A Versatile Tripodal Cu(I) Reagent for C-N Bond Construction via Nitrene-Transfer Chemistry: Catalytic Perspectives and Mechanistic Insights on C-H Aminations/amidinations and Olefin Aziridinations


A CuI catalyst (1), supported by a framework of strongly basic guanidinato moieties, mediates nitrene-transfer from PhI=NR sources to a wide variety of aliphatic hydrocarbons (C-H amination or amidination in the presence of nitriles) and olefins (aziridination). Product profiles are consistent with a stepwise rather than concerted C-N bond formation. Mechanistic investigations with the aid of Hammett plots, kinetic isotope effects, labeled stereochemical probes, and radical traps and clocks allow us to conclude that carboradical intermediates play a major role and are generated by hydrogen-atom abstraction from substrate C-H bonds or initial nitrene-addition to one of the olefinic carbons. Subsequent processes include solvent-caged radical recombination to afford the major amination and aziridination products but also one-electron oxidation of diffusively free carboradicals to generate amidination products due to carbocation participation. Analyses of metal- and ligand-centered events by variable temperature electrospray mass spectrometry, cyclic voltammetry, and electron paramagnetic resonance spectroscopy, coupled with computational studies, indicate that an active, but still elusive, copper-nitrene (S = 1) intermediate initially abstracts a hydrogen atom from, or adds nitrene to, C-H and C=C bonds, respectively, followed by a spin flip and radical rebound to afford intra- and intermolecular C-N containing products.



Keywords and Phrases

Abstracting; Amines; Atoms; Cyclic voltammetry; Electron spin resonance spectroscopy; Hydrogen; Hydrogen bonds; Isotopes; Olefins; Aliphatic hydrocarbons; Computational studies; Electron paramagnetic resonance spectroscopy; Electrospray mass spectrometry; Kinetic isotope effects; One-electron oxidation; Radical recombination; Variable temperature; Iodine; aliphatic hydrocarbon; cuprous ion; hydrogen; amination; article; catalysis; chemical bond; chemical modification; cyclic potentiometry; electron spin resonance; electrospray mass spectrometry; heteronuclear multiple bond correlation; heteronuclear multiple quantum coherence; nuclear Overhauser effect; olefin aziridination; proton nuclear magnetic resonance; synthesis; temperature

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