Nitrene-Transfer Chemistry to Olefins Mediated by Co(III) Catalysts Supported by a Tetraamido Macrocycle

A tetraamido macrocyclic ligand scaffold (L1H4) has been synthesized and metalated with Co(III) to afford anionic metal complexes [CoIII(L1)]- (cations: K+, PPh4+) that are paramagnetic (S = 1) in solution and display semi-reversible reduction waves (CoII/III) and irreversible anodic events in cyclic voltammograms. These macrocyclic Co(III) compounds have been examined as nitrene-transfer catalysts, involving iminoiodinane precursors (PhI=NR) and olefins, to reveal efficient aziridinations and/or allylic aminations, especially with sterically unencumbered styrenes. Mechanistic studies indicate that stepwise formation of two N-C bonds is operative in aziridinations, in which both polar and radical contributions are evident, in contrast to analogous nitrene-transfer chemistry displayed by [CoIII(TAMLred)]-, the latter relying on single-electron transfer between ligand and substrate. The generation of both mono- and bis-nitrene cobalt complexes or derivatives is indicated by ESI-MS, but their precise structural identity, electronic configuration, and relevance in nitrene-transfer chemistry remains an area for further exploration.