Tellurium-oxygen rings

SULFUR-, SELENIUM- AND TELLURIUM-OXYGEN RINGS AND POLYMERS... 

The Si=Si double bonds of the five-membered ring compounds 154-156 also exhibit a similar low reactivity and, for example, are not attacked by atmospheric oxygen. However, the tellurium compound 156 is photochemically labile and decomposes on exposure to daylight with deposition of tellurium142. 

By contrast, 1,2,4-triazole carbene 354 displays electrophilic character. Thus, it reacts with alcohols and amines producing triazoline derivatives 355 in quantitative yields. Oxygen or sulfur gives triazolinone and triazolinethione derivatives 356 (similar reaction with tellurium is known for imidazol-2-ylidenes). Reactions of 354 with dimethyl maleate or dimethyl fumarate lead to compounds 357, probably via ring opening of a cyclopropane intermediate with subsequent 1,2-hydrogen shift. 

Figure 24 The structure of [Te6N8(TeCl4)4-(thf)4]. Tellurium atoms are indicated in grey, nitrogen, oxygen, and chlorine in white, and carbon atoms from the tetrahydrofiiran rings in dark grey...

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