A biomimetic study for S/Se oxygenation in Ni(μ-EPh)(μ-SN 2 )Fe, (E = S or Se; SN 2 = Me-diazacycloheptane-CH 2 CH 2 S); Fe = (η 5 -C 5 H 5 )Fe II (CO) complexes related to the oxygen-damaged active sites of [NiFeS]/[NiFeSe]-H 2 ases is described. Mono- and di-oxygenates (major and minor species, respectively) of the chalcogens result from exposure of the heterobimetallics to O 2 ; one was isolated and structurally characterized to have Ni–O–Se Ph –Fe–S connectivity within a 5-membered ring. A compositionally analogous mono-oxy species was implicated by ν (CO) IR spectroscopy to be the corresponding Ni–O–S Ph –Fe–S complex; treatment with O-abstraction agents such as P( o -tolyl) 3 or PMe 3 remediated the O damage. Computational studies (DFT) found that the lowest energy isomers of mono-oxygen derivatives of Ni(μ-EPh)(μ-SN 2 )Fe complexes were those with O attachment to Ni rather than Fe, a result consonant with experimental findings, but at odds with oxygenates found in oxygen-damaged [NiFeS]/[NiFeSe]-H 2 ase structures. A computer-generated model based on substituting − SMe for the N-CH 2 CH 2 S − sulfur donor of the N 2 S suggested that constraint within the chelate hindered O-atom uptake at that sulfur site.
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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.
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- Award ID(s):
- 1665258
- NSF-PAR ID:
- 10199349
- Date Published:
- Journal Name:
- Chemical Science
- Volume:
- 11
- Issue:
- 35
- ISSN:
- 2041-6520
- Page Range / eLocation ID:
- 9366 to 9377
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D0SC02584D
