Preparation, Characterization, and Physical Properties of Bis(imidazole)sulfur Difluoride and Bis(4-phenylimidazole)sulfur Difluoride. New Compositions with Unexpected Thermal Stability

Two new bis(imidazole)sulfur difluoride compositions, (imid)(2)SF(2) (2) and (4-Ph-imid)(2)SF(2) (4), have been prepared in high yields from the reactions involving the corresponding TMS precursors and excess SF(4) in anhydrous solvent. Mechanisms are proposed to account for the formation of 2 and 4 preferentially over the corresponding SF(3) derivatives or other isomers containing the SF(2) moiety. These new compositions are stable solids which melt at high temperatures and have been characterized in solution by (1)H, (13)C, and (19)F NMR spectroscopy and in the solid state by MS (EI), elemental analysis, and single-crystal X-ray diffraction. The crystal structures of 2 and 4 are each based on a pseudo-trigonal-bipyramidal arrangement of two fluorines and two imidazole groups around the central sulfur, with the fluorines occupying axial positions and the imidazole groups in equatorial positions as predicted for these AX(4)E compounds by the VSEPR model. Thermal decomposition properties of 2 and 4 have been studied using the Radex-Solo thermal hazards screening system. Compounds 2 and 4 have decomposition onset temperatures similar to those of several common R(2)NSF(3) compounds; however, the thermal decomposition of 2 and 4 occurs at much slower rates than that of the R(2)NSF(3) compounds and without the rapid release of gaseous byproducts, which is generally characteristic of explosive decomposition events. Therefore, by comparison, compounds 2 and 4 are inherently safer to handle and use.