Manipulating Terminal Iron-Hydroxide Nucleophilicity through Redox

High Resolution Image Download MS PowerPoint Slide We report changes in the reactivity profile of a high-spin, terminal ferrous hydroxo complex ( Em L)Fe(OH) as a function of oxidation states (i.e., Fe II /Fe III ). The terminal, high-spin Fe–OH adducts were isolated within a sterically hindered dipyrrin ligand scaffold. In the ferrous state, ( Em L)Fe(OH) exhibits nucleophilic reactivity toward carbon-based electrophiles (e.g., CS 2, CO 2, nitrile, isocyanate), highlighted by the reversible capture of CO 2 to generate ( Em L)Fe(κ 2 -O,O-HCO 3 ) (Δ G ° = −2.0 kcal/mol) both in solution and solid state as characterized by single-crystal X-ray crystallography, 57 Fe Mössbauer spectroscopy, and IR spectroscopy. We probed the nucleophilic character of ferrous analogues with different terminal ligand motifs (X: −CH 3, −NH 2, −F, −SH, −H) through a comparison of their reactivity with CO 2 . In contrast to the nucleophilic character exhibited by ( Em L)Fe II (OH), its high-spin ferric analogue ( Em L)Fe III I(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.