ELECTROCHEMISTRY OF [M6(CO)15]2- ANIONIC CLUSTERS (M=CO AND IR) - PREPARATION AND CHEMICAL CHARACTERIZATION OF [IR6(CO)14(NCO)]- AND OF THE RADICAL-ANION [IR6(CO)15]- - PROPOSED MECHANISM OF FORMATION OF THE HEXANUCLEAR SUBSTITUTED CLUSTER [IR6(CO)15CL]-

Electrochemical studies performed on [Ir6(CO)15]2- show that the dianion undergoes stepwise oxidation to the congeners [Ir6(CO)15]n (n = - 1 or 0); only the monoanion is notably long-lived. By contrast the electrochemical oxidation of [Co6(CO)15]2- shows that both the corresponding monoanion and neutral clusters are transient species. Information gained on the oxidation of [Ir6(CO)15]2- in the presence of halide ions has enabled establishment of the mechanism of formation of the anion [Ir6(CO)15Cl]-, previously characterized by an X-ray study. This process of oxidation of [Ir6(CO)15]2- can be also initiated by treating the hexanuclear complex with chemical oxidants such as [Fe(C5H5)2]+ and FeCl3. The characterization of [N(PPh3)2][Ir6(CO)14(NCO)], obtained by chemical oxidation of [N(PPh3)2]2[Ir6(CO)15] in the presence of [N(PPh3)2]N3, is also reported.