Two hexacarbonyl diiron compounds featuring dithiolate bridges with strong electron-withdrawing groups (CO(2)Me, tetrachloro-biphenyl) were synthesized and structurally characterized. Electrochemical study of these compounds demonstrates that such electron-withdrawing groups have a pronounced effect on both the reduction potentials and the electron transfer process. The reduced forms of these compounds catalyze the reduction of protons in dichloromethane. However, the tetrachloro-biphenyl derivative is the only one able to work in the potential range of its primary reduction process. A catalytic reaction scheme is proposed.