Tellurium diimides

The corresponding tellurium diimide BuNTe( -N Bu)2TeN Bu (10.7) may be obtained in good yields from the reaction of lithium tert-butylamide with TeCU in THE (Eq. 10.3). °" In toluene solution this reaction also produces the cyclic tellurium(II) imide (TcN Bu)3. The dimer 10.7 is obtained as an orange solid, which can be purified by vacuum sublimation at ca. 90°C. 

In general, it was found that this process is strongly endothermic for sulfur diimides, approximately thermoneutral for selenium diimides and strongly exothermic for tellurium diimides, consistent with experimental observations. These differences can be attributed to the expected trend to lower r-bond energies for chalcogen-nitrogen (np-2p) r-bonds along the series S (n = 3), Se (n = 4) and Te (n = 5). 

The dimeric tellurium diimide 10.7 undergoes a cycloaddition reaction with BuNCO to generate the Ai,iV -ureatotellurium imide 10.11, which is converted to the corresponding telluroxide 10.12 by reaction with excess BuNCO. " By contrast, BuN=S=N Bu undergoes exchange reactions with isocyanates. 

Because of the lower stability of Se(IV) compounds as compared with their Te(IV) analogues (95UK527), the reaction of the disilyldiimine with SeCU ends up in phenanthro[9,10-c]-l,2,5-selenadiazole. 3,4-(2,4-Di-terr-butylbenzo)-l,2,5-telluradiazole 75 was obtained by a treatment of the tellurium diimide 76 with a lithium salt of tris(rerr-butyl)aniline. Dimer 77 is an intermediate in this reaction (96IC9). 

The dimeric tellurium diimides can act as chelating or bridging ligands. In the cis,exo,exo conformation, the formation of A. TV -chclated complexes is... 

The first structural characterization of a tellurium diimide RNTe(p-N Bu)2TeNR (R = PPh2NSiMe3) was reported in 1994. Subsequently, the synthesis of the symmetric derivative, R = Bu, was achieved by the reaction of Li[HN Bu] with TeClq in a 4 1 molar ratio in toluene. Several LiCl-containing byproducts are also obtained in this solvent. In THF, however, the tellurium diimide, BuN-Te(p-N Bu)2TeN Bu, is obtained in 90% yield and is readily purified." Unlike sulfur or selenium diimides, the tellurium diimides are dimeric and form either cis or... 

Other imine-like adduct structures reported include the phosphinimine of Entry 30149 and the coordinated nitrile in the vanadocene complex shown in Entry 31.150 The tellurium diimide dimer (Entry 32) also coordinates one equivalent of B(C6F5)3 and this adduct has been crystallographically characterized.151 The structure features weak... 

An exchange reaction of a tellurium diimide dimer with t-butyl isocyanate affords di-t-butylcarbodiimide and N,N -bis(t-butyl)ureato dimer. ... 

Tellurium diimide dimers are thermally stable. For instance, BuNTe(/x-N Bu)2TeN Bu sublimes at 85 °C, 10 Torr and melts at 100-102 °C without decomposition. This is a marked contrast to selenium diimides. (RN)2Se (R = Bu 468 qj. adamantyP 470 gj.g monomeric species that are thermally unstable and decompose spontaneously in solution to a variety of selenium-nitrogen species. 

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