Ru Nanoparticles-Loaded Covalent Organic Framework for Solvent-Free One-Pot Tandem Reactions in Air

Article abstract of DOI:10.1021/acs.inorgchem.7b03077

Condensation of benzene-1,3,5-tricarbohydrazide with benzene-1,4-dicarboxaldehyde generated a new covalent organic framework, COF-ASB (1), in which the organic units are held together via hydrazone linkage to form porous frameworks. COF-ASB (1) is highly crystalline and displays good chemical and thermal stability and is permanently porous. In addition, 1 can be an ideal support to load Ru nanoparticles (Ru NPs) to generate Ru@COF-ASB (2). The obtained composite material is able to highly promote one-pot tandem synthesis of imine products from benzyl alcohols and corresponding amines under solvent-free conditions in air.

Full text of DOI:10.1021/acs.inorgchem.7b03077

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Ru Nanoparticles-Loaded Covalent Organic Framework for Solvent-
Free One-Pot Tandem Reactions in Air
Gong-Jun Chen,*,† Xiao-Bo Li,† Chen-Chen Zhao,† Hui-Chao Ma,† Jing-Lan Kan,† Yu-Bin Xin,†
Cheng-Xia Chen,‡ and Yu-Bin Dong*,†
†College of Chemistry, Chemical Engineering and Materials Science, Collaborative Innovation Center of Functionalized Probes for
Chemical Imaging in Universities of Shandong, Key Laboratory of Molecular and Nano Probes, Ministry of Education, Shandong
Normal University, Jinan 250014, P. R. China
‡MOE Laboratory of Bioinorganic and Synthetic Chemistry Lehn Institute of Functional Materials, School of Chemistry and
Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, P. R. China
S
* Supporting Information
ABSTRACT: Condensation of benzene-1,3,5-tricarbohydrazide with benzene-1,4-
dicarboxaldehyde generated a new covalent organic framework, COF-ASB (1), in
which the organic units are held together via hydrazone linkage to form porous
frameworks. COF-ASB (1) is highly crystalline and displays good chemical and
thermal stability and is permanently porous. In addition, 1 can be an ideal support
to load Ru nanoparticles (Ru NPs) to generate Ru@COF-ASB (2). The obtained
composite material is able to highly promote one-pot tandem synthesis of imine
products from benzyl alcohols and corresponding amines under solvent-free
conditions in air.
functional groups such as triazole, imine, and hydrazone
could be facilely introduced into COFs during their synthetic
processes. Therefore, COFs should meet the requirement at
this point and are the ideal solid scaffolds to support MNPs for
heterogeneous catalysis.
In this contribution, we report a heteroatom-rich COF
material COF-ASB (1) which is generated from benzene-1,3,5-
tricarbohydrazide (BTCH) and benzene-1,4-dicarboxaldehyde
(TPAL) via the Schiff base condensation reaction. The
obtained COF-ASB (1) can be an ideal support to upload Ru
NPs to generate Ru@COF-ASB (2) composite material which
can highly promote one-pot tandem synthesis of imines from
alcohols and amines in heterogeneous way under solvent-free
conditions.
INTRODUCTION
■
As an emerging class of porous crystalline solid materials,
covalent organic frameworks (COFs) exhibit potential
applications in gas adsorption and separation, sensing, catalysis,
and proton conductivity.1 As a promising alternative to MOF
materials, the robustness of COFs is improved, and they are
more stable to aqueous and organic media, and even strong
acidic or alkaline environment.2 These inherent advantages of
COFs would make them more beneficial than MOF-based
supports to upload active catalytic species, such as metal
nanoparticles (MNPs), for catalysis, especially those catalytic
reactions that are performed under relatively rigorous
conditions. As the counterpart of MOFs,3 the study of COF-
supported MNPs@COFs with heterogeneous catalytic nature,
however, has received very limited investigation.4
As one important type of MNPs, ruthenium nanoparticles
(Ru NPs) have attracted more attention owing to their
excellent catalytic performance.5 Such highly active MNPs,
however, tend to lose their catalytic activity as a consequence of
the formation of aggregates due to their high surface energy.6
The alternative way for addressing such a problem is to
immobilize MNPs in the porous supports which are decorated
with heteroatom functionalities.7 For example, nitrogen-
modified activated carbon supported Pt and Pd NPs exhibited
high catalytic performance toward the alcohol oxidation.8
Notably, COFs are formed by means of reversible covalent
bond formation reactions, and the heteroatom-involved
EXPERIMENTAL SECTION
■
Materials and Instrumentation. The reagents and solvents are
commercially available and used without further purification. The X-
ray powder diffractometer (XRPD) patterns were collected by a D8
ADVANCEX-ray with Cu Kα radiation (λ = 1.5405 Å). ICP-LC was
performed on an IRIS Interpid-II XSP and NU AttoM. High
resolution transmission electron microscopy (HRTEM) analysis was
performed on a JEOL 2100 electron microscope at an operating
voltage of 200 kV. Mass spectra analysis was performed on API 200
LC/MS system (Applied Biosystems Co. Ltd.). 1H NMR and 13C
Received: December 6, 2017
© XXXX American Chemical Society
A
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a
Scheme 1. Synthesis of 1 and 2
a
Their photographs and SEM images are inserted.
NMR spectra were recorded on Bruker Avance 400 MHz
spectrometer. Gas chromatography (GC) analysis was performed on
an Agilent 7890B GC. XPS spectra were obtained from PHI
Versaprobe II. Thermogravimetric analysis (TGA) was performed
on TGA/SDTA851e under N2 atmosphere from 50 to 650 °C. The
structural modeling was conducted with the software of Materials
Studio (ver. 5.0).
Synthesis of COF-ASB (1). A mixture of benzene-1,3,5-
tricarbohydrazide (504 mg, 2 mmol) and benzene-1,4-dicarboxalde-
hyde (402 mg, 3 mmol) and a drop of HOAc in DMF (3 mL) was
stirred at 120 °C for 72 h to generate 1 as bright yellow crystalline
solids. The obtained crystalline solids were completely washed with
water and MeOH and dried in air (Yield, 85%). IR: 3200 (m), 3065
(m), 1659 (s), 1603 (w), 1550 (s), 1256 (s), 830(w), 731(w).
Elemental Analysis (%) calcd for C7H5N2O: C, 63.15; N, 21.04; H,
3.79. Found (%): C, 62.76; N, 20.87; H, 4.04.
Synthesis of Ru@COF-ASB (2). 1 (15 mg) and HCl (0.3 mL) was
added to a CH3CN (2 mL) solution of ruthenium(III) chloride
hydrate (10 mg, 0.05 mmol). The mixture was stirred for 24 h at room
temperature. The resulting solid was isolated by centrifugation and
washed with CH2Cl2. The obtained black crystalline solids (Scheme 1)
were mixed with NaBH4 (1 mg, 0.026 mmol) in water (2 mL), and the
mixture was stirred for additional 5 h to afford Ru@COF-ASB (2) as
black crystalline solids. The obtained solids were completely washed
with water and MeOH and dried in air. IR: 3200 (m), 3065 (m), 1659
(s), 1603 (w), 1550 (s), 1256 (s), 830(w), 731(w). ICP measurement
indicated that the encapsulated amount of Ru NPs in 2 is 4.1% (mass
fraction).
Solvent-Free Oxidation of Benzyl Alcohols. A mixture of
benzyl alcohol (1 mmol) and 2 (70 mg, 5% mol Ru) was stirred at 80
°C for 24 h to afford benzaldehydes with yield 80−93% (the products
were diluted with methylene chloride and determined by GC).
Leaching Test. Ru@COF-ASB (2) was separated from the
reaction solution by centrifugation, and the reaction solution was
transferred to another reaction vial under the same conditions.
One-Pot Tandem Synthesis of Imines from Alcohols and
Amines. A mixture of benzyl alcohol (1 mmol), corresponding amine
(1.2 mmol), and Ru@COF-ASB (2) (70 mg, 5 mol % Ru) was stirred
at 80 °C for 22 h. The yields of obtained imines were determined by
GC.
dichloromethane (3.0 mL) (3 times), and dried in vacuum at 90 °C for
the next run under the same reaction conditions.
RESULTS AND DISCUSSION
■
Synthesis and Structural Analysis of COF-ASB (1) and
Ru@COF-ASB (2). As shown in Scheme 1, COF-ASB (1) was
prepared in good yield (85%) by heating the mixture of
benzene-1,3,5-tricarbohydrazide and benzene-1,4-dicarboxalde-
hyde with catalytic amount of HOAc in DMF at 120 °C for 72
h. 1 was obtained by filtration and successively washed with
water, dichloromethane, and ethanol to afford yellow powders
that were insoluble in common organic solvents and water. The
morphology of the as-prepared 1 was examined by scanning
electron microscopy (SEM), and their particle morphology was
observed (Scheme 1). Thermogravimetric analysis (TGA)
showed that no weight loss of 1 was observed until 350 °C
(Figure S1, Supporting Information).
Furthermore, COF-ASB (1) was characterized by Fourier
transform infrared (FT-IR) and 13C cross-polarization magic
angle spinning (CP-MAS) spectroscopies. The IR spectrum of
1 showed the >CO band at 1698 cm−1 of benzene-1,4-
dicarboxaldehyde disappeared after the condensation reaction.
Meanwhile the >CN− band at 1603 cm−1 that is
characteristic of the >CN− group appeared, indicating that
the acylhydrazone Schiff base linkage formed9 from the
condensation of benzene-1,3,5-tricarbohydrazide and benzene-
1,4-dicarboxaldehyde. In 1, the >CO band was observed at
1659 cm−1 while the corresponding band in the starting
material of benzene-1,3,5-tricarbohydrazide was located at 1624
cm−1. This shift could be considered as a weakening of the
>CO bonds as a result of resonance with the imine group,
which is similar to that of molecular hydrazones.9,10 In addition,
the signals at 731 and 830 cm−1 indicated that both sym-tri-
and para-substituted phenyl moieties exist in 1. Solid-state 13C
CP-MAS NMR was also used to establish the connectivity of
the COF species. The existence of the phenyl (141 ppm) and
acylhydrazone Schiff base (173, 158 ppm) groups in 1 was well
Recycle and Activation of Ru@COF-ASB (2). 2 was recovered
by centrifugation, then was washed with ethanol (3.0 mL) and
B
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Figure 1. (a) IR spectra of benzene-1,4-dicarboxaldehyde (purple), benzene-1,3,5-tricarbohydrazide (cyan), COF-ASB (1, blue), Ru(III)@COF-
ASB (red), and Ru@COF-ASB (black, 2). (b) 13C NMR of 2.
Figure 2. Left: The simulated (black line) and measured PXRD patterns of 1 (red line) and 2 (purple). Riveted refinement (blue line), and the
difference plot between measured and Rietveld-refined PXRD patterns (dark green line). Right: HRTEM images and the electron diffraction of 1.
Figure 3. (a) Crystal packing pattern viewed down the crystallographic c axis. (b) Single hexagonal unit. (c) Crystal packing pattern viewed down the
crystallographic a axis.
confirmed via the characteristic resonances, respectively (Figure
1b).
the optimized parameters of a = b = 31.823 Å and c = 3.700 Å,
α = β = 90°, and γ = 120° (residuals wRp = 5.08% and Rp =
3.86%, Supporting Information). Its typical hexagonal crystal
system is further supported by the electron diffraction (Figure
2). The calculated PXRD pattern of this hexagonal unit cell well
matches with the experimental profile, including the peak
location and intensity. As shown in Figure 2, 1 displays intense
peaks at 5.54°, 6.40°, 8.48°, and 24.05° that correspond to the
(2,−1,0), (2,0,0), (3,−2,0) and (0,0,1) planes, respectively. The
observed PXRD patterns of 1 exhibited peaks with the d
spacing of 15.93, 13.79, 10.41, and 3.70 Å, respectively. In
As revealed by its powder X-ray diffraction (PXRD) pattern
(Figure 2), COF-ASB (1) features a microcrystalline material
with a long-range structure, and no diffraction peaks related to
the substrates of benzene-1,3,5-tricarbohydrazide and benzene-
1,4-dicarboxaldehyde were observed, indicating the sole
formation of 1. The structural modeling was then conducted
with the software of Materials Studio (ver. 5.0).11 The most
probable structure of 1 was simulated, analogous to that of 1 as
a 2D eclipsed layered sheets using the space group of P6 with
C
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Figure 4. (a) XPS spectrum of 2. (b) HR-TEM image of 2. (c) N2 adsorption isotherms of 1 and 2 at 77 K. (d) The pore widths of 1 (black line)
and 2 (red line) are centered at 2.5 and 2.0 nm, respectively.
addition, the observed peak at 24.5° is correlated to the value of
the interlayer distance. The d spacing of 1 was calculated to be
3.7 Å, which is well consistent with the high-resolution
transmission electron microscope (TEM) characterization
(Figure 2).
In the full XPS spectrum of 2 (Figure 4a), the referencing of
the binding energy scale is complicated by the superposition of
the C(1s) and the Ru (3d) signals. The two bands at 280.2 and
284.4 eV can readily be assigned of Ru (0) 3d3/2 and 3d5/2
,
respectively.12 In addition, the Ru (0) 3p3/2 and 3p1/2 peaks
were also observed at 461.5 and 483.5 eV in the Ru 3p region.
All these measured values are comparable to those of
ruthenium metal, 280, 285, 461, and 483 eV for the Ru(0)
3d5/2, 3d3/2, 3p3/2, and 3p1/2, respectively.12 In addition, we
used HR-TEM to investigate the Ru NPs dispersion and size in
2. As indicated in Figure 4b, the Ru NPs in 2 were highly
dispersed with particle sizes of 2−5 nm. The atomic lattice
fringes with an interplanar spacing of 0.23 nm, which was
corresponding to the lattice spacing of (100) plane of hcp
metallic Ru.13
The AA stacking model in 1 was determined by the force-
field-based molecular mechanics calculations (Figure 3a).
Compared to AB-type staggered structure, the eclipsed model
is more energetic preferential (Figure S2, Supporting
Information). As shown in Figure 3b, the eclipsed 2D structure
contains a hexagonal structural unit, in which the opposite
Ocarbonyl···Ocarbonyl distance is ca. 3.1 nm. The close-packed 2D
layers with an interlayer distance of 3.7 Å indicated that
adjacent layers in 1 are in a weak π−π contact (Figure 3c).
Ru NPs embedded Ru@COF-ASB (2) was simply prepared
by the reduction (NaBH4, H2O, 5 h, r.t.) of Ru(III)@COF-ASB
that was obtained by impregnating of 1 in a solution of RuCl3
in MeOH at room temperature for 1 h. The color of 1 changed
from yellow to dark of 2 after the impregnation and reduction
processes (Scheme 1). The total uploaded Ru amount, as
determined by in inductively coupled plasma (ICP) measure-
ment, is up to 4.1 wt %. The EDS mapping images of Ru(III)@
COF-ASB and Ru@COF-ASB (2) indicated that the Ru
species homogeneously distributed in the COF matrix (Figures
S3−S4, Supporting Information).
The oxidation state of the Ru NPs in 2 was determined by X-
ray photoelectron spectroscopy (XPS, Figure 4a). Notably, if
Ru(III)@COF-ASB was treated by large excess amount of
NaBH4 under the given reaction conditions, the >CN- Schiff
base linkage would also be reduced, and the peak at 55 ppm in
solid-state 13C CP-MAS NMR spectrum clearly indicated the
formation of the secondary amino group (Figure S5,
Supporting Information). Therefore, the hydrazone linkage in
1 could be kept intact during the reduction process with
controlled amount of NaBH4. This selective reducing approach
would be very useful to construct many more new metal NPs-
loaded catalytic systems based on imine-linked COFs.
The porosity difference before and after Ru loading was
further supported by the gas adsorption−desorption measure-
ment. As shown in Figure 4c, N2 adsorption at 77 K revealed
absorption amounts of 357.88 and 122.66 cm3/g by COF-ASB
(1) and Ru@COF-ASB (2), respectively. The surface area
calculated on the basis of the BET model is 233.15 m2/g for 1
and 101.92 m2/g for 2. The hysteresis in some reported
microporous 2D COFs was also observed, which might be
attributed to the dynamic response of the flexible framework.2c
Part of the surface area loss and pore volume decrease can be
attributed to the embedded Ru NPs. The pore size distribution
curves, calculated from Barrett−Joyner−Halenda analysis,
showed that 1 and 2 with pore widths of ca. 2.5 (1) and 2.0
nm (2), respectively (Figure 4d). The PXRD pattern after Ru
NPs loading was well in agreement with that of 1 but with
reduced crystallinity, indicating that the structural integrity of 1
well preserved (Figure 2).
Oxidation of Benzyl Alcohol under Solvent-Free
Conditions in Air. For one-pot tandem imine synthesis
from alcohols and amines, we first examine the catalytic
behavior of Ru@COF-ASB (2) for catalytic benzyl alcohol to
benzaldehyde. The best result was observed when the benzyl
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alcohol oxidation reaction in air was carried out in the presence
of 2 (5 mol % Ru) under solvent-free conditions at 80 °C
(monitored by GC). As shown in Figure 5a, with the increase
that the doped Ru NPs in the COF-ASB matrix are responsible
for the catalytic activity (Figure S10, Supporting Information).
As a heterogeneous catalyst, the recyclability of 2 was also
examined. As shown in Figure 5b, 2 can be recycled five times.
After each catalytic run, the solid catalyst was collected by
centrifugation, washed with acetonitrile, dried at 90 °C, and
reused in the next run under the same conditions. The reaction
conversion was still up to 87% at the fifth catalytic run with
100% selectivity (Figure S11, Supporting Information). After
five runs, XPS spectrum indicated that the valence state of Ru
remains unchanged. HR-TEM image showed that the size of
the Ru NPs in 2 was basically unchanged after five runs, and the
PXRD pattern of 2 after recycling demonstrated that the COF
structural integrity and crystallinity of 1 was preserved, so 2 was
very stable during this oxidation recycling process (Figure S12,
Supporting Information).
With the optimized conditions in hand, we investigated the
scope of the 2-catalyzed oxidation reactions utilizing different
liquid benzyl alcohols. As shown in Table 1, the benzyl alcohols
Figure 5. Solvent-free oxidation of benzyl alcohol. (a) Reaction time
examination (black line) and leaching test (red line) for solvent-free
oxidation of benzyl alcohol reaction. The solid catalyst was filtrated
from the reaction solution after 4 h, whereas the filtrate was transferred
to a new vial, and reaction was carried out under the same conditions
for an additional 16 h. (b) Catalytic cycles. After each run, the catalyst
was collected by centrifugation, washed with ethanol and dichloro-
methane, and dried at 90 °C in vacuum for the next catalytic run under
the same conditions. Reaction conditions: benzyl alcohol (104 μL, 1
mmol), 2 (70 mg, 5 mol % Ru), temperature 80 °C.
Table 1. Summary of the Liquid Benzyl Alcohols Oxidation
Catalyzed by 2
in time from 2 to 25 h, the yield of benzaldehyde significantly
enhanced. It should be noted that an excellent yield of 90% was
achieved at 24 h (conversion 90%, selectivity 100%). However,
no more changes in the yield can be observed after extending
the reaction time (Figure S6, Supporting Information). In
addition, when the reactions were performed at 90 and 100 °C,
the oxidation product yields were 90 and 91%, respectively.
Also, when benzyl alcohol oxidation was carried out at 60 and
70 °C, benzaldehyde was obtained in lower 49 and 69% yields,
respectively. In view of the following condensation reaction
between amine and the in situ generated benzaldehyde, the
optimum reaction temperature of 80 °C was adopted (Figure
S7, Supporting Information). It is known that the direct
synthesis of −RCN− from amines and alcohols via one-pot
tandem reaction is challenging because the optimal reaction
conditions for the first aerobic alcohol oxidation step and the
second anaerobic condensation step largely differ from each
other. The higher temperature would be beneficial to the
aerobic alcohol oxidation but detrimental to the stability of the
co-existing amine substrate (Figure S8, Supporting Informa-
tion).
It therefore, appears that 24 h and 80 °C are the optimum
reaction time and temperature for the maximum yield of
benzaldehyde under solvent free conditions. The total number
(TON) is 18 h−1, and turnover frequency (TOF) is 0.75 h−1
under the optimized conditions. In order to show the
heterogeneous nature of 2, the hot leaching test was examined.
As shown in Figure 5a, the yield did not increase without 2 after
ignition of the oxidation reaction at 6 h (Figure S9, Supporting
Information), indicating 2 exhibited a typical heterogeneous
catalyst nature.
with electron-withdrawing nitro group showed less reactivity
and gave a relatively lower conversion (80%), whereas the
electron-donating group of methoxy-substituted benzyl alcohols
proved to be more active and furnished the desired products in
93% conversion. Notably, the reaction selectivity toward
benzaldehydes is 100% in all cases (Figure S13, Supporting
Information). Comparing this work with other catalysts for the
solvent-free selective oxidation of benzyl alcohol (Table S1,
Supporting Information), 2 exhibits excellent catalytic activity
and selectivity for benzyl alcohol oxidation.
One-Pot Tandem Synthesis of Imines from Benzyl
Alcohols and Amines. As known, imine is a very important
class of compounds in organic synthesis, biomedicine, and
materials science. As shown above, 2 is a highly efficient and
stable catalyst for benzyl alcohol oxidation under solvent-free
conditions in air. Thus, we wondered if the imine species could
be one-pot synthesized from alcohols and amines in the
presence of 2 under reaction conditions.
For this, benzyl alcohol and phenylamine amine were chosen
as model substrates. To our delight, when the mixture of benzyl
alcohol (1 mmol) and phenylamine (1.2 mmol) was stirred at
80 °C in the presence of 2 (5 mol % Ru) for 22 h (monitored
by TLC) under solvent-free conditions, the corresponding
imine product was generated in 90% yield (conversion 90%,
selectivity 100%) (Figure S14, Supporting Information). As
shown in Figure 6, the conversion began to decrease after 22 h.
The TON and TOF at 22 h for N-benzylideneaniline formation
from alcohol and amine were 18 and 0.82 h−1, respectively,
In addition, only tiny amounts of benzaldehyde (Yield, 2%)
was generated when the oxidation reaction was performed in
the presence of 1 under the optimized conditions, indicating
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Figure 6. Solvent-free one-pot tandem reaction from benzyl alcohol. (a) Reaction time examination (black line) and leaching test (red line) for
solvent free one-pot tandem synthesis of imine. The solid catalyst was filtrated from the reaction solution after 6 h, whereas the filtrate was
transferred to a new vial, and reaction was carried out under the same conditions for an additional 12 h. (b) Catalytic cycles. After each run, the
catalyst was collected by centrifugation, washed with ethanol and dichloromethane, and dried at 90 °C in vacuum for the next catalytic run under the
same conditions. Reaction conditions: Ru@COF-ASB (2) (70 mg, 5 mol % Ru), benzyl alcohol (104 μL, 1 mmol), phenylamine (109 μL, 1.2
mmol), and 80 °C.
under the optimized reaction conditions (Figure S15,
Supporting Information). Again, the heterogeneous catalytic
nature of 2 was confirmed by the hot leaching test. As shown in
Figure 6, no further reaction occurred in the absence of 2 after
ignition of the reaction at 6 h, indicating that 2 is a
heterogeneous catalyst for this one-pot tandem reaction (Figure
S16, Supporting Information).
Table 2. Summary of the One-Pot Tandem Reactions Based
on Substituted Benzyl Alcohols and Phenylamines and
Benzylamines
a
In addition, the second condensation step between
benzaldehyde and phenylamine was very fast, and the reaction
could be finished in several minutes under the given reaction
conditions with or without 2. For example, the desired N-
benzylideneaniline was obtained in 94% yield after 3 min with 2
under solvent-free condition at 80 °C, meanwhile high reaction
efficiency (3 min, 93%) was also observed in the absence of 2
under the same reaction conditions (Figure S17, Supporting
Information). Therefore, 2, as an alcohol oxidation catalyst, did
not affect and inhibit the second step of the condensation
reaction under the reaction conditions.
The recyclability of 2 was examined for this one-pot tandem
reaction. After each catalytic run, the solid catalyst of 2 was
collected by centrifugation, washed with acetonitrile, dried at 90
°C, and reused in the next run under the same conditions. As
shown in Figure 6, the conversion was still up to 88% with
100% selectivity for the fifth catalytic run (Figure S18,
Supporting Information). Notably, the size and valence of the
Ru NPs in 2 remain unchanged after five runs (Figure S19,
Supporting Information). In addition, the amount of Ru species
in 2 was examined by ICP. The result showed the amount of
Ru is 4.0%, indicating that basically no Ru species loss occurred
after five catalytic cycles. Moreover, the PXRD pattern of 2
after reused for five cycles demonstrated that the structural
integrity of 2 was well preserved (Figure S19, Supporting
Information). Therefore, 2 herein is able to tolerate relatively
rigorous reaction conditions, such as higher temperature, air
atmosphere, and relatively long reaction time. So COF-ASB (1)
is an ideal platform to support Ru NPs for this tandem reaction.
After that, we examined the scope of this one-pot tandem
reaction under the optimized reaction conditions. Table 2
summarized the results of these tandem reactions. We found
that the combination of benzyl alcohols without substituted
a
Reaction conditions: Ru@COF-ASB (2) (70 mg, 5 mol % Ru),
benzyl alcohol (1 mmol), amine (1.2 mmol), 80 °C, solvent-free, in
air, 22 h. Yields were determined by GC (Figure S20, Supporting
Information).
group or electron-donating groups with aminobenzenes
without substituent group or with electron-withdrawing groups
generally afforded the desired products in higher yields (80−
91%). However, a combination of the aminobenzene bearing
electron-withdrawing group such as −Cl with either electron-
donating or electron-withdrawing groups attached benzyl
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benzylamines. As shown in Table 2, N-benzylidenebenzyl-
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groups or without substituted groups afforded the correspond-
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electron-withdrawing groups (70−75%) (Figure S20, Support-
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CONCLUSION
■
In summary, we successfully prepared a new porous COF-ASB
(1)-supported Ru NPs catalytic composite system that was
demonstrated to be a highly efficient heterogeneous catalyst for
the one-pot tandem synthesis of imines from benzyl alcohols
and anilines and from benzyl alcohols and benzylamines. We
expect this approach will be useful for the fabrication of many
more new and attractive COF-supported meal NPs heteroge-
neous catalysts, and studies toward the synthesis of new metal
NPs-loaded COF composite catalytic heterogeneous systems
are underway.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b03077.
Additional characterization of 1 and 2, GC results for the
benzyl alcohols oxidation and one-pot syntheses of N-
benzylidenebenzylamine and N-benzylideneaniline, and
the characterization of 2 after catalysis (PDF)
AUTHOR INFORMATION
Corresponding Authors
*E-mail: gongjchen@126.com.
*E-mail: yubindong@sdnu.edu.cn.
■
ORCID
Yu-Bin Dong: 0000-0002-9698-8863
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are grateful for financial support from NSFC (grant nos.
21671122, 21475078, 21301109, 21501111) and Taishan
scholar’s construction project.
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