Article | Published:

Direct observation of a borane–silane complex involved in frustrated Lewis-pair-mediated hydrosilylations

Nature Chemistry volume 6, pages 983988 (2014) | Download Citation

Abstract

Perfluorarylborane Lewis acids catalyse the addition of silicon–hydrogen bonds across C=C, C=N and C=O double bonds. This ‘metal-free’ hydrosilylation has been proposed to occur via borane activation of the silane Si–H bond, rather than through classical Lewis acid/base adducts with the substrate. However, the key borane/silane adduct had not been observed experimentally. Here it is shown that the strongly Lewis acidic, antiaromatic 1,2,3-tris(pentafluorophenyl)-4,5,6,7-tetrafluoro-1-boraindene forms an observable, isolable adduct with triethylsilane. The equilibrium for adduct formation was studied quantitatively through variable-temperature NMR spectroscopic investigations. The interaction of the silane with the borane occurs through the Si–H bond, as evidenced by trends in the Si–H coupling constant and the infrared stretching frequency of the Si–H bond, as well as by X-ray crystallography and theoretical calculations. The adduct's reactivity with nucleophiles demonstrates conclusively the role of this species in metal-free ‘frustrated-Lewis-pair’ hydrosilylation reactions.

  • Compound C26BF19

    1,2,3-Tris(pentafluorophenyl)-4,5,6,7-tetrafluoro-1-boraindene

  • Compound C32H16BF19Si

    Triethylsilane 1,2,3-tris(pentafluorophenyl)-4,5,6,7-tetrafluoro-1-boraindene adduct

  • Compound C62H31BF19NP2

    Bis(triphenylphosphine)iminium 1,2,3-tris(pentafluorophenyl)-4,5,6,7-tetrafluoro-1-hydrido-1-borataindene

  • Compound C62H30BClF19NP2

    Bis(triphenylphosphine)iminium 1,2,3-tris(pentafluorophenyl)-4,5,6,7-tetrafluoro-1-chlorido-1-borataindene

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Acknowledgements

Funding for the experimental work described was provided by the Natural Sciences and Engineering Research Council of Canada in the form of a Discovery Grant to W.E.P. Funding for the computational work described was provided by the Academy of Finland in the form of a Research Grant and Fellowship to H.M.T.

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Affiliations

  1. Department of Chemistry, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada

    • Adrian Y. Houghton
    •  & Warren E. Piers
  2. Department of Chemistry, Nanoscience Center, University of Jyväskylä, PO Box 35, FI-40014 Jyväskylä, Finland

    • Juha Hurmalainen
    • , Akseli Mansikkamäki
    •  & Heikki M. Tuononen

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Contributions

A.Y.H. and W.E.P. conceived and designed the experiments, A.Y.H. performed the experiments and determined the X-ray structure, H.M.T. and A.M. conceived and designed the computational work, J.H. and A.M. executed the calculations and performed data analyses. A.Y.H., W.E.P. and A.M. co-wrote the paper with input from J.H. and H.M.T.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Warren E. Piers or Heikki M. Tuononen.

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DOI

https://doi.org/10.1038/nchem.2063

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