A phosphine-free heterogeneous formylation of aryl halides catalyzed by a thioether-functionalized MCM-41-immobilized palladium complex

Article abstract of DOI:10.1016/j.catcom.2014.03.027

Thioether-functionalized MCM-41-immobilized palladium(II) complex [MCM-41-S-PdCl₂] was found to be a highly efficient catalyst for the formylation of aryl iodides or bromides with CO (1 atm) using HCO₂Na as a hydrogen source. This phosphine-free heterogeneous palladium complex can be easily recovered by simple filtration and reused for at least 10 consecutive trials without any decreases in activity.

Full text of DOI:10.1016/j.catcom.2014.03.027

Catalysis Communications 51 (2014) 53–57
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
A phosphine-free heterogeneous formylation of aryl halides catalyzed by
a thioether-functionalized MCM-41-immobilized palladium complex
Wenyan Hao, Guodong Ding, Mingzhong Cai ⁎
Department of Chemistry, Jiangxi Normal University, Nanchang 330022, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Thioether-functionalized MCM-41-immobilized palladium(II) complex [MCM-41-S-PdCl ] was found to be a
2
Received 1 December 2013
Received in revised form 9 February 2014
Accepted 21 March 2014
2
highly efficient catalyst for the formylation of aryl iodides or bromides with CO (1 atm) using HCO Na as a hydro-
gen source. This phosphine-free heterogeneous palladium complex can be easily recovered by simple filtration
and reused for at least 10 consecutive trials without any decreases in activity.
Available online 27 March 2014
©
2014 Elsevier B.V. All rights reserved.
Keywords:
Supported palladium catalyst
Thioether palladium complex
MCM-41
Formylation
Heterogeneous catalysis
1
. Introduction
palladium-catalyzed formylation of aryl halides since they are very
weak reducing agents, cheap and readily available [13,14]. Okano
Aromatic aldehydes are important building blocks for the synthesis
2 3 2
et al. reported that PdCl (PPh ) -catalyzed formylation of aryl halides
of biologically active molecules or their intermediates [1] and are usual-
ly prepared by the electrophilic formylation reactions, however, these
methods often suffer from several drawbacks such as the use of unac-
ceptable amount of reagents and producing large quantities of side
products and wastes [2,3]. The palladium-catalyzed formylation of
aryl halides with carbon monoxide would offer significant advantages
over those conventional methods. Schoenberg and Heck reported the
with HCO Na under CO (1 atm) readily proceeded in DMF to afford
2
the corresponding aldehydes in good yields [15]. However, industrial
applications of homogeneous palladium complexes remain a challenge
because they are expensive, cannot be recycled, and difficult to separate
from the product mixture, which is a particularly significant drawback
for their application in the pharmaceutical industry. The immobilization
of catalytically active species, i.e. organometallic complexes, onto a solid
support to produce a molecular heterogeneous catalyst is one potential
solution to the latter two problems [16]. Heterogeneous catalysis also
helps to minimize wastes derived from reaction workup, contributing
to the development of green chemical processes [17]. Very recently,
Tokunaga and coworkers reported a phosphine-free heterogeneous
formylation of aryl iodides in the presence of palladium nanoparticles
on cobalt oxide under a syngas atmosphere (4 MPa); the catalyst
could be reused at least 7 times without significant loss of activity [18].
Developments on the mesoporous material MCM-41 provided a
new possible candidate for a solid support for immobilization of homo-
geneous catalysts [19,20]. To date, some palladium complexes on func-
tionalized MCM-41 support have been prepared and successfully used
in carbon–carbon coupling reactions [21–24]. However, to the best of
our knowledge, the formylation of aryl halides with carbon monoxide
catalyzed by immobilization of palladium in MCM-41 has not been re-
ported in the previous literature. In continuing our efforts to develop
greener synthetic pathways for organic transformations, our new ap-
proach, described in this paper, was to design and synthesize a
thioether-functionalized MCM-41-immobilized palladium(II) complex,
first example of PdX
2 3 2
(PPh ) -catalyzed formylation of aryl halides
using H as a hydrogen source under high pressures of CO (80–100
2
bar) at high temperatures (125–150 °C) [4]. The palladium-catalyzed
formylation of aryl halides could also be achieved under a lower
pressure of carbon monoxide, however, the use of expensive re-
agents such as silyl [5,6] and tin [7,8] hydrides was required and
the formylation with these hydrides is often accompanied by
overreduction of the aldehyde and other functional groups due to
their high reducing abilities. Singh et al. described reductive carbon-
ylation of aryl and heteroaryl iodides under a syngas atmosphere
using Pd(acac)
an industrially applicable catalytic system containing Pd(OAc)
P(1-adamantyl) nBu (cataCXum®A) for the reductive carbonylation
2
/dppm as an efficient catalyst [9]. Beller et al. reported
2
and
2
of aryl and heteroaryl bromides using synthesis gas as an environmen-
tally benign formylation source at a comparably low pressure (5 bar)
[10–12]. The use of formate salts is probably the best variant to perform
⁎
Corresponding author. Tel./fax: +86 791 88120388.
E-mail address: caimzhong@163.com (M. Cai).
http://dx.doi.org/10.1016/j.catcom.2014.03.027
566-7367/© 2014 Elsevier B.V. All rights reserved.
1

54
W. Hao et al. / Catalysis Communications 51 (2014) 53–57
which was used as an effective, phosphine-free heterogeneous palla-
dium catalyst for the formylation of aryl halides under an atmo-
100
spheric pressure of carbon monoxide using HCO
source.
2
Na as a hydrogen
2
. Experimental
All chemicals were obtained from commercial suppliers and used as
received, unless otherwise noted. The mesoporous material MCM-41
25] and ω-(methylmercapto)undecyltrimethoxysilane [26] were pre-
[
1
pared according to literature procedures. All solvents were distilled
and dried before use.
110
2
200
2
2
6
.1. Preparation of the catalyst
.1.1. Preparation of MCM-41-S
A solution of ω-(methylmercapto)undecyltrimethoxysilane (2.0 g,
.2 mmol) in dry chloroform (18 mL) was added to a suspension of
1
2
3
4
5
6
7
8
2θ (degrees)
the MCM-41 (2.5 g) in dry toluene (180 mL). The mixture was stirred
for 24 h at 100 °C. Then the solid was filtered and washed by CHCl
2
Fig. 1. XRD patterns of the parent MCM-41 (1) and MCM-41-S-PdCl (2).
3
(
2 × 20 mL), and dried in vacuum at 160 °C for 5 h. The dried white
2.3. General procedure for the formylation of aryl iodides or bromides
3
solid was then soaked in a solution of Me SiCl (3.05 g, 28 mmol) in
dry toluene (100 mL) at room temperature under stirring for 24 h.
Then the solid was filtered, washed with acetone (3 × 20 mL) and
diethyl ether (3 × 20 mL), and dried in vacuum at 120 °C for 5 h to
obtain 3.64 g of hybrid material MCM-41-S. The sulfur content was
found to be 1.07 mmol g− by elemental analysis.
A 50 mL round-bottomed flask equipped with a gas inlet tube, a
reflux condenser, and a magnetic stirring bar was charged with
MCM-41-S-PdCl (173 mg, 0.05 mmol Pd), aryl halide (5.0 mmol)
2
and HCOONa (7.5 mmol). The flask was flushed with carbon monoxide.
DMF (5 mL) was added by syringe and a slow stream of CO was passed
into the suspension. The mixture was vigorously stirred at 100–110
°C for 4–24 h, cooled to room temperature, and diluted with diethyl
ether (50 mL). The palladium catalyst was separated from the mix-
ture by filtration, washed with distilled water (2 × 10 mL), ethanol
(2 × 10 mL) and ether (2 × 10 mL) and reused in the next run. The
ethereal solution was washed with water (3 × 20 mL) and dried
over anhydrous magnesium sulfate and concentrated under reduced
pressure. The residue was purified by flash column chromatography
on silica gel (hexane–ethyl acetate = 10:1).
1
2
.1.2. Preparation of MCM-41-S-PdCl
In a small Schlenk tube, MCM-41-S (2.5 g) was mixed with PdCl
0.158 g, 0.89 mmol) in dry acetone (50 mL). The mixture was
2
2
(
refluxed for 72 h under Ar. The solid product was filtered by suction,
washed with distilled water and acetone and dried at 70 °C/26.7 Pa
under Ar for 5 h to give 2.57 g of a yellow palladium complex
[
2
MCM-41-S-PdCl ]. The sulfur and palladium contents were found
−
1
−1
to be 0.91 mmol g
and 0.29 mmol g , respectively.
All formylation products were characterized by comparison of their
spectra and physical data with authentic samples. IR spectra were deter-
2
.2. Characterization techniques of the catalyst
1
13
mined on a Perkin-Elmer 683 instrument. H NMR (400 MHz) and
NMR (100 MHz) spectra were recorded on a Bruker Avance 400 MHz
spectrometer with TMS as an internal standard and CDCl as solvent.
C
Microanalyses were measured by using a PerkinElmer 2400 II
CHNS elemental analyzer. Palladium content was determined with an
inductively coupled plasma atom emission Atomscan16 (ICP-AES,
TJA). X-ray photoelectron spectra were recorded on XSAM 800 (Kratos).
X-ray powder diffraction patterns were obtained on D/Max-rA
3
3. Results and discussion
(
Rigaku). The BET surface area and pore analysis were performed
Although phosphine ligands stabilize palladium and influence its
reactivity, the simplest and cheapest palladium catalysts are of
course phosphine-free systems. It is known that the catalysts
on ASAP2010 (micromeritics) by N
at 77.4 K.
2
physical adsorption–desorption
2
Scheme 1. Preparation of the MCM-41-S-PdCl complex.

W. Hao et al. / Catalysis Communications 51 (2014) 53–57
55
Table 1
MCM-41-S-PdCl
is 0.8 eV less than that in PdCl
, but 2.3 eV larger
2
2
2 2
XPS data for MCM-41-S-PdCl , MCM-41-S, PdCl
, metal Pd and used catalyst.a
than that in metal Pd. These results show that a coordination bond be-
tween S and Pd is formed in the MCM-41-S-PdCl . To verify whether
the resting state of the catalyst is Pd(0) or Pd(II), the XPS of used catalyst
was also measured and listed in Table 1. The shift (lower) of the Pd3d5/2
binding energy of used catalyst indicated that the resting state of the
catalyst should be Pd(0).
Sample
Pd3d5/2
337.5
S
2p
Si2p
O
1s
Cl2p
2
MCM-41-S-PdCl
MCM-41-S
2
164.2
163.7
103.2
103.2
533.1
533.0
199.3
PdCl
2
338.3
335.2
336.5
199.2
Metal Pd
Used catalyst
164.3
103.1
533.2
2
The formylation of iodobenzene with HCO Na was chosen as a
a
The binding energies are referenced to C1s (284.6 eV) and the energy differences were
determined with an accuracy of ± 0.2 eV.
model reaction, and the influences of solvents, reaction tempera-
tures, and catalyst quantities on the reaction were tested. The results
are summarized in Table 2. For the temperatures tested [25, 60, 80, 100,
and 110 °C], 100 °C gave the best result. Among the solvents evaluated
[
toluene, dioxane, pyridine, propionitrile, DMF, and DMSO], DMF was
Table 2
found to be the most effective. Less polar solvents such as toluene, diox-
ane, pyridine and propionitrile were not favorable for the formylation,
and DMSO afforded a moderate yield (entry 8). The amount of palladi-
um catalyst was also screened, and 1.0 mol% loading of palladium was
found to be optimal (entry 4), a lower yield was observed when the
amount of the catalyst was decreased (entry 12). Increasing the amount
of palladium catalyst could shorten the reaction time, but did not in-
crease the yield of benzaldehyde (entry 11). Thus, the optimized re-
action condition for this formylation reaction is the MCM-41-S-PdCl
(1.0 mol%) with DMF as solvent at 100 °C under CO (1 atm) for 8 h
(entry 4).
To examine the scope for this heterogeneous formylation, we
have investigated the reaction of a variety of aryl iodides or bromides
with HCO
and the results are outlined in Table 3. As shown in Table 3, the
formylation reactions of a variety of aryl iodides with HCO Na
Reaction condition screening for the formylation reaction of iodobenzene with HCO
2
Na.a
TON TOF
Entry Solvent
Pd catalyst
mol%)
Temp.
(°C)
Time
(h)
Yieldb
(%)
(
1
2
3
4
5
6
7
8
9
1
1
1
DMF
DMF
DMF
DMF
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
25
60
80
24
24
24
8
0
0
0
0
0
Trace
56
84
81
0
Trace
51
Trace
7
83
78
56
84
81
0
2.3
10.5
16.2
0
100
110
100
100
100
100
100
100
100
DMF
5
2
Toluene
Dioxane
DMSO
24
24
12
24
24
5
0
0
51
0
4.3
0
Propionitrile 1.0
0
1
2
Pyridine
DMF
DMF
1.0
2.0
0.5
7
0.3
41.5 8.3
156 7.8
2
Na under the optimized reaction conditions (Scheme 2)
20
a
2
All reactions were performed using PhI (5.0 mmol) and HCO Na (7.5 mmol) in a sol-
2
vent (5.0 mL) under CO (1 atm).
b
Isolated yield.
under CO (1 atm) proceeded smoothly in DMF at 100 °C affording the
corresponding aromatic aldehydes 2a–l in good to excellent yields (en-
tries 1–12). Various electron-donating and electron-withdrawing groups
3 3 2 3 2 3 3
such as \OCH , \CH , \Cl, \CN, \CO CH , \NO , \CF , and \COCH
containing phosphine ligands at higher temperatures are unstable
27] and the procedure for preparing the supported phosphine palla-
dium complexes is rather complicated. Therefore, the development
of novel phosphine-free heterogeneous palladium catalysts having
a high activity and good stability is a topic of enormous importance.
A new thioether-functionalized MCM-41-immobilized palladium(II)
complex [MCM-41-S-PdCl ] was prepared from ω-(methylmercapto)-
2
undecyltrimethoxysilane via immobilization on MCM-41, followed by
reacting with palladium chloride (Scheme 1). The X-ray powder diffrac-
on aryl iodides were well tolerated. The reactivity of electron-deficient
aryl iodides was higher than that of electron-rich aryl iodides. The reac-
tions of sterically hindered aryl iodides such as 2-iodoanisole, methyl 2-
iodobenzoate and 2-trifluoromethyliodobenzene could also give the
corresponding aromatic aldehydes 2m–o in good yields on longer
times (entries 13–15). The formylation of the bulky 1-iodonaphthalene
afforded 1-naphthaldehyde 2p in 86% yield (entry 16). The heteroaryl
iodides such as 3-iodopyridine and 2-iodothiophene could undergo the
formylation to give pyridine-3-carboxaldehyde 2q and thiophene-2-
carboxaldehyde 2r in 79% and 85% yields, respectively (entries 17 and
18). Aryl bromides were less reactive than the iodides, and underwent
the formylation at 110 °C to give the corresponding aromatic aldehydes
in good yields along with about 4–9% yields of reductive dehalogenation
by-products (entries 19–25). Benzyl bromide could also undergo the
formylation at 100 °C to afford phenylacetaldehyde 2s in an 84% yield
[
2
tion (XRD) analysis of the MCM-41-S-PdCl indicated that, in addition
to an intense diffraction peak (100), two higher order peaks (110)
and (200) with lower intensities were also detected, and therefore the
chemical bonding procedure did not diminish the structural ordering
of the MCM-41 (Fig. 1). The nitrogen adsorption studies demonstrated
that significant decreases in surface area and pore size by virtue of mod-
ification of the MCM-41 were observed. The MCM-41 had a surface area
2
(entry 26). To compare the reactivity of the MCM-41-S-PdCl with that
2
−1
of 906.4 m g and a diameter of 2.8 nm, however, MCM-41-S-PdCl
2
of some commercially available heterogeneous palladium catalysts
such as Pd/C (from Aldrich), we also performed the formylation of
iodobenzene using Pd/C as the catalyst under the same conditions.
It was found that the formylation reaction did not occur with Pd/C
2
−1
had a surface area of 642.7 m g and a diameter of 2.1 nm.
Elemental analyses and X-ray photoelectron spectroscopy (XPS)
were used to characterize the new thioether-functionalized MCM-41-
immobilized palladium(II) complex. The S:Pd mole ratio of the MCM-
2
instead of MCM-41-S-PdCl . In contrast to the iodides and bro-
4
1-S-PdCl
PdCl , MCM-41-S, PdCl
seen that the difference of S2p binding energies between MCM-41-S-
PdCl and MCM-41-S is 0.5 eV, and the binding energy of Pd3d5/2 in
2
was determined to be 3.14. The XPS data for MCM-41-S-
mides, the chlorides were inactive under these conditions. There-
fore, both 4-chloroiodobenzene and 4-bromochlorobenzene were
formylated selectively to 4-chlorobenzaldehyde 2b in high yields
(entries 2 and 20).
2
2
and metal Pd are listed in Table 1. It can be
2
2
Scheme 2. Heterogeneous formylation of aryl halides with HCO Na.

56
W. Hao et al. / Catalysis Communications 51 (2014) 53–57
Table 3
Formylation of aryl halides with HCO
Na under CO (1 atm) catalyzed by MCM-41-S-PdCl
2 2
.a
Entry
Ar
X
Temp. (°C)
Time (h)
Product
Yieldb (%)
TON
TOF
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
Ph
4-ClC
4-MeC
4-MeOC
4-CNC
3-MeC
3-MeOC
4-MeCOC
4-MeOCOC
4-NO
3-NO
3-CF
2-MeOC
2-MeOCOC
2-CF
1-Naphthyl
3-Pyridinyl
2-Thienyl
Ph
4-ClC
4-CNC
4-MeCOC
4-MeOCOC
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
110
110
110
110
110
110
110
100
8
6
10
12
6
10
12
6
6
4
6
7
24
20
24
12
10
12
12
10
10
10
10
16
24
6
2a
2b
2c
2d
2e
2f
2g
2h
2i
84
88
83
81
90
84
82
91
89
93
87
85
75
80
72
86
79
85
75
79
82
83
81
74
71
84
84
88
83
81
90
84
82
91
89
93
87
85
75
80
72
86
79
85
75
79
82
83
81
74
71
84
10.5
14.7
8.3
6.8
15.0
8.4
6
H
4
6
H
4
6
H
4
6
H
4
6
H
4
6
H
4
6.8
6
H
4
15.2
14.8
23.3
14.5
12.1
3.1
4.0
3.0
7.2
7.9
7.1
6.3
7.9
8.2
8.3
8.1
4.6
2.9
6
H
4
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
2
C
C
6
H
H
4
2j
2k
2l
2
6
4
3
6
C H
4
6
H
4
2m
2n
2o
2p
2q
2r
2a
2b
2e
2h
2i
6
H
4
3
6
C H
4
I
I
Br
Br
Br
Br
Br
Br
Br
Br
H
6 4
6
H
4
6
H
4
6
H
4
4-MeC
4-MeOC
PhCH
6
H
4
2c
2d
2s
6
H
4
2
14.0
a
All reactions were performed using aryl halide (5.0 mmol), HCO
Isolated yield.
2 2
Na (7.5 mmol), and MCM-41-S-PdCl (0.05 mmol) in DMF (5.0 mL) under CO (1 atm).
b
To verify whether the observed catalysis was due to the heteroge-
neous catalyst or to a leached palladium species in a solution, we per-
under CO (1 atm) by using thioether-functionalized MCM-41-
immobilized palladium complex as the catalyst with HCO Na as a hy-
2
formed the hot filtration test [28]. We focused on the formylation of
iodobenzene with HCO Na. We filtered off the MCM-41-S-PdCl com-
2 2
drogen source. The reactions generated a variety of aromatic aldehydes
in good to excellent yields. This novel phosphine-free heterogeneous
palladium catalyst can be easily prepared and exhibits high catalytic ac-
tivity and can be reused at least 10 times without any decreases in
activity.
plex after 4 h of reaction time and allowed the filtrate to react further.
We found that, after this hot filtration, no further reaction was observed,
indicating that leached palladium species from the catalyst (if any) are
not responsible for the observed activity. It was confirmed by ICP-AES
analysis that no palladium could be detected in the hot filtered solution.
Acknowledgments
2
The MCM-41-S-PdCl complex can be easily recovered by a simple
filtration of a reaction solution. We also investigated the possibility to
reuse the catalyst by using the formylation of 4-iodoacetophenone.
It was found that when the reaction of 4-iodoacetophenone with
We gratefully acknowledge the financial support of this work by the
National Natural Science Foundation of China (Project No. 20862008).
HCO
MCM-41-S-PdCl
2
Na under CO (1 atm) was performed even with 1.0 mol% of
, the catalyst could be recycled 10 times without any
2
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TON
TOF
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91
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