Heterogeneous Fe-MIL-101 catalysts for efficient one-pot four-component coupling synthesis of highly substituted pyrroles

Article abstract of DOI:10.1039/c5nj00632e

Four-component coupling reactions (4CRs) of 1,3-dicarbonyl compounds, amines, aldehydes and nitromethane have been carried out for substituted pyrroles using iron-containing metal organic frameworks (MOFs) as heterogeneous catalysts. Due to its higher sur

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Fe-MIL-101 as an efficient heterogeneous catalyst for four-component coupling
synthesis of highly substituted pyrroles

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DOI: 10.1039/C5NJ00632E
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ARTICLE TYPE
Heterogeneous Fe-MIL-101 catalyst for efficient one-pot four-
component coupling synthesis of highly substituted pyrroles
Jia Tang, Mu Yang, Ming Yang, Jingjing Wang, Wenjun Dong* and Ge Wang
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x
A four-component coupling reactions (4CRs) of 1,3-dicarbonyl compounds, amines, aldehydes and
nitromethane has been carried out for substituted pyrroles using Iron-containing metal organic
frameworks (MOFs) as heterogeneous catalysts. Due to the higher surface area and larger pore size, the
Fe-MIL-101 catalyst exhibits a higher activity than that of Fe-MIL-88B and Fe-MIL-53. The reusability
10 and heterogeneity of Fe-MIL-101 catalyst was demonstrated, and over five cycles no significant reduction
of its catalytic activity was observed. The structural stability of the fresh and recovered catalyst was
further studied by characterization with thermogravimetric analysis, powder X-ray diffraction, and fourier
transform infrared spectra. The MOFs have been demonstrated to be highly active heterogeneous
catalysts for substituted pyrroles via 4CRs.
become one hot topic in heterogeneous catalysis.29-30 The large
surface area and pore size of MOFs allow the access of organic
substrates to the transition metal ions inside the crystal structure
of MOFs. Furthermore the highly dispersed metals ions, which
50 are involved in the coordination of MOFs, can interact with
organic substrates and be used as active sites to promote
catalyzed reactions such as oxidation of alcohol, alkylation of
aldehyde, suzuki–miyaura coupling and reduction of
nitroaromatic.29,31 However, to the best of our knowledge, there
55 have been no reports on the synthesis of functionalized pyrroles
catalyzed by MOFs via MCRs.
15 1. Introduction
Pyrrole and its derivatives, as
a class of heterocyclic
compounds in many natural products and medicinal compounds,1
have been widely used in pharmaceutical industries due to their
biological and pharmacological applications as antibacterial,
20 antitumor, antioxidant, anti-inflammatory and antifungal
components.2-4 Up to now, many synthetic methods such as
hantzsch reaction,5-6 3-dipolar cycloaddition reaction,7
annulations reactions,8 and paal–knorr reaction have been
developed.9-10 Although classical reactions are very useful and
25 effective in synthesizing common pyrroles, they often suffer from
some drawbacks such as multistep synthetic operation, functional
group compatibility, regiospecificity, and harsh reaction
conditions.
In the mind of the good catalytic performance of Fe3+ in FeCl3
as a homogeneous catalyst for the MCRs,19 we envisioned the
one-pot four-component coupling reactions (4CRs) to result in
60 functionalized pyrroles by using Fe-MOFs as heterogeneous
catalysts. In this paper, the highly porous Fe-MOF (Fe-MIL-101)
To overcome those problems, recently Multi-component
30 reactions (MCRs) have been developed in the systhesis of
pyrroles.11-18 Advantages of the MCRs include no need of
isolation or purifications for intermediate products, superior
atom-economy, and high variability of substrates. Meanwhile
various catalysts for the synthesis of substituted pyrroles via
35 MCRs have been employed including metal chlorides,19-21
iodine,22 amberlyst-15,23 nano-CoFe2O4 supported Mo catalyst or
Sb (III) catalyst,24-25 nano copper oxide,26 Clay K10,27 and Pd
catalyst.28 While these methods have their own advantages, they
still suffer from several disadvantages such as use of toxic metal
40 catalyst, tedious workup and purifications with low yield, and
long reaction time. In particular, the separation and reuse of
catalysts still remain a challenge. Hence, the development of
efficient and recoverable heterogeneous catalysts to synthesize
highly substituted pyrroles becomes a very important subject.
65
70
Scheme 1 Synthesis of substituted pyrroles catalyzed by Fe-MIL-
101.
was chosen as a new heterogeneous catalyst for the one-pot four-
75 component coupling reactions (4CRs) of 1,3-dicarbonyl
compounds, amines, aldehydes and nitroalkanes (Scheme 1). The
mesoporous system of Fe-MIL-101 defines nano cages of about
45
In recent years, metal organic frameworks (MOFs) have
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o
o
2.9 and 3.4 nm with windows of 1.2 and 1.6 nm,32 which allow 50 temperature, the 4CRs were carried out at from 60 C to 100 C.
bulky molecules to access freely. Furthermore, Fe (III) in Fe-
MIL-101 has a free coordination position around the Fe (III)
ion.31 Therefore the Fe-MIL-101 can be act as a heterogeneous
catalyst to promote the 4CRs for substituted pyrroles.
The results indicate that the temperature greatly affects the
conversion and especially the selectivity of the reaction. When
o
the reaction temperature was raised from 60 C to 100 oC and the
5
reaction time was 20h, the selectivity increases from 49.5% to
55 99.5%. It can be observed that the selectivity rises steadily as
time or temperature increased. In order to get a high yield of the
desired products, the reaction temperature and time were kept at
2. Results and discussion
As shown in Fig S1 and Table S1, the Fe-MIL-101
nanoparticles showed the octahedral structure and the octahedral
length was 300-400 nm, and the Fe-MIL-101 has high surface
o
100 C and 20h in subsequent reactions. In addition, the reaction
was also carried out with different molar ratios of the reactants
60 (Table 2, entries 9-12). There is no obvious change for the
selectivity while the conversion slightly changes. For
convenience, the molar ratio of n (1): n (2): n (3) =1:1:1 was
chosen in following reactions.
10 areas (2670.5 m2/g) and large pore volumes (0.75 cm3/g). With
the advantages of Fe-MIL-101 such as high dispersion of active
Fe (III) ion and large pore size in the structure, the comparison of
Fe-MIL-101 with Fe (III) homogeneous catalysts for the reaction
Table 2 Effect of reaction conditions on the 4CRs.a
of aniline
1 with benzaldehyde 2, acetylacetone 3 and
15 nitromethane 4 was explored firstly. The results are given in
65
Table 1.
Table 1 Comparison the catalytic activity of Fe-MIL-101 with some Fe
(III) homogeneous catalysts and other MOFs for 4CRs. a
Entry n(1):n(2):n(3)
T (oC)
60
60
60
80
80
80
100
100
100
100
100
100
Time (h)
4
8
20
4
8
20
4
Conv.(%) b
91.9
89.14
87.08
83.2
85.9
81.69
96.1
84.4
93.14
87.9
82.2
90
Sel. (%)
0
20
1
2
3
4
5
6
7
8
9
1:1.2:1
1:1.2:1
1:1.2:1
1:1.2:1
1:1.2:1
1:1.2:1
1:1.2:1
1:1.2:1
1:1.2:1
1:1.2:1.2
1:1:1.2
1:1:1
7.26
49.52
17.2
85.4
92.13
56.8
98.7
99.5
98.6
99.1
99.4
Entry
Catalyst
None
Conv. (%)
21
Sel. (%) c
1
2
3
4
5
6
7
8
87
99
98
96
98
99
99
98
FeCl3.6H2O
Fe(NO3)3.9H2O
Fe2(SO4)3
Fe(C5H5)2
Fe-MIL-101
Fe-MIL-88B
Fe-MIL-53
98 b
94 b
95 b
80 b
90
8
20
20
20
20
10
11
12
85
67
a
70 Reaction conditions: Fe-MIL-101(50 mg), aniline, acetylacetone, and
benzaldehyde were added in nitromethane (1 mL), 100oC, 20h;
bDetermined by GC using toluene as an internal standard.
a Reaction conditions: catalyst (50 mg), aniline (1 mmol), benzaldehyde
o
25 (1.2 mmol), nitromethane (1 mL), and acetylacetone (1 mmol) at 100 C
for 20 h; b Reaction conditions: catalyst (0.2 mmol), aniline (1 mmol),
To investigate the efficient scope of Fe-MIL-101
heterogeneous catalyst for the 4CRs, various aromatic amines,
75 primary aldehydes and keto esters were subjected to the protocol
in the presence of Fe-MIL-101, and the results are shown in
Table 3. In general, the reactions are performed well with various
aromatic and aliphatic amines (Table 3, entries 1-5). Compared
with m- and p-toluidine (Table 3, entries 2-3), o-toluidine (Table
80 3, entry 1) shows less reactive in the presence of Fe-MIL-101 and
gives lower conversion, due to the steric hindrance of -CH3. The
weakly electron deficient aromatic aniline such as p-fluoroaniline
was also applied to this reaction and the corresponding pyrrole is
obtained in moderate yield (Table 3, entry 4). Compared to
85 aromatic amines, aliphatic amines such as 1-butylamine exhibit
slightly better reactions with a higher conversion of 99% and
excellent selectivity (Table 3, entry 5). Subsequently, different
kinds of aldehydes were surveyed for these 4CRs. Aromatic
aldehydes bearing electron-donating groups such as -OMe and -
90 Me are converted to the corresponding pyrroles with high
conversions (Table 3, entries 6-7), while weak electron
withdrawing aromatic aldehydes show less reactive in the 4CRs
(Table 3, entries 8-9). Heteroaromatic aldehyde such as 2-
formylfuran also react efficiently to obtain the corresponding
95 product with good conversion and high selectivity (Table 3, entry
benzaldehyde (1.2 mmol), nitromethane (1 mL), acetylacetone (1 mmol)
c
at 100 oC for 20 h;
standard.
Determined by GC using toluene as an internal
30
As can be seen (Table 1, entries 1-6), Fe-MIL-101 as a
heterogeneous catalyst for 4CRs exhibited high activity which
was like that of the homogeneous Fe (III) catalysts. Aniline was
converted to the corresponding product with 90% conversion
after 20h’s reaction (Table 1, entry 6). Other Fe-MOFs as
35 catalysts such as Fe-MIL-88B, Fe-MIL-53 were also applied to
the reaction in similar reaction condition (Table 1, entries 7-8).
Both Fe-MIL-88B and Fe-MIL-53 showed lower reactivity than
Fe-MIL-101. Compared to Fe-MIL-101, the pore sizes of the Fe-
MIL-88B and Fe-MIL-53 structure are much smaller. The unit
40 cell parameters for Fe -MIL-88B in closed states are a =9.5 Å, c
=19.0 Å, V =1485 Å3, 34 and the MIL-53 structure has flexibility
pore size about 8.6 Å.32 Since reactants could not fully contact
with iron ions in both MIL-88B and MIL-53 structure, the active
site cannot catalyze the reaction effectively, which causes a lower
45 conversion.
Exhaustive studies of the optimal reaction conditions for the
synthesis of pyrrole 5 from aniline 1 with benzaldehyde 2,
acetylacetone 3 and nitromethane 4 in the presence of Fe-MIL-
101 were conducted (Table 2). To identify the suitable reaction
2
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10). Moreover, other 1,3-dicarbonyl compounds such as methyl
acetoacetate and ethyl acetoacetate were also evaluated in the
4CRs (Table 3, entries 12-13), methyl acetoacetate undergoes
smooth reaction and affords 85% conversion after 20 h, however,
ethyl acetoacetate is found to be less reactive in the 4CRs and
only 47% conversion is observed, probably due to the steric
hindrance of the pore in Fe-MIL-101 hampers the reaction. The
results suggest that Fe-MIL-101 as a heterogeneous catalyst
exhibits high activity in the 4CRs for broad substrates.
5
50
55
60
10 Table 3 Synthesis of different substituted pyrroles catalyzed by Fe-MIL-
101.a
15
Entry R1
R2
R3
Conv. (%) b Sel. (%)
Fig 2 X-ray diffraction patterns of fresh and recovered Fe-MIL-
101.
1
2
3
4
5
6
7
8
o-CH3Ph
Ph
Ph
Ph
Ph
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
63.7
93.2
92.2
78.0
99
89.9
89.2
69.4
61.8
90.1
87.2
97
m-CH3Ph
p-CH3Ph
p-FPh
CH3(CH2)3
4-FPh
4-FPh
4-FPh
4-FPh
4-FPh
Ph
97.2
96.5
98.1
99.4
96.7
96.3
95.8
84.2
89.2
99.1
90.8
91.1
After reaction, the catalyst was recovered and analyzed by
65 powder XRD and FT-IR. XRD results show that the recovered
Fe-MIL-101 catalyst have the same peak positions as the fresh
material (Figure 2), but the peaks become slightly broaden, which
indicates some defect of Fe-MIL-101 structure, it’s probably due
to some of the coordination bonds between metal ions and
70 organic ligands breaking,38 which caused the surface area of the
Fe-MIL-101 much less, and the total volume was also increased
from 0.754 to 0.899 cm3/g after one time used. Their FT-IR
spectra have the same curves, and the sharp peak assigned to the
organic linkers at 1660 cm-1 remains unaltered (Figure 3). The
75 FT-IR and XRD results further confirm that the main structure of
Fe-MIL-101 is stable under the reaction conditions.
Ph
4-CH3OPh
4-CH3Ph
4-FPh
2-FPh
Furanyl
Ph
9
10
11
12
13
Ph
Ph
Ph
Ph
OMe 85.3
OEt 47
a Reaction conditions: Fe-MIL-101(50 mg), amine (1 mmol), aldehyde (1
mmol), nitromethane (1 mL), 1,3-dicarbonyl compound (1 mmol) and
toluene (1mmol), 100 C, 20 h; Determined by GC using toluene as an
internal standard.
o
b
20
25
30
35
80
85
90
Fig 1 TGA curve of fresh Fe-MIL-101.
Fig 3 FT-IR spectra of fresh and recovered Fe-MIL-101.
In order to investigate the stability of Fe-MIL-101, the thermal
stability of Fe-MIL-101 was first evaluated by thermogravimetric
As one key feature of heterogeneous catalysts, the recyclability
95 of the Fe-MIL-101 catalyst was studied. After the catalytic
reaction for pyrroles, the catalyst was recovered, and stirred in
analysis (Figure 1), The TGA curve under a N2 atmosphere
o
o
40 shows about 8% weight loss at 40-200 C, which is due to the
loss of guest solvent molecules from the pores of Fe-MIL-101.
The 37% weight loss at 300-600 oC can be due to the partial
decomposition of Fe-MIL-101. It implies that the catalyst shows
good thermal stability in the catalytic reaction conditions (100
45 oC).
DMF (8 mL) at 100 C for 24 h twice to active the pores of the
catalyst efficiently, then washed with methanol three times, dried
at 80oC for 24h and used in subsequent reaction. It is found that
100 Fe-MIL-101 can be recovered and reused five times without
obvious loss of catalytic activity. Indeed, the conversion of 84.8%
and the selectivity of 98.5% are still achieved in the 5th run (Fig
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4). XRD results indicate some defect of Fe-MIL-101 structure
MIL-101 catalyst, and these characteristics of Fe-MIL-101
(Fig S2) after the 4th recycling experiment, which may be due to 60 guarantee the excellent catalytic activity for the 4CRs.
some of the coordination bonds breaking between metal ions and
organic ligands. However, the defect of the structure doesn’t
cause a significant decrease of its catalytic performance or
influence the Fe-MIL-101 to be a highly active heterogeneous
catalyst for substituted pyrroles via the four-component coupling
reactions.
3. Conclusions
5
10
15
A porous metal organic framework (Fe-MIL-101) is used as a
heterogeneous catalyst for the synthesis of highly substituted
pyrroles via a one-pot four-component coupling reactions (4CRs).
65 The highly dispersed Fe (III) ions, large surface area, and big
pore size of Fe-MIL-101 ensure that the catalyst has high activity
for 4CRs. The Fe-MIL-101 has high stability under the reaction
conditions and the recovered catalyst can be reused over five
cycles without a significant decrease in activity. Therefore, for
70 the first time we have demonstrated that MOFs can act as good
heterogeneous catalysts to catalyze the MCRs for highly
functionalized pyrroles.
4. Experimental methods
4.1. General information
20 Fig 4 Reusability of Fe-MIL-101 in the 4CRs. Reaction
conditions: Fe-MIL-101 (50 mg), aniline (1 mmol), benzaldehyde
(1 mmol), nitromethane (1 mL), and acetylacetone (1 mmol), 100
oC, 20 h, determined by GC using toluene as an internal standard.
75
All the solvents and chemicals were of reagent grade and used
without further purification. Powder X-ray diffraction (XRD) of
Fe-MIL-101 was performed on M21X Cu Kα radiation
o
(λ=0.154178 nm) in a scanning rang of 5-60o at 10 /min. The
surface morphology was studied on scanning electron microscopy
25
30
35
80 (SEM, ZEISS SUPRA55). The specific surface areas, total pore
volume and average pore size of Fe-MIL-101were measured by a
Micromeritics ASAP 2420 adsorption analyzer with nitrogen
sorption-desorption
isotherms
(N2
adsorption).
Thermogravimetric analysis (TGA) was conducted with an
o
85 instrument (Netzsch STA449F) at a heating rate of 10 C min-1
under a N2 flow. Fourier transform infrared spectra (FTIR) were
obtained on Nicolet 6700 using the KBr pellet technique at room
temperature. The catalytic results were monitored by a gas
chromatography-mass (GC-MS) spectrum on Agilent7890/
90 5975C-GC/MSD.
4.2. Synthesis of Fe-MIL-101
Fe-MIL-101 was synthesized according to the literature with
some modifications.33 Typically, 0.658 g (3.96 mmol) of
terephthalic acid and 1.07 g (3.96 mmol) of FeCl3.6H2O were
95 dissolved into 90 mL of DMF in a 250 mL round-bottomed flask,
and 3.6 mL of acetic acid was added. The reaction mixture was
heated at 110 °C for 24 h, and then cooled to room temperature.
The product was centrifuged and washed with DMF two times
each day for two days to activate the MOF, and the brick-red
100 solid was washed with methanol in the same way to replace
DMF. Finally, the solid was dried at 80 oC for 24 h.
40 Fig 5 Proposed reaction mechanism for the formation of highly
substituted pyrrole catalyzed by Fe-MIL-101.
According to the Grob and Cameisch reaction as well as the
Michael reaction, pyrroles can be obtained in the presence of
nitroalkenes and β-enamino ketones or esters followed by
45 cyclization.35 The nitroalkenes can be obtained via the reaction of
aldehyde with nitroalkane, and the β-enamino ketones or esters
can be generated via the reaction of 1,3-dicarbonyl compound
with amines which can be catalyzed by Fe(III) ion (Fig 5).36-37
The large surface area and pore size of Fe-MIL-101 allow the
50 organic substrates to access the Fe (III) ions inside the crystal
structure, and the highly dispersed Fe (III) in Fe-MIL-101 has a
free coordination position, which makes the Fe (III) ions as high
active sites to promote the 4CRs, while the coordination between
ligands and Fe (III) ions could keep the physical and chemical
55 stability of Fe (III) ions in the metal organic framework during
the catalytic procedure. Therefore, the construction of the pyrrole
ring via the Michael reaction of β-enamino ketones or esters and
nitroalkenes followed could be completed in the presence of Fe-
4.3. General procedure for the synthesis of pyrrole
derivatives.
To a mixed solution of amine 1 (1 mmol), aldehyde 2 (1.2
105 mmol), nitromethane 3 (1 mL), 1,3-dicarbonyl compound 4 (1
mmol) and toluene (1 mmol, as an internal standard) was added
Fe-MIL-101(50 mg). The mixture was stirred at 100 °C for 20 h.
After the reaction, the mixture was cooled to room temperature
and 5 mL ethanol was added, the pyrrole derivatives were
110 dissolved in ethanol. Then the mixture was centrifuged to get the
supernatant solution, and the solution was analyzed by Agilent
4
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31 A. Dhakshinamoorthy, M. Alvaro, H, Garcia, Adv. Synth. Catal.,
2010, 352, 3022.
7890/5975C-GC/MSD.
32 P. Horcajada, T. Chalati, C. Serre, B. Gillet, C. Sebrie, T. Baati, J. F.
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Acknowledgment
The work was supported by the Co-building Special Project of
Beijing Municipal Education and the National High Technology
Research and Development Program of China (no.
2013AA031702).
5
75
80
133, 17839.
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Notes and references
School of Materials Science and Engineering, University of Science and
Technology Beijing, Beijing 100083, P.R. China
10 Tel: +86-010-62333827; E-mail: wdong@ustb.edu.cn
† Electronic Supplementary Information (ESI) available: SEM and BET
of Fe-MIL-101. See DOI: 10.1039/b000000x/
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