5,5'-BI(1,3,2,4-DITHIADIAZOLYLIUM)(2+) BIS[HEXAFLUORO-ARSENATE(V)] - A GENERAL SYNTHETIC STRATEGY TO MOLECULES AND RADICALS CONTAINING THIAZYL RINGS

The salt [SNS][AsF6] undergoes a quantitative multiple cycloaddition reaction with cyanogen to give the planar, centrosymmetric dication (CNSNS)22+, which has been characterised by vibrational and C-13 NMR spectroscopy, chemical analysis and X-ray crystallography. While the reaction between cyanogen and SNS+ must proceed via a 1 : 1 cycloadduct, NCCNSNS+, this was not prepared or observed. The cycloaddition of SNS + to NCCNSNS+ must therefore be kinetically preferred, contrary to arguments based on simple frontier molecular orbital (FMO) theory. By contrast, the reaction of [SNS][AsF6] with [N=CCNSNSCH][AsF6]to give [HCSNSC-CNSNS][AsF6]2 was complete only after 10 weeks at 50-degrees-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 CNSNS+ ring, which facilitates the second cycloaddition. The salt [(CNSNS)2][AsF6]2 potentially provides access to a new family of eight other bicyclic CNS dications, radical cations and diradicals, of which .SNSNC-CNSNS+, +SNSNC-CNSSN. and +NSSNC-CNSNS+ are reported.