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Boron-catalysed hydrogenolysis of unactivated C(aryl)–C(alkyl) bonds

Nature Catalysis volume 6, pages 16–22 (2023)Cite this article

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Abstract

The hydrogenolysis of C–C bonds is one of the most important processes in the petroleum industry. These transformations typically rely on heterogeneous catalysts and take place at high temperatures and high pressures with limited selectivity. Employing homogeneous transition metal catalysts, while allowing the hydrogenolysis of C–C bonds to proceed under much milder conditions, is only suitable for substrates containing strained C–C bonds or directing groups. Here we report that a borenium complex can catalyse the selective hydrogenolysis of unstrained C(aryl)–C(alkyl) bonds of alkylarenes in the absence of directing groups at ambient temperature, affording the corresponding alkanes and arenes. Mechanistic studies suggest a reaction pathway that involves a synergistic activation of dihydrogen by the borenium complex and alkylarenes, followed by retro-Friedel–Crafts reaction to cleave the C(aryl)–C(alkyl) bonds. The synthetic utility of this protocol is demonstrated by the conversion of post-consumer polystyrene into valuable benzene and phenylalkanes with mass recovery rates above 90%.

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Fig. 1: Different approaches to hydrodealkylation.
Fig. 2: Substrate scope of hydrodealkylation.
Fig. 3: Mechanism investigation of the hydrogenolysis of 6.
Fig. 4: Hydrogenolysis of polystyrene with 1a as catalyst.

Data availability

All data supporting the findings of this study are available within the Article and its Supplementary Information or from the corresponding authors upon reasonable request.

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Acknowledgements

We thank G. Tang, L. Wang and Y. Zhao for their assistance with GC–MS, NMR and inductively coupled plass mass spectrometry experiments. Financial support for this work was provided by the National Natural Science Foundation of China (21871051 (H.W.), 21873019 (Z.H.L.) and 22071027 (H.W.)), the Shanghai Science and Technology Committee (19DZ2270100) and Fudan University.

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Author notes

  1. These authors contributed equally: Yuliang Xu, Yizhou Yang.

Authors and Affiliations

  1. Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Department of Chemistry, Fudan University, Shanghai, China

    Yuliang Xu, Yizhou Yang, Yizhen Liu, Zhen Hua Li & Huadong Wang

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  1. Yuliang Xu
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Contributions

H.W. conceived the research and designed the project. Y.X. and Y.L. optimized the reaction conditions. Y.X. studied the substrate scope and carried out experimental mechanism investigation. Y.Y studied the hydrogenolysis of polystyrene. Z.H.L. undertook the density functional theory calculations. H.W. wrote the manuscript with input from all authors. All authors analysed the results and commented on the manuscript.

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Correspondence to Huadong Wang.

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Nature Catalysis thanks Ning Yan and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Information

Supplementary Figs. 1–140, Tables 1–25 and Methods.

Supplementary Data 1

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Xu, Y., Yang, Y., Liu, Y. et al. Boron-catalysed hydrogenolysis of unactivated C(aryl)–C(alkyl) bonds. Nat Catal 6, 16–22 (2023). https://doi.org/10.1038/s41929-022-00888-y

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