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)15]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·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)2Co 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 [Co10(C2)­(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–, [Co11(C2)­(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–, [Co10(C2)­(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).