Electrocatalytic proton reduction by dithiolate-bridged diiron carbonyl complexes: a connection to the H-cluster?

Spectroscopic and electrochemical investigation of electrocatalytic proton reduction by Fe₂(μ-pdt)(CO)₆, 1, have been interpreted in terms of a reaction scheme involving sequential electron–proton reactions to give a two-electron, two-proton product that undergoes rate-limiting dihydrogen elimination. Further reduction, at slightly higher negative potentials, gives a more reactive product and this process dominates reactions conducted at higher acid concentrations. Inhibition of the electrocatalytic reaction by CO is due to the more efficient loss of catalyst and this is best modelled by a reaction that is second order in terms of 1⁻. During electrocatalytic proton reduction a new species is observed, which features a bridging CO group and the wavenumbers of the ν(CO) modes of the terminally bound carbonyl groups are similar to those of the carbonyl groups bound to the oxidized form of the H-cluster.