Selenium selenolates

Hydrazine155,156 or samarium diiodide157-162 are other useful reagents for the synthesis of selenolates, but electrochemical methods163,164 have also been employed for their selective synthesis from diselenides. Starting from elemental selenium, selenolates 80 can easily be prepared by insertion reactions of selenium into organolithium... 

Although the oxoacids of selenium and sulfur have comparable acid strengths (pITai 2.6 vs. p fa 1-9, respectively, for the quadrivalent species pA a 3 for both the hexavalent species), the hydride H2Se is much more acidic than H2S (pATai 3.9 vs. 7.0). Thus, while thiols such as cysteine are mainly protonated at physiological pH, selenols such as selenocysteine are predominantly dissociated under the same conditions. 

Metal-Sulfur, -Selenium, and -Tellurium Bond Lengths, M—E—C Angles, and Torsion Angles for Three-Coordinate Aluminum, Gallium, and Indium Thiolates, Selenolates and Tellurolates", and Related Compounds... 

Nickel-selenium coordination compounds have received attention in recent years, because a unique Ni-selenocysteine interaction was revealed in the active site of [FeNiSe]-hydrogenases.1083,1084 Of particular interest in this regard are mixed CO/selenolate complexes. Distorted square planar (393) was prepared from [CpNi(CO)]2, PhSeSePh, and [Fe(CO)3(SePh)3] and provides the first example of CO bound to a square planar Ni11 center in thiolate/selenolate environment.1085,1086 Upon addition of RSSR, species of the series [Ni(CO)(SR) (SePh)3 ] are formed. //(CO) ranges from 2,023 cm-1 to 2,043 cm-1 and is regarded as a spectroscopic reference for the CO binding site in [NiFeSe] hydrogenases. 

The lO-E-4 chalcogen(IV) species diphenylselenium(IV) dibromide (1, Fig. 1) and diphenyltellurium(IV) dibromide (2, Fig. 1) oxidize thiophenol to diphenyl disulfide in nearly quantitative yield as shown in equations (13) and (14). Tellurium(IV) dihalides 6-11 also oxidize thiophenol to diphenyl disulfide and benzene selenol to diphenyl diselenide. Similarly, the 12-Te-5 molecule dioxatellurapentalene 45 (Fig. 19) is a mild oxidant for ethylmercaptan, thiophenol, and benzene selenol giving diethyl disulfide, diphenyl disulfide, and diphenyl diselenide in essentially quantitative yield. As shown in equation (15), 1,1,5,5,9,9-hexachloro-1,5,9-tritelluracyclododecane oxidizes six molecules of thiophenol to diphenyl disulfide and 1,5,9-tritelluracyclododecane in 90% yield. In contrast, 12-Te-5 pertellurane 44 and 12-Se-5 perselenane 46 do not oxidize thiophenol to diphenyl disulfide. Instead, these molecules undergo a nucleophilic addition of thiophenol followed by cleavage of the tellurium-carbon or selenium-carbon bond. ... 

Although in humans only MsrBl is a selenoprotein, the depletion of selenium from the diet of mice led to increases in both R and S stereoisomers. This was not initially explained, yet a subsequent study has shown that small molecule selenols (organic selenocysteine homologues) could act as efficient electron donors in vitro for MsrA enzymes. ° This effect has only been shown in vitro, but the possibility that small molecular selenium reductants, or more likely that some selenoproteins that contain reduced selenols (in redox-active motifs) is quite intriguing. Several small selenoproteins do not have real roles and reside in nearly all subcompartments of the cell (mitochondria, ER) where electron donors for Msr enzymes are probably critical to maintain protein stability. Low selenium nutritional status would then have a significant impact on all methionine oxidation, as Future studies to address selenium nutrition and methionine oxidation could prove to be... 

The most common reaction of selenolates is the nucleophilic substitution of halide compounds. For the synthesis of selenides 82 the selenolates 80 can be reacted with halides. Nucleophilic selenium species can also be reacted with a variety of other electrophilic compounds. The reaction with acid chlorides, chloroformates, or carbamoyl chlorides leads to the corresponding selenoesters 83 (R" = R ), selenocarbonates 83 (R" = OR ), or selenoamides 83 (R" = NR 2), respectively (Scheme 17).166... 

Selenolate 77, prepared from diselenides with sodium borohydride, is also not reactive enough for reactions with esters or lactones. Only under higher reaction temperatures, lactones 90 can be ring opened with selenolates to the corresponding carboxylic acids 91.173,174 The selenium moiety can then be used for further manipulations. Using similar reaction conditions, esters 92 can be converted to the corresponding carboxylic acids 93 and selenides 94 (Scheme 21).149... 

Also widely employed are organoselenium compounds containing group 14 elements. Phenyl trimethylsilyl selenide 102 can be easily prepared from diphenyl diselenide 8 and is a good source for selenium nucleophiles (Scheme 24). In the presence of methanol selenols are generated for use in Michael reactions or in ring-... 

The strontium selenolate Sr(Se(2,4,6-t-Bu3C6H2))2(THF)4 has been synthesized by reaction of Srl2 with KSe(2,4,6-t-Bu3C6H2) in THF. The compound is low melting (120-125°C) and soluble in THF.227 Tellurium- and selenium-containing salts, Ca(DMF)6(Te4)228 and Ba(en)4(SbSe2)2 229 with mono- and bidentate bases such as dimethylformamide and ethylenedi-... 

Carbonsulfur bonds can be formed by the reaction of elemental sulfur with a lithio derivative, as illustrated by the preparation of thiophene-2-thiol 446. If dialkyl or diaryl disulfides are used as reagents to introduce sulfur, then alkyl or aryl sulfides are formed sulfinic acids are available by reaction of lithium derivatives with sulfur dioxide. In the pyrrole series, a 2-thiol and the corresponding selenol can be prepared via reaction of 2-lithio-l-methylpyrrole with sulfur or selenium, then trapping with Me3SiCl leading to the 2-Me3SiX-substituted derivatives <1997T13079>. 

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