A simple and efficient recyclable phosphine-free catalytic system for alkoxycarbonylation and carbonylative Sonogashira coupling reactions of aryl iodides

Article abstract of DOI:10.1016/j.jcat.2007.10.021

Using palladium on charcoal (Pd/C) and triethylamine as a novel, efficient, versatile, recyclable, and phosphine-free catalytic system, we carried out the alkoxycarbonylation of aryl iodides (alcohols or phenols as nucleophiles) and the carbonylative Sonogashira coupling reaction of aryl iodides with terminal alkynes, affording the corresponding aryl esters and α, β-alkynyl ketones in good to excellent yields under mild conditions. We found that both electron-withdrawing and electron-donating substituents on phenol enhanced the phenoxycarbonylation of iodobenzene. The recyclability of Pd/C was also demonstrated.

Full text of DOI:10.1016/j.jcat.2007.10.021

Journal of Catalysis 253 (2008) 50–56
www.elsevier.com/locate/jcat
A simple and efficient recyclable phosphine-free catalytic system
for alkoxycarbonylation and carbonylative Sonogashira coupling reactions
of aryl iodides
Jianhua Liu, Jing Chen ∗, Chungu Xia ∗
State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences
and Graduate School of the Chinese Academy of Sciences, Lanzhou 730000, People’s Republic of China
Received 5 September 2007; revised 24 October 2007; accepted 25 October 2007
Available online 26 November 2007
Abstract
Using palladium on charcoal (Pd/C) and triethylamine as a novel, efficient, versatile, recyclable, and phosphine-free catalytic system, we carried
out the alkoxycarbonylation of aryl iodides (alcohols or phenols as nucleophiles) and the carbonylative Sonogashira coupling reaction of aryl
iodides with terminal alkynes, affording the corresponding aryl esters and α,β-alkynyl ketones in good to excellent yields under mild conditions.
We found that both electron-withdrawing and electron-donating substituents on phenol enhanced the phenoxycarbonylation of iodobenzene. The
recyclability of Pd/C was also demonstrated.
© 2007 Elsevier Inc. All rights reserved.
Keywords: Palladium on charcoal; Alkoxycarbonylation; Carbonylative Sonogashira coupling; Aryl iodides; Aryl esters; α,β-Alkynyl ketones; Recycle
1. Introduction
lic reagents with acid chlorides [9]. Recently reported meth-
ods have used Pd- or Cu-catalyzed coupling reactions of acid
halides and terminal alkynes [10]; however, these methods must
be use dry solvents under an inert atmosphere. Evidently, the
conventional synthesis processes for these compounds are not
so eco-friendly and atom-economical; thus, in this regard, the
carbonylation of aryl halides with alcohol, phenol, or alkyne as
a nucleophile provides an alternative approach to the synthesis
of aryl esters and α,β-alkynyl ketones with atom economy.
Over the last decade, significant efforts have focused on the
development of Pd-phosphine complexes for the one-step syn-
thesis of phenyl esters [11,12] and α,β-alkynyl ketones [13–19]
via carbonylation of aryl iodides under homogeneous condi-
tions. However, as a result of the notorious phosphine degra-
dation by P–C bond cleavage, an excess of phosphine is often
necessary to avoid catalyst deactivation. Furthermore, homo-
geneous palladium catalysts usually are not reusable, and the
products are frequently contaminated by residual palladium
and toxic phosphine ligands, which can be difficult to sepa-
rate from the products and starting materials in an efficient
and simple manner. Recently, Leadbeater and Kormos [20]
reported phosphine-free Pd(OAc)2-catalyzed alkoxycarbony-
The transition metal-catalyzed carbonylation of aryl halides
in the presence of nucleophiles is an important methodology
for the preparation of aromatic carbonyl compounds [1–3], in-
cluding esters, acids, amides, ketones, and others. Of particular
interest among these important carbonyl intermediates are the
aryl esters and α,β-alkynyl ketones, because aryl esters (es-
pecially phenyl esters) are widely used in liquid crystals [4],
photosensitizers [5], and biologically active compounds [6],
whereas α,β-alkynyl ketones are crucial moieties in many bio-
logically active molecules, natural products, and pharmaceuti-
cals [7]. Traditionally, phenyl esters were obtained by the acy-
lation of arenes by chloroformates, the acylation of phenols by
anhydrides and acyl chlorides, or by acids themselves in the
presence of dicyclohexylcarbodiimide [8]. The main drawbacks
of the acylation technique are the harsh conditions, low yields,
and serious environmental problems. α,β-Alkynyl ketones are
generally synthesized via the coupling of alkynyl organometal-
*
Corresponding authors. Fax: +86 931 8277088.
E-mail addresses: chenj@lzb.ac.cn (J. Chen), cgxia@lzb.ac.cn (C. Xia).
0021-9517/$ – see front matter © 2007 Elsevier Inc. All rights reserved.
doi:10.1016/j.jcat.2007.10.021

J. Liu et al. / Journal of Catalysis 253 (2008) 50–56
51
lation of aryl iodides using heavy-walled quartz reaction ves-
sels with CO in conjunction with microwave heating. But this
requires special vessels with a microwave oven specifically de-
signed for this purpose, which is a particular problem if the
reaction is to be realized on an industrial scale.
Several approaches [21] to overcome the inherent diffi-
culty of separating and recycling homogeneous palladium cat-
alysts have been developed. Multiphasic systems [22], such as
fluorous-biphasic, ionic liquids, scCO2, and a combination of
the latter two, show very promising results, but their high cost
has restricted their commercial application. Anchoring the cat-
alyst on a solid support allows separation of the catalyst by
filtration or by using a fixed catalyst bed and continuous oper-
ation. One of the most common heterogeneous supported pal-
ladium catalysts, Pd/C has been widely used in hydrogenation
processes [23], carbon–carbon bond forming reactions [24–26],
and some carbonylation reactions [27–33]. It is especially note-
worthy that Kotschy and co-workers [34] established that only
a minor portion of the bound palladium (<2%) is released
into the solution in the Pd/C-catalyzed Sonogashira coupling of
aryl halides in aqueous dimethyl acetamide. These authors also
suggested that by using solid-supported palladium in coupling
reactions, one might be able to exploit the benefits of homoge-
neous catalysis but still retain the ease of heterogeneous catalyst
separation. Recently, we reported a mild protocol for the oxida-
tive cyclocarbonylation of β-aminoalcohols and 2-aminophenol
to synthesize corresponding 2-oxazolidinones [27] with high
turnover frequency (TOF) using a Pd/C-I2 heterogeneous cat-
alytic system.
Up to now, only one report has described the use of het-
erogeneous catalyst (Pd/C) in the alkoxycarbonylation of aryl
iodides. But in that work, the reaction required using carcino-
genic benzene as a solvent, and the aryloxycarbonylation reac-
tion has low nucleophile availability [28]. To the best of our
knowledge, no heterogeneous catalyst systems have been in-
vestigated in the carbonylative Sonogashira coupling reaction
of aryl halides with alkynes. In view of the importance and ap-
plications of palladium-catalyzed carbonylation reactions from
industrial as well as academic viewpoints, it is urgent to find
an efficient, inexpensive, recyclable, versatile, and environmen-
tally benign catalyst system for those interesting reactions.
As a part of our ongoing efforts to extend the scope of the use
of Pd/C in carbonylation reactions, we report Pd/C-catalyzed
alkoxycarbonylation and carbonylative Sonogashira coupling
reactions of aryl iodides (Scheme 1) in the absence of copper
and phosphine under mild conditions to afford aryl esters and
α,β-alkynyl ketones efficiently. The recyclability of the catalyst
also was investigated.
Scheme 1. Alkoxycarbonylation and carbonylative Sonogashira reactions of
aryl iodides.
ical grade. Anhydrous methanol, triethylamine (Et3N), toluene,
and other solvents were freshly distilled from appropriate dry-
ing agents under an argon atmosphere before use. CO with a
purity of 99.99% was commercially available.
2.2. General procedures for the carbonylation reactions
2.2.1. General procedure for the alkoxycarbonylation reaction
[Scheme 1, Eq. (1)]
A magnetic stirring bar, aryl iodide (2.5 mmol), alcohol
(4.0 mL), 5% Pd/C (5 mg), and Et3N (7.2 mmol, 1 mL)
were placed in a 35-mL stainless autoclave. The autoclave was
closed, purged three times with 0.2 MPa of CO, pressurized
to 0.5 MPa with CO, and then stirred at 130 ◦C for 2 h. After
the reaction, the autoclave was cooled, and excess CO was dis-
charged at room temperature. The reaction mixture was then
analyzed by gas chromatography (GC) with biphenyl as the
internal standard, using an Agilent 6820 gas chromatograph
equipped with a SE-54 capillary column and a flame ioniza-
tion detector, along with GC/mass spectroscopy (GC-MS). The
crude product was purified by column chromatography on sil-
ica gel (eluting solvent, petroleum ether:ethyl acetate = 20:1)
to give the desired product.
2.2.2. Recycling of Pd/C in the methoxycarbonylation of
iodobenzene in methanol
A magnetic stirring bar, iodobenzene (2.5 mmol, 510 mg),
CH3OH (4.0 mL), 5% Pd/C (10 mg), and Et3N (7.2 mmol,
1 mL) were placed in a 35-mL stainless autoclave. The au-
toclave was closed, purged three times with 0.2 MPa of CO,
pressurized to 0.5 MPa with CO, and then stirred at 130 ◦C for
2 h.
After the reaction, the reaction mixture was separated
by centrifugation. The liquid was transferred by a syringe;
any Pd/C remaining in the vessel was washed with anhy-
drous methanol (2 × 2 mL). Then the combined liquid was
qualitatively and quantitatively analyzed by GC-MS (Agi-
lent 6890/5973) and GC (Agilent 6820), respectively, using
biphenyl as the internal standard. The Pd/C was used in the
next run under the same conditions.
2. Experimental
2.1. Materials
2.3. General procedure for the phenoxycarbonylation reaction
[Scheme 1, Eq. (2)]
The catalyst, consisting of 5% Pd/C, was purchased from
Shanghai Sinopham Chemical Reagent Co. Ltd. (China); aryl
iodides and alkynes were purchased from Aldrich, Fluka, or
Alfa Aesar and used as received; other reagents were of analyt-
A magnetic stirring bar, aryl iodide (2.5 mmol), ArOH
(3.0 mmol), 5% Pd/C (30 mg), Et3N (7.2 mmol, 1 mL), and

52
J. Liu et al. / Journal of Catalysis 253 (2008) 50–56
toluene (4.0 mL) were placed in a 35-mL stainless autoclave.
The autoclave was closed, purged three times with 0.5 MPa
of CO, pressurized to 2.0 MPa with CO, and then stirred at
130 ◦C for 8 h. After the reaction, the autoclave was cooled,
excess CO was discharged at room temperature. The reaction
mixture was qualitatively and quantitatively analyzed by GC-
MS (Agilent 6890/5973) and GC (Agilent 6820), respectively,
using biphenyl as the internal standard. The crude product was
purified by column chromatography on silica gel (eluting sol-
vent hexane:ethyl acetate = 10:1) to give the desired prod-
uct.
(2 × 2 mL). Then the combined liquid was qualitatively and
quantitatively analyzed by Agilent 6890/5973 GC-MS and Ag-
ilent 6820 GC, respectively, using biphenyl as the internal stan-
dard. The solid residue was used in the next run under the same
conditions.
3. Results and discussion
3.1. Pd/C-catalyzed alkoxycarbonylation reaction
For the optimization of the reaction conditions, we chose the
methoxycarbonylation of iodobenzene (1a) as the model reac-
tion, and examined the effects of different parameters on the
reaction; the results are given in Table 1. First, the compari-
son experiments were carried out using Pd/C as catalyst with
and without base, Et3N (Table 1, entries 1 and 2). It was ob-
served that in the absence of Et3N, only a 22.8% yield of methyl
benzoate (2a) was obtained, whereas with Et3N, a 94.2% yield
of 2a was seen. To further evaluate the effects of bases on
the reaction, various other organic bases, including pyridine,
2,6-lutidine, and 4-dimethylaminopyridine (DMAP), also were
investigated and were all found to be less effective than Et3N
with regard to the yields (Table 1, entries 3–5). CO pressure
was found to play an important role in the reaction; increasing
the CO pressure from 0.1 MPa to 0.5 MPa did significantly in-
crease the yield of the desired product (Table 1, entries 2, 6,
and 7), but, there was a slight increase in the yield of 2a when
the reaction was operated at 1.0 MPa (Table 1, entry 8). In-
creasing the reaction temperature had a positive effect on the
catalytic activity (Table 1, entries 9–12). When the quantity of
iodobenzene was increased to 5.0 mmol (i.e., a molar ratio of
2.3.1. Recycling of Pd/C in the phenoxycarbonylation of
iodobenzene
A magnetic stirring bar, iodobenzene (2.5 mmol, 510 mg),
phenol (3.0 mmol, 282 mg), 5% Pd/C (30 mg), Et3N (7.2 mmol,
1 mL), and toluene (4.0 mL) were placed in a 35-mL stain-
less autoclave. The autoclave was closed, purged three times
with 0.5 MPa of CO, pressurized to 2.0 MPa with CO, and then
stirred at 130 ◦C for 8 h.
After the reaction, the reaction mixture was separated by
centrifugation. The liquid was transferred by a syringe. The
solid residue remaining in the vessel was washed with toluene
(2 × 2 mL). Then the combined liquid was qualitatively and
quantitatively analyzed by Agilent 6890/5973 GC-MS and Ag-
ilent 6820 GC, respectively, using biphenyl as the internal stan-
dard. The solid residue was used in the next run under the same
conditions.
2.4. General procedure for the carbonylative Sonogashira
coupling reaction [Scheme 1, Eq. (3)]
A magnetic stirring bar, aryl iodide (2.5 mmol), alkyne
(3.0 mmol), 5% Pd/C (10 mg), Et3N (7.2 mmol, 1 mL), and
toluene (4.0 mL) were placed in a 35-mL stainless autoclave.
The autoclave was closed, purged three times with 0.5 MPa
of CO, pressurized to 2.0 MPa with CO, and then stirred for
4 h at 130 ◦C. After the reaction, the autoclave was cooled, and
excess CO was discharged at room temperature. The reaction
mixture was then qualitatively and quantitatively analyzed by
Agilent 6890/5973 GC-MS and Agilent 6820 GC, respectively,
using biphenyl as the internal standard. The crude product was
purified by column chromatography on silica gel (eluting sol-
vent hexane:ethyl acetate = 10:1) to give the desired prod-
uct.
Table 1
Pd/C-catalyzed methoxycarbonylation of iodobenzene under different condi-
a
tions
Entry
Base
Temperature
( C)
Pressure
(MPa)
Yield of 2a
(%)
◦
b
1
2
3
4
5
6
7
8
9
None
130
130
130
130
130
130
130
130
100
110
120
140
130
130
0.5
0.5
0.5
0.5
0.5
0.1
0.25
1.0
0.5
0.5
0.5
0.5
0.5
0.5
22.8
94.4
26.0
26.9
72.4
37.6
79.7
95.5
73.6
82.2
93.5
96.9
88.7
96.6
Et N
3
Pyridine
2,6-Lutidine
DMAP
Et N
3
Et N
3
2.4.1. Recycling of Pd/C in the carbonylative Sonogashira
coupling reaction
Et N
3
Et N
3
10
11
12
Et N
3
A magnetic stirring bar, iodobenzene (2.5 mmol, 510 mg),
phenylacetylene (3.0 mmol, 306 mg), 5% Pd/C (10 mg), Et3N
(7.2 mmol, 1 mL), and toluene (4.0 mL) were placed in a
35-mL stainless autoclave. The autoclave was closed, purged
three times with 0.5 MPa of CO, pressurized to 2.0 MPa with
CO, and then stirred for 4 h at 130 ◦C.
After the reaction, the reaction mixture was separated by
centrifugation. The liquid was transferred by a syringe. The
solid residue remaining the vessel was washed with toluene
Et N
3
Et N
3
c
13
d
Et N
3
Et N
3
14
a
Reaction conditions: iodobenzene: 2.5 mmol, 5% Pd/C: 5 mg (2.4 ×
−3
10 mmol), base: 7.2 mmol, CH OH: 4 mL, reaction time: 2 h.
3
b
Determined by GC using biphenyl as internal standard.
5.0 mmol iodobenzene was used.
10 mg 5% Pd/C was used.
c
d

J. Liu et al. / Journal of Catalysis 253 (2008) 50–56
53
Table 2
Table 3
Pd/C-catalyzed methoxycarbonylation of aryl halides
a
a
Alkoxycarbonylation of iodobenzene in various alcohols
b
1
b
Entry
1
Aryl-X
Product
–
Yield (%)
Entry
1
R OH
Product
Yield (%)
0
0
CH OH
82
3
2
3
–
c
2
3
4
5
C H OH
2
89 (95)
5
69
89
d
n-C H OH
92 (32)
7
3
4
5
d
n-C H OH
89 (32)
4
9
77
i-C H OH
75
0
7
3
6
a
t-C H OH
–
4
9
6
7
8
96
98
94
Reaction conditions: iodobenzene: 2.5 mmol, 5% Pd/C: 5 mg, Et N:
3
7.2 mmol, alcohol: 4 mL, 0.5 MPa of CO, 130 C, 2 h.
◦
b
Isolated yield after silica gel chromatography.
Determined by GC using biphenyl as internal standard.
Determined by GC, 3 mmol alcohol, 4 mL toluene was used as solvent.
c
d
substrate/catalyst of 2128), only a 88.7% yield of methyl ben-
zoate was obtained under the same reaction conditions (Table 1,
entry 13).
9
92
99
To determine the scope of this process, various aryl iodides
and diverse alcohols were used as substrates; the results are
summarized in Tables 2 and 3. The results of alkoxycarbony-
lation of iodobenzene (Table 2) demonstrate that changing the
alcohol substrate from methanol to n-butanol had no signifi-
cant effect on product yield (Table 2, entries 1–4). But with
a secondary alcohol (2-propanol), a lower yield (75%) of car-
bonylation product was obtained (Table 2, entry 5). Unfortu-
nately, when tert-butanol was used as a nucleophile, no desired
product was detected by GC-MS, presumably due to steric bulk
(Table 2, entry 6).
As shown in Table 3, a wide range of aryl iodides bearing an
electron-withdrawing group or an electron-donating group were
clearly carbonylated in methanol providing that the ester prod-
ucts, bromobenzene and chlorobenzene, were unreactive (Ta-
ble 3, entries 1 and 2). Iodobenzenes containing substituents at
the 2-position gave poorer results because of the steric influence
(Table 3, entries 3 and 5). 2-Iodoanisole (1d), 3-iodoanisole
(1e), and 4-iodoanisole (1f) were converted smoothly to the cor-
responding products 2d, 2e, and 2f in 77%, 96%, 98% yields,
respectively (Table 3, entries 5–7). Remarkably, 4-chloroiodo-
benzene (1g) was subjected to the methoxycarbonylation re-
action to produce selectively methyl 4-chlorobenzoate (2g) at
a 94% yield (Table 3, entry 8). The carbonylation of 1-iodo-
naphthalene (1h) and 4-iodoacetophenone (1i) also gave cor-
responding carbonylated products in excellent yields (Table 3,
entries 9 and 10).
10
a
Reaction conditions: aryl halide: 2.5 mmol, 5% Pd/C: 5 mg, Et N:
3
◦
7.2 mmol, CH OH: 4 mL, 0.5 MPa of CO, 130 C, 2 h.
3
b
Isolated yield after silica gel chromatography.
bonylation of iodobenzene (reaction conditions: iodobenzene,
2.5 mmol; 5% Pd/C, 10 mg, Et3N, 7.2 mmol; CH3OH, 4 mL;
0.5 MPa of CO; temperature, 130 ◦C; time, 2 h), after the com-
pletion the catalyst was recovered by centrifugation and reused
for the next reaction under the same reaction condition; no sig-
nificant loss of catalytic activity and selectivity were found even
after 10 reuses.
3.2. Pd/C-catalyzed phenoxycarbonylation reaction
Successful application of Pd/C in the alkoxycarbonylation of
aryl iodides has inspired us to explore its use in the phenoxycar-
bonylation reaction. Initially, the influence of critical reaction
parameters (i.e., base, temperature, CO pressure, solvent) on
the carbonylation of iodobenzene using phenol as a nucleophile
had been investigated for reaction optimization (Table 4). It was
noteworthy that in all cases, >99% selectivity of phenyl ben-
zoate was observed. A survey of various bases determined that
Et3N provided the highest conversion (Table 4, entries 1–4).
The conversion of iodobenzene increased with increasing CO
In addition to the high activity, the Pd/C-Et3N catalytic
system also demonstrated good stability in the methoxycar-

54
J. Liu et al. / Journal of Catalysis 253 (2008) 50–56
Table 4
Table 5
Effects of substituted phenol on phenoxycarbonylation of iodobenzene
a
a
Phenoxycarbonylation of iodobenzene under different conditions
Entry
Ar
Conversion
of PhI (%)
Product
Yield
(%)
Entry Solvent Base
Temperature Pressure Conversion
b
c
◦
b
( C)
(MPa)
of 1a (%)
1
2
3
4
5
6
7
8
9
a
Ph
96.9
100
100
100
100
100
98.6
100
100
3a
3b
3c
3d
3e
3f
3g
3h
3i
96
93
96
97
95
97
97
94
94
1
2
3
4
5
6
7
8
Toluene Et N
3
Toluene Pyridine
Toluene 2,6-lutidine
130
130
130
2.0
2.0
2.0
2.0
1.0
2.5
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
96.9
36.0
30.7
49.9
70.1
98.2
89.0
56.3
39.6
83.9
66.6
84.8
100
2-CH C H
3-CH C H
4-CH C H
4-(CH ) CC H
6 4
4-(CH ) C-2-CH C H
2-(CH ) C-4-CH C H
4-CH OC H
4-ClC H
6
3
6
4
4
4
3
6
Toluene HCO Na·2H O 130
3
6
2
2
Toluene Et N
3
130
130
120
100
90
130
130
130
130
130
130
3 3
Toluene Et N
3
Toluene Et N
3
Toluene Et N
3
Toluene Et N
3
3 3
3
6
3
3
3 3
3 6
3
6
4
9
c
4
10
11
12
13
14
15
a
Toluene Et N
3
Reaction conditions: iodobenzene: 2.5 mmol, ArOH: 3 mmol, 5% Pd/C:
d
◦
Toluene Et N
3
30 mg, Et N: 7.2 mmol, toluene: 4 mL, 2.0 MPa of CO, 130 C, 8 h.
3
b
Et N
3
Et N
3
Determined by GC using biphenyl as internal standard.
Isolated yield after silica gel chromatography.
c
THF
Et N
3
DMF
DCM
Et N
Et N
3
100
29.6
3
Table 6
Reaction conditions: iodobenzene: 2.5 mmol, phenol: 3 mmol, 5% Pd/C:
a
Pd/C-catalyzed phenoxycarbonylation of aryl iodides
30 mg (0.0141 mmol), base: 7.2 mmol, solvent: 4 mL, reaction time: 8 h.
b
Determined by GC using biphenyl as internal standard.
20 mg 5% Pd/C was used.
10 mg 5% Pd/C was used.
c
d
b
Entry
Aryl-I
Product
Yield (%)
1
2
3
4
5
6
7
a
1b
1c
1d
1e
1f
4b
4c
4d
4e
4f
87
95
95
95
95
94
98
pressure (Table 4, entries 1, 5, and 6). The catalyst system was
sensitive to reaction temperature; conversion decreased dramat-
ically when the temperature was decreased from 130 to 90 ◦C
(Table 4, entries 7–9). Decreasing the amount of Pd/C resulted
in a lower conversion (Table 4, entries 10 and 11). Besides these
conditions, a series of solvents were also examined using Et3N
as a base and solvent, and only 84.8% conversion was achieved
(Table 4, entry 12). Quantitative conversion of iodobenzene was
observed when the reaction was performed in tetrahyrofuran
(THF) or N,N-dimethylformamide (DMF) (Table 4, entries 13
and 14). However, poor result was obtained when the reaction
was carried out in dichloromethane (DCM) (Table 4, entry 15).
Considering the solvent cost as well as the subsequent handling,
toluene may be the appropriate reaction medium.
1g
1h
4g
4h
Reaction conditions: aryl iodide: 2.5 mmol, phenol: 3 mmol, 5% Pd/C:
◦
30 mg, Et N: 7.2 mmol, toluene: 4 mL, 2.0 MPa of CO, 130 C, 8 h.
3
b
Isolated yield after silica gel chromatography.
As shown in Table 6, the phenoxycarbonylation of various
aryl iodides proceeded well and led to the corresponding car-
bonylated product in high yields.
To determine the scope and limitation of this reaction, the
phenoxycarbonylation of iodobenzene using substituted phe-
nol as the nucleophile, as well as the reaction of various aryl
halides, was studied. The results are given in Tables 5 and 6,
respectively.
As shown in Table 5, Pd/C-Et3N as the catalytic system
for the phenoxycarbonylation reactions of iodobenzene with
phenols proved exceptionally active. Obviously, both electron-
withdrawing and electron-donating substituents on the nucle-
ophile may enhance the reaction, giving the desired products in
excellent yields. It is possibly reasonable to consider that a phe-
nol exists in an acid–base dissociation equilibrium in the pres-
ence of Et3N in the reaction medium. An electron-withdrawing
substituent attached to phenol may enhance its acidity; on the
other hand, an electron-donating substituent may increase elec-
tron density on the O atom of phenol to enhance the reactiv-
ity.
3.3. Pd/C-catalyzed carbonylative Sonogashira coupling
reaction
To further expand the scope of carbonylation reactions us-
ing Pd/C as a catalyst, we also evaluated the carbonylative
Sonogashira coupling reaction of aryl halides with terminal
alkynes. First, we examined effects of different parameters on
the carbonylative Sonogashira coupling reaction of iodoben-
zene with phenylacetylene to optimize reaction conditions (Ta-
ble 7). When using Pd/C as the sole catalyst, the carbonylative
Sonogashira coupling reaction did not occur (Table 7, entry 1).
Most strikingly, a 95.9% conversion of iodobenzene was ob-
tained when 7.2 mmol Et3N was added to the reaction system
(Table 7, entry 2); decreasing the amount of Et3N decreased
the conversion (Table 7, entry 3). As in the methoxycarbony-
lation and phenoxycarbonylation of iodobenzene, pyridine and

J. Liu et al. / Journal of Catalysis 253 (2008) 50–56
55
Table 7
Table 8
Pd/C-catalyzed carbonylative coupling of iodobenzene with phenylacetylene
under different conditions
Pd/C-catalyzed carbonylative coupling of aryl iodides with terminal alkynes in
the presence Et N
3
a
a
2
b
◦
Entry
Aryl-I
R
Product
Yield (%)
Entry
Solvent
Base
T ( C)/
Conversion
of 1a (%)
Selectivity
of 5a (%)
b
b
P (MPa)
1
2
1a
1b
1c
1d
1e
1f
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
5a
5b
5c
5d
5e
5f
84
93
96
80
90
97
91
94
83
63
1
2
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
None
130/2.0
130/2.0
130/2.0
130/2.0
130/2.0
100/2.0
110/2.0
120/2.0
130/1.0
130/3.0
130/2.0
130/2.0
130/2.0
130/2.0
–
–
3
Et N
3
Et N
3
Pyridine
95.9
85.7
27.6
17.6
50.9
68.0
82.4
67.3
99.4
85.8
91.8
100
>99
>99
>99
>99
>99
>99
>99
>99
>99
93.0
>99
91.2
96.8
c
4
3
5
4
5
6
2,6-Lutidine
7
1g
1h
1a
1a
5g
5h
5i
6
Et N
3
Et N
3
Et N
3
Et N
3
Et N
3
Et N
3
Et N
3
Et N
3
8
7
9
4-(CH ) CC H
3 3 6 4
CH (CH )
8
10
a
5j
3
2 3
9
10
11
12
13
14
a
Reaction conditions: aryl iodide: 2.5 mmol, alkyne: 3 mmol, 5% Pd/C:
10 mg, Et N: 7.2 mmol, toluene: 4 mL, 2.0 MPa of CO, 130 C, 4 h.
3
◦
Et N
3
THF
b
Isolated yield after silica gel chromatography.
DMF
DCM
Et N
3
41.4
Reaction conditions: iodobenzene: 2.5 mmol, phenylacetylene: 3 mmol,
5% Pd/C: 10 mg, base: 7.2 mmol, solvent: 4 mL, reaction time: 4 h.
b
Determined by GC using biphenyl as internal standard.
c
3.6 mmol Et N was used.
3
2,6-lutidine also did not work well (Table 7, entries 4 and 5).
Increasing both the reaction temperature and CO pressure had
a pronounced positive effect on the catalytic activity (Table 7,
entries 6–10).
We also investigated the effects of different solvents on the
reaction with Pd/C-Et3N as the catalytic system (Table 7, en-
tries 3, 11–14). The solvent was found to play an important
role in activity and selectivity. DMF displayed excellent per-
formance in the conversion of iodobenzene, while affording a
lower selectivity of 1,3-diphenylprop-2-yn-1-one (5a) (Table 7,
entry 13). Thus, from a practical standpoint, toluene was deter-
mined to be the best choice.
To explore the generality and scope of the carbonylative
three-component coupling reaction, we also evaluated various
aryl iodides and terminal alkynes as substrates. Some results
are given in Table 8. It is noteworthy that only small percent-
age (not above 1%) of the noncarbonylative coupling products
was observed; we reasoned that in the absence of copper, the
less reactive alkyne (compared with its corresponding alkynyl
copper gate complex) would easily react with the electron-
deficient acylpalladium (II) rather than its precursor aryl pal-
ladium iodide species (I) derived from the oxidative addition
of aryl iodide to Pd(0) [16,17] (Scheme 2). As a result, the
carbonylative coupling reaction product was obtained through
(IIIA). Alternatively, insertion of an arylalkyne to the acylpal-
ladium species giving (IIIB), followed by β-hydrogen elimina-
tion, might be a plausible pathway [35]. It should be pointed out
that the carbonylative coupling reaction of chlorobenzene (or
bromobenzene) with phenylacetylene did not occur, because the
dissociation energy of the sp2-C–Cl or sp2-C–Br bond is com-
paratively high (402, 339, and 272 kJ mol−1 for PhCl, PhBr,
Scheme 2. Possible explanation for carbonylative coupling reactions.
and PhI, respectively, at 298 K) [36]. The reaction of substi-
tuted aryl iodides gave the corresponding alkynyl ketones in
good to excellent yields. When the terminal alkyne bearing
an alkyl substituent was used (Table 8, entry 10), the reaction
was found to be slower than that of arylalkynes, whose relative
reactivity was similar to the noncarbonylative coupling reac-
tions.
3.4. Recyclability of Pd/C in the phenoxycarbonylation and
carbonylative three-component coupling reactions
The key property of heterogeneous catalysts is their recovery
and reuse, an essential perspective for green chemistry involv-
ing both ecologic and economic considerations. As mentioned
above, Pd/C could reused at least 10 times in the methoxy-
carbonylation of iodobenzene with only a slight decrease in
efficiency; the slight change may be due to the loss of catalyst
during handling and transferring of catalyst. We also evaluated
the activity and recyclability of Pd/C in the phenoxycarbony-
lation of iodobenzene and the carbonylative three-component
coupling reaction of iodobenzene with phenylacetylene; the re-

56
J. Liu et al. / Journal of Catalysis 253 (2008) 50–56
Supplementary material
The online version of this article contains additional supple-
mentary material.
Please visit DOI: 10.1016/j.cat.2007.10.021.
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Acknowledgments
The authors thank the National Natural Science Fund for
Distinguished Young Scholars (No. 20625308) for financial
support.