Synthesis of a palladium complex bearing 2-phenylbenzothiazole and its application to Suzuki–Miyaura coupling reaction

Article abstract of DOI:10.1002/jccs.201800145

The palladacycle complex [L^sPdOAc]₂ bearing 2-phenyl benzothiazole was synthesized and characterized by NMR and X-ray crystallography. [L^sPdOAc]₂ was used as a catalyst in the Suzuki–Miyaura cross coupling reaction of 4-bromotoluene with phenylboronic acid, which resulted in a conversion of >90% with 5 mol% of the Pd complex within 10 min at 60°C.

Full text of DOI:10.1002/jccs.201800145

Received: 18 April 2018
Revised: 11 August 2018
Accepted: 24 August 2018
DOI: 10.1002/jccs.201800145
A R T I C L E
Synthesis of a palladium complex bearing 2-phenylbenzothiazole
and its application to Suzuki–Miyaura coupling reaction
1
1
1
2
Someswara Rao Kosuru | Hsin-Yu Lai | Chien-Yi Yang | Gopal Chandru Senadi |
1
1,3,4
Yi-Chun Lai | Hsuan-Ying Chen
1
Department of Medicinal and Applied Chemistry,
s
The palladacycle complex [L PdOAc] bearing 2-phenyl benzothiazole was synthe-
Kaohsiung Medical University, Kaohsiung,
Taiwan, Republic of China
2
s
sized and characterized by NMR and X-ray crystallography. [L PdOAc] was used
as a catalyst in the Suzuki–Miyaura cross coupling reaction of 4-bromotoluene with
phenylboronic acid, which resulted in a conversion of >90% with 5 mol% of the
Pd complex within 10 min at 60 C.
2
2
Department of Chemistry, SRM Research
Institute, SRM University, Chennai, Tamilnadu,
India
ꢀ
3
Department of Medical Research, Kaohsiung
Medical University Hospital, Kaohsiung, Taiwan,
Republic of China
KEYWORDS
4
Department of Chemistry, National Sun Yat-sen
palladium, Suzuki–Miyaura cross coupling reaction
University, Kaohsiung, Taiwan, Republic of China
Correspondence
Hsuan-Ying Chen, Department of Medicinal and
Applied Chemistry, Kaohsiung Medical University,
Kaohsiung 80708, Taiwan, Republic of China.
Email: hchen@kmu.edu.tw
Funding information
Kaohsiung Medical University, Grant/Award
Number: NSYSUKMU 107-P010; Ministry of
Science and Technology, Taiwan, Grant/Award
Number: MOST 106-2113-M-037 -002
[
6]
1
| INTRODUCTION
revealed great catalytic activity. A palladacycle complex
bearing benzothiazole was reported, but no catalytic activity
toward the Suzuki coupling reaction was studied. In this
Transition-metal-mediated catalytic cross-coupling reactions,
such as Mizoroki–Heck,[1d] Negishi,[1f] Suzuki–
paper, we report the synthesis of a 2-phenyl benzothiazole-
s
Miyaura,[1e]
Sonogashira,[1g]
Kumada–Corriu,[1h]
derived Pd complex [L PdOAc]
2
and its application toward
Hiyama,[1i] and Stille[1c] coupling reactions, are powerful
Suzuki coupling reactions (Figure 1).
methods for the construction of Caryl–Caryl or Caryl–Calkyl
[
1]
bonds
and other functions.[1b] Among these cross-
2
2
| RESULTS AND DISCUSSION
coupling reactions, Suzuki coupling reaction[1e,2] is one of
the most important methods for the synthesis of biaryl com-
pounds because boronic acids, which are less toxic and safer
to the environment, are used as the precursor under mild
s
.1 | Synthesis and characterization of [L PdOAc]2
s
[L PdOAc] was synthesized from Pd(OAc) and 2-phenyl
2
2
[3]
ꢀ
reaction conditions. Phosphines and N-heterocyclic car-
benzothiazole in acetic acid at 60 C and crystalized in THF
at −20 C. The anti and syn isomers of [L PdOAc] were
clearly observed by H NMR spectroscopy (Figure 2), which
were consistent with those reported in the literature. In
Figure 2, the anti isomer shows a larger ratio than the syn
isomer. The crystal structure of [L PdOAc] (Figure 3) was
analyzed by X-ray crystallography, which revealed a square-
[
4]
s
ꢀ
benes (NHCs) are the commonly employed ligands for
Suzuki coupling reactions because they adjust the electron
density surrounding the metal center, facilitating steps such
as oxidative addition and reductive elimination (through ste-
2
1
[
6]
[
5]
s
ric bulk). Recently, cyclometalated Pd complexes were
used as catalysts for the Suzuki coupling reaction, and they
2
©
2018 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
J Chin Chem Soc. 2018;1–4.
http://www.jccs.wiley-vch.de
1

2
KOSURU ET AL.
s
2
FIGURE 1 Synthesis of palladacycle complex ([L PdOAc] )
s
FIGURE 3 Molecular structure of [L PdOAc]
2
(CCDC 1826155) as 20%
ellipsoids and all hydrogen atoms were omitted for clarity. Selected
distances and angles: d(C(5)-Pd(1)) = 1.960(4) Å, d(C(18)-Pd(2)) = 1.972
(4) Å, d(N(1)-Pd(1)) = 2.023(3) Å, d(N(2)-Pd(2)) = 2.043(3) Å, d(O(1)-Pd
(1)) = 2.132(3) Å, d(O(2)-Pd(2)) = 2.046(3) Å, d(O(3)-Pd(2)) = 2.153
(3) Å, d(O(4)-Pd(1)) = 2.035(3) Å, d(Pd(1)-Pd(2)) = 2.8577(5) Å, d(C(10)-
C(11)) = 1.450(6) Å, d(C(23)-C(24)) = 1.441(6) Å, ∠C(5)-Pd(1)-N
ꢀ
ꢀ
ꢀ
(
(
1) = 81.03(16) , ∠C(18)-Pd(2)-N(2) = 81.82(16) , ∠O(4)-Pd(1)-O
ꢀ
1) = 87.31(13) , ∠O(2)-Pd(2)-O(3) = 88.55(12)
1
s
FIGURE 2
H NMR spectrum of [L PdOAc]
2
planar geometry of the dinuclear Pd complex with two
-phenyl benzothiazoles and two bridging acetates. The
bond lengths and bond angles were compared with those of
2
ꢀ
s
FIGURE 4 Select bond distances (Å) and bond angles ( ) of [L PdOAc]
2
o
and [L PdOAc]
2
o
[5]
2
(
-phenyl benzoxazole-derived Pd complex [L PdOAc]2
Figure 4). The data revealed that the two complexes have
similar geometry. The only differences are that the angles
mixed solvent CH CN + H O [1:1] with NaOH as the base
showed lower catalytic activity (conversion 66%, entry 7 in
Table 1) than in the mixed solvent DMF + H O (1:1, con-
version 91%, entry 6 in Table 1). Using the mixed solvent
system reduced the reaction time to 10 min (conversion 90%
for the mixed solvent DMF + H O (entry 8) and 86% for
CH CN + H O (entry 9)). When the reaction temperature
was brought down to 30 C, the conversion was 85% in a 1:1
3
2
s
ꢀ
ꢀ
∠
N–Pd–C of [L PdOAc] (81.02 and 81.82 ) are smaller
2
2
o
than those of [L PdOAc] (90.50, 90.47, 90.59, and 89.24),
2
and the distances between the phenyl and benzothiazolyl
s
groups of [L PdOAc] (d(C(10)–C(11)) = 1.450(6) Å, d(C
2
2
(
23) –C(24)) = 1.441(6) Å in Figure 4) are smaller than
3
2
o
those of [L PdOAc] (1.389–1.409 Å).
ꢀ
2
mixture of DMF + H O after 60 min (entry 10), 80% after
2
2
.2 | Suzuki coupling reaction
3
0 min (entry 11), and 68% after 10 min (entry 12). How-
s
ever, the conversion was only 17% while using a 1:1 mixture
[L PdOAc] was tested as a catalyst for the Suzuki cross-
2
ꢀ
of CH CN + H O at 30 C after 60 min (entry 13). With
coupling reaction of 4-bromotoluene with phenylbronic acid
to synthesize 4-methyl-1,1 -biphenyl. We first performed the
optimization of solvents and bases for the coupling reaction
of 4-bomotoluene and phenylboronic acid with 5 mol% of
3
2
0
reduced Pd loading of 1 mol% in the solvent mixture
DMF + H O, the conversion was 62%. It showed that
[L PdOAc] was a great catalyst for the Suzuki coupling
2
2
s
s
s
[L PdOAc] as catalyst (Table 1). As shown in entries 1–5
reaction. [L PdOAc]
was tested as the catalyst of choice for
2
2
in Table 1, Cs CO was used as the base and the solvent sys-
tem was varied. The mixed solvents DMF + H O (1:1, entry
an entire set of substrates (Table 2). In the condition of entry
2
3
s
8 of Table 1, [L PdOAc]
was also effective with various
2
2
4
) and CH CN + H O (1:1, entry 5) both revealed the high-
substrates in Table 2. However, aryl chlorides were inactive
3 2
ꢀ
s
est catalytic activity with conversions of >90% at 60 C after
hr. However, performing the coupling reaction in the
when using [L PdOAc]
as catalyst in this reaction condi-
2
3
tion, and therefore their results are not reported.

KOSURU ET AL.
3
s
2
TABLE 1 Suzuki coupling reaction of 4-bromotoluene and phenylboronic acid by using the complex [L PdOAc] as catalyst
ꢀ
a
Entry
Base
Solvent
DMSO
Time (min)
360
360
360
180
180
180
180
10
Temperature ( C)
Yield (%)
Trace
79/60
34/20
91/85
91/83
91/86
66/50
90/80
86/79
85/75
80/70
68/55
1
2
3
4
5
6
7
8
9
Cs
2
Cs
2
Cs
2
Cs
2
Cs
2
CO
CO
CO
CO
CO
3
3
3
3
3
60
60
60
60
60
60
60
60
60
30
30
30
30
30
DMF
1,4-Dioxane
DMF + H
CH CN + H
DMF + H
CH CN + H
DMF + H
CH CN+ H
2
O
3
2
O
O
NaOH
NaOH
2
O
3
2
Cs
2
Cs
2
Cs
2
Cs
2
Cs
2
Cs
2
Cs
2
CO
CO
CO
CO
CO
CO
CO
3
3
3
3
3
3
3
2
O
3
2
O
10
10
11
12
13
14
DMF + H
DMF + H
DMF + H
2
O
2
O
2
O
60
30
10
c
CH
3
CN + H
2
O
60
17/ –
b
DMF + H
2
O
10
62/50
s
Reaction conditions: 4-Bromotoluene 0.5 mmol, phenylboronic acid 0.5 mmol, base 1 mmol, and [L PdOAc]
2
5 mol% in solvent (3 mL).
a
GC yield/isolated yield.
b
c
s
[
L PdOAc]
2
1 mmol%.
Not available.
s
TABLE 2 Suzuki coupling reaction of various aryl halides and phenylboronic acid by using the complex [L PdOAc]
2
as a catalyst
a
Entry
Aryl halide
Product
Conversion yield (%)
Isolated yield (%)
1
95
91
2
90
85
3
4
5
6
95
86
90
90
91
80
83
85
s
ꢀ
Reaction conditions: aryl halide 0.5 mmol, phenylboronic acid 0.5 mmol, Cs
2
CO
3
1 mmol, and [L PdOAc]
2
5 mol% in solvent (3 mL, DMF + H
2
O (1:1)) at 60 C in
1
0 min.
H NMR yield.
a 1
3
| CONCLUSIONS
4 | EXPERIMENTAL
s
The palladacycle [L PdOAc] was synthesized and charac-
2
4
.1 | General
Standard Schlenk techniques and a N -filled glove box were
2
terized. Its structure was identified by X-ray crystallography.
s
The exceptional catalytic reactivity of [L PdOAc] was dem-
2
used throughout the isolation and handling of all the com-
pounds. Solvents and deuterated solvents were purified prior
to use. Deuterated chloroform was purchased from Acros.
onstrated with the Suzuki cross-coupling reaction of
4
-bromotoluene with phenylboronic acid, with 80% conver-
ꢀ
sion at 30 C after 1 hr.

4
KOSURU ET AL.
Adv. 2014, 4, 53442. (c) C. Cordovilla, C. Bartolomé,
J. M. Martínez-Ilarduya, P. Espinet, ACS Catal. 2015, 5, 3040.
3
4
4
-Iodobenzotrifluoride, 2-bromobenzaldehyde, 4-iodophenol,
-fluoroiodobenzene, 1,4-dibromobenzene, 4-bromoanisole,
-bromotoluene, phenylboronic acid, 2-aminothiophenol,
(d) G.-Y. Yang, S.-S. Wang, Catal. Sci. Technol. 2016, 6, 2862.
e) A. D. Zotto, D. Zuccaccia, Catal. Sci. Technol. 2017, 7, 3934. (f )
(
benzaldehyde, and palladium acetate were purchased from
Aldrich. Cesium carbonate and sodium hydroxide were pur-
D. Haas, J. M. Hammann, R. Greiner, P. Knochel, ACS Catal. 2016, 6,
540. (g) G. Evano, K. Jouvin, C. Theunissen, C. Guissart, A. Laouiti,
1
C. Tresse, J. Heimburger, Y. Bouhoute, R. Veillard, M. Lecomte, A. Nitelet,
S. Schweizer, N. Blanchard, C. Alayrace, A.-C. Gaumont, Chem. Commun.
2014, 50, 10008. (h) X. Y. Hua, J. Masson-Makdissi, R. J. Sullivan,
S. G. Newman, Org. Lett. 2016, 18, 5312. (i) A. B. Smith III. , A. T. Hoye,
D. Martinez-Solorio, W.-S. Kim, R. Tong, J. Am. Chem. Soc. 2012, 134,
1
13
chased from Alfa. H and C NMR spectra were recorded on
1
a Varian Gemini2000-200 (200 MHz for H and 50 MHz for
1
3
C) spectrometer with chemical shifts given in ppm from the
internal TMS or center line of CDCl . 2-Phenylbenzothiazole
3
4
533.
[2] (a) R. Martin, S. L. Buchwald, Accounts Chem. Res. 2008, 41, 1461.
b) A. Suzuki, Angew. Chem. Int. Ed. 2011, 50, 6723. (c) G. A. Molander,
[7]
was prepared following literature procedures.
(
B. Canturk, Angew. Chem. Int. Ed. 2009, 48, 9240. (d) A. Kumar,
G. K. Rao, S. Kumar, A. K. Singh, Dalton Trans. 2013, 42, 5200.
[3] C. C. C. Johansson, T. Sperger, T. G. Scrase, F. Schoenebeck, T. J. Colacot,
J. Am. Chem. Soc. 2017, 139, 5194.
4
.2 | General procedure for the Suzuki–Miyaura cross-
coupling reaction of 4-bromotoluene with
phenylbronic acid
[
[
4] Q. Deng, Y. Shen, H. Zhu, T. Tu, Chem. Commun. 2017, 53, 13063.
5] (a) P. Agarwal, N. Thirupathi, M. Nethaji, Organometallics 2016, 35, 3112.
A typical procedure is exemplified by the synthesis of entry
1
(
(
b) R. H. Fath, S. J. Hoseini, J. Organomet. Chem. 2017, 828, 16.
c) A. Avila-Sorrosa, H. A. Jiménez-Vázquez, A. Reyes-Arellano,
(Table 1). 4-Bromotoluene (0.5 mmol), phenylboronic acid
s
(0.5 mmol), and Cs CO (1 mmol) with [L PdOAc] (5 mol
2 3 2
J. R. Pioquinto-Mendoza, R. A. Toscano, L. González-Sebastián,
D. Morales-Morales, J. Organomet. Chem. 2016, 819, 69. (d) C. Xu,
H.-M. Li, Z.-Q. Xiao, Z.-Q. Wang, S.-F. Tang, B.-M. Ji, X.-Q. Hao,
M.-P. Song, Dalton Trans. 2014, 43, 10235. (e) P. G. Gildner, T. J. Colacot,
ꢀ
%
) as a catalyst were stirred at 60 C in DMSO (3 mL). After
360 min, the solution was cooled to room temperature,
diluted with CH Cl , and filtered through silica gel with
copious washing (CH Cl ). The yield was determined by
gas chromatography (GC).
2
2
ꢀ
Organometallics 2015, 34, 5497. (f ) K. Muniz, Angew. Chem. Int. Ed.
2009, 48, 9412. (g) R. Mamidala, V. Mukundam, K. Dhanunjayarao,
K. Venkatasubbaiah, Dalton Trans. 2015, 44, 5805. (h) N. C. Bruno,
N. Niljianskul, S. L. Buchwald, J. Org. Chem. 2014, 79, 4161.
2
2
[
6] C. Navarro-Ranninger, F. Zamora, L. A. Martínez-Cruz, R. Isea,
J. R. Masaguer, J. Organomet. Chem. 1996, 518, 29.
ACKNOWLEDGMENTS
[7] Y.-T. Huang, W.-C. Wang, C.-P. Hsu, W.-Y. Lu, W.-J. Chuang,
M. Y. Chiang, Y.-C. Lai, H.-Y. Chen, Polym. Chem. 2016, 7, 4367.
This study was supported by Kaohsiung Medical University,
NSYSU-KMU Joint Research Project (#NSYSUKMU
107-P010), and the Ministry of Science and Technology
(Grant MOST 106-2113-M-037-002). We thank the Center
How to cite this article: Kosuru SR, Lai H-Y,
for Research Resources and Development, Kaohsiung Medi-
cal University, for instrumentation and equipment support.
Yang C-Y, Senadi GC, Lai Y-C, Chen H-Y. Synthesis
of
a
palladium
complex
bearing
2-
phenylbenzothiazole and its application to Suzuki–
Miyaura coupling reaction. J Chin Chem Soc. 2018;
REFERENCES
1–4. https://doi.org/10.1002/jccs.201800145
[1] (a) J. Hassan, M. Sévignon, C. Gozzi, E. Schulz, M. Lemaire, Chem. Rev.
2
002, 102, 1359. (b) M. Karak, L. C. A. Barbosa, G. C. Hargadenc, RSC