Redox-active ligand facilitates HNO generation in a super-reduced dinitrosyl iron complex

Dinitrosyl iron complexes (DNICs) are widespread biological nitric oxide (NO) storage and delivery motifs, yet their highly delocalized electronic structure generally resists NO-centered reductive chemistry. Here, we establish ligandcentered reduction as a strategy for unlocking nitroxyl (HNO)-generating DNIC reactivity. A redox-active formazanate ligand (L) stabilizes a super-reduced formal {LFe(NO) 2 } 11 state beyond the conventional {Fe(NO) 2 } 9/10 redox pair. EPR and Mössbauer spectroscopy, together with density functional theory calculations, identify predominantly ligand-centered reduction, yielding an {Fe(NO) 2 } 10 unit coupled to a formazanate radical dianion, L 2−• . Electronic communication between the reduced ligand and the [Fe(NO) 2 ] unit enhances Fe-to-NO π backbonding, consistent with experimental ν(NO) redshifts. Importantly, protonation triggers HNO release, representing an unprecedented example of HNO generation from the super reduced DNIC scaffold. Isotopically distinct H 14 NO/H 15 NO is trapped with PPh 3 , along with the 14/15 N 2 O characterization. Calculations support direct nitrosyl protonation to form an Fe-bound HNO intermediate, followed by solvent-assisted HNO release and subsequent N 2 O formation. These findings establish that ligand-centered electron accommodation coupled to nitrosyl protonation enables HNO generation from a formally super-reduced DNIC, extending DNIC reactivity beyond conventional NO donation.