Addition of the cyanide ion to cyclopentadienyliron complexes of arenes containing an electron-withdrawing substituent

Reactions of cyclopentadienyliron (CpFe) complexes of arenes containing an electron-withdrawing substituent with NaCN in DMF resulted in a regiospecific addition of the cyanide ion at a position ortho to the substituent, giving rise to CpFe complexes of cyanocyclohexadienyl systems. For example, the addition of the cyanide ion to η⁶-nitrobenzene-η⁵-cyclopentadienyliron hexafluorophosphate (Ia) gave the neutral complex, 1-5-η⁵-exo-6-cyano-1-nitrocyclohexadienyl-η⁵-cyclopentadienyliron (IIa). Similar cyanide additions also took place with the CpFe complexes of benzophenone and of methyl benzoate. Reactions with η⁶-anthraquinone, xanthone, thioxanthone, or thioxanthone-10,10-dioxide-η⁵-cyclopentadienyliron hexafluorophosphate (IIIa, IIIb, IIIc or IIId, respectively) resulted in the addition of the cyanide ion solely to C(1), a position ortho to the keto substituent; for example, from IIIa, the adduct was 2,3,4,4a,9a-η⁵,-exo-1-cyano-1H-anthraquinone-η⁵-cyclopentadienyliron (IVa). With the CpFe complex of fluorenone (V), however, a 3/1 mixture of products was obtained, arising from cyanide additions to C(1) and C(4a), both positions being ortho to the keto substituent in V. A possible explanation is suggested for the failure of the cyanide ion adding to C(4a) in reactions with IIIa to IIId.