Synthesis and Molecular Structures of Monosubstituted Pentamethylcobaltocenium Cations

(Amino-η5-cyclopentadienyl)(pentamethyl-η5-cyclopentadienyl)cobalt(III) hexafluorophosphate (6PF6) was prepared by a route that started with the synthesis of the zwitterion (oxycarbonyl-η5-cyclopentadienyl)(pentamethyl-η5-cyclopentadienyl)cobalt(III) (1). The acidification of 1 created the carboxylic acid 2PF6, which was converted into the acyl chloride 3PF6. The reaction with NaN3 afforded the azide 4PF6, which was transformed to the carbamate 5PF6. The hydrolysis of 5PF6 afforded the desired aminocobaltocenium compound 6PF6. The oxidation of 6PF6 yielded the (nitro-η5-cyclopentadienyl)(pentamethyl-η5-cyclopentadienyl)cobalt(III) cation 7+. For 1, 2+, 4PF6, 6PF6, and 7PF6, X-ray structure analyses were performed. The electronic structure of 6+ calculated by DFT methods revealed a short C–N bond, which is in agreement with the molecular structure obtained from X-ray structure analysis. The pKa value of 6PF6 was estimated from aqueous solution. Cyclic voltammetry studies show a reversible one-electron reduction and an irreversible one-electron oxidation.