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: Fe-2(mu-pdt)(CO)(4)(PMe3)(2), Fe-2(mu-edt)(CO)(4)(PMe3)(2), (NEt4)(2)[Fe-2(mu-pdt)(CO)(4)(CN)(2)], (NEt4)(2)[Fe-2(mu-edt)(CO)(4)(PMe3)(2)] and (NEt4)[Fe-2(mu-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.