A Mononuclear Side-on Peroxocobalt(III) Complex in Nitrile Activation

Abstract

Oxidation processes mediated by metal-oxygen adducts have attracted much attention in biomimetic and enzymatic reactions. Although a number of metal-oxygen species has been prepared and investigated in oxidation reactions toward diverse organic substrates under mild conditions, activation of nitriles has rarely been examined in oxidation process of metal-oxygen complexes. Herein, we report the first example of nitrile activation by a side-on peroxocobalt(III) complex with a tetradentate macrocyclic ligand. The peroxocobalt(III) complex is capable of performing nitrile activation of CH3CN to give a mononuclear hydroximatocobalt(III) complex where the nitrile is oxidized by two oxygen atoms of the peroxo group. 18O labeling experiments indicate dioxygenase-like reactivity of the peroxocobalt(III) complex in nitrile activation. Such an unprecedented nitrile activation was confirmed by the activation of other nitrile compounds (e.g., CH3CH2CN and C6H5CN), which gives corresponding hydroximatocobalt(III) complexes. Kinetic studies including the Hammett analysis and isotope labeling experiments proposed that the nitrile activation occurs via a concerted mechanism. These results will expand the range of nitrile activation processes. ⓒ 2017 DGIST