Nobel Gas Chemistry Derived from N≡SF3 and Related Sulfur-Nritrogen-Flourine Chemistry

Abstract

<p>The chemistry of xenon(II) has been significantly extended by the syntheses and characterizations of new examples of xenon bound to nitrogen having formal sp, sp2, and sp3 hybridization, namely the F3S≡NXeF+, F4S=NXe+, and F5SN(H)Xe+ cations. The F4S=NXe---N≡SF3+ adduct-cation is the first example of an N-Xe-N linkage to be structurally characterized by X-ray crystallography. Until recently, all of the known compounds containing xenon bound to formally sp-hybridized nitrogen have been prepared using organic nitrogen bases. The inorganic nitrogen Lewis base thiazyl trifluoride, N≡SF3, was reacted with the AsF6- salt of the Lewis-acidic XeF+ cation at -20 °C to synthesize the donor-acceptor adduct [F3S≡NXeF][AsF6]. Displacement of XeF2 from [FXeOXeFXeF][AsF6] by N≡SF3 at -60 °C led to the formation of the FXeOXe---N≡SF 3 + adduct-cation, providing a rare example of a xenon(II) oxide fluoride, which was characterized by Raman spectroscopy of natural abundance and 180-enriched salts. The solid-state rearrangement of [F3S≡NXeF][AsF6] at 22 °C yielded [F4S=NXe][AsF6], which was characterized by Raman spectroscopy. This is the first example of xenon bonded to an imido-nitrogen and the first example ofthe F4S=N- group bonded to a noble gas. The HF solvolysis of [F3S≡NXeF][AsF6] at -20 °C in aHF or BrF5 solvents generated [F5SN(H)Xe][AsF6], which, in addition to F5TeN(H)Xe+, provides the only other example of xenon bonded to an sp3 -hybridized nitrogen centre.</p> <p>Through further study of the HF solvolysis of [F3S≡NXeF][AsF6] in aHF or BrF5 solutions, it was shown that the F 4S=NXe+ cation was also formed, and may be understood in terms of an HF -catalyzed mechanism. The F 4S=NXe + cation subsequently underwent HF solvolysis, forming F4S=NH2+, XeF2, and F5SN(H)Xe+. Both cations underwent further HF solvolyses to form the F5SNH3+ cation. The F4S=NXe+ and F4S=NH2+ cations were characterized by NMR spectroscopy and single-crystal X-ray diffraction, and exhibit high barriers to rotation about their S=N double bonds. They are the first cations known to contain the F4S=N- group, significantly extending the chemistry of this ligand. The rearrangement of [F3S≡NXeF][AsF6] in N≡SF3 solution at 0 °C yielded [F4S=NXe---N≡SF3][AsF6], which was characterized by Raman spectroscopy and X-ray crystallography.</p> <p>Solvolysis of N≡SF3 m aHF is known to give the primary amme, F5SNH2, whereas solvolysis in the superacid medium AsF5/aHF results in amine protonation to give [F5SNH3][AsF6]. Until recently, definitive structural characterizations were not known for either of these fundamental species. Isolation of F5SNH2·nHF from the reaction of N≡SF3 with HF has provided a structural characterization of F5SNH2 by Raman spectroscopy. Crystal growth by sublimation of F5SNH2·nHF at -30 to -40 °C provided single crystals of F5SNH2·2[F5SNH3][HF2]·4HF, and recrystallization of [F5SNH3][AsF6] from N≡SF3 solution at -70 °C afforded crystalline [F5SNH3][AsF6]-2N≡SF3 and resulted in the structural characterization of these salts by X-ray crystallography. The redox decomposition of [F4S=NXe---N≡SF3][AsF6] in N≡SF3 at 0 °C generated Xe, cis-N2F2, and [F3S(N≡SF3)2][AsF6] which was characterized by Raman spectroscopy and single-crystal X-ray diffraction. These X-ray crystal structure determinations, in themselves, represent a significant extension of sulfur-nitrogen-fluorine chemistry, providing the first definitive characterizations of F5SNH2 and FsSNH3+, only the second known example of unadducted N≡SF3, and rare examples of main-group coordination compounds of N≡SF3.</p> <p>The F5SNH3+ cation protonated CH3CN to CH3CNH+ which is proposed to initiate the cyclotrimerization of CH3CN, generating F5SNH2 and [s-C3(CH3)3N3H][AsF6], as characterized by NMR spectroscopy at -10 °C in CH3CN solvent. Crystal growth from CH3CN at -10 to -35 °C enabled the determination of the X-ray crystal structure of [s-C3(CH3)3N3H---NCCH3][AsF6]-CH3CN. This represents the first known crystal structure of a sym-2,4,6-trialkyl-1 ,3,5-triazinium cation.</p> <p>The final objective of this research was to extend the chemistry of krypton-nitrogen bonded species. The nitrile cations RC≡NKrF+ (R = H, CF3, C2F5, n-C3F7) are currently the only known examples containing Kr-N bonds. The syntheses of the F3S≡NKrF+ and F5SN(H)Kr+ cations as their AsF6- salts were attempted by the reaction ofKrF2 with F3S≡NAsF5 and [F5SNH3][AsF6], respectively, for characterization by NMR spectroscopy in BrF5 solvent at -70 to -60 °C. No conclusive evidence for Kr-N bond formation was found, however, in each case, the fluorination and oxidation products SF6, NF3, NF4+ and AsF6- were observed instead.</p>