Polymer polystannane

Most of the reactions that can be used to prepare distannanes can be extended to the preparation of oligo- and polystannanes, which have attracted interest for potential use in electronic and optical devices.455 The structures of the products are not necessarily those of completely linear catenanes, (R2Sn) , and different degrees of branching confer different properties. The formation of polymers is also frequently accompanied by the formation of cyclic pentamers or hexamers, and samples prepared by different methods may show substantially different properties. 

In recent years, dehydrocoupling reactions catalysed by early transition metal complexes have become an increasingly important method for generating catenated species of the p-block elements. In addition to producing cyclic oligomers, this approach is used to prepare linear oligomers and polymers such as polysilanes and polystannanes of the type H(MR2) H (M = Si, Sn) (see Section 10.1.4). ... 

Currently, there is growing interest in polymers the frameworks of which are constructed from the Group 14 elements silicon, germanium and tin. Several reviews on polysilanes have appeared in the literature . In the first section of this article we focus on recent developments in the chemistry of polygermanes and polystannanes. The chemistry and structure-property relationship of oligostannanes and low molecular weight polystannanes was the subject of earlier reviews . ... 

The silyl chloride complexes ( / -C5H4SiMe3)2Zr[Si (SiMe3)3]Cl is a catalyst for the dehydropolymerization of both PhSiH3 and -Bu2SnH2 to relatively low-molecular weight polymers. Thus, polysilanes and polystannanes can be obtained. 

Polystannanes are routinely characterized by and spectroscopy, and (GPC) against polystyrene standards of different molecular weights in THF. However, it is often " Sn NMR in particular that is a valuable tool to determine the structure of the linear oligomeric and polymeric chains and provides useful information regarding purity of polymer chains and ratios and types of cyclic oligomers. 

Even smaller band gaps are present in polystannanes with aryl substituents at tin" " For example, dehydropolymerization of R2SnH2 (R =/>- BuG6H4 or />- HexG6H4) afforded linear polymers (contaminated with some cyclics) with values up to 20,000. The materials, which are yellow in color, possess A ax values for the Sn a-a transition of 423-436 nm, that is red-shifted by 30 0 nm compared to those for poly(dialkylstannanes) and suggest that significant cr-7r-conjugation that involves the Sn backbone and the aryl substituents is present. 

Table 7 Calculated band parameters for polystannane [SnHJn 215 and analogous group 14 polymers [SiHJn 212, and [GeHdn 213...

A significant drawback for the practical application of polystannanes is their air and moisture sensitivity. This is not so significant in the solid state but the materials are appreciably sensitive in solution. Nevertheless, the properties of these fascinating materials are under detailed scrutiny." The polymers are reasonably thermally stable up to ca. 270 °G, and polystannane 215 (R = y>-TuG6H4) yields tin metal, when heated under nitrogen to 400 °G, and tin oxides in air, with a decomposition onset at around 225 °G. Polystannanes are highly photosensitive and exhibit... 

---