[FeFe] Hydrogenase: Protonation of {2Fe3S} Systems and Formation of Super‐reduced Hydride States

The synthesis and crystallographic characterization of a complex possessing a well-defined {2Fe3S(μ-H)} core gives access to a paramagnetic bridging hydride with retention of the core geometry. Chemistry of this 35-electron species within the confines of a thin-layer FTIR spectro-electrochemistry cell provides evidence for a unprecedented super-reduced FeI(μ-H)FeI intermediate.