Reactions of trifluorovinyl-trifluoromethylboron derivatives, structure of (F2C=CF)(F3C)2B·NHMe2 and (HOOC)(F3C)2B·NHMe2

Article abstract of DOI:10.1016/S0022-328X(00)00199-6

Dimethylamino-bis(trifluoromethyl)borane, (F₃C)₂BNMe₂ (1) reacts with 1,1,1,2-tetrafluoroethane in the presence of tBuLi to yield the dimethylamine borane (F₂C=CF)(F₃C)₂B·NHMe₂ (2). Compound 2 was alkylated at nitrogen with CH₃I/KOH or benzyl chloride/KOH in ether to yield the amine boranes (F₂C=CF)(F₃C)₂B·NMe₃ (2a) or (F₂C=CF)(F₃C)₂B·NMe₂Bzl (2b). Both 2 and 2a add bromine across the C=C bond to form the respective F₂BrC-CFBr derivatives 3 and 3a. A solution of 2 in CHCl₃ reacts with ozone to give a 9:1 mixture of (cyclo-O-CF₂-CF)(F₃C)₂B·NHMe₂ (4) and (HOOC)(F₃C)₂B·NHMe₂ (5), and the reaction of ozone with 2a yields a mixture of the analogous trimethylamine adducts 3b and 5a. Compound 4 further hydrolyzes to form the oxocarboxyborane (HOOC-CO)(F₃C)₂B·NHMe₂ (6). The B-N bond of 2a is cleaved by either NEt₃×3HF or NMe₄F to form the fluoroborate anion [(F₂C=CF)B(CF₃)₂F]^- (7). The structures of 2 and 5 have been investigated by single-crystal X-ray diffraction. The B-C bond involving the trifluorovinyl group in 2 is 1.598(3) A? long, and the associated B-C-C bond angle of 134.4(2)° is remarkably large. The B-C linkage to the carboxy group in 5 is 1.620(2) A? long.

Full text of DOI:10.1016/S0022-328X(00)00199-6

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 604 (2000) 43–51
Reactions of trifluorovinyl-trifluoromethylboron derivatives,
structure of (F2CꢀCF)(F3C)2B·NHMe2 and
(HOOC)(F3C)2B·NHMe2
David J. Brauer, Gottfried Pawelke *
Anorganische Chemie, Fachberiech 9, Bergische Uni6ersita¨t-Gesamthochschule, D-42097 Wuppertal, Germany
Received 1 December 1999; received in revised form 15 March 2000
Dedicated to Professor Othmar Stelzer on the occasion of his 60th birthday
Abstract
Dimethylamino-bis(trifluoromethyl)borane, (F3C)2BNMe2 (1) reacts with 1,1,1,2-tetrafluoroethane in the presence of tBuLi to
yield the dimethylamine borane (F2CꢀCF)(F3C)2B·NHMe2 (2). Compound 2 was alkylated at nitrogen with CH3I/KOH or benzyl
chloride/KOH in ether to yield the amine boranes (F2CꢀCF)(F3C)2B·NMe3 (2a) or (F2CꢀCF)(F3C)2B·NMe2Bzl (2b). Both 2 and
2a add bromine across the CꢀC bond to form the respective F2BrCꢁCFBr derivatives 3 and 3a. A solution of 2 in CHCl3 reacts
with ozone to give a 9:1 mixture of (cyclo-O-CF2ꢁCF)(F3C)2B·NHMe2 (4) and (HOOC)(F3C)2B·NHMe2 (5), and the reaction of
ozone with 2a yields a mixture of the analogous trimethylamine adducts 3b and 5a. Compound 4 further hydrolyzes to form the
oxocarboxyborane (HOOCꢁCO)(F3C)2B·NHMe2 (6). The BꢁN bond of 2a is cleaved by either NEt3×3HF or NMe4F to form
the fluoroborate anion [(F2CꢀCF)B(CF3)2F]− (7). The structures of 2 and 5 have been investigated by single-crystal X-ray
,
diffraction. The BꢁC bond involving the trifluorovinyl group in 2 is 1.598(3) A long, and the associated BꢁCꢁC bond angle of
,
134.4(2)° is remarkably large. The BꢁC linkage to the carboxy group in 5 is 1.620(2) A long. © 2000 Elsevier Science S.A. All
rights reserved.
Keywords: Boron; Trifluoromethyl group; Crystal structure; Small rings; Ionic liquid
1. Introduction
Grignard reagents [2]. Thus, dimethylamine boranes of
the general formula R(F3C)2B·NHMe2 are accessible
with R=alkyl, alkenyl, alkinyl and aryl. The only
perfluorinated group that has been added to 1 is the
CF3 group, and adducts of (F3C)3B with numerous
amines have been shown to be thermally robust com-
pounds [3]. We are interested in attaching functional
perfluorinated groups, and the trifluorovinyl group
would be one such candidate. Trifluorovinyl boranes
(F2CꢀCF)BX2 (X=F, Cl, Br, Me), (F2CꢀCF)2BX
(X=F, Cl, Br, Me) and (F2CꢀCF)3B are well charac-
terized compounds [4–6] despite their limited thermal
stability and elaborate synthesis. Little seems to be
known about the chemistry of these compounds. Ex-
cept for their tendency to hydrolyze under formation of
HCFꢀCF2, no reactions of a trifluorovinyl group
bonded to boron have been reported. In the current
study we have carried on the chemistry of the unique
trifluoromethylboron group by adding a trifluorovinyl
Previous studies have shown that dimethylamino-
bis(trifluoromethyl)borane, (F3C)2BNMe2 (1), enters
into numerous, novel reactions in which the boron
atom increases its coordination number from three to
four [1]. This electrophilic character of 1 is the driving
force for its ene-type reactions with nitriles or carbonyl
compounds, which readily take place to form dimethyl-
amine boranes by C-alkylation. However, such ene-
type reactions of 1 require a reactant that has
sufficiently activated hydrogen atoms. Reactants that
do not dispose over such hydrogen atoms can be at-
tached to the boron atom of 1 using alkyl lithium or
* Corresponding author. Tel.: +49-202-4392576.
E-mail address: pawelke@mailgate.urz.uni-wuppertal.de (G.
Pawelke).
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00199-6

44
D.J. Brauer, G. Pawelke / Journal of Organometallic Chemistry 604 (2000) 43–51
group to 1 and have investigated the properties and
chemistry of the resulting borane.
was also formed when 2a was treated with hypochlorite
in acetonitrile–water; however, the yield was lower due
to hydrolytic cleavage of the BꢁC2F3 bond.
2. Results
In 1997 Brisdon et al. [7] described a convenient
method to generate and attach a trifluorovinyl group to
elements like Hg, Sn, etc. They used 1,1,1,2-te-
trafluoroethane, which is a substitute for the banned
CFCs, and nBuLi to generate a solution of F2CꢀCFLi
in ether at dry ice temperature. We have modified their
method by using tBuLi for deprotonation. This turned
out to be necessary because the deprotonation of
1,1,1,2-tetrafluoroethane with nBuLi was incomplete,
and nBuLi, which was still present, also reacted with 1.
As a result a 2:8 mixture of nBu(F3C)2B·NHMe2 and
(F2CꢀCF)(F3C)2B·NHMe2 (2) was obtained, and sepa-
ration of the two components was difficult. Because a
tBu group does not add to 1, tBuLi proved to be the
preferred deprotonating reagent; thus 2 was obtained in
quantitative yield (Eq. (1)).
(4)
In principle, the ozonolysis of 2 proceeds analogously.
If the reaction is carried out in CHCl3 which has not
been carefully dried, the carboxyborane (HOOC)-
(F3C)2B·NHMe2 (5) precipitates from the solution. The
initially colorless mother liquor, which contains the
trifluorooxiranylborane
(cyclo-O-CF2ꢁCF)(F3C)2B·
NHMe2 (4), slowly turns yellow. This color change
results from the hydrolysis of 4 to form the yellow
oxocarboxyborane (HOOCꢁCO)(F3C)2B·NHMe2 (6)
according to Eq. (5).
(5)
(F3C)2BNMe2
In the course of the hydrolysis HF is formed; accord-
ingly, once the hydrolysis has started in a glass vessel, it
proceeds rapidly until all of 4 is converted into 6. If the
ozonolysis of 2 is carried out under absolutely water
free conditions in a Teflon PFA reaction vessel, 4 is
obtained as an oily liquid contaminated with ca. 10% of
(FOC)(F3C)2B·NHMe2 — the complete separation of
which failed. Therefore only NMR data of 4 are
reported.
1. tBuLi/−78°C
+F3CCFH2 ꢁꢁꢁꢁꢁꢁꢁꢁꢁꢁꢁꢂ (F2CꢀCF)2B·NHMe2 (1)
2. H O/−78°C
2
2
In order to test the reactivity of the CꢀC bond towards
bases and nucleophiles, it was necessary to methylate
the acidic NꢁH function of 2. This was achieved by
deprotonation of the nitrogen atom with KOH in ether
and subsequent alkylation of the aminoborates with
CH3I or benzyl chloride. Thus the corresponding tri-
alkylamine boranes 2a and 2b were obtained (Eq. (2)).
We found that 2a reacts with NEt3×3HF at 200°C
according to Eq. (6) to form the fluoroborate ion
[(F2CꢀCF)B(CF3)2F]− (7)
(2)
Like a typical alkene, both compounds 2 and 2a
slowly add bromine at 20°C across the CꢀC bond to
form the respective boranes (F2BrCꢁCFBr)(F3C)2-
B·NHMe2 (3) and (F2BrCꢁCFBr)(F3C)2B·NMe3 (3a) in
high yield (Eq. (3)).
(6)
Anion 7 is also formed when 2a is treated in 2-bu-
tanone at 80°C with NMe4F, prepared according to the
procedure of Christe [8]. It seems that two mechanisms
for the formation of 7 have to be considered. First, at
200°C the BN bond of 2a is cleaved thermally, and the
borane thus generated rapidly reacts with HF of
NEt3×3HF to form the fluoroborate anion 7. Second,
at 80°C fluoride adds first to the terminal CF2 group of
2a, and this adduct subsequently releases trimethyl-
amine to form an intermediate alkylidene borate anion.
This anion rearranges to yield 7. The latter mechanism
is typical of perfluorinated alkenes where ‘naked’
(F2CꢀCF)(F3C)2B·LB“r2(F2BrCꢁCFBr)(F3C)2B·L
(3)
L=NHMe2 (3), NMe2 (3a)
Treatment of 2a with O2/O3 in a CHCl3 solution
furnished both the trifluorooxiranylborane (cyclo-O-
CF2ꢁCF)(F3C)2B·NMe3 (3b) and the carboxyborane
(HOOC)(F3C)2B·NMe3 (5a) in an approximately 9:1
ratio according to Eq. (4). The latter (5a) results from
oxidative cleavage of the CꢀC bond and subsequent
hydrolysis of the resulting BꢁC(ꢀO)F group by traces of
water which were present. It should be noted that 3b

D.J. Brauer, G. Pawelke / Journal of Organometallic Chemistry 604 (2000) 43–51
45
fluoride is known to add to the carbon–carbon double
bond to yield perfluorinated carbanions. Despite the
drastic reaction conditions, the reaction of 2a with
NEt3×3HF is more convenient than that with NMe4F
because the trimethylammonium salt is readily con-
verted in acetone solution into Cs or Li salts using
Cs2CO3 or LiOH×H2O, respectively.
atoms of the B(CF3)2 groups, whereas the other fluorine
atom, resonating at −114 ppm, shows no such cou-
pling. An analogous coupling pattern is observed for
perfluoropropene oxide, where the downfield signal is
also split by coupling with the CF3 group. However,
based on the assumption that 3J(FF)trans isB0, whereas
3J(FF)cis is\0, the high field signal was assigned to the
fluorine atom cis to the CF3 group and the down field
signal, which shows coupling with the CF3 groups, was
ascribed to the trans fluorine atom [11]. We would
suggest a reversal of this assignment for the following
reason. In the parent molecules 2 and 2a, where the
assignment of the C2F3 fluorine atoms is unequivocal,
the B(CF3)2 group shows long range coupling to the
fluorine atom cis to the boron substituent but not to the
trans fluorine atom. We see no reason why this behav-
ior should change upon epoxidation.
The EI mass spectra of 2–2b were recorded. When
the M+ peaks (which are generally weak) could not be
detected, the [M+−Br] (3 and 3a), [M+−CF3] (3b)
and [M+−C2F5] peaks were taken as indicators of the
molecular weight. A typical fragment of the carboxybo-
ranes is m/z=222 [Me2HNꢁB(CF3)2ꢁCO+] and m/z=
236 [Me3NꢁB(CF3)2ꢁCO+].
The miscibility of Cs[(F2CꢀCF)B(CF3)2F] (Cs7),
which is a liquid at 20°C, with acetone and ether is
remarkable. Attempts to obtain single crystals at low
temperature have so far failed. The specific conductivity
of a 0.01 M solution of the salt in acetone was deter-
mined to be 0.14 V−1 m−1 at 25°C. Thus, the conduc-
tivity is approximately the same as an aqueous KCl
solution of equal molar concentration. However, in dry
ether the specific conductivity of a 0.07 M solution of
Cs7 was determined to be only ca. 0.0015 V−1 m−1 at
25°C. This indicates that the salt dissolves as an ion
pair in ether.
2.1. Properties and spectra
All of the novel boron compounds are air-stable
solids or oily liquids (3, 4, and the cesium and lithium
salts of 7). With the exception of 5, 5a, 6, and 7, they
are volatile and sublime at 40°C 10−3 mbar. Only 4 is
sensitive to water. All species mentioned here are solu-
ble in polar solvents like acetone or acetonitrile. Com-
pounds 5 and 5a are weak acids with pKa values of 5.9
and 5.4, and they are much less soluble in cold water
than their sodium salts. Compound 6 is a stronger acid
(pKa 2.6), which is typical for a ketocarboxylic acid.
The NMR chemical shifts and coupling constants of
2–7 (Table 1) are consistent with the proposed struc-
tures. Except for the carbon atom of the trifluorovinyl
group which is directly bonded to boron, all 13C reso-
nances were detected. We assume that this signal is
veiled by the resonance of the CF3 groups at 130 ppm.
The assignment of the three fluorine atoms of the
trifluorovinyl group was made on the generally ac-
cepted assumption that 2J(FF)\0, 3J(FF)transB0,
3
3
3J(FF)cis\0 and ꢀ J(FF)transꢀ\ꢀ J(FF)cisꢀ [9]. In tri-
fluorovinyl derivatives F2CꢀCFX, the 3J(FF)cis cou-
pling constant is sensitive to the electronegativity of
X — varying from 58 Hz for X=Cl [10] to 23 Hz for
3
X=B(CH3)2 [6]. The J(FF)cis coupling constants of 2,
2a and 7 (ca. 26 Hz) all lie in this range. Thus the
replacement of CH3 groups by CF3 groups and subse-
quent coordination to the amine has little influence on
the electronegativity of the boron atom. Furthermore,
we note that the fluorine atom cis to the B(CF3)2 group
shows a 5J(FF) coupling of 9–14 Hz for the amine
boranes 2, 2a and 2b and a coupling of 4.6 Hz for the
fluoroborate anion 7.
2.2. Description of the crystal structures of
(F2CꢀCF)(F3C)2B·NHMe2 and
(HOOC)(F3C)2B·NHMe2
The structure of 2 is shown in Fig. 1, and selected
structural parameters are given in Table 3. Of particu-
lar interest is the interaction between the boron atom
and the trifluorovinyl group. The BC2F3 fragment is
In 4 and 3b the location of the 19F-NMR signals of
the C2F3O group is in good agreement with those
reported for perfluoropropene oxide: −110.95,
−114.11 and −157.69 ppm [11] versus −107.0, −
114.8, −140.8 ppm (4) and −108.8, −113.2, −132.8
ppm (3b). The assignment of the resonance close to
−135 ppm to the BCF fluorine atom is unambiguous
due to the broadening by the boron nucleus, whereas
the assignment of the terminal CF2 group is debatable.
,
planar to within90.02 A, and its orientation with
respect to the rest of the molecule, as shown by the
anticlinal value [144.0(2)°] of the NꢁBꢁC(1)ꢁC(2) tor-
sion angle, precludes a nontrivial symmetry for this
compound in the solid state. The BꢁC(1) bond length
,
(1.598(3) A) is not significantly shorter than that
2
,
The geminal coupling constants J(FF) of 4 and 3b are
(1.608(4) A) found for the attachment to the diazoacetic
50.1 and 47.1 Hz, respectively. These values are in line
with those observed for perfluoropropene oxide (+43.5
Hz). The fluorine atom of the CF2 group with the
resonance at −108 ppm shows coupling to the fluorine
acid ester group in B(CF3)2[C(N2)C(O)OEt]·NHMe2
(A) [12], which is the only previously reported structure
of a B(CF3)2R·NHMe2 derivative having the R group
bonded to boron via an sp2-hybridized carbon atom.

46
D.J. Brauer, G. Pawelke / Journal of Organometallic Chemistry 604 (2000) 43–51
Differences in the electronic and steric nature of the
borate and fluoride substituents of the C(1) atom are
reflected in its bond angles. Thus the BꢁC(1)ꢁC(2) and
F(1)ꢁC(1)ꢁC(2) angles assume relatively large and small
values, 134.4(2) and 112.6(2)°, respectively. The latter is
much smaller than that reported for tetrafluoroethene
(B) in the gas phase, 123.8(6)° [13]. Substitution of a
fluorine in B by the boryl group in 2 also leads to a
marked lengthening of the C(1)ꢁF(1) bond from
,
1.319(6) to 1.383(2) A.
When the amine ligand in amine(trifluoro-
methyl)borates possesses an NꢁH bond, this bond is
sufficiently acidic to take part in hydrogen bonding [1].
Three types of fluorine atoms, namely those of the CF,
CF2 and CF3 groups, are possible proton acceptors in
2. In order to determine if any of them take part in
Table 1
NMR spectral data for 2–7 a
2
2a
2b
3
3a
4
4a
5
5a
6
6a
7
1H
l(NCH3)
l(NCH2)
l(C6H5)
2.87
2.88
2.75
4.37
7.39
7.53
3.04
3.10
2.97
3.01
2.79
2.97
2.69
2.62
l(NH)
l(OH)
4.4
4.98
4.5
6.5
6.7
6.50
9.05
19F
l(BCF3)
−63.2
−59.7
−58.4
−59.9
−58.8
−62.6
−61.6
−62.8
−60.3
−61.8
−60.6
−70.8
−60.2
−59.6
−63.4
−61.9
2J(BF)
l(CF2)
2J(FF)
3J(FF)cis
l(CF2)
3J(FF)trans
4J(FF)
5J(FF)
3J(FF)
l(CFB)
4J(FF)
2J(BF)
l(BF)
29
28
28.4
−99.5
+87.7
+25.5
−124.3
−110.9
17.8
−91.7
+71.7
+25.9
−115.9
−111.4
−91.4
+64.2
+26.3
−111.6
−111.4
−90.5
+62.6
+27.5
−110.6
−111.4
−51.8
172.9
26.5
−46.1
162.8
31.8
−114.8
+50.1
26.9
−113.2
+50.6
28.2
−52.6
−54.1
−107.0
−108.8
9.5
13.6
13.7
11
10
10
−132.8
4.6
−196.8
−187.3
−186.4
−124.9
−131.2
−140.8
−195.7
8.4
5.4
23
−229.9
56.9
1J(BF)
11B
l(B)
−11.1
−9.0
−8.1
−9.7
−7.4
−12.1
−9.6
−12.4
−10.8
−10.8
−11.4
−6.4
13C
l(NCH3)
40.6
52.7
46.7
64.2
131
42.6
55.4
41.1
41.2
53.8
41.1
53.4
41.2
40.8
l(NCH2)
l(CO)
l(BCF3)
165.0
131.6
174.5
131.9
130.4
130
131.1
129.5
304
130.8
131.1
304.2
81.4
79.7
107.3
266
130
98
131.1
132.3
132.2
134.3
133
1J(CF)
1J(BC)
305
78.
301.1
79.7
304
74
305.0
77.1
300
76
l(CB)
1J(CF)
1J(BC)
l(CF2)
1J(CF)
130
130
106.0
265
99.5
301
74
112.2
289.4
295.5
19.3
186.5
72
184.4
73.7
221.3
59
234.1
58
160.5
297.2
278.4
43.2
161.5
280
280
47
161.4
297.5
283.3
45.3
124.4
308.2
312.3
37.6
127.3
312.3
316.4
38.15
110.5
294.5
161.6
274
275
2J(CF)
18.4
42.2
l(C6H5)
127.4
129.1
130.4
133.2
a 2, 2a, 2b, 3, 4, in CDCl3, 6, 3a, 3b, 7 in [D3]acetonitrile; 5, 5a in [D6]acetone; 6a in D2O/[D3]acetonitrile.

D.J. Brauer, G. Pawelke / Journal of Organometallic Chemistry 604 (2000) 43–51
47
Table 2
Crystal data
A view of 5 is given in Fig. 2, and selected distances
and angles are listed in Table 4. While the CF3 and
NMe2H groups adopt roughly staggered conformations
Compound
2
5
Empirical
formula
C6H7BF9N
C5H8BF6NO2
Formula weight 274.94
238.93
Crystal system
Space group
Monoclinic
P21/c
Triclinic
(
P1
,
a (A)
10.1079(13)
8.2451(10)
12.545(2)
90
106.597(10)
90
1002.0(2)
4
1.823
6.904(2)
7.308(2)
10.825(2)
89.78(2)
74.50(2)
61.947(14)
459.6(2)
2
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
V (A )
Z
Dcalc (g cm−3
Radiation
)
1.726
Mo–Ka
Mo–Ka
0.71073
293(2)
Siemens P3
q–2q
,
Wavelength (A) 0.71073
T (K) 295(2)
Diffractometer Siemens P3
Scan mode q–2q
Fig. 1. A perspective drawing showing two screw-related molecules of
2. Broken lines delineate hydrogen bonds, and the positions of the
non-hydrogen atoms are indicated by 20% probability thermal ellip-
soids.
Theta range (°) 2.10–25.04
Limiting indices 05h512,
05k59,
3.19–25.05
−85h58,
−85k58,
−125l512
3566
−145l514
Table 3
Reflections
collected
Unique
Rint
1865
,
Selected bond lengths (A) and angles (°) for 2
1765
0.0122
1297
1636
0.0262
1261
Bond lengths
BꢁN
1.608(2)
1.598(3)
1.622(3)
1.627(3)
1.493(2)
1.496(2)
NꢁH
0.84(2)
Observed
(I\2|)
Crystal size
(mm)
BꢁC(1)
BꢁC(3)
BꢁC(4)
NꢁC(6)
NꢁC(5)
C(1)ꢁC(2)
C(1)ꢁF(1)
C(2)ꢁF(2)
C(2)ꢁF(3)
1.293(3)
1.383(2)
1.314(2)
1.313(3)
0.46×0.24×0.20
0.42×0.20×0.10
v (mm−1
)
0.225
0.201
0.9776–0.9639
0.0441
0.0848
1.018
Transmission
R1 (all data)
wR2 (all data)
0.9590–0.9495
0.0454
0.0818
Bond angles
NꢁBꢁC(1)
NꢁBꢁC(3)
105.66(14)
111.4(2)
108.62(14)
113.6(2)
108.44(14)
108.93(14)
109.6(2)
BꢁNꢁC(6)
BꢁNꢁH
113.2(2)
101.9(14)
134.4(2)
112.99(14)
112.6(2)
126.2(2)
124.2(2)
109.6(2)
Goodness-of-fit 1.044
on F2
NꢁBꢁC(4)
BꢁC(1)ꢁC(2)
BꢁC(1)ꢁF(1)
F(1)ꢁC(1)ꢁC(2)
C(1)ꢁC(2)ꢁF(2)
C(1)ꢁC(2)ꢁF(3)
F(2)ꢁC(2)ꢁF(3)
Parameters
167
153
C(1)ꢁBꢁC(3)
C(1)ꢁBꢁC(4)
C(3)ꢁBꢁC(4)
C(5)ꢁNꢁC(6)
BꢁNꢁC(5)
DF map
0.200 to −0.137
0.251 to −0.145
−3
,
(e A
)
Extinction
coefficient
0.020(2)
0.020(6)
118.0(2)
hydrogen bonding, the coordinates of the hydrogen
atom were first corrected for the systematic shortening
of the NꢁH bond, which arises in an X-ray experiment
[14]. Accordingly, the hydrogen atom was pushed along
,
the NꢁH vector to a position 1.033 A [15] from the
nitrogen atom. The nearest fluorine atoms to this posi-
,
tion are F(1) (2.21 A) and F(9) (1−x, y−0.5, 1.5−z)
,
(2.23 A). These hydrogen bonds are shown in Fig. 1.
The former completes a five-membered ring and ac-
cordingly is sharply bent (111°), while the latter links
the molecules to chains and is more stretched (161°).
While the basicity of the F(1) and F(9) atoms should be
enhanced over those of the CF2 group by the inductive
effect of the boron atom, the lengths involved in this
bifurcated interaction indicate that the hydrogen bond-
ing must be considered feeble [16].
Fig. 2. A perspective drawing of 5 employing 20% probability thermal
ellipsoids for the non-hydrogen atoms.

48
D.J. Brauer, G. Pawelke / Journal of Organometallic Chemistry 604 (2000) 43–51
Table 4
to form a centrosymmetric, ten-membered ring, Fig. 3.
Thus hydrogen bonding couples the molecules to zigzag
chains, which propagate in the b direction. This struc-
ture further underscores the weak hydrogen-acceptor
properties of organic fluorine [16] because the O(1)
atoms accepts both protons although it is outnumbered
by fluorine by a factor of six.
,
Selected bond lengths (A) and angles (°) for 5
Bond lengths
BꢁN
BꢁC(1)
BꢁC(2)
BꢁC(3)
O(1)ꢁC(3)
1.589(2)
1.630(2)
1.620(3)
1.620(2)
1.231(2)
O(2)ꢁC(3)
NꢁC(4)
NꢁC(5)
NꢁH(N)
O(2)ꢁH(O2)
1.315(2)
1.498(2)
1.503(2)
0.85(2)
0.83(2)
Bond angles
NꢁBꢁC(1)
NꢁBꢁC(2)
112.45(14)
109.22(14)
107.82(13)
109.7(2)
110.02(14)
107.53(14)
123.86(14)
BꢁC(3)ꢁO(2)
O(1)ꢁC(3)ꢁO(2)
BꢁNꢁC(4)
BꢁNꢁC(5)
BꢁNꢁH(N)
C(4)ꢁNꢁC(5)
C(3)ꢁO(2)ꢁH(O2)
115.10(14)
121.0(2)
114.12(14)
117.1(2)
104.5(13)
108.8(2)
112(2)
3. Discussion
NꢁBꢁC(3)
The thermal stability and chemical inertness of the
amine trifluorovinylboranes 2 and 2a is in contrast to
the sensitivity of the uncomplexed trifluorovinylboranes
reported in the literature. It has been mentioned that
C2F3BMe2 and (C2F3)2BMe react with NMe3 to form
the corresponding trimethylamine boranes [6]. How-
ever, no information about the properties of these
adducts was given. A comparison of the properties of
(F2CꢀCF)Me2B·NMe3 with those of 2a should give
further insight into the CH3/CF3 substitution effect.
Although a direct comparison is not possible, the C2F3
group at tetracoordinated boron is drastically stabilized
by the CF3 groups in 2 and 2a. The addition of
bromine to the CꢀC bond of 2a is a typical reaction of
both fluorinated and nonfluorinated alkenes. The epox-
idation of 2 and 2a using ozone is typical for perfluori-
nated terminal alkenes, e.g. tetrafluoro-oxirane has
been obtained from tetrafluoroethene and ozone [17].
The side reaction with oxidative cleavage of the CꢀC
bond and the formation of a C(ꢀO)F group, which
hydrolyses to form 5 and 5a, is also known in per-
fluoroalkene chemistry [17,18]. Amine carboxyboranes,
R1R2R3NꢁBH2ꢁCOOH (R1R2R3=H, Me), are well
characterized compounds which exhibit remarkable
physiological properties [19]. They are very weak acids
with pKa values of 8.14–8.38. Compounds 5 and 5a are
related derivatives in which the boron-bonded hydro-
gen has been substituted by CF3 groups. The electron
withdrawing power of these two groups increases the
acid strength considerably — the pKa values being 5.9
and 5.4, respectively.
C(1)ꢁBꢁC(2)
C(1)ꢁBꢁC(3)
C(2)ꢁBꢁC(3)
BꢁC(3)ꢁO(1)
Fig. 3. A packing diagram of 5 showing the formation of centrosym-
metric hydrogen-bonded eight- and ten-membered rings.
with respect to the bonds radiating from the boron
atom, the plane of the carboxy group is oriented nearly
perpendicular to the BꢁCF3 bond of the C(2) atom. The
,
attachment of the carboxy group to boron, 1.620(2) A,
is slightly but significantly longer than the BꢁC(sp2)
bond in 2 and is probably longer than that of A.
Bonding to the boryl fragment does not lead to signifi-
cant lengthening of the CꢁO bonds in 5, 1.231(2) and
Compounds 4 and 3b are the first well-characterized
species in which an epoxide ring is directly attached to
boron. It has been reported that styrylboranes add
molecular oxygen to form epoxides according to Eq. (7)
[20], but these products were only characterized by their
refractive indices, densities, boiling points and elemen-
tal analyses.
,
1.315(2) A, when compared with those of carboxy
groups that are directly bonded to a saturated carbon
,
atom, 1.214(19) and 1.308(19) A, respectively [15].
Before checking for possible proton acceptors in 5,
the NꢁH(N) and O(2)ꢁH(O2) bond lengths were length-
,
ened as described for 2 to 1.033 and 0.967 A, respec-
tively. A scan of the interatomic distances showed that
only the O(1) atom is functioning as a hydrogen bond
acceptor. It interacts weakly with the H(N) atom (2.14
(7)
,
A, 154°) to form a centrosymmetric, eight-membered
,
ring and stronger with the H(O2) atom (1.81 A, 169°)
R=iPr, Pr, (CH2)2CHMe2, pentyl, ibutyl, heptyl

D.J. Brauer, G. Pawelke / Journal of Organometallic Chemistry 604 (2000) 43–51
49
Thus the characterization of these compounds gave
4.3. Preparation of compounds
no indication of the oxygen connectivity. In light of
boron chemistry this reaction seems strange because
trialkylboranes are known to react readily with oxygen
under insertion into the carbonꢁboron bond.
4.3.1. Dimethylamine-trifluoroethenylbis-
(trifluoromethyl)borane (2)
To a stirred solution of 20 g of 1,1,1,2-tetra-
fluoroethane in 100 ml of dry ether, (CF3)2BNMe2 (1)
(7.1 g, 36.8 mmol) and 50 g tBuLi (15% solution in
pentane) were added dropwise at −78°C. The reaction
mixture was stirred for 20 min, 30 ml of water added at
−78°C and the mixture was allowed to warm to r.t.
The pH was adjusted to ca. 4 using diluted HCl, the
organic phase separated, dried over Na2SO4 and taken
to dryness. The brown oily residue was sublimed in
vacuo at 50°C. Yield: 9.0 g (32.7 mmol) 89% colorless
solid, m.p. 48°C. IR (film)/Ra: 3272 cm−1 s/- (NH),
1753 s/m (CꢀC), 1104 vs/- (CF). —MS (70 eV); m/z
(%): 275 (22) [M+], 206 (11) [M+−CF3], 156 (93)
[M+−C2F5], 94 (100) [F2BNH(CH3)+2 ], 44 (66)
[C2H6N+]. —C6H7BF9N (274.92): Anal. Calc.: H, 2.57;
C, 26.21; N, 5.09. Found: H, 2.6; C, 25.6; N, 4.8%.
The difference in the hydrolytic stability of 3b and 4
is remarkable. Whereas 3b is water-stable, 4 rapidly
adds water, the epoxide ring being cleaved. We assume
that this divergent behavior is due to either intramolec-
ular or intermolecular hydrogen bridging between the
acidic NH function and the oxygen atom of the epoxide
ring. Such bridging increases the nucleophilicity of the
CF2 group and lowers the barrier for a nucleophilic
attack. That the hydrolytic stability of the epoxide ring
is due to the quaternization of the nitrogen is further
established by the fact that the ozonolysis of 2b results
in the formation of a stable oxiranylborane. This was
shown by epoxidation experiments run on an NMR
scale.
4. Experimental
4.3.2. Trimethylamine-trifluoroethenylbis-
(trifluoromethyl)borane (2a), benzyldimethylamine-
trifluoroethenylbis(trifluoromethyl)borane (2b)
4.1. General
A solution of 2 (8 g, 29 mmol) in 100 ml of ether
(dried over KOH) was stirred with 4.0 g of KOH pellets
and 10 ml of CH3I at 20°C for ca. 2 h. The reaction
mixture was filtered, all volatile material removed in
vacuo and 2a crystallized from CHCl3. 2a: Yield 7.9 g
(27 mmol) 94% colorless solid, m.p. 94°C. IR (film)/Ra:
1741 cm−1 s/m (CꢀC), 1105 vs/- (CF). —MS (70 eV);
m/z (%): 289 (5) [M+], 220 (2) [M+−CF3], 170 (53)
[M+−C2F5], 108 (100) [F2BN(CH3)+3 ], 58 (91)
[C3H8N+]. —C7H9BF9N (288.95): Anal. Calc.: H, 3.14;
C, 29.10; N, 4.85. Found: H, 3.1; C, 28.8; N, 4.6%.
Compound 2b was prepared analogously by stirring 3.9
g (14 mmol) of 2, 4.4 g of benzyl chloride and 4 g of
KOH pellets in 60 ml of ether for 14 h. Crystallization
from ether at −78°C furnished 2b (4.6 g, 12.9 mmol) in
90% yield as a colorless solid, m.p. 59°C. —IR 1736
cm−1 (CꢀC), 1112, 1090 (CF). —MS (70 eV); m/z (%):
365 (3) [M+], 246 (1) [M+−C2F5], 135 (19) [C9H13N+],
134 (10) [C9H12N+], 92 (21) [F2BNCH2(CH3)+], 91
(100) [C7H+7 ], 58 (59) [C3H8N+]. —C13H13BF9N
(365.05): Anal. Calc.: H, 3.59; C, 42.77; N, 3.84.
Found: H, 3.5; C, 42.6; N, 4.0%.
NMR: Bruker ARX 400 (400, 100.6 and 376.5 MHz,
1
for H, 13C and 19F, respectively), Bruker AC 250 (79.8
MHz for 11B): CDCl3 (1H: lH=7.27, 13C: lC=77.0),
[D3]acetonitrile (1H: lH=1.95, 13C: lC=1.30),
[D6]acetone (1H: lH=2.05, 13C: lC=30.5) as solvent
and internal standard, 19F: external standard CFCl3,
11B: external standard BF3. OEt2. —IR: Bruker IFS 25;
—Raman: Cary 82 Kr+ 647.1 nm. —UV–vis: Schi-
madzu UV-160 A. —MS: Varian MAT 311 (70 eV).
—Thermogravimetry: Netzsch STA 409. —Ozone
Generator: Fischer 501.
4.2. X-ray structural determination
Crystals of 2 were grown by sublimation and sealed
in a glass capillary while those of 5, which crystallized
from a solution in acetonitrile, were glued to a glass
fiber. Diffraction measurements were made at room
temperature (r.t.) using a Siemens P3 diffractometer
employing graphite monochromatized Mo–Ka radia-
tion. Intensities were derived by profile analysis and
corrected for absorption. The structures were solved by
direct methods and refined with all non-hydrogen
atoms assigned anisotropic temperature factors. The
hydrogen atoms bonded to the nitrogen and oxygen
atoms were located by difference Fourier techniques
and refined isotropically, while those of the methyl
groups were idealized. Crystal data are given in Table
2. Structural solution, refinement and display were car-
ried out with a SHELXTL, version 5.03, program pack-
age.
4.3.3. Dimethylamine-1,2-dibromotrifluoroethylbis-
(trifluoromethyl)borane (3), trimethylamine-1,2-
dibromotrifluoroethylbis(trifluoromethyl)borane (3a)
A solution of 2 (1.1 mmol) or 2a in 5 ml of CHCl3
was mixed with 0.4 g (2.5 mmol) of Br2 and kept for 3
days at 20°C. All volatile material was removed in
−3
vacuo. Compound 3 was distilled at 50°C 10
mbar
and 3a was crystallized from CHCl3. Yield 3a: 0.38 g

50
D.J. Brauer, G. Pawelke / Journal of Organometallic Chemistry 604 (2000) 43–51
organic phase was taken to dryness and 6 dried at
60°C. Yield: 2.0 g (7.56 mmol) 52% yellow powder;
m.p. 108°C; pKa 2.6. IR: w=3343 cm−1 (OH), 3185
(NH), 1746, 1686 (CꢀO), 1102 (CF). —MS (70 eV);
m/z (%): 222 (10) [M+−CO2H], 94 (100)
[F2BNH(CH3)+2 ], 74 (3) [FBN(CH3)+2 ], 44 (15)
[C2H6N+]. Elemental analyses C6H8BF6NO3 (266.93):
Anal. Calc. H, 3.02; C, 27.00; N, 5.25. Found: H, 2.9;
C, 26.5; N, 4.9%. Cs[HMe2NꢁB(CF3)2ꢁCOꢁCO2] (6a):
UV–vis (water): umax (m)=365 nm (27), 410 nm (14).
Elemental analyses C6H7CsBF6NO3 (398.83): Anal.
Calc.: H, 1.77; C, 18.07; N, 3.51. Found: H, 1.7; C,
17.7; N, 3.5%.
Crystals of 5 were grown from acetonitrile. Yield 5:
0.42 g (1.74 mmol) 12%: dec. 144°C IR (KBr): 3202
cm−1 m (NH), 1691 m, 1664 s (CꢀO), 1099 vs (CF).
—MS (70 eV); m/z (%): 239 (4) [M+], 222 (1) [M+−
OH], 175 (2) [M+−CO2ꢁHF], 156 (1) [M+−
CO2ꢁHF2], 94 (100) [F2BNH(CH3)+2 ], 44 (22)
[C2H6N+]. —C5H8BF6NO2 (238.92): Anal. Calc.: H,
3.37; C, 25.14; N, 5.86. Found: H, 3.3; C, 24.7; N,
5.8%. —pKa 5.4.
(0.85 mmol) 77% colorless solid, m.p. 112°C. IR (KBr)/
Ra: 1110 vs/- (CF), −/296 vs (CBr). —MS (70 eV);
m/z (%): 370 (30) [M+−Br], 289 (1) [M+−Br2], 222
(10) [C2F2Br2+], 170 (16) [M+−C2F5ꢁBr2], 108 (100)
[F2BN(CH3)+3 ], 58 (98) [C3H8N+]. —C7H9BBr2F9N
(448.76): Anal. Calc.: H, 2.02; C, 18.74; N, 3.12.
Found: H, 2.0; C, 18.5; N; 3.6%. Yield 3: 0.35 g (0.80
mmol) 73% colorless oil. —IR (film)/Ra: 1110 vs/-
(CF), −/295 vs (CBr). MS (70 eV); m/z (%): 356 (1)
[M+−Br], 275 (5) [M+−Br2], 222 (37) [C2F2Br+2 ], 162
(28) [C2F3Br+], 156 (23) [M+−C2F5ꢁBr2], 94 (100)
[F2BNH(CH3)+2 ], 44 (92) [C2H4N+]. —C6H7BBr2F9N
(434.73): Anal. Calc.: H, 1.62; C, 16.58; N, 3.22.
Found: H, 1.6; C, 16.8; N, 3.2%.
4.3.4. Trimethylamine-bis(trifluoromethyl)-
trifluorooxiranylborane (3b), trimethylamine-
carboxybis(trifluoromethyl)borane (5a),
dimethylamine-carboxybis(trifluoromethyl)borane (5),
dimethylamine-bis(trifluoromethyl)oxocarboxyborane (6)
A flow of ozone/oxygen (ca. 2 g O3/h) was intro-
duced into a solution of 2 (4.0 g, 13.8 mmol) in 10 ml
of CHCl3 at 20°C. The progress of the reaction was
monitored by running 19F-NMR spectra and stopped
when the signals of 2a had disappeared. The solution
was cooled to 0°C and 5a was removed by filtration.
The filtrate was concentrated to 5 ml and upon cooling
to −20°C most of 3b crystallized (colorless thin
plates). Yield 3b: 3.1 g (10.1 mmol) 73%: m.p. 113°C.
—IR/Ra: 1500 cm−1 s/- (CꢁO), 1123, 1095 vs/- (CF).
—MS (70 eV); m/z (%): 236 (3) [M+−CF3], 186 (3)
[M+−C2F5], 170 (3) [M+−OC2F5], 108 (100)
[F2BN(CH3)+3 ], 58 (74) [C3H8N+]. —C7H9BF9NO
(304.95): Anal. Calc.: H, 2.97; C, 27.57; N, 4.59.
Found: H, 3.1; C, 27.4; N, 4.6%.
Yield 5a: 0.49 g (1.9 mmol) 14%: dec. 201°C. —IR
(KBr): 1671 cm−1 s, 1629 m (CꢀO), 1105 vs (CF).
—MS (70 eV); m/z (%): 253 (10) [M+], 236 (6) [M+−
OH], 189 (4) [M+−CO2ꢁHF], 170 (3) [M+−
CO2ꢁHF2], 139 (3) [M+−CO2ꢁHCF3], 108 (100)
[F2BN(CH3)+3 ], 58 (76) [C3H8N+]. —C6H10BF6NO2
(252.95): Anal. Calc.: H, 3.98; C, 28.49; N, 5.54.
Found: H, 3.9; C, 28.5; N; 5.3%. —pKa 5.9.
The epoxidation of 2 was carried out analogously
with 4.0 g (14.5 mmol). After 5 has been isolated by
filtration, the filtrate became yellow and was stirred for
2 h with aqueous CsOH solution. The pH was of the
aqueous phase was adjusted to 9 using CsOH, and the
reaction mixture was taken to dryness in vacuo. The
residue was stirred with 150 ml of hot acetonitrile, and
the slurry was hot filtered. Upon cooling the filtrate to
−20°C Cs[HMe2NꢁB(CF3)2ꢁCOꢁCO2] (6a) precipi-
tated. The salt was dissolved in 50 ml of 2 M HCl and
the acid extracted with two portions of ether. The
4.3.5. Tetramethylammonium-fluoro-
(trifluoroethenyl)bis(trifluoromethyl)borate (NMe47)
Anhydrous tetramethylammonium fluoride (6 g), pre-
pared according to Ref. [8], was stirred with 30 ml of
anhydrous 2-butanone and 2 g (6.9 mmol) of 2a at
reflux for 20 min. Most of the solvent was removed in
vacuo, and the residue was stirred with ca. 60 ml of
anhydrous acetone and filtered. The filtrate was taken
to dryness in vacuo. Yield: 1.2 g (3.7 mmol) 54% light
yellow waxy solid. IR (KBr): 1746 cm−1 s (CꢀC), 1488
s (lasCH3), 1277, 1091, 1034 vs (CF). —C8H12BF10N
(322.98): Anal. Calc.: H, 3.74; C, 29.75; N, 4.34.
Found: H, 4.1; C, 30.4; N, 4.5%.
4.3.6. Cesium-fluoro(trifluoroethenyl)bis-
(trifluoromethyl)borate (Cs7)
Compound 2a (0.85 g, 2.94 mmol) and NEt3×3HF
(2.0 g, 12.4 mmol) were heated in a Teflon PFA reac-
tion vessel to 200°C for 7 h. The excess of NEt3×3HF
and eventually unreacted 2a were distilled off in vacuo
at 150–160°C, and the residue was stirred with 4 g
of Cs2CO3 in 30 ml of acetone for 4 h to remove
NEt3×3HF and to prepare the Cs salt. The slurry
was filtered over charcoal and the filtrate was taken
to dryness in vacuo at 60°C. Yield: 0.96 g (2.53
mmol) 86% colorless oil, dec.170–175°C. IR (film):
1751 cm−1 vs (CꢀC), 1283, 1093, 1031 vs (CF). —
C4CsF10B (381.74): Anal. Calc.: C, 12.59. Found: C,
12.2%.

D.J. Brauer, G. Pawelke / Journal of Organometallic Chemistry 604 (2000) 43–51
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5. Supplementary material
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Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC nos. 134641 and 134642, respec-
tively, for compounds 2 and 5. Copies of the data can
be obtained free of charge from The Director, CCDC,
12 Union Road, Cambridge CB2 1EZ, UK (Fax: +44-
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
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