Practical syntheses of N-hexylcarbazol-2-yl- and -3-yl-boronic acids, their cross-coupled products and a derived tris-cyclometalated (pyridin-2-yl) carbazole iridium(III) complex

Article abstract of DOI:10.1055/s-2005-865307

The syntheses of N-hexylcarbazol-2-yl- and -3-yl-boronic acids (1 and 2) are described on a ca. 7 g scale, starting from commercially available 2,5-dibromonitrobenzene (4) and carbazole (11), respectively. Compounds 1 and 2 underwent efficient palladium-catalyzed cross-coupling reactions under Suzuki-Miyaura conditions to yield products 17,18 and 20. Compound 18 reacted with IrCl₃ to give the tris-cyclometalated (pyridin-2-yl)carbazole iridium(III) complex 21, the X-ray crystal structure of which is reported. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2005-865307

PAPER
1619
Practical Syntheses of N-Hexylcarbazol-2-yl- and -3-yl-boronic Acids, Their
Cross-Coupled Products and a Derived Tris-cyclometalated (Pyridin-2-yl)car-
bazole Iridium(III) Complex
S
ynthese
s
and
R
eactio
u
ns of
N
-Hexy
s
lcarbazol
t
ylboron
a
ic
A
cids fa Tavasli,a Sylvia Bettington,a Martin R. Bryce,*a Andrei S. Batsanov,a Andrew P. Monkmanb
a
b
Received 10 January 2005
B(OH)2
Abstract: The syntheses of N-hexylcarbazol-2-yl- and -3-yl-boron-
ic acids (1 and 2) are described on a ca. 7 g scale, starting from com-
mercially available 2,5-dibromonitrobenzene (4) and carbazole
(11), respectively. Compounds 1 and 2 underwent efficient palladi-
um-catalyzed cross-coupling reactions under Suzuki–Miyaura con-
ditions to yield products 17, 18 and 20. Compound 18 reacted with
IrCl3 to give the tris-cyclometalated (pyridin-2-yl)carbazole iridi-
um(III) complex 21, the X-ray crystal structure of which is reported.
B(OH)2
N
N
C6H13
C6H13
1
2
Figure 1 N-Hexylcarbazol-2-yl- and -3-yl-boronic acids (1 and 2).
Key words: carbazole, boronic acid, fluorene, cross-coupling reac-
tion, cyclometalating ligands, iridium complex
ing from a two-fold reaction. Optimized conditions (5.5 h
at 90 °C) gave a mixture of the desired product 5 (77%), 6
(8%) and unreacted 4 (15%). This mixture was heated in
triethylphosphine under Cadogan’s reductive cyclization
conditions10 to afford 2-bromocarbazole (7) (57% yield
based on 5) contaminated with 2-phenylcarbazole (8)
(6%) which was derived from 6.
Functionalized carbazoles are of considerable interest as
bioactive compounds that display a broad spectrum of
pharmacological properties.1 Many condensed ring sys-
tems are known, and some derivatives with pendant aryl
or heteroaryl derivatives have been investigated. For ex-
ample, hyellazole (2-phenyl-3-methyl-4-methoxycarba-
zole) has been widely studied,1 and pyrazolyl and quinolyl
derivatives have been reported very recently.2 Carbazole
derivatives bearing aryl and heteroaryl substituents are
very important in organic materials chemistry due to their
high stability, processability and the hole-transporting
properties of the carbazole unit.3 For example, they are
key building blocks for photorefractive materials,4 liquid
crystals,5 field effect transistors,6 and light-emitting poly-
mers.7 Carbazole-2,7-diboronic acid (or diboronate ester)
has been used for the synthesis of symmetrical 2,7-diaryl-
carbazole derivatives.3,8 We now report the efficient syn-
theses of N-hexylcarbazol-2-yl- and -3-yl-boronic acids
(1 and 2) (Figure 1) and establish that they undergo clean
Suzuki–Miyaura cross-coupling reactions to yield prod-
ucts 17, 18 and 20, which are ligands for cyclometalation
studies.
2-Bromocarbazole (7) has been synthesized by Percec et
al.11 in two steps (13% overall yield) starting from 2-nitro-
biphenyl, which was converted into 4-bromo-2¢-nitrobi-
phenyl followed by ring-closure. Our cross-coupling
strategy provided a considerably higher overall yield of 7
(36%) and the by-product 8 was readily removed at the
next stage. Thus the mixture of 7 and 8 was subjected to a
standard alkylation reaction12 with hexyl bromide; chro-
matography cleanly separated N-hexyl-2-bromocarbazole
(9) (99% based on 7) from N-hexyl-2-phenylcarbazole
(10). Compound 9 was hydroxyborolylated12 by lithiation
with n-BuLi, addition of triisopropylborate and then hy-
drolysis with HCl, to give the boronic acid 1 in 83% yield
(Scheme 1).
For the synthesis of carbazol-3-ylboronic acid (2), the key
intermediate was 3-bromocarbazole (12), which has been
obtained previously by treatment of carbazole (11) with
bromine in pyridine.11,13 In our hands carbazole (11) was
not soluble in pyridine, and we prepared 12 by a modifi-
cation of the procedure of Smith et al.,14 replacing trimeth-
yltin chloride with the less toxic trimethylsilyl chloride.
Lithiation of carbazole (11) with n-BuLi, followed by si-
lylation and bromination gave mixtures of 11, 12 and 13
in a ratio of 4:5:1, respectively, after chromatography (by
1H NMR data). Recrystallization removed 13 to give a
mixture of 11 and 12 in a 2:3 ratio. This enabled us to
complete the synthesis of boronic acid 2 successfully, in
13% overall yield from 11.
The first step in our route to carbazol-2-yl-boronic acid
(1) (Scheme 1) was Suzuki–Miyaura coupling9 of phenyl-
boronic acid (3) with 2,5-dibromonitrobenzene (4) (both
of which are commercially available) in the presence of
catalytic Pd(PPh3)4. Under a variety of conditions, prod-
uct mixtures were obtained. Longer reaction times (e.g. 22
h) favored formation of compound 6 (ca. 50% yield) aris-
SYNTHESIS 2005, No. 10, pp 1619–1624
x
x.
x
x
.
2
0
0
5
Advanced online publication: 12.04.2005
DOI: 10.1055/s-2005-865307; Art ID: P00705SS
© Georg Thieme Verlag Stuttgart · New York

1620
M. Tavasli et al.
PAPER
i
+ 6
+
B(OH)2
Br
Br
Br
66%
O2N
O2N
3
4
5
57%
ii
N
H
8
O2N
+ 8
6
Br
N
H
N
C6H13
7
10
99%
iii
iv
+ 10
B(OH)2
Br
83%
N
N
C6H13
C6H13
1
9
Scheme 1 Reagents and conditions: (i) Pd(PPh3)4 (3% equiv), aq 2 M Na2CO3 (3 equiv), toluene, 90 °C, 5.5 h; (ii) (EtO)3P, reflux, 10 h; (iii)
t-BuOK (1.2 equiv), DMF, 20 °C, 2 h; 1-bromohexane (1.5 equiv), 130 °C, 65 h; (iv) n-BuLi (1.2 equiv), THF, –78 °C, 2 h; (i-PrO)3B (3.0
equiv), –78 to 20 °C, 16 h; concd HCl, 20 °C, 2 h.
However, we have found that bromine in dimethylform- Compounds 17, 18 and 20 are new ligands for cyclometa-
amide at room temperature (conditions which have not lated complexes for use in electrophosphorescent devices.
been reported previously) is the best way to prepare 12 To illustrate their ability to form metal complexes, follow-
from 11 (Scheme 2), and is preferable to all other proce- ing a modified literature method,18 an excess of 18 was
dures.15 Upon simple filtration, compound 12 was thereby treated with iridium(III) chloride under microwave irradi-
obtained in >90% yield, contaminated with ca. 10% of un- ation. The triply cyclometalated iridium(III) complex 21
reacted 11 and on some occasions with ca. 2% of 3,6-di- was obtained in 14% yield (Scheme 4). This complex rep-
bromocarbazole (13). Recrystallization from chloroform resents a rare example of a triply cyclometalated iridi-
lowered the yield of 12 (35%) and removed the traces of um(III) complex in which a carbazole unit is directly
13. The single-crystal X-ray structure of 12 was obtained
Br
(Scheme 2, inset). The mixture of 11 and 12 was alkylat-
ed, as above, to give a mixture of 14 and 15 (ca. 9:1 ratio;
Method A (i), 22%; or
+
13
91% yield of 14, based on 12). Hydroxyborolylation of
14, as above, gave N-hexylcarbazol-3-ylboronic acid (2)
in 67% yield, after easy separation from 15. A borolane
derivative of 2, namely 2-(9-hexylcarbazol-3-yl)-4,4,5,5-
tetramethyl-1,3,2-dioxaborolane, has been reported re-
cently,16 without any experimental details. The routes in
Schemes 1 and 2 have reproducibly provided pure prod-
ucts 1 and 2 on ca. 7 g scales, with straightforward purifi-
cation steps.
Method B (ii), 35%
N
H
12
N
H
11
iii
91%
Br
15
+
N
Single-crystal X-ray structure of 12
C6H13
14
Br
Br
To confirm the suitability of reagents 1 and 2 for cross-
coupling reactions, 2-bromopyridine (16) and 2-(7-bro-
mo-9,9-dihexylfluoren-2-yl)pyridine (19)17 were chosen
as the halogenated partners. Standard Suzuki–Miyaura
conditions [either Pd(PPh3)4 or Pd(PPh3)2Cl2 as catalyst,
toluene, Na2CO3 (aq 2 M), 90 °C, 21–54 h] gave 17, 18
and 20 (60%, 70% and 77% yields, respectively;
Scheme 3). Shorter reaction times gave lower yields of
products.
N
C6H13
15
67%
iv
N
H
13
2
Scheme 2 Reagents and conditions: (i) n-BuLi (1.0 equiv), –78 °C,
15 min; Me3SiCl (1.0 equiv), 20 °C, 3 h; Br2 (1.0 equiv), –78 °C, 1 h;
20 °C, 2 h (ii) Br2 (1.1 equiv), DMF, 0–20 °C, 1–27 h; (iii) t-BuOK
(1.2 equiv), DMF, 20 °C, 1 h; 1-bromohexane (1.5 equiv) 130 °C, 65
h; (iv) n-BuLi (1.2 equiv), THF, –78 °C, 1 h; (i-PrO)3B (3.0 equiv),
–78 to 20 °C, 22 h; concd HCl (5.0 equiv), 20 °C, 2 h.
Synthesis 2005, No. 10, 1619–1624 © Thieme Stuttgart · New York

PAPER
Syntheses and Reactions of N-Hexylcarbazolboronic Acids
1621
ally perpendicular), while the n-hexyl chains and solvent
molecules are intensely disordered. The crystals instantly
lost solvent and decomposed if taken out of the mother li-
quor. In the same experiment, unsolvated and air-stable
crystals of 21 were also formed. Remarkably, the crystal
lattice and the packing of the molecules are essentially the
same as in the solvate, but loose packing without solvent
resulted in even stronger disorder of the n-hexyl chains
and librational disorder of the entire molecules as well. A
facial structure of complex 21 is also supported by the
NMR data.
i
Br
N
60%
N
N
16
C6H13
(1.2 equiv)
17
N
ii
Br
N
70%
N
16
C6H13
(2.5 equiv)
18
In summary, efficient and inexpensive routes have been
developed for the synthesis of the carbazolyl-boronic ac-
ids 1 and 2, which are versatile reagents for the construc-
tion of new aryl- and heteroaryl-carbazole derivatives. In
addition, we have established that pyridinyl-carbazole
ligand 18 bonds directly through the carbazole unit to
form facial tris-cyclometalated iridium(III) complexes
which will be studied as electrophosphorescent dopants in
organic light emitting devices (OLEDs). Iridium(III)
complexes of ligands 17 and 20 and the photophysical
properties of this family of compounds will be described
in a forthcoming paper.
Br
N
C6H13
C6H13
19
N
77%
iii
C6H13
C6H13
N
C6H13
20
Scheme 3 Reagents and conditions: (i) boronic acid 1, Pd(PPh3)2Cl2
(4% equiv), aq 2 M Na2CO3 (4 equiv), toluene, 90 °C, 21 h; (ii) boro-
nic acid 2, Pd(PPh3)2Cl2 (6% equiv), aq 2 M Na2CO3 (10 equiv), to-
luene, 90 °C, 40 h; (iii) boronic acid 2 (1.5 equiv), Pd(PPh3)4 (7%
equiv), aq 2 M Na2CO3 (17 equiv), toluene, 90 °C, 54 h.
All reactions were performed under argon, which was dried by pas-
sage through a column of P2O5. All reagents were of standard re-
agent grade and purchased from Aldrich, Lancaster and Fluorochem
and used as supplied. THF was dried and distilled prior to use over
potassium or sodium metal. All other solvents were used without
prior purification. Petroleum ether used had bp 40–60 °C. Column
chromatography was carried out on silica gel (40–60 mm). 1H NMR
spectra were recorded on a Varian Unity 300 at 300 MHz, a Varian
VXR 400s at 400 MHz or a Varian Inova 500 spectrometer at 500
MHz using deuteriated solvent as the lock and tetramethylsilane as
the internal reference. 13C NMR spectra were recorded using broad-
band decoupling on the above spectrometers at 75, 100 and 125
MHz, respectively. Mass spectra were recorded on a Micromass
Autospec spectrometer operating at 70 eV with the ionization mode
as indicated. Electrospray high-resolution mass spectra were ob-
tained on a Micromass LCT (TOF). Elemental analyses were ob-
tained on an Exeter Analytical Inc. CE-440 elemental analyzer.
Melting points were recorded on a Stuart Scientific SMP3 apparatus
and are uncorrected.
bonded to the metal core.19 By analogy, we anticipate that
other ligands of this family will form similar cyclometa-
lated complexes.
The structure of 21 was confirmed by a single-crystal
X-ray
diffraction
study
of
the
solvate
21·2CH2Cl2·0.5Me2CO (Scheme 4, H atoms and minor
positions of the disordered n-hexyl groups are omitted).
The iridium atom has fac-octahedral coordination with the
three 9-hexyl-3-(pyridin-2-yl)carbazole ligands, whose
pyridinyl-carbazole moieties are nearly planar (and mutu-
4-Bromo-2-nitrobiphenyl (5)20
18
Phenylboronic acid (3; 10.0 g, 82.0 mmol), 2,5-dibromonitroben-
zene (4; 23.1 g, 82.3 mmol) and Pd(PPh3)4 (2.8 g, 2.5 mmol) were
dissolved in a mixture of toluene (250 mL) and aq 2 M Na2CO3 (124
mL). The degassed mixture was heated at 90 °C for 5.5 h, cooled to
20 °C and then diluted with distilled H2O. The organic phase was
separated and the organic products were extracted into CH2Cl2
(4 × 50 mL). The combined extracts were dried (MgSO4) and con-
centrated under reduced pressure to give a dark brown liquid. Dis-
tillation under high vacuum (72 °C/3 × 10–2 mm Hg) gave an
inseparable mixture of 4, 5 and 6 as a light-orange semi-solid (19.2
(1.7 equiv)
14%
i
N
Ir
1
g). The H NMR analyses indicated that 77% of the mixture was
compound 5 (14.8 g, 66%). The mixture was used in the next step
without further purification.
N
C6H13
3
Single crystal X-ray structure of 21.
Mean bond lengths Ir–C 2.017(8), Ir–N 2.128(8) Å.
5
21
1H NMR (400 MHz, CDCl3): d = 8.00 (d, 1 H, J = 2.0 Hz, H-3),
7.75 (dd, 1 H, J = 8.2, 2.0 Hz, H-5), 7.45–7.41 (m, 3 H), 7.33 (d, 1
H, J = 8.2 Hz, H-6), 7.31–7.27 (m, 2 H).
Scheme 4 Reagents and conditions: (i) IrCl3, Na2CO3 (2 equiv),
ethylene glycol–H2O, 220 °C, microwave (220 W), 30 min.
Synthesis 2005, No. 10, 1619–1624 © Thieme Stuttgart · New York

1622
M. Tavasli et al.
PAPER
13C NMR (CDCl3, 75 MHz): d = 136.5, 135.6, 135.5, 133.5, 131.8,
8), 7.29 (t, 1 H, J = 7.6 Hz, H-6), 4.47 (t, 2 H, J = 7.3 Hz, NCH2),
2.02 (p, 2 H, J = 7.6 Hz, NCH2CH2), 1.60–1.25 (m, 6 H,
CH2CH2CH2), 0.91 (t, 3 H, J = 7.4 Hz, CH3).
13C NMR (125 MHz, CDCl3): d = 141.5, 140.4, 127.6, 126.8, 126.7,
125.9, 122.8, 121.3, 120.1, 119.1, 116.3, 109.3, 43.4, 31.9, 29.4,
27.4, 22.9, 14.3.
129.5, 129.1, 128.8, 128.0, 127.3, 124.2, 121.6.
MS (EI): m/z (%) = 280 (5, [M+]), 279 (40, [M+]), 278 (8, [M+]), 277
(36, [M+]), 153 (31), 152 (100), 151 (72), 150 (42).
HRMS (EI+): m/z calcd for C12H8BrNO2: 276.9738; found:
276.9733.
Anal. Calcd for C54H60B3N3O3: C, 78.0; H, 7.3; N, 5.1. Found: C,
77.8; H, 7.2; N, 5.0.
2-Bromocarbazole (7)
The above mixture of 4, 5 and 6 [19.2 g, ≡ 5 (14.8 g, 53.1 mmol)]
and (EtO)3P (61.8 g, 371.9 mmol) was refluxed for 10 h. Excess
(EtO)3P was distilled off under vacuum (72–76 °C/9 mm Hg). The
remaining residue was diluted with a 1:1 mixture of MeOH and dis-
tilled H2O to give a precipitate which was filtered off and washed
several times with a 1:1 mixture of MeOH–H2O, and with petro-
leum ether. Column chromatography (petroleum ether and CH2Cl2)
3-Bromocarbazole (12)
Method A: A solution of n-BuLi (2.5 M in hexanes, 2.4 mL, 6.0
mmol) was added to a solution of carbazole (11; 1.0 g, 6.0 mmol) in
THF (50 mL) at –78 °C. The mixture was stirred for 15 min both at
–78 °C and at 20 °C, then cooled to –78 °C and chlorotrimethylsi-
lane (650 mg, 6.0 mmol) was added. The mixture was stirred at
20 °C for 3 h, cooled to –78 °C and Br2 (956 mg, 6.0 mmol) was
added. The mixture was stirred at –78 °C for 1 h, at 20 °C for 2 h
and then quenched with distilled H2O. After removal of solvents,
the solid residue was washed with aq 2 M NaHCO3 (3 × 50 mL),
distilled H2O (3 × 50 mL) and hexane (4 × 100 mL) to give a light-
brown solid. Column chromatography (petroleum ether and
CH2Cl2) gave a mixture of 11, 12 and 13 (1.1 g) in a ratio of 4:5:1,
respectively (by 1H NMR data). After removal of 13 by recrystalli-
zation from CHCl3, a mixture of 11 and 12 was obtained as a white-
1
gave a mixture of 7 and 8 as a white amorphous solid (8.0 g). H
NMR analyses indicated that 94% of the mixture was product 7 (7.5
g, 57% based on 5); Rf 0.38 (petroleum ether–CH2Cl2, 1:1). The 1H,
13C NMR and MS data were in agreement with the literature data.11
The mixture was used in the next step without further purification.
2-Bromo-9-hexylcarbazole (9)
Solid t-BuOK (4.2 g, 37.4 mmol) was added to a solution of the
above product mixture of 7 and 8 [8.0 g, ≡ 7 (7.5 g, 31.2 mmol)] in
anhyd DMF (150 mL). The mixture was stirred for 2 h at 20 °C, and
then 1-bromohexane (7.7 g, 46.8 mmol) was added, followed by
heating at 130 °C for 65 h. The solvent and excess 1-bromohexane
were removed under vacuum (40 °C/9 mm Hg) to leave a light
brown liquid, which was diluted with H2O, and the organic products
were extracted into CH2Cl2 (4 × 50 mL). The combined extracts
were dried (MgSO4) and evaporated under reduced pressure to give
a light brown liquid. Chromatographic purification by eluting with
a mixture of hexane and CH2Cl2 (9:1) gave 9 (10.3 g, 99% based on
7) as a clear oil; Rf 0.39 (petroleum ether–CH2Cl2, 8:1).
1H NMR (500 MHz, CDCl3): d = 8.07 (d, 1 H, J = 7.9 Hz, H-5),
7.94 (d, 1 H, J = 8.3 Hz, H-4), 7.55 (d, 1 H, J = 1.6 Hz, H-1), 7.50
(t, 1 H, J = 7.7 Hz, H-7), 7.40 (d, 1 H, J = 8.2 Hz, H-8), 7.34 (dd, 1
H, J = 8.2, 1.6 Hz, H-3), 7.26 (t, 1 H, J = 7.9 Hz, H-6), 4.23 (t, 2 H,
J = 7.4 Hz, NCH2), 1.85 (p, 2 H, J = 7.4 Hz, NCH2CH2), 1.45–1.25
(m, 6 H, CH2CH2CH2), 0.90 (t, 3 H, J = 6.9 Hz, CH3).
1
floppy solid. H NMR established that 60% of this mixture was
compound 12 (0.32 g, 22%); Rf 0.37 (petroleum ether–CH2Cl2, 1:1).
This mixture was used in the next step without further purification.
The 1H, 13C NMR and MS data for 12 were in agreement with the
literature data.13c,14
Method B: Br2 (30.8 g, 192.5 mmol) was added to a solution of car-
bazole (11; 29.3 g, 175.0 mmol) in DMF (150 mL) at 0 °C and the
mixture stirred for 21 h, while gradually warming to 20 °C. The
mixture was quenched with aq 15% Na2S2O3 solution and then di-
luted with distilled H2O until the products precipitated. The solid
was washed with distilled H2O (4 × 100 mL) and hexane (4 × 100
mL). Recrystallization from CHCl3 gave mixtures of 11 and 12
(16.1 g) as a white solid, 93% of which was the desired compound
12 (15.0 g, 35%) based on 1H NMR data. This mixture was used in
the next step without further purification. The 1H NMR data were in
agreement with the literature.13c,14 Compound 12 was characterized
by single crystal X-ray structural analysis.
13C NMR (125 MHz, CDCl3): d = 141.3, 140.6, 126.0, 122.4, 121.9,
121.8, 121.5, 120.3, 119.3, 119.2, 111.8, 108.9, 43.2, 31.6, 28.8,
26.9, 22.6, 14.0.
12
Crystal Data21
MS (EI): m/z (%) = 332 (16, [M+]), 331 (83, [M+]), 330 (18, [M+]),
C12H8BrN, M = 246.10, monoclinic, space group P21/c (No. 14),
T = 120 K, a = 20.312(3), b = 5.8017(8), c = 7.805(1) Å,
b = 91.75(1)°, V = 919.3(2) Å3, Z = 4, m = 4.42 mm–1, R = 0.037 on
1985 unique data with I>2s(I).
329 (86, [M+]), 261 (15), 260 (97), 259 (17), 258 (100).
HRMS (EI+): m/z calcd for C18H20BrN: 329.0779; found: 329.0779.
9-Hexylcarbazol-2-ylboronic Acid (1)
3-Bromo-9-hexylcarbazole (14)
n-BuLi (1.6 M in hexanes, 23.3 mL, 37.3 mmol) was added drop-
wise to a solution of 2-bromo-9-hexylcarbazole (9; 10.3 g, 31.1
mmol) in anhyd THF (150 mL) at –78 °C. The light-green mixture
was stirred at –78 °C for 2 h, then (i-PrO)3B (17.5 g, 93.2 mmol)
was added and the mixture was stirred for 16 h while allowing the
temperature to rise to 20 °C. Conc. HCl (13.2 mL) was added and
stirring was continued for 2 h to give a clear light-brown solution
which was neutralized (pH 7) with aq 2 M Na2CO3 (85 mL) and
then concentrated under reduced pressure to give a precipitate. The
precipitate was washed several times with H2O and petroleum ether,
respectively, to give compound 1 (7.6 g, 83%) as a white solid, mp
179–181 °C. The C, H, N analysis was obtained upon converting 1
into its boroxine derivative by heating at 70 °C for 2 days.
Solid t-BuOK (1.8 g, 15.6 mmol) was added to a solution of a mix-
ture of 11 and 12 [3.2 g, ≡ 12 (2.9 g, 11.8 mmol)] in anhyd DMF (60
mL). The mixture was stirred for 1 h at 20 °C and then 1-bromohex-
ane (3.2 g, 19.7 mmol) was added. The mixture was heated at
130 °C for 65 h, cooled to 20 °C and quenched with distilled H2O.
Upon evaporation, the residue was diluted with H2O and the organic
products were extracted into CH2Cl2 (4 × 40 mL). The combined
extracts were dried (MgSO4) and evaporated under reduced pres-
sure to give a light-brown liquid. This was chromatographed, elut-
ing with a mixture of hexane and CH2Cl2 (9:1) to give mixtures of
14 and 15 (4.0.g) as a clear oil. 1H NMR data indicated that 90% of
the mixture was compound 14 (3.6 g, 91% based on 12); Rf 0.42
(petroleum ether–CH2Cl2, 8:2). This mixture was used in the next
step without further purification.
1H NMR (500 MHz, CDCl3): d = 8.37 (s, 1 H, H-1), 8.29 (d, 1 H,
J = 7.6 Hz, H-4), 8.22 (d, 1 H, J = 7.6 Hz, H-5), 8.21 (d, 1 H, J = 7.9
Hz, H-3), 7.55 (t, 1 H, J = 7.7 Hz, H-7), 7.48 (d, 1 H, J = 8.3 Hz, H-
Synthesis 2005, No. 10, 1619–1624 © Thieme Stuttgart · New York

PAPER
Syntheses and Reactions of N-Hexylcarbazolboronic Acids
1623
14
13C NMR (125 MHz, CDCl3): d = 158.5, 149.9, 141.5, 141.2, 137.2,
137.1, 126.2, 123.8, 122.8, 122.1, 121.3, 120.9, 120.7, 119.2, 118.1,
109.1, 107.6, 43.4, 31.9, 29.3, 27.2, 22.8, 14.3.
MS (EI+): m/z (%) = 328 (72, [M+]), 257 (100), 244 (26), 129 (30).
HRMS (EI+): m/z calcd for C23H24N2: 328.1940; found: 328.1944.
1H NMR (500 MHz, CDCl3): d = 8.24 (s, 1 H, H-4), 8.07 (d, 1 H,
J = 7.8 Hz, H-5), 7.56 (dd, 1 H, J = 8.6, 1.6 Hz, H-2), 7.52 (t, 1 H,
J = 7.8 Hz, H-7), 7.43 (d, 1 H, J = 8.3 Hz, H-8), 7.29 (d, 1 H, J = 8.6
Hz, H-1), 7.28 (t, 1 H, J = 7.8 Hz, H-6), 4.27 (t, 2 H, J = 7.4 Hz,
NCH2), 1.87 (p, 2 H, J = 7.4 Hz, NCH2CH2), 1.46–1.27 (m, 6 H,
CH2CH2CH2), 0.90 (t, 3 H, J = 7.0 Hz, CH3).
9-Hexyl-3-(pyridin-2-yl)carbazole (18)
13C NMR (125 MHz, CDCl3): d = 141.0, 139.3, 128.5, 126.6, 124.8,
123.3, 122.1, 120.8, 119.4, 111.8, 110.4, 109.2, 43.5, 31.8, 29.1,
27.2, 22.8, 14.3.
Compound 2 (1.9 g, 6.3 mmol), 2-bromopyridine 16 (2.5 g, 15.8
mmol) and Pd(PPh3)2Cl2 (0.3 g, 0.4 mmol) were dissolved in a mix-
ture of toluene (64 mL) and aq 2 M Na2CO3 (32 mL, 64 mmol). The
mixture was degassed several times, heated at 90 °C for 40 h, then
cooled to 20 °C and diluted with distilled H2O. The organic prod-
ucts were extracted with EtOAc (4 × 30 mL). The combined ex-
tracts were dried (MgSO4) and concentrated under reduced pressure
to give a dark-brown solid, which was chromatographed, eluting
with a mixture of petroleum ether and EtOAc (4:1). This was fol-
lowed by Kugelrohr distillation (110 °C/6 × 10–2 mm Hg) to re-
move traces of 16, giving compound 18 (1.5 g, 70%) as a pale
orange oil; Rf 0.24 (CH2Cl2). (Reaction time of 8 h gave 18 in 13%
yield).
1H NMR (300 MHz, CDCl3): d = 8.89 (1 H, s), 8.82 (1 H, d, J = 3.9
Hz), 8.29 (1 H, d, J = 7.5 Hz), 8.20 (1 H, d, J = 8.7 Hz), 7.88 (1 H,
d, J = 6.0 Hz), 7.76 (1 H, m), 7.58–7.46 (3 H, m), 7.35 (1 H, m),
7.23 (1 H, m), 4.29 (t, 2 H, J = 7.4 Hz, NCH2), 1.89 (p, 2 H, J = 6.8
Hz, NCH2CH2), 1.49–1.22 (m, 6 H, CH2CH2CH2), 0.92 (t, 3 H,
J = 7.6 Hz, CH3).
MS (EI): m/z (%) = 332 (12, [M+]), 331 (56, [M+]), 330 (12, [M+]),
329 (56, [M+]), 261 (20), 260 (98), 259 (20), 258 (100).
HRMS (EI+): m/z calcd for C18H20BrN: 329.0779; found: 329.0779.
9-Hexylcarbazol-3-ylboronic Acid (2)
n-BuLi (2.5 M in hexanes, 5.2 mL, 12.9 mmol) was added dropwise
to a mixture of 14 and 15 [4.0 g, ≡ 14 (3.6 g, 10.8 mmol)] in anhyd
THF (100 mL) at –78 °C. The mixture was stirred at –78 °C for 1 h
and then (i-PrO)3B (6.1 g, 32.3 mmol) was added. The mixture was
stirred for 22 h, while gradually warming to 20 °C. Conc. HCl (4.3
mL) was added and stirring continued for 2 h to give a clear blue so-
lution, which was neutralized (pH 7) with aq 2M Na2CO3. The or-
ganic phase was separated and the organic products were extracted
into CH2Cl2 (4 × 30 mL). The combined extracts were dried
(MgSO4) and concentrated under reduced pressure to give a light-
blue solid which was chromatographed (petroleum ether–EtOAc,
1:1) and then recrystallized from EtOAc to afford 2 (2.1 g, 67%
based on 14) as a white solid; mp 182–184 °C. C, H and N analyses
were obtained upon converting 2 into its boroxine derivative by
heating at 70 °C for 2 days; Rf 0.53 (petroleum ether–EtOAc, 1:1).
13C NMR (75 MHz, CDCl3): d = 158.5, 149.7, 141.3, 141.2, 136.9,
130.5, 126.0, 125.0, 123.5, 123.4, 121.3, 120.4, 119.32, 119.29,
109.1, 109.0, 43.3, 31.8, 29.1, 27.2, 22.8, 14.3.
MS (EI+): m/z (%) = 328 (76, [M+]), 257 (100), 243 (25).
HRMS (EI+): m/z calcd for C23H24N2: 328.1940; found: 328.1938.
1H NMR (300 MHz, DMSO-d6): d = 8.55 (s, 1 H, H-4), 7.99 (d, 1
H, J = 7.8 Hz, H-5), 7.87 (dd, 1 H, J = 8.2, 1.6 Hz, H-2), 7.58 [s, 1
H, B(OH)2], 7.41–7.25 (m, 3 H), 7.12 (m, 1 H, H-6), 4.22 (t, 2 H,
J = 7.4 Hz, NCH2), 1.76 (p, 2 H, J = 7.5 Hz, NCH2CH2), 1.38–1.09
(m, 6 H, CH2CH2CH2), 0.76 (t, 3 H, J = 7.1 Hz, CH3).
Anal. Calcd for C23H24N2: C, 84.1; H, 7.4; N, 8.5. Found: C, 83.9;
H, 7.4; N, 8.2.
13C NMR (125 MHz, CDCl3): d = 143.7, 141.0, 133.4, 129.1, 126.1,
123.6, 123.1, 121.0, 120.6, 119.7, 109.2, 108.5, 43.5, 31.9, 29.3,
27.4, 22.9, 14.4.
3-[9,9-Dihexyl-7-(pyridine-2-yl)fluoren-2-yl]-9-hexylcarbazole
(20)
A mixture of 2 (1.0 g, 3.5 mmol), 19 (1.2 g, 2.4 mmol) and
Pd(PPh3)4 (195 mg, 0.17 mmol) dissolved in toluene (40 mL) and
aq 2 M Na2CO3 (20 mL, 40 mmol) was heated at 90 °C for 54 h.
Work-up as described for 18 gave a black liquid. Chromatographic
purification by eluting with a mixture of petroleum ether and
CH2Cl2 removed a fast-running impurity, then gave a foamy white
solid which contained a minor impurity with a similar Rf value. Fur-
ther purification, both by Kugelrohr distillation (140 °C/0.02 mm
Hg) and by column chromatography (petroleum ether–EtOAc,
95:5), afforded 20 (1.22 g, 77%) as a glassy solid; mp 53–54 °C;
Rf 0.23 (petroleum ether–EtOAc, 9:1).
1H NMR (500 MHz, acetone-d6): d = 8.69 (d, 1 H, J = 4.7 Hz, py-
ridyl H-6), 8.55 (s, 1 H), 8.28 (s, 1 H, carbazolyl H-4), 8.23 (d, 1 H,
J = 7.9 Hz), 8.16 (d, 1 H, J = 7.9 Hz, carbazolyl H-5), 8.02 (d, 1 H,
J = 7.9 Hz), 7.96–7.90 (m, 3 H), 7.89–7.83 (m, 2 H), 7.80 (d, 1 H,
J = 7.9 Hz), 7.68 (d, 1 H, J = 8.4 Hz), 7.59 (d, 1 H, J = 8.2 Hz), 7.48
(t, 1 H, J = 7.5 Hz, carbazolyl H-7), 7.31 (t, 1 H, J = 4.7 Hz, pyridyl
H-5), 7.23 (t, 1 H, J = 7.5 Hz, carbazolyl H-6), 4.47 (t, 2 H, J = 7.2
Hz, NCH2), 2.30–2.15 (m, 4 H), 1.91 (p, 2 H, J = 7.5 Hz,
NCH2CH2), 1.42 (p, 2 H, J = 7.6 Hz), 1.38–1.23 (m, 4 H, CH2CH2),
1.16–0.98 (m, 12 H), 0.84 (t, 3 H, J = 7.2 Hz, CH3), 0.80–0.69 (m,
4 H), 0.71 (t, 6 H, J = 7.1 Hz, CH3).
Anal. Calcd for C54H60B3N3O3: C, 78.0; H, 7.3; N, 5.1. Found: C,
78.1; H, 7.4; N, 5.1.
9-Hexyl-2-(pyridin-2-yl)carbazole (17)
Compound 1 (1.5 g, 5.1 mmol), 2-bromopyridine (16; 1.0 g, 6.1
mmol) and Pd(PPh3)2Cl2 (143 mg, 0.2 mmol) were dissolved in a
mixture of toluene (20 mL) and aq 2 M Na2CO3 (10 mL, 20 mmol).
The mixture was degassed several times, then heated at 90 °C for 21
h, cooled to 20 °C and then diluted with distilled H2O. The organic
phase was separated and the organic products were extracted into
CH2Cl2 (4 × 30 mL). The combined extracts were dried (MgSO4)
and concentrated under reduced pressure to give a light-orange liq-
uid, which was chromatographed, eluting with a mixture of petro-
leum ether and CH2Cl2. This was followed by a Kugelrohr
distillation (110 °C/6 × 10–2 mm Hg) to remove traces of 16, giving
compound 17 (1.0 g, 60%) as a pale orange liquid; Rf 0.36 (CH2Cl2).
(Reaction time 8 h gave 17 in 9% yield).
1H NMR (500 MHz, CDCl3): d = 8.77 (d, 1 H, J = 4.5 Hz, pyridyl
H-6), 8.18 (d, 1 H, J = 8.2 Hz, H-4), 8.16 (d, 1 H, J = 0.9 Hz, H-1),
8.14 (d, 1 H, J = 7.6 Hz, H-5), 7.89 (d, 1 H, J = 8.2 Hz, pyridyl H-
3), 7.83 (dd, 1 H, J = 8.2, 1.6 Hz, H-3), 7.80 (t, 1 H, J = 7.8, 1.9 Hz,
pyridyl H-4), 7.50 (dt, 1 H, J = 7.0, 1.2 Hz, H-7), 7.44 (d, 1 H,
J = 8.2 Hz, H-8), 7.28–7.24 (m, 2 H, H-6 and pyridyl H-5), 4.40 (t,
2 H, J = 7.4 Hz, NCH2), 1.93 (p, 2 H, J = 7.4 Hz, NCH2CH2), 1.44
(p, 2 H, J = 7.4 Hz, NCH2CH2CH2), 1.39–1.23 (m, 4 H, CH2CH2),
0.88 (t, 3 H, J = 7.2 Hz, CH3).
13C NMR (125 MHz, CDCl3): d = 158.0, 152.3, 151.9, 149.7, 142.5,
141.7, 141.2, 140.2, 139.3, 137.8, 137.2, 132.9, 126.4, 126.2, 126.1,
125.6, 123.6, 123.2, 122.1, 121.9, 121.5, 121.0, 120.7, 120.5, 120.1,
119.1, 109.2, 109.1, 55.7, 43.5, 40.8, 31.9, 31.8, 30.0, 29.3, 27.3,
24.1, 22.9, 22.8, 14.3.
Synthesis 2005, No. 10, 1619–1624 © Thieme Stuttgart · New York

1624
M. Tavasli et al.
PAPER
Anal. Calcd for C48H56N2: C, 87.22; H, 8.54; N, 4.24. Found: C,
87.24; H, 8.51; N, 4.45.
(3) Wakim, S.; Bouchard, J.; Blouin, N.; Michaud, A.; Leclerc,
M. Org. Lett. 2004, 6, 3413.
(4) (a) Review: Zhang, Y.; Wada, T.; Sasabe, H. J. Mater.
Chem. 1998, 8, 809. (b) Belloni, M.; Manickam, M.; Preece,
J. A. Ferroelectrics 2002, 276, 103.
MS (EI): m/z (%) = 663 (20, [M+]), 662 (66, [M+]), 661 (100, [M+]),
660 (44, [M+]).
(5) (a) Manickam, M.; Cooke, G.; Kumar, S.; Ashton, P. R.;
Preece, J. A.; Spencer, N. Mol. Cryst. Liq. Cryst. 2003, 397,
399. (b) Perea, E.; Lopez-Calahorra, F.; Velasco, D. Liq.
Cryst. 2002, 29, 421.
(6) Bouchard, J.; Wakim, S.; Leclerc, M. J. Org. Chem. 2004,
69, 5705.
fac-Tris[9-Hexyl-3-(pyridin-2-yl)carbazole]iridium(III) (21)
IrCl3 (42.9 mg, 0.12 mmol), 9-hexyl-3-(pyridin-2-yl)carbazole (18;
200 mg, 0.61 mmol), and Na2CO3 (26 mg, 0.24 mmol) in a mixture
of ethylene glycol (4 mL) and distilled H2O (1 mL) were placed in
a reaction vessel and blanketed with argon. The mixture was heated
to 220 °C by microwave irradiation (Personal Chemistry, Emrys
Optimizer, Microwave reactor, 200 W) for 30 min. The mixture was
diluted with H2O (10 mL) and the organic products were extracted
with EtOAc (3 × 15 mL). The combined extracts were dried
(MgSO4) and concentrated under reduced pressure to give the crude
product. The crude product was purified by chromatography by
eluting with a mixture of n-hexane and EtOAc (8:2) to afford 21 (20
mg, 14%) as a bright yellow solid; Rf 0.48 (petroleum ether–
CH2Cl2, 1:1). A pure and a solvated form of 21, grown from a mix-
ture of CH2Cl2 and acetone, was characterized by single crystal
X-ray structural analysis.
(7) (a) Cho, N. S.; Hwang, D.-H.; Jung, B.-J.; Oh, J.; Chu, H. Y.;
Shim, H.-K. Synth. Met. 2004, 143, 277. (b) Kim, B. S.;
Joo, S.-H.; Oh, D.; Cha, S. W.; Choi, D. S.; Lee, C. E.; Jin,
J.-I. Synth. Met. 2004, 145, 229. (c) van Dijken, A.;
Bastiaansen, J. J. A. M.; Kiggen, N. M. M.; Langeveld, B.
M. W.; Rothe, C.; Monkman, A. P.; Bach, I.; Stossel, P.;
Brunner, K. J. Am. Chem. Soc. 2004, 126, 7718.
(8) Dierschke, F.; Grimsdale, A. C.; Müllen, K. Macromol.
Chem. Phys. 2004, 205, 1147.
(9) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.
(10) (a) Cadogan, J. I. G.; Cameron-Wood, M. J. Chem. Soc.
1962, 361. (b) Cadogan, J. I. G.; Cameron-Wood, M.;
Mackie, R. K.; Searle, R. J. G. J. Chem. Soc. 1965, 4831.
(c) Morin, J.-F.; Leclerc, M. Macromolecules 2001, 34,
4680. (d) Dierschke, F.; Grimsdale, A. C.; Müllen, K.
Synthesis 2003, 2470.
1H NMR (500 MHz, acetone-d6): d = 8.63 (s, 3 H), 8.26 (d, 3 H,
J = 8.0 Hz), 8.06 (d, 3 H, J = 8.0 Hz), 7.81 (dd, 3 H, J = 5.5 Hz),
7.73 (td, 3 H, J = 8.5 Hz), 7.26 (m, 6 H), 7.06 (t, 3 H, J = 7.0 Hz),
6.98 (t, 3 H, J = 4.5 Hz), 6.91 (s, 3 H), 3.76 (m, 6 H), 1.43 (m, 6 H),
0.89 (m, 18 H), 0.63 (m, 9 H).
13C NMR (125 MHz, acetone-d6): d = 168.1, 161.9, 148.2, 147.5,
144.4, 140.9, 137.5, 137.0, 125.4, 124.6, 121.8, 119.5, 119.2, 117.8,
117.1, 116.3, 109.2, 43.2, 32.0, 29.2, 27.4, 23.0, 14.2.
MS (MALDI-TOF): m/z calcd for C69H69IrN6 (M+) 1174.5; found:
1774.4.
(11) Percec, V.; Obata, M.; Rudic, J. G.; De B, B.; Glodde, M.;
Bera, T. K.; Magonow, S. N.; Balagurusamy, V. S. K.;
Heiney, P. A. J. Poly. Sci. Part A, Polym. Chem. 2002, 40,
3509.
(12) Li, Y.; Ding, J.; Day, M.; Tao, Y.; Lu, J.; D’iorio, M. Chem.
Mater. 2004, 16, 2165.
Anal. Calcd for C69H69IrN6: C, 70.6; H, 5.9; N, 7.2. Found: C, 70.5;
H, 6.1; N, 6.9.
(13) (a) Kuroki, M. Kogyo Kagaku Zasshi 1967, 70, 63; Chem.
Abstr. 1968, 68, 12802. (b) Pielichowski, J.; Kyzio, J.
Monatsh. Chem. 1974, 105, 1306. (c) Ribou, A.-C.; Wada,
T.; Sasabe, H. Inorg. Chim. Acta. 1999, 288, 134.
(14) Smith, M. B.; Guo, L. (C.).; Okeyo, S.; Stenzel, J.; Yanella,
J.; LaChapelle, E. Org. Lett. 2002, 4, 2321.
(15) (a) Spanggaard, H.; Jørgensen, M.; Almdal, K.
Macromolecules 2003, 36, 1701. (b) Smith, K.; James, D.
M.; Mistry, A. G.; Bye, M. R.; Faulkner, D. J. Tetrahedron
1992, 48, 7479. (c) Bogdal, D.; Lukasiewicz, M.;
Pielichowski, J. Green Chem. 2004, 6, 110.
Crystal Data22
21
C69H69IrN6, M = 1174.50, triclinic, space group P–1 (No. 2),
T = 120 K, a = 13.031(2), b = 20.049(2), c = 23.621(3) Å,
a = 82.45(1), b = 78.17(1), g = 72.15(1)°, V = 5734(1) Å3, Z = 4,
m = 2.38 mm–1, R = 0.082 on 10322 unique data with I>2 s(I).
21·2CH2Cl2·0.5Me2CO
(16) Paliulis, O.; Ostrauskaite, J.; Gaidelis, V.; Jankauskas, V.;
Strohriegl, P. Macromol. Chem. Phys. 2003, 204, 1706.
(17) Tavasli, M.; Bettington, S.; Bryce, M. R.; Al Attar, H. A.;
Dias, F. B.; King, S.; Monkman, A. P. manuscript submitted.
(18) Konno, H.; Sasaki, Y. Chem. Lett. 2003, 32, 252.
(19) For structurally different cyclometalated carbazole
derivatives, see: Igawa S., Takiguchi T., Kamatani A.,
Okada S., Tsuboyama A., Miura K., Moriyama T., Iwawaki
H.; Japanese Patent 2003342284, 2002; Chem. Abstr. 2004,
140, 21334.
(20) For a different synthesis of 5 with no reported spectroscopic
data, see: Badger, G. M.; Sasse, W. F. H. J. Chem. Soc. 1957,
4.
(21) CCDC No.: 257962. Supplementary data available in CIF
format from the authors.
M = 1373.39, triclinic, space group P–1 (No. 2), T = 120 K,
a = 15.331(2), b = 19.532(3), c = 23.946(3) Å, a = 82.57(1),
b = 77.56(1), g = 69.72(1)°, V = 6557(1) Å3, Z = 4, m = 2.25 mm–1,
R = 0.053 on 22361 unique data with I>2s(I).
Acknowledgment
We thank Durham County Council (Project SP/082), CENAMPS
and the University of Durham Photonic Materials Institute for fun-
ding this work.
References
(1) Review: Knölker, H.-J.; Reddy, K. R. Chem. Rev. 2002, 102,
4303.
(2) Nagarajan, R.; Perumal, P. T. Synthesis 2004, 1269; and
references cited therein.
(22) Compound 21, CCDC No.: 260850; compound
21·2CH2Cl2·0.5Me2CO, CCDC No.: 260851.
Supplementary data available in CIF format from the
authors.
Synthesis 2005, No. 10, 1619–1624 © Thieme Stuttgart · New York