Perstanna- -prismanes

All of the polycyclic polystannanes reported to date are thermally robust in solution to temperatures of at least 200°C. For the bicyclo[2.2.0]hexa-slannane derivative 87, this is not too surprising, since the calculated strain-energy value for the parent compound is still ca. 12 kcal mol" less than the parent cyclotristannane system (102). However, the parent perstanna-[ ]-prismanes for n = 4 and 5 are expected to be more ring-strained than cyclotristannane (cf. 73.2 and 61.0 kcal mol" , respectively) (99,I04) therefore, the thermal stability of the two compounds, 90 and 91, suggest that these compounds are kinetically stable by virtue of signifi-... 

Fig. 14. Molecular structures of the perstanna-[n]-prismanes (a) compound 90, and (b) compound 91. Reprinted with permission from Sita and Kinoshita (98,99).

We have found that if the thermolysis of the cyclotristannane 1 is carried out with benzophenone at 200° C, two new polycyclic polystannanes, 7 and 8, which are members of the perstanna-[n]-prismane, [RSn]2n, series of compounds, can be isolated by column chromatograpy in a 1 2.3 ratio for a combined yield of 12% [11,12]. Since the octastanna-[4]-prismane 7 and the decastanna-[5]-prismane 8 display different physici and chemical properties, an investigation of these compounds reveals important information concerning the impact that bond angle distortions have on the electronic structure and thermodynamic stability of heavy atom Group IVA polycyclic compounds. 

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