Synthesis and characterization of dibenzannulated silole dianions. The 1,1-dilithiosilafluorene and 1,1′-dilithiobis(silafluorene) dianions

Stirring of 1,1-dichloro-SiFl (1), (SiFl, silafluorene) in THF with excess lithium for 1 h gave a dark green solution of 1,1-dilithio-SiFl (2) in high yield. The dark red solution of the intermediate 1,1′-dilithio-(SiFl)2 (3) was also observed from this reaction within 10 min. Treatment of 2 with excess trimethylchlorosilane gave the 1,1-bis(trimethylsilyl)-SiFl derivative (4) in 95% yield. Treatment of the dark red solution of 3 and 2 with excess methyliodide gave the 1,1′-dimethyl-bis(SiFl) (5) and 1,1-dimethyl-SiFl (6) derivatives in a 4:1 ratio. The upfield locations of the 29Si resonances of dianions 2 and 3 (−1.09 ppm and −39.25 ppm, respectively) are consistent with π-electron localization on the silicon atoms.