UiO-66 microcrystals catalyzed direct arylation of enol acetates and heteroarenes with aryl diazonium salts in water

Article abstract of DOI:10.1002/aoc.5482

UiO-66 is a classic Metal–organic framework (MOF) that constructed by zirconium cations and terephthalate with high chemical and thermal stability. Using pristine UiO-66 nanocrystals as the catalysts, the carbon–carbon bond formation based on denitrogenat

Full text of DOI:10.1002/aoc.5482

Received: 29 September 2019
DOI: 10.1002/aoc.5482
Revised: 2 December 2019
Accepted: 3 December 2019
F U L L P A P E R
UiO-66 microcrystals catalyzed direct arylation of enol
acetates and heteroarenes with aryl diazonium salts in
water
Zhong-Hua Sun | Wang Chen | Bing-Bing Qian | Liang Wang
Binxun Yu | Qun Chen | Ming-Yang He | Zhi-Hui Zhang
|
Jiangsu Key Laboratory of Advanced
UiO-66 is a classic Metal–organic framework (MOF) that constructed by zirco-
nium cations and terephthalate with high chemical and thermal stability.
Using pristine UiO-66 nanocrystals as the catalysts, the carbon–carbon bond
formation based on denitrogenative substitution of aryl diazonium salts has
been achieved under mild condition. The C–H arylation of both enol acetates
and heteroarenes could be performed in aqueous medium without other metal
assistance. The UiO-66 catalyst shows good water stability and reusability as
well as impressive functional group tolerance.
Catalytic Materials & Technology,
Advanced Catalysis and Green
Manufacturing Collaborative Innovation
Center, Changzhou University,
Changzhou, 213164, China
Correspondence
Ming-Yang He and Zhi-Hui Zhang,
Jiangsu Key Laboratory of Advanced
Catalytic Materials & Technology,
Advanced Catalysis and Green
Manufacturing Collaborative Innovation
Center, Changzhou University,
Changzhou, 213164, P.R. China.
Email: hemingyangjpu@yahoo.com;
zhangzh@cczu.edu.cn
K E Y W O R D S
C–H arylation, Diazonium salts, heterogeneous catalysts, metal–organic frameworks, UiO-66
Funding information
Natural Science Foundation of the Jiangsu
Higher Education Institutions, Grant/
Award Number: 19KJA150001; Jiangsu
Key Laboratory of Advanced Catalytic
Materials and Technology, Grant/Award
Number: BM2012110; National Natural
Science Foundation of China, Grant/
Award Numbers: 11775037, 21676030
1
| INTRODUCTION
suffered from the drawbacks of homogeneous transition
metal catalysts such as CuCl in Meerwein arylation,
unfriendly solvents and unsatisfactory yields.
[
9,10]
Diazonium salts are widely used in the radical arylations
of arenes and heteroarenes coupling reactions, due to
their low cost, ready availability and high reactivity.
As an ideal generator of aryl radicals, aryl diazonium salts
have attracted more and more attention in cross coupling,
C–H-arylation and annulation reactions.
direct arylation of enol acetates and heteroarenes with
aryl diazonium salts is of significant importance since the
arylated products are ubiquitous with diverse applica-
Metal–organic frameworks (MOFs) are built from var-
[
1,2]
ious organic linkers and metal ions with well-defined
[
11]
porous coordination networks.
They have become an
important class of heterogeneous catalysts because of
their large surface area and tunable functionalized
[2–7]
Particularly,
[
12–15]
linkers.
Many classic MOFs promote the formation
of catalytic sites and provide size- shape- and even
enantio-selective supports for C-C formations, oxidations,
reductions and hydrogen evolutions. Some of the catalytic
[8]
tions.
However, the reported procedures usually
Appl Organometal Chem. 2020;e5482.
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© 2020 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5482

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SUN ET AL.
centers are metals while some of them are metal clus-
2
2
| EXPERIMENTAL SECTION
.1 | Preparation of UiO-66 nanoparticles
[13]
ters.
Among the classic MOFs, UiO-66 (UiO for Uni-
versity of Oslo) shows exceptional thermal stability (up to
ꢀ
3
50 C) and acid/base resistance owing to its Zr O (OH)
6
4
4
[16]
inorganic cores.
in [Zr (μ -O) (μ -OH) (BDC) ]
The synthesis of UiO-66 was performed in a Teflon-lined
6
3
4
3
4
6
(
H BDC = terephthalic acid). The metal-cluster based
stainless steel autoclave. ZrCl (0.56 g, 2.4 mmol) and ter-
2
4
Lewis acidity endows UiO-66 favorable in the synthesis of
a large variety of aromatic compounds including hetero-
ephthalic acid (0.399 g, 2.4 mmol) were dissolved in
140 ml DMF using ultrasound for about 1 min before
being transformed to a 200 ml Teflon-lined stainless steel
[17–19]
cycles by the introduction of defects.
On the other
ꢀ
hand, the composition of UiO-66 or amino-functionalized
autoclave. The autoclave was kept in an oven at 120 C
NH -UiO-66 with noble metals, such as Ag, Pd and Pt,
for 24 hr under autogenous pressure. The solution was
cooled to room temperature and the precipitates were iso-
lated by filtration. The obtained particles were further
purified with ethanol (10 ml) for 3 times and the off-
white UiO-66 products were dried at 80 C for 24 hr
(yield: 0.63 g for UiO-66-1). For UiO-66-2, the synthesis
2
lead to good catalysis performance in carboxylation,
reduction of nitroarenes, esterification, dehydrogenation
[20–23]
of formic acid, and Suzuki coupling.
At this stage,
ꢀ
the catalysis application of the pristine UiO-66 materials
still need to be paid more attention.
In continuation of our interest of MOFs catalysts in
green chemistry, we report herein a UiO-66 catalyzed
arylation of enol acetates and heteroarenes with aryl dia-
zonium salts in water at room temperature. This protocol
is simple, green, and scalable. The UiO-66 catalyst
showed good catalytic activity and superior chemical sta-
bility. Also, it could be readily recovered and reused for
several runs with slight decreasing in its activity. This
work demonstrates the great potential of using porous
MOFs-based materials not only as a carrier but also as an
electron acceptor to induce the coupling of MOFs with C-
C bonds and to increase their stability and catalytic
activity.
protocol is the same as that of UiO-66-1, with the excep-
ꢀ
tion of the reaction time at 120 C being 48 hr ZrCl
4
(0.65 g, 2.8 mmol) and terephthalic acid (0.47 g,
2.8 mmol), giving the yield of 0.86 g.
2.2 | General procedure for the synthesis
of R-aryl methyl ketones
At room temperature, a water (6 ml) solution of
p-nitrodiazonium salt (0.6 mmol) was sequentially added
by isopropenyl acetate (9 mmol) and UiO-66 (20 mol%).
The mixture was allowed to react at room temperature
FIGURE 1 TEM image of UiO-66-1 (a,c) and UiO-66-2 (b,d)

SUN ET AL.
3 of 8
for 12 hr. After the reaction was completed, the system
was extracted with ethyl acetate, the organic phase was
dried over anhydrous sodium sulfate, and rotary evapo-
rated under reduced pressure. The mixture was purified
by column chromatography with petroleum ether/ethyl
acetate (10: 1) as eluent to give the product.
particles of UiO-66-2 are mostly cubic nanocrystals with
somewhat aggregation. The TEM results indicate that
longer aging time leads to more regular shapes of the
nanoparticles in the similar sizes. Powder X-ray diffrac-
tion (PXRD) of UiO-66 microcrystals indicated their crys-
talline property with all the diffraction peaks well
1
6
matching with the simulated PXRD patterns of UiO-66
Figure 2a). The successful syntheses of both materials
(
3
| RESULTS AND DISCUSSION
were also verified by FT-IR spectroscopy (Figure 2b) with
typical peaks at 1580 and 1400 cm− that assigned to the
asymmetric and symmetric stretching of carboxylic
1
For the synthesis, solvothermal reaction of equivalents of
ZrCl and terephthalic acid in DMF leads to nano-sized
[
27]
groups.
4
UiO-66 particles. By comparison with the litera-
As evidenced by thermalgravimetric analysis (TGA,
Figure 2c), both of the UiO-66 samples show several
[24–26]
tures,
scale up reactions of the reagents was con-
ꢀ
ducted in the same equimolar ratio but different
containers (Teflon-lined stainless steel autoclaves
weight losses in the temperature range of 50 to 800 C.
ꢀ
The first gradual mass loss occurs up to100 C,
[24,25]
vs. Teflon-capped glass flasks
). Upon different reac-
corresponding to the volatilization of guest molecules
(ca. 25%) followed by the pyrolysis of the possible
unbounded. Then a plateau is shown in the temperature
tion time, the products were denoted as UiO-66-1 and
UiO-66-2 for the synthesis time of 24 and 48 hr, respec-
tively. The TEM images of UiO-66-1 and UiO-66-2 sam-
ples are shown in Figure 1. Both of the samples exhibit
nanoparticles in the size range of 50 nm to 100 nm. UiO-
ꢀ
range of 300–480 C, indicating high thermal stability of
the samples, which is followed by the decomposition of
ꢀ
the frameworks at around 500 C. Surface areas and pore
6
6-1 shows the spherical morphology, whereas the
structure of the as-prepared samples were investigated
2
FIGURE 2 (a) PXRD patterns, (b) FT-IR spectra, (c) TG curves, and (d) N adsorption/desorption isotherms

4
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SUN ET AL.
[
32,33]
using
N2
adsorption–desorption
measurements
catalysts.
Among them, seldom reactions were per-
(
Figure 2d). The nitrogen adsorption isotherms of the as-
formed under mild conditions nevertheless in environ-
[
29]
synthesized samples indicate a steep nitrogen gas uptake
at low relative pressure, displaying typical type I adsorp-
tion of microporous structure. The BET surface areas of
UiO-66-1 and UiO-66-2 are 603 and 812 m g , respec-
tively. The average pore sizes of them are about 2.32 nm
and 2.25 nm (Figure S1, Supporting Information). When
crystallization time elongated, UiO-66 could slightly
increase the surface area, due to the morphology chang-
ing from sphere to cube with almost similar sizes.
With these catalysts in hand, we initially explored
their catalytic activity toward the C–H arylation of
enol acetates using 4-nitrobenzenediazonium tet-
rafluoroborate (1a) and enol acetate (2) as the substrates
ment friendly aqueous medium.
So we firstly
investigated the solvent media at room temperature of
the model reaction. As shown in Table 1, the solvent
plays an important role in this series of reactions. Reac-
tions in acetonitrile, ethanol, acetone and DMSO gave
very low yields (Table 1, entries 1~4). Only slightly
higher yields were observed by using methanol and DMF
as the solvent (Table 1, entries 5 and 6). Given that the
addition of water could enhance the solubility of aryl dia-
zonium salt 1a, several reactions were then carried out in
the aqueous medium. Actually, the introduction of water
solvent could significantly promote this reaction
(Table 1, entries 7~10). Pleasingly, reaction in pure water
afforded the desired product in 63% yield (Table 1, entry
11). The catalyst loading was then evaluated (Table 1,
entries 12~18). Trace amount of the product was
observed in the absence of any catalyst. The reaction
2
−1
(Table 1). Notably, C–H arylation reactions employing
diazonium salts as the arylating reagents have been car-
ried out under different conditions with transition metal
catalysts,
[28,29]
[8,10,30,31]
photocatalysts,
or metal-free
TABLE 1 Optimization of the reaction conditions
a
Entry
Solvent
CH CN
Catalyst
UiO-66-2
UiO-66-2
UiO-66-2
UiO-66-2
UiO-66-2
UiO-66-2
UiO-66-2
UiO-66-2
UiO-66-2
UiO-66-2
UiO-66-2
UiO-66-1
–
Amount of the catalyst (mol %)
Yield (%)
trace
7
1
2
3
4
5
6
7
8
9
3
3
3
ethanol
acetone
DMSO
MeOH
DMF
3
trace
12
3
3
24
3
24
DMF: H
2
O (1:1)
O (1:1)
Acetone: H O (1:1)
CH CN: H O (1:1)
3
47
DMSO: H
2
3
35
2
3
48
10
11
12
13
14
15
16
17
18
19
3
2
3
43
H
H
H
H
H
H
H
H
H
2
2
2
2
2
2
2
2
2
O
O
O
O
O
O
O
O
O
3
63
3
43
0
trace
65
UiO-66-2
UiO-66-2
UiO-66-2
UiO-66-2
UiO-66-2
5
10
15
20
25
20
75
87
b
96 (92)
94
53
ZrO
2
Reaction conditions: 1a (0.6 mmol), 2 (15 equiv), solvent (6 ml), catalyst, room temperature, 12 hr.
a
1
Yields determined by H-NMR.
b
Isolated yields.

SUN ET AL.
5 of 8
yield increased with the increasing of catalyst loading.
Results clearly showed that 20 mol % of UiO-66-2 were
sufficient. The catalysis performance of UiO-66-2 is better
than that of UiO-66-1, which may be due to the larger
BET surface area of UiO-66-2.
electron-withdrawing groups such as nitro, cyano,
trifluoromethyl, acetyl and ester group successfully sur-
vived the reaction conditions. Due to the triangular win-
[
16]
dows (0.6 nm) of UiO-66 network,
the reactions of
para-substituted substrates likely occur in different cages
within the networks of UiO-66 catalysts.
[34–36]
Zirconia and zirconia-related catalysts,
such as
sulfated, molybdated and tungstated zirconia solid acids,
in the liquid phase which include condensation, isomeri-
zation, esterification and transesterification. But the reac-
tion of diazonium salts with enolacetates has never been
disclosed with the catalysis of zirconia. To identify the
catalysis capacity and the catalytic active sites of UiO-66,
commercial zirconia nanoparticles (<100 nm, BET Sur-
The ortho-substituted aryl diazonium salts showed
less activities owing to the hindrance effect, affording
the products 3c, 3d, and 3 h in relatively lower yields
(63%, 67% and 62%, respectively). Moreover, 1-naphthyl
diazonium salt also survived the reaction conditions to
give 3 l in 45% yield.
The arylation of heteroarenes is an important reaction
to access heteribiaryl intermediates and products in fine
2
−1
face area of 70 m g ) was used to catalyze the model
reaction (Table 1, entry 19). The desired product was
obtained in a modest yield (53%), indicating the catalytic
active sites of zirconium. A substantial drop of yield indi-
cated that the nanosize zirconia catalyst leads to larger
mass transport limitations than that of UiO-66 catalysts.
Apparently, larger surface areas can increase mass trans-
[
38]
chemical industries.
So this protocol was extended to
C–H arylation of heteroarenes. Generally, few examples
of heterogeneous catalysts can promote this reaction,
[
10,31,39]
especially in an aqueous system.
In this work,
both furan and thiophene reacted with aryl diazonium
salts smoothly to yield the target products as shown in
Table 3. A wide range of functional groups, such as nitro,
cyano, ester, and trifluoromethyl, keto, and halo were
compatible with the reaction conditions.
The C–Cl bonds in product 5e and 5 s keep intact,
enabling further manipulation of the initial compounds.
The ortho-substituted aryl diazonium salts also showed
good activities, giving the desired products in moderate
to good yields (5d, 5e, 5i, 5 k and 5o). Notably, this
protocol was not compatible for the electron-donating
aryl diazonium salts, which show low yields of the
[37]
fer in the reaction.
The porosity of UiO-66 particles
results in higher surface areas than that of zirconia,
which may render advantage on the substrate diffusion
and promote the mass transport.
Employing the optimized reaction conditions, we
started to explore the scope and generality of the present
method (Table 2). As shown in the table, a series of aryl
diazonium salts could be efficiently transformed into the
corresponding aryl methyl ketones 3a~3 l in moderate to
good yields. Generally, aryl diazonium salt containing
a
TABLE 2 Reaction scope
a
2
Reaction conditions: 1 (0.6 mmol), 2 (15 equiv), H O (6 ml), UiO-66-2 (20 mol%), room temperature, 12 hr, isolated yields.

6
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SUN ET AL.
a
TABLE 3 Reaction scope of heteroarenes
a
Reaction conditions: 1 (0.6 mmol), 4 (15 equiv), H
2
O (6 ml), UiO-66-2 (20 mol%), room temperature, 12 hr, isolated yields.
FIGURE 3 (a)
Recyclability of UiO-66-2 for the
synthesis of 3a under standard
reaction conditions. (b) PXRD
patterns of UiO-66-2 before and
after catalysis
[
40]
corresponding products. Nevertheless, 1-naphthyl diazo-
nium salt survived the reaction conditions to give product
previous literatures,
which may due to the difficulty of
the reduction of aryl diazonium salts bearing electron-
[
10,39]
5
l in 55% yield. This result was in according with the
rich groups.

SUN ET AL.
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FIGURE 4 TEM images of
the used UiO-66-2 catalysts
Furthermore, a scale-up reaction toward 3a was
performed with initial 12 mmol of 1a under the opti-
mized conditions. Then product 3a was obtained in
Education Institutions (Grant 19KJA150001) is also
acknowledged.
7
6% yield (1.63 g), indicating the potential application
ORCID
in the practical synthesis. Heterogeneous catalysts take
advantages of the facile separation and the reusability.
So in this work, the recovery and recycling investiga-
tion of UiO-66-2 was carried out (Figure 3) using the
model reaction in Table 1. A slight decreasing of the
product yields was observed after six catalysis runs
Liang Wang https://orcid.org/0000-0002-5367-1516
Zhi-Hui Zhang https://orcid.org/0000-0002-8744-7897
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How to cite this article: Sun Z-H, Chen W,
Qian B-B, et al. UiO-66 microcrystals catalyzed
direct arylation of enol acetates and heteroarenes
with aryl diazonium salts in water. Appl
[
[
Organometal Chem. 2020;e5482. https://doi.org/10.
2
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1002/aoc.5482
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2