An electrochemical and spectroelectrochemical study of an iridium-buckminsterfullerene complex. Evidence for C₆₀-localized reductions

The complex (η⁵-C₉H₇)Ir(CO)(η²-C ₆₀) has been studied by cyclic voltammetry (CV) in dichloromethane, tetrahydrofuran, and benzene. The CV in dichloromethane shows two quasi-reversible waves (E_1/2 = -1.08 and -1.43 V vs internal ferrocene), which are assigned to C₆₀-localized redox processes, and an irreversible oxidation (E_p = +0.72 V vs Fc⁺/Fc) apparently occurring at the metal atom. Modified potentials are observed in tetrahydrofuran, an effect very similar to that reported for free C₆₀. Infrared spectroelectrochemistry shows that reduction of the complex by one and two electrons causes the v_CO IR band to shift to lower energy by 12 and 23 cm^-1, respectively. These relatively small changes in frequency reflect small changes in electron density at the iridium center, thereby indicating ligand-centered rather than metal-centered reductions. Oxidation leads to irreversible loss of carbon monoxide from the complex. Small changes in the UV-vis spectrum of the complex also are observed upon reduction. Analysis of the electrochemical and spectral data suggests that complexation of C₆₀ with the (η⁵-C₉H₇)Ir(CO) moiety causes distinct but relatively minor perturbations in its electronic structure.