Oxygen uptake in complexes related to [NiFeS]- and [NiFeSe]-hydrogenase active sites.

A biomimetic study for S/Se oxygenation in Ni(μ-EPh)(μ-SN)Fe, (E = S or Se; SN = Me-diazacycloheptane-CHCHS); Fe = (η-CH)Fe(CO) complexes related to the oxygen-damaged active sites of [NiFeS]/[NiFeSe]-Hases is described. Mono- and di-oxygenates (major and minor species, respectively) of the chalcogens result from exposure of the heterobimetallics to O; one was isolated and structurally characterized to have Ni-O-Se-Fe-S connectivity within a 5-membered ring. A compositionally analogous mono-oxy species was implicated by (CO) IR spectroscopy to be the corresponding Ni-O-S-Fe-S complex; treatment with O-abstraction agents such as P(-tolyl) or PMe remediated the O damage. Computational studies (DFT) found that the lowest energy isomers of mono-oxygen derivatives of Ni(μ-EPh)(μ-SN)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]-Hase structures. A computer-generated model based on substituting SMe for the N-CHCHS sulfur donor of the NS suggested that constraint within the chelate hindered O-atom uptake at that sulfur site.