1.3- Dithiolium salts structure

The same uncertainty exists with regard to the bonding in the addition products of trithiones with Cl2, Br2, and I2,82 84 and with the acid chlorides S02C12, S0C12,83, 84 and S2C12.88 The relatively high melting points of all these crystalline adducts, many of which decompose very readily, but which have very definite compositions, can be taken as evidence for the 1,2-dithiolium salt structures (e.g., 41 or 42) however, physical measurements that could conclusively establish the saltlike character have not so far been carried out. 

The unstable yellow salt obtained by the action of hydrogen sulphide and hydrogen chloride on the triketone (40) has been assigned the dithiolium salt structure (41). On treatment with bases it yields the intensely coloured meso-ionic compound (42), which is also obtained by the... 

The first recorded attempt to prepare a thio derivative of a /1-diketone resulted in the isolation of the colourless dimer (57 R = R = Me) from the reaction of acetylacetone and hydrogen sulfide in hydrochloric acid.243 Similar dimers with various R and R groups have been reported244 and the structure (57) has been confirmed from NMR and MS data.245 Other attempts to prepare dithio-/ -diketones (58) yielded 1,2-dithiolium salts (59).246... 

The 1,2-dithiolium salts are electron-deficient compounds, and as such are very reactive and unselective towards nucleophilic reagents. Qualitative considerations based on the simple resonance theory, as well as refined quantum mechanical approximations (Section II, C, 1), indicate that the resonance hybrid is most closely described by the carbonium and sulfonium structures (1 and 60), whereas the decet (61) and long-bond (62) structures appear to be of little importance. As would be expected for a charge distribution indicated in 1, protons attached in positions 3 and 5 experience a relatively weak electron screening effect (Section II, C, 4).79c... 

Thus the 1,2-dithiafulvene (155) liberated from the 3-methyl-5-phenyl-1,2-dithiolium salt (154) by ammonia is unstable, and could not be characterized even in solution. It is doubtful whether 155 can in fact be obtained by this method, since 154 reacts even with the weak base pyridine to yield a product which has been assumed to possess the structure 159. The formation of this product has been plausibly explained by the reaction sequence shown in Scheme 9.110... 

The electrophilic character of the 1,3-dithiolium salts is distinctly stronger than that of the 1,2-dithiolium isomers. This has been very qualitatively explained by assuming that the positive charge is largely localized on the S—C—S grouping, i.e., that the most important of the limiting structures 2 and 269-273 are the carbonium-sulfonium... 

Among the nucleophilic reagents that react with 1,3-dithiolium salts, tertiary aliphatic amines have given interesting results. Numerous TTF derivatives have been prepared by treatment of 2-unsubstituted 1,3-dithiolium salts by triethylamine or A-ethyldiisopropylamine (Section III,B,6,a).The 1,3-dithioliumcation probably first undergoes adeprotonation leading to a cyclic carbene which can also be represented by dipolar structures (Eq. 36). 

Few IR data of 1,3-dithiolium salts have been reported.1,3-Dithiolium-4-olates have been studied more in relation to their mesoionic and resonance hybrid structure 97. They show a strong absorption band whose position varies between 1575 and 1610 cm according to the substituents. This is also observed in the spectra of other mesoionic... 

No data appears to be available for 1,2-dithiolium salts, but for mesoionic 1,2-dithioles, IR studies indicate that the cyclic structure (20) is favored over an acyclic structure (21), except where R is an amino substituent <87PS(3l)l09>. 

Because of structural contributors such as (101), ring substituents on dithiole rings with exocyclic double bonds at C(3) or C(5) should have a reactivity similar to that of 1,2-dithiolium salts (3). 

Vilsmeier-Haack formylation of 2,5-diaryl-6a-thiathiophthens leads to the 3-formyl compounds, which are also obtainable from 3-aryl-l,2-dithiolium salts by treatment with triethylamine, and details have been given for the bromination of 2,5-disubstituted thiathiophthens. Nitration of 2-methylthio-5-phenyl-6a-thiathiophthen gives the 3-nitro-compound in poor yield, and attempted nitrosation experiments lead, in several examples, to rearranged structures of type (19), although the first stage of these reactions is presumed to be electrophilic attack on the 3-position. 

Reviews have appeared on structure and bonding in unsaturated five-membered cyclic disulphides, and on the chemistry of 1,3-dithiolium salts. Although published in 1970, these reviews contain few references to work published after 1966. 

Studies on chlorinated dithiole derivatives have continued. 4-Chloro-l,2-dithiol-3-ones of type (21) are converted by the action of oxalyl chloride into dichloro-l,2-dithiolium salts (22), which react at the 3-position with aromatic amines to give 3-arylimino-l,2-dithioles (23 R = Ar). Related structures (23 R = PhS02, MeSOa, or EtO CO) are obtained from... 

Ri =s R2 = Ph). 4-Aryl-l,2-dithiolium salts of type (36 R = Me or Ph, R = H) yield 1,2-dithiolylidene ketones (37) when heated in ethanol, but this reaction fails when the dithiolium salt has a 5-amino-substituent (36 R = NRa). The 5-amino-compounds have been found to give 1,3-dithiole derivatives on treatment with phosphorus pentasulphide in pyridine. The structure of one of the products (38) was established by conversion into the 6a-thiathiophthen (39), which was also prepared by sulphurization of the dithiolylidene ketone (37 R = Ar = Ph, R = MeaN) obtained by the triethylamine-acetic acid route. 

Earlier work on the crystal structures of dithiolium salts has been continued by a study of 4-phenyl-l,2-dithiolium chloride monohydrate. ... 

Related structures, for example (62), are prepared by condensation of 2-piperidino-l,3-dithiolium salts with active-methylene compounds. ... 

When the tetracation salt 33c was prepared by chemical oxidation with NOBF, it showed five signals reflecting an apparent Cj structure in its NMR chemical shifts. In addition, the chemical shifts of DT rings correspond to DT rings in the tetracationic species and are quite similar to those of 4,5-benzo-1,3-dithiolium salt 34e" -BF4 . Thus, the simultaneous four-electron transfer process in 33e is attributed to a particular stabilization of 33c, whose central five-membered ring strongly contributes to the aromatic cyclopentadienide characteristic (Figure 8.15). The same interpretation can be applied to the redox behavior of 33a and 33b. 

Diazo-coupling reactions of thiathiophthens, 1,2 dithiolylidene aldehydes (see Section 3), and 6,6a-dithia-l-azapentalenes (29) all lead to 6,6a-dithia-l,2-diazapentalene derivatives (17), which can also be obtained from 2-methyl- (or methylene)- ,2-dithiolium salts by coupling with diazonium fluoroborates. " When R = H in structure (17), further coupling can take place at this position. 1,2-Diselenolium salts give similar products but in poor yields. Preliminary A -ray data on the 5-t-butyl-l-phenyl compound (17 = Bu, R2 = R = H,... 

Dithiolylidene derivatives of malonic acid (26) decarboxylate in perchloric acid-acetic acid to give 5-ary 1-1,2-dithiolium perchlorates. Vilsmeier salts of type (27) are produced by condensation of 5-methyl-1,2-dithiolium salts with dimethylthioformamide, and a similar trans-structure (28) is formed when 6-methyl-l,6a-dithia-6-azapentalene (see Chapter9) is protonated. 

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