Deciphering Iron‐Catalyzed C−H Amination with Organic Azides: N2 Cleavage from a Stable Organoazide Complex

Abstract

AbstractCatalytic C−N bond formation by direct activation of C−H bonds offers wide synthetic potential. En route to C−H amination, complexes with organic azides are critical precursors towards the reactive nitrene intermediate. Despite their relevance, α‐N coordinated organoazide complexes are scarce in general, and elusive with iron, although iron complexes are by far the most active catalysts for C−H amination with organoazides. Herein, we report the synthesis of a stable iron α‐N coordinated organoazide complex from [Fe(N(SiMe3)2)2] and AdN3 (Ad=1‐adamantyl) and its crystallographic, IR, NMR and zero‐field 57Fe Mössbauer spectroscopic characterization. These analyses revealed that the organoazide is in fast equilibrium between the free and coordinated state (Keq=62). Photo‐crystallography experiments showed gradual dissociation of N2, which imparted an Fe−N bond shortening and correspond to structural snapshots of the formation of an iron imido/nitrene complex. Reactivity of the organoazide complex in solution showed complete loss of N2, and subsequent formation of a C−H aminated product via nitrene insertion into a C−H bond of the N(SiMe3)2 ligand. Monitoring this reaction by 1H NMR spectroscopy indicates the transient formation of the imido/nitrene intermediate, which was supported by Mössbauer spectroscopy in frozen solution.