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⁾⁺–OIPh] 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.