Résumé
We have previously investigated cis/trans isomerization processes in phenoxido-bridged mixed-valent Fe$^{II}$Fe$^{III}$ complexes that contain either one aniline or one anilide ligand. In this work, we compare the properties of similar complexes bearing one terminal protic ligand, either aniline or 1H-benzimidazole. Whatever the ligand, $^1$H NMR spectroscopy clearly evidences that the complexes are present in CH$_3$CN as a mixture of cis- and trans-isomers in a close to 1:1 ratio. We show here that addition of NEt$_3$ indeed allows the deprotonation of these ligands, the resulting complexes bearing either anilide or benzimidazolide that are coordinated to the ferric site. The latter are singular examples of a high-spin ferric ion coordinated to a benzimidazolide ligand. Whereas the trans-isomer of the anilide complex is the overwhelming species, benzimidazolide species are mixtures of cis- and trans-isomers in equal proportions. Moreover, cyclic voltammametry studies show that Fe$^{II}$Fe$^{III}$ complexes with 1H-benzimidazole are more stable than their aniline counterparts, whereas the reverse is observed for the deprotonated species.