Reduction of 1-chloro-1,2,3,4,5-pentaphenylsilole: formation of silole monoanion and dianion

The reduction of 1-chloro-1,2,3,4,5-pentaphenylsilole, (C₄Ph₄SiPhCl, 1) with 2 equiv lithium gave the pentaphenylsilole anion C₄Ph₄SiPh]⁻ (2), silole dianion C₄Ph₄Si]²⁻ (3), and hexaphenylsilole C₄Ph₄SiPh₂ (4). 2, 3, and 4 from the reaction mixture were characterized by ²⁹Si NMR spectroscopy. The ²⁹Si chemical shift of 3.7 ppm for 2 is shifted upfield as compared to that of previously reported t -butyltetraphenylsilole anion LiC₄Ph₄SitBu], but shifted downfield compared to that of the other silole monoanion such as LiC₄Me₄SiSiMe₃], indicating the delocalization of silole anion through the 5-membered ring. Derivatization of the reaction mixture with iodomathane gave C₄Ph₄SiPh₂ (4), C₄Ph₄SiMePh (5), and C₄Ph₄SiMe₂ (6), which were characterized by ¹H, ¹³C, and ²⁹Si NMR spectroscopy. The silole dianion 3 could be either from the continuous reduction of 1 with lithium or from the disproportionation of 2. The reduction of 1 with excess lithium in THF gave the silole dianion C₄Ph₄Si]²⁻ in about 70% yield.