Lewis acid trapping of an elusive copper-tosylnitrene intermediate using scandium triflate

J Am Chem Soc. 2012 Sep 12;134(36):14710-3. doi: 10.1021/ja306674h. Epub 2012 Aug 31.

Abstract

High-valent copper-nitrene intermediates have long been proposed to play a role in copper-catalyzed aziridination and amination reactions. However, such intermediates have eluded detection for decades, preventing the unambiguous assignments of mechanisms. Moreover, the electronic structure of the proposed copper-nitrene intermediates has also been controversially discussed in the literature. These mechanistic questions and controversy have provided tremendous motivation to probe the accessibility and reactivity of Cu(III)-NR/Cu(II)N(•)R species. In this paper, we report a breakthrough in this field that was achieved by trapping a transient copper-tosylnitrene species, 3-Sc, in the presence of scandium triflate. The sufficient stability of 3-Sc at -90 °C enabled its characterization with optical, resonance Raman, NMR, and X-ray absorption near-edge spectroscopies, which helped to establish its electronic structure as Cu(II)N(•)Ts (Ts = tosyl group) and not Cu(III)NTs. 3-Sc can initiate tosylamination of cyclohexane, thereby suggesting Cu(II)N(•)Ts cores as viable reactants in oxidation catalysis.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Copper / chemistry*
  • Imines / chemistry*
  • Lewis Acids / chemistry*
  • Mesylates / chemistry*
  • Models, Molecular
  • Molecular Structure
  • Organometallic Compounds / chemical synthesis
  • Organometallic Compounds / chemistry*
  • Scandium / chemistry*
  • Tosyl Compounds / chemistry*

Substances

  • Imines
  • Lewis Acids
  • Mesylates
  • Organometallic Compounds
  • Tosyl Compounds
  • scandium triflate
  • Copper
  • Scandium