Porous aromatic framework with mesopores as a platform for a super-efficient heterogeneous Pd-based organometallic catalysis

Article abstract of DOI:10.1039/c8sc00510a

A strategy using a mesoporous amine-tagged porous aromatic framework (PAF70-NH₂) to immobilize a palladium (Pd)-based molecular catalyst has been developed. The resulting immobilized catalyst PAF70-Pd, in which the framework is entirely constructed by phenyl rings linked with stable carbon-carbon bonds, has high structural rigidity and stability. Compared with the known porous organic material immobilized Pd-based catalysts, PAF70-Pd has the highest Pd content so far. Moreover, PAF70-Pd has extremely high catalytic activity with good size selectivity and very easy recyclability in catalyzing the Suzuki-Miyaura coupling reaction. In the current system, the catalyst loading could be as low as 0.001 mol% and the TOF value could go up to 28800 h^-1 which is far higher than those of the known porous organic material immobilized Pd-based catalysts. In order to elucidate the particularly high catalytic efficiency of PAF70-Pd, we prepared PAF1-Pd from PAF1-NH₂ for comparison. PAF1-Pd has a higher Pd content than PAF70-Pd. However, due to the absence of large enough mesopores in PAF1-NH₂, PAF1-Pd has almost no catalytic activity under the same conditions, which definitely demonstrated that the intrinsic mesoporosity of PAF70-NH₂ plays a crucial role in the superb catalytic efficiency of PAF70-Pd. This strategy to immobilize Pd-based molecular catalysts has very good expansibility to be applied in the immobilization of different organometallic catalysts into the pores of PAFs, which also has very high potential in the chemical and pharmaceutical industry.

Full text of DOI:10.1039/c8sc00510a

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Porous aromatic framework with mesopores as a platform for a
super-efficient heterogeneous Pd-based organometallic catalysis
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
*a
*b
Li-Ping Jing, Jin-Shi Sun, Fuxing Sun, Peng Chen, and Guangshan Zhu
DOI: 10.1039/x0xx00000x
2
A strategy using a mesoporous amine-tagged porous aromatic framework (PAF70-NH ) to immobilize palladium (Pd)-based
molecular catalyst has been developed. The resulting immobilized catalyst PAF70-Pd, in which the framework is entirely
constructed by phenyl rings linked with stable carbon-carbon bonds, has high structural rigidity and stability. Compared
with the known porous organic material immobilized Pd-based catalysts, PAF70-Pd has the highest Pd content so far.
Moreover, PAF70-Pd has extremely high catalytic activity with good size selectivity and very easy recyclability in catalyzing
Suzuki-Miyaura coupling reaction. In the current system, the catalyst loading could be as low as 0.001 mol% and the TOF
www.rsc.org/
-1
value could be upto 28800 h which is far higher than the known porous organic material immobilized Pd-based catalysts.
In order to elucidate the particularly high catalytic efficiency of PAF70-Pd, we prepared PAF1-Pd from PAF1-NH for
comparison. PAF1-Pd has a higher Pd content than PAF70-Pd. However, due to the absence of large enough mesopores in
PAF1-NH , PAF1-Pd has almost no catalytic activity under the same conditions, which definitely demonstrated that the
intrinsic mesoporosity of PAF70-NH plays a crucial role on the superb catalytic efficiency of PAF70-Pd. This strategy to
2
2
2
immobilize Pd-based molecular catalysts has very good expansibility to be applied in immobilization of different
organometallic catalysts into the pores of PAFs, which also has very high potential in chemical and pharmaceutical
industry.
1
0-29
metal loadings.
1
. Introduction
Using porous materials such as metal-organic frameworks
MOFs), covalent organic frameworks (COFs) or porous organic
(
Organometallic catalysis, which used a metal-based molecular
catalyst to catalyze an organic reaction, is a very important
field of organic chemistry. The excellent catalytic activity of the
organometallic catalysts (metal-based molecular catalysts) has
attracted intensive interest from chemists in diverse research
fields. Thereinto, palladium (Pd)-based organometallic
catalysts are versatile tools that can catalyze various organic
reactions such as Suzuki-Miyaura coupling reaction and Heck
polymers (POPs) as supported materials has begun to appear
in the last decade, which is a good idea because of their
6
, 7, 30-36
porosity and high surface area.
However, the intrinsic
instability of MOFs and COFs or the flexibility of the
frameworks of POPs makes this related research field still face
many difficulties. In 2009, a new type of porous organic
material with robust regular frameworks constructed entirely
from rigid aromatic building blocks linked by stable covalent
bonds, named porous aromatic frameworks (PAFs), has been
developed by our group and achieved intensive interest from
the researchers in diverse fields due to their wide range of
1
-3
reaction. However, the high price of Pd-based catalysts and
the Pd-residue in the products, have greatly limited their
applications in the academia and industry. Immobilization of
the Pd-based catalyst onto some supported solid materials
such as activated carbon or inert inorganic zeolites or organic
3
7-45
structures and potential applications in gas sorption,
4
6, 47
48-54
separation
and catalysis
, etc. Owing to the robust
polymers, typically by physical adsorption or chemical grafting
4
-9 structure together with high stability in most organic solvents,
PAFs are extremely suitable platforms for catalysis of organic
reactions. Noteworthily, due to containing Pd center and
organic ligand, the Pd-based organometallic catalysts usually
have relatively large sizes. Hence, immobilization of Pd-based
molecular catalysts into the porous materials often needs large
enough pore size. Most of the reported porous organic
material immobilized Pd-based catalysts always suffer from a
low Pd utilization efficiency which might be due to that the
pore space after introduction of the Pd-based catalyst is too
small to accommodate the catalytic reaction. Apparently, for
application of PAFs as the platforms for Pd-based
(
binding), is a good method to solve the above problems.
Although the rapid development of immobilization of Pd-based
catalysts was achieved, this field still suffers from the reduced
catalytic activity caused by the poor accessibility or the low
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organometallic catalysts, PAFs with large enough mesopores demonstrate the importance of the mesopores in PAF70-NH
2
,
are needed. However, the synthesis of narrowly distributed another amine-tagged PAF (PAF1-NH ) without mesopores
2
mesoporous PAFs is still a challenge because of the was also used as a platform to immobilize the same Pd-based
interpenetration when using large-size monomers. Thus using molecular catalyst, affording PAF1-Pd for comparison with
PAFs as the platforms for covalent anchoring of organometallic PAF70-Pd
catalysts into the pores still remains rare up to now. In this
paper, we will make an attempt in this area.
.
2
. Results and discussion
Considering the need of large enough pore space for
accommodating the Pd-based molecular catalysts and the
2
.1 Synthesis of the materials.
followed catalysis, in this paper, PAF70-NH
2
, an amine-tagged
PAF with narrowly distributed mesopores which was recently Firstly, as shown in Scheme 1, via the pre-modification
5
5
55
reported by our group , was selected as the platform for Pd- procedure used in our previous literature, we synthesized
based organometallic catalysis. In this paper, a strategy PAF70-NH which contains mesopores with 3.8 nm diameter
2
,
containing two post-synthesis modification steps for and amine anchors in the pores. Then, via the amine anchors
introduction of the Pd-based organometallic catalyst into the using a condensation reaction with picolinaldehyde, the
pores of PAF70-NH
material and the catalytic performance of the desired material obtaining the PAF which was named PAF70-N=CPy. After a
PAF70-Pd) was systematically studied. In order to further
2
was used for synthesis of our desired chelating ligand unit for Pd was introduced into the material,
(
Scheme 1 Synthetic route for PAF70-Pd and PAF1-Pd.
2
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second post-treatment of PAF70-N=CPy with palladium
acetate, the PAF material containing Pd-based molecular
catalyst was achieved, which was named PAF70-Pd
.
Noteworthily, N, N-bidentate ligand is one of the most
versatile coordination systems in organometallic catalysis,
which can coordinate with various metal ions and has been
widely used in homogeneous catalysis. In addition, the post-
synthesis modification was very facile and efficient. The above
features of our synthetic method could expand the application
value of the PAF material. In addition, for the purpose of
comparison, we prepared PAF1-NH
2
according to literature
step, and using a similar two post-synthesis method PAF1-Pd
the counterpart of PAF70-Pd) was prepared (Scheme 1).
5
1
(
2.2 Characterization of the materials.
As shown in Fig. 1a, compared with the (Fourier transform
infrared) FT-IR spectrum of PAF70-NH2, the strong attenuation
-
of the characteristic double peaks of –NH (3464 and 3377 cm
2
1
)
and the appearance of the characteristic peaks of Schiff base
-1
(the new peaks at around 1600 cm ) in the FT-IR spectrum of
PAF70-N=CPy, indicated the formation of imine bond and thus
the successful construction of PAF70-N=CPy. In comparison
with PAF70-N=CPy, in the FT-IR spectrum (Fig. 1a) of PAF70-Pd,
Fig. 1 FT-IR spectra (a), Nitrogen adsorption (solid symbols)–desorption (open symbols)
the appearance and enhancement of the bands at the region isotherms measured at 77 K (b), and TGA plots (c) of PAF70-NH , PAF70-N=CPy and
2
-
1
of 1520-1750 cm could be attributed to the C
＝
O stretching PAF70-Pd. XPS spectra (d) of free Pd(OAc)
2
, PAF70-Pd and PAF1-Pd.
-1
vibration and the new peaks at 1321 cm could be attributed
o
to C–O stretching vibration, which obviously indicated that PAF70-NH2 and PAF70-N=CPy. At about 400 C, the framework
PAF70-Pd was successfully obtained through our strategy. In decomposition started and when the temperature was above
o
addition, the successful synthesis of PAF1-Pd was also 500 C the decomposition became obvious. The 3.96 wt%
confirmed through the similar analysis of the FT-IR spectra residue for PAF70-NH2 and 2.15 wt% residue for PAF70-N=CPy
(more details could be found in Fig. S15 in the ESI†).
o
at 800 C could be ascribed to some palladium oxide residue
Nitrogen adsorption–desorption isotherms for the obtained which originated from the Pd catalysts in the preparation
materials were measured at 77 K. As shown in Fig. 1b, at low process of PAF70-NH2. As shown in Fig. 1c, PAF70-Pd (blue
o
, PAF70-N=CPy and PAF70-Pd all curve) had a 56 % weight loss at 277-320 C. This weight loss
relative pressures, PAF70-NH2
showed sharp uptakes, indicating the existence of micropores could be attributed to the decomposition of both
-
N, N-
in the materials. Noteworthily, in the desorption branch of bidentate ligand and AcO species which directly connect to
PAF70-NH2, a relatively sharp hysteresis demonstrated the the Pd center. Compared with PAF70-N=CPy
PAF70-Pd
presence of narrowly distributed mesopores. Compared with showed a lower stability, which might be due to that the Pd
,
PAF70-NH2, the corresponding hysteresis disappeared in the species could catalyze the cleavage of carbon–carbon bonds
5
desorption branches of PAF70-N=CPy and PAF70-Pd, which around the Pd centers in the PAF material. After a further
6
indicated the disappearance of the mesopores after post- obvious decomposition of the framework that started at 450
o
o
modifications of PAF70-NH2. The apparent surface area
calculated from the Brunauer–Emmett–Teller (BET) model was In addition, all the three PAF materials could not be dissolved
C, there was a 26.2 wt% palladium oxide residue left at 800 C.
2
-1
2
-1
2
99 m g for PAF70-NH2, 263 m g for PAF70-N=CPy, 172 m or decomposed in almost all common solvents such as water,
5
-
1
g for PAF70-Pd. Through the change of pore size distributions ethanol, dichloromethane, toluene, tetrahydrofuran, ethyl
calculated by non-local density functional theory (NLDFT), it acetate, hexane, diethyl ether, etc. The high thermal stability
was clear that the mesopores with pore width of 3.8 nm of and chemical stability made PAF70-Pd fully satisfy the
PAF70-NH
The decrease of BET surface area and the disappearance of found in the ESI† (Fig. S17). The Pd content was further
mesopores from PAF70-NH to PAF70-Pd further proved the determined by Inductively Coupled Plasma (ICP) analysis,
successful introduction of the Pd-based functional groups into which revealed that 23.0 wt% of Pd was incorporated to
the pores of the PAF.
PAF70-Pd and 25.1 wt% of Pd was incorporated to PAF1-Pd
2
disappeared in PAF70-Pd (see Fig. S10 in the ESI†). demands of catalysis. The TGA analysis of PAF1-Pd could be
2
.
Thermogravimetric analysis (TGA) was performed to test the These were in agreement with their TGA analysis. Importantly,
thermal stabilities of the above PAF materials. As shown in Fig. to the best of our knowledge, PAF70-Pd and PAF1-Pd have
1c, PAF70-NH
2
(black curve) and PAF70-N=CPy (red curve) higher Pd contents than other reported porous organic
showed similar TGA curve. There is almost no weight loss material immobilized Pd catalysts, which significantly profits
o
before 300 C, which suggested the high thermal stability of
from that the pores of our PAF materials could endow high
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Table 1 The control experiments for PAF70-Pd catalyzed Suzuki-Miyaura coupling
a
reaction.
o
b
entry catalyst (catalyst loading) solvent
T [ C]
Time
12h
yield
1
2
3
4
5
6
PAF70-Pd (0.5 mol%)
PAF70-Pd (0.5 mol%)
PAF70-Pd (0.5 mol%)
PAF70-Pd (0.5 mol%)
PAF70-Pd (0.5 mol%)
PAF70-Pd (0.5 mol%)
PAF70-Pd (0.1mol%)
PAF70-Pd (0.01 mol%)
PAF70-Pd (0.001 mol%)
No catalyst
CH
2
Cl
2
40
150
25
40
60
80
80
80
80
80
80
0
p-xylene
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
4h
92%
92%
96%
95%
97%
96%
97%
93%
0
1h
45min
20min
7min
15min
25min
4h
Fig. 2 TEM images of PAF70-N=CPy (a), PAF70-Pd (b), PAF1-N=CPy (c) and PAF1-Pd (d).
surface area for immobilizing the Pd coordination system.
In order to further investigate the incorporation of
c
7
8
c
palladium within PAF70-N=CPy and PAF1-N=CPy
, X-ray
photoelectron spectroscopy (XPS) was performed. As shown in
Fig. 1d, the binding energy (BE) at 337.80 eV, assigned to
Pd3d5/2 orbital, indicated that the Pd species in PAF70-Pd and
PAF1-Pd are present in +2 state. Compared with the BE of
d
9
1
0
12h
3
38.55 eV for free Pd(OAc)
and PAF1-Pd negatively shifted 0.75 eV. This negative shift
indicated that Pd(OAc) has strong coordination with the
bidentate ligand in PAF70-N=CPy and PAF1-N=CPy
2
, the BE for Pd species in PAF70-Pd
11
PAF70-N=CPy
12h
0
The supernatant liquid of
the EtOH suspension of
e
2
N
,
N
-
1
2
EtOH
EtOH
80
80
12h
0
1
1, 26
.
PAF70–Pd and K
2 3
CO
Transmission electron microscope (TEM) images obviously
showed the successful introduction of Pd species into the PAF
materials. As shown in Fig. 2a and Fig. 2b, compared with
1
3
PAF1-Pd (0.01 mol%)
25min
<5%
a
Reaction conditions (unless other noted):
CO (1.0 mmol), and the catalysts (for entry
0, no catalyst was added; for entry 11, 1.2 mg PAF70-N=CPy was added as
a solution of 1a (0.5 mmol),
PAF70-N=CPy, some evenly distributed black dots with a mean phenylboronic acid (0.75 mmol), K
2
3
1
diameter of about 1 nm emerged in the TEM images of PAF70-
Pd, indicating that the Pd species are uniformly dispersed in
the frameworks of the PAF material, which was in accordance
catalyst; for other entries, the catalysts were added at the indicated loadings
based on Pd) in 2 mL of solvent was stirred at indicated temperature for indicated
b
c
d
time. The isolated yield. The reaction scale was 2.5 mmol of 1a. The reaction
with the above analysis of the TGA curve of PAF70-Pd
.
e
2 3
scale was 25.0 mmol of 1a. 1.2 mg PAF70-Pd and K CO (1.0 mmol) was
o
Similarly, compared with PAF1-N=CPy (Fig. 2c), the TEM image immersed in 2 mL of EtOH for 2h at 80 C, after centrifugation, to the supernatant
liquid was added 0.5 mmol 1a, 0.75 mmol phenylboronic acid and 1.0 mmol
of PAF1-Pd (Fig. 2d) also showed uniformly dispersed Pd
o
K
2
3
CO , then the resulted mixture was stirred at 80 C for 12h.
species. This demonstrated that the Pd-based catalyst could
also be anchored into the pores of PAF1-NH material.
2
exciting to note that when the catalyst loading of PAF70-Pd
was reduced to 0.01 mol% the current catalytic reaction could
still react rapidly (Table 1, entry 8) and when the catalyst
loading of PAF70-Pd was reduced to 0.001 mol% the current
catalytic reaction could still occur smoothly (Table 1, entry 9).
Under the best condition (Table 1, entry 8) obtained from the
above screenings, the current reaction could not occur without
catalyst (Table 1, entry 10). In addition, PAF70-N=CPy (Table 1,
2
.3 Catalytic performance of PAF70-Pd.
After confirming the formation of desired PAF70-Pd and PAF1-
Pd, the catalytic properties of them were then studied. Suzuki-
Miyaura coupling reaction, one of the representative Pd-
catalyzed reactions, was selected as the model reaction to
study their catalytic performance. First, some control
experiments were conducted using p-bromonitrobenzene and
entry 11) with the palladium residue in the material could not
phenylboronic acid as model substrates and PAF70-Pd as
catalyze the reaction, indicating the Pd residue from the
preparation process in these materials has not catalytic activity.
The above results demonstrated that PAF70-Pd is indeed
efficient catalyst for the Suzuki-Miyaura coupling reaction.
Furthermore, the supernatant liquid of the EtOH suspension of
PAF70-Pd showed no catalytic activity for the coupling
reaction (Table 1, entry 12) even in a much longer time, which
indicated no leakage of catalytically active species from the
PAF70-Pd catalyst during the catalysis process. Thus the
catalyst. As shown in entries 1-3 of Table 1, among the
2 2
screened solvents (CH Cl , p-xylene and EtOH), EtOH gave the
best results in terms of the reaction rate and yield of the
current catalytic Suzuki-Miyaura coupling reaction. Increasing
o
o
the reaction temperature from 25 C to 80 C improved the
reaction rate significantly (Table 1, entries 3-6). The catalyst
loading screening showed that increasing the catalyst loading
could improve the reaction rate (Table 1, entries 6-9). It was
4
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a
Table 2 PAF70-Pd catalyzed Suzuki-Miyaura coupling reaction.
-Br, -F and –CN, entries 1-5) or an electron-donating-group
such as –OMe, -Me and –(OH)CHCH , entries 6-8) afforded the
cross-coupling products in excellent yields (upto >99%) with
(
3
-
1
Time
b
-1
c
high turnover frequency (TOF) value (all >= 14700 h ),
demonstrating the wide generality and functional tolerance of
the current system.
Entry
1
Ar-X
Product
Yield TOF(h )
(
min)
25
97%
96%
95%
90%
23280
18432
19000
18000
For the porous material immobilized catalysts with narrowly
distributed pore size, the size selectivity is a signature feature
for that the catalyzed reaction could occur in the pores. In
order to investigate the size selectivity of PAF70-Pd, some
contrast tests were performed as shown in entries 9-11 of
Table 2. Compared with that 9a could smoothly transform to
2
3
4
5
6
7
8
9
30
30
30
40
40
35
40
20
9b completely (Table 2, entry 9), the larger-size 10a reacted
more slowly under the same conditions in the same time (35%
yield, Table 2, entry 10). When 10a reacted with the larger-size
4
-biphenylboronic acid, the reaction rate further decreased
>99% >14850
and even almost no product was obtained under the same
conditions in the same time (Table 2, entry 11). The above size
selectivity obviously indicated that the catalytic reaction could
98%
92%
14700
15771
occur inside the pores of the PAF70-Pd
.
As a heterogeneous catalyst, the recyclability is an
important factor. Then the recyclability of PAF70-Pd as catalyst
was tested by subjecting it to 3 cycles of the Suzuki-Miyaura
coupling reaction of 4-bromonitrobenzene 1a and
>99% >14850
phenylboronic acid (Table S1 in the ESI†). After each cycle,
PAF70-Pd was easily recovered by centrifugation followed by
washing and could be directly used in the next cycle for cycles
96%
28800
2
-3, in which the substrate dosages were the same as that in
cycle 1. After 3 cycles, the recovered PAF70-Pd was dried in
vacuo at 120 °C for 18h. ICP analysis showed that the
recovered PAF70-Pd had 22.7 wt% of Pd content, which had
no obvious change compared with the fresh PAF70-Pd (23.0 wt%
of Pd content). These indicated that there is very low metal
leaching during the reaction process. The results
demonstrated that PAF70-Pd could undergo at least 3 cycles of
the reaction without obvious loss of catalytic activity.
1
0
20
20
35%
<5%
--
--
d
1
1
a
Reaction conditions: a solution of 2.5 mmol 1a, 3.75 mmol phenylboronic acid,
o
5
2 3
.0 mmol K CO and PAF70-Pd (0.01 mol%) in 10 mL of EtOH was stirred at 80 C
b
c
for indicated time. The isolated yield. TOF = (moles of product)/(moles of Pd in
d
the catalyst * reaction time). For entry 11, 4-biphenylboronic acid was used
2
.4 Comparison with the previously reported porous organic
instead of phenylboronic acid.
material (POPs and COFs) immobilized Pd catalysts.
current PAF70-Pd catalyzed reaction proceeds via
a
Data on the Pd contents and the TOF values of corresponding
heterogeneous catalytic process.
catalytic systems of PAF70-Pd, PAF1-Pd and previously
For comparison, PAF1-Pd was then employed as catalyst of reported porous organic material immobilized Pd catalysts are
the current Suzuki-Miyaura coupling reaction under the best given in Fig. 3 and Table S2 in the ESI†. The TOF values were all
condition as entry 8 in Table 1. Compared with PAF70-Pd calculated through the whole reaction process after complete
which gave a 97% yield (Table 1, entry 8), PAF1-Pd had almost conversion of the reactant under their respective optimum
no catalytic activity (<5% yield, Table 1, entry 13) under the conditions. It is very noticeable that PAF70-Pd and PAF1-Pd
same condition which should be due to that the remanent have the highest Pd contents, which might be due to the high
space in the pores after introducing Pd-catalyst was too small effective surface areas of our materials. Moreover, PAF70-Pd
to accommodate the current catalysis. This comparison fully showed far higher TOF values than other catalysts in Fig. 3. In
demonstrated the importance of the large enough mesopores addition, PAF70-Pd gave a rare example of catalytic system
in PAF70-NH
metal-based molecular catalysts.
2
for its application in immobilizing large-size with size selectivity in this field (Table S2 in the ESI†). These
excellent catalytic properties of PAF70-Pd are inferred to be
The catalytic performance of PAF70-Pd was further tested attributed to the large enough remanent pore space after
using a series of aryl bromides as the reaction substrates at a introduction of the catalytic sites. That is, the remanent pore
0
.01 mol% catalyst loading. As shown in Table 2, space could accommodate the reactants entering into the
bromobenzene 9a (entry 9) or the substituted aryl bromides pores and the products exiting outside of the pores.
2
with either an electron-withdrawing group (such as –NO , CHO,
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There are no conflicts to declare.
Acknowledgements
We are grateful for the financial support of the National Basic
Research Program of China (973 Program, grant no.
2
014CB931804) and the National Natural Science Foundation
of China (NSFC Project, grant nos. 21302061 and 21531003).
Notes and references
1
2
3
4
.
.
.
.
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Fig. 3 Pd contents and the catalytic performances for catalyzing Suzuki-Miyaura 8. H. Zhong, C. Liu, Y. Wang, R. Wang and M. Hong, Chemical
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. Conclusions
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the narrowly distributed mesopores (3.8 nm) in PAF70-NH
2
1
1
1
1
endow sufficient pore space for immobilizing Pd-based
molecular catalyst with relatively large size, the resulting
immobilized catalyst PAF70-Pd has evenly distributed Pd
species and high Pd content (23.0 wt%). Furthermore, PAF70-
Pd showed superb catalytic activity for catalyzing Suzuki-
Miyaura coupling reaction with good size selectivity and very
easy recyclability. Compared with the reported porous organic
3
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in PAF70-NH are very important to the high activity of PAF70-
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Conflicts of interest
6
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Chemical Science
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DOI: 10.1039/C8SC00510A
Table of Contents Entry:
A porous aromatic framework with mesopores was used as a platform for an immobilized Pd
catalyst with superb catalytic activity and size selectivity for Suzuki-Miyaura coupling reaction.
1