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Phenyllithium

Names
IUPAC name Phenyllithium
Other names PhLi, phenyl lithium
Identifiers
CAS Number	591-51-5
ECHA InfoCard	100.008.838
PubChem CID	24845894
CompTox Dashboard (EPA)	DTXSID70938503 DTXSID20883453, DTXSID70938503
Properties
Chemical formula	C6H5Li
Molar mass	84.05 g/mol
Appearance	Colorless crystals, solutions in cyclohexane/ether are dark brown, solutions in THF are reddish
Density	0.828 g/cm
Boiling point	140-143 °C
Solubility in water	Severe reaction with water
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Y verify (what is  ?) Infobox references

Phenyllithium is an organometallic agent with the empirical formula C₆H₅Li. It is most commonly used as a metalating agent in organic syntheses and a substitute for Grignard reagents for introducing phenyl groups in organic syntheses. Crystalline phenyllithium is colorless; however, solutions of phenyllithium are various shades of brown or red depending on the solvent used and the impurities present in the solute.

Structure and properties

Phenyllithium is an organolithium compound that forms monoclinic crystals. Solid phenyllithium can be described as consisting of dimeric Li₂Ph₂ subunits. The Li atoms and the ipso carbons of the phenyl rings form a planar four-membered ring. The plane of the phenyl groups are perpendicular to the plane of this Li₂C₂ ring. Additional intermolecular bonding occurs between these phenyllithium dimers and the π-electrons of the phenyl groups in the adjacent dimers.

In solution, it takes a variety of structures dependent on the organic solvent. In tetrahydrofuran, it equilibrates between monomer and dimer states. In ether, as it is commonly sold, phenyllithium exists as a tetramer. Four Li atoms and four ipso carbon centers occupy alternating vertices of a distorted cube. Phenyl groups are at the faces of the tetrahedron and bind to three of the nearest Li atoms.

The C-Li bond lengths are an average of 2.33 Å. An ether molecule binds to each of the Li sites through its oxygen atom. In the presence of LiBr, a byproduct of directly reacting lithium with a phenyl halide, the complex instead becomes [(PhLi • Et₂O)₃ • LiBr). The Li atom of LiBr occupies one of the lithium sites in the cubane-like frame, and Br atom sits in an adjacent carbon site.

Preparation

Phenyllithium was first produced by the reaction of lithium metal with diphenylmercury:

(C₆Η₅)₂Ηg + 2Li → 2C₆Η₅Li + Ηg

The synthesis was improved soon afterward by directly reacting lithium with phenyl halides.

C₆H₅X + 2Li → C₆H₅Li + LiX

Phenyllithium can also be synthesized with a metal-halogen exchange reaction:

n-BuLi + X-Ph → n-BuX + Ph-Li

The predominant method of producing phenyllithium today are the latter two syntheses.

Reactions

The primary use of PhLi is to facilitate formation of carbon-carbon single bonds by nucleophilic addition and substitution reactions:

PhLi + R₂C=O → PhR₂COLi

References

1. Wietelmann, U.; Bauer, R.J. “Lithium and Lithium Compounds“ in Ullmann’s Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a15
2. Gilman, H.; Zoellner, E.A.; Selby, W.M. An Improved Procedure for the Preparation of Organolithium Compounds. J. Am. Chem. Soc. 1932 54 (5), 1957-1962. doi:10.1021/ja01344a033
3. Hope, H.; Power, P.P. Isolation and Crystal Structures of the Halide-Free and Halide-Rich Phenyllithium Etherate Complexes and . J. Am. Chem. Soc. 1983 105 (16), 5320-5324. doi:10.1021/ja00354a022
4. Green, D.P.; Zuev, D. “Phenyllithium” in Encyclopedia of Reagents for Organic Synthesis, 2008, Wiley and Sons. doi:10.1002/047084289X.rp076.pub2
5. Dinnebier, R.E.; Behrens, U.; Olbrich, F. Lewis Base-Free Phenyllithium: Determination of the Solid-State Structure by Synchrotron Powder Diffraction. J. Am. Chem. Soc. 1998 120 (7), 1430-1433. doi:10.1021/ja972816e

• Organolithium compounds