Combination of carbon nanotube and cyclodextrin nanosponge chemistry to develop a heterogeneous Pd-based catalyst for ligand and copper free C-C coupling reactions

Article abstract of DOI:10.1016/j.carbpol.2018.01.020

Carbon nanotubes and cyclodextrin nanosponge were hybridized and used as a support for embedding Pd(0) nanoparticles and developing a novel and heterogeneous catalyst, Pd@CDNS-CNT, for promoting ligand and copper-free Sonogashira and Heck coupling reactio

Full text of DOI:10.1016/j.carbpol.2018.01.020

Accepted Manuscript
Title: Combination of carbon nanotube and cyclodextrin
nanosponge chemistry to develop a heterogeneous Pd-based
catalyst for ligand and copper free C-C coupling reactions
Authors: Samahe Sadjadi, Majid M. Heravi, Maryam Raja
PII:
S0144-8617(18)30020-1
DOI:
Reference:
https://doi.org/10.1016/j.carbpol.2018.01.020
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Accepted date:
1-12-2017
5-1-2018
5-1-2018
Please cite this article as: Sadjadi, Samahe., Heravi, Majid M., & Raja, Maryam.,
Combination of carbon nanotube and cyclodextrin nanosponge chemistry to develop
a heterogeneous Pd-based catalyst for ligand and copper free C-C coupling
reactions.Carbohydrate Polymers https://doi.org/10.1016/j.carbpol.2018.01.020
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Combination of carbon nanotube and cyclodextrin nanosponge chemistry to
develop a heterogeneous Pd-based catalyst for ligand and copper free C-C
coupling reactions
*
a
*b
b
Samahe Sadjadi , Majid, M. Heravi , Maryam Raja
a
Gas Conversion Department, Faculty of Petrochemicals, Iran Polymer and Petrochemicals
Institute, PO Box 14975-112, Tehran, Iran. Tel.;+982148666; Fax; +982144787021-3; E-mail:
samahesadjadi@yahoo.com and s.sadjadi@ippi.ac.ir
b
Department of Chemistry, School of Science, Alzahra University, PO Box 1993891176,
Vanak, Tehran, Iran. Tel.: +98 21 88044051; fax: +982188041344; E-mail:
mmh1331@yahoo.com and m.heravi@alzahra.ac.ir
Highlight

A novel hybrid system composed of carbon nanotubes and cyclodextrin nanosponge have
been prepared and used for immobilization of Pd nanoparticle.
The synergism between carbon nanotubes and cyclodextrin nanosponge was confirmed.
A novel procedure for ligand and copper-free Sonogashira and Heck reaction is
developed.



The catalyst was highly recyclable with negligible Pd leaching.
Abstract
1

Carbon nanotubes and cyclodextrin nanosponge were hybridized and used as a support for
embedding Pd(0) nanoparticles and developing a novel and heterogeneous catalyst, Pd@CDNS-
CNT, for promoting ligand and copper-free Sonogashira and Heck coupling reactions in aqueous
media and mild reaction condition. Cyclodextrin nanosponge could contribute to catalysis
through encapsulating the reagents and transferring them in the vicinity of Pd nanoparticles. The
results established that the catalytic activity of Pd@CDNS-CNT was superior to those of
Pd@CNT, Pd@CDNS and Pd@CNT+CDNS, indicating the synergism between the components
of the hybrid system. Notably, various aryl halides including aryl iodide, bromide and chloride
were useful substrates for the coupling reactions and affording the corresponding products in
high to excellent yields in short reaction times. Moreover, the catalyst was recyclable up to six
reaction runs with negligible Pd leaching.
Keywords: Carbon nanotubes, Cyclodextrin nanosponge, Pd nanoparticles, Hybrid catalyst, C-C
coupling reactions.
1
. Introduction
Recently, the utility of cyclodextrins, CDs, as monomers for preparation of hyper-cross linked
polymers, referred as cyclodextrin nanosponges (CDNS), has been disclosed. Using various
types of cross-linking agents and CDs, synthetic procedure and the ratio of CDs to cross-linking
agents, the crystallinity, morphology and the cavities of CDNS can be tuned (Trotta, 2011;
Tejashri, Amrita&Darshana, 2013). The presence of both cavities of CDs and the cavities of 3D
polymeric network makes CDNS a proper candidate for accommodating various guest molecules
with diverse range of size, shape and polarity (Swaminathan, Pastero, Serpe, Trotta, Vavia,
Aquilano, Trotta, Zara&Cavalli, 2010; Trotta, Cavalli, Martina, Biasizzo, Vitillo, Bordiga,
Vavia&Ansari, 2011). Besides this feature, CDNS exhibited high thermal and pH stability and
2

biocompatibility (Trotta, 2011; Shende, Deshmukh, Trotta&Caldera, 2013; Torne, Darandale,
Vavia, Trotta&Cavalli, 2013; Shringirishi, Prajapati, Mahor, Alok, Yadav&Verma, 2014).
Hence, they have been widely used for developing drug delivery systems (Cavalli,
Trotta&Tumiatti, 2006; Anandam&Selvamuthukumar, 2014). Moreover, CDNS have attracted
growing attention in the field of waste water treatment and catalysis (Arkas, Allabashi,
Tsiourvas, Mattausch&Perfle, 2006; Di Nardo, Roggero, Campolongo, Valetti, Trotta&Gilardi,
2
2
009; Boscolo, Trotta&Ghibaudi, 2010; Trotta, 2011; Cintas, Cravotto, Gaudino, Orio&Boffa,
012; Cravotto, Calcio Gaudino, Tagliapietra, Carnaroglio&Procopio, 2012).
Carbon-based nanomaterials such as graphene sheets, carbon nanotubes, carbon nanofibers,
carbon spheres have been widely used as support for development of various photo, electro-
catalysts. Among carbon nanomaterials, single and multi-walled carbon nanotubes, CNTs, have
been considered as promising supports due to their outstanding properties such as high surface
area, electric conductivity, inertness, surface tune-ability through functionalization, and thermal
and chemical stability (Ombaka, Ndungu&Nyamori, 2013; Hiltrop, Masa, Maljusch, Xia,
Schuhmann&Muhler, 2016; Wang, Chu, Wang, Yang&Jiang, 2016; Fan, Fan, Wang, Xiang,
Tanga&Sun, 2017).
Heck and Sonogashira reactions are of Pd catalyzed C-C coupling reactions. The importance of
these reactions lies in their utilities for the synthesis of diverse range of complex organic
compounds, including natural products and biologically active chemicals (Lin, Huang , Wu, Mou
&Tsai 2010). Traditionally, phosphine ligands as well as copper co-catalysts have been
employed together with homogeneous Pd catalysts (Chinchilla&Nájera, 2011; Hajipour,
Shirdashtzade&Azizi, 2014). Use of homogeneous catalysts can make the recyclability of the
catalyst tedious. Hence, development of a heterogeneous Pd catalyst which could promote the C-
3

C coupling reactions in the absence of co-catalysts and ligands under green and eco-friendly
conditions has gained tremendous attention (Gholap, Venkatesan, Pasricha, Daniel,
Lahoti&Srinivasan, 2005; Thorwirth, Stolle&Ondruschka, 2010; Bakherad, 2013; Hajipour,
Shirdashtzade&Azizi, 2014; Nasrollahzadeh, Khalaj&Ehsani, 2014; Nasrollahzadeh,
Maham&Tohidi, 2014; Roya, Mondal, Banerjee, Mondal, Bhaumik&Manirul Islam, 2014; Zhou,
Wang, Jiang, Fu, Zheng, Zhang, Chen&Li, 2014; Nasrollahzadeh, Sajadi, Maham&Ehsani,
2
015; Shunmughanathan, Puthiaraj&Pitchumani, 2015; Esmaeilpour, Sardarian&Javidi, 2016;
Bakherad, Doosti, Mirzaee&Jadidi, 2017; Rathod&Jadhav, 2017). In this line, immobilization of
Pd nanoparticles supported on tubular inorganic functionalized materials such as poly(N-
isopropylacrylamide)-functionalized halloysite nanotubes (Massaro, Schembri, Campisciano,
Cavallaro, Lazzara, Milioto, Noto, Parisi&Riela, 2016) as well as organic nanotubes such as
CNT (Siamaki, Lin, Woodberry, Connell&Gupton, 2013; Ohtaka, Sansano, Nájera, Miguel-
García, Berenguer-Murcia&Cazorla-Amorós, 2015) has been reported.
In continuation of our efforts to develop novel heterogeneous catalysts (Sadjad, Heravi,
Zadsirjan&Farzaneh, 2017; Sadjadi, Heravi&Malmir, 2017; Sadjadi, Hosseinnejad,
Malmir&Heravi, 2017; Sadjadi, Malmir&Heravi, 2017), recently we focused on the utility of
CDNS for embedding catalytic active species (Sadjadi, Heravi&Daraie, 2016; Sadjadi,
Heravi&Daraie, 2017). The promising performance of CDNS can be attributed to its capability
to encapsulate the catalytic active species as well as substrates within its cavities and bringing
them in close contact to the catalytic species. On the other hand, the utility of CNT as catalyst
support has been well-established. However, one of the drawbacks of CNT is its insolubility in
aqueous media, which can limit its applications. To furnish a solution to this problem and
develop a heterogeneous catalyst with high catalytic activity in aqueous media, a novel hybrid
4

system, CDNS-CNT, was designed and used for immobilizing Pd(0) nanoparticles. As CDNS
can host the hydrophobic substrates in its cavities and bringing them in the vicinity of the
catalytic active sites, it can act as phase transfer agent. The catalytic activity of the catalyst,
Pd@CDNS-CNT, for two important C-C coupling reactions, Sonogashira and Heck reactions
(Schemes 1 and 2 in supporting information), was investigated. Moreover, the catalyst
recyclability and Pd leaching was examined.
2
. Experimental
.1. Materials and Instruments
2
The catalyst was prepared using multi-walled carbon nanotubes, MWCNTs (provided from US
NANO), (3-chloropropyl) trimethoxysilane, N-[3-(trimethoxysilyl)propyl] ethylenediamine
(AEAPTMS), diphenyl carbonate, β-cyclodextrin, Pd(OAc)
2
, NaBH
4
, HNO
3
, H
2
SO , toluene and
4
MeOH. All the chemicals were purchased from Sigma-Aldrich and used without any
purification.
The chemicals employed for studying the catalytic activity of Pd@CDNS-CNT included K
2
CO ,
3
acetylenes, aryl halides, alkenes and distilled water. All were provided from Merck and used as
received.
Characterization of Pd@CDNS-CNT was performed by using BET, XRD, FTIR, TEM, TGA,
SEM/EDS and ICP-AES. N -adsorption-desorption isotherm of Pd@CDNS-CNT was recorded
2
by using BELSORP Mini II apparatus. The catalyst and other samples subjected to BET analyses
were degassed by pre-heating at 423 K for 3 h. TEM images were obtained by using Philips
CM30300Kv field emission transmission electron microscope. To record SEM/EDS images,
Tescan instrument, using Au-coated samples and acceleration voltage of 20 kV was applied.
Thermo gravimetric analyses (TGA) was carried out by using a METTLER TOLEDO thermo
5

-1
gravimetric analysis instrument with a heating rate of 10°C min from 40 to 730°C under N
2
atmosphere. X-ray diffraction pattern of the catalyst was achieved by using a Siemens, D5000.
CuKα radiation from a sealed tube. To obtain FTIR spectra of the catalyst and other components,
PERKIN-ELMER- Spectrum 65 instrument was used. The ultrasonic apparatus used for the
synthesis of Pd@CDNS-CNT was Bandelin HD 3200 with output power of 150 W and tip TT13.
The progress of Sonogashira and C-C coupling reactions was monitored by using thin layer
chromatography (TLC) on commercial aluminum-backed plates of silica gel 60 F254, visualized,
using ultraviolet light. All the obtained coupling products were known and their formation was
confirmed by comparing their melting points, determined in open capillaries using an
Electrothermal 9100 without further corrections, and FTIR spectra with authentic samples.
1
13
Moreover, HNMR and CNMR spectra of some selected products were recorded by applying
Bruker DRX-400 spectrometer at 400 and 100 MHz, respectively.
2
.2. Synthesis of CDNS
CDNS, 1, was prepared through previously reported melting methodology (Cavalli,
Trotta&Tumiatti, 2006; Swaminathan, Pastero, Serpe, Trotta, Vavia, Aquilano, Trotta,
Zara&Cavalli, 2010; Trotta, Cavalli, Martina, Biasizzo, Vitillo, Bordiga, Vavia&Ansari, 2011).
Typically, cross-linking agent, diphenyl carbonate, (8 mmol) was heated at 100°C to melt. Then,
the monomer, β-cyclodextrin (1 mmol) was added slowly to the melted diphenyl carbonate. To
allow the cross-linking reaction between the two components to proceed, the mixture was stirred
at 120 °C for 12 h. Subsequently, the resulting precipitate was cooled to ambient temperature and
crushed. Then the product was purified by washing with acetone and distilled water. Further
6

purification was accomplished by Soxhlet extraction with EtOH for 4 h. Finally, CDNS was
dried in an oven at 80 °C overnight.
2
.3.
Amine-functionalization of CDNS: CDNS-N
CDNS (1.2 g) was suspended in dry toluene and homogenized by using ultrasonic irradiation of
power 100 W for 15 min. Then, a solution of AEAPTMS (4 mL in 20 mL dry toluene) was
added to the homogenized CDNS suspension dropwise and the resulting mixture was refluxed
overnight. Upon completion of the reaction, the white precipitate, 2, was filtered and washed
several times with dry toluene and dried at 90 °C overnight.
2
.4. Modification of CNTs surface: synthesis of CNT-OH
MWCNTs (1.5 g) was suspended in acidic mixture of H SO and HNO
C for 24 h. Then, the resulting mixture was diluted 5 times with distilled water to reach the
2
4
3
(1:1) and refluxed at 55
°
neutral pH. After filtration via centrifuge, the sample was dried in vacuum oven at 50 °C for 24
h. To reduce the acidic and other carbonyl functionalities on the surface of CNT and provide –
OH functionalities, the solid was treated with NaBH
.5. Synthesis of CNTs-Cl :
To introduce Cl functionality on the surface of CNT, CNT-OH (2.1 g) was suspended in xylene
100 mL) and then 3-chloropropyltrimethoxysilane (2.5 mL) was added. The resulting mixture
4
in methanol for 24 h.
2
(
was then refluxed for 24 h. Upon completion of the reaction, the obtained solid was washed with
methanol in order to remove the un-reacted residue of organosilane. Finally, CNT-Cl was
obtained by drying in vacuum oven at 80 °C overnight.
2
.6. Synthesis of CNT-CDNS hybrid
7

To hybridize CNT-Cl and CDNS-N, CNTs-Cl (2.25 g), CDNS-N (0.75 g) and catalytic amount
of ammonia (0.5 mL) were mixed in toluene (100 mL). The resulting mixture was then refluxed
for 24 h. CNT-CDNS hybrid was obtained by drying in vacuum oven at 110 °C.
2
.7. Immobilization of Pd nanoparticles: Synthesis of Pd@CDNS-CNT
To immobilize palladium nanoparticles, CDNS-CNT (1.2 g) was dispersed in dry toluene (15
mL) and then a solution of Pd(OAc) (0.02 g) in MeOH (10 mL) was added dropwise. The
resulting mixture was then stirred at room temperature for 8 h. To reduce Pd salt to Pd(0), a
solution of NaBH in a mixture of toluene and MeOH (10 mL, 0.2 N) was added dropwise into
2
4
the above-mentioned mixture and the suspension was mixed for 3 h. Finally, Pd@CDNS-CNT
o
was obtained by washing with MeOH and drying in oven at 60 C for 12 h, Figure 1 in
supporting information.
To prepare Pd@CNT and Pd@CDNS, the similar procedures were used except, CNT-OH and
CDNS-N were used as supports.
2
.8. Typical procedure for Sonogashira reaction
Pd@CDNS-CNT (25 mg) as catalyst, K
2
CO (2.0 mmol) as base, aryl halide (1.0 mmol) and
3
acetylene (1.2 mmol) as reagents were mixed in distilled water and then heated at 50 °C under
stirring condition. The progress of the reaction was traced by TLC. At the end of the reaction,
Pd@CDNS-CNT was filtered off and the reaction mixture was cooled to ambient temperature.
Subsequently, the organic layer was extracted with diethyl ether, purified by column
chromatography over silica gel by using-hexane/ethyl acetate (4:1) as eluent to furnish the
corresponding coupling product.
8

2
.9. Typical procedure for the Catalytic Mizoroki–Heck Reaction
Arylhalide (1.0 mmol), alkene (1.5 mmol), K CO (2 mmol) and Pd@CDNS-CNT (30 mg)
2
3
were mixed in water (4.0 mL). Then, the obtained mixture was stirred at 100°C for appropriate
reaction time. At the end of the reaction (traced by TLC), Pd@CDNS-CNT was filtered, washed
with ethanol and dried at 90°C and used for the consecutive reaction run. Then, the organic
layer, extracted with diethyl ether, was washed with H
2
O, separated and dried over anhydrous
Na SO . Purification was achieved by recrystallization.
2
4
3
. Result and discussion
.1. Catalyst characterization
3
To confirm the formation of CDNS-N, CNT-Cl, CDNS-CNT and Pd@CDNS-CNT, their FTIR
spectra were recorded and compared, Figure 1. As depicted, the FTIR spectrum of CDNS-N,
-
1
-1
Figure 1, showed the characteristic bands of CD, i.e. the bands at 3370 cm , 1621 cm , as well
-1
as a band at 1747 cm , which is the characteristic band of (-C=O) and confirm the cross-linking
-1
-1
of CDs with diphenyl carbonate. Moreover, the bands at 2926 cm and 1030 cm can be
attributed to the –CH and Si–O stretching, indicating the conjugation of AEAPTMS. The FTIR
spectrum of CNT-Cl also contains the bands at 1000 cm (Si–O stretching) and 2921 cm (–CH
2
-1
-1
2
stretching), implying the successful attachment of 3-chloropropyltrimethoxysilane on the surface
of CNT. The FTIR spectra of both CDNS-CNT and Pd@CDNS-CNT exhibited the characteristic
bands of CDNS-N and CNT, confirming the successful formation of hybrid system. Comparing
the FTIR spectra of CDNS-CNT and Pd@CDNS-CNT, showed that the intensities of the bands
of the latter were slightly lower than those of the former. This can be indicative of Pd
nanoparticle incorporation.
9

Figure 1. The FTIR spectra of CDNS-N, CNT-Cl, CDNS-CNT, Pd@CDNS-CNT
The XRD patterns of CNT-F, CDNS-CNT and Pd@CDNS-CNT are shown in Figure 2. The
XRD pattern of CNT-F exhibited the characteristic peaks at 2θ = 22°, 23.4°, 26°, 31°, 34°, 37°,
4
3°, 46° and 52°. The XRD pattern of CDNS-CNT showed the characteristic bands of CNT-F as
well as broad halo 2θ = 20°, which can be assigned to CDNS. The XRD pattern of the catalyst is
similar to that of CDNS-CNT and no characteristic peaks for Pd(0) nanoparticles was observed.
According to the literature, this issue can be due to the low amount of Pd loading (as it was
confirmed by ICP-AES analysis) and high distribution and small particle size of Pd nanoparticles
(Mallik, Dash, Parida&Mohapatra, 2006).
10

Figure 2. The XRD pattern of CNT-F, CDNS-CNT and Pd@CDNS-CNT
To elucidate the morphology of CDNS-N, CDNS-CNT and Pd@CDNS-CNT and study the
effect of hybridization with CDNS and incorporation of Pd, the SEM images of CDNS-N,
CDNS-CNT and Pd@CDNS-CNT were recorded and compared, Figure 3. CDNS-N, Figure 3-
A-1, exhibited the small particulates packed together to form small aggregates. The morphology
of CDNS-CNT hybrid (Figure 3-A-2), however, is totally different. In the hybrid system, the
carbon nanotubes are clearly observable and it can be seen that the CNT and CDNS intertwined
to form aggregates. Although the SEM images of CDNS-CNT and Pd@CDNS-CNT are almost
similar, it can be detected that incorporation of Pd nanoparticles (Figure 4-A3 and 4) can slightly
induce more aggregation. In Figure 3-A-5 the EDS analysis of the catalyst is illustrated. As
shown, the incorporation of Pd nanoparticles (the presence of Pd atom) can be confirmed. The
presence of Si, C, N and O atoms can prove the functionalization of CDNS and CNT with
organosilanes. Moreover, the observation of C and O can be attributed to the CDNS component.
11

Notably, EDS solely was not adequate for confirming the formation the catalyst. Hence, the
structure of Pd@CDNS-CNT was confirmed by other analyses.
12

A
13

B
Figure 3. A: SEM images of A: CDNS, B: CDNS-CNTC and D: Pd@CDNS-CNT, E: EDS
analysis of Pd@CDNS-CNT, B: TEM images of Pd@CDNS-CNT
The morphology of the catalyst was also studied by TEM. The TEM images of Pd@CDNS-CNT
are depicted in Figure 3-B. As shown, the carbon nanotubes are covered with CDNS in some
parts. Moreover, the black spots can be attributed to the Pd nanoparticles. Using TEM analysis,
the average size of Pd nanoparticles were calculated to be ~10 nm.
To measure the amount of Pd nanoparticles on Pd@CDNS-CNT, the catalyst was subjected to
ICP-AES analysis. For preparing the sample for analysis, Pd@CDNS-CNT was fully digested in
concentrated acidic solution of HCl and HNO
3
and the extract was analyzed by ICP-AES. The
result revealed that the content of Pd nanoparticles was about 0.5 w/w %.
14

In the next step, the catalyst was subjected to the BET analysis. Nitrogen adsorption–desorption
isotherm of Pd@CDNS-CNT, Figure 2 in supporting information, corresponds to the type II
nitrogen adsorption–desorption isotherm with H3 hysteresis loops (Yuan, Southon, Liu, Green,
Hook, Antill&Kepert, 2008), indicating the porous nature of Pd@CDNS-CNT. Notably, the
nitrogen adsorption–desorption isotherm of the catalyst is different from that of CDNS, Figure 3
in supporting information.
The BET analyses of Pd@CDNS-CNT and CDNS-CNT established that the specific surface area
2
-1
2 -1
of CDNS-CNT (32.9 m g ) reduced to 29.2 m g upon incorporation of Pd nanoparticles. This
observation was consistent with the hypothesis that Pd nanoparticles located on the surface of the
hybrid system. The average pore diameter of CDNS-CNT exhibited a slight increase upon
incorporation of Pd nanoparticles.
Next, thermal stability of Pd@CDNS-CNT was investigated by TGA analysis of Pd@CDNS-
CNT, Figure 4. As depicted, the catalyst exhibited several weight losses. The first one occurring
below 150 °C, can be attributed to the loss of water molecules. According to the literature
(Sadjadi, Heravi&Daraie, 2017), the weight loss observed at about 340 °C can be assigned to the
degradation of CDNS. To further confirm this issue and also estimate the weight percent of
AEAPTMS, the thermogram of CDNS-N was also obtained, Figure 4. It was shown that CDNS-
N exhibited three weight losses in the range of 120-340 °C. The first weight loss can be
attributed to the loss of water, the second one can be due to loss of AEAPTMS and the last one
can be assigned to the degradation of CDNS. Using this thermogram the content of AEAPTMS
was estimated to be about 3 w/w%. It was also confirmed that AEAPTMS degraded before 350
°
C.
15

Figure 4. The TGA analyses of CDNS-N, CNT-Cl and Pd@CDNS-CNT
In the thermogram of the catalyst another weight loss was observed at about 370 °C. To elucidate
whether it can be attributed to the loss of functionalities on the CNT, the thermogram of CNT-Cl
was recorded, Figure 4. Besides loss of water, three more weight losses were observed in the
range of 350- 620 °C in the thermogram of CNT-Cl. According to the literature, the weight loss
at 620 °C, can be due to the decomposition of CNT (Lehman, Terrones, Mansfield,
Hurst&Meunier, 2011). The other losses can be due to the degradation of functionalities on
CNT. The percent of these functionalities were estimated to be about 15 w/w%.
The last weight loss in the thermogram of the catalyst was observed at 623 °C. As described
above, this can be due to the oxidation of CNT. Using comparing the thermograms, the content
of CDNS in the catalyst was calculated to be about 12 w/w%.
3
.2. Catalytic activity
16

The catalytic activity of Pd@CDNS-CNT was examined. Considering the importance of
developing an efficient and eco-friendly procedure for C-C coupling reactions, Sonogashira and
Heck coupling reactions were targeted as model organic transformations. Initially, the reactions
of iodobenzene with acetylene and styrene were selected as model Sonogashira and Heck
reactions respectively. The efficiency of Pd@CDNS-CNT for promoting these two model
reactions in the absence of copper co-catalyst and ligand in the aqueous media was studied.
Gratifyingly, these two reactions could proceed in the presence of catalytic amount of the
catalyst and K
2
CO to afford the corresponding model products in high yields, Table 1 in
3
supporting information. Motivated by these results, Sonogashira and Heck reactions were
optimized by altering the reaction variables, i.e. reaction temperature, catalyst amount, solvent
and type of the applied base, and investigating their effects on the yield of desired products,
Tables 1 and 2 in supporting information. The results showed that the best solvent and base for
both reactions were water and K
2
CO respectively. However, the Heck coupling reaction
3
required more amount of the catalyst and elevated reaction temperature compared to Sonogashira
reaction. More precisely, Sonogashira reaction could proceed at 50 °C, while the optimum
temperature for Heck reaction was 100 °C. Moreover, the optimum amount of the catalyst for
Sonogashira and Heck reactions were 25 and 30 mg respectively.
Generality of the developed procedures for Sonogashira and Heck coupling reactions was
examined by using various alkenes, alkyenes and aryl halides with electron withdrawing and
electron donating groups, Table 3 in supporting information. It was found that all the reagents
were useful substrates and afford the corresponding products in high to excellent yields. As
expected, in the case of using less reactive aryl chlorides and bromides, lower yields were
obtained in longer reaction times compared to aryl iodide. Moreover, reagents with steric
17

hindrance led to lower yields. In the case of Sonogashira coupling reaction, use of aromatic
alkenes resulted in higher yields compared to aliphatic ones.
To elucidate whether CDNS can contribute to the catalysis, Pd@CNT was synthesized, see
experimental section, and used as a catalyst for promoting the model Sonogashira and Heck
coupling reactions. The comparison of the catalytic activity of Pd@CDNS-CNT and Pd@CNT,
Table 1, established the superior catalytic activity of the former. This observation confirmed the
contribution of CDNS to catalysis. According to the literature (Swaminathan, Pastero, Serpe,
Trotta, Vavia, Aquilano, Trotta, Zara&Cavalli, 2010; Trotta, 2011), the role of CDNS in
catalysis can be explained based on the potential of CDNS for encapsulation of the substrates in
its cavities and bringing them in the vicinity of Pd nanoparticles.
Next, the possibility of the synergistic effect between CDNS and CNT was investigated. Initially,
the effect of co-addition of CDNS in the Pd@CNT-catalyzed model Sonogashira and Heck
reactions was investigated. More precisely, the model reactions were performed in the presence
of Pd@CNT and a catalytic amount of CDNS (Pd@CDNS+CNT), Table 1. The result showed
that in the case of use of Pd@CNT, co-addition of CDNS can improve the yield of the products.
However, the comparison of the effect of co-addition of CDNS and its inclusion in a single
composite on the catalytic activity, i.e. comparison of the catalytic activity of Pd@CDNS+CNT
with Pd@CDNS-CNT, established the superior catalytic activity of the latter. This observation
indicates the synergistic effects between two components.
In the following, the catalytic activity of Pd@CDNS was investigated and compared with those
of Pd@CNT and Pd@CDNS-CNT, Table 1. It was found that the catalytic activity of these
catalysts increased in the following order: Pd@CDNS-CNT> Pd@CNT> Pd@CDNS.
18

Finally, to compare the efficiency of Pd@CDNS-CNT for promoting coupling reactions with
those of previously reported catalysts, the yields of the model Sonogashira and Heck reactions
under Pd@CDNS-CNT catalysis and previously described condition was compared with some of
catalysts and conditions reported in the literature, Table 4 in supporting information. It was
found that using Pd@CDNS-CNT as catalysts comparative or higher yields of the products could
be achieved in shorter or comparative reaction time with no need to toxic or harmful co-catalyst,
ligand, or base.
Table 1. Comparison of catalytic activity of the present catalyst with Pd@CNT and
Pd@CNT+CDNS in the Sonogashira coupling reaction of iodobenzene and phenyl and Heck
coupling reaction of iodobenzene and methyl acrylate
Yield
%)
Sonogashira reaction
Time
(h)
Entry
Catalyst
Reaction conditions
[Ref]
(
1
2
Pd@CDNS
Pd@CNT
H
H
2
O/ K
O/ K
2
CO
CO
3
/ 50 °C
/ 50 °C
86
2
This work
This work
2
2
3
88
1.40
H
H
2
O/ K
O/ K
2
2
CO
CO
3
3
/ 50 °C
/ 50 °C
This work
This work
3
4
Pd@CNT+CDNS
Pd@CDNS-CNT
90
93
1.30
1.20
2
Heck reaction
5
6
Pd@CDNS
Pd@CNT
H
H
2
2
O/ K
O/ K
2
2
CO
3
/ 100 °C
/ 100 °C
85
88
2.50
2.40
This work
This work
CO
CO
CO
3
3
3
H
H
2
2
O/ K
O/ K
2
2
/ 100 °C
/ 100 °C
This work
This work
7
8
Pd@CNT+CDNS
Pd@ CDNS-CNT
92
94
2.25
2.10
3
.3. Catalyst recyclability
19

In the following, the recyclability of Pd@CDNS-CNT was investigated. To this purpose, the
yields of the model Sonogashira and Heck products, catalyzed by fresh Pd@CDNS-CNT, were
compared with the yields obtained through using recycled catalysts. More precisely, upon
completion of the first reaction run, the catalyst was recovered by simple filtration and then
washed, dried, see experimental section, and subjected to the next reaction run. This recycling
was performed up to six reaction cycles, Figure 5, and the yields of the model products were
compared. The results established that the catalyst could be successfully recycled for six
consecutive reaction runs with only 10% loss of the catalytic activity.
To investigate the effect of recycling of the catalyst on the Pd leaching, Pd content after each
reaction run was measured, Figure 5. The results established that this value up to third recycling
was negligible. Upon recycling for forth to sixth runs, slight Pd leaching was detected.
20

Figure 5. The yields Sonogashira model reaction (a) and Heck model reaction (b) upon recycling
of the catalyst and the Pd content in the catalyst in each consecutive reaction run.
To elucidate the stability of Pd@CDNS-CNT upon recovery and recycling, the FTIR spectra of
fresh and recycled Pd@CDNS-CNT were recorded and compared, Figure 4 in supporting
information. The comparison of two spectra can clearly confirm their similarity, indicating that
Pd@CDNS-CNT preserved its structure upon recycling and did not collapse or destruct through
recycling.
Finally, to elucidate the effect of recycling on the morphology of Pd@CDNS-CNT, the SEM and
TEM images of recycled catalyst was recorded, Figure 6, and compared with those of fresh
Pd@CDNS-CNT. As depicted, the SEM images of both fresh and recycled catalysts are similar.
The comparison of TEM images also showed the similarity of the morphologies of both fresh
and recycled catalysts. However, a slight aggregation was observed. Hence, the slight decrease in
the catalytic activity up to six reaction runs can be attributed to both slight Pd leaching and
aggregation of Pd nanoparticles upon recycling.
21

Figure 6. SEM and TEM images of the recycled catalyst.
Conclusion
Combining the capability for CDNS to form inclusion complex with substrate and the
outstanding features of CNT as catalyst support, a novel hybrid system, CDNS-CNT, was
designed and prepared through reaction of CDNS-N and CNT-Cl. The resulting CDNS-CNT was
applied as a support for immobilization of Pd(0) nanoparticles. The obtained catalyst,
Pd@CDNS-CNT, was characterized and used for promoting Heck and Sonogashira coupling
reactions in aqueous media.
The contribution of CDNS in catalysis was through accommodation of the organic reagent into
its hydrophobic cavities and bringing them in the vicinity of the catalytic active sites. On the
other hand, the hydrophilic nature of the CDNS, which stems from the presence of hydroxyl
groups on the surface of CDs monomers, can allow the reaction proceed in aqueous media.
Moreover, comparison of the catalytic activities of the catalyst with those of the control samples,
22

i.e. Pd@CDNS, Pd@CNT and Pd@CNT+CDNS confirmed the superior catalytic activity of the
catalyst, indicating the synergism between CDNS and CNT. Notably, Pd@CDNS-CNT exhibited
high recyclability (up to six reaction runs) with low Pd leaching and loss of the catalytic activity.
The cauterization of the reused catalyst showed that the catalyst was stable upon recycling.
However, recycling could cause slight aggregation.
Acknowledgements
The authors appreciate partial financial supports from Iran Polymer and Petrochemical Institute
and Alzahra University. MMH is also thankful to Iran National Science Foundation for the
Individual given grant. The contribution of Mrs. Malmir for performing the catalytic tests are
fully appreciated.
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