Selenium derivs

Comparison of the ultraviolet spectra of analogous sulfur and selenium compounds shows that there is very little difference in the absorption curves, except for a slight bathochromic shift in the case of the selenium derivatives-... 

A large number of selenium derivatives such as the selenium analog of vitamin B] have been tested for physiological activity (91). 

Despite the inconveniences, a certain number of studies have been carried out, particularly concerning dyes containing azomethine groups. Such as hydrazones, pyrazolones, formazans, and selenazoles quinoids. Saturated heterocycles, that is, selenazolines and selenazolidines. have also been tackled. Selenium derivatives for pharmacological or physiological applications are little developed by comparison with their thiazole homologs. 

This section will focus primarily on a comparison of these ring systems with their heavier chalcogen analogues. The first selenium derivative benzo-l,2,5-selenadiazole was prepared more than 115 years ago by the condensation reaction of selenium dioxide with 1,2-diaminobenzene (Eq. 11.12) and other benzo derivatives may be prepared in a similar manner. The parent 1,2,5-selenadiazole has also been reported. This reagent has been employed to make the tellurium analogue via treatment with ethylmagnesium bromide followed by the addition of tellurium tetrachloride (Eq. 11.13). ... 

Examples of the C2N3S ring system containing three- or four-coordinate sulfur are also well known. The monohalogenated derivatives 12.2 (E = S, Se), are best prepared by the condensation of imidoyl amidines with SCI2 or SeCU, respectively (Scheme 12.1)." In the case of the selenium derivative, the initial product is heated at 60°C and then at 120°C in order to convert it to 12.2 (E = Se) via (PhC)2(NH)N2SeCl2. In the solid state this intermediate is a weakly associated, centrosymmetric dimer with Se-Cl and Se Cl distances of 2.42 and 3.39 A, respectively. ... 

Diazenes of the type REN=C(R )N=NC(R )=NER have a rich structural chemistry. The selenium derivatives 15.11a,b display a cis,trans,cis conformation with two short l,5-Se N contacts (2.65 A). Several sulfur analogues, e.g., 15.1c, have the same structure, but a different cis,trans,cis conformer 15.12 with two 1,4-S N contacts (2.83 A) has also been characterized. A third type of diazene is the trans,trans,trans isomer 15.13a,b with no intramolecular short contacts. ... 

Only one dangerous reaction was mentioned for selenium derivatives. When it is... 

Thiotraamidophosphoric acids (35) are isoelectronic with phosphoric acids and were initially reported from the reaction of phosphorus pentasulfide with primary amines at high temperatures.62 Subsequently, an improved synthesis for 35 with increased yields and milder conditions has been reported involving the room temperature reaction of thiophosphoryl chloride and primary amines (Equation 50).63 The most convenient route to the analogous selenium derivatives SeP(NHPh)3 is from the oxidation of P(NHPh)3 with elemental selenium (Equation 51).63 Also isoelectronic with phosphoric acids are dithio wamido-phosphoric acids (36), which can be prepared from the reaction of phosphorus pentasulfide with an excess of primary amine at 30°C in toluene (Equation 52).62 The selenium derivatives of 36 can be prepared in a similar reaction from phosphorus (V) selenide, although due to their increased acidity... 

Common synthesis of disulfonium dications involves formation of a S-S bond by oxidative coupling of two sulfide moieties. Involving for oxidative generation of S-S bond, thiocarbonyl compounds can lead to new-type dications containing disulfide moieties between two positively charged fragments. There are several disulfide dications of this type derived from thioureas, thiocarbon-ates and thioketones as well as selenium derivatives.137 148... 

In the course of the quest for new Fe(III) spin crossover compounds, systems related to N,N-disubstituted-dithiocarbamates have been explored. This section deals with oxygen and selenium derivatives of this parent ligand system, as displayed in Fig. 2. 

Tin and selenium derivatives (runs 11 and 12) undergo lithium-tellurium exchange preferentially to lithium-tin and lithium-selenium exchange. - ... 

For example, recently some selenium derivatives of TTF (i.e., TMTSF) were found to become superconductors around 1... 

The brown material, insoluble in water, examined more carefully [said he], was recognized to be the cause of the peculiar odor we mentioned above and by means of some experiments which we shall report soon, it was found that it was a combustible, elementary substance hitherto unknown, to which I have given the name selenium, derived from Selene (the moon), to recall its analogy with tellurium. According to its chemical properties, this substance belongs between sulfur and tellurium, although it has more properties in common with sulfur than with tellurium (9,17). 

The organoselenium compounds, their chemistry, and methods of preparation are discussed in the literature (3,4,7,11,12,14,59). Selenium-containing polymers are of interest because of their semiconducting and plastic properties. The biologically important compounds include selenoaminocarboxylic acids and derivatives, selenium-containing peptides, and selenium derivatives of pyrimidines, purines, cholines, steroids, coenzyme A, and other compounds (4,14). The biochemical and medical aspects and uses of oiganoselenium compounds have also been discussed (13,14,60—62). 

The tetranuclear sulfur and selenium derivatives [E(AuPPh3)4]2+ show a square pyramidal geometry with the chalcogen atom in the apical position [241]. These cations dimerize in the solid state through Au-E interactions (Figure 1.40). Further auration of sulfur and selenium to give the penta- and hexa-nudear species has been achieved and trigonal bipyramidal and octahedral structures have been proposed [242]. 

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