Cyclopentadienyl magnesium bromide

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Cyclopentadienyl magnesium bromide
Skeletal formula
3D model (JSmol)
  • InChI=1S/C5H5.BrH.Mg/c1-2-4-5-3-1;;/h1-3H,4H2;1H;/q-1;;+2/p-1
  • C1C=CC=[C-]1.[Mg+2].[Br-]
Molar mass 169.304 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Cyclopentadienyl magnesium bromide is a chemical compound with the molecular formula C5H5MgBr. The molecule consists of a magnesium atom bonded to a bromine atom and a cyclopentadienyl group, a ring of five carbons each with one hydrogen atom.

The compound is a Grignard reagent, a type of organometallic compound that features a magnesium atom bonded to a halogen atom and to a carbon atom of some organic functional group.

This compound is of historic importance as the starting material for the first published synthesis of ferrocene by Peter Pauson and Thomas J. Kealy in 1951.[1]


The compound can be prepared by reacting cyclopentadiene with magnesium and bromoethane in anhydrous benzene.[2]


  1. ^ H. Werner (2012): "At Least 60 Years of Ferrocene: The Discovery and Rediscovery of the Sandwich Complexes". Angewandte Chemie International Edition, volume 51, issue 25, pages 6052–6058. doi:10.1002/anie.201201598
  2. ^ P. L. Pauson and T. J. Kealy (1951): "A New Type of Organo-Iron Compound". Nature, volume 168, issue 4285, pages 1039–1040. doi:10.1038/1681039b0