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, [F(4)S=NXe][AsF(6)], has been synthesized by the solid-state rearrangement of [F(3)S[triple bond]NXeF][AsF(6)] and by HF-catalyzed rearrangement of [F(3)S[triple bond]NXeF][AsF(6)] in anhydrous HF (aHF) and HF/BrF(5) solvents. The F(4)S=NXe(+) cation undergoes HF solvolysis to form F(4)S=NH(2)(+), XeF(2), and the recently reported F(5)SN(H)Xe(+) cation. Both [F(4)S=NXe][AsF(6)] and [F(4)S=NH(2)][AsF(6)] have been characterized by (129)Xe and (19)F NMR spectroscopy in aHF and HF/BrF(5) solvents and by single-crystal X-ray diffraction. The [F(4)S=NXe][AsF(6)] salt was also characterized by Raman spectroscopy. The Xe-N bond of F(4)S=NXe(+) is among the shortest Xe-N bonds presently known (2.084(3) A), and the cation interacts with the AsF(6)(-) anion by means of a Xe---F-As bridge in which the Xe---F distance (2.618(2) A) is significantly less than the sum of the Xe and F van der Waals radii. Both F(4)S=NXe(+) and F(4)S=NH(2)(+) 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 F(4)S=NH(2)(+) cation is isoelectronic with F(4)S=CH(2) and, like F(4)S=CH(2), has a high barrier to rotation about the S=N double bond and to pseudorotation of the trigonal bipyramidal F(4)S=N- moiety. The solution and solid-state rearrangements of F(3)S[triple bond]NXeF(+) to F(4)S=NXe(+) are proposed to result from attack at sulfur by fluoride ion arising from HF in solution and from the AsF(6)(-) anion in the solid state. Quantum-chemical calculations were employed to calculate the gas-phase geometries, charges, bond orders, valencies, and vibrational frequencies of F(4)S=NXe(+) and F(4)S=NH(2)(+). The F(4)S=NXe(+) cation provides the first example of xenon bonded to an imido-nitrogen, and together with the F(4)S=NH(2)(+) cation are presently the only cations known to contain the F(4)S=N-group. Both cations are intermediates in the HF solvolysis pathways of F(3)S[triple bond]NXeF(+) which lead to F(5)SN(H)Xe(+) and F(5)SNH(3)(+), and significantly extend the chemistry of the F(4)S=N-group.