Polysulfide complex synthesis

NQR, 22 216 olefin complexes of, 4 85 in organogermanium compounds, 27 141,143 oxyfluoride, properties of, 11 29 pentacarbonyl dimets of sulfur oxydifluoride imide, 19 203-205 pentafluoride, structure, 27 102 peroxides, 6 325-326 phthalocyanine, 7 54 physical properties of, 11 18 polysulfide complexes, 31 100, 102 envelope conformation, 31 115 synthesis, 31 103-104 [Pt[15]aneS5) f, 35 75, 77 reaction with fluorinated peroxides, 16 120 salts, lattice energy and thermochemistry, 22 52-56... 

Reactions of metal halides with polysulfide dianions are useful methods for the synthesis of polysulfido complexes of main group elements and transition metals. In most of these reactions, similarly to other methods, the chain lengths and coordination types of the polysulfide ligands depend on the other ligands coordinated to the metal, on the ratio between the metal and sulfur, on the reaction temperature, and other parameters. 

Scheme 20 Synthesis of group 13 polysulfido complexes by the reaction of the corresponding metal halides with polysulfide dianions...

The technically most important polysulfide is poly thiophenylene or poly(p-phe-nylene sulfide), PPS. It is obtained by reacting sodium sulfide and p-dichlo-robenzene in a polar solvent, for example, l-methyl-2-pyrrolidone at about 280 °C under pressure. The mechanism of the reaction is very complex and cannot be described by a simple aromatic substitution. This synthesis requires special autoclaves and is therefore not suitable for a laboratory course (for an experimental procedure see Table 2.3). 

Preparation and Structure. Many minerals exist as sulfides, and these have been outlined in Section 2.1.1. The alkali and alkali earth metals form simple ionic sulfides that are water soluble. Many sulfides, polysulfides, and their complexes are known and there have been a number of reviews illustrating their structures, catalytic uses, and biological significance. Excellent reviews illustrate the complexity of this area for the chemistry of Cr, Mo, and W sulfides. Many of the sulfides exist in different phases depending upon the conditions used in their synthesis and they may be interconverted by anneaUng, etc. M0S2 is used as a high-temperature lubricant. 

A great variety of binary Mo-S complex anions is formed and can be isolated in reactions of the tetrathiomolybdate anion [MoS ] " with various suinde and polysulfide anions. The nature of the anionic products that can be isolated from these reactions depends on (a) the amount of excess sulfur used (and the types of ligands present in the reaction mixtures), (b) the type of counterion used in the isolation of the complex anions, and (c) the type of solvent employed in the synthetic procedure. In a recent article, we described a scheme that interrelates the various [Mo2(S),(S2)6-,] anions. In this scheme (Fig. 1), any of the six homologs can hypothetically be obtained from any other by either the addition of sulfur, or the abstraction of sulfur by triphenylphosphine. Experimentally, the correctness of this scheme has been verified by the successful synthesis of most of the [Mo2(S) (S2)6 ] complexes, or of their internal redox isomers. In the [Mo2(S), (82)6 series, the homologs with n = 4, 5, and 6 have been characterized structurally. Those with n = 2 and 3 have been characterized structurally as the internal-redox isomers, [(S4)Mo(S)(//-S)2(S)Mo S2)] (ref. 3) and... 

Synthesis ofMo-Dithiolene Complexes in Reactions of Alkynes and Metal Polysulfides... 

Pendent sulfur groups are the supposed precursors prior to an interchain crosslink formation. The synthesis of model pendent groups containing benzothiazolyl functions [132,133] has enabled their thermal behavior to be studied directly. Again, the experiments evidenced that the zinc complexes play an important active role in the desulfuration reaction of the pendent polysulfidic groups. 

The concentration of zinc accelerator-thiolate complexes in the rubber is not the only factor determining the balance of the two reactions in NR. Both the rate of desulfuration of polysulfide crosslinks and the rate of their thermal decomposition depend upon the positions of attachment of the sulfur chains to the backbone rubber chains and the detailed structure of the hydrocarbon at the ends of the crosslinks. In the course of normal accelerated vulcanization there are three different positions of attack on the polyisoprene backbone two of these are methylene groups in the main chain (labelled d and a in 3), and the third is the side chain methyl group (labelled b in 3). Direct analysis of the distribution of the sites of attack cannot yet be made on actual rubber vulcanizates, and information has had to be obtained solely by sulfuration of the model alkene 2-methyl-2-pentene and, more recently, 2,6-dimethyl-2,6-octadiene. The former (4) models the a-methylic site but only one of the two a-methylenic sites of polyisoprene the latter (5) models all three sites, but at the present time these are not all supported by the synthesis of relevant sulfides. Because allylic rearrangements are common in subsequent reactions of the sulfurated rubber, sulfur substituents appear not only on allylic carbon atoms but on isoallylic carbon atoms. Thus, from 2-methyl-2-pentene, the groups shown in Scheme 2 are formed. 

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