Ferrocene and Metallocenes

Ferrocene organomercurials were also used to prepare a number of other derivatives, namely, halogen-, sulfur-, or selenium-containing compounds, biferrocenyl, or triphenylmethylferrocene [Nesmeyanov, Perevalova, 0. A. Nesmeyanova 258,259)]. Lithiation or sodium metalation provided even more versatile reagents, the reactions being used by other investigators as well. 

Of this research, I will mention here only aminoferrocene. We were very glad to obtain the compound through the Kocheshkov reaction of ferrocenyllithium and hydroxylamine 0-ether [Nesmeyanov, Perevalova, Shilovtseva 260)] later, we synthesized aminoferrocene via other paths 261, 262). 

Our first ferrocene papers described one more reaction the synthesis of bis(tetrahydroindenyl)iron through the acylation of ferrocene with succinic anhydride, reduction, then closure of the six-membered ring followed by reduction again. The compound was identical with that obtained by 

Fischer from tetrahydroindcne [253). In a similar manner, we obtained ferrocene analogs of anthronc and anthraquinone from ferrocene and phthalic anhydride. 

Now let me come back to primary substitutions at the ferrocene nucleus. Together with Vil chevskaya, we phosphorylated ferrocene and its derivatives to triferrocenylphosphine oxides [263, 264). An unusual reaction, discovered in collaboration with Perevalova and Yur eva, was the direct cyanation of ferrocene with hydrocyanic acid in the presence of ferric chloride [265,272). Initially, cyanide attacks the iron atom of the ferricinium cation, then the cyanide group transfers to the ring while the iron is simultaneously reduced. The reaction was termed by us as the ricochet (from the metal to the nucleus) substitution it may be applied to many substituted ferrocenes and to the ruthenocenium cation [273), and it is now the simplest route to ferrocene carboxylic acids through their nitriles. Further, ferrocene was studied in acid-medium reactions with oxo compounds. With aldehydes [274), the reaction was complicated by the transformation of ferro-cenylalkyl carbinol formed Initially via the carbonium ion, followed by transformation to a radical which, in its turn, was coupled to 1,2-bis-(ferrocenylalkyl)ethane (27.5). The reaction with acetone led to 2,2-di-ferrocenylpropane (276). 

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