Valence tautomerism in a high-valent manganese-oxo porphyrinoid complex induced by a Lewis acid.

Department of Chemistry, The Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA.
Journal of the American Chemical Society (Impact Factor: 10.68). 06/2012; 134(25):10397-400. DOI: 10.1021/ja304609n
Source: PubMed

ABSTRACT Addition of the Lewis acid Zn(2+) to (TBP(8)Cz)Mn(V)(O) induces valence tautomerization, resulting in the formation of [(TBP(8)Cz(+•))Mn(IV)(O)-Zn(2+)]. This new species was characterized by UV-vis, EPR, the Evans method, and (1)H NMR and supported by DFT calculations. Removal of Zn(2+) quantitatively restores the starting material. Electron-transfer and hydrogen-atom-transfer reactions are strongly influenced by the presence of Zn(2+).

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    ABSTRACT: High-valent cobalt-oxo intermediates are proposed as reactive intermediates in a number of cobalt-complex-mediated oxidation reactions. Herein we report the spectroscopic capture of low-spin (S=1/2) CoIV-oxo species in the presence of redox-inactive metal ions, such as Sc3+, Ce3+, Y3+, and Zn2+, and the investigation of their reactivity in CH bond activation and sulfoxidation reactions. Theoretical calculations predict that the binding of Lewis acidic metal ions to the cobalt-oxo core increases the electrophilicity of the oxygen atom, resulting in the redox tautomerism of a highly unstable [(TAML)CoIII(O.)]2− species to a more stable [(TAML)CoIV(O)(Mn+)] core. The present report supports the proposed role of the redox-inactive metal ions in facilitating the formation of high-valent metal–oxo cores as a necessary step for oxygen evolution in chemistry and biology.
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