A mononuclear nonheme iron complex with higher affinity for O2 than CO via hydrogen bonding
- Matthias Jux
- Stefan Mebs
- Michael Haumann
- Sagie Katz
- Ricardo Garcia-Serres
- Peter Hildebrandt
- Yong Wang
- Wonwoo Nam
- Kallol Ray
2026-05-05
Dioxygen activation at iron centers is central to many biological and synthetic oxidation processes. In proteins, the reactivity and stability of iron–dioxygen intermediates are often controlled by secondary-sphere interactions such as hydrogen bonding. For example, hemoglobin stabilizes a Fe−O 2 adduct through distal hydrogen bonding, while hemerythrin employs hydrogen bonding to stabilize reduced oxygen species within a diiron active site, enabling reversible O 2 binding. Here we show that a mononuclear nonheme iron complex, [Fe II (DIG 3 tren)] 2+ (DIG 3 tren = tris(N’,N”-diisopropylguanidinyl-2-ethyl)amine), reversibly reduces O 2 by two electrons to generate an iron(IV)-peroxido species. Strong hydrogen bonds from N − H groups of the ligand stabilize the O 2 2− ligand, while the electron-rich guanidine donors promote the unusual Fe II -mediated two-electron reduction of O 2 . As a result, the complex exhibits higher affinity for O 2 than for CO due to preferential hydrogen-bond stabilization of the peroxido intermediate. These results demonstrate how secondary-sphere design can control both O 2 activation and ligand selectivity at iron centers.