The palladium-catalysed cross-coupling reaction of lithium polyfluorophenyltrimethoxyborates with 4-fluoroiodobenzene

Article abstract of DOI:10.1016/S0022-1139(03)00088-5

Li[C₆F₅B(OMe)₃], Li[C₆ HF₄B(OMe)₃] (all three isomers) and Li[3,4,5-C₆H₂F₃B(OMe)₃] are the first examples of polyfluorophenyltrimethoxyborate salts which have been applied as reagents to Pd-catalysed cross-coupling reactions. A series of polyfluorinated biphenyls C₆H_5-n F_n-C₆H₄F-4′ were obtained from Li[C₆H_5-nF_nB(OMe)₃] and the model substrate 4-FC₆H₄I in the presence of Pd catalysts. The influence of the number and the position of fluorine atoms in the polyfluorophenyltrimethoxyborate salts on the reactivity in the coupling reaction was elucidated.

Full text of DOI:10.1016/S0022-1139(03)00088-5

Journal of Fluorine Chemistry 122 (2003) 195–199
The palladium-catalysed cross-coupling reaction of lithium
polyfluorophenyltrimethoxyborates with 4-fluoroiodobenzene$
Hermann-Josef Frohna,*, Nicolay Yu. Adoninb, Vadim V. Bardinb,
Vladimir F. Starichenkob
aInstitute of Chemistry, Inorganic Chemistry, University Duisburg-Essen, Lotharstr. 1, MC 363, D-47048 Duisburg, Germany
bN.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, SB RAS, Acad. Lavrentjev Avenue 9, 630090 Novosibirsk, Russia
Received 6 January 2003; received in revised form 13 March 2003; accepted 13 March 2003
Abstract
Li[C6F5B(OMe)3], Li[C6HF4B(OMe)3] (all three isomers) and Li[3,4,5-C6H2F3B(OMe)3] are the first examples of polyfluorophenyl-
trimethoxyborate salts which have been applied as reagents to Pd-catalysed cross-coupling reactions. A series of polyfluorinated biphenyls
C6H5ꢀnFn-C6H4F-40 were obtained from Li[C6H5ꢀnFnB(OMe)3] and the model substrate 4-FC6H4I in the presence of Pd catalysts. The
influence of the number and the position of fluorine atoms in the polyfluorophenyltrimethoxyborate salts on the reactivity in the coupling
reaction was elucidated.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Polyfluoroarylborates; Methoxyborates; Cross-coupling; Polyfluorobiphenyls; Palladium catalysis; Silver oxide
1. Introduction
Pentafluorophenyldihydroxyborane belongs to this group
of reagents. Only recently, two unsuccessful attempts to
apply it to cross-coupling reactions have been reported, both
under basic conditions [6]. This behaviour is in agreement
with our recent results on the reactivity of fluorine-contain-
ing aryldihydroxyboranes, C6H5ꢀnFnB(OH)2, towards bases
which revealed the significant acceleration of hydrodebora-
tion with an increasing number of fluorine atoms from n ¼ 1
to 5 [1].
To avoid this property, we used potassium polyfluorophe-
nyltrifluoroborates, K[C6H5ꢀnFnBF3], instead of the corre-
sponding polyfluorophenyldihydroxyboranes and succeeded
in the first cross-coupling of polyfluoroorganoboron com-
pounds with arenediazonium tetrafluoroborates as carbon
electrophiles [7]. Continuing our efforts in this field, we
decided to study the reactivity of the closely related salts
Li[C6H5ꢀnFnB(OMe)3] in cross-coupling reactions with 4-
fluoroiodobenzene as a model substrate. To our knowledge,
only the non-fluorinated salts M[RB(OMe)3] (M ¼ Li, Na)
were used previously in cross-coupling reactions with
R ¼ alkynyl [8] and hetaryl [9] groups.
The palladium-catalysed cross-coupling reaction of
organic halides with organoboron compounds is a convenient
method for synthesising biaryl, ethenylarene, and ethynylar-
ene skeletons, which are useful intermediates, e.g. for biolo-
gically activecompounds, chiral ligands, liquid crystals, dyes,
etc. [2]. The wide use of this synthetic method is favoured for
several reasons, as a rule, organoboron compounds are easily
accessible, not expensive, not moisture and air sensitive and
do not demand special handling conditions. Furthermore, the
inorganic by-products of the reaction are non-toxic and can be
easily separated from the target products.
The original procedure of Suzuki and co-workers [3] was
developed primarily for organodihydroxyboranes (organo-
boronic acids) and for organodialkoxyboranes and was later
modified [4]. Frequently, these reactions are carried out in
the presence of aqueous bases. However, aryldihydroxybor-
anes and aryldialkoxyboranes with electron-withdrawing
substituents in the ortho-positions often do not give
satisfactory results under these conditions or they are
consumed in competitive hydrodeboration reactions [5].
2. Results and discussion
$ Part 3 in the series ‘‘polyfluoroorganoboron oxygen compounds’’ [1].
* Corresponding author. Tel.: þ49-203-379-3310;
fax: þ49-203-379-2231.
The previously unknown salts Li[ArFB(OMe)3] (ArF ¼
C6F5 (1a), 2,3,4,5-C6HF4 (1b), 2,3,5,6-C6HF4 (1c), 2,3,4,
E-mail address: frohn@uni-duisburg.de (H.-J. Frohn).
0022-1139/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-1139(03)00088-5

196
H.-J. Frohn et al. / Journal of Fluorine Chemistry 122 (2003) 195–199
Scheme 1.
6-C6HF4 (1d) and 3,4,5-C6H2F3 (1e)) were prepared by the
nucleophilic arylation of B(OMe)3 with ArLi and isolated as
white moisture-sensitive solids (see also preliminary com-
munication [10]) (Scheme 1).
We examined the reaction of 1a with 4-fluoroiodobenzene
(2) under different conditions (solvent, temperature, cata-
lyst, additives) and monitored these reactions (Eq. (1)) by
19F NMR spectroscopy (Table 1).
12 h at 20 8C (entry 4). The reaction in toluene at 100–
110 8C resulted in 50% conversion of substrate 2 after 7 h,
but the yield of biphenyl 3a was only 23% (entry 5). In
addition, we studied the influence of DME on the lithium
salts and of the amount of catalyst on the effectiveness of the
cross-coupling both at the fixed temperature of 80 8C in
toluene. The influence of the amount of DME was lower in
comparison to that of the amount of catalyst (entries 6–8).
In the presence of 10 mol% of palladium acetate, the yield
of the target biphenyl was 50% (entry 6). When the reaction
was carried out in toluene at 100 8C without addition of
DME, 2,3,4,40,5,6-hexafluorobiphenyl (3a) was obtained in
25% yield only (26% conversion of 2 (entry 9)). Carrying
out the reaction in DME in the presence of the ligand
P(o-Tol)3 resulted in lower yields of 3a (entry 10). The
addition of the Lewis acid B(OMe)3 (entry 11) or of the hard
base KF (entry 12) gave no satisfactory results. In all
reactions with Pd(OAc)2 as catalyst (entries 1–12) beside
signals due to expected biphenyls, a C6F5-Pd species was
observed in the 19F NMR spectra. The highest yield of 3a
was achieved when [Pd(PPh3)4] was used as catalyst, being
60% (90% conversion of 2 (entry 13)).
Li½C6F5BðOMeÞ Š þ 4-FC6H4I catalysts
!
C6F5-C6H4F-40 (1)
3a
3
conditions
2
1a
The reaction of 1a with 2 in DME at 65–70 8C in the
presence of palladium acetate (5 mol%) gave 2,3,4,40,5,6-
hexafluorobiphenyl (3a) in 26% yield (40% conversion of
substrate 2 within 1 h (entry 1)). The use of toluene instead
of DME as solvent under the same conditions yielded 9% of
the target product 3a (21% conversion of 2) (entry 2).
Carrying out the reaction in boiling DME (85 8C) decreased
both, the yield of 3a and the conversion of 2 (entry 3). A
similar disadvantageous influence on the reactivity was
observed when the cross-coupling was carried out for
Table 1
Reactions of lithium polyfluorophenyltrimethoxyborates Li[ArFB(OMe)3] (1a–1e) with 4-fluoroiodobenzene (2)
Entry ArF
1a–1e
(mmol)
2
(mmol)
Catalyst
(mmol)
Solvent (ml) and
additives (mmol)
Temperature
(8C)
Time
(h)
Conversion Yield of
3 (%)a
of 2 (%)
1
2
C6F5 (1a)
0.75
0.75
0.75
0.67
0.75
0.75
0.75
0.86
0.75
0.75
0.75
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
Pd(OAc)2 (0.027)
Pd(OAc)2 (0.027)
Pd(OAc)2 (0.027)
Pd(OAc)2 (0.027)
Pd(OAc)2 (0.027)
Pd(OAc)2 (0.054)
Pd(OAc)2 (0.027)
Pd(OAc)2 (0.027)
Pd(OAc)2 (0.054)
Pd(OAc)2 (0.060)
Pd(OAc)2 (0.031)
DME (1)
65–70
65–70
1
40
26 (66)
9 (43)
7 (51)
6 (28)
23 (46)
50
C6F5 (1a)
C6F5 (1a)
C6F5 (1a)
C6F5 (1a)
C6F5 (1a)
C6F5 (1a)
C6F5 (1a)
C6F5 (1a)
C6F5 (1a)
C6F5 (1a)
Toluene (1)
DME (1)
1
21
3
ꢁ85 (reflux)
20
100–110
1
13
4
DME (1)
Toluene (1)
ꢁ12
7
23
50
5
6
Toluene (1) þ DME (0.078) 80
Toluene (1) þ DME (0.078) 80
3
ND
ND
ND
26
7
3
18
19
8
Toluene (1) þ DME (0.16)
80
3
9
Toluene (1)
100
4
25 (96)
9 (95)
20
10
11
DME (1) þ P(o-Tol)3 (0.12) 80
1
10
DME (1)
(0.028)
þ
B(OMe)3 80
3
ND
12
13
14
15
16
17
18
19
20
21
C6F5 (1a)
C6F5 (1a)
0.75
0.75
0.89
0.89
0.9
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
Pd(OAc)2 (0.050)
DME (1) þ KF (1.5)
65
100
100
80
1
20
98
60
73
82
42
63
35
60
45
17 (83)
60 (63)
8 (13)
[Pd(PPh3)4] (0.050) Toluene (1)
[Pd(PPh3)4] (0.050) Toluene (1)
2.5
2,3,4,5-F4C6H (1b)
2,3,4,5-F4C6H (1b)
2,3,5,6-F4C6H (1c)
2,3,5,6-F4C6H (1c)
2,3,4,6-F4C6H (1d)
2,3,4,6-F4C6H (1d)
3,4,5-F3C6H2 (1e)
3,4,5-F3C6H2 (1e)
3
3
3
3
3
3
3
3
Pd(OAc)2 (0.050)
[Pd(PPh3)4] (0.050) Toluene (1)
Pd(OAc)2 (0.050) DME (1)
[Pd(PPh3)4] (0.050) Toluene (1)
Pd(OAc)2 (0.050) DME (1)
[Pd(PPh3)4] (0.050) Toluene (1)
Pd(OAc)2 (0.050) DME (1)
DME (1)
70 (96)b
34 (42)
40 (95)
22 (35)
32 (91)
3 (5)
100
80
0.9
0.92
0.85
0.8
100
80
100
80
0.8
32 (98)c
a Based on initial 4-FC6H4I (on reacted 4-FC6H4I).
b Biphenyl 4 (11% yield) was obtained beside 3b.
c Biphenyl 5 (22% yield) was obtained beside 3e.

H.-J. Frohn et al. / Journal of Fluorine Chemistry 122 (2003) 195–199
197
Thus, the conversion of substrate 2 and the yield of the
target biphenyl 3a depend on different factors. The most
essential seems to be the stability of the reagent, lithium
pentafluorophenyltrimethoxyborate (1a), in the solvent
used. Apparently, in DME at 65–70 8C, there is an optimal
ratio of the cross-coupling reaction rate over the rate of
decomposition of 1a and, consequently, the best yield (entry
1). Salt 1a is nearly insoluble in toluene (19F NMR). The
addition of stoichiometric amounts of DME increased the
reactivity of the reagent by higher solubility in toluene on
one hand, but on the other hand the rate of destruction of 1a
was raised also (entries 6–8).
This behaviour is quite similar to the recently published
results with salts K[C6H5ꢀnFnBF3] [12].
Li½C6F5BðOMeÞ3Š þ 4-FC6H4I
2
1a
½PdðPPh3Þ4Š
!
C6F5-C6H4F-40 ð90%Þ
(3)
Ag2O; toluene; 100 ꢂC;3 h
3a
Further investigations of polyfluoroorganoboron compounds
in cross-coupling reactions are in progress.
3. Conclusion
The nature and quantity of the catalyst were important
factors which determined the out come of the coupling
reaction. With palladium acetate as catalyst, formation of
a C6F5Pd-containing compound was observed [11]. Prob-
ably, the concurrent formation of a C6F5Pd compound was
the main reason why only moderate yields of 3a were
achieved in entries 1–12. With [Pd(PPh3)4] as catalyst we
observed no C6F5Pd compound and obtained biphenyl 3a in
a reasonable yield (entry 13).
For the first time lithium salts of polyfluorophenyltri-
methoxyborates were used as polyfluorophenylating reagents
in Pd-catalysed cross-coupling reactions. Generally, salts of
polyfluoroorgano alkoxyborates should be suitable fluoroor-
gano reagents in coupling reactions under aprotic conditions.
4. Experimental
It was interesting to study the influence of one or two
hydrogen atoms in the polyfluorinated phenyl group on the
effectiveness of cross-coupling. Therefore, we compared the
reactivity of lithium 2,3,4,5-tetrafluorophenyltrimethoxybo-
rate (1b), 2,3,5,6-tetrafluorophenyltrimethoxyborate (1c),
2,3,4,6-tetrafluorophenyltrimethoxyborate (1d) and 3,4,5-
trifluorophenyltrimethoxyborate (1e) with that of borate
1a (Eq. (2)).
The 1H and 19F NMR spectra were recorded on BRUKER
WP 80 SY (1H at 80.13 MHz and 19F at 75.39 MHz at 32 8C)
7
and BRUKER AVANCE 300 (1H at 300.13 MHz, Li at
116.64 MHz, 11B at 96.29 MHz and 19F at 282.40 MHz at
24 8C) spectrometers. The chemical shifts are referenced to
TMS (1H), 1.0 M LiBr in D2O (7Li), 15 vol.% BF3ꢃOEt2 in
CDCl3 (11B) and CFCl3 (19F, with C6F6 as secondary
reference (ꢀ162.9 ppm)). Raman spectra were recorded
on a BRUKER RFS 100/S FT spectrometer. For measuring
the infrared spectra (BRUKER IFS 66 FT spectrometer) of
salts 1a and 1c, the samples were deposited on a polished
silicon disc in a glove box. High resolution mass spectra
were recorded on an AMD 604 spectrometer (EI mode,
70 eV).
Li½C6H5ꢀnFnBðOMeÞ Šþ4-FC6H4I catalysts
!
C6H5ꢀnFn-C6H4F-40
3
conditions
2
3bꢀ3e
1bꢀ1e
ðn¼1ꢀ4Þ
(2)
Lithium polyfluorophenyltrimethoxyborates (1b–1e) reac-
ted easily in DME with 4-fluoroiodobenzene (2) in the
presence of palladium acetate, forming the cross-coupling
products 3b–3e in satisfactory to good yields (entries 15, 17,
19 and 21). The tetrakis(triphenylphosphine)palladium(0)
catalysed reactions in toluene delivered the target biphenyls
3b–3e in significant lower yields (entries 14, 16, 18 and 20).
For lithium 2,3,4,5-tetrafluorotrimethoxyborate and
3,4,5-trifluorotrimethoxyborate, both with H-atoms in the
ortho-position(s), the formation of the corresponding sym-
metrical biphenyls (2,20,3,30,4,40,5,50-octafluorobiphenyl
and 3,30,4,40,5,50-hexafluorobiphenyl) was observed in addi-
tion to the cross-coupling products 3b and 3e.
Toluene, ether and B(OMe)3 were distilled over sodium.
Dichloromethane was distilled over P4O10 and stored over
˚
molecular sieve (4 A). DME was distilled over Li[AlH4]
and stored under an atmosphere of dry argon. Pd(OAc)2,
P(o-Tol)3, 2.5 M butyllithium in hexanes (all Aldrich) and
KF (spray-dried) (Morita, Japan) were used as supplied.
Tetrakis(triphenylphosphine)palladium(0) was prepared
using the literature method [13]. All manipulations with
lithium polyfluorophenyltrimethoxyborates were performed
under an atmosphere of dry argon. Biphenyls 3a–3e were
identified by 19F NMR spectroscopy [7].
The comparison of the results presented here with the
data obtained in the cross-coupling of K[C6H5ꢀnFnBF3] [7]
revealed the higher reactivity of the salts Li[C6H5ꢀnFn-
B(OMe)3]. Indeed, salt 1a forms biphenyl 3a when reacted
with 2 while the related salt K[C6F5BF3] did not react with 2
under the same conditions [7]. Less differentiated reactivity
of both classes was found in the presence of the additive
Ag2O. We were able to improve significantly the yield of 3a
in the cross-coupling of 1a with 2 by using the additive Ag2O.
4.1. Preparation of lithium
polyfluorophenyltrimethoxyborates 1a–1e
4.1.1. Lithium pentafluorophenyltrimethoxyborate (1a)
Pentafluorobenzene (7.6 g, 45 mmol) was dissolved in dry
ether (40 ml) and cooled to ꢀ78 8C. Butyllithium (2.5 M) in
hexane (16 ml) was added within 30 min, and after 2 h,
a white suspension had been formed which was slowly

198
H.-J. Frohn et al. / Journal of Fluorine Chemistry 122 (2003) 195–199
added to the cold solution (ꢀ78 8C) of B(OMe)3 (6.21 g,
59.8 mmol) in pentane (100 ml). The reaction mixture was
stirred at ꢀ78 8C for 0.5 h, than warmed up to ꢀ40 8C
slowly, stirred at this temperature for 5–10 min, before it
was cooled down to ꢀ78 8C and kept without stirring for
30 min for phase separation. The upper layer was decanted
and the residue was washed with pentane (3ꢄ 60 ml) with
stirring at 0–20 8C. After each washing, the flask was cooled
to ꢀ78 8C, kept without stirring for 15 min, before the upper
layer was decanted. Finally, all volatile products were
removed from the solid residue in high vacuum for 3 h
yielding 8.36 g (75%) of Li[C6F5B(OMe)3] (white solid, mp
(capillary) 110–115 8C (dec.).
ꢀ78 8C and added to the cold solution (ꢀ78 8C) of
B(OMe)3 (6.50 g, 62.5 mmol) in pentane (150 ml). After
the procedure above for working up, salt 1d (4.54 g, 44%)
was obtained (mp (capillary) 115–125 8C (dec.).
1H NMR (CD2Cl2) d ¼ 6:75 (1H, H5), 3.20 (9H, OCH3).
19F NMR (CD2Cl2) d ¼ ꢀ119:31 (1F, F6), ꢀ135.00 (1F, F2),
ꢀ137.74 (1F, F4), ꢀ168.01 (1F, F3) and additional
resonances at ꢀ119.72, ꢀ136.15, ꢀ138.31 and ꢀ168.01
(1:1:1:1) (ca. 5%). 11B NMR (CD2Cl2) d ¼ 4:18
(s, t1=2 ¼ 42 Hz). 7Li NMR (CD2Cl2) d ¼ ꢀ0:21
(s, t1=2 ¼ 18 Hz).
IR (powder on Si) u, cmꢀ1: 2933 (w), 2890 (w), 2824 (w)
ꢀ
(C–H), 1633 (m), 1606 (m), 1500 (m), 1488 (m), 1416 (s),
1275 (w), 1230 (w), 1195 (w), 1136 (w), 1080 (s), 1046 (m),
1014 (m), 968 (m), 936 (m), 825 (m), 809 (m), 728 (w).
Raman (glass capillary) ꢀu, cmꢀ1: 3082 (CAr–H), 2969,
2965, 2958, 2906, 2832 (C–H), 1609, 1600, 1471, 1197,
1031, 833, 684, 580, 566, 458, 410, 398, 389, 368, 343, 290,
284, 256, 221,171, 164.
Because of the hygroscopicity of salts 1a–1e, we were not
able to obtain correct analytical results (C, H, F) using
standard analytical procedures in air. For instance, after
10–15 min exposure of 1a (ꢁ10 mg) to air, the analysis
gave C 28.06%, H 6.82% and F 2.39% (cf. with calculated
values for Li[B(OCH3)3OH]: C 28.18% and H 7.88%).
1H NMR (CD2Cl2) d ¼ 3:21 (OCH3). 19F NMR (CD2Cl2)
d ¼ ꢀ143:89 (2F, F2,6), ꢀ158.83 (1F, F4), ꢀ163.87 (2F, F3,5
)
4.1.4. Lithium 2,3,5,6-
tetrafluorophenyltrimethoxyborate (1c)
and additional resonances at ꢀ144.64, ꢀ159.16 and ꢀ163.87
(2:1:2) (ca. 7%). 11B NMR (CD2Cl2) d ¼ 4:23 (s, t1=2
¼
2,3,5,6-Tetrafluorophenyllithium was prepared from
1,2,4,5-tetrafluorobenzene (6.75 g, 45 mmol) and 2.5 M
BuLi in hexane (16 ml, 40 mmol) in ether (40 ml) at
ꢀ78 8C (2 h) and added to the cold solution (ꢀ78 8C) of
B(OMe)3 (6.50 g, 62.5 mmol) in pentane (100 ml). After
working up (see the procedure above), salt 1c (8.80 g, 85%)
was obtained (mp (capillary) 125–130 8C (dec.).
1H NMR (CD2Cl2) d ¼ 6:96 (1H, H4), 3.20 (9H, OCH3).
19F NMR (CD2Cl2) d ¼ ꢀ144:66 (2F, F2,6), ꢀ141.14 (2F,
F3,5) and additional resonances at ꢀ145.15 and ꢀ141.36
7
36 Hz). Li NMR (CD2Cl2) d ¼ ꢀ0:25 (s, t1=2 ¼ 21 Hz).
IR (powder on Si) u, cmꢀ1: 2946 (w), 2913 (w), 2834 (w)
ꢀ
(C–H), 1648 (w), 1534 (m), 1518 (m), 1464 (s), 1386 (w),
1280 (m), 1198 (m), 1180 (m), 1133 (m), 1086 (m), 1046 (s),
955 (s), 779 (m), 751 (w), 718 (w), 708 (w), 627 (w), 584
(w), 556 (w), 530 (w).
Raman (glass capillary) u, cmꢀ1: 2947, 2837 (C–H), 1648,
ꢀ
1460, 1359, 1133, 1046, 938, 787, 665, 582, 492, 450, 401,
248.
(1:1) (ca. 6%). 11B NMR (CD2Cl2) d ¼ 4:27 (s, t1=2
¼
7
4.1.2. Lithium 2,3,4,5-
tetrafluorophenyltrimethoxyborate (1b)
42 Hz). Li NMR (CD2Cl2) d ¼ ꢀ0:17 (s, t1=2 ¼ 19 Hz).
Raman (glass capillary) u, cmꢀ1: 3101 (CAr–H), 2939,
ꢀ
2,3,4,5-Tetrafluorophenyllithium was prepared from
1,2,3,4-tetrafluorobenzene (3.40 g, 22.7 mmol) and 2.5 M
BuLi in hexane (8 ml, 20 mmol) in ether (40 ml) at ꢀ78 8C
(3 h) and added to the cold solution (ꢀ78 8C) of B(OMe)3
(3.24 g, 31.3 mmol) in pentane (50 ml). After working up
(see above), salt 1b (2.40 g, 46%) was obtained.
1H NMR (CD2Cl2) d ¼ 7:00 (1H, H6), 3.18 (9H, OCH3).
19F NMR (CD2Cl2) d ¼ ꢀ140:83 (1F, F5), ꢀ148.21 (1F, F2),
ꢀ158.86 (1F, F4), ꢀ160.24 (1F, F3). 11B NMR (CD2Cl2)
d ¼ 4:44 (s, t1=2 ¼ 113 Hz). 7Li NMR (CD2Cl2) d ¼ ꢀ0:15
(s, t1=2 ¼ 16 Hz).
2848, 2829 (C–H), 1641, 1462, 1451, 1427, 1351, 1167,
1136, 1102, 1047, 981, 956, 796, 723, 707, 672, 586, 495,
453, 442, 421, 383, 360, 336, 306, 241, 163.
4.1.5. Lithium 3,4,5-trifluorophenyltrimethoxyborate (1e)
3,4,5-Trifluorophenyllithium was prepared from 1-bromo-
3,4,5-trifluorobenzene (9 g, 42.7 mmol) and 2.5 M BuLi in
hexane (16 ml, 40 mmol) in ether (40 ml) at ꢀ78 8C (2 h)
and added to the cold solution (ꢀ78 8C) of B(OMe)3 (6.50 g,
62.5 mmol) in pentane (100 ml). After working up (see
above), salt 1e (9.60 g, 99%) was obtained (mp (capillary)
105–110 8C (dec.).
Raman (glass capillary) u, cmꢀ1: 3067 (CAr–H), 2944,
ꢀ
2836 (C–H), 1650, 1459, 1326, 1189, 1158, 1138, 1132,
1088, 1059, 706, 685, 657, 525, 505, 467, 453, 414, 361,
332, 312, 304, 290, 276, 249, 234.
1H NMR (CD2Cl2) d ¼ 7:07 (2H, H2,6), 3.25 (9H, OCH3).
19F NMR (CD2Cl2) d ¼ ꢀ138:33 (2F, F3,5), ꢀ165.67 (1F,
F4) and additional resonances at ꢀ139.16 and ꢀ167.46 (2:1)
(ca. 8%). 11B NMR (CD2Cl2) d ¼ 5:92 (s, t1=2 ¼ 204 Hz).
7Li NMR (CD2Cl2) d ¼ ꢀ0:22 (s, t1=2 ¼ 12 Hz).
4.1.3. Lithium 2,3,4,6-
tetrafluorophenyltrimethoxyborate (1d)
Raman (glass capillary) u, cmꢀ1: 3058 (CAr–H), 2980,
ꢀ
2,3,4,6-Tetrafluorophenyllithium was prepared from
1,2,3,5-tetrafluorobenzene (6.75 g, 45 mmol) and 2.5 M
BuLi in hexane (16 ml, 40 mmol) in ether (60 ml) at
2943, 2893, 2873, 2835 (C–H), 1621, 1608, 1520, 1471,
1453, 1281, 1131, 1110, 1050, 1026, 1012, 998, 916, 838,
730, 643, 610, 567, 542, 502, 445, 377, 309, 268, 141.

H.-J. Frohn et al. / Journal of Fluorine Chemistry 122 (2003) 195–199
199
4.2. The cross-coupling reaction of lithium
polyfluorophenyltrimethoxyborates (1aꢀ1e) with
Acknowledgements
4-FC6H4I (2) (general procedure)
We gratefully acknowledge financial support by the
Deutsche Forschungsgemeinschaft, the Russian Foundation
for Basic Research, and the Fonds der Chemischen Industrie.
Lithium polyfluorophenyltrimethoxyborate and the palla-
dium catalyst (see Table 1) were placed in a flask under an
atmosphere of dry argon. 4-Fluoroiodobenzene and the
degassed solvent were added and the reaction mixture was
stirred under the described reaction conditions (Table 1).
After cooling to 20 8C, CF3C(O)OCH3 (quantitative stan-
dard) (10 ml, 0.1 mmol) was added and the solution was
analysed by 19F NMR spectroscopy.
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