Concerted proton-electron transfer oxidation of phenols and hydrocarbons by a high-valent nickel complex

Katherine J. Fisher, Margalit L. Feuer, Hannah M.C. Lant, Brandon Q. Mercado, Robert H. Crabtree, Gary W. Brudvig

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The high-valent nickel(iii) complex Ni(pyalk)2+ (2) was prepared by oxidation of a nickel(ii) complex, Ni(pyalk)2 (1) (pyalk = 2-pyridyl-2-propanoate). 2 and derivatives were fully characterized by mass spectrometry and X-ray crystallography. Electron paramagnetic resonance spectroscopy and X-ray photoelectron spectroscopy confirm that the oxidation is metal-centered. 2 was found to react with a variety of phenolic and hydrocarbon substrates. A linear correlation between the measured rate constant and the substrate bond dissociation enthalpy (BDE) was found for both phenolic and hydrocarbon substrates. Large H/D kinetic isotope effects were also observed for both sets of substrates. These results suggest that 2 reacts through concerted proton-electron transfer (CPET). Analysis of measured thermodynamic parameters allows us to calculate a bond dissociation free energy (BDFE) of ∼91 kcal mol-1 for the O-H bond of the bound pyalk ligand. These findings may shed light onto CPET steps in oxidative catalysis and have implications for ligand design in catalytic systems.

Original languageEnglish
Pages (from-to)1683-1690
Number of pages8
JournalChemical Science
Issue number6
Publication statusPublished - Feb 14 2020


ASJC Scopus subject areas

  • Chemistry(all)

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