Organoethynylxenon(II) tetrafluoroborates, [RC≡CXe][BF4] - The first examples of isolated alkynylxenonium salts: Preparation and multi-NMR characterisation

Article abstract of DOI:10.1002/ejic.200600366

The perfluorinated organoethynylxenon(II) salts, [RC≡CXe][BF ₄] [R = CF₃, C₃F₇, (CF ₃)₂CF, cis-, trans-CF₃CF=CF, C ₆F₅], were prepared by the reaction of Xe

Full text of DOI:10.1002/ejic.200600366

FULL PAPER
DOI: 10.1002/ejic.200600366
Organoethynylxenon(II) Tetrafluoroborates, [RCϵCXe][BF4] – The First
Examples of Isolated Alkynylxenonium Salts: Preparation and Multi-NMR
Characterisation
Hermann-Josef Frohn*[a] and Vadim V. Bardin[b]
Keywords: Alkynes / Boranes / Xenon / NMR spectroscopy
The
perfluorinated
organoethynylxenon(II)
CF3, C3F7, (CF3)2CF, cis-, trans-
salts,
tained in 20 to 40% yield. All [RCϵCXe][BF4] salts are solu-
ble in anhydrous HF (aHF) and the salts with R = C4H9 or R
= (CH3)3C display sufficient solubility in the weakly coordi-
nating solvents CH2Cl2 and PFP. The xenonium salts
[RCϵCXe][BF4] were unambiguously characterised by their
1H-, 11B-, 13C-, 19F-, and 129Xe NMR spectra in solution.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
[RCϵCXe][BF4] [R
=
CF3CF=CF, C6F5], were prepared by the reaction of XeF2
with the corresponding perfluoroorganoethynyldifluorobor-
anes, RCϵCBF2, in 1,1,1,3,3-pentafluoropropane (PFP) or
CH2Cl2 at –60 to –40 °C and isolated in 30–98% yield. Simi-
larly, the non-fluorinated organoethynylxenon(II) salts
[C4H9CϵCXe][BF4] and [(CH3)3CCϵCXe][BF4] were ob-
2004 Naumann et al. observed RCϵCXeF molecules (R =
Me, Bu, Ph) in the fluoride-catalysed reaction of XeF2 and
Me3SiCϵCR. The authors reported a significant decompo-
sition of RCϵCXeF in solution above –60 °C.[10]
In 1992, Zhdankin et al. published a short communica-
tion on the salt [tBuCϵCXe][BF4] obtained by the reaction
of Li[tBuCϵCBF3] with BF3 and XeF2 in CH2Cl2
(Scheme 1).[11] This salt, which could not be isolated be-
cause of its decomposition at –30 °C, was characterised by
1H-, 11B-, 13C-, and 129Xe NMR spectroscopy at –40 °C, by
IR spectroscopy at 0 °C, and by the alkynylation of PPh3
to [tBuCϵCPPh3][BF4] at –78 °C.
Introduction
The preparative chemistry of organoxenon compounds
was established in 1989 with the synthesis of pentafluo-
rophenylxenon(II) salts, [C6F5Xe][Y], obtained by the reac-
tion of XeF2 with (C6F5)3B.[1,2] In the subsequent years xe-
nonium salts, [RXe][Y], with different types of organo
groups in the cation (R = substituted phenyl, polyfluorocy-
cloalk-1-enyl) as well as arylxenon(II) molecules ArXeX (X
= F, Cl, O2CC6F5, CN, C6F5) and the first example of a
Xe(IV)–C compound, [C6F5XeF2][BF4], were investigated.
The achievements made in the first decade of xenon–carbon
chemistry are compiled in some reviews published in 1999–
In the analogous reactions of XeF2 with alkynylsilanes,
2002.[3] In the following years reactivities of arylxenon(II) RCϵCSiMe3 (R = Et, Pr, tBu, and Me3Si), and BF3·OEt2
salts,[4,5] of diarylxenon ArXeArЈ,[6] and the preparation in CD2Cl2 at –45 °C, the authors reported no multi-NMR
and reactivity of a series of acyclic polyfluoroalk-1-en- spectroscopic data of the desired products, the xenonium
ylxenon(II) salts [RCF=CRЈXe][BF4][7–9] were reported. In salts. Each reaction solution was only characterised by a
Scheme 1.
singlet in the 129Xe NMR spectrum. No 129Xe resonances
[a] Department of Chemistry, Inorganic Chemistry, University
were found in the spectra of the reaction solutions for R =
Duisburg-Essen,
H, Me, Ph, CF3, 4-CH3C6H4SO2, (iPr)3Si, PhMe2Si.[11]
Lotharstr. 1, 47048 Duisburg, Germany
Fax: +49-203-379-2231
We published a preliminarily report of the first isolation
of an alkynylxenon(II) salt in 2003 when we succeeded in
preparing trifluoropropynylxenon(II) tetrafluoroborate
[CF3CϵCXe][BF4].[12] We employed the previously devel-
oped approach to polyfluorinated arylxenon(II) and alk-1-
enylxenon(II) salts: the reaction of xenon difluoride with
E-mail: frohn@uni-duisburg.de
[b] N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry,
SB RAS,
Acad. Lavrentjev Ave. 9, 630090 Novosibirsk, Russia
E-mail: bardin@nioch.nsc.ru
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
3948
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 3948–3953

[RCϵCXe][BF4] – The First Examples of Isolated Alkynylxenonium Salts
FULL PAPER
polyfluoroorganoboron difluoride in the appropriate sol-
vent.[3b] This preparative method allowed for the isolation
of the new salt as a pure product and opened the possibility
of extensive and unambiguous characterisation. Sub-
sequently, we extended this preparative method to a repre-
sentative series of alkynylxenon(II) salts, [RCϵCXe][BF4],
where R represents any alkyl chain, a perfluoroalkyl group,
a perfluoroalk-1-enyl group or a perfluoroaryl group.
Scheme 4.
Results and Discussion
tetrafluoroborate (7b), respectively (Scheme 5). Surpris-
ingly, these salts are significantly soluble in PFP even be-
low –40 °C. Salt 6b is more soluble than salt 7b. Thus, under
comparable reaction conditions in PFP at –50 °C, 6b re-
mained in solution whereas half of isomer 7b precipitated.
When borane 6a reacted with XeF2 in CH2Cl2 at –65 °C
solely a solution of 6b was obtained.
The addition of XeF2 to the solution of either trifluoro-
propynyldifluoroborane (1a) or heptafluoropent-1-ynyldi-
fluoroborane (2a) in PFP[13] at –40 to –55 °C was ac-
companied by the precipitation of trifluoropropyn-
ylxenon(II) tetrafluoroborate (1b) or heptafluoropent-1-yn-
ylxenon(II) tetrafluoroborate (2b), respectively. Both salts
are insoluble in PFP and form white solids. After decan-
tation of the mother liquors and removal of the residual
volatiles in vacuo, alkynylxenon salts 1b and 2b were iso-
lated in 60–90% yield (Scheme 2).
Scheme 5.
In contrast to the reaction of alk-1-enyldifluoroboranes,
RCF=CFBF2, with XeF2,[7] neither the alk-1-enyltrifluo-
roborate anions, [RCF=CFBF3]–, nor their fluorination
products, [XBF3]– (X = RCF=CF, RCF2CF2), were ob-
served.
The results demonstrate the easy xenodeborylation (re-
placement of the three-coordinate boron atom by xenon)
of both non-fluorinated organoethynyldifluoroboranes and
perfluoroorganoethynyldifluoroboranes, RCϵCBF2, in re-
actions with xenon difluoride. Significant differences be-
tween the present reactions and the previously studied reac-
tions of XeF2 with alk-1-enyldifluoroboranes are their in-
sensitivity to the type of R group attached to C-2 of the
multiple C–C bond. It is worth mentioning that in the reac-
Scheme 2.
In a similar way, the reaction of heptafluoro-3-meth-
ylbut-1-ynyldifluoroborane (3a) with XeF2 gave hep-
tafluoro-3-methylbut-1-ynylxenon(II) tetrafluoroborate (3b)
in 82% yield (Scheme 3).
Scheme 3.
The replacement of the perfluorinated alkyl group at C- tions of hydrocarbon alk-1-enyldifluoroboranes with XeF2
2 of boranes 1a, 2a, and 3a by the pentafluoropropenyl or no xenonium salts were obtained. Thus under the same re-
pentafluorophenyl group did not affect the course of the action conditions as those of alkynyldifluoroboranes, cis-
reaction. Both pentafluoropent-3-en-1-ynyldifluoroboranes and trans-hex-1-enyldifluoroboranes, C4H9CH=CHBF2,
(cis-4a) and (trans-4a) and pentafluorophenylethynyldifluo- only gave complex mixtures but no hexenylxenon com-
roborane (5a) were successfully converted into pentafluo- pounds.[7]
ropent-3-en-1-ynylxenon(II) tetrafluoroborates (cis-4b) and
The novel alkynylxenon(II) compounds 1b–5b were iso-
(trans-4b) and pentafluorophenylethynylxenon(II) tetrafluo- lated as white solids at low temperatures (Ͻ–40 °C). When
roborate (5b), respectively. No addition of fluorine to the warmed from –40 °C the solutions took on a brown col-
double bond in the perfluorinated propenyl or phenyl moi- ouration, and at 20 °C the conversion into dark liquids took
ety of 4a or 5a occurred. The ratio cis-4b/trans-4b = 1:2 was place within a few minutes (4b, 5b) or a few hours (1b–3b).
equal to that in the parent boranes 4a (Scheme 4).
Salts 1b–5b are very soluble in aHF and insoluble in PFP
To complete the investigations of xenon difluoride with and CH2Cl2. A characteristic property of solutions of 1b–
alkynyldifluoroboranes, we studied the reaction of XeF2 5b in aHF is their longer lifetime at room temperature than
with boranes that contained a hydrocarbon alkynyl chain. that of the salts themselves in the solid state. In detail, no
XeF2 was treated with hex-1-ynyldifluoroborane (6a) and decomposition of perfluoroalkynylxenon tetrafluoroborates
3,3-dimethylbut-1-ynyldifluoroborane (7a) under the condi- 1b–3b was detected in aHF solutions within 20–24 h. The
tions mentioned above and formed hex-1-ynylxenon(II) tet- salts 4b and 5b, which contain the unsaturated perfluoro
rafluoroborate (6b) and 3,3-dimethylbut-1-ynylxenon(II) groups R = CF3CF=CF and R = C6F5, respectively, at C–
Eur. J. Inorg. Chem. 2006, 3948–3953
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3949

H.-J. Frohn, V. V. Bardin
FULL PAPER
2, decomposed much faster than 1b–3b. Salt 5b totally de-
The 129Xe NMR signals of salts [RCϵCXe][BF4] 1b–5b
composed in aHF at –40 °C within 1 h, whereas the total in aHF at –60 °C are singlets located between δ = –3600
decomposition of 4b in aHF at 22–24 °C took ca. 4 h. The and –3662 ppm (Table 1). The influence of the type of the
complete decomposition of pure solids 4b and 5b at 20 °C perfluorinated R group in [RCϵCXe]+ on the 129Xe NMR
led to the formation of brown materials, insoluble in aHF, chemical shifts is demonstrated by the remarkably high-fre-
which consisted of non-volatile complex mixtures (19F quency shift (deshielding) of the xenon atom parallel to the
NMR).
Hex-1-ynylxenon(II) tetrafluoroborate 6b and its isomer roalkyl groups: δ(129Xe)
7b were isolated as brownish powders (probably contami- –3609 ppm (RF=CF3CF2CF2)
replacement of fluorine atoms in [CF3CϵCXe]+ by perfluo-
=
–3636 ppm (RF=CF3)
–3600 ppm [RF
Ͻ
Ͻ
=
nated with impurities) which were easily liquefied above (CF3)2CF]. Furthermore, there is yet a very small but still
–40 °C (cf.[11]). Solutions or suspensions of these salts in experimentally detectable distinction in the 129Xe NMR
either PFP or CH2Cl2 decomposed in a manner similar to chemical shifts caused by configurational distinctions at C-
that of the salts in the solid state. Surprisingly, solutions of 4 as shown in the case of the isomeric cations [cis-
6b and 7b in aHF are stable at 22–25 °C for more than CF3CF=CFCϵCXe]+ (δ
=
–3613.2 ppm) and [trans-
12 h. After 22 h, 38% of 6b and 80% of 7b still remained CF3CF=CFCϵCXe]+ (δ = –3613.4 ppm).
unchanged. Finally the complete decomposition led to tar.
Solutions of the salts [C4H9CϵCXe][BF4] and [(CH3)3-
Salts 1b–7b were unambiguously characterised by multi- CCϵCXe][BF4] in aHF (–60 °C) displayed the most shi-
NMR spectroscopy. The 19F NMR spectra of fluoroor- elded xenon nuclei in the series of alkynylxenonium salts
ganoethynylxenon(II) tetrafluoroborates 1b–5b in aHF dis- with 129Xe resonances at δ = –3775 ppm and δ =
played signals for the fluoroorgano groups and for the –3781 ppm, respectively (Table 1).
[BF4]– anion (at approximately δ = –148 ppm) with the ex-
The 13C NMR spectra of [RCϵCXe][BF4] are of particu-
were lar interest because they should allow a direct and unam-
19F,129Xe
pected integrations. Long-range couplings J
observed in the spectra of both isomers of biguous proof of the C–Xe bond in alkynylxenon(II) salts.
[CF3CF=CFCϵCXe][BF4]. The signal for F-4 at δ = To our surprise, the resonances C-1 are located at unusually
–128.2 ppm (cis-4b) and F-3 at δ = –149.3 ppm (trans-4b) low frequencies between 8 and –24 ppm. The shielding of
4
displayed 129Xe satellites (5JF-4,Xe = 17 Hz and JF-3,Xe
=
C-1 in aHF solutions of alkynylxenon(II) salts bearing
6 Hz, respectively) in accordance with the natural abun- either hydrocarbon or perfluoroalkyl groups increases in
dance of the 129Xe isotope of 26%. The assignment of the the same order as the shielding of the xenon atom, e.g. from
4
coupling JF-3,Xe = 8 Hz in the 19F NMR spectrum of R = (CF3)2CF to R = (CH3)3C (Table 1). Salts 4b and 5b
[(CF3)2CFCϵCXe][BF4] was confirmed in a 19F{19F(CF3)} with unsaturated perfluoro R groups attached to C-2 pos-
homodecoupling NMR experiment. In the 19F NMR spec- sess the most deshielded C-1, which is probably the result
trum of salts with unbranched perfluoroalkyl R groups, as of a π-electron interaction of the CF3CF=CF group or the
in 1b (signal for the CF3 group at δ = –52.5 ppm, τ1/2
=
C6F5 group with the CϵC triple bond. The 13C NMR spec-
1.5 Hz) or 2b [19F{19F(CF3)} spectrum of the CF3CF2CF2 tra for C-1 of the cations [RCϵCXe]+ contains satellites
group] such couplings were not observed. For comparison, from the 13C–129Xe coupling, which increases from ca. JC-
1
in the case of cis-perfluoroalk-1-enylxenonium salts, larger 1,Xe = 265 Hz [R = C4H9, (CH3)3C] to 1JC-1,Xe = 308 Hz (R
4JF-3,Xe couplings are known. In the spectra of = C6F5) to approximately 1JC-1,Xe = 345 Hz (R = perfluoro-
4
[cis-YCF2CF=CFXe][BF4], JF-3,Xe = 40 Hz (Y = F) and alkyl). An opposite course of couplings is found for
4JF-3,Xe = 56 Hz (Y = CF3) were measured.[7]
2JC-2,Xe. In addition, it is worth mentioning that the chemi-
Table 1. 129Xe and selected 13C NMR spectroscopic data for [RCϵCXe][BF4].
R
Solvent
T [°C]
δ(Xe) [ppm]
δ(C-1) [ppm]
–23.7
1JC-1,Xe [Hz]
δ(C-2) [ppm]
2JC-2,Xe [Hz]
(CH3)3C
(CH3)3C
(CH3)3C
(CH3)3C[11]
C4H9
aHF
PFP
CH2Cl2
CDCl3
aHF
–60
–60
–40
–40
–30
–60
–60
–60
–60
–60
–60
–60
–20
–20
–3781
–3773
–3719
–3631
–3783
–3775
–3762
–3698
–3662
267
107.0
76
[a]
[a]
–15.7
26.9
–24.0
105.7
105.2
101.6
120
264
79
69
C4H9
C4H9
C6F5
CF3
cis-CF3CF=CF
trans-CF3CF=CF
C3F7
PFP
CH2Cl2
aHF
aHF
aHF
aHF
aHF
aHF
–21.2
–16.7
0.6
–5.2
6.9
7.9
–0.7
–0.5
279
288
308
99.3
98.7
81.0
81.2
79.8
79.8
80.9
80.4
73
75
62
69
64
64
70
68
–3636
343
[a]
–3613.2
–3613.4
–3619
332
349
343
(CF3)2CF
–3610
(–3601)[b]
[a] The coupling 13C–129Xe was not observed because of the low intensity of the parent signal. [b] Extrapolated to –60 °C from the
equation: ∆δ(129Xe)/∆T = –0.22 ppmK–1.[20]
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Eur. J. Inorg. Chem. 2006, 3948–3953

[RCϵCXe][BF4] – The First Examples of Isolated Alkynylxenonium Salts
FULL PAPER
difluoroboranes 1a–7a were prepared from the corresponding po-
tassium organoethynyltrifluoroborate salts.[18] All manipulations
with organoethynyldifluoroboranes, organoethynylxenon(II) salts
and anhydrous HF were performed in FEP (block copolymer of
tetrafluoroethylene and hexafluoropropylene) equipment under an
atmosphere of dry argon.
cal shift values for C-2 in the above series show an opposite
trend to that of C-1 and diminish from δ = 107 ppm to
approximately δ = 80 ppm.
In contrast to 1b–5b, the salts [C4H9CϵCXe][BF4] and
[(CH3)3CCϵCXe][BF4] are soluble in weakly coordinating
solvents such as CH2Cl2 and PFP and do not decompose
in these solutions below –60 °C over the course of several
weeks. The 129Xe resonances of 6b and 7b in PFP are sim-
ilar to those in aHF but are slightly shifted by (9–13 ppm)
to higher frequencies. In contrast, the NMR spectra of 6b
and 7b in CH2Cl2 display significant distinctions relative to
those in aHF. Thus, in CH2Cl2 the 129Xe NMR spectra
show signals that are shifted by 67 ppm (7b) and 77 ppm
(6b) to higher frequencies. In the 13C NMR spectra of both
salts, the resonance for C-1 is even shifted by 8 ppm into
the same direction, whereas the resonance for C-2 moves
Trifluoropropynylxenon(II) Tetrafluoroborate, [CF3CϵCXe][BF4],
(1b): A solution of CF3CϵCBF2 (0.45 mmol) in PFP (1.5 mL) was
cooled to –47 °C, and xenon difluoride (83 mg, 0.49 mmol) was
added in one portion. Within a few minutes, a white suspension
was formed which was stirred at –45 °C for an additional 1.5 h
before all volatiles were removed in vacuo at –45 °C to give 1b
(82 mg, 59%). Similarly, salt 1b (123 mg, 57%) was prepared in
CH2Cl2 (4.8 mL) at –55 °C from CF3CϵCBF2 (0.80 mmol) and xe-
non difluoride (120 mg, 0.71 mmol).
1b: 11B NMR (96.29 MHz, aHF, –20 °C): δ = –2.4 (s, [BF4]–) ppm.
13C{19F} NMR (75.46 MHz, aHF, –20 °C): δ = 112.2 (C-3), 80.5
by 2 ppm in the opposite direction. The position of the res- (d*, 2JC,Xe = 69 Hz, C-2), –5.2 (d*, 1JC,Xe = 345 Hz, C-1) ppm. 19
F
onance for the [BF4]– anion in the 19F NMR spectra of 6b
and 7b is shifted to δ = –144 1 ppm in CH2Cl2 and to δ
= –140 1 ppm in PFP. For comparison, solutions of
[Bu4N][BF4] in aHF (–20 °C), CH2Cl2 (24 °C) and PFP
(–10 °C) display the 19F NMR signal at δ = –148.3, –151.8
and –148.4 ppm, respectively. The deshielding of the signal
for the anion in the 19F NMR spectra of the solutions of
salts 6b and 7b in CH2Cl2 and PFP is attributed to a signifi-
cant cation–anion interaction (borderline description as
contact or tight ion pair). This is in contrast to their behav-
iour in aHF solutions where the salts exist as solvent-shared
ion pairs. The solvation of [BF4]– in aHF can be described
as the protonation of the fluorine terminus by the superacid
aHF or by the formation of a hydrogen bridge between
[BF4]– and the fluorine atom of the HF molecule. Recently
the related phenomena have been reported for solutions of
NMR (282.40 MHz, aHF, –20 °C): δ = –52.5 (s, 3 F, CF3), –148.0
(s, 4 F, [BF4]–) ppm.
Heptafluoropent-1-ynylxenon(II) Tetrafluoroborate, [C3F7CϵCXe]-
[BF4], (2b): A solution of C3F7CϵCBF2 (0.66 mmol) in PFP
(1.5 mL) was cooled to –40 °C, and xenon difluoride (99 mg,
0.58 mmol) was added in one portion. The resulting white suspen-
sion was stirred at –40 °C for 2 h before the volatiles were removed
in vacuo (0.13 hPa) at –40 °C to give 2b (237 mg, 98%).
2b: 11B NMR (96.29 MHz, aHF, –20 °C): δ = –1.3 (s, [BF4]–) ppm.
13C{19F} NMR (75.46 MHz, aHF, –20 °C): δ = 117.5 (C-5), 107.9
2
and 106.9 (C-3 and C-4), 80.9 (d*, JC,Xe = 70 Hz, C-2), –0.7 (d*,
1JC,Xe = 349 Hz, C-1) ppm. 19F NMR (282.40 MHz, aHF, –20 °C):
δ = –78.6 (t, 4JF,F = 9 Hz, 3 F, F-5), –101.1 (t, 3JF,F = 3 Hz, q, 4JF,F
3
= 9 Hz, 2 F, F-3), –124.2 (t, JF,F = 3 Hz, 2 F, F-4), –147.2 (s, 4 F,
[BF4]–) ppm.
Heptafluoro-3-methylbut-1-ynylxenon(II) Tetrafluoroborate, [(CF3)2-
CFCϵCXe][BF4], (3b):
A
solution of (CF3)2CFCϵCBF2
(aryl)(pentafluorophenyl)iodonium
tetrafluoroborates[14]
(0.73 mmol) in PFP (2 mL) was cooled to –45 °C before solid xe-
non difluoride (128 mg, 0.75 mmol) was added in one portion.
Within a few minutes, a white suspension was formed which was
stirred at –40 °C for an additional 1.5 h. The mother liquor was
decanted, and the residue was washed with cold (–40 °C) PFP
(1 mL). After drying in vacuo (0.13 hPa) at –40 °C, salt 3b (207 mg,
69%) was obtained. The mother liquor contained borane 3a
(0.16 mmol) along with traces of (CF3)2CFCϵCH and unknown
products (19F NMR).
and (pentafluorophenyl)(perfluoroalkenyl)iodonium tetra-
fluoroborates[15] in CH2Cl2 and aHF.
Finally, we have to mention that some of the NMR spec-
troscopic data of salt 7b presented here differ (see Table 1)
from those reported for the product solution obtained in
accordance with Scheme 1.[11]
3b: 11B NMR (96.29 MHz, aHF, –20 °C): δ = –1.3 (s, [BF4]–) ppm.
13C{19F} NMR (75.46 MHz, aHF, –20 °C): δ = 118.8 (CF3), 85.9
(C-3), 80.4 (d*, 2JC,Xe = 68 Hz, C-2), –0.5 (d*, 1JC,Xe = 343 Hz, C-
Experimental Section
The NMR spectra were recorded with an AVANCE 300 Bruker
spectrometer. The chemical shifts are referenced to TMS (1H, 13C),
BF3·OEt2/CDCl3 (15% v/v) (11B), CCl3F (19F) [with C6F6 as a sec-
ondary reference, δ = –162.9 ppm], and XeOF4 (129Xe) [with XeF2
3
1) ppm. 19F NMR (282.40 MHz, aHF, –20 °C): δ = –74.0 (d, JF,F
= 10 Hz, 6 F, CF3), –170.9 (3JF,F = 10 Hz, d*, 4JF,Xe = 8 Hz, septet,
1 F, F-3), –147.6 (s, 4 F, [BF4]–) ppm.
as
a secondary reference, XeF2/MeCN/24 °C (cǞ0), δ = –
Pentafluoropent-3-en-1-ynylxenon(II)
Tetrafluoroborate,
[CF3-
1813.28 ppm].[16] The multiplicities of the 13C- and 19F NMR sig-
nals caused by couplings with the 129Xe nucleus (satellites) are de-
noted by (*). The composition of the reaction mixtures and the
yields of the products were determined by NMR spectroscopy by
using the internal quantitative standard 1,1,2-trichlorotrifluoroe-
thane.
CF=CFCϵCXe][BF4], (4b): A solution of CF3CF=CFCϵCBF2
(0.50 mmol) (cis/trans = 1:2) in PFP (2 mL) was cooled to –55 °C,
and solid xenon difluoride (84 mg, 0.50 mmol) was added in one
portion. Within a few minutes, a white suspension was formed
which was stirred at –55 °C for an additional 1 h. After centrifuga-
tion at –78 °C, the mother liquor was decanted at –60 °C, the resi-
due was washed with cold (–60 °C) PFP (2 mL) and dried in vacuo
at –55 °C to give 4b (130 mg, 70%).
1,1,1,3,3-Pentafluoropropane (Honeywell), 1,1,2-trichlorotrifluoro-
ethane (Merck) were used as supplied. Dichloromethane (Fluka)
was purified and dried by standard procedures.[17] Anhydrous hy-
drogen fluoride was stored over CoF3. Solutions of organoethynyl-
cis-4b: 11B NMR (96.29 MHz, aHF, –20 °C): δ = –1.3 (s, [BF4]–)
ppm. 13C{19F} NMR (75.46 MHz, aHF, –60 °C): δ = 150.3 and
Eur. J. Inorg. Chem. 2006, 3948–3953
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3951

H.-J. Frohn, V. V. Bardin
FULL PAPER
135.1 (C-3 and C-4), 119.5 (C-5), 79.8 (d*, JC,Xe = 64 Hz, C-2),
6.9 (C-1) (the signal was too low in intensity to detect 1JC,Xe) ppm.
2
2
–60 °C): δ = 98.7 (d*, JC,Xe = 75 Hz, C-2), 28.7, 21.8, 20.5 (C-3,
C-4, C-5), 13.4 (C-6), –16.7 (d*, JC,Xe = 288 Hz, C-1) ppm. 19F
1
19F NMR (282.40 MHz, aHF, –60 °C): δ = –68.1 (d, 3JF,F = 12 Hz, NMR (282.40 MHz, CH2Cl2, –60 °C): δ = –143.0 (s, [BF4]–) ppm.
d, 4JF,F = 6 Hz, 3 F, F-5), –128.2 (d, q, 3JF,F = 12 Hz, 3JF,F = 3 Hz,
aHF (0.4 mL) was added to a solution of 6b in CH2Cl2 and stirred
at –45 °C for 10 min before the acidic phase was decanted.
5
3
4
d*, JF,Xe = 17 Hz, 1 F, F-4), –134.4 (d, JF,F = 3 Hz, q, JF,F
6 Hz, 1 F, F-3), –147.5 (s, 4 F, [BF4]–) ppm.
=
6b: 1H NMR (300.13 MHz, aHF, –30 °C): δ = 2.68 (t, 3JH,H = 7 Hz,
trans-4b: 11B NMR (96.29 MHz, aHF, –20 °C): δ = –1.3 (s, [BF4]–)
ppm. 13C{19F} NMR (75.46 MHz, aHF, –60 °C): δ = 148.0 and
3
3
2 H, 3-H), 1.66 (t, JH,H = 7 Hz, t, JH,H = 7 Hz, 2 H, 4-H), 1.46
3
(t, 3JH,H = 7 Hz, q, 3JH,H = 7 Hz, 2 H, H-5), 0.95 (t, JH,H = 7 Hz,
2
133.2 (C-3 and C-4), 116.3 (C-5), 79.8 (d*, JC,Xe = 64 Hz, C-2),
3 H, 6-H) ppm. 11B NMR (96.29 MHz, aHF, –30 °C): δ = –1.2 (s,
[BF4]–) ppm. 13C{1H} NMR (75.46 MHz, aHF, –30 °C): δ = 101.6
(d*, 2JC,Xe = 69 Hz, C-2), 29.0, 21.9, 20.1 (C-3, C-4, C-5), 12.0 (C-
1
7.9 (d*, JC,Xe = 332 Hz, C-1) ppm. 19F NMR (282.40 MHz,
3
4
aHF, –60 °C): δ = –67.9 (d, JF,F = 7 Hz, d, JF,F = 18 Hz, 3 F, F-
3
3
5), –150.0 (d, JF,F = 139 Hz, q, JF,F = 7 Hz, 1 F, F-4), –149.3 (d,
6), –24.0 (d*, JC,Xe = 264 Hz, C-1) ppm. 19F NMR (282.40 MHz,
1
4
4
3JF,F = 139 Hz, q, JF,F = 18 Hz, d*, JF,Xe = 6 Hz, 1 F, F-3),
aHF, –30 °C): δ = –147.8 (s, [BF4]–) ppm.
–147.5 (s, 4 F, [BF4]–) ppm.
B: A solution of C4H9CϵCBF2 (0.25 mmol) in PFP (0.7 mL) was
cooled to –70 °C and added in one portion to the cold (–70 °C)
suspension of xenon difluoride (54 mg, 0.32 mmol) in PFP
(0.2 mL). The brown reaction mixture was stirred at –65 °C for 1 h.
The NMR spectra of the suspension showed the total conversion
of 6a and the formation of 6b in Ͼ25% yield.
Pentafluorophenylethynylxenon(II) Tetrafluoroborate, [C6F5CϵCXe]-
[BF4], (5b)
A: A solution of C6F5CϵCBF2 (0.34 mmol) in PFP (0.9 mL) was
cooled to –55 °C, and xenon difluoride (50 mg, 0.29 mmol) was
added in one portion. The resulting suspension was stirred at –50
to –55 °C for 1 h. After centrifugation at –78 °C the brown mother
liquor was decanted at –45 °C. The residue was dried in vacuo
(0.13 hPa) at –45 °C, and pale brownish 5b was obtained (37 mg,
31%). The dissolution in aHF at –40 °C was accompanied by de-
composition of 5b. Total decomposition occurred within 30–50 min
(19F and 129Xe NMR).
1
6b: H NMR (300.13 MHz, PFP, –60 °C): δ = 1.58 (m, 2 H, 4-H),
1.42 (m, 2 H, 5-H), 0.91 (t, 3JH,H = 7 Hz, 3 H, 6-H) ppm (the signal
for 3-H overlapped with the resonance of PFP at 2.6 ppm). 11B
NMR (96.29 MHz, PFP, –60 °C): δ = –0.1 (s, [BF4]–) ppm. 13C{1H}
2
NMR (75.46 MHz, PFP, –60 °C): δ = 99.3 (d*, JC,Xe = 73 Hz, C-
1
2), 28.5, 21.4, 19.6 (C-3, C-4, C-5), 12.1 (C-6), –21.2 (d*, JC,Xe
=
B: A solution of C6F5CϵCBF2 (0.26 mmol) in CH2Cl2 (1.5 mL)
was cooled to –60 °C and xenon difluoride (38 mg, 0.22 mmol) was
added in one portion. The white suspension was stirred at –60 °C
for 1 h, and subsequently 5b (0.15 mmol, 68%) (19F NMR) was
extracted with cold (–65 °C) aHF (0.5 mL).
279 Hz, C-1) ppm. 19F NMR (282.40 MHz, PFP, –60 °C): δ =
–140.7 (s, [BF4]–) ppm. No changes were found in a solution of 6b
in CH2Cl2 after storage at –70 °C over 5 months. When 6b was
stored as aHF solution at 22 °C the content of 6b was reduced
from 95–100% (after 2 h) to 38% (after 22 h) to 10% (after 46 h).
1
5b: 11B NMR (96.29 MHz, aHF, –60 °C): δ = –1.7 (q, JB,F
=
3,3-Dimethylbut-1-ynylxenon(II)
Tetrafluoroborate,
[(CH3)3-
11 Hz, [BF4]–) ppm. 13C{19F} NMR (75.46 MHz, aHF, –60 °C): δ
= 149.5, 145.7, 137.9, 95.2 (C-2,6, C-4, C-3,5, and C-ipso, C6F5),
81.0 (d*, 2JC,Xe = 62 Hz, C-2), 0.6 (d*, 1JC,Xe = 308 Hz, C-1) ppm.
19F NMR (282.40 MHz, aHF, –60 °C): δ = –131.7 (m, 2 F, F-or-
CCϵCXe][BF4], (7b)
A: A cold (–60 °C) solution of (CH3)3CCϵCBF2 (0.44 mmol) in
PFP (1.7 mL) was added in one portion to the cold (–60 °C) stirred
suspension of xenon difluoride (69 mg, 0.40 mmol) in PFP
(0.1 mL). After 2 h, the reaction mixture was centrifuged at –78 °C
and subsequently the brown mother liquor was decanted at –65 °C.
The precipitate was dried at –60 °C in vacuo to give 7b (37 mg,
0.12 mmol). The mother liquor still contained borane 7a
(0.05 mmol) along with product 7b (0.15 mmol) (1H-, 11B-, 19F
NMR).
3
4
tho), –142.4 (t, JF,F = 19 Hz, t, JF,F = 6 Hz, 1 F, F-para), –159.0
(m, 2 F, F-meta), –148.1 (s, 4 F, [BF4]–) ppm.
The solution of 5b in aHF obtained as described under B showed
no significant decomposition at –60 °C over 13 h (19F-, 129Xe
NMR), but when the temperature was raised above –30 °C, 5b
quickly decomposed to give mainly cis-C6F5CF=CHF.[19]
cis-C6F5CF2=CHF1: 1H NMR (300.13 MHz, CDCl3, 24 °C): δ =
1
7b: H NMR (300.13 MHz, PFP, –50 °C): δ = 1.30 (s, CH3) ppm.
2
3
6.80 (d, JH,F-1 = 71 Hz, d, JH,F-2 = 16 Hz) ppm. 19F NMR
11B NMR (96.29 MHz, PFP, –50 °C): δ = –1.4 (s, [BF4]–) ppm. 19F
NMR (282.40 MHz, PFP, –50 °C): δ = –138.9 (s, [BF4]–) ppm.
(282.40 MHz, CDCl3, 24 °C): δ = –135.9 (d, 3JF,H = 16 Hz, d, 3JF,F
= 15 Hz, t, JF,F-ortho = 15 Hz, 1 F, F-2), –138.0 (m, 2 F, F-ortho),
4
2
3
5
1
–149.1 (d, JF,H = 71 Hz, d, JF,F = 15 Hz, t, JF,F-ortho = 5, d,
7b: H NMR (300.13 MHz, aHF, –60 °C): δ = 1.26 (s, CH3) ppm.
7JF,F-para = 3 Hz, 1 F, F-1), –149.8 (t, JF,F = 21 Hz, 1 F, F-para),
3
1
11B NMR (96.29 MHz, aHF, –50 °C): δ = –1.2 (quintet, JB,F
=
10 Hz, [BF4]–) ppm. 13C{1H} NMR (75.46 MHz, aHF, –60 °C): δ
–160.4 (m, 2 F, F-meta) ppm.
2
= 107.0 (d*, JC,Xe = 76 Hz, C-2), 30.9 (C-3), 27.6 (CH3), –23.7
Hex-1-ynylxenon(II) Tetrafluoroborate, [C4H9CϵCXe][BF4], (6b)
(d*, JC,Xe = 267 Hz, C-1) ppm. 19F NMR (282.40 MHz, aHF,
1
A: A solution of C4H9CϵCBF2 (0.25 mmol) in CH2Cl2 (0.6 mL)
was cooled to –70 °C and added in one portion to the cold (–70 °C)
suspension of xenon difluoride (60 mg, 0.35 mmol) in CH2Cl2
(0.2 mL). The dark reaction mixture was stirred at –65 to –70 °C
for 1 h. The 1H- and 19F NMR spectra showed the quantitative
conversion of 6a into 6b.
–50 °C): δ = –148.0 (s, [BF4]–) ppm.
B: When a solution of 7b in PFP was warmed to 20 °C, it became
dark, and a black precipitate was formed within 5–10 min. The
decomposition of the colourless solution of 7b in aHF proceeded
slowly at 20 °C and led to a dark colouration. The intensity of the
129Xe NMR signal was also reduced to 80% (after 24 h) and then
to 11% (after 44 h).
1
3
6b: H NMR (300.13 MHz, CH2Cl2, –60 °C): δ = 2.59 (t, JH,H
=
3
3
7 Hz, 2 H, 3-H), 1.55 (t, JH,H = 7 Hz, t, JH,H = 7 Hz, 2 H, 4-H),
3
3
3
1.35 (t, JH,H = 7 Hz, q, JH,H = 7 Hz, 2 H, 5-H), 0.87 (t, JH,H
=
7b: 1H NMR (300.13 MHz, CH2Cl2, –60 °C): δ = 1.28 (s, CH3)
ppm. 11B NMR (96.29 MHz, CH2Cl2, –60 °C): δ = –1.4 (s, [BF4]–)
7 Hz, 3 H, 6-H) ppm. 11B NMR (96.29 MHz, CH2Cl2, –60 °C): δ
= –1.4 (s, [BF4]–) ppm. 13C{1H} NMR (75.46 MHz, CH2Cl2, ppm. 13C{1H} NMR (75.46 MHz, CH2Cl2, –40 °C): δ = 105.7 (C-
3952
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 3948–3953

[RCϵCXe][BF4] – The First Examples of Isolated Alkynylxenonium Salts
FULL PAPER
2), 30.4 (C-3), 28.9 (CH3), –15.7 (C-1) ppm. 19F NMR
(282.40 MHz, CH2Cl2, –60 °C): δ = –144.7 (s, [BF4]–) ppm.
[6] H.-J. Frohn, M. Theissen, J. Fluorine Chem. 2004, 125, 981–
988.
[7] H.-J. Frohn, N. Yu. Adonin, V. V. Bardin, Z. Anorg. Allg.
Chem. 2003, 629, 2499–2508.
[8] H.-J. Frohn, V. V. Bardin, Z. Anorg. Allg. Chem. 2003, 629,
2465–2469.
Supporting Information (see also the footnote on the first page of
this article): Multi-NMR spectra of the [RCϵCXe][BF4] salts.
[9] H.-J. Frohn, V. V. Bardin, Z. Anorg. Allg. Chem. 2004, 630,
1022–1024.
Acknowledgments
[10] H. Schmidt, H. Scherer, W. Tyrra, J. Hahn, D. Naumann, In-
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[11] V. V. Zhdankin, P. J. Stang, N. S. Zefirov, J. Chem. Soc., Chem.
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[12] H.-J. Frohn, V. V. Bardin, Chem. Commun. 2003, 2352–2353.
[13] The choice of an appropriate solvent for the reaction of XeF2
with highly acidic organodifluoroboranes was discussed in
ref.[7]
We gratefully acknowledge financial support from the Deutsche
Forschungsgemeinschaft, the Russian Foundation for Basic Re-
search (Grant 04–03–04002 NNIO_a) and the Fonds der Chem-
ischen Industrie. We thank Honeywell Specialty Chemicals Seelze
GmbH for the generous donation of chemicals.
[14] F. Bailly, P. Barthen, H.-J. Frohn, M. Koeckerling, Z. Anorg.
Allg. Chem. 2000, 626, 2419–2427.
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[17] D. D. Perrin, W. L. F. Armarego (Eds.), Purification of Labora-
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[3] a) J. H. Holloway, E. G. Hope, Adv. Inorg. Chem. 1999, 46, 51–
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[20] V. V. Bardin, H.-J. Frohn, Magn. Res. Chem, accepted for pub-
lication.
Received: April 24, 2006
Published Online: August 7, 2006
Eur. J. Inorg. Chem. 2006, 3948–3953
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3953