Selenium diimides

The only selenium diimide to be structurally characterized in the solid state, Se(NAd)2 (Ad = adamantyl), ° adopts the cis, trans conformation consistent with conclusions based on H and C NMR studies for Se(N Bu)2. ... 

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). 

A redox process also occurs in the reaction of selenium diimides with bis(amino)stannylenes. Eor example, the cyclic stannylene McaSi)//-N Bu)2Su reacts in a 1 1 molar ratio with BuN=Sc=N Bu to give a spirocyclic tin complex, which reacts with a second equivalent of the stannylene to generate a Sn-Sn bond [d(Sn-Sn) = 2.85 A, /( Sn- Sn) = 13,865 Hz)] (Scheme 10.6). ... 

Scheme 10.6 Reaction of a selenium diimide with a bis(amino)stannylene...

Selenium diimides react in a manner similar to SeOa with unsaturated organic compounds. The first report of BuN=Sc=N Bu described its use as an in situ reagent for allylic amination of olefins and acetylenes. Improved procedures for this process (Eq. 10.5) and for the diamination of 1,3-dienes (Eq. 10.6) have been developed using the reagents RN=Se=NR [R = para-toluenesulfonyl (Ts), ort/io-nitrobenzenesulfonyl (Ns)]. ... 

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... 

A similar cycloaddition reaction occurs between the glycal (36) and the substituted selenium diimide (37) (Equation (10)) <83ZORl622>. 

TeUnrium diimide dimers are thermally stable. For instance, BnNTe(/u.-lSfBn)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 = 0 167,168 oj- adamantyl ) re monomeric species that are thermally imstable and decompose spontaneously in solution to a variety of selenium-nitrogen species. 

For asymmetric allylic amination reactions, chiral sulfur diimides and selenium diimides are efficient chiral reagents (Sections D.7.4. and D.7.6.). The synthesis uses (S)-l-phenylethylamine as a chiral auxiliary26. 

Diamination of 1,3-dienes. Sharpless and Singer allowed this selenium diimide species to react with 2,3-dimethyIbutadiene with the expectation of obtaining a [4 + 2] cycloadduct. Instead, a t>/e-disulfonamide (2) was formed... 

The accessibility of the +4 and +6 oxidation states for sulfur and, to a lesser extent, selenium gives rise to both acyclic and cyclic molecules that have no parallels in N-O chemistry. Thus there is an extensive chemistry of chalcogen diimides RN=E=NR (E = S, Se, Te) (Section 10.4). In the case of Te these unsaturated molecules form dimeric structures reflecting the increasing reluctance for the heavier chalcogens to form multiple bonds to nitrogen. The acyclic molecule N=Sp3,... 

The Se NMR chemical shifts of Se-N compounds cover a range of >1500 ppm and the value of the shift is characteristic of the local environment of the selenium atom. As a result, Se NMR spectra can be used to analyse the composition of a complex mixture of Se-N compounds. For example, Se NMR provides a convenient probe for analyzing the decomposition of selenium(IV) diimides RN=Se=NR e.g., R = Bu). By this method it was shown that the major decomposition products are the six-membered ring (SeN Bujs, the five-membered ring Sc3(N Bu)2 and fifteen-membered ring Sc9(N Bu)6 (Figure 3.2 and Section 6.3). 

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. ... 

Although selenium(IV) diimides RN=Se=NR (R = adamantyl) and sulfi-nylamines RN=S=0 are monomeric in the solid state, the seleninylamine OSe(p-N Bu)2SeO crystallises as the cis dimer (Figure 12.33). " ° Calculations reveal that the cyclodimerisation of RNSeO ([2 + 2] cycloaddition) is energetically favoured. " ... 

Physical Properties. - Naphtho[2,3-c][1,2,5]thiadiazol-4,9-dione and its selenium analogue have been studied by X-ray crystallography. Both show significant ir interaction of the chalcogen diimide with the it system of the naphthoquinone. ... 

Pericyclic reactions provide some of the most elegant examples of the importance of orbital symmetry in chemical reactions. Unlike in organic chemistry, however, pericyclic reactions are not of great importance in inorganic chemistry. That said, we will encounter a few significant examples in this book, including the reduction of carbon-carbon double bonds by diimide (Section 5.7a) and certain selenium dioxide oxidations (Section 6.16). 

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