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.