One-pot synthesis of Pd nanoparticle catalysts supported on N-doped carbon and application in the domino carbonylation

Article abstract of DOI:10.1021/cs400077r

In this work, we report a novel and facile procedure for a one-pot preparation of palladium nanoparticle catalysts supported on porous N-doped carbon (Pd@CN^T) by direct carbonization of palladium-N-heterocyclic carbene coordination polymer (P-Pd-NHC). This method could be conveniently extended to the synthesis of the Ni and alloy (Pd_xNi_y) nanoparticle catalysts (Ni@CN⁸⁰⁰, Pd_xNi _y@CN⁸⁰⁰). The treatment temperature played an important role on the growth and properties of the resultant M@CN^T, wherein M@CN⁸⁰⁰ carbonized at 800 C showed well-monodispersed metal nanoparticles (MNPs), graphene-like layers of the N-doped carbon supports, and strong interaction between MNPs and the support. Pd@CN⁸⁰⁰ displayed high efficiency and stable recyclability toward the domino carbonylative synthesis of pyrazole derivatives. Interestingly, its catalytic performance has been even higher than that of the representative PdCl₂(PPh ₃)₂ within six runs.

Full text of DOI:10.1021/cs400077r

Subscriber access provided by Columbia Univ Libraries
Article
One-pot synthesis of Pd nanoparticle catalysts supported on N-
doped carbon and the application in the domino carbonylation
Zelong Li, Jianhua Liu, Zhiwei Huang, Ying Yang, Chungu Xia, and Fuwei Li
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/cs400077r • Publication Date (Web): 19 Mar 2013
Downloaded from http://pubs.acs.org on March 20, 2013
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
ACS Catalysis is published by the American Chemical Society. 1155 Sixteenth Street
N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 9
ACS Catalysis
1
2
3
4
5
6
7
8
One-pot synthesis of Pd nanoparticle catalysts supported on
N-doped carbon and the application in the domino carbonyla-
tion
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Zelong Li,† ‡ Jianhua Liu,† Zhiwei Huang,† Ying Yang,† Chungu Xia*† and Fuwei Li*†
† State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Acadeꢀ
my of Sciences, Lanzhou, Gansu 730000, P. R. China
‡ University of the Chinese Academy of Sciences, Beijing, P. R. China
KEYWORDS: N-doped carbon, N-heterocyclic carbenes, supported catalysts, nanoparticles, carbonylation
ABSTRACT: In this work, we report a novel and facile procedure to one pot prepare palladium nanoparticles catalysts supported
on porous Nꢀdoped carbon (Pd@CNT) by direct carbonization of palladiumꢀNꢀheterocyclic carbene coordination polymer (PꢀPdꢀ
NHC). This method could be conveniently extended to the synthesis of the Ni and alloy (PdxNiy) nanoparticles catalysts
(Ni@CN800, PdxNiy@CN800). The treatment temperature played an important role on the growth and properties of the resultant
M@CNT, wherein M@CN800 carbonized at 800oC showed well monodispersed metal nanoparticles (MNPs), grapheneꢀlike layers
of the Nꢀdoped carbon supports and strong interaction between MNPs and the support. Pd@CN800 displayed high efficiency and
stable recyclability toward the domino carbonylative synthesis of pyrazole derivatives. Interestingly, its catalytic performance has
been even higher than that of the representative PdCl2(PPh3)2 within six runs.
synthesize nitrogenꢀdoped (Nꢀdoped) carbons, in situ doping
by using nitrogenꢀcontaining precursors can realize
1. INTRODUCTION
a
homogeneous incorporation of nitrogen into carbons.
Following such direct carbonization method, Antonietti, Dai
and their coauthors have prepared functional Nꢀdoped
carbons.20ꢀ24 These Nꢀdoped carbon materials themselves have
shown novel physicochemical properties and could be better
supports to stabilize and disperse MNPs for the postꢀ
preparation.10,12,25,26 However, to the best of our knowledge, no
oneꢀpot synthesis of MNPs catalysts supported on Nꢀdoped
carbon without using any reducing agents has ever been
reported.
Recently, the synthesis of supported MNPs as
heterogeneous catalyst for liquid phase reactions has attracted
extensive
research
interests.1ꢀ3
Impregnation
and
coprecipitation are commonly used methods to prepare these
supported catalysts, however, either the aggregation of MNPs
or the irreversible leaching of metal atoms from the supports
during the reaction will inevitably reduce their catalytic
activity and stability, which are also the limitations of the
postꢀloading methodology to the practical applications.
Additionally, the preparation of such kind of catalysts usually
needs to use excess reducing reagents such as NaBH4 and
LiAlH4 resulting inorganic wastes. Therefore, the development
of methodology to expediently synthesize active and stable
supported MNPs for liquid phase reactions is highly
desirable.1,4
Transformations of rationally synthesized molecular
compounds to materials constitute an important new direction
in both structural inorganic chemistry and materials chemistry,
which will enable possible pathways for the rational design of
materials.27 Based on this concept, in situ carbonization of
structurally defined organometallic coordination polymers
containing both nitrogen and metal atoms could possibly be an
option for oneꢀstep preparation of metalꢀsupported Nꢀdoped
carbon catalytic materials. Additionally, high carbonization
yields, certain amount of functional groups loading and
homogeneous distributions of MNPs in the carbon matrix, are
also the important key factors for the development of a
procedure to synthesize such catalytic material.23 In the last
decade, Nꢀheterocyclic carbene (NHC) metal complexes have
found wide range of applications in catalysis and material. 28,29
Nanostructured porous carbon materials have been the
popular catalytic supports due to their high surface area and
good stability.5ꢀ15 It is known that traditional carbons
(including carbon black, activated carbon, carbon nanofibers
and carbon nanotubes) are poor in functional groups, and so
their supported MNPs by ordinary impregnation often result in
aggregation or leaching of the particles in the liquid solution
because of the weak interaction between MNPs and the carbon
supports. A possible solution to enhance the catalytic
performance and the stability of such kind of catalysts is the
introduction of functional groups (e.g. nitrogen groups) on the
surface of the supports.16ꢀ19 Among the procedures used to
We herein report
a
facile oneꢀpot synthesis of
(hetero)metallic(Ni, Pd or NixPdy) nanoparticles supported Nꢀ
ACS Paragon Plus Environment

ACS Catalysis
Page 2 of 9
1
2
doped carbon catalytic materials from the corresponding
peak multiplications. High resolution mass spectra (HRMS)
(hetero)metalꢀNHC coordination polymers. Such kind of
supported catalysts displayed narrow metal size distribution,
good stability and efficient catalytic activity toward a fourꢀ
component cascade carbonylation reaction to yield
heterocyclic pyrazole.
were recorded by Bruker microTOFꢀII (ESI). Elemental
analyses were carried out on a Vario EL analyzer. Inductively
coupled plasma atomic emission spectrometry (ICPꢀAES)
was performed on a Shimadzu ICPSꢀ8100 equipment by the
chemical analysis team in RIKEN. The detection of palladium
content was carried out on an Atomic absorption spectroscopy
(AAS) and its model is 180ꢀ80. Powder Xꢀray diffraction
(XRD) measurements were performed using an X’Pert Pro
multipurpose diffractometer (PANalytical, Inc.) with Niꢀ
filtered CuKα radiation (0.15046 nm) at room temperature
from 10.0 ° to 80.0 ° (wide angle). Measurements were
conducted using a voltage of 40 kV, current setting of 40 mA,
step size of 0.02 °, and count time of 4 s. The nitrogen
adsorption and desorption isotherms at –196 oC were recorded
on an AutosorbꢀiQ analyzer (Quantachrome Instruments,
Boynton Beach, FL). Prior to the tests, samples were degassed
3
4
5
6
7
8
9
Based on our and other reported knowledge30ꢀ33, transition
metal acetate salts, such as Pd(OAc)2 and Ni(OAc)2, could
easily react with imidazolium C2ꢀH of the NHC precursor to
form a MꢀC bond, which could be a bridge to intermolecularly
link polydentate NHCs and generate a coordination polymer.
Meanwhile, Dai and coworkers have found that the nitrile arm
of an ionic liquid is a key to attain high carbon yields of the
resultant metalꢀfree carbon nitride materials.34,35 It is assumed
that a metalꢀNHC coordination polymer with functional nitrile
arms could be an ideal precursor for the oneꢀpot preparation of
metalꢀsupported Nꢀdoped carbon catalysts via high
temperature carbonization, by which the carbon, nitrogen
atoms and MNPs would be homogeneously reassembled to
form MNPs embedded Nꢀdoped carbon catalysts.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
o
at 200 C for 4 h. The specific surface areas were calculated
via the BET method in the relative pressure range of 0.05−0.3,
the singleꢀpoint pore volume was calculated from the
adsorption isotherm at
a relative pressure of 0.990.
Transmission electron microscopy and High resolution
transmission electron microscope (TEM, HRTEM)
experiments were conducted in a JEMꢀ2010 TEM with an
accelerating voltage of 300 kV. Xꢀray photoelectron
spectroscopy (XPS) analyses of the catalysts were performed
2. EXPERIMENTAL SECTION
2.1 Synthesis of P-M-NHC. A novel and tridentate
NHC precursor, [TPBAIm][NTf2]3, with functional nitrile
arms was initially prepared in high yield from readily
accessible starting materials [Scheme S1 in the Supporting
Information (SI)]. Subsequently, as shown in Scheme 1,
[TPBAIm][NTf2]3 and 1.5 equivalent of Pd(OAc)2 or
Ni(OAc)2 or their mixture with certain mole ratio were
dissolved in 10 mL of DMF with the presence of 3.6
on
a
Thermo Fisher Scientific KꢀAlpha spectrometer.
scanning calorimetry
Thermograviꢀmetric−differential
(TG−DSC) measurements were carried out on a NETZSCH
STA 449F3 thermogravimetric analyzer from room
o
o
temperature to 800 C at a rate of 10 C/min under nitrogen
atmosphere.
o
equivalent of NaOAc and were stirred at 110 C for 24 h. A
pale yellow precipitate was formed, and the precipitate was
isolated by filtration and rinsed with DMF (3 × 30 mL) and
EtOH (3 × 30 mL) to remove unreacted salts. Solvent was
2.4 Catalytic application in the domino
carbonylation. Representative Pd@CN800 (0.01 mmol),
iodobenzene (0.5 mmol), phenylacetylene (0.60 mmol),
phenyhydrazine (0.65 mmol), Et3N (1.0 mmol) and 1.5 mL of
MeOH were introduced into a 50 mL Schlenk tube with a
magnetic bar, then the glass tube was vacuumed and purged
with CO (99.99 % purity) three times before it was finally
pressurized with 1.0 atm of CO gas. Subsequently, the
o
removed by heating the material at 150 C for 24 h under
vaccum to yield the desired PꢀMꢀNHC. Taking PꢀPdꢀNHC as
an example, [TPBAIm][NTf2]3 (1.0 mmol) reacted with
Pd(OAc)2 (1.5 mmol) in the presence of NaOAc (3.6 mmol) in
o
10 mL of DMF at 110 C. Finally, 970 mg of PꢀPdꢀNHC was
isolated.
o
reaction mixture was stirred at 70 C for 6 h. After cooling to
2.2 Synthesis of M@CNT. The carbonization was
room temperature, excess CO was carefully released and the
crude product was purified by flash chromatography on silica
gel with petroleum ether/ethyl acetate (10:1) as eluent to
afford the pyrazole product.
performed under N2 atmosphere.
A certain amount of specific
PꢀMꢀNHC was introduced into a quartz tube and the
temperature was controllably ramped at a rate of 10 C minꢀ1
o
o
to a final temperature (300, 400 and 800 C), and then the
After the completion of the fresh reaction performed as
above typical procedure, the liquid reaction mixture was
seperated from Pd@CN800 catalyst through centrifugation, and
the residual solid catalyst could be reused for the next run after
addition of fresh reactants.
final temperature was maintained for 1 h to finish the oneꢀpot
synthesis of monometallic or bimetallic nanoparticle catalysts
supported Nꢀdoped porous carbon, generally named as
M@CNT, wherein CN represents Nꢀdoped carbon support and
M stands for Ni or Pd or PdxNiy, and T is the carbonization
temperature. Additionally, for the sake of comparison, the
ligand precursor [TPBAIm][NTf2]3 was also similarly
3. RESULTS AND DISCUSSION
o
carbonized at 800 C under N2 for 1 h, and the product was
named as LP800
.
The MNPs catalysts supported on Nꢀdoped carbon,
o
M@CN800 (M = Pd, Ni), carbonized at 800 C were initially
2.3 Material Characterization. NMR spectra were
prepared and their structure and morphology were
characterized by transmission electron microscopy (TEM), as
shown in Figure 1a, 1e and Figure S1, S2, the PdNPs in
Pd@CN800 and NiNPs in Ni@CN800 are well monodispersed
in different grapheneꢀlike layers of the Nꢀdoped carbon
obtained on a BRUKER DRX spectrometer operating at 400
1
MHz for H NMR and 100 MHz for 13C NMR. Chemical
shifts are reported in parts per million (ppm) down field from
TMS with the solvent resonance as the internal standard.
Coupling constants (J) are reported in Hz and refer to apparent
ACS Paragon Plus Environment

Page 3 of 9
ACS Catalysis
1
2
3
4
5
6
7
8
9
supports and possess a uniform size ditribution, which are
quite narrow with 12.3±1.1 nm for PdNPs (300 nanoparticles,
speculated that the formation of PdNPs was initiated by the
cleavage of PdꢀC bond and then Pd, C and N atoms were
assembling to grow to the optimal structured PdNPs
Figure 1b) and 3.0 ± 0.5 nm for NiNPs (Figure 1f ),
respectively. Interestingly, this facile method could not only
apply to the synthesis of monometallic MNPsꢀsupported Nꢀ
doped carbons, but also to the preparation of bimetallic
nanostructured catalytic materials by carbonization
corresponding PꢀPdxNiyꢀNHC with certain metal ratio. It is
revealed in Figure 1g, 1h and Figure S3 that the Pd80Ni20NPs
of Pd80Ni20@CN800 are also homogeneously dispersed in the
Nꢀdoped carbon matrix and its diameter is finely controlled at
around 9.0 ± 1.0 nm, which is between the diameter of
monometalic NiNPs and PdNPs. Susequently, representative
PdxNiy@CN800 with different Pd and Ni ratio could be easily
prepared in high yields. TEM analysis of Pd50Ni50@CN800 and
Pd20Ni80@CN800 in Figure S4 and S5 showed that the alloy
nanoparticles could also be well monodispersed in the
resultant Nꢀdoped carbon supports. Additionally, as presented
supported Nꢀfunctional carbon with the increasing temperature.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
in Figure 2, the Xꢀray diffraction (XRD) patterns of Ni@CN800
Pd@CN800 and PdxNiy@CN800 further proved that the
,
monometallic PdNPs, NiNPs and bimetallic PdxNiy alloy
nanoparticles have been successfully obtained. All these
characterizations indicate that the direct carbonization of
structureꢀdefined and readily synthesized metalꢀNHC
coordination polymers is a facile and general methodology to
prepare monometallicꢀ and heterometallicꢀMNPs supported Nꢀ
doping carbon materials.
Scheme 1. Synthesis of PꢀMꢀNHC and M@CNT.
To gain more information about the formation of the
nanoparticles, monometallic Pd@CNT were taken as model
samples to investigate further. Though the PdNPs loading for
Pd@CN800 was as high as 24 % estimated by atomic
absorption spectroscopy (AAS), it was observed that the
PdNPs were homogeneously embedded on the nanostructured
Nꢀdoped carbon supports from the TEM results. Furthermore,
the well dispersed small metal nanoparticles could also be
clearly seen from the STEMꢀHAADF image (Figure S1c) of
Pd@CN800. It could be calculated from the highꢀresolution
TEM (HRTEM, figure S1d) image of the Pd@CN800 that the
interplanar spacing of the PdNPs particle lattices is 0.23 nm,
which matched well with the (111) lattice spacing of faceꢀ
centered cubic (fcc) Pd. A good indication of the growth
mechanism of such kind of MNPs supported carbon catalysts
came from the differences of PdNPs size distribution and Nꢀ
doped carbon matrix morphology of Pd@CN400 and
Pd@CN800, smaller and narrower PdNPs size distribution with
8.2±0.8 nm could be obtained in Pd@CN400 (figure 1d),
however, its supports displayed an amorphous morphology
while the supporting matrix of Pd@CN800 exhibited layered
grapheneꢀlike structure (Figure 1c), which suggested that the
carbonization temperture played an crucial role in the
syntheses of these catalytic materials. Additionally, it could be
Figure 1. TEM pictures and metal nanoparticle size distribution
of: a) and b) Pd@CN800. c ) and d) Pd@CN400. e) and f)
Ni@CN800. g) and h) Pd80Ni20@CN800. i) and j) recycled catalyst
(Pd@CN800) after six runs.
The carbonization yield is also an important factor for the
material synthetic method, as shown in Table 1, the yield of
o
LP800 through carbonization of [TPBAIm][NTf2]3 at 800 C is
37 wt %, and the formation of organometallic coordination
polymer (PꢀPdꢀNHC) could effectively enhance the
carbonization yield to 58 wt %, affording structually
optimized Pd@CN800. Due to the similar manipulation
procedure, thermogravimetric analysis (TGA) could be a good
tool to detect the carbonization process of [TPBAIm][NTf2]3
ACS Paragon Plus Environment

ACS Catalysis
Page 4 of 9
1
2
3
4
5
6
7
8
and PꢀPdꢀNHC. It is revealled in Figure 3A that their
Pd@CN400 shifted to lower values, which indicated PdCx
o o
decomposition occured in two distinct steps, the first stage of
phase was formed during carbonization at 300 C and 400 C.
These phenomena were consistent with the previous reports
that the littice parameter of bulk Pd with carbon occupying
interstitial octahedral sites has increased.36ꢀ38 And when
[TPBAIm][NTf2]3 started at 337 oC, and PꢀPdꢀNHC proceeded
o
to decompose at a lower temperature (225 C) possibly due to
the initial disconnection of coordinative PdꢀOAc bonds in the
PꢀPdꢀNHC, and both of their first decomposition stage
o
enhancing the treatment temperature to 800 C under innert
o
completed untill 500 C. Their second decomposition phase
atmosphere, the interstitial carbon atoms would be expelled
o
o
were similar, ranging from 500 C to 800 C. The C, N and H
content variations of PꢀPdꢀNHC, Pd@CN400 and Pd@CN800
detected by EA are shown in Figure 3B, when temperature
from the palladium lattice to form pure PdNPs.36ꢀ38
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
o
o
increased from 400 C to 800 C, N content decreased from
7.15 to 4.45 wt% and H content decreased to 0.85 wt%. These
variations possibly indicated that the carbon nitride matrix
reconstructed to form the proper ring system to fit the
requirements of the locally graphitized structure, which is also
in accordance with the TEM results showing the carbon nitride
matrix changing from amorphous morphology for Pd@CN400
to the layered grapheneꢀlike structure of Pd@CN800. N2
adsorptionꢀdesorption isotherms for LP800, Pd@CN400 and
Pd@CN800 are given in Figure 4. Compared with Pd@CN400
,
the nitrogen sorption isotherms of Pd@CN800 and LP800
exhibit a typeꢀH2 hysteresis loop, indicating the presence of
mesoporosity. However, when the Pd nanoparticles are
introduced into Pd@CN800, its specific surface area and the
pore volume fell dramatically (Table 1).
Figure 3. A): TG curves of a): [TPBAIm][NTf2]3; b): PꢀPdꢀNHC
under N2 with a heating rate of 2 oC minꢀ1. B): C, N and H content
of PꢀPdꢀNHC, Pd@CN400, Pd@CN800 determined by elemental
analysis (EA).
Figure 4. Nitrogen sorption of (a) LP800, (b) Pd@CN400 and (c)
Figure 2. Wideꢀangle XRD patterns of PdxNiy@CN800
.
Pd@CN800
.
Table 1. Characteristics of LP800 and Pd@CNT
Xꢀray photoelectron spectroscopy (XPS) analysis was also
used to study the variation of the Pd oxidation state in the
precursor and resultant Pd@CNT catalysts. As shown in Figure
5b, the Pd 3d photoelectron spectrum of PꢀPdꢀNHC showed
two peaks around 342.8 and 337.6 eV in the 3d3/2 and 3d5/2
levels, indicating the Pd species in the polymer precursor are
Pd2+ state, which was also proved by previous XRD analysis.
Although the XPS patterns of Pd@CN300 was still dominated
by Pd2+ oxidation state, characteristic Pd0 species with 3d5/2
spinꢀorbit components at 335.0 and 335.5 ev assignable to
metallic Pd and carbonꢀdiffused PdCx surface phace,
respectively, started to be generated after heat treatment for Pꢀ
PdꢀNHC at 300 oC (Figure S6a). XPS measurment of
Pd@CN400 showed most of the Pd species presented as Pd0
nanoparticles with small amount of oxidized Pd atoms in the
Nꢀdoped carbon matrix (Figure S6b). Upon enhancing the
carbonization temperature to 800 oC, the characteristic Pd
photoelectron peaks indicated that the majority (roughly 81%
based on XPS) of the Pd species are wellꢀcrystallized Pd0
nanoparicles (Figure S6c). It was reported that the introduction
Sample
Carbonization SBET
VBJH
Yield (%)
(m2g-1)
(cm3g-1)
LP800
37
90
58
667
344
395
0.50
Pd@CN400
Pd@CN800
0.17
0.19
Figure 5a showed the XRD patterns of PꢀPdꢀNHC and its
carbonized Pd@CNT at different temperatures. PꢀPdꢀNHC
precursor only displayed a broad band at ca. 25 °, indicating
its amorphous nature and Pd2+ oxidation state of the
coordination polymer. After PꢀPdꢀNHC was carbonized to
Pd@CNT, three wellꢀresolved peaks were obversed in
Pd@CN300, Pd@CN400, and Pd@CN800, respectively. The
sharpper peaks of the XRD patterns for Pd@CN800 proved that
the highly crystalline faceꢀcenterd cubic (fcc) Pd nanoparticles
were obtained. The slightly broad peaks for Pd@CN300 and
ACS Paragon Plus Environment

Page 5 of 9
ACS Catalysis
1
2
3
4
5
6
7
8
9
of amine groups possessing electronꢀdonor properties in the
carbon carrier can stabilize highꢀdispersed Pd0 and prevented
its reꢀoxidation.39 In our case, the status of N in Pd@CN300
nanoparticles. Therefore, treatment of the organometallic
coordination polymers homogeneously containing nitrogen
and metal atoms could possibly be an alternative to realize the
high dispersion of the nitrogen and MNPs in the carbon
materials through their chemically assembling growth and thus
increase the interaction between MNPs and supports. It is
important to note that, comparing with PdCx species, the pure
Pd nanoparticles possibly show higher reactivity toward the
oxidative addtion of Pd0 onto CꢀX bond during the catalytic
transformation of aryl halide.
,
Pd@CN400 and Pd@CN800 can also be explored by XPS
analysis of N1s, as shown in Figure 6a and Figure S7, the N1s
spectra could be divided into two peaks, one peak at 398.4 eV
ascribed to pyridineꢀlike sp2 nitrogen and another 400.9 eV
peak attributed to the quaternary nitrogen.40,41 Therefore, the
pyridinic nitrogen atoms along with the quaternary nitrogen in
planar CꢀNꢀCꢀlayers in our system can stailize highꢀdispersed
Pd0 prevent efficiently the reꢀoxidation of the Pd atoms.26,39
When a nitrogen atom is doped into carbon materials, the
charge distribution of the carbon atoms will be influenced by
the neighbor nitrogen dopants.42 Hence, the C1s spectrum for
Pd@CN800 could also be deconvoluted into two peaks
centered at 284.6 and 285.8 eV, corresponding to pure
graphitic sites in the CN matrix and sp2 carbon atoms bonded
to the nitrogen inside the aromatic structure, respectively
(Figure 6b).43,44
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 6. XPS analysis of Pd@CN800: a) N1s and b) C1s.
Multicomponent domino reactions are among the most
powerful synthetic tools available because they allow rapid
access to structural variation and complexity in a single
reaction vessel without intermediary purification steps.48ꢀ50
However, those transformations are mainly achieved by the
homogeneous catalysis of a noble metal catalyst and thus a
recyclable catalyst system will promote it to be a more
competitive and economical tool, especially in the preparation
Figure 5. a) Wideꢀangle XRD pattern of Pd@CNT; b) The Pd 3d
of heterocyclic compounds. Pyrazole,
a fiveꢀmembered
XPS spectra of Pd@CNT.
heterocycle with two adjacent nitrogen atoms, has attracted
considerable interests in medicinal and coordination
In present series of Pd@CNT catalysts, strong metalꢀsupport
interaction between Pd nanoparticle and the carbon nitride
support can be speculated by the characteristic XPS peak at
335.5 eV, which could be attributed to the PdCx phase
formation45,46 and the interactions47 between Pd nanoparticles
and the carbon nitride matrix in Pd@CN300 and Pd@CN400, Pd
3d5/2 XPS peak at 335.5 eV of Pd@CN800 was exclusively
induced by the strong interaction between Pd nanoparticles
and Nꢀdoped carbon support since PdCx phase formed in
lower temperature has been transferred into metallic Pd
chemistry.51ꢀ54 Mori and coauthors55 developed
a
homogeneous
Pdꢀcatalyzed
fourꢀcomponent
coupling
carbonylation of aryl iodide, terminal alkyne and hydrazine to
yield substituted pyrazole (see Table 2), but such method
failed in the reaction with arylhydrazine. Later, Stonehouse et
al.56 disclosed another similar catalytic procedure replacing
CO gas with solid Mo(CO)6 as carbonyl resource, however,
phenylhydrazine only giving 47% yield of the corresponding
triaryl substituted pyrazole. One of the key factor of this
tandem catalytic syntheis is to develop an active Pd0 catalyst to
ACS Paragon Plus Environment

ACS Catalysis
Page 6 of 9
1
2
initiate its oxidative addition onto the aryl CꢀX bond, this
higher proportion of well dispersed metallic Pd nanoparticles
catalyst requirement matches well with the property of present
Pd@CN800, which has very high and widely dispered Pd0
metallic naniparticle proportion as well as the stability support
through the interaction with the Nꢀdoped porous carbon
materials. To verify this assumption and proceed our ongoing
interest on the Pdꢀcatalyzed carbonylation reactions,57ꢀ61 fourꢀ
component carbonylation of iodobenzene, phenylacetylene,
phenylhydrazine and CO gas was selected as a model reaction
to test the catalytic performance of the heterogeneous
Pd@CNT catalysts. Such cascade reaction would be an initial
carbonylative Sonogashira coupling between benzene iodide
and aryl alkyne to yield α, βꢀalkynyl ketone55,62, followed by
the addition and cyclic condensation with phenylhydrazine to
give the desired pyrazole product.63ꢀ66
and stronger support stabilization effect. Surprisingly, the
current heterogeneous catalytic system even presented higher
reactivity than that of the representative homogeneous
carbonylation catalyst, PdCl2(PPh3)2, which yielded 85 % of
the triphenylꢀsubstituted pyrazole (Entry 4). This is possibly
because the current cascade reaction is initiated by a Pd0
species and the homogeneous Pd2+ complex need to be
reduced to Pd0 before it can undergo the oxidative addition
onto the CꢀX bond of aryl halide. Furthermore, the present Pd
nanoparticles catalysts supported Nꢀdoped carbon displayed
good substrate tolerance, iodobenzenes and phenylacetylenes
with different electronic donating or withdrawing substituents
all worked perfectly with high isolated yields of the desirable
pyrazoles (Entries 5ꢀ12, 81ꢀ93 %). Besides phenylhydrazine,
the cascade carbonylative coupling reaction with the simple
hydrazine could also proceed efficiently, giving an 84 % yield
of the expected biarylꢀsubstituted pyrazole (Entry 13).
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table 2. One-pot four-component synthesis of pyrazoles[a].
Entry
1
catalyst
R1
H
R2
H
Yields[b] (%)
Pd@CN800
Pd@CN300
Pd@CN400
PdCl2(PPh3)2
Pd@CN800
Pd@CN800
Pd@CN800
Pd@CN800
Pd@CN800
Pd@CN800
Pd@CN800
Pd@CN800
Pd@CN800
92
36
62
83
88
81
83
93
86
92
93
88
84
2
H
H
3
H
H
4
H
H
Figure 7. Recycle of the catalyst Pd@CN800. Reaction conditions:
iodobenzene (0.5 mmol), phenylacetylene (0.60 mmol),
phenyhydrazine (0.65 mmol), Pd@CN800 (2.0 mol%), Et3N (1.0
mmol), MeOH (1.5 mL), CO (0.1 MPa), temperature (110 oC) and
reaction duration (6 h).
5
H
F
6
H
t-Bu
H
7
Cl
Cl
Cl
Me
Me
Me
H
Besides efficient catalytic acitivity, stable recyclability is
also crucial for an outstanding heterogeneous catalyst from the
viewpoint of both academic research and industrial
applications. As shown in figure 7, Pd@CN800 demonstrated
high stability and could be used at least six times by simple
centrifugation without a significant loss of its catalytic
performance. To further verify its stability, Pd concentration in
the reaction solution was determined by ICPꢀAES to be less
than 0.1 ppm, indicating that leaching of Pd into the liquid
phase is negligible. Moreover, TEM anlaysis of the reused
catalyst revealed that the dispersion and size distribution of
PdNPs did not show any obvious change after six runs (Figure
1g and 1f) comparing with the fresh catalysts (Figure 1a and
1b). As expected, the nitrogen functionalities on the carbon
matrix might act as a coordination donor ligand to tune the
electronic property of PdNPs and thus enhance its stability as
well as the catalytic activity.
8
F
9
t-Bu
H
10
11
12
13[c]
F
t-Bu
H
[a] Reaction conditions: iodobenzene (0.5 mmol), arylacetylene
(0.60 mmol), phenyhydrazine (0.65 mmol), catalyst (2.0 mol %),
Et3N (1.0 mmol), MeOH (1.5 mL), CO (1.0 atm), temperature (110
oC) and reaction duration (6 h). [b] Isolated yield. [c] Hydrazine
hydrate.
To our delight, as shown in Table 2, Pd@CN800
demonstrated efficient activity toward the oneꢀpot synthesis of
triaryl substituted pyrazole, giving a 92 % yield under 1.0 atm
pressure of CO gas (Entry 1). However, its analogues
4. CONCLUSION
In summary, a facile one pot methodology to prepare
metallic and heterometallic nanoparticles catalysts supported
on porous Nꢀdoped carbon by direct carbonization of a metalꢀ
NHC coordination polymer has been successfully developed.
Deep investigations revealed that treatment temperature played
an important role on the growth and properties of the resultant
carbonized at lower temperature, Pd@CN300 and Pd@CN400
,
only showed low to moderate activities (Entry 2 and 3). These
catalytic activity differences are consistent with their
properties of the corresponding Pd@CNT based on TEM,
XRD and XPS analysis, which revealed that Pd@CN800 has
ACS Paragon Plus Environment

Page 7 of 9
ACS Catalysis
1
2
3
4
5
6
7
8
9
M@CNT. The novel Pd catalyst, Pd@CN800, displayed high
(19) Stein, A.; Wang, Z.; Fierke, M. A., Adv. Mater. 2009, 21, 265ꢀ293.
(20) Hu, B.; Wang, K.; Wu, L.; Yu, S.ꢀH.; Antonietti, M.; Titirici, M.ꢀ
M., Adv. Mater. 2010, 22, 813ꢀ828.
activity and selectivity toward the domino carbonylative
synthesis of pyrazole derivatives from three simple substrates
and an atmosphere pressure of CO gas. Its outstanding
catalytic performance has been even higher than that of the
representative Pd2+ homogeneous catalyst within six runs.
These promising characters of M@CNT and their facile
preparative method will prompt us to prepare more (hetero)
metallic nanoparticles supported catalysts and investigate their
sustainable catalysis in the further research.
(21) Paraknowitsch, J. P.; Zhang, J.; Su, D.; Thomas, A.; Antonietti, M.,
Adv. Mater. 2010, 22, 87ꢀ92.
(22) Zhai, Y.; Dou, Y.; Zhao, D.; Fulvio, P. F.; Mayes, R. T.; Dai, S.,
Adv. Mater. 2011, 23, 4828ꢀ4850.
(23) Lee, J. S.; Wang, X.; Luo, H.; Baker, G. A.; Dai, S., J. Am. Chem.
Soc. 2009, 131, 4596ꢀ4597.
(24) Yang, W.; Fellinger, T.ꢀP.; Antonietti, M., J. Am. Chem. Soc. 2010,
133, 206ꢀ209.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(25) Li, X.ꢀH.; Wang, X.; Antonietti, M., Chem. Sci. 2012, 3, 2170ꢀ2174.
(26) Wang, Y.; Yao, J.; Li, H.; Su, D.; Antonietti, M., J. Am. Chem. Soc.
2011, 133, 2362ꢀ2365.
(27) Murugavel, R.; Walawalkar, M. G.; Dan, M.; Roesky, H. W.; Rao,
C. N. R., Acc. Chem. Res. 2004, 37, 763ꢀ774.
(28) Powell, A. B.; Suzuki, Y.; Ueda, M.; Bielawski, C. W.; Cowley, A.
H., J. Am. Chem. Soc. 2011, 133, 5218ꢀ5220.
(29) Choi, J.; Yang, H. Y.; Kim, H. J.; Son, S. U., Angew. Chem. Int.
Ed. 2010, 49, 7718ꢀ7722.
(30) Kantchev, E. A. B.; O'Brien, C. J.; Organ, M. G., Angew. Chem. Int.
Ed. 2007, 46, 2768ꢀ2813.
(31) Wittmann, S.; Schätz, A.; Grass, R. N.; Stark, W. J.; Reiser, O.,
Angew. Chem. Int. Ed. 2010, 49, 1867ꢀ1870.
(32) Fortman, G. C.; Nolan, S. P., Chem. Soc. Rev. 2011, 40, 5151ꢀ5169.
(33) Li, F.; Hu, J. J.; Koh, L. L.; Hor, T. S. A., Dalton Trans. 2010, 39,
5231ꢀ5241.
(34) Lee, J. S.; Wang, X.; Luo, H.; Dai, S., Adv. Mater. 2010, 22, 1004ꢀ
1007.
ASSOCIATED CONTENT
SUPPORTING INFORMATION
The details of the preparation of materials and their characterizaꢀ
tions, catalytic procedures and NMR spectra for the pyazole
products. This material is available free of charge via the Internet
at http://pubs.acs.org.
Corresponding Author
*Eꢀmail: fuweili@licp.cas.cn, cgxia@licp.cas.cn
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
This work was supported by the Chinese Academy of Sciences
and the National Natural Science Foundation of China (21002106
and 21133011).
(35) Lee, J. S.; Luo, H.; Baker, G. A.; Dai, S., Chem. Mater. 2009, 21,
4756ꢀ4758.
(36) Ziemecki, S. B.; Jones, G. A.; Swartzfager, D. G.; Harlow, R. L.;
Faber, J., J. Am. Chem. Soc. 1985, 107, 4547ꢀ4548.
(37) Zlemecki, S. B.; Jones, G. A., J. Catal. 1985, 95, 621ꢀ622.
(38) Krishnankutty, N.; Vannice, M. A., J. Catal. 1995, 155, 312ꢀ326.
(39) Radkevich, V. Z.; Senko, T. L.; Wilson, K.; Grishenko, L. M.;
Zaderko, A. N.; Diyuk, V. Y.,, Appl. Catal., A 2008, 335, 241ꢀ251.
(40) Khabashesku, V. N.; Zimmerman, J. L.; Margrave, J. L., Chem.
Mater. 2000, 12, 3264ꢀ3270.
REFERENCES
(1) De Rogatis, L.; Cargnello, M.; Gombac, V.; Lorenzut, B.; Montini,
T.; Fornasiero, P., ChemSusChem 2010, 3, 24ꢀ42.
(2) Molnár, A. r. d., Chem. Rev. 2011, 111, 2251ꢀ2320.
(3) Guerra, J.; Herrero, M. A., Nanoscale 2010, 2, 1390ꢀ1400.
(41) Li, X.; Wang, H.; Robinson, J. T.; Sanchez, H.; Diankov, G.; Dai,
H., J. Am. Chem. Soc. 2009, 131, 15939ꢀ15944.
(4)
Balanta, A.; Godard, C.; Claver, C., Chem. Soc. Rev. 2011, 40,
4973ꢀ4985.
(42) Zhang, L.; Xia, Z., J. Phys. Chem. C. 2011, 115, 11170ꢀ11176.
(43) SanchezꢀLopez, J. C.; Donnet, C.; Lefebvre, F.; FernandezꢀRamos,
C.; Fernandez A., J. Appl. Phys. 2001, 90, 675ꢀ681.
(44) Marton, D.; Boyd, K. J.; AlꢀBayati, A. H.; Todorov, S. S.; Rabalais,
J. W., Phys. Rev. Lett. 1994, 73, 118ꢀ121.
(45) Teschner, D.; Revay, Z.; Borsodi, J.; Havecker, M.; KnopꢀGericke,
A.; Schlogl, R.; Milroy, D.; Jackson, S. D.; Torres, D.; Sautet, P.,
Angew. Chem. Int. Ed. 2008, 47, 9274ꢀ9278.
(46) Teschner, D.; Borsodi, J.; Wootsch, A.; Revay, Z.; Havecker, M.;
KnopꢀGericke, A.; Jackson, S. D.; Schlogl, R., Science 2008, 320,
86ꢀ89.
(47) CrespoꢀQuesada, M.; Dykeman, R. R.; Laurenczy, G.; Dyson, P. J.;
KiwiꢀMinsker, L., J. Catal. 2011, 279, 66ꢀ74.
(48) Staben, S. T.; Blaquiere, N., Angew. Chem. 2010, 122, 335ꢀ338;
Angew. Chem. Int. Ed., 2010, 49, 325ꢀ328.
(49) Dong, G.; Teo, P.; Wickens, Z. K.; Grubbs, R. H., Science, 2011,
333, 1609ꢀ1612.
(50) D'Souza, D. M.; Müller, T. J. J., Chem. Soc. Rev. 2007, 36, 1095ꢀ
1108.
(5) Zlotea, C.; Cuevas, F.; PaulꢀBoncour, V. r.; Leroy, E.; Dibandjo, P.;
Gadiou, R.; VixꢀGuterl, C.; Latroche, M., J. Am. Chem. Soc. 2010,
132, 7720ꢀ7729.
(6)
Scheuermann, G. M.; Rumi, L.; Steurer, P.; Bannwarth, W.;
Mu lhaupt, R., J. Am. Chem. Soc. 2009, 131, 8262ꢀ8270.
(7) ChanꢀThaw, C. E.; Villa, A.; Katekomol, P.; Su, D.; Thomas, A.;
Prati, L., Nano Lett. 2010, 10, 537ꢀ541.
(8)
Chan, C. W. A.; Xie, Y.; Cailuo, N.; Yu, K. M. K.; Cookson, J.;
Bishop, P.; Tsang, S. C., Chem. Commun. 2011, 47, 7971ꢀ7973.
(9) Wang, W.; Wang, H.ꢀy.; Wei, W.; Xiao, Z.ꢀG.; Wan, Y., Chem. Eur.
J. 2011, 17, 13461ꢀ13472.
(10) Datta, K. K. R.; Reddy, B. V. S.; Ariga, K.; Vinu, A., Angew. Chem.
Int. Ed. 2010, 49, 5961ꢀ5965.
(11) Sun, Z.; Sun, B.; Qiao, M.; Wei, J.; Yue, Q.; Wang, C.; Deng, Y.;
Kaliaguine, S.; Zhao, D., J. Am. Chem. Soc. 2012, 134, 17653ꢀ
17660.
(12) Xu, X.; Li, Y.; Gong, Y.; Zhang, P.; Li, H.; Wang, Y., J. Am. Chem.
Soc. 2012, 134, 16987ꢀ16990.
(13) Yang, Y.; Chiang, K.; Burke, N., Catal. Today 2011, 178, 197ꢀ205.
(14) Ma, T.ꢀY.; Liu, L.; Yuan, Z.ꢀY., Chem. Soc. Rev. 2013, DOI:
10.1039/C2CS35301F.
(15) Shen, W.; Fan, W., J. Mater. Chem. A 2013, 1, 999ꢀ1013.
(16) Goettmann, F.; Fischer, A.; Antonietti, M.; Thomas, A., Angew.
Chem. Int. Ed. 2006, 45, 4467ꢀ4471.
(17) Groenewolt, M.; Antonietti, M., Adv. Mater. 2005, 17, 1789ꢀ1792.
(18) Jiang, L.; Gao, L., Carbon 2003, 41, 2923ꢀ2929.
(51) Bellarosa, L.; Diez, J.; Gimeno, J.; Lledos, A.; Suarez, F. J.; Ujaque,
G.; Vicent, C., Chem. Eur. J. 2012, 18, 7749ꢀ7765.
(52) Kuwata, S.; Ikariya, T., Chem. Eur. J. 2011, 17, 3542ꢀ3556.
(53) Liu, X. M.; McAllister, J. A.; de Miranda, M. P.; McInnes, E. J. L.;
Kilner, C. A.; Halcrow, M. A., Chem. Eur. J. 2004, 10, 1827ꢀ1837.
(54) Trofimen.S., Chem. Rev. 1972, 72, 497ꢀ509.
ACS Paragon Plus Environment

ACS Catalysis
Page 8 of 9
1
2
(55) Mohamed Ahmed, M. S.; Kobayashi, K.; Mori, A., Org. Lett. 2005,
3
4
5
6
7
8
9
7, 4487ꢀ4489.
(56) Stonehouse, J. P.; Chekmarev, D. S.; Ivanova, N. V.; Lang, S.;
Pairaudeau, G.; Smith, N.; Stocks, M. J.; Sviridov, S. I.; Utkina, L.
M., Synlett 2008, 100, 100ꢀ104.
(57) Liu, J.; Zhang, R.; Wang, S.; Sun, W.; Xia, C., Org. Lett. 2009, 11,
1321ꢀ1324.
(58) Xue, L.; Shi, L.; Han, Y.; Xia, C.; Huynh, H. V.; Li, F., Dalton
Trans. 2011, 40, 7632ꢀ7638.
(59) Lang, R.; Wu, J.; Shi, L.; Xia, C.; Li, F., Chem.Commun. 2011, 47,
12553ꢀ12555.
(60) Lang, R.; Shi, L.; Li, D.; Xia, C.; Li, F., Org. Lett. 2012, 14, 4130ꢀ
4133.
(61) Xing, Q.; Shi, L.; Lang, R.; Xia, C.; Li, F., Chem.Commun. 2012,
48, 11023ꢀ11025.
(62) Mohamed Ahmed, M. S.; Mori, A., Org. Lett. 2003, 5, 3057ꢀ3060.
(63) Wasilke, J.ꢀC.; Obrey, S. J.; Baker, R. T.; Bazan, G. C., Chem. Rev.
2005, 105, 1001ꢀ1020.
(64) Tietze, L. F., Chem. Rev. 1996, 96, 115ꢀ136.
(65) Negishi, E.ꢀi.; Copéret, C.; Ma, S.; Liou, S.ꢀY.; Liu, F., Chem.
Rev.1996, 96, 365ꢀ394.
(66) Grotjahn, D. B.; Van, S.; Combs, D.; Lev, D. A.; Schneider, C.;
Rideout, M.; Meyer, C.; Hernandez, G.; Mejorado, L., J. Org.
Chem. 2002, 67, 9200ꢀ9209.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ACS Paragon Plus Environment

Page 9 of 9
ACS Catalysis
1
2
3
4
5
6
7
8
9
A facile one pot procedure to prepare metallic
and heterometallic nanoparticles catalysts
supported on porous Nꢀdoped carbon by direct
carbonization of novel metalꢀNHC coordinaꢀ
tion polymers has been developed. The repreꢀ
sentative Pd@CN800 exhibited high activity
and stability toward the carbonylative domino
syntheses of pyrazole derivatives under mild
reaction conditions.
Zelong Li, Jianhua Liu, Zhiwei Huang,
Ying Yang, Chungu Xia* and Fuwei Li*
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Oneꢀpot synthesis of Pd nanoparticle catalysts
supported on Nꢀdoped carbon and the applicaꢀ
tion in the domino carbonylation
N
N
NTf2
N
M
M(OAc)2
M
M
800 oC
M
N2
M
M
M
NTf2
NTf2
N
M
N
N
N
N
N
M@CN800
M = Pd or Ni or both
M = Pd
NHNH2
I
CO
+
+
+
R2
R1
R2
R1
N
N
ACS Paragon Plus Environment