A highly efficient memantine-modified palladium catalyst for Suzuki-Miyaura cross-coupling reaction

Article abstract of DOI:10.1016/j.tet.2014.03.064

A new simple Pd(memantine)₂Cl₂ complex was synthesized and characterized by ¹H NMR, ¹³C NMR and X-ray single crystal structure determination. The Suzuki-Miyaura reaction of aryl bromides catalyzed by Pd(memantine)₂Cl₂ complex was investigated in air with different temperature. The high turnover numbers of 650,000 have been obtained in the reaction of 4-bromonitrobenzene with phenylboronic acid at 80 °C. At room temperature, the complex also showed high activity for Suzuki-Miyaura cross-coupling reaction of aryl bromides with a wide range of functional groups under air, and the turnover number of up to 99,000 was achieved. The catalytic system also gives good yields toward the reaction of several heteroaryl bromides with thiophenylboronic acid.

Full text of DOI:10.1016/j.tet.2014.03.064

Tetrahedron 70 (2014) 3471e3477
Contents lists available at ScienceDirect
Tetrahedron
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A highly efficient memantine-modified palladium catalyst for
SuzukieMiyaura cross-coupling reaction
,
Qinxu Wu a, Leilei Wu b, Lei Zhang a, Haiyan Fu a, Xueli Zheng a, Hua Chen a
*
,
Ruixiang Li a
a Key Laboratory of Green Chemistry and Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu 610065, China
b Analysis & Testing Center of Sichuan Province, Chengdu, Sichuan 610023, China
a r t i c l e i n f o
a b s t r a c t
A new simple Pd(memantine)2Cl2 complex was synthesized and characterized by 1H NMR, 13C NMR and
X-ray single crystal structure determination. The SuzukieMiyaura reaction of aryl bromides catalyzed by
Pd(memantine)2Cl2 complex was investigated in air with different temperature. The high turnover
numbers of 650,000 have been obtained in the reaction of 4-bromonitrobenzene with phenylboronic
acid at 80 ꢀC. At room temperature, the complex also showed high activity for SuzukieMiyaura cross-
coupling reaction of aryl bromides with a wide range of functional groups under air, and the turnover
number of up to 99,000 was achieved. The catalytic system also gives good yields toward the reaction of
several heteroaryl bromides with thiophenylboronic acid.
Article history:
Received 1 January 2014
Received in revised form 8 March 2014
Accepted 19 March 2014
Available online 26 March 2014
Keywords:
SuzukieMiyaura reaction
Pd(memantine)2Cl2
Aryl bromides
Ó 2014 Elsevier Ltd. All rights reserved.
Heteroaryl bromides
At room temperature
1. Introduction
oxazolines,8 aryloximes,16 arylimines,17 and diazabutadine de-
rivatives,18 pyridine-piperidine bidentate ligands19 and so on have
Palladium-catalyzed CeC bond forming reactions continues to
be the most important method to synthesize the biaryls,1,2 which
are ubiquitous motifs found in conducting polymers,3 bioactive
compounds,4 catalyst ligands,5 and natural products.6 Among these
reactions, the SuzukieMiyaura cross-coupling reaction have re-
ceived extensive attention due to the advantages, such as a good
functional group tolerance, mild reaction conditions, and easy
handling of by-products.7 In general, an active and selective Suzuki
reaction catalyst could be achieved by using an appropriate sup-
porting ligand8 and the phosphines have proved to be the most
common9 and efficient ligands.10 However, the phosphorous-based
ligands are often air- and/or moisture-sensitive, hence require an
inert-atmosphere technology during operation, and in some cases,
it was plagued by the degradation caused by PeC bond cleavage.11
To address these problems, many non-phosphorous C- or N-based
ligands have been developed.12e15 Particularly, given the fact that
the atoms N and P are in the same column of Periodic Table, the N-
based ligand exhibited similar properties with the P-based ligand to
some extent, but relatively insensitive to air and moisture. There-
fore, in the past decades, the N-type ligands including aryl-2-
been extensively explored in this reaction as an alternative to
phosphine. In most cases, a high active catalyst could be achieved.
For example, an oxime-derived palladacycle (containing a N-donor)
proved to be a high efficient SuzukieMiyaura coupling reaction
catalyst for challenging substrate arylchloride, which can enable
a set of (hetero) aryl chlorides to undergo the reaction in air.20
A palladium precatalyst based on a piperazine-derived diamino-
diol also proved to be an excellent catalyst for both bromide
and chloride derivatives, and a high TON of 548,400 for 4-
bromobenzonitriles could be achieved.21
However, the commercially available simple amine have been
under-developed as supporting ligand in Suzuki reaction.8 The first
successful example was reported by D. W. Boykin and co-workers
in 2004, which demonstrated that the bulky secondary amine
Cy2NH modified catalyst trans-(Cy2NH)2Pd(OAc)2 could catalyzed
Suzuki cross-coupling of 4-bromoanisole at room temperature with
2 mol % catalyst loading. Following that work, J. H. Li et al. reported
that an in situ generated Pd(OAc)2/Dabco (Dabco: 4-diazabicyclo
[2.2.2]octane) catalyst exhibited an extremely high activity for
Suzuki reaction, and up to 950,000 TONs could be achieved for the
coupling reaction of PhI with p-chlorophenylboronic acid.22 Re-
cently, another simple amine, 2,20-diamino-6,60-dimethylbiphenyl
(L) was also found a useful ligand for this reaction. Even the less
active aryl chlorides could readily react with arylboronic acid in
* Corresponding author. Tel./fax: þ86 28 85412904; e-mail addresses: scuh-
chen@163.com, scuhchen@scu.edu.cn (H. Chen).
0040-4020/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2014.03.064

3472
Q. Wu et al. / Tetrahedron 70 (2014) 3471e3477
DMF at 110 ꢀC with 5 mol % of palladium loading.23 According to the
literature, a bulky and electronically rich ligand is beneficial for
improving the catalyst activity and selectivity of these palladium
catalysts.24 As our continuous effort to develop high efficient and
robust catalyst for Suzuki reaction, herein we first report our result
on catalytic properties of complex 1(Pd(memantine)2Cl2) in Suzu-
kieMiyaura cross-coupling reaction.
Table 2
Selected bond lengths (nm) and angles (ꢀ) for complex 1
Pd(1)eCl(1)1
Pd(1)eCl(1)
Pd(1)eN(1)
N(1)1ePdeCl(1)1
N(1)ePdeCl(1)1
N(1)ePdeCl(1)
N(1)1ePdeCl(1)
N(1)ePdeN(1)1
2.3001(10)
2.3001(10)
2.051(3)
90.08(10)
89.92(10)
90.08(10)
89.92(10)
180
Pd(1)eN(1)1
N(1)eC(1)
2.051(3)
1.497(5)
180
123.7(2)
110.1(3)
107.7(3)
110.8(3)
Cl(1)1ePdeCl(1)
C(1)eN(1)ePd(1)
N(1)eC(1)eC(2)
N(1)eC(1)eC(6)
N(1)eC(1)eC(9)
2. Results and discussion
2.1. The properties and molecular structure of complex 1
2.2. The SuzukieMiyaura cross-coupling reaction
The new simple complex Pd(memantine)2Cl2 was synthesized
by the reaction of Pd(OAc)2 with memantine hydrochloride, and
a single crystal of complex 1 was grown by slow evaporation of
CH2Cl2/n-Hexane solvent system, allowing for structural elucida-
tion by X-ray single crystal analysis. The molecular structure is il-
lustrated in Fig. 1. Crystal data are presented in Table 1. The acetate
was replaced by chloride ion based on the X-ray single crystal de-
termined. Selected bond lengths and angles are given in Table 2.
The bond lengths and angles are all within the expected range,
without distorted square-planar geometry (the dihedral angle be-
tween the plane of Cl(1)ePd(1)eCl(2) and the plane of N(1)e
Pd(1)eN(2) is 90ꢀ). The PdeCl(1) and PdeCl(2) bond distances
(2.3001(10) nm and 2.3001(10) nm, respectively) are identical.
The Suzuki-Miyaura coupling reactions of aryl bromides with
phenylboronic acid were investigated by employing the complex 1
as catalyst. Firstly, the coupling of 4-bromoanisole with 1.5 equiv of
phenylboronic acid in the presence of 1.5 equiv of base at 80 ꢀC was
chosen as a model reaction to evaluate the catalytic properties of
complex 1 in the Suzuki-Miyaura coupling reactions (Table 3, en-
tries 1e15). Satisfyingly, a moderate GC yield (62%) of desired
product was obtained in EtOH with KOH as base, upon
0.0002 mol % Pd loading (Table 3, entry 1). Increasing the catalyst
loading to 0.002 mol % could improve the yield to 80%. Sub-
sequently, several bases including NaOH, K3PO4, Na2CO3, NaHCO3
and Cs2CO3 were scanned for this system, and NaOH proved to be
the best. The product could be obtained in 91% yield (Table 3, entry
7), which could be further increased to 96% by decreasing the NaOH
amount to 1.2 equiv (Table 3, entry 8). Solvent also plays a crucial
role in the reaction rate of Suzuki coupling reactions. Polar protic
solvents, such as EtOH, i-PrOH and n-BuOH afforded higher activity
than either polar aprotic solvents, such as DMF, DMA, and dioxane,
or nonpolar solvent toluene. It was worthy of note that the complex
1 could also be operated in green solvent water, although the yield
(50%) is lower than that in ethanol (Table 3, entry 15).
Table 3
Effect of reaction conditions on the Suzuki coupling reaction catalyzed by complex 1
Fig. 1. The molecular structure and ORTEP representation of complex 1.
Entry
Catalyst loading (mol %)
Solvent
Base
Yield (%)a
Table 1
1
2
3
4
5
6
7
8
0.0002
0.002
0.002
0.002
0.002
0.002
0.002b
0.002
0.002
0.002
0.002
0.002
0.002
0.002
0.002
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
i-PrOH
n-BuOH
Toluene
DMF
DMA
Dioxane
H2O
KOH
KOH
62
80
72
76
24
91
96
Trace
90
93
61
0
Crystal and refinement data for complex 1
K3PO4
Na2CO3
NaHCO3
NaOH
NaOH
CsCO3
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
C24H42Cl2N2Pd
535.89
293.15
Triclinic
P-1
6.6333(7)
7.6678(8)
12.507(3)
85.124(14)
79.886(15)
75.155(9)
604.80(16)
1
ꢀ
a/A
ꢀ
9
b/A
ꢀ
10
11
12
13
14
15
c/A
ꢀ
ꢀ
ꢀ
/
a
/
b
/
10
3
50
g
3
ꢀ
Volume/A
Z
r
calcd mg/mm3
1.471
1.002
280.0
0.2ꢂ0.15ꢂ0.1
Reaction conditions: catalyst: complex 1, 4-bromoanisole (0.5 mmol), phenyl-
m/mmꢁ1
boronic acid (0.75 mmol), base (0.75 mmol), solvent (3 mL), 24 h, 80 ꢀC.
F(000)
a
GC yield.
Base: 0.6 mmol.
Crystal size/mm3
Radiation
b
Mo K
a
(
l
¼0.7107)
2
Q
range for data collection
6.302e52.734ꢀ
ꢁ8ꢃhꢃ8, ꢁ9ꢃkꢃ9, ꢁ15ꢃlꢃ15
5265
Index ranges
With the optimal conditions in hand, the scope and
limitations of the present catalytic system was investigated for
SuzukieMiyaura reaction. Firstly, the substrate scope and limita-
tions regard to the aryl bromide were tested. As shown in Table 4,
the established complex 1 catalytic system displayed high activity
in this cross-coupling reaction. Various aryl bromides, regardless of
electronically rich, neutral and deficient properties, reacted
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
5265[R(int)¼?]
5265/0/144
1.047
Final R indexes [Iꢄ2
Final R indexes [all data]
ꢀꢁ3
s
(I)]
R1¼0.0358, wR2¼0.0877
R1¼0.0382, wR2¼0.0890
0.68/ꢁ0.68
Largest diff. peak/hole/e A

Q. Wu et al. / Tetrahedron 70 (2014) 3471e3477
3473
Table 4
Suzuki reaction of various aryl bromides with phenylboronic acid catalyzed by complex 1
Entry
1
Aryl bromide
Catalyst loading (mol %)
Time (h)
24
Yield (%)a
0.002
98
91
2
3
0.0002
24
0.001
0.0002
6
24
99
96
4
0.0002
0.0001
6
48
97
65
5
0.001
0.001
0.002
0.002
0.002
0.002
0.002
6
6
98
99
96
85
90
94
99
6
7
24
24
24
24
24
8
9
10
11
12
13
0.001
0.002
6
51
90
24
14
15
16
17
18
0.002
0.002
0.001
0.002
0.002
24
24
6
15b
55
18
90
24
24
46
(continued on next page)

3474
Q. Wu et al. / Tetrahedron 70 (2014) 3471e3477
Table 4 (continued )
Entry
Aryl bromide
Catalyst loading (mol %)
Time (h)
24
Yield (%)a
19
20
0.002
0.002
80
24
25b
21
22
0.002
0.002
24
24
94
97
23
24
0.01
0.01
6
6
91
40
Reaction conditions: catalyst: complex 1, aryl bromide 0.5 mmol, phenylboronic acid 0.75 mmol, NaOH 0.75 mmol, EtOH 3 mL, 80 ꢀC.
a
Isolated yield.
GC yield.
b
smoothly with phenylboronic acid to afford the corresponding
coupling products in excellent isolated yields (80e99%, Table 4,
entries 1e23). Additionally, the system proved to be compatible
with a wide range of functional groups, such as eCN, eCF3, eNO2,
eCHO, eCOCH3, eF, eNMe2 and eNH2 etc. although a relatively
strong basic conditions was employed. The position of substituent
on the aryl bromide was also influenced the activity. Generally, the
activity of different aryl bromides followed a sequence: para-
Meanwhile, the homo-coupling product of phenylboronic acid was
also observed with about 20% GC yield.
Subsequently, the scope of complex 1 catalytic system was fur-
ther explored with respect to arylboronic acids (Table 5, entries
1e3). Electron-deficient and sterically hindered boronic acids led to
a significant decrease in yields even with increased catalyst loading,
however, in the case of the electron-rich 4-methoxyphenyl-boronic
acid, 4-bromoanisole could be converted to the desired product
with yield of 96% even the catalyst loading was low as 0.001 mol %
(Table 5, entry 3).
We were happy to discover that the scope of the protocol could
be extended to the Suzuki coupling reaction of heteroaryl bromides
with heteroarylboronic acid, and so the products of heteroaryl-aryl
and biheteroaryls could be obtained with good yield when EtOH
was employed as the media (Table 5, entries 4, 5 and 6). Although
phosphine ligands, palladacycles, and PdeNHC catalysts have been
successfully used for the Suzuki reaction of heteroaryl bromides
with heteroarylboronic acids,25e27 to the best of our knowledge, the
efficiency of simple N-ligands for such couplings has not been
demonstrated. And thiophene is an important motif, which can be
found in a variety of natural products as well as pharmaceutically
interesting compounds. Thiophenylboronic acids are prone to de-
composition under polar solvents, possibly by undergoing the
protodeboronation,28 which becomes the limitation plaguing the
reactions involving these substrates. We were pleased to find that
Suzuki reaction of thiophenylboronic acid could be performed well
in the present catalytic system. And a moderate to excellent yield of
desired products could be obtained by using 1 mol % catalyst (Table
5, entries 4e6).
>meta->ortho-.
For
example,
4-bromobenzaldehyde,
3-
bromobenzaldehyde and 2-bromo- benzaldehyde gave the prod-
uct in 98%, 51% and 18% yield, respectively (Table 4, entries 5, 12 and
16). This substituent-position-dependent activity is presumably
related to the congested coordinative environment around the
palladium centre, which was created by large volume of ligand
memantine. This trend was again observed in disubstituted aryl
bromides. A satisfying yield of 80% was obtained in case of 2-
bromo-1,4-dimethylbenzene as substrate, while only a low GC
yield 25% was obtained from 2-bromo-1,3-dimethylbenzene (Table
4, entries 19 and 20). The 1-naphthyl and 2-naphthyl bromides also
reacted with phenylboronic acid smoothly. In both cases, almost
a quantitative yield can be reached after 24 h. Moreover, the het-
eroaryl bromides, such as 2- and 3-bromopyridine also proved to be
viable for the present catalytic system and proceed nicely to give
product 2-phenylpyridine and 3-phenylpyridine in 40% and 91%
yield, respectively (Table 4, entries 21e24).
Encouraged by the excellent catalytic activity of complex 1 in
the Suzuki coupling reaction of aryl bromides with phenylboric
acid, the reaction of electron-deficient aryl chlorides with phenyl-
boronic acid catalyzed by complex 1 was investigated. In the case of
4-chloronitrobenzene,
4-chlorobenzotrifluoride
and
4-
Based on the above efficient results, the catalyst system was
investigated at room temperature. The desired coupling products
were still obtained in excellent isolated yields (Table 6, entries
1e13). And compared to Boykin’s reported system of DAPCy (trans-
(Cy2NH)2Pd(OAc)2) in room temperature, the desired product of the
chloroacetophenone as substrate, the cross-coupling products
could be obtained in isolated yields of 42%, 60% and 66%, re-
spectively, when the catalyst loading increased to 1 mol % and the
reaction temperature was elevated to 110 ꢀC for 24 h in n-butanol.

Q. Wu et al. / Tetrahedron 70 (2014) 3471e3477
3475
Table 5
Suzuki reaction of aryl bromides with arylboronic acids catalyzed by complex 1
Entry
1
Aryl bromide
Arylbonoric acid
Catalyst loading (mol %)
0.002
Yield (%)a
53
2
3
4
0.001
0.001
1
86
96
92
5
6
1
1
50
90
Reaction conditions: catalyst: complex 1, aryl bromide 0.5 mmol, arylboronic acid 0.75 mmol, NaOH 0.75 mmol, EtOH 3 ml, 80 ꢀC, 24 h.
a
Isolated yield.
4-Bromoanisole with phenylboronic acid could not be obtained
even in the presence of 2 mol % DAPCy at room temperature for
30 h. However, the reaction could perform smoothly in our catalytic
system and 82% yield of desired product was obtained in the
presence of 0.01 mol % catalyst 1 with 24 h (Table 6, entry 8). When
catalyst loading reduced to 0.001 mol %, the reaction of 4-
bromonitrobenzene, 4-bromobenzotrifluoride and 4-bromo-
benzonitrile with phenylboronic acid also gave the desired prod-
ucts in high yields of 99%, 88% and 97% in 24 h, respectively (Table 6,
entries 1e3). A high TON of up to 99,000 was achieved. Thus, the
results indicated that the complex 1 was still efficient in the cata-
lytic process at room temperature.
(30 mꢂ0.32 mmꢂ0.25
mm). The GC yields of the cross-coupling
reactions were determined from normalized peak areas using an
internal standard.
4.2. General procedure for the Suzuki reaction
In the reaction tube with a magnetic bar was added the solution
of aryl bromides (0.5 mmol) and phenylboronic acid (91 mg,
0.75 mmol), NaOH (24 mg, 0.6 mmol), complex
1
(0.0001e0.02 mol %, dissolved in DMA) and ethanol (3 mL). After
stirred for the required time in the preset conditions, the reaction
mixture was cooled to room temperature, and then quenched by
1 mL brine and 3 mL water, and extracted with ethyl acetate
(3ꢂ5 mL). The combined organic layer was dried over anhydrous
MgSO4 and the filtrate was concentrated to dryness under reduced
pressure. The crude products were purified by column chroma-
tography (petroleum ether, ethyl acetate) on silica gel.
3. Conclusions
An easy-to-handle catalytic system was reported for the Suzuki-
Miyaura coupling reaction using a new simple Pd(memantine)2Cl2
complex as catalyst. The new catalytic system provided a mild and
aerial condition for the coupling reaction of aryl bromides with
arylboronic acid. A wide range of substrates could be coupled with
arylboronic acids to afford the desired products in good to excellent
yields. Furthermore, the catalytic system also gives excellent yields
toward several heteroaryls. The catalytic reaction results demon-
strated that the complex 1 is a highly efficient catalyst in Suzuki
cross-coupling reaction.
4.3. Preparation of complex 1
A solution of memantine hydrochloride (86.3 mg, 0.4 mmol) in
dichloromethane (20 mL) was added dropwise to the 50 mL bottom
flask charged with Pd(OAc)2 (44.9 mg, 0.2 mmol) in dichloro-
methane (5 mL) at room temperature. After the reaction mixture
was stirred for 4 h at room temperature, the solvent was evapo-
rated in the reduced pressure to give a pale yellow solid. The crude
product was purified by column chromatography (petroleum ether/
ethyl acetate¼1:3 v/v) on silica gel. Yield: 50% (53.6 mg, 0.1 mmol)
4. Experiment section
4.1. General information
(mp>250 ꢀC). 1H NMR (400 MHz, CDCl3)
d 2.67 (s, 4H, NH2);
All the chemicals received from commercial suppliers were used
without further purifications unless noted. 1H and 13C NMR spectra
were recorded on a 400 MHz spectrometer using TMS as the in-
ternal standard. Gas chromatographic analyses were performed on
an Agilent 6890N GC System equipped with a SE-30 GC column
2.22e2.24 (m, 2H, CH); 1.86 (s, 4H, CH2); 1.64e1.74 (m, 8H, CH2);
1.28e1.39 (M, 8H, CH2); 1.17 (s, 4H, CH2); 0.92 (s,12H, CH3). 13C NMR
(101 MHz, CDCl3)
d 55.67, 51.09, 50.12, 43.43, 42.17, 33.04, 30.42,
29.95. HRMS-ESI. calcd for C24H42Cl2N2Pd (MþNa)þ¼557.1658,
found 557.1661.

3476
Q. Wu et al. / Tetrahedron 70 (2014) 3471e3477
Table 6
Suzuki reaction of various aryl bromides with phenylboronic acids catalyzed by complex 1 at room temperature
Entry
Aryl bromide
Pd (mol %)
Time (h)
Yield (%)a
1
2
3
4
5
6
7
8
9
0.001
0.001
0.001
0.01
0.01
0.01
0.01
0.01
0.01
24
24
24
24
24
24
24
24
24
99
88
97
95
95
97
71
82
94
10
11
12
0.01
0.01
0.01
24
24
24
81
73
65
Reaction conditions: catalyst: complex 1, aryl bromide 0.5 mmol, phenylboronic acid 0.75 mmol, NaOH 0.75 mmol, EtOH 3 ml, 25 ꢀC.
a
Isolated yield.
4.4. Crystal structure determination of complex 1
Supplementary data
A single crystal of complex 1 was grown by slow evaporation
of CH2Cl2/n-Hexane solvent system, the X-ray intensity data were
measured at 293 K on a Xcalibur, Eos diffractometer using
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.tet.2014.03.064.
graphite monochromated Mo Ka radiation (0.071070 nm). Using
References and notes
Olex2,29 the structure was solved with the Superflip30 structure
solution program using Charge Flipping and refined with the
ShelXL-201231 refinement package using Least Squares
minimisation.
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3185.
CCDC 968898 contains the supplementary crystallographic data
for complex 1. These data can be obtained free of charge from the
Cambridge Crystallographic Centre via www.ccdc.cam.ac.uk/
data_request/cif.
3. Kertesz, M.; Choi, C. H.; Yang, S. Chem. Rev. 2005, 105, 3448.
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E., Eds.; Springer: New York, NY, 2001; Vol. 82, pp 1e293.
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We are grateful to the Analytical and Testing Center of Sichuan
University for providing support with the characterization of
compounds.

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3477
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