Thermolyse et photolyse d'heterocycles a liaison GeS. Mise en evidence de la formation de germylenes et germathiones

Abstract The photolysis and thermolysis of 2,3-digerma-1,4-dithianes, 2,3,5-trigerma-1,4-dithiolanes and tetragerma-1,4-dithianes have been studied. 2,2,3,3-Tetramethyl-2,3-digerma-1,4-dithiane (I) decomposes slowly at room temperature by α-elimination to yield dimethylgermylene (Me 2 Ge:) and 2,2-dimethyl-2-germa-1,3-dithiolane (II). 2,2,3,3,4,4-Hexamethyl-2,3,4-trigerma-1,5-dithiepane (III) is obtained by the insertion of Me 2 Ge: into the sulfur-germanium bond of I. At 200°C, I undergoes thermal fragmentation leading to II, III and 2,2,3,3,5,5-hexamethyl-2,3,5-trigerma-1,4-dithiolane. These results are explained by two concurrent mechanisms of decomposition of I, involving formation of dimethylgermylene (Me 2 Ge:) and dimethylgermathione (Me 2 GeS), respectively. Photolysis of I or 2,2,3,3,5,5,6,6-octamethyl-2,3,5,6-tetragerma-1,4-dithiane and thermolysis of the latter heterocycle generate dimethylgermylene and heterocycles resulting from dimethylgermylene expulsion. 2,2,3,3,5,5-Hexamethyl-2,3,5-trigerma-1,4-dithiolane is thermally and photochemically stable.