Kinetic, Spectroscopic, and Computational Investigation of Oxidative Aminative Alkene Cleavage Reveals an N -Iodonium-Iminoiodinane Pathway

The combination of hypervalent iodine(III) oxidants and ammonia sources has been applied in various oxidative aminative transformations of high synthetic value. Central to these reactions is the proposed in situ generation of a four-electron oxidizing intermediate, commonly referred to as iodonitrene. However, this species' mechanism of formation, nature, and relevance to N-atom transfer remains uncertain. Furthermore, evidence for its direct implication as the key reactive intermediate remains elusive. Herein, we present an extensive mechanistic study of a recently published oxidative aminative cleavage of alkenes, which allowed us to obtain key insights into these understudied aspects of hypervalent iodine-mediated nitrogen atom insertion. Through in situ ¹⁹F nuclear magnetic resonance (NMR), initial rate kinetics, linear free energy relationships (LFER), H/D and ¹²C/¹³C kinetic isotope effect (KIE) determination, electrospray ionization mass spectrometry (ESI-MS) and density functional theory (DFT) studies, we show that the formation of an N-iodonium-iminoiodinane is rate-determining in this reaction. This species is highly electrophilic and capable of concerted, asynchronous transfer of a [PhI-N]⁺ unit to double bonds. These findings point toward the N-iodonium-iminoiodinane, not an iodonitrene, being the active N-atom transfer agent generated from the combination of hypervalent iodine(III) oxidants and ammonia. This ultimately deepens our understanding of this commonly used reagent combination and will help to inform the development of methods and reagents for oxidative amination reactions using this reactive manifold.