Copper-catalyzed synthesis of triarylamines from aryl halides and arylamines

Article abstract of DOI:10.1002/cjoc.201200247

A simple and efficient methodology for the synthesis of triphenylamines has been demonstrated using copper catalyst with a ligand and tripotassium phosphate as the base. The effect of parameters such as catalyst precursors, ligands, bases and solvents were studied and a series of triphenylamines were obtained with moderate to excellent yields in DMF. This reaction displays great functional groups compatibility in the presence of a broad range of functional groups.

Full text of DOI:10.1002/cjoc.201200247

FULL PAPER
DOI: 10.1002/cjoc.201200247
Copper-Catalyzed Synthesis of Triarylamines from Aryl Halides
and Arylamines
Qian, Cunwei*,a(钱存卫)
Xu, Shaojiea(许少杰)
Fang, Donga(方东)
Zong, Qianshou*,b(宗乾收)
a School of Chemistry and Chemical Engineering, Yancheng Teachers University, Yancheng, Jiangsu 224051,
China
b School of Biological and Chemical Engineering, Jiaxing University, Jiaxing, Zhejiang 314001, China
A simple and efficient methodology for the synthesis of triphenylamines has been demonstrated using copper
catalyst with a ligand and tripotassium phosphate as the base. The effect of parameters such as catalyst precursors,
ligands, bases and solvents were studied and a series of triphenylamines were obtained with moderate to excellent
yields in DMF. This reaction displays great functional groups compatibility in the presence of a broad range of
functional groups.
Keywords copper catalyst, Ullmann coupling, triphenylamine, synthesis
Introduction
fully selected combinations of a catalytic amount of
copper sources, bases, and supporting ligands, triaryl-
amines were obtained by the coupling of arylamines
with aryl iodides with good yields under mild conditions.
In addition, bisarylation of substituted anilines with 2
equiv. of an aromatic halide to produce triarylamine
derivatives has been reported with the conventional
Ullmann catalyst, however yields are substantially
poor.[6a] Therefore, the further discovery of new facile
catalytic system for the synthesis of substituted triaryl-
amines is still an area of considerable interest. In this
paper, we report a simple, inexpensive, and effective
catalytic system for the synthesis of substituted triaryl-
amines under mild reaction conditions.
High purity triarylamines find applications in xero-
graphic photoreceptors, as constituents of non-linear
optical chromophores useful in the design of integrated
electrooptic switches and modulators, and as hole-
transport materials for organic electroluminiscent (EL)
display devices.[1] The palladium-catalyzed formation of
carbon-nitrogen bonds is one of the two major methods
available for the synthesis of triphenylamines. However,
palladium-based protocols, although successful,[2] have
some inherent limitations such as moisture sensitivity,
costly metal catalysts, and environmental toxicity. The
other one is the copper-mediated Ullmann triarylamine
synthesis.[3] Major drawbacks of this method are the
requirement of high temperature (200 ℃), sensitivity to
catalyst type and low to moderate yield of amines.[4] In
the past years, significant advances have been achieved
for the copper-catalyzed formation of C—N bond by
use of the new ligands explored, such as organic phos-
phanes,[5a,5b] N-containing aromatic heterocycles,[5c,5d]
diamines,[5e,5f] diols,[5g] triols,[5h] rac-binols,[5i] salicyla-
mides,[5j] β-diketones,[5k,5l] β-keto esters,[5m] imines,[5n]
amino acids,[5o] amino phosphates,[5p] diazaphos-
pholanes,[5q] and (S)-pyrrolidinyl-methylimidazole.[5r]
These advances promote the study of triarylamine syn-
thesis. Some new ligands (e.g. organic phosphanes,[5a]
1,10-phenanthroline,[6a,5b] diazabutadiene,[6b] pyridine,[6c]
2,2'-bipyridine,[6c] 2,2,6,6-tetramethyl-3,5-heptanedio-
nate,[6d] 2-aminophenol,[6e] ect.[6]) have been applied to
the synthesis of various triarylamines. With the care-
Results and Discussion
Since our group have reported that methenamine dis-
played great activity to promote CuI catalyzed C—O
bond fortmation,[7] we reasoned that the coupling of
iodobenzenes and diarylamines could formate C—N
bond by the use of methenamines as a ligand. The in-
vestigation was initiated by using the coupling of iodo-
benzenes and diarylamines as a model reaction.
As shown in Table 1, methenamines showed moder-
ate potency for the copper-catalyzed coupling of iodo-
benzenes and diarylamides with 2 equiv. of K3PO4 as
bases at 140 ℃ (Table 1, Entry 1). However, when the
reaction was carried out with 3.0 mmol of K3PO4 as
base, an excellent yield (93%) was obtained without
other changes (Table 1, Entry 2). While the reaction
*
E-mail: qiancunwei@163.com, zongqs@iccas.ac.cn; Tel.: 18962033519; Fax: 0086-0515-88233188
Received March 13, 2012; accepted May 29, 2012.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201200247 or from the author.
Chin. J. Chem. 2012, 30, 1881—1885
© 2012 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Qian et al.
FULL PAPER
OH
gave low yields at 120 ℃ (Table 1, Entry 3). Then the
catalytic efficiency of L1 (methenamine), L2 (TMEDA),
L3 (8-hydroxyquinoline), L4 (quinoline) and L5 (2,4-
dihydroxyquinoline) for the N-arylation of diaryl-
amimes was compared under the combination of 5%
CuI, 5% ligands and 300% tripotassium phosphate in
DMF at 120 ℃. The results disclosed that the desired
triphenylamines could be obtained in yields ranging
from 33%—72% when L1, L2, L3, L4 and L5 was em-
ployed (Table 1, Entries 3 and 5—8). The best results
were achieved when the reaction was performed in the
presence of L3, furnishing triphenylamines in 72% yield
(Table 1, Entry 6). However, only trace amounts of the
product could be obtained in the absence of the ligand
(Table 1, Entry 4). The catalytic activity of cuprous salts
was compared and the choice of the copper catalyst did
not appear to be critical; CuCl, CuBr, CuI and CuCl2
gave similar results (Table 1, Entries 6 and 9—11). The
use of Cu2O led to slightly low conversions (Table 1,
Entry 12). This might be due to the low solubility of
Cu2O. Whereas no desired coupling product was ob-
tained in the absence of copper salts (Table 1, Entry 13).
Base influenced the progress of the reaction greatly. The
highest yield was obtained when 300% K3PO4 was used
(Table 1, Entries 10 and 17). While other bases (K2CO3,
Cs2CO3 and Na2CO3) were tested, triphenylamine was
obtained in much lower yields (Table 1, Entries 14—16).
Of the solvents investigated, DMF was found to be the
most effective, whereas toluene was ineffective (Table 1,
Entries 18 and 21) and low yield was achieved in
1,4-dioxane or CH3CN (Table 1, Entries 19 and 20). A
slight excess of the phenol was employed (0.5 equiv.
excess) since the use of 1.0 equiv. resulted in very slow
conversion as the reaction neared completion. Moreover,
the results also showed that a better yield (86%) was
acquired when the amount of CuCl and L3 added up to
7.5 mol% relative to iodobenzene (Table 1, Entry 22).
As previously reported,[6] aryl iodides displayed higher
reactivity than aryl bromides, and aryl chlorides were
unreactive in the coupling reactions (Table 1, Entries 23
and 24). Therefore, the optimized conditions employed
7.5 mol% of CuI, 7.5 mol% of L3 (8-hydroxyquinoline),
and 3 equiv. of K3PO4 relative to iodobenzene in DMF
under argon.
N
N
N
N
N
N
N
L1 Methenamine
N
L3 8-Hydroxyquinoline
L
2 TMEDA
HO
N
OH
L5 2,4-Dihydroxyquinoline
L
4 Quinoline
Figure 1 Structures of ligands.
Table 1 Effect of ligand, catalyst, base, and solvent on the cou-
pling of diarylamides with iodobenzene
I
ligand, Cu salt, T
+
NH
N
solvent, base, 24 h
Entry Ligand/mol%
Copper salt/mol%
CuCl, 5%
CuCl, 5%
CuCl, 5%
CuCl, 5%
CuCl, 5%
CuCl, 5%
CuCl, 5%
CuCl, 5%
CuCl2, 5%
CuI, 5%
Yieldb/%
62
1c,d
2d
3
L1, 5%
L1, 5%
L1, 5%
—
93
58
4
Trace
51
5
L2, 5%
L3, 5%
L4, 5%
L5, 5%
L3, 5%
L3, 5%
L3, 5%
L3, 5%
L3, 5%
L3, 5%
L3, 5%
L3, 5%
L3, 5%
L3, 5%
6
72
7
33
8
53
9
74
10
11
12
13
14e
15f
16g
17h
18i
76
CuBr, 5%
Cu2O, 5%
—
70
44
0
CuI, 5%
38
CuI, 5%
26
CuI, 5%
Trace
51
CuI, 5%
CuI, 5%
36
19j,k L3, 5%
20 i,l L3, 5%
21i,m L3, 5%
CuI, 5%
26
CuI, 5%
10
With the optimal conditions, the reactivities of sev-
eral representative substituted aryl iodides in the reac-
tions with diarylamines were examined. As shown in
Table 2, the couping of 2-iodotoluene and methyl
2-iodobenzoate with diarylamine gave corresponding
products in 62% and 46% yields (Table 2, Entries 2 and
6). This might be attributable to the influence of steric
hindrance. Electronic effects were observed when vari-
ous iodobenzenes were submitted to coupling with di-
arylamines. For instance, N-arylation of aryl iodides
bearing electron-donating substituents with diaryl-
amines was shown to give the corresponding products in
yields of 55%—76% (Table 2, Entries 1, 4 and 5),
whereas the coupling of 1-iodo-4-chlorobenzene with
CuI, 5%
0
22
23n
24r
a
L3, 7.5%
L3, 7.5%
L3, 7.5%
CuCl, 7.5%
CuCl, 7.5%
CuCl, 7.5%
86
32
0
General reaction conditions: 1.5 mmol of diphenylamine, 1.0
mmol of ArX, 3.0 mmol of K3PO4, 1.5 mL of anhydrous DMF at
b
c
120 ℃. Isolated yield. Reaction carried out with 2.0 mmol of
K3PO4 as base. d At 140 ℃. e K2CO3 was used in place of K3PO4.
f Cs2CO3 was used in place of K3PO4. g Na2CO3 was used in place
of K3PO4. h Reaction carried out with 4.0 mmol of K3PO4 as base.
At 100 ℃. At 80 ℃. k In acetonitrile. In 1,4-dioxane. m In
toluene. bromobenzene was used in place of iodobenzene.
r Chlorobenzene was used in place of iodobenzene.
i
j
l
n
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Chin. J. Chem. 2012, 30, 1881—1885

Copper-Catalyzed Synthesis of Triarylamines from Aryl Halides and Arylamines
diarylamines gave excellent yield of the desired product
under our optimal conditions (Table 2, Entry 3).
Table 3 Cu-catalyzed double N-arylation of anilines with aryl
iodides
I
NH2
R1
R1
Table 2 Cu-catalyzed coupling reaction of aryl iodides with
diarylamines.
K3PO4, 120 oC
L3, CuCl, DMF
N
2
2R1
+
R
R2
I
R
L3, CuCl, 120 oC
+
NH
N
DMF, K3PO4, 24 h
Entry R1
R2
H
Product
Yieldb/%
68
R
Yieldb/%
76
N
Entry
1
R
Product
1
H
p-CH3
o-CH3
p-Cl
Cl
N
N
2
p-Cl
H
H
76
2
3
4
5
6
62
89
55
69
46
N
Cl
N
O
3
4
o-OCH3
59
91
O
N
Cl
O
H
o-OCH3
o-OCH3
o-OCH3
o-OCH3
N
N
p-OCH3
N
O
O
N
O
O
5
6
7
p-CH3
o-CH3
p-Cl
85
68
90
o-OCH3
COOCH3
o-COOCH3
N
N
a General reaction conditions: 1.5 mmol of diphenylamine, 1.0
mmol of ArX, 3.0 mmol of K3PO4, 0.075 mmol CuCl, 0.075
mmol L3, 1.5 mL of anhydrous DMF at 120 ℃. b Isolated yield.
Cl
N
O
O
Next, our interest turned to extending the scope of
this protocol to the double N-arylation of anilines for the
preparation of triarylamines. To lessen the byproduct
(diphenylamines), 4 equiv. of K3PO4 and 2.5 equiv. of
substituted iodobenzenes, relative to anilines, were used
in the reaction. Likewise, to gain good results of the
double N-arylation of anilines in 24 h, 15 mol% copper
salts and 8-hydroxyquinoline, relative to anilines, were
introduced. So that the modified standard conditions
employed 15 mol% of CuI, 15 mol% of methenamine,
Cl
O
N
O
8
o-OCH3
o-OCH3
48
Chin. J. Chem. 2012, 30, 1881—1885
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Qian et al.
FULL PAPER
Continued
Yieldb/%
Continued
Yieldb/%
Entry R1
R2
Product
Entry R1
R2
Product
O
N
O
O
17
o-OCH3
p-Cl
56
N
9
p-OCH3
o-OCH3
66
O
Cl
a General reaction conditions: 1 mmol of aniline, 2.5 mmol of
ArX, 4 mmol of K3PO4, 0.15 mmol CuCl, 0.15 mmol L3, 2.5 mL
of anhydrous DMF at 120 ℃. b Isolated yield.
O
COOCH3
N
and 4 equiv. of K3PO4 relative to anilines in DMF under
argon. Using this modified protocol, we were able to
synthesize a variety of triphenylamines in good yields
from the readily available anilines and aryl iodides. The
results were listed in Table 3. The results indicated the
double N-arylation of anilines with various substituted
aryl iodides gave only moderate to good product yields
(59%—76%) (Table 3, Entries 1—3). The results re-
vealed that an electron-donating group in the aniline
favored the coupling reactions. For example, when
o-methoxyaniline was submitted to coupling with vari-
ous aryl iodides, the reaction gave good to excellent
yields (66% — 91%) with the exception of methyl
2-iodobenzoate and 2-iodoanisole, which led to moder-
ate yields (43%, 48%) (Table 3, Entries 4—10). As
above mentioned, this might be due to the influence of
steric hindrance. p-Methoxyaniline, as a reactant, gave
the expected product in 61%—79% yields (Table 3,
Entries 11 and 12) too. Similarly, the coupling of
o-toluidine and 1-iodo-4-chlorobenzene (or 2-iodoto-
luene) gave a good yield of the desired product under
our modified optimal conditions (Table 3, Entries 13
and 14). It was noteworthy that the coupling reaction of
p-chloroaniline with varied substituted aryl iodides ob-
tained good yields (56%—76%), albeit p-chloroaniline
is less reactive than anilines bearing electron-donating
substituents for arylation (Table 3, Entries 15—17).
In summary, an efficient and convenient method for
the synthesis of triarylamines has been developed
through N-arylation of secondary and primary aryl-
amines catalyzed by the copper salt. The protocol dis-
plays excellent functional group compatibility in the
presence of a broad range of functional groups under
mild conditions. The further study on design and appli-
cation of new ligands in copper based Ullmann-type
coupling reaction is currently ongoing.
10
11
o-COOCH3 o-OCH3
43
61
O
COOCH3
H
p-OCH3
N
O
O
Cl
N
12
p-Cl
p-OCH3
79
Cl
O
N
13
o-OCH3
o-CH3
58
O
Cl
N
14
15
p-Cl
o-CH3
76
71
76
Cl
Cl
Cl
N
H
p-Cl
Experimental
Cl
All the reactions were carried out in reaction tube
under argon atmosphere. Reaction temperatures were
controlled by temperature modulator; Thin-layer
chromatography (TLC) was performed using silica gel
60 F254 precoated plates (0.25 mm) and visualized by
N
16
p-Cl
p-Cl
Cl
1
UV fluorescence lamp. H NMR and 13C NMR spectra
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Chin. J. Chem. 2012, 30, 1881—1885

Copper-Catalyzed Synthesis of Triarylamines from Aryl Halides and Arylamines
were recorded on a 400 MHz instrument. Spectra were
reported relative to Me4Si (δ 0.0) or residual CDCl3 (δ
7.26). 13C NMR were reported relative to CHCl3 (δ
77.16). High resolution mass spectra (HRMS) were re-
corded on mass spectrometer.
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Typical representative experimental procedure
(a) 8-Hydroxyquinoline (0.075 mmol, 10.8 mg),
CuCl (0.075 mmol, 7.5 mg), diphenylamine (1.5 mmol,
255 mg) and K3PO4 (3.0 mmol, 638 mg) were added to
a screw-capped Schlenk tube. The tube was then evacu-
ated and backfilled with argon (three cycles). Iodoben-
zene (1 mmol, 0.11 mL) and dry DMF (1.5 mL) were
added by syringe at room temperature. The reaction
mixture was stirred at needed temperature (120 ℃) for
24 h. The reaction mixture was allowed to reach room
temperature and then diluted with dichloromethane (10
mL). The slurry was filtered, and filter cake was washed
with 10 mL of dichloromethane. The solvent was re-
moved in vacuo, and the residue was purified by column
chromatography on silica gel to afford the desired
product (triarylamine).
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(b) 8-Hydroxyquinoline (0.15 mmol, 21.6 mg), CuCl
(0.15 mmol, 15 mg) and K3PO4 (4.0 mmol, 0.85 g) were
added to a screw-capped Schlenk tube. The tube was
then evacuated and backfilled with argon (three cycles).
Anilines (1 mmol, 0.091 mL), iodobenzene (2.5 mmol,
0.275 mL) and dry DMF (2.5 mL) were added by sy-
ringe at room temperature. The reaction mixture was
stirred at needed temperature (120 ℃) for 24 h. The
reaction mixture was allowed to reach room temperature
and then diluted with dichloromethane (10 mL). The
slurry was filtered, and filter cake was washed with 10
mL of dichloromethane. The solvent was removed in
vacuo, and the residue was purified by column chroma-
tography on silica gel to afford the desired product (tri-
arylamine).
Triarylamine (Table 1 and Table 3, Entry 1)
1
White solid, m.p. 126—127 ℃; H NMR (400 MHz,
CDCl3) δ: 7.01—7.05 (m, 3H), 7.12 (d, J＝7.2 Hz, 6H),
7.27 (t, J＝7.6 Hz, 6H); 13C NMR (100 MHz, CDCl3) δ:
147.8, 129.2, 124.1, 122.6.[8]
Acknowledgement
We are grateful to Yancheng Teachers University
and Key Laboratory of Organic Synthesis of Jiangsu
Province for the financial support (Nos. 6106053058,
620610C448, KJS1112).
(Cheng, F.)
Chin. J. Chem. 2012, 30, 1881—1885
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1885