The first hydrogen containing (polyfluorocycloalken-1-yl)xenon(II) salts

Article abstract of DOI:10.1515/znb-1998-5-612

(2-H-Hexafluoro-1,4-cyclohexadien-1-yl)xenon(II) and (2-H-octafluorocyclohexen-1-yl)xenon(II) hexafluoroarsenates and tetrafluoroborates were obtained together with their perfluorinated analogues on reacting the corresponding (2,3,4,5-tetrarluorophenyl)xenon(II) salts with XeF₂ in anhydrous HF (aHF). The fluorinated (cyclohexen-1-yl)xenon(II) cations react with bromide and iodide anions in MeCN and aHF under alkenylation of the halide anions.

Full text of DOI:10.1515/znb-1998-5-612

The First Hydrogen Containing (Polyfluorocycloalken-l-yl)xenon(II) Salts
H.-J. Frohn*,a, V. V. Bardinb
a Fachgebiet Anorganische Chemie, Gerhard-Mercator-Universität Duisburg,
Lotharstr. 1, D-47048 Duisburg, Germany
b Institute of Organic Chemistry, Russian Academy of Sciences, 630090 Novosibirsk, Russia
Z. Naturforsch. 53 b, 562-564 (1998); received February 23, 1998
Xenon Difluoride, Fluorinated Alkenylxenon(II) Salts, Fluorinated Arylxenon(II) Salts,
Oxidative Fluorination
(2-H-Hexafluoro-l ,4-cyclohexadien-l-yl)xenon(II) and (2-H-octafluorocyclohexen-l-yl)xe-
non(II) hexafluoroarsenates and tetrafluoroborates were obtained together with their perfluori-
nated analogues on reacting the corresponding (2,3,4,5-tetrafluorophenyl)xenon(II) salts with
XeF2 in anhydrous HF (aHF). The fluorinated (cyclohexen-l-yl)xenon(II) cations react with
bromide and iodide anions in MeCN and aHF under alkenylation of the halide anions.
Introduction
l-yl)xenon(II) (6a, b) salts as final products in a ca.
2 : 1 molar ratio.
In 1993 we have reported the first preparation
of perfluorinated cycloalken-l-ylxenon(II) com-
pounds. [l-Xe+-l,4-CöF7] [AsFö]~ and [1-Xe+-
CöFg] [AsFö]- were formed by fluorine addi-
tion to [C6F5Xe]+ [AsFö]- using XeF2 in anhy-
drous HF [1]. Until recently hydrogen-containing
alkenylxenon(II) derivatives were unknown. Their
preparation is of interest in order to study the rel-
ative influence of hydrogen versus fluorine in vic-
inal position to xenon [2], here in a vinylic moi-
ety. This study gives inter alia an experimental an-
swer to the proposed Xe-C bond stabilisation by
“through-space” or chelate-like vie-F-Xe interac-
tions (see [3]).
The formation of the perfluorinated compounds
3, 4, and 6 is in agreement with the general picture
of fluorination of tetrafluorobenzenes C6HF4R by
xenon difluoride via 1-R-hexafiuorocyclohexadiene
and its dehydrofluorination [5]. Indeed, NMR mon-
itoring of the reaction mixture of lb and XeF2 (1.3
to 1.7 equivalents) showed, besides the resonances
of compounds 2, 4, 5 and 6 [1], signals at 6.5 ppm
('H , d 47 Hz, H-C-F), at ca. -186 ppm (19F, d 40-
45 Hz, F-C-H) and at -2235 ppm (129Xe, d ca.
70 Hz, V(Xe, F-2) which are assigned to one of
the isomeric cations [CöHFöXe]* 7 with a gem-
inal CHF-fragment; the (2,3,3,4,5,6-hexafluoro-
l,4-cyclohexadien-l-yl)xenon(II) or (2,3,4,5,5,6-
hexafluoro-1,3-cyclohexadien-1-yl)xenon(II) cat-
ion. After further XeF2 addition (2.53 equivalents in
total) the oxidative fluorination was complete and
compounds 5 and 6 were the only products. It is
necessary to emphasize that no conversion of hex-
ene 5 into hexene 6 was observed in the presence of
XeF2 during one week at room temperature.
In the couples of cyclohexadienylxenon(II) 4b,
2b and cyclohexenylxenon(II) 6b, 5b tetrafluorobo-
rates the hydrogen-containing alkenylxenon cation
shows a substantial shift of the l29Xe resonance to
higher frequency with corresponding _\(l29Xe) val-
ues of 131 and 137 ppm, respectively. The deshield-
ing of the xenon nucleus is comparable with the
one observed for the transition from cation 3 to [X-
C6H4Xe]+ (X = w-CF3 [6], p-CF3, m-F, p-F) [7].
Substitution of F by H in the perfluorophenyl or
Results
The addition of XeF2 in small portions (ca.
1.5 equivalents) into
a solution of (2,3,4,5-
tetrafluorophenyl)xenon(II) hexafluoroarsenate la
or tetrafluoroborate lb [4] in anhydrous HF at -15 °C
and warming to room temperature resulted in Xe°
evolution and formation of (3,3,4,5,6,6-hexafluoro-
l,4-cyclohexadien-l-yl)xenon(II) (2a, b), minor
amounts of (pentafluorophenyl)xenon(II) (3a. b),
and (heptafluoro-1,4-cyclohexadien-1-yl)xenon(II)
(4a. b) salts. Further fluorine addition using excess
XeF2 gave (3,3,4,4,5,5,6,6-octafluorocyclohexen-
l-yl)xenon(II) (5a. b) and (nonafluorocyclohexen-
Reprint requests to Prof. Dr. H.-J. Frohn.
0939-5075/98/0500-0562 $ 06.00 (c) 1998 Verlag der Zeitschrift für Naturforschung. All rights reserved.
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H.-J. Frohn - V. V. Bardin • The First Hydrogen Containing (Polyfluorocycloalken-l-yl)xenon(II) Salts_________563
5b
+
6b
+
NaBr
- Na[BF4],-Xe"
10
+
11
-vinyl group bonded to Xe(II) leads to a stronger
polarisation of the phenyl or vinyl group by the
positively charged Xe atom and weakens the Xe-C
bond [8].
Experimental
The NMR spectra were measured on Bruker spectro-
meters WP 80 SY ('H at 80.13 and ,9F at 75.39 MHz)
and Avance DRX 500 ('H at 500.130, 19F at 470.593
and 129Xe at 138.338 MHz). The chemical shifts 6(F)
were referred to internal CöF6 and related to CFCI3 [6(F)
(CöFö) = -162.9 ppm)], <5(l29Xe) to external XeF2/aHF
and to XeOF4 (neat, 24 °C) (given in braces (<$(XeOF4) } ) -
The molecular formulas of the iodoalkenes 8 and 9 and
of the bromoalkenes 10 and 11 were determined from
the high resolution mass spectra of their mixtures using a
Finnigan MAT 8200 mass spectrometer.
However, the weakening of the Xe-C bond in 2
and 5 is probably not very significant, since there
is no direct correspondence of the large differ-
ence in the l29Xe NMR chemical shift of the cou-
ple 5/6 to the reactivity or thermal stability in the
solid state or in solution. A mixture of (cyclohex-
enyl)xenon(II) hexafluoroarsenates 5a and 6a could
be stored at room temperature (FEP container under
argon) over more than 2 months without decompo-
sition. No changes were observed in the solution
of the tetrafluoroborates 5b and 6b in anhydrous
HF after one week (l9F NMR). The treatment of
a mixture of 5 and 6 (2 : 1, molar) with NaBr or
Nal in anhydrous HF as well as in MeCN solu-
tion resulted in the fast quantitative conversion of
both alkenylxenon cations into the corresponding
polyfluorinated 1-bromo- or 1-iodocyclohexenes in
the same molar ratio (cf [9]).
Anhydrous HF (aHF) was dried electrolytically (stain-
less steel cell, Ni electrodes). All experiments were per-
formed in FEP tubes under a dry Ar-atmosphere.
Fluorination ofarylxenon(II) salts la, b
A. Xenon difluoride (52 mg, 0.31 mmol) was added in
three portions to the solution of lb (65 mg, 0.18 mmol) in
aHF (0.2 ml) at -15 °C. After each addition the reaction
mixture was warmed to room temperature and maintained
until the gas evolution stopped. The molar ratio of 2 : 4 :
5 : 7 was 6.6 : 2.0 : 1.0 : 0.5 (19F NMR) besides traces of
6. A further amount of XeF2 was added (a total of 74 mg,
0.44 mmol) and the reaction mixture was maintained at
room temperature for 1.5 h. Compounds 5b and 6b were
obtained in 2 : 1 molar ratio (l9F NMR). This solution
which contains small amounts of XeF2 was kept at room
temperature for 1week without any changes. Hexafluoro-
The close similarity of the hydrogen-containing
cycloalkenylxenon(II) cations 2, 5 and the perflu-
orinated analogues 4, 6 indicates the absence of a
specific participation of the vinylic fluorine atom in
neighbourhood to xenon in a "‘through space"’ or
chelate-like stabilisation of the carbon-xenon bond.
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564
H.-J. Frohn - V. V. Bardin • The First Hydrogen Containing (Polyfluorocycloalken-1-yl)xenon(II) Salts
8: l9F NMR (CH3CN): -101.9 (F-6,6 ), -107.6 (F-
3,3), -131.5 and -133.8 (F-4,4,5,5) ppm. MS: found: M+'
351.9005; calculated (C6HF8I): M+' 351.8995.
9: l9F NMR (CH3CN): -98.1 (F-2), -100.4 (F-6 ,6 ),
-117.3 (F-3,3), -131.1 and -133.1 (F-4,4,5,5) ppm (cf.
[9]). MS: found: M+' 369.8909; calculated (C6F9I): M+’
369.8901.
B. Similarly, bromopolyfluorocyclohexenes 10 and 11
( 2 : 1 , molar) were obtained in quantitative yield (l9F
NMR) from 5a and 6a (2 :1, molar) (99 mg) and NaBr
(165 mg) in MeCN (0.5 ml).
benzene was added in excess at -20 °C to remove the
residual XeF2. After warming to room temperature the
volatile compounds were removed in a vacuum to give 68
mg of salts 5b and 6b (yields 58 and 28 %, respectively).
B.
The reaction of la (130 mg, 0.28 mmol) with
XeF2(232 mg, 1.37 mmol) in aHF (0.3 ml) was performed
in a similar manner. The solution of 5a and 6a (60 and 30
% yields, respectively, based on la) (19F NMR) was kept
at room temperature for further 2 days without changes.
2a: i9F NMR (aHF, -15 °C): -93.0 (F-3,3), -98.0 (F-
6 .6), -147.7 (F-4), -148.9 (F-5) ppm.
10: 19F NMR (CH3CN): -107.2 and -107.7 (F-3,3,6 ,6 ),
-131.8 and -133.7 (F-4,4,5,5) ppm.
11: 19F NMR (CH3CN): -106.3 (F-6 ,6), -111.5 (F-2),
-117.4 (F-3,3), -130.3 and -132.8 (F-4,4,5,5) ppm (cf.
[10]).
C. A solution of 5b and 6b (2: 1, molar) (68 mg) in aHF
(0.2 ml) was treated with NaBr (100 mg) at -35 °C and
warmed to room temperature. After 15 min the reaction
mixture was extracted with CH2CI2 (0.1 ml). The l9F
NMR spectrum showed the quantitative conversion of
both compounds 5b and 6b into the bromocyclohexenes
10 and 11 (2 : 1, molar).
2b: 19F NMR (aHF, -40 °C): -94.6 (F-3,3), -99.6 (F-
6 .6 ), -149.6 (F-5) ppm (the resonance of F-4 overlaps
with the resonance of the [BF4]~ anion at -148.1 ppm);
J/ Hz: (3,4) 20, (3,5) 9.7, (5,6) 21.5. ]H NMR (aHF, -40
°C): 8.31 ppm (m). l29Xe NMR (aHF, -40 °C): -2208 ppm
{<5(XeOF4) = -3772 ppm}, d, V(Xe, H-2) ca. 15 Hz.
5a: 19F NMR (S 0 2, -50 °C): -101.7 (F-3,3), -106.9 (F-
6.6), -129.7 and -134.2 (F-4,4,5,5) ppm. 19F NMR (aHF,
-15 °C): -99.1 (F-3,3), -104.7 (F-6 ,6), -127.3 and -132.0
(F-4,4,5,5) ppm. 19F NMR (CH3CN, -25 °C): -101.9 (F-
3,3), -107.1 (F-6 ,6 ), -129.6 and -133.2 (F-4,4,5,5) ppm.
'H NMR (S 02, -50 °C): 7.63 ppm.
5b: ,9F NMR (aHF, -40 °C): -100.5 (F-3,3), -105.8 (F-
6 .6), -128.3 and -132.7 (F-4,4,5,5) ppm. 'H NMR (aHF,
-40 °C): 8.46 ppm (m).129Xe NMR (aHF, -40 °C): -2150
ppm, d, 3J(Xe, H-2) ca. 15 Hz; {<$(XeOF4) = -3714 ppm}.
10: 19F NMR (CH2CI2): -108.5 and -109.5 (F-3,3,6 ,6 ),
-133.2 and -135.3 (F-4,4,5,5) ppm. 'H NMR (CH2C12):
6.40 ppm (m). MS: found: M+ 303.9126; calculated
(C6HBrF8): M+ 303.9134.
11: ,9F NMR (CH2CI2): -108.0 (F-6 ,6), -112.6 (F-2),
-118.8 (F-3,3), -133.2 and -134.6 (F-4,4,5,5) ppm (cf.
[10]) MS: found: M+ 321.9042; calculated (C6BrF9): M+
321.9040.
Reactions with NaX (X = Br, I).
A.
The solution of 5a and 6a (2 :1, molar) (60 mg) in
MeCN (0.2 ml) was treated with Nal (120 mg) at -30 °C
(immediate Xe evolution and I2 formation). The reaction
mixture was warmed to room temperature, the mother
liquor was decanted and the iodopolyfluorocyclohexenes
8 and 9(1.8: 1, molar) were obtained in quantitative yield
(19FNM R).
Acknowledgements
We gratefully acknowledge financial support by Volks-
wagen Stiftung and Fonds der Chemischen Industrie.
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