A green approach for the synthesis of 2-oxazolidinones using gold(I) complex immobilized on KCC-1 as nanocatalyst at room temperature

Article abstract of DOI:10.1002/aoc.3511

A novel gold(I)-containing ionic liquid-based KCC-1 catalyst was applied for the cyclization of propargylic amines with CO₂ to provide 2-oxazolidinones. High catalytic activity and ease of recovery from the reaction mixture using an external ma

Full text of DOI:10.1002/aoc.3511

Full paper
Received: 26 February 2016
Revised: 7 April 2016
Accepted: 17 April 2016
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.3511
A green approach for the synthesis of 2-
oxazolidinones using gold(I) complex
immobilized on KCC-1 as nanocatalyst at
room temperature
Seyed Mohsen Sadeghzadeh*
A novel gold(I)-containing ionic liquid-based KCC-1 catalyst was applied for the cyclization of propargylic amines with CO2 to
provide 2-oxazolidinones. High catalytic activity and ease of recovery from the reaction mixture using an external magnet, and
several recycle runs without significant loss in performance are additional eco-friendly attributes of this catalytic system.
Copyright © 2016 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web site.
Keywords: KCC-1; nanocatalyst; one-pot synthesis; green chemistry; fibrous nanosilica
important role as chemical intermediates[22] and chiral auxiliaries[23]
Introduction
in organic synthesis, and as antibacterial drugs[24] in pharmaceu-
Organic shell–inorganic core composite particles have received a
lot of attention in a wide range of industrial fields due to their func-
tional properties, high dispersibility and stability after a certain
thickness of polymer coating. The core–shell nanostructure is an
ideal composite system that combines the advantages of both
the core and the shell to offer enhanced physical and chemical
properties. In recent years, Fe3O4 magnetic nanoparticles (MNPs)
have been extensively investigated as inorganic cores for the
synthesis of organic–inorganic core–shell composite particles, due
to their potential applications in many industrial and biological
fields.[1–13] Fe3O4 nanoparticles are naturally hydrophilic because
of the existence of plentiful hydroxyl groups on the particle surface.
Since they are prone to aggregate and their dispersion in organic
media is difficult, the surface coating or modification of iron oxide
nanoparticles is very important in many applications. Surface-
functionalized mesoporous materials have emerged as one of the
most important research areas in the field of advanced functional
materials. Fibrous nanosilica (KCC-1), which features a high surface
area and easy accessibility through its fibres (as opposed to the
traditional use of pores), has been reported by Polshettiwar et al.[14]
Development of green processes based on chemical stabilization
of carbon dioxide has received a great deal of interest in recent
years because CO2 could be used as a safe, cheap and renew-
able C1 building block to synthesize useful organic compounds.
Various useful chemicals, such as dimethyl carbonate,[15]
urethanes,[16] formic acid,[17] methanol,[18] cyclic carbonates,[19]
polycarbonates[20] and others have been prepared by using CO2
as a feedstock. One of the useful developments in which CO2
has been utilized as a substrate is through the carboxylative cycli-
zation of propargylic amines to provide 2-oxazolidinones.[21]
2-Oxazolidinones are important heterocyclic chemicals playing an
tical chemistry. One of the most promising examples of CO2 fixation
to access 2-oxazolidinones is the carboxylative cyclization of
propargylic amines with CO2, which represents an important clean
and atom-economic reaction.
Gold catalysis has quickly become a hot topic in chemistry in the
past decade.[25] Gold species are equally impressive as hetero-
geneous or homogeneous catalysts,[26,27] which show excellent
results in diverse reactions.[28,29] Gold complexes have been
employed as highly efficient catalysts for the formation of C–O, C–
C, C–S, C–N, C–P and C–F bonds starting from alkenes and
alkynes.[30–32] From the viewpoint of reactivity, gold complexes in-
volving phosphorus ligands are one of the reactive classes of gold
catalysts. Supporting these ligands on a recyclable support is one
of the most important approaches for improving their applicability
in organic reactions.[33] In recent years, it has been revealed that
the use of gold complexes grafted on solid supports plays an impor-
tant role in preventing the aggregation of gold.[34]
Herein, we report a simple and efficient synthesis of a
nanoferrite-supported, magnetically recyclable and ionic liquid
catalyst and a study of the effectiveness of KCC-1 for the perfor-
mance of a new magnetic catalyst. The superior performance of
the Fe3O4/KCC-1/tetrazolylidene/Au catalyst has been attributed
to gold complex units incorporated into the fibres, which pre-
vent the formation of agglomerated gold whilst maintaining
*
Correspondence to: Seyed Mohsen Sadeghzadeh, Department of Chemistry,
College of Sciences, Sina Masihabadi Student Research, Neishabour, Iran. E-mail:
seyedmohsen.sadeghzadeh@gmail.com
Department of Chemistry, College of Sciences, Sina Masihabadi Student Research,
Neishabour, Iran
Appl. Organometal. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.

S. M. Sadeghzadeh
the catalytic activity of gold species. Considering the importance
of the chemical stabilization of carbon dioxide as well as the re-
markable properties of gold(I) complex-based nanomaterials in
MNPs is also improved, and the average size increases to about
35–45 nm (Fig. 1(b)). As expected, uniform and monodisperse
Fe3O4/KCC-1/tetrazolylidene/Au materials with radial-like channels,
as shown in Fig. 1(c), were synthesized successfully. The length of
the silica fibres coming out of the centre of Fe3O4/KCC-1/
tetrazolylidene/Au and distributed in all directions is estimated to
be 180–200 nm (Fig. 1(c)). The TEM image shown in Fig. 1(c) further
clarifies that the distance between two fibres is about 10–15 nm.
Comparison of TEM image of used catalyst (Fig. 1(d)) with that of
fresh catalyst (Fig. 1(c)) shows that the morphology and structure
of Fe3O4/KCC-1/tetrazolylidene/Au MNPs remain intact after ten
recoveries. Agglomeration of Fe3O4/KCC-1/tetrazolylidene/Au
MNPs can be seen.
organic transformations, we prepared
(tetrazolylidene)-functionalized ordered mesofibre organosilica
material by using 3-chloropropyltriethoxysilane and
a
novel bis
tetramethoxysilane as silica precursors on a magnetic core
(Fe3O4/KCC-1/tetrazolylidene). The Fe3O4/KCC-1/tetrazolylidene
material was then used as an efficient support for the immobili-
zation of gold(I) (Fe3O4/KCC-1/tetrazolylidene/Au) as a catalyst
for the synthesis of 2-oxazolidinone Scheme 1. The recyclability,
reusability and stability of the catalyst were also investigated.
The successful synthesis of the Fe3O4/KCC-1/tetrazolylidene/
Au MNPs was confirmed from Fourier transform infrared (FT-IR)
spectra (Fig. 2). The peaks at 3415 and 590 cmꢀ1 appear in all
FT-IR spectra, which are assigned to the –OH group and the
Fe–O group, respectively (Fig. 2(a)). In the FT-IR spectrum of
the Fe3O4/KCC-1 MNPs, the absorption intensity of Fe–O group
decreases with the addition of silica portion and a strong absorp-
tion band of the Si–O–Si group appears at 1090 cmꢀ1 owing to
the silica coat (Fig. 2(b)). The O–H stretching vibration at
3415 cmꢀ1, the Si–O stretching at 1110 cmꢀ1, the C¼N
stretching at 1635 cmꢀ1 and CH2 stretching at 2905 cmꢀ1 are ob-
served for the Fe3O4/KCC-1/tetrazolylidene/Au MNPs (Fig. 2(c)).
These results indicate that the organic compound had been suc-
cessfully introduced onto the surface of KCC-1.
Results and discussion
We report the synthesis of a MNP-based solid gold(I) complex with
a high density of gold(I) groups and discuss its performance as a
novel strong and stable magnetic nanocatalyst.
The morphologies and structural features of Fe3O4, Fe3O4/SiO2
and Fe3O4/KCC-1/tetrazolylidene/Au MNPs were evaluated using
transmission electron microscopy (TEM) images (Fig. 1). The aver-
age size of Fe3O4 MNPs is about 10–20 nm (Fig. 1(a)). After being
coated with a SiO2 layer, the typical core–shell structure of the
Fe3O4/SiO2 MNPs can be observed. The dispersity of Fe3O4/SiO2
The structural properties of synthesized Fe3O4/KCC-1/
tetrazolylidene/Au MNPs were analysed using powder X-ray diffrac-
tion (XRD). As shown in Fig. 3, XRD pattern of the synthesized
Fe3O4/KCC-1/tetrazolylidene/Au MNPs displays several relatively
strong reflection peaks in the 2θ range 20–70°, which is quite similar
to those of Fe3O4 nanoparticles reported by other groups. The six
discernible diffraction peaks in Fig. 3(a) can be indexed to (220),
Scheme 1. Synthesis of 2-oxazolidinone in the presence of Fe3O4/KCC-1/
tetrazolylidene/Au MNPs.
Figure 1. TEM images of Fe3O4 (a), Fe3O4/SiO2 (b), Fe3O4/KCC-1/
tetrazolylidene/Au MNPs (c) and Fe3O4/KCC-1/tetrazolylidene/Au MNPs
after ten runs (d).
Figure 2. FT-IR spectra of Fe3O4 MNPs (a), Fe3O4/KCC-1 MNPs (b) and
Fe3O4/KCC-1/tetrazolylidene/Au MNPs (c).
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Appl. Organometal. Chem. (2016)

gold (I) complex immobilized on KCC-1 as nano catalysts
Figure 3. XRD analysis of Fe3O4 MNPs (a), Fe3O4/KCC-1 MNPs (b) and
Fe3O4/KCC-1/tetrazolylidene/Au MNPs (c).
Figure 5. Room-temperature magnetization curves of Fe3O4 and Fe3O4/
KCC-1/tetrazolylidene/Au MNPs.
(311), (400), (422), (511) and (440) which match well with the
database of magnetite in JCPDS (card no. 19–0629) file. Besides
the peak of iron oxide, the XRD pattern of Fe3O4/KCC-1 core–shell
nanoparticles presents a broad featureless peak at low diffraction
angle, which corresponds to amorphous silica (Fig. 3(b)).
Figure 3(c) shows a typical XRD pattern of the Fe3O4/KCC-1/
tetrazolylidene/Au MNPs indicating that there is no change in it.
The thermal behaviour of Fe3O4/KCC-1/tetrazolylidene/Au MNPs
is shown in Fig. 4. A significant decrease in the weight percentage
of the Fe3O4/KCC-1/tetrazolylidene/Au MNPs at about 130 °C is
related to desorption of water molecules from the catalyst surface.
This is evaluated to be 1–3% according to the thermogravimetric
analysis (TGA). In addition, the analysis shows two other decreasing
peaks. The first peak appears at around 250–280 °C due to the
decomposition of gold. This is followed by a second peak at 420–
620 °C, corresponding to the loss of the organic group derivatives.
The magnetic properties of the nanoparticles were characterized
using a vibrating sample magnetometer. The magnetization curves
of the obtained nanocomposite recorded at 300 K show nearly no
residual magnetism (Fig. 5), which means that the nanocomposite
exhibits paramagnetic characteristics. Magnetic measurement
shows that pure Fe3O4, and Fe3O4/KCC-1/tetrazolylidene/Au MNPs
nanocomposite exhibits good magnetic response, which suggests
a potential application for targeting and separation.
First examined was the effect of solvent on the synthesis of
2-oxazolidinone from propargylic amine and CO2 using the
Fe3O4/KCC-1/tetrazolylidene/Au MNPs at 1.5 atm and heating
under reflux (Table 1). Solvent does have an effect on catalyst per-
formance. n-Hexane, a non-polar solvent, gives 2-oxazolidinone in a
lower yield than that obtained under solvent-free conditions
(Table 1, entries 9 and 15). CH3CN, tetrahydrofuran (THF), CH2Cl2,
dimethylformamide (DMF), toluene, dioxane, CHCl3, EtOAc and
dimethylsulfoxide (DMSO), aprotic polar solvents, also give 2-
oxazolidinone in low yields. These results suggest that the aprotic
polar solvents cannot activate propargylic amine. The reaction
was better in protic solvent. i-PrOH and ethanol give 2-
oxazolidinone in average yields (Table 1, entries 13 and 14). In
contrast, the use of methanol results in an increased yield of 75%,
and the yield is markedly increased up to 94% when H2O is used
as the solvent. The protic solvents can activate propargylic amine
Table 1. Synthesis of 2-oxazolidinone catalysed by Fe3O4/KCC-1/
tetrazolylidene/Au MNPs in various solventsa
have saturation magnetization values of 46.2 and 16.8 emu gꢀ1
,
Entry
Solvent
Yield (%)b
respectively. These nanocomposites with paramagnetic character-
istics and high magnetization values can quickly respond to an
external magnetic field and quickly redisperse once the external
magnetic field is removed. The result reveals that the
1
Dioxane
H2O
16
94
—
23
30
41
25
31
11
43
34
75
69
63
23
2
3
CH3CN
THF
4
5
CH2Cl2
EtOAc
DMF
6
7
8
Toluene
n-Hexane
CHCl3
9
10
11
12
13
14
15
DMSO
MeOH
EtOH
i-PrOH
Solvent-free
aReaction conditions: propargylic amine (1 mmol), Fe3O4/KCC-1/
tetrazolylidene/Au MNPs (0.2 mg) and CO2 (1.5 MPa), under reflux of
solvents after 48 h.
bIsolated yield.
Figure 4. TGA diagram of Fe3O4/KCC-1/tetrazolylidene/Au MNPs.
Appl. Organometal. Chem. (2016)
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S. M. Sadeghzadeh
via hydrogen bonds formed between the hydroxyl and the acet-
ylene groups. In this study, it is found that water is more efficient
(Table 1, entry 2) compared to other organic solvents.
At this stage, the amount of catalyst necessary to promote the re-
action efficiently was examined. It is observed that the variation of
the amount of Fe3O4/KCC-1/tetrazolylidene/Au MNPs has an effec-
tive influence. The best amount of Fe3O4/KCC-1/tetrazolylidene/Au
MNPs is 0.08 mg which affords the desired product in 94% yield
(Fig. 6). Using this catalyst system, excellent yields of 2-
oxazolidinone can be achieved in 18 h and in the presence of
0.08 mg of Fe3O4/KCC-1/tetrazolylidene/Au MNPs (Fig. 7).
Also investigated was the crucial role of temperature and pres-
sure in the fixation of CO2 with propargylic amine in the presence
of Fe3O4/KCC-1/tetrazolylidene/Au MNPs as a catalyst. It is clear that
the catalytic activity is not sensitive to reaction temperature. The best
temperature for this reaction is room temperature. Temperatures
greater than room temperature do not cause changes in the
efficiency of the reaction. Pressure is a significant parameter with re-
spect to safety concerns and connected costs, especially for industrial
plants. Hence, conversion at low pressures is desirable. To investigate
the effect of pressure, the conversion of propargylic amine was
examined at 0–1.4 bar CO2 pressure and under isobaric conditions
(Fig. 8). In the pressure range 0.4–1.4 bar, there is no notable effect
of pressure on the yield of 2-oxazolidinone in the presence of
Fe3O4/KCC-1/tetrazolylidene/Au MNPs (blue line). These results
indicate that the synthesis of 2-oxazolidinone in the presence of
Fe3O4/SiO2/tetrazolylidene/Au MNP (red line) had already been real-
ized in excellent yields (94%) with a constant pressure (≥0.8 bar).
However, by performing the reaction at extremely low pressures
(≤0.5 bar), conversions and yields decrease significantly to 0%. This
Figure 8. Effect of pressure on yield of 2-oxazolidinone.
prominent catalytic performance of Fe3O4/KCC-1/tetrazolylidene/Au
MNPs as compared with Fe3O4/SiO2/tetrazolylidene/Au MNPs might
be attributed to a great extent to the crucial promoting effect of con-
fined KCC-1 in obtaining high catalytic activity possibly through sup-
pressing catalyst deactivation and enabling easy CO2 delivery via a
phase transfer mechanism. It should be noted that the promoting ef-
fect of tetrazolylidene on the catalyst performance is, however,
closely dependent on its content inside the fibrous catalyst.
To further evaluate the efficiency of the catalyst, various control
experiments were performed and the obtained data are summa-
rized in Table 2. Firstly, the reaction was examined in the presence
of Fe3O4 MNPs. The result of this study shows that any amount of
the desired product was not formed (Table 2, entry 1). When
Fe3O4/KCC-1 or Fe3O4/KCC-1/tetrazolylidene is used as the catalyst,
a reaction is still not observed (Table 2, entries 2 and 3). Based on
these frustrating results, research was continued to improve
the yield of the product by the optimization of the reaction
conditions. To our delight, the reaction proceeds smoothly with
the use of Fe3O4/KCC-1/tetrazolylidene/Au MNPs and bis
(1-benzyl-4-methyl-4,5-dihydro-1H-1,2,3,4-tetrazol-5-ylidene)gold(I)
chloride (compound 1; Scheme 2) as homogeneous catalyst, and
their catalytic activities are identical (Table 2, entries 4 and 5).
The nano-sized particles increase the exposed surface area of
the active component of the catalyst, thereby enhancing mark-
edly the contact between reactants and catalyst and mimicking
homogeneous catalysts. Also, the activity and selectivity of the
nanocatalyst can be manipulated by tailoring chemical and
physical properties like size, shape, composition and morphol-
ogy. As a result, Fe3O4/KCC-1/tetrazolylidene/Au MNPs were used
in the subsequent investigations because of their high reactivity,
high selectivity and easy separation.
Figure 6. Effect of increasing amount of Fe3O4/KCC-1/tetrazolylidene/Au
MNPs on yield of 2-oxazolidinone.
Table 2. Influence of different catalysts in the synthesis of 2-
oxazolidinonea
Entry
Catalyst
Yield (%)b
1
2
3
4
5
Fe3O4
—
—
—
94
94
Fe3O4/KCC-1
Fe3O4/KCC-1/tetrazolylidene
Fe3O4/KCC-1/tetrazolylidene/Au
Compound 1
aReaction conditions: propargylic amine (1 mmol), catalyst (0.1 mg) and
CO2 (1.5 MPa), in water at room temperature after 24 h.
bIsolated yield.
Figure 7. Effect of time on yield of 2-oxazolidinone.
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Appl. Organometal. Chem. (2016)

gold (I) complex immobilized on KCC-1 as nano catalysts
carboxylative cyclization reaction for an obviously high efficiency
of 94% (Table 4, entries 6–8). High yields and excellent turnover
numbers (TONs) are achieved in all cases.
We compared the catalytic performance of our catalyst with cat-
alysts reported in the literature for the synthesis of 2-oxazolidinone
(Table 5). Table 5 clearly demonstrates that the most favourable
terms are required for the synthesis of 2-oxazolidinone, using
Fe3O4/KCC-1/tetrazolylidene/Au MNPs, while an appropriate, highly
perfect, performance of the present catalyst is observed for the
reaction.
Scheme 2. Structure of bis(1-benzyl-4-methyl-4,5-dihydro-1H-1,2,3,4-
tetrazol-5-ylidene)gold(I) chloride (compound 1).
A plausible mechanism for the catalytic synthesis of 2-
oxazolidinone is shown in Scheme 3. Initially, the catalyst activates
propargylic amine. Subsequent nucleophilic attack on CO2 leads to
the acetylene. Finally, ring closure gives the 2-oxazolidinone.
It is important to note that the heterogeneous nature of Fe3O4/
KCC-1/tetrazolylidene/Au facilitates its efficient recovery from the
reaction mixture during work-up procedure. The activity of the
recycled catalyst was also examined under the optimized condi-
tions. After the completion of reaction, the catalyst was separated
by magnetic filtration, washed with methanol and dried at a pump.
The recovered catalyst was reused for ten consecutive cycles with-
out any significant loss in catalytic activity (Fig. 9). For a poisoning
test, we added higher than stoichiometric amount of mercury, Hg
(0), to the catalytic reaction. The reaction shows weak activity in
the presence of excess Hg(0) which confirms the existence of gold
as soluble species in the reaction. No significant reduction in the ac-
tivity of the catalyst is observed. To test if any gold is leached from
the solid catalyst during the process, a hot filtration test was per-
formed for the reaction of propargylic amine with CO2 after ca
50% of the coupling reaction was completed. Interestingly, no gold
species is detected in the filtrate using atomic absorption spectros-
copy. Also, in order to know whether the reaction takes place at the
surface of Fe3O4/KCC-1/tetrazolylidene/Au MNPs, ICP-MS analysis
was conducted of the remaining mixture after catalyst and product
separation upon reaction completion. The amount of gold after ten
repeated recycles is 6.4% and the amount of gold leaching into the
reaction mixture is very low (about 0.2 ppm). These observations in-
dicate that the catalyst is stable and can tolerate the present reac-
tion conditions.
To assess the exact impact of the presence of KCC-1 in the
catalyst, the Fe3O4/KCC-1/tetrazolylidene/Au MNPs were com-
pared with Fe3O4/SiO2/tetrazolylidene/Au MNPs. The loading
amount of gold(I) in Fe3O4/KCC-1/tetrazolylidene/Au and
Fe3O4/SiO2/tetrazolylidene/Au
was
determined
using
inductively coupled plasma mass spectrometry (ICP-MS). The
amount of gold(I) in Fe3O4/KCC-1/tetrazolylidene/Au is more
than double the amount of gold(I) in Fe3O4/SiO2/
tetrazolylidene/Au (Table 3). But it is interesting that, after reuse
for ten consecutive cycles of catalysts, still the amount of gold(I)
in Fe3O4/KCC-1/tetrazolylidene/Au MNPs is more than about
double that in Fe3O4/SiO2/tetrazolylidene/Au MNPs. This re-
markable ability of the Fe3O4/SiO2/tetrazolylidene/Au MNP
mesostructure may be attributed to KCC-1 units that effectively
manage the reaction through preventing gold agglomeration
and releasing and recapturing gold during the reaction process.
Since Fe3O4/KCC-1/tetrazolylidene/Au MNPs were the most
active of the one-component catalysts, they were tested in the con-
version of other terminal propargylic amines (1a–h) into the corre-
sponding 2-oxazolidinones (2a–h) Scheme 1, the results being
summarized in Table 4. In each case, the 2-oxazolidinones are
obtained with good to excellent isolated yield after 18 h using
0.08 mg of catalyst under solvent-free conditions at room tempera-
ture under a constant pressure of carbon dioxide. Notably, benzene
ring of the terminal position increases the reactivity for the
Table 3. Loading amount of nanometric gold in Fe3O4/KCC-1/
tetrazolylidene/Au and Fe3O4/SiO2/tetrazolylidene/Au MNPs
Entry
Catalyst
Amount (wt%)
Experimental
1
2
3
4
Fe3O4/SiO2/tetrazolylidene/Au
2.9
6.6
1.9
6.4
Fe3O4/KCC-1/tetrazolylidene/Au
Materials and methods
Fe3O4/SiO2/tetrazolylidene/Au after ten runs
Fe3O4/KCC-1/tetrazolylidene/Au after ten runs
Chemical materials were purchased from Fluka and Merck in high
purity. Melting points were determined in open capillaries using
Table 4. Synthesis of 2-oxazolidinone derivatives Scheme 1 catalysed by Fe3O4/KCC-1/tetrazolylidene/Au MNPsa
Entry
R1
R2
R3
Product
Yield (%)b
TON
M.p. (°C)
1
2
3
4
5
6
7
8
H
H
H
|H
H
H
H
H
CH3CH2CH2CH2
CH3
2a
2b
2c
95
91
84
92
91
94
96
95
11.9 × 102
11.4 × 102
10 × 102
Yellow oil
Yellow oil
74–76
H
CH3
CH3
CH3
CH3
C6H5CH2
(CH3)2CH
CH3
2d
2e
2f
11.5 × 102
11.4 × 102
11.8 × 102
12 × 102
40–42
Yellow oil
139–141
134–136
Yellow oil
C6H5
4-CH3C6H4
C6H5
CH3
2 g
2 h
CH3CH2
CH3CH2CH2CH2
11.9 × 102
aReaction conditions: propargylic amine derivatives (1 mmol), catalyst (0.08 mg) and CO2 (0.5 MPa), in water at room temperature after 18 h.
bRefers to isolated product.
Appl. Organometal. Chem. (2016)
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S. M. Sadeghzadeh
Table 5. Comparison of catalytic efficiency of Fe3O4/KCC-1/tetrazolylidene/Au MNPs and various other catalysts
Entry
Catalyst
SiO2–(CH2)3–NEt2
CO2 (MPa)
Solvent
Temperature (°C)
Amount of catalyst
Time (h)
Yield (%)
1
80
—
—
90
90
90
90
90
60
60
60
60
60
60
60
60
60
60
60
40
60
60
60
60
60
60
60
60
60
60
60
r.t.
0.09 g
0.09 g
21
21
21
21
21
240
120
114
24
18
16
17
33
48
27
20
48
20
20
20
20
20
20
20
20
20
20
20
18
72[35]
88[35]
67[35]
58[35]
85[35]
69[36]
63[36]
78[36]
86[36]
90[36]
92[36]
95[36]
94[36]
8[36]
2
SiO2–TBD
80
3
Hydrotalcite MG30
Hydrotalcite MG70
Al2O3
80
—
0.09 g
4
80
—
0.09 g
5
80
—
0.09 g
6
PtCl2/DBU
—
DMSO/H2O
DMSO/H2O
DMSO/H2O
DMSO/H2O
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
MeOH
—
200 mol%
200 mol%
200 mol%
200 mol%
200 mol%
200 mol%
200 mol%
10 mol%
10 mol%
10 mol%
10 mol%
2 mol%
7
CuI/DBU
—
8
Cu(OAc)2/DBU
AgOAc/DBU
AgOAc/DBU
Ag2O/DBU
—
9
—
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
—
—
AgNO3/DBU
AgNO3/DBU
AgNO3/DBU
AgNO3/DBU
AgNO3/DBU
AuCl(IPr)
—
—
—
—
95[36]
95[36]
76[37]
—
0.1
(nC7H15)4NBr
99.999%, balloon
99.999%, balloon
99.999%, balloon
99.999%, balloon
99.999%, balloon
99.999%, balloon
99.999%, balloon
99.999%, balloon
99.999%, balloon
99.999%, balloon
99.999%, balloon
0.5
2.5 mol%
2.5 mol%
2.5 mol%
2.5 mol%
2.5 mol%
2.5 mol%
2.5 mol%
2.5 mol%
2.5 mol%
2.5 mol%
2.5 mol%
0.08 mg
—
[38]
[38]
K8[α-SiW11O39
]
—
—
K6[SiW11O39Cu]
—
43[38]
67[38]
68[38]
66[38]
18[38]
16[38]
45[38]
43[38]
73[38]
95
CuCl2
CuCl2 + (nC7H15)4NBr
—
—
[(nC7H15)4N]6[α-SiW11O39Co]
[(nC7H15)4N]6[α-SiW11O39Fe]
[(nC7H15)4N]6[α-SiW11O39Ni]
[(nC7H15)4N]6[α-SiW11O39Zn]
[(nC7H15)4N]6[α-SiW11O39Mn]
[(nC7H15)4N]6[α-SiW11O39Cu]
Fe3O4/KCC-1/tetrazolylidene/Au
—
—
—
—
—
—
H2O
aReaction conditions: propargylic amine (1 mmol) and CO2 in various solvents and with various amounts of catalyst, temperature, and time.
Scheme 3. A plausible mechanism.
Figure 9. Recycling performance of the catalyst.
an Electrothermal 9100 apparatus and are uncorrected. FT-IR spec-
tra were recorded with a VERTEX 70 spectrometer (Bruker) in trans-
mission mode with spectroscopic grade KBr pellets for all powders.
Morphology was analysed using high-resolution TEM with a JEOL
transmission electron microscope operating at 200 kV. The content
of phosphorus in the catalyst was determined using an OPTIMA
7300DV ICP analyser. Powder XRD data were obtained using a
Bruker D8 Advance model with Cu Kα radiation. TGA was carried
out with a Netzsch STA449F3 at a heating rate of 10 °C minꢀ1 under
nitrogen. Magnetic measurements were carried out with a vibrating
sample magnetometer (4 inch, Daghigh Meghnatis Kashan Co.,
Kashan, Iran) at room temperature. NMR spectra were recorded in
CDCl3 with
a Bruker Avance DRX-400 instrument using
tetramethylsilane as internal standard. Determination of purity of
products and reaction monitoring were accomplished using TLC
with silica gel polygram SILG/UV 254 plates.
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Copyright © 2016 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. (2016)

gold (I) complex immobilized on KCC-1 as nano catalysts
General procedure for preparation of Fe3O4 MNPs
1/3-chloropropylsilane (0.5 mmol) at ꢀ78 °C, reacted for 1 h, and
slowly allowed to reach room temperature. Then the Fe3O4/KCC-
1/tetrazolylidene/Au MNPs were separated from the reaction mix-
ture using an external magnet and washed several times with de-
ionized water and acetone. Finally, Fe3O4/KCC-1/tetrazolylidene/
Au MNPs were dried under vacuum at 50 °C.
The synthesis procedure was as follows. (1) 0.01 mol FeCl2ꢁ4H2O
and 0.03 mol FeCl3ꢁ6H2O were dissolved in 200 ml of distilled water,
followed by the addition of poly(ethylene glycol) (1.0 g, MW
6000 g molꢀ1). (2) Sodium hydroxide (NaOH) was added to the
solution and the pH value was controlled in the range 12–13. (3)
Various amounts of hydrazine hydrate (N2H4ꢁH2O, 80% con-
centration) were added to the suspension. The reaction was
continued for about 24 h at room temperature. During this period,
the pH value was adjusted using NaOH and kept in the range
12–13. The black Fe3O4 MNPs were then rinsed several times with
deionized water.
General procedures for preparation of 2-Oxazolidinones
To a Schlenk tube were successively added Fe3O4/KCC-1/
tetrazolylidene/Au MNPs (0.08 mg), degassed water (1 ml) and a
propargylic amine (1 mmol) under an argon atmosphere, and the
inside of the Schlenk tube was replaced with CO2 (0.5 MPa). The
carboxylative cyclization of the propargylic amine with CO2
proceeded by the stirring of the resulting mixture at room temper-
ature. The progress of the reaction was monitored by TLC. When
the reaction was completed, methanol and dichloromethane were
added to the reaction mixture and the catalyst was separated using
an external magnet under vacuum. Then the solvent was removed
from solution under reduced pressure and the resulting product
purified by recrystallization from methanol.
General procedure for preparation of Fe3O4/SiO2 MNPs
Fe3O4 MNPs (0.02 mol) were dispersed in a mixture of 80 ml of
ethanol, 20 ml of deionized water and 2.0 ml of 28 wt.% concen-
trated ammonia aqueous solution (NH3ꢁH2O), followed by the
addition of 0.20 g of tetraethyl orthosilicate (TEOS). After vigorous
stirring for 24 h, the final suspension was repeatedly washed,
filtered several times and dried at 60 °C in air.
General procedure for preparation of Fe3O4/SiO2/KCC-1 MNPs
Conclusions
The Fe3O4/SiO2/KCC-1 core–shell microspheres were synthesized
according to a previously reported method.[39] Fe3O4/SiO2 (0.25 g)
was dispersed in an aqueous solution (30 ml) containing urea
(0.3 g) to form solution A under ultrasonication for 1 h.
Cetylpyridinium bromide (0.5 g) was added to 0.75 ml of n-pentanol
and 30 ml of cyclohexane to form solution B. Solution A was added
to solution B under stirring at room temperature. Then 1.25 g of
TEOS was added dropwise to the resulting solution. The resulting
mixture was continually stirred for 1 h at room temperature and
then placed into a 120 °C environment for 5 h, thus initiating the re-
action. After the reaction was completed, the mixture was allowed
to cool to room temperature, and the Fe3O4/SiO2/KCC-1 core–shell
microspheres were isolated by strong magnetic suction, washed
with deionized water and acetone, and dried overnight in a drying
oven at 40°oC. This material was then calcined at 550 °C for 5 h in air.
In summary, the design and preparation of a novel gold(I) complex
containing KCC-1-based ordered mesofibre organosilica (Fe3O4/
KCC-1/tetrazolylidene/Au MNPs) and its catalytic application for
the cyclization of propargylic amines with CO2 to provide 2-
oxazolidinones have been described. Interestingly, it was found
that while hot filtration tests and selective catalyst poisons showed
the presence of soluble gold species during the reaction process,
recovery studies illustrated that no significant decrease occurred
in the activity and metal content of recovered Fe3O4/SiO2/
tetrazolylidene/Au MNPs. In addition, the catalyst could be recov-
ered and reused at least ten times with no decrease in its activity
and selectivity. Based on these results, it is concluded that although
the KCC-1 nanostructure acts as ‘cobweb’ for the soluble gold
species, it can also operate as a nanoscaffold to re-uptake the
gold(I) into the mesofibres, thereby avoiding agglomeration of
gold(I) complex. This superior effectiveness of the Fe3O4/KCC-1/
tetrazolylidene/Au nanocatalyst may be ascribed to isolated KCC-
1 units incorporated in the mesofibres which can control the
reaction mechanism through preventing the formation of agglom-
erated gold(I) complex as well as stabilization of active catalytic
gold species.
General procedure for preparation of Fe3O4/SiO2/KCC-1/3-
chloropropylsilane MNPs
KCC-1 NPs (2 mmol) and THF (20 ml) were mixed together in a bea-
ker, and then NaH (20 mmol) was dispersed into the mixture by
ultrasonication. 3-Chloropropyltriethoxysilane (22 mmol) was
added dropwise at room temperature and stirred for another 16 h
at 60 °C. The resultant products were collected and washed sequen-
tially with ethanol and deionized water, and then dried under vac-
uum at 60 °C for 2 h for further use.
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Appl. Organometal. Chem. (2016)