The role of aziridines as intermediates and end products of synthetic and biological chemistry is hard to overstate. Not only do aziridines afford avenues for further structural development by taking advantage of the energetic content and stereochemical disposition of their strained three-atom ring (ring opening, expansion or rearrangement), but also constitute valuable functionalities in the framework of several natural products possessing antibiotic or antineoplastic activities. In addition to the central role exercised by aziridines as fine chemicals and pharmaceutical agents, their contribution to the chemistry of materials has been increasingly recognized, especially as key entities for the development and post-modification of polymeric scaffolds.In the present work, we examine a library of high-spin Co(II) reagents (S = 3/2), supported by a modular trisphenylamido-amine ligand framework, giving rise to a weak equatorial field,The present work significantly enlarges the scope of high-spin Co(II) compounds as nitrene-transfer reagents, and provides insights in their operational characteristics, not only vis-à-vis the reported low-spin (Por)Co(II) paradigms, but also in comparison with the previously examined libraries of Mn(II) and Fe(II) reagents, supported by the same trisphenylamido-amine ligand framework. Whereas the nitrene-transfer reactivity of the Mn(II) reagents in alkene aziridinations largely depends on the electrophilicity of the presumptive MnIII–NR (S = 3/2) moiety, underscoring the crucial role of the electron affinity of the metal nitrene as a dominant factor, the reactivity of the corresponding, much faster, Co(II) reagents is affected by additional subtle electronic and steric factors arising from the tighter disposition of the reaction cavity, resulting in ligand-coordination flexibility, electronic rearrangement, and possible secondary interactions. We showed that even an otherwise small change in ligand substitution can have a significant effect on nitrene-transfer reactivity in aziridination reactions, occasionally overriding the preponderance of the metal-nitrene electrophilicity as a driving force.

Synthesis and characterization of a library of Co(II) triphenylamido-amine reagents and its application to the catalytic aziridination of olefinic substrates

ACS Spring Meeting 2021

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