Lithium bis(trimethylsilyl)amide
| Lithium bis(trimethylsilyl)amide | |
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lithium bis(trimethylsilyl)azanide |
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Other names
Lithium bis(trimethylsilyl)amide and lithium hexamethyldisilazide |
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| Identifiers | |
| CAS number | 4039-32-1  |
| Jmol-3D images | Image 1 |
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| 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 |
| Solubility | THF, hexane |
| Hazards | |
| Main hazards | flammable |
| Related compounds | |
| Related compounds | Sodium bis(trimethylsilyl)amide, Potassium bis(trimethylsilyl)amide |
 (verify) (what is:  / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Lithium bis(trimethylsilyl)amide (commonly abbreviated as LiHMDS, Lithium HexaMethylDiSilazide) is the organosilicon compound with the formula [(CH3)3Si]2NLi. This colourless volatile solid is a strong non-nucleophilic base used for deprotonation reactions and as a ligand.
Contents |
Structure [edit]
When solvent-free, this compound is dimeric in solution, and trimeric in solid state.[1][2]
Preparation [edit]
LiHMDS is commercially available, but it can also be prepared by deprotonation of bis(trimethylsilyl)amine with n-butyllithium:[3]
- [(CH3)3Si]2NH + C4H9Li → [(CH3)3Si]2NLi + C4H10
The compound can be purified by sublimation or distillation.
LiHMDS can be prepared in situ then reacted. This method is illustrated in the preparation of the enolate shown below under "reactions".[4]
Reactions [edit]
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).[5] 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,[6] or to form a lithium enolate, as here with benzylideneacetone:[4]
It is volatile and has been discussed for use for atomic layer deposition of lithium compounds.
See also [edit]
References [edit]
- ^ 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.
- ^ Rogers, Robin D.; Atwood, Jerry L.; Grüning, Rainer (1978). "The crystal structure of N-lithiohexamethyldisilazane, [LiN(SiMe3)2]3". J. Organomet. Chem. 157 (2): 229–237. doi:10.1016/S0022-328X(00)92291-5.
- ^ Amonoo-Neizer, E. H.; Shaw, R. A.; Skovlin, D. O.; Smith, B. C. (1966). "Lithium Bis(Trimethylsilyl)Amide and Tris(Trimethylsilyl)Amine". Inorg. Synth. Inorganic Syntheses 8: 19–22. doi:10.1002/9780470132395.ch6. ISBN 978-0-470-13239-5.
- ^ 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; Coll. Vol. 9: 197
- ^ 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
- ^ 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. Retrieved 5 September 2010.
