Phenylmagnesium bromide

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Phenylmagnesium bromide
Image:PhMrBrL2.png Image:Phenylmagnesium-bromide-3D-balls.png OR2 = ether or THF
General
Systematic name	?
Other names	PMB
Molecular formula	C6H5MgBr
SMILES	Br[Mg]c1ccccc1
Molar mass	181.31 g/mol
Appearance	Colorless crystals
CAS number	[100-58-3]
Properties
Density and phase	solid
Solubility in water	Reacts violently
Basicity (pKb)	strong base
Structure
Hazards
MSDS	External MSDS
Main hazards	inflammable
NFPA 704
Flash point	?°C
R/S statement	R: R12 R14 R15 R20 R22 R35 R41 S: S16 S26 S30 S33 S36 S37 S39 S42 S45
RTECS number	?
Supplementary data page
Structure and properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Related compounds
Related compounds	Phenyllithium Magnesium bromide Methylmagnesium chloride
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Phenylmagnesium bromide, with the simplified formula C₆H₅MgBr, is a a magnesium-containing organometallic compound. It is so commonly used that it is commercially available as a solution in diethyl ether or tetrahydrofuran (THF). Phenylmagnesium bromide is a Grignard reagent. It is often used as a synthetic equivalent for the "Ph⁻" phenyl synthon.

Contents 1 Preparation and structure 2 Chemistry 3 References 4 Further reading

Preparation and structure

Phenylmagnesium bromide can be prepared in the laboratory by treating bromobenzene with magnesium metal, usually in the form of ribbon. A polar solvent is required to solvate the magnesium portion of the molecule, hence the use of ether or THF. Protic solvents such as alcohols and water react with phenylmagnesium bromide to give benzene, and halogenated solvents are also incompatible with the synthesis. A small amount of iodine may be used to activate the magnesium by removing the oxide surface.

Although in organic synthesis it is convenient to represent this species as C₆H₅MgBr, the molecule is more complex as shown in the figure. The compound invariably forms an adduct with two OR₂ ligands from the ether or THF solvent. Thus the Mg is tetrahedral and obeys the octet rule. The Mg-O distances are 2.01 and 2.06 Å whereas the Mg-C and Mg-Br distances are 2.2 and 2.44 Å, respectively.^[1]

Chemistry

Phenylmagnesium bromide is a strong nucleophile as well as a strong base. It can abstract many labile protons, thus the substrate must be protected where necessary. It often adds to carbonyls, which are electron-deficient, such as in the laboratory synthesis of benzoic acid and triphenylmethanol.

References

1. ↑ Stucky, G. D.; Rundle, R. E. "The Structure of Phenylmagnesium Bromide Diethyletherate and the Nature of Grignard Reagents" Journal of the American Chemical Society 1963, volume 85, pp1002. DOI 10.1021/ja00890a039

Further reading

• Oxford University, Phenylmagnesium bromide in ether, Aug 19 2005. Accessed 28 Oct 2006.