Highly Active Urea-Functionalized Zr(IV)-UiO-67 Metal-Organic Framework as Hydrogen Bonding Heterogeneous Catalyst for Friedel-Crafts Alkylation

Article abstract of DOI:10.1021/acs.inorgchem.9b00259

A new Zr(IV)-based UiO-67 metal-organic framework (1) was prepared with urea-functionalized biphenyl-4,4′-dicarboxylic acid (BPDC-urea) as the linker using conventional solvothermal technique and thoroughly characterized using X-ray powder diffraction (XR

Full text of DOI:10.1021/acs.inorgchem.9b00259

Article
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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Highly Active Urea-Functionalized Zr(IV)-UiO-67 Metal−Organic
Framework as Hydrogen Bonding Heterogeneous Catalyst for
Friedel−Crafts Alkylation
Aniruddha Das,† Nagaraj Anbu,‡ Mostakim SK,† Amarajothi Dhakshinamoorthy,*,‡
and Shyam Biswas*,†
†Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati, 781039 Assam, India
‡School of Chemistry, Madurai Kamaraj University, Madurai 625021, Tamil Nadu, India
S
* Supporting Information
ABSTRACT: A new Zr(IV)-based UiO-67 metal−organic
framework (1) was prepared with urea-functionalized
biphenyl-4,4′-dicarboxylic acid (BPDC-urea) as the linker
using conventional solvothermal technique and thoroughly
characterized using X-ray powder diffraction (XRPD), Fourier
transform infrared (FT-IR) spectroscopy, thermogravimetric
(TG), and N2 sorption analyses. The activated form of 1
(called 1′) exhibited excellent BET surface area in spite of
having a large functional moiety (urea) in the linker side. The
activated form of this material (1′) was successfully employed
for the Friedel−Crafts alkylation of indole with β-nitrostyrene
to achieve 97% yield in toluene at 70 °C for 24 h.
Furthermore, the catalyst was used for four cycles, with no
significant loss in its activity, and the reaction was heterogeneous in nature. The activity of 1′ was comparable to UiO-67-
(NH2)2, whereas the activity was 2-fold higher compared to the parent UiO-67. Further, the activity of the BPDC-urea linker
was nearly 2-fold higher than that of ZrCl4, suggesting the crucial role played by the urea moiety than the metal node. In
addition, the catalyst (1′) exhibited a wide substrate scope, allowing the preparation of a series of compounds with moderate to
high yields under the optimized reaction conditions. The roles of metal salt and linker in the catalysis have also been studied
separately, and the mechanism for the catalysis has been clarified.
including Strecker reactions,19 Diels−Alder reactions,20
INTRODUCTION
■
Claisen rearrangements,21 Mannich reactions,22 and Friedel−
The Friedel−Crafts alkylation reaction of indoles with β-
Crafts reactions.23 Although HBD catalysts have been
frequently employed in many reactions as commented earlier,
nitrostyrene is one of the fundamental organic reactions often
catalyzed by the presence of Lewis acids, leading to C−C bond
formation.1−4 Among these substrates, nitroalkenes are one of
the competency of H-bond donors present in HBD catalysts
significantly lead to dimerization and oligomerization through
the preferred Michael acceptors widely used in this reaction
due to the strong electron-withdrawing nature of nitro group5
hydrogen bonding of catalyst molecules to each other (Scheme
1).24,25 As a result, HBD catalysts undergo self-quenching to
and have been extensively used in organic synthesis.6
produce unproductive interactions, thus, strongly affecting the
Furthermore, Friedel−Crafts alkylation reactions between
arenes and nitroalkenes have been reported with a wide
catalyst solubility and reactivity. One of the effective strategies
range of homogeneous Lewis acid catalysts.7−11 Although this
to overcome these issues in HBD catalysis is to incorporate in
MOFs with defined environments and accessibility (Scheme
reaction can afford an asymmetric product, there are limited
1). With this aim, the present work reports the synthesis of
examples of these types of reactions catalyzed by Lewis acids
UiO-67 MOF using BPDC-urea as the linker and ZrCl4 as a
with high enantiomeric values due to the significant restrictions
on the substrates.12−15
source of central metal ion with accessible N−H bonds to form
hydrogen bonding to activate the substrate in the Friedel−
Crafts reaction between indole and β-nitrostyrene.
The growing interests in metal−organic frameworks
(MOFs) have originated from their structural varieties, the
Hydrogen-bond-donating (HBD) catalysis has been shown
to be an effective approach as an alternative to Lewis acid
activation.16−18 This type of catalysis typically uses urea or
thiourea as the core moieties capable of forming two-point
hydrogen bonding with their acidic N−H bonds (Scheme 1).
For example, a wide range of reactions have been reported with
very high yield and selectivity by employing HBD catalysis,
Received: January 28, 2019
© XXXX American Chemical Society
A
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bands were labeled with the following notations: very strong (vs),
strong (s), medium (m), weak (w), shoulder (sh), and broad (br).
The thermogravimetric (TG) data were recorded with the SDT Q600
thermogravimetric analyzer with a heating rate of 10 °C/min under a
stream of argon. The measurement of XRPD patterns was carried out
with the Bruker D2 Phaser X-ray diffractometer (30 kV, 10 mA) by
means of Cu Kα (λ = 1.5406 Å) radiation. The recording of the
nitrogen sorption isotherms at −196 °C was performed by utilizing
the Quantachrome Autosorb iQMP instrument. Before performing
the nitrogen sorption measurement, the MOF sample was degassed
under dynamic vacuum at 70 °C for 16 h.
Scheme 1. Substrate Activation by Urea Moiety through
Hydrogen Bonding, Self-Quenching of Urea Moieties in
Homogeneous Catalysis and Immobilization of Urea-
a
Functionalized Linkers in MOFs
Synthesis of [Zr6O4(OH)4(L)6]·7H2O·3DMF (1). ZrCl4 (40 mg,
0.134 mmol), H2L linker (40 mg, 0.134 mmol) and trifluoroacetic
acid (310 μL, 4.02 mmol) were added into a glass tube having 3 mL
of N,N-dimethylformamide (DMF). After sealing the tube with a cap,
it was heated at 150 °C by utilizing an aluminum block heater for 24
h. After the completion of heating, the sealed glass tube was cooled
down to ambient temperature and the yellow precipitate was collected
over a membrane filter paper by vacuum filtration. The powder
sample was then washed with acetone (2 × 3 mL) and air-dried.
Additional drying of the material was carried out inside an oven at 80
°C for 8 h. The yield was 45 mg (0.02 mmol, 63%) based on the Zr
salt. Elem. anal. Calcd for 1: C, 42.43; H, 3.12; N, 7.49%. Found: C,
42.20; H, 3.06; N, 7.23%. FT-IR (KBr pellet, cm−1): 3436 (br), 2924
(w), 2851 (w), 1689 (s), 1658 (w), 1620 (s), 1551 (vs), 1415 (vs),
1418 (vs), 1376 (m), 1264 (s), 1224 (s), 1114 (m), 1034 (w), 906
(w), 779 (vs), 665 (vs).
a
Reprinted with permission from ref 26. Copyright 2012 ACS.
Activation of Material 1. Material 1 (100 mg) was first placed
into a 50 mL round-bottom flask and 20 mL of methanol was added
to it. The mixture was allowed to stir for 24 h at room temperature.
Subsequently, collection of the powder sample by vacuum filtration
and drying in air resulted in the methanol-exchanged form of the
material. Heating of this powder material under vacuum at 70 °C for
16 h resulted in the thermally activated form of the material, which
was named as 1′. Elem. anal. Calcd for 1′: C, 43.26; H, 2.97; N,
7.64%. Found: C, 43.12; H, 2.56; N, 7.41%.
Catalytic Studies. In a typical reaction, a Schlenk tube (10 mL)
was charged with 10 mg of 1′, 0.1 mmol of indole, 0.105 mmol of β-
nitrostyrene, and 0.1 mL of solvent. Then, this mixture was
homogeneously mixed and placed in a preheated oil bath which
was maintained at 70 °C for the required reaction time mentioned in
Table 1. The progress of the reaction was monitored by Agilent
7820A gas chromatography system by sampling aliquots at different
time intervals. The purity and selectivity of the products were also
checked by gas chromatography. The determination of yield was
carried out by gas chromatography by means of the internal standard
method. The GC-MS technique was employed for the character-
ization of the obtained products. For the recyclability experiments, the
same catalytic reaction procedure was repeated except that the
catalyst was filtered after the reaction, washed thrice with fresh
toluene and dried at 80 °C in an oven for 5 h. The dried catalyst was
utilized in the consecutive cycles with the fresh reactants.
possibility of incorporation of various functional groups (which
can act as recognition sites for different molecules and ions)
without hampering the framework topology, and likely
applications in the field of gas storage and separation,
magnetism, drug delivery, optoelectronics, heterogeneous
catalysis, and sensing of small organic molecules, metal ions,
toxic anions, toxic molecules, nitroaromatic explosives,
gasotransmitters, and so on.27−37 In particular, Zr(IV) MOFs
have some special features like huge surface area, high thermal
and chemical stability, and low toxicity.38−49 These features of
Zr(IV)-based MOFs are highly preferred for applications in
heterogeneous catalysis.
In this report, a new Zr(IV) MOF material (1) is presented,
which has an analogous structure as UiO-6750 and consists of a
BPDC-urea (H2L) linker. The incorporation of the urea
functionality in the organic linker helps the activated MOF
material (1′) through HBD catalysis to accomplish Friedel−
Crafts alkylation of indole with β-nitrostyrene to achieve
industrially relevant pharmaceutical analogues.26,51−58 In
addition, the catalyst stability has been also surveyed by
performing reusability and hot filtration experiments. The
substrate scope and the effect of metal salt as well as linker in
the catalysis have been also presented here separately. Catalyst
1′ has been demonstrated to result in extremely high yield
(97%) for the Friedel−Crafts alkylation reaction of indoles
with β-nitrostyrene.
RESULTS AND DISCUSSION
■
Synthesis and Activation Procedure. Solvothermal
reactions were performed in all the probable combinations
by using three zirconium salts (ZrCl4, ZrOCl2·8H2O, Zr-
(SO4)2·4H2O), three solvents (DMF, N,N-diethylformamide
and N,N-dimethylacetamide), and four modulators59 (acetic
acid, formic acid, benzoic acid, and trifluoroacetic acid). The
reaction temperature and time were also varied, keeping the
molar ratio of ZrCl4 to H2L linker fixed at 1:1. A yellow
powder of 1 with optimum crystallinity was obtained when
ZrCl4, DMF, and trifluoroacetic acid were utilized as metal salt,
solvent, and modulator, respectively. The optimized reaction
temperature and time was 150 °C and 24 h, respectively. The
activation of the as-synthesized product involved solvent-
EXPERIMENTAL SECTION
■
Materials and Characterization Methods. The BPDC-urea
linker (H2L) was synthesized by following the reported procedure.56
For the characterization of H2L linker, 1H and 13C NMR spectra were
collected, which are provided in Figures S1 and S2, Supporting
Information. All the other chemicals and starting materials including
the indole derivatives and β-nitrostyrene used in the present study
were purchased from the commercial sources and they were used as
received. The recording of the Fourier transform infrared spectra in
the region 400−4000 cm−1 was conducted at room temperature with
the PerkinElmer Spectrum Two FT-IR spectrometer. The absorption
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exchange with methanol and subsequent heating under
vacuum. The activated compound was named as 1′.
parameters. The results of indexing are displayed in Table S1,
Supporting Information. The unit cell parameters obtained
from indexing are in well agreement with the reported
unfunctionalized and functionalized Zr-UiO-67 MOFs.60,61
We have also conducted a Pawley fit (Figure S4, Supporting
Information) of the observed XRPD pattern of compound 1.
The results obtained from Pawley fit showed quite good
similarity with the simulated XRPD pattern of UiO-67 MOF.
Hence, it can be inferred that compound 1 has UiO-67
framework topology. The comparison between the XRPD
patterns of the activated and as-synthesized materials (Figure
1) also reveals noticeable similarity in terms of peak positions,
indicating the high stability of the framework after the removal
of guest molecules from the microporous cages.
Infrared Spectroscopy. In the FT-IR spectra (Figure S3,
Supporting Information) of as-synthesized and activated 1, the
strong peaks at 1415 and 1565 cm−1 belong to the symmetric
and antisymmetric stretching vibrations of the coordinated
carboxylate groups from the H2L linker molecules, respectively.
The peak at 1660 cm−1 in the FT-IR spectrum of as-
synthesized material correspond to the carbonyl stretching
vibration of the guest DMF molecules.28 The peak attributable
to the DMF molecules is absent in the activated material,
which indicates that the complete activation of the material has
been achieved.28 The peak at 1719 cm−1 is present in H2L
ligand, 1 and 1′ due to the presence of carbonyl group of urea
moiety (Figure S3, Supporting Information).
Structure Description. As confirmed by the XRPD
experiment (Figure 1), compound 1 has shown similar
XRPD pattern with the unfunctionalized Zr-UiO-67 com-
pound. Hence, it can be inferred that the framework topology
of 1 is similar as the pristine Zr-UiO-67 compound.50 The
comprehensive description of the crystal structure of Zr-UiO-
67 compound has been already reported in the literature.50
The framework structure of Zr-UiO-67 contains hexanuclear
[Zr6O4(OH)4]12+ secondary building units (SBUs). The SBUs
are interconnected by the carboxylates of twelve 4,4′-
biphenyldicarboxylate (BPDC) linkers resulting in the
construction of a 3D cubic framework. Within this cubic
framework, there exists both tetrahedral (smaller) and
octahedral (larger) cages. Every central octahedral cage is
surrounded by eight tetrahedral cages at the corners. The
connection between the tetrahedral and octahedral cages
occurs via narrow triangular windows which have a free
diameter of ∼8 Å. In the structure of Zr-UiO-67, each Zr atom
is eight-coordinated and features square antiprismatic geom-
etry. The structure of 1 consists of the BPDC-urea (L) linkers
instead of unfunctionalized BPDC linkers, which are present in
Zr-UiO-67 compound. Figure 2 reveals the structures of the
tetrahedral and octahedral cages present within the framework
of 1.
XRPD Analysis. As shown in Figure 1, there is a nice
agreement between the XRPD pattern of as-synthesized 1 and
Figure 1. XRPD patterns of (a) simulated Zr-UiO-67 and (b) as-
synthesized (experimental) 1 and (c) activated 1′.
For confirmation of the presence of H2L linker in the
1
framework of 1′, we have carried out both H and 13C NMR
experiments with digested 1′ (1′ was digested with CsF in
D2O) (Figure S5 and S6, Supporting Information). The 13C
NMR spectrum shows peaks for eight different carbon atoms
the calculated XPRD pattern of the parent Zr-UiO-67
material.50 We have performed indexing of the experimental
XRPD pattern of compound 1 to deduce the unit cell
1
and the H NMR spectrum displays peaks for six aromatic
Figure 2. Ball-and-stick representation of the (a) H2L linker, (b) tetrahedral and (c) octahedral cages present within the framework structure of 1.
Color codes: Zr, cyan polyhedra; C, gray; O, red; N, blue; H, white. The cavities are represented by yellow spheres. The structure of 1 was modeled
and drawn by using the Materials Studio (version 5.0, Accelrys Inc., San Diego, 2009) software package.
C
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1
protons. In the H NMR spectrum, the peaks for two − NH
immersion in 1 M HCl for 4 h. It should be noted that the
chemical stability of 1′ is in good agreement with the chemical
stability of the existing functionalized and pristine Zr-based
UiO-67 MOF compounds.64
protons are absent due to the abstraction of these protons by
F− ion during digestion with CsF in D2O. These NMR spectra
clearly indicate that the H2L linker is present in the framework
of 1′.
Surface Area Analysis. The permanent porosity of 1′ was
demonstrated by conducting the nitrogen sorption experi-
ments at −196 °C. The resulting sorption isotherms (Figure
S9, Supporting Information) showed type-I behavior, indicat-
ing microporosity. From the adsorption isotherm, the BET
surface area and micropore volume were calculated. The
respective values are 1300 m2 g−1 and 0.75 cm3 g−1 at p/p0 =
0.5. A noticeable similarity can be also observed when the BET
surface area of 1′ is compared with the parent, functionalized
Zr-UiO-67 materials.63,65
Catalytic Studies. The Friedel−Crafts reaction between
indole and β-nitrostyrene has received considerable attention
due to its importance in the synthesis of tryptamine
derivatives.66 On the other hand, the Friedel−Crafts reaction
between β-nitrostyrene and indole is relatively slow due to the
lower nucleophilicity of indole. One of the possible ways to
overcome this issue is to develop heterogeneous catalysts to
activate electrophilic β-nitrostyrene toward nucleophilic
addition of indole through hydrogen bonding. This reaction
has been previously exploited using a series of MOF catalysts,
which include squaramide-functionalized UiO-67 MOF,67 NU-
601,26 Cr-MIL-101-UR3,58 Cu-UBTA,54 Cu(dbda),68 [Zn4O-
(4,4′-ureylene-benzenedicarboxylate) (DMF)2]·3DMF,52 and
Cu3(BTC)2.69
Thermal Stability. The thermogravimetric (TG) analyses,
which were performed under air atmosphere, disclose that the
compound is stable up to 290 °C. Three distinct weight loss
steps were observed in the TG profile of as-synthesized 1
(Figure S7, Supporting Information). The first and second
weight losses are 4.5 and 8.3 wt % in the temperature range of
25−150 and 150−290 °C, respectively. Such losses in weight
could be attributed to the elimination of seven water (cald.: 4.5
wt %) and three DMF (cald.: 7.8 wt %) molecules per formula
unit, respectively. The weight loss step starting at 290 °C was
observed due to the removal of coordinated linker molecules
from the structural framework of 1. The physisorbed water
molecules gave rise to the first weight loss step of 2.8 wt %
from 25 to 130 °C in the TG trace 1′. The second weight loss
of 7.8 wt % was found in the temperature range of 130−290
°C in the TG trace of 1′. The first and second weight loss steps
in the TG curve of 1′ correspond to the elimination of four
water (cald.: 2.6 wt %) and three DMF (cald.: 8.0 wt %)
molecules per formula unit, respectively. After 290 °C, the
organic linker molecules start to leave the framework of 1′. A
comparison of the thermal stability of 1 with pristine and
functionalized Zr-UiO-67 compounds revealed considerable
similarity.62,63
Initially, the catalytic activity of 1′ was studied in the
Friedel−Crafts reaction between β-nitrostyrene and indole as
model substrates and the reaction was optimized by the
variation of catalyst loading, reaction temperature and reaction
medium. The catalytic reaction between β-nitrostyrene and
indole was conducted in the presence of 1′ at different catalyst
loadings such as 3 (1.2 mol %), 6 (2.3 mol %), and 10 mg (3.8
mol %) in toluene at 70 °C. The time−conversion plots for
these catalyst loadings are provided in Figure 3. The results
indicate that the initial reaction rate and the final yield of the
Table 1. Optimization of Reaction Conditions for the
Friedel-Crafts Alkylation Reaction between Indole and β-
Nitrostyrene Using 1′ as a Solid Heterogeneous Catalyst
a
b
entry
solvent
toluene
toluene
toluene
toluene
acetonitrile
dichloroethane
dichloromethane
toluene
temp. (°C)
yield (%)
1
2
3
25
50
70
70
70
70
25
70
70
53
60
97
11
87
81
52
69
43
c
4
5
6
7
d
8
e
9
toluene
a
Reaction conditions: indole (0.1 mmol), β-nitrostyrene (0.105
mmol), solvent (0.1 mL), catalyst (10 mg, 3.8 mol %), 70 °C, 24 h.
b
c
Yield was determined by GC. Blank experiment (in the absence of
d
e
catalyst). 7 mg of H2L linker was used. 5.5 mg of ZrCl4 was used.
Chemical Stability. The chemical stability of 1′ was
examined via XRPD analysis (Figure S8, Supporting
Information). Initially, the samples of 1′ were separately
immersed in water, glacial acetic acid, and 1 M HCl at room
temperature for 4 h. After 4 h, the solid materials were
collected via vacuum filtration and XRPD data of the dry
powdered samples were recorded. The XRPD studies revealed
no significant change in the crystallinity of 1′ in water and
acetic acid, whereas 1′ slightly lost its crystallinity after
Figure 3. Effect of catalyst loading on the Friedel−Crafts alkylation
reaction between indole and β-nitrostyrene with (a) 3 mg (1.2 mol
%), (b) 6 mg (2.3 mol %), and (c) 10 mg (3.8 mol %) of 1′. Catalyst
mol % was calculated with respect to β-nitrostyrene.
D
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product are higher with 3.8 mol % catalyst than the other two
loadings. Therefore, the optimization of this reaction with
respect to temperature and solvent was performed using 3.8
mol % catalyst loading. The observed catalytic data are
summarized in Table 1. The reaction between indole and β-
nitrostyrene afforded 53% yield at room temperature in
toluene. The same reaction has shown 60% yield at 50 °C in
toluene as solvent. Additionally, the increment in the reaction
temperature from 50 to 70 °C resulted in significant
enhancement in the activity of 1′ to achieve 97% yield of
the desired product under identical experimental conditions. In
contrast, a blank control experiment in the absence of catalyst
between indole and β-nitrostyrene provided 11% yield at 70
°C in toluene as a solvent. These catalytic results clearly
indicate that 1′ plays the active role to promote this reaction.
On the other hand, the Friedel−Crafts reaction between indole
and β-nitrostyrene using 1′ as a catalyst exhibited 87% and
81% yields in acetonitrile and dichloroethane as solvents,
respectively, at 70 °C. Similarly, the reaction of indole and β-
nitrostyrene using 1′ as a catalyst gave 52% yield in
dichloromethane at room temperature after 24 h. All these
catalytic data conclude that the use of toluene as a solvent and
the reaction temperature of 70 °C are the optimum reaction
conditions to achieve 97% yield of the desired product and
hence further reactions were performed under these reaction
conditions. Figure 4 shows the time−conversion plot for the
between the reactions with and without catalyst suggests that
the reaction rate is completely stopped upon removal of 1′
from the reaction mixture. These kinetic data indicate that 1′ is
highly essential to promote the reaction toward completion.
Having demonstrated the activity of 1′ in promoting the
reaction between β-nitrostyrene and indole in a heterogeneous
manner under the optimized conditions, we were also
interested to compare the activity of 1′ with a series of
analogous catalysts. The results are shown in Figure 5. The
Figure 5. Time-conversion plots for the Friedel−Crafts alkylation
■
reaction between indole and β-nitrostyrene using (black, ) 1′, (blue,
▲
▼
●
) UiO-67-(NH2)2, (purple, ) BPDC-urea ligand, (red, ) UiO-
⧫
67 and (green, ) ZrCl4.
activity of UiO-67-(NH2)2 was identical to that of 1′. This may
be ascribed to the presence of N−H bonds, which can activate
β-nitrostyrene. Furthermore, the use of BPDC-urea linker
afforded 69% yield, which is lower than the activity of the
above catalysts. This lower activity of the linker compared to 1′
may be due to the self-quenching of the N−H bonds between
each molecule through dimerization.24 In contrast, the activity
of UiO-67 was much lower than the activities of 1′, UiO-67-
(NH2)2, and BPDC-urea. This activity difference may be due
to the lack of hydrogen bonding groups in UiO-67. However,
the activity of UiO-67 arises due to the Lewis acidity around
central metal ions, which is in accordance with earlier
precedents.70,71 Finally, ZrCl4 as a homogeneous catalyst
showed 43% yield under identical conditions, and it is the
lowest activity in these series of catalysts. Although the
activities of ZrCl4 and BPDC-urea linker are comparatively
lower than 1′, the observed catalytic data using 1′ as a catalyst
serve to illustrate the synergism between these two
components located in the framework structure and the
operation of HBD catalysis in promoting this reaction in an
efficient manner.
■
Figure 4. Time-conversion plot in the presence of 1′ (black, ) and
●
hot filtration test (red, ) upon filtration of catalyst after 1 h from the
reaction mixture, and the reaction mixture maintained under identical
conditions for the remaining time in the absence of catalyst.
Friedel−Crafts reaction between indole and β-nitrostyrene
using 1′ as a solid catalyst. It can be realized from this figure
that 1′ is highly effective in catalyzing the Friedel−Crafts
reaction between indole and β-nitrostyrene to achieve 97%
yield after 24 h. In order to verify the heterogeneity of the
reaction under these experimental conditions, hot filtration test
was conducted by removing the catalyst through filtration at
the reaction temperature after 1 h. Subsequently, the reaction
in the absence of solid catalyst was continued for another 23 h
under identical reaction conditions. The progress of the
reaction in the absence of catalyst was examined by sampling at
different time intervals. The comparison of the kinetic curves
Figure 6 shows the catalytic data of reusability experiments
for the Friedel−Crafts reaction between indole and β-
nitrostyrene using 1′ as a catalyst. This figure demonstrates
that the catalytic activity of 1′ is retained up to four cycles.
Although there is a slight decrease in the catalytic performance
of 1′, the catalytic data in the third cycle reveal that 90% of the
initial activity is still retained. This slight decrease in the
product yield can be ascribed to the loss of catalyst during the
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from the FT-IR spectrum (Figure S3, Supporting Informa-
tion), it is obvious that the peak for the carbonyl stretching of
the urea moiety is present in 1′ used up to the fourth catalytic
cycle at 1715 cm−1. The IR spectrum also shows that the
asymmetric and symmetric carboxylate stretching peaks are
present in 1′ used up to the fourth catalytic cycle at similar
positions as that of 1′ before catalysis. The stability of the
catalyst was further supported by FE-SEM images (Figures S10
and S11, Supporting Information), which revealed that the
morphology of 1′ was similar before and after the catalytic
study. Furthermore, EDX analysis with elemental mapping was
performed for compound 1′ before and after catalysis to check
the presence of different elements in the compound. Figures
S12−S15 (Supporting Information) reveal that the different
elements present in compound 1′ before catalysis remained
intact after catalysis.
After optimizing the conditions for the Friedel−Crafts
reaction between indole and β-nitrostyrene using 1′ as a
heterogeneous catalyst, the scope of 1′ was further examined
with substituted indoles under the identical reaction
conditions. The observed catalytic data are provided in
Table 2. The Friedel−Crafts reaction between N-methylindole
and β-nitrostyrene produced 86% yield. Similarly, the reaction
between 2-methylindole and β-nitrostyrene was efficiently
promoted by 1′ to achieve 96% of the desired adduct.
Furthermore, the reaction of 5-methylindole and β-nitro-
styrene in the presence of 1′ exhibited 96% yield. Similarly, an
encouraging yield of 94% was also observed for the reaction
between 5-methoxyindole and β-nitrostyrene under identical
reaction conditions. In contrast, the reaction of 5-chloro and 5-
bromoindoles with β-nitrostyrene in the presence of 1′
resulted in the formation of desired products with 61 and
55% of yields, respectively. On the other hand, a poor yield of
only 6% was observed for the reaction between 5-nitroindole
and β-nitrostyrene under identical experimental conditions.
This low yield may be explained from the fact that the presence
of a nitro substituent largely reduces the nucleophilicity at the
C3 carbon of indole moiety, whereas the presence of methyl
and methoxy substituents at the indole moiety afforded the
highest yield as discussed above. In addition, the moderate
yield observed for the halogen-substituted indoles may be
explained from the electronic factor as well as the steric nature
of these substrates to reach the active site in the MOF.
Interestingly, the reaction of pyrrole with β-nitrostyrene also
afforded the expected product in 97% yield under the
optimized reaction conditions. Finally, the Friedel−Crafts
reaction between N,N-dimethylaniline and β-nitrostyrene
provided the expected product in 22% yield. The results of
these catalytic investigations undoubtedly demonstrate that the
MOF catalyst 1′ plays the key role in carrying out the reactions
proficiently under the optimized reaction conditions. In any
case, the data presented in Table 2 and Figures S16−S34
(Supporting Information) clearly point out that the solid
catalyst 1′ can be conveniently used to perform the Friedel−
Crafts alkylation reaction at 70 °C within a short reaction time.
The operation of size-selective catalysis using 1′ as catalyst
was examined for the reaction between the N-Boc-protected
indole derivative and β-nitrostyrene as substrates under the
present experimental conditions. The catalytic data in Table 2
indicate that this reaction does not lead to any product
formation. This may be ascribed to the diffusion limitation of
the N-Boc-protected indole derivative to reach the active site
in 1′. This experiment clearly suggests that the catalytic
Figure 6. Reusability experiment for the Friedel−Crafts reaction of
indole with β-nitrostyrene using 1′ as a solid heterogeneous catalyst.
recovery process in every catalytic cycle. In addition, a control
experiment was performed to ensure that the recovered
catalyst is free from the reactants or products. This hypothesis
was confirmed by treating the three times reused 1′ with
toluene at 70 °C for 3 h. This solution was analyzed by GC-
MS and no evidence for the existence of either reactant or
product was observed. This experimental result indirectly
supports that the slight reduction in the catalytic performance
of 1′ is not due to the catalyst deactivation under the present
experimental conditions and furthermore the decrease in yield
during the reusability experiment can be related to the loss of
catalyst during the recovery process. This hypothesis was
further supported by comparing the XRPD pattern between
the fresh and four cycles used 1′. Figure 7 shows that the
crystalline nature of the four times used catalyst is certainly
retained and no significant change in the XRPD pattern is
noticed as compared to the fresh solid material. Moreover,
Figure 7. XRPD patterns of 1′ (a) before catalysis, (b) after the 1st
cycle, (c) after the 2nd cycle, (d) after the 3rd cycle, and (e) after the
4th cycle.
F
DOI: 10.1021/acs.inorgchem.9b00259
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
a
Table 2. Friedel-Crafts Alkylation Reaction of Indoles with β-Nitrostyrene Using 1′ as a Solid Heterogeneous Catalyst
a
b
Reaction conditions: indoles (0.1 mmol), β-nitrostyrene (0.105 mmol), toluene (0.1 mL), and 1′ (10 mg), 70 °C, 24 h. Yield was determined by
GC.
reaction occurs within the pores of 1′, demonstrating the size-
selective catalysis. The pore-size distribution plot of 1′ is
displayed in Figure S35 (Supporting Information). The plot
shows that the micropores of 1′ are centered at around 7.7 Å.
The catalytic performance of 1′ has been assessed by
comparing the yield, reaction time, temperature and catalyst
stability in terms of multiple reuses with earlier reports on
MOF catalysts in the literature. The comparison data are
presented in Table 3. These data clearly indicate that the
activity of 1′ is comparable or superior to some existing MOF
catalysts as the present catalyst requires short reaction time
and can be reused for more cycles. Furthermore, the reported
catalysts require 50−60 °C as the reaction temperature for this
catalytic reaction, whereas the present catalyst requires 70 °C,
which is not too high from the reported catalysts. Some of the
salient features of this catalytic system include a wide substrate
scope of 1′, as compared to the earlier catalysts, and an easy
synthesis procedure of 1′, without tedious functionalization of
the linker.
Scheme 2 provides the possible mechanism for the Friedel−
Crafts alkylation of indole with β-nitrostyrene using 1′ as a
solid catalyst. As stated earlier, the BPDC-urea linker in 1′
interacts with β-nitrostyrene through hydrogen bonding. The
formation of this type of hydrogen bonding with substrates
have been proposed in many studies involving HBD
catalysis.20,23,26,73,74 Hence, the activities of 1′, UiO-67-
(NH2)2, and BPDC-urea were much higher than UiO-67
and ZrCl4 under identical reaction conditions. Furthermore,
this interaction creates electron deficiency in the CC double
bond of β-nitrostyrene. Later, indole attacks β-nitrostyrene
through the C3 carbon atom to provide the expected product.
Table 3. Comparison of the Catalytic Performance of 1′
with the MOF Catalysts of Earlier Reports
No.
time temp. yield
of
entry
catalyst
(h)
(°C)
(%) uses
ref.
26
58
67
54
72
52
1
2
3
4
5
6
NU-601
36
30
24
48
24
24
60
60
50
60
50
60
98
96
95
85
99
90
5
4
4
3
5
3
Cr-MIL-101-UR3
UiO-67-Squar/bpdc
Cu-UBTA
Cu(dbda)
[Zn4O(4,4′-ureylene-
benzenedicarboxylate)
(DMF)2]·3DMF
CONCLUSIONS
■
7
[Zr6O4(OH)4
(L)6]·7H2O·3DMF
(1′)
24
70
97
4
present
work
In summary, a new Zr(IV)-based urea-functionalized UiO-67
MOF has been synthesized and characterized thoroughly by
G
DOI: 10.1021/acs.inorgchem.9b00259
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
ORCID
Scheme 2. Possible Mechanism for the Friedel-Crafts
Alkylation of Indole with β-Nitrostyrene Catalyzed by 1′
Mostakim SK: 0000-0003-4896-5154
Amarajothi Dhakshinamoorthy: 0000-0003-0991-6608
Shyam Biswas: 0000-0001-7103-9939
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
S.B. is thankful to the Science and Engineering Research
Board, New Delhi, for financial support (Grant No. EEQ/
2016/000012). A.D.M. is grateful to the University Grants
Commission, New Delhi, for the award of Assistant Professor-
ship under its Faculty Recharge Program. A.D.M. also
acknowledges financial assistance from the Science and
Engineering Research Board, New Delhi, through EMR Project
(EMR/2016/006500).
REFERENCES
■
(1) Olah, G. A.; Khrisnamurti, R.; Prakash, G. K. S. Comprehensive
Organic Synthesis, 1st ed.; Pergamon: New York, 1991; Vol. 3, pp
293−339.
(2) Halimehjani, A. Z.; Farvardin, M. V.; Zanussi, H. P.; Ranjbari, M.
A.; Fattahi, M. Friedel−Crafts alkylation of N,N-dialkylanilines with
nitroalkenes catalyzed by heteropolyphosphotungstic acid in water. J.
Mol. Catal. A: Chem. 2014, 381, 21−25.
(3) You, S.-L.; Cai, Q.; Zeng, M. Chiral Brønsted acid catalyzed
Friedel−Crafts alkylation reactions. Chem. Soc. Rev. 2009, 38, 2190−
2201.
(4) Shi, Z.-H.; Sheng, H.; Yang, K.-F.; Jiang, J.-X.; Lai, G.-Q.; Lu, Y.;
Xu, L.-W. Diarylprolinol Silyl Ether Catalyzed Asymmetric Friedel−
Crafts Alkylation of Indoles with α,β-Unsaturated Aldehydes:
Enhanced Enantioselectivity and Mechanistic Investigations. Eur. J.
Org. Chem. 2011, 2011, 66−70.
appropriate techniques to understand its structural features.
The material showed high chemical and thermal stability, as
well as considerable specific BET surface area. The solid
material 1′ was successfully employed in the Friedel−Crafts
alkylation reaction between β-nitrostyrene and indole. In this
reaction, a promising yield of 97% for the desired product was
achieved in toluene at 70 °C for 24 h. The active role of urea
moiety in the linker was established by performing a series of
experiments with UiO-67-(NH2)2, BPDC-urea linker, UiO-67,
and ZrCl4. The activity of the catalyst possessing urea moiety
was higher or comparable to the other tested catalysts. These
control experiments clearly suggest the active participation of
HBD catalysis through the presence of N−H bonds in the
linker. The solid MOF catalyst (1′) was utilized up to four
cycles with an insignificant reduction in its catalytic perform-
ance. However, the control experiments and XRPD analysis
confirmed that this loss in catalytic activity is not due to the
deactivation of the MOF catalyst. Moreover, the reaction is
found to be heterogeneous in nature. This catalyst also exhibits
a wide substrate scope in providing a series of products with
moderate to high yields.
(5) Kastl, R.; Wennemers, H. Peptide-Catalyzed Stereoselective
Conjugate Addition ReactionsGenerating All-Carbon Quaternary
Stereogenic Centers. Angew. Chem., Int. Ed. 2013, 52, 7228−7232.
(6) Berner, O. M.; Tedeschi, L.; Enders, D. Asymmetric Michael
Additions to Nitroalkenes. Eur. J. Org. Chem. 2002, 2002, 1877−1894.
(7) Firouzabadi, H.; Iranpoor, N.; Nowrouzi, F. The facile and
efficient Michael addition of indoles and pyrrole to α,β-unsaturated
electron-deficient compounds catalyzed by aluminium dodecyl sulfate
trihydrate [Al(DS)3]·3H2O in water. Chem. Commun. 2005, 6, 789−
791.
(8) Bartoli, G.; Bosco, M.; Giuli, S.; Giuliani, A.; Lucarelli, L.;
Marcantoni, E.; Sambri, L.; Torregiani, E. Efficient Preparation of 2-
Indolyl-1-nitroalkane Derivatives Employing Nitroalkenes as Versatile
Michael Acceptors: New Practical Linear Approach to Alkyl 9H-β-
Carboline-4-carboxylate. J. Org. Chem. 2005, 70, 1941−1944.
(9) Komoto, I.; Kobayashi, S. Lewis Acid Catalysis in Supercritical
Carbon Dioxide. Use of Poly(ethylene glycol) Derivatives and
Perfluoroalkylbenzenes as Surfactant Molecules Which Enable
Efficient Catalysis in ScCO2. J. Org. Chem. 2004, 69, 680−688.
(10) Harrington, P. E.; Kerr, M. A. Reaction of Indoles with Electron
Deficient Olefins Catalyzed by Yb(OTf)3·3H2O. Synlett 1996, 1996,
1047−1048.
(11) Bandini, M.; Melchiorre, P.; Melloni, A.; Umani-Ronchi, A. A
Practical Indium Tribromide Catalysed Addition of Indoles to
Nitroalkenes in Aqueous Media. Synthesis 2002, 2002, 1110−1114.
(12) Bandini, M.; Melloni, A.; Umani-Ronchi, A. New Catalytic
Approaches in the Stereoselective Friedel−Crafts Alkylation Reaction.
Angew. Chem., Int. Ed. 2004, 43, 550−556.
(13) Bandini, M.; Fagioli, M.; Garavelli, M.; Melloni, A.; Trigari, V.;
Umani-Ronchi, A. Can Simple Enones Be Useful Partners for the
Catalytic Stereoselective Alkylation of Indoles? J. Org. Chem. 2004,
69, 7511−7518.
(14) Jensen, K. B.; Thorhauge, J.; Hazell, R. G.; Jørgensen, K. A.
Catalytic Asymmetric Friedel-Crafts Alkylation of beta, gamma-
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.9b00259.
■
S
NMR, mass, IR and EDX spectra, TG and GC-MS
traces, XRPD patterns and Pawley fits, nitrogen
adsorption isotherms, FE-SEM images, pore size
distribution plot, and table containing indexing results
(PDF)
AUTHOR INFORMATION
Corresponding Authors
*E-mail: sbiswas@iitg.ac.in.
*E-mail: admguru@gmail.com.
■
H
DOI: 10.1021/acs.inorgchem.9b00259
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Unsaturated alpha-Ketoesters: Enantioselective Addition of Aromatic
C-H Bonds to Alkenes This work was made possible by a grant from
the Danish National Research Foundation. Angew. Chem., Int. Ed.
2001, 40, 160−163.
(15) Zhou, J.; Tang, Y. Sidearm Effect: Improvement of the
Enantiomeric Excess in the Asymmetric Michael Addition‡ of Indoles
to Alkylidene Malonates. J. Am. Chem. Soc. 2002, 124, 9030−9031.
(16) Schreiner, P. R. Metal-free organocatalysis through explicit
hydrogen bonding interactions. Chem. Soc. Rev. 2003, 32, 289−296.
(17) Taylor, M. S.; Jacobsen, E. N. Asymmetric Catalysis by Chiral
Hydrogen-Bond Donors. Angew. Chem., Int. Ed. 2006, 45, 1520−
1543.
(18) Doyle, A. G.; Jacobsen, E. N. Small-Molecule H-Bond Donors
in Asymmetric Catalysis. Chem. Rev. 2007, 107, 5713−5743.
(19) Sigman, M. S.; Jacobsen, E. N. Schiff Base Catalysts for the
Asymmetric Strecker Reaction Identified and Optimized from Parallel
Synthetic Libraries. J. Am. Chem. Soc. 1998, 120, 4901−4902.
(20) Schreiner, P. R.; Wittkopp, A. H-Bonding Additives Act Like
Lewis Acid Catalysts. Org. Lett. 2002, 4, 217−220.
(21) Etter, M. C.; Reutzel, S. M. Hydrogen bond directed
cocrystallization and molecular recognition properties of acyclic
imides. J. Am. Chem. Soc. 1991, 113, 2586−2598.
(22) Wenzel, A. G.; Jacobsen, E. N. Asymmetric Catalytic Mannich
Reactions Catalyzed by Urea Derivatives: Enantioselective Synthesis
of β-Aryl-β-Amino Acids. J. Am. Chem. Soc. 2002, 124, 12964−12965.
(23) Dessole, G.; Herrera, R. P.; Ricci, A. H-Bonding Organo-
catalysed Friedel-Crafts Alkylation of Aromatic and Heteroaromatic
Systems with Nitroolefins. Synlett 2004, 13, 2374−2378.
(24) Deshapande, S. V.; Meredith, C. C.; Pasternak, R. A.
Crystallographic data on disubstituted symmetric ureas. Acta
Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1968, 24, 1396.
(25) Stankovic, S.; Andreetti, G. D. N,N’-Bis(3,4-dichlorophenyl)-
urea. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1978,
B34, 3787−3790.
(26) Roberts, J. M.; Fini, B. M.; Sarjeant, A. A.; Farha, O. K.; Hupp,
J. T.; Scheidt, K. A. Urea Metal−Organic Frameworks as Effective and
Size-Selective Hydrogen-Bond Catalysts. J. Am. Chem. Soc. 2012, 134,
3334−3337.
(27) Das, A.; Biswas, S. A multi-responsive carbazole-functionalized
Zr(IV)-based metal-organic framework for selective sensing of
Fe(III), cyanide and p-nitrophenol. Sens. Actuators, B 2017, 250,
121−131.
(28) Das, A.; Banesh, S.; Trivedi, V.; Biswas, S. Extraordinary
sensitivity for H2S and Fe(III) sensing in aqueous medium by Al-
MIL-53-N3 metal−organic framework: in vitro and in vivo
applications of H2S sensing. Dalton Trans. 2018, 47, 2690−2700.
(29) Ricco, R.; Malfatti, L.; Takahashi, M.; Hill, A. J.; Falcaro, P.
Applications of magnetic metal−organic framework composites. J.
Mater. Chem. A 2013, 1, 13033−13045.
(30) Stavila, V.; Talin, A. A.; Allendorf, M. D. MOF-based electronic
and opto-electronic devices. Chem. Soc. Rev. 2014, 43, 5994−6010.
(31) Dalapati, R.; Sakthivel, B.; Ghosalya, M. K.; Dhakshinamoorthy,
A.; Biswas, S. A cerium-based metal−organic framework having
inherent oxidase-like activity applicable for colorimetric sensing of
biothiols and aerobic oxidation of thiols. CrystEngComm 2017, 19,
5915−5925.
(32) Wang, L.; Zheng, M.; Xie, Z. Nanoscale metal−organic
frameworks for drug delivery: a conventional platform with new
promise. J. Mater. Chem. B 2018, 6, 707−717.
(33) Nagarkar, S. S.; Desai, A. V.; Ghosh, S. K. A fluorescent metal−
organic framework for highly selective detection of nitro explosives in
the aqueous phase. Chem. Commun. 2014, 50, 8915−8918.
(34) Karmakar, A.; Kumar, N.; Samanta, P.; Desai, A. V.; Ghosh, S.
K. A Post-Synthetically Modified MOF for Selective and Sensitive
Aqueous-Phase Detection of Highly Toxic Cyanide Ions. Chem. - Eur.
J. 2016, 22, 864−868.
(35) Sharma, S.; Ghosh, S. K. Metal−Organic Framework-Based
Selective Sensing of Biothiols via Chemidosimetric Approach in
Water. ACS Omega 2018, 3, 254−258.
(36) Gole, B.; Bar, A. K.; Mallick, A.; Banerjee, R.; Mukherjee, P. S.
An electron rich porous extended framework as a heterogeneous
catalyst for Diels−Alder reactions. Chem. Commun. 2013, 49, 7439−
7441.
(37) Gole, B.; Bar, A. K.; Mukherjee, P. S. Fluorescent metal−
organic framework for selective sensing of nitroaromatic explosives.
Chem. Commun. 2011, 47, 12137−12139.
́
́
(38) Wang, T. C.; Bury, W.; Gomez-Gualdron, D. A.; Vermeulen, N.
A.; Mondloch, J. E.; Deria, P.; Zhang, K.; Moghadam, P. Z.; Sarjeant,
A. A.; Snurr, R. Q.; Stoddart, J. F.; Hupp, J. T.; Farha, O. K. Ultrahigh
Surface Area Zirconium MOFs and Insights into the Applicability of
the BET Theory. J. Am. Chem. Soc. 2015, 137, 3585−3591.
(39) Wang, T. C.; Hod, I.; Audu, C. O.; Vermeulen, N. A.; Nguyen,
S. B. T.; Farha, O. K.; Hupp, J. T. Rendering High Surface Area,
Mesoporous Metal−Organic Frameworks Electronically Conductive.
ACS Appl. Mater. Interfaces 2017, 9, 12584−12591.
(40) Stewart, L.; Lu, W.; Wei, Z.-W.; Ila, D.; Padilla, C.; Zhou, H.-C.
A zirconium metal−organic framework with an exceptionally high
volumetric surface area. Dalton Trans. 2017, 46, 14270−14276.
(41) Gutov, O. V.; Bury, W.; Gomez Gualdron, D. A.;
Krungleviciute, V.; Fairen Jimenez, D.; Mondloch, J. E.; Sarjeant, A.
A.; Al Juaid, S. S.; Snurr, R. Q.; Hupp, J. T.; Yildirim, T.; Farha, O. K.
Water Stable Zirconium Based Metal−Organic Framework Material
with High Surface Area and Gas Storage Capacities. Chem. - Eur. J.
2014, 20, 12389−12393.
(42) Feng, D.; Chung, W. C.; Wei, Z.; Gu, Z. Y.; Jiang, H. L.; Chen,
Y. P.; Darensbourg, D. J.; Zhou, H. C. Construction of Ultrastable
Porphyrin Zr Metal−Organic Frameworks through Linker Elimi-
nation. J. Am. Chem. Soc. 2013, 135, 17105−17110.
(43) SK, M.; Nandi, S.; Singh, R. K.; Trivedi, V.; Biswas, S. Selective
Sensing of Peroxynitrite by Hf-Based UiO-66-B(OH)2 Metal−
Organic Framework: Applicability to Cell Imaging. Inorg. Chem.
2018, 57, 10128−10136.
(44) Dalapati, R.; Nandi, S.; Reinsch, H.; Bhunia, B. K.; Mandal, B.
B.; Stock, N.; Biswas, S. Fluorogenic Naked-Eye Sensing and Live-
Cell Imaging of Cyanide by Hydrazine-Functionalized CAU-10
Metal-Organic Framework. CrystEngComm 2018, 20, 4194−4201.
(45) Nandi, S.; Banesh, S.; Trivedi, V.; Biswas, S. A dinitro-
functionalized metal-organic framework featuring visual and fluoro-
genic sensing of H2S in living cells, human blood plasma and
environmental samples. Analyst 2018, 143, 1482−1491.
(46) Wong, Y.-L.; Yee, K.-K.; Hou, Y.-L.; Li, J.; Wang, Z.; Zeller, M.;
Hunter, A. D.; Xu, Z. Single-Crystalline UiO-67-Type Porous
Network Stable to Boiling Water, Solvent Loss, and Oxidation.
Inorg. Chem. 2018, 57, 6198−6201.
(47) Kandiah, M.; Nilsen, M. H.; Usseglio, S.; Jakobsen, S.; Olsbye,
U.; Tilset, M.; Larabi, C.; Quadrelli, E. A.; Bonino, F.; Lillerud, K. P.
Synthesis and Stability of Tagged UiO-66 Zr-MOFs. Chem. Mater.
2010, 22, 6632−6640.
(48) Farha, O. K.; Eryazici, I.; Jeong, N. C.; Hauser, B. G.; Wilmer,
C. E.; Sarjeant, A. A.; Snurr, R. Q.; Nguyen, S. B. T.; Yazaydın, A. O.;
Hupp, J. T. Metal−Organic Framework Materials with Ultrahigh
Surface Areas: Is the Sky the Limit? J. Am. Chem. Soc. 2012, 134,
15016−15021.
(49) Nagarkar, S. S.; Saha, T.; Desai, A. V.; Talukdar, P.; Ghosh, S.
K. Metal-organic framework based highly selective fluorescence turn-
on probe for hydrogen sulphide. Sci. Rep. 2015, 4, 7053−7058.
(50) Cavka, J. H.; Jakobsen, S.; Olsbye, U.; Guillou, N.; Lamberti,
C.; Bordiga, S.; Lillerud, K. P. A new zirconium inorganic building
brick forming metal organic frameworks with exceptional stability. J.
Am. Chem. Soc. 2008, 130, 13850−13851.
́
́
̈
(51) Sonsona, I. G.; Marques-Lopez, E.; Haring, M.; Díaz, D. D.;
Herrera, R. P. Urea Activation by an External Brønsted Acid: Breaking
Self-Association and Tuning Catalytic Performance. Catalysts 2018, 8,
305−320.
(52) Rao, P. C.; Mandal, S. Friedel−Crafts Alkylation of Indoles
with Nitroalkenes through Hydrogen Bond Donating Metal−Organic
Framework. ChemCatChem 2017, 9, 1172−1176.
I
DOI: 10.1021/acs.inorgchem.9b00259
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(53) Raja, E. K.; Nilsson Lill, S. O.; Klumpp, D. A. Friedel−Crafts-
type reactions with ureas and thioureas. Chem. Commun. 2012, 48,
8141−8143.
(54) Wang, X.-J.; Li, J.; Li, Q.-Y.; Li, P.-Z.; Lu, H.; Lao, Q.; Ni, R.;
Shi, Y.; Zhao, Y. A urea decorated (3,24)-connected rht-type metal−
organic framework exhibiting high gas uptake capability and catalytic
activity. CrystEngComm 2015, 17, 4632−4636.
(55) Zhu, C.; Mao, Q.; Li, D.; Li, C.; Zhou, Y.; Wu, X.; Luo, Y.; Li,
Y. A readily available urea based MOF that act as a highly active
heterogeneous catalyst for Friedel-Crafts reaction of indoles and
nitrostryenes. Catal. Commun. 2018, 104, 123−127.
(56) Glomb, S.; Woschko, D.; Makhloufi, G.; Janiak, C. Metal-
Organic Frameworks with Internal Urea-Functionalized Dicarboxylate
Linkers for SO2 and NH3 Adsorption. ACS Appl. Mater. Interfaces
2017, 9, 37419−37434.
and beneficial influence of water in the catalysis of Fischer
esterification. J. Catal. 2017, 352, 401−414.
(72) Wang, X.-J.; Li, J.; Li, Q.-Y.; Li, P.-Z.; Lu, H.; Lao, Q.; Ni, R.;
Shi, Y.; Zhao, Y. A urea decorated (3,24)-connected rht-type metal−
organic framework exhibiting high gas uptake capability and catalytic
activity. CrystEngComm 2015, 17, 4632−4636.
(73) Curran, D. P.; Kuo, L. H. Altering the Stereochemistry of
Allylation Reactions of Cyclic.alpha.-Sulfinyl Radicals with Diary-
lureas. J. Org. Chem. 1994, 59 (s), 3259−3261.
(74) Fan, E.; Arman, S. A. V.; Kincaid, S.; Hamilton, A. D. Molecular
recognition: hydrogen-bonding receptors that function in highly
competitive solvents. J. Am. Chem. Soc. 1993, 115, 369−370.
(57) Hall, E. A.; Redfern, L. R.; Wang, M. H.; Scheidt, K. A. Lewis
Acid Activation of a Hydrogen Bond Donor Metal−Organic
Framework for Catalysis. ACS Catal. 2016, 6, 3248−3252.
(58) Dong, X.-W.; Liu, T.; Hu, Y.-Z.; Liu, X.-Y.; Che, C.-M. Urea
postmodified in a metal−organic framework as a catalytically active
hydrogen-bond-donating heterogeneous catalyst. Chem. Commun.
2013, 49, 7681−7683.
(59) Stock, N.; Biswas, S. Synthesis of Metal-Organic Frameworks
(MOFs): Routes to Various MOF Topologies, Morphologies, and
Composites. Chem. Rev. 2012, 112, 933−969.
(60) Øien-Ødegaard, S.; Bouchevreau, B.; Hylland, K.; Wu, L.;
Blom, R.; Grande, C.; Olsbye, U.; Tilset, M.; Lillerud, K. P. UiO-67-
type Metal−Organic Frameworks with Enhanced Water Stability and
Methane Adsorption Capacity. Inorg. Chem. 2016, 55, 1986−1991.
(61) Ko, N.; Hong, J.; Sung, S.; Cordova, K. E.; Park, H. J.; Yang, J.
K.; Kim, J. A significant enhancement of water vapour uptake at low
pressure by amine-functionalization of UiO-67. Dalton Trans. 2015,
44, 2047−2051.
(62) Schaate, A.; Roy, P.; Godt, A.; Lippke, J.; Waltz, F.; Wiebcke,
M.; Behrens, P. Modulated synthesis of Zr-based metal−organic
frameworks: from nano to single crystals. Chem. - Eur. J. 2011, 17,
6643−6651.
(63) Xu, Z.; Zhao, G.; Ullah, L.; Wang, M.; Wang, A.; Zhang, Y.;
Zhang, S. Acidic ionic liquid based UiO-67 type MOFs: a stable and
efficient heterogeneous catalyst for esterification. RSC Adv. 2018, 8,
10009−10016.
(64) Ødegaard, S. Ø.; Bouchevreau, B.; Hylland, K.; Wu, L.; Blom,
R.; Grande, C.; Olsbye, U.; Tilset, M.; Lillerud, K. P. UiO-67-type
Metal−Organic Frameworks with Enhanced Water Stability and
Methane Adsorption Capacity. Inorg. Chem. 2016, 55, 1986−1991.
(65) Fei, H.; Cohen, S. M. A robust, catalytic metal−organic
framework with open 2,2′-bipyridine sites. Chem. Commun. 2014, 50,
4810−4812.
(66) Lancianesi, S.; Palmieri, A.; Petrini, M. Synthetic Approaches to
3-(2-Nitroalkyl) Indoles and Their Use to Access Tryptamines and
Related Bioactive Compounds. Chem. Rev. 2014, 114, 7108−7149.
(67) McGuirk, C. M.; Katz, M. J.; Stern, C. L.; Sarjeant, A. A.; Hupp,
J. T.; Farha, O. K.; Mirkin, C. A. Turning On Catalysis: Incorporation
of a Hydrogen-Bond-Donating Squaramide Moiety into a Zr Metal−
Organic Framework. J. Am. Chem. Soc. 2015, 137, 919−925.
(68) Zhang, X.; Zhang, Z.; Boissonnault, J.; Cohen, S. M. Design
and synthesis of squaramide-based MOFs as efficient MOF-supported
hydrogen-bonding organocatalysts. Chem. Commun. 2016, 52, 8585−
8588.
(69) Nagaraj, A.; Amarajothi, D. Cu3(BTC)2 as a viable
heterogeneous solid catalyst for Friedel-Crafts alkylation of indoles
with nitroalkenes. J. Colloid Interface Sci. 2017, 494, 282−289.
(70) Rimoldi, M.; Howarth, A. J.; DeStefano, M. R.; Lin, L.;
Goswami, S.; Li, P.; Hupp, J. T.; Farha, O. K. Catalytic Zirconium/
Hafnium-Based Metal−Organic Frameworks. ACS Catal. 2017, 7,
997−1014.
(71) Caratelli, C.; Hajek, J.; Cirujano, F. G.; Waroquier, M.;
Xamena, F. X. L.; Speybroeck, V. V. Nature of active sites on UiO-66
J
DOI: 10.1021/acs.inorgchem.9b00259
Inorg. Chem. XXXX, XXX, XXX−XXX