Palladium Nanoparticles Supported on Nitrogen-rich Containing Melamine-based Microporous Covalent Triazine Polymers as Efficient Heterogeneous Catalyst for C?Se Coupling Reactions

Article abstract of DOI:10.1002/cctc.201800400

In the present work, microporous nitrogen containing covalent triazine polymers (CTPs) TATAM was synthesized from condensation of 4,4′4′′-(1,3,5-triazine-2,4,6-triyl) tribenzaldehyde (TATA) and melamine under solvothermal conditions to obtain nitrogen- rich triazine containing polymeric supported materials (TATAM). Further, palladium nanoparticles (Pd NPs) were supported on TATAM polymeric networks (Pd@TATAM). The synthesized Pd@TATAM CTPs material was thoroughly characterized by FT-IR, UV-DRS, solid state ¹³C-CPMAS, XPS, powder X-ray diffraction, TGA, SEM, TEM. In addition, the characterized Pd@TATAM CTPs were applied to check the catalytic application. The Pd@TATAM was shown to be an efficient and reusable heterogeneous solid catalyst for the formation of C?Se bond through coupling of aryl halide and elemental selenium, dimethyl sulfoxide as a solvent at 100 °C for about 6 h. Besides the absence of metal leaching for catalytic system, it is also observed that the catalyst can be reused for three consecutive cycles with a minimal decrease in its activity.

Full text of DOI:10.1002/cctc.201800400

Accepted Article
Title: Palladium Nanoparticles Supported on Nitrogen-rich Containing
Melamine-Based Microporous Covalent Triazine Polymers as
Efficient Heterogeneous Catalyst for C-Se Coupling Reactions
Authors: Sadhasivam Velu, Balasaravanan Rajendiran, Chithiraikumar
Chinnadurai, and Siva Ayyanar
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the VoR from the journal website shown below when it is published
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To be cited as: ChemCatChem 10.1002/cctc.201800400
Link to VoR: http://dx.doi.org/10.1002/cctc.201800400
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ChemCatChem
Palladium Nanoparticles Supported on Nitrogen-rich Containing Melamine-
based Microporous Covalent Triazine Polymers as Efficient Heterogeneous
Catalyst for C-Se Coupling Reactions
Mr. Velu Sadhasivam, Dr. Rajendiran Balasaravanan, Mr. Chinnadurai Chithiraikumar
and Prof. Dr. Ayyanar Siva*
Supramolecular and Organometallic Chemistry Lab, Department of Inorganic Chemistry, School
of Chemistry, Madurai Kamaraj University, Madurai-625021, Tamil Nadu, India.
E-mail: drasiva@gmail.com.
Abstract
In the present work, microporous nitrogen containing covalent triazine polymers (CTPs)
TATAM
was
synthesized
from
condensation
of
4,4′,4′′-(1,3,5-triazine-2,4,6-
triyl)tribenzaldehyde (TATA) and melamine under solvothermal conditions to obtain nitrogen-
rich triazine containing polymeric supported materials (TATAM). Further, palladium
nanoparticles (Pd NPs) were supported on TATAM polymeric networks (Pd@TATAM). The
synthesized Pd@TATAM CTPs material was thoroughly characterized by FT-IR, UV-DRS,
solid state 13C-CPMAS, XPS, powder X-ray diffraction, TGA, SEM, TEM. In addition, the
characterized Pd@TATAM CTPs were applied to check the catalytic application. The
Pd@TATAM showed to be an efficient and reusable heterogeneous solid catalyst for the
formation of C-Se bond through coupling of aryl halide and elemental selenium,
dimethylsulfoxide as a solvent at 100 °C for about 6 hrs. Besides the absence of metal leaching
for catalytic system, it is also observed that the catalyst can be reused for three consecutive
cycles with a minimal decrease in its activity.
1
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Introduction
Carbon and nitrogen-rich containing covalent organic frameworks (COFs) have grown
into a major research field of material science, because of its remarkable potential applications
such as photo catalyst, hydrogen storages, hydrogen production, gas storages,[1] membranes,
electrodes, optoelectronic, gas separation, drug delivery, super hydrophobic interface and mainly
used to heterogeneous catalysis.[2-9] The molecular building blocks of COFs materials are
composed by light weight elements such as C, B, N, O linked by covalent bonds into a well-
defined predictable two or three-dimensional (2D or 3D) porous crystalline networks.[10-15] These
COFs materials are found to be efficient catalyst in organic synthesis due to their low density,
high specific surface areas, large porosity and easy structural tunable functionality that can lead
to efficient performances and selectivity of the organic reactions.[16] As some of the porous
materials like COFs, porous silica and zeolites are used to supports incorporate metal nano
particles (NPs) are unstable, metal leaching in aqueous and most organic solvents.[17] In order to
overcome these issues, newly synthesized highly stable nitrogen containing porous materials in
which there is a strong interaction between the metal support and the loaded materials (NPs).[18]
Covalent triazine polymers (CTPs) are one of the nitrogen containing COFs, formed by the
trimerization reaction of cyano-functionalized aromatic compounds to obtain triazine based
linkages. CTPs have some remarkable properties due to their periodic columnar π-π stacking,
ordered nano channels, high surface area and high amount of nitrogen atom present in the
networks, which is beneficial to incorporate a large number of metal binding sites, namely,
nitrogen on the surfaces of the supported materials to enhance the high catalytic activity as well
as the stability of the supported materials.[19-21] Palkovits et al., applied a CTPs loaded with a
platinum metal as a catalyst for methane oxidation in concentrated sulfuric acid at harsh
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condition.[22] Recently, in our group also reported triazine based microporous covalent imine
functionalized polymers as a novel solid supports for palladium mediated Suzuki-Miyaura
coupling reaction.[23] In addition to that, CTPs supported catalyst showed no detectable
degradation and change the structural integrity even after use to several reaction cycles.
In recent years, transition metal catalyzed cross coupling reactions such as C-C, C-N,
C-O, C-Se bond formation reactions have achieved considerable progress in synthetic organic
transformations, pharmaceutical and medicinal applications.[24] Over the decades, various
homogeneous catalytic systems, which exhibit better activity and high selectivity have been
developed for this transformations.[25] However, the homogeneous catalyst suffer from
drawbacks such as expensive phosphine ligands, use of various additives, contamination of
products, metal leaching, recyclability and tedious multistep protocol necessary for the ligand
synthesis and to difficult work-up process and also phosphine ligands are very toxic in nature. In
this manner, the heterogenization of the Pd catalyst has to overcome the above difficulties and
make the process to green protocols. Recently, there has been an increasing demand for efficient
methods to synthesize mono selenide and diselenides for organoselenium compounds, especially,
these carbon-selenium bonds have been a fascinating topic for current research field, mainly
these compounds are vital role in biological system for antioxidant, antimicrobial, antiviral for
the pharmaceutical industry and material science applications.[26-28] Selenium is an one of the
most important component for amino acids such as selenocysteine and selenomethionine, so the
construction of C-Se bond formed by using various selenium sources, such as selenols,[29]
[31]
diselenide,[30] ArSeSnR3
under basic conditions.[32] Most of the aryl selenols suffer from
trouble for handling, because of unpleasant odours, high sensitive to air and moisture, expensive
and instability, which hamper their applications in pharmaceutical industry. In order to overcome
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the important shortcoming of organoselenium reagent, recently, the elemental selenium powder
has been used as a selenating agent,[33] due to easy to handle, commercial available, stable
material and low cost. Huayue Wu et al., reported aryl and heteroaryl selenation of indole using
the elemental selenium as a selenating agent to obtain regioselective and high yield of product
was observed.[34]
Scheme 1. Synthesis of Pd NPs supported on nitrogen rich covalent triazine polymer networks
(Pd@TATAM).
Scheme 2. Synthesis of diarylmonoselenide from aryl halide for C-Se coupling reactions.
In this work, we have successfully synthesized nitrogen rich covalent triazine based CTPs
may incorporate a large number of metal binding sites and robust stability. Herein, we report a
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novel strategy for the synthesis of palladium nanoparticles supported on nitrogen rich melamine-
based microporous covalent triazine polymers as efficient heterogeneous catalyst for selenation
of aryl halide (C-Se) coupling reactions and good catalytic activity with excellent yield under
eco-friendly conditions. To the best of our knowledge, there are no reports describing the
selenation of aryl halide using tiny amounts of Pd@TATAM CTPs (20 mg, 0.5 mol%)
heterogeneous catalytic system for the clean synthesis of C-Se bond formations.
Results and Discussion
A new series of triazine based nitrogen containing TATAM and Pd@TATAM was
synthesized under solvothermal conditions by condensation reaction between 4,4',4"-(1,3,5-
triazine-2,4,6-triyl)tribenzaldehyde (TATA) and melamine, DMSO/dioxane (1:2) solvent in the
presence of glacial acetic acid at 150 °C for about 3 days to obtain nitrogen rich triazine
supported materials (TATAM). After that, Pd NPs successfully incorporated into the TATAM
polymeric materials (Pd@TATAM). The prepared CTPs materials were confirmed by FT-IR
spectroscopy (Fig. 1). In this spectrum of raw materials, the core triazine ring C=N stretching
and the primary amine group (NH2 stretching) of melamine was appeared at 1520 and 3468 cm-1
respectively. Further, the carbonyl functional group of aldehyde C-H at 2830 cm-1 as well as
(C=O stretching) at 1670 cm-1 (see SI Figure S1) was completely diminished in TATAM. It is
suggested that the successfully conversion of starting material of melamine into TATAM
through aminal linkage to form three-dimensional network polymers (see SI Figure S1)[35]
compared with these materials (TATAM and Pd@TATAM) revealed that both are similar
pattern observed and the Pd@TATAM does not show any changes for absorption position, it is
clearly indicated that the structural regularity was well maintained after incorporating Pd NPs.
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Figure 1. FT-IR Spectra of compounds TATA, TATAM and Pd@TATAM.
Solid state UV-Visible spectroscopy is an effective technique to investigate whether the
metal precursors are completely reduced or not and the metal NPs are supported or not. The
absorption spectra of both the TATAM and Pd@TATAM shows the two absorption band
appeared at 217 nm and 250 nm, which may be attributed to π-π* and n-π* transition of C=C,
C=N respectively, which are shown in Fig. 2. In addition to that, Pd@TATAM shows the new
broad absorption band appeared at near 335 nm, which is due to the charge-transfer transitions of
an electron excited from the triazine nitrogen lone pair to a vacant d-orbitals of the metallic
nanoparticles.[36, 37] Thus the solid state UV-DRS clearly stipulate all the palladium precursor is
completely reduced to Pd NPs, hence it is clearly revealed that all Pd NPs are successfully
incorporated on nitrogen-rich containing TATAM networks.
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Figure 2. UV-DRS spectra of TATAM and Pd@TATAM.
The crystalline nature and structural regularity of both TATAM and Pd@TATAM were
determined by powder XRD analysis which is shown in Fig. 3. The obtained powder XRD
pattern TATAM shows partial crystallinity of the material, due to the range of 16 to 30 2
values. This set of broad peaks suggests that TATAM material has a certain degree of order.[38]
The comparison of TATAM and Pd@TATAM revealed that TATAM was well maintained after
the synthesis of Pd@TATAM, because of these both materials have similar patterns was
observed. It is also confirmed by FTIR spectrum, but the Pd@TATAM additionally new small
peak was observed in these 2values at 12.62, 40.07 and 46.13, which are assigned to the
refractions from the corresponding (100), (111) and (200) planes, indicating the face centered
cubic (fcc) lattice for Pd NPs,[39] the broad diffraction peak at 12.62º ascribed to Pd NPs strongly
binding/interaction with triazine unit as well π-π stacking between aromatic ring and triazine unit
to form certain degree of order, which is consistent with our reported literature.[23] These powder
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XRD results clearly indicating the synthesized materials (Pd@TATAM) are partial crystalline in
nature and Pd NPs high dispersion on TATAM network.
Figure 3. Powder XRD pattern of TATAM and Pd@TATAM.
13
The C CP-MAS solid state NMR spectrum is further utilized to confirm the molecular
structure of TATAM. As shown in Fig. 4, a five characteristic resonance signals at 167.93,
137.25, 126.66, 50.17, 13.09 ppm were observed. The signal at 167.93 corresponds to aromatic
ring of core triazine carbon, whereas the signals appeared at 137.25 and 126.66 ppm originates
from the aromatic C-H phenyl ring carbons. Furthermore, the carbonyl carbon at 190 ppm was
greatly attenuated and the signal at 50.17 ppm corresponds to carbon attached to the aminal
linked polymeric network was formed instead of imine linkage. The C=N characteristic
13
resonance peak of imine bond at 160 ppm was not observed. Thus the C CP-MAS solid state
NMR spectrum clearly indicating melamine incorporated into TATAM polymeric network
through an aminal linkage via the condensation of triazine aldehydes and primary amine of
melamine. Which is consistent with the previous literature.[40, 41]
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Figure 4.13C-CP MAS NMR spectrum of TATAM.
The thermal stability of TATAM and Pd@TATAM were measured by thermo gravimetric
analysis (TGA) under nitrogen atmosphere, the temperature up to 800 C and heating flow rate is
5 C/min shown in Fig. 5. From this figure, both materials have exhibits 4% of weight loss
within a temperature near 135 C, this is due to desorption takes place the physisorbed molecule
loss of moisture and solvent molecules trapped inside the polymeric frame. Furthermore, the
second weight loss of these materials takes place above 350 C (and continuing to 365 C) is
related to the decomposition of the melamine linker from the Pd@TATAM covalent organic
polymeric network. From the observed results, it is confirmed that the Pd@TATAM stable up to
365 C. Pd@TATAM is also revealed that high thermal stability similar to that of TATAM
materials.
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Figure 5. Thermogravimetric analysis of compounds TATAM and Pd@TATAM.
The surface area, pore volume and microporous nature of nitrogen-rich CTPs were
further supported by the N2 adsorption/desorption isotherm measurement at 77K (Fig. 6). The
application of the Brunauer Emmett Teller (BET) resulted in the surface areas and pore volume
of these material was found to be 213 m2 g-1 and 0.5492cm2g-1 (P/Po= 0.985) respectively for
Pd@TATAM. The pore size distribution of Pd@TATAM was calculated via NLDFT (nonlocal
density functional theory) methods applied to the N2 isotherms presented at (Fig. 6b) the pore
size value 5.2 Å and it’s a microporous material.
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Figure 6. (a) N2 adsorption (filled symbol) / desorption (empty symbol) and (b) pore size
distribution of Pd@TATAM.
The oxidation state and binding affinity of Pd NPs in the Pd@TATAM catalyst was
confirmed by the XPS spectrum as shown in the Fig. 7. The two binding energy peaks appeared
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at 335.5 eV and 340.7 eV corresponds to Pd3d5/2 and Pd3d3/2 core level respectively and these
values are matched with some reported literature (Fig. 7a),[42,43] which clearly indicating that the
Pd@TATAM catalyst was incorporated by palladium species and all are presented in metallic
state of Pd(0). In addition to that, there is an another component peak at 285.22 eV
corresponding to the C1s in the C=N bonds for triazine is observed and one additional small
peak at 288.19 eV is appeared corresponds to sp3 bond of C-N single bonds.[44,41] These results
are clearly suggested that the aldehyde and amine are coupled with aminal linkages in TATAM
covalent triazine network polymer and further survey scan of the Pd@TATAM material also
support the palladium was bind with CTPs material as shown in Fig. 8g.
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Figure 7. XPS analysis of (a) Pd3d and (b) C1S spectra for Pd@TATAM.
The structural morphology of TATAM and Pd@TATAM were confirmed by SEM and
TEM analysis which are shown in Fig. 8. SEM images and elemental mapping of both materials
showed direct visualization of porous cross-linked polymers with partially crystalline structures
and distribution of Pd NPs. (see SI Figures S6, S7 and S8). In addition, transmission electron
microscopy (TEM) analysis was further used to predict the dispersion of palladium nanoparticles
in the Pd@TATAM catalyst. TEM images showed that Pd nanoparticles are dispersed (black
dots) on TATAM, sponge cake like porous structure was observed (Fig. 8c-8f). Moreover, the
average particle size of Pd@TATAM approximately 2.90 nm, and mean particle size of
Pd/TATAE around 2.40 nm calculated from the XRD full width at half maximum (FWHM)
using the Debye-Scherrer equation. Pd Nps are highly dispersed within the porous TATAM
network (see SI Figure S9). Furthermore, the elemental composition of both materials was
confirmed by EDS analysis (see SI Figures S3 & S4).
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Figure 8. (a, b) SEM images of TATAM and Pd@TATAM, (c, d, e, f) TEM images of
Pd@TATAM, (g) the overall survey scan of XPS analysis for Pd@TATAM.
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Catalytic studies of Pd@TATAM in selenation of aryl halide for C-Se coupling reactions
In order to check the potential catalytic activity of Pd@TATAM material, we first
optimize the reaction condition for monoselenation of aryl halide, starting from the reaction
between aryl halide 1a with elemental selenium in DMSO as a solvent and K3PO4 as a base in an
air atmosphere at 100 °C to obtain diphenylmonoselenide (2a) as a major product and small
amount of Ullmann homo coupled byproduct (3a) were obtained. Herein, bromobenzene and
elemental selenium were chosen as model substrates to determine the optimal reaction
conditions. The results are summarized in Table 1. Under controlled experimental condition the
reaction was performed, no product was formed either in the presence of TATAM or absence of
Pd incorporated catalyst (Table 1, entries 1, 2). Moreover, the reaction was performed without
base (Table 1, entry 21) to obtain the less amount of yield (24%). This is confirmed that Pd NPs
and base plays an important role in the catalytic reactions and further, the reaction was carried
out in room temperature (Table 1, entry 20), we observed no product was obtained. Moreover,
the elemental selenium does not activate in room temperature, so increase temperature up to 100
°C then only reaction was undergoes. Next optimization of the solvent condition, we chosen
different polar/non polar solvents, such as DMF, DMSO, toluene, acetonitrile, dioxane and
DMSO/H2O mixture (Table 1, entries 3-8). Among the solvents DMSO gave an excellent
amount of yield (84%) of the product observed at 100°C temperature (Table 1, entry 7). Other
solvents like toluene, acetonitrile, and dioxane are provided trace amount of the products (Table
1, entries 3, 4 and 6). This may be due to the DMSO is more polar aprotic solvent that dissolve
polar and non polar reactants and also the sulfur centre in DMSO is nucleophilic toward soft
electrophiles and the oxygen is nucleophilic toward hard electrophiles with aryl/alkyl halide to
form alkylated/arylatedsulfoxonium halide, which is more efficient intermediate in this selenium
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insertion reaction. In addition, various organic and inorganic bases were also studied like K2CO3,
Cs2CO3, NEt3, NaOH and K3PO4 (Table 1, entries 9-12). All bases gave a moderate amount of
yield except K3PO4 which gave an excellent amount of yield 84% (Table 1, entries 13), due to
the efficiency of the reaction was strongly dependent on their base strength, probably K3PO4
base was involved in the activation of the Se-Se bond of the elemental selenium (Se8) and base
K3PO4 was required to promote Se2- anion with Pd@TATAM catalyst to activate the reaction.
Next, we further examine the various substrate scope, the elemental selenium with
various substituted aryl halides (X = I, Br) were studied and the results are listed in Table 2,
(entries 1-12). The reaction was conducted with a wide range of substrates containing both
electron-withdrawing and donating groups substituted on bromobenzene gave diaryl substituted
monoselenide products with excellent yield up to 84% and high turnover number upto1127
(Table 2, entry 1). The substituent’s electron donating and electron withdrawing groups did not
show any significant influence during the course of the reactions, which suggests that electronic
character has no obvious effect on the catalytic system. In addition, the electronic properties of
ortho and meta substituted aryl halide had little influence of yield (Table 2, entry 5), due to steric
hindrance between the aryl halide and palladium catalyst, only less amount of substrate
approaches to Pd@TATAM. Moreover, the synthesis of unsymmetrical diarylselenides to give
less amount of yields (38%, 42%, 46%), because of symmetric diaryl selenides by-products also
obtained during the course of these reactions (Table 2, entry 13,14,15).
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Table 1. Optimization of Pd@TATAM-Catalyzed Mono-selenation of aryl halide with elemental
Selenium [a]
Entry Catalyst
Solvent
Base
Temperature
(°C)
100
Yield[b]
2a (%)
NR[d]
NR[d]
21
Yield[c]
3a (%)
NR[d]
NR[d]
11
1
2
TATAM
DMSO
K3PO4
-
DMSO
Dioxane
Toluene
DMF
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K2CO3
Cs2CO3
NaOH
TEA
100
3
Pd@TATAM
Pd@TATAM
Pd@TATAM
Pd@TATAM
Pd@TATAM
100
4
100
-
5
5
100
50
22
6
ACN
75
-
trace
15
7
DMSO
100
82
8
Pd@TATAM DMSO-H2O
100
-
10
9
Pd@TATAM
Pd@TATAM
Pd@TATAM
Pd@TATAM
Pd@TATAM
Pd@TATAM
PdCl2
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
100
29
trace
trace
14
10
11
12
13
14[e]
15
16
17
100
42
100
59
100
51
14
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
100
84
15
100
50
15
100
5
8
Pd(OAC)2
100
24
trace
15
Pd@TATAM
100
83
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18
19
20
21
Pd@TATAM
Pd@TATAM
Pd@TATAM
Pd@TATAM
DMSO
DMSO
DMSO
DMSO
K3PO4
K3PO4
K3PO4
-
90
82
84
16
trace
NR
-
120
RT
100
NR
24
[a]
Reaction condition: bromo benzene (1 mmol), elemental selenium (1 mmol), base (1.5 mmol), solvent (2 mL),
[c]
catalyst (20 mg of Pd@TATAM thePd content 0.034 mg), 100°C, 6 h. [b] Isolated yield based on bromo benzene.
Small amount of biphenyl homo coupled product, [d] NR = no reaction, [e] 10 mg of Pd@TATAM.
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Table 2. Pd@TATAM-catalyzed mono-selenation of various aryl halides[a] with elemental
selenium.
Entry
R-X
Product
code Yield (%) TON
1
2a
2b
84
82
70
1127
1115
757
2
3
2c
4
5
6
7
2d
2e
2f
76
76
78
71
910
644
927
701
2g
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8
2h
72
795
9
2i
2j
67
62
81
75
648
825
963
895
10
11
12
2k
2l
13b
2m
38
368
406
14b
15b
2n
2o
42
46
[a]
Ar
yl
438
halid
es (1mmol), elemental selenium (1 mmol), K3PO4 (1.5 mmol), DMSO (2 mL), Pd@TATAM (20 mg, 0.034 mg of Pd content), 100°C, 6h,
Isolated yield based on aryl bromide. [b] synthesis of unsymmetrical diaryl selenides from 4-substituted aryl halide (1mmol), bromobenzene (1
mmol), elemental selenium (1 mmol), K3PO4 (1.5 mmol).
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Shelton test
In order to check the heterogeneity of Pd@TATAM catalyst in our system were analyzed
by the Shelton test under the optimized reaction conditions. Shelton test was performed in
selenation of bromobenzene with elemental selenium as a model substrate (Figure 9a). The solid
catalyst Pd@TATAM was separated from the reaction mixture by simple centrifugation at this
time 2 hrs (conversion 25.5%); then filtrate solution was performed for a further 4 h and the
reaction mixture was analyzed by gas chromatographic technique, which showed no
improvement in the product conversion. This result indicates that no leaching of Pd NPs in the
filtrate solution and confirmed that the catalyst is truly heterogeneous in nature and Pd NPs are
strongly supported in the TATAM network.
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Figure 9. (a) Effect of reaction time and the percentage of bromo benzene conversion in
Pd@TATAM catalyzed C-Se coupling reactions and Hot filtration test for Pd@TATAM catalyst,
(b) Reusability experiment of Pd/TATAE catalyst.
Reusability test
Generally, the solid catalyst is one of the major important issues in metal supported
heterogeneous catalysis while during the course of the reactions. Some of the metal supported
catalysts are not reusable, unstable, tricky work up procedure and remarkable decreasing in
catalyst efficiency. In our catalytic system the reusability test was performed in the mono
selenation (C-Se) reaction and it was carried out with optimized reaction conditions to obtain
84% of yield. After that the catalyst was filtered and washed with water and to add the excess
amount of acetone to remove the inorganic base, unreacted selenates and other impurities.
Finally, the recovered catalyst was dried in a vacuum oven for 30 minutes. After the catalyst was
reused for another three consecutive cycles under the same reaction conditions, no significant
loss of catalytic activity (84%, 83%, 80% and 72% of yield) observed. On the basis of the above
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results, and also in accordance with previous literature reports,[45, 32] a plausible mechanism is
proposed and shown in Scheme 4.
Scheme 4. Plausible mechanism for the Pd@TATAM catalyzed C-Se coupling reactions.
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Table 5. Previously reported catalytic performance of different transition metal based catalyst
selenation reaction between bromobenzene with diselinide reagent or selenium powder.
S.No
Catalyst
Solvent
Base
Additive Catalyst Temp Time Yield
Ref
(mol%)
15
(°C)
110
120
100
110
90
(hrs)
24
20
6
(%)
84
80
97
92
96
85
95
85
92
82
84
1
2
CuI-bpy
Cu-TC
DMF
DMSO
DMSO
Na2CO3 Al, MgC
[32]
[33]
[46]
[47]
[48]
[49]
[50]
[51]
[52]
[53]
-
-
bipy
20
3
CuNPs/AC
CuO
-
10
4
DMSO Na3PO4
-
10
24
2
5
CuO NPs
DMSO
KOH
-
-
10
6
PdCl2(NCPh) DMSO
-
PPh3
-
10
120
120
140
150
45
12
24
24
24
12
6
7
Ni(OAc)2
CuCl2
Cu(OAc)2
-
DMF
DMF
Na2CO3
Na2CO3
10
8
10
9
Toluene K2CO3 1,10-Phe
15
10
11
H2O
KOH
TBAI
-
-
Pd@TATAM DMSO
K3PO4
0.5
100
Present
-work
Conclusions
In summary, we have demonstrated a facile synthesis of nitrogen containing covalent
triazine polymer which have developed from condensation reactions between melamine and
4,4',4"-(1,3,5-Triazine-2,4,6-triyl)tribenzaldehyde of commercially available and cheap starting
materials under solvothermal conditions. The CTPs have an accessible surface area, pore size
24
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10.1002/cctc.201800400
ChemCatChem
and good solid support for palladium NPs and Pd@TATAM with efficient, recyclable
heterogeneous catalytic activity towards mono selenation of arylhalide C-Se coupling reactions
to performed K3PO4 base, dimethylsulfoxide as a solvent at 100 °C for about 6 hrs. The C-Se
coupling reaction was using elemental selenium powder act as a selenating agent. In addition, the
reaction was carried out in the absence of any additional stabilizes ligand and also we got a very
good product yield over a very short reaction time. The reaction system shows tolerance toward
numerous substituted arylhalide to obtain the corresponding products in good to excellent yield,
the reactions employs environmentally friendly solvent and no additives/inert atmosphere/ligand
free protocol.
Experimental section
Materials and methods
All the chemicals and reagents were purchased from commercial reagent suppliers, used
without further purification as commercially available unless otherwise noted. All the solvents
1
13
were obtained from laboratory reagent grade. The H and C NMR spectra were recorded on a
Bruker (Avance) 300 and 400 MHz NMR instrument using TMS as an internal standard and
CDCl3 as a solvent. Chemical shifts are given in ppm (δ-scale) and the coupling constants are
13
given in Hz. C CP-MASNMR was recorded using a Burker Avance 500 MHz operating at 75
13
MHz for C nuclei. The thermal stability of the samples were evaluated by TGA (SCINCO
thermal gravimeter S-1000, Japan) under the Argon (Ar) atmosphere over the temperature range
o
o
upto 30-800 C, in flowing argon gas at heating rate of 5 C min-1. Powder X-ray diffraction
(PXRD) patterns were obtained on a Rigaku diffractometer using CuKα ( =1.5404 Å) source
with a scan rate of 0.5o min-1. The N2 adsorption-desorption isotherms were measured on a
25
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10.1002/cctc.201800400
ChemCatChem
BELsorp-Max (BEL, Japan) at 77 K. The surface area of the samples was calculated by using the
Brunauer–Emmett–Teller (BET) method and the pore sizes of the samples were calculated using
the NL-DFT model. The morphology and particle size of the polymerized materials were
examined by SEM and TEM. The scanning electron microscopy (SEM) measurements were
performed by VEGA3 TESCAN, CZECH REPUBLIC. Energy dispersive X-ray spectroscopy
(EDX) was carried out using Bruker Nano, Germany. The FT-IR spectra were obtained from a
JASCO FT/IR-410 spectrometer. Silica gel-G plates (Merck) were used for TLC analysis with a
mixture of n-hexanes and ethyl acetate as an eluent. Column chromatography was carried out on
silica gel (60-120 mesh) using n-hexanes and ethyl acetate as an eluent.
Synthesis of TATAM polymer
A 100 mL Schlenk tube was charged with melamine (30 mg, 0.13 mmol) and 15 mL (1:2)
of dioxane/DMSO mixture, and stirred well under nitrogen atmosphere. The resultant
homogeneous solution was treated with drop wise addition of 4,4',4"-(1,3,5-triazine-2,4,6-
triyl)tribenzaldehyde (100 mg, 0.132 mmol) dissolved in anhydrous THF (2 mL) and then finally
glacial acetic acid (6 M) was slowly added during this course of the reaction until the colorless
homogeneous solution was appeared. The reaction tube was capped tightly and then transferred
to oil bath, heated at 150 °C for about 3 days. After completion of the reaction, the mixture was
poured into 100 mL of water and stirred for 2 hrs, the colorless solid was completely settled in
the bottom of aqueous solution. In addition, the solid was filtered and subsequently washed with
water, DMF, acetone, THF, DCM, to remove the unreacted starting materials. After that, the
solid was immersed in acetone for one day and filtered, then dried at 80 °C under the vacuum
oven for 8 hrs to get 85% yield of colorless solid product. FT-IR (powder cm-1) 3325, 1640,
26
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10.1002/cctc.201800400
ChemCatChem
1546, 1490, 1341, 1127, 1034, 876, 783, 614. Elemental analysis calculated from EDS analysis
(Atomic %) for C27N13H15:C 52.31, N 37.27, H 3.45; found C 46.94, N 38.06, O 13.29, H 3.02.
Synthesis of Pd@TATAM polymer
To a stirred solution of solid TATAM (100 mg) was dispersed methanol (15 mL) in a 25
mL round bottom flask. PdCl2 (20 mg) was added into the reaction mixture then stirred at room
temperature for 30 minutes, meanwhile the colorless solid was changed to light brown color.
After that, the reducing agent hydrazine monohydrate (L) was subsequently added into the
reaction mixture and also maintained constant stirring for about 6 hrs, and then filtered, washed
with methanol (3 × 20 mL), acetone (3×20 mL) and water to remove the unreacted PdCl2. In
addition, the solid was dried in a vacuum oven at 70 °C for 8 hrs to obtain Pd@TATAM as a
light black colored powder (93 mg, 93% yield). FT-IR (powder cm-1) 3342, 1652, 1520, 1490,
1201, 1117, 1043, 810, 783, 614; Elemental analysis calculated from EDS analysis (Atomic %)
for C 48.42, N 37.09, O 12.47, Pd 0.65.
General procedure for selenation of Aryl halide to C-Se coupling reactions
Aryl bromide (1 mmol), elemental selenium (1 mmol), K3PO4 (1.5 mmol), Pd@TATAM
(20 mg) were taken in DMSO and the reaction mixture was stirred at 100°C for about 6 hrs.
After completion of the reaction (monitored by TLC), the reaction mixture was diluted with 5
mL ethyl acetate and then the catalyst was removed by simple filtration through celite bed. The
filtrate was washed with brine solution and extracted with an excess amount of ethyl acetate and
then concentrated under reduced pressure. The crude product was further purified by silica gel
(60-120 mesh) column chromatography (petroleum ether/ethyl acetate) to afford the
corresponding diarylmonoselinide and tiny amount of homo coupled byproduct was observed.
27
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10.1002/cctc.201800400
ChemCatChem
Acknowledgments
AS and VS acknowledge the financial support of the Department of Science and Technology,
SERB, Extramural Major Research Project (Grant No. EMR/2015/000969), Council of Scientific
and Industrial Research (CSIR), HRDG, No. 01(2901)/17/EMR-II, New Delhi, Department of
Science and Technology DST/TM/CERI/C130(G), New Delhi, India.
Keywords: Melamine, Elemental selenium, Diarylmonoselinide, Monoselinide, Solvothermal.
References
[1] P. Puthiaraj, S. M. Cho, Y. R. Lee, W. S. Ahn, J. Mater. Chem. A, 2015, 3, 6792-6797.
[2] L. Stegbauer, K. Schwinghammer, B. V. Lotsch, Chem. Sci., 2014, 5, 2789-2793.
[3] H. Furukawa, O. M. Yaghi, J. Am. Chem. Soc., 2009, 131, 8875-8883.
[4] S. B. Kalidindi, H. Oh, M. Hirscher, D. Esken, C. Wiktor, S. Turner, G. V. Tendeloo, R. A.
Fischer, Chem. Eur. J., 2012, 18, 10848-10856.
[5] Z. Li, X. Feng, Y. Zou, Y. Zhang, H. Xia, X. Liu, Y. Mu, Chem. Commun., 2014, 50, 13825-
13828.
[6] S. Wan, F. Gandara, A. Asano, H. Furukawa, A. Saeki, S. K. Dey, L. Liao, M. W.
Ambrogio, Y. Y. Botros, X. Duan, S. Seki, J. F. Stoddart, O. M. Yaghi, Chem. Mater., 2011,
23, 4094-4097.
[7] P. Puthiaraj, W. Seung Ahn, Catal. Commun., 2015, 65, 91-95.
[8] P. Puthiaraj, S. Sung Kim, W. Seung Ahn, Chem. Eng. J., 2016, 283, 184-192.
[9] P. Puthiaraj, K. Pitchumani, Chem. Eur. J., 2014, 20, 8761-8770.
[10] C. J. Doonan, D. J. Tranchemontagne, T. G. Glover, J. R. Hunt, O. M. Yaghi, Nat. Chem.,
2010, 2, 235-238.
28
This article is protected by copyright. All rights reserved.

10.1002/cctc.201800400
ChemCatChem
[11] N. L. Campbell, R. Clowes, L. K. Ritchie, A. I. Cooper, Chem. Mater., 2009, 21, 204-206.
[12] S. Y. Ding, W. Wang, Chem. Soc. Rev., 2013, 42, 548-568.
[13] Q. Fang, S. Gu, J. Zheng, Z. Zhuang, S. Qiu, Y. Yan, Angew. Chem. Int. Ed., 2014, 53,
2878-2882.
[14] L. Xu, L. Cao, Z. Guo, Z. Zha, S. Lei, Chem. Commun., 2015, 51, 8664-8667.
[15] F. J. Uribe-Romo, J. R. Hunt, H. Furukawa, C. Klock, M. OKeeffe, O. M. Yaghi, J. Am.
Chem. Soc., 2009, 131, 4570-4571.
[16] K. Sakaushi, M. Antonietti, Acc. Chem. Res., 2015, 48, 1591-1600.
[17] J. Long, H. Liu, S. Wu, S. Liao, Y. Li, ACS Catal., 2013, 3, 647-654.
[18] C. E. Chan-Thaw, A. Villa, P. Katekomol, D. Su, A. Thomas, L. Prati, Nano Lett., 2010,
10, 537-541.
[19] P. Kuhn, M. Antonietti, A. Thomas, Angew. Chem., Int. Ed., 2008, 47, 3450-3453.
[20] M. J. Bojdys, J. Jeromenok, A. Thomas, M. Antonietti, Adv. Mater., 2010, 22, 2202-2205.
[21] P. Katekomol, J. Roeser, M. Bojdys, J. Weber, A. Thomas, Chem. Mater., 2013, 25, 1542-
1548.
[22] R. Palkovits, M. Antonietti, P. Kuhn, A. Thomas, F. Schuth, Angew. Chem., Int. Ed., 2009,
48, 6909-6912.
[23] V. Sadhasivam, R. Balasaravanan, C. Chithiraikumar, A. Siva, chemistry select, 2017, 2,
1063-1070.
[24] P. Puthiaraja, K. Pitchumani, Green Chem., 2014, 16, 4223-4233.
[25] R. Imran Khana, K. Pitchumani, Green Chem., 2016, 18, 5518-5528.
[26] S. Patai, Z. Rappoport, The Chemistry of Organic Selenium and Tellurium Compounds,
John Wiley & Sons: New York, Vol 1, 1986-1987.
29
This article is protected by copyright. All rights reserved.