Cu2(BDC)2(BPY)-MOF: An efficient and reusable heterogeneous catalyst for the aerobic Chan-Lam coupling prepared via ball-milling strategy

Article abstract of DOI:10.1039/c7ra09772g

Nanoporous Cu₂(BDC)₂(BPY)-MOF was used as efficient and reusable heterogeneous catalyst to effect the aerobic cross-coupling of aromatic amines and phenyl boronic acid (Chan-Lam coupling). Ball-milling strategy was utilized for the first as a powerful green and energy-efficient method for the synthesis of this nanoporous metal-organic framework. Certain ratio of metal ion and organic linkers were held to improve the quality of nanostructures. Cu₂(BDC)₂(BPY) were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) surface area analysis.

Full text of DOI:10.1039/c7ra09772g

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Cu (BDC) (BPY)–MOF: an efficient and reusable
2
2
heterogeneous catalyst for the aerobic Chan–Lam
coupling prepared via ball-milling strategy†
Cite this: RSC Adv., 2017, 7, 46022
Armaqan Khosravi, Javad Mokhtari, *a Mohammad Reza Naimi-Jamal,*b
a
a
b
Sharareh Tahmasebi and Leila Panahi
2 2
Nanoporous Cu (BDC) (BPY)–MOF was used as efficient and reusable heterogeneous catalyst to effect the
aerobic cross-coupling of aromatic amines and phenyl boronic acid (Chan–Lam coupling). Ball-milling
strategy was utilized for the first as a powerful green and energy-efficient method for the synthesis of
this nanoporous metal–organic framework. Certain ratio of metal ion and organic linkers were held to
Received 2nd September 2017
Accepted 14th September 2017
improve the quality of nanostructures. Cu
2
(BDC)
2
(BPY) were characterized by X-ray powder diffraction
DOI: 10.1039/c7ra09772g
(XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–
rsc.li/rsc-advances
Emmett–Teller (BET) surface area analysis.
23–26
catalysis.
In particular, applications in energy technologies
Introduction
such as fuel cells, supercapacitors, and catalytic conversions
Crystalline microporous and mesoporous metal–organic have made them objects of extensive study, industrial-scale
27
frameworks (MOFs) are constructed by joining metal- production, and application. The variety of synthesis proce-
containing units [secondary building units (SBUs)] with dures was extended in the past years with the introduction of
2
8
29
organic linkers, using strong bonds (reticular synthesis) to chemical vapour deposition mechanochemical procedures,
create open crystalline frameworks with permanent porosity.
1
30
31
ow reactors, and spray drying for the synthesis of MOFs.
Bivalent or trivalent aromatic carboxylic acids or N-containing Waste-free sustainable syntheses require quantitative yields of
aromatics are commonly used to form frameworks with zinc, products without solvent-consuming, waste-producing workup
32
copper, chromium, aluminum, zirconium, and other procedures. Organic and inorganic solid–solid syntheses by
2
–5
elements. During the past century, extensive work was done ball-milling are most useful in this aim, and already hundreds
on crystalline extended structures in which metal ions are of examples of waste-free procedures, including industrial
33
joined by organic linkers containing Lewis base – binding scale-up processes, are available. These solid–solid reactions
6,7
atoms such as nitriles and bipyridines. A great variety of are comparable to solvothermal reactions at higher tempera-
cations can be incorporated into the framework and a wide tures, although there is a risk of inferior results because the
34
choice of functionalized organic linkers provides many possi- benet of self-assembled packing is lost. Nevertheless, there is
bilities to design the structures and tune the properties of the also urgency for solvent-free reactions under efficient kneading
8
,9
35

nal porous materials. They encompassed void space and conditions in the absence of solvents, because the common
therefore were viewed to have the potential to be permanently syntheses based on solvothermal methods oen lead to the
10
porous, as is the case for zeolites. Since MOFs have low incorporation of solvent molecules in the network. Conse-
density, very high surface area with a large percentage of tran- quently, the subsequent removal of solvent can even cause the
sition metals, they have emerged as interesting materials for collapse of the network. In addition, sufficient amounts of pure
1
1
12,13
various applications in energy storage, CO
hydrocarbon adsorption/separation,
2
adsorption,
material for broad range testing can be easily obtained typically
in quantitative yields. Mechanochemistry for preparation of
14,15
16,17
18
36
catalysis,
sensor,
19
20
21
22
magnetism, drug delivery, luminescence, gas storage and porous MOFs was rst reported in 2006 by Pichon and
37
coworkers. The application of mechanochemistry for the
synthesis of MOFs is relatively unusual synthesis possibility,
a
Department of Chemistry, Science and Research Branch, Islamic Azad University, P.O. although it is currently employed by several researchers as an
Box 14515/775, Tehran, Iran. E-mail: j.mokhtari@srbiau.ac.ir
b
38,39
approach for the synthesis of metal organic compounds.
Ullmann reaction (copper catalyzed N-arylation of amines)
and the related Goldberg reaction (copper-catalyzed N-arylation
Department of Chemistry, Research Laboratory of Green Organic Synthesis &
40
Polymers, Iran University of Science and Technology, P.O. Box 16846-13114,
Tehran, Iran. E-mail: Naimi@iust.ac.ir
41
of amides) are traditional methods for C–N bond formation in
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c7ra09772g
organic synthesis and pharmaceutical industry. However, the
1
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2 2
Scheme 1 Synthesis of Cu (BDC) (BPY) by ball-milling and application
as catalyst in cross-coupling of aromatic amines and phenyl boronic
acid.
classic Ullmann amination requires high reaction tempera-
tures, stoichiometric amounts of copper reagents, strong bases
and harsh reaction condition. During the past years, great Fig. 1 (a) PXRD patterns of prepared Cu
2
0
2
(BDC)
2
(BPY) in literature (b)
(BDC) (BPY) (this
PXRD patterns of mechanochemically prepared Cu
work).
2
2
progress on the palladium-based modied Ullmann and Gold-
42
berg coupling reactions protocols have been made, but the
drawbacks of the catalyst systems, such as air sensitivity and
high cost, limit their applications. On the other hand, in 1998,
the groups of Chan, Evans, and Lam independently developed
Cu-mediated oxidative amination of aryl boronic acids with
the reactants. Also, XRD results indicated that Cu
2 2
(BDC) (BPY)
was formed mutually interpenetrating structure of a pair of
three-dimensional frameworks. The loading percent of Cu was
measured by means of ICP. The measured amount of copper
found: 20.83%) corresponds well with the calculated
percentage for Cu (BDC) (BPY) (calcd 20.80%). FT-IR spectros-
copy technique was employed to characterize vibrational modes
of the MOF. In bidentate bridged carboxylate–Cu(II) complexes,
the intense band of (COO) is usually characterized by a wave-
5
1
43
amines and other nucleophiles in the presence of Cu(OAc)2,
providing a valuable alternative to traditional cross-couplings in
the construction of carbon heteroatom bonds. Recently, many
applications of this new method have been reported based on
(
2
2
44
45
3 4
copper catalysts supported on the resin, cellulose, Fe O
4
6
47
magnetic nanoparticles, and uorapatite, in heterogeneous
48
3
systems and fac-[Ir(ppy) ]-assisted Cu(II), in homogenous
ꢀ
1
number in the 1600–1625 cm region.
systems. However, despite these important contributions, more
work still needs to be done to identify new heterogeneous
systems for a highly effective catalyst. As part of our ongoing
work on the mechanochemistry synthesis of metal organic
The asymmetric stretching mode of COO appears at
614 cm . The bands at 1563, 1508 cm are associated with
the phenyl and pyridine modes, based on the comparison with
pure BDC and 4,4 -bipyridine ligands. SEM images of Cu–MOF
showed a narrow particle size distribution. Most of the particles
size was in the range of 60–90 nm (Fig. 2).
TEM micrograph (Fig. 3), conrmed that a crystalline and
nano-scaled material was produced. It is also to emphasize that
ball milling technique has resulted in producing uniformly
ꢀ1
ꢀ1
1
0
49
framework and application as catalyst in organic synthesis,
herein we report an efficient protocol for the synthesis of
Cu (BDC) (BPY) by ball milling technique and application of it
2
2
in the cross-coupling of aromatic amines and phenyl boronic
acid (Scheme 1).
Results and discussion
The choice of an appropriate ratio of reactants is critical for the
successful synthesis of desired MOFs. The best ratio of
0
Cu(OAc) $H O, terephthalic acid and 4,4 -bipyridine for the
2
2
2 2
synthesis of Cu (BDC) (BPY) with good crystalline structure and
high surface area was 1 : 1 : 0.5 respectively. The MOF was
synthesized by room temperature solvent-free ball-milling. The
process was completed within 2 hours resulting in a green
powder. To conrm the mechanochemically preparation of
Cu
2 2
(BDC) (BPY), X-ray powder diffraction was performed. The
observed sharp peaks at 2theta of 8, 12, 14, 16, 18, and 28 (Fig. 1)
50
are in a good agreement with reported in literature. The
diffraction patterns of the mechanochemically prepared MOF
Fig.
2
Scanning electron microscopy (SEM) images of the
samples (as synthesized and aer activation) show no reexes of Cu
2
(BDC) (BPY).
2
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Fig.
Cu
3
Transmission Electron Microscopy (TEM) images of the
2
(BDC) (BPY).
2
2 2
Fig. 5 MP-plot of as-synthesized Cu (BDC) (BPY).
distributed nano-scale particles. As can be observed, the
appearance of squares units in the TEM images reveal the
a
Table 1 Optimization of reaction conditions
formation of Cu
nano-cubic morphology.
2 2
(BDC) (BPY) framework structure and shown
51
The
N
2
adsorption–desorption
isotherm of the MOF exhibits an intermediate mode between
type I and type IV (Fig. 4) which is related to mesoporous
52
materials and microporous materials, respectively.
The BET surface area and total specic pore volume are
2
ꢀ1
ꢀ3 ꢀ1
3
05.5 m g and 0.462 cm
g
, respectively (Fig. 4).
Entry
Catalyst (mg)
Ratio 1a/2
Solvent
Yield (%)
The mesopore size distribution curve, calculated from Bar-
1
2
3
4
5
6
7
20
20
20
20
20
30
40
1
1
1
1
0.5
0.5
0.5
H
EtOH
MeOH
H O/MeOH
H
H
H
2
O
35
40
35
65
82
83
85
rett Joyner–Halenda analysis, shows a pore size distribution
centered at around 2.5 nm (inset of Fig. 4). The micropore
diameter was calculated to be 0.6 nm by MP plot (Fig. 5).
2
The synthetic Cu
2
(BDC)
2
(BPY) was employed as a catalyst in
2
O/MeOH
2
O/MeOH
2
O/MeOH
the aerobic cross-coupling of aromatic amines and phenyl
boronic acid. It is noticeable that the nature of base and solvent
greatly affect the efficiency of the coupling reaction (Table 1).
The coupling reaction of aniline and phenyl boronic acid was
chosen as model reaction for optimization of reaction condi-
a
Reaction condition: aniline (1 mmol), phenyl boronic acid (2 mmol),
CO (1.5 mmol), H O/MeOH (1 : 1), time: 1 h.
K
2
3
2
tion. With respect to the applicability and availability, K
was employed as the base in this study. The best solvent for this
coupling reaction is mixture of H O and methanol (1 : 1) (entry
–7). As shown in Table 2 the molar ratio of aniline and phenyl
boronic acid affect the yield of reaction and the best ratio is
.5 : 1 of aniline and phenyl boronic acid (entry 7). In another
attempt, when the reaction was carried out in the presences of
0 and 40 mg of catalyst, no observable change in yield is Table 2 Evaluation of catalyst scopea
2 3
CO
With the optimum reaction conditions in hand, the catalytic
system was efficient for the coupling reaction of different
aromatic amines with phenyl boronic acid and showed high
selectivity for monoarylation vs. diarylation. Aromatic amines
2
4
0
3
obtained.
Entry
Ar
Yield
1
1
1
1
1
1
1
a
b
c
d
e
f
Ph
4-Me–C
85
80
81
75
79
82
84
6
H
4
4-NO
4-Br–C
4-Cl–C
2-Pyrimidine
1-Naphthyl
2
–C
6
H
4
6
H
4
H
4
6
g
Fig. 4 (a) The N
2
adsorption–desorption isotherms of the meso-
(BPY)] and (b) the BJH isotherm and DA plot of
a
2
porous [Cu (BDC)
2
Reaction condition: aromatic amines (1 mmol), phenyl boronic acid
CO (1.5 mmol), H O/MeOH (1 : 1), time: 1 h.
2
mesoporous [Cu (BDC)
2
(BPY)].
(2 mmol), K
2
3
2
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Table 3 Comparison of activity for different catalytic systems in the cross-coupling of aromatic amines and phenyl boronic acid
Entry
Catalyst
Reaction condition
Cat. 10 mol%, CH Cl
Cat. 10 mol%, toluene/MeCN, 35 C, blue LED irradiation
Cat. 100 mg, MeOH, r.t.
Time
Yield
Ref. no.
1
2
3
4
5
6
Resin supported Cu(II)
2
2
, 1 atm O
2
, r.t.
24 h
20
3
2
2.5
1
32
95
90
95
87
85
23
27
26
25
ꢁ
Cu(OAc)
Cu-supported-uorapatite
Fe –EDTA–Cu(II)
Cellulose supported Cu(0)
Cu (BDC) DABCO–MOF
2
/fac-[Ir(ppy)
3
]
ꢁ
3
O
4
Cat. 5 mol%, H
Cat. 25 mg, Et
Cat. 20 mg, K
2
O, 50 C
3
N, MeOH, reux
CO , MeOH/H O, r.t.
24
2
2
2
3
2
Present work
with electron-withdrawing and electron-releasing groups gave Cu amide 3 by oxygen gives a copper(III) intermediate 4, which
the corresponding biphenyls in good yield and the results are undergoes reductive elimination to give product 5. The mech-
52
53
summarized in Table 2. Only in case of 4-nitro aniline rate of the anism is based on those proposed by Collman, Buchwald.
reaction increased and reaction completed within 20 minutes. The structures of all products were elucidated from their
1
This shown that electron-withdrawing group increased the rate mass, and H-NMR spectra and melting point as described for
of cross-coupling. Moreover, the cross-coupling of 2-amino- diphenyl amine. The mass spectrum of diphenyl amine
pyrimidine, 1-naphthylamine with phenylboronic acid was also (Table 3, entry 1) displayed the molecular ion peak at m/z ¼ 169.
1
accomplished with a high yield under the same conditions The H-NMR spectrum of diphenyl amine showed the aromatic
(
Table 2, entry 1f, 1g).
protons gave rise to multiplets in the region d ¼ 6.92–7.28 ppm
A comparison with other catalytic systems in the cross- and N–H in 5.65 ppm.
coupling reaction of aniline with phenylboronic acids demon-
strated that our present Cu–MOF catalyst system exhibited
a higher conversion and yield under milder conditions
Conclusions
(
Table 3).
2 2
Nanoporous metal–organic framework Cu (BDC) (BPY) was
For a heterogeneous catalyst, the recycling of the catalyst are
successfully synthesized by a solvent-free ball milling process.
The advantages of this procedure are solvent-free conditions,
short reaction times, high yield and easy work up. Also,
prepared MOF samples (as synthesized and aer activation)
show no reexes of the reactants and XRD results indicated that
Cu (BDC) (BPY) was formed mutually interpenetrating struc-
important issues to be reviewed. To address these issues, the
catalyst was recovered by simple ltration and washed with
methanol and oven dried. The recovered catalyst was reused for
cross-coupling of aniline and phenyl boronic acids. The result
indicates that the Cu (BDC) BPY can be used for several cycles
2
2
2
2
successfully with minimal loss of activity. A tentative mecha-
nism for the Cu–MOF Chan–Lam coupling reaction of aromatic
amines and phenyl boronic acids is shown in Scheme 2. The
proposed mechanism is shown in Scheme 2.
Initially, the Cu(II)–MOF catalyst could undergo ligand
exchange and transmetalation with aromatic amine 1 and
phenyl boronic acid 2 to generate Cu amide 3. The oxidation of
ture of a pair of three-dimensional frameworks. The synthesized
Cu (BDC) (BPY) offered high catalytic activity for cross-coupling
2
2
of aromatic amines and phenyl boronic acid. So, a different
range of aryl amines applicable in this reaction. Further studies
on mechanochemical synthesis of other useful MOFs and
development of its catalytic scope are in progress and would be
presented in the future.
Experimental section
1.
Materials and instruments
All reagents and starting materials including organic linker
H
2
BDC, metal salt Cu(OAc)
2
$H
2
O, 1,4-benzenedicarboxylate
0
(BDC, 99%), 4,4 -bipyridine (BPY) were obtained from
commercially available sources such as Sigma-Aldrich and
Merck and used without any further purication. X-ray powder
diffraction (XRD) patterns recorded using an X'pert MPD. The
sample was characterized using a scanning electron microscope
(
SEM) with a ZEISS scanning electron microscope at 30 kV with
gold coating. FT-IR spectra were recorded with a Shimadzu
400s FT-IR spectrometer using potassium bromide pellets.
8
Brunauer–Emmett–Teller (BET) surface area of the samples was
determined from N2 adsorption–desorption isotherms using
a Quantachrome NovaWin2 analyzer. Transmission electron
microscopy (TEM) was carried out using an EM10C-100 kV
series microscope from the ZEISS Company, German and the
Scheme
2
Proposed mechanism for cross-coupling by the
Cu (BDC)
2
2
BPY–MOF catalyst.
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Coupled Plasma (ICP) analysis on sequential plasma spec-
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recorded at 500.1 MHz on a BRUKER DRX 500-AVANCE FT-NMR
3
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Cu
.
Ball-milling synthesis of the metal–organic framework
(BDC) (BPY)
2
A mixture of Cu(OAc) $H O (0.6 mmol), H2BDC (0.6 mmol) and
2
2
2
BPY (0.3 mmol) with molar ratio of 1 : 1 : 0.5 were ball-milled
vigorously at 30 Hz without any solvent at room temperature
for 2 h. The obtained green powder was washed with DMF (2 ꢂ
1
1
0 mL). Solvent exchange was carried out with methanol (2 ꢂ
0 mL) at room temperature. To remove the guest molecules of
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monitored by TLC) catalyst was ltered and washed by H O/
(
2
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2
4
2
puried by column chromatography (silica gel, n-hexane/EtOAc)
to afford diarylamines 3a–g structure of all product was char-
1
acterized by melting point and H-NMR spectra.
2
Conflicts of interest
There are no conicts to declare.
2
Acknowledgements
2
The authors gratefully acknowledge from Science and Research
Branch, Islamic Azad University and Iran university of Science
and Technology (IUST) for partial nancial support of this work.
2
2
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