Increased stability of (μ-1,3-propanedithiolato)-diironhexacarbonyl anion, and new electrocatalytic pathways for molecular hydrogen production

Inexpensive and efficient production of molecular hydrogen is crucial to a renewable energy economy. Hydrogen production catalyzed by [μ-1,3-C₃H₆S₂]Fe2(CO)6 (1), and [μ-1,3-C₃H₄(1,3-CH₃)₂S₂]Fe₂(CO)₆ (2), which have features similar to the active sites of [FeFe]hydrogenases, are being studied. The electronic structure of 2 is found to be very similar to that of the previously studied catalyst 1 as probed by photoelectron and infrared spectroscopies. However, reduction of 1 is largely irreversible on the cyclic voltammetry (CV) time scale and has been shown to form a dimer, whereas the reduction of 2 is reversible on the CV time scale. The catalyzed reduction of protons from weak acids with pK_a values from 18 to 25 in acetonitrile has revealed new catalytic mechanisms occurring at significantly less negative reduction potentials than previously observed. Possible pathways of these new mechanisms are examined by density functional theory and simulation of the electrochemical data.