Polyalkynes capped by sulfur and selenium

The synthesis of sulfur- and selenium-capped polyalkynes with two to four triple bonds was achieved. As starting materials the bis(trimethylsilyl)-protected polyalkynes were used, which were treated with MeLi/LiBr. The reaction of the resulting lithium salts with thiocyanatomethane and selenium/methyl iodide afforded 2(n) and 3(n), respectively. Spectroscopic (PE and UV) and quantum chemical investigations show significant interaction between the chalcogen atoms. The structure of 3(4) was investigated in the solid state, showing relatively short intermolecular Se...Se interactions.     

Access to new Janus head ligands: linking sulfur diimides and phosphanes for hemilabile tripodal scorpionates

Reactions of lithium dialkyl/phenyl phosphanylmethylides, RR'PCH(X)Li (R, R' = Me, Et, Ph and R = Me, R' = Ph; X = H or Me), with sulfur diimides S(NR')2 (R' = (t)Bu or SiMe3) in an equimolar ratio yielded Janus head complexes with the structural motif [Li{RR'PCH(X)S(NR')2}]2 (R' = (t)Bu, SiMe3). The basic core of these dimeric complexes is composed of a (LiN)(2) four-membered ring containing two four-coordinated lithium atoms. A lithium complex of the new Janus head ligand with another structural motif [TMEDA·Li{Ph(2)PCH(2)S(NSiMe3)2}] (6) could be isolated from the reaction of [Ph2PCH2Li·TMEDA] with S(NSiMe3)2. Two monomeric complexes [Mg{Me2PCH2S(NR')2}2] (7, 8) were synthesised by a straightforward reaction of [Li{Me2PCH2S(NR')2}2] with MgCl2 in pentane. The magnesium atom is chelated by one phosphorus atom and two nitrogen atoms of each unit of the hemilabile ligand in a tripodal manner, leading to octahedral geometry around the magnesium cation. A complete analysis of [Ph2PCH2(SNSiMe3)(HNSiMe3)] (9) is also described in which one nitrogen atom of the imido moiety is protonated.     

Condensed thiophenes and selenophenes: thionyl chloride and selenium oxychloride as sulfur and selenium transfer reagents

3,4-Cyanomethyl substituted thiophenes reacted with thionyl chloride in the presence of base to give dicyano substituted thieno(3,4-c)thiophenes. The use of selenium oxychloride furnished the corresponding cyano substituted seleno(3,4-c)thiophene. 1,2-Phenylenediacetonitriles gave the corresponding cyano substituted benzo(c)thiophenes and benzo(c)selenenophenes, respectively, upon reaction with thionyl chloride and selenium oxychloride in the presence of base.     

Thermal stability of selenium, sulfur and nitrogen analogous phthalazine derivatives

Differential scanning calorimetry (DSC) and thermogravimetry (TG) are analytical and quantitative methods capable of providing reliable, fast and reproducible results. These data allow establishing the thermal stability, purity degree and the polymorphic behavior of organic compounds. Thermal analysis of fusion and degradation processes was carried out on organonitrogen, organosulfur and organoselenium phthalazine derivatives to establish thermal stability criteria. Decomposition and fusion temperatures of 27 biological active compounds, synthesized by our research group were determined using TG and DSC. Analysis of the thermal data indicated that: (a) in general, nitrogen compounds are more stable than sulfur and selenium compounds; (b) thioderivatives possess degradation temperatures higher than selenium compounds; (c) the presence of selenium atoms in molecular structure has associated a minor thermal stability; (d) sulfide derivatives decomposition process have higher T_onset values than disulfide compounds; (e) there are differences in the stability due to groups selenol, methylseleno, and cyanoseleno; (f) the nature of the substituent located on the benzyl ring has no effects on selenophthalazines thermal stability.     

The insertion of sulfur and selenium into the 1,2-dihydrophosphete ring

Sulfur and selenium react with a 1,2-dihydrophosphete P-W(CO)₅ complex at ca. 120°C to give the corresponding 2,5-dihydro-1,2-thiaphosphole and 2,5-dihydro-1,2-selenaphosphole complexes, respectively. These products result from an insertion of S or Se into the P C sp³ bond of the four-membered ring.     

Evaluation of sulfur, selenium and tellurium catalysts with antioxidant potential

Oxidative stress is implicated, either directly or indirectly, in the pathology of a range of human diseases. As a consequence, the development of efficient antioxidants for medical use has become increasingly important. We have synthesised a range of structurally related organo-sulfur, -selenium and -tellurium agents and demonstrated that a combination of electrochemical methodology, in vitro assays and cell culture tests can be used to rationalise the antioxidant activity of these catalytic agents. Based on its exceptionally low anodic oxidation potential (Epa) and high activity against the representative oxidative stressors tert-butyl hydroperoxide and peroxynitrite, 4,4'-dihydroxydiphenyltelluride is predicted to be a potent antioxidant. This compound exhibits a correspondingly high activity with a remarkably low IC50 value of 20 nM, when tested in PC12 cell culture using a bioassay indicative of the early stages of Alzheimer's disease.     

Vertical and nonvertical participation by sulfur,selenium, and tellurium

The mechanism of stabilization of positive charge on carbon by sulfur, selenium, or tellurium at the beta-position has been investigated kinetically, by measurement of rate enhancements, and structurally, by variation of the bond strength to the leaving group. Stabilization can occur either nonvertically with formation of a bridged intermediate or vertically through hyperconjugation within an open carbocation. We observed large rate enhancements (10(5) for S, 10(6) for Se) in 97% aqueous trifluoroethanol with trifluoroacetate as the leaving group. These enhancements are consistent with either mechanism. Product structures also are consistent with either mechanism. Nine crystal structures revealed that the bond to the leaving group (C-O) is lengthened by the presence of S or Se at the beta-position, in proportion to the basicity of the leaving group. This lengthening is not accompanied by angle distortions expected for the bridging mechanism. The crystallographic data support vertical (hyperconjugative) character along the reaction coordinate, more so for selenium than sulfur.     

Chemistry of naphthalene diimides

This tutorial review surveys recent developments in the chemistry of naphthalene diimides (NDIs) and explores their application in the fields of material and supramolecular science. It begins with a discussion of their general uses, methods of syntheses and their electronic and spectroscopic properties. Of interest to their application in the fields of conducting thin films and molecular sensors is the structure-function relationships that exist either as co-components of supramolecular ensembles as in the case of "nanotubes", or as the sole components in molecular wires. Also discussed are advances in NDI research within the areas of energy and electron transfer (covalent and non-covalent systems) and in host-guest chemistry including foldamer, mechanically-interlocked and ligand-gated ion channel examples. Finally, we explore the developments in the recent field of core-substituted NDIs, their photophysical properties and applications in artificial photosynthesis. We conclude with our views on the prospects of NDIs for future research endeavours.     

The substitution of polychlorotrifluoroethylene with sulfur,selenium, and phosphorus nucleophiles

The substitution of polychlorotrifluoroethylene (PCTFE) with sulfur, selenium, and phosphorus nucleophiles is reported. The primary reaction, which extends throughout the bulk of the polymer, is the incorporation of the nucleophile with concommitant loss of chloride. The substituted PCTFE's are studied by ¹H-, ¹³C-, ¹⁹F-, and ³¹P-NMR, as well as IR, and elemental analysis.     

Dzhemilev reaction in the synthesis of five-membered sulfur and selenium heterocycles*

A one-pot methods were developed for the synthesis of five-membered sulfur and selenium heterocycles based on the consecutive cyclometallation of olefins, allenes, and acetylenes using alkyl and haloalkyl derivatives of Al and Mg in the presence of catalytic amounts of titanium and zirconium complexes to give the corresponding alumina- and magnesacarbocycles in situ, which, without further purification, were introduced into reaction with sulfur or selenium, leading to various tetrahydrothiophenes, thiophenes, tetrahydroselenophenes, and selenophenes. * Dedicated to Academician B. A. Trofimov of the Russian Academy of Sciences on the occasion of his seventieth jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 393–403, March, 2009.     

Novel reactions of 1,1,4,4-tetraaryl-1,2,3-butatrienes with elemental sulfur and selenium

Sulfurization and selenation reactions of 1,1,4,4-tetraaryl-1,2,3-butatrienes were examined to give novel 1,2,3,4,5-pentathiepane and 1,2,5-triselenepane ring systems. Further degradation of these new heterocycles using DBU/DMF was also described.     

Thin-layer chromatography of some organic selenium compounds and their oxygen and sulfur analogs

The Chromatographic behavior of some series of organic selenium compounds and their oxygen and sulfur analogs (urea, thiourea, selenourea; xanthene, thioxanthene, selenoxanthene; xanthone, thioxanthone, selenoxanthone) has been examined by thin-layer chromatography (TLC) on silica gel. The experimental results show the possibility of attaining fast separations on very small amounts of substance (at the microgram level) by simple monodimensional TLC techniques. Urea and its S and Se analogs as well as xanthones are well separated by two- or three-component eluting solvents; xanthenes are not easily screened even by solvent mixtures. The separation of xanthenes from xanthones by the two-dimensional TLC technique is also described. A further result is the possibility of detecting species in trace amounts in the matrix being examined.     

The effect of sulfur and selenium substitutents on the regiochemistry of diels-alder reactions

2-Phenylthio-1,3-butadiene (1) and 2-phenylseleno-1,3-butadiene (2) have been generated in situ from their SO₂ adducts and reacted with a series of unsymmetrical dienophiles. The regiochemical results have been analyzed in terms of qualitative perturbation theory.     

Fluorine-induced chemiluminescence detection of biologically methylated tellurium,selenium, and sulfur compounds

Summary The sensitive detection of volatile, methylated selenium and tellurium compounds based on capillary gas chromatography coupled to fluorine-induced chemiluminescence detection is described. The method requires no sample derivatization, and the detection limits for selenides and tellurides (low pg range) are the lowest reported to date. This technique can resolve and speciate complex mixtures of methylated tellurium, selenium, and sulfur gases and is useful for analysis of selenium and tellurium gases in environmental samples that also contain usually interfering reduced sulfur gases. Applications of the technique for analysis of bacterial and fungal headspace samples are presented.