Bis(pentafluorophenylxenonium) tetrafluoroterephthalate, p-C6F5XeO(O)CC6F4C(O)OXeC6F5, a hypervalent compound with two xenon-carbon bonds

Article abstract of DOI:10.1016/j.jfluchem.2009.05.010

Bis(pentafluorophenylxenonium) tetrafluoroterephthalate (1) was obtained by metathesis reactions of pentafluorophenylxenonium and tetrafluoroterephthalate salts. The availability of suitable solvents for the metatheses hampered the optimization of the rea

Full text of DOI:10.1016/j.jfluchem.2009.05.010

Journal of Fluorine Chemistry 130 (2009) 824–829
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Bis(pentafluorophenylxenonium) tetrafluoroterephthalate,
p-C6F5XeO(O)CC6F4C(O)OXeC6F5, a hypervalent compound with two
xenon–carbon bonds
*
Vural Bilir, Dieter Bla¨ser, Roland Boese, Hermann-Josef Frohn
Inorganic Chemistry, University of Duisburg-Essen, Lotharstr. 1, D-47048 Duisburg, Germany
A R T I C L E I N F O
A B S T R A C T
Article history:
Bis(pentafluorophenylxenonium) tetrafluoroterephthalate (1) was obtained by metathesis reactions of
pentafluorophenylxenonium and tetrafluoroterephthalate salts. The availability of suitable solvents for
the metatheses hampered the optimization of the reaction. The new xenon–carbon compound with two
polar Xe–O bonds was characterized by NMR spectroscopy in solution and by Raman spectroscopy in the
solid state. From (CF3)2CHOH/MeCN solutions single crystals were obtained with four alcohol molecules
attached to 1 by hydrogen bridges. The thermal properties of the intrinsically unstable title compound
are reported.
Received 23 April 2009
Received in revised form 11 May 2009
Accepted 11 May 2009
Available online 19 May 2009
Keywords:
Noble gas compound
Perfluoroarylxenon compounds
Tetrafluoroterephthalates
NMR
ß 2009 Elsevier B.V. All rights reserved.
Structure
Dedicated to Professor Henry
Selig on the occasion of his receipt
of the 2009 ACS Award for Creative
Work in Fluorine Chemistry.
1. Introduction
2. Results and discussion
The methodology applied for the synthesis of C6F5XeO(O)CC6F5
– the reaction of [C6F5Xe][AsF6] with Cs[O2CC6F5] in water [3,10] –
failed in the case of a 2:1 reaction with bifunctional Cs2[p-
(O2C)2C6F4]. An insoluble product resulted already from the
interaction of one [C6F5Xe]+ cation with one tetrafluoroterephtha-
late anion and was very unstable. Even at 0 8C it decomposed
rapidly despite attempts to rapidly isolate it. Alternative reaction
conditions were therefore investigated.
At present, three prototypes for Xe–C compounds – the major
number are arylxenon compounds – can be distinguished by
their bonding: arylxenonium salts [ArXe][Y] with weakly
coordinating anions [Y]ꢀ(Ar55C6F5 or C6H5ꢀnFn; Y = BF4,
BF4ꢀn(C6F5)n, B(CN)4, B(CF3)4, B(OTeF5)4, AsF6) [1–5], diaryl
xenon molecules Ar2Xe or ArXeAr’ [2,3,6–8], and finally
arylxenon compounds ArXeZ (Z = CN [3,6,8,12], Cl [1–3,9,11],
F [1–3,6,8,12], C6F5CO2 [3,10], Br [11]) with asymmetrical 3c–4e
(hypervalent) C–Xe–Z bonds. In both salts [(C6F5Xe)2Cl][AsF6]
[1–3,9] and [(C6F5Xe)2F][BF4] [3,6], two electrophilic [C6F5Xe]+
cations are bridged by a monoatomic, singly charged anion. The
present study is focused on the bifunctional coordinating
tetrafluoroterephthalate anion [p-(O2C)2C6F4]2ꢀ, which in the
presence of two electrophilic [C6F5Xe]+ cations forms the neutral
title compound, p-C6F5XeO(O)CC6F4C(O)OXeC6F5 (1).
2.1. Alternative procedures for the synthesis of 1 by metatheses
We have chosen three types of solvents (strongly coordinating
MeCN, weakly coordinating CH2Cl2, and the proton-donor solvent,
CF3CH2OH) which allowed all reactions to be carried out at ꢀ40 8C
and below. In MeCN, we used [C6F5Xe][BF4] and [N(nBu)4]2[p-
(O2C)2C6F4] as soluble starting materials (Eq. (1)).
MeCN
n
2½C6F5Xeꢁ½BF4ꢁ þ ½Nð BuÞ4ꢁ2½ pꢀðO2CÞ2C6F4ꢁꢀꢀ4!0 ꢂC
n
pꢀC6F5XeOðOÞCC6 F4 CðOÞOXeC6F5 ꢃ 2MeCN # þ 2½Nð BuÞ4ꢁ½BF4ꢁ
1
* Corresponding author.
(1)
E-mail address: h-j.frohn@uni-due.de (H.-J. Frohn).
0022-1139/$ – see front matter ß 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2009.05.010

V. Bilir et al. / Journal of Fluorine Chemistry 130 (2009) 824–829
825
In the 2:1 reaction at ꢀ40 8C, product 1 precipitated and the co-
product [N(nBu)4][BF4] remained in solution. Product 1 contained 2
MeCN, presumably co-crystallized. But MeCN could not be
removed over a period of more than 50 h under vacuum despite
warming to 0 8C. At 20 8C, the decomposition of 1 occurred parallel
to the removal of MeCN. The decomposition is discussed later.
When the precipitate of the 2:1 reaction product in MeCN, 1ꢃ2
MeCN, was repeatedly washed with CH2Cl2 while vigorously
stirring (ꢀ78 8C), 1 could be isolated free of MeCN.
product of 1. This effect was confirmed for an isolated sample of the
diester.
We have found two types of solvents suitable for 1: basic
nitriles like MeCN (poor solubility) and acidic alcohols like
CF3CH2OH (mp ꢀ44 8C) or (CF3)2CHOH (mp ꢀ4 8C) (satisfactory
solubilities). The thermal stability of 1 in both alcohol solutions is
lower than in MeCN solution. Thus, at ꢀ40 8C the decomposition of
1 in CF3CH2OH resulted in 20% C6F5H after 20 min whereas in more
acidic (CF3)2CHOH after 20 min at 0 8C, only 6% C6F5H was detected
In order to start the synthesis in the absence of coordinating
solvents, e.g., in polar CH2Cl2 [C6F5Xe]+ salts with weakly
coordinating anions having a sphere of fluoroorganic ligands like
[B(CF3)4]ꢀ or [B(C6F5)4]ꢀ [4,5] were required. When a cold
solution of [N(nBu)4]2[p-(O2C)2C6F4] in CH2Cl2 (ꢀ78 8C) was
added to a cold suspension of poorly soluble [C6F5Xe][B(CF3)4], 1
was formed as an insoluble product. After repeated washings at
low temperature and drying, pure 1 could be isolated free of
solvent (Eq. (2)).
(
19F NMR). The addition of MeCN to (CF3)2CHOH (1:1, vol) lowered
the melting point significantly (mp ꢀ86 8C) and provided an
acceptable stability and solubility of 1. After 21 h at ꢀ30 8C, only 3%
C6F5H had been formed. MeCN solutions of
1 showed no
decomposition at ꢀ20 8C after 4 h but were decomposed com-
pletely after 5.5 h at 20 8C. The complex mixture showed three
main products derived from the tetrafluoroterephthalate unit:
p-(C6F5O(O)C)2C6F4 (24%), p-C6F5O(O)CC6F4CO2H (43%), and
p-(HO2C)2C6F4 (30%). 30% of the C6F5 groups (C6F5Xe unit) were
not found in the products. This may be caused by diffusion of
volatile C6F5H (only 79% observed) through the trap material.
CH2Cl2
n
2½C6F5Xeꢁ½BðCF3Þ4ꢁ þ ½Nð BuÞ4ꢁ2½ pꢀðO2CÞ2C6F4ꢁꢀꢀ7!8 ꢂ
C
n
pꢀC6F5XeOðOÞCC6 F4 CðOÞOXeC6F5 # þ 2½Nð BuÞ4ꢁ½BðCF3Þ4ꢁ
(2)
2.3. NMR and Raman spectroscopic characterizations of
1
1 and 1ꢃ2 MeCN
The analogous reaction with the [C6F5Xe][B(C6F5)4] salt at
ꢀ78 8C suffered from the handicap that one MeCN molecule is
coordinated to the cation of [C6F5Xe][B(C6F5)4] [4,5]. MeCN could
be removed from the product after the reaction of [N(nBu)4]2[p-
(O2C)2C6F4] with [C6F5XeꢃNCMe][B(C6F5)4] by extensive washing
with CH2Cl2.
The solubility of 1 in MeCN is very poor. Therefore, the 13C and
129Xe NMR data were only measured in a (CF3)2CHOH/MeCN-
mixture (1:1, vol). Table 1 allows a comparison of the C6F5Xe unit
in 1 with the ionic species [C6F5Xe][BF4] in the same solvent
mixture at the same temperature and of the tetrafluoroterephtha-
late group in related compounds. The shieldings of the m- and p-F
1 could also be obtained from the 2:1 reaction of [C6F5Xe][BF4]
and Cs2[p-(O2C)2C6F4] in CF3CH2OH at ꢀ40 8C (Eq. (3))
resonances (C6F5Xe unit) in
1 are indicative for a strong
arylxenonium tetrafluoroterephthalate interaction which can be
described as an asymmetric 3c–4e C–X–O bond with significant
polarity for the Xe–O part. In addition to the Xe–O covalency, the
low frequency shift of o-F in 1 is caused by the proximity of the
‘‘keto’’ oxygen of the carboxylate group to XeII. The covalent
contribution in the Xe–O bond is supported by the large 3J(19F,
129Xe) coupling of 81 Hz which is 11 Hz larger than in
[C6F5Xe][BF4] and has a magnitude that is similar in C6F5XeF
(82 Hz) where the covalency of Xe–F was proven by a 1J(19F, 129Xe)
coupling of 4014 Hz [6]. The 129Xe NMR resonance of 1 appears to
low frequency (ꢀ3857 ppm) to that of [C6F5Xe][BF4] (ꢀ3825 ppm).
C1 in 1 (89.2 ppm, 1J(13C, 129Xe) = 168 Hz) shows a resonance at
higher frequency than in [C6F5Xe][BF4] (84.8 ppm, 1J(13C,
129Xe) = 132 Hz) and C6F5XeF (in CH2Cl2 at ꢀ78 8C: 86.4 ppm,
1J(13C, 129Xe) = 111 Hz) but at lower frequency relative to (C6F5)2Xe
(in (CD3)2CO at ꢀ60 8C: 123.2 ppm, 1J(13C, 129Xe) = 315 Hz); the
latter having a symmetrical 3c–4e bond. The influence of the less
usual solvents CF3CH2OH and (CF3)2CHOH on the shift values of the
C6F5Xe unit in 1 differs from that of the cation in the [C6F5Xe][BF4]
salt (Table 1). In the latter case, the m-F and p-F resonances appear
deshielded and are comparable to those in aHF solutions [4].
It is worth mentioning that all 19F NMR resonances of 1 in
MeCN solution at ꢀ40 8C are shifted to low frequencies relative
to those in (CF3)2CHOH solutions. This tendency may be
explained by a strong interaction between the tetrafluoroter-
ephthalate group and C6F5Xe moiety under basic conditions. The
presence of (CF3)2CHOH lowers the nucleophilicity of the
carboxylate groups in 1. In accordance with this assumption,
the 3J(19F, 129Xe) coupling constant in 1 increases in MeCN
solution to 85 Hz and the C6F4 resonance of the tetrafluoroter-
ephthalate anion becomes deshielded when changing from
MeCN to CF3CH2OH solutions (see also the solvent influence on
[N(nBu)4] and Cs salts, Table 1)
CF3CH2OH
2½C6F5Xeꢁ½BF4ꢁ þ Cs2½ p ꢀ ðO2CÞ2C6F4ꢁ ꢀ!
ꢄ ꢀ40 ꢂC
p ꢀ C6F5XeOðOÞCC6F4CðOÞOXeC6F5 þ 2Cs½BF4ꢁ #
(3)
1
This approach, however, has disadvantages. The insoluble co-
product, Cs[BF4], is micro-crystalline and transparent. Thus, its
separation from the mother liquor could not be easily followed
visually and was very time consuming. After 5 h at <ꢀ35 8C,
ꢅ34% of 1 was decomposed. Only one type of C6F5 and C6F4
groups was present in the product besides C6F5H (38% related to
C6F4). The ratio was C6F5:C6F4 = 1.66 instead of 2.0 (for 1) and
the presence of C6F5H are in agreement with a mixture of 1
(major) and p-C6F5XeO(O)CC6F4CO2H (minor). The presence of
p-(HO2C)2C6F4 can be excluded based on the 19F NMR spectrum.
2.2. Thermal stability: neat and in solution
The neat compound, 1ꢃ2 MeCN, is less stable than base-free 1, but
both are intrinsically unstable. When 1ꢃ2 MeCN was handled for less
than 30 min at 20 8C, no change could be detected by NMR
spectroscopy after dissolution. After 2 weeks at 20 8C, the total
decomposition led in a clean reaction (elimination of Xe0) to the
diester, p-(C6F5O(O)C)2C6F4. The absence of C6F5H is indicative of the
absence of MeCN in the coordination sphere of XeII [4] in 1ꢃ2 MeCN.
The decomposition of solid 1ꢃ2 MeCN was characterized by an
exothermic process at 89 8C (DSC, Tonset). In base-free 1, Tonset of the
exothermic process increased to 118 8C. One sample of 1 was stored
inside the glove box and the stability was checked periodically at
20 8C by Raman spectroscopy after 1 d, 6 d, and 10 d. In the latter
case, only small amounts of 1 had not decomposed.
The DSC measurements of 1 and 1ꢃ2 MeCN featured an
endothermic process at 145 and 141 8C, respectively, which
followed the decomposition and can be attributed to the melting
point of the diester, p-(C6F5O(O)C)2C6F4, the primary decomposition
In the Raman spectrum of 1, the most intense vibration at
180 cmꢀ1 is tentatively assigned to the Xe–C stretching mode. For

826
V. Bilir et al. / Journal of Fluorine Chemistry 130 (2009) 824–829
Table 1
19F NMR spectral data for p-(C6F5XeO(O)C)2C6F4 (1) and related compounds (
d
in ppm, J in Hz).
Compound
Solvent
T (8C)
C6F5 fragment
2,3,5,6-C6F4 fragment
o-F
3J(19F, 129Xe)
p-F
3J(19F, 19F)
m-F
F2,6
F3,5
p-(C6F5XeO(O)C)2C6F4
p-(C6F5XeO(O)C)2C6F4
p-(C6F5XeO(O)C)2C6F4
p-(C6F5XeO(O)C)2C6F4
[C6F5Xe][BF4]
CH3CN
–40
ꢀ30
ꢀ40
0
ꢀ128.7
ꢀ127.9
ꢀ127.2
ꢀ128.2
ꢀ125.5
ꢀ125.7
ꢀ124.8
ꢀ124.6
ꢀ152.0
ꢀ152.0
ꢀ152.2
ꢀ152.1
85
81
78
77
68
70
63
61
ꢀ146.3
ꢀ145.1
ꢀ143.1
ꢀ142.8
ꢀ142.3
ꢀ142.3
ꢀ139.6
ꢀ137.6
ꢀ156.8
ꢀ156.6
ꢀ157.0
ꢀ157.1
20
19
ꢀ156.6
ꢀ155.8
ꢀ154.4
ꢀ154.0
ꢀ155.1
ꢀ154.7
ꢀ152.6
ꢀ151.0
ꢀ161.8
ꢀ161.9
ꢀ161.9
ꢀ162.2
ꢀ142.4a
(CF3)2CHOH/CH3CNb
CF3CH2OH
ꢀ141.3a
ꢀ140.7
ꢀ140.4
18
(CF3)2CHOH
CH3CN
(CF3)2CHOH/CH3CNb
CF3CH2OH
18
ꢀ40
ꢀ30
ꢀ30
0
20; 5c
20; 5c
19
[C6F5Xe][BF4]
[C6F5Xe][BF4]
[C6F5Xe][BF4]
(CF3)2CHOH
CH3CN
18; 6c
21
p-(C6F5O(O)C)2C6F4
p-(C6F5O(O)C)2C6F4
p-C6F5O(O)CC6F4CO2H
p-C6F5O(O)CC6F4CO2H
p-((CF3)2HCO(O)C)2C6F4
p-((CF3)2HCO(O)C)2C6F4
p-(HO2C)2C6F4
ꢀ40
ꢀ40
ꢀ40
ꢀ40
24
ꢀ135.0
ꢀ134.7
(CF3)2CHOH/CH3CNb
CH3CN
21
21
ꢀ135.8
ꢀ135.7
ꢀ138.9
ꢀ140.6
(CF3)2CHOH/CH3CNb
CH3CN
21
d
e
ꢀ135.6
ꢀ135.4
ꢀ138.9
ꢀ141.4
ꢀ145.7f
ꢀ140.4
(CF3)2CHOH/CH3CNb
CH3CN
ꢀ40
ꢀ40
ꢀ40
ꢀ40
0
Cs2[p-(O2C)2C6F4]
CF3CH2OH
[N(n-C4H9)4]2[p-(O2C)2C6F4]
[N(n-C4H9)4]2[p-(O2C)2C6F4]
CH3CN
(CF3)2CHOH
a
Dn1/2 = 5 Hz.
Mixture: 1:1 vol.
4J(19F, 19F).
b
c
d
d
(CF3) = ꢀ72.2 ppm.
(CF3) = ꢀ72.4 ppm.
Dn1/2 = 2 Hz.
e
f
d
˚
comparison, in [C6F5Xe][BF4] with a stronger C–Xe bond, this
vibration was found at 205 cmꢀ1 [5]. When comparing 1 with 1ꢃ2
MeCN, no significant shift of this vibration (181 cmꢀ1) was noticed.
The vibrational frequencies of 1ꢃ2 MeCN at 2253, 2946, and 3005
are assigned to CBB N and C–H stretches, respectively.
and that in the [C6F5Xe]+ cation of [C6F5Xe][AsF6] (2.083(5) A,
average) [12]. The Xe–O distances behave opposite and were
˚
measured to be 2.503(6) A (average) in 1ꢃ4 (CF3)2CHOH compared
˚
˚
to 2.367(3) A in C6F5XeO(O)CC6F5 and 2.687(9) A in the salt [2,6-
C6H3F2Xe][OS(O)2CF3] [13]. A special feature of 1ꢃ4 (CF3)2CHOH are
the four contacts via hydrogen bridges of the alcohols to both types
of carboxylate oxygen atoms, the ‘‘keto’’ and the ‘‘ester’’ oxygen
2.4. The molecular structure of 1ꢃ4 (CF3)2CHOH
˚
atoms with Oꢃ ꢃ ꢃO distances of 2.608(6) to 2.650(6) A, respectively.
Single crystals of 1ꢃ4 (CF3)2CHOH were obtained from a
The different distances do not correlate with both types of oxygen
atoms (vide supra). The hydrogen bridges lower the nucleophili-
cities of the oxygen atoms bonded to XeII and are responsible for
the differences in the molecular structures between 1ꢃ4
(CF3)2CHOH and C6F5XeO(O)CC6F5. Also, the deshielding of the
C6F5Xe unit in the 19F NMR spectra of 1 in alcohol solutions can be
explained by a weaker Xe–O interaction caused by hydrogen
bridges. Their influence is supported by a comparison of both types
of carbon-oxygen bonds. In the carboxylate group, the C55O bonds
(CF3)2CHOH/MeCN (2:1, vol) solution of
1
at ꢀ70 8C. 1ꢃ4
(CF3)2CHOH crystallizes in the space group P21/c with four
molecules in the unit cell (Table 2). Fig. 1 shows the important
molecular parameters and the interaction between 1 and the acidic
solvent molecules. The typical structural features of 1ꢃ4
(CF3)2CHOH are briefly compared with that of C6F5XeO(O)CC6F5
(no acidic alcohol was present in the crystal) [10]. XeII has a nearly
linear environment (C–Xe–O: 175.0(3)8, average) in 1ꢃ4
(CF3)2CHOH compared with 178.1(1)8 in C6F5XeO(O)CC6F5. The
˚
are 1.232 and 1.228(6) and the C–O bonds 1.273 and 1.268(6) A,
˚
C–Xe distance in 1ꢃ4 (CF3)2CHOH is 2.103(4) A (average) and
respectively. These parameters are related to 1.220(3) and 1.271(4)
˚
˚
should be compared with that in C6F5XeO(O)CC6F5 (2.122(4) A)
A in C6F5XeO(O)CC6F5. The dihedral angles between the carboxy-
late groups are 158 (average) and the dihedral angles between the
C6F4 planes are 428 and 588 (average). The two alcohol molecules
coordinated to each carboxylate group did not lie exactly in the CO2
plane, but were positioned slightly above and below of this plane.
Table 2
Crystallographic and refinement data for p-(C6F5XeO(O)C)2C6F4 (1)ꢃ4 (CF3)2CHOH.
Compound
p-(C6F5XeO(O)C)2C6F4ꢃ4 (CF3)2CHOH
Empirical formula
Crystal size
C
20F14O4Xe2ꢃ4 C3H2F6O
2.5. Attempts to use 1 as a [C6F5Xe]+ source in a metathesis reaction
0.26 mm ꢆ 0.21 mm ꢆ 0.08 mm
Crystal system
Space group
Monoclinic
P21/c
The borderline bonding situation (covalent Xe–O bond with
significant polarity) in 1 prompted us to investigate the substitu-
tion of the [p-(O2C)2C6F4]2–anion by two weakly coordinating
singly charged anions in order to displace the C6F5Xe unit as cation
from 1 (Eq. (4)). Thus we combined a solution of Cs[B(C6F5)4] in
MeCN with a suspension of partially soluble 1 in MeCN.
˚
a = 16.0126(8) A
Unit cell dimensions
˚
b = 14.7397(8) A
˚
c = 21.2081(11) A
b
= 112.171(2)8
3
˚
Volume
4635.5(4) A
4
Z (molecules/unit cell)
Density (calculated)
Temperature
2.156 g cmꢀ3
183 ꢇ 2 K
MeCN
pꢀC6F5XeOðOÞCC6F4CðOÞOXeC6F5 þ 2Cs½BðC6F5Þ4ꢁꢀ= !
2½C6F5Xeꢁ½BðC6F5Þ4ꢁ þ Cs2½ pꢀðO2CÞ2C6F4ꢁ #
˚
(l = 0.71073 A)
a
Radiation
Mo K
2856
(4)
F(0 0 0)
Theta range for data collection
Final R indices
1.04–30.518
R1 = 0.0390, wR2 = 0.0945
The desired co-product, Cs2[p-(O2C)2C6F4], is insoluble in MeCN
at 20 8C. This fact was expected to be a driving force for the

V. Bilir et al. / Journal of Fluorine Chemistry 130 (2009) 824–829
827
Fig. 1. Molecular structure of p-(C6F5XeO(O)C)2C6F4 (1)ꢃ4 (CF3)2CHOH.
˚
Selected distances (A) and angles (8): Xe(1)–C(8) 2.101(4), Xe(2)–C(15) 2.105(5), Xe(1)–O(1) 2.495(3), Xe(2)–O(3) 2.511(4), Xe(1)- -O(2) 3.156(5), Xe(2)- -O(4) 3.120(5), O(1)–
C(7) 1.273(6), O(2)–C(7) 1.232(6), O(3)–C(14) 1.268(6), O(4)–C(14) 1.228(6), O(1)ꢃ ꢃ ꢃO(21_1) 2.622(6), O(2)ꢃ ꢃ ꢃO(21_2) 2.649(6), O(3)ꢃ ꢃ ꢃO(21_3) 2.650(6), O(4)ꢃ ꢃ ꢃO(21_4)
2.608(6), C(8)–Xe(1)–O(1) 174.7(2), C(15)–Xe(2)–O(3) 175.4(2).
metathesis reaction. At ꢀ40 8C (1 h) as well as at 20 8C (5 min), no
metathesis proceeded. A longer reaction time at 20 8C (18 h) was
accompanied by decomposition of 1. Thus, 1 is not a source of
[C6F5Xe]+ under basic conditions.
3.2. Crystal structure determination
X-ray diffraction data were collected at 183 ꢇ 2 K using a
diffractometer measurement device with a Siemens SMART three-
axis goniometer and an APEX II area detector system. Crystal
structure solution by Direct Methods and refinement on F2 were
performed using the Bruker AXS SHELXTL software suite Version 6.12
after data reduction, and empirical absorption correction was
performed using the Bruker AXS SAINT program Version 6.0. For
crystallographic and refinement details see Table 2.
The structure of 1ꢃ4 (CF3)2CHOH was pseudo orthorhombic
twinned by the twin law 1 0 0 0 ꢀ1 0 ꢀ 1 0 ꢀ1. Crystal structure
data have been deposited at the Cambridge Crystallographic Data
Centre (CCDC). Enquiries for data can be directed to Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge, U.K., CB2
1EZ or (e-mail) deposit@ccdc.cam.ac.uk or fax: +44 0 1223 336033.
Any requests sent to the Cambridge Crystallographic Data Centre
for this material should quote the full literature citation and the
reference number CCDC 735093.
2.6. Transesterification of p-(C6F5O(O)C)2C6F4 to
p-((CF3)2CHO(O)C)2C6F4
The dissolution of p-(C6F5O(O)C)2C6F4 in a 1:1 mixture of
(CF3)2CHOH/MeCN was accompanied by the complete trans-
formation of p-(C6F5O(O)C)2C6F4 into p-((CF3)2CHO(O)C)2C6F4
(Eq. (5)).
a
pꢀðC6F5OðOÞCÞ2C6F4ꢀ! pꢀððCF3Þ2CHOðOÞCÞ2C6F4 þ 2C6F5OH
(5)
a ¼ ðCF3Þ2CHOH=MeCN ð1 : 1; volÞ
The acidic property of the alcohol is responsible for this reaction.
Additionally, the transesterification may be supported by the
interaction of MeCN with the electrophilic carbonyl centre.
3. Experimental
3.3. Solvents and starting materials
3.1. Instrumentation
1,1,1,3,3-pentafluorobutane (PFB) (Solvay Fluor und Derivate
˚
GmbH) was dried over molecular sieves (3 A). CH3CN (KMF) was
The NMR spectra were recorded on a Bruker spectrometer
AVANCE 300 (1H at 300.13 MHz, 13C at 75.46 MHz, 19F at
282.40 MHz, and 129Xe at 83.46 MHz). The chemical shifts are
referenced to TMS (1H, 13C), CCl3F (19F) [with C6F6 as a secondary
refluxed and distilled from KMnO4 and repeatedly refluxed and
distilled from P4O10. CH2Cl2 (KMF) was treated in sequence with
conc. H2SO4, Na2CO3(aq), and H2O and finally refluxed and
˚
distilled from P4O10 and stored over molecular sieves type 3 A.
reference,
d
= ꢀ162.9 ppm], and XeOF4
(
129Xe) [with XeF2 as a
CF3CH2OH and (CF3)2CHOH were distilled and stored over
˚
secondary reference, XeF2/MeCN/24 8C at infinite dilution,
molecular sieves (3 A). [C6F5Xe][BF4] [15] [C6F5Xe][B(CF3)4] [4],
d
= ꢀ1813.28 ppm] [14]. Raman spectra were measured in FEP
and [C6F5XeꢃCH3CN][B(C6F5)4] [4] were prepared using literature
protocols. All manipulations with XeF2 and xenonium salts were
performed in FEP (block copolymer of tetrafluoroethylene and
hexafluoropropylene) equipment under an atmosphere of dry
argon. The glove box was operated with dry argon
(H2O < 1 ppm). Cs2[p-(O2C)2C6F4] and [NnBu4]2[p-(O2C)2C6F4]
were obtained by neutralization of the corresponding acid in
H2O.
or glass capillaries on a Bruker RFS 100/S spectrometer and IR
spectra as films between KBr plates on a Nicolet Impact 400
spectrometer. DSC analyses were performed using a Netzsch 204
Phoenix instrument equipped with a CC220 controller; a TASC414/
3A microprocessor system, and a personal computer. The solid
samples (2–7 mg) were weighed inside a glove box into aluminum
pans which were closed by
temperature difference between the sample and the empty
reference pan with pierced lid was measured choosing
a pierced aluminum lid. The
a
3.3.1. Analytical data of the ammonium salt
[NnBu4]2[p-(O2C)2C6F4] (ref. [16] reports no experimental or
analytical details).
temperature program of 10 K/min. The raw data were processed
using the Netzsch Proteus Software Version 4.2.

828
V. Bilir et al. / Journal of Fluorine Chemistry 130 (2009) 824–829
DSC:Tonset 158 8C(endothermiceffect), Tonset at184 8C(endother-
500
m
L MeCN at ꢀ40 8C was washed free of [N(nBu)4][BF4] with
mic effect followed by an exothermic). The visual melting point at
160 8C was accompanied by partial decarboxylation: formation of
[2,3,5,6-C6HF4CO2]ꢀ, 2,3,5,6-C6H2F4, and N(nBu)3 (1H, 19F).
MeCN (three times 500
m
L,ꢀ40 8C). The product was washed seven
times at ꢀ78 8C with CH2Cl2 (500
mL each) with vigorous stirring
and finally dried in vacuum (4 ꢆ 10ꢀ2 hPa, 0 8C for 3 h). Raman and
Raman (20 8C): 120 (19), 164 (9), 253 (21), 313 (11), 409 (10),
442 (13), 501 (25), 753 (7), 778 (3), 791 (3), 800 (2), 878 (11), 907
(15), 986 (2), 1010 (3), 1036 (5), 1055 (14), 1112 (4), 1134 (11),
1150 (7), 1279 (3), 1329 (26), 1374 (6), 1452 (30), 1469 (20), 1487
(12), 1643 (28), 2712 (2), 2734 (4), 2749 (3), 2874 (85), 2922 (94),
NMR spectra confirmed the absence of MeCN and CH2Cl2. Yield of
1: 10 mg, 12
mmol, 47%. The solubility of 1 showed the following
trend: (CF3)2CHOH (mp ꢀ4 8C) > CF3CH2OH > MeCN. Solvent
mixtures of (CF3)2CHOH/MeCN (2:1, mp ꢀ83 8C or 1:1, mp
ꢀ86 8C or 1:2, mp ꢀ67 8C) allowed the formation of solutions of
1 having satisfactory solubilities at low temperatures. For physical
and spectroscopic data of 1, see Section 3.6.1.
2937 (100), 2962 (80) cmꢀ1
13C NMR (MeCN, 24 8C)
.
d
(ppm): 161.1 (s, Dn1/2 = 3 Hz, CO2),
141.8 (dm, 1J(C, F = 245 Hz, C6F4, C2,3,5,6), 121.9 (m, C6F4, C1,4), 58.5
(tm, 1J(C1, H1) = 143 Hz, nC4H9, C1), 23.8 (tm, 1J(C2, H2) = 125 Hz,
nC4H9, C2), 19.6 (tm, 1J(C3, H3) = 124 Hz, nC4H9, C3);
13.3 (qtt, 1J(C4, H4) = 125 Hz, 3J(C4, H3) = 4 Hz, 4J(C4, H2) = 4 Hz,
nC4H9, C4).
3.6. Synthesis of p-C6F5XeO(O)CC6F4C(O)OXeC6F5 (1) in CH2Cl2
[N(nBu)4]2[p-(O2C)2C6F4] (9.71 mg, 13.5
m
mol) in a FEP trap
(3.5 mm i.d.) was dissolved in CH2Cl2 (300
m
L, ꢀ78 8C). This cold
19F NMR: see Table 1
solution was added to the suspension of [C6F5Xe][B(CF3)4]
(16.6 mg, 28.4 mol) in CH2Cl2 (300
m
m
L, ꢀ78 8C) and vigorously
3.4. Synthesis of p-C6F5XeO(O)CC6F4C(O)OXeC6F5ꢃ2 MeCN
(1ꢃ2 MeCN) in MeCN
mixed. After 45 min, the suspension was centrifuged (ꢀ78 8C) and
the mother liquor was separated. Solid product 1 was washed nine
times with CH2Cl2 (500
PFB (350
L aliquots at ꢀ30 8C). The last washing still contained a
trace amount of [C6F5Xe][B(CF3)4] (19F NMR). Therefore, washing
(four times) with MeCN (250
m
L aliquots at ꢀ40 8C) and four times with
[C6F5Xe][BF4] (203 mg, 0.528 mmol) and [N(nBu)4]2[p-
(O2C)2C6F4] (177 mg, 0.245 mmol) were combined in a FEP trap
(8 mm i.d.) and cooled to ꢀ40 8C. MeCN (1.5 mL,ꢀ40 8C) was added
under vigorous stirring. In concert with dissolution of the starting
materials, precipitation of product 1 resulted. After 2 h, the
suspension was centrifuged at ꢀ35 8C. The mother liquor was
separated, the solid was suspended and stirred in MeCN
(0.5 mL,ꢀ45 8C), and the solution phase was separated again. This
washingprocedurewas repeated (23times)till[N(nBu)4]+ and [BF4]ꢀ
ions could not be detected in the NMR spectra (1H, 19F). The purified
solid product was dried under vacuum (4 ꢆ 10ꢀ2 hPa) for 6 h at ꢀ35
to ꢀ25 8C (151 mg, 0.165 mmol, 67%), transferred into the glove box
and divided in portions in FEP tubes (3.5 mm i.d.). This procedure at
20 8C took less than 30 min. All samples were stored at ꢀ70 8C. One
sample was checked by Raman spectroscopy and showed that MeCN
m
m
L aliquots at ꢀ30 8C) with a high
solubility for [C6F5Xe][B(CF3)4] followed. The suspension was
centrifuged at ꢀ29 8C. The last MeCN washing contained no
[C6F5Xe][B(CF3)4]. After repeated treatment with CH2Cl2 the solid
product was dried in vacuum (4 ꢆ 10ꢀ2 hPa, ꢈꢀ25 8C and 0 8C for
1.5 h at each temperature). The absence of MeCN and other
solvents was proven by Raman and NMR spectroscopy.
In
a
similar procedure,
1
was prepared from [C6F5Xeꢃ
NCMe][B(C6F5)4] and [N(nBu)4]2[p-(O2C)2C6F4].
3.6.1. p-C6F5XeO(O)CC6F4C(O)OXeC6F5 (1).
DSC: Tonset 118 8C (exothermic dec.), Tonset 145 8C (endothermic
effect).
was still present (n(C–H) 2946,
n
(CBB N) 2253 cmꢀ1). This sample was
Raman (20 8C): 138 (2), 180 (100), 226 (2), 278 (11), 292 (5), 347
(29), 383 (5), 410 (6), 440 (5), 488 (50), 503 (6), 606 (1), 720 (3), 732
(9), 764 (29), 782 (30), 1017 (1), 1071 (2), 1083 (9), 1284 (7), 1336
again pumped under vacuum at ꢀ35 to ꢀ25 8C for 33 h (no decrease
in MeCN) and at 0 8C for 20 h (only a small reduction of MeCN). After
15 h of evacuation at 20 8C, MeCN was removed but significant
changes in the Raman spectrum indicated partial decomposition.
After storage for an additional 3 h at 20 8C, the composition of the
sample was checked by 19F NMR spectroscopy in a (CF3)2CHOH/
MeCN mixture (1:1, vol, ꢀ40 8C) (1 (83%), p-C6F5O(O)CC6F4CO2H
(13%), p-(C6F5O(O)C)2C6F4 (4%), C6F5H (3%) and five unknown
products ((CF3)2CXY derived from the solvent (5%)).
(2), 1371 (2), 1387 (11), 1409 (14), 1625 (15), 1641 (7) cmꢀ1
.
13C and 13C{19F} NMR (CF3)2CHOH/CH3CN (1:1, vol, ꢀ30 8C)
d
(ppm): 145.4 (dm, 1J(C4, F4) = 260 Hz, C4), 144.0 (dm, 1J(C2, F2; C6,
F6) = 252 Hz, C2,6), 139.0 (dm, 1J(C3, F3; C5, F5) = 258 Hz, C3,5), 89.2
(m, 1J(C1, 129Xe) = 168 Hz, C1), 166.0 (s, Dn1/2 = 4 Hz, CO2), 144.9
0
0
0
0
0
0
(dm, 1J(C’, F’) = 252 Hz, C6F4, C2 ,3 ,5 ,6 ), 125.8 (m, C6F4, C1 ,4 ).
129Xe NMR ((CF3)2CHOH/CH3CN (1:1, vol, ꢀ30 8C)
d (ppm):
Another sample (15 mg, 16
ratio, 1:MeCN, by comparison of the integrated intensities with
C6H5CF3 (5
L) from the 1H and 19F NMR spectra in a CF3CH2OH
(300
L) solution at ꢀ40 8C. The ratio 1:MeCN was calculated to be
1:1.9. The ideal value for this product is 1ꢃ2 MeCN.
mol/mL
mmol) was used to determine the
ꢀ3857 (t, 3J(Xe–F2,6) = 81 Hz).
19F NMR see Table 1.
m
m
3.7. Synthesis of p-C6F5XeO(O)CC6F4C(O)OXeC6F5 (1) in CF3CH2OH
1ꢃ2 MeCN: solubility in MeCN at ꢀ40 8C: 1.48
m
Due to the slow dissolution in cold CF3CH2OH [C6F5Xe][BF4]
DSC: Tonset 89 8C (exothermic dec.), Tonset 141 8C (endothermic
effect), Tonset 173 8C (weakly exothermic effect), Tonset 219 8C
(endothermic effect).
(19.8 mg, 51.5
at 20 8C within 5 min and cooled to ꢀ40 8C before a solution of
Cs2[(p-O2C)2C6F4] (13.1 mg, 26.0 mol) in CF3CH2OH (1 mL,
mmol) was dissolved in 500 mL of CF3CH2OH
m
Raman (ꢀ40 8C): 136 (3), 181 (100), 253 (2), 277 (12), 290 (12),
347 (27), 356 (23), 386 (10), 408 (5), 442 (8), 490 (57), 509 (11), 520
(20), 766 (57), 784 (30), 918 (1), 1012 (2), 1080 (4), 1082 (19), 1280
(10), 1333 (2), 1388 (17), 1407 (30), 1617 (34), 1658 (4), 2253 (7),
ꢀ43 8C) was added. The reaction mixture was stirred for 3 h at
ꢀ35 to ꢀ40 8C in a FEP trap (8 mm i.d.). Despite the fact that no
precipitation of Cs[BF4] could be detected in CF3CH2OH, the
mixture was centrifuged (ꢀ35 8C) several times. Hints of small
amounts of transparent solid were observed. After 5 h, a sample of
the upper one third of volume was taken for 19F NMR analysis and
proved the absence of [BF4]ꢀ in this part. A significant amount of
C6F5H (38%) besides 1 was found. The fact that the ratio C6F5:C6F4
2946 (10), 3005 (1) cmꢀ1
19F NMR: see Table 1
.
3.5. Removal of MeCN from 1ꢃ2 MeCN by extraction with CH2Cl2
Freshly prepared 1ꢃ2 MeCN from [C6F5Xe][BF4] (21.9 mg,
of 1.66 deviated from 2.0 implies that pure
1 cannot be
differentiated from p-C6F5XeO(O)CC6F4CO2H in CF3CH2OH. Finally,
the mother liquor was separated and evaporated at <ꢀ20 C,
56.9
m mmol) in
mol) and [N(nBu)4]2[p-(O2C)2C6F4] (18.7 mg, 25.8

V. Bilir et al. / Journal of Fluorine Chemistry 130 (2009) 824–829
829
4 ꢆ 10ꢀ2 hPa and the solid residue was suspended in MeCN and
3.10. Transesterification of p-(C6F5O(O)C)2C6F4 into p-
showed the presence of [BF4]ꢀ
(
19F NMR). It should be noted that in
((CF3)2CHO(O)C)2C6F4
all experiments our attempts to separate the very fine particles of
Cs[BF4] failed even with a 50 m Teflon frit.
m
A sample of p-(C6F5O(O)C)2C6F4 (5.0 mg, 8.8
m
mol) dissolved in
a 1:1 mixture of (CF3)2CHOH/MeCN (300
(
mL) showed after 30 min
3.8. Thermal behavior of 1 and 1ꢃ2 MeCN, neat and in solution
A sample of 1 (10.0 mg, 12 mol) in a FEP trap (3.5 mm i.d.) was
19F NMR) complete conversion into p-((CF3)2CHO(O)C)2C6F4 and
C6F5OH (ꢀ163.2 (o-F), ꢀ166.4 (m-F), ꢀ173.4 (p-F)).
m
stored inside a glove box at 20 8C. The progress of the decom-
3.10.1. p-((CF3)2CHO)2C6F4
position was followed by Raman spectroscopy
(
n
(C–Xe) at
IR (20 8C): 690 (m), 750 (w), 760 (vw, sh), 799 (vw, br), 859 (w),
906 (m), 930 (s), 995 (s), 1072 (s), 1108 (vs), 1157 (m), 1205 (vs),
1247 (m, sh), 1260 (s), 1282 (s), 1364 (m), 1380 (m), 1487 (s), 1511
180 cmꢀ1). After 1 d, no decomposition was detected. After 10
d, the majority of 1 was decomposed. After storage of a sample of
1ꢃ2 MeCN (8.3 mg, 9.1
m
mol) in a FEP trap (3.5 mm i.d.) inside a
(w), 1774 (vs) cmꢀ1
.
glove box at 20 8C over 14 d, a solid white decomposition product
resulted which was soluble in n-pentane. 19F NMR confirmed that
p-(C6F5O(O)C)2C6F4 was formed as the only product in the residue.
The thermal stability of 1 in solution was monitored in MeCN,
CF3CH2OH, (CF3)2CHOH, and (CF3)2CHOH/MeCN (1:1, vol).
After 5.5 h at 20 8C, the MeCN solution of 1 showed the
following composition related to the C6F4 fragment: C6F5H
(79%), C6F5O(O)CC6F4CO2H (43%), p-(HO2C)2C6F4 (30%),
p-(C6F5O(O)C)2C6F4 (24%) [p-(O2C)2C6F4]2–(3%). 1 was partially
decomposed in CF3CH2OH at ꢀ40 8C after 20 min: C6F5H (20%).
In the (CF3)2CHOH solution of 1 after 20 min at 0 8C C6F5H (6%)
was detected. A satisfactory stability of 1 was found in a
(CF3)2CHOH/MeCN mixture (1:1). After 21 h at ꢀ30 8C only 3% of
C6F5H was formed.
19F NMR: see Table 1.
4. Conclusions
The nucleophilicity of the tetrafluoroterephthalate anion is high
enough to bind two electrophilic [C6F5Xe]+ cations forming the
molecular compound p-C6F5XeO(O)CC6F4C(O)OXeC6F5 (1). When
the synthesis of 1 was performed in MeCN, two solvent molecules
were co-crystallized without coordination to XeII. Crystals were
obtained from (CF3)2CHOH/MeCN (1:1, vol) solutions that had four
(CF3)2CHOH molecules bonded by hydrogen bridges to the four
oxygen atoms in 1. Solvent coordination makes the carboxylate
groups less nucleophilic, shifting the Xe–O bond polarity towards
the ionic side. The polarity of the Xe–O bond in 1 is not itself high
enough to allow metathesis of the tetrafluoroterephthalate anion
by two weakly coordinating [B(C6F5)4]ꢀanions under basic
conditions. 1 is an intrinsically unstable compound and eliminates
two Xe0 when stored at ambient temperature forming the diester,
p-C6F5O(O)CC6F4C(O)OC6F5. The latter underwent rapid trans-
esterification at 20 8C when dissolved in (CF3)2CHOH/MeCN.
3.8.1. p-(C6F5O(O)C)2C6F4 [17]
DSC: Tonset 141 8C (endothermic melting), Tonset 181 8C (weakly
exothermic dec.), Tonset 250 8C (endothermic boiling).
Raman (20 8C): 147 (4), 156 (3), 253 (5), 274 (11), 280 (10), 313
(12), 330 (5), 379 (55), 394 (37), 402 (43), 440 (53), 476 (21), 506
(70), 571 (100), 636 (4), 662 (5), 715 (3), 769 (2), 779 (3), 828 (11),
950 (5), 1014 (4), 1150 (4), 1158 (3), 1227 (25), 1237 (18), 1412
Acknowledgements
(56), 1471 (6), 1656 (70), 1769 (48) cmꢀ1
.
IR (20 8C): 638 (vw), 667 (vw), 713 (vw), 755 (vw), 772 (vw),
793 (vw), 895 (vw), 984 (s), 996 (s), 1007 (s), 1123 (m), 1149 (m),
1261 (vw), 1314 (m), 1335 (s), 1494 (s), 1520 (vs), 1682 (w), 1767
We gratefully acknowledge the financial support by the Fonds
der Chemischen Industrie.
(s) cmꢀ1
13C NMR (CH2Cl2, 24 8C)
.
References
d
(ppm): 145.9 (dm, 1J(C2, F2; C6,
F6) = 266 Hz, C6F5, C2,6), 140.8 (dtt, 1J(C4, F4) = 255 Hz, 2J(C4,
F3,5) = 14 Hz, 3J(C4, F2,6) = 4 Hz, C6F5, C4), 138.5 (dm, 1J(C3, F3; C5,
F5) = 252 Hz, C6F5, C3,5), 114.0 (m, C6F5, C1), 155.1 (s, Dn1/2 = 4 Hz,
[1] H.-J. Frohn, V.V. Bardin, in: K.K. Laali (Ed.), Recent Developments in Carbocation
and Onium ion chemistry., ACS Symposium Series, vol. 965, American Chemical
Society, Washington, DC, 2007, pp. 428–457.
[2] W. Tyrra, D. Naumann, in: G. Meyer, D. Naumann, L. Wesemann (Eds.), Inorganic
Chemistry Highlights, Wiley-VCH, Weinheim, 2002, pp. 297–316.
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(2007) 9425–9437.
0
0
0
0
CO2), 141.4 (dm, 1J(C’-F’) = 253 Hz, C6F4, C2 ,3 ,5 ,6 ), 124.4 (m, C6F4,
0
0
C1 ,4 ).
19F NMR: see Table 1.
[5] K. Koppe, H.-J. Frohn, H.P.A. Mercier, G.J. Schrobilgen, Inorg. Chem. 47 (2008)
3205–3217.
[6] H.-J. Frohn, M. Theißen, Angew. Chem. Int. Ed. 39 (2000) 4591–4593.
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[8] H.-J. Frohn, M. Theißen, J. Fluorine Chem. 125 (2004) 981–988.
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[10] H.-J. Frohn, A. Klose, G. Henkel, Angew. Chem. Int. Ed. 32 (1993) 99–100.
[11] H. Bock, H. Scherer, W. Tyrra, D. Naumann, J. Fluorine Chem. 127 (2006) 1440–
1445.
[12] H.-J. Frohn, A. Klose, T. Schroer, G. Henkel, V. Buss, D. Opitz, R. Vahrenhorst, Inorg.
Chem. 37 (1998) 4884–4890.
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[14] G.A. Schumacher, G.J. Schrobilgen, Inorg. Chem. 23 (1984) 2923–2929.
[15] H.-J. Frohn, H. Franke, V.V. Bardin, Z. Naturforsch. 54b (1999) 1495–1498.
[16] D.J. Brown, M.H. Chisholm, C.W. Gribble, Dalton Trans. (2007) 1793–1801.
[17] E.R. Lynch, W. Cummings, British Patent 1,099,646 (1968).
3.9. Attempt to use 1 as a [C6F5Xe]+ source in a metathesis reaction
In a FEP trap (3.5 mm i.d.) a solution (200
Cs[B(C6F5)4] (30.9 mg, 38.1 mol) was added to partially soluble 1
(16.0 mg, 19.2 mol) in MeCN (300
m
L, ꢀ40 8C) of
m
m
m
L, ꢀ40 8C). After 1 h and
efficient mixing at ꢀ40 8C no reaction could be detected. After
5 min at 20 8C 77% of 1 was dissolved but no conversion
was observed. After 18 h decomposition of 1 dominated and after
48 h at 20 8C the decomposition of
1 was completed. No
[C6F5Xe][B(C6F5)4] was detected at any time. The composition of
the final solution is related to the sum of C6F4 groups: [B(C6F5)4]ꢀ
(200%), p-(C6F5O(O)C)2C6F4 (83%), p-C6F5O(O)CC6F4CO2H (12%),
p-(HO2C)2C6F4 (5%), C6F5H (6%).