The roles of chalcogenides in O(2) protection of H(2)ase active sites

At some point, all HER (Hydrogen Evolution Reaction) catalysts, important in sustainable H(2)O splitting technology, will encounter O(2) and O(2)-damage. The [NiFeSe]-H(2)ases and some of the [NiFeS]–H(2)ases, biocatalysts for reversible H(2) production from protons and electrons, are exemplars of oxygen tolerant HER catalysts in nature. In the hydrogenase active sites oxygen damage may be extensive (irreversible) as it is for the [FeFe]–H(2)ase or moderate (reversible) for the [NiFe]–H(2)ases. The affinity of oxygen for sulfur, in [NiFeS]–H(2)ase, and selenium, in [NiFeSe]–H(2)ase, yielding oxygenated chalcogens results in maintenance of the core NiFe unit, and myriad observable but inactive states, which can be reductively repaired. In contrast, the [FeFe]–H(2)ase active site has less possibilities for chalcogen-oxygen uptake and a greater chance for O(2)-attack on iron. Exposure to O(2) typically leads to irreversible damage. Despite the evidence of S/Se-oxygenation in the active sites of hydrogenases, there are limited reported synthetic models. This perspective will give an overview of the studies of O(2) reactions with the hydrogenases and biomimetics with focus on our recent studies that compare sulfur and selenium containing synthetic analogues of the [NiFe]–H(2)ase active sites.