Germanium compounds, double effect

A number of cyclic structures with Se-Si bonds have been contributed in recent years (Scheme 11). Beside one substituted three-membered ring consisting of C, Si, and Se (3 = 4-49), some four- and five-membered rings (24-28) were published. Further examples are 29-31 and 33 36, 37, 39, 41, the propellane-type 43 and the double-decker tricyclus 44. For many of the silicon compounds, corresponding germanium analogues have been reported as well 32, " 38, 40, 42, and 45 (Scheme 11). Evidently, the effects of Ge are mostly less shielding as compared to Si. 

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