Electrophilic ipso-iodination of silylated arylboronic acids

Article abstract of DOI:10.1016/j.jorganchem.2010.08.016

Silylated functionalized arylboronic acids were converted into corresponding iodinated arylboronic acids in good yields via the electrophilic ipso-desilylation effected with iodine chloride in refluxing CHCl₃. Disilylated arylboronic acids were susceptible to diiodination. In addition, the structural characterization and reactivity of a novel sterically hindered ortho-silylated diarylborinic ester were reported. The potential of selected iodinated phenylboronic acids as monomers for the Suzuki-Miyaura cross-coupling polymerization was demonstrated.

Full text of DOI:10.1016/j.jorganchem.2010.08.016

Journal of Organometallic Chemistry 695 (2010) 2635e2643
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Journal of Organometallic Chemistry
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Electrophilic ipso-iodination of silylated arylboronic acids
*
ꢀ
K. Durka, J. Górka, P. Kurach, S. Lulinski , J. Serwatowski
Physical Chemistry Department, Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Silylated functionalized arylboronic acids were converted into corresponding iodinated arylboronic acids
in good yields via the electrophilic ipso-desilylation effected with iodine chloride in refluxing CHCl3.
Disilylated arylboronic acids were susceptible to diiodination. In addition, the structural characterization
and reactivity of a novel sterically hindered ortho-silylated diarylborinic ester were reported. The
potential of selected iodinated phenylboronic acids as monomers for the SuzukieMiyaura cross-coupling
polymerization was demonstrated.
Received 16 June 2010
Received in revised form
11 August 2010
Accepted 12 August 2010
Available online 20 August 2010
Ó 2010 Elsevier B.V. All rights reserved.
Keywords:
Arylboronic acids
Arylborinic compounds
Arylsilanes
Iodination
Electrophilic ipso-substitution
Suzuki cross-coupling
1. Introduction
2. Results and discussion
Arylboronic acids are extremely important reagents due to their
wide and diverse applications in organic synthesis, catalysis and
supramolecular chemistry. Iodinated arylboronic acids are attrac-
tive synthetic intermediates as they possess two sites, which can be
employed in coupling reactions. Thus, pinacol esters of simple
iodophenylboronic acids were used as precursors of magne-
siumeboron bimetallics followed by the treatment with electro-
philes to give functionalized arylboronic esters [1,2]. Recently,
2-iodophenylboronic acid was found to be an effective catalyst for
the direct formation of amides from carboxylic acids and
amines [3].
2.1. Synthesis of silylated arylboronic acids
In most cases, the classical approach involving the trans-
metalation of silylated aryllithiums with trialkyl borate followed by
hydrolysis was employed (Scheme 1) as described previously for
substrates 8a, 9a, 12a, and 15a [9,10]. Alternatively, silylated
difluorophenylboronic acids 1a and 2a were obtained by the
treatment of appropriate lithiated arylboronic derivatives with
Me3SiCl as reported recently [7]. In most cases crude acids were
used in subsequent synthetic step as the isolation of well-defined
crystalline materials proved problematic.
Simple iodophenylboronic acids and esters are readily prepared
from the corresponding diiodobenzenes via I/Li or I/Mg exchange
followed by boronation [4]. Alternative approach based on the
treatment of lithiumeboron bimetallics with elemental iodine has
also been described [5e7]. However, many functionalized iodoar-
ylboronic acids cannot be obtained using these routes due to the
limited access to the appropriate aryllithium or arylmagnesium
precursors. This has prompted us to investigate the general
potential of silylated arylboronic acids as starting materials in the
approach involving electrophilic ipso-desilylation with ICl [8].
The reaction of ortho-silylated aryllithiums with B(OMe)3 under
standard conditions (Et2O/THF, ꢀ70 ꢁC) leads to mixtures of boronic
and borinic acid derivatives (Scheme 2) [9]. For the selective
formation of arylboronic acids a lower temperature is required
during the boronation step. As reported recently, this can be
attributed to the decreased stability of the highly strained inter-
mediate anionic ortho-silylated boronate. It tends to dissociate to
some extent to form the boronic ester which is immediately trap-
ped with excessive aryllithium. Interestingly, the borinic ester 4c
was formed as a major product from the reaction of 3-fluoro-2-
(trimethylsilyl)phenyllithium 4-Li with B(OMe)3 whereas the cor-
responding 3-chloro and 3-bromo derivatives (5-Li and 6-Li) were
converted mainly to boronic acids 5ae6a. Initially, we expected the
reversed product distribution as we assumed that larger substitu-
ents adjacent to Me3Si will increase the steric pressure on the
* Corresponding author. Tel.: þ48 22 2347575; fax: þ48 22 6282741.
ꢀ
E-mail address: serek@ch.pw.edu.pl (S. Lulinski).
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.08.016

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K. Durka et al. / Journal of Organometallic Chemistry 695 (2010) 2635e2643
Scheme 1. General synthetic approaches to silylated arylboronic acids 1ae16a.
boronate group. Our results may suggest that irrespective of steric
factors the more potent long-range inductive effects of heavier
halogens are operative to provide additional electronic stabilization
for the intermediate “ate” complex.
atoms of the adjacent Me3Si groups (Fig. 1). The geometry of these
interactions is presented in Table 1. In order to extend our investi-
gations we performed theoretical calculations at DFT(B3LYP) [14]
level of theory using 6 ꢀ 311 þ G* basis set [15] at the experi-
mental geometry of isolated molecule. The Bond Critical Points and
linking bond paths were found in all CeH/O interactions. The
2.2. Structural characterization of bis(3-fluoro-2-(trimethylsilyl)
phenyl)methoxyborane (4c)
values of electron density (r) at these BCPs range from 0.06 to
0.08 e Åꢀ3. Local potential energy density, which is the quantity
proportional to the hydrogen bond energy, is close to
ꢀ6 kJ molꢀ1 bohrꢀ3 and is in good agreement with the literature
values [16]. The values of Laplacian of electron density range from
0.8 to 1.0 e Åꢀ5 and are characteristic for such interactions. The
stabilization of the methoxy function via CeH/O interactions may
also account for its higher kinetic resistance against hydrolytic
cleavage.
The borinic ester 4c can be isolated from the reaction mixtures by
fractional distillation followed by recrystallization from pentane. It
shouldbenotedthatunlikeothermethyl estersof boronic and borinic
acids, 4c is fairly stable towards water and does not rapidly hydrolyze
to give corresponding borinic acid and methanol [11]. The 1H NMR
spectrum of 4c shows a broad Me3Si resonance at 0.35 ppm which
splits into two sharp signals at 0.41 and 0.28 ppm on cooling to 227 K.
The signal at 0.41 ppm is a doublet, apparently due to the long-range
coupling 5JHꢀF ¼ 2 Hz. This points to the non-equivalence of aromatic
rings, which is also demonstrated by the appropriate changes in the
aromatic range of the spectrum. Similarly, broad resonances are also
observed in the 13C NMR spectrum of 4c. This points to the restricted
rotation of aryl groups around the BeC bonds.
The molecular structure of 4c has been determined by single-
crystal X-ray diffraction analysis and is shown in Fig.1. Two aromatic
rings are almost perpendicular to each other due to the steric
hindrance of ortho trimethysilyl groups. The boron centre adopts
trigonal, planar geometry. Interestingly, the C(1)eB(1)eC(7) angle is
120 ꢁ, whereas for other sterically hindered borinic derivatives, this
angle is close to 125 ꢁ [11e13]. The C(1)eB(1)eO(1) and C(7)eB(1)e
O(1) angles are equal to 124.1(1) ꢁ and 115.8(1) ꢁ, respectively, which
differ significantly from ideal 120 ꢁ. Both trimethylsilyl groups show
significant deviations either in plane or out of plane of aromatic ring
(both Si atoms are out of the least-squares planes of the corre-
sponding phenyl rings byabout 0.22 Å). The oxygen atom is involved
in the intramolecular CeH/O interactions with selected hydrogen
2.3. Electrophilic ipso-substitution of silylated arylboronic acids
with ICl
There are only a few reported reactions of related silylated
pinacol arylboronates and phenyldichloroboranes with iodine
chloride [17,18]. They were carried out in dichloromethane at room
or lower temperature. We found that the conversion of silylated
boronic acids was incomplete using this solvent even under pro-
longed reflux conditions, which may be due to their limited solu-
bility. Fortunately, good yields of iodinated arylboronic acids were
obtained in general using a slight excess of ICl (1.1 equiv.) in
refluxing chloroform (Scheme 3). The results are summarized
in Table 2. However, in the case of 13a, the use of excess ICl resulted
in the formation of a significant amount of a 3,5-diiodo-2-
methoxyphenylboronic acid resulting from electrophilic iodination
of the ring at C5 owing to the para-activating effect of the methoxy
group. The selective synthesis of 13b was performed using a stoi-
chiometric amount of ICl at 0 ꢁC. Finally, the general protocol was
Scheme 2. Synthesis of ortho-silylated arylboronic acids.

K. Durka et al. / Journal of Organometallic Chemistry 695 (2010) 2635e2643
2637
Fig. 1. Molecular structure of 4c. Labelling of atoms and estimation of atomic thermal motions as Anisotropic Displacement Parameters (ADPs). Ellipsoids are drawn at 50%
probability level. Weak intramolecular CeH/O interactions are presented as dashed lines.
successfully extended for the preparation of diiodinated products
14be16b from their disilylated precursors. Among them, 16b is the
first example of iodinated phenylenediboronic acid.
Iodination of borinic ester was performed in a similar way and
the resulting product was isolated after complexation with
8-hydroxyquinoline (Scheme 4).
heated at 100 ꢁC. The resulting product 16c was isolated as a yellow
amorphous powder insoluble in common solvents. Based on
elemental analysis data ca. 80% of boronic and iodine groups were
involved in the cross-coupling. This indicates that 16c must have
a highly branched structure (Scheme 6). It does not melt up to
425 ꢁC, although partial decomposition manifested by the extru-
sion of elemental iodine was observed above 370 ꢁC. It seems that
the starting boronic acid 1c could be used as a comonomer for the
synthesis of branched poly(phenylenes), e.g., via copolymerization
with other phenylenediboronic acids. Further studies on the
synthesis and characterization of polymers 1c and 16c and their
analogues will be reported in due course.
2.4. Polymerization of 3,5-difluoro-4-iodophenylboronic acid (1b)
and 2,5-diiodo-1,4-phenylenediboronic acid (16b)
We have probed the potential of 1b for the synthesis of fluori-
nated poly(p-phenylene) via Pd-catalyzed polymerization. The
reaction was performed at room temperature (rt) using Pd(OAc)2
(0.5 mol%)/K2CO3 (1.1 equiv) in 2-methoxyethanol/H2O (3:1)
(Scheme 5) [19].
3. Conclusions
The resulting polymer 1c was obtained in a good yield as a white
powder after removal of palladium black with concentrated HNO3
and washing with water and acetone. It is completely insoluble in
common solvents which preclude the characterization by NMR and
ESI MS. The XPRD analysis revealed that 1c is essentially amor-
phous. Based on elemental analysis and assuming the presence of
iodine and B(OH)2 end groups the average molecular weight was
calculated to be ca. 1600, which corresponds to an average value of
13 difluorophenylene units in the polymer chain. IR spectrum of
a vacuum-dried sample shows no bands of OH absorption, which
indicates that the triangle-shaped polymer with a central boroxine
core is formed upon condensation of three B(OH)2 end groups
[20,21]. TG/DTA analysis revealed that no significant mass loss
occurred when the sample of 1c was heated up to 300 ꢁC. In the
range 300e600 ꢁC the mass loss was ca. 30% followed by extensive
degradation in the range 600e700 ꢁC (over 95% of the initial mass).
The polymerization of 16b was performed using the same
catalytic system as that applied for 1b. The reaction proceeds at
room temperature although the mixture was then additionally
In conclusion, silylated arylboronic acids can be readily prepared
from the appropriate bimetallic aromatic siliconelithium or borone
lithium precursors by lithiumeboron or lithiumesilicon trans-
metalation, respectively. The sterically hindered arylborinic esters are
formed to a significant extent from the reactions of ortho-silylated
aryllithiums with B(OMe)3. Silylated arylboronic acids are effi-
ciently converted into iodinated arylboronic acids using the ipso-
iododesilylation protocol involving ICl in CHCl3 as the iodinating
agent. Similarly, diiodinated arylboronic acids as well as bis
(iodoaryl)borinic derivatives were obtained. The preliminary
results indicate the potential of iodinated arylboronic acids in the
synthesis of boroxine-based and branched poly(phenylenes).
4. Experimental
All reactions involving air- or moisture-sensitive reagents were
carried out under argon. Et2O and THF were stored over sodium
wire before use. Key reagents including nBuLi (10 M solution in
hexanes), diisopropylamine, 2,2,6,6-tetramethylpiperidine, chloro-
trimethylsilane, iodine chloride, acyl chlorides, trimethoxyborane,
Pd(OAc)2 and solvents were received from Aldrich and used
without additional purification. The synthesis of silylated arylbor-
onic acids 1a, 2a, 8a, 9a, 12a, and 15a was described previously
[7,9,10]. The remaining silylated arylboronic acids were obtained
from appropriate silylated bromobenzenes [22e24], in most cases
as crude materials and hence their combustion analyses were not
performed. NMR spectra were recorded on a Varian Mercury 400
Table 1
Geometry of weak intramolecular interactions (D denotes a donor and A an acceptor
of DeH/A interactions; d and
q denote distance and angle, respectively).
o
Interaction
dH/A/Å
dD/A/Å
qDeH/A/
C(14)eH(14C)/O(1)
C(16)eH(16A)/O(1)
C(17)eH(17C)/O(1)
2.525
2.457
2.477
3.279 (2)
3.170 (1)
3.182 (2)
133.7
129.3
128.7

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K. Durka et al. / Journal of Organometallic Chemistry 695 (2010) 2635e2643
Scheme 3. Preparation of iodoarylboronic acids 1be16b.
spectrometer. The NMR chemical shifts are given relative to TMS
with the aid of known chemical shifts of residual proton (1H) or
carbon (13C) solvent resonances. In the 13C NMR spectra the reso-
nances of boron-bound carbon atoms were not observed in most
cases (except for compounds 2b, 11b and 16b), due to their
broadening by quadrupolar boron nuclei.
4.1.3. Bis(3-fluoro-2-(trimethylsilyl)phenyl)methoxyborane (4c)
The suspension of 4-Li was prepared from 1-bromo-3-fluoro-2-
(trimethylsilyl)benzene (20.0 g, 0.08 mol) and nBuLi (10 M, 8 mL,
0.08 mol) at ꢀ70 ꢁC in Et2O/THF (2:1,100 mL). Then, B(OMe)3 (10.4 g,
0.1 mol) was added at ꢀ60 ꢁC and the resulting mixture was warmed
up to the room temperature. 2 M HCl solution in Et2O (40 mL) was
added followed by the filtration of theresulting slurry. The filtratewas
concentrated in vacuo and the residue was subjected to vacuum
distillation to give impured (3-fluoro-2-(trimethylsilyl)phenyl)
dimethoxyborane (5.5 g, b.p. 60e110 ꢁC, 1 Tr) and 4c (11.0 g, b.p.
130e135 ꢁC, 1 Tr) which slowly crystallized and was purified by
recrystallization from pentane at ꢀ20 ꢁC, m.p. 78e80 ꢁC. Yield: 9.3 g
4.1. Synthesis of silylated arylboronic acids
4.1.1. 4-Fluoro-3-(trimethylsilyl)phenylboronic acid (3a)
A
solution of 1-bromo-4-fluorobenzene-3-(trimethylsilyl)-
(62%). 1H NMR (CDCl3, 400 MHz)
d
: 7.29 (2H, broad, Ph), 7.10e6.98
(4H, m, Ph), 3.64 (3H, s, OMe), 0.35 (18H, broad, SiMe3); 13C{1H} NMR
(CDCl3, 100.6 MHz) : 167.8 (d, J 241 Hz), 147 (broad), 134.7 (broad)
130.9(broad),130.0(broad),125.4(broad),117.5(broad),114.5(broad),
2.1 (broad), 0.1 (broad); 11B NMR (CDCl3, 64.16 MHz)
: 42. Anal. Calcd.
benzene (6.35 g, 25 mmol) was added at ꢀ75 ꢁC to a stirred solution
of nBuLi (10 M, 2.5 mL, 25 mmol) in Et2O (30 mL). THF (10 mL) was
added. After ca. 30 min of stirring at ca. ꢀ75 ꢁC a mixture containing
the lithiate was quenched with B(OMe)3 (3.2 g, 3.5 mL, 0.30 mmol).
The mixture was stirred for 30 min at ꢀ75 ꢁC and was then
hydrolyzed with 2 M aq. H2SO4 (10 mL). The water phase was
separated, followed by extraction with diethyl ether (2 ꢂ 15 mL).
The extracts were added to the organic phase, which was concen-
trated under reduced pressure. A solid residue was filtered and
washed consecutively with water (2 ꢂ 10 mL) and hexane
(2 ꢂ 10 mL). Drying in vacuo afforded the title compound as a white
d
d
for C19H27BF2OSi2 (376.40): C, 60.63; H, 7.23. Found: C, 60.45; H, 7.11.
4.1.4. 3-Chloro-2-(trimethylsilyl)phenylboronic acid (5a)
The synthesis was performed as described for 3a starting with
1-bromo-3-chloro-2-(trimethylsilyl)benzene (21.0 g, 0.08 mol).
Vacuum distillation gave crude (3-chloro-2-(trimethylsilyl)phenyl)
dimethoxyborane (10.5 g, b.p. 75e80 ꢁC, 1 Tr). It was mixed with
water (10 mL) and acetone (10 mL). The solvent was removed and
the resulting white solid was filtered, washed with water and
hexane and dried to give pure boronic acid, m.p. 94e96 ꢁC. Yield:
powder. Yield: 4.9 g (93%). 1H NMR (CDCl3, 400 MHz)
d: 8.31 (1H,
dd, J 6.5, J 1.0 Hz, Ph), 8.20 (1H, t, J 8.5 Hz, Ph), 7.13 (1H, t, J 8.5 Hz,
Ph), 0.40 (9H, s, CH3) ppm. 11B NMR ([D6]acetone, 64.16 MHz)
d: 30.
9.5 g (52%). 1H NMR ([D6]acetone, 400 MHz)
(OH)2), 7.28 (3H, m, Ph), 0.41 (9H, s, SiMe3); 13C{1H} NMR ([D6]
acetone, 100.6 MHz)
: 141.9, 140.6, 130.4, 130.3, 129.6, 1.1; 11B NMR
([D6]acetone, 64.16 MHz) : 29.
d: 7.35 (2H, broad, B
4.1.2. 3-Fluoro-2-(trimethylsilyl)phenylboronic acid (4a)
The synthesis was performed as described for 3a starting with
1-bromo-3-fluoro-2-(trimethylsilyl)benzene. The lithiate was
quenched with B(OMe)3 below ꢀ90 ꢁC. Yield: 4.3 g (80%). 1H NMR
d
d
(CDCl3, 400 MHz)
d
: 7.37e7.31 (1H, m, Ph), 7.26e7.21 (1H, m, Ph),
4.1.5. 3-Bromo-2-(trimethylsilyl)phenylboronic acid (6a)
7.02e6.97 (1H, m, Ph), 0.36 (9H, s, CH3); 13C{1H} NMR ([D6]acetone,
100.6 MHz) : 167.6 (d, J 242.0 Hz), 130.8 (d, J 8.3 Hz), 128.5 (d, J
27.5 Hz), 127.1 (d, J 2.3 Hz), 115.8 (d, J 27.4 Hz), 0.4 (d, J 3.0 Hz); 11B
NMR ([D6]acetone, 64.16 MHz) : 28.5.
The synthesis was performed as described for 3a starting with
1,3-dibromo-2-(trimethylsilyl)benzene (15.5 g, 0.05 mol), m.p.
d
95e97 ꢁC. Yield: 6.5 g (48%). 1H NMR ([D6]acetone, 400 MHz)
d
: 7.49
d
(1H, dd, J 8.0, 1.5 Hz, Ph), 7.35 (2H, broad, B(OH)2), 7.33 (1H, dd, J 7.0,

K. Durka et al. / Journal of Organometallic Chemistry 695 (2010) 2635e2643
2639
Table 2
Preparation of functionalized iodophenylboronic acids via electrophilic ipso-substitution of silylated arylboronic acids with iodine chloride.
Substrate
Product
Yield, %
63
Substrate
Product
yield, %
64
B(OH)2
B(OH)2
B(OH)2
B(OH)2
I
SiMe3
F
F
F
F
CN
CN
9a
9b
SiMe3
I
1a
1b
1b
[9]
[7]
86
72
B(OH)2
F
B(OH)2
F
B(OH)2
SiMe3
B(OH)2
I
F
F
I
SiMe3
CF3
CF3
2b
2a
10a
10b
[7]
79
79
B(OH)2
B(OH)2
B(OH)2
SiMe3
B(OH)2
I
F3C
F3C
SiMe3
I
11a
11b
F
F
3a
3b
91
88
84
85
94
87
B(OH)2
B(OH)2
I
B(OH)2
CHO
B(OH)2
CHO
SiMe3
SiMe3
I
F
F
12b
4a
4b
5b
6b
12a
13a
[10]
B(OH)2
B(OH)2
I
B(OH)2
B(OH)2
SiMe3
OMe
OMe
SiMe3
Cl
Cl
I
5a
6a
13b
B(OH)2
B(OH)2
I
B(OH)2
B(OH)2
SiMe3
Me3Si
SiMe3
I
I
I
I
Br
Br
F
F
14a
15a
14b
15b
84
68
B(OH)2
B(OH)2
BOH)2
SiMe3
B(OH)2
I
Me3Si
I
Me3Si
Br
Br
7b
7a
CN
CN
[9]
79
86
B(OH)2
B(OH)2
BOH)2
B(OH)2
I
SiMe3
SiMe3
I
Me3Si
CN
CN
B(OH)2
B(OH)2
8a
8b
16a
16b
[9]

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K. Durka et al. / Journal of Organometallic Chemistry 695 (2010) 2635e2643
Scheme 4. Electrophilic ipso-iodination of 4c.
1.5 Hz, Ph), 7.18 (1H, dd, J 8.0, 7.0 Hz, Ph), 0.44 (9H, s, SiMe3); 13C{1H}
NMR ([D6]acetone, 100.6 MHz) : 142.9, 133.3, 132.1, 130.7, 130.5,
1.4; 11B NMR ([D6]acetone, 64.16 MHz)
: 29.
acetone, 400 MHz)
0.30 (18H, d,
100.6 MHz) d: 174.7 (d, J 236.0, 11.5 Hz), 144.3 (d, J 12.0 Hz), 124.3 (d,
d
: 8.03 (2H, d, J 1.0 Hz, Ph), 7.29 (2H, s, B(OH)2),
d
J
1.0 Hz, SiMe3); 13C{1H} NMR ([D6]acetone,
d
J 34.0 Hz), ꢀ0.8; 11B NMR ([D6]acetone, 64.16 MHz)
d: 28.
4.1.6. 3-Bromo-5-(trimethylsilyl)phenylboronic acid (7a)
Yield: 5.9 g (86%), m.p. 145e147 ꢁC. The synthesis was per-
formed as described for 3a starting with 1,3-dibromo-5-(trime-
thylsilyl)benzene (7.7 g, 25 mmol). 1H NMR ([D6]acetone, 400 MHz)
4.1.11. 2,5-Bis(trimethylsilyl)-1,4-phenylenediboronic acid (16a)
The synthesis was performed as described for 3a starting with
1,4-diiodo-2,5-bis(trimethylsilyl)benzene (4.8 g, 0.01 mol). Yield:
d
: 8.03 (1H, t, J 1.0 Hz, Ph), 7.97 (1H, dd, J 2.0 Hz, J 1.0 Hz, Ph), 7.69
(1H, d, J 2.0 Hz, J 1.0 Hz, Ph), 0.27 (9H, s, SiMe3); 11B NMR ([D6]
acetone, 64.16 MHz) : 29.
2.5 g (80%), m.p. >310 ꢁC (dec). 1H NMR ([D6]acetone, 400 MHz)
d:
7.78 (2H, s, Ph), 7.20 (4H, s, B(OH)2), 0.29 (18H, d, SiMe3); 13C{1H}
NMR ([D6]acetone, 100.6 MHz)
: 143.0, 138.5, 0.5; 11B NMR ([D6]
acetone, 64.16 MHz) : 28.0.
d
d
d
4.1.7. 5-(Trifluoromethyl)-2-(trimethylsilyl)phenylboronic acid (10a)
The synthesis was performed as described for 3a starting with
1-bromo-5-(trifluoromethyl)-2-(trimethylsilyl)benzene.
2.8 g (42%). 1H NMR (CDCl3, 400 MHz)
: 8.29 (1H, s, Ph), 7.86 (1H, d,
J 8.0, Ph), 7.74 (1H, d, J 8.0, Ph), 0.37 (9H, s, SiMe3); 11B NMR (CDCl3,
64.16 MHz)
¼ 29.
Yield:
4.2. Synthesis of iodinated arylboronic acids
d
4.2.1. 3,5-Difluoro-4-iodophenylboronic acid (1b)
d
A mixture of 1a (2.44 g, 10 mmol), ICl (1.8 g, 11 mmol) and
CHCl3 (50 mL) was stirred under reflux for 6 h. The resulting
mixture was concentrated under reduced pressure. Et2O (50 mL)
was added and the dark-coloured solution was treated with 10%
aq. Na2S2O3 (10 mL). The almost colourless organic phase was
separated and ether was removed under reduced pressure. The
crude product was filtered and washed with CHCl3 (5 mL). Yield:
1.80 g (63%), m.p. 304e307 ꢁC 1H NMR ([D6]acetone, 400 MHz)
4.1.8. 4-(Trifluoromethyl)-2-(trimethylsilyl)phenylboronic acid (11a)
The synthesis was performed as described for 3a starting with
1-bromo-4-(trifluoromethyl)-2-(trimethylsilyl)benzene.
3.0 g (46%). 1H NMR (CDCl3, 400 MHz)
: 8.03 (d, J 7.5 Hz, 1H, Ph),
7.65 (d, J 7.5 Hz,1H, Ph), 7.46 (s,1H, Ph), 0.33 (s, 9H, SiMe3); 11B NMR
(CDCl3, 64.16 MHz) : 29.
Yield:
d
d
d
: 7.63 [2H, broad, B(OH)2], 7.41 (2H, d, J 7.0 Hz, Ph); 13C{1H}
NMR ([D6]acetone, 100.6 MHz) : 163.2 (d, J 250.5 Hz), 116.8
(d, J 23.0 Hz), 73.9 (t, J 29.0 Hz); 11B NMR ([D6]acetone, 64.16 MHz)
: 28.5. Anal. Calcd. for C6H4BF2IO2 (283.81): C, 25.39; H, 1.42.
4.1.9. 2-Methoxy-3-(trimethylsilyl)phenylboronic acid (13a)
The synthesis was performed as described for 3a starting with
1-bromo-2-methoxy-3-(trimethylsilyl)benzene (6.5 g, 25 mmol).
d
d
Yield: 4.5 g (81%), m.p. 79e82 ꢁC 1H NMR ([D6]acetone, 400 MHz)
d:
Found: C, 25.05; H, 1.39.
7.67 (1H, dd, J 7.5, J 1.5 Hz, Ph), 7.45 (1H, dd, J 7.5, J 1.5 Hz, Ph), 7.21
(2H, broad, B(OH)2), 7.07 (1H, t, J 7.5 Hz, Ph), 3.80 (1H, s, Ph), 0.27
4.2.2. 2,3-Difluoro-4-iodophenylboronic acid (2b)
(9H, s, SiMe3); 11B NMR ([D6]acetone, 64.16 MHz)
d: 29.
Yield: 2.45 g (86%), m.p. >400 ꢁC 1H NMR ([D6]acetone,
400 MHz)
NMR ([D6]acetone, 100.6 MHz)
150.8 (dd, J 244.0 Hz, J 16.0 Hz), 134.6, 132.5, 125.0 (broad), 84.7 (d, J
21.5 Hz); 11B NMR ([D6]acetone, 64.16 MHz)
: 23.0. Anal. Calcd. for
C6H4BF2IO2 (283.81): C, 25.39; H, 1.42. Found: C, 25.18; H, 1.77.
d
: 7.55e7.52 (1H, m, Ph), 7.23e7.20 (1H, m, Ph); 13C{1H}
4.1.10. 3,5-Bis(trimethylsilyl)-4-fluorophenylboronic acid (14a)
The synthesis was performed as described for 3a starting with
d
: 153.6 (dd, J 252.0 Hz, J 14.0 Hz),
1-bromo-4-fluoro-3,5-bis(trimethylsilyl)benzene
(25.5
g,
d
0.08 mol), m.p. 288e291 ꢁC. Yield 20.5 g (90%). 1H NMR ([D6]
Scheme 5. Polymerization of 1b.

K. Durka et al. / Journal of Organometallic Chemistry 695 (2010) 2635e2643
2641
Scheme 6. Polymerization of 16b.
4.2.3. 4-Fluoro-3-iodophenylboronic acid (3b)
7.57 (1H, s, Ph), 7.56 (1H, d, J 7.0 Hz); 13C{1H} NMR ([D6]acetone,
100.6 MHz)
: 137.5, 134.5, 128.6, 121.3, 120.6; 11B NMR ([D6]
acetone, 64.16 MHz) : 29.0. Anal. Calcd. for C7H5BINO2 (272.84): C,
Yield: 2.10 g (79%), m.p. 240e241 ꢁC 1H NMR ([D6]acetone,
d
400 MHz)
Ph), 7.39 [2H, broad, B(OH)2], 7.17 (1H, t, J 8.4 Hz, Ph); 13C{1H} NMR
([D6]acetone, 100.6 MHz): : 163.9 (d, J 245.5 Hz), 146.4, 137.3 (d, J
7.5 Hz), 115.8 (d, J 23.0 Hz), 81.26 (d, J 24.5 Hz); 11B NMR ([D6]
acetone, 64.16 MHz) : 29.0; Anal. Calcd. for C6H5BFIO2 (265.82): C,
d
: 8.30 (1H, dd, J 7.5 Hz, J 1.5 Hz, Ph), 7.90e7.86 (1H, m,
d
30.82; H, 1.85; N, 5.13. Found: C, 30.95; H, 2.00; N, 5.07.
d
4.2.10. 5-(Trifluoromethyl)-2-iodophenylboronic acid (10b)
d
Yield: 2.30 g (72%), m.p. 139e142 ꢁC 1H NMR ([D6]acetone,
30.81; H 1.85. Found: C, 28.40; H, 1.47.
400 MHz)
(1H, d, J 2.0 Hz, Ph), 7.17 (1H, dd, J 8.5 Hz, J 3.0 Hz, Ph); 13C{1H} NMR
([D6]acetone, 100.6 MHz) : 140.1, 130.5 (d, J 4.0 Hz), 129.5 (q, J
32.5 Hz), 127.3, 125.3 (q, J 277.0 Hz), 104.0; 11B NMR ([D6]acetone,
64.16 MHz) : 28.4. Anal. Calcd. for C7H5BF3IO2 (315.82): C, 26.62; H,
d: 8.03 (1H, d, J 8.5 Hz, Ph), 7.67 [2H, broad, B(OH)2], 7.64
4.2.4. 3-Fluoro-2-iodophenylboronic acid (4b)
d
Yield: 2.42 g (91%), m.p. 199e202 ꢁC 1H NMR ([D6]acetone,
400 MHz)
(2H, m, Ph); 13C{1H} NMR ([D6]acetone, 100.6 MHz):
243.5 Hz),130.4 (d, J 7.0 Hz),129.9 (d, J 3.0 Hz),116.0 (d, J 24.5 Hz), 85.6
(d, J 23.5 Hz); 11B NMR ([D6]acetone, 64.16 MHz):
: 28.7. Anal. Calcd.
d: 7.55 [2H, broad, B(OH)2], 7.39e7.34 (1H, m, Ph), 7.17e7.09
d
d: 161.6 (d, J
1.60. Found: C, 26.38; H, 1.73.
d
4.2.11. 4-(Trifluoromethyl)-2-iodophenylboronic acid (11b)
for C6H5BFIO2 (265.82): C, 27.11; H, 1.90. Found: C, 27.76; H, 2.04.
Yield: 2.50 g (79%), m.p. 205e208 ꢁC 1H NMR ([D6]acetone,
400 MHz)
s, Ph); 13C{1H} NMR ([D6]acetone, 100.6 MHz)
132.1 (q, J 32 Hz), 125.4 (q, J 270 Hz), 124.8 (q, J 4.0 Hz), 124.3 (q, J
4.0 Hz), 98.6; 11B NMR ([D6]acetone, 64.16 MHz):
: 28.7. Anal. Calcd.
d
: 8.05 (1H, d, J 7.5 Hz, Ph), 7.67 (1H, d, J 7.5 Hz, Ph), 7.54 (1H,
4.2.5. 3-Chloro-2-iodophenylboronic acid (5b)
d: 139.4 (broad), 135.5,
Yield: 2.48 g (88%), m.p. 130e132 ꢁC 1H NMR ([D6]acetone,
400 MHz)
Ph), 7.35 (1H, t, J 7.2 Hz, Ph), 7.18 (1H, dd, J 7.0 Hz, J 1.5 Hz, Ph); 13C
{1H} NMR ([D6]acetone, 100.6 MHz):
: 138.6, 131.6, 129.9, 129.7,
101.9; 11B NMR ([D6]acetone, 64.16 MHz):
: 28.1. Anal. Calcd. for
d: 7.49 [2H, broad, B(OH)2], 7.47 (1H, dd, J 8.0 Hz, J 1.5 Hz,
d
for C7H5BF3IO2 (315.82): C, 26.62; H, 1.60. Found: C, 26.87; H, 1.80.
d
d
4.2.12. 3-Iodo-2-formylphenylboronic acid (12b)
C6H4BF2IO2 (282.27): C, 25.53; H, 1.79. Found: C, 25.86; H, 1.83.
Yield:2.25g(85%), m.p. 80e83ꢁC 1HNMR ([D6]acetone, 400MHz)
d
: 7.86 (1H, d, J 7.6 Hz, Ph), 7.71 (1H, d, J 7.6 Hz, Ph), 7.14 (1H, t, J 7.6 Hz,
Ph); 13C{1H}NMR ([D6]acetone,100.6MHz)
:157.4,141.8,131.3,130.7,
99.9, 91.0; 11B NMR ([D6]acetone, 64.16 MHz)
: 27.5. Anal. Calcd. for
4.2.6. 3-Bromo-2-iodophenylboronic acid (6b)
d
Yield: 2.54 g (78%), m.p. 127e128 ꢁC 1H NMR ([D6]acetone,
d
400 MHz)
(OH)2], 7.31e7.20 (2H, m, Ph); 13C{1H} NMR ([D6]acetone,
100.6 MHz)
: 133.1, 132.0, 130.5, 129.9, 104.8; 11B NMR ([D6]
acetone, 64.16 MHz) : 29.5. Anal. Calcd. for C6H5BBrIO2 (326.72): C,
d
: 7.64 (1H, dd, J 7.5 Hz, J 2.0 Hz, Ph), 7.48 [2H, broad, B
C7H6BIO3 (275.84): C, 30.48; H, 2.19. Found: C, 30.31; H, 2.04.
d
4.2.13. 3-Iodo-2-methoxyphenylboronic acid (13b)
d
The synthesis was carried out using a stoichiometric amount of ICl
22.06; H, 1.54. Found: C, 21.92; H, 1.70.
at 0 ꢁC. Yield: 2.6 g (94%), m.p. 89e91 ꢁC 1H NMR ([D6]acetone,
400 MHz)
1.5 Hz, Ph), 7.25 [2H, broad, B(OH)2], 6.93 (1H, t, J 7.5 Hz, Ph), 3.83 (3H,
s, Ph); 13C{1H} NMR ([D6]acetone, 100.6 MHz)
: 164.9, 142.6, 136.9,
126.7, 91.6, 62.6; 11B NMR ([D6]acetone, 64.16 MHz)
: 29.0. Anal.
d: 7.88 (1H, dd, J 8.0 Hz, J 2.0 Hz, Ph), 7.73 (1H, dd, J 7.0 Hz, J
4.2.7. 3-Bromo-5-iodophenylboronic acid (7b)
Yield: 2.75 g (84%), m.p. 323e324 ꢁC 1H NMR ([D6]acetone,
d
400 MHz)
(OH)2]; 13C{1H} NMR ([D6]acetone,100.6 MHz)
123.3, 95.2; 11B NMR ([D6]acetone, 64.16 MHz)
d
: 8.16 (1H, m, Ph) 7.96 (2H, m, Ph), 7.60 [2H, broad, B
: 142.6,141.5,136.9,
: 28.0. Anal. Calcd.
d
d
Calcd. for C7H8BIO3 (277.85): C, 30.26;H, 2.90. Found:C, 30.10;H, 2.73.
d
for C6H5BBrIO2 (326.72): C, 22.06; H, 1.54. Found: C, 21.85; H, 1.65.
4.2.14. 4-Fluoro-3,5-diiodophenylboronic acid (14b)
Yield: 3.40 g (87%), m.p. 352e354 ꢁC 1H NMR ([D6]acetone,
4.2.8. 3-Cyano-2-iodophenylboronic acid (8b)
400 MHz)
NMR ([D6]acetone,100.6 MHz)
27.7 Hz); 11B NMR ([D6]acetone, 64.16 MHz)
d
d
: 8.24 (2H, d, J 6.4 Hz, Ph), 7.61 [2H, broad, B(OH)2]; 13C{1H}
Yield: 2.15 g (79%), m.p. 141e143 ꢁC 1H NMR ([D6]acetone,
d: 162.1 (d, J 242.5 Hz),146.5, 80.9 (d, J
400 MHz)
(OH)2], 7.57 (1H, s, Ph), 7.56 (1H, d, J 2.0 Hz, Ph). 13C{1H} NMR ([D6]
acetone, 100.6 MHz):
: 147.5, 145.0, 138.6, 131.3, 130.6, 112.3; 11B
NMR ([D6]acetone, 64.16 MHz): : 29.2. Anal. Calcd. for C7H5BINO2
d: 7.70 (1H, dd, J 5.6 Hz, J 4.0 Hz, Ph), 7.68 [2H, broad, B
: 27.5. Anal. Calcd. for
C6H4BFI2O2 (391.71): C, 18.39; H, 1.03. Found: C, 18.21; H, 1.10.
d
d
4.2.15. 4-Cyano-2,5-diiodophenylboronic acid (15b)
(272.84): C, 30.82; H, 1.85; N, 5.13. Found: C, 30.50; H, 1.85; N, 5.20.
Yield: 2.70 g (68%), m.p. 151e153 ꢁC 1H NMR ([D6]acetone,
400 MHz)
acetone, 100.6 MHz)
([D6]acetone, 64.16 MHz)
(398.73): C, 21.08; H, 1.01, N, 3.51. Found: C, 21.31; H, 1.12; N, 3.28.
d
: 8.13 (1H, s, Ph), 7.92 (1H, s, Ph); 13C{1H} NMR ([D6]
4.2.9. 4-Cyano-3-iodophenylboronic acid (9b)
d
: 144.2, 143.7, 122.3, 118.5, 97.9, 97.5; 11B NMR
: 28.5. Anal. Calcd. for C7H4BI2NO2
Yield: 1.75 g (64%), m.p. 137e138 ꢁC 1H NMR ([D6]acetone,
d
400 MHz) d: 7.70 (1H, dd, J 5.5 Hz, J 3.5 Hz), 7.69 [2H, broad, B(OH)2],

2642
K. Durka et al. / Journal of Organometallic Chemistry 695 (2010) 2635e2643
4.2.16. 2,5-Diiodo-1,4-phenylenediboronic acid (16b)
polarization effects. The structure was solved by direct methods
using SHELXS-97 and refined using SHELXL-97 [26]. The refine-
ment was based on F2 for all reflections except those with very
negative F2. Weighted R factors (wR) and all goodness-of-fit (GooF)
values are based on F2. Conventional R factors are based on F with F
Yield: 2.3 g (86%), m.p. >400 ꢁC 1H NMR ([D6]acetone, 400 MHz)
d
: 7.72 (s, 2H, Ph), 7.48 (s, 4H, B(OH)2); 13C{1H} NMR ([D6]acetone,
100.6 MHz)
64.16 MHz)
d
: 148.0 (broad), 144.3, 98.9; 11B NMR ([D6]acetone,
: 28.0; Anal. Calcd. for C6H6B2I2O4 (417.54): C, 17.26; H,
d
1.45. Found: C, 17.14; H, 1.53.
set to zero for negative F2. The Fo2 > 2 (Fo2) criterion was used only
s
for calculating R factors and is not relevant to the choice of reflec-
tions for the refinement. The R factors based on F2 are about twice
as large as those based on F. Scattering factors were taken from
International Tables for Crystallography [27]. All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms of CeH bond
were placed in idealized positions (all these hydrogen atoms were
visible on difference density map).
4.2.17. Bis(3-fluoro-2-iodophenyl)borinic acid 8-hydroxyquinoline
ester (4d)
The borinic ester 4c was iodinated as described for 1b. The crude
iodinated borinic ester was dissolved in Et2O (50 mL) followed by
the addition of 8-hydroxyquinoline (1.45 g, 0.01 mol). The mixture
was stirred for 12 h and a yellow suspension was formed. The
resulting yellow solid was filtered and washed with Et2O (10 mL)
and hexane (10 mL). Yield: 3.50 g (58%), m.p. 211e212 ꢁC 1H NMR
4.6. DFT study of 4c
([D6]acetone, 400 MHz) d: 9.00 (1H, d, J 5.5 Hz, Q), 8.90 (1H, d, J
8.0 Hz, Q), 8.00 (1H, dd, J 8.5 Hz, J 5.0 Hz, Q), 7.74 (1H, t, J 8.0 Hz, Q),
7.50 (1H, d, J 8.5 Hz, Q), 7.21 (3H, m, Ph, Q), 7.01 (2H, m, Ph), 6.73
(2H, dd, J 7.5 Hz, J 1.6 Hz, Ph); 13C{1H} NMR ([D6]acetone,
Calculations were carried out with Gaussian 03 suite of
programs [28]. Electron density calculations were performed with
Becke-style 3-parameter density functional method using the Lee-
Yang-Parr correlation functional [14] (B3LYP) with 6 ꢀ 311 þ G*
basis set [15]. Topological analysis of electron density distributions
was investigated in terms of Bader’s Quantum-Theory-of-Atoms-
In-Molecules [29] (QTAIM) using AIM2000 programs [30].
100.6 MHz)
132.5, 129.9, 129.3 (d, J 7.5 Hz), 128.0, 124.4, 113.8, 109.8, 89.4 (d, J
23.0 Hz); 11B NMR ([D6]acetone, 64.16 MHz)
: 9.5. Anal. Calcd. for
d: 160.2 (d, J 241.0 Hz), 159.4, 157.1, 142.6, 141.2, 137.1,
d
C21H12BF2I2NO (596.94): C, 42.25; H, 2.03; N; 2.35. Found: C, 42.18;
H, 1.98; N, 2.42.
Acknowledgements
4.3. Polymerization of 1b
This work was supported by the by the Polish Ministry of
Science and Higher Education (Grant No. N N205 055633). The
support by Aldrich Chemical Co., Milwaukee, WI, U.S.A., through
continuous donation of chemicals and equipment is gratefully
acknowledged. The authors thank Dr. W. Fabianowski for helpful
remarks regarding characterization of polymers 1c and 16c. Dr. A.
Ostrowski is thanked for performing XPRD analyses. The X-ray
measurements were undertaken in the Crystallographic Unit of the
Physical Chemistry Laboratory at the Chemistry Department of the
University of Warsaw.
A mixture of 1b (1.5 g, 5.3 mmol), K2CO3 (0.85 g, 6.1 mmol) and
Pd(OAc)2 (5 mg, 0.03 mmol) in 2-methoxyethanol/H2O (3:1, 10 mL)
was stirred for 24 h at rt. A clear solution turned gradually turbid
and a grey suspension was formed. The crude product was filtered
and washed with water and Et2O. Then it was heated with conc.
HNO3 (3 mL) to remove palladium. Water (5 mL) was added and the
white suspension was filtered and washed with water (3 ꢂ 5 mL)
and acetone (3 ꢂ 5 mL) and dried in air. Yield of polymer 1c:
420 mg. It was obtained as a white powder insoluble in common
solvents, which precluded characterization by the solution NMR
spectroscopy. IR (KBr) n
/cmꢀ1: 3105 (w),1634 (s),1584 (s),1457 (m),
Appendix A. Supplementary material
1391 (s), 1350 (w), 1272 (m), 1009 (s), 868 (s), 736 (m), 564 (m).
Anal. found: C, 57.57; H, 1.94.
Crystallographic data for the structural analysis has been
deposited with the Cambridge Crystallographic Data Centre, CCDC
No 776555 for compound 4c. Copies of this information may be
obtained free of charge from: The Director, CCDC 12 Union Road,
Cambridge, CB2 1EZ UK, Fax. (int code) þ44(1223)336 033 or Email:
deposit@ccdc.cam.ac.uk or www:http://www.ccdc.cam.ac.uk.
4.4. Polymerization of 16b
A mixture of 16b (1.5 g, 3.6 mmol), K2CO3 (1.38 g, 10 mmol) and
Pd(OAc)2 (5 mg, 0.03 mmol) in 2-methoxyethanol/H2O (3:1, 12 mL)
was stirred for 12 h at rt and then for 12 h at 100 ꢁC. The crude
product was filtered and washed with conc. aq. HCl (3 mL), water
(3 ꢂ 5 mL) and acetone (3 ꢂ 5 mL). Yield of polymer 16c: 470 mg. IR
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