Electronic structure of a benzylidyne-capped tricobalt cluster, [Co3Cp3(μ3-CPh)2]. X-ray structures and 1H NMR paramagnetic shifts of its cation and DFT calculations of its model complex

The cationic tricobalt cluster [Co3Cp3(μ3-CPh)2]+ (1+) was synthesized by the electrochemical oxidation of [Co3Cp3(μ3-CPh)2] (1). A large structural change was observed not only in the Co–Co, but also in the Co–C(cap) bonds upon oxidation of 1 to 1ClO4. 1H NMR paramagnetic shifts of this salt were measured in CD2Cl2. The π spin density on each sp2 carbon atom was estimated to be 0.0089 (o-Ph), −0.0012 (m-Ph), 0.0087 (p-Ph), and 0.0053 (Cp). These values on the phenyl carbon atoms are similar to ca. 1/25 of those of the benzyl radical. It indicates that there is significant spin density on the capping carbon atom, which is delocalized onto the benzylidyne groups from the Co3C2 oxidation center by π conjugation between them. These results are consistent with the e′′ (in the idealized D3h symmetry) singly occupied molecular orbital (SOMO) of 1+, and are reproduced by B3LYP-DFT calculations of a model complex, [Co3Cp3(μ3-CH)2] (2), and its cation.