Pd Nanoparticles Decorated on Hypercrosslinked Microporous Polymer: A Highly Efficient Catalyst for the Formylation of Amines through Carbon Dioxide Fixation

Article abstract of DOI:10.1002/cctc.201700069

CO₂ fixation reaction is one of the most challenging chemical transformations not only in the context of environmental remediation but also for effective utilization of abundant carbon sources in nature. Here, we have stabilized palladium nanoparticles (NPs) at the surfaces of a hypercrosslinked porous polymer bearing carbazole and α,α′-dibromo-p-xylene monomeric units to obtain a Pd@HMP-1 nanocatalyst. The material has been thoroughly characterized by powder XRD, high-resolution (HR)-TEM, field-emission (FE)-SEM, Brunauer–Emmett–Teller (BET), thermogravimetric (TGA), and FTIR analysis. Pd@HMP-1 showed excellent catalytic activity towards formylation of amines by carbon dioxide fixation under mild reaction conditions. The high surface area and nitrogen-rich porous surface make the polymer a suitable support for the palladium nanoparticles and endow it with high recycling efficiency in this CO₂ fixation reaction.

Full text of DOI:10.1002/cctc.201700069

Accepted Article
Title: Pd NPs decorated over hypercrosslinked microporous polymer:
a highly efficient catalyst for the formylation of amines via carbon
dioxide fixation reaction
Authors: Rostam A Molla, Piyali Bhanja, Kajari Ghosh, Sk Safikul
Islam, Sk. Manirul Islam, and Asim Bhaumik
This manuscript has been accepted after peer review and appears as an
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of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: ChemCatChem 10.1002/cctc.201700069
Link to VoR: http://dx.doi.org/10.1002/cctc.201700069
A Journal of
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10.1002/cctc.201700069
ChemCatChem
FULL PAPERS
Pd NPs decorated over hypercrosslinked microporous
polymer: a highly efficient catalyst for the formylation of
amines via carbon dioxide fixation reaction
Rostam Ali Molla,[a] Piyali Bhanja,[b] Kajari Ghosh,[a,c] Sk Safikul Islam,[a,d] Asim Bhaumik,*[b] Sk Manirul Islam*[a]
Abstract: CO2 fixation reaction is one of the most challenging
chemical transformations not only in the context of environmental
remediation but for effective utilization of abundant carbon sources of
nature. Here, we have stabilized palladium nanoparticles (NPs) at the
surfaces of a hypercrosslinked porous polymer bearing carbazole and
ꢀ,ꢀ’-dibromo-p-xylene monomeric units to obtain Pd@HMP-1
nanocatalyst. The material has been thoroughly characterized by
powder XRD, HR TEM, FE-SEM, BET, TGA and FTIR analysis.
Pd@HMP-1 showed excellent catalytic activity towards formylation of
amines via carbon dioxide fixation reaction under mild reaction
conditions. High surface area and nitrogen rich porous surface make
the polymer suitable support for the palladium nanoparticles and its
high recycling efficiency in this CO2 fixation reaction.
1. Introduction
been reported. However, utilization of H2 as a reducing agent
required harsh reaction conditions[27] compared to hydrosilanes.
The carbon dioxide fixation reactions and its transformation to the
value added chemicals are very demanding in the context of
greenhouse gas control[1] and cost-effectiveness and green
organic synthesis as CO2 is a nontoxic, cheap and abundant
renewable C1 source.[2] Substitution of hazardous and toxic
carbon monoxide as a C1 source with carbon dioxide, is a
greener and sustainable move towards the production of carbonyl
group containing various important chemicals.[3] Up till now a wide
range of methodologies have been developed for the carbon
dioxide fixation reactions such as carboxylation of aryl
halides/alkynes,[4,5] formylation of aryl halides,[6,7] formylation of
amines,[8-10] methylation of amines and cyclization with epoxides
or aziridines.[11-15] Formylation of amines using carbon dioxide as
the C1 source is a very useful reaction as most of the N-
formylated products are used as the intermediates of various
agrochemicals, fragrances, drugs and dyes.[16-20] There are two
pathways to produce formylated amines, one is non carbon
dioxide pathway and the second one is carbon dioxide fixation
pathway. In case of non CO2 pathway either formaldehyde or
methanol is used as a CHO source.[21-23] On the other hand,
carbon dioxide fixation pathway involving CO2 as C-source is
more attractive than non CO2 pathway in terms of economy and
environmental concerns.
In last few years, the utilization of hydrosilanes as reducing agent
of carbon dioxide has increased tremendously.[28-30] Cantat et al
have used the hydrosilane for the formylation of amines via CO2
fixation reaction.[31-32] Latter on some other catalytic systems such
as imidazolium-based ionic liquids[33] and thiazolium carbine[34]
were reported. The former catalytic system showed good
recyclability. Non recyclable and homogeneous metal salts based
catalysts make the separation process difficult and costly. To
avoid the separation difficulties and also to make process cost
effective Gao et al. have reported covalent organic frameworks as
heterogeneous catalyst for this CO2 fixation reaction in the
presence of immobilized ionic liquids.[35] On the other hand, high
surface area, excellent stability of the polymeric framework and
tunable functional groups at the pore surface has made the
porous organic polymers a very demanding material for a wide
range of frontline applications. Recently, hypercrosslinked porous
organic polymers have been used as a solid support for noble
metal nanoparticles.[36-39] The synergy of the porous organic
polymer bearing metal binding sites and nanoparticles offer
exceptional recyclability and high activity in several catalytic
reactions.
First homogeneous catalytic system for N-formylation has been
reported by Haynes et al. using CO2 and H2 for the production of
DMF[24] followed by Noyori and co-workers using ruthenium
based homogeneous catalyst.[25,26] Recently, synthesis of
formamides from amines via CO2 fixation reaction using
hydrosilane or molecular hydrogen as the hydrogen source has
Herein, we report the synthesis of
a
hypercrosslinked
microporous polymer via Friedel-Crafts alkylation reaction
between ꢀ,ꢀ’-dibromo-p-xylene and carbazole. The resulting
hypercrosslinked microporous polymer HMP-1 is used as support
to stabilize tiny palladium nanoparticles to obtain Pd@HMP-1.
The Pd@HMP-1 material showed excellent catalytic activity for
the carbon dioxide fixation reaction with amines under mild
reaction conditions. The excellent stability, recyclability and
efficiency of the catalyst could be attributed due to the strong
binding of reactive Pd NPs on nitrogen containing
hypercrosslinked microporous structure.
[a]R. A. Molla, Dr. K. Ghosh, Prof. S. M. Islam
Department of Chemistry, University of Kalyani ,Kalyani, Nadia,
741235, W.B., India. E-mail: manir65@rediffmail.com
[b]P. Bhanja. Prof. A. Bhaumik
Department of Material Science, Indian Association for the Cultivation
of Science, Kolkata –700032, India. E-mail: msab@iacs..res.in
[c]Dr. K. Ghosh
2. Experimental
Department of Chemistry, University of Burdwan ,Burdwan, W.B.,
India
Synthesis of hypercrosslinked microporous polycarbazole
supported palladium nanomaterial (Pd@HMP-1):
[d]S. S. Islam
Department of Chemistry, Aliah University, Kolkata, W.B., India
Supporting information for this article is given via a link at the end of
the document. ((Please delete this text if not appropriate))
1
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10.1002/cctc.201700069
ChemCatChem
For synthesizing microporous polycarbazole based organic
framework we have explored the Friedel-Crafts alkylation
reaction.[40] ꢀ,ꢀ’-dibromo-p-xylene and carbazole undergoes the
Friedel-Crafts alkylation reaction in the presence of FeCl3
catalyst. In a typical reaction 50 mmol of ꢀ,ꢀ’-dibromo-p-xylene
(13.2 gm) and 25 mmol of carbazole (4.15 gm) and 8.5 gm FeCl3
were mixed in anhydrous dichloroethane (DCE) and stirred for 6 h
under N2 atmosphere at room temperature. After that the
the monomers suggested full incorporation of carbazol moieties in
the crosslinked polymeric backbone.
Pd(111)
Pd@HMP
0
temperature of the reaction mixture was increased to 80 C and
refluxed for 18 h. A brown colored precipitate was obtained and to
remove iron completely the precipitate was washed with methanol
by soxhlet apparatus. Again it was washed with acetone and
hexane consecutively and then dried in vacuum for overnight to
obtain HMP-1.
Pd (200)
500 mg HMP-1 was taken in a round bottomed flask and 60 mg
PdCl2 and 10 ml distilled water was added to it and stirred for 1h
at 100 0C. After that temperature was increased for complete
evaporation of water. It was then cooled to room temperature
followed by addition of 10 ml ethylene glycol and then stirring for
5 h at 160 0C. Finally the product was washed with methanol and
dried (Scheme 1) to obtain Pd@HMP=1.
Pd(220)
10
20
30
40
50
60
70
80
2
θ (degree)
Figure. 1 XRD analysis of Pd@HMP-1 material
Powder X-ray diffraction pattern of Pd@HMP-1 material is shown
in Figure 1. Microporous HMP-1 showed its distinguishing wide
diffraction hump located at 2ꢁ=19-21 degree which suggested the
amorphous nature of the polymeric material. High surface area of
the material is capable to bind the nanoparticles at its surface
with the help of nitrogen donor sites. Accordingly, Pd@HMP-1
material showed three additional prominent diffraction peaks at
40.20, 46.35 and 68.10 degrees corresponding to Pd(111),
Pd(200) and Pd(220) FCC crystal planes of metallic palladium.[41]
Microscopic analysis
Scheme 1: Schematic synthesis procedure polycarbazole supported
Pd NPs (Pd@HMP-1)
General procedure of formylation of amine:
Figure 2. The FE-SEM images of Pd@HMP-1 material at two
Formylation of amines was carried out in a 50 ml stainless-steel
reactor outfitted with a temperature controller and stirrer. 1.0
mmol of amine, 2.0 mmol of dimethylphenylsilane, 5 ml dioxane,
and 60 mg catalyst (Pd@HMP-1) were added in the high-
pressure reactor and then reactor was pressurized with CO2 (1
MPa) at 60 0C for 9h and then 0.3 ml of distilled water injected in
the reactor and continued for total 20 h. After completion of
reaction, the reactor was cooled, the CO2 was vented from the
reactor and the product was analyzed by GC.
different magnifications
In order to understand the morphological features of Pd@HMP-1,
field emission scanning electron microscopic (FE-SEM) image
analysis has been carried out. In Figures 2a and 2b the SEM
images of Pd@HMP-1 material are shown at two different
magnifications. It is noticed from Figure 2b the Pd@HMP-1
particles have spherical particle morphology with dimensions of
ca. 80-90 nm. These spherical particles are agglomerated to form
larger particles and this could be responsible for inter-particle
porosity as seen from the BET analysis.
3. Results and Discussion
3.1. Characterizations
The loading of palladium in Pd@HMP-1 has been estimated
through the AAS analysis and the observed palladium loading in
the catalyst was 4.52 weight %. We have carried out CHN
analysis to investigate the carbon, hydrogen and nitrogen content
in Pd@HMP-1, where observed C = 80.43 %, H = 5.72 % and N
= 4.26 %. Theoretically the carbon, hydrogen and nitrogen
content have been estimated to be 89.54 %, 5.86 %, 4.60 %,
respectively. Close N contents in Pd@HMP-1 with respect to the
proposed model structure of Scheme 1 with stoichiometric ratio of
Specific surface area, porosity:
The nitrogen adsorption/desorption isotherm of Pd@HMP-1
material is shown in Figure 3. As seen from the figure that the
isotherm can be classified as mixture of type I and IV according to
IUPAC nomenclature.[42,43] Initially the gradual N2 uptake at 0 to
0.1 partial pressure P/P0 region suggests the presence of
micropores in the material. This is followed by gradual increase in
N2 uptake in the partial pressure P/P0 region 0.20 to 0.90
2
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10.1002/cctc.201700069
ChemCatChem
suggested the presence of mesopores. These mesopores could
be attributed to the inter-particle porosity in the nanoscale. BET
~10-15 nm has been grafted successfully over the polymer
surface.
Thermal analysis
Figure 5. The TGA (a) and (b) DTA profile diagrams of
Figure 3. The N2 adsorption/desorption isotherm of Pd@HMP-1
material where filled circle represents adsorption and empty circle
defines desorption. The pore size distributions plot, obtained by
using NLDFT (Non Local Density Functional Theory) method, is
shown in the inset.
Pd@HMP-1 material.
To check the thermal stability of Pd@HMP-1 material
thermogravimetric analysis has been performed at 10 0C
temperature ramp under N2 flow up to 700 °C. Figure
5
represents the TG/DTA profile diagram for Pd@HMP-1 material.
0
The initial weight loss at ca. 90-120 C could be attributed to the
evaporation of adsorbed moisture from the material surface.
(Brunauer, Emmett and Teller) surface area and the pore volume
were 384 m2g-1 and 0.2171 ccg-1, respectively. Utilizing NLDFT
(non-local density functional theory) method the pore size
distribution plot has been demonstrated in the inset of Figure 3
where the peak pore diameters for Pd@HMP-1 of 0.6, 1.1 and
1.9 nm is observed. Peak pore diameter of parent HMP-1 as
observed at 1.6 nm[40] has been reduced to 1.1 nm after Pd
loading in Pd@HMP-1. From De Boer statistical thickness (t-plot)
the microporosity and mesoporosity contribution to the total BET
surface area of material are calculated as 338 and 46 m2g-1,
respectively.
Further,
a second weight loss has been observed in the
temperature region of 240 to 440 °C due to decomposition of
organic functional groups of polymeric framework. The third
weight loss started at 480 °C is for the decomposition of residual
part of material. The thermal analysis data revealed the good
thermal stability of Pd@HMP-1 material upto 240 °C.
HR TEM analysis:
Figure 4 HR TEM images of Pd@HMP-1 material.
In Figure 4, high resolution TEM images of the Pd@HMP-1
material are shown. The TEM images provide a clear idea about
the morphology of the Pd NPs in the material. Spherical nature
polymeric material with interconnected morphology is seen in this
TEM image (Fig. 4b). On the other hand, black dots at the surface
of the round shaped polymer are due to the deposition of the
palladium nanoparticles on the surface of the HMP-1 material.
Figure 4b confirms the palladium nanoparticles with a diameter of
Figure 6. Narrow range XPS spectra of Pd@HMP-1 material
containing elements Pd 3d (a), C 1s (b), N 1s (c), and full scale
XPS survey spectrum (d).
To get a better idea about the oxidation state of metal centre as
well as binding sites with organic part XPS analysis has been
performed. Figure 6 represents the narrow range XPS spectrum
of Pd@HMP-1 material, which suggested the presence of
3
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10.1002/cctc.201700069
ChemCatChem
elements C 1s (a), N 1s (b), Pd 3d (c), and Pd 3p (d). Figure 6c
shows the XPS spectrum of Pd 3d with two binding energy values
at 334.8 eV and 340.5 eV, corresponding to two splitting
component 3d5/2 and 3d3/2, respectively.[44] Further, since the
material is devoid of O, two peaks in the binding energy range
530-570 eV corresponds to the Pd 3p3/2 and 3p1/2.This result
suggested the presence of zero oxidation state of palladium (Pd0)
in Pd@HMP-1. The N 1s peak at 399.3 eV is attributed to the
presence of carbazole moiety, which can coordinate with the Pd
centres.
have injected small amount of water in the reactor under the
given reaction condition (Table 1, entry 5) which may produce
formic acid and it can further react with N-methylaniline to
generate N-phenylformamide.
Table 1: Effect of solvent and reducing agent on the N-
formylation reaction.
Entry Solvent
Reducing agent
GC yield
(%)
Catalytic Activity:
1
Toluene
THF
diphenylmethylsilane
diphenylmethylsilane
diphenylmethylsilane
H2 (1.5MPa)
15
58
87
23
93
Recently we have synthesized few porous nanomaterials and
utilized them in the carbon dioxide fixation reactions.[45,46] In this
work we have synthesized palladium nanoparticles supported on
nitrogen bearing crosslinked porous polymer and this catalyst has
been explored in the formylation of amines using CO2. Literature
reports suggested that there are two ways to produce formylated
amines via carbon dioxide fixation reaction. Molecular H2 was
used as reducing agent in one path and in another alternative
pathway, where hydrosilane was used as the reducing agent
using simple tetrabutylammonium fluoride or hydroxide as
catalyst.[47]
2
3
Dioxane
Dioxane
4
5a
Dioxane/H2O diphenylmethylsilane
Reaction conditions: N-methylaniline (1.0 mmol), Dioxane (5
ml), CO2 (1MPa), diphenylmethylsilane (2.5 mmol), Pd@HMP-1
(50 mg), Temperature (60 0C), time 20h. Reaction condition: 0.3
a
Iꢁ
ml water was added after 9h
I/hhIꢌCꢈꢇꢍꢂ ꢋ
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I
/ꢂ ꢂꢃꢄꢅ
b
The reaction parameters such temperature and catalyst amount
are also important in terms of conversion and selectivity. Both the
parameters are optimized (Table 2). We have tested the reaction
even at low temperature (30 0C) and got moderately good yield.
Conversion of the N-methylaniline increases with temperature, at
60 0C temperature maximum yield was obtained. Beyond this
temperature selectivity of the N-methyl-N-phenylformamide started
to decrease slightly and N, N-dimethylaniline was started to form.
The amount of catalyst which was required to get maximum yield
was optimized. When catalyst loading was low (20 mg) the amount
of desired yield was also low (36 %). The highest yield of N-
formylated product was obtained when catalyst amount was 50mg.
Reaction time was also optimized and at 20 h maximum yield was
obtained.
bIꢁ
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/Ih
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/ꢂ ꢂꢃꢄꢅ
wꢀ ꢑ ꢂꢃꢒꢄꢃꢌꢂꢇꢄꢃ ꢓꢇꢈꢔꢕ ꢈ ꢂꢍꢉꢊꢋ ꢂꢊꢆ wꢁ ꢑ ꢂꢃꢒꢄꢃꢌꢂꢇꢄꢃ ꢓꢇꢈꢔꢕ ꢈ !ꢄꢆꢇꢈꢅꢉꢃꢂꢊꢋ
Scheme 2: Formylation of amine through different pathways.
We have started the formylation reaction of the N-methylaniline
with diphenylmethylsilane as the reducing agent of carbon
dioxide. Initially we have taken 1 mmol of N-methylaniline, 2
mmol of diphenylmethylsilane and 5 ml of dioxane at 1 MPa CO2
pressure. The outcome of the result was interesting and we have
got 87 % of formylated product of N-methylaniline.
Table 2: Effect of catalyst amount and temperature on the N-
formylation reaction
Entry
Catalyst amount
(mg)
Temperature
(0C)
GC yield
(%)
CHO
HN
1
2
3
4
5
6
7
8
50
50
50
50
50
20
40
-
30
40
50
60
80
60
60
60
56
68
85
93
88
36
79
-
N
Pd@HMP-1
diphenylmethylsilane
Carbon dioxide (1MPa)
Scheme 3: Formylation of N-methylaniline catalyzed by Pd@HMP-1
For optimization we have screened all the parameters. Solvent is
very important parameter for the reaction. Thus we have tested
some other solvents like THF and toluene but these solvents
were not superior to dioxane for the reaction. Similarly reducing
agent is also important. We have employed hydrogen as a
reducing agent but desired yield was low. Detailed study is given
in the Table 1. To increase the desired yield we have injected 0.5
ml water after 6h (Table 1, entry 5). The increase in yield (%) can
be explained on the basis of previous literatures which suggested
that formic acid or formate salt formed in the reaction medium,
reacted with amine to produce formylated amine.[48,49] Thus we
9a
50
60
90
Reaction
conditions:
N-methylaniline
(1.0
mmol),
diphenylmethylsilane (2.5 mmol), dioxane (5 ml + 0.3 ml water
was added after 9h), CO2 (1Mpa), time 20h. aReaction time (15
h).
4
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10.1002/cctc.201700069
ChemCatChem
Effect of CO2 pressure on the reaction was checked by varying
pressure from 0.1 MPa to 1.2 MPa. When CO2 pressure was low
(near 1 atmosphere) yield of N-methyl-N-phenylformamide was
below 20 %. But when CO2 pressure was increased, yield was
also increased. Maximum yield was formed at 1 MPa pressure,
after that yield remained almost constant (Fig.7).
Under the optimized reaction conditions we have tested some
other amines such as substituted aniline, morpholine and
piperidine. All the mentioned substrates (Table 4, entries 1-7)
produced their corresponding formamide with excellent yield.
Based on our experimental results and literature reports[50,51] we
can propose a mechanistic pathway for the N-formylation reaction
over Pd@HMP-1 and this is shown in Scheme 4. Main role of the
support is immobilization of the active centres. Initially Si-H bond
of Me2PhSiH has been activated by palladium nanoparticle
present in Pd@HMP-1 and consequently activated silane reacts
with carbon dioxide to form formyloxysilane intermediate (i)
which further reacts with amine to form desired product. On the
other hand, intermediate (i) reacts with water to form HCOOH.
Microporous polymer containing the free N-donor sites of
carbazole can catalyze the reaction between formic acid and
amine to produce N-fomylated product (Scheme 4).
100
80
60
40
20
0
CO
2
MPa
mmol
1.8
7.2
10.8
16.2
18.0
21.6
0.1
0.4
0.6
0.9
1.0
1.2
Table 4. Formylation of various amines under optimized reaction
conditions
Entry
Substrate
Product
GC
yield
(%)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
CO Pressure (MPa)
2
H
N
93
91
88
N
H
1
2
Figure 7. Effect of CO2 pressure on the N-formylation reaction.
Reaction conditions: N-methylaniline (1.0 mmol),
diphenylmethylsilane (2.5 mmol), Dioxane (5 ml + 0.3 ml water
was added after 9h), time 20 h.
O
H
N
N
H
We have also tested the effect of some other supports on this N-
formylation reaction (Table 3). We have loaded Pd NPs over the
TiO2 nanoparticles. When Pd/TiO2 was employed as catalyst the
selectivity of formylated yield was decreased due to the formation
of N-methylated product (Table 3, product-B). Commercially
purchased Pd/C was also active for the reaction but the yield (%)
was low compared to Pd@HMP-1. In the absence of PdNPs,
HMP-1 was also gave the desired the product (22%), which could
be attributed due to the presence of N-donor siltes present at the
HMP-1 surface. Only trace amount of the desired product was
obtained in the absence of any catalyst (Table 3, entry 6). HMP-1
alone can also catalyze the reaction to a certain extent. Basic
nitrogen sites are present inside the pore and as well as outside
the pore i.e on the external surface. These basic nitrogens is also
be able to promote the interation between amine and silane which
facilitated the reaction to some extent and thus produced small
amount desired N-formylated product.
O
H
N
N
H
3
4
O
F
F
NH2
H
79
N
H
O
H
NH2
5
6
87
97
N
H
Table 3. Effect of different catalysts on formylation of aniline
O
H3CO
R-NH2
RNHCHO
A
Catalyst
RNHCH3
B
B (%)
H3CO
Entry
A (%)
NH
N
O
1
2
4
5
6
Pd@TiO2
Pd@C
58
84
22
93
0.4
36
-
O
O
HMP-1
-
7
95
Pd@HMP-1
-
N
NH
O
without
catalyst
-
Reaction conditions: Amine (1.0 mmol), diphenylmethylsilane
(2.5 mmol), Dioxane (5 ml + 0.3 ml water was added after 9h),
CO2 (1MPa),temperature (60 0C), Pd@HMP-1 (50 mg), amine:
palladium molar ratio is 1:0.021, time 20h.
Reaction conditions: aniline (1.0 mmol), diphenylmethylsilane
(2.5 mmol), Dioxane (5 ml + 0.3 ml water was added after 9h),
CO2 (1MPa),temperature (60 0C), Catalyst (50 mg), time 20h.
5
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10.1002/cctc.201700069
ChemCatChem
Catalyst reusability:
Table 3 entry 4 showed that the reaction may also carried out
some extent in the presence of microporous HMP-1 polymer
alone. But reactivity of the catalyst is much higher when Pd
nanoparticles are loaded on HMP-1. So, the nitrogen present in
the microporous material (HMP-1) can plays two important role;
first is to stabilize the Pd nanoparticles on the porous surface
(mainly through outer surface nitrogen) and secondly is helps to
catalyze the reaction. Recently, Gao et al have reported the
formylation reaction using microporous COF material
([Et4NBr]50%-py-COF, pore size 1.6 nm).[53] Thus, this formylation
can also be carried out within the micropores bearing the active
sites. So, the main role of Pd@HMP-1 material with nitrogen
containing micropores is to act as a supporting centre to enhance
the overall productivity of the reaction.
The Pd-HMP-1 catalyst showed very good recyclability in this N-
formylation reaction. At the end of the reaction the catalyst was
removed by plain filtration washing with acetone. The catalyst
was dried up in oven at 80 0C. Under the optimized reaction
condition the catalyst employed for 2nd run and it was observed
that efficiency of the catalyst was lowered by only 2%. In this way
the catalyst can be reused upto 5 times. In these successive
cycles almost similar reactivity was observed (Fig. 8). This result
suggested that Pd@HMP-1 is a very efficient catalyst for the N-
formylation reaction. We have carried out the same recycling
experiments with 10 mg catalyst instead of 50 mg catalyst. In that
perticular case we have got 28% yield for the 1st cycle and 21%
for the 5th reaction cycle. Little decrease in the product yield
during the recycling experiment could be attributed to minor
deactivation and loss of catalysts during the workup.
Conclusion
In conclusion, palladium nanoparticles are supported efficiently
over a hypercrosslinked microporous polycarbazole (Pd@HMP-1)
and the resulting material can catalyze the formylation of amines
in the presence of carbon dioxide as C1 source. In this reaction
diphenylmethylsilane is used as effective reducing agent in the
presence of CO2. Various aromatic and non aromatic amines
produced their corresponding formylated amines. The crosslinked
polymer containing nitrogen sites can bind the palladium
nanoparticle at the surface of the polymer very strongly. The
catalyst can be recycled several times without much decrease in
its activity. Thus, the protocol reported herein for the synthesis of
Pd NPs decorated hypercrosslinked microporous polymer and its
efficient use in the CO2 fixation reaction under green conditions
for the N-formylated products may open new avenues in
environmental and catalysis research in near future.
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Acknowledgements
/
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wꢆwꢄ
I/hhI
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SMI gratefully acknowledges Department of Science and
Technology, (DST-SERB, Ref. EMR/2016/004956), New Delhi,
Govt. of India, Council of Scientific and Industrial Research
(CSIR, Sanction No. 02(6206)/16 dated 01/12/16), New Delhi,
Govt. of India, for financial support. RAM acknowledges
University Grant Commission (UGC) New Delhi, India for his
Maulana Azad National Fellowship (F1-17.1/2012-13/MANF-
2012-13-MUS-WES-9628/SA-III). KG acknowledges DST (SERB-
t$ꢀ
Ia
Scheme: 4: Probable reaction path way of N-formylation of
amines.
NPDF),
for
her
National
Post
Doctoral
Fellowship
(PDF/2016/000160). SSI acknowledges UGC for his for his
Maulana Azad National Fellowship. SMI also acknowledges DST
and UGC for providing funds to the Department of Chemistry,
University of Kalyani through PURSE, FIST and SAP
programmes. PB thanks CSIR, New Delhi for a senior research
fellowship.
100
80
60
40
20
0
Catalyst amount 50mg
Catalyst amount 10 mg
Keywords: Polycarbazole; cross-linked porous polymers; palladium
NPs; carbon dioxide fixation; formylation reaction.
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10.1002/cctc.201700069
ChemCatChem
Table of Contents
FULL PAPER
Rostam Ali Molla, Piyali Bhanja, Kajari
Ghosh,
Sk Safikul Islam, Asim
Bhaumik,* Sk Manirul Islam*
Pd
NPs
decorated
over
hypercrosslinked
microporous
polymer: a highly efficient catalyst for
the formylation of amines via carbon
dioxide fixation reaction
CO2 fixation via formylation of material showed high catalytic activity
amines: Pd nanoparticles are grafted towards formylation of a wide range of
at the surface of a hypercrosslinked aromatic amines via carbon dioxide
porous polymer and the resulting
fixation reaction under mild conditions.
8
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