Reactions of organosulphur ligands on tungsten centres. Evidence for carbonium ion formation in the degradation of alkanethiolatopentachlorotungsten(VI) species

Abstract

The monothiolate derivatives of tungsten(VI) chloride, [WCl₅(SR)](R = Me, Et, cyclohexyl, Bu^t, Bu^t, CH₂,Ph, or Ph), have been found to be unstable with respect to at least two modes of degradation. Heterolytic cleavage of the carbon–sulphur bond to generate a carbonium ion, which can further abstract chloride to give WSCl₄+ RCl, is the preferred pathway if the R⁺ ion is relatively stable. The intermolecular elimination of R₂S₂ is the alternative route for degradation and is the exclusive one for R = Ph, where the carbonium ion is very unstable. The only pure [WCl₅(SR)] compounds which have been isolated are [WCl₅(SMe)] and [WCl₅(SPh)] and even these slowly decompose at room temperature over a period of a few weeks.