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

Abstract

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.