As possibly biomimetic species, small-molecule mononuclear copper(III) hydroxo-, peroxo-, and carboxylate species have been shown to activate C–H bonds, this typically being the first step of overall enzymatic catalysis of hydrocarbon oxidation. Such reactivity can be characterized as a hydrogen atom transfer (HAT) or as a concerted proton-coupled electron transfer (cPCET). The distinction between these two cases generally focuses on whether the electron and proton travel together as a true H-atom, HAT, or whether the proton and electron are transferred in concert, but travel between different donor/acceptor centers, cPCET. We find both mechanisms to be associated with C–H bond activation by Cu(III)–OH, –OOR, and –O2CR compounds, with interesting variations as a function of substrate and copper functionality. We use theoretical tools to distinguish these mechanisms, for different reagent/substrate combinations, including an analysis of the total dipole moment vector projected along the H-donor-acceptor axis, as well as an even more direct visualization approach using the intrinsic bond orbital (IBO) method of Knizia and co-workers, where IBOs representing relevant α- and β-spin are monitored as they evolve along the overall reaction-coordinate.

HAT vs cPCET mechanisms for C–H bond activations by LCu(III)–OH, –OOR, and –O2CR compounds

2019 Spring National Meeting

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