Synthesis and Handling Properties
The first reported synthesis of ferrocene used the Grignard reagent cyclopentadienyl magnesium bromide, which can be prepared by reacting cyclopentadiene with magnesium and bromoethane in anhydrous benzene. Iron(II) chloride is then suspended in anhydrous diethyl ether and added to the Grignard reagent. The reaction sequence is:
- 2 C5H5MgBr + FeCl2 → Fe(C5H5)2 + MgCl2 + MgBr2
Numerous other syntheses have been reported, including the direct reaction of gas-phase cyclopentadiene with metallic iron at 350 °C or with iron pentacarbonyl.
- Fe + 2 C5H6(g) → Fe(C5H5)2 + H2(g)
- Fe(CO)5 + 2 C5H6(g) → Fe(C5H5)2 + 5 CO(g) + H2(g)
More efficient preparative methods are generally a modification of the original transmetalation sequence using either commercially available sodium cyclopentadienide or freshly cracked cyclopentadiene and potassium hydroxide with anhydrous iron(II) chloride in ethereal solvents:
- 2 NaC5H5 + FeCl2 → Fe(C5H5)2 + 2 NaCl
- FeCl2.4H2O + 2 C5H6 + 2 KOH → Fe(C5H5)2 + 2 KCl + 6 H2O
Direct transmetalation can also be used to prepare ferrocene from other metallocenes, such as manganocene:
- FeCl2 + Mn(C5H5)2 → MnCl2 + Fe(C5H5)2
As expected for a symmetric and uncharged species, ferrocene is soluble in normal organic solvents, such as benzene, but is insoluble in water. Ferrocene is an air-stable orange solid that readily sublimes, especially upon heating in a vacuum. It is stable to temperatures as high as 400 °C. The following table gives typical values of vapor pressure of ferrocene at different temperatures:
| Pressure (Pa) | 1 | 10 | 100 |
|---|---|---|---|
| Temperature (K) | 298 | 323 | 353 |
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