Cyclopentadienyl magnesium bromide is a chemical compound with the molecular formula C5H5MgBr.

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] MgCpBr (TiCp2Cl)2 TiCpCl3 TiCp2S5 TiCp2(CO)2 TiCp2Me2 VCpCh VCp2Cl2 VCp(CO)4 (CrCp(CO)3)2 Fe(η5-C5H4Li)2 ((C5H5)Fe(C5H4))2 (C5H4-C5H4)2Fe2 FeCp2PF6 FeCp(CO)2I CoCp(CO)2 NiCpNO ZrCp2ClH MoCp2Cl2 (MoCp(CO)3)2 RuCp(PPh3)2Cl RuCp(MeCN)3PF6