Synthesis of triphenylamine-modified arylates and ketones via suzuki coupling reactions

Article abstract of DOI:10.1080/00397911003706982

A series of triphenylamine-mdified arylates and ketones were synthesized via Pd-catalyzed Suzuki coupling reaction of triphenylamine boronic acid with aryl bromide. The triphenylamine boronic acid was synthesized by iodization of 4-bromoaniline, Ullmann reaction of 1-bromo-4-iodobenzene with diphenylamine, and boronic acidification of 4-bromotriphenylamine.

Full text of DOI:10.1080/00397911003706982

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Synthesis of Triphenylamine-Modified
Arylates and Ketones via Suzuki Coupling
Reactions
Jian Wang a , Chang-Jian Yang a , Hua-Nan Peng a , Yang-Sheng Deng
a & Xi-Cun Gao a
a Department of Chemistry, School of Science, Nanchang University,
Nanchang, China
Published online: 25 Feb 2011.
To cite this article: Jian Wang , Chang-Jian Yang , Hua-Nan Peng , Yang-Sheng Deng & Xi-Cun Gao
(2011) Synthesis of Triphenylamine-Modified Arylates and Ketones via Suzuki Coupling Reactions,
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 41:6, 832-840
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Synthetic Communications1, 41: 832–840, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911003706982
SYNTHESIS OF TRIPHENYLAMINE-MODIFIED
ARYLATES AND KETONES VIA SUZUKI COUPLING
REACTIONS
Jian Wang, Chang-Jian Yang, Hua-Nan Peng,
Yang-Sheng Deng, and Xi-Cun Gao
Department of Chemistry, School of Science, Nanchang University,
Nanchang, China
GRAPHICAL ABSTRACT
Abstract A series of triphenylamine-mdified arylates and ketones were synthesized via
Pd-catalyzed Suzuki coupling reaction of triphenylamine boronic acid with aryl bromide.
The triphenylamine boronic acid was synthesized by iodization of 4-bromoaniline, Ullmann
reaction of 1-bromo-4-iodobenzene with diphenylamine, and boronic acidification of
4-bromotriphenylamine.
Keywords Arylates; ketones; Suzuki-coupling; triphenylamine; triphenylamine boronic
acid
INTRODUCTION
Triphenylamine derivatives have potential applications in two-photon dynamic
therapy,[1] holographic optical devices,[2] and three-dimensional optical data
storage[3] and have been used extensively as hole transport materials in organic
light-emitting diodes (OLEDs).[4,6] In OLEDs, the triphenylamine moiety can also
be used to chemically modify the emissive material with charge-transporting
property for a balance of charge injection and transport.[7–10] The general way of
synthesizing triphenylamine derivatives is the Ullmann reaction.[11–13] However,
the reaction requires high temperatures and a long time, yet the yield is not always
satisfactory.[13] For example, if the reaction system contains aromatic heterocycles,
the heterocycle ring may become unstable because of the high reaction temperature
Received December 9, 2007.
Address correspondence to Xi-Cun Gao, Department of Chemistry, School of Science, Nanchang
University, 999 Xue Fu Road, Hong-Gu-Tan New District, Nanchang 330031, China. E-mail: xcgao@
ncu.edu.cn
832

TRIPHENYLAMINE-MODIFIED ARYLATES AND KETONES
833
and the base. Suzuki coupling recently has become a widely used synthetic tool for
the formation of sp2-sp2 carbon–carbon bonds on account of its moderate reactive
condition and good yields.[14–16] Research groups[17–19] have concentrated their
efforts on the development of new and more efficient catalytic systems for Suzuki
coupling, yet very few results have been reported on the Suzuki coupling reaction
of triphenylamine boronic acid and b-diketone derivatives. In this communication,
we report the synthesis of a series of triphenylamine-modified arylates and ketones
via Suzuki coupling reactions. b-Diketones have been widely used as extraction
reagents[20] and coordinating ligands with a variety of metal ions for optoelectronic
materials.[21–26]
RESULTS AND DISCUSSION
The reaction route and conditions are summarized in Schemes 1 and 2 and
Table 1 respectively. We furnished the synthesis by varying the solvent, catalyst, tem-
perature, base, and amount of reagent. As shown in Scheme 1, compound 3 was eas-
ily obtained by diazotization and iodination. The key to synthesis of 4 via Ullmann
reaction is the choice of catalyst. If the catalyst is too active (e.g., CuI, Cu powder,[11]
Pd[27]), both the –Br and the –I atom in
will react with diphenylamine by a
C-N coupling reaction, leading to impurity and poor yield. In our experiment, CuCl
is an appropriate catalyst to obtain 4.
Recently, 5 was prepared by Grignard reaction of 4, but the yield is poor (only
50%).[28] When we use trimethyl borate and n-butyl lithium, the yield increased to
83%. In our experience, n-butyl lithium should be added dropwise via a syringe over
1 h, and the mixture should be stirred for an additional 2 h while the temperature is
held at ꢀ78 ꢁC. Otherwise, the yield would be reduced markedly.
In synthesizing the materials listed in Scheme 2, three general rules can be con-
cluded from our experiment: (1) both the original material and the product must
endure the base and solvent; otherwise, decomposition caused by base and solvent
will severely cut the yield, as in the cases of 7e–g. In these cases, we previously used
the popular toluene=ethanol=H2O as the solvent, but nothing was obtained. When
the solvent was changed to anhydrous tetrahydrofuran (THF) for 7f and 7g or anhy-
drous ethanol for 7e and Na2CO3, was changed to K2CO3, the yield was markedly
Scheme 1. The synthetic route to 4-(diphenylamino)benzene boronic acid.

834
J. WANG ET AL.
Scheme 2. Reaction routes to the triphenylamine-modified arylates and ketones.

TRIPHENYLAMINE-MODIFIED ARYLATES AND KETONES
835
Table 1. Suzuki coupling reactions of 5 and 6
Aryl
Entrya bromides
Temp. Time
(ꢁC)
Yield
Product (%)b
Catalyst
Base
Solvent
(h)
1c
6a
6b
6c
6d
Pd(PPh3)4 Na2CO3 Toluene=ethanol=H2O
Pd(PPh3)4 Na2CO3 Toluene=ethanol=H2O
Pd(PPh3)4 Na2CO3 Toluene=ethanol=H2O
Pd(PPh3)4 Na2CO3 Toluene=ethanol=H2O
90
90
90
90
80
80
90
60
60
90
50
50
50
90
12
20
24
24
24
8
7a
7b
7c
7d
90
80
88
21
52
84
0
2c
3c
4c,d,e
Pd(PPh3)4 Ethanol=H2O
Pd(OAc)2 Ethanol=H2O
Pd(PPh3)4 Na2CO3 Toluene=ethanol=H2O
5c
6e
6f
24
36
36
24
36
36
36
24
7e
7f
Pd(PPh3)4 K2CO3 Anhydrous ethanol
Pd(OAc)2 K2CO3 Anhydrous ethanol
Pd(PPh3)4 Na2CO3 Toluene=ethanol=H2O
21
76
0
6c,e
Pd(PPh3)4 K2CO3
Pd(OAc)2 K2CO3
Pd(OAc)2 K2CO3
Anhydrous THF
Anhydrous THF
Anhydrous THF
25
73
75
60
7e
8c,e
6g
6h
7g
7h
Pd(PPh3)4 Na2CO3 Toluene=ethanol=H2O
aThe reactions were carried out utilizing 3% (mol) of Pd catalyst, 1.0 equiv. of 5, 1.5 equiv. of 6, and 3
equiv. of base under N2.
bIsolated yield.
cThe ratio in volume for toluene, ethanol, and H2O was 5:3:1.
dThe ratio in volume for ethanol and H2O was 3:1.
e4 equiv. of base was used.
increased to more than 70%. However, as the anhydrous solvent was used, the solu-
bility of K2CO3 was reduced and more reaction time was needed (Table 1). (2) The
bulky triphenylamine moiety has negligible steric effect on the overall production
yield. In the cases of 7a–d, our yields are comparable to those reported in the litera-
ture[16–18] in which no such bulky moiety was used. The slightly lower yield for 7b
might be caused by the two additional active sites of –Br in 6b. The three –Br atoms
will inevitably react with the boric acid with equal chances and result in undesirable
products. Therefore, product 7b cannot be controlled simply by the 1:1 ratio of the
reaction materials. Because of the weak acidity of 7d and 7f–7h, increased amounts
of CO23ꢀ were used (refer to the enol form and ketone form of 7f–h in the literature).
(3), Pd(OAc)2 is better than Pd(PPh3)4 for 7d–g, in which the solvent was changed
from toluene to ethanol.
In summary, we have synthesized eight triphenylamine-modified arylates con-
taining ketones using the Suzuki coupling reaction. The reaction conditions have
been slightly modified in view of the structure of the product, which includes the
appropriate choice of solvent, catalyst, and base and lengthened reaction time. Both
the arylates and ketones can be further tuned for optoelectronic materials.
EXPERIMENTAL
All the reagents are commercially available and used as purchased. Infrared
1
(IR) spectra were measured either in liquid or as a KBr pellet. H NMR was col-
lected by a Bruker 400-MHz spectrometer in CDCl3 or dimethylsulfoxide (DMSO).
Elemental analyses were obtained using a flash EA 1112 automatic elemental
analysis instrument.

836
J. WANG ET AL.
1-Bromo-4-iodobenzene (3)
A 250-mL, three-necked, round-bottomed flask fitted with an electromagnetic
stirrer was charged with 17.2 g of 1 (0.1 mol) and 21 mL of hydrochloric acid
(12 mol ꢂ Lꢀ1). This solution was then cooled in a beaker with an ice–salt mixture.
With vigorous stirring, a solution of 7 g (0.1 mol) sodium nitrite (2.5 mol ꢂ Lꢀ1) was
added (temp. ꢀ5 ꢁC). Two hours later, the diazonium salt was added into a solution
of 16 g (0.1 mol) potassium iodide (2 mol ꢂ Lꢀ1). The reaction mixture was stirred for
about 3 hs. The crude product was filtered out, washed with water, and purified by
silica-gel column chromatography using petroleum ether as the eluent. Recrystalliza-
tion from ethanol afforded 22.9 g (81%) of white crystalline powder. Mp 90–92 ꢁC.
N,N-Diphenyl-4-bromoaniline (4)
A 250-ml, three-necked, round-bottomed flask fitted with an electromagnetic
stirrer, a reflux condenser, and a nitrogen inlet was charged with 11.3 g of 3
(0.04 mol), 6.76 g of diphenylamine (0.04 mol), 6.8 g of potassium hydroxide (KOH,
0.12 mol), 2.01 g of CuCl (0.02 mol), 0.7 g of phenanthroline (4 mmol), and toluene=
o-xylene (v=v, 1:1, 100 mL). The resulting mixture was heated to reflux with stirring
under nitrogen at approximately 120 ꢁC for 48 h. After cooling down, the crude pro-
duct was isolated by filtering off the inorganic soilds, distilling out solvent under
reduced pressure, then purifing by silica-gel column chromatography using petroleum
ether as the eluent. Recrystallization from hexane=ethylacetate (10:1) afforded 6.9 g
1
(61%) of white crystalline powder. Mp 112–114 ꢁC; H NMR (400 Mz, CDCl3) d:
6.92–6.94 (d, 2H), 7.00–7.07 (m, 6H), 7.22–7.26 (t, 4H), 7.3–7.32 (d, 2H). Anal. calcd.
for C18H14BrN: C, 66.67; H, 4.32; N, 4.32. Found: C, 66.64; H, 4.16; N, 4.45.
4-(Diphenylamino)benzene Boronic Acid (5)
A 250-mL, three-necked flask fitted with an electromagnetic stirrer and a nitrogen
inlet was charged with 9.7 g of 4 (0.03 mol), 10mL of trimethy borate (0.09 mol), and
80 mL anhydrous tetrahydrofuran (THF). The mixture was cooled to ꢀ78 ꢁC using a
dry ice = ethanol bath under nitrogen. n-Butyl lithium (2.86 M in hexanes, 13.45 mL,
0.039 mol) was added dropwise via a syringe pump over 1 h, and the mixture was stirred
for an additional 2 h while the temperature was held at ꢀ78ꢁC. The ethanol =
dry ice bath was removed, and the reaction mixture was then allowed to warm to
ꢀ10ꢁC before a 2 N HCl solution (110mL) was added, and the mixture was stirred
for 8 h at room temperature. This mixture was extracted three times with ether and
once with saturated NaCl solution. The combined organic layers were evaporated in
vacuo to provide a solid and were washed with hexane, then purified by silica-gel
column chromatography using ether as the eluent to afford 7.23 g (83%) of white crys-
talline powder. Mp 219–222 ꢁC. IR (KBr) nmax 3437 (OH); 1H NMR (400 Mz, CDCl3)
d: 7.04–7.09 (t, 4H), 7.14–7.16 (d, 4H), 7.25–7.30 (m, 6H), 7.99–8.01 (d, 2H).
General Procedure for the Preparation of 7
A 250-mL, three-necked flask was fitted with an electromagnetic stirrer, a
reflux condenser, and a nitrogen inlet and charged with 125 mL solvent, base, aryl

TRIPHENYLAMINE-MODIFIED ARYLATES AND KETONES
837
bromides, triphenylamine boronic acid, and catalyst. The reaction mixture was stir-
red at a suitable temperature until the starting triphenylamine boronic acid had been
completely consumed. The reaction mixture was extracted three times with ether.
The combined organic layer was evaporated in vacuo to provide a solid. The crude
product was purified by silica-gel column chromatography.
4’-(Diphenylamino)-4-methyl-1,1’-biphenyl (7a). The coupling of 6a with
5 was effective using the general procedure. The crude product was purified by
silica-gel column chromatography using petroleum ether as the eluent. Recrystalliza-
tion from hexane afforded white crystalline powder. Mp 100–102 ꢁC; 1H NMR (400
Mz, CDCl3) d: 2.38 (s, 3H), 7.00–7.03 (t, 2H), 7.11–7.13 (d, 6H), 7.21–7.27 (m, 6H),
7.44–7.47 (m, 4H). Anal. calcd. for C25H21N: C, 89.55; H, 6.27; N, 4.18. Found: C,
89.03; H, 6.45; N, 3.91.
3,5-Dibromo,4’-(diphenylamino)-1,1’-biphenyl (7b). The coupling of 6b
with 5 was effective using the general procedure. The crude product was purified
by silica-gel column chromatography using petroleum ether = toluene (1:1) as the
eluent. Recrystallization from hexane = toluene (1:1) afforded white crystalline pow-
1
der. Mp 181–184 ꢁC; H NMR (400 Mz, CDCl3) d: 7.04–7.08 (t, 2H), 7.10–7.13 (t,
6H), 7.26–7.30 (t, 4H), 7.37–7.39 (d, 2H), 7.58 (s, H), 7.62–7.62 (d, 2H). Anal. calcd.
for C24H17Br2N: C, 60.15; H, 3.58; N, 2.92. Found: C, 59.93; H, 3.56; N, 2.99.
4-Acetyl-4’-(diphenylamino)-1,1’-biphenyl (7c). The coupling of 6c with 5
was effective using the general procedure. The crude product was purified by
silica-gel column chromatography using dichloromethane as the eluent. Recrystalli-
zation from hexane afforded yellow crystalline powder. Mp 112–114 ꢁC; IR (KBr)
1
nmax 1674 cmꢀ1 (C O); H NMR (400 Mz, CDCl3) d: 2.62 (s, 3H), 7.04–7.07 (t,
=
2H), 7.13–7.15 (d, 6H), 7.26–7.30 (t, 4H), 7.50–7.51 (d, 2H), 7.64–7.66 (d, 2H),
7.99–8.01 (d, 2H). Anal. calcd. for C26H21NO: C, 85.95; H, 3.86; N, 4.18. Found:
C, 85.51; H, 3.92; N, 3.92.
4’-(Diphenylamino)-1,1’-biphenyl-4-carboxylic acid (7d). The coupling of
6d with 5 was effective using the general procedure. After cooling, hydrochloric acid
was dropped into the reaction mixture until its pH increased to 3. The reaction mix-
ture was extracted three times with ether. The combined organic layer was evapo-
rated in vacuo to provide a solid. The crude product was purified by silica-gel
column chromatography using ether as the eluent. Recrystallization from ethanol=
dichloromethane (3:1) afforded yellow crystalline powder. Mp 229–231 ꢁC; IR
(KBr) nmax 3439 (OH), 1692 cmꢀ1 (C O); 1H NMR (400 Mz, DMSO) d:
=
7.04–7.07 (m, 8H), 7.32–7.34 (t, 4H), 7.66 (d, 2H), 7.75 (d, 2H), 7.98 (d, 2H),
12.87–12.88 (s, H). Anal. calcd. for C25H19NO2: C, 82.19; H, 5.20; N, 3.83. Found:
C, 82.24; H, 5.18; N, 3.91.
4’-Diphenylamino-4-phenyl ethyl benzoate (7e). The coupling of 6e with
5 was effective using the general procedure. After cooling, the crude product was iso-
lated by filtering off the inorganic solids, washing with dichloromethane, distilling
the solvent under reduced pressure, then purifing by silica-gel column chromato-
graphy using toluene as the eluent. Recrystallization from ethanol afforded white
crystalline powder. Mp 115–116 ꢁC; IR (KBr) nmax 1589 cmꢀ1 (C O); H NMR
1
=

838
J. WANG ET AL.
(400 Mz, CDCl3) d: 1.39–1.42 (t, 3H), 4.37–4.42 (m, 2H), 7.03–7.07 (t, 2H), 7.12–7.14
(d, 6H), 7.25–7.30 (t, 4H), 7.49 ꢀ 7.51 (d, 2H), 7.61–7.64 (d, 2H), 8.07–8.09 (d, 2H).
Anal. calcd. for C27H23NO2: C, 82.44; H, 5.85; N, 3.56. Found: C, 82.06; H, 5.99;
N, 3.53.
4’-Diphenylamino-1-(1,1’-biphenyl)-1,3-butanedione (7f). The coupling
of 6f with 5 was effective using the general procedure. After cooling, the crude pro-
duct was isolated by filtering off the inorganic solids, washing with dichloromethane,
distilling the solvent under reduced pressure, and then purifing by silica-gel column
chromatography using toluene as the eluent. Recrystallization from hexane afforded
white crystalline powder. Mp 126–127 ꢁC; IR (KBr) nmax 3444 (OH), 1588 (C O),
=
and 1486 cmꢀ1 (C O); 1H NMR (400 Mz, CDCl3) d: 2.22 (s, H), 6.22 (s, H),
=
7.04–7.08 (t, 2H), 7.13–7.15 (d, 6H), 7.26–7.30 (t, 4H), 7.50–7.52 (d, 2H),
7.64–7.66 (d, 2H), 7.92–7.94 (d, 2H). Anal. calcd. for C28H23NO2: C, 82.96; H,
5.68; N, 3.45. Found: C, 82.45; H, 5.70; N, 3.36.
4’-Diphenylamino-1-(1,1’-biphenyl)-3-phenyl-1,3-propanedione (7g). The
coupling of 6 g with 5 was effective using the general procedure. After cooling, the
crude product was isolated by filtering off the inorganic solids, washing with dichlor-
omethane, distilling the solvent under reduced pressure, and then purifing by
silica-gel column chromatography using toluene as the eluent. Recrystallization from
ethanol afforded white crystalline powder. Mp 135–136 ꢁC. IR (KBr) nmax 3443
ꢀ1
1
=
=
(OH), 1589 (C O), and 1485 cm (C O); H NMR (400 Mz, CDCl3) d: 6.90 (s,
H), 7.05–7.08 (t, 2H), 7.14–7.16 (d, 6H), 7.26–7.31 (t, 4H), 7.49–7.57 (m, 5H),
8.00–8.06 (m, 4H). Anal. calcd. for C31H25NO2: C, 83.97; H, 5.64; N, 3.16. Found:
C, 84.16; H, 5.46; N, 3.26.
1-(4’-Diphenylamino-1,1’-biphenyl)-3-methyl-4-isobutyl-5-pyrazolone (7h).
The coupling of 6 h with 5 was effective using the general procedure. After cooling,
hydrochloric acid was dropped into the reaction mixture until its pH increased to 3.
The reaction mixture was extracted three times with ether. The combined organic
layer was evaporated in vacuo to provide a solid. The crude product was purified
by silica-gel column chromatography using dichloromethane as the eluent. Recrys-
tallization from hexane=ethanol (1:1) afforded white crystalline ꢀp1 owder. Mp
1
149–151 ꢁC; IR (KBr) nmax 3453 (OH), 1594 (C O), and 1499 cm (C O); H
NMR (400 Mz, CDCl3) d: 1.26–1.27 (s, 6H), 2.50 (s, 2H), 3.15–3.18 (m, H),
7.02–7.06 (t, 2H), 7.13–7.15 (d, 6H), 7.26–7.29 (t, 4H), 7.48–7.50 (d, 2H),
7.63–7.65 (d, 2H), 7.88–7.90 (d, 2H). Anal. calcd. for C32H29N3O2: C, 78.85; H,
5.95; N, 8.62. Found: C, 78.85; H, 5.98; N, 8.62.
=
=
ACKNOWLEDGMENTS
This work was financially supported by NSFC 60868001.
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