Hydrogen Evolution by Fe^III Molecular Electrocatalysts Interconverting between Mono and Di-Nuclear Structures in Aqueous Phase

A new FeL/Fe₂ L₂ 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 Fe₂ L₂ μ-oxo dimer in acetate buffer (pH 4.9), with an overpotential of about 1 V and faradaic yield up to 75 %. The resulting i_cat /i_p values in the range 15-28 are among the highest reported for Fe-based electrocatalysts (i_cat is the catalytic current, whereas i_p is the current of an Fe-based redox event).