Chalcogen imides

2 Cyclic Sulfur Liiides 6.2.1 Eight-membered rings 

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Cyclic chalcogen imides in which sulfur is in the formal -f2 oxidation state (or lower) can, in the case of sulfur, act as a source of binary S-N... 

The 15-membered ring Se9(N Bu)6 (6.9) is a unique member of the series of cyclic chalcogen imides (see Section 12.8.1). It was first obtained as the major product of the reaction of LiN( Bu)SiMe3 with Se2Cl2 or SeOCl2. It is also formed, in addition to smaller cyclic selenium imides, in the cyclocondensation of SeCl2 with er -butylamine in THF or from the decomposition of the sele-nium(IV) diimide BuN=Se=N Bu. ... 

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., Se3(NR)2 (74, R= Bu, Ad),30,152 Se3(N Bu)3 (75),160 Se Bu (76)208 and Se9(N Bu)6 (77).208 The only known cyclic tellurium imide is Te3(NtBu)3.150... 

The pyramidal inversion energies of chalcogen-onium imides were estimated by MO calculations.28 The values for model compounds, dimethyl chalcogen-onium imides, were evaluated to be 34, 44, and 54 kcal mol-1 for S, Se, and Te, respectively, indicating that among the chalcogen-onium imides, telluronium imides are those that are most stable toward pyramidal inversion. 

The very strong polarization of the Te=X —> Te+ - X (X = C,N,0) bonds accounts for the enhanced electrophilicity of the tellurium center in 7r-telluranes, which markedly exceeds that of other chalcogen centers in respective 7r-chalcogenuranes (ylides, imides, oxides). Such a polarization provides also for the highest nucleophilcity and basicity of the X-centers in ir-telluranes. 

The ligands that have been used in the preparation of metal nitride complexes are quite varied. They include halides, carbogenic groups (alkyl moiety and Cp ), pnic-togens (amine, amide, imide, phosphine, and arsine), and chalcogens (ether, alkox-ide, oxo, thioalkoxide, and selenides). Chart 1 provides a listing of the various ligands and the associated nitrido metal complexes. 

By far the most frequently used method is the deprotonation with potassium tert-butoxide, which gives the potassium salts in nearly quantitative yields. The method seems to be usable for any bis(chalcogenophosphinyl and -phosphoryl)imide and has been employed for a broad diversity of derivatives, regardless of the nature of the chalcogen.2,26,30,33,36-38,49,89,91,99 If the salts are needed for further use in reactions with metal halides to form complexes, the potassium salt can be used in situ, without isolation, e.g., with zinc(II) chloride or palladium and platinum chloro complexes.41,43 Potassium metal in THF also forms the salt K[SPh2PNPPh2S] in 82% yield, 38 but the method is not practical for preparative purposes. Potassium-crown ether complexes, [K(18-crown-6)][Q1Ph2PNPPh2Q1] with Q1 = O,92 Q1 = S,93 and Q1 = Se,98 have been prepared by direct complexation of the potassium salt with the macrocyclic ligand. 

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