KCC-1 Supported Ruthenium-Salen-Bridged Ionic Networks as a Reusable Catalyst for the Cycloaddition of Propargylic Amines and CO2

Article abstract of DOI:10.1007/s10562-018-2349-9

Abstract: This study investigates the potential application of an efficient, easily recoverable and reusable KCC-1 nanoparticle-supported Salen/Ru(II) catalyst in the synthesis of 2-oxazolidinones from CO₂, and propargylic amines. The KCC-1/Salen/Ru(II) NPs were thoroughly characterized by using TEM, SEM, TGA, FT-IR, ICP-MS, and BET. This observation was exploited in the direct and selective chemical fixation of CO₂, affording high degrees of CO₂ capture and conversion. The recycled catalyst has been analyzed by ICP-MS showing only minor changes in the morphology after the reaction, thus confirming the robustness of the catalyst.

Full text of DOI:10.1007/s10562-018-2349-9

Catalysis Letters
https://doi.org/10.1007/s10562-018-2349-9
KCC-1 Supported Ruthenium-Salen-Bridged Ionic Networks
as a Reusable Catalyst for the Cycloaddition of Propargylic Amines
and CO2
Seyed Mahdi Saadati1 · Seyed Mohsen Sadeghzadeh2
Received: 27 December 2017 / Accepted: 24 February 2018
© Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract
This study investigates the potential application of an efficient, easily recoverable and reusable KCC-1 nanoparticle-supported
Salen/Ru(II) catalyst in the synthesis of 2-oxazolidinones from CO2, and propargylic amines. The KCC-1/Salen/Ru(II)
NPs were thoroughly characterized by using TEM, SEM, TGA, FT-IR, ICP-MS, and BET. This observation was exploited
in the direct and selective chemical fixation of CO2, affording high degrees of CO2 capture and conversion. The recycled
catalyst has been analyzed by ICP-MS showing only minor changes in the morphology after the reaction, thus confirming
the robustness of the catalyst.
Graphical Abstract
Keywords Nano catalyst · KCC-1 · One-pot synthesis · Green chemistry · CO2
1 Introduction
Morphology-controlled nanomaterials such as silica play a
decisive role in the development of technologies for address-
* Seyed Mahdi Saadati
ing challenges in the fields of wellness, environment, and
energy. Mesoporous silica materials discovery such as
MCM-41 and SBA-15, a notable increase in the design. The
synthesis of nano silica with different sizes, shapes, mor-
phologies, and tissue properties have been observed in late
years. KCC-1 is dendritic fibrous nanosilica as one notable
smsaadati@bojnourdiau.ac.ir
1
Department of Chemistry, Bojnourd Branch, Islamic Azad
University, Bojnourd, Iran
2
Young Researchers and Elite Club, Neyshabur Branch,
Islamic Azad university, Neyshabur, Iran
Vol.:(0123456789)
1 3

S. M. Saadati, S. M. Sadeghzadeh
invention that have a unique fibrous morphology, unlike the
tubular porous structure of various customary silica materi-
als. It has a high surface area with improved accessibility
to the internal surface, tunable pore size and pore volume,
controllable particle size, and, importantly, improved stabil-
ity [1–10].
plan logically transformations catalyzed by ruthenium-salen
complexes, the science of their redox and structural attrib-
utes is desirable [43].
Lately, organometallic ionic complexes (OICs) have
emerged as very marvelous catalysts because they can be
created from readily available and highly tailorable metal
and ligand forerunners for multifunctional integration [44,
45]. Many researchers have showned OICs that contain a
Lewis acidic metal center and a nucleophilic halogen anion
(X−) portion as highly impressive bifunctional catalysts for
the coupling reaction between carbon dioxide and other
organic compound under co-catalyst free circumstances
owing to the cooperative effects of the catalytic functional
groups [46–48]. Having this point in mind, we envisioned a
way in which the preface of Lewis acid (metal center) active
sites to a halogen anion (X−) based ionic polymer could
provide highly active, recyclable catalysts for the synthe-
sis of cyclic carbonates. Herein, we report the design and
synthesis of a novel bifunctional complex composed of the
cross-linked KCC-1 as a substrate with the N,N″-bis{(4-
dimethylamino)salicylidene}ethylenediamino ruthenium(II)
[Salen-Ru(II)] Schiff base outer shell to serve as a catalyst
for the synthesis 2-oxazolidinones from CO2, and propar-
gylic amines under solvent-free (Scheme 1).
Carbon dioxide as a recyclable, non-toxic, easily avail-
able, naturally abundant, non-flammable and inexpensive
C1 resource and considered as one of the most substantial
greenhouse gases which caused the global warming and cli-
mate change [11–16]. As a result, the efficient change of
carbon dioxide into useful chemicals is an important con-
tribution from the opinion of environmental conservation
and exploitation of resources [17–20]. The reaction of CO2
with other organic compound to form the multi-membered
cyclic carbonates has been extensively studied [21]. One
of the useful methods for chemical fixation of CO2 is the
carboxylative cyclization of propargylic amines with CO2
to provide 2-oxazolidinones [22–26]. Various investigations
have been conducted for this reaction catalyzed by orga-
nometallic complexes of noble metals such as ruthenium
[27], palladium [28], silver [29], and gold [30]. Organome-
tallic complexes can reduce the cost and avoid the pollu-
tion caused by metals have been used for the carboxylative
cyclization of propargylic amines with CO2.
Ruthenium complexes are at the moment investigated
because of their interesting structural, electrochemical, cat-
alytic, and biological attributes [31–36] including research
of ruthenium complexes containing diimino tetradentate
Schiff bases, such as salen and salophen ligands [37, 38].
Recently, a number of ruthenium-salen complexes have
also been found to be active catalysts in various chemical
transformations [39, 40]. Specifically, ruthenium macrocy-
clic complexes which are stable to the side demetalation
have been found to show a reversible electrochemistry and
provide good model systems for mech-anistic researches of
proton-coupled multielectron transfer reactions [41, 42]. To
2 Experimental
2.1 Materials and Methods
Chemical materials were purchased from Fluka and Merck
in high purity. Melting points were determined in open
capillaries using an Electrothermal 9100 apparatus and are
uncorrected. FTIR spectra were recorded on a VERTEX 70
spectrometer (Bruker) in the transmission modein spectro-
scopic grade KBr pellets for all the powders. The particle
size and structure of nano particle was observed by using
O
N
Br-
O
Me
O
N
O
O
N
N
Ru
N
Me
Br-
N
O
O
i
O
S
O
HN R3
R3
O
N
CO2
+
R1
R2
R2
R1
Scheme 1 Synthesis of 2-oxazolidinones in the presence of KCC-1/Salen/Ru(II) NPs
1 3

KCC-1 Supported Ruthenium-Salen-Bridged Ionic Networks as a Reusable Catalyst for the…
a Philips CM10 transmission electron microscope operat-
ing at 100 kV. Powder X-ray diffraction data were obtained
using Bruker D8 Advance model with Cu ka radition. The
thermogravimetric analysis (TGA) was carried out on a
NETZSCH STA449F3 at a heating rate of 10 °C min−1
under nitrogen. 1H and 13C NMR spectra were recorded on
a BRUKER DRX-300 AVANCE spectrometer at 300.13 and
75.46 MHz, BRUKER DRX-400 AVANCE spectrometer at
400.22 and 100.63 MHz, respectively. Elemental analyses
for C, H, and N were performed using a Heraeus CHN–O-
rapid analyzer. The purity determination of the products and
reaction monitoring were accomplished by TLC on silica gel
polygram SILG/UV 254 plates. Mass spectra were recorded
on Shimadzu GCMS-QP5050 mass spectrometer.
2.5 General Procedure for the Preparation of KCC‑1/
Salen NPs
The salen ligand (0.41 g) was dissolved in toluene (5 mL)
and methanol (5 mL), respectively. The two solutions were
combined and the reaction mixture was vigorously stirred
at 60 °C for 24 h then KCC-1/3-bromopropyl (0.6 g) was
added. After stirring at 60 °C for 24 h, the brown solid was
separated by filtration, washed with ethanol, and dried under
vacuum at 60 °C for 24 h to afford KCC-1/Salen.
2.6 General Procedure for the Preparation of KCC‑1/
Salen/Ru(II) NPs
A mixture of KCC-1/Salen (0.45 g), Ru(DMSO)4Cl2 (0.5 g),
and Et3N (0.8 ml) in methanol (10 ml) was degassed with
N2 and refluxed for 4 h. After cooling to room tempera-
ture, the precipitate was filtered and washed with methanol
(10 mL× 3) and ether (10 mL× 3) to get a reddish-brown
powder. The powder was mixed with an excess of 4-meth-
ylpyridine in methanol (0.5 mL) and heated to reflux for
2 h. The final particle was separated from the solution by
applying a magnetic field, washed three times with water
to remove any ions present, and dried under vacuum [42].
2.2 General Procedure for the Preparation of KCC‑1
NPs
Tetraethyl orthosilicate (TEOS) (2.5 g) was dissolved in a
solution of cyclohexane (30 mL) and 1-pentanol (1.5 mL).
A stirred solution of cetylpyridinium bromide (CPB 1 g) and
urea (0.6 g) in water (30 mL) was then added. The resulting
mixture was continually stirred for 45 min at room tempera-
ture and then placed in a Teflon-sealed hydrothermal reactor
and heated 120 °C for 5 h. The silica formed was isolated
by centrifugation then washed with a mixture of deionized
water and acetone, and dried in a drying oven. This material
was then calcined at 550 °C for 5 h in air.
2.7 General Procedures for Preparation
of 2‑oxazolidinones
In a 100 mL stainless-steel reactor, CO2 (1.0 MPa), propar-
gylic amine (10 mmol), and KCC-1/Salen/Ru(II) (1 mg) were
added at room temperature. Then, the temperature was raised
to 100 °C with the addition of CO2 from a reservoir tank to
maintain a constant pressure (2.0 MPa). The remaining CO2
was removed slowly. After reaction, the catalyst was separated
by filtration under vacuum and reused for further recycling
experiment. The crude product mixture was dried over anhy-
drous sodium sulphate, and then subjected to column chro-
matography using a 6:1 petroleum ether/EtOAc eluent system
on silica gel to give 2-oxazolidinones as a colorless liquid.
2.3 General Procedure for the Preparation of Salen
The salen ligand was prepared by modification of a previ-
ously reported procedure [49]. Diethylamine (0.30 g) was
added to a solution of 4-(diethylamino)salicylaldehyde
(2.00 g) in ethanol (30 mL). The reaction mixture was heated
at reflux for 24 h then the mixture was cooled to room tem-
perature. After 48 h, the precipitated yellow crystals were
separated by filtration, washed with ethanol, and dried at
80 °C for 12 h to give the salen ligand.
2.8 Spectral Data of Synthesized Compounds
3-butyl-5-methyleneoxazolidin-2-one (Compound 2a):
Yellow oil; 1H NMR δ=0.90 (t, J=7.2 Hz, 3H), 1.31–1.22
(m, 2H), 1.50–1.44 (m, 2H), 3.20 (t, J=7.2 Hz, 2H), 4.14 (d,
J=2.4 Hz, 2H), 4.22 (d, J=2.4 Hz, 2H), 4.64 (d, J=2.4 Hz,
1H) ppm. 13C NMR δ = 13.6, 19.5, 28.9, 43.5, 47.4, 85.9,
150.0, 155.2 ppm. GC-MS m/z (%)=155 (90), 113 (27), 112
(100), 98 (11), 84 (37).
2.4 General Procedure for the Preparation
of KCC‑1/3‑Bromopropyl NPs
Under nitrogen atmosphere, 2 ml of 3-Bromopropyltrimeth-
oxysilane is added to 5.0 g of KCC-1 in suspension with
50 mL of freshly distilled toluene. After 24 h of reaction
under reflux, the solid is filtered, washed thoroughly with
toluene, ethanol, toluene, diethylether and then subjected
to toluene Soxhlet extraction. The functionalized KCC-1 is
finally dried in vacuum at 70 °C.
3-Methyl-5-methylene-1,3-oxazolidin-2-one (Com-
pound 2b): Yellow oil; 1H NMR δ=2.89 (s, 3H), 4.14 (dd,
J=2.4 Hz, 2H), 4.30 (dt, J=3.1 Hz, 1H), 4.72 (dt, J=3.1 Hz,
1H) ppm. 13C NMR δ=30.4, 50.8, 86.5, 149.0, 156.1 ppm.
1 3

S. M. Saadati, S. M. Sadeghzadeh
3-Methyl-5-ethylidene-1,3-oxazolidin-2-one (Com-
pound 2c): White powder; mp 74–76 °C. 1H NMR δ=1.64
(dt, J=7.0 Hz, 3H), 2.89 (s, 3H), 4.10 (dq, J=2.2 Hz, 2H),
4.60 (qt, J=7.0 Hz, 1H) ppm. 13C NMR δ=9.6, 30.3, 50.0,
97.3, 141.3, 156.0 ppm.
58.9, 102.2, 126.5, 128.1, 133.8, 146.6, 155.3 ppm. GC-MS
m/z (%)=259 (14), 230 (100), 174 (51), 118 (26), 90 (22).
3-Benzyl-5-ethylidene-1,3-oxazolidin-2-one (Com-
pound 2d): White powder; mp 40–42 °C. 1H NMR δ=1.65
(dt, J=7.0 Hz, 3H), 3.92 (dq, J=2.2 Hz, 2H), 4.42 (s, 2H),
3 Results and Discussion
The Salen-Ru Schiff base was covalently attached onto the
surface of KCC-1 by a nucleophilic reaction, which resulted
in dual catalytically active centers with a synergistic effect to
greatly enhance the catalytic productivity. Furthermore, the
catalyst can be easily recovered from the reaction mixture
by centrifugation for steady reuse (Scheme 2).
4.53 (qt, J=7.0 Hz, 1H), 7.24–7.40 (m, 5H, Ar) ppm. 13
C
NMR δ=9.9, 47.4, 47.9, 97.9, 128.0, 128.8, 135.2, 141.6,
156.3 ppm.
3-Isopropyl-5-ethylidene-1,3-oxazolidin-2-one (Com-
pound 2e): Yellow oil; 1H NMR δ=1.15 (d, J=6.5 Hz, 6H),
1.69 (dt, J = 6.9 Hz, 3H), 4.02 (dq, J = 2.2 Hz, 2H), 4.12
The morphology and structure of the KCC-1 and KCC-1/
Salen/Ru(II) NPs are further characterized by SEM. Fig-
ure 1a shows an SEM image of highly textured KCC-1
samples, where the samples have spheres of uniform size
with diameters of ~ 300 nm and a wrinkled radial struc-
ture. A close inspection of these images shows that wrin-
kled fibers (with thicknesses of ~ 8.5 nm) grow out from
the center of the spheres and are arranged radially in three
dimensions. Also, the overlapping of the wrinkled radial
structure forms cone-shaped open pores. The SEM image
shows that the entire sphere is solid and composed of fibers.
Furthermore, this open hierarchical channel structure and
fibers are more easily for the mass transfer of reactants and
increase the accessibility of active sites. The SEM images
of KCC-1/Salen/Ru(II) NPs showed that after modification
the morphology of KCC-1 is not change (Fig. 1b). After
being reused ten times, the dandelion-like structure of the
catalyst could be still observed although the dandelion-like
structure collapsed to some extent. The structure similar
between fresh KCC-1/Salen/Ru NPs and the KCC-1/Salen/
Ru(II) NPs reused ten times, accounted for high power in
recyclability (Fig. 1c).
(septet, J=6.7 Hz, 1H), 4.60 (qt, J=7.0 Hz, 1H) ppm. 13
NMR δ=9.9, 19.7 ,42.9, 44.8, 97.3, 142.1, 155.3 ppm.
C
3-Methyl-5-benzylidene-1,3-oxazolidin-2-one (Com-
pound 2f): White powder; mp 139–141 °C. 1H NMR δ=2.94
(s, 3H), 4.30 (d, J= 2.1 Hz, 2H), 5.49 (t, J= 2.1 Hz, 1H),
7.19 (t, J = 7.3 Hz, 1H), 7.30 (dd, J = 7.3 Hz, J = 7.6 Hz,
2H), 7.54 (d, J=7.6 Hz, 1H) ppm. 13C NMR δ=30.5, 50.9,
102.9, 127.0, 128.2, 128.7, 133.5, 141.7, 155.6 ppm.
5-(4′-Methylbenzylidene)-3-methyl-1,3-oxazolidin-
2-one (Compound 2 g): White powder; mp 134–136 °C. 1H
NMR δ=7.47 (d, J=8.1 Hz, 2H), 7.15 (d, J=8.0 Hz, 2H),
5.50 (t, J = 2.0 Hz, 1H), 4.30 (d, J = 2.0 Hz, 2H), 3.00 (s,
3H), 2.31 (s, 3 H). 13C NMR δ=155.6, 140.6, 136.3, 130.5,
129.0, 127.9, 102.9, 50.8, 30.2, 21.0 ppm.
5-benzylidene-3-butyl-4-ethyloxazolidin-2-one (Com-
pound 2 h): Yellow oil; 1H NMR δ=1.09 (m, 6H), 1.31–1.40
(m, 2H), 1.52–1.59 (m, 2H), 1.73–1.75 (m, 1H), 1.97–2.01
(m, 1H), 3.01–3.06 (m, 1H), 3.54–3.65 (m, 1H), 4.54 (s,
1H), 5.50 (s, 1H), 7.20 (dd, J = 6.8 Hz, J = 12.8 Hz, 1H),
7.34 (dd, J=7.2 Hz, J=12.8 Hz, 2H), 7.61 (d, J=7.6 Hz,
2H) ppm. 13C NMR δ = 6.3, 13.5, 20.1, 25.0, 29.1, 41.0,
O
O
i
S
O
Br
Br
H2N
N
NH2
OH
EtO
EtO Si
EtO
+
Br
O
H
O
i
O
S
KCC-1
O
Me
N
O
N
O
i
N
Br-
O
Me
Br-
O
i
S
S
O
O
N
O
O
N
N
OH N
OH
Et3N, CH3OH
reflux, 4 h
, CH3OH
Ru
Ru(DMSO)4Cl2
+
N
N
reflux, 2 h
Me
Br-
N
Br-
N
O
O
i
O
S
O
O
O
Scheme 2 Schematic illustration of the synthesis for KCC-1/Salen/Ru(II) NPs
1 3

KCC-1 Supported Ruthenium-Salen-Bridged Ionic Networks as a Reusable Catalyst for the…
Fig. 1 SEM images of KCC-1 NPs (a); fresh KCC-1/Salen/Ru(II) NPs NPs (b); KCC-1/Salen/Ru(II) NPs NPs after ten reuses (c); TEM images
of KCC-1 NPs (d); fresh KCC-1/Salen/Ru(II) NPs NPs (e); KCC-1/Salen/Ru(II) NPs NPs after ten reuses (f)
100
98
96
94
92
90
88
0
100
200
300
400
500
600
700
T / o
C
Fig. 2 TGA diagram of KCC-1/Salen/Ru(II) NPs
The thermal stability of the synthesized KCC-1/Salen/
Ru(II) NPs catalyst was detected through TGA and the
results are depicted in Fig. 2. The weight loss below 250 °C
was ascribed to the elimination of the physisorbed and
chemisorbed solvent on the surface of the silica material.
About 8.2% of the weight loss, in the temperature range
250–450 °C, was due to the organic group derivatives.
The N2 adsorption–desorption isotherms of KCC-1/
Salen/Ru(II) NPs showed characteristic type IV curve
Fig. 3 Adsorption–desorption isotherms of KCC-1/Salen/Ru(II) NPs
(Fig. 3), which isconsistent with literature reports on stand-
ard fibrous silica spheres. As for KCC-1, the BET surface
area, total pore volume, and BJH pore diameter are obtained
1 3

S. M. Saadati, S. M. Sadeghzadeh
as 439 m2/g, 1.49 cm3/g, and 14.78 nm respectively, whereas
the corresponding parameters of KCC-1/Salen/Ru(II) NPs
have decreased to 328 m2/g, 1.22 cm3/g, and 13.49 nm. The
nitrogen sorption analysis of KCC-1/Salen/Ru NPs also con-
firms a regular and uniform mesostructure with a decrease in
surface area, pore diameter and pore volume parameters in
comparison with that of pristine KCC-1. With the function-
alization by Salen/Ru-Si, the corresponding pore volumes
are drastically reduced. This could be ascribed to increased
loading with the sensing probe, which occupies a large vol-
ume inside the silica spheres (Fig. 3; Table 1).
at 802 and 1103 cm−1 and the O–H stretching vibration
at 3444 cm−1 were observed for the KCC-1 (Fig. 4a). The
bands observed at 3121 and 2929 cm−1 are assigned to C–H
stretching of aromatic and aliphatic moieties. Moreover, the
signals cleared at 1463 and 1535 cm−1 are, respectively,
attributed to C=C and C=N. (Fig. 4b). These results indi-
cated that the salen had been successfully introduced onto
the surface of KCC-1.
To optimize the reaction conditions, the carbon dioxide
and propargylic amine were used for the synthesis 2-oxa-
zolidinone in the presence of KCC-1/Salen/Ru(II) NPs
as a catalyst was chosen as a model system. The effect of
various parameters such as solvent, and time (Table 2)
were examined on the model reaction. To investigate the
effect of solvents for the synthesis 2-oxazolidinone, differ-
ent solvents have been used (Table 2, Entries 1–15) and the
obtained results reveal that when the polar protic solvents,
such as methanol, isopropanol, ethanol, and water are used,
the expected product is not formed. However, the yield of
the crosscoupling product was relatively average in polar
aprotic solvents, such as DMF, EtOAc, and DMSO. When
the reaction was conducted in less polar solvents, such as
FT-IR spectroscopy was employed to determine the sur-
face modification of the synthesized catalyst (Fig. 4). The
Si–O–Si symmetric and asymmetric stretching vibrations
Table 1 Structural parameters of KCC-1 and KCC-1/Salen/Ru(II)
NPs materials determined from nitrogen sorption experiments
Catalysts
SBET (m2 g−1
)
Va (cm3 g−1
)
DBJH (nm)
KCC-1
KCC-1/Salen/
Ru NPs
439
328
1.49
1.22
14.78
13.49
Fig. 4 FTIR spectra of a KCC-1 NPs, b KCC-1/Salen/Ru(II) NPs
1 3

KCC-1 Supported Ruthenium-Salen-Bridged Ionic Networks as a Reusable Catalyst for the…
100
Table 2 Synthesis of 2-oxazolidinone by KCC-1/Salen/Ru(II) NPs in
different solvents
90
80
70
60
50
40
30
20
10
0
Entry
Solvent
Time (min)
Yield (%)a
1
2
3
4
5
6
7
8
EtOH
H2O
CH3CN
DMF
CH2Cl2
EtOAc
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
60
30
20
10
–
–
47
32
35
46
36
50
–
35
40
–
0
20
40
60
80
100
120
THF
Temperature oC
Toluene
n-Hexane
CHCl3
DMSO
MeOH
Dioxane
i-PrOH
Anisole
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
9
Fig. 5 Effect of temperature on yield of 2-oxazolidinone
10
11
12
13
14
15
16
17
18
19
20
100
90
80
70
60
50
40
30
20
10
0
–
–
59
97
97
89
54
21
Reaction conditions: CO2 (1.0 MPa), propargylic amine (10 mmol),
KCC-1/Salen/Ru(II) NPs (1 mg), solvent (10 mL), at reflux or 100 °C
0
0.2
0.4
0.6
0.8
1
1.2 1.4
1.6
1.8
2
CO2 Pressure (MPa)
aIsolated yields
Fig. 6 Effect of CO2 pressure on the synthesis of 2-oxazolidinone
anisole or toluene, average yields were isolated. However,
the carbonylative cross-coupling product was obtained in
low yield in polar solvents. In this study, it was found that
conventional heating under solvent free is more efficient than
using solvents (Table 2, Entries 16). Under the optimal con-
ditions, the reaction progress for the shortest time necessary
in the presence of 1 mg of of KCC-1/Salen/Ru(II) NPs was
monitored by GC, that excellent yields of synthesis of 2-oxa-
zolidinone can be achieved in 60 min (Table 2, Entries 17).
To optimize reaction conditions for the KCC-1/Salen/
Ru(II) NPs catalyst system, the effects of various reaction
parameters were investigated. The influence of temperature
on this reaction is exhibited in Fig. 5. It is obvious that the
2-oxazolidinone yield increased up to 97% at 100 °C under
2.0 MPa CO2 pressure over 60 min. Whereas further increase
in the temperature resulted in a slight decrease in the product
yield due to formation of a small amount of by-products.
Therefore, the optimal temperature for the coupling reaction
of CO2, and propargylic amine are 100 °C.
pressure was propitious to produce 2-oxazolidinone when
the reaction pressure was less than 1.8 MPa. Too high pres-
sures would reduce the propargylic amine concentration to
give low 2-oxazolidinone yields. Therefore, the CO2 pres-
sure of 1.0 MPa was considered as suitable condition.
For further investigation the efficiency of the cata-
lyst, different control experiments were performed and
the obtained information is shown in Table 3. Initially, a
Table 3 Influence of different catalysts for synthesis of 2-oxazolidi-
none
Entry
Catalyst
Yield (%)a
1
2
3
4
5
6
7
KCC-1
KCC-1/Salen
KCC-1/Salen/Ru(II)
Nano-SiO2/Salen/Ru(II)
MCM-41/Salen/Ru(II)
SBA-15/Salen/Ru(II)
Salen/Ru(II)
–
–
97
49
81
86
98
As shown in Fig. 6, the CO2 pressure also has a signifi-
cant effect on the coupling reaction. The reaction rate was
accelerated quickly in the range 0.8–1.0 MPa. However, the
yield decreased when the pressure reached 2.0 MPa. Based
on these report, it can be inferred that increasing reaction
Reaction conditions: CO2 (1.0 MPa), propargylic amine (10 mmol),
KCC-1/Salen/Ru(II) NPs (1 mg) at 100 °C
aIsolated yield
1 3

S. M. Saadati, S. M. Sadeghzadeh
Table 4 Synthesis of 2-oxazolidinone derivatives catalyzed by KCC-1/Salen/Ru(II) NPs
Entry
Amines
2-oxazolidinones
Products
2a
Yield (%)a
94
1
O
HN
H
H
O
N
H
H
2
2b
97
O
HN
H
H
O
N
H
H
3
4
2c
2d
93
92
O
HN
H
O
O
O
N
H
O
HN
H
N
H
5
6
2e
2f
98
95
O
HN
H
N
H
O
HN
H
O
N
H
7
2 g
96
O
HN
H
O
N
H
1 3

KCC-1 Supported Ruthenium-Salen-Bridged Ionic Networks as a Reusable Catalyst for the…
Table 4 (continued)
Entry
Amines
2-oxazolidinones
Products
2f
Yield (%)a
93
8
O
HN
O
N
Reaction condition: propargylic amine derivatives (1 mmol), and CO2 1 MPa, KCC-1/Salen/Ru(II) NPs (1 mg), 60 min and at 100 °C
aYield refers to isolated product
standard reaction was carried out using KCC-1 showed that
any amount of the desired product was not formed after
60 min of reaction time (Table 3, entries 1). Also, when
KCC-1/Salen was used as the catalyst, a reaction was not
observed (Table 3, entries 2). The Salen could not give the
satisfactory catalytic activity under mild reactions. Based
on these disappointing results, we continued the studies to
improve the yield of the product by added the Ru(II). Nota-
bly, there was not much difference in the reaction yields
when reaction was carried out using KCC-1/Salen/Ru(II)
NPs and Salen/Ru(II) catalyst (Table 3, entries 3 and 7),
However, Salen/Ru(II) is not recoverable and reusable for
the next runs. These observations show that the reaction
cycle is mainly catalyzed by Ru(II) species complexed on
the KCC-1/Salen nanostructure. The nano-sized particles
increase the exposed surface area of the active site of the
catalyst, thereby enhancing the contact between reactants
and catalyst dramatically and mimicking the homogeneous
catalysts. As a result, KCC-1/Salen/Ru(II) NPs was used in
the subsequent investigations because of its high reactivity,
high selectivity and easy separation. Also, the activity and
selectivity of nano-catalyst can be manipulated by tailoring
chemical and physical properties like size, shape, compo-
sition and morphology. To assess the exact impact of the
presence of KCC-1 in the catalyst, the KCC-1/Salen/Ru(II)
NPs compared with MCM-41/Salen/Ru(II), SBA-15/Salen/
Ru(II), and nano-SiO2/Salen/Ru(II). When nano-SiO2/
Salen/Ru(II), MCM-41/Salen/Ru(II) or SBA-15/Salen/
Ru(II) was used as the catalyst, the yield of the desired
product was average to good, but the yield for KCC-1/
Salen/Ru(II) NPs was excellent. Non-negligible activity
of the silica was attributed to its shape, composition and
morphology. Besides, the large space between fibers can
significantly increase the accessibility of the active sites
of the KCC-1. That is why, the KCC-1 was more effective
than nano-SiO2, MCM-41, and SBA-15 (Table 3, entries
3–6). As a result, KCC-1 NPs were used in the subsequent
investigations because of its high reactivity, high selectiv-
ity and easy separation (Table 3).
The carboxylative cyclization for a variety of propargylic
amines was then under taken to explore the scope of this
well developed KCC-1/Salen/Ru(II) NPs catalytic system.
As shown in Table 4, both aromatic and aliphatic propar-
gylic amines performed smoothly to give the corresponding
2-oxazolidinones in excellent yields.
For further investigation the possibility of the hetero-
geneous nature of KCC-1/Salen/Ru(II) NPs, a kinetic
study was performed. For this purpose, ruthenium
leaching was study for synthesis of 2-oxazolidinone
under the optimized reaction condition. To determine
the Ru(II) concentration in solution, six samples of the
reaction mixture were taken during the reaction. The
samples were analyzed by ICP-MS as well as the yield
of the reaction was monitored by GC. The results were
described in Fig. 7. No obvious leaching was observed,
according to the ICP-MS data. According to the obtained
results, the conclusion could be derived that the heter-
ogenous ruthenium species aren’t the catalyst promoter
in this reaction.
To gain insight into the nature of the nanocatalyst,
a three-phase test was designed. Three-phase test is a
powerful technique that allows the catalyst to be in its
nature habitat. To conduct the test, the model synthesis
of 2-oxazolidinone was carried out in the absence and in
the presence of salen as a strong scavenger to capture the
homogeneous soluble ruthenium ions. The reaction pro-
gress was monitored by GC. As it is evident in Fig. 8, the
presence of scavenger has no effect on the yield of the
reaction. All of the results obtained from heterogeneity
tests confirmed that the KCC-1/Salen/Ru(II) NPs had a
high catalytic activity with a truly stable heterogeneous
nature under the described reaction conditions.
It is important to note that the heterogeneous prop-
erty of KCC-1/Salen/Ru(II) NPs facilitates its efficient
recovery from the reaction mixture during work-up pro-
cedure. The activity of the recycled catalyst was also
examined under the optimized conditions. After the
completion of reaction, the catalyst was separated by
1 3

S. M. Saadati, S. M. Sadeghzadeh
100
90
80
70
60
50
40
30
20
10
0
0
5
10
15
20
25
30
35
40
Time (min)
Fig. 7 Time-dependent correlation of the ruthenium leaching in
model reaction
Fig. 9 The reusability of catalysts for synthesis of 2-oxazolidinone
4 Conclusions
100
(a)
80
60
40
20
0
In the present study KCC-1/Salen/Ru(II) NPs was syn-
thesized and characterized as an environmentally-friendly
nanocatalyst for the synthesis of 2-oxazolidinones with
various electronically diverse substrates. The experimental
results displayed the core–shell structure of the synthe-
sized catalyst with a mean size range of 250–300 nm. In
addition, the catalyst was easily recoverable and reusable.
Subsequently, high yields in short reaction times were
achieved without the need for an expensive catalyst as well
as excellent reusability for at least ten times in the corre-
sponding reaction without a reduction in catalytic activity.
0
5
10
15
20
25
30
35
40
45
Time (min)
100
80
60
40
20
0
(b)
Acknowledgements The authors gratefully acknowledge the financial
support of Islamic Azad University, Bojnourd Branch, Bojnourd, Iran.
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