Dithiolates structure

There are single examples of sulfur and selenium xanthates with the remaining structures to be described in this section featuring tellurium as the central element. There are a significant number of binary xanthates and, in common with these, their organotellurium xanthates feature extensive supra-molecular association, usually, but not exclusively, via Te- S secondary bond interactions. A rare example of mixed-ligand 1,1-dithiolate structure is available where the odd dithiolate ligand is a dithiocarbamate. 

This situation has been widely discussed [592a-c] and has not been finally resolved [592d]. At the same time, there is experimental data (reactions with halogens) in favor of the existence of dithiol structures of type 318b containing M — S bonds (M = Ni, Pd, Pt) with metal oxidation number +4 [592e,f]. 

A special derivatization reaction is required for lewisite 1, which is so reactive that it cannot be determined by GC/MS in low quantities (e.g. below 10 ng per injection). It has been known for a long time that lewisite 1 reacts with compounds having an a, P-dithiol structure, such as 2,3-dimercaptopropanol-l (British-Anti-Lewisite (BAL) also used for medical treatment). The derivatization reaction can be performed at an analytical level and several examples have been described (29). The reaction product of lewisite 1 with 3,4-dimercaptotoluene, 2-(2-chlorovinyl)-5-methyl-l,3,2-benzodithiarsole (see (1)), is a useful derivative for GC/MS analysis. Its mass spectrum is simple with molecular ion peaks at m/z 290/292 and the base peak at m/z 229 due to the loss of the 2-chlorovinyl group (30). 

Potential 2-hydroxy- and 2-mercapto-l,3,4-thiadiazoles have been examined both by infrared and by ultraviolet spectra in the solid state and in solution by Sheinker et They concluded that these compounds exist in the 2-oxo and 2-thione forms, respectively. To 2,5-dimercapto-l,3,4-thiadiazole the 2-mercapto-5-thione structure (155) was given. The structure of this compound has been the subject of some controversy. Stanovnik and TiSler have added some valuable arguments to the discussion. They measured the pKfl values of 155, its iV-methyl, iV -phenyl, and iV -phenyl-/S-methyl derivatives (156), and of the conjugate acids of these and the S-methyl derivative (pKn ) (Table III). In all compounds 156 with R = H, the infrared spectrum showed an absorption band near 2300 cm characteristic of the SH group. They also had pK i values near —1.5, Avhich in connection with the infrared evidence was taken as characteristic of an SH group in this situation. Since the 2,5-dithiol structure is excluded by ultraviolet spectral evidence, the 2-mercapto-5-thione structure (155) seems rather well established. It has previously been shown bj Thorn to predominate in chloroform solution, whereas he concluded that the dithione form (157) should predominate in ethanol solution. However, the pK i value for 155, — 1.36, makes it rather probable that Thorn used the monoanion of 155 instead of the acid itself for spectral comparison, and in that case his conclusions have a very weak foundation. 

Consistent with the dithiolene structure proposed for the oxidized derivative of molybdopterin (3), no nonexchangeable H resonances are observed in the region expected for the CH protons of a dithiolate structure (5b). The mass spectrum of 3 is also consistent with the proposed dithiolene structure (19, 34). Resonance Raman spectra of DMSO reductase show bands at 1575 cm (oxidized form) and 1568 cm (reduced form) that are assigned to the C=C stretch of the dithiolene unit of 2 (40). However, the delocalized electronic structure of dithiolene ligands makes it difficult to assign the C=C stretch with certainty. As Rajagopalan notes (19), ultimate proof of the structure [of molybdopterin] will have to await either X-ray studies on a molyb-doenzyme or unequivocal chemical synthesis of the molecule. ... 

Ab initio 3-21G and 6-31G calculations on trithiapentalenes favor a bicyclic structure (6), whereas a monocyclic dithiole structure (10) is favored by SCF calculations <9UA6449>. 

The monomeric nickel dithiolates, structures 8h-81, have yielded electrochemical data relating to the three-oxidation-state hypothesis expressed in the Introduction. Complexes 8h-8k show S-based reactivity, including the S-based uptake and binding of gaseous molecules, SO2, O2, and I2 in complex 8k. " Complex 8h " was used in an intensive analysis of requirements to achieve the... 

Under UV irradiation, allene (16 gm, 0.4 mole) was bubbled for 11 hr into 54 gm (0.5 mole) of trimethylenedithiol contained in a quartz tube at 15°C. At the end of this time 0.4 mole of allene was absorbed and the reaction mixture solidified to yield the raw polytrimethylenesulfidedithiol. The polymer was repeatedly dissolved in benzene and reprecipitated with methanol to give 50 gm (84.5%) of a polymer with MW 837 by potentiometric titration assuming a dithiol structure. 

Scheme 2.41 Asymmetry of the dithiolene chelates explained by an admixture of resonance forms, the thione-thiolate (structure B) and the dithiolate (structure A).

Diisopentyl thiomalate Dithiols Structural class 1 1672 N No safety concern... 

Thieno[3,4-d][l,3]dithiol-2-one, 1-nitro-synthesis, 6, 1013 Thieno[3,4-c]furan, 4,6-dichloro-synthesis, 6, 1013 Thieno[3,4-c]furan, tetraphenyl-formation, 4, 1060 synthesis, 4, 1060 UV spectra, 4, 1044 Thieno[3,2-6]furans structure, 4, 1039 synthesis, 6, 1020 Thieno[3,4-c]furans... 

Tire reaction of the lead dithiolate 18 with elemental sulfur was claimed, without unambiguous structure proof, to give a dithiirane 19 in 75% yield (96ZOR1881). 

Bidentate dithiolate ligands afford complexes like Au(S2CNR2) (R = Et, Pr, Bu) and Au(S2PR2) (R = Pr), which have dimeric structures based on 8-membered rings with linear S—Au—S coordination and short Au-Au distances. These in turn are associated into chains (Figure 4.16) (Au-Au c. 3.0-3.4 A) [99],... 

The photochemical behavior of a number of substituted derivatives of thiochroman-4-one 1-oxides has been examined by Still and coworkers192-194. These authors also report that rearrangement to cyclic sulfenates, with subsequent reaction by homolysis of the S—O bond, appears to be a particularly favorable process. For example, ultraviolet irradiation of a solution of 8-methylthiochroman-4-one 1-oxide (133) in benzene for 24h afforded a single crystalline product which was assigned the disulfide structure 134 (equation 54). More recently, Kobayashi and Mutai195 have also suggested a sulfoxide-sulfenate rearrangement for the photochemical conversion of 2,5-diphenyl-l,4-dithiin 1-oxide (135) to the 1,3-dithiole derivatives 136 and 137 (equation 55). 

Metal complexes of 1,1-dithiolates have been reviewed by Coucou-vanis (1) Eisenberg (2) presented a systematic, structural review of dithiolato chelates, and Stokolosa ct al. (3) reviewed dithiophosphate complexes in detail. Earlier reviews (4-3) covered less recent work in greater detail. Following initial work by Delepine (9), 1,1-dithiolato complexes were more intensively studied between 1930 and 1941 (10-16). There is, however, continuous interest in the synthesis, characterization, electronic structures, and bonding of these complexes. 

The structure of [Mo3S4(dmit)3] (dmit=l,3-dithiole-2-thione-4,5-dithiolate) represents one of the rare examples of M3S4 clusters where each metal atom appears as pentacoordinate instead of its more common type-I structure octahedral environment [39]. Complexes [M3Q4(dmit)3] (M = Mo, W Q = S, Se) degrade in air with an almost quantitative yield and afford a series of M(V) dimers of formula [M202(//-Q)2(dmit)2] where the oxygen atoms are in a syn configuration. 

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