Synthesis of symmetrical dicarbazole-biphenyls, components of phosphorescentorganic light-emitting diodes (PHOLEDs) using organocuprates

Article abstract of DOI:10.1007/s10593-011-0800-6

An effective one-stage method is proposed for obtaining symmetrical dicarbazole-biphenyls, components of phosphorescent organic light-emitting diodes through organocuprates of the corresponding N-(bromophenyl)carbazoles. The reaction products were obtained in moderate to high yields.

Full text of DOI:10.1007/s10593-011-0800-6

Chemistry of Heterocyclic Compounds, Vol. 47, No. 5, August 2011 (Russian original Vol. 47, No. 5, May, 2011)
SYNTHESIS OF SYMMETRICAL
DICARBAZOLE-BIPHENYLS,
COMPONENTS OF PHOSPHORESCENT
ORGANIC LIGHT-EMITTING DIODES (PHOLEDs)
USING ORGANOCUPRATES
1
,2
1
1
G. V. Zyryanov *, I. S. Kovalev , I. N. Egorov ,
1
1,2
V. L. Rusinov , and O. N. Chupakhin
An effective one-stage method is proposed for obtaining symmetrical dicarbazole-biphenyls, compo-
nents of phosphorescent organic light-emitting diodes through organocuprates of the corresponding
N-(bromophenyl)carbazoles. The reaction products were obtained in moderate to high yields.
Keywords: dicarbazole-biphenyl, Gilman cuprate, Lipshutz cuprate, cross coupling, lithiation, energy of
the triplet state.
Recently phosphorescent organic light-emitting diodes (PHOLEDs) have attracted significant attention
due to the theoretical possibility of achieving high (up to 100%) quantum efficiency through simultaneous
electrogeneration of triplet and singlet excitons [1–4]. With the aim of achieving highly efficient electrophos-
phorescence and reducing such undesirable factors as triplet–triplet annihilation or concentration quenching of
luminescence, phosphorescent emitters, which as a rule are complexes of heavy metals, are introduced into basic
material [5–7]. 4,4'-Dicarbazole-biphenyls are traditionally used as basic material for PHOLEDs due to the high
energy of the triplet state and a high capacity for transporting holes [8–10]. In addition, isomeric dicarbazole-
biphenyls such as 3,3'- and particularly 2,2'-dicarbazole-biphenyls, theoretically are more promising materials
for PHOLEDs in connection with potentially higher values of triplet state energy, due to the lower conjugation
degree of (hetero)aromatic rings. However, the use of traditional synthetic methods successfully applied for the
synthesis of 4,4'-dicarbazole-biphenyl namely cross coupling of commercially available diiodo- or dibromobi-
phenyl according to Ullman or to Buchwald, is significantly limited by the commercial availability
_
______________
Dedicated to Academician V. N. Charushin on his 60th birthday.
*
To whom correspondence should be addressed, e-mail: gvzyryanov@gmail.com.
1
Ural Federal University named after First President of Russia B. N. Yeltsin, 19 Mira Str., Yekaterinburg
20002, Russia.
6
2
I. Ya. Postovskii Institute of Organic Synthesis, Ural Branch of the Russian Academy of Sciences,
2 Akademicheskaya/20 S. Kovalevskoi Str., Ekaterinburg 620990, Russia; e-mail: chupakhin@ios.uran.ru
2
______________________________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 692–695, May, 2011. Original
article submitted March 29, 2011.
0
009-3122/11/4705-0571©2011 Springer Science+Business Media, Inc.
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of the starting 3,3'- and 2,2'-dihalobiphenyls and also by low yields, as a result of significant steric difficulties
11].
[
In the present study we have proposed a highly effective one-stage procedure for obtaining symmetrical
,2'-, 3,3'-dicarbazole-biphenyls 1a,b and also 4,4'-dicarbazole-biphenyl (1c) consisting of the direct cross
2
coupling of corresponding aromatic Gilman [12] cuprates 2a–c and Lipshutz [13, 14] cuprates 3a–c in THF
o
solution in an argon atmosphere at –78 C with subsequent warming to room temperature. The cross-coupling
products were obtained in 50–76% yield. Cuprates were generated in situ by the action of copper(II) chloride or
copper(I) cyanide/benzoquinone on solutions of lithium salts obtained by interacting the appropriate
o
N-(bromophenyl)carbazoles 4a–c with a solution of t-BuLi in THF in an argon atmosphere at –78 C.
1
Characteristic signals for the carbazole fragment were observed in the H NMR spectra of compounds
1
a–c as multiplets in the regions of 8.10–8.19, 7.60–7.90, and 7.24–7.34 together with the resonance of protons
of the aromatic fragment as a multiplet in the 7.30–7.60 ppm region. A peak for the molecular ion was present in
the electron impact (EI) mass spectra of compounds 1a–c.
Theoretical calculations and preliminary experimental data have demonstrated the high prospects of
using dicarbazole-biphenyls 1a–c as components of PHOLED.
EXPERIMENTAL
1
The H NMR spectra were recorded on a Bruker DRX-400 (at 400 MHz) in CDCl
3
, internal standard
was TMS. The TLC analysis was carried out on Merck silica gel 60 F254 plates using UV light. Column
chromatography was carried out using Merck silica gel 60. Melting points were measured on a Boetius
instrument. Electron-impact mass spectra were recorded on a Varian MAT 311A instrument. All synthetic
procedures were carried out in an atmosphere of dry argon.
The starting substances were synthesized by known procedures or are commercially available.
Dicarbazole-biphenyls 1a–c. A. A 1.5 M solution (0.4 ml, 0.6 mmol) of t-BuLi in pentane was added
o
dropwise to a solution of compound 4a–c (0.32 g, 1 mmol) in dry freshly distilled THF (30 ml) at –78 C during
o
3
0
0 min. The obtained solution was maintained for 1 h at –78 C, after which freshly calcined CuCl
2
(0.067 g,
.5 mmol) was added. The mixture was stirred until complete solution of the solid, then stirred at room
temperature for 12 h. Water (30 ml) was added, and the mixture extracted with ethyl acetate (3×10 ml). The
organic extracts were washed with water (2×10 ml), with 10% aqueous citric acid solution (2×10 ml), with
saturated NaCl solution (10 ml), and dried over Na SO for 24 h. The solution was filtered, evaporated to dry-
2
4
ness in vacuum, and the residue recrystallized from acetonitrile.
B. A 1.5 M solution (0.75 ml, 1.1 mmol) of t-BuLi in pentane was added during 30 min to a solution of
o
compound 4a–c (0.32 g, 1 mmol) in dry freshly distilled THF at –78 C. The obtained solution was maintained
o
for 1 h at –78 C, after which CuCN (0.045 g, 0.5 mmol) was added. The mixture was warmed to room
temperature and stirred until complete solution of the solid. After this 1,4-benzoquinone or 2,3,5,6-tetramethyl-
1
,4-benzoquinone (1.5 mmol) was added at room temperature and the obtained solution stirred for 3 h. The
reaction mixture was then worked up as in method A.
,2'-Dicarbazole-1,1'-biphenyl (1a) [11]. Yield 0.1 g (41%, method A), 0.3 g (62%, method B);
2
o
o
mp 242–244 C) (lit. mp 243–244.6 C [11]).
,3'-Dicarbazole-1,1'-biphenyl (1b). Yield 0.15 g (61%, method A), 0.41 g (85%, method B);
mp >250 C (acetonitrile). H NMR spectrum, δ, ppm (J, Hz): 7.24–7.34 (8H, m, (ArH+CDCl )); 7.39–7.53 (8H,
3
o
1
3
1
3
m, 2C
6
H
4
6 4
); 7.60–7.90 (8H, m, 2C H ); 8.19 (4H, d, J = 7.6, H Ar). C NMR spectrum, δ, ppm: 109.8; 120.0;
1
20.3; 123.4; 125.7; 126.0; 126.3; 126.7; 130.3; 134.5; 140.9; 142.8. Mass spectrum (70 eV), m/z (I ,%): 484
rel
+
(
100) [M] . Found, %: C 89.01; H 5.05. C H N . Calculated, %: C 89.23; H 4.95.
3
6
24
2
4
,4'-Dicarbazole-1,1'-biphenyl (1c) [15, 16]. Yield 0.22 g (91%, method A), 0.45 g (93%, method B);
o
o
mp > 250 C (lit. mp 272 C [17]).
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The work was carried out with the support of a grant from the State Foundation for Leading Scientific
Schools (НШ-65261.2010.3) and State contract of the Ministry of Education and Science of the Russian
Federation No. 02.740.11.0260.
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