Trifluorovinylxenon(II) tetrafluoroborate

Article abstract of DOI:10.1039/a901380f

The first acyclic alkenylxenon(II) compound, trifluorovinylxenon(II) tetrafluoroborate, was prepared from XeF₂ and trifluorovinylboron difluoride and characterized by ¹³C, ¹⁹F and ¹²⁹Xe NMR spectroscopy.

Full text of DOI:10.1039/a901380f

Trifluorovinylxenon(ii) tetrafluoroborate
H.-J. Frohn*a and V. V. Bardinb
a Fachgebiet Anorganische Chemie, Gerhard-Mercator-Universität Duisburg, Lotharstr. 1, D-47048 Duisburg,
Germany. E-mail: frohn@uni-duisburg.de
b Institute of Organic Chemistry, Lotharstr. 1, 630090 Novosibirsk, Russia
Received (in Basel, Switzerland) 18th February 1999, Accepted 2nd April 1999
3
The first acyclic alkenylxenon(ii) compound, trifluorovi-
nylxenon(ii) tetrafluoroborate, was prepared from XeF2 and
trans)-(F-2 cis) 42 Hz, J(F-2 trans)–(F-1) 105 Hz], 2100.13
(F-2 cis) [3J(F-2 cis)–(F-1) 126 Hz], 2126.36 (F-1), 2148.22
([BF4]2, br) and HF at d 2190.83. All resonances of fluorine
atoms bonded to carbon have 129Xe satellites corresponding to
the natural abundance of 129Xe (I = 1/2) of 26.4%: 3J(F-2 cis)-
(
(
trifluorovinylboron difluoride and characterized by 13C, 19
and 129Xe NMR spectroscopy.
F
In 1993 we reported the first preparation of the cyclic
alkenylxenon(ii) compounds, (heptafluorocyclohexa-1,4-dien-
1-yl)xenon(ii) 1 and (nonafluorocyclohexen-1-yl)xenon(ii) 2
hexafluoroarsenates by stepwise fluorine addition to
[C6F5Xe]+[AsF6]2 using XeF2 in anhydrous HF (aHF).1 Later
(2-H-hexafluorocyclohexa-1,4-dien-1-yl)xenon(ii) 3 and (2-H-
octafluorocyclohexen-1-yl)xenon(ii) 4 tetrafluoroborates2 were
obtained in a similar manner from (2,3,4,5-tetrafluorophe-
nyl)xenon(ii) tetrafluoroborate. Electrophilic oxygenation of
[C6F5Xe]+[AsF6]2 with XeF2 and stoichiometric amounts of
H2O in HF gave (3-oxopentafluorocyclohexa-1,4-dien-1-yl)xe-
non(ii) 5 and (3-oxo-4,5-epoxypentafluorocyclohexen-1-yl)xe-
non(ii) 6 hexafluoroarsenates.3
129Xe) 30 Hz, 3J(F-2 trans)–(129Xe) 146 Hz and 2J(F-1)–
129Xe) 248 Hz.
Resonances4 of the carbon atoms C-1 and C-2 in the 19F-
decoupled 13C NMR spectrum of 7 were located at d 100.60
and 148.77, respectively and both displayed 129Xe satellites:
1J(C-1)–(129Xe) 131 Hz and 2J(C-2)–(129Xe) 18 Hz. For
comparison, the resonance of the carbon atom C-1 in the 13C
NMR spectrum of (nonafluorocyclohexen-1-yl)xenon(ii) hexa-
fluoroarsenate 2 in aHF (210 °C) occurs at d 96.28 and
1J(C-1)–(129Xe) is 114 Hz.1
The 129Xe NMR spectrum4 of compound 7 in aHF (230 °C)
displays a doublet of doublets of doublets at d 23636.1(Dn1/2
=
13 Hz) [2J(129Xe)–(F-1) 248 Hz, J(129Xe)–(F-2 cis) 30 Hz,
3J(129Xe)–(F-2 trans) 146 Hz] (Fig. 1). This deshielding of the
xenon atom in 7 is remarkable when compared to d(129Xe)
values of the (polyfluorocycloalken-1-yl)xenon(ii) compounds
1–6 (d 23912.3, 23858.4, 23771.8, 23714.0, 23916.2 and
23900.3, respectively)1–3 and is probably the result of a strong
‘through-space’ electronic interaction of the xenon atom with
the geminal fluorine atom F-1. This consideration is also in
agreement with the large value of 2J(129Xe)–(F-1), which is the
largest of the the known coupling constants in organoxenon
compounds.
3
Y
Y
F
F
A–
A–
Xe+
Xe+
1 Y = F, A– = [AsF6]–
3 Y = H, A– = [BF4]–
2 Y = F, A– = [AsF6]–
4 Y = H, A– = [BF4]–
O
F
O
F
O
A–
A–
Xe+
Xe+
The 19
F NMR spectrum of a solution of 7 in EtCN at 240 °C
consists of resonances at d 284.97 (F-2 trans) [2J(F-2 trans)–
(F-2 cis) 46 Hz, 3J(F-2 trans)–(F-1) 90 Hz], 2103.36 (F-2 cis)
[3J(F-2 cis)–(F-1) 124 Hz], 2137.81 (F-1) and 2149.59
([BF4]2) [3J(F-2 cis)–( 129Xe) 29 Hz, 3J(F-2 trans)–(129Xe) 139
Hz, 2J(F-1)–(129Xe) 191 Hz]. The 129Xe NMR signal was
located at d 23510.6 [2J(129Xe)–(F-1) 197 Hz, 3J(129Xe)–(F-2
5 A– = [AsF6]–
6 A– = [AsF6]–
All these synthetic routes to cyclic alkenylxenon(ii) salts are
based on the functionalization of arylxenon(ii) salts and are
restricted to the preparation of compounds with cyclohexa-
dienyl- and cyclohexenyl-xenon(ii) skeletons.
The topic of this paper is the elaboration of an alternative and
new strategy and a more general approach to the synthesis of
fluoroalkenylxenon(ii) compounds: the reaction of XeF2 with
polyfluoroalkenylboron difluorides. When XeF2 was reacted
with trifluorovinylboron difluoride at 240 °C in CH2Cl2 the
first acyclic alkenylxenon(ii) salt, trifluorovinylxenon(ii) tetra-
fluoroborate 7,† was obtained in very good yield [eqn. (1)].
F2trans
F2cis
F1
CH2Cl2
–40 °C
(1)
CF2 CFBF2 + XeF2
+ [BF4]–
Xe
7
Salt 7 is a white solid which decomposes above ca. 0 °C. It is
insoluble in CH2Cl2 but dissolves well in anhydrous HF (aHF),
MeCN and EtCN. Its solution in aHF is stable at room
temperature for some hours (monitored by 19F NMR), whereas
in MeCN (basic medium) 7 decomposes slowly above 220 °C
and rapidly at room temperature with formation of xenon and
some uncharacterized polyfluoroolefins.
Fig. 1 129Xe NMR resonance of 7 (aHF, 230 °C, 5 mm glass tube with FEP
inliner, measured on a Bruker DRX 500 spectrometer at 138.34 MHz; shift
values relative to neat XeOF4 at 24 °C.
The 19F NMR spectrum4 of the vinylxenon salt 7 in aHF
(230 °C) consists of resonances at d 281.91 (F-2 trans) [2J(F-2
Chem. Commun., 1999, 919–920
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cis) 27 Hz, 3J(129Xe)–(F-2 trans) 136 Hz]. Cooling to 270 °C
led to shielding of the fluorine atom F-1 and a decrease of 2J(F-
1)–(129Xe) to 188 Hz resulting from a favoured cation–anion
interaction over the cation–EtCN interaction:5 d 284.09 (F-2
We gratefully acknowledge Volkswagen Stiftung and Fonds
der Chemischen Industrie for financial support.
Notes and references
3
trans) [2J(F-2 trans)–(F-2 cis) 46 Hz, J(F-2 trans)–(F-1) 88
† Synthesis of trifluorovinylxenon(ii) tetrafluoroborate 7: a solution of XeF2
(1.83 mmol) in CH2Cl2 (15 ml) was cooled to 240 °C and added to a
solution of trifluorovinylboron difluoride (1.54 mmol) in dichloromethane
(10 ml) at 240 °C under a dry argon atmosphere. After stirring at 240 to
250 °C for 5 h the mother liquor was decanted and the residual product was
washed and dried under vacuum to yield compound 7 (1.30 mmol, 85
%).
Hz], 2102.62 (F-2 cis) [3J(F-2 cis)–(F-1) 123 Hz], 2138.27 (F-
3
1) and 2150.31 ([BF4]2) [3J(F-2 cis)–( 129Xe) 28 Hz, J(F-2
trans)–(129Xe) 136 Hz].
Chemical proof of the carbon–xenon bond and of the
electrophilic nature of the vinylxenon(ii) cation in 7 was
obtained by conversion into trifluoroiodoethene with loss of
Xe0 when a solution of 7 in EtCN was treated with NaI in excess
at @230 °C [eqn. (2)] (cf. ref. 6).
1 H.-J. Frohn and V. V. Bardin, J. Chem. Soc., Chem. Commun., 1993,
1072.
2 H.-J. Frohn and V. V. Bardin, Z. Naturforsch., Teil B, 1998, 53, 562.
3 H.-J. Frohn and V. V. Bardin, Z. Naturforsch., Teil B, 1996, 51, 1011.
4 The NMR shift values are relative to CCl3F (19F), TMS (13C) and XeOF4
F
F
F
F
+ excess NaI
EtCN/–30 °C
+ Xe + Na [BF4]
(2)
+ [BF4]–
F
Xe
F
I
(
129Xe).
5 H.-J. Frohn, A. Klose, T. Schroer, G. Henkel, V. Buss, D. Opitz and R.
Vahrenhorst, Inorg. Chem., 1998, 37, 4884.
6 H.-J. Frohn and V. V. Bardin, Z. Anorg. Allg. Chem., 1996, 622, 2031.
In summary, the trifluorovinylxenon cation is of great
importance for preparative and theoretical chemistry because it
is an unique precursor for the trifluorovinyl radical and
cation.
Communication 9/01380F
920
Chem. Commun., 1999, 919–920