A-chalcogenation

Dibismuthines are very sensitive to oxidation. Thus tetramethyldibismuthine fumes ia air, and tetraphenyldibismuthine ia toluene solution rapidly absorbs oxygen. Under controlled conditions, dibismuthines react with chalcogens resulting ia cleavage of the bismuth—bismuth bond and iasertion of a chalcogen atom (105,138,140—142) ... 

The involvement of a chalcogen atom in an intramolecular interaction may influence the reactivity of the chalcogen centre as a result of steric or electronic effects. This feature may lead to unique reaction patterns. Eor example, the sulfur(II) centre involved in an intramolecular contact... 

The chalcogenides are binary compounds of a chalcogen (i.e., the elements of Group Ilb zinc, cadmium, mercury) with a less electropositive element, such as those of Group VIb (oxygen, sulfur, selenium, and tellurium). This section covers the sulfides, selenides, andtellurides. Oxides are reviewed above in Ch. 11. Most of the chalcogenides have useful optical characteristics and their applications are usually found in optics. 

The electrochemical preparation of metal chalcogenide compounds has been demonstrated by numerous research groups and reviewed in a number of publications [ 1-3]. For the most part, the methods that have been used comprise (a) cathodic co-reduction of the metal ion and a chalcogen oxoanion in aqueous solution onto an inert substrate (b) cathodic deposition from a solvent containing metal ions and the chalcogen in elemental form (the chalcogens are not soluble in water under normal conditions, so these reactions are carried out in non-aqueous solvents) (c) anodic oxidation of the parent metal in a chalconide-containing aqueous electrolyte. 

The induced co-deposition concept has been successfully exemplified in the formation of metal selenides and tellurides (sulfur has a different behavior) by a chalcogen ion diffusion-limited process, carried out typically in acidic aqueous solutions of oxochalcogenide species containing quadrivalent selenium or tellurium and metal salts with the metal normally in its highest valence state. This is rather the earliest and most studied method for electrodeposition of compound semiconductors [1]. For MX deposition, a simple (4H-2)e reduction process may be considered to describe the overall reaction at the cathode, as for example in... 

TABLE 2.2. Impact of a-Chalcogen Substitution on Fluorine Chemical Shifts ... 

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 nitrido and phosphido complexes of TMs have been the subjects of intensive experimental studies in the recent years. Of particular interest has been the issue of Lewis basicity of the nitrogen and phosphorus atoms in the TM=N and TM=P groups. Table 7.17 lists the BDEs calculated at the MP2/II, B3LYP/B and CCSD(T)/B levels of theory for LnMN-X and LnMP-X, where X is a group-13 Lewis acid or a chalcogen atom [86, 87]. 

The presence of a fragment corresponding to the loss of selenium in mass spectroscopy under electronic impact of germaneselone 179 points to a thermal instability of the Ge = Se bond.132 Heating a solution of 179 in benzene at 80°C in the presence of sulfur leads to a chalcogen exchange, likely via the divalent species (ArO)2Ge 141 [Eq. (38)]. 

Scheme 4.2 Possible mechanistic paths for the displacement of a chalcogen group (R X, where X = S or Se) by (TMS)3Si radicals...

In ABj compounds where B is a halogen other than fluorine or a chalcogen (S, Se, Te), the A—B bond is considerably covalent and a different set of structures is encountered. Some of the important structures are shown in Fig. 1.8. 

Several approaches have been used for the synthesis of heteroatomic chalcogen cations, including (a) direct oxidation of a mixture of two chalcogens with oleum, MF5 (M = As, Sb) or transition metal halides, (b) reaction of a chalcogen with a homoatomic cation of another chalcogen and (c) compro-portionation of the homoatomic cations of two different chalcogens. 

In this section I will comment on some examples of gold complexes that display supramolecular entities in the solid state, although in these cases the metal atom is not directly involved in the van der Waals interactions. As in the previous section, the electron density donor can be a non-metal different from hydrogen, which can be a halogen or a chalcogen a hydrogen atom of a covalent NM — H bond or a doud of n electron density. 

The first examples of a chalcogen insertion into a transition metal-carbene bond were reported in 1981. Stirring solutions of the pentacarbonyl-(diarylcarbene)tungsten complexes 39 in pentane in the presence of solid sulfur afforded the thioketone complexes 40 [Eq. (8)].171 The reaction rate increased considerably when pentane was replaced by CS2 as the solvent due to the higher solubility of elemental sulfur in CS2. 

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