Synthesis and Molecular Structures of Monosubstituted Pentamethylcobaltocenium Cations

(Amino‐η 5 ‐cyclopentadienyl)(pentamethyl‐η 5 ‐cyclopentadienyl)cobalt(III) hexafluorophosphate ( 6 PF 6 ) was prepared by a route that started with the synthesis of the zwitterion (oxycarbonyl‐η 5 ‐cyclopentadienyl)(pentamethyl‐η 5 ‐cyclopentadienyl)cobalt(III) ( 1 ). The acidification of 1 created the carboxylic acid 2 PF 6 , which was converted into the acyl chloride 3 PF 6 . The reaction with NaN 3 afforded the azide 4 PF 6 , which was transformed to the carbamate 5 PF 6 . The hydrolysis of 5 PF 6 afforded the desired aminocobaltocenium compound 6 PF 6 . The oxidation of 6 PF 6 yielded the (nitro‐η 5 ‐cyclopentadienyl)(pentamethyl‐η 5 ‐cyclopentadienyl)cobalt(III) cation 7 + . For 1 , 2 + , 4 PF 6 , 6 PF 6 , and 7 PF 6 , 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 p K a value of 6 PF 6 was estimated from aqueous solution. Cyclic voltammetry studies show a reversible one‐electron reduction and an irreversible one‐electron oxidation.