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From Si(II) to Si(IV) and Back: Reversible Intramolecular Carbon–Carbon Bond Activation by an Acyclic Iminosilylene

Wendel, Daniel, Porzelt, Amelie, Herz, Fabian A. D., Sarkar, Debotra, Jandl, Christian, Inoue, Shigeyoshi, Rieger, Bernhard
Journal of the American Chemical Society 2017 v.139 no.24 pp. 8134-8137
carbon dioxide, catalytic activity, chemical bonding, density functional theory, ethylene, hydrogen, ligands, silicon, silicon compounds, temperature
Reversibility is fundamental for transition metal catalysis, but equally for main group chemistry and especially low-valent silicon compounds, the interplay between oxidative addition and reductive elimination is key for a potential catalytic cycle. Herein, we report a highly reactive acyclic iminosilylsilylene 1, which readily performs an intramolecular insertion into a C═C bond of its aromatic ligand framework to give silacycloheptatriene (silepin) 2. UV–vis studies of this Si(IV) compound indicated a facile transformation back to Si(II) at elevated temperatures, further supported by density functional theory calculations and experimentally demonstrated by isolation of a silylene–borane adduct 3 following addition of B(C₆F₅)₃. This tendency to undergo reductive elimination was exploited in the investigation of silepin 2 as a synthetic equivalent of silylene in the activation of small molecules. In fact, the first monomeric, four-coordinate silicon carbonate complex 4 was isolated and fully characterized in the reaction with carbon dioxide under mild conditions. Additionally, the exposure of 2 to ethylene or molecular hydrogen gave silirane 5 and Si(IV) dihydride 6, respectively.