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: [Fe-2(mu-S2C6H4-xClx)(CO)(6)], where x = 0, 2-4, and [Fe-2(mu-S2C6H3Me)(CO)(6)]. Among this series the novel compounds [Fe-2(mu-S2C6Cl3H)(CO)(6)] (4) and [Fe-2(mu-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 (pK(a) = 22.3 in acetonitrile).