Reduction of Terphenyltrifluorosilanes: C−C Insertion Products and Possible Formation of a Disilyne

The new terphenyl trifluorosilanes Mes2C6H3SiF3 (1) and Tip2C6H3SiF3 (2) have been
synthesized, and their reduction behavior has been investigated in detail. Reduction with
sodium in both cases results in insertion of the silicon center into C−C bonds of the
substituent. The reactive intermediates giving rise to the C−C insertion most likely involve
fluorosilylene or disilyne species. The final product is a bis-silafluorenyl (3) in the case of 1
and a silafluorenyl anion in the case of 2. The anion can be protonated to give a stable
silafluorene. The reduction of 1 and 2 with potassium gives a completely different result,
and radical species are formed instead. The different reaction pathway is probably caused
by the existence of a poorly soluble intermediate [2Mes2C6H3SiF3·3KF] (10) that lowers the
concentration of the starting material and therefore influences the reaction kinetics. Crystal
structures are presented for 1, 2, the insertion product 3, and the intermediate adduct 10.