Solid-State and Solution Rearrangements of F₃SNXeF⁺ Leading to the F₄SNXe⁺ Cation; Syntheses, HF Solvolyses, and Structural Characterizations of [F₄SNXe][AsF₆] and [F₄SNH₂][AsF₆]

The salt, [F4SNXe][AsF6], has been synthesized by the solid-state rearrangement of [F3SNXeF][AsF6] and by HF-catalyzed rearrangement of [F3SNXeF][AsF6] in anhydrous HF (aHF) and HF/BrF5 solvents. The F4SNXe+ cation undergoes HF solvolysis to form F4SNH2+, XeF2, and the recently reported F5SN(H)Xe+ cation. Both [F4SNXe][AsF6] and [F4SNH2][AsF6] have been characterized by 129Xe and 19F NMR spectroscopy in aHF and HF/BrF5 solvents and by single-crystal X-ray diffraction. The [F4SNXe][AsF6] salt was also characterized by Raman spectroscopy. The Xe−N bond of F4SNXe+ is among the shortest Xe−N bonds presently known (2.084(3) Å), and the cation interacts with the AsF6− anion by means of a Xe---FAs bridge in which the Xe---F distance (2.618(2) Å) is significantly less than the sum of the Xe and F van der Waals radii. Both F4SNXe+ and F4SNH2+ exhibit trigonal bipyramidal geometries about sulfur, with nitrogen in the equatorial plane and the nitrogen substituents coplanar with the axial fluorine ligands of sulfur. The F4SNH2+ cation is isoelectronic with F4SCH2 and, like F4SCH2, has a high barrier to rotation about the SN double bond and to pseudorotation of the trigonal bipyramidal F4SN− moiety. The solution and solid-state rearrangements of F3SNXeF+ to F4SNXe+ are proposed to result from attack at sulfur by fluoride ion arising from HF in solution and from the AsF6− anion in the solid state. Quantum-chemical calculations were employed to calculate the gas-phase geometries, charges, bond orders, valencies, and vibrational frequencies of F4SNXe+ and F4SNH2+. The F4SNXe+ cation provides the first example of xenon bonded to an imido-nitrogen, and together with the F4SNH2+ cation are presently the only cations known to contain the F4SN-group. Both cations are intermediates in the HF solvolysis pathways of F3SNXeF+ which lead to F5SN(H)Xe+ and F5SNH3+, and significantly extend the chemistry of the F4SN-group.