Michael Gerken

On the XeF+/H2O System: Synthesis and Characterization of the Xenon(II) Oxide Fluoride Cation, FXeOXeFXeF+

The reported synthesis of the H(2)OF(+) cation as a product of the oxidative fluorination of H(2)O by [XeF][PnF(6)] (Pn = As, Sb) in HF solution has been reinvestigated. The system exhibits complex equilibria, producing two new Xe(II) compounds, [Xe(3)OF(3)][PnF(6)] and [H(3)O][PnF(6)] x 2 XeF(2), refuting the original claim for the synthesis of the H(2)OF(+) cation. Both compounds have been isolated and characterized by vibrational spectroscopy and single-crystal X-ray diffraction. The X-ray crystal structures of the [Xe(3)OF(3)][PnF(6)] salts contain the Z-shaped FXeOXeFXeF(+) cation, which represents the first example of an isolated Xe(II) oxide fluoride. The crystal structure of the [H(3)O][AsF(6)] x 2 XeF(2) adduct contains XeF(2) molecules that interact with the H(3)O(+) cations. The vibrational assignments for the Xe(3)OF(3)(+) cation have been made with the aid of quantum-chemical calculations and were confirmed by (18)O-enrichment, and the assignments for [H(3)O][AsF(6)] x 2 XeF(2) were confirmed by (2)D- and (18)O-enrichment. Quantum-chemical calculations have also been carried out for H(3)O(+) x nXeF(2) (n = 1-4) and have been used to interpret the X-ray crystal structure and vibrational spectra of [H(3)O][AsF(6)] x 2 XeF(2). The energy-minimized geometries and vibrational frequencies for HOF and H(2)OF(+) have been calculated, further disproving the original report of the H(2)OF(+) cation. Both FXeOH and FXeOH(2)(+) have also been computed and are viable intermediates in the proposed equilibria between XeF(+) and H(2)O that lead to the Xe(3)OF(3)(+) cation.

Syntheses and Characterization of (C2F5)3BCO and (C3F7)3BCO

The new tris(perfluoroalkyl)borane carbonyls, (C(2)F(5))(3)BCO and (C(3)F(7))(3)BCO, were prepared by means of a novel synthetic route using commercially available precursors by reacting K[(C(2)F(5))(3)BCOOH] and K[(C(3)F(7))(3)BCOOH] with concentrated sulfuric acid in the last step. The carboxylic acids, K[(C(2)F(5))(3)BCOOH] and K[(C(3)F(7))(3)BCOOH], were prepared by oxidative cleavage of the C[triple bond]C triple bonds in Cs[(C(2)F(5))(3)BC[triple bond]CPh] and Cs[(C(3)F(7))(3)BC[triple bond]CPh] in a two-step process to yield K[(C(2)F(5))(3)BCO-COPh] and K[(C(3)F(7))(3)BCO-COPh] as isolable intermediates. Crystal structures were obtained of K[(C(2)F(5))(3)BCO-COPh], K[(C(2)F(5))(3)BCOOH].H(2)O, (C(2)F(5))(3)BCO, K[(C(3)F(7))(3)BCOOH].2H(2)O, and (C(3)F(7))(3)BCO. In the crystal structures of (C(2)F(5))(3)BCO and (C(3)F(7))(3)BCO the C[triple bond]O bond lengths are 1.109(2) and 1.103(5) A, respectively, which are among the shortest observed to date. Tris(pentafluoroethyl)borane carbonyl and (C(3)F(7))(3)BCO slowly decompose at room temperature to yield CO, difluoroperfluoroalkylboranes and perfluoroalkenes. The decomposition of (C(2)F(5))(3)BCO was found to follow a first-order rate law with E(a)=107 kJ mol(-1).

Anomeric Effects in Sulfonyl Compounds: An Experimental and Computational Study of Fluorosulfonyl Azide, FSO2N3, and Trifluoromethylsulfonyl Azide, CF3SO2N3

Fluorosulfonyl azide, FSO(2)N(3), was characterized by IR (gas phase, Ar matrix), and Raman (liquid) spectroscopy. According to the matrix IR spectrum of (18)O-labeled FSO(2)N(3), its two oxygen atoms are nonequivalent. This assumption was confirmed by the X-ray crystal structure of FSO(2)N(3) at -123 degrees C, as only one conformer was observed with one of the S=O bonds in synperiplanar position to the N(3) group (phi(OS-NN) = -14.8(3) degrees) with respect to the S-N bond. The same conformation was found for trifluoromethylsulfonyl azide, CF(3)SO(2)N(3) (phi(OS-NN) = -23.74(15) degrees), in the solid state. The preference of such a synperiplanar configuration between S=O and N(3) was rationalized by a predominant anomeric interaction of n(sigma)(N) --> sigma*(S-O), as supported by the experiment and quantum chemical calculations.

Spectroscopic and structural studies of difluorophosphoryl azide F2P(O)N3, difluorophosphoryl isocyanate F2P(O)NCO, and difluorophosphoric acid anhydride, F2(O)POP(O)F2.

Difluorophosphoryl azide, F(2)P(O)N(3), was fully characterized by (19)F, (31)P, (14)N, and (15)N NMR, as well as by IR (gas, Ar-matrix), and Raman (liquid, solid) spectroscopy. For comparison the vibrational spectra of the isoelectronic difluorophosphoryl isocyanate, F(2)P(O)NCO was also studied. Both molecules were found to exist as single rotamers in the gas, liquid, and solid states. Their solid-state structures were determined by X-ray crystallography as the rotamers with the P=O bond being cis to the pseudohalide groups (with respect to the P-N bond). The F(2)P(O)N(3) molecule exhibits approximate C(s) symmetry (phi(O1P1-N1N2) = -0.7(3) degrees), while F(2)P(O)NCO is significantly distorted from C(s) symmetry (phi(O1P1-N1C1) = -18.9(5) degrees) because of intermolecular C...O contacts. The crystal structure of difluorophosphoric acid anhydride, F(2)(O)POP(O)F(2), was also determined, possessing crystallographic C(2) symmetry with the two F(2)PO groups slightly staggered by 10.66(7) degrees along the P...P vector, and a P-O-P angle of 140.89(10) degrees for the bridging oxygen atom. The experimental results are supported by quantum chemical calculations, and the conformational properties of F(2)P(O)N(3) and F(2)P(O)NCO are discussed.

Syntheses, Characterization, and Computational Study of WSF4 and WSF4-CH3CN

A new and improved synthetic route to WSF(4) was developed from the reaction of WF(6) and Sb(2)S(3) in anhydrous HF. Tungsten sulfide tetrafluoride was characterized by Raman and (19)F NMR spectroscopy for the first time in HF solvent. Both studies provided evidence for its monomeric form in HF solution. In the solid state, WSF(4) was also characterized by Raman and infrared spectroscopy. The WSF(4) x CH(3)CN adduct was prepared from WSF(4) and CH(3)CN in anhydrous HF solvent and by the direct combination of WSF(4) with excess CH(3)CN, and was characterized by Raman and infrared spectroscopy in the solid state and (19)F NMR spectroscopy in CH(3)CN solution. The crystal structure of WSF(4) x CH(3)CN was obtained and showed that CH(3)CN coordinates to W in an end-on fashion and trans to the W-S bond. Quantum-chemical calculations using B3LYP and PBE1PBE methods were used to calculate the gas-phase geometries and vibrational frequencies of WSF(4) and WSF(4) x CH(3)CN.

Fluoride-Ion Acceptor Properties of WSF4: Synthesis, Characterization, and Computational Study of the WSF5– and W2S2F9– Anions and 19F NMR Spectroscopic Characterization of the W2OSF9– Anion

The new [N(CH(3))(4)][WSF(5)] salt was synthesized by two preparative methods: (a) by reaction of WSF(4) with [N(CH(3))(4)][F] in CH(3)CN and (b) directly from WF(6) using the new sulfide-transfer reagent [N(CH(3))(4)][SSi(CH(3))(3)]. The [N(CH(3))(4)][WSF(5)] salt was characterized by Raman, IR, and (19)F NMR spectroscopy and [N(CH(3))(4)][WSF(5)]·CH(3)CN by X-ray crystallography. The reaction of WSF(4) with half an aliquot of [N(CH(3))(4)][F] yielded [N(CH(3))(4)][W(2)S(2)F(9)], which was characterized by Raman and (19)F NMR spectroscopy and by X-ray crystallography. The WSF(5)(-) and W(2)S(2)F(9)(-) anions were studied by density functional theory calculations. The novel [W(2)OSF(9)](-) anion was observed by (19)F NMR spectroscopy in a CH(3)CN solution of WOF(4) and WSF(5)(-), as well as CH(3)CN solutions of WSF(4) and WOF(5)(-).

Synthesis, characterization, and computational study of MoSF4.

Molybdenum sulfide tetrafluoride was synthesized from MoF(6) and S(Si(CH(3))(3))(2) in CFCl(3) at low temperature and was fully characterized by Raman, infrared, and (19)F NMR spectroscopy and by X-ray crystallography. The crystal structure revealed that MoSF(4) forms infinite fluorine-bridged chains. Quantum-chemical calculations using B3LYP and PBE1PBE methods were used to calculate the gas-phase geometry and vibrational frequencies of monomeric MoSF(4) and (MoSF(4))(3)F(-). The vibrational frequencies of (MoSF(4))(3)F(-) have been used in the assignment of the vibrational spectra of solid MoSF(4). Natural bond order analyses were carried out for monomeric MoSF(4) and, for comparison, for WSF(4).

Syntheses and Multi-NMR Study of fac- and mer-OsO3F2(NCCH3) and the X-ray Crystal Structure (n = 2) and Raman Spectrum (n = 0) of fac-OsO3F2(NCCH3)·nCH3CN

Dissolution of the infinite chain polymer, (OsO(3)F(2))(infinity), in CH(3)CN solvent at -40 degrees C followed by solvent removal under vacuum at -40 degrees C yielded fac-OsO(3)F(2)(NCCH(3)).nCH(3)CN (n >/= 2). Continued pumping at -40 degrees C with removal of uncoordinated CH(3)CN yielded fac-OsO(3)F(2)(NCCH(3)). Both fac-OsO(3)F(2)(NCCH(3)).nCH(3)CN and fac-OsO(3)F(2)(NCCH(3)) are yellow-brown solids and were characterized by low-temperature (-150 degrees C) Raman spectroscopy. The crystal structure (-173 degrees C) of fac-OsO(3)F(2)(NCCH(3)).2CH(3)CN consists of two co-crystallized CH(3)CN molecules and a pseudo-octahedral OsO(3)F(2).NCCH(3) molecule in which three oxygen atoms are in a facial arrangement and CH(3)CN is coordinated trans to an oxygen atom in an end-on fashion. The Os---N bond length (2.205(3) A) is among the shortest M---N adduct bonds observed for a d(0) transition metal oxide fluoride. The (19)F NMR spectrum of (OsO(3)F(2))(infinity) in CH(3)CN solvent (-40 degrees C) is a singlet (-99.6 ppm) corresponding to fac-OsO(3)F(2)(NCCH(3)). The (1)H, (15)N, (13)C, and (19)F NMR spectra of (15)N-enriched OsO(3)F(2)(NCCH(3)) were recorded in SO(2)ClF solvent (-84 degrees C). Nitrogen-15 enrichment resulted in splitting of the (19)F resonance of fac-OsO(3)F(2)((15)NCCH(3)) into a doublet ((2)J((15)N-(19)F), 21 Hz). In addition, a doublet of doublets ((2)J((19)F(ax)-(19)F(eq)), 134 Hz; (2)J((15)N-(19)F(eq)), 18 Hz) and a doublet ((2)J((19)F(ax)-(19)F(eq)), 134 Hz) were observed in the (19)F NMR spectrum that have been assigned to mer-OsO(3)F(2)((15)NCCH(3)); however, coupling of (15)N to the axial fluorine-on-osmium environment could not be resolved. The nitrogen atom of CH(3)CN is coordinated trans to a fluorine ligand in the mer-isomer. Quantum-chemical calculations at the SVWN and B3LYP levels of theory were used to calculate the energy-minimized gas-phase geometries, vibrational frequencies of fac- and mer-OsO(3)F(2)(NCCH(3)) and of CH(3)CN. The relative stabilities of the mer- and fac-isomers have been determined and are in accordance with the solution NMR assignments.

Improved Synthesis of CsN3Dedicated to Professor Joachim Strähle on the Occasion of his 65th Birthday

Abstract : Cesium azide can conveniently be prepared from anhydrous CsF and (CH3)3SiN3 in SO2 solvent in high purity and yield. In this reaction, the initially generated SO2F(-) anion is converted in SO2 solvent to solvated azide, (SO2)(sub n)N3(-), which is labile and releases S02 under dynamic vacuum yielding pure CsN3.

Preparation, structures and preliminary host–guest studies of fluorinated syn-bis-quinoxaline molecular tweezers

Summary A series of polycyclic frameworks with fluorinated syn-facial quinoxaline sidewalls has been prepared as potential molecular tweezers for electron-rich guest compounds. Our synthetic route to the cyclooctadiene-derived scaffolds 16a–d takes advantage of the facile isolation of a novel spirocyclic precursor 9b with the crucial syn-orientation of its two alkene moieties. The crystal structure of 16c displays two features typical of a molecular tweezer: inclusion of a solvent molecule in the molecular cleft and self-association of the self-complementary scaffolds. Furthermore, host–guest NMR studies of compound 16c in solution show chemical exchange between the unbound and bound electron-rich guest, N,N,N′,N′-tetramethyl-p-phenylenediamine.