Mechanism and Reaction Channels of Iron-Catalyzed Primary Amination of Alkenes by Hydroxylamine Reagents

Iron-catalyzed N-transfer by hydroxylamine-derived reagents has emerged as an appealing method for the straightforward synthesis of unprotected primary amines. Here, we studied the detailed reaction mechanism of the FePc-catalyzed aminofunctionalization of styrene with AcO-NH3OTf and PivO-NH3OTf by quantum chemical calculations and mass spectrometry experiments. An inner-sphere heterolytic N-O cleavage mechanism was proposed for the hydroxylamine activation. It affords an unprotected iron-amido species ([PcFeNH2]+), which has been detected by mass spectrometry. The iron-amido species acts as the active aminating intermediate and reacts with styrene to form a radical intermediate, followed by nucleophilic addition with methanol to generate the product. Electronic structure analysis revealed sigma- and pi- channels in the N-transfer process for the iron-amido species. This reported iron- nitrogen complex resembles the iron-oxo species to possess both sigma- and pi-channels, unveiling the mechanistic connections with iron-oxo chemistry.