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.