The Redox Chemistry of [Co6C(CO)15]2–: A Synthetic Route to New Co-Carbide Carbonyl Clusters

The oxidation and reduction reactions of [Co6C(CO)(13)](2-) have been studied in detail, leading to the isolation of several new Co-carbide carbonyl clusters. Thus, [Co6C(CO)(15)](2-) reacts in tetrahydrofuran (THF) with oxidants such as HBF4 center dot Et2O and [Cp2Fe][PF6], resulting first in the formation of the previously reported [Co6C(CO)(14)](-); then, in CH2Cl2, the new dicarbide [Co11C2(CO)(23)](2-) is formed. The latter may be further oxidized, yielding the isostructural monoanion [Co11C2(CO)(23)](-), whereas its reduction with (cyclopentadienyl)(2)Co affords the unstable trianion [Co11C2(CO)(23)](3-), which decomposes during workup. Oxidation of [Co6C(CO)(15)](2-) in CH3CN with [C7H7][BF4] affords the same major products, and besides, the new monoacetylide [Co-10(C-2)(CO)(21)](2-) was obtained as side-product. Conversely, the reduction of [Co6C(CO)(15)](2-) in THF with increasing amounts of Na/naphthalene results in the following species: [Co6C(CO)(13)](2-), [Co-11(C-2)(CO)(22)](3-), [Co7C(CO)(15)](3-), [Co8C(CO)(17)](4-), [Co6C(CO)(12)](3-), and [Co(CO)(4)](-). The new [Co11C2(CO)(23)](-), [Co11C2(CO)(23)](2-), [Co-10(C-2)(CO)(21)](2-), [Co8C(CO)(17)](4-), [CO6C(CO)(12)](3-), and [Co7C(CO)(15)](3-) clusters were structurally characterized. Moreover, the paramagnetic species [Co11C2(CO)(23)](2-) and [Co6C(CO)(12)](3-) were investigated by means of electron paramagnetic resonance spectroscopy. Finally, electrochemical studies were performed on [Co11C2(CO)(23)](n-) (n = 1-3).