Hydrodeboration of potassium polyfluoroaryl(fluoro)borates with alcohols

Article abstract of DOI:10.1016/j.jfluchem.2014.09.016

Potassium polyfluoroaryltrifluoroborates, K[Ar_FBF₃] (Ar_F = C₆F₅, HC₆F₄, MeC₆F₄, 4-MeOC₆F₄, 4-indol-1-ylC₆F₄, 4-i

Full text of DOI:10.1016/j.jfluchem.2014.09.016

Journal of Fluorine Chemistry 168 (2014) 111–120
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Hydrodeboration of potassium polyfluoroaryl(fluoro)borates
with alcohols§
a
b,c
Nicolay Yu. Adonin a,b, , Anton Yu. Shabalin , Vadim V. Bardin
*
a G.K. Boreskov Institute of Catalysis, SB RAS, Acad. Lavrentjev Avenue 5, 630090 Novosibirsk, Russian Federation
b Novosibirsk State University, Pirogova Street, 2, 630090 Novosibirsk, Russian Federation
c N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, SB RAS, Acad. Lavrentjev Avenue 9, 630090 Novosibirsk, Russian Federation
A R T I C L E I N F O
A B S T R A C T
Article history:
Potassium polyfluoroaryltrifluoroborates, K[ArFBF3] (ArF = C6F5, HC6F4, MeC6F4, 4-MeOC6F4, 4-indol-1-
ylC6F4, 4-imidazol-1-ylC6F4, 4-pyrazol-1-ylC6F4, 2,4,6-C6F3H2 and 4-tetrafluoropyridyl), and K[(C6F5)2BF2]
undergo hydrodeboration to ArFH in aliphatic alcohols at elevated temperature. At the same conditions,
borates K[3,4,5-C6F3H2BF3], K[4-FC6H4BF3] and K[C6H5BF3] remain intact. The presence of base (Et3N,
K2CO3 and NaOMe) retards or prevents conversion of K[C6F5BF3]. Attempted hydrodeboration of
K[C6F5BF3] in MeCN failed.
Received 28 July 2014
Received in revised form 12 September 2014
Accepted 15 September 2014
Available online 28 September 2014
Keywords:
ß 2014 Elsevier B.V. All rights reserved.
Pentafluorophenyltrifluoroborate
Hydrodeboration
NMR spectroscopy
1. Introduction
and then to ArH. The rate of consumption of aryltrifluoroborates
diminished with increase of electron-withdrawing character of
The carbon–carbon bond formation based on transition metal-
catalyzed cross-coupling reactions of organoboron compounds
with appropriate carbon electrophiles is one of the most effective
and intensively studied modern preparative methods [1–6]. The
matter of importance is the nature of key reactive boron-
containing species and their role within catalytic cycle. In general,
two sorts of organoboron compounds are used as partners for
cross-coupling: borane derivatives, OrgBX2 and borate derivatives,
K[OrgBX3] [4,7]. Both of them have advantages and disadvantages
in preparation and efficiency in application, but the latter are
moisture-resistant and thermally stable substances and thus they
are more convenient for routine syntheses [4,8].
Several researches described detailed evaluation of the
hydrolysis of potassium aryltrifluoroborates in aqueous buffer
(pHꢀ7), aqueous THF or aqueous MeCN under conditions of cross-
coupling reactions (without the Pd catalyst) [9–14]. Despite of
distinction in substrates and reaction conditions, the common
conclusion was consisted in conversion of K[ArBF3] to ArB(OH)2
aryl groups.
In course of systematic research of the low-reactive poly-
fluorinated organoboron compounds as partners in the Pd-
catalyzed cross-coupling reactions, we explored reactivity of
K[C6F5BF3] and related borates towards alcohols (alcoholysis/
hydrodeboration under basic conditions) as a part of mechanistic
aspect of cross-coupling. It is important that in contrast to
organo(fluoro)borates, their polyfluorinated analogs are the less
investigated although significant progress in this field was
achieved in last two decades [15–27]. Salts K[C6F5BF3] and
K[CF2 = CFBF3] can be involved in cross-coupling but underwent
fast hydrodeboration under reaction conditions typical for
hydrocarbon organotrifluoroborates [28–31] (detail discussion
see [5,16]). Hydrodeboration of polyfluorinated organoboranes are
better described. Polyfluorophenylboronic acids, C6FnH5ꢁnB(OH)2
(n ꢂ 2), (except 3,4,5-C6F3H2B(OH)2) were converted to the
corresponding arenes in MeOH, aqueous MeOH, aqueous pyridine
and by action of KOH in aqueous MeOH [32]. Heating of (C6F5)2BOH
in CD2Cl2 in the presence of 1,8-bis(dimethylamino)naphthalene
[33] as well as in methanol [34] gave C6F5H. Tris(pentafluorophe-
nyl)borane is slowly decomposed with water under rather drastic
conditions (water–toluene, 100 8C) [35]. The formation of C6F5H
(90%) from C6F5B(OH)2 and diethylamine in DMF (25 8C, 24 h) was
well documented [36]. Arylboronic acids bearing the more
electron-rich aryl moiety are tolerant towards hydrodeboration
§
Dedicated to Prof. Hermann-Josef Frohn (Germany) on the occasion of his 70th
birthday.
*
Corresponding author at: G.K. Boreskov Institute of Catalysis, SB RAS, Acad.
Lavrentjev Avenue 5, 630090 Novosibirsk, Russian Federation.
Tel.: +7 383 326 9674; fax: +7 383 330 8056.
E-mail address: adonin@catalysis.ru (N.Yu. Adonin).
http://dx.doi.org/10.1016/j.jfluchem.2014.09.016
0022-1139/ß 2014 Elsevier B.V. All rights reserved.

112
N.Y. Adonin et al. / Journal of Fluorine Chemistry 168 (2014) 111–120
under basic conditions [37]. It should be noted that the rate of
hydrodeboration of potassium organotrifluoroborates under acidic
conditions increases in opposite mode [16,38]. Hydrodeboration of
K[C6F5BF3] in refluxed water (1 h) was assumed to produce KHF2
and H3BO3 although the formation of pentafluorobenzene was not
proved [39]. Reaction of K[C6F5BF3] with MeOH at 70–90 8C [40] or
with secondary amines in DMF, diglyme or DMSO at higher
temperature (150 8C) [41] leads to total or partial hydrodeboration
to C6F5H. Hydrodeboration of Li[C6F5B(OMe)3] to C6F5H in MeOH,
HOCH2CH2OH, acetone and MeCN should be mentioned too
[42,43].
F
F
F
F
F
F
AlkOH
90-95 °C
- K[BFn(OAlk)4-n
K
F
BF3
F
H
]
F
F
1
2
Scheme 2. Hydrodeboration of K[C6F5BF3] (1) in different alcohols.
Table 2
The picture presented above demonstrates the peculiar
reactivity of perfluoroorganoboranes and borates towards their
hydrocarbon analogues and requires clear experimental data for
unambiguous interpretation of the observed phenomena.
Results on hydrodeboration of K[C6F5BF3] (1) in different alcohols after 4 h at 90–
95 8C (Scheme 2).
Run
Alk
Conversion of 1, %
1
2
3
4
5
6
7
CH3OH
100
93
29
6–7
29
4
HOCH2CH2
CH3OCH2CH2
CH3CH2CH2
(CH3)2CH
(CH3)3C
2. Results
2.1. Effect of solvent
(CF3)2CH
<1
Potassium pentafluorophenyltrifluoroborate (1) does not react
with methanol at 20–25 8C over a period of 30 h [40] but undergoes
hydrodeboration to pentafluorobenzene (2) at elevated tempera-
ture (Scheme 1). At 50–55 8C the reaction is slow: conversion of 1 is
17% and 62% after 4 h and 11 h, respectively. At 90–95 8C 1
disappears within less than 4 h. Formation of K[BF4], K[BF3OMe]
and in some cases K[BF2(OMe)2] was detected by 19FNMR
spectroscopy (Table 1). It is important to note that reaction in a
glass ampoule and in a FEP (block copolymer of tetrafluoroethylene
and hexafluoropropylene) made trap gives the equal result,
e.g. glass wall does not affect on the mode and rate of the
process (cf. [9]).
Hydrodeboration of 1 under the action of other alcohols
proceeds similarly although there are distinctions in the rate
(Scheme 2). Thus, heating 1 in ethylene glycol at 90–95 8C results
in consumption of 1 within 4 h. Conversion of 1 to C6F5H in
2-methoxyethanol is 7% and 29% after 1 h and 4 h, respectively.
The use of propanol, iso-propanol or tert-butanol leads to the
further decreasing of the hydrodeboration rate: conversion of 1 in
these alcohols does not exceed 7%. In (CF3)2CHOH borate 1 remains
intact after stirring at 90–95 8C over a period of 4 h (Table 2).
2.2. Effect of additives
We explored the effect of some additives on the relative
hydrodeboration rate of 1 in methanol (Scheme 3). In aqueous
methanol conversion of 1 at 90–95 8C is less than in the anhydrous
solvent although difference is small (Table 3).
An additive of base stronger than MeOH tends to slow down the
hydrodeboration rate of K[C6F5BF3]. Borate 1 remains intact
towards triethylamine in methanol at 50–55 8C within 11 h. At
higher temperature pentafluorobenzene is formed although
conversion is lower than in the absence of the base (27% vs.
100%, Table 1). Stirring of 1 with K2CO3 in MeOH or in neat MeCN at
90–95 8C does not affect this borate (Scheme 4).
An additive of lithium chloride accelerates the consumption of 1
(Scheme 5). This is demonstrated by reactions at temperatures
lower than 90–95 8C at which the above mentioned reactions do
not proceed. Conversion of 1 in the presence of hydrate LiClꢃH2O at
50–55 8C (Table 4, run 2) is closely related to that in neat MeOH
(Table 1, run 1), but besides of pentafluorobenzene (the hydro-
deboration product), significant amounts of pentafluorophenyldi-
fluoro(methoxy)borate (3) form in this case. Prolongation of
heating up to 6 h causes disappearance of 3 and production of 2 at
86% conversion of 1 (Table 4, run 4; cf. Table 1, run 2). Anhydrous
F
F
F
F
F
F
F
F
MeOH
- K[BFn(OMe)4-n
K
F
BF3
F
H
]
F
F
F
F
F
F
F
F
MeOH - H2O
(9:1 v/v)
90-95 °C
- K[BFn(OAlk)4-n
1
2
K
F
BF3
F
H
Scheme 1. Hydrodeboration of K[C6F5BF3] (1) in MeOH.
]
1
2
Table 1
Results on hydrodeboration of K[C6F5BF3] (1) in MeOH (Scheme 1).
Scheme 3. Hydrodeboration of K[C6F5BF3] (1) in aqueous MeOH.
Run
Temperature, 8C
Time, h
Conversion of 1, %
Notes
1
2
3a
4a
5
50–55
50–55
50–55
50–55
70
4
11
4
17
62
This work
This work
This work
This work
See [40]
Table 3
Results on hydrodeboration of K[C6F5BF3] (1) in aqueous MeOH at 90–95 8C
(Scheme 3).
21
6
29
4
80
Run
Time, h
Conversion of 1, %
6
90–95
90–95
1
81
See [40]
1
2
1
4
72
7
4
100
See [40]
100
a
The reaction is performed in a FEP made trap.

N.Y. Adonin et al. / Journal of Fluorine Chemistry 168 (2014) 111–120
113
F
F
Table 5
Results on hydrodeboration of K[2,3,5,6-C6F4HBF3] (4) in MeOH at 90–95 8C
(Scheme 6).
5 Et3N, MeOH
50-55 °C, conversion 0 % (11 h)
90-95 °C, conversion 27 % (4 h)
F
H
F
F
F
F
Run
Time, h
Conversion of 4, %
F
F
1
2
1
4
40
K
F
BF3
2
100
K2CO3 in MeOH, 90-95 °C, 2 h
or MeCN, 90-95 °C, 6 h
1
No reaction
F
F
F
F
F
F
F
F
F
Scheme 4. Hydrodeboration of K[C6F5BF3] (1) in the presence of base.
MeOH
90-95 °C
- K[BFn(OMe)4-n
+
K
F
BF3
K
F
BF2OMe
F
H
]
H
H
H
6
7
8
Scheme 7. Reaction of K[2,3,4,5-C6F4HBF3] (6) in MeOH.
Scheme 5. Reactions of K[C6F5BF3] (1) with MeOH in the presence of LiClꢃnH2O.
Table 6
Results of reaction of K[2,3,4,5-C6F4HBF3] (7) with MeOH at 90–95 8C (Scheme 7).
Run
Time, h
Conversion of 6, %
Molar ratio
Table 4
7
8
Results of reactions of K[C6F5BF3] (1) with MeOH in the presence of LiClꢃnH2O at 50–
55 8C (Scheme 5).
1
2
3
1
11
30
<1
32a
100
1
0
1
1
0.6
0
Run
n
Time, h
Conversion of 1, %a
Molar ratio
a
3
2
Conversion on both routes.
1
2
3
4
0
1
0
1
3
3
6
6
60
14
0.16
0.75
0
1
1
1
1
reaction with MeOH at 100 8C complete hydrodeboration of all
borates to 1-(20,30,50,60-tetrafluorophenyl)imidazole (11), C6F5H
and 1,2-bis(1-imidazolino)-3,5,6-trifluorobenzene (12) was ob-
served after 6 h (Scheme 8).
100
86
0
a
Conversion on both routes.
These examples demonstrate the common transformation
route of potassium polyfluoroaryltrifluoroborates but do not
display the quantitative distinctions in their reactivity relative
to K[C6F5BF3]. To obtain this information we performed hydro-
deboration of binary mixtures of K[C6F5BF3] and salts from a series
of different borates in MeOH at 90–95 8C and compared conversion
of each borate to C6F5H and ArH, respectively, using 19FNMR
spectroscopy with quantitative internal standard (Scheme 9).
Potassium 4-methoxytetrafluorophenyltrifluoroborate (13) is
the more reactive than K[C6F5BF3] and forms 2,3,5,6-tetrafluor-
oanisole (14) in a quantitative yield within 2 h whereas 1 is
still present under these conditions. K[C6F5BF3] and potassium
LiCl proved to be the much more effective reagent than LiClꢃH2O. In
this case at 50–55 8C conversion of 1 to 2 and 3 is 60% for 3 h and
the latter borate is formed in low yield (Table 4, run 1). After 6 h
both borates 1 and 3 disappear and pentafluorobenzene was
obtained in quantitative yield (Table 4, run 3).
2.3. Effect of aryl group in K[ArBF3]
Preliminary experiments displayed the remarkable effect of
substituent X in K[XC6F4BF3] on the reactivity of these borates
relating to parent K[C6F5BF3]. Heating of potassium 2,3,5,6-
tetrafluorophenyltrifluoroborate (4) in MeOH for 1 h leads to the
less conversion of 4 to 1,2,4,5-tetrafluorobenzene (5) than in the
case of the related reaction of 1 (Scheme 6). Nevertheless, after 4 h
complete conversion of 4 to 5 was observed (Table 5).
Potassium 2,3,4,5-tetrafluorophenyltrifluoroborate (6) is more
tolerant towards MeOH than 4 (Scheme 7). The reaction is very
slow and leads to 2,3,4,5-tetrafluorophenyldifluoro(methoxy)bo-
rate (7) and 1,2,3,4-tetrafluorobenzene (8) (Table 6).
F
F
F
F
F
F
MeOH
100 °C, 6 h
- K[BFn(OMe)4-n
K
F
Im
Im
BF3
BF3
BF3
F
H
]
]
]
F
F
F
F
1
2
When a mixture of potassium 4-imidazol-1-yltetrafluorophe-
nyltrifluoroborate (9), K[C6F5BF3] and potassium 3,4-bis(imidazol-
1-yl)trifluorophenyltrifluoroborate (10) was involved in the
F
F
MeOH
100 °C, 6 h
- K[BFn(OMe)4-n
Im =
Im
Im
H
N
K
N
F
F
F
F
F
F
9
11
12
F
F
F
F
F
F
F
F
Im
Im
MeOH
90-95 °C
- K[BFn(OMe)4-n
MeOH
100 °C, 6 h
- K[BFn(OMe)4-n
K
H
BF3
H
H
K
H
]
F
F
F
F
10
4
5
Scheme 8. Hydrodeboration of a mixture of K[4-XC6F4BF3] (X = F, imidazol-1-yl)
and K[3,4-Im2C6F3BF3] in MeOH.
Scheme 6. Hydrodeboration of K[2,3,5,6-C6F4HBF3] (4) in MeOH.

114
N.Y. Adonin et al. / Journal of Fluorine Chemistry 168 (2014) 111–120
F
F
F
F
F
F
F
F
MeOH
90-95 °C, 2 h
- K[BFn(OMe)4-n
Prz =
Ind =
K
F
X
BF3
BF3
F
X
H
H
N
N
MeOH
90-95 °C, 40 min
- K[BFn(OMe)4-n
N
K
K
F
X
BF3
BF3
F
X
F
H
H
H
]
]
F
F
F
F
F
F
F
F
]
1
F
F
F
F
F
F
F
F
1
MeOH
90-95 °C, 2 h
- K[BFn(OMe)4-n
K
F
F
F
F
MeOH
90-95 °C, 40 min
- K[BFn(OMe)4-n
OMe (
X = Prz (17), Ind (18)
X =
13), Me (15), H (4),
X = OMe (14), Me (16), H (5),
X = Prz (19), Ind (20)
]
F
X
F
F
F
F
Scheme 9. Hydrodeboration of a mixture of 1 and K[4-XC6F4BF3] (X = OMe, Me, H,
pyrazol-1-yl and indol-1-yl) in MeOH.
X = H (4), Me (15)
X
F
4-methyltetrafluorophenyltrifluoroborate (15) shows the equal
reactivity towards MeOH producing pentafluorobenzene and
2,3,5,6-tetrafluorotoluene (16). Potassium 2,3,5,6-tetrafluorophe-
nyltrifluoroborate (4), potassium 4-pyrazol-1-yltetrafluorophe-
nyltrifluoroborate (17) and potassium 4-indol-1-yltetrafluor-
ophenyltrifluoroborate (18) are the less reactive than 1. Difference
in the reactivity of 1 and 4 is not significant, but both borates 17
and 18 undergo hydrodeboration much more slowly relative to 1
and give 1-(2,3,5,6-tetrafluorophenyl)pyrazole (19) and 1-(2,3,5,
6-tetrafluorophenyl)indole (20), respectively (Table 7).
MeOH
90-95 °C, 40 min
- K[BFn(OMe)4-n
K
F
BF3
]
F
F
F
F
X = Me (21), H (22)
Scheme 10. Hydrodeboration of a mixture of 1 and salts K[XC6F4BF3] (X = H and Me)
in MeOH.
Table 8
To estimate the reactivity of K[5-XC6F4BF3] relative to reactivity
of K[4-XC6F4BF3] and K[C6F5BF3], a mixture of these borates was
heated in MeOH at 90–95 8C for 40 min (Scheme 10). When X = Me,
conversion of borates diminishes in the following order: from 1 to
15 and to K[5-MeC6F4BF3] (21). The closed similarity was found for
the structurally related borates K[4-HC6F4BF3] and K[5-HC6F4BF3]
(22) (Table 8).
Results on hydrodeboration of K[XC6F4BF3] (X = F, H and Me) in MeOH after 40 min
at 90–95 8C (Scheme 10).
Run
X
Conversion, %
1
K[4-XC6F4BF3]
K[5-XC6F4BF3]
1
2
H
83
93
43
67
36
42
Me
Borates with the less fluorinated phenyl groups, K[C6FnH5ꢁnBF3]
(n ꢄ 3), react with methanol more slowly than K[C6F5BF3], and the
rate of their consumption depends on the number and mutual
disposition of fluorine atoms. Thus, heating of potassium 2,4,6-
trifluorophenyltrifluoroborate (23) at 90–95 8C for 2 h results in
mainly 2,4,6-trifluorophenyl(fluoro)(methoxy)borates 24 and 25
besides traces of 1,3,5-trifluorobenzene (26) (Scheme 11). Com-
plete conversion of 23 to 26 was achieved over a period of 6 h
(Table 9).
Potassium 3,4,5-trifluorophenyltrifluoroborate (27) does not
react with MeOH over 12 h (Scheme 12).
Potassium 4-fluorophenyltrifluoroborate (28) and potassium
phenyltrifluoroborate (29) do not react with MeOH at 90–95 8C
over a period of 10–12 h, although the former gives traces of the
corresponding aryldifluoro(methoxy)borate (30) (Scheme 13).
routes the initial step is dissociation of [ArBF3]ꢁ to aryldifluor-
oborane and fluoride anion assisted by AlkOH (Scheme 14, Eq. (1)).
Then ArBF2 and AlkOH form adduct A (Scheme 14, Eq. (2)). The
subsequent intramolecular substitution of boron atom by hydrogen
(hydrodeboration) gives ArH (Scheme 14, Eq. (3)). Alternatively,
elimination of H+ from adduct A leads to aryldifluoro(alkoxy)borate
(alcoholysis) (Scheme 14, Eq. (4)). The products of alcoholysis can
be also involved in the above reactions forming ArH and BF(OAlk)2
(these routes are not presented on Scheme 14 because closed
similarity with conversions of [ArBF3]ꢁ). Attachment of a fluoride
anion to BFn(OAlk)3ꢁn gives [BFn+1(OAlk)3ꢁn]
ꢁ (Scheme 14, Eq. (5)).
In the presence of species able to bind the fluoride anion
equilibrium (Scheme 14, Eq. (1)) is shifted to right and thereby
subsequent reactions facilitates. This is illustrated by the
significant acceleration of the K[C6F5BF3] consumption in the
presence of anhydrous LiCl (Tables 1 and 4). Here LiCl acts as a
scavenger of the fluoride anion because the large crystal lattice
energy of formed LiF (1027 kJ molꢁ1) [44] and its low solubility.
Hydrate LiClꢃH2O is the less effective and initially produces much
more M[C6F5BF2OMe] than anhydrous LiCl (Table 4, runs 1, 2).
The role of water (3–4 equivalents) in this phenomenon is not
3. Discussion
The obtained results allow us to distinguish two routes of
consumption of K[ArBF3] in alcohols: (a) hydrodeboration to ArH
and (b) alcoholysis to K[ArBFn(OAlk)3ꢁn]ꢁ. We assume that in both
Table 7
Results on hydrodeboration of K[4-XC6F4BF3] (X = F, OMe, Me, H, pyrazol-1-yl and
indol-1-yl) in MeOH after 2 h at 90–95 8C (Scheme 9).
clear. If aryl(fluoro)borate is
a very weak fluoride donor,
concentration of the corresponding aryl(fluoro)borane (very
strong Lewis acid) is too low for the subsequent conversions
with the remarkable rate. Thus, heating of a mixture of 1 with
potassium bis(pentafluorophenyl)difluoroborate (31) at 90–
95 8C for 6 h leads to quantitative hydrodeboration of K[C6F5BF3]
(1) while K[(C6F5)2BF2] (31) remains intact (Scheme 15).
Formation of 2 from 31 in MeOH occurs slowly at 120 8C and
after 6 h conversion does not exceed 17% (Scheme 16).
Run
X
K[4-XC6F4BF3]
4-XC6F4H
Conversion, %
1
K[4-XC6F4BF3]
1
2
3
4
5
OMe
Me
H
13
15
4
14
16
5
80
87
82
41
89
100
87
73
19
61
Prz
Ind
17
18
19
20

N.Y. Adonin et al. / Journal of Fluorine Chemistry 168 (2014) 111–120
115
H
H
F
H
F
H
H
F
F
MeOH
90-95 °C
- K[BFn(OMe)4-n
+
K
F
BF3
K
F
BFn(OMe)3-n
F
H
]
F
H
F
24 (n = 2), 25 (n = 1)
Scheme 11. Reaction of K[2,4,6-C6F3H2BF3] (23) with MeOH.
23
26
Table 9
Results of reaction of K[2,4,6-C6F3H2BF3] (23) with MeOH at 90–95 8C (Scheme 11).
Analogously, hydrodeboration of potassium 2,3,5,6-tetrafluor-
opyridyltrifluoroborate (32) proceeds at 90–95 8C much more
slowly than hydrodeboration of 1 (cf. Table 1 and Scheme 17).
Here elimination of fluoride anion from both [(C6F5)2BF2]ꢁand
[2,3,5,6-C5NF4BF3]ꢁaryl(fluoro)borates is the rate-determining
step. These borates are much weaker fluoride donors than
[C6F5BF3]ꢁ [45]), and the negligible concentration of the corre-
sponding perfluoroaryl(fluoro)borane is the key factor hindering
the subsequent transformations (Scheme 14).
Run
Time, h
Conversion of 23, %a
Molar ratio, %
24 and 25
26
1
2
2
6
21
4 (n = 1–3)
ꢀ0
1
1
100
a
Conversion on both routes.
Tolerance of 31 and 32 towards MeOH is in agreement with
the published data on hydrolysis of aryltrifluoroborates to
arylboronic acids. Perrin et al. presented kinetics of hydrolysis
of K[ArBF3] in aqueous phosphate buffer (pH 6.9–7.0) (22 8C):
Ar (half-life) = C6H5 (2 min) < 3,4-C6F2H3 (9 min) < 4-CF3C6H4
(29 min) = 4-CNC6H4
(29 min) < 4-O2NC6H4
(42 min) < 2,4-
C6F2H3 (43 min) < 2-FC6H4 (50 min) < 2,4,6-C6F3H2 (280 min)
[10] < 4-C5NH4 (346 min) < 2-FC5NH3 (364 min) < 2,6-C5NCl2H2
(866 min) < 2,6-C5NF2H2 (1155 min) [11]. The strong tolerance
against hydrolysis is attributed to zwitterionic aryltrifluorobo-
rates, 2-XC6H4BF3 (X is positively charged substituent (Me3N,
MePh2P, and Me2S) (phosphate buffer in 80% aqueous acetonitrile,
pH 7.5) (20 8C) [12] and (1-methylpyridinium-4-yl)trifluoroborate
(pH 6.9–7.0) (22 8C) [11]. Hydrolysis products [ArBF3ꢁn(OH)n]ꢁ
(n = 1, 2) are better fluoride anion donors than [ArBF3]ꢁ and they
Scheme 12. Attempted reaction of K[3,4,5-C6F3H2BF3] (27) with MeOH.
MeOH
K
X
BF3
K
X
BF2OMe
90-95 °C, 10-12 h
X = F (28)
X = H (29)
Traces
No reaction
Scheme 13. Attempted reaction of K[4-C6H4FBF3] (29) and K[C6H5BF3] (28) with
MeOH.
Scheme 15. Hydrodeboration of K[(C6F5)nBF4-n] (n = 1 and 2) in MeOH.
Scheme 16. Hydrodeboration of K[(C6F5)2BF2] in MeOH.
Scheme 14. Mechanism of the K[C6F5BF3] hydrodeboration.
Scheme 17. Hydrodeboration of K[2,3,5,6-C5NF4BF3] (32) in MeOH.

116
N.Y. Adonin et al. / Journal of Fluorine Chemistry 168 (2014) 111–120
were not detected by the 19FNMR spectroscopy. Thus, the loss of
the first fluoride anion was outlined as a single rate-determining
step. Under basic conditions (D2O, ꢂ3 equivalents of K2CO3, Cs2CO3
or ꢂ6 equivalents of KOH), borate M[4-FC6H4BF3] undergoes
hydrolysis and such intermediates M[4-FC6H4BFn(OH)3ꢁn] (n = 0–
2) were detected [13]. Closely related conversion of K[ArBF3]
(Ar = C6H5, 2-XC6H4 (X = Cl, OH, OMe, OTs and CHO), 4-XC6H4
(X = F, Me and OMe) to the arylboronic acid occurs under the action
of MOH, MHCO3 and M2CO3 (M = Li, Na and K) in aqueous
acetonitrile at room temperature while no hydrodeboration was
observed [46]. More detailed evaluation of the hydrolysis with
Cs2CO3 (three equivalents) in aqueous THF (THF:H2O = 10:1)
(55 8C) revealed the following order of the half-life of K[ArBF3]:
Ar (half-life) = 4-MeOC6H4 (19 min) < 4-MeC6H4 (51 min) < C6H5
Ar (half-life) = 2,6-C6F2H3 (28 min) > 2,4,6-C6F3H2 (10 min) > 3-
Bu-2,6-C6F2H2 (6 min) > 2,3,6-C6F3H2 (2 min) [14]. The fast
hydrodeboration of both C6F5B(OH)2 and Li[C6F5B(OMe)3] in
methanol [32,42] as well as both 2,3,5,6-C5NF4B(OH)2, and
Li[2,3,5,6-C5NF4B(OMe)3] in cold (ꢁ40 8C) aqueous MeOH acidified
with HCl [47] proceeds by the similar pathways. In contrast, 3,
5-C6F2H3B(OH)2 (no fluorine atoms at ortho-position) reacts with
hot iso-propanol to give 3,5-C6F2H3B(OCHMe2)2 that is converted
to Na[3,5-C6F2H3B(OCHMe2)3] in 79% yield by reflux with
NaOCHMe2 in iso-propanol without hydrodeboration [48]. More-
over, many arylboronic acids bearing electron-rich aryl group are
resistant towards hydrodeboration in saturated aqueous NaOH or
KOH in a water–toluene mixture producing aryltrihydroxyborates
in preparative yields, and these borates are stable in aqueous
alkali [49].
(100 min) < 4-FC6H4 (200 min) < 4-CF3C6H4 (2
d
18 h) < 3-
O2NC6H4 (5 d) < 3,5-(CF3)2C6H3 (54 d) [9]. Thus, electron-
withdrawing aryl groups slow down hydrolysis of K[ArBF3]
relative to K[C6H5BF3] while electron-donating groups accelerate
hydrolysis. If transformation of fluoro-containing borates
K[C6FnH4ꢁnBF3] to C6FnH5ꢁn in alcohols followed this way,
K[C6H5BF3] would be the most reactive compound while lowest
reactivity would be attributed to K[C6F5BF3]. However, the real
picture is another: borates 29, 28 and 27 do not react with MeOH at
90–95 8C, and the relative rate of consumption of other borates are
graded in order: Ar = C6H5–4-FC6H4–3,4,5-C6F3H2 << 2,4,6-
C6F3H2 < XC6F4.
This paradox arises from two factors which determine the
observed rate of consumption of K[ArBF3] in AlkOH. They act
opposite to each other, and final result depends on balance of them.
The first one is the reversible conversion of [ArBF3]ꢁ to ArBF2ꢃOHAlk
(adduct A) (Scheme 14, Eqs. (1) and (2)) and to [ArBF2(OAlk)]ꢁ
(Scheme 14, Eq. (4)). Some of species like ArBF2ꢃOHAlk or
[ArBF2(OAlk)]ꢁ were detected by 19FNMR spectroscopy
(Ar = 2,3,4,6-C6F4H; 2,3,4,5-C6F4H, 2,4,6-C6F3H2, 4-FC6H4; OAlk = -
OMe). The following cascade of dissociative exchanges of F for OR
would yield the aryl(dialkoxy)borane or aryl(trialkoxy)borate, and
rate of the reaction would rise from Ar = C6F5 to Ar = C6H5 as
suggested above.
The second factor deals with rearrangement of adduct A to
species B (or structurally related transition state) which loss
BF2OMe giving ArH (Scheme 14, Eq. (3)). The driving forces of the
reversible conversion of electrically neutral adduct A to zwitter-
ion B is necessity of sufficiently large negative charge at carbon
atom C–1. If it is too small, contribution of B in equilibrium is too
low and the irreversible formation of ArH from B occurs very slowly.
Unfortunately, the charge distribution in adducts ArBF2ꢃOHAlk has
not been reported so far. We assume that the presence of 1–2
fluorine atom(s) at the ortho position to boron atom in A increases
the negative charge at carbon atom C–1. This consideration is
based on experimental facts. Indeed, substituent X in borates like
K[4-X-2,3,5,6-C6F4BF3] is located far from reaction site C–1 and the
effect of different X on the rate of hydrodeboration is weak relative
to the effect of fluorine in K[C6F5BF3] (Table 7). The consumption
rate of borates K[5-X-2,3,5,6-C6F4BF3] (X = H or Me) diminishes
relative to that for 1 (Table 8), whereas K[2,3,4,5-C6F4HBF3] (one
fluorine atom at ortho-position) is the least reactive (Table 6).
K[2,4,6-C6F3H2BF3] (two electron-acceptors at ortho-position)
reacts with MeOH much faster than isomer K[3,4,5-C6F3H2BF3]
(no electron-acceptors at ortho-position) (Schemes 11 and 12). It
should be mentioned the kinetic investigation of hydrodeboration
of fluoro-containing phenylboronic acids, ArB(OH)2, in 9% D2O–
pyridine [32] that revealed the same order of reactivity of
The important role plays the nature of solvent or reaction media
as whole. Basicity of alcohols (pKBH+) increases with elongation
and branching of hydrocarbon chain from methanol to tert-
butanol, CH3OH (ꢁ4.86) < (CH3)2CHOH (ꢁ4.72) < (CH3)3COH
(ꢁ3.80) (water, 25 8E) [50], and the rate of hydrodeboration of
K[C6F5BF3] diminishes in parallel way giving decrease of conver-
sion from 81% to 4% (Table 2). Steric requirements around the
three-coordinated boron atom (Scheme 14, eq. 2) are not so strong
to discriminate CH3OH vs. RCH2CH2OH (R = H, CH3 and CH3O) on
their coordination ability, although the steric factor can be decisive
for coordination of ArBF2 with (CH3)2CHOH, (CH3)3COH and
(CF3)2CHOH. An additive of base stronger than MeOH retards
+
reaction. In the presence of Et3N (pKBH 10.6 [50]) the rate of
hydrodeboration diminishes in three times, while in the presence
of NaOMe (24 8C, 28 h and 68 8C, 4 h) [40], K2CO3 or in neat MeCN
(pKBH+ 0.80 [50]) consumption of 1 was not observed. Presumably,
these bases form the hydrogen bond with AlkOH + Base = Alk-
O. . .H. . .Base, and a competition with Fꢁ inhibits dissociation of
K[C6F5BF3] to C6F5BF2 and Fꢁ (Scheme 14, Eq. (1)). This elucidates
moderate conversion of 1 and 17 during hydrodeboration (Table 7,
run 4) as a consequence of increased basicity of reaction media by
borate 17 as well as arylated heterocycle 19 [51]. On the other side,
reaction of K[4-FC6H4BF3] with Et3N in CD3OH (rt, 1 h) results in
only [Et3NH][4-FC6H4BF2OCD3] [52], e.g. the fluoride anion donor
stronger than K[C6FnH4ꢁnBF3] (n ꢂ 3) does not require the
hydrogen bond assistance (Scheme 14, run 1) and the correspond-
ing adduct A undergoes deprotonation rather than rearrangement
to B. The formation of strong adduct C6F5BF2ꢃBase (Base = NEt3,
NCCH3) as a reason of tolerance of 1 was rejected on the basis of
the 19FNMR data [16,53].
4. Conclusion
Despite on apparent similarity with reported hydrolysis/
hydrodeboration of K[ArBF3] (Ar is aryl or hetaryl group) in H2O,
aqueous THF or aqueous MeCN [9–14], reaction of fluorinated
potassium aryl(fluoro)borates with alcohols proceeds in more
complex way. The highest rate of hydrodeboration of K[C6F5BF3]
was observed for reactions carried out in MeOH. The reaction rate
slightly reduces in aqueous 90% MeOH and in HOCH2CH2OH
whereas hydrodeboration in MeOCH2CH2OH, CH3CH2CH2OH,
(Me)2CHOH, (Me)3COH and (CF3)2CHOH proceeds slowly. The
presence of LiCl (fluoride anion scavenger) accelerates the
reaction while in the more basic media (MeCN) or with additives
like Et3N, K2CO3, and NaOMe hydrodeboration retards or does not
occur. Reactivity of borates K[C6FnH5ꢁnBF3] increases with number
of fluorine atoms n. In a series of isomers, the borate with
maximum number of fluorine atoms at positions 2,3,5,6 is the most
reactive. However, K[2,3,5,6-C5NF4BF3] and K[(C6F5)2BF2] are
more resistant than K[C6F5BF3] due to the high fluoride affinity
of the corresponding perfluoroaryl(fluoro)boranes.
substrates
{Ar = 3,4,5-C6F3H2 << 2,4,6-C6F3H2 < 2,3,4,5-C6F4H
< 2,3,5,6-C6F4H < C6F5} as one obtained in this paper. The similar
hydrodeboration of arylboronic acids, ArB(OH)2, with K3PO4 in
aqueous THF occurs with the rates ranked in the following order:

N.Y. Adonin et al. / Journal of Fluorine Chemistry 168 (2014) 111–120
117
5. Experimental
of the resulted solution showed the resonances of C6F5H
(0.11 mmol) beside the signals of K[BF3OMe], K[BF2(OMe)2] and
traces of K[C6F5BF3].
5.1. General
The NMR spectra were recorded using a Bruker AVANCE
300 spectrometer (1H at 300.13 MHz, 19F at 282.40 MHz, and 11B at
96.29 MHz). The chemical shifts are referenced to TMS (1H), CCl3F
5.5. With ethylene glycol
Solution of K[C6F5BF3] (89 mg, 0.32 mmol) in ethylene glycol
(1.3 mL) was kept for 4 h in a sealed tube to give C6F5H (0.30 mmol)
(
19FNMR).
(
19F, with C6F6 as secondary reference (ꢁ162.9 ppm)), and
BF3ꢃOEt2/CDCl3 (15% v/v) (11B), respectively. The high resolution
mass spectra were recorded using a Thermo Scientific DFS
spectrometer in EI mode (70 eV). These analyses as well as
elemental analysis were performed in the Collective Service
Center of SB RAS (Novosibirsk).
5.5.1. With 2-methoxyethanol for 1 h
Solution of K[C6F5BF3] (40 mg, 0.15 mmol) in 2-methoxyetha-
nol (0.9 mL) was kept for 1 h in a sealed tube. Conversion of 1 to
C6F5H (0.010 mmol) was 7%.
Methanol, ethylene glycol, propanol, iso-propanol, tert-butanol,
and triethylamine were refluxed with CaO and distilled. 2-
Methoxyethanol (Acros) and (CF3)2CHOH (ABCR) were used as
supplied. LiCl was prepared by calcination of LiClꢃH2O at 200–250 8C
over 4 h K[C6F5BF3] [54], K[2,3,5,6-C5NF4BF3] [47], K[2,3,4,
5-C6F4HBF3] [30], K[2,3,4,6-C6F4HBF3] [30], K[2,3,5,6-C6F4HBF3]
[55], K[2,4,6-C6F3H2BF3] [55], K[3,4,5-C6F3H2BF3] [55], K[4-
C6FH4BF3] [55], K[C6H5BF3] [38], K[4-PrzC6F4BF3] [41], K[4-
ImC6F4BF3] [41], K[4-IndC6F4BF3] [41], K[4-CH3OC6F4BF3] [40],
K[(C6F5)2BF2] [56] and a mixture of n-HC6F4CF3 (n = 4, 5 and 6 in
molar ratio 23:70:7) [57] were prepared as described. Known
products 2,3,5,6-C6F4HOCH3 (14) [58], 1-(2,3,5,6-tetrafluorophe-
nyl)pyrazole (19) [59], 1,2,4,5-C6F4H2 (5), 1,2,3,5-C6F4H2 (34),
1,2,3,4-C6F4H2 (8), 1,3,5-C6F3H3 (26), 2,3,5,6-C5NF4H (33) [60] were
identified by their 19FNMR spectra. Synthesis of K[n-CH3C6F4BF3]
(n = 5, 6) described below. Quantitative analysis of products in
reaction mixtures were performed by the 19FNMR with C6F6 or
C6H5F as an internal reference. Because of limited solubility of some
K[ArBF3]inAlkOH, conversionofboratetoArH wascalculatedfroma
ratio {ArH}/{K[ArBF3]0} where {ArH} is quantity of produced ArH
5.5.2. With 2-methoxyethanol for 4 h
Solution of K[C6F5BF3] (38 mg, 0.14 mmol) in 2-methoxyetha-
nol (0.9 mL) was kept for 4 h in a sealed tube. Conversion of 1 to
C6F5H (0.040 mmol) was 29%.
5.6. With n-propanol
Suspension of K[C6F5BF3] (41 mg, 0.150 mmol) in PrOH (1 mL)
was stirred for 4 h in a sealed tube forming C6F5H (0.009 mmol)
(
19FNMR).
5.7. With iso-propanol
Suspension of K[C6F5BF3] (48 mg, 0.175 mmol) in (Me)2CHOH
(1 mL) was stirred for 4 h in a sealed tube forming C6F5H
(0.012 mmol) (19FNMR).
5.8. With tert-BuOH
(
19FNMR) and {K[ArBF3]0} is initial quantity of borate (in mmol).
Solubility of K[C6F5BF3] (mg {mmol}) per mL of alcohol: 1
Suspension of K[C6F5BF3] (30 mg, 0.109 mmol) in tert-BuOH
(0.8 mL) was stirred for 4 h in a sealed tube forming C6F5H
(0.004 mmol) (19FNMR).
{0.004} in PrOH, 0.8 {0.003} in (CH3)2CHOH, 0.3 {0.001} in tert-
BuOH, >80 {>0.29} in MeOCH2CH2OH).
5.2. Reaction of K[C6F5BF3] with MeOH at 50–55 8C
5.9. With (CF3)2CHOH
5.2.1. In a glass tube
Suspension of K[C6F5BF3] (41 mg, 0.150 mmol) in (CF3)2CHOH
(1 mL) was stirred for 4 h in a sealed tube. After cooling, trace of
C6F5H was detected (19FNMR).
Suspension of K[C6F5BF3] (24 mg, 0.087 mmol) in MeOH
(0.83 mL) was kept at 50–55 8C for 4 h in a sealed tube. The
19FNMR spectrum of resulted solution showed the resonances of
C6F5H (0.015 mmol) and K[C6F5BF3] (0.072 mmol). Heating for the
next 7 h (total 11 h) gave C6F5H (0.054 mmol) and K[C6F5BF3]
(0.033 mmol). In both cases, the 19FNMR signals of K[BF3OMe] and
K[BF2(OMe)2] were present.
5.9.1. Reaction in aqueous MeOH for 1 h
Suspension of K[C6F5BF3] (31 mg, 0.11 mmol) in aqueous MeOH
(H2O:MeOH = 1:9, v/v) (0.83 mL) was kept for 1 h in a sealed tube.
The 19FNMR spectrum of resulted solution showed resonances of
C6F5H (0.080 mmol) beside the signals of K[C6F5BF3], K[BF3OMe],
K[BF2(OMe)2] and traces of K[BF3OH].
5.3. In a FEP made trap
K[C6F5BF3] (58 mg, 0.211 mmol) and MeOH (1.5 mL) were
loaded into a FEP made trap (o.d. = 9.0 mm, i.d = 8.0 mm) equipped
with a Teflon-coated magnetic bar and the trap was deposited in a
bath (50–55 8C). The suspension was stirred for 4 h, cooled to 22 8C
and a probe of the mother liquid was taken. The 19FNMR spectrum
displayed the resonances of C6F5H (0.044 mmol) beside the signals
of K[C6F5BF3], K[BF4] and K[BF3OMe]. After 6 h at 50–55 8C,
0.062 mmol of C6F5H were formed.
5.9.2. Reaction in aqueous MeOH for 4 h
Suspension of K[C6F5BF3] (28 mg, 0.10 mmol) in aqueous MeOH
(H2O:MeOH = 1:9, v/v) (0.83 mL) was kept for 4 h in a sealed tube.
The 19FNMR spectrum of the resulted solution showed the
resonances of C6F5H (0.10 mmol) beside the signals of K[BF3OMe],
K[BF2(OMe)2] and traces of K[BF3OH] [
B) = 15 Hz] [61,62].
d
ꢁ144.4 (q (1:1:1:1), 1J(F,
5.10. Reaction of K[C6F5BF3] with Et3N in MeOH
5.4. Reaction of K[C6F5BF3] with alcohols at 90–95 8C
K[C6F5BF3] (61 mg, 0.22 mmol) and Et3N (122 mg, 1.20 mmol)
in MeOH (1.5 mL) was kept in a sealed tube at 50–55 8C for 11 h (no
reaction) and 4 h at 90–95 8C to produce C6F5H (0.06 mmol)
5.4.1. With MeOH
Suspension of K[C6F5BF3] (31 mg, 0.11 mmol) in MeOH
(0.76 mL) was kept for 4 h in a sealed tube. The 19FNMR spectrum
(
19FNMR).

118
N.Y. Adonin et al. / Journal of Fluorine Chemistry 168 (2014) 111–120
5.11. Attempted reaction of K[C6F5BF3] and K2CO3 with MeOH
5.15.4. Reactions of K[RC6F4BF3] (R = F and Me)
Solution of K[C6F5BF3] (0.030 mmol) and K[4-MeC6F4BF3]
(0.070 mmol) in MeOH (1.5 mL) was stirred in a sealed tube for
2 h. The 19FNMR spectroscopy showed the resonances of C6F5H
(0.026 mmol) and 2,3,5,6-C6F4HMe (0.061 mmol) beside the
signals of traces of K[C6F5BF3], K[4-MeC6F4BF3], K[4-MeC6F4B-
F2(OMe)], K[BF4] and K[BF3OMe].
Suspension of K[C6F5BF3] (28 mg, 0.10 mmol) and K2CO3 (21 mg,
0.15 mmol) in MeOH (0.8 mL) was magnetically stirred at 90–95 8C
for 2 h in a sealed tube. The 19FNMR spectrum of the mother liquor
showed the resonances of K[C6F5BF3] and C6F5H (trace).
5.12. Attempted reaction of K[C6F5BF3] with MeCN
K[4-MeC6F4BF2OMe]. 19FNMR (MeOH):
d
ꢁ136.1 (m, 2F, F2,6),
ꢁ147.4 (dd, 3J(F3, F2) = 23 Hz, 3J(F3, F6) = 14 Hz, 2F, F3,5), ꢁ142 (br
Suspension of K[C6F5BF3] (22 mg, 0.08 mmol) in anhydrous
MeCN (0.8 mL) was kept in a sealed tube at 90–95 8C for 6 h (no
reaction) (19FNMR).
m, 2F, BF2OMe).
5.15.5. Reaction of K[C6F5BF3] and K[2,3,5,6-C6F4HBF3] (4)
Suspension of
1
(34 mg, 0.126 mmol) and
4
(17 mg,
5.13. Reaction of K[C6F5BF3] with LiCl in MeOH at 50–55 8C
0.066 mmol) in MeOH (1 mL) was kept for 1 h in a sealed tube.
The formed solution contained 1, 2, 4 and 5 in molar ratio
1.0:4.5:0.8:2.1 (conversion of 1 to 2 and 4 to 5 was 82% and 73%,
respectively) besides K[BF4] and K[BF3OMe].
5.13.1. Reaction with anhydrous LiCl
K[C6F5BF3] (56 mg, 0.20 mmol), LiCl (35 mg, 0.83 mmol) and
MeOH (1 mL) were loaded into a glass ampoule. The ampoule was
sealed by flame and kept at 50–55 8C. After 3 h, a probe of the
mother liquor showed the resonances of [C6F5BF3]ꢁ (0.06 mmol),
[C6F5BF2(OMe)]ꢁ (0.02 mmol) and C6F5H (0.12 mmol). After 6 h
signals of C6F5H (0.19 mmol) beside the signals of traces of
[C6F5BF3]ꢁ were present.
5.15.6. Reaction of K[C6F5BF3] and potassium 4-pyrazol-1-
yltetrafluorophenyltrifluoroborate (17)
Suspension of
1 (28 mg, 0.102 mmol) and 17 (24 mg,
0.075 mmol) in MeOH (1 mL) was heated for 2 h to produce
colorless solution. The 19FNMR spectrum showed the resonances of
C6F5H (0.042 mmol), 1-(2,3,5,6-tetrafluorophenyl)pyrazole 035
(0.014 mmol) beside the signals of 1, 17, K[BF4] and K[BF3OMe].
Admixture of K[3,4-Prz2C6F3BF3] (0.008 mmol) in initial borate 17
did not react.
5.14. Reaction with LiClꢃH2O
LiClꢃH2O (162 mg, 2.7 mmol) was dissolved in MeOH (3 mL)
and K[C6F5BF3] (230 mg, 0.83 mmol) was added. The suspension
was stirred at 50–55 8C. A probe of the mother liquor showed
the resonances of [C6F5BF3]ꢁ (0.57 mmol), [C6F5BF2(OMe)]ꢁ
(0.09 mmol), C6F5H (0.12 mmol) after 3 h and C6F5H (0.72 mmol)
besidethesignalsoftraces of [C6F5BF(OMe)2]ꢁ after6 h, respectively.
5.15.7. Reaction of K[C6F5BF3] and potassium 4-indol-1-
yltetrafluorophenyltrifluoroborate (18)
Suspension of
1 (51 mg, 0.18 mmol) and 18 (103 mg,
0.28 mmol) in MeOH (8 mL) was heated for 12 h. A probe of the
mother liquor contained C6F5H (0.16 mmol), 1-(2,3,5,6-tetrafluor-
ophenyl)indol 20 (0.17 mmol) besides 18, K[BF4] (0.021 mmol) and
K[BF3OMe].
M[C6F5BF2OMe] (3). 19FNMR (MeOH):
d
ꢁ133.8 (m, 2F, F2,6),
ꢁ141.9 (q (1:1:1:1), 1J(F, B) = 47 Hz, 2F, BF2OMe), ꢁ161.0 (t, 3J(F4,
F3,5) = 20 Hz, 1F, F4), ꢁ165.7 (m, 2F, F3,5).
5.15. Reaction of potassium polyfluoroaryl(fluoro)borates with MeOH
5.15.8. Reaction of K[XC6F4BF3](X = F, 4-Me (15) and 5-Me (21))
at 90–95 8C
Suspension
of
K[C6F5BF3]
(21 mg,
0.076 mmol), K[4-
MeC6F4BF3] (13 mg, 0.048 mmol) and K[5-MeC6F4BF3] (32 mg,
0.118 mmol) in MeOH (1 mL) was stirred in a sealed ampoule for
40 min. After cooling to 22 8C, white suspension formed. A probe of
the mother liquor contained C6F5H (0.071 mmol), 2,3,5,6-C6F4HMe
(16) (0.032 mmol) and 2,3,4,6-C6F4HMe (34) (0.049 mmol) besides
K[C6F5BF3], K[4-MeC6F4BF3], K[5-MeC6F4BF3], K[BF4] and
K[BF3OMe] (19FNMR). Conversion of 1 to 2, 15 to 16 and 21 to
34 was 93%, 67% and 42%, respectively.
5.15.1. Reaction of K[2,3,5,6-C6F4HBF3] (4)
A mixture of K[2,3,5,6-C6F4HBF3] (34 mg, 0.13 mmol) and MeOH
(0.8 mL) was heated for 1 h in a sealed tube. Cooling the colorless
solution resulted in formation of white crystals. The 19FNMR
spectrum of the mother liquor showed the resonances of 1,2,4,
5-C6F4H2 (0.052 mmol) beside the signals of K[2,3,5,6-C6F4HBF3],
K[BF3OMe] and K[BF2(OMe)2]. After 4 h, reaction of 4 (29 mg,
0.11 mmol) and MeOH (0.8 mL) gave the colorless solution of 1,2,4,
5-C6F4H2 (0.11 mmol), K[BF3OMe] and K[BF2(OMe)2] (19FNMR).
5.15.9. Reaction of K[XC6F4BF3](X = F, 4-H (4) and 5-H (22))
Suspension of K[C6F5BF3] (18 mg, 0.065 mmol), K[2,3,5,6-
C6F4HBF3] (32 mg, 0.125 mmol) and K[2,3,4,6-MeC6F4BF3]
(17 mg, 0.066 mmol) in MeOH (0.9 mL) was stirred in a sealed
ampoule for 40 min. After cooling to 22 8C, white suspension
5.15.2. Reaction of K[2,3,4,5-C6F4HBF3] (6)
Solution of 6 (0.19 mmol) (10 mg, 0.05 mmol) in MeOH (0.7 mL)
was heated in a sealed tube The solution contained 6 (0.18 mmol)
and K[2,3,4,5-C6F4HBF2(OMe)] 7 (0.01 mmol) after 1 h, and 6
formed.
A probe of the mother liquor contained C6F5H
(0.09 mmol),
7
(0.04 mmol), and 1,2,3,4-C6F4H2 (0.06 mmol)
(0.054 mmol), 1,2,4,5-C6F4H2 (5) (0.054 mmol) and 1,2,3,5-
C6F4H2 (34) (0.024 mmol) besides the started borates, K[BF4]
and K[BF3OMe] (19FNMR). Conversion of 1 to 2, 4 to 5 and 22 to 34
was 83%, 43% and 36%, respectively.
besides K[BF3OMe] and K[BF2(OMe)2] after 11 h. Heating for
30 h led to complete conversion of 6 to 1,2,3,4-C6F4H2 (0.19 mmol).
K[2,3,4,5-C6F4HBF2OMe] (7). 19FNMR (MeOH):
d
ꢁ135.1 (m, 1F,
F2), ꢁ143.1 (m, 1F, F5), ꢁ146.8 (q (1:1:1:1), 1J(F, B) = 47 Hz, 2F,
BF2OMe), ꢁ160.0 (m, 1F, F3), ꢁ162.3 (ddd, 4J(F4, F2) = 9 Hz, 3J(F4,
F3) = 19 Hz, 3J(F4, F5) = 19 Hz, 1F, F4).
5.15.10. Reaction of K[2,4,6-C6F3H2BF3] (23)
Suspension of 23 (33 mg, 0.14 mmol) in MeOH (1.0 mL) was
kept in a sealed tube. After 2 h, the 19FNMR spectrum of the mother
liquor showed resonances of 23, K[2,4,6-C6F3H2BF2(OMe)] (24),
K[2,4,6-C6F3H2BF(OMe)2] (25) (1:2:2), 1,3,5-C6F3H3 (26)
(0.03 mmol) beside the signals of K[BF3OMe] and K[BF2(OMe)2].
After 6 h, the formed solution contained 26 (0.14 mmol) besides
K[BF3OMe], K[BF2(OMe)2] and traces of 23, 24 and 25.
5.15.3. Reaction of K[C6F5BF3] and K[4-MeOC6F4BF3] (13)
Suspension of 1 (27 mg, 0.10 mmol) and 16 (30 mg, 0.10 mmol)
in MeOH (1 mL) was kept for 2 h in a sealed tube to produce
solution. This contained C6F5H (0.08 mmol) and 2,3,5,6-C6F4HOMe
(14) (0.10 mmol) besides K[BF3OMe] and K[BF2(OMe)2] (19FNMR).

N.Y. Adonin et al. / Journal of Fluorine Chemistry 168 (2014) 111–120
119
K[2,4,6-C6F3H2BF2OMe] (24). 19FNMR (MeOH):
d
ꢁ100.5 (m, 2F,
5.18. Preparation of K[4-MeC6F4BF3] and K[5-MeC6F4BF3] (isomer
F2,6), ꢁ113.8 (tt, 4J(F4, F2,6) = 9 Hz, 3J(F4,H3,5) = 8 Hz, 1F, F4), ꢁ141.8
mixture)
(q (1:1:1:1), 1J(F, B) = 42 Hz, 2F, BF2OMe).
K[2,4,6-C6F3H2BF(OMe)2] (25). 19FNMR (MeOH):
d
ꢁ101.8 (m,
5.18.1. Preparation of C6F4HCCl3 (isomer mixture)
2F, F2,6), ꢁ114.6 (m, 1F, F4), ꢁ146.5 (br, 1F, BF(OMe)2).
A three-necked flask equipped with a reflux condenser
topped with bubbler and gas inlet/outlet tube, dropping funnel,
thermometer and a Teflon-coated magnetic bar was flushed
with dry argon and charged with anhydrous AlCl3 (14.5 g,
0.11 mol) and CH2Cl2 (60 mL). The stirred suspension was cooled
5.15.11. Attempted reaction of K[3,4,5-C6F3H2BF3] (27)
Solution of 27 (0.25 mmol) in MeOH (1.0 mL) was kept for 12 h
in a sealed tube. Borate 27 did not react (19FNMR).
with ice bath and
a solution of n-HC6F4CF3 (4-H:5-H:6-
5.15.12. Reaction of K[4-C6FH4BF3] (28)
H = 23:70:7) (22 g, 0.10 mol) in CH2Cl2 (10 mL) was added
dropwise within 30 min at <14 8C. The red reaction mixture was
stirred at 20–22 8C for 2 h, cooled with ice bath, and water
(100 mL) was added. The organic phase was separated, washed
with water till neutral and dried with MgSO4. The solvent was
removed on rotary evaporator and the residue was evacuated at
95 8C for 1 h to give n-HC6F4CCl3 (4-H:5-H:6-H = 24:69:7) (22 g,
0.08 mol).
Suspension of 28 (31 mg, 0.15 mmol) in MeOH (0.9 mL) was
kept for 12 h in a sealed tube. Cooling the formed solution led to
precipitation of white solid. The mother liquor contained 28, K[4-
C6FH4BF2(OMe)] 30 (10:1), while C6H5F was not detected
(
19FNMR).
K[4-C6FH4BF2OMe] (30). 19FNMR (MeOH):
d
ꢁ117.9 (m, 1F, F4),
ꢁ148.5 (br q (1:1:1:1), 1J(F, B)ꢀ40 Hz, 2F, BF2OMe).
2,3,5,6-C6F4HCCl3. 19FNMR (CDCl3):
ꢁ137.6 (m, 2F, F3,5).
d
ꢁ134.5 (m, 2F, F2,6),
5.15.13. Attempted reaction of K[C6H5BF3] (29)
Suspension of 29 (15 mg, 0.08 mmol) in MeOH (0.8 mL) was
kept for 10 h in a sealed tube. Borate 29 did not react (19FNMR).
2,3,4,6-C6F4HCCl3. 19FNMR (CDCl3):
d
ꢁ106.3 (dddd, 5J(F6,
F3) = 11 Hz, 3J(F6, H5) = 11 Hz, 4J(F6, F4) = 6 Hz, 4J(F6, F2) = 5 Hz, 1F,
F6), ꢁ125.2 (dddd, 3J(F2, F3) = 20 Hz, 5J(F2, H5) = 2 Hz, 4J(F2,
F4) = 11 Hz, 4J(F2, F6) = 5 Hz, 1F, F2), ꢁ127.8 (dddd, 3J(F4,
F3) = 22 Hz, 4J(F4, H5) = 11 Hz, 4J(F4,F2) = 11 Hz, 4J(F4, F6) = 6 Hz,
1F, F4), ꢁ162.7 (dddd, 3J(F3, F2) = 20 Hz, 4J(F3, H5) = 6 Hz, 3J(F3,
F4) = 22 Hz, 5J(F3, F6) = 11 Hz, 1F, F3).
5.15.14. Reaction of K[2,3,5,6-C5NF4BF3] (32)
Suspension of 32 (66 mg, 0.25 mmol) in MeOH (0.8 mL) was
kept for 6 h in a sealed tube. The 19FNMR spectrum of the mother
liquor showed the resonances of 2,3,5,6-C5NF4H 33 (0.017 mmol)
beside the signals of 32, K[BF3OMe] and K[BF2(OMe)2].
2,3,4,5-C6F4HCCl3. 19FNMR (CDCl3):
d
ꢁ130.2 (ddd, 3J(F5,
F4) = 20 Hz, 3J(F5, H6) = 8 Hz, 5J(F5, F2) = 12 Hz, 1F, F5), ꢁ138.3
(dddd, 3J(F2, F3) = 20 Hz, 5J(F2, F5) = 12 Hz, 4J(F2, F4) = 8 Hz, 4J(F2,
H6) = 3 Hz, 1F, F2), ꢁ150.9 (dddd, 3J(F4, F3) = 21 Hz, 3J(F4,
F5) = 20 Hz, 4J(F4, F2) = 8 Hz, 4J(F4, H6) = 8 Hz, 1F, F4), ꢁ153.0 (dddd,
3J(F3, F2) = 20 Hz, 4J(F3, F5) = 3 Hz, 3J(F3, F4) = 21 Hz, 5J(F3,
H6) = 3 Hz, 1F, F3).
5.15.15. Reaction of K[C6F5BF3] and K[(C6F5)2BF2] (31)
Suspension of K[C6F5BF3] (0.066 mmol) and K[(C6F5)2BF2]
(0.101 mmol) in MeOH (0.76 mL) was kept for 6 h in a sealed
tube. The 19FNMR spectrum of resulted solution showed the
resonances of C6F5H (0.060 mmol) beside the signals of 31,
K[BF3OMe] and K[BF2(OMe)2].
HRMS (ESI) (mixture of C6F4HCCl3), m/z: calcd. for C7HCl3F4
265.9075 (35Cl); found 265.9074.
5.16. Reaction of K[C6F5BF3], K[4-ImC6F4BF3] (9) and K[3,4-
Im2C6F3BF3] (10) at 100 8C
5.18.2. Preparation of C6F4HCH3 (isomer mixture)
A three-necked flask equipped with a reflux condenser topped
with bubbler, dropping funnel, thermometer and Teflon-coated
magnetic bar was charged with zinc powder (13 g, 0.20 mol) and
glacial CH3COOH (90 mL). The stirred suspension was cooled with
ice bath and n-HC6F4CCl3 (22 g, 0.08 mol) (4-H:5-H:6-H = 24:69:7)
was added dropwise within 30 min at 15–22 8C. The suspension
was stirred at 20–22 8C for 1 h, at 50–53 8C (bath) for 5 h and left
overnight. Then water (100 mL) was added and products were
steam distilled. The organic phase was separated, washed with
water till neutral and dried with MgSO4 to yield colorless liquid
(11 g). The 1H and 19FNMR spectra showed the presence of
C6F4HCH2Cl besides C6F4HCH3. This mixture was reduced again
with zinc powder (11 g, 0.17 mol) and glacial CH3COOH (50 mL) as
above to give n-HC6F4CH3 (8 g, total yield 61%) (4-H:5-H:
6-H = 32:64:4).
A
mixture of K[4-ImC6F4BF3], K[C6F5BF3] and K[3,4-
Im2C6F3BF3] (100:7:7) (110 mg) was dissolved in MeOH (1 mL)
and heated in a sealed tube for 6 h. The 19FNMR spectrum showed
formation of 2,3,5,6-C6F4HIm 11, C6F5H and 1,2-Im2-3,5,6-C6F3H
12 (100:16:21), [BF4]ꢁ and [BF3OMe]ꢁ. The solution was
evaporated to dryness under reduced pressure, the residue was
extracted with acetone. The solution contained 11 (73%) and 12
(23%) (GC–MS).
1-(20,30,50,60-Tetrafluorophenyl)imidazole (11). 19FNMR (ace-
0
0
0
0
0
tone):
d
ꢁ137.5 (dddd, 3J(F3 , F2 ) = 21 Hz, 5J(F3 , F6 ) = 11 Hz, 3J(F3 ,
0
0
0
0
0
0
0
H4 ) = 10 Hz, 4J(F3 , F5 ) = 3 Hz, 2F, F3 ,5 ), ꢁ148.9 (m, 2F, F2 ,6 ) {lit.
d
0
0
ꢁ136.5 (d 22 Hz, d 12 Hz, d 10 Hz, d 4 Hz, 2F, F3 ,5 ), ꢁ147.1 (d
0
0
22 Hz, d 12 Hz, d 4 Hz, 2F, F2 ,6 ) [63]}.
1,2-Bis(1-imidazolino)-3,5,6-trifluorobenzene (12). 19FNMR
0
0
0
0
(acetone):
d
ꢁ121.6 (ddd, 5J(F3 , F6 ) = 12 Hz, 3J(F3 , H4 ) = 10 Hz,
2,3,5,6-C6F4HCH3 (16). 1HNMR (neat): 6.72 (tt, 3J(H4,
d
0
0
0
0
0
0
4J(F3 , F5 ) = 4 Hz, 1F, F3 ), ꢁ129.4 (ddd, 3J(F5 , F6 ) = 22 Hz, 4J(F5 ,
F3,5) = 10 Hz, 4J(H4, F3,5) = 8 Hz, 1H, H4), 2.16 (t, 4J(CH3,
0
0
0
0
0
F3 ) = 4 Hz, 3J(F5 , H4 ) = 10 Hz, 1F, F5 ),–148.0 (ddd, 3J(F6 ,
F2,6) = 2 Hz, 3H, CH3). 19FNMR (neat):
d
ꢁ140.5 (ddd, 3J(F3,
0
0
0
0
0
0
F5 ) = 22 Hz, 5J(F6 , F3 ) = 12 Hz, 4J(F6 , H4 ) = 7 Hz, 1F, F6 ).
HRMS (ESI) (a mixture of 11 and 12). Calcd. for C9H4F4N2:
216.0310; found 216.0321; Calcd. for C12H7F3N4: 264.0622; found
264.0617.
F2) = 21 Hz, 3J(F3, H4) = 10 Hz, 5J(F3, F6) = 13 Hz, 2F, F3,5), ꢁ144.0
(dddq, 3J(F2, F3) = 21 Hz, 4J(F2, H4) = 8 Hz, 5J(F2, F5) = 13 Hz,
4J(F2,CH3) = 2 Hz, 2F, F2,6) (cf. 19FNMR (neat):
ꢁ140.6) [64].
d
ꢁ139.1 and
2,3,4,6-C6F4HCH3 (36). 1HNMR (neat):
d
6.54 (dddd, 3J(H5,
5.17. Reaction of K[(C6F5)2BF2] (31) with MeOH at 120 8C
F4) = 9 Hz, 3J(H5, F6) = 10 Hz, 4J(H5, F3) = 6 Hz, 5J(H5, F2) = 3 Hz, 1H,
H5), 2.07 (s, 3H, CH3). 19FNMR (neat):
d
ꢁ118.5 (dd, 3J(F6,
Solution of 31 (67 mg, 0.158 mmol) in MeOH (1 mL) was stirred
at 120 8C for 6 h in a sealed tube to yield C6F5H (0.055 mmol)
besides 31, K[BF3OMe] and K[BF2(OMe)2].
H5) = 10 Hz, 5J(F6, F3) = 10 Hz, 1F, F6), ꢁ136.2 (d, 3J(F2,
F3) = 20 Hz, 1F, F2), ꢁ137.0 (ddd, 3J(F4, F3) = 20 Hz, 4J(F4,
H5) = 10 Hz, 4J(F4, F6) = 4 Hz, 1F, F4), ꢁ166.7 (dddd, 3J(F3,

120
N.Y. Adonin et al. / Journal of Fluorine Chemistry 168 (2014) 111–120
F2) = 20 Hz, 4J(F3, H5) = 6 Hz, 3J(F3, F4) = 20 Hz, 5J(F3, F6) = 10 Hz, 1F,
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F3).
2,3,4,5-C6F4HCH3. 1H NMR (neat): 6.66 (m, 1H, H6), 1.97 (s, 3H,
d
CH3) [65]. 19FNMR (neat):
d
ꢁ140.9 (dddd, 3J(F5, F4) = 20 Hz, 3J(F5,
H6) = 11 Hz, 4J(F5, F3) = 2 Hz, 5J(F5, F2) = 12 Hz, 1F, F5), ꢁ143.1 (m,
1F, F2), ꢁ157.5 (dddd, 3J(F3, F2) = 19 Hz, 4J(F3, F5) = 2 Hz, 3J(F3,
F4) = 19 Hz, 5J(F3, H6) = 2 Hz, 1F, F3), ꢁ160.5 (ddd, 3J(F4, F3) = 19 Hz,
3J(F4, F5) = 20 Hz, 4J(F4, F2) = 8 Hz, 1F, F4) [65].
Anal. calcd for C7H4F4 (164.10): C, 51.23; H, 2.46; F, 46.31;
found: C, 51.9; H, 2.46; F, 45.9.
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8111–8114.
5.18.3. Preparation of K[4-MeC6F4BF3] and K[5-MeC6F4BF3] (isomer
mixture)
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3725.
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Chem. 125 (2004) 1771–1778.
A solution of n-HC6F4CH3 (4-H:5-H:6-H = 32:64:4) (1.37 g,
8.4 mmol) in ether (17 mL) was cooled to ꢁ80 8C, and 2.0 M BuLi
in hexanes (5 mL, 10 mmol) was added using a syringe within
20 min, ensuring that the internal temperature did not rise above
ꢁ73 8C. The solution was stirred at ꢁ75 8C for 1 h and then
transferred with a cannula into the cold (ꢁ75 8C) stirred solution of
B(OMe)3 (1.0 g, 10 mmol) in ether (20 mL). After additional stirring
at ꢁ70 8C for 1 h, the solution was warmed to 0 8C within 2 h and
poured out onto stirred solution of K[HF2] (6 g, 79 mmol) in water
(15 mL) and MeOH (30 mL). The reaction mixture was stirred for
16 h, saturated with KF (5 g), and extracted with acetone
(2 ꢅ 23 mL). The combined extracts were dried with MgSO4 and
evaporated to dryness. Subsequent drying in a vacuum desiccator
over Sicapent1 gave the white solid (2.0 g, 88%) consisted from
K[4-MeC6F4BF3] and K[5-MeC6F4BF3] (3:7).
K[4-MeC6F4BF3] (15). 19FNMR (acetone):
d
ꢁ133.8 (tq, 4J(BF3,
F2,6) = 11 Hz, 1J(F, B) = 44 Hz, BF3), ꢁ136.0 (ddq, 3J(F2, F3) = 23 Hz,
5J(F2, F5) = 12 Hz, 4J(F2, BF3) = 11 Hz, 2F, F2,6), ꢁ147.2 (dd, 3J(F3,
F2) = 23 Hz, 5J(F3, F6) = 12 Hz, 2F, F3,5). 11BNMR (acetone-d6):
(q, 1J(B, F) = 45 Hz, BF3).
d
1.90
K[5-MeC6F4BF3] (21). 19FNMR (acetone):
d
ꢁ111.7 (m, 1F, F6),
ꢁ132.5 (m, 1F, F2), ꢁ133.8 (BF3) (overlapped on signal of 15),
ꢁ143.4 (d, 3J(F4, F3) = 20 Hz, 1F, F4), ꢁ170.2 (ddd, 3J(F3, F4) = 20 Hz,
3J(F3, F2) = 22 Hz, 1F, F3), 5J(F3, F6) = 13 Hz, 2F, F3,5). 11BNMR
[48] T. Muller, K. Djanashvili, I.W.C.E. Arends, J.A. Peters, U. Hanefeld, Chem. Commun.
49 (2013) 361–363.
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Reactions, 1(2), 1975.
[51] Basicities of 17 and 19 are not reported, but basicities of structurally related 1-
methylpyrazole (pKBH+ 1.9) [44], 2.0 [66,67]) and 1-phenylpyrazole (pKBH+ 0.43
[67]) are comparative with that of MeCN (see above).
(acetone-d6):
d
1.97 (q, 1J(B, F) = 45 Hz, BF3).
Anal. calcd for C7H3BF7K (270.0) (a mixture of 15 and (21): C,
31.14; H, 1.12; F, 49.26; found: C, 31.7; H, 1.38; F, 48.8.[66,67]
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