A Polymer-Bound Monodentate-P-Ligated Palladium Complex as a Recyclable Catalyst for the Suzuki-Miyaura Coupling Reaction of Aryl Chlorides

Article abstract of DOI:10.1002/adsc.201500070

A three-fold cross-linked polymer-bound phosphine (POL-Ph₃P) with high phosphorus content has been prepared. The phosphorus-containing polymer forms a monodentate-P-ligated palladium complex, which shows excellent activity in Suzuki-Miyaura cross-coupling reactions of aryl chlorides. Importantly, the catalyst Pd/POL-Ph₃P is highly stable and can be reused for at least 10 times without losing reactivity.

Full text of DOI:10.1002/adsc.201500070

FULL PAPERS
DOI: 10.1002/adsc.201500070
A Polymer-Bound Monodentate-P-Ligated Palladium Complex as
a Recyclable Catalyst for the Suzuki–Miyaura Coupling Reaction
of Aryl Chlorides
Yun-Bing Zhou,+a Cun-Yao Li,+b Min Lin,a Yun-Jie Ding,b,*
and Zhuang-Ping Zhana,*
a
Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, Fujian,
Peopleꢀs Republic of China
E-mail: zpzhan@xmu.edu.cn
b
Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Science, Dalian
116023, Peopleꢀs Republic of China
E-mail: dyj@dicp.ac.cn
+
These authors contributed equally to this work.
Received: January 26, 2015; Revised: March 22, 2015; Published online: July 29, 2015
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201500070.
Abstract: A three-fold cross-linked polymer-bound stable and can be reused for at least 10 times without
phosphine (POL-Ph3P) with high phosphorus content losing reactivity.
has been prepared. The phosphorus-containing poly-
mer forms a monodentate-P-ligated palladium com-
plex, which shows excellent activity in Suzuki– Keywords: heterogeneous catalysts; metal binding
Miyaura cross-coupling reactions of aryl chlorides. ability; monodentate-P-ligated palladium complex;
Importantly, the catalyst Pd/POL-Ph3P is highly phosphines; Suzuki–Miyaura cross-coupling reaction
Introduction
ficult to activate the less reactive aryl chlorides using
catalysts derived from palladium and single-pointed
Palladium-catalyzed cross-coupling reactions, such as PS-Ph3P (Figure 1a) or two-fold cross-linked PS-
Suzuki–Miyaura, Sonogashira–Hagihara and Heck re- Ph3P, [6] probably because of the multidentate-P-ligat-
actions, have played a crucial role in the construction ing behavior of the polymeric ligand and the steric ef-
of carbon-carbon bonds.[1] Great efforts have been de- fects of the flexible PS backbone. Over the last few
voted to develop homogeneous palladium catalysts in years, monoligation of many phosphine ligands in ho-
the presence of phosphine ligands.[2] However, appli- mogeneous catalysis system has been achieved
cation of these homogeneous catalysts in industrial through different strategies and the resulting com-
settings is still limited because of their high cost and plexes have successfully induced cross-coupling reac-
the difficulty in recycling them from the products. tions of aryl chlorides.[7,8] Recently, Sawamuraꢀs group
Transition metal catalysts can be bound to ligand-con- reported a three-fold cross-linked PS-Ph3P covalently
taining polymers to form metal-polymer complexes.[3,4] bound hybrid (Figure 1b, PS-L3) which merely formed
These complexes are used as heterogeneous catalysts monodentate-P-ligated transition metal complexs as
to overcome some of the drawbacks of homogeneous a heterogeneous catalyst and showed high catalytic
catalysts. In this regard, polystyrene-supported phos- activity in Suzuki–Miyaura cross-coupling reactions of
phines (PS-Ph3P) have been used as ligands for heter- aryl chlorides.[9] However, the catalytic activity was
ogeneous catalysts.[4] For example, PS-Ph3P in com- reduced dramatically after being recycled for four
plex with palladium is employed for the cross-cou- times. Therefore, the development of heterogeneous
pling reactions of aryl iodides or bromides and aryl- catalysts with high reactivity and stability remains
boronic acids.[5] From an industrial point of view, the a big challenge.
use of aryl chlorides is attractive because they are rel-
Recently, we reported a porous organic ligand
atively cheap and readily available. However, it is dif- (POL-Ph3P, Figure 1c) supported rhodium species
Adv. Synth. Catal. 2015, 357, 2503 – 2508
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2503

FULL PAPERS
Yun-Bing Zhou et al.
Figure 1. (a) The single-pointed PS-L1. (b) The three-fold
cross-linked PS-L2 (R=H); PS-L3 (R=t-Bu). (c) The three-
fold cross-linked POL-Ph3P synthesized by us.
Scheme 1. Preparation of POL-Ph3P.
which exhibits high activity in the hydroformylation
of 1-octene.[10] We now hope to employ this polymer
as
a
supporting ligand for palladium-catalyzed
Suzuki–Miyaura cross-coupling reactions. POL-Ph3P POL-Ph3P was characterized by solid NMR, thermo-
is a new type of three-fold cross-linked polymer- gravimetry (TG), nitrogen adsorption-desorption
bound phosphine[11] and can be prepared through sol- analysis, X-ray diffraction (XRD) and X-ray photo-
vothermal polymerization of tris(p-vinylphenyl)phos- electron spectroscopy analysis (XPS). The 31P MAS
phine in the absence of styrene and divinylbenzene NMR spectrum of fresh POL-Ph3P exhibits an addi-
(see Scheme 1). Compared with polystyrene-support- tional small peak at 27 ppm corresponding to an oxi-
ed phosphine, this novel phosphine possesses a much dation state of phosphorus (P=O), which indicates ox-
higher P content and enhances metal binding ability. idation of P atom took place during the polymeri-
The POL-Ph3P-metal complex maintains high catalyt- zation (see the Supporting Information, Figure S3).
ic activities over many cycles. Furthermore, the three- Remarkably, the 31P MAS NMR spectrum of fresh
fold cross-linking results in an increased density of Pd/POL-Ph3P shows that the peak at 27 ppm is as-
the polymer chain around the P atom, limiting multi- signed to both the P atom in complex with palladium
dentate P-coordination to the palladium. In addition, and oxidation state of phosphorus (P=O) (see the
the monodentate-P-ligated palladium complex (Pd/ Supporting Information, Figure S6). The 31P MAS
POL-Ph3P) can be accessed easily by the substrates NMR spectrum of used Pd/POL-Ph3P shows the peak
because of the spacer effect of the three aromatic at 27 ppm with a relatively large peak area, compared
rings. Herein, we report the catalytic behavior of the with that of fresh Pd/POL-Ph3P, which can be attrib-
Pd/POL-Ph3P complex in Suzuki–Miyaura cross-cou- uted to oxidation of the P atom during the recycling
pling reactions employing aryl chlorides as substrates. as well (see the Supporting Information, Figure S7).
TG shows that the Pd/POL-Ph3P complex remains
intact at temperatures up to 4308C, demonstrating its
Results and Discussion
superior thermal stability (Figure 2c). Nitrogen ad-
sorption-desorption analysis shows that Pd/POL-Ph3P
PS-L1 (Figure 1a) and PS-L2 (Figure 1b) were synthe- possesses a high surface area and large pore volume,
sized in accordance with the reported procedure.[9] which are desirable for effective catalyst-substrate in-
The catalyst Pd/POL-Ph3P was prepared by impregna- teractions (Figure 2a and Figure 2b). XPS shows that
tion of POL-Ph3P with PdCl2(PhCN)2 in THF for 4 h. the binding energies of Pd 3d3/2 and Pd 3d5/2 in the
The palladium loading was measured to be fresh Pd/POL-Ph3P decrease to 342.7 eV and 337.4 eV
0.23 mmolgÀ1 by inductively coupled plasma atomic from 343.5 eV and 338.2 eV of PdCl2(PhCN)2, respec-
emission spectrometry (ICP-AES). The resulting Pd/ tively, as a result of coordination of PdCl2(PhCN)2
2504
asc.wiley-vch.de
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2015, 357, 2503 – 2508

FULL PAPERS
A Polymer-Bound Monodentate-P-Ligated Palladium Complex
Figure 2. (a) N2 sorption isotherms of Pd/POL-Ph3P. (b) Pore size distribution of Pd/POL-Ph3P (c) TG curve of Pd/POL-
.
Ph3P.
with POL-Ph3P (see the Supporting Information, Fig- reactions were conducted in toluene at 1008C using
ure S12a and Figure S12b). Interestingly, the XPS K2CO3 as a base. Remarkably, Pd/POL-Ph3P exhibit-
spectra of P 2d show that the fresh and used Pd/POL- ed a high catalytic activity and afforded the cross-cou-
Ph3P give the same binding energy of 132.2 eV (see pling product in 97% yield (Table 1, entry 1). In con-
the Supporting Information, Figure S12e and Fig- trast, Pd/PS-L1 provided the desired product in only
ure S12f). Additionally, the used Pd/POL-Ph3P gives 5% yield (Table 1, entry 2). Low activity was also ob-
a relatively high binding energy, compared with that served for Pd/PS-L2 under the same reaction condi-
of POL-Ph3P (131.9 eV), demonstrating coordination tions (Table 1, entry 3). It should be pointed out that
of Pd nanoparticles with POL-Ph3P (see the Support- no conversion of 4-chloroanisole was observed by
ing Information, Figure S12d).
using the homogeneous catalyst derived from
and tris(4-vinylphenyl)phosphane
To compare the reactivity of different catalysts, we PdCl2(PhCN)2
selected as a model reaction the cross-coupling of 4- (Table 1, entry 7). No conversion of 4-chloroanisole
chloroanisole and phenylboronic acid (Table 1). The was also obtained on using a commercial Pd/C
(5 wt% palladium) (Table 1, entry 4). Traditional ho-
mogeneous catalysts such as PdCl2(PPh3)2 and
Pd(PPh3)4 also failed (Table 1, entries 5 and 6).
Table 1. Suzuki–Miyaura coupling reactions using different
Pd catalysts.[a]
The catalytic efficiency of Pd/POL-Ph3P was inves-
tigated by employing various substituted aryl chlor-
ides for the cross-coupling reaction (Table 2). The ac-
tivated aryl chlorides were converted smoothly to the
desired products in excellent yields (Table 2, en-
tries 1–5). Deactivated aryl chlorides are usually diffi-
cult substrates for palladium-catalyzed cross-coupling
reactions.[12] However, under the standard conditions,
these substrates also reacted efficiently with phenyl-
boronic acids (Table 2, entries 6–11). Note that the
catalyst Pd/POL-Ph3P promoted the cross-coupling
reaction of 4-chloroaniline and 2-chloro-6-methylpyri-
dine with phenylboronic acids (Table 2, entries 10 and
11), which is difficult to achieve under other condi-
tions.[13]
Next, we examined the scope of the arylboronic
acids (Table 3). A substrate bearing a fused ring such
as naphthylboronic acid was successfully coupled with
aryl chloride (Table 3, entry 1). Arylboronic acids
containing electron-withdrawing groups (Table 3, en-
tries 2 and 3) or electron-donation groups (Table 3,
entries 4 and 5) were converted to the desired biphen-
yls in high yield. In addition, our Pd/POL-Ph3P cata-
lyst exhibited outstanding catalytic activity for the
[a]
Reaction conditions: 4-chloroanisole (0.50 mmol), phenyl-
boronic acid (0.75 mmol), Pd/POL-Ph3P (0.01 mmol Pd),
K2CO3 (1.00 mmol), toluene (3 mL), 1008C, 10 h.
[b]
Yield determined by 1H NMR analysis based on 4- coupling of n-butylboronic acid with 4-chloroaceto-
chloroanisole.
Tris(4-vinylphenyl)phosphane (0.02 mmol) was added.
phenone (Table 3, entry 6). To the best of our knowl-
edge, there are currently no reports on the cross-cou-
[c]
Adv. Synth. Catal. 2015, 357, 2503 – 2508
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
2505

FULL PAPERS
Yun-Bing Zhou et al.
Table 2. Suzuki cross-coupling reactions of aryl chlorides
Table 3. Suzuki coupling reactions of aryl chlorides with var-
with phenylboronic acids.[a]
ious arylboronic acids.[a]
[a]
Reaction conditions: aryl chloride (1.00 mmol), boronic
acid (1.50 mmol), Pd/POL-Ph3P (0.02 mmol Pd), K2CO3
(2.00 mmol), toluene (6 mL), 1008C.
[b]
Yield of isolated product (1H NMR yield in parenthesis).
porting Information, Figure S11). However, the TEM
images showed that the Pd nanoparticles with a mean
diameter of about 5 nm were formed after the third
run (Figure 3b and Figure 3c). Interestingly, no obvi-
ous aggregation of these nanoparticles occurred up to
the 10th run (Figure 3d). With a high ratio of P/Pd
(12:1), Pd/POL-Ph3P could maintain high catalytic ac-
tivities, although oxidation of a small number of P
atoms took place during the recycling.
[a]
Reaction conditions: aryl chloride (1.00 mmol), phenyl-
boronic acid (1.50 mmol), Pd/POL-Ph3P (0.02 mmol Pd),
K2CO3 (2.00 mmol), toluene (6 mL), 1008C.
[b]
Yield of isolated product (1H NMR yield in parenthesis).
pling reaction of alkylboronic acids with aryl chlorides Conclusions
using a heterogeneous catalyst.
The reaction of 4-chloroacetophenone with phenyl- In conclusion, we have prepared a three-fold cross-
boronic acid was selected to evaluate the reusability linked polymer-bound phosphine with a high content
of Pd/POL-Ph3P (Table 4). After each run, the cata- of P. This phosphorus ligand-containing polymer
lyst was recovered by filtration and washed with H2O, forms a monodentate-P-ligated palladium complex,
THF, and toluene. The catalyst could be effectively which displays excellent reactivity in Suzuki–Miyaura
used for at least 10 cycles without losing efficiency. cross-coupling reactions of aryl chlorides. Importantly,
During the recycling, the Pd species in the filtrate are the catalyst complex is highly stable as demonstrated
undetectable (<10 ppb), suggesting there is almost no by the negligible metal leaching and excellent reusa-
Pd leaching, which is desirable in the synthesis of fine bility. These desirable properties of Pd/POL-Ph3P can
chemicals and pharmaceutical intermediates.[14] The be attributed to its high P content, which prevents ag-
morphology of the catalyst after each run was studied gregation and agglomeration of Pd nanoparticles.
by transmission electron microscopy. There were no Studies on the application of POL-Ph3P to other
Pd nanoparticles on the fresh catalyst, as evidenced metal-catalyzed reactions are underway in our labora-
by TEM image (Figure 3a) and XRD (see the Sup- tory.
2506
asc.wiley-vch.de
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2015, 357, 2503 – 2508

FULL PAPERS
A Polymer-Bound Monodentate-P-Ligated Palladium Complex
Table 4. Recycling studies of Pd/POL-PPh3.[a]
[a]
[b]
Reaction conditions: 4-chloroacetophenone (1.00 mmol), phenylboronic acid (1.50 mmol),
Pd/POL-Ph3P (0.02 mmol Pd), K2CO3 (2.00 mmol), toluene (6 mL), 1008C, 3 h.
Yield determined by H NMR analysis based on 4-chloroacetophenone.
1
Figure 3. (a) TEM image of Pd/POL-Ph3P before use. (b)and (c) TEM images of Pd/POL-Ph3P recovered after third run. (d)
TEM image of Pd/POL-Ph3P recovered after tenth run.
closed with Kel-F cap which was spun at 12 kHz. 1H CP/
MAS and 13C CP/MAS spectra were referenced to adaman-
tane (C10H16) as standard (1.63 ppm). 31P CP/MAS were ref-
erenced to adenosine diphosphate (ADP) (0.0 ppm). Nitro-
gen sorption isotherms at the temperature of liquid nitrogen
were peformed on a Quantachrome Autosorb-1. ICP-AES
analyses of solid samples were peformed on a Perkin–Elmer
ICP-OES 7300DV while ICP-AES analyses of liquid sam-
ples were peformed on a Perkin–Elmer ICP-MS 300D. Ther-
mogravimetry analyses were peformed on a Netzsch TG-
DSC. Transmission electron microscope (TEM) images were
performed using a JEM-2100 with an accelerating voltage of
200 kV. The XRD was peformed on a XRD X,pertPro. The
XPS were conducted using a Thermo Scientific and the
spectrometer binding energy was calibrated through the ref-
erence C 1s (284.6 eV).
Experimental Section
General Methods and Materials
The liquid-state NMR spectra were recorded on a 400 MHz
spectrometer. Chemical shifts were reported in ppm.
1H NMR spectra were referenced to CDCl3 (7.28 ppm), and
13C NMR spectra were referenced to CDCl3 (77.0 ppm). All
13C NMR spectra were measured with complete proton de-
coupling. Peak multiplicities were designated by the follow-
ing abbreviations: s, singlet; d, doublet; t, triplet; m, multip-
let; brs, broad singlet and J, coupling constant in Hz. The
solid-state NMR was recorded on a Bruker AVANCE III
400 WB spectrometer equipped with a 4 mm standard bore
CP/MAS probehead whose channel was tuned to
400.18 MHz. The samples were packed in the ZrO2 rotor
Adv. Synth. Catal. 2015, 357, 2503 – 2508
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
2507

FULL PAPERS
Yun-Bing Zhou et al.
Chem. 2005, 117, 4516–4563; Angew. Chem. Int. Ed.
2005, 44, 4442–4489; c) K. W. Anderson, S. L. Buch-
wald, Angew. Chem. 2005, 117, 6329–6333; Angew.
Chem. Int. Ed. 2005, 44, 6173–6177; d) R. Martin, S. L.
Buchwald, Acc. Chem. Res. 2008, 41, 1555–1564.
[3] a) J. N. Lu, P. H. Toy, Chem. Rev. 2009, 109, 815–838;
b) Y. Zhang, S. N. Riduan, Chem. Soc. Rev. 2012, 41,
2083–2094.
Preparation of POL-Ph3P
Under nitrogen, tris(4-vinylphenyl)phosphane (10.0 g) was
dissolved in THF (100 mL), followed by the addition of
AIBN (1.0 g) at room temperature. Next, the mixture was
transferred into an autoclave at 1008C for 24 h. After evap-
oration of THF under vacuum, a white solid was obtained;
yield: 9.6 g (96%).
[4] N. E. Leadbeater, M. Marco, Chem. Rev. 2002, 102,
3217–3274.
Preparation of Pd/POL-Ph3P
[5] a) I. Fenger, C. L. Drian, Tetrahedron Lett. 1998, 39,
4287–4290; b) T. Y. Zhang, M. J. Allen, Tetrahedron
Lett. 1999, 40, 5813–5816.
Under nitrogen, PdCl2(PhCN)2 (104 mg) was dissolved in
THF (40 mL), followed by the addition of POL-Ph3P (1.0 g).
Next, the mixture was stirred 4 h at room temperature.
After filtration and evaporation under vacuum, a yellow
solid was obtained; yield: 1.1 g (99%).
[6] W. M. McKenzie, D. C. Sherrington, J. Polym. Sci.
Polym. Chem. Ed. 1982, 20, 431–441.
[7] a) Q.-S. Hu, Y. Lu, Z.-Y. Tang, H.-B. Yu, J. Am. Chem.
Soc. 2003, 125, 2856–2857; b) T. Yamamoto, Y. Akai, Y.
Nagata, M. Suginome, Angew. Chem. 2011, 123, 9006–
9009; Angew. Chem. Int. Ed. 2011, 50, 8844–8847.
[8] a) T. Iwasawa, T. Komano, A. Tajima, M. Tokunaga, Y.
Obora, T. Fujihara, Y. Tsuji, Organometallics 2006, 25,
4665–4669; b) H. Ohta, M. Tokunaga, Y. Obora, T.
Iwai, T. Iwasawa, T. Fujihara, Y. Tsuji, Org. Lett. 2007,
9, 89–92; c) T. Fujihara, S. Yoshida, H. Ohta, Y. Tsuji,
Angew. Chem. 2008, 120, 8434–8438; Angew. Chem.
Int. Ed. 2008, 47, 8310–8314; d) T. Fujihara, S. Yoshida,
J. Terao, Y. Tsuji, Org. Lett. 2009, 11, 2121–2124;
e) D. J. M. Snelders, G. van Koten, R. J. M. K. Gebbink,
J. Am. Chem. Soc. 2009, 131, 11407–11416; f) W. K.
Chow, O. Y. Yuen, C. M. So, W. T. Wong, W. Y. Kwong,
J. Org. Chem. 2012, 77, 3543–3548.
General Procedure for Suzuki–Miyaura Cross-
Coupling Reactions
Typically, aryl chloride (1.0 mmol), arylboronic acid
(1.5 mmol), K2CO3 (2.0 mmol) and palladium catalyst
(2 mol%) were added to toluene (6 mL) under an N2 atmos-
phere, and the reaction mixture was stirred at 1008C for the
desired number of hours. When the reaction was completed,
the solution was filtered and washed with toluene and ether.
The filtered solution was subsequently dried over Na2SO4
and evaporated under vacuum. The crude was purified di-
rectly by silica gel column chromatography eluting with pe-
troleum ether and ethyl acetate to afford the corresponding
product.
[9] T. Iwai, T. Harada, K. Hara, M. Sawamura, Angew.
Chem. 2013, 125, 12546–12552; Angew. Chem. Int. Ed.
2013, 52, 12322–12326.
[10] Q. Sun, M. Jiang, Z. J. Shen, Y. Y. Jin, S. X. Pan, L.
Wang, X. J. Meng, W. Z. Chen, Y. J. Ding, J. X. Li, F.-S.
Xiao, Chem. Commun. 2014, 50, 11844–11847.
[11] J. Lloret, M. Stern, F. Estevan, M. Sanau, M. A. Ubeda,
Organometallics 2008, 27, 850–856.
Acknowledgements
Financial support from National Natural Science Foundation
of China (No. 21272190) and PCSIRT in University.
[12] A. F. Littke, G. C. Fu, Angew. Chem. 2002, 114, 4350–
4386; Angew. Chem. Int. Ed. 2002, 41, 4176–4211.
[13] a) N. Kudo, M. Perseghini, G. C. Fu, Angew. Chem.
2006, 118, 1304–1306; Angew. Chem. Int. Ed. 2006, 45,
1282–1284; b) K. L. Billingsley, K. W. Anderson, S. L.
Buchwald, Angew. Chem. 2006, 118, 3564–3568;
Angew. Chem. Int. Ed. 2006, 45, 3484–3488; c) C. A.
Fleckenstein, H. Plenio, Chem. Eur. J. 2008, 14, 4267–
4279.
References
[1] a) N. Miyaura, A. Suzuki, Chem. Rev. 1995, 95, 2457–
2483; b) L. X. Yin, J. Liebscher, Chem. Rev. 2007, 107,
133–173; c) P. Das, D. Sharma, A. K. Shil, A. Kumari,
Tetrahedron Lett. 2011, 52, 1176–1178; d) A. K. Shil,
N. R. Guha, D. Sharma, P. Das, RSC Adv. 2013, 3,
13671–13676.
[2] a) U. Christmann, R. Vilar, Angew. Chem. 2005, 117,
370–378; Angew. Chem. Int. Ed. 2005, 44, 366–374;
b) K. C. Nicolaou, P. G. Bulger, D. Sarlah, Angew.
[14] C. E. Garrett, K. Prasad, Adv. Synth. Catal. 2004, 346,
889–900.
2508
asc.wiley-vch.de
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2015, 357, 2503 – 2508