Mechanistic Insights into the Reductive N–O Bond Cleavage of O-Acyl Hydroxylamines: Dual Reactivity as Potent Oxidants and Nitrogen Transfer Agents

Hydroxylamine (NH₂OH), an N-O containing moiety and a pivotal intermediate in the nitrogen biogeochemical cycle, typically functions under reducing conditions, in stark contrast to its isoelectronic O-O analogue, hydrogen peroxide (H₂O₂). Oxygen-substituted hydroxylamine derivatives, widely employed in organic synthesis, utilize electron-withdrawing substituents (R) to weaken the N-O bond, thereby enabling the generation of reactive "N-transfer" intermediates. Although these reagents are increasingly recognized for their dual roles as masked "amine" donors and potential "oxidants", direct experimental validation of their oxidative capacity has remained elusive. Herein, we report a detailed mechanistic investigation integrating kinetic, spectroscopic, electrochemical, and computational approaches to establish the dual functionality of O-acyl-substituted hydroxylamine derivatives in iron-catalyzed N-transfer processes. Using a series of O-benzoyloxy hydroxylamine-derived triflic acid salts bearing electronically varied substituents (Ox_Me, Ox_OMe, Ox_H, and Ox_NO2 ) along with the O-pivaloyl hydroxylamine derivative (PivONH₃OTf), (Ox_OPiv), a clear structure-function relationship was uncovered, where the modulation of the electron density on the oxygen substituent tunes the redox potential and thus the oxidizing strength of the O-acyl-substituted hydroxylamine-derived N-O reagents. Mechanistic probing using well-defined outer-sphere Fe-(II) redox probesferrocene (Fc) and decamethylferrocene (DMFc)demonstrates that O-acyl-substituted hydroxylamine derivatives promote Fe-(II) to Fe-(III) oxidation via the outer sphere electron-transfer process. However, while Fc undergoes oxidation to ferrocenium ion (Fc⁺) along with the formation of putative iron-nitrogen/N-inserted intermediates (detected by high-resolution mass spectrometry), the sterically hindered, methyl-substituted DMFc exhibits a pure outer sphere redox event to form decamethylferrocenium ion (DMFc⁺) without competing N-substitution reactivity on the cyclopentadienyl (Cp) backbone. Together, these results provide the first direct experimental evidence for the oxidative capability of O-acyl-substituted hydroxylamine derivatives via a reductive N-O bond cleavage. This study unveils a mechanistically distinct pathway for the advancement of catalytic amination reactions and guides the design of sustainable nitrogen-transfer methodologies.