Postsynthetic modification of single Pd sites into uncoordinated polypyridine groups of a MOF as the highly efficient catalyst for Heck and Suzuki reactions

Article abstract of DOI:10.1039/c8nj00518d

A novel holmium(iii) metal-organic framework (Ho-MOF), namely, [Ho(2-TriPP-COO)₃] (2) has been hydrothermally obtained using 4′-(4-carboxyphenyl)-2,2′:6′,2′′-terpyridine (2-TriPP-COOH) and Ho(NO₃)₃·5H₂O, and it is structurally characterized by single-crystal XRD, powder XRD as well as elemental analysis. The postsynthetic modification of Ho-MOF is based on the utilization of a strong coordination effect between Pd²⁺ ions and free polypyridine groups in the skeleton of Ho-MOF, which play a critical role to access the highly efficient Pd-HoMOF catalyst. Also, Pd-HoMOF exhibits very high activity in Heck and Suzuki-Miyaura cross-coupling reactions. Moreover, the MOF catalyst displays good thermal stability (up to 400 °C), and it can be recovered and reused for five reaction cycles. The bridging between the MOF structure and homogeneous molecular Pd catalyst represents a good example in designing highly efficient catalysts for various fine chemical transformations.

Full text of DOI:10.1039/c8nj00518d

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PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Postsynthetic modification of single Pd sites into uncoordinated
polypyridine groups of a MOF as the highly efficient catalyst for
Heck and Suzuki reactions
Received 00th January 20xx,
a
a
a
a
a
b
a
Dapeng Dong, Zhenghua Li, Dedi Liu, Naisen Yu, Haiyan Zhao, Huiying Chen* Jia Liu and
a
Dongping Liu*
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
A novel holmium (III) metal-organic framework (Ho-MOF), namely, [Ho(2-TriPP-COO)
obtained by using 4′-(4-carboxyphenyl)-2,2′: 6′,2″-terpyridine (2-TriPP-COOH) and Ho(NO
characterized by the single-crystal XRD, powder XRD as well as the elemental analysis. The postsynthetic modification of
3
] (2) had been hydrothermally
)
3 3
•5H O and structurally
2
2
+
Ho–MOF was based on the utilization of strong coordination effect between Pd ions and the free polypyridine groups at
the skeleton of Ho–MOF, which played a critical role to access the highly efficient Pd-HoMOF catalyst. And the Pd-HoMOF
exhibited impressively high activity in Heck and Suzuki–Miyaura cross-coupling reactions. Moreover, the MOF catalyst
displayed well thermal stability (up to 400 °C), and could be recovered and reused for five reaction cycles. The bridging
between MOF structures and homogeneous molecular Pd catalyst could represent a good example in designing highly
efficient catalysts for various fine chemical transformations.
date, some materials such as membranes, organic polymers
and inorganic materials have been used as carrier to
Introduction
1
3-17
incorporate noble metal catalysts.
But very few high
The development of surface-characterization techniques and
advanced synthesis methods have evolved the synthesis of
solid catalysts from trial-and-error methodologies into a
density and uniform distribution of single site catalysts were
obtained by the traditional anchoring method. Metal-organic
frameworks (MOFs), known as hybrid solid materials with
periodic network structures built from inorganic connecting
points and organic bridging ligands, are crystalline material for
which the detailed structures and compositions are known and
1
-5
multidisciplinary science.
From the global motif of
sustainable development in energy and environment area
point of view it is vitally important to prepare single metal site
catalysts that take full advantage of metal active site, so they
1
8-34
6
-8
handled to present the well-defined multiple active sites.
have superior reactivity and selectivity. As an ideal model
combination of homogeneous and heterogeneous catalysis,
the performance of catalysts based on single atoms has the
high activities of characteristics for the homogeneous catalyst,
MOFs thus are particularly attractive candidates of single site
3
heterogeneous catalysts.
5, 36
Palladium-catalyzed C-C coupling, including Suzuki and Heck
-11 reactions, etc. are the reaction of great concern as a versatile
9
as well as the advantages of facile separation and recycling.
route to aryl compounds for pharmaceuticals and fine
To date, the classical synthesis methods for single site catalysts
are commonly based on an initial adsorption of metal
3
7
chemicals. These catalytic reactions usually take place in
homogeneous conditions which become difficult reuse of the
products and separation of the catalysts after reactions that
causes particular economic and environmental concern in
1
2
precursor with a subsequent reduction process. Therefore,
the final properties of single site catalysts are highly
dependent upon the binding and stabilization of support. To
3
8-40
large scale synthesis.
To solve this problem, considerable
efforts have been put in the development of heterogeneous
catalyst that can be efficiently reused whilst without affecting
a.
Liaoning Key Laboratory of Optoelectronic Films and Materials, School of Physics
4
1-46
and Materials Engineering, Dalian Nationalities University, Dalian 116600, PR
China. E-mail: dongping.liu@dlnu.edu.cn
College of Life Science, Dalian Nationalities University, Dalian 116600, PR China.
E-mail: chy@dlnu.edu.cn Supporting information for this article is given via a link
at the end of the document
the inherent activity of the catalytic centers.
Since one of
b.
the extremely serious problem to be overcome in the Pd-
based catalysts for fine chemicals and pharmaceuticals is the
leaching of palladium from heterogeneous supports/ligand.
Accordingly, strategies for introducing coordination bound
units in which palladium centers are directly bound to MOFs is
1
Electronic Supplementary Informaꢀon (ESI) available: Crystal structure; IR, TG, H-
†
NMR, PXRD and GC-MS spectra. CCDC 1571951. For ESI and crystallographic data in
CIF or other electronic format See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
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high desirable. Recent reports have showed some examples Scheme 2. Schematic representation of the synthetic route for PdꢀHoMOF
catalyst. The structure model (down) of PdꢀHoMOF shows the incorporation of
the palladium(II) ions into the MOF framework. Atomic scheme: holmium, rose;
that post-synthetic modification approach has been applied to
incorporate single-site Pd(II) on pre-synthesized MOFs, which palladium, azure; oxygen, red; nitrogen, blue; carbon, grey.
is limited typically by the overall stability of the framework
7,48
under the reaction conditions.
4
Recently, the terpyridine derivatives, as multidentate Experimental section
polypyridine ligands with efficient and stable chelating ability
Materials and general methods
to metal ions, has been intensively explored because of its
4
versatility as building blocks for metal-organic frameworks.
The 2-TriPP-COOH = 4
′-(4-carboxyphenyl)-2,2′: 6′,2″-
9
terpyridine was synthesized according to procedures described
55
Moreover, the terpyridine derivatives have been applied for
selective metal ion sensing that can be further used in the
previously.
All other chemicals were obtained from
commercial sources and used without further purification.
5
0
creation of some novel optical materials. Besides the
integration of terpyridine derivatives into organic polymers,
incorporating these functional groups into solid carriers is also
an crucial step for the preparation of catalytic materials. For
Elemental analyses of C, H and N were carried out with a PE–
1
400 elemental analyzer. H NMR spectra were recorded on a
2
VARIAN INOVA-400 spectrometer with chemical shifts reported as
6
ppm (in d -DMSO, TMS as internal standard). Pd content of Pd–
5
1
instance, polymer-supported terpyridine palladium complex,
silica supported terpyridine palladium(II) complex,
HoMOF was determined using an inductively coupled plasma
5
2
(ICP) atomic absorption spectrometer. The leaching amount of
5
3
terpyridine-functionalized MCM-41 nanoporous silica
and
Pd–HoMOF in the C-C coupling reactions was determined
quantitatively by AAS on the HITACHI Z-2300 instrument.
Transmission electron microscopy (TEM; JEOL JEM-2100) were
used to acquire the morphology of the catalyst. X-ray
photoelectron spectroscopy (XPS) was conducted on an
ESCALAB250Xi spectrometer system with an Mg Kα ADES
5
4
the SBA-15-supported iron terpyridine complexes have been
used to catalyze alkyl cross-coupling reactions. Herein we wish
to describe the synthesis of MOF supported terpyridine
palladium(II) complex (Pd–HoMOF, Scheme 1-2) without
affecting the integrity of the MOF and demonstrate its
catalytic activity in Heck and Suzuki–Miyaura cross-coupling
reactions for the high-efficiency activation of C–X bond.
Furthermore, the highly active single-site MOF catalyst
displayed well thermal stability, negligible Pd(II) cations
leaching, and could be recovered and reused for five reaction
cycles.
(hν=1253.6 eV) source. IR spectra were recorded on a Thermo
Scientific Nicolet iS10 FT-IR Spectrometer with KBr pellets in
-1
the range 4000–400 cm . Powder XRD patterns were obtained
using a Bruker D8 ADVANCE XRD diffractometer with CuKα
radiation (λ = 1.54056 Å). The thermogravimetric (TG) analysis
were performed using a Perkin–Elmer Pyris Diamond TG-DTA
thermal analyses system in a nitrogen atmosphere on
−1
polycrystalline samples with a heating rate of 20 K min from
4
0 to 800 °C.
Synthesis of 2-TriPP-COOH (1). The 2-acetylpyridine (5.0 g, 41.25
3
mmol) was added to PEG300 (60 cm ) containing NaOH (1.65 g,
4
4
1.25 mmol), and the suspensions was tirred at 0 ℃for 15 minutes.
-(Methoxycarbonyl)benzaldehyde (3.38 g, 20.6 mmol) was then
added and the resulting solution was stirred for about 2h at 0 ℃.
After 2 h, NH OAc (10 g, excess) was added to reaction mixture
4
which was further heated at 100 ℃ for another 2 h. Then the 200
Scheme 1. Schematic representation of the synthetic route for 2ꢀTriPPꢀCOOH
ligand.
3
cm water was added reaction mixture and the resultant brown
solid crude product 2-TriPP-COOCH3 was collected by filtration,
3
3
washed two times with 80 cm water, 20 cm cold EtOH (Yield 3.5 g,
4
8%). Then the 3.5 g 2-TriPP-COOCH was added 20 ml HCl (50%)
3
aqueous solution and was heated to 100 ℃and stirred for 8h. After
cooling to room temperature, the precipitate 2-TriPP-COOH was
filtered and washed by 30 mL cold EtOH for three times and dried in
1
air (Brown microcrystals, yield 3.22 g, 92%). H NMR (400 MHz,
DMSO) δ 9.16 – 8.84 (m, 3H), 8.42 (d, J = 6.3 Hz, 1H), 8.19 (q, J = 8.4
Hz, 2H), 7.93 – 7.75 (m, 1H).
Synthesis of [Ho(2-TriPP-COO)
Ho(NO •5H O(0.0353 g, 0.1 mmol), 2-TriPP-COOH (0.0441 g,
.1 mmol) and KOH (0.0224 g, 0.4 mmol) was dissolved in 7 mL
3
]
(2).
A
mixture of
3
)
3
2
0
distilled water and 3ml DMF with continuous stirring for about
2
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1
2
1
h at room temperature. The resulting solution was sealed in a bond lengths and angles of compounds HoMOF were listed in
0 mL stainless steel reactor with a Teflon liner and heated at Table S2.
20 °C for 3 days under autogenous pressure and then cooled
to room temperature, the pink block crystals of 2 were
obtained. Yield: 55.2% (based on Ho). Anal. Calcd for
Results and discussion
66 9 6
3 3 2
C H42HoN O : C, 64.87; H, 3.46; N, 10.32; Found: C, 64.91; H, By using the 2-TriPP-COOH and Ho(NO ) •5H O, a novel Ho-
3
1
1
1
7
5
.49; N, 10.35%; IR (KBr, cm-1): 3479(br), 1609(w), 1598(w), MOF had been synthesized under hydrothermal conditions.
582(m), 1560(s), 1549(w), 1521(w), 1463(m), 1427(s), 1411(s), Through postsynthetic modification from the PdCl (CH CN)
2
3
2
262(w), 1163(w), 1116(w), 1092(w), 1070(w), 1039(w), palladium precursor with of the Ho–MOF, a well-defined
017(w), 990(w), 898(w), 862(w), 821(w), 784(m), 738(w), palladium metal-organic framework Pd-HoMOF was obtained.
26(w), 711(w), 704(w), 668(w), 661(w), 639(w), 620(w), The powder XRD patterns for Ho–MOF and Pd-HoMOF, and
02(w), 482(w), 419(w).
Synthesis of Pd-HoMOF (3). The Pd-HoMOF was sythesized by 1. The diffraction peaks of the powder XRD could be well
stirring a mixture of PdCl (CH CN) (285 mg, 1.1 mmol) and [Ho(2- consistent with simulated XRD patterns, indicating that the
TriPP-COO) ] (Ho-MOF, 611 mg, 0.5 mmol) in dry CH CN (10 ml) at title compounds were in the homogeneous phase and the
5 °C. After stirring for 24 h, the resulting yellow solid was filtered structural integrity after the postsynthetic modification.
the simulated XRD patterns of Ho-MOF were shown in the Fig.
2
3
2
3
3
6
and washed with CH CN. Finally, the Pd-HoMOF was dried at 90 °C Inductively coupled plasma mass spectrometry (ICP-MS)
3
for 10 h under vacuum. IR (KBr, cm-1): 3479(br), 1609(w), 1601(w), experiment with Pd–HoMOF indicated more than 2.51 wt% of
1
1
9
7
583(m), 1560(s), 1550(w), 1529(w), 1465(m), 1426(s), 1411(s), the palladium was anchored to Ho-MOF. The TEM experiment
264(w), 1162(w), 1116(w), 1091(w), 1072(w), 1037(w), 1017(w), was carried out on the Pd–HoMOF to survey the dispersion
89(w), 897(w), 861(w), 819(w), 784(m), 738(w), 727(w), 711(w), morphology after incorporating Pd(II) sites into uncoordinated
05(w), 668(w), 661(w), 639(w), 620(w), 502(w), 483(w), 419(w)
General Experimental Procedure for the Heck Reaction. The Pd- there were no distinct aggregation of the Pd particles during
HoMOF (0.4 mol%) and K CO (1.5 mmol) was stirred in DMF the Pd–HoMOF synthesis (Fig. 2a). The C-O bands between
5.0 ml) for 10 min. Then aryl halide (0.5 mmol) and olefin 1410 and 1610 cm were not changed in the reaction process,
0.75 mmol) were added and magnetically stirred for an which demonstrated the MOF material constructed by Ho ions
.
polypyridine groups of MOFs, and the results indicated that
2
3
-1
(
(
appropriate time (Table 2) at 100 °C. At the end of reaction, and carboxylate ligand was preserved in the post-synthetic
the reaction solution was cooled to room temperature and the process (Fig. S1). In addition, the appearance of two peaks (at
-1
Pd-HoMOF was separated by filtration. The yields of the crude 477 and 496 cm ) for Pd–N in IR spectra supported the loading
products were carried out by GC-MS.
of Pd on Ho-MOF through the palladium–polypyridine complex
5
7
General Experimental Procedure for the Suzuki Reaction. The Pd- (Fig. S2). It was further confirmed by the PXRD patterns after
HoMOF (0.4 mol%) and KOH (1.5 mmol) was stirred in DMF the post-synthetic modification. To determine the
(5.0 ml) for 10 min. Then aryl halide (0.5 mmol) and coordination environment for Pd(II) ions within the materials,
phenylboronic acid (0.75 mmol) were added and magnetically we did XPS analysis on Pd–HoMOF (Fig. 3). The results
stirred for an appropriate time (Table 3) at 100 °C. At the end suggested that the material exhibited the Pd 3d5/2 band and Pd
of reaction, the reaction solution was cooled to room 3d3/2 band at around 338 eV and 343 eV, respectively. These
temperature and the Pd-HoMOF was separated by filtration. values correspond to the Pd(II) binding energy of Pd–HoMOF.
The yields of the crude products were carried out by GC-MS.
Furthermore, the XPS measurement revealed that the atomic
Prep-HPLC Separation. Prep-HPLC separation was performed ratio of Cl:Pd is 2:1, which were good agreement with previous
5
8
with YMC-C18 column (250 × 10 mm i.d., 5 μm, Shimadzu LC- studies. Thermogravimetric analysis of the compounds
0AR, Tokyo, Japan) with a solvent of methanol–water (90:10) HoMOF and Pd-HoMOF revealed that they are thermally stable
at a flow rate of 5 mL/min and monitored at 254 nm.
2
up to above 400 °C (Fig. S3, S4), and that demonstrated the
high stability of the materials.
X–ray date collection and structure determination.
Data collection of compound HoMOF was performed on a
Bruker AXS Smart APEX II CCD X-diffractometer equipped with
graphite monochromated MoKα radiation ((λ = 0.71073 Å) at
2
93 ± 2K. The structure was solved by direct methods and
2
refined by full matrix least-squares fitting on F by using
5
6
SHELXS–2014/7. All non–hydrogen atoms were refined
anisotropically. Hydrogen atoms were generated geometrically
with fixed isotropic thermal parameters, and included in the
structure factor calculations. Details of crystallographic data of
compounds HoMOF were summarized in Table S1. Selected
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Single-crystal XRD analysis revealed that the compound Ho-
MOF crystallized in the monoclinic C2/c space group. There
5
4
3
2
1
00
00
00
00
00
0
3
were one crystallographically Ho ions and three 2-TriPP-COO-
+
Simulation
HoꢀMOF
PdꢀHoꢀMOF
3+
ligands in the structure unit (Fig. S5). Each Ho ion exhibited
nine–coordinated environment that was coordinated by six
oxygen atoms from three 2-TriPP-COO- ligands and three
nitrogen atoms from one 2-TriPP-COO- ligand with the
distorted tricapped trigonal prism geometric configuration.
The 2-TriPP-COO- anions acted as the pentadentate ligands
and showed two coordination modes which were the
pentadentate coordination mode on the backbone and
bidentate coordination mode on the arms, respectively.
Interestingly, in the bidentate coordination mode, oxygen
atoms from the carboxylate group coordinated with the
holmium (III) ions by the bidentate chelating coordination
mode and the terpyridyl moiety acted as the tridentate-
chelating coordination mode was free, these uncoordinated
terpyridyl coordination sites were expected to accept
palladium(II) ions through post-synthetic modification.
Furthermore, the neighboring chains arranged each other
through the π•••π stacking and C−H•••π interactions to form
a 3D supramolecular structure that was well arranged the
uncoordinated terpyridyl sites for coordinating with
palladium(II) ions (Fig. 4). The values of the Ho–O and Ho–N
bond lengths were in the range of 2.3721(18)-2.467(2)Å and
5
10
15
20
25
30
35
40
45
50
2
θ (degree)
Fig. 1. XRD patterns of the simulated XRD patterns (black line), preꢀsynthetic
HoꢀMOF (red line), and the postꢀsynthetic PdꢀHoMOF (blue line).
Fig. 2. TEM micrographs of PdꢀHoMOF before the reaction (left) and after five
catalytic cycles (right).
2
.475(2)-2.486(3)Å respectively, they were well agreement
5
9
with previous studies.
a
Table 1. Optimization of Heck reaction
b
Entry
Base
Solvent
EtOH
T(℃)
Time(h)
Yield(%)
Fig. 3. (a) XPS spectra of PdꢀHoMOF; (b) XPS spectra of Pd 3d3/2 and 3d5/2
peak positions for PdꢀHoMOF.
1
2
K
K
2
2
CO
CO
3
3
80
1
1
<10
<10
H
2
O
100
3
4
5
6
7
8
K
K
2
2
CO
CO
3
DMF+EtOH
DMF
100
80
1
1
1
1
1
1
6
1
1
64.2
84.8
92.7
88.8
>99
3
Cs
2
CO
3
DMF
100
100
100
120
100
100
100
KOH
CO
DMF
K
2
3
DMF
K
K
K
K
2
2
2
2
CO
CO
CO
CO
3
3
3
3
DMF
>99
9
DMF
>99
c
1
1
0
1
a
DMF
none
88.6
d
DMF
Reaction conditions: Ph–I (0.5 mmol), methyl acrylate (0.75mmol), base (1.2
Fig. 4. Polyhedral views of 3D supramolecular framework structures of
b
compound HoMOF in the bc−plane. Pink polyhedra: {HoO
6
N
3
}.
mmol), Pd–HoMOF (0.4 mol% Pd). Yield determined by GCꢀMS analysis.
c
d
2 3 2
Parent HoMOF as the catalyst. PdCl (CH CN) as the catalyst (0.4 mol% Pd).
Heck coupling reaction. The palladium-catalyzed Heck cross-
coupling reaction between aryl halides derivatives and various
olefins had been considered one of the most popular methods to
Crystal structures of Ho-MOF
4
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synthesize arylated alkenes in organic chemical reaction. To chlorobenzene as substrate, only little coupling products were
evaluate the reaction activity of the Pd–HoMOF catalyst, we initially obtained even after a reaction time of 6 h (<20%; entries 10-
explored the reactions for the palladium catalyzed heck reaction of 12). That's because the higher bond energy of the C–Cl bond,
aryl halides and olefins. The coupling reaction of iodobenzene with so it was difficult to activate the aromatic chlorides.
methyl acrylate was used as a model reaction to determine the
The recyclability of the Pd–HoMOF catalyst (0.4 mol%) was
optimum reaction conditions. Through the change of reaction also surveyed by the coupling reaction of iodobenzene with
conditions such as reaction time, temperature, solvent and the methyl acrylate as a test model. As shown in Table S3,
base, the optimum reaction conditions were confirmed (Table 1), recovery was achieved in five successive reaction runs. To
which typically involved an iodobenzene, methyl acrylate and K
in the solution of DMF in the presence of Pd–HoMOF catalyst at 100 MOF carrier to the solution, we performed the typical hot
C. Furthermore, it was found that by increasing the amount of Pd– filtration experiment in the model reaction. The reaction
HoMOF catalyst from 0.4 to 1.2 mol% could not improve the yield. mixture was heated at 100
for 0.5 h, then the Pd HoMOF
2
CO
3
evaluate whether palladium ions were leaching out from the
°
℃
–
Moreover, parent HoMOF exhibited no conversion was observed, catalyst was removed by hot filtration and the yield for final
this indicated that the catalytic activity of the coupling reaction product was 88%. Only a trace of palladium (ca. 86 ppb) could
came from the Pd-HoMOF (entry 10)
.
be detected in the hot filtrate, which was determined by AAS.
Although the resulting filtrate was continue heated for another
6
h, no further conversion took place in the filtrate after
a
Table 2. Results for the Heck reaction catalyzed by Pd–HoMOF
separation of the Pd–HoMOF catalyst. Since no further
conversion was observed, it indicated that Pd–HoMOF was a
true heterogeneous catalyst and the soluble species might not
be involved in the reactions.
b
Entry
X
R1
R2
Time(h)
Yield(%)
Table 3 Results for the Suzuki–Miyaura coupling reactions catalyzed by Pd–
a
HoMOF
1
2
I
I
H
COOCH
3
3
1
1
99(>99)
CH
3
COOCH
95(96.5)
99(>99)
99(>99)
99(>99)
95(96.7)
99(>99)
96(97.3)
96(97.7)
trace
3
4
5
6
7
8
9
I
COCH
3
COOCH
COOCH
Ph
3
1
1
1
1
2
2
2
6
6
6
b
Entry
X
R
Time(h)
Yield(%)
I
NO
H
2
3
1
2
I
I
H
1
1
99(>99)
99 (>99)
I
CH
3
I
CH
3
Ph
3
I
OCH
3
1
1
1
2
2
2
2
2
6
6
6
99 (>99)
99 (>99)
99 (>99)
99 (>99)
92(93.5)
95(96.6)
99 (>99)
99 (>99)
99 (>99)
92(93.4)
97(98.4)
Br
Br
Br
Cl
Cl
Cl
H
COOCH
COOCH
COOCH
COOCH
COOCH
COOCH
3
3
3
3
3
3
4
I
COCH
3
COCH
3
5
I
NO
H
2
CHO
H
6
Br
Br
Br
Br
Br
Cl
Cl
Cl
1
1
1
0
1
7
CH
3
CH
3
trace
8
OCH
3
2
CHO
17(19.1)
9
CHO
a
2 3
Reaction conditions: aryl halide (0.5 mmol), olefins (0.75 mmol), K CO (1.2
b
mmol), DMF (5 mL), Pd–HoMOF (0.4 mol% Pd), 100 °C. Yield of isolated
product after the purification of prepꢀHPLC (GCꢀMS yield in parenthesis).
10
COCH
3
1
1
1
2
3
H
As shown in Table 2, a series of aryl halide derivatives and
different olefins had been used as reactants in the Heck cross-
coupling to assess the catalytic activity of the Pd–HoMOF. The
Heck reaction of iodobenzene with methyl acrylate and
styrene both had the high yield (99%; entries 1, 3, 4, 5) in only
an hour. When the methyl group presented on the aromatic
halide, although it had the negative effect on the yield, it still
had the high yield (95%; entries 2 and 6) in only 1 h, which
suggested it was the excellent heterogeneous catalyst for the
Heck coupling reaction. Furthermore, the coupling of
bromobenzene with methyl acrylate also led to an excellent
yield (>96%; entries 7-9) in 2 h. However, using the sluggish
CH
3
1
CHO
a
Reaction conditions: phenylboronic acid (0.75 mmol), aryl halide (0.5 mmol),
b
KOH (1.5 mmol), DMF (5 mL), Pd–HoMOF (0.4 mol% Pd), 100 °C. Yield of
isolated product after the purification of prepꢀHPLC (GCꢀMS yield in parenthesis).
Suzuki–Miyaura coupling reaction. The Suzuki–Miyaura reaction
was also a significant organic reaction for the formation of carbon–
carbon bonds in fine chemical synthesis. Encouraged by the
interesting results for the Heck reaction, we further evaluated the
catalytic activity of the Pd–HoMOF for the Suzuki cross-coupling
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ARTICLE
Journal Name
reaction of aryl halide derivatives with phenylboronic acid in the coupling reaction of halide benzene with the reusable palladium
presence of the Pd–HoMOF (0.4 mol%) using KOH as a base in DMF catalyst synthesized by using the postsynthetic modification
under stirring at 100 °C (Table S4). Our initial exploration of method, the super high yield (100%) of substrates derived from
reactions for the palladium catalyzed Suzuki reaction of aryl halides iodobenzene was obtained, however, the little product yields (25%)
48
was focused on the coupling of iodobenzene and phenylboronic was obtained using chlorobenzene derivatives as substrate.
acid. Within 1 h, a more than 99% isolated yield of the biphenyl was Suzuka et al. reported the Suzuki−Miyaura coupling of
obtained. Other aryl iodides involving electron-donating and bromobenzene by the terpyridine palladium complex anchored to
electron-withdrawing substituents were also studied and the polymer in DMF, which had a lower yield (74%), even heated at
5
1
reaction proceeded with a short time (1 h), with good yield (99%; 100℃ for 6 hours. Because the grafting of terpyridine palladium
Table 3). Then we further studied the reaction extending to complex onto polymer often resulted in random incorporating the
bromobenzenes and the substituted bromobenzenes that active Pd(II) units into the carrier, so they were mutual deactivated
contained electron-donating and electron-withdrawing substituents. between active Pd(II) sites as they were too close to each other.
With the optimum reaction conditions, it obtained the excellent
yields with the corresponding coupling products when different aryl Table 4 Comparison of the catalytic performances of Pd–HoMOF and other
known catalysts in the suzuki−miyaura reactions of phenylboronic acid with aryl
halide
bromide reacted with phenylboronic acid (Table 3, entries 6–10).
Furthermore, the coupling of chlorobenzene also provided the
Aryl halide
Catalyst
Yield
wt%]
Ref.
target products with excellent yields in the same reaction
conditions (Table 3, entries 11–13).
[
a
Chlorobenzene Molecular Pd(II) complex
90
36
43
anchored to UiO-67
Recyclability of the Pd–HoMOF catalyst (0.4 mol%) was examined
in the model reaction of iodobenzene and phenylboronic acid. After
completion of the catalytic reaction, the insoluble Pd–HoMOF
catalyst could be easily isolated from the reaction mixtures by
b
Chlorobenzene Pd nanoparticles embedded in
97
MIL-101
Postsynthetic modification of
c
Iodobenzene
100
48
PdCl anchored to Sr-MOF-1
2
d
simple hot filtration alone and could be reused at least five Chlorobenzene Postsynthetic modification of
PdCl anchored to Sr-MOF-1
25
48
successive reaction runs with not a slight decrease in the reactivity
Table S5). The TEM experiment was carried out on the reused Pd–
2
e
Bromobenzene Polymer-supported terpyridine
palladium complex
74
51
(
HoMOF to survey the dispersion morphology of the Pd cations after
the catalytic reaction, which were very similar to that before
f
Iodobenzene
Silica supported terpyridine
palladium(II) complex
Pd-containing MOF
88
52
g
reaction, but there were a few Pd particles aggregation occurred in Iodobenzene
97
60
the Pd–HoMOF while the reaction was progressing (Fig. 2b). This
h
Iodobenzene
Pd–HoMOF
99
This work
This work
This work
was further confirmed by the similar PXRD patterns after the
catalytic reaction (Fig. S6). These experiments indicated that Pd–
i
Bromobenzene Pd–HoMOF
Chlorobenzene Pd–HoMOF
99
HoMOF was a true heterogeneous catalyst and the soluble species
might not be involved in the reactions.
j
99
A probable reaction mechanism by Pd–HoMOF had been
a
b
c
DMFꢀEtOH, KOH, 100℃, 20 h;
H
2
O, NaOMe, 80℃, 20 h; EtOHꢀH
2
O, K
2
CO
3
3
,
,
proposed (Scheme S1). An oxidative addition of iodobenzene on the
d
e
f
+
80℃, 2 h; EtOHꢀH
2
O, K
2
CO
3
, 80℃, 6 h;
H
2
O, K
2
CO
3
, 100℃, 6 h; H
2
O, K
2
CO
exposed Pd(II) center of [Pd(II)(N) Cl] from the Pd–HoMOF
3
g
h
i
9
1
0℃, 1.5 h; Toluene, K
2
CO
3
, 95℃, 4 h; DMF, KOH, 100℃, 1 h; DMF, KOH,
followed by ligand exchange with the phenylboronic acid and KOH
were considered as sequential steps. Reductive elimination of
biphenyl regenerated the active naked Pd and thereby the hetero-
j
00℃, 2 h; DMF, KOH, 100℃, 6 h.
coupling of iodobenzene and phenylboronic acid took place Conclusions
consecutively. Since the active Pd species was generated, no further
In conclusion, the highly dispersed Pd(II) cations had been
regeneration step was required and thus the product with a high
anchored on the robust HoMOF framework by using the
postsynthetic modification coordination incorporation method.
The prepared highly efficient single Pd sites heterogeneous
catalyst exhibited impressively high activity in Heck and Suzuki
5
7
yield was afforded.
In search of highly active MOF catalysts for Suzuki reactions, a
few excellent works deserved particular mention. Suzuki cross-
coupling reaction catalyzed by Pd–HoMOF and other various known cross-coupling reactions for the high-efficiency activation of C–
heterogeneous palladium catalysts were listed in the Table 4. X bond. Furthermore, the catalyst displayed well thermal
Various solid-supported palladium complexes were studied, they stability, negligible Pd(II) cations leaching, and could be
could catalyze the Suzuki coupling reaction under heterogeneous recovered and reused for five reaction cycles. The successful
2
+
conditions and they could be used several times without loss of the utilization of strong coordination effect between Pd ions and
4
1-45
the free polypyridine groups at the skeleton of Ho–MOF could
represent a good example in designing highly efficient
catalysts for various fine chemical transformations.
activity.
Chen et al. studied the Suzuki coupling of
chlorobenzene by the molecular Pd(II) complex anchored to UiO-67
in DMF-EtOH at 100℃, which had a high yield (90%), but it required
3
6
a longer reaction time (20 h). Sen et al. reported the Suzuki
6
| J. Name., 2012, 00, 1-3
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ARTICLE
2
8 G. Xiong, B. Yu, J. Dong, Y. Shi, B. Zhao and L.N. He, Chem.
Commun., 2017, 53, 6013−6016.
This work was financially supported by the Natural Science 29 J. Jing, X. Huo, J. Shen, J. Fu, Q. Meng and W. Zhang, Chem.
Acknowledgements
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0 K. Xie, Y. He, Q. Zhao, J. Shang, Q. Gu, G.G. Qiao and P.A.
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Research Funds for the Central Universities.
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Table of Contents Entry
Postsynthetic modification of single Pd sites into uncoordinated
polypyridine groups of a MOF as the highly efficient catalyst for Heck
and Suzuki reactions
a
a
a
a
a
b
a
Dapeng Dong, Zhenghua Li, Dedi Liu, Naisen Yu, Haiyan Zhao, Huiying Chen* Jia Liu and
a
Dongping Liu*
a
Liaoning Key Laboratory of Optoelectronic Films and Materials, School of Physics and Materials Engineering,
Dalian Nationalities University, Dalian 116600, PR China
b
College of Life Science, Dalian Nationalities University, Dalian 116600, PR China
A novel Pd-HoMOF catalyst was prepared, which displayed well thermal stability and high
activity in Heck and Suzuki cross-coupling reactions.