Synthesis of Polystannanes

The dehydrogenative coupling of hydrosilanes and hydrogermanes catalyzed by the early transition metal complexes is an attractive route for the synthesis of derivative polymers. A major advantage of this 

Early studies on dehydropolymerization suggested that metallocene dichlorides CP2MCI2, (M = Ti, Zr, Hf) could be used as catalysts, but they were not very effective only low molecular weight polymers were 

Further research is still required in this area to discover more effective and reproducible reaction conditions/catalyst systems. Such an approach could optimize formation of only the high molecular weight linear polystannananes with better structural control and suppression of cyclic oligomer formation. 

Sn-H bond, as shown by Sita, see above, then lower molecular weight oligomers and/or cycles would be expected. 

The structure of the copolymer, poly(di-n-butylstannane-co-methylphenylsilane) with a Sn Si ratio of 1 3 was determined with X-ray absorption fine-structure spectroscopy (EXAES) and X-ray absorption near-edge spectroscopy (XANES). The bond distances of Sn-Sn (2.82 A), Sn-Si (2.58 A), and Sn-C (2.15 A) in the copolymer were comparable with the cyclooligostannylsilane, illustrated in Eigure 3.8.1. 

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Although the initial efforts of the synthesis of polystannanes by the Wurtz-eoupling methodology did not appear to be successful, Molloy and coworkers have shown that a carefully controlled reaction involving Bu2SnCl2 with sodium dispersion in the presence of 15-crown-5-ether in toluene at 60 °C affords the polymer [ Bu2Sn]n in optimum yields after 4 h of reaction [17] (see Eq. 8.8). 

The condensation of diorganotin dihydrides with diorganotin diamides is another route to cyclic polystannanes. This method is especially useful for the high-yield synthesis of the dimethyl derivative (Me2Sn)g [eqn (10.5)], which cannot be obtained by the dehydrocoupling process. 

Recently, Deacon, Price, and coworkers reported the synthesis and study of polymers containing triphenyl and tributyltin as side chains and of polystannanes produced using the Wurtz polymerization [59]. The polystannanes were characterized employing Mossbauer spectroscopy. The polystannane shown below exhibits some liquid-crystal behavior. The products have weight average molecular weights of 2.5 10. The coordination number for tin is 4 with the tin present as a distorted tetrahedral geometry (4). 

Synthesis and photochemical reactions of polystannanes, Chem. Lett. 91-92. 

Sita, L. R. (1992) A new strategy for the synthesis of homologously pure linear polystannane oligomers, Organometallics 11,1442-1444. 

Other methods of polystannane synthesis include electrochemical methods [22], Thus, [ Bu2Sn]n 10,900 MJM = 2.6) and [ Oet2Sn]n (M = 5900 MJMn = 1.7) were prepared by the eleetroehemieal polymerization of dibutyldichlorostannane and dioctyldiehlorostannane, respectively, by using a platinum cathode and a silver anode. Tetrabutylammonium perchlorate is used as the supporting electrolyte and dimethoxy ethane is used as the solvent. 

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