ELECTROCHEMISTRY OF METALLOCENES AT VERY NEGATIVE AND VERY POSITIVE POTENTIALS - ELECTROGENERATION OF 17-ELECTRON CP2CO(2-), AND CP2NI(2-) SPECIES(), CP2CO(2)

Cyclic voltammetry (CV) with Pt ultramicroelectrodes and coulometry we re used to study the electrooxidation of the Cp2Co+ cation in liquid S O2/(TBA)AsF6 solution in the temperature range from -70 to +25-degrees -C. The Cp2Co+ cation was shown to undergo reversible one-electron oxi dation with formation of the Cp2Co2+ dication, which is stable on the CV time scale. The chemical and electrochemical reversibility of Cp2Co + oxidation suggests retention of the sandwich structure in the dicati on. The E-degrees value for the Cp2Co+/2+ redox couple is +3.15 V (vs SCE) and the rate constant of heterogeneous electron transfer is great er-than-or-equal-to 0.03 +/- 0.01 cm/s. Electrochemically generated in the THF/(TBA)PF6 medium at T < -60-degrees-C, Cp2Co- and Cp2Ni- anion s, at E < -3.1 V, are reduced to Cp2Co2- and Cp2Ni2- dianions (or are reduced with simultaneous electron transfer and bond rupture); these d ianions are unstable on the CV time scale for T down to -100-degrees-C . The relationship between the E-degrees values of redox reaction of m etallocenes and the ionization potentials of the corresponding metals is discussed.