water
Solubility THF, hexane
Hazards
Main hazards flammable
Related compounds
Related compounds Sodium bis(trimethylsilyl)amide, Potassium bis(trimethylsilyl)amide
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Lithium bis(trimethylsilyl)amide (commonly abbreviated as LiHMDS, Lithium HexaMethylDiSilazide) is the organosilicon compound with the formula [(CH3)3Si]2NLi. This colourless solid is a strong non-nucleophilic base used for deprotonation reactions and as a ligand. When solvent-free, this compound is dimeric in solution, and trimeric in solid state.[1]

Contents

Preparation

LiHMDS is commercially available but can also be prepared by deprotonation of bis(trimethylsilyl)amine with n-butyllithium:[2]

[(CH3)3Si]2NH + C4H9Li → [(CH3)3Si]2NLi + C4H10

The compound can be purified by sublimation.

LiHMDS can often be prepared in situ then reacted, as in the enolate preparation shown below under "reactions".[3]

Reactions

LiHMDS is used to generate coordination complexes with low-coordination numbers, taking advantage of the steric bulk of the (tms)2N- ligand. Examples include M[N(tms)2]3 for M = Sc, Ti, V, Fe (tms = (CH3)3Si).[4] Treatment with trimethylsilyl chloride gives tris(trimethylsilyl)amine, which features a planar, 3-coordinate nitrogen.

In organic chemistry, LiHMDS is often used as a strong base, for example to form lithium acetylide,[5] or to form a lithium enolate, as here with benzylideneacetone:[3]

See also

References

  1. ^ Mootz, D.; Zinnius, A.; Böttcher, B. (1969). "Assoziation im festen Zustand von Bis(trimethylsilyl)amidolithium und Methyltrimethylsilanolatoberyllium". Angew. Chem. 81 (10): 398–399. doi:10.1002/ange.19690811015. 
  2. ^ Amonoo-Neizer, E. H.; Shaw, R. A.; Skovlin, D. O.; Smith, B. C.; Rosenthal, Joel W.; Jolly, William L. (1966). "Lithium Bis(Trimethylsilyl)Amide and Tris(Trimethylsilyl)Amine". Inorg. Synth.. Inorganic Syntheses 8: 19–22. doi:10.1002/9780470132395.ch6. ISBN 9780470132395. 
  3. ^ a b Danheiser, R. L.; Miller, R. F.; Brisbois, R. G. (1990), "Detrifluoroacetylative Diazo Group Transfer: (E)-1-Diazo-4-phenyl-3-buten-2-one", Org. Synth. 73: 134, http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV9P0197 ; Coll. Vol. 9: 197 
  4. ^ Donald C. Bradley, Richard G. Copperthwaite “Transition Metal Complexes of Bis(Trimethyl-silyl)Amine (1,1,1,3,3,3-Hexamethyldisilazane)” Inorganic Syntheses 1978, Volume 18, 112. doi:10.1002/9780470132494.ch18
  5. ^ Reich, Melanie (Aug 24, 2001). "Addition of a lithium acetylide to an aldehyde; 1-(2-pentyn-4-ol)-cyclopent-2-en-1-ol". ChemSpider Synthetic Pages. p. 137. http://cssp.chemspider.com/137. Retrieved 5 September 2010.