We report changes in the reactivity profile of a high-spin, terminal ferrous hydroxo complex (EmL)Fe(OH) as a function of oxidation states (i.e., FeII/FeIII). The terminal, high-spin Fe–OH adducts were isolated within a sterically hindered dipyrrin ligand scaffold. In the ferrous state, (EmL)Fe(OH) exhibits nucleophilic reactivity toward carbon-based electrophiles (e.g., CS2, CO2, nitrile, isocyanate), highlighted by the reversible capture of CO2 to generate (EmL)Fe(κ2-O,O-HCO3) (ΔG° = −2.0 kcal/mol) both in solution and solid state as characterized by single-crystal X-ray crystallography, 57Fe Mössbauer spectroscopy, and IR spectroscopy. We probed the nucleophilic character of ferrous analogues with different terminal ligand motifs (X: −CH3, −NH2, −F, −SH, −H) through a comparison of their reactivity with CO2. In contrast to the nucleophilic character exhibited by (EmL)FeII(OH), its high-spin ferric analogue (EmL)FeIIII(OH) exhibited electrophilic reactivity at the hydroxo ligand, undergoing radical recombination with carboradicals, akin to the radical recombination reactivity observed in hydroxylation from high-valent iron oxenoids. These results highlight the effect of the oxidation level, ligand electronegativity, and basicity on the resulting nucleophilic/electrophilic character of the terminal Fe–X pair.

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Transition metal nitrides are reactive intermediates in biological and industrial processes. Chemists have synthesized molecular model complexes of such reactive species to understand their function a...