Hydrogen Evolution by FeIII Molecular Electrocatalysts Interconverting between Mono and Di‐Nuclear Structures in Aqueous Phase

A new FeL/Fe2L2 manifold, with HL=2‐({[di(2‐pyridyl)methyl](methyl)amino}methyl)phenol, was prepared in gram scale (>50 % yield) and characterized in solution and solid state. The monomer/dimer interconversion is controlled in aqueous phase, upon varying the pH conditions. The electrocatalytic hydrogen evolution reaction (HER) occurs through the FeL monomer with added trifluoroacetic acid (TFA) and through the Fe2L2 μ‐oxo dimer in acetate buffer (pH 4.9), with an overpotential of about 1 V and faradaic yield up to 75 %. The resulting icat/ip values in the range 15–28 are among the highest reported for Fe‐based electrocatalysts (icat is the catalytic current, whereas ip is the current of an Fe‐based redox event). Iron for Hydrogen: Mononuclear/ dinuclear Fe species under pH‐triggered equilibrium catalyze electrocatalytic hydrogen evolution in trifluoroacetic acid (TFA)/CH3CN or CH3CN/acetate buffer with icat/ip values in the range 15–28 (icat is the catalytic current, whereas ip is the current of an Fe‐based redox event).