1,2,3-Dithiazolyls

A direct comparison of the signals of the thiadiazolopyrazine-fused 1,3,2-dithiazolyl and 1,2,3-dithiazolyl isomers 34 and 35 <1999JA969> showed that radical 35 had a considerably more complex signal with hyperfine coupling to all five nitrogen nuclei. 

Closely related to the 1,3,2-dithiazolyl radicals are the isomeric 1,2,3-dithiazolyl radicals. The benzo-fused derivatives were originally prepared by Herz in 192276 from the reaction of aniline and its derivatives with an excess of S2C12 (Scheme 10). Almost invariably the aromatic ring becomes substituted by chlorine para to the amine N atom. 

Reduction of 38 leads to the formation of the corresponding 1,2,3-dithiazolyl radical. The simple benzo-derivatives have long lifetimes and have been studied extensively by EPR spectroscopy, although attempts to isolate radicals to date appear to have been broadly unsuccessful. The only 1,2,3-dithiazolyl which has been structurally characterised is the non-fused 4-chloro-5-pentafluorophenyl-... 

Known 1,2,3-dithiazoles are represented by the structures in row (a) of Figure 1. Strictly, these are 1,2,3-dithiazolines, the first one being 1,2,3-dithiazoline-5-one. 1,2,5-Oxathiazoles are represented by l,2,5-oxathiazolidine-4-ones (b) and 3-methylene 1,2,5-oxathiazolines (c). 1,2,3-Oxathiazoles have been obtained only in the form of their S-oxides (d), which should rather be termed -azolidines and -azolidinones. Experimentally prepared S-oxides of 1,2,3-dithiazoles and 1,2,5-oxathiazoles are depicted in row (e) and should be termed dithiazolines and oxathiazolines. 1,2,3-Dithiazolyl radicals (f) are known, as well as 1,2,3-dithiazolium cations (g) which are the only formally aromatic examples of the ring system and which may be represented by a number of resonance structures (h). 

Dithiazoles investigated are given in Figure 1(a) these are 1,2,3-dithiazolium cations 1, 1,2,3-dithiazolyl radicals 2, l,2,3-dithiazole-3-ones 3 and related compounds 4, their 2-oxides 5. 1,2,3-Oxathiazoles have been obtained and investigated in the form of their A-oxides (Figure 1(b) and named as cyclic sulfamidates 7 and 8 and sulfimidates 6, 9, and 10. 

Dispersion of the valence and conduction bands in the bis( 1,2,3-dithiazolyl) radical 14 has been determined by extended Htickel band structure calculations which suggest that the band gap (ca. 0.4 eV) has a value which is considerably smaller than that found in other radical dimer structures and arises from the weakness of the intradimer interaction <1999JA969>. 

The crystals of radical 29, which are diamagnetic by electron spin resonance (ESR), consist of cofacial dimers with four dimers per unit cell linked by two long, albeit unequal (3.053 and 3.309 A), interannular S-S bond <2005IC1837>. This mode of association has not hitherto been observed for 1,2,3-dithiazolyls. Dimers of radical 29 do not form 7i-stacked arrays instead, they adopt the closed packed herringbone arrangement which allows for a clustering of the radical heads so as to maximize S- -S and S- -N contacts. 

The ay, constants and g-values of known 1,2,3-dithiazolyl radicals are listed in Table 1. 

Table 1 ESR g-values, hyperfine coupling constants (aN) of 1,2,3-dithiazolyl radicals and cation radicals, and half-wave potentials of 1,2,3-dithiazolyls...

Various sulfur-nitrogen heterocycles can serve as a source of 1,2,3-dithiazolyl radicals. The thermolysis of benzo-trithiadiazepin 158 and dibenzotetrathiadiazecine 159 in hydrocarbons afforded the 1,2,3-benzodithiazolyl radical 15 (Scheme 30) <2003MG178>. 

Primary enaminones 178 (R1 = Me or PhCH2 R2 = Me, Ph or MeO) are converted into stabilized 1,2,3-dithiazolyl radicals 179 by the joint action of chlorine and sulphur (equation 76)97. 

Dithiazolyl free radicals, formation from amines and halosulfur compounds 85PS(23)277. 

Monocyclic neutral It 1,2,3-dithiazolyls 34 can be prepared by one-electron reduction of the readily prepared 1,2,3-dithiazoHum salts 33 using decamethylferrocene or triphenylantimony (Scheme 7) (1999CC531, 2002CC1872). These radicals have significant spin density at the C, N,... 

Benzo-fiised 1,2,3-dithiazolyls 38 are prepared by the reduction of readily prepared Herz salts 37 using decamethylferrocene in acetonitrile (Scheme 8) (1999JA969, 2001CJC1352, 2005IC1837). Se and Te derivatives of fused 1,2,3-dithiazolyls can also be prepared in a similar manner and a wide variety of reductants can be used such as octamethylferrocene, hexamethylferrocene, tetramethyl-p-phenylenediamine, and electrochemical reduction (2008IC10100). 

Resonance-stabilized 1,2,3-dithiazolyls form TT-shpped stacks and show modest conductivity but with magnetically ordered phases. The... 

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