To investigate further, a different reductant without radical character but with an oxidation potential similar to TEMPO was selected for reaction with the non-redox diazonium dC12. Based on a cyclic voltammetry study, carboxy-ferrocene (Fc-COOH) was identified as a suitable candidate due to its reversible oxidation system centered at +0.32 V vs. Ag/AgNO₃ 0.01 M, which is close to TEMPO's oxidation potential (+0.33 V vs. Ag/AgNO₃ 0.01 M). When dC 12 and Fc-COOH were mixed in stoichiometric amounts, the ¹H NMR spectrum showed a similar effect to that observed with TEMPO: the aromatic proton signals shifted to lower chemical shifts (Figure , top). This finding indicates that the diazonium group was transformed into a less electron-withdrawing form, just as observed with TEMPO radical species. These results strongly suggest that this transformation involves a redox reaction, as it occurs even in the presence of the non-radical reductant Fc-COOH.