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

Abstract

The reduction of 1-chloro-1,2,3,4,5-pentaphenylsilole, (C 4Ph 4SiPhCl, 1) with 2 equiv lithium gave the pentaphenylsilole anion [C 4Ph 4SiPh] − ( 2), silole dianion [C 4Ph 4Si] 2− ( 3), and hexaphenylsilole C 4Ph 4SiPh 2 ( 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 Li[C 4Ph 4Si tBu], but shifted downfield compared to that of the other silole monoanion such as Li[C 4Me 4SiSiMe 3], indicating the delocalization of silole anion through the 5-membered ring. Derivatization of the reaction mixture with iodomathane gave C 4Ph 4SiPh 2 ( 4), C 4Ph 4SiMePh ( 5), and C 4Ph 4SiMe 2 ( 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 [C 4Ph 4Si] 2− in about 70% yield.