Diselenane

As shown in Fig. 5, the initial fast reaction is the association of bromine with the chalcogen atom to form the -complex of bromine with diphenylselenide, dicyanomethylidene telluropyran 20, and telluropyranone 22. These structures are analogous to the 1,4-diselenane iodine complex 15 (Fig. 3), whose structure has been characterized by X-ray crystallography. The second-order rate constants are on the... 

Coordination compounds of selenium-containing heterocycles with an Se — M bond are represented by the complexes of 1,4-diselenane 346 348 [634] and seleno-phene 349 [8,643]. Among these complexes, while the Se — M coordination 350 was proposed [634] for the complexes on the basis of 1,2,3-benzoselenodiazole, only N—M binding 351 was found in these compounds [13,644] ... 

Das cyklische 1,4-Diselenandioxid ist aus dem 1,4-Diselenan mit Per-oxoessigsaure dargestellt worden (80) ... 

Interessante Eigenschaften besitzt das einzige bekannte cyclische An-hydrid, das 1,2-Athandiseleninsaureanhydrid. Es wurde zuerst auf muh-same Weise durch Oxydation von 1,4-Diselenan mit Peroxoessigsaure neben 1,4-Diselenandioxid in mg-Mengen erhalten (80) ... 

Valence group (2,6). Simple examples of this valence group include ions such as Se(CH3)3 and Te(CH3)3 (see later) and SeF. In crystalline Se(CH3)3l there are pyramidal cations but each is associated rather closely with only one I . Although Se- T is only a weak bond (3 78 A) this is less than the estimated van der Waals separation (4T5 A) and in fact shorter than S-T (3-89 A) in the sulphur analogue. Moreover this weak Se -T bond is almost collinear with one of the Se-C bonds, and the ion pair has been described as a charge-transfer complex. Similarly, the Se-I distance in the complex of I2 with 1,4-diselenane is slightly less than the S"T distance in the S analogue. At the same time there is an increase in I—I from the value 2-66 A in the free I2 molecule to 2-79 A in the S compound and to 2-87 A in... 

The mass spectra of 1,4-oxaselenane, 1,4-oxatellurane, and 1,4-diselenane are dominated by the molecular ion peaks, but in the case of 1,4-oxaselenane dichloride (1) (and of the dichloride of 1,4-oxatellurane) major fragmentations involve the stepwise loss of two chlorine atoms, or loss of Cl-followed by loss of ethene (Scheme 6) <80JHC929>. 

Diselenane, like 1,4-oxatellurane and the other compounds of the group, is alkylated by treatment with methyl iodide to give a methiodide (9) (Scheme 8) <45JCSi i, 56JA5825,65IC862, 87SR359>. 

Diselenane (31) was first obtained in very low yield by the reaction of lithium selenide and bis(2-chlorodiethyl)selenide (30) in acetone (Equation (5)) <51JA1105>. A better approach is to heat a mixture of aluminum selenide and 1,2-dibromoethane at 80-140°C over some hours. Even using this method, the yield is only 10% <56JA5825>. 

Fluoro- and 2,5-difluoroselenophenes were prepared by reaction of the corresponding selenophene lithium derivatives with FC103 in 73% and 11% yield, respectively. " The first polyfluorinated derivatives of selenophene-octafluorosele-nonane 168 and octafluoro-1,4-diselenane- were isolated in low yields in the reaction of selenium, tetrafluoroethylene, and iodine. " Selenonane 169 was prepared in low... 

Diselenane has been oxidized with Z equiv of nitrosonium tetrafluoroborate to afford the stable diselenide dication,... 

Dithians, 1,4-Diselenans, 1,4-Dithiepans, and 1,5-Dithiocans.—Formation. The ratio of 2-methyl-1,4-dithian (172) to 1,4-dithiepan (173) obtained on photocatalysed cyclization of the unsaturated thiol (174) was sensitive to... 

The stereochemical requirements of adjacent lone electron pairs and polar bonds have been discussed in an important paper which analysed the considerable volume of available data, including those pertaining to 1,4-dithians and similar systems. The Edwards-Lemieux effect in substituted 1,4-dithians was accounted for satisfactorily by calculations using fluoromethanol as a model compound. The temperature-dependence of the F n.m.r. spectrum of perfluoro-1,4-dithian indicated a barrier to ring-inversion of 10.05 0.10 kcalmol. The fluorine chemical-shift differences at — 90 °C appeared to be consistent with a preferred chair conformation, possibly strongly puckered as in 1,4-dithian. The i.r. and Raman spectra of 1,4-dithian and 1,4-diselenan have received detailed attention, and the crystal and molecular structures of... 

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