Fluorinated Tetrathiafulvalenes with Preserved Electron-Donor Properties and Segregated Fluorous Bilayer Structures Based on F···F Nonbonded Interactions
Résumé
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 < E11/2 < 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 1H and 19F NMR experiments, allowing for the identification of two independent folding processes, whose coalescence temperatures (Tc) and activation energies (G) were determined (Tc = -15 C, G = 50.2 kJ mol-1 and Tc = 47 C, G = 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 bonds.