Carbonylative Sonogashira coupling of terminal alkynes with aryl iodides under atmospheric pressure of CO using Pd(II)@MOF as the catalyst

Article abstract of DOI:10.1039/c4cy00488d

A novel, highly efficient, and phosphine-free heterogeneous palladium-MOF catalytic system for the carbonylative Sonogashira coupling of terminal alkynes with aryl iodides was developed. The catalyst could efficiently promote the carbonylative coupling reaction under atmospheric pressure of CO, affording the corresponding aryl α,β-alkynyl ketones in good to excellent yields. Besides high activity and selectivity, the proposed catalytic system features a broad substrate scope for both alkynes and aryl iodides. Moreover, the heterogeneous catalyst was recyclable, showed negligible metal leaching, and could be reused at least five times without significant loss in catalytic efficiency under the investigated conditions. the Partner Organisations 2014.

Full text of DOI:10.1039/c4cy00488d

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Carbonylative Sonogashira coupling of terminal
alkynes with aryl iodides under atmospheric
pressure of CO using Pd(II)@MOF as the catalyst†
Cite this: Catal. Sci. Technol., 2014,
4, 3261
*
Cuihua Bai, Siping Jian, Xianfang Yao and Yingwei Li
A novel, highly efficient, and phosphine-free heterogeneous palladium-MOF catalytic system for the
carbonylative Sonogashira coupling of terminal alkynes with aryl iodides was developed. The catalyst
could efficiently promote the carbonylative coupling reaction under atmospheric pressure of CO,
affording the corresponding aryl α,β-alkynyl ketones in good to excellent yields. Besides high activity and
selectivity, the proposed catalytic system features a broad substrate scope for both alkynes and aryl
iodides. Moreover, the heterogeneous catalyst was recyclable, showed negligible metal leaching, and
could be reused at least five times without significant loss in catalytic efficiency under the investigated
conditions.
Received 15th April 2014,
Accepted 11th June 2014
DOI: 10.1039/c4cy00488d
www.rsc.org/catalysis
Heterogenization of the homogeneous palladium catalyst
is an attractive solution to these problems. In this respect, a
Introduction
α,β-Acetylenic carbonyl derivatives (ynones) are important
structural units found in many biologically active molecules,
natural products, and pharmaceuticals.1 They are extremely
versatile intermediates for the synthesis of heterocyclic deriv-
atives such as pyrimidine,2 quinolone,3 furan,4 pyrazole,5
pyrrole,6 and flavone.7 Traditionally, ynones are synthesized
via the coupling of acyl halides with alkynyl organometallic
reagents8 or terminal alkynes.9 Although acyl halides have
shown good reactivity in this transformation, they suffer from
inherent problems such as low stability and limited commer-
cial availability.10
An alternative route for ynones is the Pd-catalyzed
Sonogashira-type carbonylation of terminal alkynes with aryl
halides in the presence of carbon monoxide.11 Since the first
example of carbonylative Sonogashira coupling reaction was
reported,11a significant efforts have been devoted to the
improvement of the original work of Tanaka et al. during the
past three decades.12 Among the developed methodologies
for the carbonylative Sonogashira coupling, homogeneous Pd
catalysts (usually with the addition of homogeneous phosphine
ligands) have been shown to be the most efficient catalytic
systems for ynones. However, these homogeneous systems
are normally not reusable and it is difficult to separate the
expensive palladium catalysts from the reaction mixture.9f
few phosphane-free heterogeneous palladium catalysts, such
as commercial Pd/C, Pd/Fe3O4, and Pd complexes grafted on
MCM-41 silica, have been developed for the carbonylative
coupling reactions.13,14 Indeed, the reusability of the expen-
sive Pd catalysts was mostly achieved; however, their catalytic
efficiencies are not satisfactory and still need to be largely
improved. In particular, a high CO pressure is always
required to achieve efficient carbonylative coupling for the
preparation of ynones.
Here, we report a novel and highly efficient heterogeneous
palladium-MOF system for carbonylative Sonogashira cou-
pling of terminal alkynes with aryl iodides. To the best of our
knowledge, this work represents the first example of a highly
active heterogeneous catalyst for the synthesis of ynones via
carbonylative Sonogashira coupling under atmospheric pres-
sure of CO without the addition of any phosphine ligands.
Besides high activity and selectivity to the target products,
the proposed catalytic system features a broad substrate
scope for both alkynes and aryl iodides. Furthermore, the cat-
alyst is reusable and shows negligible metal leaching under
the investigated conditions.
MOFs are a new class of porous materials that have shown
interesting catalytic properties in a number of chemical
transformations.15 In particular, functionalization of MOFs
with active metal species has been demonstrated to be a very
useful approach to optimize MOFs for specialized catalytic
applications.16 Recently, we have reported the use of the
uncoordinated 2,2′-bipyridine (bpy) moieties in MOF-253 for
the immobilization of CuI as an efficient heterogeneous
catalyst for the O-arylation of phenols or alcohols with aryl
Key Laboratory of Fuel Cell Technology of Guangdong Province, School of
Chemistry and Chemical Engineering, South China University of Technology,
Guangzhou 510640, China. E-mail: liyw@scut.edu.cn
† Electronic supplementary information (ESI) available: Experimental details,
catalyst characterization and reaction results, and spectra data of the products.
See DOI: 10.1039/c4cy00488d
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halides under ligand-free conditions.17 Herein we extend the
methodology to the heterogenization of palladium species by
using a different MOF, ZrMOF-BIPY (Zr6O4(OH)4(bpydc)6,
bpydc = 2,2′-bipyridine-5,5′-dicarboxylate) as a support, which
also features uncoordinated bpy moieties in the MOF frame-
work.18 A careful literature survey shows that so far there is
no report of employing MOFs as catalysts for carbonylative
Sonogashira-type coupling reactions, although MOFs sup-
ported Pd nanoparticles (e.g., Pd/MOF-5) for the Sonogashira
coupling of terminal alkynes with aryl halides have been
reported.19
Results and discussion
Fig. 2 XPS spectra of the Pd 3d region for (a) Pd(II)@ZrMOF-BIPY and
(b) PdCl2(CH3CN)2.
ZrMOF-BIPY was prepared according to the reported
procedures.18 ZrMOF-BIPY is isostructural to UiO-67
(Zr6O4(OH)4(bpdc)6, bpdc = para-biphenyldicarboxylate), as
confirmed by PXRD measurements (Fig. 1). The activated
ZrMOF-BIPY was soaked in an acetonitrile solution of
PdCl2(CH3CN)2 to afford Pd(II)@ZrMOF-BIPY. After modifica-
tion with Pd (1.0 wt%), the crystallinity of the MOF was
mostly maintained (Fig. 1). The intermolecular interaction
between the bpydc ligand and Pd and their coordination
environment were investigated by X-ray photoelectron spec-
troscopy (XPS). Both PdCl2(CH3CN)2 and Pd(II)@ZrMOF-BIPY
samples exhibited Pd 3d5/2 and Pd 3d3/2 bands at around
338 eV and 343 eV (Fig. 2), respectively, characteristics
of divalent Pd cations.20 However, the Pd 3d lines of
Pd(II)@ZrMOF-BIPY were shifted by ca. 0.5 eV toward lower
binding energies, as compared to the pristine PdCl2(CH3CN)2.
Such shifts reflected an increase in the electron density of
Pd,21 suggesting a strong coordination interaction between
the bpydc ligand and the Pd atom in Pd(II)@ZrMOF-BIPY.
The N 1s spectra (Fig. 3) showed two binding energies for the
N 1s peaks of Pd(II)@ZrMOF-BIPY, which implied the pres-
ence of two types of coordination environments for N atoms.
The small N 1s peak at a higher binding energy could not be
attributed to the N atom in PdCl2(CH3CN)2 because FT-IR
analysis has shown that the characteristic absorbance band
Fig. 3 XPS spectra of the N 1s region for (a) ZrMOF-BIPY and
(b) Pd(II)@ZrMOF-BIPY.
for a CN bond at ca. 2340 cm−1 was absent (Fig. 4). The
results confirmed that a small amount of the uncoordinated
bpy units was bonded to Pd in Pd(II)@ZrMOF-BIPY. Ele-
mental analysis indicated that the N : Pd molar ratio in
Pd(II)@ZrMOF-BIPY was ca. 54.0, suggesting that ca. 3.7% of
the bpydc ligands were coordinated with Pd(II). EDX analysis
Fig. 1 Powder XRD patterns of the ZrMOF-BIPY samples: simulated
UiO-67 (a); as-synthesized ZrMOF-BIPY (b); 1 wt% Pd(II)@ZrMOF-BIPY
before (c) and after (d) catalytic reaction.
Fig. 4 FT-IR spectra of (a) Pd(II)@ZrMOF-BIPY and (b) PdCl2(CH3CN)2.
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showed that the atomic ratio of Pd : Cl was ca. 1 : 2 (see the
ESI†), which indicated that all of the palladium remained in
its dichloride form in Pd(II)@ZrMOF-BIPY.
For initial optimization of the reaction conditions,
the carbonylative Sonogashira coupling reaction of
4-methoxyiodobenzene with phenylacetylene was selected as
the model reaction, and the results are summarized in
Table 1. First, the effect of solvents on the coupling reaction
was investigated. It is well known that MOFs are not as stable
as other porous materials such as zeolites, so we should pay
special attention to the selection of reaction parameters when
using MOFs for catalytic reactions. Therefore, we carefully
examined the stability of ZrMOF-BIPY in various commonly
used solvents before performing the reaction over the
Pd(II)@ZrMOF-BIPY catalyst. It was found that the MOF mate-
rial was stable in DMF, DMA, DMSO, acetonitrile, benzene,
and toluene (Fig. 5), while its structure was destroyed when
immersed in some solvents such as water, acetone, 1,4-dioxane,
chloroform, and THF (see the ESI†). Using the appropriate
solvents, the reactions were carried out at 373 K and 5 atm of
CO pressure with 1 wt% Pd(II)@ZrMOF-BIPY as the catalyst
and Et3N as the base. It was observed that DMF was the best
solvent among the five other solvents used, affording the
desired product, 1-(4-methoxyphenyl)-3-phenylprop-2-yn-1-one
(3a) in quantitative yield (Table 1, entries 1–6).
Fig. 5 PXRD patterns of ZrMOF-BIPY (a) as-synthesized and after
exposure to a variety of solvents at 393 K for 24 h: (b) DMA, (c) DMF,
(d) DMSO, (e) acetonitrile, (f) benzene, (g) toluene.
Using DMF as the solvent, we further investigated the
influence of bases on the carbonylative Sonogashira coupling
reaction. It can be seen that in the absence of a base, only a
5% yield of 3a was obtained (Table 1, entry 7), indicating that
a base was necessary for the coupling reaction to proceed. As
with Et3N, the use of Cs2CO3 as the base also furnished 3a in
quantitative yield under 5 atm of CO (Table 1, entry 10).
Notably, Pd(II)@ZrMOF-BIPY retained its high activity and
selectivity even though the CO pressure was lowered to atmo-
spheric pressure with Cs2CO3 as the base (Table 1, entry 13),
which was apparently superior to the result in the presence
of Et3N (Table 1, entry 14). Moreover, ca. 15% of the total Pd
in the fresh catalyst was observed to have leached into the
solution after reaction, leading to a much lower conversion
(68%) and selectivity (73%) when reusing the catalyst under
identical conditions as compared to the fresh one (Table 1,
entry 14). Therefore, Cs2CO3 was selected as the base for the
next reaction tests.
Table
1 Carbonylative coupling of 4-methoxyiodobenzene with
phenylacetylene under different reaction conditionsa
CO
(atm)
Conversionb
(%)
Selectivityb
(%)
Entry
Base
Solvent
Under optimized conditions, blank runs and those using
the parent MOF (without Pd grafting) showed no conversion
in the reaction (Table 1, entries 15 and 16), confirming the
need for a metal to perform the carbonylative Sonogashira
coupling. We also investigated the effect of metal content
and proved that 1 wt% Pd was the best catalyst with respect
to conversion and selectivity (Table 1, entries 13, 17, and 18).
An increase in Pd loading on the MOF led to a remarkable
decrease in selectivity to the desired product 3a (entry 18).
We also investigated the carbonylative Sonogashira coupling
at a much higher substrate/metal molar ratio (0.2 mol% Pd).
The reaction also proceeded smoothly, furnishing a conver-
sion of 95% with a good selectivity (∼99%) to 3a after 6 h of
reaction (entry 19).
The scope of this novel heterogeneous Pd-catalyzed
carbonylative coupling of phenylacetylene with a variety of
aryl iodides was investigated. Aryl iodides containing an
electron-donating group at the para, meta, and ortho posi-
tions afforded the corresponding substituted α,β-alkynyl
ketones in excellent isolated yields (Table 2, entries 1–5).
1-Iodonaphthalene also underwent carbonylative coupling
smoothly and afforded 3f in 94% yield (entry 6). In general,
1
2
3
4
5
6
7
8
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
—
K2CO3
K3PO4
Cs2CO3
DABCO
CH3ONa
Cs2CO3
Et3N
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
CH3CN
DMF
5
5
5
5
5
5
5
5
5
5
5
5
1
1
1
1
1
1
1
89
>99
91
13
20
>99
5
78
88
>99
80
65
>99
85
—
—
>99
>99
95
98
>99
>99
>99
98
77
>99
70
DMA
toluene
Benzene
DMSO
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
9
90
10
11
12
13
14
15c
16d
17e
18f
19g
>99
>99
95
>99
99
—
—
97
90
99
a
Reaction conditions: 1a (0.5 mmol), 2a (0.6 mmol), catalyst (1 mol% Pd),
b
base (0.5 mmol), solvent (2 mL), 373 K, 3 h. Conversions and
selectivities were determined by GC-MS analysis. No catalyst
was used. ZrMOF-BIPY was used as the catalyst. 0.5 wt%
c
d
e
f
Pd(II)@ZrMOF-BIPY was used. 2 wt% Pd(II)@ZrMOF-BIPY was used.
g
1a (10 mmol), 2a (11 mmol), catalyst (0.2 mol% Pd), base (10 mmol),
solvent (6 mL), 373 K, 6 h.
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electron-deficient aryl iodides exhibited slightly lower activity
than electron-rich ones (entries 7–13). Under optimized
conditions, 4-fluoro, 4-chloro, and 4-bromo substituted
iodobenzenes were selectively carbonylated at the iodo moiety
to give the corresponding ynones in satisfactory yields
(entries 11–13). However, when the reaction time is prolonged
to 12 h, it was interesting to note that for the coupling of
4-bromoiodobenzene, both the iodo and bromo groups on
the benzene ring could undergo carbon monoxide insertion,
giving the double-coupling product 3n in 62% yield (entry 14).
Heteroaryl iodides, such as 2-iodothiophene, were also
coupled with phenylacetylene smoothly to provide the desired
ynones in excellent yields (Table 2, entry 15). It is note-
worthy that only small amounts (ca. 1%) of the non-
carbonylative coupling products were observed for all of the
runs in Table 2. This could be related to the lesser reactivity
of alkyne (compared with its corresponding alkynyl copper
gate complex) in the absence of copper. Under these con-
ditions, alkyne would react with the electron-deficient
acylpalladium intermediates more easily than with aryl palla-
dium iodide species, leading to the production of the
carbonylative coupling reaction product.10,12b,14a
We also attempted to expand this catalytic system for the
carbonylative coupling of aryl bromides. We tried several aryl
bromides, such as bromobenzene, 4-bromobenzaldehyde,
4-bromoanisole, and 4-bromotoluene. However, no desired
coupling products were found even though the reaction time
was prolonged to 24 h under the optimized conditions. Aryl
bromides or chlorides have been reported to be poor sub-
strates for carbonylative Sonogashira coupling, because the
dissociation energy of the sp2-C–Cl or sp2-C–Br bond is com-
paratively higher than that of sp2-C–I.22 So far, there is no
report on the carbonylative Sonogashira coupling of aryl
bromides or chlorides using phosphane-free heterogeneous
catalytic systems.11b–d
We further investigated the carbonylative coupling
reactions of various substituted phenylacetylenes with
iodobenzene. All phenylacetylenes bearing an electron-
withdrawing group or an electron-donating group on the aro-
matic ring were coupled with iodobenzene to afford the
desired ynones in excellent isolated yields (Table 3, entries 1–7).
The Pd(II)@ZrMOF-BIPY catalyst was also active in the
carbonylative coupling of heterocyclic acetylenes, giving the
corresponding ynones in excellent yields (Table 3, entry 8).
The reaction with 1-ethynylcyclohex-1-ene (2j) provided the
carbonylated products 3x in 88% isolated yield (Table 3, entry 9).
In a final set of experiments, we evaluated the reusability
of the Pd(II)@ZrMOF-BIPY catalyst in the carbonylative
Sonogashira coupling reaction because it is crucial to con-
firm that the highly active catalyst is recyclable. It can be
seen from Table S1 and Fig. S5 (see the ESI†) that the catalyst
could be reused five times without apparent loss of activity
and yield. The results were in accordance with AAS experi-
ments for which only traces of Pd (less than 0.2% of the total
palladium) were detected in the solution collected by hot
filtration after reaction, as well as with the PXRD patterns of
Table 2 Carbonylative coupling of phenylacetylene with various aryl
iodidesa
Entry
1
Substrate
1a
Product
Yieldb
97
3a
2
3
4
98
95
95
1b
3b
1c
3c
1d
1e
3d
5
6
92
94
3e
1f
3f
7
92
86
91
87
92
93
1g
3g
8
1h
1i
3h
9
3i
10
11
12
1j
3j
1k
1l
3k
3l
13
92
62
1m
3m
14c
1m
3n
15
92
1o
3o
a
Reaction conditions: 1 (0.5 mmol), 2a (0.6 mmol), catalyst (1 mol%),
b
Cs2CO3 (0.5 mmol), DMF (2 mL), CO 1 atm, 373 K, 3 h. Isolated
yield. c 1m (0.5 mmol), 2a (1.5 mmol), 373 K, 12 h.
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Table 3 Carbonylative coupling of iodobenzene with various alkynesa
Entry
1
Substrate
Product
Yieldb
96
2b
3p
2
3
4
5
6
7
92
90
91
90
93
82
2c
3q
2d
2e
2f
3r
3s
3t
Fig. 6 Activity profile for the carbonylative Sonogashira coupling
of 4-iodoanisole with phenylacetylene. Reaction conditions: 1a
(0.5 mmol), 2a (0.6 mmol), catalyst (1 mol%), Cs2CO3 (0.5 mmol), DMF
(2 mL), CO 1 atm, 373 K. (a) With catalyst, and (b) with filtrate.
2g
3u
2h
3v
8
9
90
88
2i
3w
3x
2j
Fig. 7 SEM images of 1 wt% Pd(II)@ZrMOF-BIPY before (a and b) and
after (c and d) catalytic reaction.
a
Reaction conditions: 1a (0.5 mmol), 2 (0.6 mmol), catalyst (1 mol%),
Cs2CO3 (0.5 mmol), DMF (2 mL), CO 1 atm, 373 K, 3 h. b Isolated yield.
We reasoned that iodine could be deposited on the catalyst
surface from the oxidative addition of aryl iodides to the Pd
center and subsequent reductive elimination of the products.
the catalyst after the fifth run which showed no apparent
changes in the crystallinity of the ZrMOF-BIPY material
(Fig. 1). TEM images (Fig. S3†) showed that no apparent Pd
aggregation could be observed after reaction. XPS analysis
of the reused catalyst confirmed that palladium remained in
its divalent form and was still coordinated to the bpy unit
(Fig. S4†). The Pd content in the recovered catalyst was
almost identical to the fresh one. Moreover, the reaction with
the solution after hot filtration at approximately 30% conver-
sion essentially stopped, strongly suggesting that the reaction
proceeded mostly on the heterogeneous surface (Fig. 6).
Pd(II)@ZrMOF-BIPY after catalytic reaction was also
characterized by scanning electronic microscopy (SEM) and
energy dispersive spectroscopy (EDS). The SEM images
recorded after the catalytic runs revealed that the morphology
of the catalyst remained almost the same as that of the fresh
one (Fig. 7). Interestingly, iodine was found in the catalyst
after the catalytic reaction as confirmed by EDS analysis.
Conclusions
In summary, we have developed a novel and highly efficient
Pd(II)@ZrMOF-BIPY system for the carbonylative Sonogashira
coupling reaction of aryl iodides with terminal alkynes
without the addition of phosphine ligands. The catalyst could
efficiently promote the carbonylative coupling reaction under
atmospheric pressure of CO to afford the corresponding aryl
α,β-alkynyl ketones in good to excellent yields. Moreover, the
heterogeneous catalyst is recoverable, shows negligible metal
leaching, and could be reused at least five times without
significant loss in catalytic activity and selectivity. The combi-
nation of high catalytic efficiency and substrate compatibility
as well as good recyclability provides a practical and environ-
mentally friendly procedure for the preparation of ynones.
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and DMF (2 mL) were added to a Schlenk tube under CO
atmosphere at room temperature. The tube was sealed and
the mixture was stirred at 373 K for 3 h. After cooling to room
temperature, the solid catalyst was isolated from the solution
by filtration and washed with ethyl acetate. The supernatant
was collected and added into 20 mL of water, subsequently
extracted with ethyl acetate (3 × 20 mL), dried over MgSO4,
and concentrated in vacuo. The crude product was purified
by silica gel chromatography using petroleum ether/ethyl
acetate (8 : 1) as the eluent to afford the desired product.
Experimental
General information
1H NMR and 13C NMR data were obtained using a Bruker
Avance III 400 spectrometer with CDCl3 as solvent and tetra-
methylsilane (TMS) as an internal standard. The reaction
products were quantified and identified by GC-MS analysis
(Shimadzu GCMS-QP5050A equipped with a 0.25 mm × 30 m
DB-WAX capillary column). Powder X-ray diffraction patterns
of the samples were obtained using a Rigaku diffractometer
(D/MAX-IIIA, 3 kW) with Cu Kα radiation (40 kV, 30 mA,
λ = 0.1543 nm). XPS data were obtained using an Axis Ultra
DLD spectroscope with Mono Al Kα (1486.6 eV, 10 mA × 15 kV)
as an X-ray source. Atomic absorption spectroscopy (AAS) was
carried out using a HITACHI Z-2300 instrument. The size and
morphology were determined by scanning electronic micro-
scope (SEM, 1530 VP of LEO) equipped with an energy disper-
sive X-ray detector (EDX, Inca 300 of Oxford).
Recycling of the Pd(II)@ZrMOF-BIPY catalyst
The recyclability of the Pd(II)@ZrMOF-BIPY catalyst was
tested in the reaction of iodobenzene with phenylacetylene
maintaining the same reaction conditions as described
above, except that the recovered catalyst was used. The
results of five runs are presented in Table S1.† Each time the
reaction mixture was allowed to settle down at the end of
reaction and the supernatant liquid was decanted. The solid
was thoroughly washed with acetonitrile, dried, and then
reused as the catalyst in the next run.
Synthesis of ZrMOF-BIPY
ZrMOF-BIPY was prepared according to the procedures devel-
oped by DeCoste et al. but with a change in the quantity of
the organic linker.18 Typically, ZrCl4 (233 mg, 1 mmol) and
2,2′-bipyridine-5,5′-dicarboxylic acid (244 mg, 1 mmol) were
dissolved in 50 mL of DMF at room temperature. The mixture
was sealed in a 100 mL scintillation vial and heated to 393 K
for 24 h. The resulting white microcrystalline powder was
then filtered and washed with DMF, collected by filtration
and finally dried at 423 K under vacuum for 12 h. Elemental
analysis, calcd (%) for Zr6O4(OH)4(O2C–(C5H3N)2–CO2)6:
C, 40.56; H, 1.89; N, 7.88. Found: C, 40.58; H, 1.90; N, 7.87.
Heterogeneity of the catalyst
To verify whether the catalysis of Pd(II)@ZrMOF-BIPY is truly
heterogeneous, the solid catalyst was hot filtered from the
reaction solution after 50 min. The reaction was continued
with the filtrate but with no solid catalyst for an additional
11 h. The solution in the absence of the solid catalyst did not
exhibit any further reactivity. The results demonstrate that
the reaction proceeds on the heterogeneous surface.
Stability of the MOF in different solvents
Time-conversion curves
As-synthesized ZrMOF-BIPY (0.2 g) was soaked in solution (20 mL)
of DMF, DMA, DMSO, acetonitrile, benzene, toluene, chloroform,
THF, acetone, 1,4-dioxane, or water at 393 K for 24 h. The sam-
ples were filtered and dried under vacuum prior to analysis.
The time-conversion measurements were performed in a
20 mL online Teflon-lined stainless-steel autoclave equipped
with a sample connection. The autoclave was connected to
a carbon monoxide gas cylinder, and the reaction pressure
was controlled with a precise gas regulator. Aryl iodides
(0.5 mmol), phenylacetylene (0.6 mmol), Pd(II)@ZrMOF-BIPY
(0.005 mmol, 1 mol%), Cs2CO3 (0.5 mol), and DMF (2 mL)
were added to the reactor. The autoclave was purged several
times with CO to remove the air. Then the reactor was filled
with CO at 1 atm and heated to the target temperature.
0.1 mL of liquid mixture was taken at each time interval. The
mixture was centrifuged and the supernatant was analyzed
by GC-MS.
Synthesis of Pd(II)@ZrMOF-BIPY
Pd(II)@ZrMOF-BIPY was prepared by addition of ZrMOF-BIPY
(212.4 mg) to a solution of PdCl2(CH3CN)2 (5.2 mg, 0.2 mmol)
in acetonitrile (25 mL) at 338 K for 24 h. After cooling to room
temperature, the resulting solid was soaked in 15 mL of aceto-
nitrile. After 24 h, the supernatant was decanted and replaced
with fresh acetonitrile. The exchanging process was repeated
two times, after which the powder was filtered and heated at
423 K for 12 h under vacuum. The molar ratio of PdCl2 to bpy
in ZrMOF-BIPY was ca. 0.037, as measured by atomic absorp-
tion spectrometry.
Acknowledgements
This work was supported by the NSF of China (20936001,
21322606, and 21073065), the Doctoral Fund of Ministry
of Education of China (20120172110012), the Guangdong
NSF (S2011020002397 and 10351064101000000), and the
Fundamental Research Funds for the Central Universities
(2013ZG0001).
General procedure for the carbonylative Sonogashira
coupling reaction
Aryl iodides (0.5 mmol), phenylacetylene (0.6 mmol),
Pd(II)@ZrMOF-BIPY (0.005 mmol, 1 mol%), Cs2CO3 (0.5 mmol)
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