Oxo-metal-halide moieties have often been implicated as C–H bond activating oxidants with the terminal oxo-metal entity identified as the electrophilic oxidant. The electrophilic reactivity of metal-halide species has not been investigated. We have prepared high-valent nickel-halide complexes [NiIII(X)(L)] (L = N,N’-(2,6-dimethylphenyl)-2,6-pyridinedicarboxamide, X = F, Cl, Br) by one-electron oxidation of the [NiII(X)(L)]– precursors. [NiIII(X)(L)] were characterized using electronic absorption, electron paramagnetic resonance, and X-ray absorption spectroscopies, and mass spectrometry. [NiIII(X)(L)] reacted readily with substrates containing either phenolic O–H or hydrocarbon C–H bonds. Analysis of the Hammett, Evans-Polanyi, and Marcus relationships between the determined rate constants and substrate pKa, X-H bond dissociation energy, and oxidation potential, respectively, was performed. It was found that [NiIII(X)(L)] reacted by a hydrogen atom transfer (HAT) mechanism. Our findings shine light on enzymatic high-valent oxo-metal-halide oxidants and open new avenues for oxidative halogenation catalyst design.

Oxidation of hydrocarbons by high-valent metal-halide complexes

2019 Fall National Meeting

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