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 Fe(III)(μ-OPh)(μ(2)-mpdp)Fe(II)(NH(2)Bn)] (1; mpdp(2-) = m-phenylenedipropionate) bearing a terminal aminobenzyl ligand can be reversibly deprotonated to the anilinate complex 2 whose core Fe(II)(μ-OPh)(μ(2)-mpdp)Fe(III)(NHBn)] features an inversion of the iron valences. This observation is supported by a combination of UV-visible, (1)H NMR, and M?ssbauer spectroscopic studies.