Carbon-carbon coupling reactions catalyzed by supported Pd porphyrins

Article abstract of DOI:10.1002/aoc.3131

The tetrakis(4-N-methylpyridinium)porphyrinatopalladium(II) iodide, [Pd(TMPyP)]I₄, supported on Dowex 50WX8 and Amberlite IR-120 ion-exchange resins, was used as heterogeneous, recyclable and active catalyst for the Suzuki-Miyaura and Heck cross-coupling reactions. These catalysts were applied to coupling of various aryl halides with phenylboronic acid and styrene in Suzuki and Heck reactions, respectively, and the corresponding products were obtained in excellent yields and short reaction times. The catalysts could be recovered easily by simple filtration and reused several times without significant loss of their catalytic activity. The catalysts were characterized by diffuse-reflectance UV-visible spectroscopy and scanning electron microscopy, and their stability was confirmed by TGA.

Full text of DOI:10.1002/aoc.3131

Full Paper
Received: 10 December 2013
Revised: 31 January 2014
Accepted: 31 January 2014
Published online in Wiley Online Library: 19 March 2014
(wileyonlinelibrary.com) DOI 10.1002/aoc.3131
Carbon–carbon coupling reactions catalyzed
by supported Pd porphyrins
Omid Bagheri, Faranak Sadegh, Majid Moghadam*, Shahram Tangestaninejad*,
Valiollah Mirkhani, Iraj Mohammadpoor-Baltork and Mahsa Safiri
The tetrakis(4-N-methylpyridinium)porphyrinatopalladium(II) iodide, [Pd(TMPyP)]I4, supported on Dowex 50WX8 and
Amberlite IR-120 ion-exchange resins, was used as heterogeneous, recyclable and active catalyst for the Suzuki–Miyaura
and Heck cross-coupling reactions. These catalysts were applied to coupling of various aryl halides with phenylboronic acid
and styrene in Suzuki and Heck reactions, respectively, and the corresponding products were obtained in excellent yields and
short reaction times. The catalysts could be recovered easily by simple filtration and reused several times without significant loss
of their catalytic activity. The catalysts were characterized by diffuse-reflectance UV–visible spectroscopy and scanning electron
microscopy, and their stability was confirmed by TGA. Copyright © 2014 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at publisher’s web-site.
Keywords: tetrakis(4-N-methylpyridinium)porphyrinatopalladium(II) iodide; heterogeneous catalyst; ion-exchange resins; C―C coupling
reactions; aryl halides
decantation. This is not the case for other powdered materials
often used as catalyst supports (e.g., silica, zeolites, carbon).
Introduction
Suzuki and Heck cross-coupling reactions catalyzed by palladium
are the most widely used carbon–carbon bond forming tools to
synthesize different unsaturated structures, many of which are
important intermediates in natural product synthesis and in the
production of fine chemicals.[1,2] The principle of palladium-
catalyzed cross-coupling is that two molecules are assembled on
the metal via the formation of metal–carbon bonds. In this way,
the carbon atoms bound to palladium are brought very close to
one another. In the next step, they couple to one another and this
leads to the formation of a new carbon–carbon single bond.[3]
With various metals being employed in coupling reactions,
palladium is probably the most versatile metal in promoting or
catalyzing reactions involving C―C and C―N bond formation due
to its excellent catalytic efficiency in these types of reaction.[4–8]
Homogenous palladium catalysts used in Suzuki and Heck
reactions cannot be recovered from reaction media.[9] The use
of heterogeneous catalysts in organic synthesis has now become
a common practice,[10,11] especially following the rapid develop-
ment of combinatorial chemistry. Solid-supported palladium
complexes having high activity and selectivity offer several signif-
icant practical advantages in synthetic and industrial chemistry;
among those, the ease of separation of the catalyst from the
desired reaction products and the ease of recovery and reuse of
the catalyst are most important.
When the particle size is about 1 μm or less, they might not settle
in the solution within a short time, and it would be very difficult
to collect them for recycling. The separation of the catalyst thus
requires centrifugation or ultrafiltration. Very fine powders may
also clog or poison the reactors or the autoclaves employed in
the catalytic experiments.
A pre-catalyst that remains stable even under the harsh condi-
tions needed for the activation and conversion of demanding
substrates (aryl chlorides) and generates sufficient amounts of
coordinatively unsaturated Pd is also essential in C―C coupling
reactions. Macrocyclic Pd complexes (e.g. phthalocyanines, porphy-
rins) have very high thermal and chemical stability, complete coor-
dinative saturation of the central atom and a preference for the Pd
(II) oxidation state. Such compounds possess a surprisingly high
complex stability, so the release of Pd under coupling reaction
conditions would be very limited and its equilibrium largely shifted
towards bound Pd. Since macrocyclic ligands are usually very rigid,
they cannot dissociate partially. Such complexes are very applica-
ble model systems for the presented new concept, since they are
not able to catalyze C―C coupling reactions in their undissociated
form, but Pd released by them would be ‘completely unsaturated’
and, thus, a highly active catalyst.[21] Examples of palladium por-
phyrins as catalysts in C―C coupling reactions are few. In recent
years Kostas and co-workers used a water-soluble Pd porphyrin as
catalyst for the Suzuki reaction of aryl bromides with phenylboronic
acid in water.[22] Wan and coworkers reported the application of a
A large number of materials including activated carbon, silica
gel, polymers containing covalently bound ligands, metal oxides,
porous aluminosilicates, clays and other inorganic materials, and
microporous and mesoporous supports have been used for
immobilization of Pd compounds.[12–20]
Ion-exchange resins are commercial products commonly avail-
able in the form of small beads (16–400 mesh, 38–1180 μm
diameter) or as membranes. Shape and size allow these materials
to be easily and quantitatively recovered by simple filtration or
*
Correspondence to: Majid Moghadam and Shahram Tangestaninejad,
Department of Chemistry, Catalysis Division, University of Isfahan, Isfahan
81746-73441, Iran. E-mail: moghadamm@sci.ui.ac.ir; stanges@sci.ui.ac.ir
Department of Chemistry, Catalysis Division, University of Isfahan, Isfahan
81746-73441, Iran
Appl. Organometal. Chem. 2014, 28, 337–346
Copyright © 2014 John Wiley & Sons, Ltd.

O. Bagheri et al.
Pd porphyrin in the Heck reaction of aryl iodides using ionic liquids
as the reaction medium. The intact Pd porphyrin, at the end of
the reaction, was detected by UV–visible spectroscopy.[23]
In the present work, the synthesis and characterization of
cationic tetrakis(4-N-methylpyridinium)- porphyrinatopalladium
(II) iodide, [Pd(TMPyP)]I4, supported on Dowex 50 WX8 and
Amberlite IR-120 ion-exchange resins via electrostatic interac-
tions, are reported. The application of these catalysts in the
reaction of phenylboronic acid with aryl halides (Suzuki reaction)
and in the reaction of aryl halides with styrene (Heck reaction)
was also investigated (Scheme 1).
from Merck, Fluka and Sigma-Aldrich chemical companies.
Tetrapyridylporphyrin was purchased from Fluka Chemical
Company. FT-IR spectra were recorded on a Jasco 6300 spectro-
photometer. 1H and 13C NMR (400 and 100 MHz) spectra were
recorded on a Bruker Avance 400 MHz spectrometer using
DMSO-d6 as solvent. TGA was carried out on a Mettler TG50 in-
strument under air flow at a uniform heating rate of 5 °C minÀ1
in the range 30–600 °C. Scanning electron micrographs were
made on a Philips XL 30 scanning electron microscope. The Pd
content of the catalyst was determined using a PerkinElmer
inductively coupled plasma (ICP) analyzer. Substances were
identified and quantified by gas chromatography (GC) on an
Agilent GC 6890 equipped with a 19096C006 80/100 WHP
packed column and a flame ionization detector (FID). UV–visible
spectra were recorded using a commercial Shimadzu UV-160
spectrophotometer. Melting points were determined with a
Stuart Scientific SMP2 apparatus. Diffuse reflectance (DR) UV-visible
spectra were recorded on a JASCO V-670 spectrophotometer.
Experimental
General Remarks
All the reagents were analytical grade and used without further
purification. The chemicals used in this work were purchased
Synthesis of tetrakis(4-N-methylpyridinium)
porphyrinatopalladium(II) iodide,
[PdTMPyP]I4
The water-soluble tetrakis(4-N-methylpyridinium)
porphyrin iodide, [H2TMPyP]I4, was prepared by
the reaction of H2TMPyP with methyl iodide.[24]
UV–visible spectrum in DMF (nm): 417 (Soret
band), 522, 553, 586 and 646nm (Q bands).The
palladium(II) complex was prepared by refluxing
a mixture of Na2Pd2Cl6 (1mmol)[25] (prepared in
Scheme 1. Suzuki–Miyaura cross-coupling and Heck reaction catalyzed by supported
situ from PdCl2 and NaCl) with [H2TMPyP]I4
(1mmol) in deionized water for 6 h. 1H NMR
(400 MHz, DMSO-d6) for [H2TMPyP]I4: δ (ppm) =
9.50–9.00 (m, 24H, aromatic and β-hydrogens),
4.73 (s, 12H, CH3), À3.11 (s, 2H, pyrrolic hydrogens)
ppm. 1H NMR (400 MHz, DMSO-d6) for [PdTMPyP]
I4: δ (ppm) = 9.50–8.96 (m, 24H, aromatic and
β-hydrogens), 4.72 (s, 12H, CH3).
Pd(II)porphyrin.
Immobilization of [PdTMPyP]I4 on Amberlit
IR-120 and Dowex 50 WX8 ion-exchange
resins
The commercial cation-exchange resin Dowex 50
WX8 was first washed with aqueous Na2CO3
(5%, w/v) and then sequentially with water,
methanol and acetone, and dried under vac-
uum. [Pd(TMPyP)]I4 (500 mg) was dissolved in
a minimum volume of DMSO and acetone–wa-
ter (1:1, 50 ml) was added to this solution. The
reaction mixture was stirred at 80 °C for 24 h.
After cooling to room temperature, the purple
solids were washed with DMSO, acetone and
water. The catalyst, [Pd(TMPyP)]@Dowex 50
WX8 (Fig. 1a), was dried under vacuum prior
to use. The same method was used for the prep-
aration of [Pd(TMPyP)]@Amberlit IR-120 (Fig. 1b).
The prepared catalysts were characterized by ICP
and DR UV–visible spectroscopic method and their
thermal stability was determined by TGA.
Figure 1. The structure of (a) [Pd(TMPyP)]@Dowex 50 WX8 and (b) [Pd(TMPyP)]
@Amberlit IR-120.
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C―C coupling reactions by supported Pd porphyrins
General Procedure for Suzuki–Miyaura Cross-Coupling Reaction
Catalyzed by Ion-Exchange Resin-Supported Pd(II) Porphyrin
50 WX8, the Soret band appeared at 419 nm and the Q bands
were observed at 529, 561 and 649 nm. These observations
clearly proved the presence of metalloporphyrinon on the
Dowex (Fig. 4a, b).
The Pd content of [Pd(TMPyP)]@Amberlit IR-120 was also
determined by ICP (0.0149 mmol gÀ1). The thermal stability of
the immobilized metal complex, [Pd(TMPyP)]@Amberlit IR-120,
A mixture of aryl halide (1 mmol), arylboronic acid (1.5 mmol),
K2CO3 (207 mg, 1.5 mmol) and catalyst (0.13 mol% for [Pd
(TMPyP)]@Dowex 50 WX8 and 0.27 mol% for [Pd(TMPyP)]
@Amberlit IR-120) in 3 ml DMF/H2O (2:1) was stirred at 95 °C for
[Pd(TMPyP)]@Dowex 50 WX8 and 110 °C for [Pd(TMPyP)]
@Amberlit IR-120 under air atmosphere. The progress of the reac-
tion was monitored by GC. After completion of the reaction, ethyl
acetate (15 ml) was added and the catalysts were filtered. The
organic phase was washed with H2O (2 × 10 ml), dried over
anhydrous MgSO4 and evaporated. The residue was recrystallized
from ethyl acetate and ether (1:3) to afford the pure product.
General Procedure for Heck Reaction Catalyzed by
Ion-Exchange Resin-Supported Pd(II) Porphyrin
In a round-bottomed flask equipped with a condenser and a
magnetic stirrer, a mixture of aryl halide (1 mmol), styrene
(2 mmol), K2CO3 (2 mmol) and catalyst (0.17 mol% for [Pd
(TMPyP)]@Dowex 50 WX8 and 0.34 mol% for [Pd(TMPyP)]
@Amberlit IR-120 in DMF (2 ml) was stirred at 120 °C under air
atmosphere. The progress of the reaction was monitored by GC.
At the end of the reaction, the reaction mixture was cooled to
room temperature, ethyl acetate (15 ml) was added and the
7catalysts were filtered. The organic layer was washed with water
(2 × 10 ml) and dried over anhydrous MgSO4. Evaporation of the
solvent and purification of the crude product by recrystallizing
from ethyl acetate and ether (1:3) afforded the pure product.
Results and Discussion
Characterization of tetrakis(4-N-methylpyridinium)
porphyrinatopalladium(II) iodide, [PdTMPyP]I4, supported on
Amberlit IR-120 and Dowex 50 WX8
The synthesis of [PdTMPyP]I4 was monitored by UV–visible and
1H NMR spectroscopy. UV–visible spectra in DMSO: 424 (Soret band)
and 513 and 588 nm (Q bands) (Fig. S1, supporting information). In
the 1H NMR spectrum of [PdTMPyP]I4 in DMSO-d6, the signal
at À3 ppm corresponding to pyrrolic hydrogens in [H2TMPyP]I4
disappeared in[PdTMPyP]I4, which confirmed the synthesis and
metallation of the ionic porphyrin (Fig. S2, supporting information).
[Pd(TMPyP)]I4, which contains methylpyridinium groups at the
meso positions of the porphyrin ligand, can be immobilized on
À
Dowex 50 WX8 and Amberlit IR-120 bearing SO3 groups on
their structures via electrostatic interactions.
The Pd content of [Pd(TMPyP)]@Dowex 50 WX8 was deter-
mined by ICP and showed a value of about 0.0131 mmol gÀ1
.
TGA was used to determine the thermal stability of immobilized
metal complex [Pd(TMPyP)]@Dowex 50 WX8. The free palladium
(II) porphyrin complex showed a 46% weight loss at temperatures
below 290 °C (Fig. 2a). However, for the corresponding supported
complex, there is a continuous weight loss that extends above
379 °C, which confirms the thermal stability of the catalyst after
immobilization (Fig. 2b, c). A clear change in the morphology of
the Dowex and [Pd(TMPyP)]@Dowex 50 WX8 was observed by
scanning electron microscopy (SEM) (Fig. 3a, b). The scanning
electron micrographs clearly show the changes that occurred
on the surface of the resin after supporting palladium porphyrin
on it. In the reflectance spectrum of the [Pd(TMPyP)]@Dowex
Figure 2. TG-DTG curve of (a) [Pd(TMPyP)]I4, (b) Dowex 50 WX8 and (c)
[Pd(TMPyP)]@Dowex50 WX8.
Appl. Organometal. Chem. 2014, 28, 337–346
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O. Bagheri et al.
was determined by TGA. The decomposition behavior of the
free palladium(II) porphyrin and the immobilized complex were
compared in order to understand the effect of immobilization.
The free palladium(II) porphyrin decomposes at temperatures
below 290 °C and a weight loss of 46% was observed.
However, for the corresponding immobilized complex, a 12%
weight loss appeared. This behavior indicates thermal stability
of the complex after immobilization on to Amberlite (Fig. S3a,
b, supporting information). A similar result, which was ob-
served for [Pd(TMPyP)]@Dowex 50 WX8, was also observed
for this catalyst by SEM (Fig. S4a, b, supporting information).
In the DR UV–visible spectrum of [Pd(TMPyP)]@Amberlit
IR-120, the Soret band appeared at 420 nm and the Q bands
were observed at 528 and 561 nm. These observations clearly
proved the presence of metalloporphyrin on the Amberlit
(Fig. S5a, b, supporting information).
were chosen as base and solvent, respectively, in the presence
of 0.13 mol% Pd complex at 95 °C under air atmosphere (Table 1,
entry 4). When Pd(TMPyP)@Amberlit IR-120 was used as catalyst
in the model reaction, the best results were obtained in DMF–
H2O (2:1, 3 ml) at 120 °C in the presence of 0.27 mol% Pd complex
using K2CO3 as base (Table 1).
It seems that by supporting [Pd(TMPyP)]I4 on the resins, the
catalyst is dispersed on their surface. This leads to isolation of
the catalytic active sites and therefore a good catalytic activity
is obtained.
The generality of this catalytic system was further examined in
the coupling of various aryl halides having different steric and
electronic properties with phenylboronic acid. The results are
summarized in Table 2. Phenylboronic acid was found to couple
smoothly with iodobenzene, providing the desired product in
excellent yields. The reaction was also carried out in a satisfactory
manner with less reactive bromobenzenes. Electron-donating
groups such as methyl and methoxy, and withdrawing groups such
as nitro, were well tolerated under the present catalytic system. The
coupling reaction of 4-chloroacetophenone also took place under
similar reaction conditions, though the reactivity was lower than
their iodo and bromo counterparts (Table 2, entry 12).
Comparison of the catalytic activity of the homogeneous
[Pd(TMPyP)]I4 and its immobilized counterparts in the Suzuki reac-
tion showed that under the optimum reaction conditions involving
4-iodoanisole (1mmol), phenylboronic acid (1.5 mmol), K2CO3
(1.5mmol) and [Pd(TMPyP)]I4 (0.11 mol% Pd) in DMF–H2O (2:1,
3 ml) at 95 °C under air, the desired product was obtained in 95%
yield after 8 min (turnover frequency (TOF) 6477 hÀ1). But the main
problem associated with [Pd(TMPyP)]I4 is its solubility under
reaction conditions, and therefore it cannot be separated from
the reaction media and reused, whereas the supported catalyst
is reusable.
Suzuki–Miyaura Cross-Coupling of Aryl Halides with
Phenylboronic Acid in the Presence of [Pd(TMPyP)]@Dowex
50 WX8 and [Pd(TMPyP)]@Amberlit IR-120
Initially, the reaction of 4-iodoanisole (1mmol) with phenylboronic
acid (1.5mmol) was studied as a model reaction, and the role of
various bases such as Na3PO4, K2CO3 and NEt3, and different mixed
solvents such as DMF, N-methylpyrrolidin-2-one (NMP), MeOH,
EtOH, MeCN, THF and toluene with water were screened. Also,
the effect of catalyst amounts and temperature was investigated.
The results are summarized in Table 1. The results showed
that when the reaction was conducted in polar solvents such
as DMF and NMP a higher product yield was obtained. Com-
parison of the inorganic bases utilized showed that carbonate
base was more reactive than other bases such as Na3PO4 and
Et3N. Therefore, K2CO3 (1.5 mmol) and DMF–H2O (2:1, 3 ml)
(A)
(B)
(C)
(D)
Figure 3. SEM image of (a, b) Dowex 50 WX8 and (c, d) [Pd(TMPyP)]@Dowex 50 WX8.
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C―C coupling reactions by supported Pd porphyrins
between catalyst and support is higher than covalent
bonding. The nature of the recovered catalysts was monitored
by diffuse reflectance UV–visible spectrophotometry. No
change was observed in the DR UV–visible spectrum of the
catalysts, which indicates the stability and robustness of the
catalysts. The DR UV–visible spectrum of recovered [Pd
(TMPyP)]@Amberlit IR-120 in the Suzuki reaction, for example,
is shown in Fig. 5.
Heck Cross-Coupling of Aryl Halides with Styrene in the
Presence of [Pd(TMPyP)]@Dowex 50 WX8 and [Pd(TMPyP)]
@Amberlit IR-120
Next, we investigated the ability of these catalytic systems in the
Heck cross-coupling reactions. First, reaction conditions such as
temperature, kind of solvent and base, and amount of catalyst
were optimized in the coupling of 4-iodoanisole (1 mmol) with
styrene (2 mmol) using [Pd(TMPyP)]@Dowex 50 WX8 as catalyst
under air atmosphere (Table 4). The reaction was conveniently
carried out at 120 °C in the presence of 0.17 mol% Pd. It was
observed that the highest yield was observed with potassium
carbonate as base and DMF as solvent. It is noteworthy that,
1
based on the H NMR spectra, in all Heck coupling reactions the
trans product was obtained with 100% selectivity.
When [Pd(TMPyP)]@Amberlit IR-120 was used as catalyst in the
Heck cross-coupling reaction, the same results were obtained ex-
cept for the catalyst amount: the best results were detected in
the presence of 0.34 mol% Pd.
The applicability of [Pd(TMPyP)]@Dowex 50 WX8 and[Pd
(TMPyP)]@Amberlit IR 120 catalysts was investigated in the Heck
cross-coupling reaction of different aryl halides with styrene
(Table 5). It was observed that aryl halides bearing electron-with-
drawing groups showed higher catalytic activity in the Heck
coupling reaction in comparison with aryl halides containing
electron-donating substituents. Clearly, chloroarenes were less
reactive than their iodo and bromo counterparts.
Figure 4. The DR UV–visible spectrum of (a) Dowex 50 WX8 and (b) [Pd
(TMPyP)]@Dowex 50 WX8.
The catalytic activity of homogeneous [Pd(TMPyP)]I4 was also
investigated in the Heck reaction of 4-iodoanisole (1 mmol) with
styrene (2 mmol) using K2CO3 (2 mmol) as base and in the pres-
ence of [Pd(TMPyP)]I4 (0.12 mol%) in DMF (2 ml) at 120 °C under
air and the desired product was produced in 93% yield after
30 min (TOF 1550 hÀ1).
As can be seen in Table 5 (entry 5), [Pd(TMPyP)]@Dowex 50
WX8 had higher catalytic activity than [Pd(TMPyP)]@Amberlit IR-
120 in the Heck reaction.
As shown in Table 2 (entry 5), the [Pd(TMPyP)]@Dowex 50 WX8
catalyst is more reactive than [Pd(TMPyP)]@Amberlit IR-120 in the
Suzuki cross-coupling reaction. This can be attributed to the
different structure of Dowex 50 WX8 with Amberlit IR-120. The
porosity of a resin affects some bulk properties that are important
in the catalytic applications.
The reusability of these catalysts was also investigated in the
model reaction. In this manner, the catalysts were recovered from
the reaction mixture by simple filtration after each cycle, and
washed thoroughly with acetone, diethyl ether and water,
successively, before being reused with fresh 4-iodoanisole and
styrene. The results showed that both catalysts could be
recovered and recycled five consecutive times. The amount of
Pd leached was determined by ICP analysis (Table 6). As can be
seen, only in the first two runs was some palladium leached from
the catalysts. The nature of the recovered catalysts was moni-
tored by diffuse-reflectance UV–visible spectrophotometry. No
change was observed in the DR UV–visible spectrum of the
catalysts, which indicates the stability and robustness of the
catalysts. For example, the DR UV–visible spectrum of recovered
[Pd(TMPyP)]@Dowex50 WX8 in the Heck reaction is shown in
Fig. S6 (supporting information).
Catalyst Recovery and Reuse
The reusability of these heterogeneous catalysts was investigated
in the Suzuki reaction of 4-iodoanisole with phenylboronic acid in
the presence of K2CO3. At the end of each reaction, the catalyst
was separated by simple filtration and washed thoroughly
with acetone, diethyl ether and water, successively, before
being reused with fresh 4-iodoanisole and phenylboronic acid.
The results showed that both catalysts could be recovered
and recycled five consecutive times. The amount of Pd
leached was determined by ICP analysis (Table 3). As can be
seen, no Pd was detected in the filtrates after two first runs.
The chelating effect prevents the releasing of Pd from the
macrocyclic porphyrin ligand [21]. However, it is obvious that
catalyst leaching in the case of electrostatic interaction
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C―C coupling reactions by supported Pd porphyrins
Table 2. Suzuki cross-coupling reaction of aryl halides and phenylboronic acid using [Pd(TMPyP)]@Dowex 50 WX8 and [Pd(TMPyP)]@Amberlit IR-120a
[Pd(TMPyP)]@Ion-Exchange Resin
DMF/H2O, K2CO3
X
B(OH)2
+
R
R
X=Cl, Br, I
Entry
R
X
[Pd(TMPyP)]@Dowex 50 WX8b
[Pd(TMPyP)]@Amberlit IR-120c
Time (min)
Yield (%)d
Time (min)
Yield (%)d
1
H
I
7
15
26
8
96
95
81
91
92e
97
76
83
96
94
79
75
17
26
36
19
20
15
23
34
25
24
35
34
97
91
79
92
93f
96
68
89
96
97
86
84
2
H
Br
Cl
I
3
H
4
4-Me
5
4-MeO
4-NO2
I
10
5
6
I
7
2-Me/4-NO2
4-MeO
4-NO2
4-Ac
I
13
21
14
15
23
22
8
Br
Br
Br
Br
Cl
9
10
11
12
2-NO2
4-Ac
aReaction conditions: aryl halide (1 mmol), phenylboronic acid (1.5 mmol), K2CO3 (1.5 mmol), DMF/H2O (2:1, 3 ml) under air atmosphere.
b95°C, catalyst (0.13 mol% Pd).
c110°C, Catalyst (0.27 mol% Pd).
dIsolated yield.
eTOF is equal to 4580 (hÀ1).
fTOF is equal to 1066 (hÀ1).
Table 3. Recycling and reuse of [Pd(TMPyP)]@Dowex 50 WX8 and
[Pd(TMPyP)]@Amberlit IR-120 in the Suzuki reactiona
Entry
[Pd(TMPyP)]@Dowex
50 WX8b
[Pd(TMPyP)]@Amberlit
IR-120c
Yield (%)d Pd leached (%)e Yield (%)d Pd leached (%)e
1
2
3
4
5
92
92
91
91
89
1.18
0.96
—
93
92
91
91
89
1.10
0.88
—
—
—
—
—
aReaction conditions: 4-iodoanisole (1 mmol), phenylboronic acid
(1.5 mmol), K2CO3 (1.5 mmol), DMF/H2O (2:1, 3 ml) under air
atmosphere.
b95°C, catalyst (0.13 mol% Pd), 10 min.
c110°C, catalyst (0.27 mol% Pd), 20 min.
dIsolated yield.
eDetermined by ICP.
Figure 5. The DR UV–visible spectra of recovered [Pd(TMPyP)]@Amberlit
IR-120 in Suzuki reaction.
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C―C coupling reactions by supported Pd porphyrins
Table 5. Heck cross-coupling reactions of aryl halides with styrene using [Pd(TMPyP)]@Dowex 50 WX8 and [Pd(TMPyP)]@Amberlit IR-120a
[Pd(TMPyP)]@Ion-Exchange Resins
DMF (2.0 ml)
K2CO3 (2.0 mmol)
120 oC
X
R
R
+
X=Cl, Br, I
Entry
R
X
[Pd(TMPyP)]@Dowex 50 WX8b
[Pd(TMPyP)]@Amberlit IR-120c
Time (min)
Yield (%)d
Time (min)
Yield (%)d
1
H
I
25
48
74
28
30
21
44
57
36
35
68
54
90
86
56
90
91e
93
72
87
92
91
65
83
38
65
91
43
45
32
60
79
55
58
83
96
91
79
52
85
88f
92
71
81
87
88
79
57
2
H
Br
Cl
I
3
H
4
4-Me
5
4-MeO
4-NO2
I
6
I
7
2-Me/4-NO2
4-MeO
4-NO2
4-Ac
I
8
Br
Br
Br
Br
Cl
9
10
11
12
2-NO2
4-Ac
aReaction conditions: aryl halide (1 mmol), styrene (2 mmol), K2CO3 (2 mmol), DMF (2 ml) at 120 °C under air atmosphere.
bCatalyst (0.17 mol% Pd).
cCatalyst (0.34 mol% Pd).
dIsolated yield.
eTOF is equal to 1176 (hÀ1).
fTOF is equal to 398 (hÀ1).
coupling reactions. Short reaction times, excellent to good yields,
simple filtration and reusability and stability of the catalysts are
noteworthy advantages of these systems.
Table 6. Recycling and reuse of [Pd(TMPyP)]@Dowex 50 WX8 and
[Pd(TMPyP)]@Amberlit IR-120 in optimum model Heck reactionsa
Entry [Pd(TAPP)]@Dowex 50 WX8b [Pd(TAPP)]@Amberlit IR-120c
Yield (%)d Pd leached (%)e Yield (%)d Pd leached (%)e
Acknowledgment
The authors are grateful to the Research Council of the University
of Isfahan for financial support of this work.
1
2
3
4
5
91
89
89
87
87
0.22
0.18
88
87
87
87
86
0.13
0.11
—
—
—
—
—
—
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