Two Sulfur Atoms

Poly-(l, 2-dithiolo[4,3-c -l,2-dithiol)-2,6-ylidene as a potential conducting material 89PS(43)165. 

2- Tetrathiafulvalenes, synthesis, chemical and physical properties of 87MI61. 

3- Dithiolate conducting complexes, molecular structures of 90UK-1179. 

3- Dithiol-2-imines, formation in 1,3-anionic cycloaddition reactions of a,/3-unsaturated thiolates 87UK267. 

3- Dithiol-2-thione, formation from tetrathioxalates 86MI28. 

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The thiosulfate ion, 820 is a stmctural analogue of the sulfate ion where one oxygen atom is replaced by one sulfur atom. The two sulfur atoms of thiosulfate thus are not equivalent. Indeed, the unique chemistry of the thiosulfate ion is dominated by the sulfide-like sulfur atom which is responsible for both the reducing properties and complexing abiUties. The abiUty of thiosulfates to dissolve silver haUdes through complex formation is the basis for their commercial appHcation in photography (qv). 

Like the reaction of ketones, the interaction of triflic anhydride with thiourea and substituted thioureas also gives dicationic triflates (equations 40 and 41) however, two sulfur atoms form the bndge in this case This result indicates that triflic anhydride is acting as an oxidizing reagent toward thiourea [89]. 

Although the structure of [SsN] has not been established by X-ray crystallography, the vibrational spectra of 30% N-enriched [SsN] suggest an unbranched [SNSS] (5.22) arrangement of atoms in contrast to the branched structure (Dsh) of the isoelectronic [CSs] and the isovalent [NOs] ion (Section 1.2). Mass spectrometric experiments also support the SNSS connectivity in the gas phase.Many metal complexes are known in which the [SsN] ion is chelated to the metal by two sulfur atoms (Section 7.3.3). Indeed the first such complex, Ni(S3N)2, was reported more than twenty years before the discovery of the anion. It was isolated as a very minor product from the reaction of NiCl2 and S4N4 in methanol. However, some of these complexes, e.g., Cu and Ag complexes, may be obtained by metathetical reactions between the [S3N] ion and metal halides. 

FIGURE 21.13 The structure of mitochou-dtial cytochrome c. The heme is shown at the center of the structure, covalently linked to the protein via its two sulfur atoms (yellow). A third sulfur from a methionine residue coordinates the iron. 

Progress in the chemistry of three- and four-membered rings containing two sulfur atoms has been rapid in the past few years. An updated survey of the chemistry of dithiiranes, 1,2-dithietanes, and 1,2-dithietes is now provided from a major center in this area by Professor J. Nakayama and Dr. A. Ishii (Saitama University, Japan). 

The (V-methyldihydrodithiazine 125 has also been used as an effective formyl anion equivalent for reaction with alkyl halides, aldehydes, and ketones (77JOC393). In this case there is exclusive alkylation between the two sulfur atoms, and hydrolysis to give the aldehyde products is considerably easier than for dithianes. However, attempts to achieve a second alkylation at C2 were unsuccessful, thus ruling out the use of this system as an acyl anion equivalent for synthesis of ketones. Despite this limitation, the compound has found some use in synthesis (82TL4995). 

Another example of resort to heteroatoms to obtain both oral potency and a split between androgenic and anabolic activities Ls tiomestrone (99). Trienone, 98, prepared in much the same way as 23, undergoes sequential 1,6 and 1,4 conjugate addition of thioacetic acid under either irradiation or free radical catalysis to afford the compound containing two sulfur atoms. 

In some sulfur extrusions from 2,7-di-/ Tt-butylthiepins a byproduct containing two sulfur atoms is obtained, along with the aromatic compound. The byproduct has been characterized as a thienothiophene by single crystal X-ray analysis.92... 

Metal ions react readily with (I) and (II) to yield complexes in which the two sulfur atoms are bound to the same metal, thus forming a four-... 

Despite the fact that natural elemental sulfur contains 0.75% of the isotope [4] with a nuclear spin of 7 = /2 no NMR spectra of elemental sulfur have ever been reported. Such spectra are however well-known for compounds containing just one or two sulfur atoms [5]. Electron spin resonance spectra of irradiated elemental sulfur samples and of quenched sulfur vapor have been reviewed elsewhere [6-8]. 

By ab initio MO and density functional theoretical (DPT) calculations it has been shown that the branched isomers of the sulfanes are local minima on the particular potential energy hypersurface. In the case of disulfane the thiosulfoxide isomer H2S=S of Cg symmetry is by 138 kj mol less stable than the chain-like molecule of C2 symmetry at the QCISD(T)/6-31+G // MP2/6-31G level of theory at 0 K [49]. At the MP2/6-311G //MP2/6-3110 level the energy difference is 143 kJ mol" and the activation energy for the isomerization is 210 kJ mol at 0 K [50]. Somewhat smaller values (117/195 kJ mor ) have been calculated with the more elaborate CCSD(T)/ ANO-L method [50]. The high barrier of ca. 80 kJ mol" for the isomerization of the pyramidal H2S=S back to the screw-like disulfane structure means that the thiosulfoxide, once it has been formed, will not decompose in an unimolecular reaction at low temperature, e.g., in a matrix-isolation experiment. The transition state structure is characterized by a hydrogen atom bridging the two sulfur atoms. 

Figure 12-6. Iron-sulfur-protein complex (Fe4S4). d acid-labile sulfur Pr,apoprotein Cys, cysteine residue. Some iron-sulfur proteins contain two iron atoms and two sulfur atoms (FejSj).

A remarkable complex with the composition Co2(R2C fc)5BF4 resulted from an attempt of Hendrickson and Martin (81) to oxidise Co(R2r/tc)3- These authors report diamagnetic, ionic complexes, in which the metal atoms are bridged by two sulfur atoms of the ligands, as is found for Ru2(Et2(irc)5BF4 (77). 

Reaction of the tri- -butylphosphine adduct 180 with compound 157 leads to cycloaddition across the two sulfur atoms to give corresponding 2-tri- -butylphosphoranylidene-l,3-dithiole 181, which can be trapped by in situ Wittig reaction with benzaldehyde to give 182 (Scheme 21) <1994CC2603, 1997T2261>. 

Longer Hg-7r interactions are observed in the /> ra-/-butylcalix[4]arene mercury complex 162. The mercury atom forms primary bonds with the two sulfur atoms and engages in weaker secondary interactions with two arene rings of the calixarene whose centroids sit at 3.07-3.11 A from the metal center.201... 

Li[Ph4P2N4S2R].274 Alkali-metal derivatives of the dianion [Ph4P2N4S2]2 are prepared by treatment of 111 (E=S, R=Ph) with alkali-metal superhydrides M[Et3BH] (M=Li, Na].275 The methylene bridge between the two sulfur atoms in 116 is introduced by the addition of diiodomethane to... 

The unusually facile formation of a disulfonium dication from sulfide 10 is the result of stereochemical features of the eight-membered ring, which favor the formation of a transannular bond.31 According to X-ray data (see in Chapter 7.1 Table 1), the distance between the two sulfur atoms in 1,5-dithiacyclooctane 10 is smaller than the sum of their van der Waals radii (3.75 A), which results in a strong non-bonded interaction between the atoms confirmed by photoelectron spectroscopy and mass spectrometry.32 33 This interaction and the sulfur-sulfur distance can be decreased as a result of bond formation with an electronegative substituent as in sulfoxide 13 or sulfoximine 14.34,35... 

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