Formation of 1-ethynyl-1 H -silole from the reaction of silicon atoms with benzene: matrix infrared spectroscopy and quantum chemical calculations.

The reaction of silicon atoms with benzene molecules in solid neon is studied using matrix isolation infrared spectroscopy. Aided by carbon-13 and deuterium isotopic shifts as well as quantum-chemical calculations, the reaction intermediates and products are safely assigned. Among them, silicon atom addition to the aromatic π-system of benzene occurs in a [1,4] fashion Si[η 2 (1,4)-C 6 H 6 ] complex (A) has been formed spontaneously on annealing, which further isomerizes to the seven-membered ring 1-silacycloheptatrienylidene (B) under UV light irradiation. A previously unconsidered five-membered ring 1-ethynyl-1 H -silole (C) is generated as the final product under broadband UV light irradiation. The underlying reaction mechanism of complex A photo-isomerizing to species B and C is discussed in detail, which shows a remarkable boron-silicon diagonal relationship as compared to the reaction of boron with benzene in forming borole derivatives. The results presented herein provide new insight into the future design and synthesis of corresponding silole derivatives.