Hypervalent nitrogen

The parent compound and a set of monosubstituted bis(acylamino)diarylspiro-X4-sulfanes (360 X = H, Me, MeO, Cl, NO2) undergo hydrolysis to the corresponding sulfoxides (361). The probable mechanism involves rate-determining cleavage of one of the S—N hypervalent bonds in the spiro ring with simultaneous proton transfer to the nitrogen atom. The hydroxide ion which is formed thereby then attacks the sulfur atom in a fast step to form a diaryl(acylamino)hydroxy-k4-sulfane (362), which is converted into the sulfoxide (361) (Scheme 47). ... 

In spite of these anticipated great similarities, the results of our SC calculations [12] reveal a completely different picture. When the reacting molecules are far apart (see the rightmost column in Fig. 2), the orbitals on the HCNO fragment ( /i, /3, /5 and /6) reproduce the well-known SC model for the electronic structure of 1,3-dipoles [33,34], according to which the central heavy atom is hypervalent . The nitrogen atom in... 

A new direction in the chemistry of hypervalent silicon compounds has recently been developed by Tacke and coworkers the chemistry of zwitterionic organosilicates28-31. In these compounds the silicon is formally negative, with a cationic nitrogen attached to it by an alkyl chain. One of the groups of products of this general class is the pentacoordinate zwitterionic fluorosilicates31. 

The use of hypervalent iodine reagents for heteroatom-heteroatom bond forming reactions is well established in the context of classical oxidation chemistry [1-11]. For example, oxidations of anilines to azobenzenes, thiols to disulfides, and sulfides to sulfoxides with aryl-A3-iodanes were documented decades ago [1-5]. During the last ten years, particular attention has also been given to oxidative transformations of compounds derived from heavier elements, including the interception of reaction intermediates or initially formed products with external nucleophiles. A second important development is the utilization of sulfonyliminoiodanes, ArI = NS02R, for heteroatom-nitrogen bond formation, especially for imidations of sulfur, selenium, phosphorus and arsenic com-... 

Azide compounds of hypervalent main group elements such as Si and Ge are also highly explosive [83,84], but their structures and energetics have not been widely explored. Quite recently, the crystal structure of the Si(N3)62 anion has been reported, which has 90% nitrogen content, enough to be a possible high-energetic material candidate[83,84]. It is noted that Si(N3)62 (E = Ge, Pb) have been synthesized and are structurally known [83],... 

CP/MAS NMR spectrum reveals an isotropic 5119Sn value of —604.0 ppm83. The increase of the coordination number at the tin atom in 4 is caused by intermolecular association via the free electron pairs at the nitrogen atoms of the hypervalent N — Sn—N systems. 

Both IL3 and IL5 iodanes may formally eliminate the equatorial ligand as a cation in the resulting IL2 and ILj species bonding is still hypervalent, with elongated weak bonds. These iodates have mostly iodine-chlorine or iodine-nitrogen bonds although some of them are useful reagents, they will not be discussed here. 

Generally, hypervalent iodine reagents are often better than traditional reagents of similar reactivity, with respect to efficiency and chemoselectivity - sometimes even stereoselectivity. Unusual reactivity is another interesting feature which has often resulted in unexpected transformation. Examples of such reactions may be found in the oxidation of nitrogen-containing compounds, the Hofmann rearrangement in acidic conditions, the acetalization of carbonyl compounds in alkali, the remote functionalization of steroids, etc. Some unique transformations were effected in the... 

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