Simple synthesis of the novel Cu-MOF catalysts for the selective alcohol oxidation and the oxidative cross-coupling of amines and alcohols

Article abstract of DOI:10.1002/aoc.5965

A novel porous metal–organic framework {Cu₂(bbda)_0.5(Hbbda)_1.5(OAc)_1.5.8H₂O} (UoB-5) was synthesized under ultrasound irradiation by employing a new Schiff base ligand H₂bbda (4,4'(1,4-phenylene bis (azanylylidene)) bis (methanylylidene))dibenzoic acid) and was fully characterized. The microporous nature of UoB-5 was confirmed by gas-sorption measurements. This framework acted as a highly effective heterogeneous catalyst for the alcohol oxidation reaction with tert-butyl hydroperoxide (t-BuOOH) as an oxidant. The presence of coordinatively unsaturated metal sites in UoB-5 could be the reason for high performance in this reaction. Furthermore, using the long linker with the free -NC group and uncoordinated -N atom on the wall of the pores created UoB-5 an excellent candidate for the catalytic activities without activation of the framework. It was confirmed with the heterogeneous catalytic experiments on the one-pot tandem synthesis of imines from benzyl alcohols and anilines. Eventually, the new Cu-MOF (UoB-5) could be an alternative catalyst as a more economically favorable and environmentally friendly in the catalysis field.

Full text of DOI:10.1002/aoc.5965

Received: 25 April 2020
DOI: 10.1002/aoc.5965
Revised: 11 July 2020
Accepted: 21 July 2020
F U L L P A P E R
Simple synthesis of the novel Cu-MOF catalysts for the
selective alcohol oxidation and the oxidative cross-coupling
of amines and alcohols
Pouya Ghamari Kargar
| Sima Aryanejad
| Ghodsieh Bagherzade
Department of Chemistry, Faculty of
Sciences, University of Birjand, Birjand,
97175-615, Iran
A
novel porous metal–organic framework {Cu2(bbda)0.5(Hbbda)1.5
(OAc)1.5.8H2O} (UoB-5) was synthesized under ultrasound irradiation by
employing
new Schiff base ligand H2bbda (4,40(1,4-phenylene bis
a
Correspondence
(azanylylidene)) bis (methanylylidene))dibenzoic acid) and was fully
characterized. The microporous nature of UoB-5 was confirmed by
gas-sorption measurements. This framework acted as a highly effective hetero-
geneous catalyst for the alcohol oxidation reaction with tert-butyl hydroperox-
ide (t-BuOOH) as an oxidant. The presence of coordinatively unsaturated
metal sites in UoB-5 could be the reason for high performance in this
reaction. Furthermore, using the long linker with the free -N C group and
uncoordinated -N atom on the wall of the pores created UoB-5 an excellent
candidate for the catalytic activities without activation of the framework. It
was confirmed with the heterogeneous catalytic experiments on the one-pot
tandem synthesis of imines from benzyl alcohols and anilines. Eventually, the
new Cu-MOF (UoB-5) could be an alternative catalyst as a more economically
favorable and environmentally friendly in the catalysis field.
Ghodsieh Bagherzade, Department of
Chemistry, Faculty of Sciences, University
of Birjand. Birjand, Iran, 97175-615.
Email: bagherzadeh@birjand.ac.ir;
gbagherzade@gmail.com
K E Y W O R D S
alcohol oxidation, imine, MOF, oxidative cross-coupling, Schiff base
1 | INTRODUCTION
oxidation is the overoxidation. To resolve these problems,
researchers are focused on catalytic oxidation reactions.
In the recent century, massive attention has been paid to
the sustainable and green processes in the various fields
of synthetic chemistry. One of the important chemical
transformations in synthetic chemistry is the oxidation
reaction, which produces the types of laboratory and
industrially chemicals.[1] The selective alcohol oxidation
to the carbonyl compound especially is of great impor-
tance in both academic research and industries.[2]
Alcohol oxidation can be performed with the diversity of
oxidants.[3,4] Most of these oxidants are commercially
available but are highly toxic and hazardous. Also, the
other major concern associated with them in the alcohol
Recently, peroxides (e.g., H2O2, TBHP) and oxygen have
attracted attention because of the advantages such as
inexpensive, green, and abundant. Furthermore, their
only by-product (water or t-butanol) in the catalysis of
the selective alcohol oxidation is environmentally
friendly.[5,6] However, it is essential to develop the suit-
able heterogeneous catalysts for the efficient activation of
these oxidants due to the dynamic inertia of them.
Another of the most important oxidation reactions is
oxidative cross-coupling reaction of alcohols with amine,
which its production is imines. Imines are well-known to
be key N-containing organic intermediates for the
Appl Organomet Chem. 2020;e5965.
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GHAMARI KARGAR ET AL.
synthesis of different biological, pharmaceuticals,
agricultural compounds, and other useful chemicals.[7–10]
The main methodologies for imine formation are
oxidative cross-coupling of alcohols with amines,[11,12]
self-coupling of primary amines,[13,14] and oxidative
dehydrogenation of secondary amines,[15,16] that the first
of them seems to be one of the most promising
approaches. Synthesis of imines in this way is associated
with many advantages such as readily available, low
toxicity, stable, inexpensive, and the wide substrate
scope.[17] Moreover, the only by-product is water in the
oxidative cross-coupling of alcohols with amines. How-
ever, the main challenge for this reaction is the selective
oxidation of alcohols into aldehyde intermediates under
mild conditions. Recently, diverse heterogeneous cata-
lysts had been reported for the oxidative cross-coupling
of alcohols whit amines, including catalysts based on
supported Au, Pd, Pt, and Ru.[18–20] However, most of
those reaction systems need pure O2 atmosphere, base
additives, high temperatures, long reaction time which
limited their large-scale application. Therefore, in the
point of view of positive environmental impact, it will be
an important breakthrough if a heterogeneous catalyst is
introduced for the synthesis of imines from alcohols and
amines via the oxidative cross-coupling reaction.
Metal–organic frameworks, a class of porous crystal-
line materials, assemble with metal ions and different
organic linkers. They are structurally tunable and
monodisperse materials that propose the capacity for the
control of the molecular-level in the solid-state.[21] Inter-
estingly, the wide spectrum of MOFs with diverse struc-
tures and porosity can be synthesized by selecting the
available various organic linkers. Recently, MOFs have
attracted the considerable attention of chemists because
they precede other heterogeneous catalysts in several
significant ways, such as more accessible catalytic
centers, high catalyst loading, and the more flexible
design of structural building units.[22–24] The active sites
of catalytically in MOFs can be achieved at the organic
linker or the inorganic component of frameworks by
direct synthesis of the envisaged framework or post-
synthetic modification. The metal sites can be created via
the removal of coordinated solvent molecules, which can
be used as catalytically active sites.[25,26] MOFs with
active metal sites have studied as a heterogeneous cata-
lyst in some reactions such as cyanosilylation, photo-
catalysis, hydrogenation/isomerization, oxidation of
organic substrates, and condensation reactions.[27,28] On
the other hand, it has been made clear that MOFs with a
smaller size display the higher catalytic activities, because
of the good exposure of active sites.[29] As regards the tra-
ditional synthetic methods of MOFs prefer to form the
large crystals of them, the preparation of MOFs with
small size is a challenging task. Therefore, the purposeful
and reasonable design of the architecture and composi-
tion of MOFs is needed to produce the desired
nanostructures with the practical catalytic applications.
Considering the above points, we have successfully
synthesized the novel Cu-MOF nanostructures,
named as UoB-5, with
a
new Schiff base
(H2bbda: 4,40(1,4-phenylene bis (azanylylidene))bis
(methanylylidene))dibenzoic acid) as an organic linker
by ultrasonic irradiation as a simple and green method.
We have selected a novel Schiff base as an organic linker
because of the basic nature of its azomethine group
which can have a positive effect on catalytic activity,
especially in the reactions that catalyzed generally in the
basic medium. Also, we have chosen the copper as the
node of MOF because the topology structure can
effectively inhibit the leaching of the active sites by using
the covalently linked metal centers as the nodes.
Therefore, UoB-5 can be used as a chemical stable het-
erogeneous catalyst in different reactions. For this reason,
and after our recent report about the synthesis and
application of MOFs, we herein report our results for the
application of UoB-5 as a suitable, efficient, and green
catalyst for the alcohol oxidation and oxidative cross-
coupling reactions (Scheme 1). Also, the reusability and
stability of the catalyst during the reaction process have
also been studied in detail.
SCHEME 1 Schematic illustration of the
catalytic efficiency of UoB-5

GHAMARI KARGAR ET AL.
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2 | EXPERIMENTAL
2.1 | General information
CH N), 13.10 (s, 2H, COOH). MS m/z (ESI) Calc. for
C22H16N2O4 [M + H]+: 372.11, found: 372.06. Anal. Cal.
for C22H16N2O4 (%): C: 70.96: H, 4.33, N: 7.52; found (%):
C: 70.43, H: 4.13, N: 7.32.
All chemicals and solvents were purchased from com-
mercial sources and used without further purification.
All of them were analytical grade. Deionized water was
used to prepare all the solutions.
2.3 | Preparation of cu-MOF nanoparticle
(UoB-5)
FTIR spectra were recorded using a JASCO FTIR-
4200 (KBr technique). CHN analyses were done by a
vario EL III element analyzer. 1H NMR and electrospray
ionization mass (ESIMS) measurements were made using
Bruker DPX-250 Avance 300 MHz (in DMSO-d6 with tet-
ramethylsilane as an internal standard.) and 3,200
QTRAP system, respectively. The content of Cu was ana-
lyzed by inductively coupled plasma optical emission
spectrometry (ICP-OES,5300 DV, Perkin Elmer). Powder
X-ray diffraction pattern was recorded on an XPert
Pro MPD diffractometer with Cu Kα radiation
(λ = 0.15406 nm) and scanning speed of 10ꢀ/min from
2 to 50ꢀ at ambient temperature. Transmission electron
microscopy (TEM) was carried out on a Philips EM 208S
model. SEM images were taken with a Nova Nano
SEM450 instrument. Thermogravimetric Analysis (TGA)
was evaluated using a TG 209 F1 Nevioꢀ system from
NaOH (1 M, 1 ml) was added dropwise to a water solu-
tion (20 ml) of H2bbda (1 mmol, 0.372 g) and the mixture
stirred until a yellow and a clear solution was obtained.
Then, a solution of copper acetate (2 mmol, 0.362 g) in
water (10 ml) was gradually added to the above mixture
at room temperature under ultrasonic irradiation. The
reaction mixture remained in the same conditions for the
more 30 min. Afterward, the product was centrifuged
and washed by ethanol and water. Finally, Cu2(bbda)0.5
(Hbbda)1.5(OAc)1.5.8H2O nanoparticles were obtained
after drying for 12 hr at 70 ꢀC.
2.4 | General procedure for alcohol
oxidation using UoB-5
ꢀ
30 to 700 C with a temperature rate of 20 C/min in air.
To a mixture of primary/secondary alcohols (1 mmol),
UoB-5 (1.5 mol%) in a glass test tube was added TBHP
The specific surface areas of the catalyst samples were
measured by N2 adsorption method at 77 K using a
Belsorp-Mini II instrument. Reactions were monitored by
thin-layer chromatography (TLC) carried out on 0.2 mm
huanghai silica gel plates using UV light as a visualizing
agent. Melting points were recorded with a Veego
VMP-D melting point apparatus and were uncorrected.
ꢀ
(2 mmol), and the mixture reaction was heated at 40 C
without any solvent for the appropriate time. After
completion of the reaction, UoB-5 was separated by
centrifuging followed by decantation (3 × 3 ml EtOAc)
and was used in the next run. The final product (liquid
phase) was identified by comparison of their physical
data with those of authentic samples because all of them
are known.
2.2 | Preparation of 4,40(1,4-phenylene bis
(azanylylidene)) bis (methanylylidene))
dibenzoic acid (H2bbda)
2.5 | General procedure for oxidative
cross-coupling using UoB-5
To a solution of 4-formylbenzoic acid (2 mmol, 300 mg)
in EtOH (10 ml) was gradually added a solution of
1,4-phenylene diamine (1 mmol, 108 mg) in EtOH
(10 ml) at room temperature. The reaction mixture was
mechanically stirred for 60 min. After that, the yellow
crystalline precipitate of the product was filtered, washed
with EtOH (3 × 10), and then dried in an oven overnight.
The structural assignments of the synthesized Schiff base
(H2bbda: 4,40(1,4-phenylene bis (azanylylidene))bis
(methanylylidene))dibenzoic acid)) were based on FT-IR,
1HNMR, Mass and analytical analysis of CHN data
(Figure S1, S2, S3). FT-IR (KBr, cm−1): ν: 1685, 1,623,
Benzyl alcohol (1 mmol), TBHP (2 mmol), and UoB-5
were magnetically stirred at 40 ꢀC for an appropriate time
under solvent-free conditions. After completion of the
reaction, aniline (1.2 mmol) was subsequently added to
the above reaction mixture and stirred for an additional
appropriate time at room temperature to afford the
corresponding products. After completion of the reaction
as indicated by TLC. The final product was purified by
recrystallization from absolute ethanol to yield pure
secondary imine as yellowish solid. Also, UoB-5 was
recovered by centrifugation, then washed several times
with EtOAc, dried, and reused for the next run under the
same reaction conditions.
1
1,490, 1,430, 1,290, 852, 778. HNMR (300 MHz, DMSO):
δ = 7.45 (s, 4H, Ar), 8.09 (m, 8H, Ar), 8.82 (s, 2H,

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GHAMARI KARGAR ET AL.
3 | RESULTS AND DISCUSSION
3.1 | Syntheses and characterization
of large-scale synthesis is the most important aspect of
this procedure; here, 6.54 grams of UoB-5 were produced
with 3.6 grams of Cu (OAc)2. The molecular formula of
Cu2(bbda)0.5(Hbbda)1.5(OAc)1.5.8H2O was proposed for
UoB-5 by the EDS analysis (Figure 1a) (calc. (%): C: 51.2;
O: 27.6; Cu: 11.45), which reasonably agrees with the real
amounts (%) of C: 51.29, O: 28.07 and Cu (10.10).
The novel Schiff base ligand was prepared by the conden-
sation of 4-formylbenzoic acid and 1,4-phenylene
diamine in EtOH at room temperature, which was then
used as a suitable organic linker for the new MOF
(Scheme 2). The Cu-MOF nanoparticles, as named
UoB-5, was obtained as a light-brown powder from the
combination of Cu (OAc)2 and H2bbda in water using
ultrasonic irradiation as a simple method. The possibility
The TGA curve of UoB-5 displayed its thermal stabil-
ꢀ
ity up to 230 C (Figure 1b). The material was released
two main weight changes. The first step slope of mass
loss happened (13.71%) around 310 ꢀC due to the
vaporization of water molecules residing in the pore
(cal. 13ꢀ.09%). The other sharp weight loss step occurred
at 490 C that signified the composition temperature of
the MOF compound.
FTIR spectrum of UoB-5 compared with H2bdda con-
firmed the coordination of linker to metal (Figure 2,
Left). The OH stretching vibration at 2300–3000 cm−1
from the organic ligand was disappeared that indicated
the ligand deprotonation occurred and the ligand was
coordinated to the metal ions. The absorption peaks at
≈3,421 cm−1 and ≈3,120 cm−1 could be attributed to the
stretching vibration of hydroxyl and the N-H groups,
respectively. Also, the peaks at 1702 and 1,414 cm−1
resulted from the symmetric and asymmetric vibration of
the coordinated acetate group. The peaks at 1167 cm−1
symmetric and 1,589 cm−1 asymmetric vibration cor-
responded to the carboxylate presence in the structure of
UoB-5. Furthermore, they have been shifted to the lower
value compared to the related vibration of the linker,
which demonstrates the presence of H2bdda as a linker
in the framework. It is worth noting that the coordina-
tion mode of carboxylate groups to Cu have determined
as a bridging mode based on the difference in the sym-
metric and asymmetric stretching vibrations of carboxyl-
ate groups (Δυ) in UoB-5 and H2bdda.[30] Based on the
SCHEME 2 Synthesis of UoB-5 by the prepared H2bbda as a
Schiff base linker
FIGURE 1 (a) EDS spectrum; (b) TGA curve of UoB-5

GHAMARI KARGAR ET AL.
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FIGURE 2 (Left) FT-IR
spectra of (a) H2bbda; (b) UoB-5;
(Right) The proposed geometry
around of the Cu center
obtained results from FT-IR, the geometry around of the
Cu center in UoB-5 was suggested (Figure 2, Right).
BET-BJH method was utilized to measure the surface
area, pore-volume, and pore-size distribution of UoB-5
(Figure 3a, 3b). Moreover, the surface area and pore
value of the synthesized UoB-5 based on N2 adsorption at
77 K were 86 m2/g and 0.67 cm3/g, respectively. The
results exhibited a type IV isotherm with an H2 hysteresis
structure of UoB-5. The relevant distribution curve of the
pore diameter, calculated by BJH method, displayed that
the dominant mesopores are centered approximately in
the range of 2–10 nm with a peak maximum of 5 nm.
The crystal structure of the as-prepared UoB-5 was
well characterized by PXRD (Figure 3c). The XRD pat-
tern of UoB-5 indicated the sharp peaks at around 2θ of
6.8ꢀ that confirmed a highly crystalline material was pro-
duced. Furthermore, the appearance of the sharp peaks
loop, which revealed
a hierarchically mesoporous
FIGURE 3 (a) The adsorption–desorption curves, (b) The pore diameter distribution, (c) PXRD pattern of UoB-5
FIGURE 4 (a) TEM, (b) SEM image, (c) the size distribution of UoB-5

6 of 12
GHAMARI KARGAR ET AL.
(UoB-5 & IRMOF-3) are isostructural with the cubic
lattice structure.
The cubic morphology of UoB-5 was confirmed via
the TEM (Figure 4a) and the SEM (Figure 4b) analysis,
which was an agreement with the obtained results of
XRD pattern. Moreover, the images displayed relatively
uniform size distribution and morphology for UoB-5.
The average particle size of UoB-5 was obtained the
range 20–21 nm by the particle size distribution based
on TEM images, that was emphasized the observed data
of SEM images (Figure 4c). Also, the TEM images rev-
ealed no amorphous component in the synthesized
nanoparticle.
SCHEME 3 Model alcohol oxidation reaction catalyzed by
UoB-5
at the low angel area (2θ< 10) displayed a high degree of
mesoscopic ordering. The overall XRD pattern of the
UoB-5 was in good agreement with those of IRMOF-3, as
reported in the literature,[31] indicating that both of them
TABLE 1 Summary of the Alcohol Oxidation Reactions Based on Substituted Primary and Secondary Alcohols [a]
1a, 95% b, 1.5 h
1e, 92% b, 1.5 h
1i, 80% b, 2 h
1b, 90% b, 2 h
1f, 95% b, 2 h
1j, 85% b, 2 h
1c, 95% b, 1.45 h
1 g, 90% b, 1.45 h
1 k, 75% b, 2 h
1d,87% b,1.45 h
1 h, 85% b, 2 h
1 l, 90% b, 1.45 h
1 m, 97% b, 1.5 h
1n, 85% b, 1.5 h
1o, 95% b, 1.5 h
1p, 97% b, 1.5 h
1q, 78% b, 1.45 h
1r, 98% b, 1.5 h
1 s, 98% b, 1.5 h
1 t, 83% b, 2 h
aReaction conditions: Alcohols (1 mmol), TBHP (2 eq), UoB-5 (1.5 mol%), Solvent-free, 40 ꢀC.
bIsolated yields.

GHAMARI KARGAR ET AL.
7 of 12
3.2 | Catalysis studies
reaction progress (Figure S6). In an effort to optimize
the oxidant amount, upon increasing TBHP amount
from 0.5–2 equivalent, the conversion of benzyl alcohol
increased. Also, it decreased with more increasing of
TBHP that can be due to the over-oxidation (Figure S7).
Moreover, the nature of the oxidant was evaluated as a
crucial factor in the activity of this reaction system, and
the results confirmed that the TBHP is the best choice
(Figure S8).
With the optimized reaction conditions in hand, the
scope and generality of the alcohol oxidation reaction
were moreover extended. The obtained results are pres-
ented in Table 1. A lot of structurally diverse primary and
secondary benzyl alcohols were oxidized by UoB-5 with
TBHP in solvent-free conditions, producing excellent
yields (75–98%) of aromatic aldehydes (2a-p, Table 1)/
ketones (2r-t, Table 1). The various benzyl alcohols with
electron-donating and electron-withdrawing groups at
ortho−/meta−/and para-position of the benzene ring
were smoothly converted to corresponding aromatic alde-
hydes in a good to excellent yields under optimized reac-
tion conditions, regardless of the electronic nature and
position of the substituent. Secondary alcohols were
effectively converted to corresponding ketones by UoB-5
with TBHP. Moreover, cinnamyl alcohol was selectively
oxidized to cinnamaldehyde without any by-products in
good yield (2q, 78%).
3.2.1 | Alcohol oxidation reaction
As commented in the introduction, MOFs are character-
ized by their prominent thermal and chemical stability
as well as providing unique catalytic activity and prod-
uct selectivity. With these precedents, the catalytic per-
formance of UoB-5 was explored for alcohol oxidation
reaction in the first step of this work (Scheme 3). The
benzyl alcohol was chosen as model substrate and the
different reaction parameters, involving temperatures,
the reaction medium, catalyst amount, and the type/
amount of oxidant, were screened. It should be noted
that only a low conversion was obtained after a reaction
time of 120 min without the addition of any catalyst or
in the presence of the precursor salt. Firstly, the investi-
gation of the reaction medium was displayed that the
solvent-free condition was more effective with respect to
the solvent medium (Figure S4). This reaction condition
has some advantages such as easy reactors, facile, and
efficient workup procedures that are often more envi-
ronmentally friendly. The evaluation of the temperature
effect revealed that the best yield of the product was
ꢀ
obtained at 40 C. With a further increase in the reac-
tion temperature, the product yield decreased, which
may be due to the decomposition of TBHP without oxi-
dizing benzyl alcohol (Figure S5). The key factor of cata-
lyst dosage investigated, the best result was achieved
with using 1.5 mol% of UoB-5. Besides, a further incre-
ment of catalyst amount had no positive effect on the
In scheme 4, a possible mechanism is presented for
the alcohol oxidation catalyzed by UoB-5 in the case of
the primary alcohol dehydrogenation. At first, the radi-
cals t-BuOO• is generated by the metal-assisted, which
SCHEME 4 The plausible mechanism for
the alcohol oxidation catalyzed by UoB-5
SCHEME 5 Model tandem oxidative cross-
coupling reaction catalyzed by UoB-5

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GHAMARI KARGAR ET AL.
the Cu (II) center is oxidized t-BuOOH. Then, the formed
Cu (I) center is reduced t-BuOOH and provided the radi-
cals t-BuO•. Finely, the both radicals behave as hydrogen
atom abstractors from the alcohols.[32]
3.2.2 | Oxidative cross-coupling reaction
The adoption of MOFs as a catalyst has been explored
extensively in recent years, due to coordinatively
TABLE 2 Comparison of the catalytic activity of UoB-5 towards the oxidative cross-coupling reaction
Catalysts
Catalyst amount
25 mg
Conditions
Time (hr)
Yield (%)
Ref
[33]
RuO2/GO
toluene/air/100 ꢀC
H2O/O2/60 ꢀC
3
63
94
91
65
92
99
92
92
97
73
95
[34]
[35]
[20]
[36]
[12]
[37]
[10]
[38]
[39]
Au6Ag1/PAAS
Ru (OH)x/TiO2
Au-Pd/resin
2 mol%
2 mol%
2 mol%
50 mg
12
2
toluene/O2/100 ꢀC
H2O/O2/40 ꢀC
12
3
Cu0.9Fe0.1@RCAC
Pd-Au@Mn (II)-MOF
MnOx/TiO2@SBA-15
γ-Fe2O3
toluene/air, LED/120 ꢀC
toluene/air/110 ꢀC
toluene/air/80 ꢀC
toluene/air/80 ꢀC
toluene/air/80 ꢀC
mesitylene/ /164 ꢀC
S.F./TBHP/40 ꢀC
2 mg
30
24
12
2
100 mg
300 mg
50 mg
M-350 (amorphous manganese oxide)
Mo (CO)6
26.4 mg
1.5 mol%
60
1
UoB-5
This work
TABLE 3 Summary of the Oxidative Cross-Coupling Reactions Based on Substituted Benzyl Alcohols and Anilines [a]
2a, 95% b, 1 h
2d, 65% b, 1.5 h
2 g, 93%, 1.45 h
2j,85% b, 1.5 h
2b, 85% b, 1.5 h
2c, 80% b, 1.5 h
2f, 96% b, 1.15 h
2i, 93%, 1.5 h
2e, 92% b, 2 h
2 h, 86%, 1.45 h
2 k, 87% b, 1.45 h
2 l, 85% b, 1.5 h
(Continues)

GHAMARI KARGAR ET AL.
9 of 12
TABLE 3 (Continued)
2 m, 90% b, 1.45 h
2n, 88% b, 1.45 h
2o, 80% b, 1.45 h
aReaction conditions: Alcohols (1 mmol), Aniline (1.2 mmol), UoB-5 (1.5 mol%), Solvent-free, 40 ꢀC.
bIsolated yields.
unsaturated metal site and the microporous nature. It is
believed that both the tunable pore structures and cata-
lytically active sites of MOFs could be used at the same
time to do the chemical synthesis in a one-pot manner.
Therefore, UoB-5 was examined for its active role as a
heterogeneous catalyst for oxidative cross-coupling reac-
tion as a one-pot tandem reaction. The challenge of oxi-
dative cross-coupling reaction is the optimization of the
reaction conditions for the first step, and the following
non-oxidation condensation step largely differ from each
other. With good precedents of UoB-5 in the alcohol
oxidation reaction, its catalytic activity was also exam-
ined in the formation imines by oxidative cross-coupling
reaction (Scheme 5).
According to having the optimized reaction condi-
tion for alcohol oxidation, the imine formation was ini-
tially investigated in the same conditions by following
to add aniline as a model substrate. Fortunately,
the good result was achieved to produce the imine as
a final product in previous conditions in terms of
SCHEME 6 The plausible mechanism for the oxidative cross-coupling reaction catalyzed by UoB-5

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GHAMARI KARGAR ET AL.
temperature, catalyst amount, and reaction medium. It
should be noted that the reaction progress was evalu-
ated in the absence of catalyst, a negligible proceed was
observed. Also, the precursor salt of Cu (OAc)2 showed
negligible catalytic activity for the oxidative cross-
coupling reaction.
For the investigation that the nature of imine groups
decorated UoB-5 and the important role of its synthetic
components in oxidative cross-coupling reaction, the
model reaction was carried out using H2bbda, Cu (OAc)2
and UoB-5 as catalysts under optimized conditions. Cu
(OAc)2, as precursor salt of UoB-5, showed lower cata-
lytic activity than UoB-5, with a conversion of 25% being
obtained after 3 hr. Also, using H2bbda, the organic
linker of UoB-5 afforded approximately 15% conversion
after 3 hr (Figure S9). These results indicated that the
simultaneous presence of the imine and metal groups in
the framework enhanced the catalytic activity. Anyway,
the role of the imine moiety in the structure of UoB-5 still
requires further investigation.
catalyst amount, high reaction time, and the usage of
organic solvents that go against green chemistry was
eliminated. Therefore, UoB-5 can be a decent system
deserved to develop further for industrial applications.
After that, the scope and limitations of UoB-5 were
investigated using different amines and alcohols
(Table 3). First, aniline was examined with the different
benzyl alcohols with various functional groups as the
coupling partner to form the desired imines. The
substituted benzyl alcohols with halides (-Cl, -Br) rev-
ealed the excellent yields for the corresponding products
(respectively 2b, 2c). p- nitoraniline gave the lowest yield
for the corresponding imine (2d) after only 1.5 hr. Salicyl
alcohol with aniline showed a high yield for the
corresponding product (2e). Second, p-anisidine and ben-
zyl alcohols with the electron-withdrawing (-NO2) and
electron-donating (-OMe) functional groups as well as
displayed the excellent yields (respectively 2j, 2 k). The
reaction of p-anisidine and other substituted benzyl alco-
hols (-OH, -Cl, -Br) gave the good yields for their prod-
ucts (respectively 2 g, 2 h, 2i). Finally, the benzyl alcohols
with different functional groups and p-bromoaniline
as the partner coupling produced the corresponding
products with pleasant yields (2 l-2o).
To manifest the supremacy of our catalytic system, a
comparison list was displayed in Table 2 to compare this
work with other analogous reaction systems. In this
work, the shortcoming of high temperatures, high
FIGURE 5 Recycling test of UoB-5 catalyst within kinetic-controlled region and under the optimized conditions

GHAMARI KARGAR ET AL.
11 of 12
The oxidative cross-coupling reaction is two steps,
which the mechanism of the first step is similar to what
is given in the previous section. With respect to the catal-
ysis of imine synthesis in the basic, a plausible mecha-
nism was proposed for the second step (Scheme 6).
Actually, the C=N groups of Schiff base linker could be
act as highly reactive base sites and a Brønsted proton of
aniline is absorbed by the nitrogen of imine. The gener-
ated stable anion is subjected to nucleophilic attack on
the carbonyl carbon atom of the substituted aromatic
aldehydes. Finally, UoB-5 come back to the initial struc-
ture after two runs of protonation and deprotonation,
the product release from the surface of the catalyst.
According to the proposed mechanism, the high catalytic
activity of UoB-5 in the oxidative cross-coupling reaction
can be attributed to the presence of the azomethine
group in linker.
toward tandem oxidative cross-coupling reaction. Besides
achieving high selectivity and activity to the target prod-
ucts, the heterogeneous nature of the catalyst was pro-
vided by the preservation of its structural integrity during
both reactions. Furthermore, this framework can be sim-
ply separated and reused for five catalytic cycles without
significant loss of its activity in both reactions. UoB-5 is
an excellent candidate as a more economically favorable
and environmentally friendly alternative to conventional
catalysts. Also, we expect the approach of this work to be
viable for the construction of many more interesting and
practical MOF catalysts like this for green organic synthe-
sis, and studies toward the synthesis of novel MOFs
containing the Schiff base as linker are underway.
ACKNOWLEDGEMENTS
We gratefully acknowledge the support of this work by
the University of Birjand.
3.3 | The recyclability tests of UoB-5
AUTHOR CONTRIBUTIONS
Pouya Ghamari Kargar: Investigation. sima
aryanejad: Investigation. ghodsieh bagherzade: Project
administration.
One of the important factors for the heterogeneous cata-
lyst in terms of sustainable chemistry is recyclability.
Therefore, the used UoB-5 after the post-treatment
(illustrated experimental section) was examined for the
recycling reactions under the optimized conditions. As
shown in Figure 5, the catalyst displayed a very stable
activity for both reactions (alcohol oxidation: 5a, oxida-
tive cross-coupling: 5c) after consecutive use of five
cycles, as good as a fresh catalyst. Any possible saturation
of catalytic sites because of the used optimized reaction
conditions was also investigated during the kinetic-
controlled region, i.e. 45 and 30 min after the starting
alcohol oxidation and oxidative cross-coupling reactions,
respectively. The catalyst indeed exhibited considerable
stability. TEM of the reused catalyst from both reactions
clearly revealed the integrity of its characteristic structure
(Figure 5b, 5d). These observations can be attributed to
the strong interaction between the nodes of Cu and
H2bbda as an organic linker which maintains the
integrity and structure of the UoB-5 during the reaction
progress.
ORCID
Pouya Ghamari Kargar https://orcid.org/0000-0002-
6284-2874
Sima Aryanejad https://orcid.org/0000-0002-5145-3734
Ghodsieh Bagherzade https://orcid.org/0000-0003-2931-
8146
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How to cite this article: Ghamari Kargar P,
Aryanejad S, Bagherzade G. Simple synthesis of the
novel Cu-MOF catalysts for the selective alcohol
oxidation and the oxidative cross-coupling of
amines and alcohols. Appl Organomet Chem. 2020;
e5965. https://doi.org/10.1002/aoc.5965