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

Abstract

[FeFe] hydrogenases demonstrate remarkable catalytic efficiency in hydrogen evolution and oxidation processes. However, susceptibility of enzymes to oxygen‐induced degradation impedes their practical deployment in hydrogen‐production devices and fuel cells. Recent investigations into the oxygen‐stable (Hinact) state of the H‐cluster revealed its inherent capacity to resist oxygen degradation. Herein, we present findings on Cl‐/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 bearing the CO bridge. Structural analysis of the t‐Cl demonstrates a striking resemblance to the Hinact state of DdHydAB and CbA5H. The t‐Cl/t‐SH exhibit reversible oxidation, with both redox species, electronically, being the first biomimetic analogs to the Htrans and Hinact states. These complexes exhibit notable resistance against oxygen‐induced decomposition, supporting the potential oxygen‐resistant nature of the Htrans and Hinact states. The swift reductive release of the Cl‐/SH‐ demonstrates its labile and kinetically controlled binding. The findings garnered from these investigations offer valuable insights into properties of the enzymatic O2‐stable state, and key factors governing deactivation and reactivation conversion. This work contributes to advancement of bio‐inspired molecular catalysts and integration of enzymes and artificial catalysts into H2‐evolution devices and fuel‐cell applications.