The reactivity of tungsten chlorides towards sulfur donor ligands
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AbstractThe reactions of various tungsten chlorides with sulfur donor ligands have been investigated as part of a general study of tungsten-sulfur chemistry. The reactions of the higher halides, tungsten hexachloride and pentachloride are quite complicated. They react with simple alkyl sulfides Me2S and Et2S to form (R3S)2[WC16] (R = Me, Et). The reactions involve S-dealkylation followed by reductive elimination of the respective R2S2 from the tungsten site. Alkylation of R2S by RCl, which probably occurs at the tungsten site, yields R3SC1, which reacts with the intermediate WCl4•2R2S to form the final product. The same halides show a different behavior towards the cyclic sulfide tetrahydrothiophene. The reactions are again complex, and involve the desulfurization of the tetrahydrothiophene and formation of two tungsten complexes, both containing inorganic sulfur. The reactions lead to the alkylation of tetrahydrothiophene molecule to yield the cationic species -(CH2)4Cl. From the reaction of WCl5 with tetrahydrothiophene, organic products such as ethylene, 2-chlorotetrahydrothiophene, 2,3-dihydrothiophene and propanethiol have been identified. A reaction mechanism has been postulated, involving the initial chlorination of sulfur, followed by two possible degradative pathways. Tungsten tetrachloride on the other hand reacts with these alkyl sulfides to form simple adducts of the type WCl4•2L. These complexes have been shown to be unstable with respect to displacement of the sulfide ligands by halide ions or neutral donors and therefore form excellent intermediates for W(IV) synthetic chemistry. These compounds exhibit an unexpected ability to interact with carbon monoxide and certain alkenes. Preliminary investigations have been carried out on the reactions of WC16 with the alkylthiotrimethylsilanes Me3SiSR (R = Me and Et). These reactions lead to the formation of several interesting, and sometimes polynuclear, tungsten complexes. The stoichiometry of the reaction and the nature of the solvent used seem to have a profound effect on the composition of the final product. It has been conclusively shown that alkylthiogroups tend to be oxidized by W(VI) to disulfides, which may be retained in the co-ordination sphere of the metal.
Bibliography: o. 154-161.