Pd(0) nanoparticles immobilized on multinitrogen functionalized halloysite for promoting Sonogashira reaction: studying the role of the number of surface nitrogens in catalytic performance

Article abstract of DOI:10.1080/00958972.2018.1554214

Halloysite nanoclay, Hal, was amine-functionalized and subsequently reacted with 2,4,6-trichloro-1,3,5-triazine, TCT, and ethylenediamine, EDA, to provide multinitrogen containing functionality on the surface of Hal. The resulting surface-modified Hal, Ha

Full text of DOI:10.1080/00958972.2018.1554214

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Pd(0) nanoparticles immobilized on multi-
nitrogen functionalized Halloysite for promoting
Sonogashira reaction: Studying the role of
the number of surface nitrogens in catalytic
performance
Samahe Sadjadi, Majid M. Heravi, Baharak Masoumi & Shaghayegh Sadat
Kazemi
To cite this article: Samahe Sadjadi, Majid M. Heravi, Baharak Masoumi & Shaghayegh Sadat
Kazemi (2018): Pd(0) nanoparticles immobilized on multi-nitrogen functionalized Halloysite for
promoting Sonogashira reaction: Studying the role of the number of surface nitrogens in catalytic
performance, Journal of Coordination Chemistry, DOI: 10.1080/00958972.2018.1554214
To link to this article: https://doi.org/10.1080/00958972.2018.1554214
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Pd(0) nanoparticles immobilized on multi-nitrogen functionalized Halloysite
for promoting Sonogashira reaction: Studying the role of the number of
surface nitrogens in catalytic performance
SAMAHE SADJADI†, MAJID M. HERAVI1‡, BAHARAK MASOUMI‡ and
SHAGHAYEGH SADAT KAZEMI‡
†
Gas Conversion Department, Faculty of Petrochemicals, Iran Polymer and Petrochemicals Institute, Tehran, Iran
Department of Chemistry, School of Science, Alzahra University, Vanak, Tehran, Iran
‡
Halloysite nanoclay, Hal, was amine-functionalized and subsequently reacted with 2,4,6-
trichloro-1,3,5-triazine, TCT, and ethylenediamine, EDA, to provide multi-nitrogen containing
functionality on the surface of Hal. The resulting surface-modified Hal, Hal-2N-TCT-EDA, was
then used for immobilization of Pd nanoparticles and affording a heterogeneous catalyst,
Pd@Hal-2N-TCT-EDA, with utility for copper and ligand-free Sonogashira coupling of alkynes
and aryl halides. The results established the efficiency of this protocol in terms of product yield,
eco-friendly nature and reaction time. Study of the reusability of the catalyst confirmed that the
catalyst could be recovered and recycled up to seven times with slight loss of catalytic activity
and Pd leaching, indicating the efficiency of Hal-2N-TCT-EDA for embedding Pd nanoparticles.
To elucidate the role of the number of surface nitrogens on the catalytic performance, the
catalytic activity and recyclability of the catalyst was compared with those of Hal-2N and Hal-
2
N-TCT. It was found that more surface nitrogen atoms gave higher loading of Pd and lower Pd
leaching. This result confirms the contribution of surface nitrogens to anchor the Pd species and
suppress leaching.
Keywords: Halloysite clay; Functionality; Pd Nanoparticles; Copper and ligand-free;
Sonogashira coupling reaction
1
. Introduction
Sonogashira cross-coupling between aryl halides and aryl alkynes is an important synthetic route
2
to construct C (sp )-C (sp) bonds, which are very important in organic synthesis [1-3]. The
products of these reactions have been widely used for synthesis of substituted alkynes [4],
1
Corresponding author. Email: mmh1331@yahoo.com

natural products [5], pharmaceutical compounds [6], polymers [7] and optical materials [8].
Palladium phosphine complexes with copper salt as co-catalyst for promoting Sonogashira
coupling reaction have been extensively investigated, mostly in homogeneous conditions, and
various ligands or additives were employed to achieve higher yields of the desired coupling
products [9]. Pd salts are expensive and homogeneous palladium catalysts suffer from several
drawbacks such as high price, low chemical and thermal stability, and tedious isolation and
recovery from the reaction mixture [10]. These problems restrict the large scale applications of
these catalysts. Attempts have been made to address the challenges by using supported Pd as
heterogeneous catalysts. In this respect, several heterogeneous palladium catalysts have been
developed for Sonogashira C-C coupling reactions [11]. Numerous solid supports, such as clay
[
12], carbon materials [13], metal oxides [14] and molecular sieves [15], have been exploited for
developing Pd-based heterogeneous catalysts, in which Pd complexes or nanoparticles are
involved as the active species in coupling reactions [16]. Supporting of Pd species on magnetic
nanoparticles [17, 18] and functionalized SBA-15 [19] led to the development of efficient, green
and mild protocols for promoting not only C-C coupling reactions, but also for diverse coupling
reactions. Notably, in the case of magnetic supports, the facile separation of the catalyst is
achievable.
Halloysite, Hal, is an alumino silicate with the chemical composition
Al (OH) Si O (2-H O) [20]. The water molecules in the structure of Hal are located between the
2
4
2
5
2
interlayer spaces [21]. As a kaolonite mineral, Hal is mined from natural deposits and formed
from amorphous allophone by long time weathering [20, 22]. The porous morphology of Hal as
well as some other features of this clay such as inertness, availability, bio-compatibility and high
mechanical and chemical stability and surface area make this clay a candidate for various
applications such as drug delivery purposes [23], separation [24], catalysis [23] and water
treatment [25]. The most interesting feature of Hal is its capability to be functionalized on its
inner and outer surfaces and the incorporation of various active species such as nanoparticles
[
26].
Taking advantage of both experimental and theoretical studies, we have tried to
understand the chemistry of functionalized Hal as a catalyst support [11, 27]. In this context, we
have investigated the role of the number of heteroatoms on the surface by comparing Hal,
functionalized with 3-aminopropyl-triethoxysilane (APTES) and N-[3-(trimethoxysilyl)propyl]

ethylenediamine (AEAPTMS) [28]. The results established that nitrogen is a potent heteroatom
with high affinity to interact catalytic species. Nitrogen can effectively anchor the catalytic
species and reduce its leaching. Additionally, the studies revealed that Hal functionalized with
AEAPTMS with two nitrogens showed lower leaching of the catalytic species compared to Hal
functionalized with APTES that possessed one nitrogen.
Thorough consideration of all these factors and in continuation of our previous studies on
the catalytic utility of functionalized Hal and further confirming the role of the number of
nitrogens on the anchoring of immobilized catalytic species [29-32], herein the preparation of a
multi-nitrogen containing Hal-based heterogeneous catalyst, Pd@Hal-2N-TCT-EDA, through
multi-step functionalization of Hal and incorporation of Pd nanoparticles (figure 1) is described
and utilized for Sonogashira cross coupling. Additionally, the recyclability of Pd@Hal-2N-TCT-
EDA as well as the role of the number of surface nitrogens in suppressing Pd leaching are
reported.
2
2
. Experimental
.1. Materials and measurements
The chemicals used for preparation of Pd@Hal-2N-TCT-EDA and studying its catalytic activity
included Hal, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPTMS), 2,4,6-trichloro-
1
,3,5-triazine (TCT), ethylenediamine (EDA), triethylamine, toluene, tetrahydrofuran (THF),
Pd(OAc) , NaBH , halobenzenes, phenylacetylene, propargyl alcohol, K CO , Cs CO , KOH,
2
4
2
3
2
3
NaOH, distilled water and EtOH, all provided from Sigma-Aldrich and used as received. The
formation of Pd@Hal-2N-TCT-EDA was confirmed by using various characterization
techniques including, transmission electron microscopy (TEM), Fourier transform infrared (FT-
IR, Perkin Elmer Spectrum 65 instrument) spectroscopy, X-ray diffraction (XRD, Siemens
D5000 with Cu Kα radiation from a sealed tube), thermogravimetric analysis (TGA, Mettler
−
1
Toledo instrument with a heating rate of 10 °C min , under nitrogen) and BET (Belsorp Mini II
instrument, with degassing for 3 h at 423 K). The amount of Pd species supported on Hal-2N-
TCT-EDA was also measured by applying an ICP analyzer (Varian, Vista-pro).

2
.2. Functionalization of Hal with AEAPTMS: Synthesis of Hal-2N
To prepare the catalyst, Hal was first functionalized with AEAPTMS. To this purpose, 2.4 g of
Hal was highly dispersed in 60 mL of dry toluene by using ultrasonic irradiation of 100 W power
for 25 min. Then, 1 mL (5 mmol) of AEAPTMS was added to the Hal suspension and the
resulting mixture was stirred at 140 °C for 24 h. After that, the solid was filtered, washed with
dried toluene three times and dried at 100 °C overnight.
2
.3. Introduction of TCT: Synthesis of Hal-2N-TCT
To introduce TCT on Hal-2N, TCT (3.24 g) was dissolved in 50 ml of THF. Then, Hal-2N
(
3.5 g) was added and the obtained mixture was stirred in ice. Subsequently, triethylamine
2 mL) was introduced dropwise. After that, the solution was stirred at 25 °C overnight. Upon
(
completion of the reaction, the precipitate was filtered off and washed with THF repeatedly. Hal-
2
N-TCT was achieved after drying for 12 h at 70 °C.
2
.4. Conjugation of EDA to Hal-2N-TCT: Synthesis of Hal-2N-TCT-EDA
To the mixture of Hal-2N-TCT (1.2 g), EDA (2 mL) was gradually added and then the resulting
mixture was refluxed at 70 °C for 24 h. After completion of the reaction, the precipitate was
filtered, washed with THF several times and dried in an oven for 4 h at 70 °C.
2
.5. Immobilization of Pd nanoparticles on Hal-2N-TCT-EDA: Pd@Hal-2N-TCT-EDA
To incorporate Pd nanoparticles on Hal-2N-TCT-EDA, Hal-2N-TCT-EDA (1.2 g) was
suspended in dry toluene (15 mL) containing Pd(OAc) (0.02 g) and then stirred at ambient
2
temperature for 10 h. Reduction of Pd(II) to Pd(0) was achieved by using NaBH . More
4
precisely, a solution of NaBH in methanol (10 mL, 0.2 N) was prepared and added to the above
4
mentioned Pd(II)@Hal-2N-TCT-EDA dropwise. To assure complete reduction, the resulting
mixture was vigorously stirred for 5 h. Pd@Hal-2N-TCT-EDA was obtained after filtration,
washing with MeOH and drying in oven at 80 °C overnight. The schematic process of synthesis
of the catalyst is illustrated in figure 1.
To prepare Pd@Hal-2N and Pd@Hal-2N-TCT, the same procedure was used, except
Hal-2N and Hal-2N-TCT were applied as Pd support.

2
.6. Sonogashira coupling reaction
The catalytic activity of the synthesized Pd@Hal-2N-TCT-EDA was investigated for promoting
the Sonogashira reaction. Pd@Hal-2N-TCT-EDA (10 mol%) and K CO (3.0 mmol) were added
2
3
to the mixture of halobenzene (1.0 mmol) and acetylene (1.2 mmol) in EtOH. The reaction
mixture was then refluxed at 90 °C for appropriate reaction time (scheme 1). The reaction was
monitored by thin layer chromatography (TLC, n-hexane/ethyl acetate; 4:1). When the reaction
was completed, Pd@Hal-2N-TCT-EDA was filtered. After that, the organic layer was extracted
with diethyl ether and purified by column chromatography over silica gel by using hexane/ethyl
acetate (4:1) as eluent to furnish the corresponding product. To recycle the catalyst, the
recovered catalyst was washed with EtOH two times and dried in an oven at 90 °C overnight.
1
The coupling products were characterized by comparing their melting points and H NMR and
1
3
C NMR spectra with authentic samples (see Supporting Information).
3
3
. Results and discussion
.1. Catalyst characterization
TEM images of Pd@Hal-2N-TCT-EDA, depicted in figure 2, were recorded to investigate the
morphology of the catalyst. The TEM images revealed that upon functionalization of the Hal
nanotubes with TCT and EDA and immobilization of Pd nanoparticles, Hal preserved its tubular
morphology. However, comparison of the TEM images of the pristine Hal (figure S1 in
Supporting Information) and Pd@Hal-2N-TCT-EDA established that the latter possessed more
compact morphology and the tubes of Hal closed together to form aggregates. This can be
attributed to the intertwining of the surface functionalities of Hal and the presence of electrostatic
interactions between surface heteroatoms and Pd nanoparticles. The observed dark spots on the
Hal tubes can be assigned to the Pd nanoparticles. In some parts, Pd nanoparticles form small
aggregations. Using TEM images, the average Pd particle size is estimated to be 15 nm.
FTIR spectroscopy was employed to establish the structure of Pd@Hal-2N-TCT-EDA
(figure 3); the FTIR spectra of Hal, Hal-2N and Hal-2N-TCT-EDA were also recorded and
compared with that of Pd@Hal-2N-TCT-EDA. In the FTIR spectrum of Hal, the bands at 538
−
1
and 1034 cm are indicative of Al-O-Si vibration and Si-O stretching. The bands at 3698 and
−
1
3
624 cm demonstrate vibration of hydroxyl groups in the inner surface of Hal. The FTIR

−
1
spectrum of Hal-2N is very similar to that of Hal, except the band at 2937 cm is more
pronounced, due to the incorporation of organosilane and presence of (-CH ) functional group.
2
The FTIR spectrum of Hal-2N-TCT-EDA (figure 3) also possesses the characteristic
bands of Hal, implying that the structure of Hal would be preserved upon functionalization with
-1
TCT and EDA. Moreover, some additional bands at 1508-1612 cm can be observed. These
bands can be attributed to –C=N functionality and confirm the conjugation of TCT. Notably, the
representative band of –NH stretch, due to the attachment of EDA, overlapped with bands of
2
Hal. Comparison of the FTIR spectra of Hal-2N-TCT-EDA and Pd@Hal-2N-TCT-EDA
established that they are similar with no dramatic shift. This observation can be attributed to the
low amount of Pd loading on the catalyst.
TGA was also exploited for analysis of Pd@Hal-2N-EDA and disclosing the content of
2
-N, TCT and EDA. Initially, the thermogram of pristine Hal and Hal-2N were recorded and
compared (figure 4). Apart from the weight losses, which were observed for Hal and can be
attributed to the loss of water and the dehydroxylation of Hal, the weight loss at 300 °C can be
assigned to the loss of silanic functionality. Using these two thermograms, the content of 2N was
calculated to be about 3 w/w%. Next, the thermogram of Hal-2N-TCT was obtained to estimate
the content of TCT (figure 4). Considering the weight losses of this thermogram, which was due
to the loss of water, loss of organosilane, TCT and dehydroxylation of Hal, the content of TCT
was measured as 18 w/w%, indicating that most of the surface 2N were reacted with TCT.
Finally, to estimate the content of EDA, the thermogram of the catalyst was obtained and
compared with that of Hal-2N-TCT (figure 4). The results revealed that the content of EDA was
about 7 w/w%.
According to the thermogram of pristine Hal, ~82 wt.% of the pristine Hal remained at
8
00 °C and the ash in the thermogram of Pd@Hal-2N-TCT-EDA is about 50 wt%.
XRD analysis, as a method for studying the structure of the catalyst, was also employed
to characterize the Pd@Hal-2N-TCT-EDA. To elucidate whether the functionalization of Hal
and immobilization of Pd can occur on the surface of Hal and whether this can destroy the
structure of the pristine Hal, the XRD pattern of Pd@Hal-2N-TCT-EDA was compared with that
of pristine Hal (figure 5). As shown in figure 5, functionalization and Pd immobilization did not
lead to any significant displacement of the characteristic reflection bands of Hal (i.e. the bands at
2
θ = 12.2°, 19.9°, 24.7°, 37.5°, 55.5°, 62° (JCPDS No. 29-1487)) [33]. Observing no change in

the interlayer space can confirm that the functionalization took place on the surface of Hal. This
fact is in accord with previous reports [33, 34]. Apart from the characteristic bands of Hal, no
distinguished bands were observed for Pd nanoparticles. According to the literature, this can be
attributed to the low loading of Pd (as confirmed via ICP analysis) and its high distribution [35].
As N adsorption-desorption of the catalyst can reveal some features of the catalyst,
2
Pd@Hal-2N-TCT-EDA was subjected to BET analysis (figure 6). Considering the types of
isotherms, the Pd@Hal-2N-TCT-EDA isotherm can be attributed to type II isotherms with H3
hysteresis loops [33]. As Hal has a porous nature, this result was expected. BET results also
2
-1
disclosed that the specific surface area of Pd@Hal-2N-TCT-EDA (24 m g ) was lower than that
2
-1
of pristine Hal (51 m g ), confirming that 2N-TCT-EDA and Pd were located on the outer
surface of Hal, not within the inner space. This result is in good agreement with the literature
[
11].
In the next step, the loading of Pd in Pd@Hal-2N-TCT-EDA was studied by using ICP
analysis. Upon digesting the organic functionalities in concentrated acidic solution of nitric and
hydrochloric acid, the extract was analyzed by ICP analysis and the calculations demonstrated
that the content of Pd was very low, about 0.15 w/w%.
3
.2. Catalytic activity
The catalytic activity of the synthesized Pd@Hal-2N-TCT-EDA was investigated for
Sonogashira C-C coupling in the absence of copper co-catalyst and ligand. Initially, the
efficiency of the catalyst was studied for the model reaction of aryl iodide and phenyl acetylene
in the presence of commercially available and cost-effective K CO as base in water. The results
2
3
showed good catalytic activity of Pd@Hal-2N-TCT-EDA. Inspired by this initial finding, the
reaction was thoroughly optimized in terms of the solvent, amount of catalyst, and bases (table
1
). The efficiency of EtOH, H O-EtOH (1:1), toluene, CH CN, CHCl , and water as solvents and
2 3 3
K CO , Cs CO , KOH and NaOH as base for promoting the synthesis of the product were
2
3
2
3
screened. EtOH and K CO were the most suitable solvent and base, respectively. Among
2
3
various tested amounts of the catalyst, the value of 10 mol% was selected as the optimum
catalyst amount (table 1). Screening the effect of reaction temperature revealed that raising
reaction temperature to 90 °C led to the highest yield of the model product.

As Sonogashira coupling can be promoted by both Pd(0) and Pd(II)-based catalysts,
initially the effect of Pd valence was investigated. To this purpose, Pd(II)@Hal-2N-TCT-EDA
was also synthesized (the synthetic procedure was similar to that of Pd@Hal-2N-TCT-EDA,
except the reduction step was omitted) and its catalytic activity was compared with that of
Pd@Hal-2N-TCT-EDA. The catalytic activity of the latter was slightly higher than that of the
former. Hence, Pd(0) was selected for further investigation. Moreover, the catalytic activity of
homogeneous Pd(OAc) and Pd(0)/Hal were also obtained for the model reaction under optimum
2
reaction conditions. The results established that the catalytic activity of homogeneous Pd(OAc)2
was the lowest. Notably, the recovery of the homogeneous catalyst was tedious. The catalytic
activity of Pd(0)/Hal (60%) was higher than that of Pd(OAc) but lower than Pd@Hal-2N-TCT-
2
EDA.
In the following, the effect of the number of the surface nitrogens on the catalytic activity
of the final catalyst was investigated. Two other catalysts, i.e. Pd@Hal-2N and Pd@Hal-2N-TCT
were prepared and their catalytic performances were compared. The results showed that the order
of the yield of the desired product in the presence of various catalysts varied in the following
order: Pd@Hal-2N-TCT-EDA (95%) > Pd@Hal-2N-TCT (75) > Pd@Hal-2N (66%). The
observed difference of the catalytic activity can be attributed to the different loading of Pd
nanoparticles on the catalyst. To verify this assumption and estimate the loading of Pd, three
prepared catalysts were subjected to ICP analysis. The loading of Pd in Pd@Hal-2N-TCT-EDA
was the highest (0.15 w/w%) while Pd@Hal-2N showed the lowest Pd content (0.05 w/w%).
Regarding Pd@Hal-2N-TCT, the loading of Pd was about 0.08 w/w%. This observation
confirms the role of the number of surface nitrogens in anchoring Pd nanoparticles.
Having the optimized reaction conditions in hand, the generality of this methodology was
confirmed by applying various alkynes and aryl halides with electron-withdrawing and electron-
donating groups (table 2 [10, 30, 36-40]). As tabulated in table 2, not only aryl iodide could
tolerate Sonogashira coupling reaction using Pd@Hal-2N-TCT-EDA, but also less active aryl
halides, i.e. aryl bromides and aryl chlorides underwent the reaction to afford the corresponding
biaryls. However, the yields of the reactions in these cases were lower than those of aryl iodides.
According to the literature, this observation can be attributed to the lower activity of aryl
bromides and aryl chlorides [40]. Comparing the yields of aryl halides with different functional
groups, it can be concluded that the substrates with electron-withdrawing groups led to higher

yields of products. Moreover, sterically demanding aryl halides (table 2, entry 10) resulted in
lower yields of the products. The results also demonstrated that both aliphatic and aromatic
alkynes could be applied in the protocol. However, the yield of the reactions by using aromatic
alkynes were slightly higher than that of aliphatic ones.
Next, the reaction versus time was studied and time-conversion profile for the model
reaction was obtained (figure 7). The slope of the plot at the start of the reaction was relatively
sharp and after 30 min, conversion reached 40%. Then, the slope of the plot decreased and
conversion reached its highest value (95%) at 120 min. After that, no further increase in the
conversion was observed.
Time-conversion profile was also studied for the less active chlorobenzene (figure 7). As
depicted, the profile of chlorobenzene is similar to that of iodobenzene. However, the reaction of
chlorobenzene is slower and at the first 30 min, the conversion reached 15%. Similar to
iodobenzene, the slope of the time-conversion plot at the beginning of the reaction is sharper and
the after reaching conversion of 55% (after 180 min), the slope of the plot decreased. In this case,
the maximum conversion was observed after 390 min and the conversion did not increase by
further reaction time.
Finally, to investigate the merit of this protocol, the catalytic activity of the catalyst for
promoting the model reaction was compared with some previously reported catalysts (table 3). A
number of protocols have been reported for Sonogashira coupling and the reported protocols for
this reaction are not limited to the cases tabulated in table 3. As shown in table 3, both Pd-based
and Pd-free catalysts have been reported for this reaction under different reaction conditions. The
comparison of the catalytic activity of Pd@Hal-2N-TCT-EDA with those catalysts indicated the
superior or comparative catalytic activity of Pd@Hal-2N-TCT-EDA. Moreover, this catalyst
could promote the model reaction in the presence of cost-effective and non-toxic K CO as base
2
3
and EtOH as solvent while some of the tabulated catalysts required expensive (table 3, entry 2)
or toxic bases and/or solvents. Furthermore, the reaction time and temperature required for the
reaction with Pd@Hal-2N-TCT-EDA catalysis were lower or comparative to the catalysts
tabulated in table 3.
The aim of this research was design and preparation of a novel heterogeneous catalyst
based on Hal and investigation of the effect of the number of surface nitrogens on the catalytic
activity. In this line, Sonogashira coupling was selected as a model reaction to investigate the

catalytic performance and the role of the number of surface nitrogens. Hence, it is not claimed
that the developed protocol is the most efficient strategy for the Sonogashira reaction and there
are other reports in which this reaction was promoted in comparative or even better yield
[
41, 42]. However, the comparison in table 3 [43-51] confirms that Pd@Hal-2N-TCT-EDA can
be considered as an efficient catalyst for the Sonogashira coupling reaction.
3
.3. Recyclability of the catalyst
The recycling of the catalyst is one of the significant aspects of catalysts for practical
applications. Therefore, the recyclability of Pd@Hal-2N-TCT-EDA was investigated in the
model reaction of phenylacetylene with iodobenzene. The results showed that after seven
consecutive reactions the yield of the model product decreased only 17% (figure 8).
To further confirm the role of the number of surface nitrogens in the immobilization of
Pd nanoparticles, the recyclability of the catalyst was compared with those of Pd@Hal-2N and
Pd@Hal-2N-TCT (figure 8). As shown, Pd@Hal-2N-TCT-EDA showed the highest catalytic
recyclability among three catalysts. Moreover, the ICP analysis confirmed the lowest leaching of
Pd in the case of Pd@Hal-2N-TCT-EDA, indicating that nitrogens on the surface of Hal can
effectively suppress the leaching of Pd.
To elucidate whether recovery and recycling of Pd@Hal-2N-TCT-EDA can result in
degradation of the catalyst structure, FTIR spectra of fresh and recycled Pd@Hal-2N-TCT-EDA
were compared (figure 8). As shown in figure 9, FTIR spectra of both fresh and recycled
Pd@Hal-2N-TCT-EDA exhibited the characteristic bands of the catalyst, implying that recycling
did not lead to destruction of the structure of Pd@Hal-2N-TCT-EDA.
Finally, to study whether the catalysis is heterogeneous, hot filtration test was performed.
The hot filtration test was accomplished according to the previously reported protocol [19]. The
reaction under optimized condition was performed and then held after short reaction time. Then,
the catalyst was filtered and the reaction in the filtrate was allowed to proceed. The results
showed no further promotion of the reaction, indicating that the catalytic process was
heterogeneous and did not proceed through leaching of Pd nanoparticles and their re-deposition
on the support.

4
. Conclusion
Considering the role of surface nitrogen functionality of Hal, a heterogeneous Hal-based catalyst
with high recyclability and low Pd leaching has been developed through conjugation of TCT on
Cl-functionalized Hal followed by introduction of EDA and immobilizing Pd nanoparticles.
Pd@Hal-2N-TCT-EDA catalyzed Sonogashira coupling in the absence of copper and ligand.
The ICP results confirmed that the loading of Pd in Pd@Hal-2N-TCT-EDA was higher than for
Pd@Hal-2N. This issue stemmed from the stronger electrostatic interaction of heteroatoms on
the surface of Hal with Pd nanoparticles. Moreover, the recyclability tests revealed that the
catalyst showed superior recyclability and lower Pd leaching compared to those of Pd@Hal-2N-
TCT and Pd@Hal-2N-TCT-EDA. This observation further confirmed the role of surface
nitrogen in anchoring Pd species. This issue was confirmed by comparing the recyclability of
Hal-2N, Hal-2N-TCT and Pd@Hal-2N-TCT-EDA. The results demonstrated superior
recyclability and inferior leaching of Pd nanoparticle of the latter, indicating the role of the
number of the surface nitrogens in anchoring Pd nanoparticles.
Supplementary materials
1
13
Reported TEM images of pristine HNTs as well as H NMR and C NMR spectra of coupling
products are provided in the Supplementary Information.
Acknowledgements
The authors appreciate partial financial supports from Iran Polymer and Petrochemical Institute
and Alzahra University. MMH and Kazemi are also grateful to Iran National Science Foundation
for the Individual given grant.
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Graphical abstract

Table 1. Optimization of reaction conditions for Sonogashira coupling of iodobenzene with
a
phenylacetylene .
Reaction
condition
Catalyst amount
mol%
b
Entry
Time (h)
Base
Yield (%)
1
2
3
EtOH/rt
4
4
4
10
10
10
K CO3
65
51
60
2
H O/rt
2
K CO3
2
H O-EtOH
2
K CO3
2
(1:1)/70
4
H O-EtOH
2
4
10
K CO3
2
75
(1:1)/100
5
6
7
8
9
EtOH/70
EtOH/90
3
2
10
10
10
10
10
10
15
7
K CO3
82
95
80
68
63
65
75
64
85
59
61
2
K CO3
2
CH OH/60
3
K CO3
2
3
Toluene/reflux
3.5
3.5
4
K CO3
2
CH CN/80
K CO3
2
3
1
1
1
1
1
1
0
1
2
3
4
5
CHCl3
K CO3
2
EtOH/90
EtOH/90
EtOH/90
EtOH/90
EtOH/90
3
K CO3
2
3
K CO3
2
2
10
10
10
Cs CO3
2
2.5
2
KOH
NaOH
a
Reactions were run in 5 ml of solvent with 1 mmol of iodobenzene, 1.2 mmol of
b
phenylacetylene and 3 mmol of base. Isolated yield.

a
Table 2. Pd@Hal-2N-TCT-EDA catalyzed Sonogashira reaction of various halides with terminal alkynes .
b
Terminal
alkyne
Time Yield
Entry
1
Aryl halide
Product
Ref.
[33]
(h)
(%)
2
95
2
3
4
5
2
97
90
91
80
[34]
[35]
[36]
[27]
3.30
2:30
5
6
7
8
9
3:30
3
87
95
83
85
85
[27]
[27]
[27]
[27]
[27]
4:30
4
1
0
5

1
1
5
80
[34]
1
1
2
3
5
78
75
[37]
[10]
6:30
Cl
1
4
7
72
[37]
a
Reaction conditions: aryl halide (1.0 mmol), terminal alkyne (1.2 mmol), Pd@Hal-2N-TCT-EDA
b
(
10 mol%) and K CO (3.0 mmol) in EtOH (5.0 mL) at 90 °C. Isolated yield
2
3

a
Table 3. Comparison of the catalytic activity of Pd@Hal-2N-TCT-EDA with some other catalysts .
Time Temp. Yield
Entry
Catalyst/Catalyst precursor
NiCl ·6H O
Solvent
Base
Ref.
(h)
(°C)
(%)
1
2
3
4
2
120
60
86
70
81
87
EG
NaOH [40]
2
2
[Pd(dppe)(OTf)2]
24
6
CH OH Cs CO3 [41]
3
2
b
[(P^C)PdCl2]
130
130
DMF
K CO3 [42]
2
c
[(C^C)PdCl2]
4.5
DMF
K CO3 [42]
2
2
[
(Pd{k -C,N)-(3-
5
6
(dimethylaminomethyl)indole)}µ-
OAc)2]
3
2
120
80
85
95
DMF/H O K CO
3
[43]
2
2
PdCl {C(N(H)-
2
EtOH
K CO3 [44]
2
NPh )@N(H)Cy}(C„NCy)
2
d
7
8
9
CuI/L
6
3
145
135
140
125
75
90
55
65
54
95
DMF
DMF
K CO3 [45]
2
+
-
[N-benzyl DABCO] [Cu Cl ]
K CO3 [46]
2
4
5
Cu(OAc)2
24
48
2
Et N
Et N
[47]
3
3
1
1
0
1
Et Zn/DMEDA
Dioxane
EtOH
K PO4 [48]
3
2
Pd@Hal-2N-TCT-EDA
K CO3 This
2
work
a
b
c
Reaction of iodobenzene with phenylacetylene. Five-membered palladacycle. Seven-membered
d
analogs. N,N`-dibenzyl BINAM.

Scheme 1. Sonogashira coupling reaction.
1
9

Figure 1. The schematic route for the preparation of Pd@Hal-2N-TCT-EDA catalyst.
2
0

Figure 2. TEM images of Pd@Hal-2N-TCT-EDA.
2
1

Figure 3. The FTIR spectra of Hal, Hal-2N, Hal-2N-TCT–EDA and Pd@Hal-2N-EDA.
2
2

Figure 4. The TGA analysis of pristine Hal, Hal-2N, Hal-2N-TCT and Pd@Hal-2N-TCT-EDA.
2
3

Figure 5. The XRD pattern of Pd@Hal-2N-TCT-EDA and pristine Hal.
2
4

Figure 6. The N2 adsorption-desorption of Pd@Hal-2N-TCT-EDA.
2
5

Figure 7. Time-conversion profile for Sonogashira coupling reaction of a) iodobenzene and
phenylacetylene and b) chlorobenzene and phenylacetylene in the presence of Pd@Hal-2N-TCT-
EDA under optimum reaction conditions.
2
6

Figure 8. Reusability of the Pd@Hal-2N-TCT-EDA (a), Pd@Hal-2N-TCT (b) and Pd@Hal-2N.
c) catalysts for Sonogashira coupling.
(
2
7

Figure 9. FTIR spectra of (a) fresh Pd@Hal-2N-TCT-EDA and (b) recycled catalyst.
2
8