A triazine-based covalent organic framework/palladium hybrid for one-pot silicon-based cross-coupling of silanes and aryl iodides

Article abstract of DOI:10.1039/c5ra04433b

A triazine-based covalent organic framework (COF-SDU1) was synthesized through facile solvothermal conditions and characterized by IR, solid state ¹³C NMR, XRD, elemental analysis and BET. By a simple solution infiltration method, Pd(ii) species were successfully immobilized into COF-SDU1 due to its two-dimensional eclipsed layer-sheet structure and nitrogen-rich content. High-resolution TEM images showed the uniform loading of the Pd species into the COF-SDU1 matrix. By using this hybrid material, Pd(ii)/COF-SDU1, as a sustainable and green catalyst, one-pot cross-coupling of silanes and aryl iodides was realized with high selectivity. The catalyst can be easily recovered by a simple separation process and recycled several times without obvious loss of activity and selectivity.

Full text of DOI:10.1039/c5ra04433b

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A triazine-based covalent organic framework-palladium hybrid for
one-pot silicon-based cross-coupling of silanes and aryl iodides
a
b
a
a
a
Sha Lin, Yuxia Hou, Xiao Deng, Haoliang Wang, Shuzhuang Sun and Xiaomei
a
Zhang*
A palladium/COF hybrid material could efficiently catalyze the silicon-based
one-pot cross-coupling reaction of silanes and aryl iodides with excellent selectivity.

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Journal Name
RSCPublishing
ARTICLE
A triazine-based covalent organic framework-
palladium hybrid for one-pot silicon-based cross-
coupling of silanes and aryl iodides
Cite this: DOI: 10.1039/x0xx00000x
a
b
a
a
a
Sha Lin, Yuxia Hou, Xiao Deng, Haoliang Wang, Shuzhuang Sun and
Received 00th January 2012,
Accepted 00th January 2012
a
Xiaomei Zhang*
DOI: 10.1039/x0xx00000x
A triazineꢀbased covalent organic framework (COF-SDU1) was synthesized through a facile
1
3
www.rsc.org/
solvothermal condition and characterized by IR, solid state C NMR, XRD, elemental analysis
and BET. By a simple solution infiltration method, Pd(II) species were successfully
immobilized into COF-SDU1 due to its twoꢀdimensional eclipsed layerꢀsheet structure and
nitrogenꢀrich content. Highꢀresolution TEM images showed the uniform loading of the Pd
species into the COF-SDU1 matrix. By using this hybrid material, Pd(II)/COF-SDU1, as a
sustainable and green catalyst, a oneꢀpot crossꢀcoupling of silanes and aryl iodides was
realized with high selectivity. The catalyst can be easily recovered by a simple separation
process and recycled for several times without obvious loss of activity and selectivity.
Introduction
is complicated. To solve these problems and further optimize
siliconꢀbased crossꢀcoupling reaction with high yield and
The carbonꢀcarbon crossꢀcoupling reactions are one of the most selectivity, design and fabrication of highly effective and
crucial transformations in synthetic chemistry due to their sustainable catalysts are of great importance.
1
7
extensive application in forming novel organic compounds.
Covalent organic frameworks (COFs), as the emerging
Among them, the siliconꢀbased crossꢀcoupling reaction is an stable and porous materials, have attracted increasing interests
emerging interesting method based on its nonꢀtoxicity, high in the past ten years due to their various applications in gas
2
8
9
10
chemical stability and broad availability. To date, many types storage, chemical sensing, and catalytic supports. The
of silicon coupling reagents have been developed, such as fascinating features of COFs, such as high surface area,
3
organo(alkoxy)silanes and organosilanols. However, the porosity and structural tunability, make them to be the brilliant
synthesis of these silicon coupling reagents often need the candidates as versatile and efficient supports for various
complicated and toxic raw materials. Meanwhile, the separation catalytically active metals. In this view, as COFs were
and the purification are difficult because some of them are easy synthesized by strong covalent bonds and elaborately designed
4
to dimerize. In recent years, oxidation of organosilanes to building blocks, their chemical functionalities and structural
fabricate silicon coupling reagents catalyzed by transition metal properties could be tuned by appropriate choice of the starting
5
has been rapidly developed. This method was more green and building block and modification of the synthetic process.
facile over the above conventional routes. Because the oxides in Therefore, COFs would be more suitable for anchoring and
these reactions are water or alcohols and the only byꢀproduct is monoꢀdispersing metal ion due to their effective interplay
H . Progressively, if the synthesis of silicon coupling reagents between metal ion and the elaborately designed functional
2
and the following crossꢀcoupling could combine in oneꢀpot, groups. In fact, a few cases of COF/metal hybrids have
separation of intermediates would be avoided and the reaction exhibited excellent catalytic activity in organic reactions, such
would be green, dexterous and environmentally friendly. Rare as Suzuki coupling,10
a
,11
12
13
glycerol oxidation, nitro reduction,
10c
related work has been investigated so far. Very recently, our HeckꢀSonogashira coupling
etc. in the last few years.
group firstly realized the siliconꢀbased oneꢀpot crossꢀcoupling Inspired by the remarkably catalytic performances of the
reaction by using ordinary organosilanes as starting materials emerging COF/metal hybrids, seeking novel COF/metal
6
catalyzed by nanoporous Pd. Although excellent yield was hybrids catalysts and expanding their catalytic applications in
reached, homocoupling side product of aryl iodides inevitably more extensive reaction types have received more and more
existed. Furthermore, the preparation of nanoporous Pd catalyst attention.
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Previous investigations have revealed that the introduction of Measurements
nitrogen functionalities on the supports could increase the
1
H NMR spectra were recorded on a Bruker DPX 400
dispersion and stability of some metal nanoparticles. In this
respect, nitrogenꢀmodified activated carbons as supports for
platinum and palladium have attracted great interest in the
spectrometer. Spectra were referenced internally using the
residual solvent resonances relative to SiMe . Solidꢀstate NMR
4
experiments were performed on Bruker AVANCE III 600
1
4
liquidꢀphase oxidation of alcohols. For COFs materials,
13
spectrometer at a resonance frequency of 150.9 MHz. C CP/
1
0
a
10b,c
12
10e
Wang,
Banerjee,
Prati,
Schüth
et al. had also
MAS NMR spectra were recorded using a 4 mm MAS probe
and a spinning rate of 8 kHz. A contact time of 2 ms, a recycle
demonstrated that imineꢀbased and triazineꢀbased COFs could
immobilize and disperse palladium, gold, and platinum well.
And these COF/metal hybrids exhibited increasing catalytic
activity in organic reactions. Based on these considerations, in
present work, we design and synthesize a nitrogenꢀrich triazine
building block triꢀ(4ꢀformacylphenoxy)ꢀ1,3,5ꢀtriazine (trif)
1
13
delay of 5 s, and 4000 accumulations were used for the Hꢀ C
CP/MAS measurement. Fourier transform infrared spectra (FTꢀ
ꢀ1
IR) were recorded in KBr pellets with 2 cm resolution using
an
αALPHAꢀT spectrometer. MALDIꢀTOF mass spectra were
taken on a Bruker BIFLEX III ultraꢀhigh resolution Fourier
transform ion cyclotron resonance (FTꢀICR) mass spectrometer
(
p
Scheme 1). By a facile solvothermal reaction between trif and
ꢀphenylenediamine, a novel COF material (COF-SDU1
)
with
αꢀcyanoꢀ4ꢀhydroxycinnamic acid as matrix. Elemental
containing both imine and triazine functional groups was
obtained. This material can sturdily stabilize and regularly
monoꢀdisperse the palladium species due to COF-SDU1’s twoꢀ
dimensional eclipsed layerꢀsheet structure and nitrogenꢀrich
content. The Pd(II)/COF-SDU1, as a sustainable and green
catalyst, exhibits excellent catalytic activity and selectivity
towards the siliconꢀbased oneꢀpot crossꢀcoupling reaction of
silanes and aryl iodide. In addition, the catalyst can be reused
several times without obvious metal leaching, sintering
behaviors and evident loss of catalytic activity.
analyses were performed on an Elementar Vavio El III
elemental analyzer. Powder Xꢀray diffraction (PXRD)
measurements were carried out on a Rigaku D/masꢀ
diffractometer with a CuꢀK sealed tube ( =1.5406 Å) at
93K. Highꢀresolution transmission electron microscopy (HRꢀ
γB Xꢀray
α
λ
2
TEM) images were measured on a JEOL JEMꢀ2100 electron
microscope operated at 200 kV. Scanning electron microscopy
(
SEM) images were obtained using a JEOL JSMꢀ6700F fieldꢀ
emission scanning electron microscopy. For TEM imaging, a
drop of freshly prepared sample solution was cast onto a carbon
copper grid. For SEM imaging, C (1ꢀ2 nm) was sputtered onto
the grids to prevent charging effects and to improve the image
clarity. The Pd contents of the COF samples were determined
by inductively coupled plasma atomic emission spectroscopy
(
ICPꢀAES) analysis with an IRIS Intrepid II XRP instrument.
N2 adsorptionꢀdesorption isotherms were measured on an
ASAP 2020 (V4.01G) apparatus at 77.3 K and the surface areas
of the COF-SDU1 and Pd(II)/COF-SDU1 were calculated by
both the Brunauer–Emmett–Teller (BET) and Langmuir
method. Xꢀray photoelectron spectroscopy (XPS) was carried
out on PHI 5300 ESCA System (PerkinꢀElmer, USA). The
excitation source is Al Ka radiation. AA stacking and AB
stacking Molecular modelings and Pawley refinement of the
COF-SDU1 were carried out at the level of PBEꢀ
3
D(Grimme)/DN(4.4) in DMol software.
Scheme 1. The preparation of COF-SDU1 by the condensation
reaction between trif and pꢀphenylenediamine.
Preparation of COF-SDU1
A mixture of trif (178 mg, 0.4 mmol) and
(65 mg, 0.6 mmol) in ꢀdichlorobenzene/
5/5/1 by vol.; 16.5 mL) was sonicated at room temperature for
p
ꢀphenylenediamine
Experimental Section
o
nꢀbutanol/6M AcOH
(
General
0
.5 h. Then, the mixture was sealed in a 25ꢀmL Teflonꢀlined
stainless steel container and heated at 85 °C for 7 days. After
the temperature of container cooled down to room temperature,
a grayish yellow solid was found. This solid was isolated by
centrifugation and washed with ethyl acetate, tetrahydrofuran
Column chromatography was carried out on silica gel (Merck,
Kieselgel 60, 200ꢀ300 mesh) with the indicated eluents.
pꢀ
hydroxybenzaldehyde and ꢀphenylenediamine were obtained
p
from Sinopharm Chemical Reagent Limited Company. Triꢀ(4ꢀ
formacylphenoxy)ꢀ1,3,5ꢀtriazine (trif) was prepared according
(
THF), acetone and chloroform to remove the trapped guest
molecules, such as unreacted starting materials, then dried at 70
C under vacuum for 12 h to yield COF-SDU1 as a grayish
yellow powder (150 mg, yield 65 %); Found: C, 66.21; H,
.307; N, 17.37. Calc. for (C H ON )n: C, 72.13; H, 3.82; N,
15
to the published procedure. All other reagents and solvents
were of analytical grade and used as received without further
purification.
°
3
1
1
7
2
2
| J. Name., 2012, 00, 1-3
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ART33ICLE
ꢀ
1
1
1
1
5.30%; IR (powder, cm ): 3405, 1695, 1620, 1565, 1504,
1
3
365, 1206, 1161, 840, 809; C CP/MAS NMR (ppm): 173,
65, 154, 149, 135, 130, 122.
Preparation of Pd(II)/COF-SDU1
Pd(OAc) (15 mg, 0.067 mmol) and COF-SDU1 (100 mg)
2
were dissolved in 10 mL of dichloromethane. The mixture was
kept stirring at room temperature for 24 h. The resulting solid
was isolated by centrifugation, washed with dichloromethane,
and then dried at 70 °C under vacuum for 12 h to obtain
Pd(II)/COF-SDU1 as a grayish yellow powder (110.8 mg, 89
%
yield). The Pd content was 4.5 % as determined by ICPꢀ
AES; Found: C, 62.55; H, 3.37; N, 15.79. Calcd for
.049nPd(OAc) @(C H ON )n: C, 68.04; H, 3.61; N, 14.43%;
0
2
11
7
2
IR (powder, cmꢀ1) 3405, 2872, 1698, 1620, 1565, 1502, 1363,
1
3
1
1
206, 1161, 841, 809, 619; C CP/MAS NMR (ppm) 180,
73, 165, 154, 149, 135, 130, 122, 22.
Fig
SDU1
formacylphenoxy)ꢀ1,3,5ꢀtriazine (trif) in the region of 500ꢀ2000
.
1. FTꢀIR spectra of (a) COF-SDU1, (b) Pd(II)/COF-
Silicon-based one-pot cross-coupling reaction
,
(c) ꢀphenylenediamine and (d) triꢀ(4ꢀ
p
Pd(II)/COF-SDU1 (20 mg) and 0.2 mL of methanol were
added into 2 mL of THF solvent at room temperature. Then
phenylsilane (108 mg, 1 mmol) was added into this mixture.
After no obvious bubbles emerging, iodobenzene derivatives
ꢀ
1
ꢀ1
cm with 2 cm resolution.
(
1.1 mmol) and tetrabutylammonium fluoride (TBAF 3 mmol)
were added into the system without changing the reaction
o
vessel and then the reaction temperature was elevated to 80 C.
After the reaction was completed, the mixture was cooled to
room temperature, filtered and washed with THF. Then the
filtrate was concentrated under vacuum. The residue was
purified by silica gel chromatography with the appointed
solvent as eluent.
Results and Discussion
Synthesis of COF-SDU1 and Pd(II)/COF-SDU1
COF-SDU1 was synthesized in
solvothermal condition through the condensation of trif and
phenylenediamine in ꢀdichlorobenzene/ ꢀbutanol/6M AcOH
5/5/1, volume ratio) at 85 C for 7 days (Scheme 1).
a
good yield under
p
ꢀ
o
n
13
Fig. 2. C CP/MAS NMR spectra of (a) COF-SDU1 and (b)
o
(
Pd(II)/COF-SDU1
.
Pd(II)/COF-SDU1 was prepared by coordinating COF-SDU1
with Pd(OAc) in dichloromethane at room temperature for 24
13
2
Fourier transform infrared (FT-IR) and C CP/MAS NMR
spectra
h. Both COF-SDU1 and Pd(II)/COF-SDU1 are insoluble in
water and some polar organic solvents such as THF, acetone
and chloroform. The thermal stability of COF-SDU1 and
Pd(II)/COF-SDU1 was monitored by thermogravimetric
analysis (TGA). Under nitrogen conditions, COF-SDU1
displayed great thermal stability and can be stable up to 450 °C.
After being coordinated with Pd(OAc)2, Pd(II)/COF-SDU1
still remained high thermal stability. The degradation of this
material started at approximately 250 °C (ESI, Fig. S1†). As the
The successful formation of the COFs was assessed by Fourier
1
3
transform infrared (FTꢀIR) and
C
CP/MAS NMR
spectroscopies. As showed in the FTꢀIR spectra of the raw
materials, the carbonyl stretching band of trif (Fig. 1c) and NꢀH
stretching band of pꢀphenylenediamine (Fig. 1d) were appeared
at 1701 and 3377 cm respectively. Compared with these
starting materials, the clearly weakening absorption bonds for
C=O and NꢀH and the appearance of a new stretching vibration
band at 1620 cm attributing to the C=N bond were observed in
the FTꢀIR spectra of COF-SDU1 (Fig. 1a), clearly indicating
the successful fabrication of the COFs material. Meantime, the
ꢀ
1
o
temperature of most liquid reaction is below 250 C, the higher
ꢀ
1
thermal stability would endow Pd(II)/COF-SDU1 more
potential application in liquid phase reactions, even in gas
phase reactions.
1
3
C CP/MAS NMR spectrum provided further confirmation for
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the formation of imine bonds in the asꢀsynthesized COFs. As highly dispersed Pd(II) species on COF-SDU1 did not damage
showed in Fig. 2a, a characteristic resonance signal at 165 ppm, the crystallinity of COF-SDU1 and the integrity of COF-SDU1
which was assigned to the C=N bond, was exhibited in the asꢀ structure was retained. Next, Materials Studio software
synthesized COFs. Furthermore, the strong resonance signals of package was used to elucidate the lattice packing of COF-
1
3
C=O bond at 191 ppm displayed in the C NMR spectrum of SDU1. Two probable structures, namely a fully eclipsed model
trif (ESI, Fig. S2†) was strongly attenuated. However, the other with an AA stacking sequence (Fig. 3B) and a staggered model
1
3
17
resonance signals appeared in the C NMR spectrum of trif with an AB stacking sequence (Fig. 3C), were simulated.
1
3
was also existed in the C CP/MAS NMR spectrum of COF- Simulations of AA stacking sequence used
SDU1
Similar with COF-SDU1, FTꢀIR and C CP/MAS NMR 120 C. As can be found in Fig. 3A, the peak positions and
spectra of Pd(II)/COF-SDU1 exhibited almost identical relative intensities of AA stacking model was in good
absorption and resonance peaks with COF-SDU1 (Fig. 1b and accordance with that of the experimentally observed one. While
P
1 space group with
a = 39.694 Å, b = 39.474 Å, c = 4.838 Å and α = β = 90 C, γ =
o
.
1
3
o
2b). This result clearly indicated that the crystal structure of the PXRD pattern of AB staggered stacking mode exhibited a
COF-SDU1 was well preserved after the coordination with largely deviation from that of the experimentally observed
2
+
13
Pd . In addition, in the C CP/MAS NMR spectrum of profile. From these results, it can be speculated that COF-
Pd(II)/COF-SDU1, two additional minor resonance signals SDU1 was composed of hexagonal layers, stacking along the
were also observed at ~180 and 22 ppm, respectively. 001 plane.
10a
According to Wang’s previous work, these two signals were
assigned to the carbonyl and methyl groups of the incorporated
2+
Pd(OAc) , further implying the effective coordination of Pd
2
with COF-SDU1 materials. Further evidences for this point
were also revealed by the PXRD, SEM and TEM results, as
detailed below.
X-ray photoelectron spectra (XPS) analysis
To confirm the incorporation of palladium within COF-SDU1
,
Xꢀray photoelectron spectroscopy (XPS) was employed to
detect the Pd ions circumstance. The XPS spectra of Pd(OAc)2
and Pd(II)/COF-SDU1 (ESI, Fig. S3†), indicated that both
Fig. 3. (A) Experimental PXRD patterns of COF-SDU1 and
Pd(II)/COF-SDU1 together with the simulated patterns
according to AA and AB stacking models. (B) Views of the AA
stacking structure along c and b axes. (C) Views of the AB
stacking structure along c and b axes.
2
+
compounds show typical signals for the Pd ion. The strong
absorption peak at 338.7 and the weak absorption peak at 344.3
2
+
2+
for Pd(OAc) attributed to the Pd
and Pd 3d3/2,
2
6
3d5/2
1
respectively. In the comparation with the XPS spectrum of
Pd(OAc) the Pd signals in the XPS spectrum of Pd(II)/COF-
2
+
Morphology of the COFs materials
2
,
SDU1 take obvious shift to the lower bonding energy direction, The morphological and structural features of the asꢀsynthesized
implying the stronger coordination of Pd(OAc) with the imine both COFs were examined by scanning electron microscopy
2
10a
and triazine groups of COF-SDU1
.
(SEM) and transmission electron microscopy (TEM). Samples
were prepared by casting a drop of sample solution onto a
carbonꢀcoated grid. As could be seen from the panoramic SEM
image of COF-SDU1 (Fig. 4A), the sample was mainly
Powder X-ray diffraction patterns of COF-SDU1 and Pd/COF-
SDU1
Powder Xꢀray diffraction (PXRD) analysis was used to composed of numerous uniform spherical clusters of about 1ꢀ2
determine the crystalline structure of COF-SDU1 and
m in diameter. A close observation (Fig. 4B) revealed that
ꢀ
Pd(II)/COF-SDU1. Fig. 3A showed the both experimental and each of the individual clusters was stacked by a large amount of
simulated PXRD patterns of asꢀsynthesized COF materials. The small and dense flake with diameter of 70ꢀ90 nm. As results,
PXRD diagram of COF-SDU1 exhibited one intense and three the surface of COF-SDU1 was rather rough and rugged, which
o
o
weak peaks at 2
(
θ
= 2.71 (corresponding to 3.26 nm), 4.69
would be favor of catalytic applications. The corresponding
o
1.88 nm), 5.41 (1.63 nm) and 7.27 (1.22 nm) respectively at TEM image of COF-SDU1 (Fig. 4C) indicated that the material
the low angle range, which are ascribed to the refractions from was formed by a crowd of homogeneous small flakes within
the (100), (110), (200), and (210) planes, indicating the longꢀ tens of nanometers range, consistent with the SEM results. In
rang molecular ordering of COF-SDU1 along these planes. the highꢀresolution transmission electron microscopy (HRꢀ
When Pd(II) species was incorporated into COF-SDU1, a well TEM) image of the COF-SDU1 (Fig. 4D), the lattice fringes
maintained PXRD diagram of Pd(II)/COF-SDU1 with that of could also be observed, clearly implying the highly ordered
COF-SDU1 was observed. No other diffraction peaks crystalline structure of the asꢀsynthesized COF-SDU1. In the
attributed to the Pd(II) species can be found, implying the high SEM and TEM images of Pd(II)/COF-SDU1, it can be seen
dispersion of Pd(II) on COF-SDU1 materials. Obviously, the that the morphology of Pd(II)/COF-SDU1 was similar with
4
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COF-SDU1 (Fig. 5). Further observation of the high resolution
TEM image revealed that the surface of the spherical clusters
was covered with the 3ꢀ4 nm sized black dots attributed to Pd(0)
nanoparticles. However, from the results shown in XPS
analysis, the oxidation state of the palladium incorporated into
the COFꢀSDU1 matrix is +2. This may be a consequence of the
high energy electron beam during TEM analyses. According to
1
0
a,c,18
2+
previous research,
the loaded Pd
would get
agglomerated first then further reduced spontaneously from
Pd(II) to Pd(0) under the action of electron beam during TEM
analyses.
Fig. 6. Nitrogen adsorptionꢀ desorption isotherms of (A) COF-
SDU1 and (C) Pd(II)/COF-SDU1. Poreꢀsize distribution of (B)
COF-SDU1 and (D) Pd(II)/COF-SDU1 from nonlocal density
functional theory.
Brunauer–Emmett–Teller (BET) surface area
In order to characterize the porosity parameters of COF-SDU1
and Pd(II)/COF-SDU1, the nitrogen adsorption isotherm were
measured at 77.3 K. As showed in Fig. 6A, COF-SDU1
displayed a sharp uptake below P/P = 0.01 and a very wellꢀ
0
defined jump between P/P = 0.04 – 0.25 was also observed,
0
1
9
indicating the high crystallinity of the porous system. This
Fig. 4. (A) SEM, (B) amplifying SEM, (C) TEM and (D) highꢀ profile is assigned to a type IV isotherm, which is characteristic
resolution TEM images of COF-SDU1
.
of mesoporous nature of the material. The Brunauer–Emmett–
Teller (BET) surface area and Langmuir surface area of COF-
2
ꢀ1
SDU1 were calculated to be 1125 and 3545 m g , respectively,
which is much higher than that of the analogous COFs
2
ꢀ1 20
materials reported previously, such as CTFꢀ1 (791 m g ). The
total pore volume and pore size distribution were calculated by
using the nonlocal density functional theory (NLDFT). The
3
ꢀ1
total pore volume was estimated to be 1.20 cm g at P/P =
0
0
.98. The average pore size was mainly centered at around 2.63
nm except a few minor peaks appeared at some smaller pore
width range. This result was slight smaller than that of the
PXRD and theoretically predicted value (3.2 nm), which may
arise from the imperfect solidꢀstate stacking of the eclipsed 2D
sheets that cannot be identified by PXRD studies as reported for
8c,21
many 2D COFs and predicated by theoretical studies.
The
nitrogen adsorption isotherm of Pd(II)/COF-SDU1 also
possessed a type IV isotherm (Fig. 6C). The total pore volume
and pore size distribution calculated by NLDFT were 1.16
3
ꢀ1
cm g at P/P = 0.98 and 2.51 nm, respectively. In comparison
0
with COF-SDU1, the pore size of Pd(II)/COF-SDU1 was
nearly parallel to COF-SDU1, which indicated that the
2+
incorporation of Pd did not disturb the internal matrix of
COF-SDU1. According to the previous investigates, when
metal ions or particles were incorporated into the COFs
Fig. 5. (A) SEM, (B) amplifying SEM, and highꢀresolution
TEM images of Pd(II)/COF-SDU1 (C) before and (D) after
reused for three times.
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materials, notable decrease of the BET surface was appeared silanes and aryl iodides catalyzed by Pd(II)/COF-SDU1
.
1
0
while the pristine COF materials were maintained. However, According to the previous research, SiꢀOH bonds in
2
2
in our present case, it is amazing that the BET surface area and organosilanols could easily dimerize, which was negative to
Langmuir surface area of Pd(II)/COF-SDU1 were calculated the following noꢀisolated continuous reaction. Therefore
2
ꢀ1
to be 1052 and 3327 m g , respectively, very closer to that of organo(alkoxy)silanes were more suitable as coupling partner.
COF-SDU1. The almost unchanged high BET surface would We finally chose methanol instead of water as oxidant to avoid
undoubtedly benefit the catalytic performance of Pd(II)/COF- the generation of organosilanols intermediate. The
SDU1
.
representative reaction conditions were methanol (5 mmol),
phenylsilane (1 mmol), 4ꢀiodotoluene (1.1 mmol), TBAF (3
mmol), Pd(II)/COF-SDU1 (20 mg) and THF (2 mL). After
methanol (5 mmol), phenylsilane (1 mmol) and Pd(II)/COF-
SDU1 (20 mg) were reacted in THF at room temperature for 3
h, 4ꢀiodotoluene (1.1 mmol) and TBAF (3 mmol) were added
Catalytic activity measurement
The catalytic activity of Pd(II)/COF-SDU1 toward oneꢀpot
siliconꢀbased crossꢀcoupling reaction of silanes and aryl halides
was accessed. To realize this reaction, oxidation of
organosilanes to organo(alkoxy)silanes or organosilanols in
good yield and then effectively crossꢀcouples between the
organo(alkoxy)silanes or organosilanols with aryl halides are
necessary. Therefore, Pd(II)/COF-SDU1’s activity towards
oxidation of organosilanes to organo(alkoxy)silanes or
organosilanols was studied firstly. The reaction was tested in
THF solution (2 mL) at room temperature with phenylsilane (1
mmol), water (0.2 mL) and Pd(II)/COF-SDU1 (20 mg, the
mole ratio of Pd species versus phenylsilane was 0.0085). After
o
into this mixture. Then the system was heated up to 80 C.
After 7 h, the corresponding crossꢀcoupling product 4ꢀmethylꢀ
bipheny (2a) was obtained in 96.5 % separated yield (Table 1,
entry 1).
We also used nanoporous Pd (npꢀPd) and commercial
available Pd/C to comparatively test this reaction. The npꢀPd
5
was prepared from the reported method, and the Pd/C (5% Pd)
was purchased from Aladdin Industrial Corporation. When
using the same condition, especially the same equivalent of 4ꢀ
iodotoluene (1.1 mmol), the yield of npꢀPd was only 50% due
to the formation of homoꢀcoupling byꢀproducts. Higher yield
2
h, phenylsilanetriol (1a) was obtained with 97.8% yield (ESI,
Table S1,† entry 1). Similar with water, when methanol or
ethanol was used as oxide, the corresponding
(
91%) was obtained when we increased the dosage of 4ꢀ
iodotoluene (1.5 mmol). As for Pd/C, 93% yield was obtained
under the same condition and a small number of homoꢀcoupling
byꢀproducts were also detected. However, it was hard to realize
the good reusability of Pd/C because of the leaching problem.
When Pd/C was reused for the second time, 70% crossꢀ
coupling product was obtained.
organo(alkoxy)silanes was also obtained in high yield, (ESI,
Table S1,† entries 4ꢀ5). Then different substrates were
explored. Aromatic organosilanes, no matter containing one,
two or three H, could be activated to corresponding
organo(alkoxy)silanes or organosilanols within 2ꢀ3 h with
almost equivalent yield (ESI, Table S1,† entries 1ꢀ3), indicating
the high activity of Pd(II)/COF-SDU1 toward the oxidation of
organosilanes.
To evaluate the stability and reusability of Pd(II)/COF-
SDU1, the recycled and leaching experiments were performed.
For leaching, when the reaction was finished, Pd(II)/COF-
SDU1 was filtered from the solution. Then the filtrate was
analyzed by inductively coupled plasma atomic emission
spectroscopy (ICPꢀAES). Results showed that the leaching of
palladium was lower than the detection limits (<0.02 ppm),
indicating the heterogeneity of Pd(II)/COF-SDU1 catalyst.
Owing to the insolubility of Pd(II)/COF-SDU1 in most of
organic solvent, the catalyst can be separated easily by simple
filtration. The recovered catalyst was washed with THF and
methanol and then reused without further treatment. No
significant loss of the catalytic activity was observed (Table 1,
entries 2–4) after Pd(II)/COF-SDU1 was reused for additional
three times. The stability of the catalyst after catalytic cycles
was further confirmed by comparing the TEM images of the
catalyst after catalytic runs with the fresh prepared one. As
shown in Fig. 6D, no obvious aggregates and change in the
morphology and feature dimensions of the Pd species were
observed. The FTꢀIR and PXRD data of the reused and fresh
Pd(II)/COF-SDU1 were also consistent, which revealed the
crystallinity and the atomicꢀlevel structure of Pd(II)/COF-
SDU1 were maintained (ESI, Fig. S4 and S5†).
Next, we tested the Pd(II)/COF-SDU1’s activity towards
siliconꢀbased
crossꢀcoupling
reaction
of
the
organo(alkoxy)silanes or organosilanols with aryl iodides.
Considering the followꢀup oneꢀpot reaction, equivalent amount
of the catalyst was used. The experiment was carried out firstly
with phenyltrimethoxylsilane (1d) (1mmol), 4ꢀiodotoluene (1.1
mmol), TBAF (3 mmol) at 80 °C in THF (2 mL). After 7 h, 4ꢀ
methylbiphenyl as the crossꢀcoupling product was obtained
(
97.8% yield, ESI, Table S2†). On the other hand, no coupling
product was obtained in the absence of Pd(II)/COF-SDU1
,
indicating that the reaction was catalyzed by Pd(II)/COF-
SDU1. Similar with 1d, other organo(alkoxy)silanes or
organosilanols can also be effectively converted into 4ꢀ
methylbiphenyl (ESI, Table S2†). Moreover, no homoꢀcoupling
byproduct was detected. These results implied the high catalytic
activity of Pd(II)/COF-SDU1 for this type of crossꢀcoupling
reaction.
Based on the above experimental observations, Pd(II)/COF-
SDU1 is active for organosilane oxidation as well as siliconꢀ
based crossꢀcoupling reaction, individually. Hence, we
investigated oneꢀpot siliconꢀbased crossꢀcoupling reaction of
6
| J. Name., 2012, 00, 1-3
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Journal Name
DOI: 10.1039/C5RA044 B
ART33ICLE
Table 1 Recycle test of Pd(II)/COF-SDU1 in oneꢀpot siliconꢀ
based crossꢀcoupling reaction of phenylsilane and 4ꢀ
iodotoluene.
Conclusions
In summary, a new covalent organic framework (COF-SDU1
)
containing both imine and triazine functional groups was
prepared. The asꢀobtained COF material possessed highly
ordered crystalline structure and large surface area. Based on its
stable, porous, nitrogenꢀrich properties, COF-SDU1 can act as
the efficient support for immobilizing and monoꢀdispersing Pd
species. The Pd(II)/COF-SDU1 showed superior performance
in oneꢀpot siliconꢀbased crossꢀcoupling reaction of silanes and
aryl iodides with high selectivity. To the best of our knowledge,
this is the first report to combine the oxidation of silanes and
the next crossꢀcoupling in one system by using COF/palladium
hybrids as catalyst. Due to the particular structural properties of
COFs materials incorporation with their easy functionalization
to combine various metal, COF/metal hybrids will exhibit more
future potential in catalytic field from both academia and
industry.
a
b
c,d
Entry
Catalyst
Fresh
t1 + t2 (h)
Yield (%)
96.5
1
2
3
4
10
10
12
10
Reused 1
Reused 2
95.1
94.6
Reused 3
95.3
a
Reaction conditions: phenylsilane (1 mmol), methanol (5
mmol), Pd(II)/COF-SDU1 (20 mg, 8.5ꢀ10 mmol of Pd)
and THF (2 mL), room temperature, 3h. 4ꢀiodotoluene (1.1
ꢀ
3
b
o
c
d
mmol), TBAF (3 mmol), 80 C, 7h. Isolated yield. The
values are the average of two independent experiments.
The substrate generality under the same reaction conditions
was also studied. Aryl iodide derivatives containing both
electronꢀdonating and electronꢀwithdrawing groups were
explored. As shown in Table 2, the coupling of aryl iodides
containing the electronꢀwithdrawing group (nitro and hydroxy)
produced relatively lower efficiencies (66.5% and 68.5%
yields, Table 2, entries 5–6). However, aryl iodides containing
the electronꢀdonating group such as methyl, methoxyl and
fluoro coupled with organo(alkoxy)silanes well, gainng the
corresponding products with good to excellent yields
Acknowledgements
Financial support from the Natural Science Foundation of
China (Grant no. 21472117 and 21171106) is gratefully
acknowledged.
Notes and references
a
Prof. Dr. X. Zhang
School of Chemistry and Chemical Engineering
Shandong University
(
91.4~96.5%, Table 2, entries 1–4). Additionally, 2ꢀiodotoluene
was also attempted to this reaction, which resulted in identically
high yield with 4ꢀiodotoluene, (Table 2, entry 2). In this way,
the steric hindrance of iodobenzene derivatives could barely
influence the reaction.
2
7 South Shan Da Road, Jinan, Shandong 250100,China
Eꢀmail: zhangxiaomei@sdu.edu.cn
b
Beijing Key Laboratory for Science and Application of Functional
Molecular and Crystalline Materials, Department of Chemistry
University of Science and Technology Beijing
Beijing, 100083, China.
Table 2 Catalytic activity test of Pd(II)/COF-SDU1 in oneꢀ
pot siliconꢀbased crossꢀcoupling reaction of silanes and aryl
iodides.
†
Electronic
Supplementary
Information
(ESI)
available:
[
Thermogravimetric analysis (TGA) data of COF-SDU1 and
13
Pd(II)/COF-SDU1
; C CP/MAS NMR spectrum of trif; XPS spectrum
of Pd(OAc)
2
and Pd(II)/COF-SDU1; PXRD patterns of Pd(II)/COF-
SDU1 before and after reused first and three times;Fourier transforms
infrared (FTꢀIR) spectra of Pd(II)/COF-SDU1 before and after reused
c,d
Entry
R
2
t1a + t2b (h)
Yield (%)
96.5
ꢀ1
ꢀ1
first and three times in the region of 500ꢀ2000 cm with 2 cm resolution;
Catalytic activity test of Pd(II)/COF-SDU1 towards oxidation of
organosilanes to organo(alkoxy)silanes or organosilanols; Catalytic
activity test of Pd(II)/COF-SDU1 towards siliconꢀbased crossꢀcoupling
reaction of the organo(alkoxy)silanes or organosilanols with aryl iodides].
See DOI: 10.1039/b000000x/
1
2
3
4
5
6
4ꢀCH3
2a
2b
2c
2d
2e
2f
10
10
12
10
16
12
2ꢀCH3
93.2
4ꢀOCH3
94.2
4ꢀF
91.4
4ꢀOH
4ꢀNO2
68.5
66.5
a
1
2
3
4
L. Yin and J. Liebscher, Chem. Rev., 2007, 107, 133ꢀ173.
Y. Nakao and T. Hiyama, Chem. Soc. Rev., 2011, 40, 4893ꢀ4901.
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Reaction conditions: phenylsilane (1 mmol), methanol (5
ꢀ
3
mmol), Pd(II)/COF-SDU1 (20 mg, 8.5
and THF (2 mL), room temperature, 3h.
ꢀ10 mmol of Pd)
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This journal is © The Royal Society of Chemistry 2012
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