Phenylmagnesium bromide

Phenylmagnesium bromide, with the simplified formula C
6H
5MgBr, is a magnesium-containing organometallic compound. 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 phenyl "Ph−" synthon.

Phenylmagnesium bromide
Phenylmagnesium bromide, OR2 = ether or THF
Complex with ethers
Ball-and-stick model of the PhMgBr-diethyl ether adduct
Complex with diethyl ether
Space-filling model of the PhMgBr-diethyl ether adduct
Names
IUPAC name
Bromido(phenyl)magnesium
Other names
PMB, (bromomagnesio)benzene
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.002.607
EC Number
  • 202-867-2
  • InChI=1S/C6H5.BrH.Mg/c1-2-4-6-5-3-1;;/h1-5H;1H;/q;;+1/p-1 ☒N
    Key: ANRQGKOBLBYXFM-UHFFFAOYSA-M ☒N
  • InChI=1/C6H5.BrH.Mg/c1-2-4-6-5-3-1;;/h1-5H;1H;/q;;+1/p-1/rC6H5BrMg/c7-8-6-4-2-1-3-5-6/h1-5H
    Key: ANRQGKOBLBYXFM-ZAQPMBKGAV
  • Br[Mg]c1ccccc1
Properties
C6H5MgBr
Molar mass 181.31 g mol−1
Appearance Colorless crystals
Density 1.14 g cm−3
Reacts with water
Solubility 3.0M in diethyl ether, 1.0M in THF, 2.9M in 2Me-THF
Acidity (pKa) 45 (conjugate acid)
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 flammable, volatile
GHS labelling:
GHS02: FlammableGHS05: Corrosive
Danger
H225, H314
P210, P233, P240, P241, P242, P243, P260, P264, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P370+P378, P403+P235, P405, P501
Flash point −45 °C (−49 °F; 228 K)
Safety data sheet (SDS) External MSDS
Related compounds
Related compounds
 Phenyllithium
Magnesium bromide
Methylmagnesium chloride
Dibutylmagnesium
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Preparation
Phenylmagnesium bromide is prepared by reaction of bromobenzene with magnesium metal.

Phenylmagnesium bromide is commercially available as solutions of diethyl ether or THF. Laboratory preparation involves treating bromobenzene with magnesium metal, usually in the form of turnings. A small amount of iodine may be used to activate the magnesium to initiate the reaction.[1]

Coordinating solvents such as ether or THF, are required to solvate (complex) the magnesium(II) center. The solvent must be aprotic since alcohols and water contain an acidic proton and thus react with phenylmagnesium bromide to give benzene. Carbonyl-containing solvents, such as acetone and ethyl acetate, are also incompatible with the reagent.

Structure

Although phenylmagnesium bromide is routinely represented as C
6H
5MgBr, the molecule is more complex. The compound invariably forms an adduct with two OR
2 ligands from the ether or THF solvent. Thus, the Mg is tetrahedral and obeys the octet rule. The Mg–O distances are 201 and 206 pm whereas the Mg–C and Mg–Br distances are 220 pm and 244 pm, respectively.[2]

Chemistry
Main article: Grignard reagent

Phenylmagnesium bromide is a strong nucleophile as well as a strong base. It can abstract even mildly acidic protons, thus the substrate must be protected where necessary. It often adds to carbonyls, such as ketones, aldehydes.[1][3] With carbon dioxide, it reacts to give benzoic acid after an acidic workup. If three equivalents are reacted with phosphorus trichloride, triphenylphosphine can be made.

References
  1. Robertson, D. L. (2007-01-03). "Grignard Synthesis: Synthesis of Benzoic Acid and of Triphenylmethanol". MiraCosta College. Retrieved 2008-01-25.
  2. Stucky, G. D.; Rundle, R. E. (1963). "The Structure of Phenylmagnesium Bromide Diethyletherate and the Nature of Grignard Reagents". J. Am. Chem. Soc. 85 (7): 1002–1003. doi:10.1021/ja00890a039.
  3. Bachmann, W. E.; Hetzner, H. P. (1955). "Triphenylcarbinol". Organic Syntheses.; Collective Volume, vol. 3, p. 839
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