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12 Ralf Steudel · Bodo Eckert The oily product of this reaction still contains some S8 besides S8Cl2 as well as other dichlorosulfanes from side-reactions. However, this product re- acts with titanocene pentasulfide at 20 C to a mixture of sulfur rings from which S13 was isolated as yellow crystals in 5% yield [36]: Cp2TiS5þS8Cl2 ! S13þCp2TiCl2 ð23Þ As other sulfur homocycles, S13 shows a very characteristic Raman spec- trum. In the solid state the molecules are of approximate C2 symmetry [38]. 2.1.1.10 Preparation of S14 S14 was first synthesized in 1998 by a novel type of ligand transfer reaction using the zinc hexasulfido complex (TMEDA)ZnS6 [45] with TME- DA=tetramethylethenediamine: ðTMEDAÞZnS6þS8Cl2 ! S14þðTMEDAÞZnCl2 ð24Þ The reaction takes place in CS2 at 0 C and S14 (m.p. 117 C) was isolated as rod-shaped intense-yellow crystals in 11% yield [46]. The S8Cl2 reagent is prepared by careful chlorination of S8; see the “Preparation of S13” above; Eq. (22). 2.1.1.11 Preparation of S15 cyclo-Pentadecasulfur is one of the few sulfur allotropes which have not been obtained yet as single crystals. Therefore the structure is unknown. S15 is formed in the reaction of titanocene pentasulfide with sulfurylchloride in CS2 which is also used to prepare S10 (see above) and S20 (see below); the three products are separated by repeated crystallization and precipitation [47]: 3Cp2TiS5þ3SO2Cl2 ! S15þ3SO2þ3Cp2TiCl2 ð25Þ S15 was obtained in 2% yield as a lemon-yellow powder (from toluene) which has a characteristic Raman spectrum. The formation of S15 probably proceeds via several intermediates as shown in Scheme 1 [14, 47]. The first step is a ring-opening reaction of the metallacycle. The Cp2Ti(Cl)S5SO2Cl intermediate is likely to loose SO2 result- ing in Cp2Ti(Cl)S5Cl which by reaction with another molecule of this type may form S10 or which may react with SO2Cl2 to S5Cl2 which in turn would react with Cp2TiS5 to S10. In the latter reaction Cp2Ti(Cl)S10Cl must be an in- termediate which will react with another molecule of this type to S20 or with S5Cl2 to S15. Several alternative pathways exist as shown in Scheme 1; cyclo- pentasulfur S5 has been excluded as an intermediate [14].PDF Image | Topics in Current Chemistry
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