Lithium naphthalene

A solution of lithium naphthalenide in tetrahydrofuran
Identifiers
3D model (JSmol)
  • InChI=1S/C10H8.Li/c1-2-6-10-8-4-3-7-9(10)5-1;/h1-8H;
    Key: PDZGAEAUKGKKDE-UHFFFAOYSA-N
  • [Li].C1=CC=C2C=CC=CC2=C1
Properties
Li+[C10H8]−
Molar mass 135.11 g·mol−1
Appearance Dark green crystals
Related compounds
Other cations
 sodium naphthalene
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Lithium naphthalene is an organic salt with the chemical formula Li+[C10H8]−. In the research laboratory, it is used as a reductant in the synthesis of organic, organometallic, and inorganic chemistry. It is usually generated in situ. Lithium naphthalene crystallizes with ligands bound to Li+.[1] The anion is a well-known example of an organic radical.

Preparation and properties

The compound is prepared by stirring the metallic lithium with naphthalene in an ethereal solvent, usually as tetrahydrofuran or dimethoxyethane. The resulting salt is dark green.[2] The reaction of naphthalene with lithium can be accelerated by sonication. Methods for assaying lithium naphthalene have been developed as well.[3] As a radical, its solutions show a strong EPR signal near g = 2.0.[4] Its deep green color arises from absorptions at 463, 735 nm.[5]

Several solvates of lithium naphthalene have been characterized by X-ray crystallography. The effects are subtle, the outer pair of HC–CH bonds contract by 3 pm and the other nine C–C bonds elongate by 2–3 pm. Net: reduction weakens the bonding.[6]

Reactions

Redox

With a reduction potential near −2.5 V versus the normal hydrogen electrode, the naphthalene radical anion is a strong reducing agent.[5]

Protonation

The anion is strongly basic, and a typical degradation pathway involves reaction with water and related protic sources such as alcohols. These reactions afford dihydronaphthalene:

2 Li+[C10H8]− + 2 H2O → C10H10 + C10H8 + 2 LiOH

As a ligand precursor

Alkali metal salts of the naphthalene radical anion are used to prepare complexes of naphthalene.[7]

Related compounds

Many related radical anions are known such as those derived from anthracene, with other alkali metals (especially sodium), and with diverse ligands attached to the alkali metal cations. Dilithium naphthalene is also known in the form [Li+(tmeda)2]2[C10H8]2−.[8][1]

References

  1. ^ a b Melero, Cristóbal; Guijarro, Albert; Yus, Miguel (2009). "Structural Characterization and Bonding Properties of Lithium Naphthalene Radical Anion, Li+(TMEDA)2C
    10    H−
    8    , and Lithium Naphthalene Dianion (Li+TMEDA)2C
    10    H2−
    8    ". Dalton Transactions (8): 1286–1289. doi:10.1039/b821119c. PMID 19462646.
  2. ^ David G. Hilmey; Leo A. Paquette (2007). "1,3-Dichloroacetone as a Cyclopropanone Equivalent: 5-Oxaspiro[3.4]Octan-1-one". Organic Syntheses. 84: 156. doi:10.15227/orgsyn.084.0156.
  3. ^ Nicholas A. Morra and Brian L. Pagenkopf (2008). "Direct Synthesis of 2,5-Dihalosiloles". Organic Syntheses. 85: 53. doi:10.15227/orgsyn.085.0053.
  4. ^ Cotton, F. Albert; Wilkinson, Geoffrey (1988), Advanced Inorganic Chemistry (5th ed.), New York: Wiley-Interscience, p. 139, ISBN 0-471-84997-9
  5. ^ a b Connelly, Neil G.; Geiger, William E. (1996). "Chemical Redox Agents for Organometallic Chemistry". Chemical Reviews. 96 (2): 877–910. doi:10.1021/cr940053x. PMID 11848774.
  6. ^ Castillo, Maximiliano; Metta-Magaña, Alejandro J.; Fortier, Skye (2016). "Isolation of Gravimetrically Quantifiable Alkali Metal Arenides Using 18-Crown-6". New Journal of Chemistry. 40 (3): 1923–1926. doi:10.1039/C5NJ02841H.
  7. ^ Ellis, John E. (2019). "The Chatt Reaction: Conventional Routes to homoleptic Arenemetalates of d-Block Elements". Dalton Transactions. 48 (26): 9538–9563. doi:10.1039/C8DT05029E. PMID 30724934. S2CID 73436073.
  8. ^ Brooks, J. J.; Rhine, Wendell; Stucky, G. D. (1972). "π-Groups in Ion Pair Bonding. Stabilization of the Dianion of Naphthalene by Lithium Tetramethylethylenediamine". Journal of the American Chemical Society. 94 (21): 7346–7351. doi:10.1021/ja00776a014.
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