Phenyllithium

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Phenyllithium
Kekulé, skeletal formula of phenyllithium
Identifiers
Abbreviations LiPh, PhLi
CAS number 591-51-5 YesY
PubChem 637932
ChemSpider 10254416 N
EC number 209-720-1
MeSH phenyllithium
ChEBI CHEBI:51470 N
Beilstein Reference 506502
Gmelin Reference 2849
Jmol-3D images Image 1
Properties
Molecular formula LiC
6
H
5
Molar mass 84.045 g mol-1
Appearance Colorless crystals
Density 828 mg cm-3
Boiling point 140 to 143 °C (284 to 289 °F; 413 to 416 K)
Solubility in water Reacts
Thermochemistry
Std enthalpy of
formation
ΔfHo298
48.3-52.5 kJ mol-1
Hazards
MSDS External MSDS
R-phrases R14, R17, R23/24/25, R48
S-phrases (S1/2), S8, S9, S16, S26, S30, S46, S36/37/39, S45
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

Phenyllithium or Lithobenzene 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.[2] 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.[3]

Structure and properties[edit]

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 strong intermolecular bonding occurs between these phenyllithium dimers and the π-electrons of the phenyl groups in the adjacent dimers, resulting in an infinite polymeric ladder structure.[4]

Ball-and-stick model of part of a ladder in the crystal structure of unsolvated phenyllithium

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.

Stick model of the crystal structure of the phenyllithium etherate tetramer - ether ethyl groups omitted for clarity

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 [(PhLi • Et2O)4] 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.[5]

Preparation[edit]

Phenyllithium was first produced by the reaction of lithium metal with diphenylmercury:[6]

(C6Η5)2Ηg + 2Li → 2C6Η5Li + Ηg

The synthesis was improved soon afterward by directly reacting lithium with phenyl halides.[7]

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[edit]

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

PhLi + R2C=O → PhR2COLi

2-Phenylpyridine is prepared by the reaction of phenyl lithium with pyridine, a process that entials an addition-elimination pathway:[8]

C6H5Li + C5H5N → C6H5-C5H4N + LiH

References[edit]

  1. ^ "phenyllithium (CHEBI:51470)". Chemical Entities of Biological Interest (ChEBI). Cambridge, UK: European Bioinformatics Institute. 2009-01-22. Main. Retrieved 2013-06-01. 
  2. ^ Wietelmann, U.; Bauer, R. J. (2005), "Lithium and Lithium Compounds", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a15_393 
  3. ^ Gilman, H.; Zoellner, E. A.; Selby, W. M. (1932). "An Improved Procedure for the Preparation of Organolithium Compounds". Journal of the American Chemical Society 54 (5): 1957–1962. doi:10.1021/ja01344a033. 
  4. ^ Dinnebier, R. E.; Behrens, U.; Olbrich, F. (1998). "Lewis Base-Free Phenyllithium: Determination of the Solid-State Structure by Synchrotron Powder Diffraction". Journal of the American Chemical Society 120 (7): 1430–1433. doi:10.1021/ja972816e. 
  5. ^ Hope, H.; Power, P. P. (1983). "Isolation and Crystal Structures of the Halide-Free and Halide-Rich Phenyllithium Etherate Complexes [(PhLi•Et2O)4] and [(PhLi•Et2O)3•LiBr]". Journal of the American Chemical Society 105 (16): 5320–5324. doi:10.1021/ja00354a022. 
  6. ^ Green, D. P.; Zuev, D. (2008). "Phenyllithium". Encyclopedia of Reagents for Organic Synthesis. Wiley and Sons. doi:10.1002/047084289X.rp076.pub2. 
  7. ^ Dinnebier, R. E.; Behrens, U.; Olbrich, F. (1998). "Lewis Base-Free Phenyllithium: Determination of the Solid-State Structure by Synchrotron Powder Diffraction". Journal of the American Chemical Society 120 (7): 1430–1433. doi:10.1021/ja972816e. 
  8. ^ Evans, J. C. W.; Allen, C. F. H. "2-Phenylpyridine" Organic Syntheses (1938), vol. 18, p. 70. doi:10.15227/orgsyn.018.0070