Synthesis and Crystal Structure of [Fe(C5H4)2S3O]: The First Organometallic Trisulfane Oxide

Abstract

1,1′-Dithia-substituted ferrocenes1 have recently received much attention, either as open-chain derivatives2 or as ferrocenophanes.3 Of the latter, the 1,2,3-trithia[3]ferrocenophane 2 has been studied most extensively, but even the [1]ferrocenophane with a single sulfur atom as a bridge has been prepared and structurally characterized.4 Ring-opening polymerization of such compounds yields interesting organometallic polymers.5 Organic trisulfane-2-oxides of type R-S-S(O)-S-R are known with various bulky organic substituents,6 while the related sulfur oxyacid H-S-S(O)-S-H and derivatives with small alkyl groups are unstable and therefore unknown as pure materials. However, the structures of (HS)2SO and (MeS)2SO have been elucidated by ab initio MO calculations.6a,7 The unsubstituted trisulfane2-oxide is believed to play a major role as an intermediate in the industrial Claus reaction between H2S and SO2 for the production of elemental sulfur.7 The only metal-containing polysulfane oxides with more than two neighboring sulfur atoms are the pentasulfane-3-oxide of titanocene [(C5H5)2TiS5O] and the platinum compound [(Ph3P)2PtS3O]; only the latter has been structurally investigated. We have now prepared the first ferrocenylene trisulfane oxide by reaction of the 1,1′-dithiol of ferrocene with thionyl chloride at 20 °C in carbon disulfide in the presence of pyridine. The dark red crystals of the 1,1′(1,2,3-trithia[3])ferrocenophane-2-oxide 1 are air-stable at 20 °C and are very well soluble in benzene, CH2Cl2, CHCl3, CS2, and THF. On melting (mp 121 °C) the sample slowly decomposes to an insoluble product without SO2 evolution, in sharp contrast to the behavior of other organic trisulfane-2-oxides. However, the EI mass spectrum exhibits the molecular ion with high intensity at a sample temperature of 105 °C. Another characteristic feature is the strong IR absorption of the solid at 1098 cm-1 originating from the SO stretching mode. The thermal stability of 1 together with the rigidity of the S3O group opens the possibility for derivatization reactions at the SO bond. For example, reduction of 1 with aminoiminomethane sulfinic acid yielded the trisulfane 2 in 86% yield: