Chalcogens reactions with

Chalcogen-nitrogen cations can be generated by the reactions of homopolyatomic chalcogen cations with azides. For example, the... 

Cycloaddition reactions also have important applications for acyclic chalcogen-nitrogen species. Extensive studies have been carried out on the cycloaddition chemistry of [NSa]" which, unlike [NOa]", undergoes quantitative, cycloaddition reactions with unsaturated molecules such as alkenes, alkynes and nitriles (Section 5.3.2). ° The frontier orbital interactions involved in the cycloaddition of [NSa]" and alkynes are illustrated in Fig. 4.13. The HOMO ( Tn) and LUMO ( r ) of the sulfur-nitrogen species are of the correct symmetry to interact with the LUMO (tt ) and HOMO (tt) of a typical alkyne, respectively. Although both... 

Although the high reactivity of metal-chalcogen double bonds of isolated heavy ketones is somewhat suppressed by the steric protecting groups, Tbt-substituted heavy ketones allow the examination of their intermolecular reactions with relatively small substrates. The most important feature in the reactivity of a carbonyl functionality is reversibility in reactions across its carbon-oxygen double bond (addition-elimination mechanism via a tetracoordinate intermediate) as is observed, for example, in reactions with water and alcohols. The energetic basis... 

Although diselenonium-, ditelluronium- and mixed sulfonium-selenonium dications can exhibit either oxidative or electrophilic properties in reactions with nucleophiles, substitution at the onium chalcogen atom is more typical.96 Owing to the increased stability of heavier dichalcogenium-dications, they react only with highly activated substrates such as aniline and tV,A-dimethylaniline, while no reaction is observed with phenol and diphenylamine.113 Reactions of ditelluronium dications with activated aromatics are also not known (Scheme 44).114... 

The chemical properties of trichalcogen dications are, in many ways, analogous to the properties of dichalcogen dications, but are considerably less studied. Hydrolysis of chalcogenurane dications occurs preferentially at the onium chalcogen atom. Similar to the usual dichalcogen dications, trichalcogen dications also display oxidative properties. For example, reduction of selenu-rane dication 135 (X = Y = Se) is observed in reactions with Sm(II) salts, triphenylphosphine or thiophenol (Scheme 54).135... 

Introduction of two different chalcogen elements to the C-C unsaturated bond is of particular interest from both synthetic and mechanistic viewpoints. Therefore, extensive studies have been carried out on the development of the (RE)2/(R E )2 binary system without using RE-E R compounds, which are difficult to prepare. (Z)-l-Seleno-2-thio-1-alkenes are produced regio- and stereoselectively when a mixture of diaryl disulfides and diaryl diselenides is subjected to a rhodium-catalyzed reaction with alkynes (Equation (68)).193... 

In the tristanna[3]ferroceneophane, the cyclopentadienyl rings are parallel but twisted, and reaction with a chalcogen gives a l,3-distanna-2-chalcogena[3]ferroceneophane.319 321... 

The chalcogenides are synthesized either by reaction of the chalcogen vapour with the actinide metal or the hydride (Faraday-method), or in reaction with compounds ... 

Although very little is known for the reactions of isolated germylenes 146, 147, and 148, diarylgermylene (150) was found to undergo a variety of reactions with olefins, dienes, acetylenes, alcohols, isothiocyanates, elemental chalcogens, and hydrosilanes as in the cases of less hindered, transient germylenes previously reported. 

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