Oxygen Sensitivity of [FeFe]-Hydrogenase: A Comparative Study of Active Site Mimics Inside vs Outside the Enzyme

[FeFe]-hydrogenase is nature’s most efficient proton reducing and H2 oxidizing enzyme. However, biotechnological applications are hampered by the pronounced O2 sensitivity of this metalloenzyme, and the mechanism of aerobic deactivation is poorly understood. Here, we explore the oxygen reactivi-ty of four mimics of the organometallic active site cofactor of [FeFe]-hydrogenase, [Fe2(adt)(CO)6-x(CN)x]x– and [Fe2(pdt)(CO)6-x(CN)x]x– (x = 1, 2) as well as the corresponding cofactor variants of the enzyme by means of molecular spectroscopy. Additionally, we describe a straightforward and scalable synthetic recipe for the active site precursor complex Fe2(adt)(CO)6. Our data indicate that the amino-dithiolate (adt) complex, which is the synthetic precursor of the natural active site cofactor, is most oxygen sensitive. This observation highlights the significance of proton transfer in aerobic degradation and facilitates the identification of the responsible reactive oxygen species (ROS). Moreover, we show that the ligand environment of the iron ions critically influences the reactivity with O2 and ROS as the oxygen sensitivity increases with the exchange of ligands from CO to CN–. In summary, our results shine light on the chemistry of oxygen-induced deactivation of [FeFe]-hydrogenase. The trends in aer-obic deactivation observed for the model complexes are in line with the respective enzyme variants. This similarity underscores the relevance of model systems in understanding the enzyme and validates their potential as important tools for elucidating the chemistry of oxygen-induced deactivation of [FeFe]-hydrogenase and hydrogen turnover.