Chemistry of Cyclopentadienyl and Related Complexes

In addition to complexes in which electron density is donated from localized a bonds to metals, many complexes are known in which electrons in aromatic molecules are donated to metals. A brief survey of the chemistry of these interesting compounds will be presented here. However, the area is so vast that the interested reader will need to consult the references listed at the end of the chapter for further details. 

Hydrogen atoms on the cyclopentadiene ring are very slightly acidic. Therefore, metallic sodium reacts with a solution of cyclopentadiene dissolved in tetrahydrofuran (THF) to liberate hydrogen, leaving 

The reaction of this product with FeCl2, which can be shown as 

Ferrocene is more correctly named as bis( 75-cyclopentadienyl)iron(II), and the molecule has a structure that can be shown as follows  

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