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(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.