Branched polystannanes

Unfortunately, very little has been done to date regarding the investigation of branched polystannanes. No structural studies have been performed, and only the electronic spectrum of compound 55 (X a 277 nm  

Selected Bond Lengths and Bond Angles FOR [PHjSnIj (O) (76,77) 

Forced to adopt formal bond angles of 60° and 90° degrees, respectively, the skeletal frameworks of cyclotristannanes and cyclotetrastannanes are of interest with regard to the information they could provide concerning the origins and manifestations of strain in polystannane structures. The 

The electronic spectrum of dodecaphenylcyclohexastannane 63 exhibits an intense absorption maximum at 280 nm -45,000). In the two cyclotristannanes, this characteristic feature is shifted to longer wavelengths and now appears at X 295 nm (e 45,000) for 17 and at X 300 nm 55,000) for 17 (2/,27). Whether this shift is a result of longer Sn-Sn bond lengths in the three-membered ring system or is an inherent property of the cyclotristannane framework itself remains a question until further studies with these compounds are performed. In this regard, it is unfortunate that the electronic spectra of other cyclopolystannanes have not been reported. 

---

Polystannanes have been shown to display very interesting properties. They are highly photosensitive and exhibit photobleaching behaviour and on UV irradiation depolymerise to yield cyclic oligomers. The materials are thermally stable to 200-270 °C in air and at more elevated temperatures function as precursors to Sn02. " By using rhodium catalysts, branched polystannanes have been prepared. 

D. Redistributive Coupling of Hydrostannanes to Highly Branched Polystannanes. 161... 

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. 

The Sn-NMR chemical shifts of the poly(alkyl-) and poly(arylstannanes), surprisingly, are quite similar the cyclic products have up field chemical shifts (Table 8.1). In contrast to the fairly linear polystannanes prepared by the catalytic action of zirconocene catalysts, branched polymers are obtained in the reaction of Bu2SnH2 with the rho-... 

---