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C(sp3)–F Bond Activation of CF3‑Substituted Anilines with Catalytically Generated Silicon Cations: Spectroscopic Evidence for a Hydride-Bridged Ru–S Dimer in the Catalytic Cycle

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journal contribution
posted on 30.01.2013 by Timo Stahl, Hendrik F. T. Klare, Martin Oestreich
Heterolytic splitting of the Si–H bond mediated by a Ru–S bond forms a sulfur-stabilized silicon cation that is sufficiently electrophilic to abstract fluoride from CF3 groups attached to selected anilines. The ability of the Ru–H complex, generated in the cooperative activation step, to intramolecularly transfer its hydride to the intermediate carbenium ion (stabilized in the form of a cationic thioether complex) is markedly dependent on the electronic nature of its phosphine ligand. An electron-deficient phosphine thwarts the reduction step but, based on the Ru-S catalyst, half of an equivalent of an added alkoxide not only facilitates but also accelerates the catalysis. The intriguing effect is rationalized by the formation of a hydride-bridged Ru–S dimer that was detected by 1H NMR spectroscopy. A refined catalytic cycle is proposed.