Cyclic Selenium and Tellurium Imides

There are very few similarities between the cyclic selenium imides and their sulfur analogues (Section 12.6.1). The selenium imides that have been structurally characterised include examples of five-, six-, eight- and 15-membered rings cyclo-Se3(NR)2 (12.17, R = Bu, Ad), cyclo-Se3(N Bu)3 (12.18), cyclo-Se6(N Bu)2 (12.19) and cyclo-Se9(N Bu)6 (12.20). All of these derivatives have bulky alkyl substituents on the nitrogen atoms the parent selenium imides (R = H) are unknown. 

The discovery of cyclic imides of the heavier chalcogens is a relatively recent development. The ring systems that have been structurally characterized all have bulky substituents attached to the nitrogen atoms, viz., Sc3(NR)2 (74, R= Bu, Ad), 2 Sc3(N Bu)3 (75), See(N Bu)2 (76) and Seg(N Bu)6 (77) 208 known cyclic tellurium imide is Tc3(N Bu)3.  

Seg(N Bu)2 (76) and Seg(N Bu)6 (77) were obtained in low yields by the reaction of LiN( Bu)SiMe3 with Se2Cl2 or SeOCl2. The reaction of tert-butylamine with SeCl2 in THF in a 1 3 molar ratio yields the smaller ring systems 74 and 75, in addition to 76 and 11 A better preparation of 75 involves the decomposition of BuN=Se=N Bu in toluene at 20 °C, which also generates 74 and 76. ° 

The Se NMR spectra provide an informative analysis of the components of the reaction mixtures in these syntheses of cyclic selenium imides. The five- and 

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