Pyrrolinium-substituted Persistent Zwitterionic Ferrocenate Derivative Enabling the Application of Ferrocene Anolyte

Here, we report the imidazolium-/pyrrolinium-substituted persistent zwitterionic ferrocenate derivatives, which were characterized by electron paramagnetic resonance (EPR) and ⁵⁷Fe Mössbauer spectroscopy. Additional theoretical studies on these zwitterionic ferrocenate derivatives clearly explain the origin of their thermal stability and the orbital interactions between iron and imidazolium-/pyrrolinium-substituted zwitterionic cyclopentadienyl ligand. Exploiting the facile Fe(II/I) redox chemistry, we successfully demonstrated that the ferrocene derivative can be applied as an example of derivatized ferrocene anolyte for redox-flow batteries. These zwitterionic ferrocenate derivatives will not only deepen our understanding of the intrinsic chemistry of ferrocenate but have the potential to open the way for the rational design of metallocenate derivatives for various applications.