ELECTROINDUCED AND SPONTANEOUS METAL-HALIDE BOND-DISSOCIATION IN [CO(ETA(5)-C5H5)(ETA(3)-2-MEC3H4)I]

The electrochemical behavior of the species [Co(eta(5)-C5H5)(eta(3)-2- MeC3H4)I] and [Co(eta(5)-C5H5)(eta(3)-2-MeC3H4)(ACN)](+) in ACN soluti ons, at 25 degrees C, is described. The kinetic analysis of the cyclic voltammetry curves indicates that the introduction of one electron in the former complex is concerted with the dissociation of the Co-I bon d. The ensuing radical undergoes fast solvation to yield the solvato c omplex [Co(eta(5)-C5H5)(eta(3)-2-MeC3H4)(ACN)](.), which then acts as an efficient electron donor toward the starting material with the form ation of[Co(eta(5)-C5H5)(eta(3)-2-MeC3H4)(ACN)](+); finally, the catio n is electroreduced at the working potentials to conclude an overall a utocatalytic sequence. The solvato complex [Co(eta(5)-C5H5)(eta(3)-2-M eC3H4)(ACN)](.), formed as a product of the above reduction process, c an be reversibly reduced to the corresponding anion at more negative p otentials. Confirmation of the above mechanism and of the fact that th e solvato complex can act as a solution electron donor toward the star ting material was obtained by studying the electrochemical behavior of the solvato complex itself and through calculations aimed to better d efine the dissociative electron-transfer process to [Co(eta(5)-C5H5)(e ta(3)-2-MeC3H4)I]. The dissociation of the metal-halide bond in the ne utral complex [Co(eta(5)-C5H5)(eta(3)-2-MeC3H4)I], with the formation of[Co(eta(5)-C5H5)(eta(3)-2-MeC3H4)(ACN)](+), was also found to occur spontaneously, in the bulk, through the observation of a progressive c hange of the cyclic voltammetric pattern. Support for the occurrence o f the reaction between the starting complex and the solvent was confir med by conductivity and spectroscopic measurements, which allowed the rate constant for the homogeneous solvolysis to be determined.