Electrochemical reduction of cobaltocenium in the presence of β-cyclodextrin

The cathodic voltammetric behavior of cobaltocenium (Cob(+)) and carboxycobaltocenium (Cob(+)-COO-) in aqueous solution was investigated in the presence of beta-cyclodextrin (beta-CD). The one-electron reduction of Cob(+) leads to the deposition on the electrode surface of the reduced, neutral form? cobaltocene (Cob). In contrast, the reduction of Cob(+)-COO- does not produce any deposits because Cob-COO- is water soluble. Upon addition of the CD host, the voltammetric waves of both compounds shift to less negative values revealing the formation of inclusion complexes between the reduced forms and the beta-CD host. In the case of Cob(+), the formation of the beta-CD.Cob complex results in the disappearance of the distortions in the current-potential curves which were associated with the deposition of free Cob. Digital simulations of the voltammetric responses in the presence of beta-CD led to the determination of the corresponding equilibrium association constants. The values obtained were 2000 and 1800 L/mol for the complexation of Cob and Cob-COO-, respectively, by beta-CD. The cobaltocenium (oxidized) forms were not appreciably bound by the beta-CD host.