Stepwise oxidation of the stannole dianion.

Tin oxidation of stannole dianion 1 with 1.3 equivalents of oxygen gave terstannole-1,3-dianion 3. The non-aromatic nature of 3 was confirmed by X-ray crystallographic analysis. Treatment of 1 with 1,2-dibromoethane (3 equiv) gave poly(1,1-stannole) 4, the formation of which was proven by reduction of 4 with lithium to revert to the starting dianion 1. Reaction of 1 with 1,2-dibromoethane (3 equiv) in the presence of phenyllithium gave phenyl-capped ter(1,1-stannole) 7. The electronic absorption spectra of newly obtained stannoles were also measured.