1.3- Dithiol-4-olates

Modified spectrophotometric procedures are described for the quantitative determination of cobalt and molybdenum as the 2-nitrosonaphth-l-olate and toluene-3,4-dithiolate complexes in carbon tetrachloride. The extraction, chelation and phase separation steps permitted rapid sample handling, controlled interferences more effectively and provided accurate assays. The molar absorptivities for cobalt and molybdenum were 5.1 x 104 and 2.5 xl04mol/lcm, respectively, and the detection limits for both elements were 4 ng/g. 

Compounds of interest are the l,2-dithiolylium-4-olates (7), 3-acylmethylene-l,2-dithioles (11) and various oxocyclohexadienylidene-l,2-dithioles (13) and (31). The compounds (7) appear by most physical data and chemical properties to be best represented by the structure shown (78AJC297,80PS(8)79>, and for the compounds of type (11) data indicate some measure of contributions from structures (lib) or (11c). However, the exact amount of polar or tetravalent sulfur contributors to each of the structures (11), (13) and (31) is a matter of some discussion (71AHC(13)161,80MI43100). 

The mesoionic l,3-dithiol-4-ones of type (2) are best represented as resonance hybrids of several limiting formulae (2a)-(2e), of which (2a) and (2b) are presumably most representative both formulae are, for example, in good agreement with the direction of the dipole moments. According to the IUPAC nomenclature rules, the mesoionic 1,3-dithiolones (2) should be named as l,3-dithiolylium-4-olates (B-79MI43202). 

Examples of these systems are the l,2-dithiole-3-thione 43 and the type A mesoionic l,3-thiazolium-4-olate 44. Important members of this class are the tetrathiafulvalenes (TTFs) 45 and related systems, which have been studied extensively because of their potentially useful electrical properties . 

Complexes of dithiolene anions, snch as maleonitriledithi-olate and tolnene dithiolate, where the delocalized S... 

Density functional theory (DFT) and post-Hartree-Fock MP2 in conjunction with the B3LYP employing the 6-31G(d) basis set were used to predict structure and correlate assignments of the fundamental vibrational modes of 3/7-1,2-dithiole-3-one la and 3/7-1,2-dithiole-3-thione lb with experimental data <1998VSP77>. These sulfur-rich heterocycles, characterized by a long and weak S-S bond, are represented in accordance to the simple 7t-MO theory by resonance contributor 8, involving a cationic 67t-l,2-dithiolylium part and an anionic thiolate or olate part, and the exocyclic C=S bond is more delocalized than the C=0 bond. However, computational evidence suggests structures with localized bonds and relatively low aromatic delocalization, which is also supported by the low values of the dipole moments, that is, 3.54 D for la and 4.12 D for lb. 

Dithiolium salts react with hydrazines similarly to amines, but further cyclization gives pyrazoles (46) or pyrazolium salts (47). When there are replaceable substituents, hydrazones and azines are formed. A mesoionic l,2-dithiole-3-olate (20 R = Ph) reacts similarly at C(3) with aniline, but with eventual formation of the products (48) and (49) <87CJC2830,92T8127). The reaction... 

Various reagents, including oxalyl chloride and thionyl chloride, convert 1,2-dithiole-3-ones (2a) and -3-thiones (2b) into 3-chloro-l,2-dithiolium salts, types (56a), some via cyclic intermediates <87PS(3l)i09>. The oxygen atom on l,2-dithiolium-3-olates (20) can be protonated or alkylated to form 4-hydroxy or 4-alkoxy-l,2-dithiolium salts respectively <86MCLC373>. 

The meso-ionic 1,3-dithiolium 4-olate (283 R = SMe) exists in equilibrium with the dimer (284 R = SMe). Complete regiospecificity is observed in the 1,3-dipolar cycloaddition of styrene to the diphenyl-derivative (283 R = Ph), which gives only compound (285 R = H,R = Ph) in contrast, methyl acrylate yields a mixture of (285 R = C02Me, R = H) and the isomeric adduct (285 R = H, R = C02Me)/ Irradiation of the diphenyl-compound (283 R = Ph) yields a mixture of 4,5-diphenyl-l,2-dithiole-3-thione (286) via the bridged intermediate shown), sulphur, diphenylacetylene, tetraphenylthiophen, and the latter s precursor, the dithiin (287). The dithiin is thought to arise from the dimeric compound (284 R = Ph) by loss of carbon oxysulphide. ... 

Synthesis.—3,5-Diaryl- and 3,5-dialkyl-1,2-dithiolium salts (121 R = Ar or Bu ) can be prepared in good yield by the sulphurization of diketones (Scheme 9). Treatment of these salts (121) with pyridine affords the corresponding 4-olates (122), which can be O-alkylated with iodomethane and similar compounds. With ammonia, ring scission and re-cyclization occurs, and the corresponding iso-thiazolium-4-olates are formed. An unusual synthesis of 1,2-dithiolium salts (124) is by the photolysis of l,2-dithiole-3-thiones (123) in benzene or acetonitrile, in the presence of aryl or alkenyl bromides or iodides. 

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