Pd-poly(N-vinyl-2-pyrrolidone)/MCM-48 nanocomposite: a novel catalyst for the Ullmann reaction

Article abstract of DOI:10.1007/s11696-018-0421-y

Abstract: Homocoupling of aryl halides (Ullmann-type reaction) promoted by a Pd-poly(N-vinyl-2-pyrrolidone)/MCM-48 (Pd–PVP/MCM-48) nanocomposite catalyst is described. In situ polymerization method was employed to prepare composite poly(N-vinyl-2-pyrrolidone)/MCM-48 (PVP/MCM-48) which was used as a support for palladium nanoparticles obtained by reducing Pd(OAc)₂ with hydrazine hydrate. FT-IR, XPS, XRD, UV–Vis, SEM, and BET techniques were used to study the chemical and physical properties of the catalyst. The catalytic performance of this heterogeneous catalyst was specified for Ullmann-type reaction between aryl halies in DMF. The catalyst was good with regard to its stability and it can be reused up to six times without significant loss of its activity.

Full text of DOI:10.1007/s11696-018-0421-y

Chemical Papers
https://doi.org/10.1007/s11696-018-0421-y
ORIGINAL PAPER
Pd‑poly(N‑vinyl‑2‑pyrrolidone)/MCM‑48 nanocomposite: a novel
catalyst for the Ullmann reaction
Neda Mosaddegh1 · Issa Yavari1
Received: 10 September 2017 / Accepted: 14 February 2018
© Institute of Chemistry, Slovak Academy of Sciences 2018
Abstract
Homocoupling of aryl halides (Ullmann-type reaction) promoted by a Pd-poly(N-vinyl-2-pyrrolidone)/MCM-48 (Pd–PVP/
MCM-48) nanocomposite catalyst is described. In situ polymerization method was employed to prepare composite poly(N-
vinyl-2-pyrrolidone)/MCM-48 (PVP/MCM-48) which was used as a support for palladium nanoparticles obtained by reducing
Pd(OAc)2 with hydrazine hydrate. FT-IR, XPS, XRD, UV–Vis, SEM, and BET techniques were used to study the chemical
and physical properties of the catalyst. The catalytic performance of this heterogeneous catalyst was specifed for Ullmann-
type reaction between aryl halies in DMF. The catalyst was good with regard to its stability and it can be reused up to six
times without signifcant loss of its activity.
Graphical abstract
I
2
DMF
,
1) Pd(OAc)2
1)N-vinyl-2-pyrrolidone, THF
HCl
K2CO3
100 °C
2)
NH2NH2
2) Benzoyl peroxide
N
O
Pd
MCM-48
Pd-PVP/MCM-48
PVP/MCM-48
N
O
O
N
N
O
N
O
N
Pd
Pd
O
Keywords MCM-48 · Pd nanoparticles · Poly(N-vinyl-2-pyrrolidone) · Polymer–inorganic hybrid material · Ullmann-type
reaction
Introduction
(Kantchev et al. 2007; Fu 2008) are the most commonly
used catalysts for such reactions. However, there are dis-
advantages such as non-reusability of catalyst, high cost,
and environmental pollution due to the presence of organic
solvents and heavy metallic ions (Mark 2006; Zheng et al.
2008; Ostapenko et al. 2008; Morales et al. 2010) in homo-
geneous catalysis. In general, because of their easy separa-
tion from the products, heterogeneous catalysts are prefer-
able to homogeneous ones. Thus, heterogeneous catalysts
could be used repeatedly, and this reduces the cost. Since
there seems to be a problem regarding their low activity and/
or selectivity (Yin and Liebscher 2007), the development of
heterogeneous palladium nanocatalysts, with high stability,
Palladium catalyzed cross-coupling reactions are famous for
generating carbon–carbon bonds (Phan et al. 2006; Segan-
ish et al. 2005). Heck, Sonogashira, Suzuki–Miyaura, and
Ullmann reactions have proved to be excellent methods for
synthesizing organic compounds (Molnar 2011; Anbarasan
et al. 2011), and homogeneous palladium (II) complexes
* Issa Yavari
yavarisa@modares.ac.ir
1
Department of Chemistry, Science and Research Branch,
Islamic Azad University, Tehran, Iran
Vol.:(0123456789)
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Chemical Papers
activity, and recyclability is an important task in nanomate-
rial researches.
Chemicals
Recently, much attention has been attracted to periodic
mesoporous materials for various applications including
drug delivery, catalysis, etc. Due to their large surface area
and pore volume and tunable pore size, these materials have
attracted much attention as catalysts (Taguchi and Schuth
2005). The cubic MCM-48 (Mobil Composition of Matter)
has two interwoven independent three-dimensional pore
systems that are suited in a mirror-plane position to each
other. Compared to MCM-41 in a one-dimensional hex-
agonal bisectional pore system (Wei et al. 2010), MCM-48
provides more favorable mass transfer kinetics in catalytic
and separation applications, but this material has not been
vastly explored as a support for catalytic reactions, and lit-
erature reports in this area are limited (Wang et al. 2012a, b).
Catalytic components are often supported on high-specifc
surface area carriers like mesoporous silica in an attempt to
increase the catalyst durability or activity.
All chemicals were obtained from Merck and were used
without further purifcation.
Preparation of poly(N‑vinyl‑2‑pyrrolidone)/MCM‑48
(PVP/MCM‑48)
MCM-48 was prepared according to the previous work
(Kalbasi and Mosaddegh 2011). N-Vinyl-2-pyrrolidone
(NVP) (0.5 mL, 4.6 mmol) and MCM-48 (0.5 g) in 7 mL
of THF were poured in a round bottom fask, and the mix-
ture was stirred for 5 h. Then, benzoyl peroxide (3% mol,
0.034 g) was added to the mixture and it was refuxed again
for 5 h while being stirred under N2 atmosphere. The result-
ing colorless fne powder composite (PVP/MCM-48) was
collected by fltration, washed with THF, and dried at 60 °C
under reduced pressure. The yield of polymerization was
75%.
Hybrid organic–inorganic polymers have attracted
increasing attention due to their unique properties (Zheng
et al. 2008; Mark 2006); however, there are few reports on
their application as a heterogeneous catalyst (Ma et al. 2009;
Alves et al. 2010). In our previous studies (Kalbasi and
Mosaddegh 2011), diferent kinds of such polymers were
used as catalysts. In this study, we concentrated on preparing
poly(N-vinyl-2-pyrrolidone)/MCM-48 as a good support for
Pd nanoparticles, and generated a suitable heterogeneous
catalyst with a large surface area. The catalytic activity of
this novel hybrid material was studied in Ullmann cross-
coupling reaction.
Preparation of Pd nanoparticle–poly(N‑vinyl‑2‑
pyrrolidone)/MCM‑48 (Pd–PVP/MCM‑48)
Poly(N-vinyl-2-pyrrolidone)/MCM-48 (PVP/MCM-
48) (0.1 g) and 10 mL of an aqueous hydrochloric acid
(CHCl = 0.09 M) solution of Pd(OAc)2 (0.053 g, 0.236 mmol)
were placed in a round bottom fask. The mixture was heated
to 80 °C for 5 h while being stirred under N2 atmosphere.
After that, 0.6 mL (9.89 mmol) aqueous solution of hydra-
zine hydrate (N2H4·H2O) (80 vol%) was added to this mix-
ture dropwise in 15–20 min, and the solution was stirred
at 60 °C for 1 h prior to being fltered and washed sequen-
tially with CHCl3 and MeOH to remove excess N2H4·H2O.
Then, it was dried at room temperature to yield palladium
nanoparticle–poly(N-vinyl-2-pyrrolidone)/MCM-48 com-
posite (Pd–PVP/MCM-48) (Scheme 1). The Pd content of
the catalyst, which was estimated by inductively coupled
plasma atomic emission spectrometry (ICP-AES), was
1.14 mmol g−1 (the yield of Pd loading is about 49%).
Experimental
General identifcation methods
The samples were all analyzed using FT-IR spectroscopy
(using a Perkin Elmer 65 in KBr matrix in the range of
4000–400 cm−1). Using a Series BEL SORP 18, their BET
specifc surface areas and BJH pore size distribution were
determined by adsorption–desorption of nitrogen at liquid
nitrogen temperature. The X-ray powder difraction (XRD)
of the catalyst was done on a Bruker D8 Advance X-ray
difractometer by employing Ni-fltered Cu Kα radiation at
40 kV and 20 mA. In addition, X-ray photo-electron spec-
tra (XPS) were recorded on ESCA SSX-100 (Shimadzu) by
employing a non-mono-chromatized Mg Ka X-ray as the
source of excitation. Scanning electron microscopic (SEM)
studies were carried out on Philips, XL30, SE detector. The
DRS UV–Vis spectra were recorded with JASCO spectrom-
eter, V-670 from 190 to 2700 nm.
General procedure for Ullmann coupling reaction
A mixture of iodobenzene (3 mmol), K2CO3 (4.5 mmol),
and catalyst (0.12 g, Pd–PVP/MCM-48) in DMF (5 mL) was
stirred at 100 °C for appropriate time (Scheme 2). The reac-
tion progress was checked by TLC using hexane or hexane/
AcOEt (4:1) as eluent. The reaction mixture was cooled to
room temperature. After extraction with water and diethyl
ether, the combined organic layer was dried over MgSO4
and solvent was removed under reduced pressure. The
crude product was purifed by fash column chromatography
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Chemical Papers
Scheme 1 Encapsulation of PVP and Pd in the 3-D interconnected pore channels of MCM-48
Scheme 2 Ullmann-type reaction of aromatic aryl halides catalyzed by Pd–PVP/MCM-48
(hexane or hexane/EtOAc) to aford the desired coupling
product. The fnal product was identifed with 1H NMR, 13
C
NMR, and FT-IR spectroscopic techniques.
Results and discussion
Figure 1 shows the powder X-ray difraction patterns of
silica MCM-48 (a), PVP/MCM-48 (b), and Pd–PVP/MCM-
48 (c). All samples exhibit a strong (211) difraction peak
at ~ 2.35° (Pedernera et al. 2009; Bandyopadhyay and Gies
2005).
The characteristic refections of a well-ordered cubic
structure are present in all cases, and this indicates that
polymerization and Pd immobilization have no adverse
efects on the ordered structure of MCM-48. However, the
intensity of the characteristic refection peaks of the PVP/
MCM-48 and Pd–PVP/MCM-48 (2θ = 0.7–10) samples is
reduced (Fig. 1) to some extent. In fact, composites have
much less MCM-48 because of the dilution of the silicious
material by PVP and Pd. This dilution can be the reason for
the decrease in the peak intensity. Figure 1 illustrates the
wide-angle XRD pattern of the Pd–PVP/MCM-48 nano-
composite (2θ = 10–85), too. Four difraction peaks in the
XRD pattern at 39.92°, 46.54°, 67.90°, and 81.84° are (111),
(200), (220), and (311) difractions of the Pd fcc lattice,
respectively (Wang et al. 2008).
Figure 2 presents the FT-IR spectra of MCM-48 (a),
PVP/MCM-48 (b), and Pd–PVP/MCM-48 (c). Just like
mesoporous silica MCM-48 (Fig. 2a), PVP/MCM-48 and
Pd–PVP/MCM-48 samples show the typical vibrations of
symmetric and asymmetric stretching in addition to the rock-
ing of Si–O–Si at around 1075, 800, and 460 cm−1 (Fig. 2).
Fig. 1 Powder XRD of a mesoporous silica MCM-48, b PVP/MCM-
48, and c Pd–PVP/MCM-48
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Chemical Papers
Pd–PVP/MCM-48 had already been calculated by
employing the Brunauer–Emmett–Teller (BET) and Bar-
rett–Joyner–Halenda (BJH) methods, respectively (Table 1).
After hybridization of MCM-48 with PVP through in situ
polymerization, PVP/MCM-48 shows a smaller specifc
area, pore size, and pore volume in comparison with those
of pure MCM-48, and this might be resulted from the pres-
ence of polymer on the surface of the MCM-48 (Table 1
and Fig. 3).
The UV–Vis spectra of Pd(OAc)2 reveal a peak at 400 nm,
indicating the existence of Pd(II) (Ahmadian-Namini et al.
2007), but UV–Vis spectra of Pd–PVP/MCM-48 showed
no characteristic peak in this region, indicating complete
reduction of Pd(II)–Pd nanoparticles.
The SEM images of the MCM-48 (a), PVP/MCM-
48 (b), and Pd–PVP/MCM-48 (c) are shown in Fig. 4.
Obviously, no change is observed on the morphology of
MCM-48 after hybridization with poly(N-vinyl-2-pyrro-
lidone) and palladium nanoparticles (Fig. 4b, c). This can
Table 1 Physicochemical properties of mesoporous silica MCM-48,
PVP/MCM-48, and Pd–PVP/MCM-48 samples obtained from N2
adsorption
Sample
BET surface VP (cm3 g−1 a
)
BJH pore
diameter
(nm)
area (m2 g−1
)
Mesoporous silica MCM- 1673
48
0.89
2.14
PVP/MCM-48
911
464
0.76
0.71
2.01
1.89
Fig. 2 FT-IR spectra of a mesoporous silica MCM-48, b PVP/MCM-
48, and c Pd–PVP/MCM-48
Pd–PVP/MCM-48
aTotal pore volume
The band at around 950 cm−1 is attributed to Si–OH
vibrations of the surface silanols (Fig. 2), which is character-
istic of mesoporous silica. The typical PVP vibration in the
FT-IR spectrum (Fig. 2b) shows the presence of PVP in the
PVP/MCM-48 composite. In the FT-IR spectrum of PVP/
MCM-48 (Fig. 2b), the new band at 1661 cm−1 is related to
the carbonyl group of PVP [23]. Furthermore, the bands at
2800–3000 cm−1 are related to the aliphatic C–H stretching
in PVP/MCM-48 (Fig. 2b).
The band around 1654 cm−1 corresponding to carbonyl
bond of PVP is shifted to lower wave number (1654 cm−1,
red shift) as shown in Pd–PVP/MCM-48 spectrum (Fig. 2c).
This may be resulted from the interaction between the Pd
nanoparticles and C=O groups, meaning that the C=O
stretching vibration becomes weaker by being coordinated
to Pd nanoparticles (Iwamoto et al. 2009; Metin and Zkar
2008).
The BET specific surface areas and the pore
size, the host MCM-48, PVP/MCM-48, and
Fig. 3 N2 adsorption–desorption isotherms of mesoporous silica
MCM-48, PVP/MCM-48, and Pd–PVP/MCM-48
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Chemical Papers
Fig. 4 Scanning electron microscopy photographs of a mesoporous MCM-48, b PVP/MCM-48, c Pd–PVP/MCM-48
Table 2 Efect of diferent bases
Base
Yield (%)a
on Ullmann reaction
K2CO3
Na3PO4
Et3N
90
73
34
Reaction conditions: Catalyst
(0.12 g), iodobenzene (3 mmol),
base (4.5 mmol), DMF (5 mL),
100 °C, 12 h, Pd loading (in
mol% referred to iodoben-
zene) = 0.046
aIsolated yield of biphenyl
Catalytic activity
Fig. 5 XPS spectrum of a Pd 3d of Pd–PVP/MCM-48, b Pd–PVP/
In the beginning, we conducted the coupling reaction of
iodobenzene (3 mmol) in the presence of Pd–PVP/MCM-
48 as catalyst and K2CO3 (4.5 mmol) as base in DMF. The
mixture was stirred under nitrogen atmosphere at 100 °C for
12 h, and the desired product (biphenyl) was obtained in 90%
yield. Because the proper combination of base and solvent
is very important, several diferent solvents and bases were
examined for the Ullmann cross-coupling reaction.
MCM-48
be attributed to the polymerization and incorporation of
PVP and Pd nanoparticles inside the pores of MCM-48.
The XPS study was carried out on the Pd–PVP/MCM-
48 catalyst (Fig. 5a). In comparison with the standard
binding energy [Pd0 with Pd 3d5/2 of about 335 eV and
Pd 3d3/2 of about 340 eV (Teranishi and Miyake 1998)],
we can conclude that the Pd peaks in Pd–PVP/MCM-48
shifted to lower binding energy than Pd0 standard bind-
ing energy.
The efects of base on homocoupling reactions were
studied. Indeed, the base is necessary for terminal reduc-
tion, and the catalytic cycle is not completed without it.
According to the results, K2CO3 was selected as an inor-
ganic and cheaper base (Table 2). This feature may be
interpreted by the fact that in the presence of an inor-
ganic base, DMF decomposes into carbon monoxide and
dimethylamine. The latter could reduce aryl halides in the
presence of Pd(0) catalysts (Zawisza and Muzart 2007).
Moreover, in the presence of K2CO3, higher selectivity
toward biphenyl was achieved (5% benzene was produced).
In the presence of Na3PO4 and Et3N, 17 and 12% benzene
was obtained, respectively. It means that the selectivity
toward biphenyl is lower in the presence of these bases.
In the next stage, the efect of the solvent was inves-
tigated. As shown in Table 3, the reaction rate is greatly
The position of Pd 3d peak is usually influenced by
the local chemical/physical environment around Pd spe-
cies in addition to the formal oxidation state, and shifts
to lower binding energy with an increase in the charge
density around it (Teranishi and Miyake 1998).
Therefore, the peaks at 333.8 and 339.1 eV should
be resulted from Pd0 species bounded directly to oxy-
gen atom of the carbonyl group of PVP. The full XPS
spectrum of Pd–PVP/MCM-48 showed peaks of carbon,
oxygen, Si, and palladium. Carbon peaks were related to
PVP structure (Fig. 5b).
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Chemical Papers
Table 3 Efect of solvent on
Table 4 Catalyst reusability for the Ullmann reaction
Solvent
Yield (%)a
Ullmann coupling reaction
Cycle
Yield (%)a
Pd content of cata-
lyst (mmol/0.12 g)
EtOH
H2O
DMF
DMSO
CH2Cl2
62
56
90
57
31
1
2
3
4
5
6
7
90
90
90
90
87
87
85
0.137
0.135
0.135
0.135
0.133
0.133
0.132
Reaction conditions: Pd–PVP/
MCM-48 (0.12 g), iodobenzene
(3 mmol), K2CO3 (4.5 mmol),
solvent (5 mL), refux, 12 h, Pd
loading (in mol% referred to
iodobenzene) = 0.046
Reaction conditions: Pd–PVP/MCM-48 (0.12 g), iodobenzene
(3 mmol), K2CO3 (4.5 mmol), DMF (5 mL), 12 h, Pd loading for
fresh catalyst (in mol% referred to iodobenzene) = 0.046
aIsolated yield of biphenyl
aIsolated yield of biphenyl
afected by the kind of solvent used. Among the commonly
used organic solvents, the best results were obtained with
DMF (Table 3). The choice of DMF is favored also by the
fact that DMF is soluble in water, which facilitates prod-
uct isolation. In case of ethanol and water, the selectivity
toward biphenyl was lower which 23 and 31% benzene as
byproduct was obtained, respectively. The yield of ben-
zene as byproduct in the presence of other solvents was
about 5% which means that the selectivity is higher in
these cases.
contribute stabilizing the palladium nanoparticles and pre-
venting aggregate formation. The mesoporous structure of
MCM-48 prevents uncontrolled growth of palladium nanopar-
ticles and make the size of nanoparticles be small which cause
enhancing in catalytic activity. In addition, simultaneous pres-
ence of polymer and mesoporous silica decreases palladium
leaching. Thus, the stability and reusability of the catalyst get
increase and this is an important advantage in compared to
catalysts which palladium nanoparticles are fxed on polymeric
substrate or supported in mesoporous cavities.
The efect of temperature was fnally examined, and it was
found that the reaction temperature has a signifcant efect.
The results showed that the yield and the rate of the reaction
are relatively low below 100 °C. It should be mentioned that
the selectivity toward biphenyl abruptly decreased when the
reaction temperature increased from 100 to 120 °C (the same
results were reported by Li , Chai et al.). Actually, at higher
temperatures, Pd leaching is increased to some extent and
hydrodehalogenation may be catalyzed by leached Pd atoms.
Therefore, 100 °C was chosen as an optimal condition.
Other important issues concerning the application of a
heterogeneous catalyst are its reusability and stability under
reaction conditions. Catalyst recycling experiments were
carried out using an Ullmann reaction of iodobenzene, and
the results are shown in Table 4. After each cycle, the cata-
lyst was fltered of, washed with water (10 mL), diethyl
ether and acetone (3 × 5 mL). Then, it was dried in an oven
at 60 °C and was reused in the Ullmann reaction. The results
show that there was very low Pd leaching during the reaction
(only about 3.5%) and the catalyst exhibited high stability
even after six recycles (Table 4). However, the selectivity
toward biphenyl was constant even after 6 cycles of the
reaction.
The general applicability of Pd–PVP/MCM-48 as catalyst
was explored with diferent arylhalids containing electron-
withdrawing or electron-donating substituents in the Ullmann
homocoupling reaction (Table 5) using the optimized reaction
conditions.
The reactions were carried out in DMF at 100 °C, and cou-
pling reactions with aryl bromides (Entries 5 and 6) proceeded
with good yields. Activation of C–Cl bond is more difcult
than C–Br and C–I bonds, and generally requires harsher reac-
tion conditions in heterogeneous catalysis systems. As shown
in Table 5, chlorobenzene was converted to biphenyl in 55%
yield. However, the yield of the reaction at 130 °C was 95%.
Thus, the catalyst aforded reasonable yields of biaryl prod-
ucts. In addition, the selectivity toward biaryl products was
high and the yield of benzene as byproduct was lower than
10%.
A comparative study was conducted for the use of Pd–PVP/
MCM-48 with some of the reported catalysts for Ullmann
reaction with respect to the catalyst, aryl halide, solvent, base,
reaction time, yield and selectivity of the products (Table 6).
The results clearly show that Pd–PVP/MCM-48 promotes
the reaction reasonably in a good yield and high selectivity.
Moreover, Pd–PVP/MCM-48 can be efectively used for the
Ullmann reaction of chloro and bromo benzene.
It should be mentioned that the catalyst consists of
mesoporous silica and polymer parts, which both parts
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Chemical Papers
Table 5 Ullmann reaction of aromatic aryl halides catalyzed by Pd–PVP/MCM-48
Entry
1
Substrate
Product
Yield (%)a
90
I
2
85
3
4
90
55
5
70
6
7
90
55
Br
Cl
Reaction conditions: Pd–PVP/MCM-48 (0.12 g), aryl halide (3 mmol), K2CO3 (5 eq), DMF (5 mL), 12 h, 100 °C, Pd loading (in mol% referred
to aryl halide) = 0.046
aIsolated yield of bi-aryl product
Table 6 Comparison of Pd–PVP/MCM-48 with some other catalysts for Ullmann reaction
Catalyst
Aryl halide
Temp (°C) Solvent
Base
Time (h) Yield (%) Selectivity Recyclability References
(%)
(times)
Pd/Ph-SBA-15
Au–Pd/PVP
PhI
PhCl/PhBr
100
35
H2O
NaHCO2/KOH 10
75
97
96
–
5
Li et al. (2007)
DMF/H2O KOH
12
Not reported Nath Dhital et al.
(2012)
Pd/Ph-MCM-41
Pd–Fe–H
Pd–PVP/MCM-48 PhI/PhBr/PhCl 100
PhI
PhI
100
90
H2O
H2O
DMF
NaHCO2/KOH 10
NaHCO2/KOH 28
74a
98
100
95
3
5
6
Wan et al. (2006)
Li et al. (2010)
This work
85
K2CO3
12
90 (95)b
aYield for chlorobenzene at ambient condition
bYield for chlorobenzene at 130 °C
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Chemical Papers
Li H, Zhu Z, Li H, Li P, Zhou X (2010) Recyclable hollow Pd–Fe
nanospheric catalyst for Sonogashira-, Heck-, and Ullmann-
type coupling reactions of aryl halide in aqueous media. J
Colloid Interface Sci 349:613–619. https://doi.org/10.1016/j.
jcis.2010.06.009
Conclusions
In summary, a novel polymer–inorganic hybrid material,
Pd nanoparticle–PVP/MCM-48, was prepared by a simple
method. The catalytic activity of this novel organic–inor-
ganic hybrid was good for Ullmann cross-coupling reaction
of aryl bromide, chloride, and iodides at 100 °C. This new
heterogeneous catalyst can practically replace soluble cata-
lysts in view of the following advantages: (a) high catalytic
activity under relatively mild reaction conditions; (b) easy
separation of the catalyst after the reaction; and (c) reus-
ability of the catalyst for several times without signifcant
loss in the yield of the reaction. Moreover, with regard to
environmental concerns, the synthetic method reported here
may be considered as an environment-friendly process.
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