Details

Autor(en) / Beteiligte

• Liu, Wen-Bo
• Schuman, David P
• Yang, Yun-Fang
• Toutov, Anton A
• Liang, Yong
• Klare, Hendrik F. T
• Nesnas, Nasri
• Oestreich, Martin
• Blackmond, Donna G
• Virgil, Scott C
• Banerjee, Shibdas
• Zare, Richard N
• Grubbs, Robert H
• Houk, K. N
• Stoltz, Brian M

Titel

Potassium tert-Butoxide-Catalyzed Dehydrogenative C–H Silylation of Heteroaromatics: A Combined Experimental and Computational Mechanistic Study

Ist Teil von

• Journal of the American Chemical Society, 2017-05, Vol.139 (20), p.6867-6879

Ort / Verlag

United States: American Chemical Society

Erscheinungsjahr

2017

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• We recently reported a new method for the direct dehydrogenative C–H silylation of hetero­aromatics utilizing Earth-abundant potassium tert-butoxide. Herein we report a systematic experimental and computational mechanistic investigation of this transformation. Our experimental results are consistent with a radical chain mechanism. A trialkylsilyl radical may be initially generated by homolytic cleavage of a weakened Si–H bond of a hyper­coordinated silicon species as detected by IR, or by traces of oxygen which can generate a reactive peroxide by reaction with [KOt-Bu]4 as indicated by density functional theory (DFT) calculations. Radical clock and kinetic isotope experiments support a mechanism in which the C–Si bond is formed through silyl radical addition to the hetero­cycle followed by subsequent β-hydrogen scission. DFT calculations reveal a reasonable energy profile for a radical mechanism and support the experimentally observed regio­selectivity. The silylation reaction is shown to be reversible, with an equilibrium favoring products due to the generation of H2 gas. In situ NMR experiments with deuterated substrates show that H2 is formed by a cross-dehydrogenative mechanism. The stereo­chemical course at the silicon center was investigated utilizing a 2H-labeled silolane probe; complete scrambling at the silicon center was observed, consistent with a number of possible radical intermediates or hyper­coordinate silicates.