A-Dithioketones

To obtain ethylenedithiols, the main options described in Scheme 1 are available. Vicinal dithio-ethers, which can be prepared from cis-dichloro- or dibromo-alkenes or from alkenes through a stepwise synthesis, can be cleaved to produce dithiols (Route A). Ethylenedithiocarbonates can be prepared by several well-established procedures and by some less general ones as well. The ethylenedithiocarbonates are central intermediates for many dithiolene syntheses and for syntheses of derivatives of the electron donor tetrathiafulvalene (TTF), which has been intensively investigated in the past decade. This has widened the synthetic possibilities for ethylenedithio-carbonates. Their cleavage by alkali metal hydroxides or alkoxides produces salts of ethylenedithiolates (Route B). As an alternate route, their photolysis with loss of CO and generation of a dithioketone has been explored. ... 

In the paradigmatic example of the bisdithiolene complexes of group 10 metals, the metal atom in the neutral compounds can be described as zerovalent if the ligand is considered to be a dithioketone (Scheme 25a), as divalent if a thione thiolato ligand is considered (Scheme 25b), and as tetravalent when the ligand is considered to be a dithiolato (Scheme 25c). 

Because the benzene resonance energy is much higher than that of an isolated double bond, the oxidation of an ethylenedithiolate to the butadiene-like dithione is easier to accomplish than the oxidation of a benzenedithiolate to the corresponding dithio-or /io-benzoquinone there is a difference in stability between the dianionic ligands (44) and (46) relative to the dithioketone forms (45) and (47) derived from them by a two-electron oxidation. 

Figure 3-20. The reaction of a 1,3-diketone with hydrogen sulfide only gives a monothio derivative, 3.11, rather than a 1,3-dithioketone.

Figure 3-21. The metal directed reaction of a monothio compound with hydrogen sulfide to yield a chelated 1,3-dithioketonate.

However, the dithioketones may be readily prepared by reaction of the metal complexes of the monothio derivatives, 3.11, with hydrogen sulfide (Fig. 3-21). In this case, the metal probably plays a dual role, both in polarising the ligand and stabilising the product. Clearly, the use of a soft metal ion such as lead(it) or platinum(u) is to be preferred in a reaction of this type. 

Sulfur participates as a donor center in sulfide complexes (Muller and Diemann, p. 515), dithiolenes (Miiller-Westerhoff and Vance, p. 595), and other S-containing ligands (thiosulfates, thiourea, mono-, and dithioketones) (Livingstone, p. 633). Some other complex compounds with Se and Te as donor centers have been described (Berry, p. 661). 

Thioketones bearing an a carbonyl have been reported [87]. As these species are produced in situ and trapped by cycloaddition, this chemistry is reported in the corresponding section (Sect. 3.8). Sulfurisation of diketones by B2S3 led to dithioketones, which were later nicely found by the Steliou group [88, 89] to be capable of ejecting diatomic disulfur (S2) via an elusive... 

Few dithiolenes are prepared via reactions involving 1,2-dithioketones, a rare class of compounds prone to oligomerization. The first stable 1,2-dithione, l,2-bis(4-dimethylaminophenyl)ethane-l,2-dithione, was generated by photolysis... 

The present section and Section IV.A.4 complement each other. The GC of metal chelates derived from monothio-/3-diketones, /3-diketones, -dithioketones and /3-keto-enamines was reviewed. The discussion includes column phenomena, analytical improvements and limitations and various applications . A study of the GC behavior of Group 13 /9-diketonates 37 shows that when the chelate contains a Mef group its volatility is enhanced, while a Ph group tends to decrease it. When R and R are alkyl groups the retention time of the chelates increases with the molecular weight, but it does not depend on the volatility however, the retention time of the chelates containing a Mef group is almost inversely correlated with the volatility . ... 

Enedithiolate anions are redox-active ligands (see equation 1), capable of coordinating with a variety of metals as neutral dithioketones (1), thioketone radical thiolate monoanions (2) and ene-l,2-dithiolate dianions (3). The complexes are named dithiolenes irrespective of their oxidation state to remind one that they are noninnocent ligands . 

There is considerable ambiguity concerning the charge on this type of ligand. This K> because it may be formulated either as a neutral dithioketone or the dianion of an ufisaturated dithiol. The diRl ence of two electrons can be represented formally as ... 

Monothiophosphates derived from the enol form of a j -dithioketone (6) give, when treated with perchloric acid, a 1,2-dithiolium cation and a dialkylphosphite (Eq. 5). ... 

The in situ photochemical generation of 1,2-dithioketones and -aldehydes including dithioglyoxal, 3,3-dimethyl-2-thioxobutanethial, and camphor dithioquinone was confirmed by the subsequent trap of the 1,2-dithiocarbonyl compounds in [4 + 2] cycloadditions. The 1,2-dithioketones and 1,2-dithioaldehydes exhibited a preference for 4ir participation in inverse electron demand (LUMOdlene controlled) Diels-Alder reactions with electron-rich dienophiles (Scheme 8-X).37... 

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