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The Fluoroacyltris(trifluoromethyl)borate Ion [(CF3)3BC(O)F] a Fluoroacylboron Complex.

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Communications
metals are known: [Ir(CO)2F{C(O)F}(PEt3)]+,[7] [Ir(CO)5{C(O)F}]2+,[8] [MF{C(O)F}(CO)2(PPh3)2] (M = Ru, Os).[9]
Recently we reported on carbonyltris(trifluoromethyl)borane, (CF3)3BCO.[10, 11] This reactive carbonyl compound is
an ideal building block for the insertion of the (CF3)3B group
into a number of different molecules. Thus, this enables the
generation of weakly coordinating anions in which in
comparison to the tetrakis(trifluoromethyl)borate ion,
[B(CF3)4] ,[12] a trifluoromethyl ligand is replaced by another
ligand. The fluoroacyltris(trifluoromethyl)borate ion,
[(CF3)3BC(O)F] , described herein is the first example of a
boron acyl fluoride; moreover, it is a better substrate than
(CF3)3BCO in a number of different chemical reactions since
it is more stable and easier to handle.
K[(CF3)3BC(O)F] and Cs[(CF3)3BC(O)F] are obtained by
the reaction of (CF3)3BCO with KF and CsF, respectively, in
liquid SO2 [Eq. (1)] as white solids, which in the absence of
SO
ðCF3 Þ3 BCO þ MF ƒƒ
ƒ2ðlÞ
! M½ðCF3 Þ3 BCðOÞF
ð1Þ
moisture are stable up to 130 8C and 140 8C, respectively
(differential scanning calorimetry).
The fluoroacyltris(trifluoromethyl)borate ion is one of the
possible intermediates in the acid hydrolysis of [B(CF3)4] to
(CF3)3BCO [Eq. (2)].
25 C; conc: H SO
2
4
ðCF3 Þ3 BCOðgÞ þ 3 HFðsolvÞ
½BðCF3 Þ4 ðsolvÞ þ H3 Oþ ƒƒƒƒƒƒƒƒƒ!
ð2Þ
Fluoroacylboron Complexes
The Fluoroacyltris(trifluoromethyl)borate Ion,
[(CF3)3BC(O)F] , a Fluoroacylboron Complex**
Maik Finze, Eduard Bernhardt, Helge Willner,* and
Christian W. Lehmann*
Although numerous acyl fluorides are known in organic
chemistry[1] no analogous isoelectronic boron compounds
have been described to date. This is surprising since acyl
fluorides of many nonmetals, such as hydrogen,[2] nitrogen,[3]
sulfur,[4] , oxygen,[4, 5] and halogens[6] exist. Whereas there are
no examples of fluoroacyl complexes of main-group metals, a
number of analogous coordination compounds of transition
The synthesis described here is the first step of the reverse
reaction, the fluorination of (CF3)3BCO to [B(CF3)4] .
Except for the oxygen atom all atoms in [(CF3)3BC(O)F]
may be investigated by NMR spectroscopy. Since both 11B
and 10B exhibit a quadrupole moment, broad signals are
usually observed in 11B NMR spectra.[13, 14] In the case of
[(CF3)3BC(O)F] , however, the observed spectra display
unusual sharp signals (see Table S1 in the Supporting
Information), which can be explained by a relatively small
electric field gradient at the central B atom.[15]
The 19F NMR spectrum of the [(CF3)3BC(O)F] ion
(Figure 1) shows two signals at d = 78.3 and 61.2 ppm with
an intensity ratio of 1:9. The signal at the lower frequency is in
[*] Prof. Dr. H. Willner, Dipl.-Chem. M. Finze, Dr. E. Bernhardt
Fakult1t 4, Anorganische Chemie
Gerhard-Mercator-Universit1t Duisburg
Lotharstrasse 1, 47048 Duisburg (Germany)
Fax: (+ 49) 203-379-2231
E-mail: willner@uni-duisburg.de
Dr. C. W. Lehmann
Max-Planck-Institut f=r Kohlenforschung
Kaiser-Wilhelm-Platz 1, 45470 M=lheim an der Ruhr (Germany)
Fax: (+ 49) 208-306-2989
E-mail: lehmann@mpi-muelheim.mpg.de
[**] This work was supported by the Deutsche Forschungsgemeinschaft,
the Fonds der Chemischen Industrie, and Merck KGaA, Darmstadt.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
1052
2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Figure 1. 19F NMR spectrum of [(CF3)3BC(O)F] in CD3CN (the signal
set at d = 78.2 ppm is amplified by a factor of 14).
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the region typical for CF3 groups (Table 1). The 19F NMR shift
of acyl fluorides, RC(O)F, is highly dependent upon the
substituent. Thus, values between d = 50 and + 50 ppm for
FC(O) groups attached to nonmetal atoms[17] and values
greater than d = + 100 ppm for transition-metal–FC(O) complexes are typical (Table 2). The measured chemical shifts of
the boron complex lie between those of fluoroacyl transitionmetal complexes and nonmetal acyl fluorides. The assignment
of the signals is confirmed by the observed coupling patterns.
The 19F nuclei couple with the 11B nucleus (quartets with the
same relative intensities for the four components), whereby
the respective coupling constants are derived from the 11B
NMR spectrum in Figure 2. The 4J coupling of the F atom of
the acyl ligand with the F atoms of the CF3 groups is 7.6 Hz
and is thus of the same order of magnitude as that in
[B(CF3)3(13CF3)] (Table 1).[12]
The 11B NMR signal of [(CF3)3BC(O)F] (Figure 2) is split
into a doublet of decets through the coupling of the F atom of
the acyl ligand and the CF3 groups. The 11B NMR shift is
similar to those of other borate complexes with three CF3
ligands (Table 1).[10, 12]
Figure 2.
B NMR spectrum of [(CF3)3BC(O)F] in CD3CN.
11
The 13C NMR spectrum of [(CF3)3BC(O)F] in Figure 3
shows two signals at d = 173.7 and 132.8 ppm with a relative
intensity ratio of 1:3. The chemical shift of the signal at higher
frequency is similar to those of carbonyl ligands in tris(trifluoromethyl)boron derivatives and
to those of other fluoroacyl groups
(Tables 1 and 2).[7, 9, 10, 17] The cou
[a, b]
Table 1: NMR data of [(CF3)3BC(O)F] and similar compounds.
pling pattern shows the interaction
Parameter
[(CF3)3BC(O)F] (CF3)3BCO[c] [(CF3)3BC(O)OH] [B(CF3)4] [(CF3)3BF]
of the acyl C atom with the directly
d(11B)
19.1
17.9
18.9
18.9
7.1
bonded F atom and the central B
132.8
126.2
133.9
132.9
132.6
d(13C) (CF3)
atom as well as the 3J coupling with
d(13C) (C(O))
173.7
159.8
186.4
–
–
the
F atoms of the CF3 groups. The
61.2
58.7
60.3
61.6
68.8
d(19F) (CF3)
position
and the coupling pattern of
78.3
–
–
–
–
d(19F) (C(O)F)
13
the
C
NMR signal of the CF3
1 11 13
J( B, CF3)
74.6
80 5
72.8
73.4
80.0
1 11 13
groups
is
comparable to those of
J( B, C(O))
73.1
30 5
68.2
–
–
1 13
similar compounds (Table 1).[10, 12]
J( CF3,C19F3)
303.9
298 3
305.5
304.3
309.4
1 13
J( C(O)F,C(O)19F)
398.0
–
–
–
–
However, in contrast to the 13C
2 11
J( B,C19F3)
27.1
36 2
25.8
25.9
28.3
signal of the fluoroacyl ligand the
2 11
J( B,C(O)19F)
51.7
–
–
–
–
3 13
J( C,19F) coupling is not resolved.
3 13
12 19
J( CF3, C F3)
4.0
n.o.
4.0
3.9
n.o.
The IR and Raman spectra of
3 13
J( CF3,12C(O)19F)
n.o.
–
–
–
–
K[(CF
shown
in
3 13
12 19
3)3BC(O)F]
J( C(O), C F3)
4.0
n.o.
3.5
–
–
4 12 19
13 19
Figure
4
confirm
the
formation
of
J( C F3, C F3)
6.3
n.o.
n.o.
5.8
n.o.
4 12 19
J( C F3,12C(O)19F)
7.6
–
–
–
–
the fluoracyl complex as shown in
ref.
this work
[10, 11]
[10]
[12]
[12, 16]
Equation (1).
The
band
at
1829 cm1 lies in a region that is
[a] J in Hz, d in ppm. [b] Unless otherwise stated the NMR spectra were measured in CD3CN.
[c] Measured in CD2Cl2. [d] n.o. = not observed.
typical of CO vibrations of fluoracyl
Table 2: Characteristic data of selected fluoroacyl compounds.
Compound
ñ [cm1]
n(CO)
ñ [cm1]
n(CF)
ñ [cm1]
d(COF)
d(19F) [ppm]
(FCO)
d(19F) [ppm]
(CF3)
4 19 19
J( F, F) [Hz]
(CF3/FCO)
d(13C) [ppm]
(FCO)
Ref.
[(CF3)3B-C(O)F] [a]
(CF3)3C-C(O)F
(CF3)2N-C(O)F
CF3O-C(O)F
F-C(O)F
H-C(O)F
[Ir(CO)5{C(O)F}]2+
[IrF(CO)2{C(O)F}(PEt3)2]+
[RuF(CO)2{C(O)F}(PPh3)2]
[OsF(CO)2{C(O)F}(PPh3)2]
1829
1880
1883
1900
1943
1837
1849
1815
n.o.
1651
1077
990
996
1020
1107[c]
1065
1049
n.o.
n.o.
n.o.
667
660
n.o.
608
626
663
n.o.
n.o.
n.o.
n.o.
78.3
42.3
5.4
13.6
23.0
42.0
n.o.
132.4
156
146
61.2
67.1
56.5
71.9
–
–
–
–
–
–
7.6
11.4
17.0
9.8
–
–
–
–
–
–
173.7
n.o.[b]
n.o.
136.9
133.6
n.o.
n.o.
154.5
n.o.
n.o.
this work
[18]
[19, 20]
[5, 21]
[17, 22]
[2, 17]
[7]
[8]
[9]
[9]
[a] K+ salt. [b] n.o. = not observed. [c] Mean value from ñ = 1249 cm1 (nas(CF)) and ñ = 965 cm1 (ns(CF)).
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Figure 5. Structure of the [(CF3)3BC(O)F] ion in K[(CF3)3BC(O)F]
(50 % probability ellipsoids).
13
Figure 3. C NMR spectrum of [(CF3)3BC(O)F] in CD3CN. The signal
at d = 173.7 ppm is amplified by a factor of 2; the enlarged sections
left and right illustrate more clearly the 3J(13C,19F) couplings.
Figure 4. FT-IR and Raman spectrum of [(CF3)3BC(O)F] .
derivatives (Table 2).[23] The characteristic band pattern of the
B(CF3)3 group lies between 1300 and 400 cm1,[11, 12] an
additional IR band at 600 cm1 can be assigned to FCO
deformation. The wavenumber of the CF vibration of the
fluoroacyl ligand in the potassium salt is 1077 cm1 and thus is
within the range (1020–1145 cm1) which is dominated by the
absorption of the nas(CF3) vibrations.
Gaussian 98 geometry and vibrational frequency calculations[24] performed for [(CF3)3BC(O)F] with the B3LYP/6311G* basis set give wavenumbers for the normal vibrations
which are in good agreement with those observed (see
Table S2 in the Supporting Information). At the energy
minimum the anion exhibits C1 symmetry (see Figure S1 in
the Supporting Information) in which the CF3 groups are
present in a staggered conformation. Since the energy difference between the C1 and the Cs symmetry conformations (see
Figure S2 in the supporting information) is only 0.3 kJ mol1
and the fluoracyl ligand in C1 symmetry is twisted by only 8.58
from the plane of symmetry it is understandable why a
conformation with Cs symmetry is present in the crystal.
As the crystal structure shows, the O atom of the FCO
group is adjacent to the CF3 group in the plane of symmetry,
1054
2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
whereas the F atom of the fluoracyl ligand protrudes into the
gap between the two remaining CF3 groups (Figure 5).[25] The
structural parameters agree well with the calculated values of
the [(CF3)3BC(O)F] ion and with the values of similar
fluoracyl
compounds,
for
example
CF3C(O)F,[26]
[27]
[28]
[5]
(CF3)2NC(O)F,
F2CO,
CF3OC(O)F, and [IrF(CO)2{C(O)F}(PEt3)2]+[7] (Table 3). The distance between the O
atom and the nearest K+ ion is 2.748(2) G. A K+ ion in the
solid is surrounded by ten F atoms at distances of 2.694(2) to
3.196(2) G. The distance between the F atom and the
fluoracyl ligand to the K+ ion is 2.729(3) G. All distances
indicate weak interionic interactions.[29]
The synthesis of K[(CF3)3BC(O)F] provides one of the
few examples of a nucleophilic attack of an F ion at a CO
ligand with the formation of a fluoracyl complex. Notably,
[(CF3)3BF] [12, 16] is not formed by exchange of the CO ligand
in (CF3)3BCO by an F ion. The observed reaction course is
attributed to two reasons: 1) the attacking F ion forms a
relatively stable bond with the C atom of the carbonyl ligand,
and 2) the BCO bond is stabilized by association with SO2
molecules.[10] The synthesis, and spectroscopic and thermal
properties of the homologous halogen acyl complexes
[(CF3)3BC(O)X] (X = Cl, Br, I) will be reported elsewhere.
Table 3: Selected bond parameters of the [(CF3)3BC(O)F] ion from the
structure of the potassium salt and DFT calculations.
Solid
B3LYP/6-311 + G*
bond lengths [J]
BC(O)F
CO
C(O)F
BCF3
CF
1.621(5)
1.208(4)
1.351(4)
1.622[a]
1.387[a]
1.6291
1.1862
1.4033
1.6377[a]
1.3678[a]
bond angles [8]
O-C-F
C(O)-B-CF3
120.5(3)
109.50[a]
116.604
108.788[a]
[a] Mean values of different bond lengths and angles.
Experimental Section
Preparation of K[(CF3)3BC(O)F]: In a dry box, KF (1.50 g,
25.8 mmol) was weighed into a 50-mL round bottom flask equipped
with a valve with PTFE piston (Young, London) and a magnetic
stirring bar. Then in vacuo (CF3)3BCO (4.86 g, 19.8 mmol) and dry
SO2 (30 mL) were condensed into the flask. The reaction mixture was
warmed to room temperature and stirred for about 1 h. All volatile
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components were removed under vacuum and a white residue
remained in the flask. This residue was extracted with diethyl ether
(2 I 40 mL) and filtered under nitrogen through a Schlenk frit packed
with celite. After removal of the diethyl ether under vacuum white
K[(CF3)3BC(O)F] remained. Yield: 5.33 g (17.5 mmol, 88 %). Elemental analysis calcd (%) for C4BF10KO: C 15.87; found: C 15.81.
Preparation of Cs[(CF3)3BC(O)F]: CsF (1.08 g, 7.1 mmol) was
allowed to react with (CF3)3BCO (1.34 g, 5.5 mmol) under the same
conditions as for the preparation of K[(CF3)3BC(O)F]. Yield: 1.89 g
(4.8 mmol, 87 %). Elemental analysis calcd (%) for C4BF10CsO: C
12.08; found: C 12.49.
[25]
Received: October 4, 2002 [Z50303]
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Nichtmetallen, vol. 4, Thieme, Stuttgart, 1994.
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[26]
[27]
[28]
[29]
[30]
[31]
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O. Farkas, J. Tomasi, V. Barone, M. Cossi, R. Cammi, B.
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Petersson, P. Y. Ayala, Q. Cui, K. Morokuma, D. K. Malick,
A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. Cioslowski,
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Piskorz, I. Komaromi, R. Gomperts, R. L. Martin, D. J. Fox, T.
Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, C.
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Chen, M. W. Wong, J. L. Andres, M. Head-Gordon, E. S.
Replogle, J. A. Pople, Gaussian, Inc., Pittsburgh, PA, 1998.
a) Crystal structure analysis of K[(CF3)3BC(O)F]: C4BF10KO,
KappaCCD diffractometer (Bruker AXS), MoKa radiation (l =
0.71073 G, graphite monochromator), measurement temperature 100 K. Colorless crystals (0.11 I 0.04 I 0.04 mm3), obtained
from Et2O/CH2Cl2, orthorhombic, space group Pnma (no. 62),
a = 9.1895(3), b = 10.2046(5), c = 9.7013(3) G, V = 909.74(6) G3,
Z = 4, 1cald = 2.219 Mg m3, m(MoKa) = 0.726 mm1, F(000) = 584,
10 992 measured reflections (3.65 < V < 30.988). Integration and
empirical absorption corrections (DENZO scalepack)[30] are
applied to obtain a structure solution by direct methods and
crystal structure refinement against F2 with 1519 independent
reflections (1199 independent reflections with I > 2s(I)) and 88
variables (SHELXS-97).[31] All atoms were refined anistropically.
R1 = 0.0514
(I > 2s(I)).
b)
CCDC-197603
(K[(CF3)3BC(O)F]) contains the supplementary crystallographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from
the Cambridge Crystallographic Data Centre, 12, Union Road,
Cambridge CB2 1EZ, UK; fax: (+ 44) 1223-336-033; or deposit@
ccdc.cam.ac.uk).
J. H. M. Brake, R. A. J. Driessen, F. C. Mijlhoff, G. H. Renes,
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Z. Otwinowski, W. Minor, Methods Enzymol. 1997, 276, 307.
G. M. Sheldrick, SHELXS-97 and SHELXL-97, Program
System for the Determination and Refinement of Crystal
Structures, University of GSttingen, 1997.
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