High-valent metal-oxo (e.g. Fe-oxo, Mn-oxo) species are postulated as key intermediates in a variety of catalytic reactions that are important to many biological and industrial processes. For example, in Photosystem II (PSII), the participation of one or more high-valent Mn-oxo species is proposed as part of the proton-coupled oxidation of water to dioxygen by the oxygen-evolving complex (OEC). In cytochrome P450, a heme enzyme that catalyzes the hydroxylation of strong C-H bonds, an iron(IV)-oxo porphyrin π-radical cation is indicated as the key C-H bond-cleaving oxidant. In this presentation, the reactivity of MnV(O) and CrV(O) corrolazine complexes are described. The synthesis, crystal structures, and spectroscopic characterization (UV-vis, EPR, 1H-NMR) of the new CrV(O)(TBP8Cz) and CrIII(TBP8Cz) complexes are presented. The H-atom abstraction reactivity of CrV(O)(TBP8Cz) is significantly weaker than MnV(O)(TBP8Cz). The reduction potential for the MV/MIV redox couple for CrV(O)(TBP8Cz) is shifted 100 mV positive relative to MnV(O)(TBP8Cz), indicating that CrV(O) should be a better one-electron oxidant, contrary to what is found in HAT and PCET reactions. These results suggest that the difference in reactivity is due to the difference in basicity of the MnIV(O) relative to the CrIV(O) complex.

Comparison of MnV(O) and CrV(O) complexes in HAT and PCET reactivity

251st National Meeting (2016)

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