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A diiron(iv) complex that cleaves strong C–H and O–H bonds

Nature Chemistry volume 1, pages 145–150 (2009)Cite this article

Abstract

The controlled cleavage of strong C–H bonds such as those of methane poses a significant and industrially important challenge for chemists. In nature, methane is oxidized to methanol by soluble methane monooxygenase via a diiron(iv) intermediate called Q. However, the only two reported diiron(iv) complexes have activities towards C–H bonds that fall far short of the activity of this biological catalyst. In this paper, we model the chemistry of MMO-Q by generating an oxo-bridged diiron(iv) complex by electrochemical oxidation. This species is a more effective oxidant. It can attack C–H bonds as strong as 100 kcal mol−1 and reacts with cyclohexane 100- to 1,000-fold faster than mononuclear FeIV=O complexes of closely related ligands. Strikingly, this species can also cleave the strong O–H bonds of methanol and t-butanol instead of their weaker C–H bonds, representing the first example of O–H bond activation for iron complexes.

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Figure 1: Structures of the complexes 1 and 3.
Figure 2: Characterization of complexes 1, 2 and 3.
Figure 3: X-ray absorption spectra of complexes 1, 2 and 3.
Figure 4: 4.2 K Mössbauer spectra of 3.
Figure 5: Oxidative reactivity study of 3 in CD3CN at 10 °C.
Figure 6: Reaction scheme of 3 in its oxidation of cyclohexane and t-butanol.

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Acknowledgements

This work was supported by NIH Grants EB-001475 (E.M.) and GM-38767 (L.Q.) and NIH Graduate Traineeship GM-08700 (E.R.F.). XAS data were collected on beamlines 7-3 and 9-3 at the Stanford Synchrotron Radiation Lightsource (SSRL), a national user facility operated by Stanford University on behalf of the US Department of Energy, Office of Basic Energy Sciences. The SSRL Structural Molecular Biology Program is supported by the Department of Energy, Office of Biological and Environmental Research, and by the National Institutes of Health, National Centre for Research Resources and the Biomedical Technology Program. We thank M. Latimer and A. Aranda for technical support and advice during XAS data collection. We also thank V.G. Young Jr and the X-ray Crystallographic Laboratory of the University of Minnesota for expert assistance in the crystal structure determination.

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Authors and Affiliations

  1. Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, 55455, Minnesota, USA

    Dong Wang, Erik R. Farquhar & Lawrence Que Jr

  2. Department of Chemistry, Carnegie Mellon University, Pittsburgh, 15213, Pennsylvania, USA

    Audria Stubna & Eckard Münck

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  1. Dong Wang
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Contributions

D.W., E.M. and L.Q. conceived and designed the experiments; D.W., E.R.F. and A.S. performed the experiments; D.W., E.R.F., A.S. and E.M. analysed the data; D.W., E.R.F., A.S., E.M. and L.Q. wrote the paper. All authors discussed the results and commented on the manuscript.

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Correspondence to Eckard Münck or Lawrence Que Jr.

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Crystallographic data for compound 1 (CIF 55 kb)

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Wang, D., Farquhar, E., Stubna, A. et al. A diiron(iv) complex that cleaves strong C–H and O–H bonds. Nature Chem 1, 145–150 (2009). https://doi.org/10.1038/nchem.162

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