A new class of organoplatinum-based DFNS for the production of cyclic carbonates from olefins and CO2

Article abstract of DOI:10.1039/d0ra01696a

We studied the potential application of an efficient, reusable, and easily recoverable catalyst of dendritic fibrous nanosilica (DFNS)-supported platinum(ii) complexes (DFNS/Pt(ii) NPs) to form cyclic carbonates in the presence of epoxides by converting carbon dioxide. Cyclic carbonates from epoxides and carbon dioxide is proposed as the most appropriate way to synthesis this C1 building block. We performed FE-SEM, TEM, TGA, BET, VSM, and ICP-MS to thoroughly characterize DFNS/Pt(ii) NPs.

Full text of DOI:10.1039/d0ra01696a

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A new class of organoplatinum-based DFNS for the
production of cyclic carbonates from olefins and
CO2
Cite this: RSC Adv., 2020, 10, 15044
Maryam Abassian, Rahele Zhiani, * Alireza Motavalizadehkakhky, *a
Hossein Eshghi
a
b
c
d
and Jamshid Mehrzad
We studied the potential application of an efficient, reusable, and easily recoverable catalyst of dendritic
fibrous nanosilica (DFNS)-supported platinum(II) complexes (DFNS/Pt(II) NPs) to form cyclic carbonates in
the presence of epoxides by converting carbon dioxide. Cyclic carbonates from epoxides and carbon
dioxide is proposed as the most appropriate way to synthesis this C1 building block. We performed FE-
SEM, TEM, TGA, BET, VSM, and ICP-MS to thoroughly characterize DFNS/Pt(II) NPs.
Received 21st February 2020
Accepted 20th March 2020
DOI: 10.1039/d0ra01696a
rsc.li/rsc-advances
CO2 to the epoxide ring still requires more studies and
evaluations.
Due to their high specic surface area, reduced dimension-
Introduction
18,19
Currently, the conversion of carbon dioxide to suitable organic
1
–5
compounds is a signicant research eld. This approach ality and remarkable properties, two-dimensional (2D) nano-
reduces greenhouse gas emission and waste materials from sheets have become an ideal platform for the design of novel
2
0–27
chemical industries and requires a non-toxic, non-ammable, electrocatalysts for CO
2
reduction.
Borophene is a novel 2D
6,7
and readily available carbon raw material. However, it is not material under active investigation due to its fascinating and
28
signicantly used in different industries because of the low diverse properties and potential. The properties of borophene
reactivity of carbon dioxide. Highly active catalysts, optimized can be enhanced and extended by alloying with other elements.
conditions, high energy inputs, etc. are the known essential This may provide new opportunities to design functional
parameters in the thermodynamic conversion of stable carbon materials or catalysts.
8
dioxide molecules.
For organic transformations, octahedral Ru(II) and Ir(III)
Cyclic carbonates can be used in many industrial elds such chromophores are commonly used as photocatalysts through
29
as lithium batteries, electrolytes in monomers and aprotic polar outer sphere interactions to substrates. A group of scholars
solvents and intermediates in organic synthesis. Currently, presented a type of Ir(III) complex that has a labile coordinated
distinct cyclic carbonate combinations have been produced ligand for photochemical reactions through the interactions of
30,31
from carbon dioxide. Among them, carbon dioxide cycloaddi- the inner sphere. Pt(II) complexes
with vacant axial coordi-
tion to epoxides is known as one of the common industrial nation sites can provide greater opportunities in comparison to
9,10
methods.
The direct synthesis of cyclic carbonates from the octahedral Ir(III) and Ru(II) chromophores since these
olens and carbon dioxide (CO ) by using oxidative carboxyla- complexes can exhibit both inner sphere and outer sphere
2
tion (refer to Scheme 1), which comprises the cycloaddition of interactions with substrates. Nevertheless, a few investigations
alkene epoxidation and the addition of CO to the synthesized in terms of photo-induced organic transformation reactions
2
32–35
epoxide, can be a cost-efficient method because it requires low- using the complexes of Pt(II) are reported.
In ref. 36, the
cost and readily available raw materials, alkenes, and does not
11–17
require epoxide separation.
Olen oxidative carboxylation
was rst presented in 1962. Nevertheless, the cycloaddition of
a
Department of Chemistry, Faculty of Science, Islamic Azad University, Neyshabur
Branch, Neyshabur, Iran. E-mail: amotavalizadeh@yahoo.com
b
New Materials Technology and Processing Research Center, Department of Chemistry,
Islamic Azad University, Neyshabur Branch, Neyshabur, Iran. E-mail: R_zhiani2006@
yahoo.com
c
Department of Chemistry, Faculty of Science, Ferdowsi University of Mashhad,
Mashhad, Iran
Scheme 1 Synthesis of cyclic carbonates through oxidative carbox-
ylation of alkenes.
d
Department of Biochemistry, Faculty of Science, Islamic Azad University, Neyshabur
Branch, Neyshabur, Iran
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scholars reported an approach for the diuoro alkylation of
cinnamic acid by harnessing the photo-redox properties of the
reductive capability of a Cu(I) catalyst and a Ru(II) complex. In
this work, we showed that DFNS core–shell NPs could be effi-
37–39
ciently functionalized using the Pt(II) complex,
which is
a novel recoverable heterogeneous nanocatalyst for the envi-
ronmentally friendly, selective and efficient production of cyclic
carbonates from olens and CO , as shown in Scheme 1.
2
Experimental
General procedure for the preparation of DFNS NPs
First, 2.5 g of tetraethyl orthosilicate (TEOS) was dissolved in
a solution of 30 mL of cyclohexane and 1.5 mL of 1-pentanol.
Then, 1 g of cetylpyridinium bromide (CPB) and 0.6 g of urea
were dissolved in 30 mL of water and added to the previous
solution. The resulting mixture was continuously stirred at
ꢀ
room temperature for 45 min and heated at 120 C for 5 h aer
placing it in a teon-sealed autoclave. Aer silica was formed, it
was centrifuged and isolated, washed with an acetone-
deionized water mixture, and dried in a drying oven. Then, Fig. 1 FESEM images of DFNS NPs (a) and DFNS/Pt(II) NPs (b); TEM
images of DFNS NPs (c) and DFNS/Pt(II) NPs (d).
ꢀ
40
the material was calcined in air at 550 C for 5 h.
General approach for the DFNS/3-iodopropylsilane NP
production
subsequently reduced by NaBH
The solution was then treated with 1 M HCl, and the organic
phase was extracted with CH Cl
(3 Â 30 mL). Aer drying over
MgSO and evaporation, 1,2-bis(benzylamino)ethane was iso-
4 3
(30 mmol) in CH OH (30 mL).
DFNS NPs (2 mmol) were added to 20 mL THF and ultra-
sonicated with 20 mmol of NaH. Then, 22 mmol of 3-iodopro-
pyltriethoxysilane was added dropwise under the temperature
2
2
4
lated as a solid. 1,2-Bis(benzylamino)ethane (0.10 mol) was
dissolved in toluene (15 mL) and N,N-dimethylformamide
dimethylacetal (0.12 mol) was added. The solution was placed
in a water bath for 3 h in an inert atmosphere. At the end of this
ꢀ
of 25 C and for 16 h, the mixture was stirred under the
ꢀ
temperature of 60 C. The resultant products were rinsed
several times with deionized water and ethanol and dried in
ꢀ
40
a vacuum oven for 2 h under the temperature of 60 C.
ꢀ
period, the mixture temperature was raised to 100 C and
allowed to stand for 1 h (Scheme 1). Toluene was removed by
putting the mixture in vacuum, and the product was used in the
synthesis of the complex, which was very sensitive to air
humidity and oxygen. The electron-rich olen (0.1 mol) was
dissolved in toluene and then, [PtCl (PEt ) ] (0.9 mol) was
General approach for the DFNS/Pt(II) NP production
DFNS/3-iodoopropylsilane (20 mmol) and ethylenediamine (10
mmol) were stirred overnight in methanol. Diimine was
collected as a white solid, ltrated and recrystallized in an
alcohol–ether mixture. The diimine (10 mmol) was
2
3 2 2
ꢀ
added and heated at 100 C for 5 h. The solution was placed in
vacuum to give a yellow solid. Aer washing with hexane, the
Scheme 2 Schematic illustration of the synthesis of KCC-1/Pt-NHC-
Py NPs.
Fig. 2 TGA diagram of DFNS/Pt(II) NPs.
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Table 1 Structural parameters of DFNS and DFNS/Pt(II) NPs deter-
mined from nitrogen sorption experiments
2
À1
3
À1
Catalysts
S
BET (m g
)
V
a
(cm g
)
DBJH (nm)
DFNS
DFNS/Pt(II)
421
348
1.34
1.11
9.89
7.01
product was crystallized in a dichloromethane–diethyl ether
mixture (1 : 2).
Catalytic reactions
Fig. 4 Three-dimensional AFM image of DFNS/Pt(II) NPs.
The reaction was performed in a stainless steel autoclave (25
mL). Eight mg of catalyst, 10 mmol of olen and 20 mmol of
TBHP were placed in the stainless steel autoclave. The ꢁ400 nm. As can be seen in Fig. 1c, the TEM image of DFNS
compound was stirred using a magnetic stirrer and then heated indicates that the wrinkled bers that have ꢁ10 nm thickness
to a proper temperature by placing in a water bath. The reactor are radially regulated in three dimensions and grow out from
was purged with carbon dioxide several times and then charged the center of the spheres. In addition, cone-shaped open pores
by carbon dioxide. Then, the stainless autoclave was heated to can be formed due to the overlapping of the wrinkled radial
a proper temperature and stirred for 10 hours. The reactor was structure. The TEM and FESEM images indicated that the
ꢀ
cooled to 25 C aer the reaction was complete, and the residual sphere was solid and composed of bers. In addition, the bers
CO2 was discharged slowly from the reactor. The reaction and also this open hierarchical channel structure provide better
solution was examined using GC-MS and GC.
mass transfer of reactants and can enhance the availability of
active sites. The TEM and FESEM images of DFNS/Pt(II) NPs
indicated that aer the modication of DFNS, the morphology
did not vary (Fig. 1b and d). Fig. 2 shows the thermal conduc-
Results and discussion
ꢀ
tivity of DFNS/Pt(II) NPs. The weight loss under 150 C was
As can be inferred from Scheme 1, DFNS core–shell NPs were
fabricated using a simple approach and then functionalized
using N-heterocyclic carbene platinum(II). We used different
analysis techniques like TGA, TEM, BET, and SEM to charac-
terize the DFNS/Pt(II) NPs produced by different methods (refer
to Scheme 2).
The structure and morphology of DFNS/Pt(II) and pristine
DFNS NPs were subsequently characterized using TEM and
FESEM. The FESEM image of the highly textured DFNS samples
is shown in Fig. 1a. As observed, the samples possess spheres of
uniform size with a wrinkled radial structure and diameters of
ascribed to the elimination of the physisorbed and chem-
isorbed solvent on the surface of the DFNS/Pt(II) material. In the
ꢀ
range of 180–350 C, the weight loss is around 37.4 wt%, which
may be due to the organic group derivatives.
For DFNS, the BET surface area, BJH pore diameter, and total
2
À1
pore volume were obtained as 421 m g , 9.89 nm, and 1.34
3
À1
cm g , respectively, while the values for DFNS/Pt (II) NPs were
Fig. 3 The EDX spectra of DFNS/Pt(II) NPs.
Fig. 5 FTIR spectra of (a) DFNS NPs and (b) DFNS/Pt(II) NPs.
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2
À1
3
À1
reduced to 348 m g , 7.01 nm and 1.11 cm g , respectively.
The nitrogen sorption evaluation of DFNS/Pt(II) NPs addition-
ally emphasized a uniform and ordered mesostructure with
a reduction in pore volume, pore diameter, and surface area
compared to that for pristine DFNS. The related pore volumes
considerably decreased due to the functionalization using Pt-
NHC-Si. This can be attributed to enhanced loading with the
sensing probe that can occupy a large volume of the silica
spheres (Table 1). As indicated in Fig. 3, the EDAX spectra
provide clear evidence for chemical evaluation. O, Si, Cl, Pt,
P, N, and C are demonstrated to be present in the DFNS/Pt(II)
NPs. The level of roughness in these NPs was determined by
analysing the samples with atomic force microscopy (AFM). The
topographic scheme can be seen in Fig. 4. Fig. 4 shows that the Fig. 6 Effect of the increasing amount of DFNS/Pt(II) NPs on the yield
of cyclic carbonate.
more heighted region indicated by brighter yellowish white
color increases by reducing T/W, proposing the enhancement in
the level of roughness of the catalyst.
parameters like solvents and time on the model reaction can be
observed from Table 2. Various solvents were utilized to study
their effect on the synthesis of cyclic carbonates. Our outcomes
proved that with the polar protic solvents like ethanol, meth-
anol, isopropanol, and water, no product could be obtained.
Polar aprotic solvents like EtOAc, DMSO, and DMF indicated
mild efficiency for cross-coupling. In the present paper, our
results proved that solvents are less efficient compared to
common heating at solvent-free conditions. The efficiency of
the cross-coupling reaction for carbonylation is higher in less
polar solvents like toluene and/or anisole. The reaction was
performed under optimum conditions in the presence of DFNS/
Pt(II) nanoparticles (10 mg) for investigating the reaction prog-
ress. Note that the effect of reaction time was analyzed by GC. It
was determined that excellent product yields were achieved
aer 5 h. The inuence of distinct factors was analyzed for
DFNS/Pt(II) NPs for the model reaction. Fig. 6 shows the effect of
the amount of the catalyst, like other factors, on the yield. In
addition, in the absence of the catalyst, low yields of the product
FTIR spectra (Fig. 5) prove the existence of organic groups in
a) the nanoparticles of DFNS along with (b) DFNS/Pt(II). The
(
À1
À1
broad absorption peaks at 3389 cm
and 1101 cm
are
attributed to OH and Si–O–Si asymmetric stretching, respec-
À1
tively, for DFNS/Pt(II). Fig. 5a shows two peaks at 802 cm and
À1
4
70 cm , corresponding to Si–O–Si symmetrical bending and
stretching. The above-mentioned peaks also demonstrated the
linkage of platinum(II) complexes on DFNS. The DFNS/Pt(II)
À1
composite shows bands at around 493, 802, and 1191 cm . A
wide and powerful absorption band observed in the range of
À1
3
000–3500 cm is related to the stretching vibrations of –OH.
In our system, for the synthesis of cyclic carbonates catalyzed
using DFNS/Pt(II) NPs, the conditions of the reaction are opti-
mized with respect to olen and CO . The inuence of different
2
Table 2 Synthesis of cyclic carbonates by DFNS/Pt(II) NPs in different
a
solvents
b
Entry
Solvent
Time (h)
Yield (%) of the cycloaddition reaction were obtained. The cyclic
carbonate products demonstrated mild yields with the weighed
1
2
3
4
5
6
7
8
9
H
i-PrOH
EtOH
MeOH
n-Hexane
Dioxane
DMF
2
O
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
7
—
quantities of DFNS/Pt(II) NPs equal to 2–8 mg. For the model
reaction, the optimum value of DFNS/Pt(II) NPs was determined
to be 10 mg.
—
—
—
—
—
35
38
33
40
37
29
46
48
50
97
97
97
84
THF
CHCl
CH Cl
DMSO
CH CN
EtOAc
Toluene
3
10
11
12
13
14
15
16
17
18
19
2
2
3
Anisole
Solvent-free
Solvent-free
Solvent-free
Solvent-free
5
3
a
2
Reaction conditions: appropriate CO (3.0 MPa), olen (10 mmol),
DFNS/Pt(II) NPs (10 mg), TBHP (20 mmol), and solvent (10 mL), under
ꢀ
b
reux or at 100 C. Isolated yields.
Fig. 7 Effect of temperature on the yield of cyclic carbonate.
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the reaction pressure to 2.0 MPa was desirable for the cyclic
production of carbonate. Hence, 2.0 MPa pressure of CO was
2
detected as a special condition. During the rst step of the
ꢀ
reaction, the temperature of 80 C for 4 h (10 mol%) was
applied. Different oxidants were also utilized to enhance the
yield of the product. The reaction yield was extremely sensitive
to the base. To be precise, catalyst basicity is not the only
parameter in determining activity. The highest yield was ob-
tained by TBHP as an oxidant based on the results reported in
Fig. 9.
Fig. 8 Effect of CO
2
pressure on the synthesis of cyclic carbonate.
a
Table 4 Cycloaddition of CO
2
with terminal olefins
Entry Olens
Products
Yield (%)
1
97
2
93
Fig. 9 The screening of the oxidant nature.
3
4
5
95
90
96
Fig. 7 indicates the effect of temperature on the yield of the
ꢀ
reaction. As observed, under 3.0 MPa CO pressure at 80
C
2
within 5 h, the cyclic carbonate production enhances to around
7%. Nevertheless, a further increase in temperature caused
slight reduction in the yield of the product because of the
production of small amounts of specic by-products like olen
isomers. Hence, the most appropriate temperature in the case
9
of the parallel reactions of CO
2
and olen was found to be about
ꢀ
1
00 C. The pressure of CO had a considerable inuence on the
2
parallel reaction. Fig. 8 shows that the reaction rate is enhanced
rapidly under pressures between 1.5 and 2.0 MPa. By taking
previous works into consideration, it was found that enhancing
a
2
Table 3 Influence of different catalysts for the cycloaddition of CO
b
Entry
Catalyst
Catalyst loading
Yield (%)
1
2
3
4
5
DFNS
10.0 mg
—
97
97
73
95
6
98
DFNS/Pt(II)
DFNS/Pt(II)
DFNS/Pt(II)
Pt(II) complex
10.0 mg (2.0 mol (%) of Pt(II))
10.0 mg (1.0 mol (%) of Pt(II))
10.0 mg (0.5 mol (%) of Pt(II))
10.0 mg
a
a
Reaction conditions: appropriate CO
2
(2.0 MPa), aniline (1.0 mmol),
Reaction conditions: appropriate CO
2
(2.0 MPa), aniline (1.0 mmol),
ꢀ
b
ꢀ
and TBHP (20 mmol), under 100 C. Isolated yield.
catalyst (10 mg), and TBHP (20 mmol), under 100 C.
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a
Table 5 Comparison of the catalytic efficiency of DFNS/Pt(II) NPs with that of various catalysts
Entry
Catalyst
Experimental conditions
Average yield (%)
ꢀ
1
2
3
4
5
6
7
8
9
[Ru(TPP)(O)
2
]
DCM as solvent, 30 C, 48 h
53 (ref. 41)
32 (ref. 42)
77 (ref. 43)
82 (ref. 44)
49 (ref. 45)
69 (ref. 46)
70 (ref. 47)
63 (ref. 48)
94
ꢀ
Manganese(III)-complex
Co(acac) -QPB@MCS
[ZnW12
Ti-MMM-E
MeCN as solvent, 100 C, 6 h
MeCN as solvent, 100 C, 10 h
Solvent-free, 50 C, 96 h
ꢀ
2
6
ÀÀ
ꢀ
ꢀ
O
40
]
Solvent-free, 70 C, 48 h
ꢀ
Fe(III)@MOF1
NBS/DBU
DCM as solvent, 50 C, 24–48 h
ꢀ
H
2
O as solvent, 60 C, 3–6 h
ꢀ
[C
n
m
C Im][HCO
3
]
TBHP as solvent, 65 C, 30 h
ꢀ
DFNS/Pt(II)
Solvent-free, 100 C, 5 h
a
Reaction conditions: pyrrolidine in different temperatures, times, and solvents.
To further study the performance of the catalyst, various
The comparison of the catalytic activity of DFNS/Pt(II) with
control measurements were obtained and the achieved results that of other recent catalysts used for the cycloaddition of CO
2
are demonstrated in Table 3. In the rst step, a standard reac- can be seen in Table 5. The results showed that our catalyst
tion performed utilizing DFNS indicated that no product was system had the highest yield of the product for the same reac-
produced aer the reaction time of 5 hours (refer to Table 3, tion time although a catalytic amount of a base was required,
entry 1). DFNS could not exhibit any catalytic activity at mild which conrmed that our catalyst was more active.
reaction conditions. In order to enhance the yield, the Pt(II)
As can be seen in Fig. 10, aer 10 runs, the catalyst may be
complex was added due to these disappointing outcomes. These reused. The yield of the cyclic carbonate product obtained in the
th
results indicated that the reaction cycle was particularly cata- 10 run was equal to 92% and was only 5% lower than that of
lyzed by using the Pt(II) complex. It should be noted that there is the fresh catalyst (97%). Also, the leached metal amount in the
no considerable variation in the reaction yields when the reac- solution for cyclic carbonate production for each run was
tion is performed in the presence of the Pt(II) complex (refer to investigated by utilizing ICP. Fig. 11 shows that the catalyst
Table 3, entries 3 and 5). The activity of the Pt(II) complex was leached very little aer 10 runs and aer every run, just 0.8% of
also analyzed by changing the amount of Pt(II). The highest the metal leached.
efficiency was achieved with 1.0 mol (%) of Pt(II), as can be
In this paper, a complete investigation of the heterogeneous
observed in Table 3, entries 2–4. In addition, the Pt(II) complex nature of the catalyst was performed. Initially, for the synthesis
could not be recovered and reused for the next runs. DFNS was of cyclic carbonate, we performed the hot ltration experiment
utilized for preventing the dispersion of the Pt(II) complex and at mild conditions and demonstrated that in situ, aer reaching
its easy separation.
about 84%, the catalyst was removed aer 3 h. In order to
In this novel one-pot approach, in order to synthesize cyclic tolerate more reaction, the reactants were permissible. The
carbonates, distinct olens were studied for the investigation of results indicated that the remnants of the free catalyst aer the
the substrate scope (refer to Table 4). For all the substrates reaction were fairly active aer removing the heterogeneous
shown in Table 4, the catalyst is active. In addition, aryl olens catalyst, and the conversion equal to 86% was obtained aer the
bearing a para-chloro group were determined as excellent cyclic carbonate production for 5 h. In the reaction, it was
substrates, affording near-quantitative products. Moreover, aryl proved that the catalyst acted as a heterogeneous catalyst during
olens and also ortho-chloro or meta groups were detected as the reaction, and only slight leaching occurred. Additionally,
excellent substrates. In contrast, an electron-donating group mercury poisoning evaluation was performed to prove the
like methyl on the aryl group reduced the product yield.
Fig. 10 The reusability of the catalyst for the synthesis of cyclic Fig. 11 Recyclability of the catalyst for the synthesis of cyclic
carbonate.
carbonate.
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Conclusions
1
In this work, we synthesized the nanoparticles of DFNS/Pt(II)
and the obtained catalyst was evaluated by BET, SEM, EDX,
TGA, TEM, ICP, and FTIR analyses. In this regard, for the
production of cyclic carbonates using the synthesized DFNS/
Pt(II) NPs, a low-cost, non-toxic, and novel stable catalytic
system was developed. The synthesized nanocomposite was
heterogeneous and possessed the simplicity of the separation of
the catalyst from the reaction mixture. For this reason, its
catalytic activity does not vary in the reaction and the selectivity
is maintained for 10 continuous runs. It is important to note
that this nanocomposite does not need reactivation, which can
mitigate economic and environmental problems. In addition,
mercury poisoning along with hot ltration experiments
affirmed negligible metal leaching and also the heterogeneous
nature of the catalyst.
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