The Reaction of 2-X-1,2-Difluoroalk-1-enyldifluoroboranes with Xenon Difluoride. A Methodical Approach to 1,2-Difluoroalk-1-enylxenon(II) Salts

Article abstract of DOI:10.1002/zaac.200300234

2-X-1,2-Difluoroalk-1-enylxenon(II) salts were prepared by the reaction of XeF₂ with XCF=CFBF₂ (X = F, trans-H, cis-Cl, trans-Cl, cis-CF₃, cis-C₂F₅) but no organoxenon(II) compounds were obtained when the trans-isomers of boranes, trans-XCF=CFBF ₂ (X = CF₃, C₄F₉, C ₄H₉, Et₃Si), were used under similar conditions.

Full text of DOI:10.1002/zaac.200300234

The Reaction of 2-X-1,2-Difluoroalk-1-enyldifluoroboranes with Xenon
Difluoride. A Methodical Approach to 1,2-Difluoroalk-1-enylxenon(II) Salts
Hermann-Josef Frohna,*, Nicolay Yu. Adoninb, and Vadim V. Bardinb
a Duisburg/Germany, Institute of Chemistry, Inorganic Chemistry, University Duisburg-Essen
b Novosibirsk/Russia, N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, SB RAS
Received July 14th, 2003.
Abstract. 2-X-1,2-Difluoroalk-1-enylxenon(II) salts were prepared by
the reaction of XeF2 with XCFϭCFBF2 (X ϭ F, trans-H, cis-Cl, trans-
Cl, cis-CF3, cis-C2F5) but no organoxenon(II) compounds were
obtained when the trans-isomers of boranes, trans-XCFϭCFBF2
(X ϭ CF3, C4F9, C4H9, Et3Si), were used under similar conditions.
Keywords: Noble gas chemistry; Xenon-carbon compounds; Poly-
fluoroalkenylboranes; Xenodeborylation; Polyfluoroalkylborate
anions; NMR spectroscopy
Reaktionen von 2-X-1,2-Difluoralk-1-enyldifluorboranen mit Xenondifluorid.
Untersuchung des methodischen Zugangs zu 1,2-Difluoralk-1-enylxenon(II)salzen
Inhaltsübersicht. 2-X-1,2-Difluoralk-1-enylxenon(II)salze wurden
bei der Reaktion von XCFϭCFBF2 (X ϭ F, trans-H, cis-Cl, trans-
Cl, cis-CF3, cis-C2F5) mit XeF2 isoliert. Bei Einsatz der trans-iso-
meren Borane trans-XCFϭCFBF2 (X ϭ CF3, C4F9, C4H9, Et3Si)
unter ähnlichen Reaktionsbedingungen wurden hingegen keine Or-
ganoxenon(II)salze erhalten.
Introduction
previously developed successful route to arylxenon(II) salts
[ArXe] [BF4]. This route started from arylmagnesium halide
or aryllithium and went via aryltrifluoroborate and aryldi-
fluoroborane compounds to the corresponding ar-
ylxenon(II) tetrafluoroborates (Scheme 1).
The chemistry of organic derivatives of xenon is a compara-
tively new field of fluoroorganoelement chemistry which
was established in 1989. In the last one and a half decade
a significant progress was achieved by synthesising salts
[RXe] [Y], covalent compounds RXeX or RXeRЈ (R and
RЈ are organic groups) and by studying their structure and
reactivity (see e.g. reviews [1, 2]). In the past the main ef-
forts were concentrated on arylxenon(II) compounds
whereas non-aromatic organoxenon compounds were less
investigated. Except of a preliminary communication on the
NMR spectroscopic observation of some alkynylxenon(II)
compounds [3] and a trifluoroethenylxenon(II) salt [4], only
the preparation of few polyfluorinated cycloalken-
ylxenon(II) salts in reactions of polyfluoroarylxenon(II)
salts with xenon difluoride in anhydrous HF (aHF) (oxidat-
ive fluorine addition) [5, 6] or with XeF2ϪH2O in HF (oxi-
dative oxygenation) was reported [7]. Evidently, the latter
routes are restricted to the preparation of compounds with
cyclohexa-1-dienyl- and cyclohex-1-enylxenon(II) skeletons.
In the framework of our systematic investigation of or-
ganoxenon compounds [1] we underwent efforts to prepare
and study fluoro-containing acyclic alk-1-enylxenon(II)
compounds. The methodical approach was grounded on the
Scheme 1
This paper is concerned with a systematic study of the
scope and the limitation of Scheme 1 applied to the syn-
thesis of 2-X-1,2-difluoroalk-1-enylxenon(II) salts. To prove
the usefulness of the last step of the reaction sequence solu-
tions of 2-X-1,2-difluoroalk-1-enyldifluoroboranes XCFϭ
CFBF2 with different substituents X were prepared by ab-
stracting fluoride from the corresponding potassium alken-
yltrifluoroborate salts in appropriate inert solvents. Follow-
ing the resulting alkenyldifluoroborane solutions were
treated with xenon difluoride. The selected substituents
X ϭ H, F, Cl, perfluoroalkyl CnF2nϩ1, C4H9, and Et3Si are
representatives of different electronic influences and steric
requirements.
Results
The starting materials, alkenyldifluoroboranes, and
their precursors and special requirements on the
solvents
* Prof. Dr. H.-J. Frohn
Anorganische Chemie, Institut für Chemie der Universität
Lotharstr. 1
D-47048 Duisburg
Fax: (ϩ49)2 03-379 22 31
e-mail: frohn@uni-duisburg.de
When we started this research, only a few fluoroalk-1-enyl-
difluoroboranes XCFϭCFBF2 were known prepared by
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H.-J. Frohn, N. Y. Adonin, V. V. Bardin
unique or very specific methods whereas alkenyltrifluoro-
borates K [XCFϭCFBF3] were an unknown class of or-
ganoelement compounds (see review [8]). Concerning
Scheme 1 the availability of polyfluoroalkenyldifluorobor-
anes as precursors for organoxenon(II) compounds depends
on the availability of the corresponding K [XCFϭCFBF3]
salts. Recently we elaborated a convenient methodical ap-
proach to these salts which starts with the nucleophilic alk-
enylation of trimethoxyborane by 2-X-1,2-difluoroalkenylli-
thium followed by the conversion of the intermediate lith-
ium alkenyltrimethoxyborates into the corresponding alk-
enyltrifluoroborates (Scheme 2).
For comparison, the related protodesilylation reaction of
1,2-difluoroalk-1-enyltrialkylsilanes RЈ3SiCFϭCFR (R ϭ
alkyl, alkenyl, phenyl) was completed at 40 °C within 1 h
[15]. Because the reaction proceeds via the initial formation
of the corresponding fluorosilicate anion [15], a very slow
conversion of 1a into 2a can be put down to the signifi-
cantly decreased Lewis acidity of the silicon atom under the
Ϫ
influence of the strong electron-donating BF3 substituent
Ϫ
trans to the Et3Si group in the CFϭCFBF3 moiety with
respect to the R substituent in alkenylsilanes RЈ3SiCFϭ
CFR.
Potassium cis- (3a) and trans- (4a) pentafluoroprop-1-en-
yltrifluoroborates were prepared by alkoxy-fluoride substi-
tution of lithium cis- and trans-pentafluoroprop-1-enyltri-
methoxyborates, respectively, applying K [HF2] in aqueous
HF (Eq. (3)) [16]. To our knowledge, this is the first ex-
ample of reactivity of an individual polyfluoroalkenyltrialk-
oxyborate salt beside the hydrodeboration reaction in protic
solvents [17].
Scheme 2
Using this path, potassium 2-X-1,2-difluoroalk-1-enyltri-
fluoroborates with X ϭ F, cis- and trans-Cl, cis-C2F5, cis-
C6F13, trans-C4F9, trans-C4H9, trans-C6H5 [9, 10], cis- and
trans-C3F7O [11] were successfully prepared. In all cases the
intermediate salts Li [XCFϭCFB(OMe)3] were used with-
out isolation.
For the present work we additionally needed several new
alkenyldifluoroboranes XCFϭCFBF2 (X ϭ cis- and trans-
CF3, trans-H, trans-Et3Si). All of them were prepared as
solution by fluoride abstraction from the corresponding bo-
rates K [XCFϭCFBF3] using boron trifluoride. Potassium
trans-triethylsilyl-1,2-difluoroeth-1-enyltrifluoroborate (1a)
was synthesised from trans-1,2-difluoroethenyltriethylsilane
[12] in accordance with Scheme 2 (Eq. (1)).
On account of the high Lewis acidity of polyfluorinated
alkenyldifluoroboranes (the oxidative fluorinating ability of
XeF2 is increased by formation of the polarised state
[FXe]ϩ) and the high reactivity of the organoxenon(II)
salts, the number of solvents, suitable for carbon-xenon
bond formation is limited. Although dichloromethane was
a good solvent for the preparation of arylxenon(II) tetra-
fluoroborates [18], it is non-stable toward XeF2 in the pre-
sence of strong Lewis acids like polyfluoroalk-1-enyldifluo-
roboranes. Whereas the aryldifluoroborane-initiated by-re-
action of XeF2 with CH2Cl2 was not significant, in the pres-
ence of XCFϭCFBF2 the reaction of XeF2 with CH2Cl2
became remarkable forming CH2ClF, CH2F2, CHCl2F, HF
etc [19]. This is accompanied by a significant loss of XeF2,
in by-reactions of XCFϭCFBF2 with HF, and in a de-
creased yield and purity of the target compounds, the alken-
ylxenon salts. Attempts to replace dichloromethane by the
oxidatively most stable solvent anhydrous HF led in some
cases to protodeborylation of alk-1-enyldifluoroboranes
(X ϭ F, Cl) and/or to the fluorine addition across the Cϭ
C double bond [20]. Fortunately, SO2ClF (m. p. Ϫ95 °C, b.
p. 8 °C) and the hydrofluorocarbons 1,1,1,3,3-pentafluoro-
butane (PFB) (m. p. approximately Ϫ35 °C, b. p. 40 °C),
1,1,1,3,3-pentafluoropropane (PFP) (m. p. Ϫ103 °C, b. p.
15 °C) are adequate solvents for either polyfluoroalkenyldi-
fluoroborane and xenon difluoride at low temperature and
are resistant to the attack of XeF2 under the reaction con-
ditions. The fluorocarbons CCl3F, CClF2CCl2F and
CF3CH2F were not suitable because of the negligible solu-
bility of XeF2 below Ϫ20 °C.
Potassium
trans-1,2-difluoroeth-1-enyltrifluoroborate
(2a) was obtained in a different manner because the direct
lithiation of trans-1,2-difluoroethene with BuLi in ether was
reported to fail [13]. An alternative pathway to trans-HCFϭ
CFLi via metalation of trans-HCFϭCFI (obtained in three
steps from CF2ϭCFCl in an overall yield of 38 % only [14])
with BuLi at Ϫ110 °C appeared to be not optimal. There-
fore we decided to perform the fluoride-assisted protodesi-
lylation of salt 1a. Indeed, the replacement of the triethylsi-
lyl group by the hydrogen atom took place but the reaction
proceeded very slowly (Eq. (2)).
The preparation of [XCFϭCFXe][Y] salts
The addition of xenon difluoride dissolved in PFP to the
solution of trans-1,2-difluoroethenyldifluoroborane (2b) in
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The Reaction of 2-X-1,2-Difluoroalk-1-enyldifluoroboranes with Xenon Difluoride
PFB at Ϫ50 °C caused the precipitation of a white solid.
The presence of BF3 had no influence on the formation
The H, 19F, and 129Xe NMR spectra of the solid dissolved
and the ratio of both products, the [cis-C2F5CFϭCFXe]ϩ
cation and the [C4F9BF3]Ϫ anion. The degree of conversion
of borane 8b in CH2Cl2 was reduced, probably caused by
the partial loss of XeF2 in the by-reaction with CH2Cl2.
It should be noted that the individual 1,2-difluoroalk-
1
in aHF proved unambiguously the formation of trans-1,2-
difluoroethenylxenon(II) tetrafluoroborate (2c) (Eq. (4)).
1-enylxenon(II) salts with simple fluoroelementate anions
Ϫ
[EFnϩ1
] can easily be prepared from salts with a mixture
of fluoroborate anions by treatment of their suspension
with a stronger Lewis acid than the corresponding fluoro-
boranes in an inert medium. For example,
trifluoroethenylxenon(II) and cis-heptafluorobut-1-en-
ylxenon(II) hexafluoroarsenates were obtained in quantita-
tive yields using AsF5 in CH2Cl2 without isolation of the
primary products (Eq. (7)).
In a similar way, the reaction of xenon difluoride with
the mixture of cis-2-chlorodifluoroethenyldifluoroborane
(5b) and trans-2-chlorodifluoroethenyldifluoroborane (6b)
(1 : 1.4) in PFB gave cis- (5c) and (6c) trans-2-chlorodi-
fluoroethenylxenon(II) tetrafluoroborates (1 : 1.3) (Eq. (5)).
In a preliminary communication [4] we have reported the
synthesis of trifluoroethenylxenon(II) tetrafluoroborate
when CF2ϭCFBF2 (7b) reacted with XeF2 in dichlorometh-
ane. However, the detailed re-examination showed that par-
allel to the formation of [CF2ϭCFXe] [BF4] (7c) fluorine
addition across the CϭC bond of a CF2ϭCF-B fragment
took place and resulted in the pentafluoroethyltrifluorobor-
ate anion (ca. 30 % with respect to [CF2ϭCFXe]ϩ). The
contribution of this competitive reaction route with respect
to the replacement of the BF2 group by xenon(II) (xenode-
borylation) increased when boranes of high acidity like cis-
pentafluoroprop-1-enyldifluoroborane (3b) and cis-hep-
tafluorobut-1-enyldifluoroborane (8b) were involved in the
reaction with XeF2. In both cases, the formation of cis-per-
fluoroalk-1-enylxenon(II) cations was accompanied by the
oxidative fluorination of the 1,2-difluoroalkenylboron moi-
ety (Eq. 6). The order of mixing of the reactants as well as
the use of different solvents did not affect the reaction
route. For instance, the cis-heptafluorobut-1-enylxenon(II)
cation, the tetrafluoroborate and the perfluorobutyltrifluo-
roborate anions were detected after the addition of a XeF2
solution in CH2Cl2 or in PFB to a solution of borane 8b in
the same solvent as well as after the addition of borane 8b
in CH2Cl2 to a suspension of XeF2 in CH2Cl2. It is remark-
able that the addition of solid XeF2 to the solution of alken-
yldifluoroboranes 3b in PFB or 8b in SO2ClF, respectively,
resulted in [cis-CnF2nϩ1CFϭCFXe] [CnF2nϩ1BF3] salts
(n ϭ 1, 2) while the desired counteranion [BF4]Ϫ was the
minor component or completely absent.
All salts [XCFϭCFXe] [Y] are white solids insoluble in
CH2Cl2, PFB, PFP, and SO2ClF but dissolve well in anhy-
drous HF, MeCN and EtCN. The reactivity of difluoroalk-
enylxenon(II) salts will be described in a forthcoming paper.
Reactions of trans-XCFϭCFBF2 (X ϭ CF3, C4F9,
C4H9, Et3Si) with XeF2
In contrast to boranes 2b, 3b, 5bϪ8b with trans-perfluoro-
alk-1-enyldifluoroboranes no trans-perfluoroalk-1-en-
ylxenon(II) salts were obtained. Thus in the reaction of
XeF2 with trans-perfluorohex-1-enyldifluoroboranes 9b in
CH2Cl2 at Ϫ45 °C XeF2 was mainly consumed in the reac-
tion with the solvent. When xenon difluoride dissolved in
PFB was added to a solution of trans-pentafluoroprop-1-
enyldifluoroborane (4b) in PFB at Ϫ25 °C the complete
consumption of both starting materials resulted and the
formation of perfluorinated propene, propane and propyl-
difluoroborane was found (Eq. (8)) instead of the C-Xe pro-
duct.
In addition to the information given before, the conver-
sion of trans-perfluorohex-1-enyldifluoroborane (9b) in
CH2Cl2 was only 15 % and resulted in perfluorohexane and
perfluorohexyldifluoroborane. After extraction of the reac-
tion mixture with aHF perfluorohexane, perfluorohexyltri-
fluoroborate, and trans-perfluorohex-1-enyltrifluoroborate
anions were detected by 19F NMR (Eq. (10)).
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H.-J. Frohn, N. Y. Adonin, V. V. Bardin
molecule XeF2 (fluoride donor) a Xe···F···B bridge is
formed (Scheme 3). If in the following transition state the
distance between carbon C(1) and the xenon atom is short
enough for a successful C-Xe bond formation, xenodebor-
ylation occurred and the [XCFϭCFXe] [BF4] salts were
formed (Scheme 3, route 1). This channel is realised for all
substituents X in cis position to the BF2 group, but in the
case of X in trans position only for small substituents (the
hydrogen, fluorine or chlorine atom) where the steric inter-
action between X and F2 (fluorine atom bonded to xenon
and not involved in the Xe···F···B bridge) is negligible.
The formation of the polyfluoroalkyltrifluoroborate
anions can be explained by a two step process. In the first
step fluoride is abstracted from the tetrafluoroborate anion
by polyfluoroalkenyldifluoroboranes, stronger Lewis acids
than BF3 (Scheme 3, route 2). Secondly the resulting anion
[XCFϭCFBF3]Ϫ which is more sensitive to oxidation than
the corresponding borane reacts with xenon difluoride,
polarised by a fluoride anion acceptor (BF3 or XCFϭ
CFBF2), to give the polyfluoroalkyltrifluoroborate anion
(Scheme 3, route 3). This is in agreement with the recently
reported conversion of both, boranes XCFϭCFBF2 and
borates [XCFϭCFBF3], into the perfluoroalkyltrifluoro-
borate salts by reaction with XeF2 in aHF [20]. In this reac-
tion anhydrous HF acts as a fluoride anion donor toward
the stronger Lewis acid XCFϭCFBF2 and additionally
xenon difluoride is polarised by the Lewis acid. In the pre-
sent case, both the tetrafluoroborate anion and XeF2 can
act as a fluoride donor. Due to the dependence of the fluor-
ide affinity of XCFϭCFBF2 on the nature of X, the relative
contribution of the routes 2 and 3 and consequently the
yield of the alkyltrifluoroborate anions [XCF2CF2BF3] de-
creases in the series X ϭ CnF2nϩ1 > F > Cl ϳ H.
If X is a bulky group, the steric interaction between X
and F2 Ϫ the terminal fluorine atom bonded to xenon Ϫ
prevents an optimal approximation of the xenon and car-
bon C(1) atoms (Scheme 4). In this case when X is a strong
electron-withdrawing substituent an alternative reaction
channel is opened. The interaction of the fluoride acceptor
(trans- XCFϭCFBF2) with the fluoride donor (XeF2) pro-
ceeds via transition state A and resulted in salt B or a struc-
turally related polarised intermediate (Scheme 4, route 1).
The oxidative addition of fluorine to the alkenyltrifluoro-
borate anion by [FXe]ϩ leads to the highly reactive species
C (Scheme 4, route 2) which can eliminate BF3 to give ole-
fin E via carbene D (Scheme 4, route 3) or can convert into
alkyldifluoroborane F via a 1,2-fluoride shift (Scheme 4,
route 4). A further reaction of F with XeF2 leads to the
alkylxenon compounds G or H which seem to be unstable
under the reaction conditions and convert into fluoroalkane
I (Scheme 4, route 5). It should be mentioned that the for-
mation of fluoroalkanes C3F8, C6F14 and C4H9C2F5 from
alkenyldifluoroboranes 4b, 9b, and 10b, respectively, cannot
be explained by the oxidative addition of fluorine to the
corresponding olefins XCFϭCF2 by XeF2. E.g., perfluoro-
hex-1-ene was not fluorinated by xenon difluoride in the
presence of boron trifluoride (Eq. (12)).
The replacement of the electron-withdrawing perfluoro-
alkyl groups X ϭ CF3, C4F9 in trans-XCFϭCFBF2 by the
electron-donating butyl or triethylsilyl groups did also not
lead to organoxenon(II) compounds. 1,1,2-trifluorohex-1-
ene, 1,1,1,2,2-pentafluorohexane and traces of 1,2-difluoro-
hex-1-ene in addition to BF3 were found in the reaction of
trans-1,2-difluorohex-1-enyldifluoroborane (10b) with XeF2
in PFB (Eq. (11)). A complex mixture was obtained from
trans-2-triethylsilyl-1,2-difluoroethenyldifluoroborane (1b)
under the same conditions.
Discussion
The results of the reactions of XCFϭCFBF2 with XeF2
show some characteristic features. There is a strong effect
of the substituent X in borane XCFϭCFBF2 on the reac-
tion route and the kind of products in reactions with xenon
difluoride. Xenodeborylation (formal substitution of the di-
fluoroboryl group by the Xeϩ substituent) occurred when
X ϭ trans-H, trans-Cl, cis-Cl, F, cis-CF3 and cis-C2F5. It
is important to mention that the configuration of the 1,2-
difluoroalk-1-enyl group was retained during this trans-
formation. Within this series, from X ϭ H and Cl (traces
of organotrifluoroborate anions) to X ϭ perfluoroalkyl
(significant to equimolar amounts of alkyltrifluoroborate
anions), an increased formation of the alkyltrifluoroborate
anions [XCF2CF2BF3]Ϫ was observed in addition to xeno-
deborylation.
When X ϭ trans-CF3, trans-C4F9, trans-C4H9 or trans-
Et3Si, no organoxenon salts were formed in the reactions
of XCFϭCFBF2 with XeF2. This peculiarity is especially
surprising in the case of the isomers with X ϭ CF3 if we
take into account the successful xenodeborylation of both
cis- and trans-2-chlorodifluoroethenyldifluoroboranes.
Moreover, we had previously prepared a series of polyfluor-
inated cyclohexa-1,4-dien-1-ylxenon(II) and cyclohex-1-en-
ylxenon(II) salts by oxidative fluorination of polyfluoroar-
ylxenon(II) salts with xenon difluoride in aHF [1]. Their
carbon-carbon chain -CF2-CFϭC(Xeϩ)CF2- shows a close
similarity to the carbon skeleton of the expected trans-
CnF2nϩ1CFϭC(Xeϩ)F salts. Therefore, the failing of xeno-
deborylation for boranes 4b and 9b cannot be rationalised
by an instability of the corresponding alkenylxenon(II) salts
rather an alternative explanation is required.
We assume that in the initial interaction of organodifluo-
roborane XCFϭCFBF2 (fluoride acceptor) with the linear
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The Reaction of 2-X-1,2-Difluoroalk-1-enyldifluoroboranes with Xenon Difluoride
route 1 (Scheme 4). It should be emphasised that both
Schemes 3 and 4 illustrate possible pathways from alkenyl-
difluoroboranes to the isolated or detected products.
All new alkenylxenon(II) compounds were unambigu-
ously characterised by multinuclear NMR spectroscopy.
Following the 19F, 13C and 129Xe NMR spectral data of
trifluoroethenylxenon(II) salts as representative examples in
either acidic (aHF) and basic (propionitrile) media are dis-
cussed.
The 19F NMR spectrum of the trifluoroethenylxenon(II)
salt [CF2ϭCFXe] [AsF6] in anhydrous HF (Ϫ10 °C) dis-
played resonances at Ϫ82.05 (dd 2J(F2trans,F2cis) 41 Hz,
J(F2trans,F1) 107 Hz, 1F, F2trans), Ϫ100.02 (dd 3J(F2cis,F1)
126 Hz, 1F, F2cis), Ϫ125.37 (dd 1F, F1), Ϫ64.39 (br,
[AsF6]Ϫ) ppm additionally to aHF at Ϫ190 ppm. All reson-
ances of the fluorine atoms bonded to carbon had 129Xe-
satellites corresponding to the natural abundance of 129Xe
Scheme 3
(I ϭ 1/2) of 26 %: J(F2trans,Xe) 147 Hz, J(F2cis,Xe) 31 Hz
and 2J(F1,Xe) 252 Hz. Remarkably, the cationic part of the
spectrum coincided completely with the corresponding part
of salts which contained the tetrafluoroborate (δ Ϫ148.2,
br) and the [C2F5BF3] [δ Ϫ82.43 (3F), Ϫ135.73 (2F),
Ϫ149.45 (3F, BF3)] counteranions [21].
3
3
The resonances of the carbon atoms C-1 and C-2 in the
19F decoupled 13C NMR spectrum of the [CF2ϭCFXe]ϩ
cation (in aHF, Ϫ30 °C) were located at δ 100.60 and
148.77 ppm, respectively, and both displayed 129Xe-satel-
1
2
lites: J(C1,Xe) 131 Hz and J(C2,Xe) 18 Hz. For compari-
son, the resonance of the carbon atom C-1 in the 13C NMR
spectrum of nonafluorocyclohex-1-enyl)xenon(II) hexa-
fluoroarsenate in aHF (Ϫ10 °C) occurs at δ 96.28 and
1J(C1,Xe) is 114 Hz [5].
The 129Xe NMR spectrum of [CF2ϭCFXe] [AsF6] in
aHF (Ϫ10 °C) displays a doublet of doublets of doublets at
δ Ϫ3641 J(Xe,F1) 252 Hz, 3J(Xe,F2cis) 31 Hz , J(Xe,F2-
trans) 147 Hz. This deshielding of the xenon atom in the
[XCFϭCFXe]ϩ cation is remarkable in comparison to the
δ(129Xe) values of the heptafluorocyclohexa-1,4-dien-1-
ylxenon(II) (δ Ϫ3912), nonafluorocyclohex-1-enylxenon(II)
(δ Ϫ3858), 2-H-hexafluorocyclohexa-1,4-dien-1-ylxenon(II)
(δ Ϫ3772) and 2-H-octafluorocyclohex-1-enylxenon(II) (δ
Ϫ3714) salts [5, 6]. Probably, this is the result of a the strong
“through-space” electronic interaction of the xenon atom
with the geminal fluorine atom F1.
2
3
Scheme 4
The strong donor-acceptor interaction between the tri-
fluoroethenylxenon(II) cation and EtCN (base) caused sig-
nificant changes in the NMR spectra with respect to the
spectra in aHF. The 19F NMR spectrum [22] of a solution
of [CF2ϭCFXe] [BF4, C2F5BF3] in EtCN at Ϫ40 °C con-
sists of resonances at δ Ϫ84.97 (ddd* 2J(F2trans,F2cis) 46 Hz,
At the first glance, the formation of alkyldifluoroborane
F (Scheme 4) looks similar to the formation of the alkyltri-
fluoroborate anion in Scheme 3. Indeed, we cannot exclude
a certain contribution of route 3 (Scheme 4) for the forma-
tion of the [XCF2CF2BF3]Ϫ anions when boranes 3b, 7b, 8b
react with XeF2. However, there are two circumstances
which minimised this possibility. First, no remarkable quan-
tities of perfluoroalkenes were found among the reaction
products of boranes 3b, 7b, 8b with XeF2. Secondly, the
amount of [XCF2CF2BF3]Ϫ in these reactions never ex-
ceeded the amount of the cation [XCFϭCFXe]ϩ. This sup-
ports our assumption that the intermediate anion [XCFϭ
CFBF3]Ϫ is formed on route 2 (Scheme 3) rather than on
3J(F2trans,F1) 90 Hz, 3J(F2trans,Xe) 139 Hz 1F, F2trans
,
3
3
Ϫ103.36 (ddd* J(F2cis,F1) 124 Hz, J(F2cis,Xe) 29 Hz, 1F,
F2cis, Ϫ137.81 (ddd* 2J(F1,Xe) 191 Hz, 1F, F1), Ϫ149.59
([BF4]Ϫ) and Ϫ83.34 (m, 3F, F2), Ϫ136.93 (q 2J(F1,B)
19 Hz, 2F, F1), Ϫ153.82 (q (1 : 1 : 1 : 1) J(F,B) 41 Hz, 3F,
1
BF3) which belong to the [C2F5BF3] counteranion. The
129Xe NMR signal was located at δ Ϫ3511 (d 2J(Xe,F1)
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3
3
197 Hz, d J(Xe,F2cis) 27 Hz and d J(Xe,F2trans) 136 Hz).
phere of dry argon before 2.5 M BuLi in hexanes (15 ml, 37 mmol)
was added drop-wise within 20 min at Ϫ100 to Ϫ95 °C. The reac-
tion mixture was stirred at this temperature for 1 h before a solu-
tion of B(OMe)3 (3.7 g, 35 mmol) in ether (6 ml) was added within
3 min using a syringe. The resulting suspension was maintained at
Ϫ83 to Ϫ78 °C for 20 min, warmed to Ϫ10 °C and poured into a
stirred solution of K [HF2] (20.6 g, 264 mmol) in 40 % HF (5 ml)
and water (50 ml) and kept overnight. After saturation with KF
the product was extracted with acetone (3 x 50 ml), the combined
extracts were dried over MgSO4. After evaporation under reduced
pressure a yellowish oil was obtained. The 19F NMR spectrum
showed the formation of both salts, K [trans-Et3SiCFϭCFBF3] and
K [trans-Et3SiCFϭCFBF2(OMe)]. The oil was dissolved in MeOH
(15 ml) and 40 % HF (5 ml) and stirred for 1 h at 20 Ϫ 22 °C. The
solution was neutralised with KOH and K2CO3. The precipitate
was filtered-off and dried over Sicapent in a vacuum desiccator to
give 3.3 g (32 %) of salt 1a.
Cooling to Ϫ70 °C led to a shielding of the fluorine atom
F1 and a decrease of J(F1,Xe) to 188 Hz, presumably, re-
2
sulting from a favoured cation-anion interaction over the
cation-EtCN interaction: δ Ϫ84.09 (ddd* 2J(F2trans,F2cis
)
46 Hz, 3J(F2trans,F1) 88 Hz, 3J(F2trans,Xe) 136 Hz, 1F,
F2trans), Ϫ102.62 (ddd* 3J(F2cis,F1) 123 Hz, 3J(F2cis,Xe)
28 Hz, 1F, F2cis), Ϫ138.27 (ddd*, 1F, F1).
Experimental Section
NMR spectra were recorded on Bruker spectrometers, AVANCE
300 (1H at 300.13 MHz, 11B at 96.29 MHz, 19F at 282.40 MHz,
129Xe at 83.01 MHz), DRX 500 (1H at 500.13 MHz, 11B at
160.46 MHz, 13C{19F} at 125.76 MHz, 129Xe at 139.08 MHz). The
chemical shifts are referenced to TMS (1H, 13C), BF3·OEt2/CDCl3
15 % v/v (11B), CCl3F (19F) (C6F6 as a secondary reference, δ ϭ
162.9) and XeOF4 (129Xe) (XeF2 as a secondary reference, XeF2/
MeCN/24 °C (cǞ0), δ ϭ Ϫ1813.28). The composition of the reac-
tion mixtures and the yields of products were determined by 1H or
19F NMR spectroscopy using quantitative standards. The IR spec-
tra were recorded on a Bruker Vector 22 FT-spectrometer using
KBr pellets. The elemental analysis was performed in the N. N.
Vorozhtsov Novosibirsk Institute of Organic Chemistry (Novosi-
birsk, Russia).
C8H15BF5KSi (284,19): calculated C 33.81, H 5.32, F 33.43; found
C 33.4, H 5.45, F 33.3 %.
1H NMR (acetone): δ ϭ 0.97 (t 3J(H2,H1) 8 Hz, 9H, H2), 0.68 (q, 6H, H1).
19F NMR (acetone): δ ϭ Ϫ141.87 (q 1J(F,B) 39 Hz, 3F, BF3), Ϫ159.66
(pseudo-dd, 1F, F1), Ϫ178.57 (dq 3J(F1,F2) 114 Hz, 4J(F2,BF) 9 Hz, 1F, F2).
11B NMR (acetone): δ ϭ 0.31 (qdd 1J(B,F) 42 Hz, 3J(B,F1) 25 Hz, 3J(B,F2)
10 Hz).
IR ν¯ (cmϪ1): 2958 (CH) (m), 2915 (CH) (m), 2879 (CH) (m), 1634 (w), 1464
(w), 1417 (w), 1380 (w), 1220 (m), 1049 (s), 1007 (s), 738 (m), 701 (m),
575 (w).
Dichloromethane (Baker), acetonitrile and propionitrile (Riedel-
deHae¨n) were purified by standard procedures. Fluorotrichloro-
methane, 1,1,1,3,3-pentafluorobutane (PFB, Solvay), 1,1,1,3,3-
pentafluoropropane (PFP, Honeywell), 1,1,2-trichlorotrifluoro-
ethane (Solvay), 40 and 48 % HF (Fluka), boron trifluoride
(Messer Griesheim), KF (Fluka), K [HF2] (Riedel-deHae¨n), chloro-
triethylsilane (Aldrich), 2.5 M BuLi in hexanes (Aldrich) were
used as supplied. After purification SO2ClF was distilled over SbF5
before use. B(OMe)3 (Fluka) was distilled over sodium. Arsenic
pentafluoride was prepared from AsF3 and elemental fluorine. Hy-
drogen fluoride was dried by electrolysis (stainless steel cell, Ni-
electrodes). All manipulations with alkenyldifluoroboranes, alken-
ylxenon(II) salts and anhydrous HF were performed in FEP (block
copolymer of tetrafluoroethylene and hexafluoropropylene) equip-
ment under an atmosphere of dry argon.
Potassium trans-H-1,2-difluoroeth-1-
enyltrifluoroborate K [trans-HCFϭCFBF3] (2a)
A suspension of K [trans-Et3SiCFϭCFBF3] 1a (2.49 g, 8.7 mmol)
and KF (1.5 g, 25.8 mmol) in DMSO (15 ml) and water (1 ml) was
stirred at 95 Ϫ 100 °C (bath). After 36 h the conversion of 1a into
2a was 80 % (19F NMR). After addition of water (0.5 ml) the reac-
tion mixture was stirred for an additional 58 h at the same tempera-
ture before it was evaporated to dryness in vacuum. CH2Cl2 (2 x
25 ml) was added to the residue and the solid was filtered-off and
extracted with MeCN (3 x 25 ml). The combined extracts were
dried over MgSO4. After evaporation of the solvent the resulting
solid was extracted once more with acetone (15 ml) and the extract
was decanted from the fine precipitate. The solvent was evaporated,
the residual product was dried in a vacuum desiccator over Sica-
pent. Salt 2a was obtained in 76 % (1.13 g) yield.
The solubility of XeF2 was determined to 24 mg (0.143 mmol)
(CCl3F, 24 °C), 23 mg (0.136 mmol) (SO2ClF, Ϫ20 °C), 15 mg
(0.091 mmol) (SO2ClF, Ϫ40 °C), < 1 mg (CF3CH2F, Ϫ40 °C),
67 mg (0.40 mmol) (PFB, 24 °C), 35 mg (0.20 mmol) (PFB, 0 °C),
30 mg (0.18 mmol) (PFB, Ϫ20 °C), 150 mg (0.89 mmol) (PFP,
24 °C), 49 mg (0.29 mmol) (PFP, Ϫ20 °C), 94 mg (0.55 mmol)
(CH2Cl2, Ϫ20 °C), and 49 mg (0.29 mmol) (CH2Cl2, Ϫ40 °C) per
ml of solvent (19F NMR).
C2HBF5K (169,93): calculated C 14.14, H 0.59, F 55.90; found C
14.1 H 0.32 F 55.0 %.
1H NMR (acetone-d6): δ ϭ 7.21 (md 2J(H,F2) 81 Hz). 19F NMR (acetone-
d6): δ ϭ Ϫ142.82 (q 1J(F,B) 41 Hz, 3F, BF3), Ϫ178.08 (dq 3J(F1,H) 9 Hz,
2J(F1,B) 26 Hz, 1F, F1), Ϫ184.80 (qdd 4J(F2,BF3) 9 Hz, 2J(F2,H) 81 Hz,
3J(F2,F1) 121 Hz, 1F, F2) (This resonance contained additional lines caused
by the 10B isotope. The 19F chemical shift of the 10B isotopomer was located
0.0084 ppm to higher frequency.). 11B NMR (acetone-d6): δ ϭ 0.39 (dq
2J(B,F1) 29 Hz, 1J(B,F) 43 Hz).
Solutions of 2-X-1,2-difluoroalk-1-enyldifluoroboranes X ϭ cis-
C2F5 (8b), trans-C4F9 (9b) and F (7b) were prepared by fluoride
abstraction from the corresponding salts K [XCFϭCFBF3] with
BF3 in CH2Cl2 [23], in PFB or SO2ClF (see below). The yields
were determined by 19F NMR spectroscopy with the quantitative
internal reference CClF2CCl2F.
IR ν (cmϪ1): 3113 (CH) (w), 1681 (m), 1671 (m), 1336 (m), 1187 (s), 1088
¯
(vs), 1043 (vs), 966 (vs), 822 (m), 463 (m).
Potassium cis-perfluoroprop-1-enyltrifluoroborate K
[cis-CF3CFϭCFBF3] (3a)
Potassium trans-triethylsilyl-1,2-difluoroeth-1-
enyltrifluoroborate K [trans-Et3SiCFϭCFBF3] (1a)
A solution of Li [cis-CF3CFϭCFB(OMe)3] (2.42 g, 10 mmol) in
MeOH (2 ml) was added to a solution of K [HF2] (2.57 g, 33 mmol)
in 48 % HF (1 ml) and water (10 ml). After stirring overnight the
reaction mixture was neutralised with solid K2CO3 and then evapo-
A solution of trans-Et3SiCFϭCFH [12] (36.5 mmol) in ether
(100 ml) and THF (25 ml) was cooled to Ϫ100 °C under an atmos-
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The Reaction of 2-X-1,2-Difluoroalk-1-enyldifluoroboranes with Xenon Difluoride
rated to dryness in vacuum. The solid was dried over Sicapent in a
vacuum desiccator for 3 days and then extracted with hot MeCN.
The solvent was evaporated to give 1.30 g (55 %) of salt 3a.
the suspension was warmed to 0 °C for 10 min under the protection
of dry argon to remove the excess of BF3. After centrifugation the
solution of borane 3b (1.1 mmol) in PFB was decanted into a pre-
cooled (Ϫ25 °C) trap.
19F NMR (PFB, Ϫ20 °C): δ ϭ Ϫ66.85 (dd 4J(F3,F1) 8 Hz, 3J(F3,F2) 11 Hz,
3F, F3), Ϫ86.20 (very br., 2F, BF2), Ϫ131.59 (br, 1F, F2), Ϫ149.31 (br, 1F,
F1). 11B NMR (PFB, Ϫ20 °C): δ ϭ 18.2 (br s).
C3BF8K (237,93): calculated C 15.14, F 63.88; found C 15.9, F
63.1 %.
19F NMR (MeCN): δ ϭ Ϫ66.14 (d 3J(F3,F2) 20 Hz, q 5J(F3,BF) 7 Hz, 3F,
F3), Ϫ142.75 (q 1J(F,B) 37 Hz, 3F, BF3), Ϫ137.11 (m,1F, F1), Ϫ158.74 (m,
1F, F2). 11B NMR (MeCN): δ ϭ Ϫ0.25 (qdd 1J(B,F) 37 Hz, 3J(B,F1) 24 Hz,
4J(B,F2) 7 Hz).
trans-Perfluoroprop-1-enyldifluoroborane trans-
CF3CFϭCFBF2 (4b) in PFB
IR ν¯ (cmϪ1): 1699 (m), 1367 (s), 1226 (s), 1207 (s), 1125 (s), 1043 (s), 1011
(s), 892 (s), 737 (m), 645 (m).
Boron trifluoride (ca. 9 mmol) was blown into a stirred suspension
of 4a (69 mg, 0.29 mmol) in PFB (1.5 ml) at Ϫ30 to Ϫ25 °C. The
suspension was kept at Ϫ20 °C for 1 h without stirring and the
mother liquor was decanted. A solution of borane 4b (0.23 mmol,
79 % based on starting borate) in PFB was obtained.
19F NMR (PFB): δ ϭ Ϫ68.01 (dd 4J(F3,F1) 9 Hz, 3J(F3,F2) 22.5 Hz, 3F, F3),
Ϫ86.0 (very br, 2F, BF2), Ϫ157.22 (d 3J(F2,F1) 138 Hz, 1F, F2), Ϫ166.36 (d,
1F, F1). 11B NMR (PFB): δ ϭ 14.7 (br s).
Potassium trans-perfluoroprop-1-enyltrifluoroborate K
[trans-CF3CFϭCFBF3] (4a)
Solid Li [trans-CF3CFϭCFB(OMe)3] (4.84 g, 20 mmol) was
added to a stirred solution of K [HF2] (5.14 g, 66 mmol) in
40 % HF (2 ml) and water (20 ml) and kept overnight. After
neutralisation with solid K2CO3 the resulting precipitate
was filtered-off, dried over Sicapent in a vacuum desiccator
for 3 days. After extraction with hot MeCN the solvent was
evaporated to give 3.70 g (78 %) of salt 4a.
Chloro-1,2-difluoroeth-1-enyldifluoroboranes cis- (5b)
and trans-ClCFϭCFBF2 (6b) in PFB
C3BF8K (237,93): calculated C 15.14, F 63.88; found C
15.7, F 63.0 %.
19F NMR (MeCN): δ ϭ Ϫ66.56 (dd 3J(F3,F2) 11 Hz, 4J(F3,F1) 24 Hz, 3F,
F3), Ϫ143.95 (qd 1J(F,B) 39 Hz, 3J(BF,F1) 11 Hz, 3F, BF3), Ϫ155.65 (dqq
3J(F1,F2) 130 Hz, 3J(F1,B) 25 Hz,1F, F1), Ϫ179.66 (dqq 4J(F2,BF) 11 Hz, 1F,
F2). 11B NMR (MeCN): δ ϭ Ϫ0.30 (qd 1J(B,F) 40 Hz, 3J(B,F1) 25 Hz).
A solution of cis- and trans-ClCFϭCFBF2 (0.24 mmol, 85 %)
(42 % cis- and 58 % trans-isomers) in PFB (2 ml) was obtained in
a similar way from K [cis- and trans-ClCFϭCFBF3] (200 mg,
0.98 mmol) (48 % cis- and 52 % trans-isomers) after reaction with
BF3 (8 mmol).
IR ν (cmϪ1): 1372 (m), 1232 (s), 1172 (s), 1142 (s), 1050 (m), 1003 (s), 832
¯
(m), 714 (w), 627 (w), 539 (vw).
cis-Perfluorobut-1-enyldifluoroborane cis-C2F5CFϭ
CFBF2 (8b) in SO2ClF
trans-Triethylsilyl-1,2-difluoroeth-1-enyldifluoroborane
trans-Et3SiCFϭCFBF2 (1b) in PFB
Boron trifluoride (8 mmol) was blown into a stirred suspension of
K [cis-C2F5CFϭCFBF3] (330 mg, 1.14 mmol) in SO2ClF (3 ml) at
Ϫ35 °C for 30 min. The resulting suspension was warmed to 0 °C
for 10 min under the atmosphere of dry argon to remove the excess
of BF3. After centrifugation at 0 °C (ice-water bath) the solution
of borane 8b (1.1 mmol) in SO2ClF was decanted into a pre-cooled
(Ϫ10 °C) trap.
Boron trifluoride (ca. 5 mmol) was blown into a stirred suspension
of 1a (100 mg, 0.35 mmol) in PFB (1.5 ml) at Ϫ33 °C. Following
the suspension was kept at 0 °C to remove the excess of BF3. The
mother liquor was transferred into a cold (0 °C) trap. The solution
of borane 1b (0.27 mmol, 77 % based on starting borate) in PFB
was characterised by NMR.
19F NMR (PFB, Ϫ20 °C): δ ϭ Ϫ85.66 (br, 2F, BF2), Ϫ139.39 (d 3J(F2,F1)
129 Hz, t 4J(F2,BF2) 36 Hz, 1F, F2), Ϫ175.56 (d, 1F, F1). 11B NMR (PFB,
Ϫ20 °C): δ ϭ 20.4 (br s).
19F NMR (SO2ClF, Ϫ10 °C): δ ϭ Ϫ81.75 (br, 2F, BF2), Ϫ85.60 (td 3J(F4,F3)
3 Hz, 4J(F4,F2) 5 Hz, 3F, F4), Ϫ121.00 (d 3J(F3,F2) 14 Hz, 2F, F3), Ϫ125.74
(m, 1F, F2), Ϫ147.25 (m, 1F, F1).
trans-Perfluorohex-1-enyldifluoroborane trans-
C4F9CFϭCFBF2 (9b) in PFB
trans-H-1,2-Difluoroeth-1-enyldifluoroborane trans-
HCFϭCFBF2 (2b) in PFB
Boron trifluoride (12 mmol) was blown into a stirred suspension
of K [trans-C4F9CFϭCFBF3] (400 mg, 1.0 mmol) in PFB (4 ml) at
Ϫ30 to Ϫ25 °C for 30 min. The excess of BF3 was removed at 20 °C
protected by dry argon. After centrifugation the mother liquor was
separated by decantation. The solution of borane 9b (0.94 mmol,
94 %) in PFB was characterised by NMR.
Salt 2a (133 mg, 0.78 mmol) was suspended in PFB (1.5 ml) at Ϫ25
to Ϫ30 °C and BF3 (7 mmol) was blown into the suspension for
20 min. The suspension was centrifuged at Ϫ23 °C and the mother
liquor was decanted in a cold (Ϫ30 °C) trap. The solution of bor-
ane 2b (0.57 mmol, 74 %) was characterised by NMR.
19F NMR (PFB): δ ϭ Ϫ80.12 (tt 4J(F6,F4) 10 Hz, 3J((F6,F5) 3 Hz, 3F, F6),
Ϫ80.20 (br s, 2F, BF2), Ϫ117.18 (m, 2F, F3), Ϫ123.09 (m, 2F, F4), Ϫ124.99
(m, 2F, F5), Ϫ148.71 (d 3J(F2,F1) 139 Hz, 1F, F2), Ϫ165.16 (d, 1F, F1). 11B
NMR (PFB): δ ϭ 19.4 (br s).
1H NMR (PFB, Ϫ20 °C): δ ϭ 7.75 (dd 3J(H,F1) 7 Hz, 2J(H,F2) 74 Hz). 19F
NMR (PFB, Ϫ20 °C): δ ϭ Ϫ85.77 (br, 2F, BF2), Ϫ151.68 (dd 2J(F2,H)
74 Hz, 3J(F2,F1) 132 Hz, 1F, F2), Ϫ189.92 (d 3J(F1,F2) 132 Hz, 1F, F1). 11B
NMR (PFB, Ϫ20 °C) δ ϭ 20.8 (br s).
trans-1,2-Difluorohex-1-enyldifluoroborane trans-
C4H9CFϭCFBF2 (10b) in PFB
cis-Perfluoroprop-1-enyldifluoroborane cis-CF3CFϭ
CFBF2 (3b) in PFB
Boron trifluoride (16 mmol) was blown into a stirred suspension
Boron trifluoride (10 mmol) was blown into a stirred suspension
of 3a (400 mg, 1.1 mmol) in PFB (3 ml) at Ϫ35 °C for 25 min. Then
of K [trans-C4H9CFϭCFBF3] (0.89 mmol) in PFB (1.5 ml) at Ϫ30
Z. Anorg. Allg. Chem. 2003, 629, 2499Ϫ2508
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H.-J. Frohn, N. Y. Adonin, V. V. Bardin
9 Hz, 3F, F3), Ϫ128.35 (m, 2F, F2), Ϫ134.91 (m, 2F, F1), Ϫ152.25 (q 1J(F,B)
39 Hz, 3F, BF3) [C3F7BF3]Ϫ.
to Ϫ35 °C for 20 min. The excess of BF3 was removed at 20 °C
under an atmosphere of dry argon. The mother liquor was sepa-
rated by decantation after centrifugation at 0 °C. The solution of
borane 10b (0.70 mmol, 79 %) in PFB was characterised by NMR.
[cis- (5c) and trans- (6c) ClCFϭCFXe] [BF4]
19F NMR (PFB, Ϫ20 °C):ϭ Ϫ86.97 (br, 2F, BF2), Ϫ124.00 (dtt 3J(F2,F1)
129 Hz, 3J(F2,H3) 24 Hz, 3J(F2,BF2) 32 Hz, 1F, F2), Ϫ183.55 (d, 1F, F1).
A pre-cooled (Ϫ12 °C) solution of XeF2 (58 mg, 0.34 mmol) in
PFB (2 ml) was added in three portions to a stirred cold (Ϫ38 °C)
solution of cis- and trans-ClCFϭCFBF2 (0.24 mmol) (cis : trans ϭ
1 : 1.4) in PFB (2 ml) within 3 min. The fine suspension was stirred
at Ϫ36 to Ϫ25 °C for 1.5 h before the solvent was removed in
vacuum at Ϫ20 °C. A white solid [ClCFϭCFXe] [BF4] (cis : trans ϭ
1 : 1.3) (60 mg, 79 %) was obtained.
Preparation of 2-X-1,2-difluoroalk-1-enylxenon(II)
salts
[trans-HCFϭCFXe] [BF4] (2c)
A solution of XeF2 (105 mg, 0.62 mmol) in PFP (1 ml) was cooled
to 5 to 10 °C and then added to a cold (Ϫ47 °C) stirred solution
of trans-HCFϭCFBF2 (2b) (0.50 mmol) in PFB (1.5 ml) and PFP
(0.5 ml). The resulting suspension was stirred at Ϫ42 to Ϫ47 °C for
1.5 h, the mother liquor was decanted. The precipitate was washed
with cold (Ϫ45 °C) PFP (2 ml). Afterwards volatile components
were removed from the residue in vacuum at Ϫ30 °C. A white solid
[trans-HCFϭCFXe] [BF4] (45 mg, 32 %) was obtained. The pro-
duct contained an admixture (4 mol %) of the [CHF2CF2BF3]Ϫ salt
{19F NMR signals at Ϫ135.68 (d 2J(F2,H) 54 Hz, 2F, F2), Ϫ136.33
(br m, 2F, F1), and Ϫ148.6 (br, [BF3]) ppm) (aHF, Ϫ40 °C)}.
[cis-ClCFϭCFXe] [BF4] (5c):
19F NMR (aHF, Ϫ10 °C): δ ϭ Ϫ80.40 (dd* 3J(F1,F2) 90 Hz, 2J(F1,Xe)
182 Hz, 1F, F1), Ϫ82.71 (dd* 3J(F2,Xe) 165 Hz, 1F, F2), Ϫ148.90 (br,
[BF4]Ϫ). 129Xe NMR (aHF, Ϫ10 °C): δ ϭ Ϫ3545 (dd 2J(Xe,F1) 181 Hz,
3J(Xe,F2) 162 Hz).
[trans-ClCFϭCFXe] [BF4] (6c):
19F NMR (aHF, Ϫ10 °C): δ ϭ Ϫ97.19 (dd* 3J(F2,F1) 127 Hz,
1H NMR (aHF, Ϫ40 °C): δ ϭ 7.75 (ddd* 3J(H,F1) 5 Hz, 2J(H,F2) 68 Hz,
3J(F2,Xe) 8 Hz, 1F, F2), Ϫ106.70 (dd* J(F1,Xe) 201 Hz, 1F, F1),
2
3J(H,Xe) 22 Hz).
Ϫ148.90 (br, [BF4]Ϫ). 129Xe NMR (aHF, Ϫ10 °C): δ ϭ Ϫ3571 (d
2J(Xe,F1) 204 Hz).
19F NMR (aHF, Ϫ40 °C): δ ϭ Ϫ106.26 (dd* 3J(F2,F1) 115 Hz, 2J(F1,Xe)
209 Hz, 1F, F1), Ϫ148.15 (ddd* 3J(F2,F1) 115 Hz, 2J(F2,H) 68 Hz, 3J(F2,Xe)
58 Hz, 1F, F2), Ϫ148.58 (br, [BF4]Ϫ). 129Xe NMR (aHF, Ϫ40 °C): δ ϭ Ϫ3693
(dd 3J(Xe,F2) 60 Hz, 2J(Xe,F1) 206 Hz).
[CF2ϭCFXe] [Y] (Y ϭ [BF4] (7c), [C2F5BF3],
and [AsF6])
[cis-CF3CFϭCFXe] [Y] (Y ϭ [BF4] (3c) and
[C3F7BF3])
1. Solid XeF2 (315 mg, 1.86 mmol) was added to a cold (Ϫ50 °C)
stirred solution of CF2ϭCFBF2 (7b) (1.87 mmol) in CH2Cl2
(10 ml). The resulting suspension was stirred for 4 h at Ϫ40 to
Ϫ50 °C, the mother liquor was decanted and the residue was dried
in vacuum at Ϫ40 °C to give a white solid. The 19F NMR spectrum
in EtCN (Ϫ70 °C) showed the presence of [CF2ϭCFXe]ϩ
(1.36 mmol), [C2F5BF3]Ϫ (0.39 mmol) and [BF4]Ϫ (1.36 mmol)
(NMR spectroscopic data, see Discussion).
1. Solid XeF2 (200 mg, 1.18 mmol) was added in one portion to a
cold (Ϫ35 °C) stirred solution of cis-CF3CFϭCFBF2 (3b)
(1.1 mmol) in PFB (3 ml). A suspension was formed and stirred at
Ϫ35 to Ϫ25 °C for 1.5 h before the mother liquid was decanted.
The volatile products were removed from the residue in vacuum at
Ϫ20 °C. [cis-CF3CFϭCFXe] [C3F7BF3] (120 mg, 48 %) was ob-
tained as a white solid.
2. A cold (Ϫ45 °C) solution of XeF2 (62 mg, 0.36 mmol) in
CH2Cl2 (1 ml) was added to a cold (Ϫ50 °C) stirred solution of
CF2ϭCFBF2 (0.30 mmol) in CH2Cl2 (2.5 ml) and PFB (2 ml). A
suspension was formed and stirred for 1 h at Ϫ40 to Ϫ45 °C. The
volatile compounds were removed in vacuum at Ϫ25 °C. The resi-
due was cooled to Ϫ70 °C and suspended in cold (Ϫ70 °C) CH2Cl2
(3 ml) before AsF5 (0.2 g) was condensed. The suspension was
stirred for 30 min at Ϫ60 to Ϫ70 °C and the volatile compounds
were removed in vacuum at Ϫ25 °C to give the white solid, [CF2ϭ
CFXe] [AsF6], (64 mg, 44 %) (NMR spectroscopic data, see Dis-
cussion).
2. A pre-cooled (Ϫ10 °C) solution of XeF2 (87 mg, 0.50 mmol) in
PFB (2.5 ml) was added in three portions to a stirred cold (Ϫ30 °C)
solution of cis-CF3CFϭCFBF2 (3b) (0.50 mmol) in PFB (1.5 ml)
within 3 min. After 10 min, a white suspension appeared. The reac-
tion mixture was stirred at Ϫ30 to Ϫ25 °C for 2 h. The mother
liquor was decanted and the residue was dried in vacuum at Ϫ25 °C
to yield a white solid (120 mg). The 19F NMR spectrum in cold
(Ϫ30 °C) aHF showed the resonances of [cis-CF3CFϭCFXe]ϩ,
[BF4]Ϫ and [C3F7BF3]Ϫ in the molar ratio 1 : 0.15 : 0.85.
[cis-CF3CFϭCFXe] [C3F7BF3]/[BF4]
[cis-C2F5CFϭCFXe] [Y] (Y ϭ [BF4] (8c),
19F NMR (aHF, Ϫ10 °C): δ ϭ Ϫ65.44 (ddd* 4J(F3,Xe) 40 Hz, 3F, F3),
Ϫ77.37 (qdd* 4J(F1,F3) 7 Hz, 3J(F1,F2) 71 Hz, 2J(F1,Xe) 153 Hz, 1F, F1),
Ϫ122.92 (qdd* 3J(F2,F3) 9 Hz, 3J(F2,F1) 71 Hz, 3J(F2,Xe) 183 Hz, 1F, F2)
[cis-CF3CFϭCFXe]ϩ; Ϫ79.57 (t 4J(F3,F1) 10 Hz, 3F, F3), Ϫ126.29 (m, 2F,
F2), Ϫ133.49 (m, 2F, F1), Ϫ149.2 (m, 3F, BF3) [C3F7BF3]Ϫ, Ϫ149.2 [BF4]Ϫ.
129Xe NMR (aHF, Ϫ10 °C): δ ϭ Ϫ3431 (qdd 4J(Xe,F3) 38 Hz, 2J(Xe,F1)
154 Hz, 3J(Xe,F2) 183 Hz).
19F NMR (EtCN, Ϫ50 °C): δ ϭ Ϫ67.25 (ddd* 4J(F3,F1) 6 Hz, 3J(F3,F2)
10.7 Hz, 4J(F3,Xe) 36 Hz, 3F, F3), Ϫ87.08 (qdd* 4J(F1,F3) 6 Hz, 3J(F1,F2)
48 Hz, 2J(F1,Xe) 84 Hz, 1F, F1), Ϫ132.73 (qdd* 3J(F2,F3) 10.7 Hz, 3J(F2,F1)
48 Hz, 3J(F2,Xe) 163 Hz, 1F, F2) [cis-CF3CFϭCFXe]ϩ; Ϫ80.62 (t 4J(F3,F1)
[C4F9BF3], and [AsF6])
1. A cold (Ϫ50 °C) solution of XeF2 (130 mg, 0.76 mmol) in
CH2Cl2 (6 ml) was added to a cold (Ϫ50 °C) stirred solution of cis-
C2F5CFϭCFBF2 (8b) (0.70 mmol) in CH2Cl2 (4 ml). Immediately
a white suspension was formed. After 1 h the mother liquor was
decanted. The solid product was washed with cold (Ϫ45 °C)
CH2Cl2 (1 ml) and dissolved in pre-cooled (Ϫ45 °C) aHF (1 ml).
The 19F NMR spectrum (Ϫ30 °C) showed the resonances of [cis-
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The Reaction of 2-X-1,2-Difluoroalk-1-enyldifluoroboranes with Xenon Difluoride
C2F5CFϭCFXe]ϩ, [BF4]Ϫ and [C4F9BF3]Ϫ in the molar ratio 1 : 1
: 1.3 in addition to the singlet of aHF (Ϫ190 ppm).
129Xe NMR (aHF, Ϫ10 °C): δ ϭ Ϫ3423 (tdd 4J(Xe,F3) 57 Hz,
3
2J(Xe,F1) 153 Hz, J(Xe,F2) 183 Hz). 19F NMR (EtCN-CD3CN (3
3
2
: 1): Ϫ60 °C): δ ϭ Ϫ81.34 (dd* J(F1,F2) 48 Hz, J(F1,Xe) 85 Hz,
2. A cold (Ϫ50 °C) solution of cis-C2F5CFϭCFBF2 (8b)
(0.65 mmol) in CH2Cl2 (1.4 ml) was added to a cold (Ϫ50 °C)
stirred suspension of XeF2 (124 mg, 0.72 mmol) in CH2Cl2 (1 ml).
Immediately a white suspension was formed. After 2 h the mother
liquor was decanted. Its 19F NMR spectrum displayed the presence
of CHCl2F (Ϫ80.90 ppm) and CH2ClF (Ϫ169.86 ppm). The re-
sidual solid was washed with cold (Ϫ50 °C) CH2Cl2 (2 x 1 ml),
dried in vacuum at Ϫ40 °C, and dissolved in pre-cooled (Ϫ50 °C)
aHF (0.7 ml). The 19F NMR spectrum (Ϫ40 °C) showed the reson-
ances of [cis-C2F5CFϭCFXe]ϩ, [BF4]Ϫ and [C4F9BF3]Ϫ in the mo-
lar ratio 1 : 1 : 1 in addition to the singlet of aHF (Ϫ190 ppm).
1F, F1), Ϫ82.89 (m, 3F, F4), Ϫ119.05 (dd* 3J(F3,F2) 12 Hz,
4J(F3,Xe) 44 Hz, 2F, F3), Ϫ129.36 (dd* J(F2,Xe) 163 Hz, 1F, F2),
3
Ϫ64.67 (q, [AsF6]Ϫ).
Reactions of trans-XCF؍CFBF2 (X ؍ CF3, C4F9,
C4H9, Et3Si) with XeF2
Reaction of trans-Et3SiCFϭCFBF2 (1b) with XeF2
Solid XeF2 (48 mg, 0.28 mmol) was added in three portions to a
cold (Ϫ33 °C) stirred solution of trans-Et3SiCFϭCFBF2 (1b)
(0.27 mmol) in PFB (1.5 ml). Each addition caused the immediate
evolution of gas and the darkening of the solution. The solution
was stirred for 1 h at Ϫ28 to Ϫ32 °C. The 19F NMR spectrum
(Ϫ10 °C) showed the presence of trans-Et3SiCFϭCFBF2
(0.12 mmol, 56 % conversion), Et3SiCFϭCF2 (0.016 mmol), Et3Si-
3. A cold (Ϫ50 °C) solution of XeF2 (230 mg, 1.36 mmol) in
CH2Cl2 (10 ml) was added to a cold (Ϫ50 °C) stirred solution of
cis-C2F5CFϭCFBF2 (8b) (1.0 mmol) in CH2Cl2 (6.4 ml). A suspen-
sion was formed and stirred for 1 h at Ϫ40 to Ϫ60 °C. Then the
mother liquor was decanted. It contained CHCl2F (0.54 mmol),
CH2ClF (0.13 mmol), and cis-C2F5CFϭCFH (0.28 mmol) (19F
NMR). Cold (Ϫ60 °C) CH2Cl2 (10 ml) was added to the residual
solid and then AsF5 (300 mg, 1.7 mmol) was condensed at Ϫ65 °C.
The yellow suspension was stirred for 40 min at Ϫ60 to Ϫ50 °C
and then kept for 10 min at Ϫ36 °C. The mother liquor was de-
canted and the solid residue was washed with cold (Ϫ50 °C) CCl3F
(8 ml) and dried in vacuum at Ϫ20 °C for 2 h to yield 137 mg
(54 %) of [cis-C2F5CFϭCFXe] [AsF6] (19F NMR spectrum in
EtCN-CD3CN (3 : 1), Ϫ60 °C).
CF2CF3
(0.008 mmol),
Et3SiF
(0.037 mmol),
Et2SiF2
(0.054 mmol), and additionally some unknown fluoroaliphatic
products.
Reaction of trans-CF3CFϭCFBF2 (4b) with XeF2
A pre-cooled (Ϫ7 °C) solution of XeF2 (40 mg, 0.23 mmol) in PFB
(1.8 ml) was added in three portions to a cold (Ϫ37 °C) stirred
solution of trans-CF3CFϭCFBF2 (4b) (0.20 mmol) in PFB (1 ml)
within 5 min. The resulting solution was stirred at Ϫ36 to Ϫ25 °C
for 3 h. A sample of the solution showed the presence of CF3CFϭ
CF2 (0.056 mmol), C3F7BF2 (0.064 mmol) and C3F8 (0.040 mmol)
(19F NMR).
4. Solid XeF2 (67 mg, 0.40 mmol) was added in one portion to
a cold (Ϫ50 °C) stirred solution of cis-C2F5CFϭCFBF2 (8b)
(0.50 mmol) in SO2ClF (1.5 ml). A suspension was formed and
warmed from Ϫ50 to Ϫ30 °C within 1.5 h. All volatile substances
were removed in vacuum at Ϫ25 °C. The sticky residue (124 mg)
was dissolved in pre-cooled (Ϫ10 °C) aHF (0.6 ml).
The 19F NMR spectrum (Ϫ10 °C) showed the resonances of [cis-
C2F5CFϭCFXe] [C4F9BF3] and [cis-C2F5CFϭCFBF3]Ϫ {Ϫ83.18
(m, 3F, F4), Ϫ118.78 (d 3J(F3,F2) 14 Hz, 2F, F3), Ϫ136.12 (m), and
Ϫ142.97 (m) (F1 and F2) (cf. with 19F NMR spectra of cis-
C2F5CFϭCFBF2 [20] and K [cis-C2F5CFϭCFBF3] [20] in aHF)}
(1 : 0.2 molar ratio).
Reactions of trans-C4F9CFϭCFBF2 (9b) with XeF2
1. Solid XeF2 (88 mg, 0.52 mmol) was added in one portion to a
cold (Ϫ45 °C) stirred emulsion of trans-C4F9CFϭCFBF2 (9b)
(0.51 mmol) in CH2Cl2 (2 ml). The yellow reaction mixture was
stirred for 3 h at Ϫ40 °C. The solution phase was decanted from
the brownish oil phase. The 19F NMR spectrum of the solution
(Ϫ40 °C) showed the presence of trans-C4F9CFϭCFBF2
(0.36 mmol) and CH2ClF. Treatment of the oil with cold (Ϫ40 °C)
aHF (0.8 ml) resulted in a solution which contained [trans-
C4F9CFϭCFBF3]Ϫ, [C6F13BF3]Ϫ and C6F14 (yields 12, 12 and 6 %,
respectively) (19F NMR, Ϫ20 °C). The total conversion of trans-
C4F9CFϭCFBF2 was Յ 15 %.
5. A cold (Ϫ50 °C) solution of cis-C2F5CFϭCFBF2 (8b)
(0.50 mmol) and CClF2CCl2F (28 mg, 0.15 mmol) (internal refer-
ence) in CH2Cl2 (4 ml) was treated with BF3 (ca. 3.3 mmol) under
stirring for 15 min. Then a cold (Ϫ50 °C) solution of XeF2 (94 mg,
0.55 mmol) in CH2Cl2 (2 ml) was added to the solution mentioned
above and a suspension was formed which was stirred for 2 h. After
decantation at Ϫ30 °C the mother liquor contained CH2ClF
(0.10 mmol), cis-C2F5CFϭCFBF2 (0.18 mmol) and cis-C2F5CFϭ
CFH (0.10 mmol) (19F NMR). The solid residue was washed with
cold (Ϫ30 °C) CH2Cl2 (4 ml) and dried in vacuum at Ϫ20 °C to
yield 110 mg of a white solid. Its solution in pre-cooled (Ϫ20 °C)
aHF (1 ml) displayed the resonances of [cis-C2F5CFϭCFXe]ϩ,
[BF4]Ϫ and [C4F9BF3]Ϫ in the molar ratio 1 : 0.6 : 1 in addition to
the singlet of aHF (Ϫ190 ppm) (19F NMR, Ϫ20 °C).
2. Solid XeF2 (174 mg, 1.0 mmol) was added in small portions to
a cold (Ϫ30 °C) stirred solution of trans-C4F9CFϭCFBF2 (9b)
(0.90 mmol) in PFB (4 ml). The resulting solution was stirred at
Ϫ30 °C for 1 h and then kept for 30 min without stirring. No solid
material was detected. The 19F NMR spectrum of the mother
liquor showed the presence of trans-C4F9CFϭCFBF2 (0.10 mmol),
C6F13BF2 (0.20 mmol), C6F14 (0.50 mmol) in addition to traces of
trans-C4F9CFϭCFH and C4F9CFϭCF2 (19F NMR).
[cis-C2F5CFϭCFXe] [AsF6]
19F NMR (aHF, Ϫ10 °C): δ ϭ Ϫ72.09 (dd* 3J(F1,F2) 70 Hz,
2J(F1,Xe) 152 Hz, 1F, F1), Ϫ81.93 (m, 3F, F4), Ϫ116.57 (dd*
3J(F3,F2) 9.5 Hz, 4J(F3,Xe) 56 Hz, 2F, F3), Ϫ119.87 (tdqd*
4J(F2,F4) 5 Hz, 3J(F2,Xe) 182 Hz, 1F, F2), Ϫ64.1 (br, [AsF6]Ϫ).
Reaction of trans-C4H9CFϭCFBF2 (10b) with XeF2
Solid XeF2 (128 mg, 0.75 mmol) was added in three portions to a
cold (Ϫ35 °C) stirred solution of trans-C4H9CFϭCFBF2
Z. Anorg. Allg. Chem. 2003, 629, 2499Ϫ2508
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 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
2507

H.-J. Frohn, N. Y. Adonin, V. V. Bardin
(0.70 mmol) in PFB (1.5 ml). Each addition immediately caused an
evolution of gas and additionally the solution became darker. The
reaction solution was stirred for 1 h at Ϫ35 to Ϫ32 °C. The 19F
NMR spectrum (Ϫ20 °C) showed the presence of trans-C4H9CFϭ
CFBF2 (0.09 mmol, 87 % conversion), C4H9CFϭCF2 (0.27 mmol),
trans-C4H9CFϭCFH (0.04 mmol), C4H9CF2CF3 (0.07 mmol) and
BF3 (0.30 mmol) in addition to PFB.
[7] H.-J. Frohn, V. V. Bardin, Z. Naturforsch. 1996, 51b,
1011Ϫ1014.
[8] V. V. Bardin, H.-J. Frohn, Main Group Metal Chemistry, 2002,
25, 589Ϫ613.
[9] H.-J. Frohn, V. V. Bardin, Z. Anorg. Allg. Chem. 2001, 627,
2499Ϫ2505.
[10] The substituent X at C-2 in [XC2FϭC1FRЈ] molecules or ions
is specified by cis or trans relative to the position of RЈ ϭ Xeϩ,
Ϫ
BF2 and BF3 group.
Reaction of C4F9CFϭCF2 with XeF2 in CCl3F in the
presence of BF3
[11] H.-J. Frohn, V. V. Bardin, J. Fluorine Chem. 2003, 123, 43Ϫ49.
[12] S. A. Fontana, C. R. Davis, Y.- B. He, D. J. Burton, Tetra-
hedron, 1996, 52, 37Ϫ44.
Perfluorohexene-1 (82 mg, 0.27 mmol) and XeF2 (69 mg,
0.41 mmol) showed no reaction (19F NMR) when stirred in CCl3F
(0.7 ml) under bubbling of BF3 at Ϫ45 °C for 20 min. The same
result was obtained after bubbling of BF3 for 30 min at 18 Ϫ 20 °C
(19F NMR).
[13] F. G. Drakesmith, R. D. Richardson, O. J. Stewart, P. Tarrant,
J. Org. Chem. 1968, 33, 286Ϫ291.
´ˇ
ˇ
[14] J. Kvıcala, R. Hrabal, J. Czernek, I. Bartosova, O. Paleta, A.
Pelter, J. Fluorine Chem. 2002, 113, 211Ϫ218.
ˆ
[15] S. Martin, R. Sauvetre, J.-F. Normant, J. Organomet. Chem.
1984, 264, 155Ϫ161.
[16] The preparation of Li [cis- and trans-CF3CFϭCFB(OMe)3]
will be presented elsewhere.
[17] H.-J. Frohn, N. Yu. Adonin, V. V. Bardin, Main Group Metal
Chemistry, 2001, 24, 845Ϫ846.
Acknowledgements. We gratefully acknowledge financial support by
the Deutsche Forschungsgemeinschaft, the Russian Foundation for
Basic Research, and the Fonds der Chemischen Industrie. The au-
thors thank Solvay for generous donation of chemicals.
[18] H.-J. Frohn, H. Franke, V. V. Bardin, Z. Naturforsch. 1999,
54b, 1495Ϫ1498.
References
[19] W. W. Dukat, J. H. Holloway, E. G. Hope, P. J. Townson, R.
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[20] H.-J. Frohn, V. V. Bardin, Z. Anorg. Allg. Chem. 2002, 628,
1853Ϫ1856.
[1] H.-J. Frohn, V. V. Bardin, Organometallics 2001, 20,
4750Ϫ4762.
[2] W. Tyrra, D. Naumann, Organoxenon compounds, in Inor-
ganic Chemistry Highlights, G. Meyer, D. Naumann, L. Wese-
mann (Eds.), Wiley-VCH, Weinheim, 2002, pp. 297Ϫ317.
[3] V. V. Zhdankin, P. J. Stang, N. S. Zefirov, J. Chem. Soc. Chem.
Commun. 1992, 578Ϫ579.
[4] H.-J. Frohn, V. V. Bardin, J. Chem. Soc., Chem. Commun.
1999, 919Ϫ920.
[5] H.-J. Frohn, V. V. Bardin, J. Chem. Soc. Chem. Commun.
1993, 1072Ϫ1074.
[21] The 19F NMR spectra of [CnF2nϩ1BF3]Ϫ anions see refs. [20,
24].
[22] As a convention the multiplicities of the 19F NMR signals
caused by couplings with the 129Xe nucleus (satellites) are de-
noted by (*).
[23] H.-J. Frohn, V. V. Bardin, J. Organomet. Chem. 2001, 631,
54Ϫ58.
[24] H.-J. Frohn, V. V. Bardin, Z. Anorg. Allg. Chem. 2001, 627,
15 Ϫ16.
[6] H.-J. Frohn, V. V. Bardin, Z. Naturforsch. 1998, 53b, 562Ϫ564.
2508
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