Synthetic and structural studies of some thiazene cations

Abstract

S(_5)N(_5)Cl has been produced by a new route and is much more stable than previously reported owing to greater purity. Its chemical reduction to (SN) and reactions with SO and BF were studied. An X-ray structure analysis (R.W.H. Small) revealed secondary cation-anion interactions; the resulting strain in the cation ring could be detected both by bond angle-bond length correlations and MNDO calculations. Electro-reduction of S(_5)N(_5)Cl in liquid SO(_2) produced finely powdered (SN)(_x) which could be used to form good quality vapour deposited films. Cyclic voltammograms in liquid SO(_2) (obtained after spending much time developing an improved procedure) indicated possible solvent participation in the reduction process and so electrocystallization of (SN) by electro-reduction of S(_5)N(_5)BF(_4) (prepared from S(_5)N(_5)Cl) in acetonitrile was investigated. Cyclic voltammetric evidence was used to propose a mechanism of reduction and bulk electrolyis experiments using bright platinum and (SN)(_x) film cathodes showed the influence of the cathode on the nature of the (SN)(_x) deposit. Small quantities of NSF were produced in ca. 80% yield by the solid state reaction of SN(^+)AsF(_6)ֿ and excess CsF; an unoptimised larger scale preparation indicated the usefulness of this route. Various gas phase reactions of NSF were studied using infrared spectroscopy. Attempts to prepare the simple fluoride S(_4)N(_3)F by metathesis from S(_4)N(_3)BF(_4) and CsF were only partially successful owing to reaction with solvent. Reaction of S(_3)N(_2)(^2+)(AsF(_6)ֿ)(_2) with CsF (1:1) produced S(_3)N(_2)F(^+)AsFֿ but further conversion to S(_3)N(_2)F(^2) was not possible owing to reaction with solvent. Attempted crystal growth experiments indicated that the S(_3)N(_2)(^2+) ion existed in an equilibrium mixture containing S(_2)N(^+) and SN(^+) ; this hypothesis was confirmed by its reactions with sulphur and hexafluorobut-2-yne. These solution equilibria were exploited by designing more convenient preparations of S(_3)N(_2)(^2+) (AsF(_6)ֿ)(_2) and S(_2)N(^+)SbCl(_6)ֿ . The chemical reactions of SN(^+)AsF(_6)ֿ were studied with a view to the preparation of new compounds. Although no such species were isolated, the results usefully indicated future experiments and the oxidising properties of the SN(^+) cation.