Oxidation of Metallocenes and Electron Transfer Reactions

All metallocenes of the transition metals may be oxidized to the [Mcp2] or [Mcp2] cations. Sometimes, the oxidation is reversible. Ferrocene may be oxidized by HNO3, H2SO4, Ce(SO)4)2, HEAuC ], Fe(III), CUCI2, quinone, etc. Other metallocenes are oxidized in a similar way  

Cobaltocene is a strong reducing agent it reduces FeCl2 and H 2Coq 2 + FeCl2— 2[Cocp2] Cl +Fe 

The cations [Cocp2], [Rhcp2], and [Ircp2] are very stable. They do not decompose even on boiling with concentrated sulfuric and nitric acids or aqua regia. Therefore, this enables the oxidation of substituents in the ring  

Between the oxidized Mcp cation and the metallocenes, there is often rapid electron transfer. The half-time for the electron transfer reaction between the ferrocenium ion and ferrocene is several milliseconds at 198 K. The exchange between Cocp and Cocp2 is also fast. 

Metallocenes may also be oxidized by halogens (CI2, Br212) and some halogenated organic compounds. 

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