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Catalytic dehydroaromatization of n-alkanes by pincer-ligated iridium complexes

Nature Chemistry volume 3, pages 167–171 (2011)Cite this article

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Abstract

Aromatic hydrocarbons are among the most important building blocks in the chemical industry. Benzene, toluene and xylenes are obtained from the high temperature thermolysis of alkanes. Higher alkylaromatics are generally derived from arene–olefin coupling, which gives branched products—that is, secondary alkyl arenes—with olefins higher than ethylene. The dehydrogenation of acyclic alkanes to give alkylaromatics can be achieved using heterogeneous catalysts at high temperatures, but with low yields and low selectivity. We present here the first catalytic conversion of n-alkanes to alkylaromatics using homogeneous or molecular catalysts—specifically ‘pincer’-ligated iridium complexes—and olefinic hydrogen acceptors. For example, the reaction of n-octane affords up to 86% yield of aromatic product, primarily o-xylene and secondarily ethylbenzene. In the case of n-decane and n-dodecane, the resulting alkylarenes are exclusively unbranched (that is, n-alkyl-substituted), with selectivity for the corresponding o-(n-alkyl)toluene.

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Figure 1: Dehydroaromatization of n-hexane catalysed by iridium pincer complexes 2, 4 or 6.
Figure 2: Dehydroaromatization of n-octane catalysed by 2, 4 or 6 (with TBE as hydrogen-acceptor).
Figure 3: Dehydroaromatization of n-octane catalysed by 2 with propene as hydrogen acceptor.
Figure 4: Dehydroaromatization of n-decane catalysed by 4.
Figure 5: Dehydroaromatization of n-dodecane.

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Acknowledgements

The authors are grateful to the National Science Foundation (grant no. CHE-0650456) for financial support for this work through the Center for Enabling New Technologies through Catalysis (CENTC).

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Authors and Affiliations

  1. Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, 08854, New Jersey, USA

    Ritu Ahuja, Benudhar Punji & Alan S. Goldman

  2. Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, 27599, North Carolina, USA

    Michael Findlater & Maurice Brookhart

  3. Department of Chemistry, Monmouth University, West Long Branch, 07764, New Jersey, USA

    Carolyn Supplee

  4. Chevron Research and Technology Co., 100 Chevron Way, Richmond, 948023, California, USA

    William Schinski

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  1. Ritu Ahuja
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Contributions

R.A., B.P., M.F., W.S., M.B. and A.S.G. conceived and designed the experiments; R.A., B.P., M.F. and C.S. performed the experiments; R.A., B.P., M.F., C.S., M.B. and A.S.G. co-wrote the paper.

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Correspondence to Maurice Brookhart or Alan S. Goldman.

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Ahuja, R., Punji, B., Findlater, M. et al. Catalytic dehydroaromatization of n-alkanes by pincer-ligated iridium complexes. Nature Chem 3, 167–171 (2011). https://doi.org/10.1038/nchem.946

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