Catalytic C-F bond activation reactions under mild conditions on using silylium-ions in presence of hydrogen sources like tertiary silanes have attracted great attention during the last years.[1] Such reactions take place in the homogeneous phase, and weakly coordination anions (WCA) are needed to generate and stabilize the catalytically active silylium-ions. C-F bond activation reactions on using heterogeneous catalysts are restricted to methods at high temperatures.Aluminum chlorofluoride (ACF)[2] and HS-AlF3[3] are two of the strongest known solid Lewis acids and both are able to catalyze numerous reactions with fluoroorganic compounds.Recently, we found that ACF and HS-AlF3 are both highly efficient heterogeneous C-F bond activation catalysts in the presence of tertiary silanes. For fluoromethanes, C-F bonds can be converted into either C-H or C-C bonds with TONs up to 400.[4] The crucial step is the formation of a �ACF���H-SiEt3� surface species with silylium-ion character.In order to gain more information on the nature of the catalytically active species, MAS NMR, Thermal Analysis and in-situ FTIR studies were performed. These studies lead to the conclusion that the surface species should be regarded as a chemically adsorbed silane species, whereas in presence of a substrate a silylium-ion like reactivity was found and the C�F bond activation reactions were observed.[1] a) Allemann, O.; Duttwyler, S.; Romanato, P.; Baldridge, K. K.; Siegel, J. S.; Science 2011  , 332, 574; b) Douvris, C.; Ozerov, O. V.; Science 2008  , 321, 1188; c) Panisch, R.; Bolte, M.; M�ller, T.; J. Am. Chem. Soc. 2006  , 128, 9676. [2] Krespan, C. G.; Dixon, D. A.; J. Fluorine Chem. 1996  , 77, 117.[3] Kemnitz, E.; Gro�, U.; R�diger, S.; Shekar, C. S.; Angew. Chem. Int. Ed. 2003  , 42, 4251.[4] Ahrens, M.; Scholz, G.; Braun, T.; Kemnitz, E.; Angew. Chem. Int. Ed. 2013  , 52, 5328.

Insights into the catalytic hydrodefluorination reaction of fluoromethanes by silylium-ion like surface species

248th National Meeting (2014)

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