Cyclic Voltammetric Studies of Chlorine-Substituted Diiron Benzenedithiolato Hexacarbonyl Electrocatalysts Inspired by the [FeFe]-Hydrogenase Active Site

Chlorine-substituted benzenedithiols have been coordinated
to iron
carbonyl to yield a series of hydrogen-producing electrocatalysts:
[Fe2(μ-S2C6H4–xClx)­(CO)6],
where x = 0, 2–4, and [Fe2(μ-S2C6H3Me)­(CO)6]. Among this
series the novel compounds [Fe2(μ-S2C6Cl3H)­(CO)6] (4) and [Fe2(μ-S2C6Cl4)­(CO)6] (5) have been characterized by X-ray crystallography.
IR spectroscopy and electrochemical analysis were used to evaluate
the electronic structure of these proton-reducing molecular electrocatalysts.
The increase in the number of electron-withdrawing groups upon the
electrocatalyst leads to an anodic shift in reduction potential and
a concomitant lowering of the overpotential of hydrogen evolution.
An overpotential of just 0.39 V is observed for 5 with
acetic acid (pKa = 22.3 in acetonitrile).