5,5′-bi(1,3,2,4-dithiadiazolylium)(2+) bis[hexafluoroarsenate(V)]: a general synthetic strategy to molecules and radicals containing thiazyl rings

Abstract

The salt [SNS][AsF₆] undergoes a quantitative multiple cycloaddition reaction with cyanogen to give the planar, centrosymmetric dication ([graphic omitted])₂²⁺, which has been characterised by vibrational and ¹³C NMR spectroscopy, chemical analysis and X-ray crystallography. While the reaction between cyanogen and SNS⁺ must proceed via a 1 : 1 cycloadduct, NC[graphic omitted]⁺, this was not prepared or observed. The cycloaddition of SNS⁺ to NC[graphic omitted]⁺ must therefore be kinetically preferred, contrary to arguments based on simple frontier molecular orbital (FMO) theory. By contrast, the reaction of [SNS][AsF₆] with [NC[graphic omitted]CH][AsF₆] to give [H [graphic omitted]]–[graphic omitted]][AsF₆]₂ was complete only after 10 weeks at 50 °C, in complete accord with FMO theory. These results are rationalised in terms of the influence of high-energy, in-plane molecular orbitals and the electrostatic interaction between SNS⁺ and the slightly negatively charged nitrogen atom (N) in the [graphic omitted]⁺ ring, which facilitates the second cycloaddition. The salt [([graphic omitted])₂][AsF₆]₂ potentially provides access to a new family of eight other bicyclic CNS dications, radical cations and diradicals, of which ^.[graphic omitted]–[graphic omitted]⁺, ⁺[graphic omitted]–[graphic omitted]˙ and ⁺[graphic omitted]–[graphic omitted]⁺ are reported.