Carbene and Alkene Analogs

Dialkyltin dichlorides couple via the Wurtz reaction (see Section 2.3) to yield long-chain polystannanes, as shown below, along with cychc byproducts. 

The polystannanes thus obtained are of interest for their semiconducting and liquid-crystalline properties. Provide a mechanistic rationale for the polymerization. 

Germanium, tin, and lead form stable dihalides with the general formula EX2. In the gas phase or in noble gas matrixes, they exhibit bent structures, reflecting their stereo-chemically active lone pairs (or based on VSEPR considerations). Like trivalent boron compounds, they are Lewis acids and readily accept a lone pair to complete their octets, as shown below for the formation of the GeCl2 dioxane complex  

In the solid state as well, the dihalides associate so as to complete their octets as shown below for crystalline SnCl2, SnCl2 2 H2O, and SnCl2 CsCl  

The divalent Ge and Sn halides are moderately reactive and insert into or add to various reactive bonds, as in the following cycloaddition  

---