Preparation and properties of inclusion compounds of ferrocene and its derivatives with cyclodextrins

Inclusion compounds of ferrocene and its derivatives with α-, β-, and γ-cyclodextrins have been prepared in a crystalline state in high yields. β-Cyclodextrin and γ-cyclodextrin formed 1 : 1 stoicheiometric inclusion compounds. α-Cyclodextrin formed 2 : 1 (host:guest) complexes with ferrocene and its monosubstituted derivatives, but did not form complexes with 1,1′-disubstituted derivatives. The complexes of α- and β-cyclodextrin with ferrocene are thermally stable and do not liberate ferrocene on heating at 100 °C in vacuo. The inclusion compounds were characterized by 1H n.m.r., i.r., u.v., and circular dichroism spectroscopy. A large positive induced Cotton effect was observed in the case of complex of β-cyclodextrin with ferrocene, while the complex of γ-cyclodextrin showed a negative spectrum. The binding mode is discussed.