Electrophilic oxygenation with XeF2 - H2O in hydrogen fluoride, Part 1. Oxygenation of [C6F5Xe]+ [AsF6]- and epoxidation of fluorinated cycloalkenylxenon(II) salts

Article abstract of DOI:10.1515/znb-1996-0717

XeF₂ and H₂O react with [C₆F₅Xe]⁺ [AsF₆]^- in HF without Xe-C bond cleavage under formation of the cyclohexadienone compound [3-O-1,4-C₆F₅Xe]⁺ [As

Full text of DOI:10.1515/znb-1996-0717

Electrophilic Oxygenation with XeF2 - H20 in Hydrogen Fluoride, Part 1.
Oxygenation of [C6F5Xe]+ [AsF6]' and Epoxidation of Fluorinated
Cycloalkenylxenon(II) Salts
H. J. Frohn*,a, V. V. Bardinh
a Fachgebiet Anorganische Chemie, Gerhard-M ercator-Universität Duisburg,
Lotharstr. 1, D-47048 Duisburg, Germany
b Institute of Organic Chemistry, Russian Academy of Sciences, 630090 Novosibirsk, Russia
Dedicated to Prof. Dr. M. Herberhold on the occasion of his 60[h birthday
Z. Naturforsch. 51 b, 1011-1014 (1996); received December 29, 1995
Xenon Difluoride, (Pentafluorophenyl)xenon(II), (Pentafluoro-l,4-cyclohexadien-3-on-l-yl)-
xenon(II), (Pentafluoro-4,5-epoxycyclohexen-3-on-l-yl)xenon(II), Electrophilic Oxygenation
XeF2 and FLO react with [C6F_<;Xe]+ [AsFb]- in HF without Xe-C bond cleavage under
formation of the cyclohexadienone compound [3 -0 -1 ,4-C6FsXe]+ [AsFf,]- . The FC=CF moiety
in this dienone is epoxidised with the same reagent. The cyclohexadiene compound [1,4-
C6F?Xe]+ [AsFft]- could also be epoxidised under the same conditions.
Introduction
From electrostatic arguments it can be expected
that the positively charged xenon atom in the
[C6FsXe]+cation should make the interaction of the
pentafluorophenyl group with electrophiles more
difficult or should inhibit it.
The fluorination of organic compounds with
xenon difluoride is well documented [1]. Reactions
of XeF2 with aromatic, polyfluoroaromatic and un-
saturated substrates in the presence of Lewis acids
(HF, BF3, SbFs or NbF5) usually lead to fluorode-
protonation of C-H bonds, or two fluorine atoms
are added to C-C double bonds. When alkenes re-
act with XeFi, methanol and HF or BF3 • OEt2,
fluoromethoxylation of the C-C double bond takes
place [2]. In the last case the intermediate forma-
tion of unstable [FXeOMe] or related species was
postulated rather than the formation of hypofluorite
MeOF. To our knowledge, the reactivity of the sys-
tem XeF2 - H2O in HF towards organic substrates
has not yet been investigated.
In the course of our systematic investiga-
tions in organoxenon chemistry, the interaction of
arylxenon(II) salt 1 with the system XeF2 - H2O in
HF was studied [4],
Results and Discussion
Treatment of (pentafluorophenyl)xenon(II) hexa-
fluoroarsenate 1 with a slight excess of xenon di-
fluoride and water in HF leads to the formation of
two new organoxenon(II) compounds, (pentafluoro-
1,4-cyclohexadien-3-on-1-yl)xenon(II) hexafluoro-
Recently we have published the first preparation
of (heptafluoro-1,4-cyclohexadien-1-yl)xenon( II)
and (nonafluorocyclohexen-l-yl)xenon(II) hexa-
fluoroarsenates by fluorination of (pentaflu-
arsenate 2, together with
a small amount of
(pentafluoro-4,5-epoxycyclohexen-3-on-1-yl)
xenon(II) hexafluoroarsenate 3. The latter substance
is the only fluoroorganylxenon(II) product when the
reaction mixture is treated with an additional equiv-
alent of XeF2 and water at room temperature, but the
epoxyhexenone 3 did not undergo any further reac-
tion when treated with an excess of xenon difluoride
and water.
orophenyl)xenon(II) hexafluoroarsenate
1 with
xenon difluoride in anhydrous HF [3J. Until now
this reaction is the only example of a transforma-
tion of the organic moiety bonded to xenon without
C-Xe bond cleavage.
The success of the preparation of the dienone 2
from 1 depends strongly on the reaction conditions.
2 was obtained by addition of xenon difluoride to
* Reprint requests to Prof. Dr. H. J. Frohn.
K
0939-5075/96/0700-1011 $ 06.00 (c) 1996 Verlag der Zeitschrift für Naturforschung. All rights reserved.
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1012
H. J. Frohn - V. V. Bardin • Electrophilic Oxygenation with XeF2 - H20 in Hydrogen Fluoride
a solution of 1 and HiO in HF at -10 °C or, alter-
natively, by addition of a freshly prepared solution
of XeF2 in HF containing H20 to a solution of 1 in
anhydrous HF at -10 °C. In both cases the result-
ing reaction mixture was subsequently warmed to
ambient temperature. When a solution of XeF? and
H20 (2 equivalent) in HF was maintained at -10 °C
for 1 h, gas slowly evolved. After the completion of
the gas evolution and disappearance of XeF2 reson-
ances in the 19F NMR spectrum no reaction had
intermediate formation of H20 2 [5], The reaction
of [XeF]+ [MFö]~ (M = Sb, As) with water in HF
at -60 °C yields the salt [H2OF]+ [MF6]~ [6]. In-
teraction of this salt with an excess of water gives
the [H30 2]+ cation. However, 1 does not react with
30 or 90 % H20 2 in HF at room temperature either
in the presence of a Lewis acid (NbF5) nor without
one. After addition of xenon difluoride to the solu-
tion containing 30 % H20 2, the formation of 2 was
observed. Salts of the monofluorooxonium cation
taken place with [CöFsXe]* [AsFö]- . But when a [H2OF]+ and HOF are stable in HF at -40 °C [6]. If
new portion of XeF2 was added, the conversion of
1 into dienone 2 proceeded.
these oxyfluorides would be the reactive intermedi-
ates, the formation of 2 from 1 should be expected
after consumption of XeF2 at least at -40 °C. But
this was not observed. It seems more probable that
the key reactive species is an unstable xenon-oxygen
containing intermediate like [HOXe]+- • [FHF]“ ,or
a structurally related oxidant which reacts as an
"HO+" equivalent. The situation may be compared
with reactions of the cation [FXe]+ which is the
equivalent of "F+" in many chemical processes.
+ XeF2 + H20
Xe+[AsF6]-
'Xe [As F6]~
+ XeF2 + H20
F
II
+XeF2
Xe+[As F6]'
"Xe+[AsFg]’
Xe [As F6]"
"Xe+[As F6]"
1
It should be noted that the solution of XeF2 in
HF is unstable in the presence of water. At -40 °C
decomposition proceeds slowly, and after 22 h the
volume of evolved gas is ca. 86 % of the theoreti-
cally expected amount of Xe°. Simultaneously with
the gas evolution the intensity of the XeF2 reson-
ance in the 19F NMR spectrum is diminished. The
resulting solution displays a correspondingly de-
creased oxygenation reactivity. When the solution
is allowed to react with 1 (0.66 equivalent with re-
spect to 1equivalent of the initial amount of XeF2),
only approximately 20 % of 1 is converted into the
dienone 2. Nevertheless, nearly total conversion of
[C6F5Xe]+ [AsFö]" is achieved by the introduc-
tion of a new portion of XeF2 into the solution.
No fluorination (addition of fluorine atoms) of the
pentafluorophenyl ring of 1, or of the C=C double
bonds of 2 was observed.
+XeF2 + H20
Xe+[As F6]‘
Xe [AsF6f
+ XeF2 + H20
Xe [AsF6]‘
The similarity of both electrophilic oxidative pro-
cesses was demonstrated by the fluorination of 1
with XeF? - HF (without water) [3] and by the
epoxidation of the (heptafluoro-1,4-cyclohexadien-
l-yl)xenon(II) salt
4 [3] to (heptafluoro-4,5-
epoxycyclohexen-1-yl)xenon(II) hexafluoroarsen-
ate 5 (in the presence of H20). The inertness of
the FC=CXe+ moieties in all alkenylxenon(II) salts
The results allow assumptions about the nature
of the reactive species in this new oxygenation
reaction. The intermediate may be HOF, H20 2
(or their protonated forms [H2OF]+ and [H3 0 2]+), 2, 3 and 5 as well as in (nonafluorocyclohexen-1-
yl)xenon(II) hexafluoroarsenate 6 toward reactions
or electrophilic xenon-oxygen species. Hydroly-
with XeF2 - H20 in HF is noteworthy.
sis of xenon difluoride in water proceeds via the
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1013
H. J. Frohn - V. V. Bardin ■Electrophilic Oxygenation with XeF2 - H20 in Hydrogen Fluoride
shows that the replacement of two fluorine atoms
in position 3 by oxygen affects the I29Xe chemi-
cal shift only slightly, while the epoxidation of the
FC=CF moiety of diene 4 and dienone 2 leads to a
more remarkable high-frequency shift of the 129Xe
resonances.
The new alkenylxenon(II) derivatives 2, 3, and 5
are stable at room temperature as solids as well as
in HF solution. Fast decomposition was observed
when epoxyhexenone 3 was dissolved in MeCN
at -10 to 20 °C. For reliable identification, 2 was
converted into the known l-bromopentafluoro-1,4-
cyclohexadien-3-one 7 by the reaction with NaBr.
Previously such regiospecific replacement of xenon
by bromine was performed on diene 4 [3] and 1 [7].
Experimental
The NMR spectra were measured on Bruker spectro-
meters: W P 80 SY (19F at 75.40 and l2yXe at 22.17 MHz)
and DRX 500 (l29Xe at 138.87 MHz) (CaF6 internal and
X eF:/HF external references). The chemical shifts 6(F)
were related to CFCI3 [6(F) (CftFa) = -162.9 ppm)].
The salt [C6F_<;Xe]+ [AsFft]- 1 was prepared as de-
scribed previously [8]. HF was freshly distilled from ca.
5% SbF«i - HF solution using a PTFE-FEP equipment. All
experiments were performed in FEP tubes.
2
7
The i9F NMR spectrum of dienone 2 in HF dis-
plays resonances at -88.9 (F-2), -96.7 (F-6,6), -130.2
(F-5), and -147.2 (F-4) ppm. The signal of atom
F-2 shows satellites due to l9F - l29Xe coupling
[V (19F-2)(129Xe) = 70.0 Hz], The other 7(FF) val-
ues are 3.5 (2,4), 5.8 (2,5), 8.3 (2,6), <1 (4,5), 8.9
(4,6) and 22.6 (5,6) Hz. The l9F NMR spectrum of
epoxyhexenone 3 (HF, -10 °C) exhibits resonances
at -82.3 (F-2), -95.1 (F-6A), -101.2 (F-6B), -166.3
(F-5), and -168.7 (F-4) ppm; [V (19F-2)(129Xe) =
73.9 Hz, J(FF): 9.0 (2,4), 8.4 (2,6A), 9.0 (2,6B),
18.1 (4,5), 4 (4,6B), 17.3 (5,6A), 14.0 (5,6B), 284
(6A, 6B) Hz]. A similar, but more complex spectrum
is found for epoxyhexene 5: The resonances of the
fluorine atoms are located at -84.8 (F-2), -95.1 (F-
6A), -101.0 (F-6B), -107.1 (F-3A), -119.4 (F-3B),
-166.2 (F-5) and -170.5 (F-4) ppm [3J( l9F-2)(129Xe)
= 74.0 Hz, J(FF): 25.5 (2,3A), 20.3 (2,3B), 9 (2,4),
8.5 (2,6), 299 (3A,3B), 15.8 (3A,4), 11.5 (3B,4), 3.5
(3B,5), 15 (4,5), 16.5 (5,6A), 13 (5,6B), 281 (6A,
6B) Hz], All 19F NMR spectra contain also the very
broad resonance of the AsFg- anion centred at -65
to -68 ppm.
Reaction of[ C(,F^Xe]+[AsFf,]~ 1 with XeFj - H2O in HF
Method A. A solution of 1 (160 mg, 0.328 mmol) in
HF (1 m l) was cooled to -10 °C and water (14 mg, 0.777
mmol) was introduced. Xenon difluoride (97 mg, 0.574
mmol) was added in portions. After each addition the
reactor was kept at room temperature till completion of
xenon evolution. Finally the reaction mixture was kept at
20 - 22 °C for 20 min. The |yF NMR spectrum showed
the complete conversion of 1 into 2 and 3 (traces). The
excess of XeF2 was destroyed by addition of CftFft, which
underwent electrophilic oxygenation in the presence of
H :0 (see part 2). After evaporation of HF and of the
volatile by-products in vacuum the residue was washed
with cold CH 2CI2 and dried in vacuum. 151 mg (91 %)
of colourless solid 2 were isolated.
Method B. Xenon difluoride (17 mg, 0.100 mmol) was
dissolved at -20 °C in 0.2 ml HF containing 5 mg (0.277
mmol) of H2O. This solution was immediately transferred
to the solution of 1 (50 mg, 0.102 mmol) in HF (0.1 ml),
and the resulting solution was kept at 20 - 22 °C for 10
min. The conversion of 1 into dienone 2 was ca. 20 %
( lyF NMR). The addition of the next portion of XeF2
(total amount 34 mg, 0.201 mmol) led to the formation of
2 and 3 (1 : 0.4, mol), some residual 1 being left in traces.
The l29Xe NMR spectra of the alkenylxenon(II)
hexafluoroarsenates 2, 3 and 5 as measured in HF
(-10 °C) show doublets at -2352.4, -2336.5 and
2321.1 ppm. respectively. The corresponding cou-
pling constants V (l29Xe)(l9F-2) are 70.5 ± 1.5,
72.0 ± 1.5 and 71.4 ± 0.6 Hz. The comparison
of these <§(l29Xe) and 7(XeF) values with those
of diene 4 [<§(129Xe) -2348.5 ppm, V (129Xe)(19F-
2) = 68 ± 1.1 Hz] and (nonafluorocyclohexen-1-
yl)xenon(II) hexafluoroarsenate 6 [(l29Xe) -2294.6
ppm, V (129Xe)(19F-2) = 69.7 ± 1.1 Hz] in HF [3]
Method C. Water (12 mg, 0.666 mmol) was added to
the solution of XeF2 (70 mg, 0.414 mmol) in HF (0.15
ml) at -40 °C. No reaction was observed within 20 min
( |l,F NMR). Gas evolution proceeded when this solution
was warmed to -10 °C. After 1 h the resonance of XeF2
disappeared in the 19F NMR spectrum. After dissolution
of 1 (80 mg, 0.164 mmol) no reaction was detected during
12 h at 20 - 22 °C. W hen a new portion of XeF2 (43 mg,
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1014
H. J. Frohn - V. V. Bardin • Electrophilic Oxygenation with XeF2 - H iO in Hydrogen Fluoride
0.254 mmol) was added, dienone 2 and traces of 1 and 3
were formed.
water (5 mg, 0.278 mmol) at -5 °C. Gas evolution was
complete within 10 min, but 6 did not react within 12 h
at room temperature.
Method D. A solution of XeF2 (48 mg, 0.284 mmol)
and H20 (10 mg, 0.556 mmol) in HF (0.2 ml) was kept
at -40 °C for 22 h. The measured volume of the evolved
gas was 5.5 ml (86 % of the theoretical amount of Xe°).
The |yF NMR spectrum showed only a residual amount of
XeF2. 1 (92 mg, 0.189 mmol) was added and the resulting
solution was warmed to ambient temperature. After 3 -
5 min the reaction was complete and give a mixture of 1
and 2 ( 1 0 :3 , mol).
Interaction of I with H2O2 in HF
Method A. The solution of 1 (50 mg, 0.102 mmol) in
HF (1.2 ml) was mixed with a solution of 30 % H20 2
(17 mg, 0.150 mmol of H2O 2) in HF (0.07 ml) at -60 °C.
No reaction was observed after 1 h at room temperature.
Addition of NbF? (50 mg, 0.266 mmol) did not induce
a reaction within 7 d at 20 - 22 °C. Treatment of the
reaction mixture with XeF2 (25 mg, 0.148 mmol) gave 1
and 2 (molar ration 1: 1, determined by l9F NMR).
Method B. 1 (75 mg, 0.154 mmol) was added to a
solution of 90 % H20 2(20m g,0.55 mmol of H2O 2) in HF
(0.1 ml) at -78 °C and then kept at room temperature for
1 h. No reaction of 1 was observed ( |l,F NMR). Addition
of NbF? (55 mg. 0.292 mmol) caused slow gas evolution
(presumably oxygen), but arylxenon(II) salt 1 remained
unchanged for 3 d.
Method E. The solution of 1 (80 mg, 0.164 mmol) and
H20 (6 mg, 0.330 mmol) in HF (0.1 ml) was treated with
XeF2(90 mg, 0.532 mmol) as described above (method A)
to give 3 (61 mg, 72 % yield) as a glassy colourless solid
after removing the excess XeF2with C&F6and evaporation
of the volatile products in a vacuum at room temperature.
Method F. The solution of 1 (50 mg, 0.102 mmol) and
H20 (15 mg, 0.816 mmol) in HF (0.15 ml) was kept at
room temperature for 7 d. No reaction took place, and
the chemical shifts in the 19F NMR spectrum were the
same as in anhydrous HF. Addition of XeF2 (21 mg.
0.124 mmol) caused gas evolution with complete con-
sumption of xenon ditiuoride and ca. 50 % conversion of
1 to dienone 2.
Reaction of 2 with NaBr
A solution of 2 obtained from 1 (80 mg, 0.164 mmol)
and XeF2(43 mg, 0.254 mmol) in HF (0.2 ml) was treated
with dry NaBr (48 mg. 0.466 mmol) at -15 °C. When
the gas evolution was complete, dichloromethane was
added, and HF was evaporated at room temperature. The
liquid phase was separated, the solid was washed with
CH2C b and the combined extracts analysed by l9F NMR
spectrometry. The spectra indicated the formation of 1-
bromopentafluoro-1.4-cyclohexadien-3-one 7 [9] (quan-
titative yield) (CftH-sCFi as internal reference).
Epoxidation of diene 4
1 (90 mg. 0.184 m m ol) was fluorinated with XeF2 (36
mg. 0.213 mmol) in anhydrous HF (0.2 ml) as described
in [3] to give 4 and a residual amount of 1 (86 : 14, mol).
This solution was treated with H20 (7 mg, 0.389 mmol)
and XeF2 (30 mg, 0.177 mmol) to yield 5, 6 and 4 (74, 11
and 15 mol %, respectively, determined by l9F NMR).
Acknowledgements
Interaction of (nonafluorocyclohexen-1-yl)xenon(II)
hexafluoroarsenate 6 with XeFz - HiO in HF
We gratefully acknowledge financial support by
Volkswagen-Stiftung and Fonds der Chemischen Indu-
strie.
A solution of 6 [3] (112 mg, 0.199 mmol) and XeF2
(35 mg, 0.207 mmol) in HF (0.2 ml) was treated with
Russ. J. Phys. Chem. 55. 927 (1981), and references
cited here.
[6] R. Minkwitz, G. Nowicki. Angew. Chem.. Int. Ed.
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[ 1] V. V. Bardin, Yu. L. Yagupolskii “Xenon Difluoride”,
in "New Fluorinating Agents in Organic Synthesis"
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berg. Berlin. New York (1989).
[7] H. J. Frohn. A. Klose. V. V. Bardin, A. J. Kruppa,
T. V. Leshina. J. Fluor. Chem. 70. 147 (1995).
[8] H. J. Frohn, St. Jacobs. G. Henkel, Angew. Chem.,
Int. Ed. Engl. 28. 1506 (1989); H. J. Frohn, A. Klose,
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[2] M. A. Tius. Tetrahedron 51. 6605 (1995).
[3] H. J. Frohn, V. V. Bardin, J. Chem. Soc., Chem.
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[4] Preliminary communication: H. J. Frohn, V. V.
Bardin, 11th European Symp. on Fluorine Chem.
Bled (Slovenia), Sept. 17-22. 1995. Abstract, p. 79.
[5] See A. A. Goncharov, Yu. N. Kozlov, A. P. Purmal,
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