A cobalt(II) iminoiodane complex and its scandium adduct: mechanistic promiscuity in hydrogen atom abstraction reactions

Abstract

In addition to oxometal [Mn+=O] and imidometal [Mn+=NR] units, transient metal-iodosylarene [M(n- 2)+-O=IPh] and metal-iminoiodane [M(n- 2)+-N(R)=IPh] adducts are often invoked as a possible "second oxidant" responsible for the oxo and imido group transfer reactivity. Although a few metal-iodosylarene adducts have been recently isolated and/or spectroscopically characterized, metal-iminoiodane adducts have remained elusive. Herein, we provide UV-Vis, EPR, NMR, XAS and DFT evidence supporting the formation of a metal-iminoiodane complex 2 and its scandium adduct 2-Sc. 2 and 2-Sc are reactive toward substrates in the hydrogen-atom and nitrene transfer reactions, which confirm their potential as active oxidants in metal-catalyzed oxidative transformations. Oxidation of para-substituted 2,6-di-tert-butylphenols by 2 and 2-Sc can occur by both coupled and uncoupled proton and electron transfer mechanisms; the exact mechanism depends on the nature of the para substituent.