A new homogeneous polymer support based on syndiotactic polystyrene and its application in palladium-catalyzed Suzuki-Miyaura cross-coupling reactions

Article abstract of DOI:10.1039/b913060h

Soluble syndiotactic polystyrene-supported triphenylphosphine (sPS-TPP) was synthesized by reacting borylated syndiotactic polystyrene with (4-bromophenyl)diphenylphosphine. A palladium catalyst, supported on sPS-TPP, effectively catalyzed Suzuki-Miyaura coupling reactions of aryl halides under homogeneous conditions. The polymer-supported palladium complex was recovered quantitatively by adding an equal volume of poor solvent to the polymer, and coupling products could be easily isolated by evaporating the solvents. The recovered polymer complex was reused several times without significant loss of activity. The Royal Society of Chemistry 2009.

Full text of DOI:10.1039/b913060h

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/greenchem | Green Chemistry
A new homogeneous polymer support based on syndiotactic polystyrene
and its application in palladium-catalyzed Suzuki–Miyaura
cross-coupling reactions
Jihoon Shin, Julie Bertoia, Kenneth R. Czerwinski and Chulsung Bae*a
a
b
a,b
Received 7th May 2009, Accepted 23rd June 2009
First published as an Advance Article on the web 17th July 2009
DOI: 10.1039/b913060h
Soluble syndiotactic polystyrene-supported triphenylphosphine (sPS–TPP) was synthesized by
reacting borylated syndiotactic polystyrene with (4-bromophenyl)diphenylphosphine. A
palladium catalyst, supported on sPS–TPP, effectively catalyzed Suzuki–Miyaura coupling
reactions of aryl halides under homogeneous conditions. The polymer-supported palladium
complex was recovered quantitatively by adding an equal volume of poor solvent to the polymer,
and coupling products could be easily isolated by evaporating the solvents. The recovered polymer
complex was reused several times without significant loss of activity.
Introduction
precipitated and filtered, allowing its expeditious recovery. Thus,
these soluble polymer supports offer the advantage of use under
homogeneous conditions and convenient catalyst separation.
Homogeneous catalysts display better efficiency and higher
selectivity than their heterogeneous counterparts, but tedious
and time-consuming purification steps are required to remove
homogeneous catalysts from the reaction mixture, making
recovery and recycling difficult. Since the introduction of the
Merrifield resin for peptide synthesis, cross-linked polystyrene-
supported catalysts have been adopted for numerous organic
Among the soluble polymer supports, oligomeric
-1 10
poly(ethylene glycol) (PEG, M
n
= 3–5 kg mol ), oligomeric
-1 11
polyethylene (PE, M
n
ª 3 kg mol ), and non-cross-linked
1
12
atactic polystyrene (aPS) are the most common supports
used in organic synthesis and combinatorial chemistry. These
supports have drawbacks that need to be addressed, however.
For example, because PEG is soluble in water, it is unsuitable
for organic reactions that involve aqueous work-up. In addition,
PEG and PE are end-functionalized polymer supports,
therefore, they have only modest loading capacity—typically
2
reactions to facilitate product purification and catalyst recovery.
Catalysts have also been supported on insoluble materials such
3
4
5
as activated carbon, zeolite, metal oxide, insoluble polymer
6
7
resin, and mesoporous silica nano particles. Despite the advan-
tage of convenient separation, however, heterogeneous catalysts
generally have slow diffusion rates, difficult characterizations,
and lower activity owing to the nature of heterogeneous reaction
-1
-1
less than 0.3 mmol g for PEG and 0.1 mmol g for PE. aPS
is difficult to recover in high yield via the precipitation method
13
and often needs membrane filtration. Thus, studies of recovery
8
conditions. It is also generally known that heterogeneous
14
yield of soluble polymer supports have often been omitted.
catalysis exhibits a lower degree of selectivity compared to
the homogeneous counterpart, even though some exceptions
of more selective heterogeneous catalysts have been found.
Soluble polymer supports have been studied as a way to
overcome the problems of insoluble supports. Soluble polymer
supports allow expeditious transfer of solution-based synthetic
protocols, circumventing the extensive optimization process
often required in heterogeneous reactions. After the addition
of an appropriate poor solvent, the polymer support can be
Herein we report a new type of soluble polymer support
derived from crystalline syndiotactic polystyrene (sPS). Al-
though various loading capacities can be achieved in aPS
by changing functional group levels in the side chain of the
polymer, the addition of excess cold poor solvent or membrane
filtration is required to recover the atactic polymer in high yield
and it often causes non-quantitative recovery on precipitation.
Compared to aPS, sPS and functionalized sPS show a more
restrictive solubility profile because of their high stereoregular
configuration of phenyl rings along the polymer main chain and
9
15
a
the resulting tendency toward crystallization. We theorized
that this solubility versus recovery relationship of crystalline
polymer—a well-known phenomenon in polymer chemistry—
could lead to better recovery yield of the polymer support when
precipitated with a poor solvent.
Department of Chemistry, University of Nevada Las Vegas, 4505
Maryland Parkway, Box 454003, Las Vegas, Nevada, 89154-4003, USA.
E-mail: chulsung.bae@unlv.edu; Fax: +1 702 8954072
b
Harry Reid Center for Environmental Studies, University of Nevada Las
Vegas, 4505 Maryland Parkway, Box 454009, Las Vegas, Nevada,
8
9154-4009, USA
Recently, we reported a controlled functionalization of sPS
via an iridium-catalyzed activation/borylation of aromatic
C–H bonds. The functionalization allowed the introduction
of a pinacolboronate ester [B(pin)] group in a quantity of up
†
Electronic supplementary information (ESI) available: Experimental
details of recycling experiment on sPS-supported catalyst without
addition of fresh Cs CO , analytical data for the characterization
of the isolated coupled products, and the spectral data of TPP–Br,
sPS–TPP, and the isolated coupled products are reported. See DOI:
2
3
16
1
0.1039/b913060h
to 42 mol%. While working on the functionalization of sPS
1
576 | Green Chem., 2009, 11, 1576–1580
This journal is © The Royal Society of Chemistry 2009

View Article Online
-
1
(
M
n
= 48.6 kg mol , M
w
/M
n
= 2.90), we found that a
Results and discussion
functionalized sPS such as pinacolboronate ester-functionalized
As shown in Scheme 1, (4-bromophenyl)diphenylphosphine
TPP–Br) was synthesized in 97% yield from the reaction of
,4-dibromobenzene and chlorodiphenylphosphine in THF. We
prepared 10 mol% functionalized sPS–B(pin) via iridium-
sPS [sPS–B(pin)] (50 mg) can be recovered quantitatively as
(
1
a fine powder when dissolved in a good solvent (CHCl
3
,
2
.5 mL) and precipitated by adding an equal volume of poor
solvent (methanol, 2.5 mL) (Fig. 1a). To compare the sol-
ubility/recovery difference of sPS and aPS, we also did the
same recovery experiment with borylated atactic polystyrene
16
catalyzed C–H borylation according to a literature method.
TPP was immobilized to sPS via the Suzuki–Miyaura coupling
reaction of TPP–Br and sPS–B(pin), and the immobilized
polymer support, sPS–TPP, was fully characterized using NMR
spectroscopy.
[
aPS–B(pin)] (50 mg). The recovery yield of sPS–B(pin) was
over 99%, whereas aPS–B(pin) was recovered only ~55% as a
sticky solid under the same condition (Fig. 1b).
The successful incorporation of the TPP moiety was con-
3
1
firmed in the P NMR spectrum, which revealed a resonance
3
1
at -5.0 ppm (Fig. 2c). The P NMR spectrum did not show
any resonance that could have resulted from aryl phosphine
1
oxide. In addition, the H NMR spectrum of sPS–TPP showed
two new resonances at 7.34 and 7.51 ppm, which correlate to
the phenyl groups of the attached TPP moiety (see Electronic
Supplementary Information†). The phosphine loading level of
1
-1
sPS–TPP determined by H NMR was 0.71 mmol g (i.e.,
1
21
0 mol%). Unlike that of end-functionalized polymer supports,
this loading capacity can be easily tuned by adjusting the
Fig. 1 Precipitation results of (a) sPS–B(pin) and (b) aPS–B(pin) after
being dissolved in CHCl
CH OH.
3
and precipitated by adding an equal volume of
3
Developing a controlled functionalization of sPS has allowed
us to prepare sPS supports of variable loading capacity without
sacrificing molecular weight and recovery yield. In this report,
we describe the first example of an sPS-supported palladium
catalyst and its use in Suzuki–Miyaura cross-coupling reactions.
Because triphenylphosphine (TPP) is a widely used ligand in
carbon–carbon bond forming coupling reactions and other
17
soluble polymer supports, we decided to synthesize sPS-
supported TPP (sPS–TPP; Scheme 1) and investigate its catalytic
activity and reusability in palladium-catalyzed Suzuki–Miyaura
18
cross-coupling reactions of aryl halides and aryl boronic acid.
Recently there has been considerable interest in developing
19
31
heterogeneous catalyst systems and recoverable homogeneous
Fig. 2
P NMR spectra of (a) chlorodiphenylphosphine (d
=
13,20
catalysts
for Suzuki–Miyaura reactions.
82.8 ppm), (b) TPP–Br (d = -5.3 ppm), and (c) sPS–TPP (d = -5.0 ppm).
Scheme 1 Synthesis of syndiotactic polystyrene-supported triphenylphosphine (sPS–TPP).
Green Chem., 2009, 11, 1576–1580 | 1577
This journal is © The Royal Society of Chemistry 2009

View Article Online
Table 1 Effect of base on the sPS–TPP-supported Suzuki–Miyaura
Table 2 sPS–TPP-supported Suzuki–Miyaura reactions of aryl halides
a
a
reactions of 4-bromoacetophenone and phenylboronic acid
with phenylboronic acid
◦
b
◦
b
c
Entry
Base
Time/h
Temp/ C
Conv. (%)
Entry
R
X
Temp/ C
Time/h
Yield (Conv.) (%)
1
2
3
4
5
6
Cs
2
CO
PO
CO
OH
3
1
1
1
1
1
1
110
110
110
110
110
110
99
92
94
18
91
52
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
H
H
Br
Br
Br
Br
Br
Br
Br
Br
Br
110
70
110
70
110
70
110
70
110
70
110
70
110
70
110
70
1
1
1
1
1
1
1
1
1
4
1
4
1
4
1
4
96 (99)
84 (93)
95 (99)
84 (94)
93 (99)
82 (93)
94 (99)
83 (95)
91 (99)
82 (90)
96 (99)
79 (89)
93 (99)
81 (87)
82 (88)
11 (20)
11 (20)
28 (41)
17 (25)
K
K
3
4
2
3
COCH3
COCH3
CF3
CF3
CHO
CHO
CH
CH
CH
CH
OCH
OCH
NMe
NMe2
H
NEt
NaOH
NaOtBu
4
a
4
-Bromoacetophenone
(0.044
mmol),
phenylboronic
(1 mol%), toluene
acid
(
(
0.066 mmol), sPS–TPP (1 mol%), Pd(OAc)
1 mL). Conversion to coupled product determined using GC-MS.
2
3
3
2
2
b
1
1
1
1
1
1
Br
OH Br
OH Br
3
Br
Br
Br
Br
Cl
Cl
Cl
pinacolboronate ester concentration in the C–H borylation step
without affecting the solubility and recovery of the polymer.
sPS–TPP is readily soluble in common organic solvents
including toluene, THF, dioxane, diglyme, DME, DMF, DMA,
3
2
16
1
1
1
7
8
9
110
110
110
24
24
24
CHO
COCH
CH
2
Cl
2
, and CHCl when heated gently; it is insoluble in hexane,
3
3
diethyl ether, and methanol. Unlike aPS support, which requires
the addition of excess cold poor solvent (e.g., 10-fold volume of
-
a
Aryl bromide or aryl chloride (0.88 mmol), phenylboronic acid
(1 mol%), toluene (2 mL).
◦
(1.32 mmol), sPS–TPP (1 mol%), Pd(OAc)
2
30 C methanol) for polymer recovery in high yield, support
b
c
Isolated yield obtained by column chromatography. Conversion to
coupled product determined using GC-MS.
with sPS–TPP requires only the addition of an equal volume of
methanol for quantitative precipitation of the polymer.
The catalyst activity of the soluble polymer-supported ligand
was tested for the Suzuki–Miyaura coupling reactions of aryl
bromides and chlorides with phenylboronic acid. The coupling
of 4-bromoacetophenone (1 equiv.) and phenylboronic acid
Table 3 Recovery/recycling of sPS–TPP-supported palladium catalyst
a
in Suzuki–Miyaura reactions and the leaching of palladium
(
1.5 equiv.) in toluene was performed as a model reaction
under varying reaction conditions using a palladium catalyst
generated in situ from the complexation of sPS–TPP (1 mol%)
b
Cycle
1st
99
96
> 99
99
2nd
96
96
> 99
98
3rd
99
97
> 99
98
4th
98
95
> 99
99
5th
and Pd(OAc)
bases tested (Cs
NaOtBu), Cs CO
h (Table 1, entry 1). Thus, Cs
2
(1 mol%) (Table 1). Among the six different
CO , K PO , K CO , NEt OH, NaOH, and
gave the highest conversion (99%) within
CO was selected as the base
c
Conversion (%)
Yield of product (%)
Purity (%)
Recovery yield of polymer
support (%)
Leaching of Pd (%)
66e
—
2
3
3
4
2
3
4
d
2
3
f
e
—
1
2
3
99
g
for polymer-catalyzed Suzuki–Miyaura reactions of various aryl
halides with phenylboronic acid (Table 2).
h
0.6
0.5
0.4
0.4
0.4
As shown in Table 2, Suzuki–Miyaura reactions of both
electron-rich and electron-deficient aryl bromides proceed with
high yields at 70 C under homogeneous conditions. As ex-
pected, the reaction rates of electron-deficient aryl bromides
were faster than those of electron-rich aryl bromides (entries
a
4
-Bromoacetophenone (14.2 mmol), phenylboronic acid (21.3 mmol),
◦
sPS–TPP (1 mol%), and Pd(OAc) (1 mol%) at 110 C for 1 h.
2
◦
b
c
No additional Pd(OAc)
Conversion to coupled product determined using GC-MS based on
2
was added in the recycling experiments.
d
an average of two experiments. Isolated yield of product based on
an average of two experiments. Not measured. Purity of product
determined from H NMR spectrum. Recovered yield (weight%) of
polymer support when precipitated by adding methanol and washed
e
f
1
g
4
, 6 and 8). Hence, the cross-coupling reactions of electron-
rich aryl bromides required a slightly longer reaction time
h
with H
2
O. Percentage of original Pd leached into the product solution.
(
i.e., 4 h) to achieve over 80% yield (entries 10, 12 and 14).
◦
When conducted at 110 C, all aryl bromides except for
p-(N,N-dimethylamino)phenyl bromide afforded more than
Because we could recover sPS–TPP quantitatively by adding
methanol, we performed the recycling experiment with the sPS-
supported palladium catalyst (Table 3). After filtering the base
and polymer-supported catalyst in the first run, we evaporated
the volatile liquid from the filtrate and retrieved pure coupled
product in 96% isolated yield. No additional purification process
such as column chromatography was necessary. Washing the
filtered solids with water removed the base and allowed measure-
ment of the recovered polymer support. As shown in Table 3,
the recovery yield of the polymer support is quantitative in each
9
9% conversion within 1 h and their products could be
conveniently isolated by simple precipitation of the sPS–TPP-
supported palladium catalyst and removal of the supported
catalyst (entries 1, 3, 5, 7, 9, 11 and 13). Aryl chlorides are
22
known to be much less reactive when TPP is used as a ligand.
Although the sPS–TPP-supported palladium catalyst furnished
the Suzuki–Miyaura reaction products of aryl chlorides, it did
◦
so in low yields even after 24 h at 110 C (11–28%; Table 2,
entries 17–19).
1
578 | Green Chem., 2009, 11, 1576–1580
This journal is © The Royal Society of Chemistry 2009

View Article Online
cycle, demonstrating the great potential of the soluble support
for use as a recoverable catalyst or reagent. The recovered
polymer-supported catalyst was reused for the next cycle with
sPS–B(pin)], Pd(OAc) [5.3 mg; 0.024 mmol; 5 mol% based
2
on the amount of boron concentration of sPS–B(pin)], S-Phos
[11.0 mg; 0.0240 mmol; 5 mol% based on the amount of boron
concentration of sPS–B(pin)], toluene (10 mL), and a magnetic
stirring bar were placed in a vial. The vial was capped with a
fresh Cs
2
CO
3
(see Table 3). Or alternatively, the filtered solid
(
i.e., a mixture of polymer-supported catalyst and base) can be
23
reused for the next cycle without adding fresh base.
The recycled sPS-supported palladium catalyst did not show
Teflon-lined septum and removed from the glovebox. NEt OH
4
solution [0.6 mL of 35% solution; 1.42 mmol; 3 equiv. based on
the amount of boron concentration of sPS–B(pin)] and water
(1 mL) were added to the vial. The vial was placed in an oil
24
any loss of catalytic activity up to a fourth cycle. When we
investigated the leaching of the palladium into the product
solution after precipitation of the polymer support, however,
we found that a very small percentage of the total amount of the
original palladium species was lost to the product solution in
each cycle [0.6%, 0.5%, 0.4%, 0.4%, and 0.4%, measured using
inductively-coupled plasma atomic emission spectroscopy (ICP-
◦
bath at 100 C for 13 h. After cooling, the reaction mixture
was diluted with chloroform (50 mL), dried with magnesium
sulfate, and filtered through a short plug of Celite. The filtrate
was concentrated using a rotary evaporator to approximately
7 mL, and methanol (7 mL) was added to precipitate polymer.
The precipitated polymer was filtered and dried under vacuum
25
AES)]. Considering the initial loading of Pd(OAc) in the first
2
◦
run of the reaction (1 mol%) and the convenience of product
purification (just precipitation and filtration), the amount of
palladium found in the product is very small (an average of
at 60 C for 12 h (589 mg; 103% yield based on polymer weight).
d
H
(400 MHz, CDCl
1.80 (1H, CH of sPS main chain), 6.53 (2H, H
in sPS side chain), 7.05 (3H, H , H , and H
3
, Me
4
Si) 1.29 (2H, CH of sPS main chain),
2
c
and H
of C
g
of C
6
H
5
46 ppm of palladium in each cycle).
d
e
f
6
H
5
in sPS
side chain), 7.34 (14H, H2,3,5,6,8,9,10 of triphenylphosphine moiety
in the polymer), 7.51 (2H, H11 of triphenylphosphine moiety in
Conclusion
the polymer). d
C
(100 MHz, CDCl
3
, Me
4
Si) 145.2 (C
c
of C
6
H
5
In summary, a soluble sPS-supported phosphine ligand was
prepared by reaction of sPS–B(pin) with TPP–Br. The loading
of the polymer support can be easily tuned by changing
the boronate ester concentration in the C–H borylation of
sPS. The sPS–TPP-supported palladium catalyst showed ex-
cellent catalytic activity in Suzuki–Miyaura coupling of aryl
halides. Moreover, it could be recovered quantitatively through a
simple precipitation/filtration process and reused multiple times
without significant loss of activity.
in sPS side chain), 137.3 (d, C , J = 10.5 Hz), 133.7 (d, C , J =
7
8
18.7 Hz), 128.7 (s, C ), 128.5 (d, C , J = 7.5 Hz), 127.9 (C of
1
0
9
e
C H in sPS side chain), 127.7 (C of C H in sPS side chain),
6
5
d
6
5
125.6 (C of C H in sPS side chain), 43.9 (CH of sPS main
f
6
5
2
chain), 40.6 (CH of sPS main chain). d (161.82 MHz, CDCl ,
P
3
85% H PO ) -5.04 (s).
3
4
General procedure of sPS-support-catalyzed Suzuki–Miyaura
cross-coupling in Table 2. In a nitrogen-filled glovebox, aryl
halide (0.880 mmol; 1 equiv.), phenylboronic acid (161 mg;
1
1
.32 mmol; 1.5 equiv.), Pd(OAc)
mol% based on the amount of aryl halide), Cs
2
(2.0 mg; 0.0088 mmol;
CO (860 mg;
Experimental
2
3
2
6
2.64 mmol; 3 equiv.), and a magnetic stirring bar were placed in
a vial. sPS–TPP (12.4 mg; 0.00880 mmol TPP; 1 mol% based on
the amount of aryl halide) and toluene (2 mL) were placed in
another vial. Both vials were capped with Teflon-lined septa and
removed from the glovebox. sPS–TPP was dissolved in toluene
by applying gentle heat. The sPS–TPP solution was transferred
to the aryl halide solution using a syringe, and the reaction
mixture was stirred in an oil bath under the specified conditions
in Table 2 (70 and 110 C for aryl bromide and 110 C for aryl
chloride). The reaction mixture was cooled to room temperature,
diluted with chloroform (2 mL), and filtered through a short plug
of Celite. The filtrate was concentrated by a rotary evaporator
to approximately 2 mL, and methanol (2 mL) was added to
precipitate the polymer. The precipitated polymer was removed
by filtration through a short plug of Celite. The filtrate was dried
under vacuum and analyzed using GC-MS to check conversion
of the coupled product. Isolation by column chromatography
afforded the pure product.
(
4-Bromophenyl)diphenylphosphine (TPP–Br)
A solution of 1,4-dibromobenzene (3.00 g; 12.7 mmol) in THF
75 mL) was cooled to -95 C using a toluene/liquid nitrogen
bath under a nitrogen atmosphere. n-BuLi (8.10 mL of 1.6 M in
hexane; 12.7 mmol) was added slowly and the resulting solution
was stirred at -95 C. After 1 h, chlorodiphenylphosphine
2.81 g; 12.7 mmol) was added. The solution was allowed
to warm to room temperature, stirred overnight, and filtered
through a short plug of Celite. The filtrate was evaporated under
reduced pressure, and the remaining solid was extracted with
hexane (300 mL) and filtered through a short plug of silica
gel. Evaporation of the solvent from the filtrate afforded a
◦
(
◦
(
◦
◦
pure, moderately air-stable white solid (4.21 g; 97% yield). d
H
(400 MHz, CDCl
3
, Me
.36–7.32 (m, 6H), 7.31–7.26 (m, 4H), 7.15 (dd, 2H, J = 6.9
(100 MHz, CDCl , Me Si) 136.6 (d, C
, J =
0.5 Hz), 136.5 (d, C , J = 20.2 Hz),
, J = 12.7 Hz), 135.2 (d, C
33.7 (d, C , J = 7.5 Hz), 129.0 (s,
, J = 19.4 Hz), 131.6 (d, C
), 128.6 (d, C ). d (161.82 MHz,
, J = 6.7 Hz), 123.4 (s, C
CDCl , 85% H PO ) -5.32 (s).
4
Si) 7.45 (dd, 2H, J = 1.2 and 8.0 Hz),
7
and 8.0 Hz). d
1
1
C
C
3
4
5
4
3
6
2
Recycling experiment of sPS-supported catalyst in Table 3.
In a nitrogen-filled glovebox, 4-bromoacetophenone (2.83 g;
8
7
1
P
3
3
4
1
4.2 mmol; 1 equiv.), phenylboronic acid (2.60 g; 21.3 mmol;
Preparation of sPS-supported triphenylphosphine (sPS–TPP).
In a nitrogen-filled glovebox, sPS–B(pin) [500 mg; 0.470 mmol
B(pin)], (4-bromophenyl)diphenylphosphine [1.30 g; 3.79 mmol;
1.5 equiv.), Cs CO (13.9 g; 42.6 mmol; 3 equiv.), Pd(OAc)
2
3
2
(31.8 mg; 0.142 mmol; 1 mol%), sPS–TPP (184 mg; 0.142 mmol
TPP; 1 mol%), toluene (33 mL), and a magnetic stirring bar
were placed in a 250 mL flask. The flask was removed from
8
equiv. based on the amount of boron concentration of
This journal is © The Royal Society of Chemistry 2009
Green Chem., 2009, 11, 1576–1580 | 1579

View Article Online
◦
the glovebox and placed in an oil bath at 110 C for 1 h.
10 Y.-Q. Kuang, S.-Y. Zhang and L.-L. Wei, Tetrahedron Lett., 2001,
4
2, 5925; R. W. Flood, T. P. Geller, S. A. Petty, S. M. Roberts, J.
The reaction mixture was cooled to room temperature, filtered,
and washed with hot toluene (100 mL). The filtered solid,
which contains base and polymer-supported palladium catalyst,
was washed with additional hot toluene (20 mL ¥ 2) and
dried under vacuum. The filtrate was concentrated by a rotary
evaporator to approximately 10 mL, and methanol (10 mL) was
added to precipitate the remaining polymer support which was
collected by centrifugation (~30 mg of polymer was recovered).
Although the remaining polymer precipitated quantitatively
with the addition of 10 mL of methanol, additional methanol
Skidmore and M. Volk, Org. Lett., 2001, 3, 683; D. E. Bergbreiter,
P. L. Osburn and Y.-S. Liu, J. Am. Chem. Soc., 1999, 121,
9531.
11 D. E. Bergbreiter and J. R. Blanton, J. Org. Chem., 1985, 50, 5828;
D. E. Bergbreiter and D. A. Weatherford, J. Org. Chem., 1989, 54,
2
1
726; D. E. Bergbreiter and R. Chandran, J. Am. Chem. Soc., 1987,
09, 174.
12 S. Doherty, E. G. Robins, I. P a´ l, C. R. Newman, C. Hardacre, D.
Rooney and D. A. Mooney, Tetrahedron: Asymmetry, 2003, 14, 1517;
A. Datta and H. Plenio, Chem. Commun., 2003, 1504; G. Giffels, J.
Beliczey, M. Felder and U. Kragl, Tetrahedron: Asymmetry, 1998, 9,
6
91.
13 A. Datta, K. Ebert and H. Plenio, Organometallics, 2003, 22,
685.
(
300 mL) was added to the toluene/methanol solution in order
4
to prevent co-precipitation of the product with the polymer
during centrifugation—because the solubility of the product in
methanol for the centrifugation process was found to be ~10 mg
mL- and the expected weight of the product was 2.78 g, it was
necessary to add 300 mL of methanol to prevent co-precipitation
of the product. After removal of the precipitated polymer,
evaporation of the centrifuged methanol solution afforded pure
product (96% yield), which was analyzed by H and C NMR
spectroscopy to check the purity, and subjected to ICP-AES
to determine the amount of leached palladium. The polymer
recovered from the centrifugation was dried, combined with the
initially filtered base and polymer-supported palladium catalyst
mixture, and washed with water (400 mL) to remove the base.
The resulting brownish polymer solid was filtered, washed with
water (50 mL ¥ 2) and methanol (10 mL ¥ 1), and dried
under vacuum. The weight percent of the brownish polymer
relative to the initial weight of sPS–TPP is provided as the
1
4 There have been reports on the recovery yield of soluble polymer
supports. See, for example:K. C. Y. Lau, H. S. He, P. Chiu and P. H.
Toy, J. Comb. Chem., 2004, 6, 955; R. Manzotti, S.-Y. Tang and K. D.
Janda, Tetrahedron, 2000, 56, 7885; E. J. Enholm, M. E. Gallagher,
K. M. Moran, J. S. Lombardi and J. P. Schulte, II, Org. Lett., 1999,
1
1
, 689.
1
1
5 M. Malanga, Adv. Mater. (Weinheim, Ger.), 2000, 12, 1869; Z. Su,
X. Li and S. L. Hsu, Macromolecules, 1994, 27, 287; J. Y. Dong, E.
Manias and T. C. Chung, Macromolecules, 2002, 35, 3439.
6 J. Shin, S. M. Jensen, J. Ju, S. Lee, Z. Xue, S. K. Noh and C. Bae,
Macromolecules, 2007, 40, 8600.
1
13
17 C. R. Harrison, P. Hodge, B. J. Hunt, E. Khoshdel and G.
Richardson, J. Org. Chem., 1983, 48, 3721; A. B. Charette, A. A.
Boezio and M. K. Janes, Org. Lett., 2000, 2, 3777; D. E. Bergbreiter
and J. R. Blanton, J. Chem. Soc., Chem. Commun., 1985, 337; D. E.
Bergbreiter and C. Li, Org. Lett., 2003, 5, 2445.
18 N. Miyaura and A. Suzuki, Chem. Rev., 1995, 95, 2457.
1
9 N. T. S. Phan, M. Van Der Sluys and C. W. Jones, Adv. Synth.
Catal., 2006, 348, 609; D.-H. Lee, J.-H. Kim, B.-H. Jun, H. Kang,
J. Park and Y.-S. Lee, Org. Lett., 2008, 10, 1609; S. Schweizer, J.-
M. Becht and C. Le Drian, Org. Lett., 2007, 9, 3777; Q. Yang, S.
Ma, J. Li, F. Xiao and H. Xiong, Chem. Commun., 2006, 2495; R.
Nishio, M. Sugiura and S. Kobayashi, Org. Lett., 2005, 7, 4831;
N. T. S. Phan, D. H. Brown and P. Styring, Tetrahedron Lett., 2004, 45,
recovery yield of polymer support in Table 3. Fresh Cs
3 equiv.), 4-bromoacetophenone (2.83 g; 14.2 mmol; 1 equiv.),
phenylboronic acid (2.60 g; 21.3 mmol; 1.5 equiv.), and toluene
33 mL) were added to the recovered polymer support, and they
2
CO
3
(
7
915.
20 W. J. Sommer and M. Weck, Adv. Synth. Catal., 2006, 348, 2101; A.
Leyva, H. Garc
(
´
ıa and A. Corma, Tetrahedron, 2007, 63, 7097; P. D.
Stevens, G. Li, J. Fan, M. Yen and Y. Gao, Chem. Commun., 2005,
435.
were used for the next run.
4
Acknowledgements
2
1 P. Wentworth, Jr., A. M. Vandersteen and K. D. Janda, Chem.
Commun., 1997, 759; F. Sieber, P. Wentworth, Jr., J. D. Toker, A. D.
Wentworth, W. A. Metz, N. N. Reed and K. D. Janda, J. Org. Chem.,
1999, 64, 5188.
We gratefully acknowledge the National Science Foundation
CAEER DMR-0747667) for generous support and Frontier
(
2
2
2 M. Joshaghani, E. Faramarzi, E. Rafiee, M. Daryanavard, J. Xiao
and C. Baillie, J. Mol. Catal. A: Chem., 2006, 259, 35; V. V. Grushin
and H. Alper, Chem. Rev., 1994, 94, 1047.
3 See Electronic Supplementary Information for detailed procedures
for the alternative recycling experiment†.
Scientific Co. for a gift of B
2
(pin) .
2
References
1
2
C. E. Song and S.-G. Lee, Chem. Rev., 2002, 102, 3495.
R. B. Merrifield, J. Am. Chem. Soc., 1963, 85, 2149; S.-S. Wang,
J. Am. Chem. Soc., 1973, 95, 1328.
M. Seki, Synthesis, 2006, 2975.
L. Djakovitch and P. Rollet, Adv. Synth. Catal., 2004, 346, 1782.
K. K o¨ hler, M. Wagner and L. Djakovitch, Catal. Today, 2001, 66,
24 It appears that the sPS–TPP–Pd complex was gradually deactivated
over the course of recycling work-up procedure (i.e., precipitation
of the polymer support with methanol and washing with water to
remove the base). The total amount of palladium leached out during
the recycling was not significant; 0.023 mol% (2.3% ¥ 1 mol%) over
the five cycles. Thus, the loss of palladium due to leaching will not
be a major culprit that causes the loss of catalytic activity. A similar
deactivation of palladium-phosphine complex supported on cross-
linked polystyrene has been reported. See C. A. Parrish and S. L.
Buchwald, J. Org. Chem., 2001, 66, 3820.
3
4
5
1
05.
P. Goyal, X. Zheng and M. Weck, Adv. Synth. Catal., 2008, 350,
816.
R. A. Shiels, K. Venkatasubbaiah and C. W. Jones, Adv. Synth. Catal.,
008, 350, 2823.
6
7
8
9
1
2
25 In the ICP-AES experiment, we also discovered that the synthesized
sPS–TPP contained a small quantity of palladium (0.37 wt%)
possibly due to the coordination of palladium to the phosphine
during sPS–TPP synthesis. However, the 1 mol% sPS–TPP alone,
although it contains 0.045 mol% of residual palladium, could not
catalyze Suzuki–Miyaura coupling reactions of aryl bromide even at
R. van Heerbeek, P. C. J. Kamer, P. W. N. M. van Leeuwen and
J. N. H. Reek, Chem. Rev., 2002, 102, 3717.
B. F. G. Johnson, S. A. Raynor, D. S. Shephard, T. Mashmeyer, J. M.
Thomas, G. Sankar, S. Bromley, R. Oldroyd, L. Gladden and M. D.
Mantle, Chem. Commun., 1999, 1167; R. Augustine, S. Tanielyan, S.
Anderson and H. Yang, Chem. Commun., 1999, 1257; S. A. Raynor,
J. M. Thomas, R. Raja, B. F. G. Johnson, R. G. Bell and M. D.
Mantle, Chem. Commun., 2000, 1925.
◦
110 C and only starting materials were observed.
26 C. M. Thomas and J. C. Peters, Inorg. Chem., 2004, 43, 8; S. E. Tunney
and J. K. Stille, J. Org. Chem., 1987, 52, 748.
1
580 | Green Chem., 2009, 11, 1576–1580
This journal is © The Royal Society of Chemistry 2009