A simple and novel amide ligand based on quinoline derivative used for palladium-catalyzed Suzuki coupling reaction

Article abstract of DOI:10.1016/j.jorganchem.2015.06.009

This paper discusses the synthesis of the amide ligand N,N-diisopropyl quinoline-2-carboxamide from quinoline-2-carboxylic acid and diisopropylamine. The prepared ligand was utilized in the palladium catalyzed Suzuki cross-coupling reaction in ethanol-wat

Full text of DOI:10.1016/j.jorganchem.2015.06.009

Journal of Organometallic Chemistry 794 (2015) 27e32
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
A simple and novel amide ligand based on quinoline derivative used
for palladium-catalyzed Suzuki coupling reaction
,
,
,
b
,
, b, *
Haiyang Liu a b, Xiaoshuang Li c, Feng Liu a b, Ying Tan a *, Yuyang Jiang a
a Department of Chemistry, Tsinghua University, Beijing 100084, China
b The Ministry-Province Jointly Constructed Base for State Key Lab-Shenzhen Key Laboratory of Chemical Biology, The Graduate School at Shenzhen,
Tsinghua University, Shenzhen, Guangdong 518055, China
c Advanced Materials Institute, Graduate School at Shenzhen, Tsinghua University, Shenzhen, Guangdong 518055, China
a r t i c l e i n f o
a b s t r a c t
Article history:
This paper discusses the synthesis of the amide ligand N,N-diisopropyl quinoline-2-carboxamide from
quinoline-2-carboxylic acid and diisopropylamine. The prepared ligand was utilized in the palladium
catalyzed Suzuki cross-coupling reaction in ethanol-water 1:1 (v/v). The reaction exhibited high catalytic
efficiency with low Pd loading (0.05 mol %) under mild reaction conditions (at 60e90 ꢀC under air at-
mosphere). In this study, the catalyst was successfully used in coupling reactions between various aryl
halides with phenylboronic acid to obtain desired products in excellent yields. Spectrometric methods of
1H NMR, 13C NMR, and HR-MS were used to characterize this amide ligand, and its binding properties
toward the Pd center were also investigated in detail via HR-MS measurements.
Received 16 February 2015
Received in revised form
29 May 2015
Accepted 6 June 2015
Available online 19 June 2015
Keywords:
Suzuki cross-coupling
Palladium catalyst
Quinoline-2-carboxylic acid
Diisopropylamine
Aryl bromides
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
diamino) [2,31e47]. The latter-mentioned heteroatoms act as
chelating sites toward a center metal in a proper chemical envi-
Palladium-catalyzed coupling reactions have played an impor-
tant role in organic synthesis in recent decades [1e5]. Among these
reactions, the Suzuki reaction stands out as one of the most
powerful, convenient, and versatile methods for cross-coupling aryl
halides with arylboronic acids [6e13]. This method has been
identified as a reliable platform for carbonecarbon bond formation
and has extensive use in the synthesis of natural products, phar-
maceuticals, and advanced materials [14e19]. Usually, the most
common ligands used for the Suzuki cross-coupling reaction are
phosphines [20e26]. However, most of them are sensitive to air
and moisture and are expensive and toxic, which significantly
limits their industrial applications [27e30]. Recently, significant
progress has been made toward the Suzuki coupling reaction
through the use of phosphine-free ligands, such as N-heterocyclic
carbene, N,N,O-tridentate, N,N,N-tridentate, N,O-bidentate, N,S-
bidentate, and N,N-bidentate ligands (including diimine and
ronment. Few studies practiced the use of amide ligands for Suzuki
cross-coupling reaction, even though it has been verified that
heteroatoms of the amide carbonyl can act as chelating sites for
transition metal [48e51].
In 1993, Minisci's group obtained N,N-diisopropyl quinoline-2-
carboxamide in order to study the introduction of a carbamoyl
group into heteroaromatic bases via the homolytic carbamoylation
of monoamides of oxalic acid [52]. It should be noted that Minisci
et al. did not report the application of this amide compound.
Herein, we report a palladium-based catalytic system for the Suzuki
reaction using this novel, simple, and efficient amide ligand (the
product of quinoline-2-carboxylic acid chloride reacting with dii-
sopropylamine, QADIA) in aqueous media (H2OeEtOH, 1:1) to
obtain the desired coupling products in good yields under mild
reaction conditions. The synthetic route of this amide ligand is
illustrated in Scheme 1. The new ligand was characterized via 1H
NMR (Fig. S1), 13C NMR (Fig. S2), and HR-MS (Fig. S3) spectrometry.
* Corresponding authors. Department of Chemistry, Tsinghua University, Beijing
100084, China.
2. Results and discussion
E-mail addresses: tan.ying@sz.tsinghua.edu.cn (Y. Tan), jiangyy@sz.tsinghua.
edu.cn (Y. Jiang).
We initially tested the reaction of phenylboronic acid with 4-
http://dx.doi.org/10.1016/j.jorganchem.2015.06.009
0022-328X/© 2015 Elsevier B.V. All rights reserved.

28
H. Liu et al. / Journal of Organometallic Chemistry 794 (2015) 27e32
Scheme 1. The synthetic route of QADIA. (a) CH2Cl2, oxalyl chloride, reflux, 4 h; (b) CH2Cl2, diisopropylamine, RT, 2 h.
Table 1
Effect of water in the palladium-catalyzed SuzukieMiyaura reactiona.
Entry
Ligand
[Pd] source
Solvent, V/V
Temp. (ꢀC)/time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
QADIA
QADIA
QADIA
QADIA
QADIA
QADIA
QADIA
QADIA
QADIA
QADIA
QADIA
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
Only EtOH
80/2
80/2
80/2
80/2
80/2
60/4
25/24
80/2
80/2
80/2
80/2
78
83
89
94
99
98
19
95
76
46
23
EtOH/H2O, 9/1
EtOH/H2O, 4/1
EtOH/H2O, 2/1
EtOH/H2O, 1/1
EtOH/H2O, 1/1
EtOH/H2O, 1/1
EtOH/H2O, 1/2
EtOH/H2O, 1/4
EtOH/H2O, 1/9
Only H2O
9
10
11
a
Reaction conditions: n (ligand)/n (Pd) ¼ 2,4-bromo anisole (1 mmol), phenylboronic acid (1.25 mmol), K3PO3 (2.0 mmol).
b
Isolated yield.
bromo anisole in 6 mL water as a model reaction to establish the
pertinent to note that DIPA, as a ligand, can also coordinate the
metal center and promote the model reaction with the same Pd-
loading to some extent, which was similar to Qiu's research [54].
Thorough understanding of the binding mechanism between
the center metal and the ligand is critical in the Pd-catalyzed Suzuki
coupling system. Eseola and Plass et al. confirmed that their 2-
(oxazol-2-yl) pyridine compounds (N,N-bidentate ligands) coordi-
nated with the Pd center in a 1:1 bonding model [43]. Amadio and
Scrivanti et al. verified that their thioether-triazole compound (N,S-
bidentate ligand) coordinated with the Pd center in a 1:1 bonding
best conditions for cross-coupling in the presence of 0.1 mol% of
PdCl2 and 0.2 mol% of ligand. The effect of various bases (LiOH,
NaOH, NaHCO3, Na2CO3, KOH, KHCO3, K2CO3, K3PO4, Cs2CO3, and
Et3N) on the Suzuki reaction was investigated in the experiment. It
was discovered that reactions with KOH, K3PO4, and Cs2CO3 pro-
duced the desired product in good yields (Table S1). With the
consideration of practical application, K3PO4 was chosen as the
optimal base for enhancing the efficiency of this protocol.
Simultaneously, commonly used solvents (H2O, DMF, THF,
Dioxane, MeOH, EtOH, i-PrOH and t-BuOH) were also tested in the
reaction. It was determined that EtOH performed best; the reaction
in EtOH afforded the desired product in 78% yield after 2 h at 80 ꢀC
oil bath in the presence of 0.1 mol% PdCl2 and 0.2 mol% ligand
(Table S2). The addition of appropriate amounts water to EtOH
promoted activity of the catalysis system and resulted in the
desired products in better yields [53] (Table 1, entries 2e10), may
be). Reasoning for this occurrence may be attributed to the possi-
bility that the proper polarity of the madia is conducive to the
Suzuki coupling reaction [5,43,53]. These results suggest that the
proper ratio of water and ethanol plays a key role in the model
reaction with good solubility of two substrates (aryl halides and
phenylboronic acid) in these mixed solvents. Ultimately, the
mixture of EtOH and H2O (1:1, v/v) was chosen as the best medium
for this catalyst system.
model [39]. Li et al. confirmed that their b-oxo amide ligand coor-
dinated with Pd center in a 2:1 bonding model [48]. In order to have
more insight into the binding properties of QADIA toward center
In this study, two different catalytic precursors (PdCl2 and
Pd(OAc)2) were tested. From Fig. 1, it can be seen that PdCl2 per-
formed better than Pd(OAc)2 in the model reaction. In order to
compare the catalytic effect of the system (QADIA/PdCl2 in EtOH
and H2O), diisopropylamine (DIPA), quinoline-2-carboxylic acid
(QLCA), and a simple combination of QLCA and DIPA were also
tested in the model reaction. It was found that QADIA performed
best and could stabilize the Pd(0) species more efficiently than
quinoline-2-carboxylic acid and diisopropylamin (Fig. 1). It is
Fig. 1. Effect of different ligands and Pd sources in the model reaction (Above:QLCA,
DIPA and “QLCA þ DIPA” are the potential ligands comparing to QADIA).

H. Liu et al. / Journal of Organometallic Chemistry 794 (2015) 27e32
29
Fig. 2. ESI mass spectra of QADIA in the presence of PdCl2 (2 equiv).
Pd, ESI mass spectrometry was used to measure of QADIA/PdCl2. As
to 0.005 mol%, and the reaction time was extended to 20 h, it also
afforded the corresponding substituted biphenyl in a yield of 82%
(Table 2, entry 4). In the QIDIA/PdCl2 catalysis system, electron-rich,
as well as electron-deficient aryl iodides and aryl bromides coupled
efficiently with phenylboronic acid under mild conditions (Table 2,
entries 1e12). Due to the steric hindrance of 2-bromotoluene and
2-bromoanisole, the desired products were obtained in medium
yields (Table 2, entries 13,15). In particular, the target products of 2-
bromotoluene and 2-bromoanisole with phenylboronic were ob-
tained in good yields when the reaction time was increased to 10 h
in the presence of 0.1 mol% PdCl2 and 0.2 mol% QADIA (Table 2,
entries 14 (85%), 16 (92%)). This phenomenon was similar to those
mentioned in previous reports concerning the use of nitrogen-
based ligands in the Suzuki coupling reaction [55]. Furthermore,
it was reported by Nolan's group that 3-bromopyridine and 3-
bromoquinoline were not as reactive as other aromatic substrates
in the Suzuki coupling reaction due to their strong coordination
ability towards the center metal [56]. Both yields of the target
products were normally lower than those of other coupling prod-
ucts under the same reaction conditions [54e56]. In this QADIA/
shown in Fig. 2, the cluster peak at m/z
¼
361.0509
(calcd ¼ 361.0527) corresponds to [QADIA þ Pd2þꢁHþ]þ, and m/
z
¼
397.0290 (calcd
¼
397.0299) corresponds to
[QADIA þ Pd2þþClꢁ]þ, both of which were clearly observed when
2 equiv of PdCl2 was added to QADIA. This indicates the formation
of a 1:1 metal-ligand catalyst. According to these results, a working
mechanism was proposed on the basis of the previously proposed
mechanism as outlined in Scheme 2 [12,31,40,43e45]. This pro-
posed catalytic cycle involves oxidative addition of Pd(0)L4 to the
halide (R1X) to form the organopalladium interme-diate Pd(L2)R1X,
transmetalation reaction of Pd(L2)R1X with the boron acid to form a
diarylpalladium species Pd(L2)R1R2, and reductive elimination of
Pd(L2)R1R2 to release the desired coupling product (R1eR2) [1,12].
In the above Pd-catalyzed Suzuki cross-coupling system, all the
substrates ran smoothly in the procedure, and the desired products
were isolated in excellent yields (Table 2). For the model reaction of
phenylboronic acid with 4-bromo anisole, a yield of 97% was ob-
tained only at 60 ꢀC in 5 h in the presence of 0.05 mol% PdCl2 and
0.1 mol% QADIA (Table 2, Entry 3). When Pd-loading was decreased
Scheme 2. A possible mechanism for QADIA coordinating toward center metal.

30
H. Liu et al. / Journal of Organometallic Chemistry 794 (2015) 27e32
Table 2
Suzuki coupling of phenylboronic acid and various aryl halidesa.
Entry
1
Ar-X
Pd loading (mol%)
0.05
Time (h)
5
Yieldb (%)
98
2
3
4
5
0.05
0.05
0.005
0.05
4
5
98
97
82c
96
20
5
6
7
0.05
0.05
5
5
97
96
0
8
0.05
0.05
0.05
0.05
5
5
5
5
97
98
98
96
9
10
11
12
13
14
15
0.05
0.05
0.1
5
5
97
53
85
61
10
5
0.05
16
17
0.1
0.1
10
10
92
89c

H. Liu et al. / Journal of Organometallic Chemistry 794 (2015) 27e32
31
Table 2 (continued )
Entry
18
Ar-X
Pd loading (mol%)
0.1
Time (h)
10
Yieldb (%)
95c
19
20
21
22
1
1
1
1
5
20
5
14c
38d
23c
44d
20
a
Reaction conditions: n (QADIA)/n (Pd) ¼ 2, aryl halides (1 mmol), phenylboronic acid (1.25 mmol), K3PO3 (2.0 mmol), H2O (3.0 mL), EtOH (3.0 mL), 60 ꢀC.
b
c
Isolated yield.
80 ꢀC.
d
90 ꢀC, with addition of 0.25 mmol TBAB in the system.
PdCl2 system, the reaction was found to produce good to excellent
spectroscopy was performed on a Brucker advance II 400 spec-
trometer operating at 400 MHz (1H NMR) and 100 MHz (13C NMR)
with CDCl3 as the solvent and TMS as internal standard. Melting
points were determined on a Thomas-Hoover capillary melting
point apparatus. The isolation of pure products was carried out via
column (Silica gel 200e300 mesh).
yields for the desired product with 3-bromopyridine and 3-
bromoquinoline when we extended the reaction time to 10 h at
80 ꢀC in the presence of 0.1 mol % PdCl2 (Table 2, entries 17, 18).
Encouraged by the obvious efficiency of this optimized catalytic
system, we also investigated the coupling of phenylboronic acid
with activated aryl chloride, which included 4-chloronitrobenzene
and 4-chlorobenzotrifluoride. It is well known that the Suzuki
cross-coupling of aryl chlorides is not as easy as it is for aryl iodides
and aryl bromides. In order to obtain the desired coupling products,
harsh reaction conditions and higher dosages of catalyst are typi-
cally required in the Suzuki reaction [47,57]. When we raised the Pd
loading up to 1.0 mol% and prolonged the reaction time to 20 h by
setting the reaction temperature to 90 ꢀC (in the presence of 25 mol
3.1. Synthesis of QADIA
Into a 250 mL three-necked flask equipped with a magnetic
stirringbar, 1.73 g (0.01 mol) of quinaldic acid and 60 mL anhydrous
dichloromethane are added. The mixture was stirred at room
temperature for 10 min and then 10 mL oxalyl chloride (0.12 mol)
was added. After thermostatting at 50 ꢀC in an oil bath and stirring
for 4 h, the reaction flask was cooled. After removing all the solvent
under reduced pressure, the mid-product quinaldic acid chloride
was obtained. The whole of the mid-product was dissolved in
50 mL anhydrous dichloromethane in the same flask, then 1.21 g
(0.012 mol) diisopropylamine was added dropwise into the mixture
in 10 min under ice-water bath. After the end of addition, the
mixture was stirred at room temperature for 6 h. The solvent was
removed under reduced pressure and the residue was purified by
recrystallization (EtOAc/Cyclohexane ¼ 1:3). Finally, a pale yellow
crystal (2.18 g) was obtained, yield: 85%. mp: 135e137 ꢀC. 1H NMR
%
TBAB, simultaneously), moderate coupling yields of 4-
chlorobenzotrifluoride (38%) and 4-chloronitrobenzene (44%)
with phenylboronic acid were obtained (Table 2, entries 20, 22).
Conclusively, we successfully developed a novel and simple
amide ligand QADIA (N,N-diisopropyl quinoline-2-carboxamide).
This compound was proved to be highly effective in the
palladium-catalyzed Suzuki coupling reaction of phenylboronic
acid with different substituted bromobenzenes, substituted iodo-
benzenes, and heteroaryl bromides in EtOHeH2O (1:1, v/v). In the
QIDIA/PdCl2 catalysis system, the reaction can be carried out at low
Pd-loading (0.05 mol %) in mild conditions (at 60e90 ꢀC under
aerobic conditions), resulting target biphenyl derivatives in good to
excellent yields. The ease of preparation of this amide ligand, its
low catalyst loading and stability toward air and moisture make it
an ideal catalytic system for the Suzuki cross-coupling reaction. In
view of the good coordinating performance of this quionline-based
amide compound towards Pd center, this amide ligand may
demonstrate useful for other kinds of metal catalyzed trans-
formations. And further effort to develop more simple and efficient
amide ligands in the catalytic system and more application of this
system are currently under investigation.
(400 MHz, CDCl3):
d
8.23 (d, J ¼ 8.4 Hz, 1H), 8.13 (d, J ¼ 8.5 Hz, 1H),
7.83 (d, J ¼ 8.1 Hz, 1H), 7.74 (t, J ¼ 8.0, 1.4 Hz, 1H), 7.57 (m, 2H), 3.97
(m, 1H), 3.61 (m, 1H), 1.62 (d, J ¼ 6.8 Hz, 6H), 1.22 (d, J ¼ 6.7 Hz, 6H)
ppm; 13C NMR (100 MHz, CDCl3):
d 168.81 (s, 1C), 155.99 (s, 1C),
146.88 (s, 1C), 136.92 (s, 1C), 129.77 (d, 2C), 127.63 (d, 2C), 127.02 (s,
1C), 119.66 (s, 1C), 50.69 (s, 1C), 46.18 (s, 1C), 20.65 (d, 4C) ppm;
HRMS calcd for C16H21N2O [QADIA þ H]þ: 257.1648, found:
257.1661 (Fig. S3). Elem anal. calcd for C16H20N2O: C, 74.97; H, 7.86;
N, 10.93%. Found: C, 74.81; H, 7.98; N, 10.74%.
Acknowledgments
3. Experimental
We thank the advice of Dr. Youwei Yao (Graduate School at
Shenzhen, Tsinghua University) and Dr. Kun Wang (Sichuan Uni-
versity). This work was supported by the National Natural Science
Foundation of China (No. 21302108), and Shenzhen Municipal
Government SZSITIC (No. JCYJ20130402145002379, ZDSY20120
619141412872, and CXB201104210013A).
All aryl halides and arylboronic acids were purchased from
Energy Chemical. Quinaldic acid and diisopropylamine were pur-
chased form Aladdin Industrial Corporation. Other chemicals were
purchased from commercial sources without any process. NMR

32
H. Liu et al. / Journal of Organometallic Chemistry 794 (2015) 27e32
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Appendix A. Supplementary data
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Supplementary data related to this article can be found at http://
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