Scientific paper
C6F5XeY Molecules (Y = F and Cl): New Synthetic Approaches. First Structural Proof of the Organoxenon
Halide Molecule C6F5XeF
Vural Bilir1 and Hermann-Josef Frohn2*
1	Universität Duisburg-Essen, Anorganische Chemie, Lotharstr. 1, 47048 Duisburg
2	Universität Duisburg-Essen, Anorganische Chemie, Lotharstr. 1, 47048 Duisburg
* Corresponding author: E-mail: h-j.frohn@uni-due.de Received: 28-06-2012 Dedicated to Professor Boris Zemva
Abstract
The arylxenonium salt [C6F5Xe][BF4] reacts with different sources of nucleophiles, Y (naked fluoride, [N(CH3)4]F, the silanes, (CH3)3SiCl and (C2H5)3SiH, and the cadmiumorganyl, Cd(C6F5)2), in coordinating solvents (C2H5CN, CH3CN, CD3CN). While the products C6F5XeF, C6F5XeCl, and (C6F5)2Xe are well defined molecules, in reactions with (C2H5)3SiH only decomposition products presumably derived from <C6F5XeH> and <C6F5XeC2H5> are found. Molecular parameters and intermolecular contacts in the single crystal X-ray structure of C6F5XeF are discussed.
Keywords: Arylxenonium tetrafluoroborate, organylxenon molecules, reactions with nucleophiles in coordinating solvents, pentafluorophenylxenon fluoride crystal structure
1. Introduction
The chemistry of organylxenonium salts [RXe][Z] is comprehensively treated in several reviews.1 The majority of available information concerns the salt [C6F5Xe][BF4] with an electrophilic cation and a moderately to weakly coordinating anion. The most frequently used procedure to obtain ArXeY started from ArXeF (Ar = C6F5, C6HnF5-n) which were reacted with alkylsilanes, Alk3SiY, (Y = Cl,2'3 Br, NCO2, CN,2'3'4'5 CF3C(O)O, CF3S(O)2O,2 C6F5,2'3'4'5 2,6-C6H3F22) in the weakly coordinating solvent CH2Cl2. The strong Si-F bond of the co-product was the driving force (Eq 1).
CH2Cl2/-78 °C
ArXeF + AlkSiY
-> ArXeY + AlkSiF
(1)
Thus, ArXeF can be regarded as a key substrate in the syntheses of ArXeY molecules. It was prepared by two routes: (a) the F- catalyzed F/Ar substitution with Me3SiAr in XeF26 (the product contained an admixture of (C6F5)2Xe) and (b) in the very slow surface reaction of [ArXe]+ salts with [N(CH3)4]F in CH2Cl2.4
In the current work we offer a useful modification of route (b) and a fast homogeneous synthesis of C6F5XeF. Furthermore, we investigate the direct reaction of [C6F5Xe][BF4] with Alk3SiY (Y = Cl, H) to C6F5XeY molecules. In case of Y = Cl, we discuss the results which differ from that obtained previously with [C6F5Xe][AsF6].7 Furthermore, it will be shown that the electrophilic cation of [C6F5Xe][BF4] can directly interact with the carbon nu-cleophile of the organometallic compound, Cd(C6F5)2.
2. Results and Discussion
2. 1. Synthesis of C6F5XeF
In 2000, we reported the surface reaction of insoluble [C6F5Xe][AsF6] with equimolar amounts of dissolved [N(CH3)4]F in CH2Cl2 at -78 °C.4 That reaction required more than 2 days for complete conversion and was accompanied by the partial decomposition of the product, C6F5XeF. A modified reaction using 1.5 equiv of [N(CH3)4]F in CH2Cl2 is described in the present work. The excess of [N(CH3)4]F can act as a HF scavenger. Finally, n-pentane was added to reduce the density of the
solvent and to precipitate all [N(CH3)4]+ salts. After distilling off the solvent mixture from C6F5XeF, the latter remained as a white powder (66% yield) which was dissolved in CH2Cl2 at -50 °C. Crystals suitable for single crystal X-ray structural determination having a plate morphology with right angles were obtained by a very slow partial removal of the solvent under vacuum.
An alternative fast synthesis of C6F5XeF started from a cold (-78 °C) C2H5CN solution of [C6F5Xe][BF4] which was added to a cold (-78 °C) CH2Cl2 solution of [N(CH3)4]F. Monitoring the reaction after 20 min revealed the total conversion of the xenonium salt with the formation of C6F5XeF (95%), C6F5H (5%), and traces of C6F6 (Eq 2).
[CfiF3Xe][RF4]/C2H3CN + [N(CH3)4]F/CH2Cl2
(2)
2. 2. The Molecular Structure of C6F5XeF and Important Intermolecular Contacts in the Solid State Structure
The compound, C6F5XeF crystallizes in the mono-clinic space group P2/n (a = 12.2038(3) Á, b = 9.9596(3) Á, c = 13.0904(4) Á, p = 101.140(1)°) with eight molecules in the unit cell and two molecules in the asymmetric unit. The crystallographic data are given in Table 1. The molecular parameters of both molecules are similar and mainly differentiated by their intermolecular contacts. The C-Xe-F arrangement of C6F5XeF is linear with a C1-Xe1-F1 angle in molecule 1 of 178.67(6)° (the analogous angle in molecule 2: 179.46(7)°). The Xe-C distance in molecule 1 is 2.132(2) Á (2.128(2) Á in molecule 2) and is longer than in the xenonium cations of [C6F5Xe][AsF6] (2.079(5) and 2.082(6) Á),8 [C^Xe][B(CN)4] (2.081(3) Á),9 [C^XeHB^^] (2.104(5) Á),9 in the acetonitrile adducts of the xenonium cation in [C6F5Xe ■ NCCH3] [B(CF3)4] (2.100(6) Á) and [C6F5Xe ■ NCCH3][B(C6F5)4] (2.100(10) Á),9 and only sligh5ly longer than in C6F5XeOC(O)C6F5 (2.122(4) Á).10 On the other hand, the Xe-F distance in C,F-XeF
65
(2.172(1) Á (molecule 1) and 2.182(1) Á (molecule 2)) is significantly shorter than the Xe-F cation-F contacts (F from the counterion) in [C6F5Xe][AsF6] (2.714(5) and 2.672(5) Á),8 [C6F5Xe][B(CF3)4] (2.913(4) Á).9 Thus, bonding in the C-Xe-F fragment is best described as an asymmetrical hypervalent bond. The C-Xe distance is shorter than in (C6F5)2Xe (2.394(9) and 2.35(1) Á)11 and the Xe-F distance longer than in XeF2 (2.00(1) Á.12 In addition to arguments based on experimental distances, the asymmetry is also supported by the partial charges on the C6F5 group and F ("Natural Population Analysis" charges (DFT method SVWN, basis set SDD): C6F5 -0.33 e-, F
-0.64 e-, Xe 0.97 e-; (RHF method, basis set LANL2DZ): C6F5 -0.37 e-, F -0.77 e-, Xe 1.13 e-. The calculated gas phase structure depends on the applied method and basis set. Using the DFT method SVWN and the basis set SDD the C-Xe distance is overestimated (2.18 Á) and the Xe-F distance underestimated (2.08 Á) when compared with the solid state experimental parameters. With the RHF method and the basis set LANL2DZ, the C-Xe distance was 2.20 Á (overestimated) and Xe-F distance was 2.13 Á (underestimated). In comparison with the symmetrical parent molecules (values from the [DFT method, SVWN and basis set SDD] and the {RHF method and basis set LANL2DZ} XeF2 [Xe-F 2.03 Á, Xe 1.10 e-, F -0.55 e], {Xe-F 2.03 Á, Xe 1.33 e-, F -0.67 e-} and (C6F5)2Xe [Xe-C 2.30 Á, Xe 0.81 e-, C6F5 -0.40 e-], {Xe-C 2.34 Á, Xe 0.98 e-, C6F5 -0.49 e-}, the molecule C6F5XeF can also be described as a close ion pair. The distribution of partial charges allows also to interpret the observed intermolecular interactions of C6F5XeF in the solid state: Xe-bonded fluorine and XeII interact in a donor acceptor manner. Two symmetry equivalent molecules 2 are arranged head to tail in a side-on mode and form a Xe2-F11-Xe2'-F11' parallelogram (Figure 1). In addition, each Xe2 of the parallelogram acts as acceptor of F1 and each F11 of the parallelogram as donor to Xe1. It is worth stressing, that the donor property of F11, which donates to two XeII, namely Xe1 and Xe2', leads to one shorter contact than in the single contact of F1''' to Xe2.
2. 3. Synthesis of C6F5XeCl
In 1999, we investigated the conversion of [C6F5Xe][AsF6] into C6F5XeCl.7 We were only successful when insoluble [C6F5Xe][AsF6] was reacted with soluble
Figure 1. The molecular structure of C^XeF (fluorine atoms of the C6F5 group are not depicted) showing the most significant intermolecular contacts. The thermal ellipsoids are drawn at the 50% probability level.
Selected distances / Â and angles / Xe1-C1 2.132(2), Xe1-F1 2.172(1), C1-Xe1-F1 178.67(6), Xe2-C11 2.128(2), Xe2-F11 2.182(1), C11-Xe2-F11 179.46(7).
Significant intermolecular contacts / Â and angles / °: Xe1-F11 3.036(1), Xe2-F1'" 3.261(1), Xe2-F11' 3.288(1), F11-Xe2-F11' 78.65(4), Xe2-F11-Xe2' 101.35(5), Xe2-F11-Xe1 146.97(6), Xe2'-F11-Xe1 90.95(4), F1-Xe1-F11 108.06(4), C1-Xe1-F11 72.38(6)
Table l. Crystallographic and refinement data for C6F5XeF
Compound Empirical formula Crystal size Crystal system Space group Unit cell dimensions
Volume
Z (molecules/unit cell)
Density (calculated)
Temperature
Radiation
F(000)
Theta range for data collection Final R indices
C6F5XeF
C6F6Xe
0.32 mm x 0.26 mm x 0.16 mm
Monoclinic
P21/n
a = 12.2038(3) Â b = 9.9596(3) Â c = 13.0904(4) Â ß= 101.140(1)o 1561.09(8)Â3 8
2.701 g cm-3
173 ± 2 K
Mo Ka (X = 0,71073 Â) 1152
2.09-30.46 o
R1 = 0.0180, wR2 = 0.0431
4-ClC5H4N ■ HCl in weakly coordinating CH2Cl2 at -78 °C. When CH3CN solutions of [C6F5Xe][AsF6] and [N(CH3)4]Cl were combined at < -20 °C, no reaction proceeded and at 0 °C, C6F5Cl was formed along with Xe0. When (CH3)3SiCl was used as a source of chlorine in CH2Cl2 at -78 °C, 3 equiv of the silane were required for the total conversion of [C6F5Xe][AsF6]. Instead of C6F5XeCl, the salt with the chlorine bridged bis(pentaflu-orophenylxenonium) cation, [(C6F5Xe)2Cl][AsF6], was isolated and established from its crystal structure.7 Under these conditions, the [AsF6]- anion also underwent F/Cl substitution followed by the elimination of chlorine from the proposed intermediate, AsCl5 (Eq 3).
(3)
[(C6FiXe)2Cl][AsFfi] + 6 (CH3)3SiF + AsCI3 + Cl2
In contrast to Eq 3, the presence of CH3CN avoided F/Cl substitution on AsF5 (Eq 4).
(4)
In the present work, we report a different mode of reactivity for [C6F5Xe][BF4] with (CH3)3SiCl. In CH2Cl2 at -40 °C (heterogeneous reaction), only 8% conversion into soluble C6F5XeCl occurred within 3 h (Eq 5), whereas in the homogenous reaction in CH3CN at -40 °C the total conversion took place in less than 20 min (Eq 6). In C2H5CN solution at -78 °C, only a slow reaction was ob-
[C6FsXe][BF4]
8% conversion/3 Ii
(5)
C„F5XeCl + BFj + (CH3)3SiF
GHjCN/-40 "C
[C6F5Xe][BF4] + (CH3)3SiCl ->
100% convcrsion/<20 min
CfiFsXeCl + BF3NCCH3 + (CH3)3SiF
(6)
served, but at -55 °C the conversion proceeded in less than 5 min.
Eqs 5 and 6 show that the [BF4]- anion was involved in the reaction with (CH3)3SiCl and that another Xe11 product resulted that differs from that formed in the presence of the [AsF6]- anion. To elucidate the interaction of the [BF4]- anion with (CH3)3SiCl, the reaction of [N(«-C4H9)4][BF4] with (CH3)3SiCl was investigated at 20 °C in CH3CN and only 17% conversion of [BF4]- to [BClF3]- within 1.5 h was found. That result underlines the participation of the electrophilic [C6F5Xe]+ cation in F/Cl-substitution (Eq 6) in the presence of CH3CN. It was reported that the [BF4]- anion was also involved in the very slow reaction (4 d) of [2,6-C6H3F2Xe][BF4] with (CH3)3SiOSO2CF3 in a CH3CN/CH2Cl2 mixture at -20 °C.13 A forthcoming paper will exemplify the general character of the participation of electrophilic cations of tetrafluoroborate salts in nucleophilic substitution reactions.
2. 4. The Reaction of [C6F5Xe][BF4] with (C2H5)3SiH in CD3CN and C2H5CN Solutions
The reaction of [C6F5Xe][BF4] with (C2H5)3SiH in CD3CN at -40 °C proceeded almost quantitatively within 20 min. The [BF4]- anion was converted into BF3 ■ NCCD3. C6F5H resulted as the main product (61%) besides traces of C6F5D (2%) only. Over and above that, five C6F5 compounds were formed: (C6F5)2Xe (5%), (C6F5)2 (1%), C6F5CH2CH3 (5%), C6F5Si(C2H5)3 (2%), and [C6F5C(CD3) = N(H,D)2]+ (19%) The above products and their molar ratio allow some reasonable conclusions. (a) C6F5H can result from the short living (not NMR spectro-scopically proven) compound C6F5XeH by Xe0 elimination or, as the in cage product of C6F/ and H radical combination, after oxidation of H- by [C6F5Xe]+ and subsequent Xe0 elimination from the [C6F5XeT radical. Abstraction of deuterium by C6F5^ (out of cage) proceeded only by a minor route. (b) (C6F5)2Xe, (C6F5)2, and C6F5C2H5 may result from the intermediate <C6F5XeC2H5>: (C6F5)2Xe as one product of the equili-
bration, C6F5C2H5 by the direct elimination of Xe0 from I5
C6F5XeC2H5 and (C6F5)2 by Xe0 elimination from
(C6F5)2Xe. The latter route is described in the literature.4 (c) The formation of large amounts of [C6F5C(CD3)= N(H,D)2]+ presumably results from the addition of C6F^ radicals to the C-N triple bond of the solvent, followed by H or D scavenging and (H,D)+ addition to the imino nitrogen atom). The high-frequently p-fluorine resonance (-141.5 ppm) is a strong indicator of the cationic nature. The 19F NMR shift values are in good agreement with that of the only related structure in the literature [C6F5C(CH3) = N(C2H5)2]Br.14 A Xe-C structure can be rejected despite the high-frequently p-F resonance, which is typical for Xe-C6F5 cations, because neither a 129Xe resonance nor 129Xe satellites in 19F signals were found nor did the compound decompose after heating to 20 °C for 1 h.
When the reaction of [C6F5Xe][BF4] with (C2H5)3SiH was performed in C2H5CN solution at -90 °C, a similar mixture of products resulted, but at a slower rate. The main difference derives from the C6F5 radical interaction with the solvent, namely the formation of the [C6F5C(C2H5)=NH2]+ cation.
Based on RHF/LANL2DZ calculations the assumed intermediate, C6F5XeH, should be described in the gas phase as H-Xe-C6F5 with a very weak Xe-C bond (2.54 A) and a Xe-H bond of 1.74 A and "Natural Population Analysis" charges of 0.80 e- (Xe), -0.08 e- (H), and -0.72 e-(C6F5).
2. 5. The Reaction of [C6F5Xe][BF4] with Cd(C6F5)2 in C2H5CN Solution
When [C6F5Xe][BF4] was reacted with Cd(C6F5)2 in the coordinating solvent C2H5CN at -78 °C the [BF4]- anion was involved in a metathesis reaction and in contrast to reactions with Alk3SiY, it did not serve as a source of fluoride for the acidic Cd11 center. (C6F5)2Xe was precipitated within less than 2 h along with small amounts of Cd[BF4]2, which could be removed by washing with cold C2H5CN (Eq 7).
:.(( : .kv4 t L; HI
(7)
It is worth mentioning that (C6F5)2Xe was found to decompose when pressure was exerted on the solid, e.g., with a spatula, even in a C2H5CN suspension at -78 °C. After decomposition, (C6F5)2 and C6F5H were found in the molar ratio of 83 to 17.
3. Experimental Section
3. 1. General
The NMR spectra were recorded on a Bruker AVANCE 300 spectrometer (1H at 300.13 MHz; 19F at
282.40 MHz; 11B at 96.29 MHz, 129Xe at 83.02 MHz, and 13C at 75.47 MHz). The chemical shifts were referenced to TMS (1H and 13C), CCl3F (19F, with C6F6 as secondary reference (-162.9 ppm)), BF3 ■ OEt2/CDCl3 (15% v/v) (11B), and XeOF4 (129Xe, with XeF2 in CH3CN (extrapolated to zero concentration) as secondary external reference (-1818.3 ppm)15, respectively. The composition of the reaction mixtures was determined by 19F NMR spec-troscopy using internal standards for integration.
X-ray diffraction data were collected at 173 ± 2 K using a diffractometer equipped with a Siemens SMART three axis goniometer and an APEX II area detector system. Crystal structure solution by Direct Methods and refinement on F2 were performed using the Bruker AXS SHELXTL software suite Version 6.12 after data reduction, and empirical absorption correction was performed using the Bruker AXS SAINT program Version 6.0. For crystallographic and refinement details see Table 1.
Crystal structure data have been deposited at the Cambridge Crystallographic Data Centre (CCDC). Enquiries for data can be directed to Cambridge Crysta-llographic Data Centre, 12 Union Road, Cambridge, U.K., CB2 1EZ or (e-mail) deposit@ccdc.cam.ac.uk or (fax) +44 (0) 1223 336033. Any requests sent to the Cambridge Crystallographic Data Centre for this material should quote the full literature citation and the reference number CCDC 889108.
[C6F5Xe][BF4] was prepared according to literature.16 CH3CN, C2H5CN, n-C5H12, and CH2Cl2 were purified and dried as described in ref 17. (C2H5)3SiH (Merck, >99%) was used as supplied. (CH3)3SiCl (Merck, >99%) was freshly distilled and [N(n-C4H9)4[BF4] (Fluka, >99%) was dried under vacuum before use. Cd(C6F5)2 and [N(CH3)4]F were prepared according to refs 18 and 19, respectively.
All reactions were performed in FEP (a block copolymer of tetrafluoroethylene and hexafluoropropyle-ne) or PFA (a block copolymer of tetrafluoroethylene and perfluoroalkoxytrifluoroethylene) vessels under an atmosphere of dry argon.
3. 2. Synthesis of C6F5XeF in CH2Cl2
An excess of [N(CH3)4]F (143.1 mg; 1.537 mmol) was partially dissolved in cold CH2Cl2 (10 mL; -78 °C) in an FEP trap (inner diameter = 23 mm). Solid [C6F5Xe][BF4] (386.4 mg; 1.003 mmol) was added and the suspension was intensively stirred for 2 d at -78 °C. Because of the lower density of the solid relative to the solution, the solid remained on the surface. n-Pentane (10 mL; -78 °C) was added till the solid precipitated. A sample (250 |jL; -78 °C) was taken and analyzed by 19F NMR spectroscopy.
19F NMR (CH2Cl2/n-C5H12 at -80 °C) 5(ppm): -129.0 (m, 3/(F2,6-129Xe) = 81 Hz, 2F, o-C6F5), -146.6 (t, 3/(F4-F3 5) = 20 Hz, 1F, p-C6F5), -156.2 (m, 2F, m-C6F5),
-2.2 (s, Av/ = 153 Hz, J(19F-129Xe) = 4030 Hz, 1F, XeF), C6F5XeF; -139.3 (m, 2F, o-C6F5), -154.5 (t, 3/(F4-F3,5) = 21 Hz, 1F, p-C6F5), -162.7 (m, 2F, m-C6F5), C6F5H; -141.3 (m, 2F, o-C6F5), -150.9 (m, 1F, p-C6F5), -161.4 (m, 2F, m-C6F5), C6F5Cl; molar ratio related to the sum of C6F5 compounds: C6F5XeF (66%); C6F5H (33%); C6F5Cl (1%).
[N(CH3)4]F and [N(CH3)4][BF4] are insoluble in CH2Cl2/n-pentane (1:1) at -78 °C and could be separated from the C6F5XeF solution by centrifugation at -78 °C. After removal of the solvents under vacuum (1.5 h; -55 to -50 °C; 8 ■ 10-2 hPa) a white powder remained, which was dissolved in CH2Cl2 (3 mL; -50 °C) in an FEP trap (inner diameter = 8 mm). For growing single crystals, the solution was slowly concentrated in vacuum (8 h; -55 to -45 °C; 8 ■ 10-2 hPa). After 8 h colorless transparent crystals (right angular plates; dimensions: 1 to 2 mm) were grown and stored under the mother liquor at -78 °C. The crystallographic data are compiled in Table 1.
3. 3. Synthesis of C6F5XeF in C2H5CN/CH2C12
A cold solution of [N(CH3)4]F (8.9 mg; 0.096 mmol) in CH2Cl2 (450 pL; -78 °C) was added to a cold solution of [C6F5Xe][BF4] (20.0 mg; 0.0519 mmol) in C2H5CN (50 pL; -78 °C) in an FEP inliner. A suspension resulted. After 20 min the total conversion into C6F5XeF (95% yield) was confirmed by 19F NMR spectroscopy. Only 5% of C6F5H and traces of C6F6 were present. The co-product [N(CH3)4][BF4] was insoluble.
19F NMR (C2H5CN at -80 °C) 5(ppm): -129.4 (m, J(F2,6-129Xe) = 81 Hz, 2F, o-C6F5), -147.1 (t, 3J(F4-F3,5) = 21 Hz, 1F, p-C6F5), -156.7 (m, 2F, m-C6F5), -4.0 (s, Av/ = 60 Hz, J(19F-129Xe) = 4007 Hz, 1F, XeF), C6F5XeF; -139.8 (m, 2F, o-C6F5), -155.1 (t, 3J(F4-F35) = 21 Hz, 1F, p-C6F5), -163.1 (m, 2F, m-C6F5), C6F5H; -162.9 (s, Av/ = 5 Hz, 6F), C6F6; -94.4 (s, Av/ = 44 Hz, 1F), F-; molar ratio related to the sum of C6F5 compounds: C6F5XeF (95%); C6F5H (5%); C6F6 (<1%); F- (82%).
3. 4. Synthesis of C6F5XeC1 in CH3CN
(CH3)3SiCl (7.1 mg; 0.065 mmol; 8.2 pL) was added to a suspension of [C6F5Xe][BF4] (22.6 mg; 0.0588 mmol) in cold CH2Cl2 (350 pL; -78 °C) in an FEP inliner. The starting materials were intensively mixed and the progress of the reaction was monitored by 19F NMR spectroscopy. After 1 h at -78 °C only traces of C6F5XeCl, BF3, and (CH3)3SiF were formed. Even after 3 h ait -40 °C the conversion reached 8% only. The mother liquor was separated from unreacted [C6F5Xe][BF4]. The salt was washed twice with cold CH2Cl2 (each 300 pL; -78 °C) and dried in vacuum (3 h; -78 to -50 °C; 4 ■ 10-2 hPa). Recovered [C6F5Xe][BF4] was dissolved in cold CH3CN (300 pL; -45 6°C5) and (C4H3)3SiCl (6.9 mg; 0.064 mm3 ol;
8.0 pL) was added. After 20 min the total conversion was confirmed by NMR.
19F NMR (CH3CN at -40 °C) §(ppm): -130.3 (m, 3/(F2'6-129Xe) = 91 Hz, 2F, o-C6F5), -146.7 (tt, 3/(F4-F3,5) =
20	Hz, 4/(F4-F2 6) = 3 Hz, 1F, p-C6F5), -156.4 (m, 2F, m-C6F5), C6F5XeCl; -156.2 (dec, 3J(F-H) = 7 Hz, J(19F-29Si) = 273 Hz, 1F), (CH3)3SiF; -141.6 (s, Avw = 31 Hz, 3F), BF3 ■ NCCH3; molar ratio related to C6F5XeCl: C6F5XeCl (100%); (CH3)3SiF (100%); BF3 ■ NCCH3 (100%). 1H NMR (CH3CN at -440 °C) 5(ppm): 0.4 (s, Av/ = 2 Hz, 9H), (CH3)3SiCl; 0.2 (d, 3J(H-F) = 7 Hz, 9H), (CH3)3SiF; molar ratio: (CH3)3SiCl (18%); (CH3)3SiF (100%)
3. 5. Synthesis of C6F5XeCl in C2H5CN
A solution of (CH3)3SiCl (11.3 mg; 0.104 mmol) in cold C2H5CN (200 pL; -78 °C) was added to a solution of [C6F5Xe][BF4] (28.5 mg; 0.0739 mmol) in cold C2H5CN (200 pL; -78 °C) in an FEP inliner. At -78 °C only 6% conversion proceeded within 80 min. After 5 min at -55 °C and following storage at -78 °C 19F NMR spec-troscopy confirmed the total conversion. At -50 °C (CH3)3SiF was removed from C6F5XeCl in vacuum without decomposition of the latter.
19F NMR (C2H5CN at -80 °C) 5(ppm): -131.1 (m, 3J(F2,6-129Xe) = 94 Hz, 2F, o-C6F5), -147.3 (t, 3J(F^-F3,5) =
21	Hz, 1F, p-C6F5), -157.1 (m, 2F, m-C6F5), C6F5XeCl; -139.5 (m, 2F, o-C6F5), -154.6 (tm, 3J(F4-F3,5) = 21 Hz, 1F, p-C6F5), -162.5 (m, 2F, m-C6F5), C6F5H*; -157.1 (dec, 3J(F-H) = 7 Hz, 1J(19F-29Si) = 213 Hz, 1F), (CH3)3SiF; -142.2 (s, Av/ = 5 Hz, 3F), BF3 ■ NCC2H5; -151.1 (br, Av/ = 19 Hz, 4F), [BF4]-; molar ratio related to the sum of C6F5 compounds: C6F5XeCl (98%), C6F5H (2%), (CH3)3SiF (100%), BF3 ■ NCC2H5 (92%), [BF4]- (3%). * C6F5H (2%) resulted during the dissolution of [C6F5Xe][BF4] in C2H5CN already and did not increase after addition of (CH3)3SiCl.
1H NMR (C2H5CN at -80 °C) 5(ppm): 7.4 (t, 3J(H-F26) = 8 Hz, 1H), C6F5H; 0.4 (s, Av/ = 4 Hz, 9H), (CH3)3SiCl; 0.2 (d, 3J(H-F) = 7 Hz, 9H), (CH3)3SiF; 0.1 (s, Av/ = 4 Hz, 18H), ((CH3)3Si)2O**; molar ratio: C6F5H (2%), (CH3)3SiCl (38%), (CH3)3SiF (100%), ((CH3)3Si)2O (2%); ** (CH3)3SiCl contained 1% ((CH3)3Si)2O.
C6F5XeCl
19F NMR (C2H5CN at -80 °C) 5(ppm): -131.1 (m, 3J(19F2,6-129Xe) = 94 Hz, 2F, o-C6F5), -147.3 (t, 3J(F4-F3,5) = 21 Hz, 1F, p-C6F5), -157.1 (n6, 2F, m-C6F5); (cf., ref 7 (CH2Cl2 at -60 °C) §(ppm): -130.8, -146.2, -155.5, (C2H5CN/CH3CN (3:1) at -60 °C) 5(ppm): -131.0, -147.5, -157.0). 13C{19F} NMR (C2H5CN at -80 °C) 5(ppm): 144.2 (s, C4), 143.8 (s, C2,6), 138.7 (s, C3,5), 103.5 (s, 1J(13C1-129Xe) = 231 Hz, C1); (cf., ref 7 (CH2Cl2 at -60 °C) 5(ppm): 143.3, 142.6, 137.6, 101.6). 129Xe NMR (C2H5CN at -80 °C) 5(ppm): -4077 (br, Av/ = 206 Hz); (cf., ref 7 (CH2Cl2 at -60 °C) 5(ppm): -4117/.
3. 6. Interaction of [N(«-C4H9)4][BF4] with (CH3)3SiCl in CH3CN
(CH3)3SiCl (16.8 mg; 0.155 mmol; 19.6 pL) was added into an FEP inliner which contained [N(n-C4H9)4][BF4] (50.8 mg; 0.154 mmol) dissolved in CH3CN (500 pL). C6H5CF3 (11.0 mg; 0.0752 mmol; 9.2 pL) was added as internal standard for integration. The progress of the reaction was monitored by 19F NMR at 24 °C. After 1.5 h the amount of [BF4]- was reduced by 17% and after 1 d by 19% only. Beside4 (CH3)3SiF, [BClF3]- was formed (broad singlet at -123.5); (cf., ref 20). The anions [BCl2F2]- (V(19F-nB) = 54 Hz) and [BCl3F]- (1/(19F-11B) = 79 Hz) with significant larger V(19F-nB) coupling constants than [BClF3]- (V(19F-nB) = 25 Hz) and smaller quantities were not observed.20
19F NMR (CH3CN at 24 °C) 5(ppm): -123.5 (s, Av/ = 177 Hz, 3F), [BClF3]-; -149.8 (s, Av/ = 20 Hz, 4F), [BF4]-; -155.9 (dec, 3/(F-H) = 7 Hz, 1F), (CH3)3SiF; molar ratio after 1.5 h: [BClF3]-: [BF4]-: (CH3)3S3F = 14 : 83 : 20, after 1 d: [BClF3]- : [BF4]- : (CH3)3SiF = 8 : 81 : 31.
1H NMR (CH3CN at 244 °C) A(ppm): 3.1 (m, ^(H-13C) = 143 Hz, 8H, C1H2), 1.6 (tm, 3/(H2-H3) = 7 Hz, 8H, C2H2), 1.4 (tq, 3/(H3-H2) = 7 Hz, 3/(H3-H4) = 7 Hz, 8H, C3H2), 1.0 (t, 3/(H4-H3) = 7 Hz, 7/(H-13C) = 125 Hz, 12H, C4H3), [N(«-C4H9)4]+; 0.4 (s, Av/ = 1 Hz, 9H), (CH3)3SiCl; 0.2 (d, 3/(H-F) = 7 Hz, 9H), (CH3)3SiF; molar ratio after 1.5 h: [N(«-C4H9)4]+ (100%); (CH3)3SiCl (73%); (CH3)3SiF (20%); after 1d: [N(«-C4H9)4]+ (100%); (CH3)3SiCl 363%); (CH3)3SiF (31%)
11B NMR (CH3CN at 24 °C) 5(ppm): 1.7 (s, Av/ = 121 Hz), [BClF3]-; -1.3 (s, Av/ = 15 Hz), [BF4]-.
3. 7. Reaction of [C6F5Xe][BF4] with (C2H5)3SiH in CD3CN
(C2H5)3SiH (9.5 mg; 0.082 mmol; 13 pL) was added to a solution of [C6F5Xe][BF4] (24.5 mg; 0.0636 mmol) in cold CD3CN (500 pL; -40 °C) in an FEP inliner. The mixture was intensively shaken and after 20 min analyzed by 19F and 11B NMR spectroscopy.
19F NMR (CD3CN at -40 °C) 5(ppm): -131.8 (m, 3/(F2'6-129Xe) = 43 Hz, 4F, o-C6F5),-153.8 (t, 3/(F4-F3,5) = 21 Hz, 2F, p-C6F5), -158.7 (m, 4F, m-C6F5), (C6F5)2Xe;4 -139.3 (m, 2F, o-C6F5), -154.8 (t, 3J(F4-I63,5) = 21 Hz, 1F, p-C6F5), -162.5 (m, 2F, m-C6F5), C6F5H; -139.6 (m, 2F, o-C6F5), -154.8 (t, 3J(F4-F35) = 21 Hz, 1F, p-C6F5), -162.6 (m, 2F, m-C6F5), C6F5D; -138.3 (m, 4F, o-C6F5), -151.0 (t, 3J(F4-F35) = 21 Hz, 2F, p-C6F5), -160.(5 (m, 4F, m-C6F5), (C6F5)2; -142.7 (m, 2F, o-C6F5), -155.8 (tm, 3J(F4-F3 5) = 21 Hz, 1F, p-C6F5), -161.9 (m, 2F, m-C6F5), C6F5CH2CH3; -134.9 (m, 2F, o-C6F5), -141.5 (tt, ^(F4-F35) = 21 Hz, 4J(F4-F26) = 8 Hz, 1F, p-C6F5), -159.6 (m, 2F, m-C6F5), [C6F5C(CD3)=N(H,D)2]+ a; -127.2 (m, 2F, o-C6F5), -152.7 (tt, 3J(F4-F3,5) = 20 Hz, 4J(F4-F2,6) = 3 Hz, 1F, p-C6F5), -161.9 (m, 2F, m-C6F5), C6F5Si(C2H5)3b; -174.4 (sep, 3J(F-H) = 6 Hz, J(19F-29Si) = 286 Hz, 1F),
(C2H5)3SiF c; -180.5 (dquin, 2/(F-H) = 53 Hz, 3/(F-H) = 7 Hz, 1F), (C2H5)2SiFH; -142.9 (quin, 3/(F-H) = 5 Hz, 2F), (C2H5)2SiF2 d; -141.7 (br, Av/ = 212 Hz, 3F), BF3 ■ NCCD3; -149.4 (br, Av/ = 438 Hz, 4F), [BF4]-; molar ratio after 20 min related to the sum of C6F5 compound: (C^Xe (5%), C6F5H (61%), C6F5D (2%), (C6F5)2 (1%), C6F5CH2CH3 (5%), [C6F5C(CD3)=N(H,D)2]+ (19%), C6F5Si(C2H5)3 (2%), (C2H5)3SiF (52%), (C2H5)2SiFH
(7%), (C2H5)2SiF2 (6%), BF3 ■ NCCH3 (94%), [BF4]-(6%). 2 5 2 2 3 3 4
(a cf., ref 14 (CDCl3) 5(ppm): -136.2, -143.9, -155.1 [C6F5C(CH3)=N(C2H5)2]+; b cf., ref 21 (CCl4) 5(ppm): -127.2, -152.6, -162.0; c cf., ref 22 (C6D6) 5(ppm): -175.2; d cf., ref 23 (CCl4) 5(ppm): -145.7). 11B NMR (CH3CN at -40 °C) §(ppm): -1.4 (s, Av/ = 10 Hz), [BF4]-; -2.2 (s, Av/ = 37 Hz), BF3 ■ NCCD3.
3. 8. Reaction of [C6F5Xe][BF4] with (C2H5)3SiH in C2H5CN
A solution of [C6F5Xe][BF4] (59.5 mg; 0.1546 mmol) in cold C2H5CN (200 pL; -90 °C) was transferred to a solution of (C2H5)3SiH (19.2 mg; 0.165 mmol; 26 pL) in cold C2H5CN (150 pL; -90 °C) and vigorously mixed before the reaction was monitored by 19F NMR spec-troscopy. After 20 min at -90 °C 63% of the [C6F5Xe]+ cation and 44% of [BF4]- was reacted. All reaction products are comparable with that in CD3CN, except the product deriving from the C6F/ radical attack on the solvent. In C2H5CN the cation [C6F5C(C2H5)=NH2]+ (5(ppm): -136.7 (br, Av/ = 45 Hz, 2F, o-C6F5), -142.4 (br, 1F, p-C6F5), -160.1 (br, Av/ = 51 Hz, 2F, m-C6F5)) was formed. Molar ratio of products related to the sum of B-F compounds after 20 min: [C6F5Xe]+ (37%); (C6F5)2Xe (4%); C6F5H (37%), (C6F5)2 (traces), [C6F5C(C2H5)=NH2]+ (9%), C6F5Si(CH3CH2)3 (1%), (CH3CH2)3SiF (31%); (CH3CH6)2SiFH (4%2; (CH3CH2)2SiF2 (6%); BF3 ■ NCC32H5 (44%); [BF4]- (56%). The ratio stayed nearly constant after 100 min at -90 °C, but changed after 5 d at -70 °C: (C6F5)2Xe (2%), C6F5H (58%), (C6F5)2 (1%), [C6F5C(C2H5)=NH2]+ (17%), C6F5Si(CH3CH2)3 (2%), (CH3CH2)3SiF (44%), (CH3CH2)2SiFH (2%), (CH3CH2)2SiF2 (8%), BF3 ■ NCC2H5 (65%), [BF4]- (35%).
129Xe NMR (CH3CH2CN at -90 °C after 55 min) 5(ppm): -3971; (m) [C6F5Xe]+; -4134 (m) (C6F5)2Xe.
3. 9. Synthesis of Bis(pentafluorophenyl) Xenon(II) in C2H5CN
Solid Cd(C6F5)2 (25.6 mg; 0.0574 mmol; -78 °C) was deposited in an FEP inliner. A cold solution of [C6F5Xe][BF4] (41.2 mg; 0.107 mmol) in C2H5CN (400 pL; -78 °C) was added and the mixture was intensively shaken at -78 °C. A white suspension resulted which was characterized by 19F NMR spectroscopy after 2.5 h at -80 °C: 5/ppm -131.8 (m, 3/(F26-129Xe) = 43 Hz, 4F, o-C6F5),
-153.5 (t, 3/(F4-F3'5) = 20 Hz, 2F, p-C6F5), -158.6 (m, 4F, m-C6F5). After separation (-78 °C), the solid fraction was repeatedly washed with cold C2H5CN (4 x 400 pL; -78 °C) and incorporated Cd(C6F5)2 and Cd[BF4]2 were removed. The product (C6F5)2Xe (almost quantitative yield) was only slightly soluble in C2H5CN (-78 °C) and shock-sensitive even in suspension. Decomposition proceeded also when pressure was exerted on the solid in suspension, e.g., with a spatula, and a yellow solution resulted which contained (C6F5)2 and C6F5H in the molar ratio 83 : 17.
4. Conclusion
Strongly coordinating nitrile molecules (CH3CN, C2H5CN) can be replaced in the coordination sphere of the electrophilic Xe11 centre of the [C6F5Xe]+ cation by anions which are stable against oxidation such as F-.
More oxidizable anions such as Cl- can be introduced into the [C6F5Xe]+ moiety with support of [BF4]- as the counterion using (CH3)3SiHal. Fluoride in the coprod-uct, (CH3)3SiF, originates from the [BF4]- anion. The latter is transformed into the solvent adduct BF3 ■ NCAlk. Anions which are sensitive to oxidation can be protected by interaction with Lewis acids such as H+ or BF3.
The reaction of [C6F5Xe]+ with (C2H5)3SiH in nitrile solvents is complex. From the observed products, two intermediates C6F5XeH and C6F5XeC2H5 can be deduced. Alternatively to C6F5XeH, a one-electron transfer in cage from H- to [C6F5Xe]+ as main reaction channel cannot be excluded.
Oxidation resistant organyl groups of organometal-lic compounds such as Cd(C6F5)2 are nucleophilic enough to replace nitrile solvent molecules coordinated at Xe11 in [C6F5Xe]+. The carbon nucleophile does not interact with the [BF4]- anion. Formally, a metathesis of the [BF4]- anion by the carbanion [C6F5]- proceeds. The reaction of or-ganylxenonium salt solutions in nitrile solvents with organometallic compounds which possess a very polar MC bond promises an interesting access to new or-ganylxenon compounds, R1-Xe-R2.
5. Acknowledgements
We have to thank Dieter Bläser and Professor Roland Boese for the X-ray structure determination.
6. References
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Povzetek
Soli [C6F5Xe][BF4] regirajo z različnimi viri nukleofilnih zvrsti Y (»goli« fluorid, [N(CH3)4]F, silani, (CH3)3SiCl in (C2H5)3SiH ter Cd(C6F5)2) v koordinirajočih topilih (C2H5CN, CH3CN, CD3CN). Produkte C6F5XeF, C6F5XeCl in (C6F5)2Xe smo uspeli jasno določiti. V primeru reakcije s (C2H5)3SiH pa smo uspeli določiti le produkte razgradnje, ki lahko izvirajo iz <C6F5XeH> in <C6F5XeC2H5>. Spojino C6F5XeF smo karakterizirali z rentgensko strkturno analizo monokristalov.