title: Direct observation of a borane-silane complex involved in frustrated Lewis-pair-mediated hydrosilylations.
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.
authors.affiliation: Department of Chemistry, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada.
authors.forename: Adrian Y
authors.initials: AY
authors.lastname: Houghton
authors.affiliation: Department of Chemistry, Nanoscience Center, University of Jyväskylä, PO Box 35, FI-40014 Jyväskylä, Finland.
authors.forename: Juha
authors.initials: J
authors.lastname: Hurmalainen
authors.affiliation: Department of Chemistry, Nanoscience Center, University of Jyväskylä, PO Box 35, FI-40014 Jyväskylä, Finland.
authors.forename: Akseli
authors.initials: A
authors.lastname: Mansikkamäki
authors.affiliation: Department of Chemistry, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada.
authors.forename: Warren E
authors.initials: WE
authors.lastname: Piers
authors.affiliation: Department of Chemistry, Nanoscience Center, University of Jyväskylä, PO Box 35, FI-40014 Jyväskylä, Finland.
authors.forename: Heikki M
authors.initials: HM
authors.lastname: Tuononen