Cp* iridium precatalysts for selective C-H oxidation via direct oxygen insertion: A joint experimental/computational study

Meng Zhou, David Balcells, Alexander R. Parent, Robert H. Crabtree, Odile Eisenstein

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    Abstract

    A series Cp*Ir complexes are active precatalysts in C-H oxidation of cis-decalin, cyclooctane, 1-acetylpyrrolidine, tetrahydrofurans, and γ-lactones. Moderate to high yields were achieved, and surprisingly, high selectivity for mono-oxidation of cyclooctane to cyclooctanone was observed. Kinetic isotope effect experiments in the C-H oxidation of ethylbenezene to acetophenone yield k H/k D = 15.4 ± 0.8 at 23 °C and 17.8 ± 1.2 at 0 °C, which are consistent with C-H oxidation being the rate-limiting step with a significant tunneling contribution. The nature of the active species was investigated by TEM, UV-vis, microfiltration, and control experiments. DFT calculations showed that the C-H oxidation of cis-decalin by Cp*Ir(ppy)(Cl) (ppy = o-phenylpyridine) follows a direct oxygen insertion mechanism on the singlet potential energy surface, rather than the radical rebound route that would be seen for the triplet, in good agreement with the retention of stereochemistry observed in this reaction. © 2011 American Chemical Society.
    Original languageEnglish
    Pages (from-to)208-218
    JournalACS Catalysis
    Volume2
    Issue number2
    DOIs
    Publication statusPublished - 3 Feb 2012

    Keywords

    • alkane activation
    • C-H oxidation
    • DFT
    • insertion
    • iridium
    • metal oxo
    • oxene
    • reaction mechanism

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    Zhou, M., Balcells, D., Parent, A. R., Crabtree, R. H., & Eisenstein, O. (2012). Cp* iridium precatalysts for selective C-H oxidation via direct oxygen insertion: A joint experimental/computational study. ACS Catalysis, 2(2), 208-218. https://doi.org/10.1021/cs2005899