Ru@PsIL-Catalyzed Synthesis of N-Formamides and Benzimidazole by using Carbon Dioxide and Dimethylamine Borane

Article abstract of DOI:10.1002/cctc.201800185

This work reports the synthesis and characterization of ruthenium nanoparticles (Ru NPs) supported on polymeric ionic liquids (PILs). This catalyst shows high catalytic activity towards the N-formylation of amines and synthesis of benzimidazoles from 1,2-diamines and carbon dioxide (CO₂) by reductive dehydrogenation of dimethylamine borane. This methodology shows excellent functional group tolerance with broad substrate scope towards the synthesis of N-formamides and benzimidazoles. Interestingly, this protocol also provides the tandem reduction of 2-nitroamines and CO₂ to synthesize benzimidazoles. It was proposed that the ionic liquid phase of the polymer plays pivotal roles such as assisting the stabilization of nanoparticles electrostatically, providing an ionic environment, and controlling the easy access of the substrates/reagents to the active sites. The developed methodology utilizes CO₂ as a C₁ source and water/ethanol as a green solvent system. Additionally, the catalyst was found to be recyclable in nature and shows five consecutive recycling runs without significant loss in its activity.

Full text of DOI:10.1002/cctc.201800185

Accepted Article
Title: Ru@PsIL Catalysed synthesis of N-formamides and
benzimidazole using Carbon Dioxide and Dimethylamine Borane
Authors: Bhalchandra Mahadeo Bhanage, Vitthal B Saptal, and
Takehiko Sasaki
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Ru@PsIL Catalysed synthesis of N-formamides and benzimidazole
using Carbon Dioxide and Dimethylamine Borane
Vitthal B. Saptal,[a] Takehiko Sasaki [b] and Bhalchandra M Bhanage*[a]
Abstract: This work reports the synthesis and characterization of
ruthenium nanoparticles (Ru NPs) supported on polymeric ionic
liquids (PILs). This catalyst shows high catalytic activity towards the
N-formylation of amines and synthesis of benzimidazoles from 1,2
diamines and carbon dioxide (CO2) by reductive dehydrogenation of
dimethylamine borane. This methodology shows excellent functional
group tolerance with broad substrate scope towards the synthesis of
N-formamides and benzimidazoles. Interestingly, this protocol also
provides the tandem reduction of 2-nitroamines and CO2 to synthesize
benzimidazoles. It was proposed that the ionic liquid phase of polymer
plays pivotal roles such as assisting the stabilization of nanoparticles
electrostatically, providing the ionic environment and controlling the
easy access of the substrates/reagents to the active sites. The
developed methodology utilizes the CO2 as C1 source and water:
ethanol as green solvents system. Additionally, the catalyst was found
to recyclable in nature and shows five consecutive recycle runs
without significant loss in its activity.
recyclability and outstanding selectivity.[7] In this regards, the
stabilization of NPs and designing of their architectures and
functionalities is an important task, which mostly depends on the
selection of the right ligands on the surface of NPs, comprised of
diverse coordinating elements and pendant moieties.[8-10] It has
been observed that the specific performance of these
nanomaterial’s for certain applications mostly depends on the
synthesis and stabilization techniques employed, suggesting the
importance of coordinating linkers on NP surfaces.[11]
The utilization of ionic liquids (ILs) for vast applications and in
many diverse fields such as chemistry, materials science and
specific catalysis have been witnessed over last few years.[12]
Further, the immobilization of ILs onto various supports has been
succeeded in order to stabilize the metal NPs that can be used for
various applications.[13-15] The ILs are well-known as a suitable
media for the synthesis of NPs, leading to a proper stabilization of
NPs by interaction with the ILs molecules.[16-20] In this context, the
polymeric materials having functionalities analogous to ILs
(polymeric ionic liquids: PILs) have been followed for the
development of innovative classes of cutting-edge materials.[21-22]
The presence of functional moieties having ionic nature in the
polymer backbone enhances the dispersion and stabilization of
NPs. Also, the immobilized ILs as supports for catalysts, not only
take benefit of excellent physicochemical properties of ILs but
also helps in increasing the recyclability of catalysts and easy the
catalyst-product separation.[23-31] The immobilization of ILs on
polymer acts like a solid support and provide the similar electronic
environment like ILs for the stabilization of NPs.[31]
Introduction
The high emission of greenhouse gas (CO2) is considered as the
biggest environmental issue, due to its negative impact on nature.
In 2014 about 36 Gt anthropogenic CO2 was emitted, which
corresponds to the 9.8 Gt of carbon.[1] Consequently, the
transformation of CO2 to value-added chemicals have attracted
intense interest.[2-3] The use of CO2 is considered as the greener,
sustainable and economical C1 source than other C1 sources not
only due to the easy to handling and low cost but also due to its
renewable and environmentally friendly nature.[2] However, due to
the high stability of CO2, the activation and subsequent
transformation of the activated form of CO2 to value-added
chemicals is highly challenging and demanding from the industrial
as well as academic perspectives.[3] Among the various reactions
reported for the transformations of CO2, the reductive
functionalization of amines with CO2 has developed as a highly
In continuation of our research interest towards the catalytic
fixation of CO2.[54-57] herein, we have synthesized and
characterized the Ru NPs (Ru@PsIL) stabilized onto the
supported ionic liquid phase. These as-synthesized NPs applied
as a multitasking catalyst for the synthesis of formamides,
benzimidazoles and one pot reduction and cyclization of
nitroaniline to benzimidazoles under the mild conditions (scheme
1). In addition, the high catalytic activity and good recyclability
observed for the Ru@PsIL have emphasized the utility of the
protocol employed.
sustainable approach that provides the most valuable products.[4-
6]
In the recent year, the use metal nanoparticles (NPs) in the field
of catalysis is highly demanding due to their high reactivity, good
Results and Discussion
The typical synthetic procedure for preparation of Ru@PsIL
is shown in scheme 2. This synthesized catalyst is
characterized by using various analytical techniques. The
SEM images of Ru@PsIL clearly show the good dispersion
of the ruthenium NPs over the spherical and wrinkled
polymer support (Figure 1a). The well-oriented spheres
clearly show the stabilization of the Ru NPs on the SILP
(Figure 1b). The closer view of the catalyst also shows the
wrinkled surface of the support where well stabilized NPs can
be visualized (Figure 1c, 1d).
[a] V. B. Saptal, Prof. B. M. Bhanage
Department of Chemistry, Institute of Chemical Technology
Matunga, Mumbai-400 019 (India)
Fax: (+91) 22-33611020
E-mail: bm.bhanage@gmail.com
[b] Prof. T. Sasaki
Department of Complexity Science and Engineering
Graduate School of Frontier Sciences
The University of Tokyo
5-1-5, Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan)
Supporting information for this article is given via a link at the end of the
document.
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10.1002/cctc.201800185
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Scheme 1. (a) N-formylation of amines and (b) N-cyclization of 1,2 diamines by
using DMAB as reducing agent and Ru@PsIL as a catalyst.
Figure 2 XPS spectrum (Ru 3p1/2 and Ru 3p3/2) of Ru@PsIL catalyst.
The shape and size of the Ru NPs were further characterized
by using the transmission electron microscopy (TEM)
analyses (Figure 3). The spherical and irregular spherical Ru
NPs having the uniform particle size 3 to 6 nm is clearly
observed in the TEM images. The majority of Ru NPs ranging
3 to 4 nm while, a small amount of 5 nm Ru NPs also
observed on PsIL (ESI, Figure S-3). The thermal stability of
any catalyst is important to avoid the product contamination
by the degradation of the catalyst. Thus, we investigated the
catalytic stability by using the thermogravimetric analysis
(TGA). We have observed that the as-synthesized Ru@PsIL
catalyst having high thermal stability up to the 350 °C (ESI,
Figure S-1).
Figure
1 SEM images of Ru@PsIL (a) and (b) showing the spherical
morphology with the wrinkled surface of Ru@PsIL, (b) and (c) shows the well
stabilized Ru NPs onto the wrinkled surface of the PsIL.
The catalyst was also characterized by using the X-ray
photoelectron spectroscopy (XPS). The XPS survey scan
spectrum of Ru@PsIL reveals the presence of all expected
elements like Ru, C, N and O (ESI, Figure S-2). In the overall
XPS survey, the overlapping of peaks around at 285ꢀeV of C
1s and Ru 3d brings the difficulties in assigning the
spectrums for C and Ru elements, the 3p of Ru was chosen
for the analysis. The metallic state of Ru is characterized by
Figure 3 (a) and (b) TEM images of the Ru@PsIL showing the very small Ru
NPs stabilized onto the support of PsIL.
In recent years, there has been increasing interest towards
the dehydrogenation of ammonia borane (AB) and its
derivatives, which are considered as a potential candidate
due to high H2 storage capacity, nontoxicity and high thermal
stability.[44-45] Recently, various nanoparticles have been
Ru 3p3/2 peak at
eV while the Ru (IV) is characterized by two peaks at
eV and
Ru@PsIL catalyst having ruthenium in the metallic state only
confirmed by Ru 3p3/2 at 462.15 eV and Ru 3p1/2 at
484.18 eV (Figure 2).
∼
462.3 eV and Ru 3p1/2 peak at
∼484.5
∼
463.7
∼
486.2 eV respectively.[69] The synthesized
∼
synthesized
and
applied
as catalysts for
the
∼
dehydrogenation of AB.[46,47] Although there are very few
reports available on the utilization of AB for transfer
hydrogenation reaction of organic compounds,[48-53] hence,
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there is a need to explore the more active catalytic systems
for the tandem dehydrogenation and transfer hydrogenation
reactions. The N-formamides are the very important class of
organic compounds, [32] which are extensively used in the
field of organic synthesis. Due to their intriguing application
as various biological intermediates and raw materials for the
synthesis of various chemicals,[33] several catalytic methods
have been developed for the synthesis of N-formamides.[34]
Among all the reported methods, the synthesis of N-
formamides by using the CO2 reduction method is
considered as one of the most prominent pathways from the
industry as well as academic point of view, where various
reducing agents such as H2,[35-36] silane,[37-42] and borane are
being used repeatedly.[43]
from 1 MPa to the 5 MPa(Table 1, entries 16-18), hence, we
concluded that the 2 MPa pressure
Table 1 Optimization of the reaction conditions for the N-formylation reaction.[a]
Entry
Solvent
Temp.
(°C)
Time
(h)
CO2
(MPa)
Yield
(%)[b]
TON/TOF
(h-1)[h]
1
-
100
100
100
100
100
100
100
100
80
10
10
10
10
10
10
10
10
10
10
10
8
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
3
4
5
2
2
2
2
2
40
74
69
80
75
70
80
93
93
68
48
93
93
41
70
92
94
94
18
71
69
78
15
-
2
THF
246/24.6
230/23
266/26.6
250/25
233/23.3
266/26.6
310/31
310/31
226/22.6
160/16
310/38.7
310/51.6
136/68.3
233/38.8
306/51.1
313/52.2
313/52.2
-
3
CH3CN
Initially, the formylation of N-methyl aniline (1a) to N-methyl-
N-phenylformamide (2a) was selected as a challenging
substrate for the optimization of the reaction parameters
(Table 1). The reactions were performed with 5 mg of
Ru@PSIL catalyst, 1 mmol of 1a, 2 MPa of CO2 and 3 mmol
of the dimethylamine borane (DMAB) by using the K2CO3 as
a base, at 100 °C for 12 h. Initially, the reaction was
performed under the solvent-free conditions and only 40 %
of 2a was observed (Table 1, entry 1). Then, to our delight,
the use of THF as a solvent provided the 74 % yield of 2a
(Table 1, entry 2). The use of CH3CN as solvent provided 69
% yield of 2a (Table 1, entry 3). However, the use of polar
solvents such as DMF and ethanol provided 78 and 71 %
yield of 2a, respectively (Table 1, entries 4-5). While, use of
a nonpolar solvent such as Toluene, provided a good yield
of 2a (70 %) (Table 1, entry 6). Later, we utilized water as a
green solvent, and about 80 % was observed (Table 1, entry
7). Next, by considering the solubility of the reactant and
DMAB, we utilized the mixture of water and ethanol in 1:1
ratio and surprisingly excellent yield (about 93 %) of 2a was
noted (Table 1, entry 8). After the solvent study, we studied
the effect of temperature on reaction system (Table 1, entries
9-11). By decreasing the temperature of the reaction system
at 80 °C, still same yield of 2a was noted (Table 1, entry 9).
Further decreasing temperature up to 60 °C, decreased the
yield (68 %), (Table 1, entry 10). Since, we have observed
that only 48 % yield of 2a was observed at the room
temperature (Table 1, entry 11), we concluded that the 80 °C
of temperature is the optimum temperature for the efficient
conversion of 1a. Next, the effect of time on the reaction
conditions was studied and it was observed that same yield
of 2a was noted when reaction proceeds up to 6 h (Table 1,
entry 13 entry). By further decreasing time, the decreased
yield of 2a has been observed (Table 1, entry14). Next, the
effect of the pressure of CO2 on the reaction system has
been explored (Table 1, entries 15-18). By decreasing the
pressure of CO2 to 1 MPa, the decreased amount of 2a was
noted (Table 1, entry 15). No, any further improved yield of
2a could be attained by further increasing the CO2 pressure
4
DMF
5
EtOH
6
Toluene
7
Water
8
Water:EtOH
Water:EtOH
Water:EtOH
Water:EtOH
Water:EtOH
Water:EtOH
Water:EtOH
Water:EtOH
Water:EtOH
Water:EtOH
Water:EtOH
Water:EtOH
Water:EtOH
Water:EtOH
Water:EtOH
Water:EtOH
9
10
11
12
13
14
15
16
17
18
19[c]
20[d]
21[e]
22[f]
23[g]
60
R.T.
80
80
6
80
3
80
6
80
6
80
6
80
6
80
6
80
6
236/39.4
138/23
780/130
-
80
6
80
6
80
6
[a] Reaction Conditions: 1a (1 mmol), Ru@PSIL (5 mg), CO2 (2 MPa), DMAB (3
mmol), Water:EtOH (3:3 ml) and K2CO3 (0.5 mmol). [b] Isolated yields. [c] Without
[d]
[e]
[f]
[g]
catalyst.
Triethylamine borane.
Ru/C (10 mg). RuCl3 (10mg).
PsIL
(10mg). [h] TON per h.
of CO2 was the optimum temperature to provide the effective
product. Next, the reaction was carried out without the catalyst
and no significant conversion of 2a noted (Table 1, entry 19).
When we used triethylamine borane as a reducing agent instead
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of DMAB the observed yield of 2a was 71 % (Table 1, entry 20).
We also tested the other commercially available heterogeneous
catalysts like Ru/C for the formylation reactions, and we have
observed the lower yield as compared to the Ru@PsIL (Table 1,
entry 21). Next, the use of RuCl3 as a homogeneous catalytic
system showed the 78 % yield which is very low as compared to
Ru@PsIL (Table 1, entry 22). In a control experiment, when only
polymer support i.e. PsIL was utilized to investigate the catalytic
activity and we have observed very low yield of 2a suggesting the
minimum contribution of support in the catalytic activities. The
turnover number (TON) and turnover frequency (TOF) of the
developed catalyst has been calculated based on the reported
method for the soluble metal nanoparticles.[70]
After the optimization reaction conditions in hands, we have
extended this protocol for the formylation of a variety of substrates
of amines (Table 2). The N-methyl aniline provides the excellent
yield of the formylated product (Table 2, entry 1). The secondary
cyclic amines, which are more nucleophile in nature, such as
morpholine, piperidine, cyclopentyl amine and 1-methylpiperazine
are found to be highly reactive and providing a very excellent yield
of the respective formylated products (Table 2, entries 2-5). Then,
we tested this methodology for the synthesis the
Table 2 Substrate study for the formylation reactions.[a]
Yield
(%)b
TOF[e]
h-1
Entry
Substrate
Product
TON
310
330
51.6
55
1
2
93
99
99
55
3
330
53.3
4
5
96
96
320
320
53.3
49
6
7
8
89
84
80
296
280
266
46.6
44.4
39.4
9c
71
236
dimethylformamide,
a well-known solvent for the organic
reactions and interestingly, it was found that dimethyl amine
provides the excellent yield (Table 2, entry 6). Other symmetric
diamines, such as diethylamine and dibutyl amine was also
providing the excellent yield of the corresponding formamides
(Table 2, entries 7-8). Then, the symmetric di-cyclic amine such
as dicyclohexyl amine showed the slightly decreased yield of N-
formylated product which could be possible due to the steric
hindrance of cyclohexyl ring (Table 2, entry 9). Methyl-substituted
benzylamine and benzylamine also well tolerated under the
optimized reaction condition and provide a better yield of
formylated products (Table 2, entries 10-11). The symmetric
benzylamine like dibenzyl amine gives the moderate yield for the
N-formylated product (Table 2, entry 12). The primary cyclic
amine like cyclohexylamine was also tested at the optimized
reaction condition and good yield of formylated product was noted
(Table 2, entry 13). Next, the challenging substrate like aniline for
the N-formylation was tested and good yield was noted (Table 2,
entry 14). Further, the substituted aniline was formylated and
good yield as compared to aniline was noted (Table 2, entries 15-
16). While, the use of diphenylamine was found sluggish to
formylate and provide very low yield (Table 2, entry 17). The
substituted amines at the para-position with electron donating
functional group such as p-methoxyaniline provide the good yield
of the N-formylated product (Table 2, entry 18). The heterocyclic
compound like indoline also tested for the formylation reaction
and showed the good yield (Table 2, entry 19). Interestingly, the
indole which containing reducible double bond, as well as amine
for CO2 for N-formylation, was tested and interestingly, the
reduction of the double bond as well as the N-formylated product
obtained (Table 2, entry 20). By such encouraging results from
the hydrogenation of double bond as well as formylation reactions,
we further utilized the isoquinoline ring system to synthesize the
biologically important N-formyl-1,2,3,4-tetrahydroisoquinoline,
and we observed the moderate yield (Table 2, entry 21). Also, the
45.5
41.6
6.25
10
11
82
75
273
250
12c
13
14
15
45
72
80
88
150
240
266
293
40
44.4
48.8
41.6
16
75
250
4.1
17c
18
30
87
100
290
48.3
46.6
19
84
280
30
20d
21d
22
54
48
77
180
160
256
26.6
42.7
[a]Reaction conditions: Amine (1 mmol), Ru@PSIL (5 mg), CO2 (2 MPa), DMAB
(3 mmol), Water:EtOH (3:3 ml) and K2CO3 (0.5 mmol), temperature (80 ˚C),
Time (6 h). [b]isolated yields. [c] Time (24 h). [d]DMAB (5 mmol). [e] TON per h.
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direct use of 1,2,3,4-tetrahydroisoquinoline provided the excellent
yield of N-formyl-1,2,3,4-tetrahydroisoquinoline (Table 2, entry
22).
After the successful synthesis of various formylation products, we
further extended this catalytic protocol for the cyclization reactions
to synthesize heterocyclic compounds. The high activity of
Ru@PsIL for N-formylation reaction encouraged us to use this
catalyst for the synthesis of bezimidazoles from o-phenyl diamine,
CO2 and DMAB as a reducing agent (Table 3). The
benzimidazoles are fundamental intermediates in the
synthesis of pharmaceutical scaffolds, and heterocycles with
a benzimidazole structure are pervasive in biologically active
compounds.[58-60] Nowadays, much progress has been
achieved for the synthesis of benzimidazoles and its
derivatives. Still, there is need to develop the efficient
catalytic method which works under simple green conditions
and utilizes the renewable material rather than the use of
toxic harmful chemicals. The direct use of CO2 and o-
phenylenediamine to synthesize the benzimidazoles are also
one of the interesting reactions, as it which utilizes the CO2
as a C1 source.[61] Initially, the reaction of an o-phenyl
diamine with CO2 (2 MPa) and DMAB (2 mmol) in the
presence of Ru@PsIL and water: ethanol (1:10) as the
solvent system was utilized, to our surprise we have
observed the excellent yield of benzimidazole (Table 3, entry
1). Interestingly, Ru@PsIL catalyzed the reaction of 2-
nitroaniline with CO2 in presence of DMAB (5 mmol), have
provided the excellent yield of the benzimidazole by
reduction of the nitro functional group as well as CO2 (Table
3, entry 2). The methyl-substituted 1,2-diamine as well as
methyl substituted 2-nitroaniline also well tolerated and
provide the excellent yield of the methyl substituted
benzimidazoles (Table 3, entries 3-4). The 4,6-dimethyl o-
phenylenediamine also provide the good yield of
corresponding benzimidazole (Table 3, entry 5). The N-
methyl substituted diamine and nitroaniline provide the
excellent yield of N-methyl benzimidazole (Table 3, entries
6-7). The electron donating group such as 4-methoxy o-
phenyldiamine and 4-methoxy 2-nitroaniline also provided
the good yield (Table 3, entries 8-9). While, the electron
withdrawing group such as chloro on 2-nitroaniline was found
sluggish to react (Table 3, entry 10). While, the methyl at the
ortho position of diamine also provide the good yield (Table
3, entry 11). The use of 2-aminophenol as starting material
Table 3 Ru@PsIL catalyzed synthesis of benzimidazoles bu using DMAB
and CO2.a
Entry
1
Substrate
Product
Yield (%)b
96
2c
3
90
93
4 c
87
93
5
6
97
81
7 c
8
88
75
9 c
10 c
11
15
83
12
15
13 c
N.D
a
Reaction conditions: Amine (1 mmol), Ru@PSIL (5 mg), CO2 (2 MPa),
b
DMAB (3 mmol), Water:EtOH (3:3 ml) and K2CO3 (0.5 mmol), Time (18 h).
isolated yield. C DMAB (5 mmol). N. D (Not detected).
Figure 4 Recyclability of Ru@PsIL catalysts for the N-formylation 1a to the 2a
at the optimized reaction conditions.
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provided only 15% yield of benzoxazolidinone suggesting the
role of electron withdrawing groups on catalytic activity
(Table 3, entry 12). No, any bezoxazolidinones was noted
when 2-nitrophenol was utilized as a substrate (Table 3,
entry 13). The recyclability of any heterogeneous catalysts
plays the crucial role to determine the suitability of the
developed catalysts for the industrial applications.[62] The
recyclability of developed catalysts was investigated for the
formylation reaction of 1a to 2a at the optimized reaction
conditions (Figure 4). The developed catalyst shows
excellent recyclability up to five recycle run with a negligible
loss in yield suggesting the promise of this reported
methodology towards the efficient and recyclable catalyst for
the industrial applications. The leaching of catalyst was also
investigated and very low leaching of Ru metal noted (0.1%).
Finally, after the fifth recycle study we characterized the
Ru@PsIL catalyst by using SEM analyses (ESI, Figure S-2).
After the eight recycle runs the stability of Ru@PsIL catalysts
investigated by using TGA analysis. The slightly decreased
stability of catalyst as compared to as-synthesized catalysts
noted (ESI, figure S1). While, very negligible shrinkage on
the polymer support observed, which indicates the high
stability and good recyclability of the catalyst.
benzimidazoles using DMAB as a green and mild reducing
agent. This synthesized catalyst shows diverse active
centers such as stable organic support and ionic
environment which is helpful for the stabilization of small
nanoparticles, which regulates the diffusion of the substrate
and product from active centers very easily. The developed
methodology is highly efficient and sustainable due to the
use of DMAB as a safe and atom economic hydrogen source,
mild CO2 pressure, low temperature and utilization of water:
ethanol as a green solvent system. Interestingly, Ru@PsIL
catalyst able to the tandem reduction of the double bond of
indole and isoquinoline to indoline-1-carbaldehyde and
biologically
important
N-formyl-1,2,3,4-
tetrahydroisoquinoline respectively. Additionally, this
developed methodology facilitates to provide a large number
of N-formylated and cyclized product of benzimidazoles with
tandem nitro reduction, with excellent recyclability.
Experimental Section
Synthetic method for the preparation of PsIL
The synthesis of Ru@PsIL catalyst has been performed by
modifying the reported procedure (ESI, S-2).[28-30] Typically,
the Ru@PsIL has been synthesized by the immobilization of
Merrifield peptide resin with 1,2-dimethyl-1H-imidazole to
give PsIL (Scheme 2). For this the simple and efficient
method utilized for the immobilization of ILs in which
Merrifield peptide resin (2% cross-linked, 2.3 mmol Cl/g,
Aldrich) (1 g, 5.34 mmol), was suspended 1,2-dimethyl-1H-
imidazole (10 mL) in Toluene (25 mL) as solvent at 100 °C
for 10 h. Then the PsIL was filtered, washed with DMF (3 ×
20 mL), MeOH (3 × 20 mL), CH2Cl2 (3 × 20 mL) and dried
under vacuum at 60 °C for 12 h.
Comparison our method with other approaches
The comparisons of our reported method with recently
reported methods used for the utilization of CO2 as a C1
source for the formylation and cyclization reaction are
summarized in Table 1 (ESI, S1). Although, the use of H2 as
a clean energy source is reported for the reduction reactions
the utility of H2 for reactions may be problematic due to their
explosive nature, the demand of elevated temperature and
high pressure and requirement of expensive transition metal
complexes for the reduction reactions.[36],[63] Although, the
silanes are well reported and active reducing agent for these
type of reactions, they are low atom-economical and require
an expensive catalyst.[36],[65] In case of silane, most of the
reaction systems are non-recyclable and expensive as
compared to the borane.[66]-[68] In case of heterogeneous
catalysts, the use of silane as reducing agents is problematic
due to the generation of solid waste, which is not soluble in
water and in common solvents. The use of toxic solvents in
these processes makes complications in catalyst separation.
In these circumstances, the use of borane is considered as
an ideal compared to gaseous hydrogen and silanes due to
the high hydrogen storage capacity, good air and moisture
stability and easy to handling.
General procedure for the immobilization of Ru@NPs
onto PsIL
The as-synthesized PsIL (100 mg,) was suspended in a
round-bottomed flask containing 2 mL of deionized water, 2
mL of ethylene glycol and RuCl3 (20.7 mg), and stirred at
room temperature for 6 h. Then the NaBH4 (1 mmol) was
dissolved water (20 ml) and slowly added with continuous
stirring at the 5 °C. The suspension then stirred for 4 h. for
the complete reduction and resulted in material filtered and
washed with deionized water (3 x 2.0 mL) and MeOH (1 x
1.70 mL). Finally, the polymer was vacuum dried at 80 °C till
constant weight. The percentage of loading of ruthenium
NPs on polymer support calculated by using the ICP-AES
analysis and 6.076 % of Ruthenium metal observed on the
polymer.
Conclusions
Experimental procedure for the formylation and
cyclization reactions
In conclusion, we have synthesized highly efficient, novel
Ru@PsIL as a heterogeneous catalytic protocol which
utilizes CO2 for the N-formylation of amines and synthesis of
The N-formylation and cyclized product were synthesized by
the reaction amines with CO2 and dimethylamine borane
(DMAB) in the presence of the Ru@PsIL catalyst. All the
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reactions were carried out in a 100 mL stainless-steel
autoclave with stirring at 600 rpm and equipped with an
automatic stirrer and temperature control system. In a typical
reaction procedure, the catalyst (5 mg) was introduced into
the reactor containing amine (1 mmol), Water: EtOH (3:3 ml)
and DMAB (2 mmol) at room temperature and then
pressurized to the respective pressure of CO2 and heated to
a particular temperature. After completion of the reaction, the
reactor was cooled in an ice-cold water bath and then CO2
was released slowly. The synthesized products were
extracted and purified by using silica column
chromatography using the pet ether and ethyl acetate and H1
& C13 spectra were recorded.
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Vitthal B. Saptal, Takehiko Sasaki and
Bhalchandra M. Bhanage*
Page No. – Page No.
Ru@PsIL Catalysed synthesis of N-
formamides and benzimidazole using
Carbon Dioxide and Dimethylamine
Borane
The highly active Ru NPs supported on polymeric ionic liquids and utilized for N-
formylation and cyclization reactions at mild reaction conditions.
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