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

Abstract 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.