Synthesis of Fluorine-Containing Aryl(halo)boranes from Potassium Aryl(fluoro)borates

Article abstract of DOI:10.1134/S1070363220010089

Fluorine-containing aryldihalogenoboranes have been obtained by the reaction of boron and aluminum chlorides and bromides with potassium aryltrifluoroborates K[ArBF₃] under mild conditions. In a similar way, bis(pentafluorophenyl)halogenoboranes have been synthesized by the reaction with K[(C₆F₅)₂BF₂]. The reaction of K[C₆F₅BF₃] with AlBr₃ affords a mixture of C₆F₅BF₂ and C₆F₅BCl₂ due to fast conversion of AlBr₃ to AlBrCl₂. The inductive and resonance parameters of BCl₂ and BBr₂ groups were calculated.

Full text of DOI:10.1134/S1070363220010089

ISSN 1070-3632, Russian Journal of General Chemistry, 2020, Vol. 90, No. 1, pp. 50–61. © Pleiades Publishing, Ltd., 2020.
Russian Text © The Author(s), 2020, published in Zhurnal Obshchei Khimii, 2020, Vol. 90, No. 1, pp. 72–84.
Synthesis of Fluorine-Containing Aryl(halo)boranes
from Potassium Aryl(fluoro)borates
V. V. Bardina,*, S. A. Prikhod’kob, M. M. Shmakovb, A. Yu. Shabalinb, and N. Yu. Adoninb
a N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences,
Novosibirsk, 630090 Russia
b Federal Research Center “G.K. Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences,”
Novosibirsk, 630090 Russia
*e-mail: bardin@nioch.nsc.ru
Received June 13, 2019; revised June 13, 2019; accepted June 20, 2019
Abstract—Fluorine-containing aryldihalogenoboranes have been obtained by the reaction of boron and aluminum
chlorides and bromides with potassium aryltrifluoroborates K[ArBF3] under mild conditions. In a similar way,
bis(pentafluorophenyl)halogenoboranes have been synthesized by the reaction with K[(C6F5)2BF2]. The reaction
of K[C6F5BF3] with AlBr3 affords a mixture of C6F5BF2 and C6F5BCl2 due to fast conversion of AlBr3 to AlBrCl2.
The inductive and resonance parameters of BCl2 and BBr2 groups were calculated.
Keywords: aryldihaloboranes, aryltrifluoroborates, boron halides, aluminum halides
DOI: 10.1134/S1070363220010089
Polyfluorinated aryl(halogeno)boranes are known
since 1963, when C6F5BF2 and C6F5BCl2 have been first
prepared [1, 2]. Till the end of 90-s, the main methods
of their synthesis consisted in the replacement of the
С–metal bond by the С–B bond, or in transformation of
the BR2 fragment into BX2 (X = F, Cl, Br). In 2000, it was
proposed to prepare aryldifluoroboranes by the reaction
of potassium aryltrifluoroborates with fluorine-containing
Lewis acids (BF3, AsF5) in an inert solvent (CH2Cl2,
fluorochlorocarbons). The method is of general character
and can be expanded to alkyl-, alkenyl- and alkynyldi-
fluoroboranes. More general picture of the studies in this
field is presented in review [3].
The solutions of nonsolvated aryldifluoroboranes
C6FnH5–nBF2 were obtained by us by defluorination of
aryltrifluoroborates K[C6FnH5–nBF3] in the two-phase
system [bmim][Al2Cl7]–hexane [6]. Despite of the fact
that chloroaluminate was chosen as the acceptor of fluo-
ride ion, no formation of chloro-containing arylboranes
was observed. It is noteworthy, that we succeeded not
only in the synthesis of compounds with the phenyl and
fluorophenyl group, but also with electron withdrawing
polyfluorinated aryl groups 4-EtOC6F4 and C6F5, because
such aryldifluoroboranes are much more strong Lewis
acids than their hydrocarbon analogues. The obtained
solutions of arylboranes showed the properties of good
homogeneous catalysts of alkylation of phenols with
olefins [6]. These results open up perspectives for their
use as mild acidic catalysts for selective transformations
of polyfunctional compounds.
Until recently, generation of aryldifluoroboranes in
solution using non-fluorinated fluoride ion acceptors was
represented only by papers [4, 5]. Aryldifluoroboranes
were obtained by the reaction of chlorotrimethylsilane
with salts K[ArBF3] (Ar = C6H5, 2-C6FH4, 2,6-C6Cl2H3,
1-naphthyl) in acetonitrile or THF and they exist in
equilibrium with the solvates ArBF2L [L = NCMe,
O(CH2CH2)2] (11B NMR) [4].According to [5], C6H5BF2
was formed from K[C6H5BF3], 18-crown-6 (cat.) and
SiCl4 in CH2Cl2, whereas in MeCN or MeCN–THF the
solvate C6H5BCl2L was obtained. In neither case the
yields of the products were reported.
To develop this approach to aryl(halogeno)boranes we
investigated defluorination of a series of easily accessible
potassium aryl(fluoro)borates with some Lewis acids.As
fluoride ion acceptors, boron and aluminum chlorides and
bromides were used, as well as silicon chlorides.
Earlier, we have described defluorination of
K[C6H5BF3] and fluorinated potassium phenyltrifluorobo-
rates with boron fluoride in CH2Cl2 [7]. Boron chloride
50

SYNTHESIS OF FLUORINE-CONTAINING ARYL(HALO)BORANES
51
Scheme 1.
CH2Cl2
3-FC6H4BCl2
K[3-FC6H4BF3] + BCl3
22°C, 2 h
1
2
CH2Cl2
K[4-FC6H4BF3] + BCl3
4-FC6H4BCl2
22°C, 2 h
3
4
Scheme 2.
BF2
BF3K
BFCl
BCl2
F
F
F
F
F
F
F
F
F
F
+
F
F
F
F
nBCl3
+
CH2Cl2, 22oC
F
F
F
F
F
F
5
6
7
8
n = 1.2
n = 1.7
:
0.2
:
:
0.2
:
:
1
:
0
0
1
Scheme 3.
F
F
F
F
F
F
F
F
F
BCl3
F
BCl
+
BF
F
BF2K
F
CH2Cl2, 22qC
F
F
F
2
2
2
9
10
11
is more strong Lewis acid (pF– 9.40, 9.60) than BF3 (pF–
8.21) [8, 9]. Upon the action of BCl3 in CH2Cl2 at room
temperature, potassium 3-fluorophenyltrifluoroborate 1
is converted to 3-fluorophenyldichloroborane 2 with the
absence of notable amounts of fluoroboranes 3-FC6H4BF2
and 3-FC6H4BFCl. (Table 1, run 1). Potassium 4-fluo-
rophenyltrifluoroborate 3 reacts similarly resulting in
4-fluorophenyldichloroborane 4 (Table 1, run 2). The
yields of fluorophenylboranes in both cases exceed 80%
(Scheme 1).
product is bis(pentafluorophenyl)chloroborane 11
(1 : 14) (Scheme 3).
Using large excess of BCl3 and increasing the duration
of the reaction to 15 h, we tried to obtain 2-heptafluoro-
naphthyldichloroborane 12 from potassium heptafluoro-
naphthyltrifluoroborate 13. Indeed, arylborane 12 was
obtained in 50% yield but it contained notable amount
of 2-heptafluoronaphthylfluorochloroborane 14 (2.6 : 1).
Both arylhalogenoboranes are very sensitive to moisture
and easily form 2-heptafluoronaphthylboronic acid 15
even with short-term exposure on wet air. The latter was
characterized by 11B and 19F NMR spectra and the data
of elemental analysis (Scheme 4).
Potassium pentafluorophenyltrifluoroborate 5 reacts
with small excess of BCl3 in CH2Cl2 at room temperature
to give a mixture of pentafluorophenylfluorophenyldi-
fluoroborane 6, pentafluorophenylfluorochloroborane 7
and, mainly, pentafluorophenyldichloroborane 8 (Table 1,
run 3). In a large excess of BCl3, fluoroboranes 6 and 7
practically were not formed (Table 1, run 4) (Scheme 2).
Treatment of borate 5 with two-fold excess of boron
bromide in CH2Cl2 gave equimolar amounts of difluo-
roborane 6 and pentafluorophenyldibromoborane 16
(Table 1, run 5) (Scheme 5).
Under similar conditions, potassium bis(pentafluoro-
phenyl)difluoroborate 9 gives a small amount of
bis(pentafluorophenyl)fluoroborane 10, while the main
Aluminum halides are more strong fluorine ac-
ceptors than the corresponding boron halides. For
example, the fluoride ion affinity (pF–) of compounds
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52
BARDIN et al.
Table 1. Parameters of the reaction of K[ArBF3] with boron and aluminum halogenides at 22°С
Yield, mmola
ArBFX
Run
no.
Ar (mmol)
MX3 (mmol)
Solvent (V, mL)
Time, h
ArBF2
0.48
ArBX2
1.4
1
3-FC6H4 (1.7)
4-FC6H4 (3.2)
C6F5 (4.70)
C6F5 (0.9)
BCl3 (2.8)
CH2Cl2 (7)
CH2Cl2 (11)
CH2Cl2 (20)
CH2Cl2 (4)
CH2Cl2 (5)
CH2Cl2 (5)
Hexane (2)
Hexane (2)
Hexane (3)b
Hexane (3)b
Hexane (3)
Hexane (3)b
Hexane (3)
Hexane (2)
Hexane (2)
Hexane (3)
Hexane (3)
Hexane (3)b
Hexane (3)
Hexane (3)
CH2Cl2 (10)
CH2Cl2 (10)
CH2Cl2 (20)
CH2Cl2 (2)
CH2Cl2 (3)
2
2
2
BCl3 (4.4)
2.8
3
BCl3 (5.5)
2
0.54
0.09
3.24
0.7
4
BCl3 (1.5)
3
5
C6F5 (1.15)
C6F5 (0.78)
C6F5 (1.2)
BBr3 (2.3)
2
0.44
0.41
0.56
0.21
0.3
6
AlCl3 (1.4)
AlCl3 (1.8)
AlCl3 (1.8)
AlCl3 (1.0)
AlCl3 (1.0)
AlBr3 (1.36)
AlBr3 (1.36)
AlBr3 (1.70)
AlBr3 (0.70)
AlBr3 (0.76)
AlBr3 (0.86)
AlBr3 (0.86)
AlBr3 (0.86)
AlBr3 (1.51)
AlBr3 (1.51)
AlBr3 (1.2)
AlBr3 (1.8)
AlBr3 (3.4)
BCl3 (0.95)
AlCl3 (2.1)
4
7
4
8
C6F5 (1.2)
24
7
0.1
0.09
0.09
0.4
9
C6F5 (0.89)
C6F5 (0.89)
3-FC6H4 (1.24)
3-FC6H4 (1.24)
3-FC6H4 (0.67)
4-FC6H4 (0.56)
4-FC6H4 (0.41)
C6F5 (0.83)
C6F5 (0.83)
C6F5 (0.83)
C6F5 (0.77)
C6F5 (0.77)
C6F5 (1.2)
0.30
0.67
0.78
0.78
0.19
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
14
3
0.08
0.08
0.26
0.26
0.50
0.22
0.29
9
4
4
0.19
0.04
0.67
0.67
0.67
0.19
0.31
1.1
0.04
0.02
4
3
24
6
3
0.03
0.06
0.28
0.05
24
2
C6F5 (1.00)
C6F5 (1.00)
4-C5NF4 (0.57)
4-C5NF4 (0.93)
1
0.84
0.14c
1.0c
24
5
0.03
0.05
0.07
0.05
0.40
0.80
5
а From 19F NMR.
b At 60–65°С.
c C6F5BCl2.
AlCl3, AlCl2F, AlClF2, and AlF3 is 11.46, 11.50, 11.47,
and 11.50, respectively [10]. Indeed, upon stirring the
suspension of borate 5 and AlCl3 in CH2Cl2 (22°С,
4 h) we obtained the solution of C6F5BF2, C6F5BFCl,
and C6F5BCl2 in the ratio 4 : 1 : 2 (Table 1, run 6).
The reaction in hexane proceeds slower. After 4 h, only
dichloroborane 8 was presented in the solution (yield
25%) (Table 1, run 7). Further stirring of the reaction
suspension for 24 h leads to the increase of the yield of
8 to 33% and the formation of difluoroborane 6 (8%)
and small amount of C6F5BClF (Table 1, run 8). Reflux
in hexane for 7 h increases the conversion of borate 5 to
65% and is accompanied by conversion of dichloroborane
8 to fluorochloroborane 7 and difluoroborane 6 (Table 1,
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SYNTHESIS OF FLUORINE-CONTAINING ARYL(HALO)BORANES
53
Scheme 4.
F
F
F
F
F
F
F
F
F
F
F
F
BXY
F
F
F
B(OH)2
F
F
F
BF3K
F
>4BCl3
H2O
CH2Cl2, 22qC
F
F
13
12, 14
15
X = Y = Cl (12); X= F, Y = Cl (14).
Scheme 5.
BF3K
BF2
BBr2
F
F
F
F
F
F
F
F
F
F
F
F
BBr3
+
CH2Cl2, 22qC
F
F
F
5
6
16
Scheme 6.
BF2
BCl2
BFCl
F
F
F
F
F
F
F
F
F
F
AlCl3
+
+
CH2Cl2, 22°C, 4 h
F
F
BF3K
F
6
4
F
8
F
7
F
F
F
F
:
1
:
2
F
0
1
:
:
0
1
:
1
AlCl3
5
:
4
hexane
22°ɋ, 4 h
22°ɋ, 24 h
60ꢀ65°ɋ, 7 h
60ꢀ65°ɋ, 14 h
1
1
:
:
0.3
0
:
:
0.6
0
run 9).After 14 h reflux, the latter becomes the only product
of the reaction (yield 75%) (Table 1, run 10) (Scheme 6).
Apparently, the lower reaction rate in hexane as compared
to that in dichloromethane is due to low solubility of the
substrate and the reagent in hydrocarbons.
(55 h) of heterogeneous mixture increased the conversion
of 9 to 76%, but, a small amount of [(C6F5)2B]2O 17 was
formed because of the contact with wet air (Scheme 7).
Although the affinity of aluminum bromide to
fluoride ion is unknown, it can be assumed to be higher
than that of aluminum chloride. The reaction of borate
1 with AlBr3 (1 equiv.) in hexane at room temperature
affords 3-fluorophenyldifluoroborane 18 (major prod-
uct), 3-fluorophenylfluorobromoborane 19 and 3-fluo-
rophenyldibromoborane 20 (Table 1, run 11). Heating
at 60°С for 9 h did not change the composition and the
ratio of the products (Table 1, run 12). With excess of
Similar changes in the rate of defluorination were
observed in the reaction of K[(C6F5)2BF2] with AlCl3 in
dichloromethane and hexane. In CH2Cl2 solution at 22°С,
this substrate was almost completely converted into the
equimolar mixture of boranes 10 and 11 in 4 h. In hexane,
the conversion of borate 9 was 40% after 5 h, and the
main product was chloroborane 11. Prolonged stirring
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54
BARDIN et al.
Scheme 7.
F
F
F
F
F
F
F
F
F
AlCl3
22oC
F
BF2K
F
BCl
F
BF
+
F
F
F
2
2
2
9
10
11
CH2Cl2, 4 h:
1
:
1
hexane, 5 h:
1
1
:
20
4
hexane, 55 h:
:
Scheme 8.
3-FC6H4BF2 + 3-FC6H4BFBr + 3-FC6H4BBr2
hexane
K[3-FC6H4BF3] + nAlBr3
22°ɋ
1
18
19
20
n = 1 (3 h):
3
0
:
:
0.3
:
:
1
1
n = 2.5 (4 h):
0
Scheme 9.
hexane
K[4-FC6H4BF3] + nAlBr3
4-FC6H4BF2 + 4-FC6H4BFBr + 4-FC6H4BBr2
22°ɋ, 4 h
3
21
23
22
n = 1:
1
:
:
0.2
0.1
:
:
1
1
n = 1.9:
0.1
AlBr3, only dibromoborane 20 is formed (Table 1, run 13)
(Scheme 8).
haloboranes 6 and 16 were obtained in the ratio 1 : 1.5
and total yield of 60% after 3 h. Also, a small amount of
pentafluorophenylbromofluoroborane 24 and unidentified
compounds were found (Table 1, run 19). More protracted
stirring led to partial transformation of aryldibromobo-
rane 16 to the corresponding aryldifluoroborane (Table 1,
run 20) (Scheme 10).
Isomeric borate 3 reacts with AlBr3 in hexane in a
similar way. With small excess of aluminum bromide,
approximately equal amounts of 4-fluorophenyldifluo-
roborane 21 and 4-fluorophenyldibromoborane 22 are
formed besides a small amount of 4-fluorophenylfluoro-
bromoborane 23 (Table 1, run 14). With two-fold excess
of AlBr3, the major product is dibromoborane 22, while
the total amount of fluorine-containing boranes 21 and
23 does not exceed 15–17% (Table, run 15) (Scheme 9).
The reaction of 5 withAlBr3 (1 equiv.) in CH2Cl2 pro-
ceeds faster than in hexane and after 2 h difluoroborane 6
is formed in almost quantitative yield (Table 1, run 21).
However, when 1.8 equiv. ofAlBr3 was used, along with
difluoroborane 6, dichloroborane 8 was unexpectedly
formed besides difluoroborane 6. With larger excess of
AlBr3 it was the only product of the reaction (Table 1,
runs 22, 23). We assumed that aluminum bromide is
converted to the chloride or bromochloride, which are
responsible for the formation of compound 8. Special
experiment has shown that dissolution ofAlBr3 (1 equiv.)
in CH2Cl2 (22°С) gives rise to the formation of dark so-
The reaction of borate 5 with AlBr3 (1 equiv.) at
22°C in hexane affords C6F5BF2 in 80% yield (Table 1,
run 16). The increase of duration of the reaction from
4 to 20 h, or heating at 60-65°C for 6 h did not lead to
arylbromoboranes (Table 1, runs 17, 18). This means
that the formed AlBr2F does not exchange the fluorine
atoms in 6 by bromine atoms under these conditions.
Upon the action of two equiv. of AlBr3 on borate 5, di-
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SYNTHESIS OF FLUORINE-CONTAINING ARYL(HALO)BORANES
55
Scheme 10.
BF2
F
F
F
F
hexane
1AlBr3,
22°C, 24 h, then
60ꢀ65°C, 6 h
BF3K
F
F
F
F
F
6
BF2
BBr2
BFBr
F
F
F
F
F
F
F
F
F
F
F
F
F
2AlBr3, hexane
22oC
+
5
+
F
F
16
F
24
6
3 h:
10
:
:
2
:
15
24 h:
10
2
:
2
Scheme 11.
BCl2
BF3K
BF2
F
F
F
F
F
F
F
F
F
F
F
F
nAlBr3
CH2Cl2, 22oC
+
F
F
F
6
8
5
n = 1 (2 h):
10
10
0
:
:
:
0
n = 1.8 (1 h):
n = 3.4 (24 h):
1.6
10
AlBr3 + CH2Cl2
"AlBrCl2"
+
2CH2BrCl
22oC
lution, from which gray precipitate is sedimented. After
4 h, 2 equiv. of CH2ClBr is formed and the composition
is not changed during the next 20 h. Stoichiometrically, it
corresponds to substitution of two bromine atoms inAlBr3
by chlorine atoms and formation ofAlBrCl2, although we
did not investigate the nature of the precipitate in detail
(Scheme 11).
AsF5 (pF– 10.59 [10]) in CH2Cl2 tetrafluoro-4-pyridyldi-
fluoroborane 25 was formed [12]. This compound along
with tetrafluoro-4-pyridylfluorochloroborane 27 is formed
from borate 26 by the action of boron chloride (pF– 9.60
[9]) or aluminum chlorides (11.46 [10]), but the main
product is tetrafluoro-4-pyridyldichloroborane 28, whose
yields exceed 70% (Table 1, runs 24, 25) (Scheme 12). In
this connection, the inertness of arylborate 26 to boron
bromide (pF– 10.24 [9]) and aluminum bromide is surpris-
ing. For example, it does not react with BBr3 in CH2Cl2
(22°C, 20 h), or with excess of AlBr3 in hexane (22°C,
96 h) or with excess of BBr3 in boiling 1,2-dichloroethane
(11B and 19F NMR). The reasons for that are unclear.
Since tetrafluoro-4-pyridyldifluoroborane 25 has the
highest affinity to fluoride ion among aryldifluoroboranes
(pF– 9.08 [11]), defluorination of potassium tetrafluoro-
4-pyridyltrifluoroborate 26 requires strong acceptor of
fluoride ion. Thus, this borate did not react with boron
fluoride (pF– 7.88 [11], 8.21 [9]), but under the action of
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56
BARDIN et al.
Scheme 12.
BCl2
BFCl
BF3K
BF2
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
MCl3
+
+
CH2Cl2, 22°C, 5 h
N
N
N
F
N
26
25
27
28
MCl3 = BCl3:
MCl3 = AlCl3:
0.7
0.6
:
1.7
0.6
:
:
10
10
:
Scheme 13.
MX3
K[ArBF3]
K[MX3F] + ArBF2
K[ArBXF2]
ArBX2
ArBXF
ꢀMXnF3ꢀn
MX2F
+
KX
X = Cl, Br.
Although silicon chlorides Me3SiCl and SiCl4 suc-
and are easily converted to the mixtures of arylboronic
acids and their anhydrides when exposed to air. This
strongly complicates the determination of their elemental
composition by classical methods. The structure of the
earlier unknown aryldihaloboranes was established using
multinuclear NMR spectroscopy, by comparing with the
spectra of known aryldifluoroboranes (Table 2). In the 11B
NMR spectrum of the solution obtained from borate 5 and
AlCl3 (Scheme 6), apart from the signals of the known
boranes C6F5BF2 and C6F5BCl2 (Table 2), a doublet with
the spin-spin coupling constant ССВ 1J(В,F) 85 Hz ap-
pears at 38.2 ppm that was assigned to the boron atom
in pentafluorophenylfluorochloroborane 7. The 19F NMR
spectrum of this solution contain the signal of the BFCl
group at –28.4 (q, 1JBF = 82 Hz) and the signals of pen-
tafluorophenyl group at –129.2 (m, 2F, F2,6), –144.9 (t. t,
1F, F4, 3J(F4, F3,5) 20.1 Hz, 4J(F4, F2,6) 6.6 Hz) and –161.1
(m, 2F, F3,5) ppm of the corresponding intensity. The 11B
NMR spectrum of tetrafluoro-4-pyridylflurochloroborane
27 contains a doublet at 37.3 ppm (1JВF = 84 Hz) belong-
ing to the boron atom in the BFCl group, whereas in the
19F NMR spectrum the signal of the fluorine atom of this
group appears at –23.6 ppm. The multiplets at –91.5 (2F,
F2,6) and –132.2 ppm (2F, F3,5) correspond to the fluo-
rine atoms of the tetrafluoropyridyl ring. The solution of
pentafluorophenyldihaloboranes in hexane (Scheme 10)
cessfully defluorinate hydrocarbon potassium aryltri-
fluoroborates [4, 5], they do not react with K[C6F5BF3]
at reflux in CHCl3 (weakly coordinating solvent) during
2–3 h. This is consistent with notable difference of the
pF– values of aryldifluoroboranes C6H5BF2 and C6F5BF2
(ΔpF– = 1.74 [11]).
The reaction of potassium aryltrifluoroborates with bo-
ron and aluminum halides can be represented by Scheme
13. Although the final product here isArBX2, the ratio of
boranes ArBF2 : ArBFX : ArBX2 depends on the stoichi-
ometry of the reagents, solubility or volatility of MFnX3–n
(n = 0–2), which can be removed from the reaction mix-
ture as precipitate or gas, and possible interconversion of
these boranes. It is known that in the mixture of phenyl-
dihaloboranes C6H5BF2 + C6H5BX2 = 2 C6H5BFX (X =
Cl, Br) the halogen atoms are exchanged and equilibrium
is established [13], but there are no data on the behavior
of their polyfluorinated analogues. Another determining
factor is heterogeneity of the reaction mixture. Defluo-
rination was carried out in weakly coordinating solvents
(hexane, dichloromethane, 1,2-dichloroethane), in which
borates K[ArBF3] are insoluble and, most probably, the
reaction occurs on the surface of the solid compound.
The products of defluorination, aryldihaloboranes, are
very sensitive to air moisture, especially in pure form,
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SYNTHESIS OF FLUORINE-CONTAINING ARYL(HALO)BORANES
Table 2. 11B and 19F NMR spectroscopy data for aryl(halogeno)boranes
57
δF, ppm
Borane
Solvent
δB, ppm
BF
2,6-F
4-Fа
3,5-F
С6F5BF2
CH2Cl2
22.4
22.8
23.2
53.0
54.0
52.3
–74.0
–74.4
–73.0
–128.6
–129.0
–128.7
–128.8
–128.6
–129.9
–128.3
–90.7
–143.6
–143.8
–144.5
–145.3
–146.1
–146.6
–145.3
–161.1
–161.3
–161.7
–161.2
–161.2
–162.4
–160.7
–132.9
–161.4
–161.0
–161.9
–161.0
–161
C6F5BF2 [17]
C6F5BF2 [6]
CH2Cl2
Hexane
CH2Cl2
Hexane
C6D6
C6F5BCl2
C6F5BCl2
C6F5BCl2 [21]
C6F5BCl2 [2]
4-C5NF4BCl2
C6F5BBr2
CCl4
CH2Cl2
CH2Cl2
Hexane
C6D6
53.9
53.6
54.8
53.3
43.3
43.2
58.3
–128.8
–129.0
–130.3
–130.0
–133
–146.5
–147.2
–147.4
–144.7
–146
C6F5BBr2
C6F5BBr2 [21]
(C6F5)2BF
CH2Cl2
CDCl3
CH2Cl2
–
(C6F5)2BF [23]
(C6F5)2BCl
–26
–129.0
–129.5
–129.6
–144.2
–145.4
–144.0
–161.0
–161.3
–161.4
(C6F5)2BCl [2]
(C6F5)2BCl [22]
(C6F5)2BBr [24]
(C6F5)2BBr
Toluene-d8
CDCl3
Hexane
CH2Cl2
CH2Cl2
–
58.8
61.2
61.6
24.5
54.9
54.3
57.6
26.2
24.7
24.5
54.1
54.9
56.7
–128.9
–145.3
–113.5
–113.8b
–161.1
3-FC6H4BF2 [17]
3-FC6H4BCl2
3-FC6H4BCl2 [25]
3-FC6H4BBr2
4-FC6H4BF2
4-FC6H4BF2 [17]
4-FC6H4BF2 [6]
4-FC6H4BCl2
4-FC6H4BCl2 [25]
4-FC6H4BBr2
–91.1
Hexane
CH2Cl2
CH2Cl2
Hexane
CH2Cl2
–
–112.6c
–92
–105.7
–104.0
–104.1
–102.2d
–92.7
–93.6
Hexane
–101.2e
a 3
J 4 3,5 = 19–20 Hz.
F F
b d. d. d, 3JF3H2 = 9.0, 3J F H
3
4 = 9.0, 4J F H
2,6 = 6.6 Hz.
d d. d. d, 3JF3H2 = 8.4, 3J F H4 = 8.4, 4J F H
e t. t, 3JF3H3,5 = 7.9, 4J F H
2,6 = 6.4 Hz.
3
5 = 5.4 Hz.
c t. t, 3JF3H3,5 = 8.1, 4J F H
4
3
3
5 = 5.2 Hz.
4
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 90 No. 1 2020

58
BARDIN et al.
contains the 11B NMR signals of boranes 6, 16 (Table 2)
and pentafluorophenylbromofluoroborane 24 at δB =
39.4 ppm (d, JBF = 98 Hz). In the F NMR spectrum
the signals of pentafluorophenyl group appear at –128.0
method [15]. The obtained values of inductive and reso-
nance constants are σI = 0.10 and σR0 = 0.39 for BCl2
and σI = 0.11 and σR0 = 0.39 for BBr2. According to the
literature data, the dichloroboryl group is characterized
by parameters σI = 0.04 [16] and σR0 = 0.31 [16] and
0.34 [15]. For the BBr2 group, the values of inductive
and resonance constants were not determined. For com-
parison, the corresponding values for substituent BF2 are
σI = 0.15 [17], 0.16 [18], 0.23, 0.26 [15] and σR0 = 0.22,
0.28 [15], 0.30 [17]. Despite of variation in the parameter
values measured by different methods, there is an evident
trend of the decrease of inductive effect and simultaneous
enhancement of the resonance effect of substituents BX2
with replacement of X = F by X = Cl and Br.
1
19
(m,2F,F2,6),–144.8(t.t.t,1F,F4,3JF4F3,5 =19.8Hz,4JF4F2,6
=
7.0 Hz, JF4BF = 2.8 Hz) and –161.0 (m, 2F, F3,5) ppm,
but a weak and broad resonance of the BBrF group
cannot be seen. In both cases, the signals of the boron
atoms and of the pentafluorophenyl group appear be-
tween the corresponding signals of boranes C6F5BF2
and C6F5BX2 (X = Cl, Br) (Table 2). The structure of
4-fluorophenylbromofluoroborane 23 (Scheme 9) fol-
lows from the presence of a doublet (1JВF = 100 Hz) at
42.1 ppm (11B) and the 19F NMR signal at –37.0 ppm
6
1
(q 1 : 1 : 1 : 1, 1F, BFBr, JBF = 100 Hz) and
In the present study, the content and the yields of
ArBX2 were determined from 19F NMR spectra. If only
total concentration of aryldihaloboranes is required, the
method described by us earlier can be used [6]. Thus, the
aliquot of the ArBX2 solution was added to the solution
of methylpyridine in hexane of known concentration, the
precipitate of the complex was filtered off and the amount
of the residual base was determined by the method of GC
or by titration with acid.
3
4
–101.6 ppm (t. t. d, 1F, F4, JF4H = 8.6 Hz, J
=
3,5
4
2,6
F H
6
1
5.8 Hz, JF4BF = 3.2 Hz) ppm. The Н NMR spectrum,
apart from signals of boranes 21 and 22, contains the
signals of borane 23: doublet of doublets at 7.96 ppm
(3JH3,5 4 = 6.0 Hz, JH3,5 = 8.1 Hz) and multiplet at
3
2
H
F
11
7.01 ppm of equal intensity. In the B NMR spectrum
of 3-fluorophenylbromofluoroborane 19 a doublet (1JВF =
100 Hz) appears at 42.4 ppm, and in the 19F NMR
spectrum, the signal of the BFBr group at –34.1 ppm
(q 1 : 1 : 1 : 1, 1F, BFBr, 1JBF ~95 Hz), whereas fluorine
atom F3 resonates close to the corresponding signals of
Therefore, we have developed a convenient method
for preparation of solutions of fluorinated aryldihalo-
boranes and diarylhaloboranes, which can be used as
homogeneous catalysts of electrophilic reactions, as well
as precursors of arylboronic and arylborinic acids and
their derivatives.
boranes 20 and 18 (δF = –112.7 ppm, 1F, t. d, 3JF3H
=
2,4
9.3 Hz, 4JF3H5 = 5.8 Hz). In the 1Н NMR spectrum of the
reaction mixture the signal of atom H6 was identified at
3
7.72 ppm (d, JH6H = 7.2 Hz), but the signals of other
5
EXPERIMENTAL
hydrogen atoms in compound 19 are overlapped with
those of boranes 20 and 18.
NMR spectra were recorded on Bruker AVANCE
300 [300.13 (1H), 282.40 МHz (19F)] and DRX 500
[160.46 MHz (11B)] spectrometers. Chemical shifts ref-
erenced to Me4Si (1H), CCl3F (19F, secondary standard
C6F6, δF = –162.9 ppm) and BF3OEt2 (15% in CDCl3,
11B).
The picture can be completed by the spectral charac-
teristics of the known boranes C6H5BFX. The 11B NMR
signal of phenylfluorochloroborane is a doublet at 41 ppm
(1JВF = 80±10 Hz) [14] or 40.4 ppm (1JВF = 90 Hz) [13].
The corresponding 19F NMR signal is very broaden and
appears at –51 [13]) or –49.5 ppm [14]. The doublet signal
of phenylbromofluoroborane in the 11B NMR spectrum is
found at 42.6 ppm (1JВF = 98 Hz), but the 19F NMR signal
was too broaden to be detected neither in the spectrum
of neat borane nor in the solution in methylcyclohexane.
Later, this compound was characterized by the following
NMR parameters: δB = 34.2 ppm (d, 1JВF = 125 Hz) and
δF = –31.5 ppm (br. s) [14].
Dichloromethane, chloroform, 1,2-dichloroethane and
hexane were distilled over P2O5. Me3SiCl and SiCl4 were
distilled over CaH2. Commercial AlCl3, AlBr3 (Acros),
BCl3 and BBr3 were used. K[C6F5BF3] [19], K[2,3,5,6-
C5NF4BF3] [12], K[3-FC6H4BF3], K[4-FC6H4BF3] [17],
K[(C6F5)2BF2] [20] were synthesized by the known
methods.Aryldihaloboranes were identified by the NMR
spectra (Table 2). Quantitative analysis of the reaction
mixtures was performed by 19F NMR spectroscopy
(internal standard C6F6 or C6H5F). All operations were
performed in dry argon atmosphere.
The data for fluorophenyldihaloboranes FC6H4BX2
(X = Cl, Br) allowed to calculate electronic parameters
of BX2 groups from the 19F NMR spectra using the Taft
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SYNTHESIS OF FLUORINE-CONTAINING ARYL(HALO)BORANES
59
5
3
75.0, JF1F4 = 18.0 Hz), –128.8 d. m (1F, F3, JF3F4 =
14.0 Hz), –142.2 d. d. d (1F, F8, 4JF1F8 = 75.0, 3JF7F8 =
17.0, 5JF5F8 = 17.0 Hz), –146.2 d. d. d (1F, F5, 4JF4F5 =
Defluorination of potassium aryltrifluoroborates
with boron chloride (bromide). To the suspension of
K[ArBF3] in CH2Cl2 the 0.9–1.1 М. solution of BX3 in
CH2Cl2 was added and stirred at 22°C. The suspension
was centrifuged and the solution of aryldihaloboranes
separated by decantation (Table 1).
3
5
59.0, JF5F6 = 15.0, JF5F8 = 15.0 Hz), –149.9 d. d. d
(1F, F4, JF4F5 = 59.0, JF3F4 = 18.0, JF1F4 = 18.0 Hz),
4
3
5
–150.3 d. d (1F, F6, JF5F6 = 18.0, JF6F7 = 18.0 Hz),
3
3
–155.3 d. d (1F, F7, 3JF6F7 = 18.0, 3JF7F8 = 18.0 Hz).
3-Fluorophenyldichloroborane (2). 1H NMR spec-
trum (CH2Cl2), δH, ppm: 7.86 d (1H, H6, 3JH6H5 = 7.4 Hz),
2-Heptafluoronaphthylfluorochloroborane (14).
11B NMR spectrum (CH2Cl2): δВ 36.4 ppm. 19F NMR
spectrum (CH2Cl2), δF, ppm: –102.8 d. d (1F, F1, 4JF1F8 =
74.0, 5JF1F4 = 20.0 Hz), –129.1 m (1F, F3), –142.2 m (1F,
F8), –146.5 d. d. d (1F, F5, JF4F5 = 59.0, JF5F6 = 19.0,
5JF5F8 = 19.0 Hz), –150.0 d. d (1F, F6, 3JF5F6 = 20.0, 3JF6F7 =
20.0 Hz), –150.6 d. d (1F, F4, 4JF4F5 = 59.0, 3JF3F4 = 19.0,
5JF1F4 = 19.0 Hz), –156.1 d. d (1F, F7, 3JF6F7 = 20.0, 3JF7F8 =
20.0 Hz).
3
7.72 d (1H, H2, JH2F3 = 9.4 Hz), 7.41 d. d. d (1H, H5,
3JH5H4 = 7.7, 3JH5H6 = 7.4, 4JH5F3 = 5.6 Hz), 7.29 d. d. d
(1H, H4, 3JH4F3 = 9.0, 3JH5H4 = 7.7, 4JH4H2 = 2.1 Hz).
4
3
4-Fluorophenyldichloroborane (4). 1H NMR spec-
3
trum (CH2Cl2), δH, ppm: 8.10 d. d (2H, H2,6, JH3H2 =
7.0, 4JH3H2 = 7.0 Hz), 7.09 d. d (2H, H3,5, 3JH3H2 = 7.0,
3JH3F4 = 9.0 Hz).
Defluorination of K[(C6F5)2BF2] with boron
chloride. The solution of (C6F5)2BCl (0.85 mmol) and
(C6F5)2BF (0.06 mmol) in CH2Cl2 was obtained from
the suspension of K[(C6F5)2BF2] (433 mg, 1.0 mmol)
in CH2Cl2 (6 mL) and 1.1 М BCl3 in CH2Cl2 (1.2 mL,
1.3 mmol) by stirring for 1 h at 22°С.
2-Heptafluoronaphthylboronic acid (15). The ob-
tained solution of naphthylhalogenoboranes in CH2Cl2
was kept in air for 2–3 h. After evaporation of solvent
the residue was washed with cold diethyl ether (1 mL)
Yield 80 mg (64%), white solid. 11B NMR spectrum
(Et2O): δВ 27.1 ppm. 19F NMR spectrum (Et2O), δF,
ppm: –108.6 d. d (1F, F1, 4JF1F8 = 69.4, 5JF1F4 = 19.5 Hz),
Defluorination of K[(C6F5)2BF2] with alumi-
num chloride. а. To the suspension of AlCl3 (118 mg,
0.88 mmol) in CH2Cl2 (3 mL) K[(C6F5)2BF2] (375 mg,
0.90 mmol) was added and stirred for 4 h at 22°C. The
suspension was centrifuged to obtain the solution of
(C6F5)2BF (0.40 mmol) and (C6F5)2BCl (0.43 mmol)
(11B, 19F NMR).
–127.6 d. m (1F, F3, JF3F4 = 18.0 Hz), –144.7 d. d. d
3
(1F, F8, JF1F8 = 69.4, JF7F8 = 16.5, JF5F8 = 16.5 Hz),
–147.1 d. d. d. d (1F, F5, 4JF4F5 = 57.4, 3JF5F6 = 16.5, 5JF5F8 =
16.5, 4JF5F7 = 3.6 Hz), –151.5 d. d. d. d. d (1F, F4, 4JF4F5 =
4
3
5
3
5
5
6
57.4, JF3F4 = 19.2, JF1F4 = 19.5, JF4F6 = 4.0, JF4F8 =
4.0 Hz), –155.1 d. d (1F, F6, JF5F6 = 16.4, JF6F7 =
3
3
18.0 Hz),–158.0 d. d (1F, F7, JF6F7 = 18.0, JF7F8 =
16.5 Hz). Found, %: C 39.5; H 1.02; F 44.2. C10H2BF7O2.
Calculated, %: C 40.32; H 0.68; F 44.64.
3
3
b. The reaction was performed similarly using AlCl3
(157 mg, 1.18 mmol), hexane (4 mL) and K[(C6F5)2BF2]
(452 mg, 1.07 mmol). After 5 h the solution contained
(C6F5)2BF (0.02 mmol) and (C6F5)2BCl (0.39 mmol).
After 55 h: (C6F5)2BF (0.13 mmol), (C6F5)2BCl
(0.56 mmol) and compound 17 (0.07 mmol) were present
in the mixture (11B, 19F NMR).
Reaction of K[2,3,5,6-C5NF4BF3] with boron bro-
mide. а. 1.1 М. solution of BBr3 in CH2Cl2 (1.5 mL,
1.27 mmol) was added to the suspension of K[2,3,5,6-
C5NF4BF3] (297 mg, 1.15 mmol) in CH2Cl2 (6 mL) and
stirred for 20 h at 22°C. No organofluorine compounds
were detected in the mother liquor (19F NMR).
Defluorination of K[2-C10F7BF3] with boron
chloride. 0.95 М solution of BCl3 in CH2Cl2 (2 mL,
1.9 mmol) was added to the suspension of K[2-C10F7BF3]
(152 mg, 0.42 mmol) in CH2Cl2 (2.5 mL) and stirred
for 15 h at 22°C. After centrifugation the solution was
decanted and concentrated at a reduced pressure to
~2 mL to obtain the solution containing 2-C10F7BFCl
(0.08 mmol) and 2-C10F7BCl2 (0.21 mmol) (11B, 19F
NMR).
b. 1.1 М. solution of BBr3 in CH2Cl2 (2 mL,
2.2mmol)wasaddedtothestirredsuspensionofK[2,3,5,6-
C5NF4BF3] (262 mg, 1.0 mmol) in dichloromethane
(7 mL) and heated to distill off the solvent. The residue
was refluxed for 3 h. No organofluorine compounds were
detected in the mother liquor (19F NMR). The suspension
was treated with 2% HCl, the precipitate dried in air to
obtain K[2,3,5,6-C5NF4BF3] (234 mg).
2-Heptafluoronaphthyldichloroborane (12). 11B
NMR spectrum (CH2Cl2), δВ: 53.7 ppm. 19F NMR spec-
Defluorination of potassium aryltrifluoroborates
with aluminum chloride (bromide). Potassium aryltri-
4
trum (CH2Cl2), δF, ppm: –103.4 d. d (1F, F1, JF1F8 =
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 90 No. 1 2020

60
BARDIN et al.
for Collective Use of Siberian Branch of Russian Academy of
Sciences for spectral and analytical measurements.
fluoroborate was added to the suspension of aluminum
halide in the solvent and stirred at a given temperature
(Table 1). The obtained mixture was centrifuged and the
solution of aryldihaloboranes decanted.
CONFLICT OF INTEREST
No conflict of interest was declared by the authors.
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3
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FUNDING
This work was supported by the Ministry of Science and
High Education of Russian Federation within the State task
of N.N. Vorozhtsov Institute of Organic Chemistry, Siberian
Branch of Russian Academy of Sciences, and G.K. Boreskov
Institute of Catalysis, Siberian Branch of Russian Academy of
Sciences. The authors are grateful to Chemical Research Center
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SYNTHESIS OF FLUORINE-CONTAINING ARYL(HALO)BORANES
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