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

Abstract

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.

Department(s)

Chemistry

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; cuprous Ion; Hydrogen; catalysis; Chemical Bond; Chemical Modification; Cyclic Potentiometry; electrospray Mass Spectrometry; Heteronuclear Multiple Bond Correlation; Heteronuclear Multiple Quantum Coherence; Nuclear Overhauser Effect; proton Nuclear Magnetic Resonance; Synthesis; Temperature

International Standard Serial Number (ISSN)

0002-7863

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2014 American Chemical Society (ACS), All rights reserved.

Publication Date

01 Aug 2014

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