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.
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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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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.
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Houghton, A., Hurmalainen, J., Mansikkamäki, A. et al. Direct observation of a borane–silane complex involved in frustrated Lewis-pair-mediated hydrosilylations. Nature Chem 6, 983–988 (2014). https://doi.org/10.1038/nchem.2063
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DOI: https://doi.org/10.1038/nchem.2063
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