Bis selenides

Diselenium dication 145a was formed by the reaction of the corresponding bis-selenide 144 with a 1 2 mixture of sulfuryl chloride and antimony pentachloride (see Equation 41) <1997JS01006>. 

Synthetic approaches to selenium, tellurium and mixed dications are similar to the methods used for disulfonium dications. Oxidation of bis-selenides to diselenonium dications 104 with two equivalents of nitrosonium salts -NOBF4, NOPfV,113 occurs more readily than the oxidation of sulfides and affords the corresponding dications in better yields (Scheme 41).96,114... 

Because the redox potential of selenides is sufficiently low, oxidative generation of Se-Se and S-Se dications on treatment with sulfuric acid is more general than in the case of disulfonium dications. For example, formation of dications 106 and 108 occurs readily when the corresponding bis-selenide 105 and... 

Just as disulfonium dication 34, diselenonium 113 and ditelluronium dication 114 do not undergo deprotonation. Instead, reaction of dication 113 with fluorenyllithium affords bis-selenide and fluorene dimer 103.96 Softer Lewis base such as ra-tolyl magnesium bromide reacts with diselenonium-dication 113 to give 127, a product of nucleophilic substitution at the onium atom (Scheme 48).129... 

Selenium and Carbon —Carbon Bi.selenide, Carbon Hiibselemdos, Carbon Oxysclenido, Carbon Sulphidoselenide. 

The tin(IV) chloride mediated addition of dimethyl diselenide to disubstituted alkenes proceeds rapidly at room temperature and affords in good yield the corresponding 1,2-bis(selenides) as single stereoisomers107. 

Transannular interactions between the two selenium atoms of cyclic bis-selenides were only demonstrated in 1989 as a result of the formation of the diselenide dication (51) from 1,5-diselenacyclooctane (52) <89CC1789>. This is the first example of an isolable dication salt containing a selenium-selenium cr-bond. Similarly, dications (53) and (55) are prepared from precursors (54) and (56). 

Diselenide dication (51) is formed via a two-electron oxidation of 1,5-diselenacyclooctane (52) with two equivalents of a one-electron oxidizing agent, nitrosyl hexafluorophosphate or nitrosyl tetrafluoroborate as shown in Equation (16). Six- and ten-membered ring bis-selenides (56) and (54) are oxidized similarly to the dications (55) and (53) respectively <93T1605>. The ease with which l,4-diselenoniabicyclo[2.2.0] salt (55) is obtained from 1,4-diselenacyclohexane (56) is somewhat surprising since the transannular interaction between the two selenium atoms at 1,4-positions is not expected to be extensive. 

Unlike the S-dication, the Se-dication (51) does not undergo hydrolysis with water and still retains its oxidant capability. The reaction of the Se-dication (51) with its precursor, the cyclic bis-selenide (52), follows the expected one-electron-transfer mechanism, shown in Equation (17), to generate the cation radical which can be detected by its UV absorption characteristics and, more importantly,... 

This is in contrast with the reactions of analogous cyclic bis-sulfides and bis-selenides where no corresponding dications are obtained upon treatment with ddq <91TL4537>. 

Treatment of the cyclic bis-selenide, 1,6-diselenacyclodecane 59, with nitrosonium tetrafluoroborate affords the ring-fused diselenide dication 27 (Equation 12) <1993T1605>. The dication ditetrafluoroborate salt was characterized spectroscopically using H, and Se NMR and gave a correct elemental analysis for the structure described (cf. Section 9.15.3). 

Corannulene cyclophane 105 was prepared by treating 36 with a mixture of 1,4-bis (mereaptomethyl)benzene and potassium tert-butoxide (Scheme 31) [32]. Similarly, l,5-pentadithiol/l,6-bis(bromomethyl)corannulene cyclophane (106) was prepared from 37 and 1,5-pentadithiol in 75% yield [129]. Synthesis of [3,3]seleno/l,6-dimethylcorannulene cyclophane (107), a cyclophane from two corannulenes, was not straightforward [129]. The key step is the in situ transformation of 37 to the bis(selenide anion), which reacts with the additional 37 to afford the seleno-bridged dimer 107. 

Gansow et al. came to the same conclusion when they recorded longitudinal Se relaxation times at different temperatures (78Gan). They reported values from 5.6 s at 278 K to 3.2 s at 313 K for Mc2Se, and 1.2 s at 278 K to 2.6 s at 328 K for Ph-Se-H. In the first case the decrease of Ti with temperature is due to SR whereas the reverse behaviour of selenophenol indicates a dominating CSA contribution. The Se longitudinal relaxation times of a series of bis-selenides MeSe-(CH2)n-SeMe (n = 0 to 2) revealed the expected decrease with temperature as well, whereas they are uniform if n = 3 (83 Abe) at low tempera-... 

In 2003, Ananikov and Beletskaya and their co workers proposed hydroselenation of terminal alkynes catalyzed by Pd(PPh3)4 and Pt(PPh3)4 [46]. In the case of Pd(PPh3)4, Markovnikov-type adducts 32 were obtained together with bis(selenide)s 33 (20). 

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