Deciphering the Stepwise N–O Activation of Nitroarenes: Electronic Structure and Reactivity of Iron-Nitrosoarene Intermediates

N-O bond activation in reductive transformation of both NOx⁻ and organic substrates with nitro functional groups has garnered significant interest because of its significance in both biological systems and synthetic chemistry. The reductive transformation of nitro groups involves sequential N-O bond cleavages, with nitrosoarenes (ArNO) as key yet often elusive intermediates. While iron is a biologically and synthetically relevant metal for such processes, the mechanistic understanding, particularly the role of multinuclear cooperation, remains underdeveloped. Herein, we report that a dinuclear iron N-heterocyclic carbene (NHC) complex, Fe2-MeCN, enables the sequential N-O bond activation of nitrobenzene, leading to the isolation and detailed characterization of two iron-nitrosoarene intermediates, Fe2-PhNO and Fe2-(PhNO)2. Spectroscopic and crystallographic studies, complemented by DFT calculations, identified strong charge-transfer interactions that polarize the N-O moiety. This electronic structure underpins a diverse suite of N-O activation pathways, including Lewis acid-induced electron transfer, hydride reduction, proton-coupled electron transfer (PCET), and oxygen atom transfer. The stoichiometric reactivity reveals that the nucleophilic oxygen of the coordinated ArNO can be efficiently attacked by electrophiles, while reactions with nucleophiles require more forcing conditions. Finally, Fe2-MeCN functions as a competent catalyst for the reduction of nitroarenes to anilines and facilitates unprecedented iron-mediated heterocyclizations, underscoring the critical role of bimetallic cooperativity in this multifunctional reactivity.