A tin analogue of propadiene with cumulated CSn double bonds

Abstract

The synthesis, structure, and properties of a stable, linear 2-stannapropadiene are reported. The identical CSn bonds in this 2-stannapropadiene are the shortest hitherto reported C–Sn bonds. This 2-stannapropadiene features a ¹¹⁹Sn NMR signal at 507 ppm for the central tin atom, indicative of an unsaturated Sn⁴⁺ oxidation state. Due to the inert-pair effect, the tin atom displays a pronounced preference for the +2 oxidation state over the +4 oxidation state. Nevertheless, by employing silyl substituents, it is possible to disrupt the inert-pair effect, leading to the formation of an isolable 2-stannapropadiene with a linear structure centered on a Sn⁴⁺ atom. Treatment of this 2-stannapropadiene with SnBr₂·dioxane resulted in the formation of a novel four-membered cyclic 1,1-dibromo-1,3-distannetane, which was subsequently reduced to afford the corresponding stable four-membered cyclic bis(stannylene).