Reversible (De)protonation-Induced Valence Inversion in Mixed-Valent Diiron(II,III) Complexes

The coupling of electron and proton transfers is currently under intense scrutiny. This Communication reports a new kind of proton-coupled electron transfer within a homodinuclear first-row transition-metal complex. The triply-bridged complex [FeIII(μ-OPh)(μ2-mpdp)FeII(NH2Bn)] (1; mpdp2– = m-phenylenedipropionate) bearing a terminal aminobenzyl ligand can be reversibly deprotonated to the anilinate complex 2 whose core [FeII(μ-OPh)(μ2-mpdp)FeIII(NHBn)] features an inversion of the iron valences. This observation is supported by a combination of UV–visible, 1H NMR, and Mössbauer spectroscopic studies.