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Issue 23, 2017
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An investigation of ligand effects on the visible light-induced formation of porphyrin–iron(IV)-oxo intermediates

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Abstract

High-valent porphyrin–iron-oxo intermediates are the central oxidizing species in heme-containing enzymes and synthetic oxidation catalysts. In this work, we investigated a new photochemical entry to porphyrin–iron(IV)-oxo derivatives in a variety of porphyrin ligands with different electronic and steric environments. In non-electron-deficient ligand systems, the visible light photolysis of porphyrin–iron(III) bromates gave porphyrin–iron(IV)-oxo radical cations (compound I analogues). In contrast, the photolysis of porphyrin–iron(III) bromates with electron-deficient and sterically encumbered ligands produced one-electron reduced iron(IV)-oxo porphyrins (compound II analogues). Formation of iron(III) μ-oxo dimers was also observed in the sterically unencumbered systems containing electron-deficient substituents. The photochemical generation of porphyrin–iron(IV)-oxo radical cations and iron(IV)-oxo porphyrins permits direct kinetic studies of their oxidations with organic reductants. As expected, more oxidized porphyrin–iron(IV)-oxo radical cations reacted 2–3 orders of magnitudes faster than the iron(IV)-oxo porphyrins, and the rate constants obtained in this work are in comparison to those of iron(IV)-oxo derivatives formed by chemical methods. A model including internal electron-transfer (ET) and comproportionation of the putative iron(V)-oxo species pathways is presented.

Graphical abstract: An investigation of ligand effects on the visible light-induced formation of porphyrin–iron(iv)-oxo intermediates

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Publication details

The article was received on 31 Aug 2017, accepted on 20 Oct 2017 and first published on 20 Oct 2017


Article type: Paper
DOI: 10.1039/C7NJ03296J
Citation: New J. Chem., 2017,41, 14334-14341
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    An investigation of ligand effects on the visible light-induced formation of porphyrin–iron(IV)-oxo intermediates

    K. W. Kwong, D. Patel, J. Malone, N. F. Lee, B. Kash and R. Zhang, New J. Chem., 2017, 41, 14334
    DOI: 10.1039/C7NJ03296J

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