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)(PMe(3))(2), Fe(2)(mu-edt)(CO)(4)(PMe(3))(2), (NEt(4))(2)[Fe(2)(mu-pdt)(CO)(4)(CN)(2)], (NEt(4))(2)[Fe(2)(mu-edt)(CO)(4)(PMe(3))(2)] and (NEt(4))[Fe(2)(mu-pdt)(CO)(4)(CN)(PMe(3))] (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.