Sulfinato Iron(III) Complex for Electrocatalytic Proton Reduction

We report the first example of a sulfinato Fe­(III) complex acting as a highly active electrocatalyst for proton reduction. The sulfinate binds to the metal through oxygen, resulting in a seven-membered chelate ring that is likely hemilabile during catalysis. Proton reduction occurs at −1.57 V versus Fc/Fc+ in CH3CN with an ic/ip = 13 in CH3CN (kobs = 3300 s–1) and an overpotential of 800 mV. The catalysis is first order with respect to [catalyst] and second order with respect to [trifluoracetic acid]. An 11% increase in catalytic activity is observed in the presence of water, suggesting that sulfinate moieties are viable functional groups for aqueous proton reduction catalysts.