Fluorinated tetrathiafulvalenes with preserved electron-donor properties and segregated fluorous bilayer structures based on F•••F nonbonded interactions

The synthesis of the fluorinated 4,5-(2,2'-difluoropropylenedithio)-1,3-dithiol-2-one heterocycle with DAST allows for the Preparation of several symmetrical and unsymmetrical di- and tetrafluoro-substituted tetrathiafulvalenes with accessible oxidation potentials (0.6 < E-1/2(1) < 0.85 V vs SCE) despite the presence of the electron-withdrawing CF2 groups. The flexibility of the fluorinated seven-membered ring identified from room-temperature NMR data has been thoroughly investigated by temperature-variable H-1 and F-19 NMR experiments, allowing for the identification of two independent folding processes, whose coalescence temperatures (T-c) and activation energies (Delta G double dagger) were determined (T-c = -15 degrees C, Delta G double dagger = 50.2 kJ mol(-1) and T-c = 47 degrees C, Delta G double dagger = 51.1 kJ mol(-1)). The analysis of the X-ray crystal structures of three of those fluorinated TTF demonstrates the efficiency of the nonbonded fluorine exclusion interactions for the stabilization of layered structures with fluorous bilayers, together with S ... S van der Waals interactions and C-H ... F hydrogen bands.