Dithiolium cations

Unlike their thiazolium, imidazolium, and oxazolium analogs, the dithiolium systems have not been extensively studied. Where measurements have been reported they indicate that hydrogen atoms at positions 2 or 3 possess considerable acidity. The 1,3-dithiolium cation (33, R = CH3) exchanged its 2-H in CF3COOD-D2O at 34°, OD probably being the effective catalyst. When 1,3-dithiolium salts dissolved in an... 

Another general method is illustrated by the preparation of [Cr(S2CNR2)3] (where R = Me, Et, Pr, Bun, Bu , CH2Bu R2 = (CH2)40, (CH2)4, (CH2)s, MePh or EtPh equation 52). In this a chromium (II) salt is added to the ligand and the mixture allowed to oxidize.1000 An alternative is to reduce a precursor, e.g. the 3,5-dimethyl-l,2-dithiolium cation, with a chromium(II) salt to the ligand which then coordinates to the Cr111 produced (equation 53).1001... 

The MS fragmentation patterns of dithio-/J-diketonato complexes differ from those of both /J-diketonato and monothio-/J-diketonato complexes. The mass spectra of bivalent dithioacetyl-acetonato complexes are characterized by a molecular ion peak M and a much stronger peak for L+ due to the formation of the 3,5-dimethyl-l,2-dithiolium ion another peak at tn/e 96 is due to the loss of HS from the dithiolium cation. The mass spectra of nickel complexes of dithio-/ -diketones are dominated by fragmentation products of the uncomplexed oxidized ligand, which is consistent with the low stability of dithio-/J-diketones and the greater stability of the 1,2-dithiolium... 

A dithiafulvene (1) can form a 1,3-dithiolium cation by an easy one-electron oxidation, as a result of its electron-donating property. The 1,3-dithiolium ion is an unsaturated five-membered-ring cation in which each sulfur atom contributes a pair of 3n electrons and, consequently, would be expected to show aromatic stability [1, 2]. The chemistry of the dithiafulvene and its... 

Phenyl- 1,2-dithiolium cation reacts with acetone and ethyl vinyl ether in the following way (Scheme 4).28... 

Most commonly, however, an oxidation takes place during the condensation, probably at the expense of some dithiolium cation, and a dithiolylidene carbonyl compound is formed directly (Eq. 8). 

Chloro-l,2-dithiolium cations can be used in the form of crystalline perchlorates.33 These compounds react with hydroxy-substituted and/or alkoxy-substituted aromatic compounds to give 3-aryl-l,2-dithiolium cations (Eq. 11). 

Methylthio-l, 2-dithiolium cations attack sodium phenoxide in the 2-position13,20 and sodium 2,6-dimethylphenoxide in the 4-position.31... 

Dimethylthioformamide reacts at a methylene group in the 3- or 5-position of a 1,2-dithiolium cation. This reaction may be performed in acetic anhydride. The resulting Vilsmeier salt (32), treated with aqueous sodium hydroxide, gives an a-(l,2-dithiol-3-ylidene) aldehyde.49... 

Methyl-1,2-dithiolium cations also react with dithio esters which serve as acylating agents (Eq. 23).41... 

An indirect method, using the reactivity of methylene groups substituted in position 3 of 1,2-dithiolium cations, is given later (Section III,E, 3). 

When a 3-aryl-l,2-dithiolium cation attacks methyl benzoyldithio-acetafce, two reactions may occur, probably with a common intermediate (41).03 In a neutral medium, 41 undergoes only dehydrogenation, probably by the action of unreacted dithiolium cations, as it is often seen with carbonyl compounds. In this way, the same trithia-pentalene 42 is obtained as with the corresponding 5-aryl-3-methyl-thio-l,2-dithiolium cation (see Section III,C,2). 

S,5-Bismethylthio-l,2-dithiolium Cations These compounds react just as the corresponding monomethylthio derivatives do.46,61 Bismethylthiotrithiapentalenes are obtained in this way (Eq. 25). 

In boiling acetic anhydride or in the presence of phosphorus oxychloride,70 1,2-dithiolium cations with 3- (or 5-) R-CH2 substituents react with dimethylthioformamide, giving a Vilsmeier salt. This compound reacts smoothly with sodium hydrogen sulfide to give a trithiapentalene (Scheme 16).49,70,71... 

Other resonance formulas can he written with the positive charge on the nitrogen atoms, giving some double bond character to the affected C-N bonds. Notwithstanding the close O-S contacts and the fact that the four O-S-S-O atoms are in a linear arrangement, the S-S bond has a length practically normal for 1,2-dithiolium cations. 

It should be noted that the ending ylium has been used, according to IUPAC recommendations, for denoting the formation of a cation by loss of a hydride ion instead of the ending ium which is increasingly being reserved for the addition of a proton. For this reason, the term 1,2-dithiolylium cation has been used for the structure often named 1,2-dithiolium cation (80AHC(27)15l). 

Other cation-pseudobase equilibrations that have received detailed spectral investigation include quaternary isoquinoline alkaloids and related isoquinolinium derivatives,910 naphthyridinium mono- and dications,26,38,42 44 50 pyridinium cations,51,52 isobenzopyrylium (isochro-mylium) cations,53 benzothiopyrylium (thiochromylium) cations,40 and 1,3-dithiolium cations.54 PMR spectroscopy has also been useful in the identification of pseudobases as reaction intermediates in several reactions in solution.55-57 While 13C-NMR spectroscopy is also potentially useful for the assignment of pseudobase structure, at present there do not appear to... 

The ring opening of the 4-phenyl-1,3-dithiolium cations (97) has been investigated, but the structure of the products (99 and/or 100) does not seem to have been established.76 The kinetics of the ring opening of a 1,3,4-... 

Hurtley and Smiles4 had isolated fused-ring derivatives of 2 as early as 1926, but were understandably unable to find a satisfactory explanation for the valence relationships on the basis of the views held at that time. Wizinger and Soder,6 in 1958, were the first to suggest that these aryl-l,3-benzodithiol-l-sulfonium salts were derivatives of the resonance-stabilized benzo-l,3-dithiolium cation. 

Fig. 1. Molecular diagrams of the 1,2-dithiolium cation.122-123 Model A a, j8ag = 0.5)S b, )Sgg=1.0)S. Model B c,, a = O.o/J d, /Jaa = 1.0/3. (Relative electron densities, bond orders, and free valences.) e, the nonoverlap case f, the overlap case. (Relative electron densities and bond orders.)...

The reaction of orthoformic ester with 1,2-benzenedithiol yields the unsubstituted benzo-l,3-dithiolium cation, which can be isolated as the hexachloroplatinate or as the tetrachlorozincate.131 139... 

Fig. 5. Molecular diagrams of the 1,3-dithiolium cation (relative electron densities and bond orders).

The benzo-1,3-dithiolium cation has also been subjected to the theoretical treatment, on the basis of model A, and using j3cs values of between 0.6 and 1.0. It was found that electrophilic substitution should occur most readily in position 4, whereas nucleophilic or free-radical attack should take place exclusively in position 2. The possibility of correlating the excitation energies as calculated by the HMO method with the values found by experiment has been studied, and the limitations of such a correlation discussed.1... 

In this section, reactions of 1,3-dithiolium cations and their precursors with carbanions (generated mostly from the corresponding C-H acids using various bases such as LDA, -BuLi, /-BuOK, EtONa, pyridine) are discussed. 

Treatment of 1,3-dithiolium cations 123 with malononitrile, in the presence of pyridine (py) to generate the corresponding carbanion, gave (l,3-dithiol-2-ylidene)dicyanomethanes 127 (Equation 1) <1998JMC1173>. 

The reaction of 1,3-dithiolium cation 133 with the anion of 1,3-indanedione afforded the l,3-dithio-2-ylidene derivative 134. Subsequent reaction of the latter with 1 or 2 equiv of the carbanion derived from 135 allowed the introduction of two further 1,3-dithiole units to give 136 and 137, respectively (Scheme 12) <1999T9915>. 

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