Cyclopentadienyl magnesium bromide

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.

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