Department of Chemistry, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada.
Department of Chemistry, Nanoscience Center, University of Jyväskylä, PO Box 35, FI-40014 Jyväskylä, Finland.
Nat Chem. 2014 Nov;6(11):983-8. doi: 10.1038/nchem.2063. Epub 2014 Sep 28.
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.
全氟芳基硼路易斯酸催化硅氢键与 C=C、C=N 和 C=O 双键的加成。这种“无金属”的硅氢化反应据称是通过硼烷对硅烷 Si-H 键的活化而发生的，而不是通过与底物的经典路易斯酸碱加合物。然而，关键的硼烷/硅烷加合物尚未在实验中观察到。本文证明，强路易斯酸性、反芳香性的 1,2,3-三(五氟苯基)-4,5,6,7-四氟-1-硼杂茚与三乙硅烷形成可观察到的、可分离的加合物。通过变温 NMR 光谱研究定量研究了加合物形成的平衡。硅烷与硼烷的相互作用通过 Si-H 键发生，这可以通过 Si-H 偶合常数和 Si-H 键的红外伸缩频率的趋势以及 X 射线晶体学和理论计算来证明。加合物与亲核试剂的反应明确证明了该物种在无金属“受阻路易斯对”硅氢化反应中的作用。
