DFT Mechanistic Insight into the Dioxygenase-like Reactivity of a CoIII-peroxo Complex: O-O Bond Cleavage via a [1,3]-Sigmatropic Rearrangement-like Mechanism.

Abstract

Dioxygen O-O bond activation is a process for oxygenases and oxidases to perform biological functions and synthetic biomimetic catalysts to carry out oxygenation reactions using molecular O2 as an oxidant. Inspired by the experimental development of a CoIII-peroxo complex (i.e., [CoIII(TBDAP)(O2)]+, TBDAP = N,N-ditert-butyl-2,11-diaza[3.3](2,6)-pyridinophane) that exhibits dioxygenase-like reactivity to activate nitriles, a density functional theory (DFT) mechanistic study has been carried out to understand how the peroxo ligand is broken to activate nitriles. The study unveils that the O-O bond cleavage takes place via conversion to a CoII-superoxo complex aided by nitrile coordination, followed by formation of a five-membered intermediate via superoxo O2 radical nucleophilic attack at the nitrile carbon. Finally, a [1,3]-sigmatropic rearrangement-like process breaks the dioxygen bond. The otherwise difficult [1,3]-sigmatropic rearrangement is enabled by the mediation of CoIII(TBDAP) which alters a concerted rearrangement to a sequential process of O-O bond cleavage and N-O bond formation. Expectedly, the unveiling of the O-O bond cleavage mechanism could offer a clue for the development of biomimetic metal oxygenation catalysts.