Dioxygen reactivity of a biomimetic [4Fe-4S] compound exhibits [4Fe-4S] to [2Fe-2S] cluster conversion

Fumarate and nitrate reductase (FNR) is a gene regulatory protein that controls anaerobic to aerobic respiration in Escherichia coli, for which O₂ serves as a control switch to induce a protein structural change by converting [4Fe-4S] cofactors to [2Fe-2S] clusters. Although biomimetic models can aid in understanding the complex functions of their protein counterparts, the inherent sensitivity of discrete [Fe-S] molecules to aerobic conditions poses a unique challenge to mimic the O₂-sensing capability of FNR. Herein, we report unprecedented biomimetic O₂ reactivity of a discrete [4Fe-4S] complex, [Fe₄S₄(SPh^F)₄]^2- (1) where SPh^F is 4-fluorothiophenolate, in which the reaction of 1 with O_2(g) in the presence of thiolate produces its [2Fe-2S] analogue, [Fe₂S₂(SPh^F)₄]^2- (2), at room temperature. The cluster conversion of 1 to 2 can also be achieved by employing disulfide as an oxidant under the same reaction conditions. The [4Fe-4S] to [2Fe-2S] cluster conversion by O₂ was found to be significantly faster than that by disulfide, while the reaction with disulfide produced higher yields of 2.