Mechanistic aspects of the protonation of [FeFe]-hydrogenase subsite analogues

The formation of transient metal hydride(s) at the metallo-sulfur active sites of [FeFe]-hydrogenase is implicated in both hydrogen evolution and uptake reactions. Using a combination of time-resolved NMR, stopped-flow UV and stopped-flow IR, we have begun to unravel the mechanisms for protonation of synthetic electron-rich analogues of the di-iron subsite of the enzyme: Fe2(μ-pdt)(CO)4(PMe3)2, Fe2(μ-edt)(CO)4(PMe3)2, (NEt4)2[Fe2(μ-pdt)(CO)4(CN)2], (NEt4)2[Fe2(μ-edt)(CO)4(PMe3)2] and (NEt4)[Fe2(μ-pdt)(CO)4(CN)(PMe3)] (pdt = propane-1,3-dithiolate, edt = ethane-1,2-dithiolate). The mechanistic role of isomer interconversion and how this critically relates to steric access to the di-iron bridge are revealed.