Chloride‐ and Hydrosulfide‐Bound 2Fe Complexes as Models of the Oxygen‐Stable State of [FeFe] Hydrogenase

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Abstract [FeFe] hydrogenases demonstrate remarkable catalytic efficiency in hydrogen evolution and oxidation processes. However, susceptibility of these enzymes to oxygen‐induced degradation impedes their practical deployment in hydrogen‐production devices and fuel cells. Recent investigations into the oxygen‐stable (H inact ) state of the H‐cluster revealed its inherent capacity to resist oxygen degradation. Herein, we present findings on Cl‐ and SH‐bound [2Fe‐2S] complexes, bearing relevance to the oxygen‐stable state within a biological context. A characteristic attribute of these complexes is the terminal Cl − /SH − ligation to the iron center bearing the CO bridge. Structural analysis of the t‐Cl demonstrates a striking resemblance to the H inact state of Dd HydAB and Cb A5H. The t‐Cl/t‐SH exhibit reversible oxidation, with both redox species, electronically, being the first biomimetic analogs to the H trans and H inact states. These complexes exhibit notable resistance against oxygen‐induced decomposition, supporting the potential oxygen‐resistant nature of the H trans and H inact states. The swift reductive release of the Cl‐/SH‐group demonstrates its labile and kinetically controlled binding. The findings garnered from these investigations offer valuable insights into properties of the enzymatic O 2 ‐stable state, and key factors governing deactivation and reactivation conversion. This work contributes to the advancement of bio‐inspired molecular catalysts and the integration of enzymes and artificial catalysts into H 2 ‐evolution devices and fuel‐cell applications.