Lithium amide

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## Contents

* 1 Overview
* 2 Lithium amides
* 2.1 Examples
* 3 See also
* 4 References
* 5 External links

## Overview

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Lithium amide is an inorganic compound with the chemical formula Li+NH2-, i.e. it is composed of a lithium cation, and the conjugate base of ammonia. It is a white solid with a tetragonal crystal structure.

## Lithium amides

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The anionic conjugate bases of amines are known as amides. Thus lithium amide may also refer to lithium salts of amines e.g. Li+NR2-. An example of a lithium amide is lithium diisopropylamide (LDA), which is quite commonly used.

Lithium amide can be made by adding lithium metal to liquid ammonia:

Li + NH3 -> LiNH2 \+ 0.5 H2

Lithium amides in general can be similarly formed, substituting ammonia with the appropriate amine:

Li + R2NH -> LiNR2 \+ 0.5 H2

Lithium amides are very reactive compounds and can act as strong  bases. Unless the nitrogen atom is hindered, as in the case of LDA, they can also act as nucleophiles.

### Examples

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The lithium salt of 2,2,6,6-tetramethylpiperidine has been crystalised as a tetramer:

File:Tetramericliamide.jpgTetrameric lithium amide.[1]

On the other hand, the lithium derivative of di-(1-phenylethyl)amine crystallises as a trimer:

File:Trimerliamide.jpgTrimeric lithium amide.[2]

It is also possible to make mixed oligomers of metal alkoxides and amides. [3] These are related to the super bases which are mixtures of metal alkoxides and alkyls. The cyclic oligomers form when the nitrogen of the amide forms a sigma bond to a lithium while the nitrogen lone pair binds to another metal centre.

Other organolithium compounds (such as BuLi) are generally considered to exist in and function via high-order, aggregated species.

## See also

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* Sodium amide
* Butyllithium
* Lithium hexamethyldisilazide

## References

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1. ↑ M.F. Lappert, M.J. Slade, A. Singh, J.L. Atwood, R.D. Rogers and R. Shakir (1983). "Structure and reactivity of sterically hindered lithium amides and their diethyl etherates: crystal and molecular structures of [[Li{N(SiMe3)2}(OEt2)]]2 and tetrakis(2,2,6,6-tetramethylpiperidinatolithium)". Journal of the American Chemical Society. 105 (2): 302–304. doi:10.1021/ja00340a031.CS1 maint: Multiple names: authors list (link)
2. ↑ D.R. Armstrong, K.W. Henderson, A.R. Kennedy, W.J. Kerr, F.S. Mair, J.H. Moir, P.H. Moran and R. Snaith, Dalton Transactions, 1999, 4063.
3. ↑ K.W. Henderson, D.S. Walther and P.G. Williard (1995). "Identification of a Unimetal Complex of Bases by 6Li NMR Spectroscopy and Single-Crystal Analysis". Journal of the American Chemical Society. 117 (33): 8680–8681. doi:10.1021/ja00138a030.

* Merck Index, 11th Edition, 5398.

## External links

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