Preparation and catalytically study of metal-organic frameworks of amine/MIL-53 (Al) as a powerful option in the rapid N-formylation condensation in neat conditions

Article abstract of DOI:10.1016/j.ica.2015.01.031

This paper reports on the preparation and application of amine/MIL-53 (Al) as highly active catalysts for the N-formylation reaction. These Al-MOFs were found to be an efficient, selective and waste-free green solid catalyst for the net condensation of amines and formic acid. The catalyst can be isolated from the reaction mixture and reused at least 6 times.

Full text of DOI:10.1016/j.ica.2015.01.031

Accepted Manuscript
Preparation and catalytically study of metal-organic frameworks of amine/
MIL-53 (Al) as a powerful option in the rapid N-formylation condensation in
neat conditions
Sadegh Rostamnia, Ziba Karimi
PII:
S0020-1693(15)00044-4
http://dx.doi.org/10.1016/j.ica.2015.01.031
ICA 16391
DOI:
Reference:
Inorganica Chimica Acta
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Received Date:
Revised Date:
Accepted Date:
26 October 2014
17 January 2015
18 January 2015
Please cite this article as: S. Rostamnia, Z. Karimi, Preparation and catalytically study of metal-organic frameworks
of amine/MIL-53 (Al) as a powerful option in the rapid N-formylation condensation in neat conditions, Inorganica
Chimica Acta (2015), doi: http://dx.doi.org/10.1016/j.ica.2015.01.031
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Preparation and catalytically study of metal-organic frameworks of amine/MIL-53 (Al) as a
powerful option in the rapid N-formylation condensation in neat conditions
Sadegh Rostamnia, Ziba Karimi
1

Preparation and catalytically study of metal-organic frameworks of amine/MIL-53 (Al) as a
powerful option in the rapid N-formylation condensation in neat conditions
Sadegh Rostamnia,*,a Ziba Karimi b
a Organic and Nano Group (ONG), Department of Chemistry, Faculty of Science, University of
Maragheh, P.O.: +98(421)2274893; Tel (+98) 4212278001-108; E.mail:
rostamnia@maragheh.ac.ir; srostamnia@gmail.com
b Department of Chemistry, Payame Noor University (PNU), Tehran, Islamic Republic of Iran.
Abstract:
This paper reports on the preparation and application of amine/MIL-53 (Al) as highly active
catalysts for the N-formylation reaction. These Al-MOFs were found to be an efficient, selective
and waste-free green solid catalyst for the net condensation of amines and formic acid. The
catalyst can be isolated from the reaction mixture and reused at least 6 times.
Keywords: Porous coordination polymers (PCPs); metal-organic framework (MOF); N-
formylation.
1. Introduction
Nanoporous metal-organic frameworks (MOFs), which are formed of inorganic building units
and organic linkers attracted more attention in past decade [1]. This new hybrid material has a
crystalline three or two and one-dimensional open framework [2]. MOFs-based structures
demonstrate numerous advantages such as high surface areas and high thermal stability [1,2].
MOFs were utilized to accelerate a number of organic reactions. They are considered as green
catalysts [3].
Recently, thermally and chemically stable amine-based porous coordination polymers (NH2-
MOFs) have been used as heterogeneous catalysts by our group and others [4]. In these
2

investigations, the well-known PCP, IRMOF-3 with non-coordinated amino groups demonstrates
that the basicity of the aniline-like amino group is increased when incorporated inside the pores
of PCP channels [4]. Recently, Gascon et al. [4] prepared a NH2-MIL-53(Al) material, in which
the organic ligands of H2BDC ligand are coordinated to the aluminum ions (Al3+). In fact, NH2-
MIL-53 is built from AlO4(OH)2 octahedra and 2-aminoterephthalate linkers. It should be noted
that the NH2-MIL-53 is stable in water and common organic solvents. For these reasons and in
our continuing interest in the material synthesis [5], we report our results on the synthesized and
application of NH2-MIL-53 (Fig. 1). Herein we investigated the catalytic potential of the NH2-
MIL-53 for the N-formylation condensation to achieve biologically and industrially interesting
formamides (methanamide) [6].
Figure 1. MOFs-catalyst N-formylation reaction.
2. Experimental Method
2.1. Catalyst preparation and characterization
NH2-MIL-53(Al) was synthesized based on previously reported Gascon method with slight
modifications [4b]. In a typical method, AlCl3.6H2O (2.55 g) and 2-amino-terephthalic acid
(H2BDC, 2.8 g) are dissolved in 25 ml DMF, then the produced mixture moved in Teflon-lined
autoclave and heated for 70 h in 423 K, then cooled slowly at a rate of 1 °C/min to room
3

temperature. The resulting product was washed one time with methanol. Then for removing
organic species trapped within the pores, the sample was washed with excess hot methanol (70
°C) for 4 h, and then it was filtered and dried at 60 ˚C overnight. The MOF was then
characterized using a variety of different techniques.
Fig. 2a and 2b show images of scanning electron microscopy (SEM) of the synthesized NH2-
MIL-53(Al) sample. Based on FT-IR spectra (Fig.2c), a broad band centered around 3620 cm-1
could be assigned to the bridging OH group of the MIL-53 [4b,8g]. Two sharp bands at 3496 and
3386 cm-1 are due to NH2. The bands at 1624 and 1389 cm-1 corresponds to asymmetric and
symmetric vibrations of carboxyl groups (C-O) [4c]. The 1256 cm-1 frequency can be assigned to
C-N vibrations. Based on Gascon and coworkers investigations [4b], the amino groups of MOF
are free of hydrogen bonding interactions (Fig. 2c). Also according to the FT-IR wavelengths
1
analysis of the hydroxyl groups (appear at 3620 cm− ) the OH groups show a stronger basicity in
the NH2-MIL-53(Al) [4b,4g].
4

Fig. 2. a and b) SEM micrographs (c) FT-IR spectra of the NH2-MIL-53(Al).
Diffraction peaks at around 2θ = 9.6o, 12.8o and 17.1o are readily recognized from the XRD
pattern (Fig. 3a). The observed diffraction peaks agree with the NH2-MIL-53(Al) [4b,4g,5]. The
crystal structure of NH2-MIL-53(Al) seems changed to amorphous through the reusing after 6
times. The BET surface area for synthesized MOF was 341 m2/g and its total pore volume was
0.53 cm3/g (Fig. 3b).
5

Fig 3. a) XRD patterns (b) BET of the synthesized NH2-MIL-53(Al).
2.2. General procedure for N-formylation of an amine
To a mixture of amine (1 mmol) and formic acid (3 mmol), 42 mg of NH2-MIL-53(Al) (2
mol%) was added and the mixture was stirred at 50 oC under solvent free condition. The progress
of the reaction was monitored by TLC. After completion of the reaction, ethyl acetate was added
to the solidified mixture and the solid catalyst was separated by filtration. The filtrate was dried
over anhydrous Na2SO4. The solvent was evaporated and the product, obtained, was subjected to
column chromatography. The isolated catalyst could be reused by addition of new portions of
substrate. The structure of products obtained had been confirmed by physical properties such as
1
1H NMR. Selected spectroscopy data: N-(4-nitrophenyl)formamide (Table 2, Entry 5): H NMR
3
(300.13 MHz, CHCl3): δ 7.40(1 H, s, CH of CHO), 7.74(2 H, d, JHH 8.7 Hz, CH of Ar), 8.24(2
H, d, 3JHH 8.7 Hz, CH of Ar), 8.49(1 H, broad, NH).
2.3. Recovery and TON study
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The recyclability of the NH2-MIL-53(Al) catalyst was studied in the N-formylation of aniline
under the optimized conditions. During this study, when the reaction was completed, the catalyst
was easily separated from the product, followed decantation of the reaction solution. The catalyst
was washed with dichloromethane and diethyl ether to remove residual product and dried under
vacuum and reused in a subsequent reaction. Turnover number (TON) represents the average
number of substrate molecules converted into the product per molecule of catalyst.
3. Results and discussion
In spite of more attention of MOFs, a few air and moisture stable MOFs have been reported [4].
Among the catalytic systems by MOFs, IRMOF-3 and NH2-MIL-53 family have been employed
[3,4]. Herein, the NH2-MIL-53(Al) material was prepared by H2ATA and aluminium chloride
hexahydrate in DMF by a solvothermal method in Teflon-lined autoclave. A schematic pathway
for synthesis of NH2-MIL-53(Al) is shown in Figure 4.
Fig. 4. Schematic synthetic process of NH2-MIL-53(Al).
Due to industrial importance of N-formylation reaction, several catalysts and precursors were
reported for these processes [6]. In this paper, we investigated the catalytic activity of NH2-MIL-
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53(Al) for amine and formic acid condensation. The nature of the catalyst can play an important
role in the synthesis of N-phenyl formamide 1. The efficiency of NH2-MIL-53 and other catalysts
in the target reaction was compared. The following catalysts were used for comparison: (i) 4
mol% neutral aluminium triacetate [Al(CH3CO2)3] as non-coordination polymeric and non-
porous carboxylic acidaluminium complex; (ii) 2-aminoterephthalic ester (NH2-TE); (iii) none-
amine MOF of the same structure [MIL-53(Al)]. The results are shown in Fig. 5. The MOF NH2-
MIL-53 has clearly demonstrated the best catalytic activity. When the model reaction was run
using NH2-MIL-53, the product 1 was obtained 73% yield during 40 minutes (Fig.5).
Fig. 5. Reaction scale (2.2 mmol/based on amine).
After achieving the successful performance of the model reaction using 4 mol% of the catalyst,
we tried to accomplish the N-formylation process with the lower amount of the MOF. The model
reaction was examined in polar and nonpolar solvents such as water, ethanol and toluene, and
water using different mol% of Al-MOF (Table 1). When the reaction was performed under neat
conditions, the product was obtained in %28 yield at room temperature for the time of 40
minutes. In solvent-less neat conditions the yield increased sharply when the temperature was
8

raised from room temperature to 50 ºC. Experimental results showed that the set-up of the
reaction at 50 ˚C within 20 min with 1/3 ratio of amine/formic acid by 2 mol% of Al-MOF is the
optimum.
Table 1. Study of model reaction in different condition. a
Entry
Solvent b
Sub.c
Mol
Time
Tem(˚C)
Yield
(%)
73
% MOF (min)
1
2
3
4
5
6
7
8
9
PhMe
PhMe
PhMe
EtOH
H2O
Neat
Neat
Neat
Neat
1/5
1/5
1/5
1/5
1/5
1/3
1/3
1/3
1/3
4
2
1
2
2
2
2
2
1
40
40
60
40
80
40
40
20
20
40
40
40
50
r.t.
r.t.
40
50
50
65
42
67
34
28
89
97
88
a Reaction conditions: Set up in 3 mmol. MOF (0.02 g). b 4 mL of solvents. c Substrate ratio
(PhNH2/HCO2H)
With these results in hand, we decided to explore the scope of our method. So, we used NH2-
MIL-53(Al) in the optimized condition for N-formylation of the various amines (Table 2). There
was no significant difference in the yield of product between electron-rich and un-substituted
aromatic and hetero aromatic amines. On the basis of the above results, to extend the scope and
generality of this method, the aliphatic amines were investigated. These results indicated that the
NH2-MIL-53(Al) is a suitable reaction inductor for N-formylation condensation in neat condition.
Table 2. MOF-catalyzed N-formylation condensation in neat condition. a
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Entry
1
Amine
Product
Yield (%) b
97
2
3
94
94
4
5
6
56c
85
72c
7
8
87
82
9
92
95
10
a Reaction conditions: Set up in 3 mmol. b Isolated yields. c Time of reaction was 5h.
In next step, we investigate reusability of NH2-MIL-53(Al), in which after completed of
reaction by adding of dichloromethane, the catalyst can be separated from reaction mixture. In
10

the model reaction, it was found that the NH2-MIL-53(Al) could be recovered and reused in five
reaction cycles, giving a total TON = 553 (Table 3).
Table 3. Recyclability and TON study on the synthesis of 1. a
Run a
1
2
3
4
5
6
Yield% 1
97
95
95
92
90
84
TON = 553
a Setup of reaction was 5 mmol.
As shown in Scheme 1, a plausible mechanism is proposed to explain the reaction process.
although this mechanism did not demonstrated by exact experimental, but in attention the
presence of Lewis acidic center of Al and week basic of OH and NH groups in the inside of pores
of NH2-MIL-53(Al) based on literature reports [3,4], this mechanism is logical for synthesis of
formamides by a N-formylation condensation process (Scheme 1).
Scheme 1. Plausible mechanisms for the N-formylation condensation.
To investigation of the chemo- and size selectivity of the Al-MOF, the N-formylation
condensation reaction was performed using an equimolecular mixture of the aniline (1 mmol) and
11

diphenylamine (1 mmol) in the optimized reaction conditions. After 1 h of reaction progress, the
yield of 1 was 67%, whereas 2 and 3 were trace and 12%, respectively (Scheme 2). This shows
that there is some amount of reactivity occurs outside of the framework or via defects present in
the crystal domains which facilitate guests diffusion [4a,4c].
Scheme 2. Test for chemo and size selectivity of the MOF.
Conclusion
In summary, we prepared NH2-MIL-53(Al) and utilized it for N-formylation condensation of
various amines to achieve biologically and industrially interest formamides. This MOF-catalyzed
heterogeneous method has many advantages such as good selectivity, short reaction time, small
amount of catalyst used and facilely recycled, especially the abstaining from toxic organic
solvents in the reaction, which provides a green and effective method for N-formylation
condensations.
Acknowledgment
The authors thank the referees for their valuable comments.
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Research highlights
► Preparation of metal-organic frameworks (MOFs) of amine/MIL-53 (Al). ► An efficient, fast and
waste-free green approach for organic synthesis. ► Amine/MIL-53 (Al) MOF family that provide a
synergistic means of a suitable mesochannels to drive out the products and water for next recycles.
►Represents advantages, operational simplicity, higher yield and environment friendly with easy
filterable workup.

The metal-organic frameworks of amine/MIL-53 (Al) was found to be an efficient, selective and
waste-free green solid catalyst for the net condensation of amines and formic acid.