Activating a Peroxo Ligand for C−O Bond Formation

Taming oxygen for effective cleavage of the O−O bond and a further C−O bond formation has been achieved through proton transfer/electron transfer steps. A free radical mechanism accounts for the transformation of peroxide complexes into water and 2‐iradaoxetane complexes (see scheme; C gray, Ir green, N blue, O red; Mepy=4‐methylpyridine).

Abstract

Dioxygen activation for effective C−O bond formation in the coordination sphere of a metal is a long‐standing challenge in chemistry for which the design of catalysts for oxygenations is slowed down by the complicated, and sometimes poorly understood, mechanistic panorama. In this context, olefin–peroxide complexes could be valuable models for the study of such reactions. Herein, we showcase the isolation of rare "Ir(cod)(peroxide)" complexes (cod=1,5‐cyclooctadiene) from reactions with oxygen, and then the activation of the peroxide ligand for O−O bond cleavage and C−O bond formation by transfer of a hydrogen atom through proton transfer/electron transfer reactions to give 2‐iradaoxetane complexes and water. 2,4,6‐Trimethylphenol, 1,4‐hydroquinone, and 1,4‐cyclohexadiene were used as hydrogen atom donors. These reactions can be key steps in the oxy‐functionalization of olefins with oxygen, and they constitute a novel mechanistic pathway for iridium, whose full reaction profile is supported by DFT calculations.

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