Synthesis of a Zeolitic Imidazolate-Zinc Metal-Organic Framework and the Combination of its Catalytic Properties with 2,2,2-Trifluoroethanol for N-Formylation

Article abstract of DOI:10.1055/s-0037-1610159

A novel protocol is reported for the N-formylation of amines with formic acid by using the nanoporous zeolitic imidazolate framework ZIF-8 as a heterogeneous catalyst in 2,2,2-trifluoroethanol.

Full text of DOI:10.1055/s-0037-1610159

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© Georg Thieme Verlag Stuttgart · New York
2018, 29, A–D
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H. Alamgholiloo et al.
Letter
Synlett
Synthesis of a Zeolitic Imidazolate–Zinc Metal–Organic Framework
and the Combination of its Catalytic Properties with 2,2,2-Trifluoro-
ethanol for N-Formylation
Hassan Alamgholilooa
Sadegh Rostamnia*a
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Asadollah Hassankhani*b
Reza Banaeia
a Organic and Nano Group (ONG), Department of Chemistry,
Faculty of Science, University of Maragheh, PO Box 55181-
83111, Maragheh, Iran
rostamnia.sadegh@nims.go.jp
srostamnia@gmail.com
rostamnia@maragheh.ac.ir
b Department of New Materials, Institute of Science and High
Technology and Environmental Sciences, Graduate Universi-
ty of Advanced Technology, Kerman, Iran
hassankhani_a@yahoo.com
Received: 11.01.2018
Accepted after revision: 25.04.2018
Published online: 30.05.2018
of bromo- or iodoarenes under phosphine-free conditions.7
Miao et al. reported a novel core–shell–shell structured cat-
alyst, Fe3O4@poly(4-vinylpyridine)@ZIF-8, as a heteroge-
neous recyclable catalyst for the Knoevenagel condensation
reaction.8 Recently, Zahmakiran investigated the synthesis
and characterization of iridium nanoparticles stabilized by
the ZIF-8 framework and their catalytic use in the hydroge-
nation of cyclohexene and ethynylbenzene under mild con-
ditions.9 Furthermore, ZIFs have recently been proposed as
interesting candidates for various applications, such as a
heterogeneous catalysts in organic transformations.
DOI: 10.1055/s-0037-1610159; Art ID: st-2018-d0214-l
Abstract A novel protocol is reported for the N-formylation of amines
with formic acid by using the nanoporous zeolitic imidazolate frame-
work ZIF-8 as a heterogeneous catalyst in 2,2,2-trifluoroethanol.
Key words metal–organic frameworks, trifluoroethanol, zeolites,
formylation, amines
Metal–organic frameworks (MOFs) are promising hy-
brid materials for host–guest studies due to their high spe-
cific surface areas, defined pore sizes, and crystalline and
tunable structures.1 MOFs offer the advantages of easy sep-
aration of product, selectivity, and ready control of the time
of contact with the catalyst.2 Despite the benefits of hetero-
geneous catalysis, disadvantages also exist, such as deacti-
vation of catalytic sites, formation of obstructing deposits
within the particles, loss of catalytic material due to the for-
mation of volatile species, and aggregation of catalyst crys-
tallites,2,3 Zeolitic imidazole frameworks (ZIFs) are a sub-
family of MOFs that consist of an imidazole linker and Zn+2,
and which are formed by a self-assembly approach.4 ZIFs
have rapidly developed in terms of finding new structures,
enhancement of their functionalities, expansion of their
pore-size range, exploration of new sorption mechanisms
for storage or separation of gases, and development of their
catalytic properties.4,5 Among the ZIF family, nanocrystal-
line ZIF-8, which contains Zn+2 ions and 2-methylimidaz-
olate as a linker, is the most prominent representative.6
The use of ZIF-based catalysts for the transformation of
organic molecules has received substantial attention in the
recent years. For example, Seayad and co-workers reported
the fabrication of Pd nanoparticles supported on ZIF-8 as an
efficient heterogeneous catalyst for the aminocarbonylation
The amide functionality is one of the most fundamental
chemical building blocks found in a wide variety of biologi-
cal and synthetic structures, such as proteins, pharmaceuti-
cals, or natural products. The most commonly used meth-
ods for the N-formylation of amines use formylating agents
such as chloral,10 formic acid,11 ammonium formate,12 for-
mic acetic anhydride,13 formate esters,14 N,N-dimethylfor-
mamide,15 formyl fluoride,16 formyl cyanide,17 or alde-
hydes.18 The use of MOF-based catalysts for the direct ami-
dation of amines and carboxylic acids has received
increased attention in recent years. Several novel MOF ma-
terials, such as the ionic [Et4NBr]50%–py covalent organic
framework19 or Zr–azobenzene-4,4′-dicarboxylic acid,20
have been reported to catalyze the N-formylation of amines
by carboxylic acids. However, the development of a novel
and mild method for N-formylation remains a desirable goal.
We recently reported the preparation of metal–organic
frameworks of amines with MIL-53 (Al), and we used them
in N-formylation in the absence of a solvent.21 We also de-
veloped catalytic applications of
a
copper-grafted
nanoporous silica (SBA-15/En-Cu) in the presence of a base
with water as a solvent for the conversion of aldehydes into
amides.22
© Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–D

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H. Alamgholiloo et al.
Letter
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In recent years, fluorinated alcohol solvents such as
2,2,2-trifluoroethanol (TFE) and 1,1,1,3,3,3-hexafluoropro-
pan-2-ol (HFIP) have been shown to have unique properties
as solvents, co-solvents, or additives in organic synthe-
sis.23,24 Bonnet-Delpon and co-workers investigated the use
of fluorinated alcohols such as TFE and HFIP as reaction me-
dia or co-solvents in oxidation reactions.24 Howard and co-
workers showed that TFE can be used in the formation of
helical elements in synthetic peptides.25 Khaksar et al. re-
ported an efficient method for the rapid synthesis of ben-
zimidazole derivatives by using HFIP as a solvent.26 We have
recently succeeded in applying SBA-15/TFE,27 SBA-
15/NHSO3H,28 and HFIP/SBA-159 as heterogeneous and re-
cyclable catalysts in organic synthesis. However, to the best
of our knowledge, N-formylation condensation reactions
catalyzed by crystalline ZIF-8 in TFE as a co-solvent have
not previously been reported.26–29 Here, we describe the
preparation of crystalline ZIF-8 and the combination of its
catalytic properties with those of TFE for N-formylation of
amines in a recyclable procedure.30 The pairing of ZIF-8 and
TFE provides a simple and mild method for direct conden-
sation of formic acid with amines.
In the structure of ZIF-8, the zinc atoms are connected
to nitrogen atoms by 2-methylimidazolate (MeIM) linkers,
creating a nanoporous structure containing four-, six-,
eight-, and twelve-membered-ring Zn4N tetrahedral clus-
ters.31 This structure is similar to that of conventional alu-
minosilicate zeolites, where the Zn+2 ions play the role of
silicon and the MeIM linkers form bridges that mimic the
role of oxygen in zeolites.32 The morphology of crystalline
ZIF-8 was examined by scanning electron microscopy and
energy-dispersive X-ray spectroscopy, and it was found to
have a typical octahedral shape with particle sizes ranging
from 2 to 4μm.
Figure 1 Reactivity of heterogeneous and homogeneous catalysts in
an N-formylation reaction. Reaction conditions: PhNH2 (1 mmol), HCO2H
(2 mmol), catalyst (3 mol%), TFE (3 mL), 50 °C.
with other nonfluorinated solvents such as toluene, MeOH,
CH2Cl2, or DMF. In the model reaction of aniline with formic
acid, TFE exhibited the best performance among the various
solvents tested, giving a >98% yield in 90 minutes (Figure 2).24
The catalytic activity of ZIF-8 in N-formylation was as-
sessed by examining the formylation of aniline with formic
acid as a model reaction. To highlight the advantages of us-
ing this zinc-based MOF as a heterogeneous catalyst, it
was compared with other MOFs [OMS-Cu(BDC), nanobelt
Cu-BTC, OMS-MIL-100(Fe), and Cu(BDC)(DABCO)] (Figure
1). The direct N-formylation reaction in TFE at 50 °C in the
presence of 3 mol% ZIF-8 catalyst gave a >99% yield after 90
min. The other MOFs exhibited poorer catalytic activity in
this transformation. The catalytic activity of ZIF-8 was also
compared with that of homogeneous catalysts [Zn(NO3)2,
Zn(OAc)2, ZnCl2, CuCl2, and FeCl3] (Figure 1). Notably,
Zn(NO3)2, the inorganic compound used to prepare ZIF-8,
exhibited a lower catalytic activity than ZIF-8.
Compared with other polar and nonpolar nonfluorinat-
ed alcohol solvents, TFE has specific properties resulting
from the presence of the trifluoromethyl group. The elec-
tron-withdrawing character of the CF3 group of TFE confers
a high activity on the hydrogen of the hydroxy group (pKa =
12.4), and it can form strong hydrogen bonds in comparison
Figure 2 Effect of solvent on the yield of the model reaction. Reaction
conditions: PhNH2 (1 mmol), HCO2H (2 mmol), ZIF-8 (5 mg), solvent
(3 mL), 40 °C, 90 min.
When the reaction was carried out in the absence of the
catalyst, the yield decreased to less than 30%, even after 120
minutes (Table 1, entry 1). The best yield was obtained
when the reaction was carried out in the presence of 5 mg
of ZIF-8 in 3 mL of TFE at 40 °C (entry 5). The effects of polar
nonfluorinated solvents (DMF and MeOH) on the progress
of the reaction progress were also examined (entries 2 and 3).
After examining the effects of various conditions on the
reaction progress, we explored the general applicability of
the catalyst with various amines containing electron-with-
drawing or electron-donating substituents and with formic
or acetic acid (Table 2). All the formylated derivatives were
isolated in good to excellent yields.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–D

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H. Alamgholiloo et al.
Letter
Synlett
Table 1 Optimization of the Reaction Conditions for the N-Formyla-
(1b) was 64%, whereas phenylformamide (2b) was present
only in a trace amount and N-formyl-N-phenylformamide
(3a′) was isolated in 19% yield (Scheme 1).
tion of Anilinea
H
O
NH2
N
H
ZIF-8/TFE
ZIF-8/TFE
HOH
+
+
CHO
N
NH2
H
OH
O
H
N
CHO
N
conditions
10 mg/8 mL
NHCHO
+
40 °C, 90 min
CHO
+
+
Entry Solvent
Substrate ZIF-8
Time (min) Temp (°C) Yieldc
(%)
HCO2H
4 mmol
ratiob
(mg)
1b, 64%
3a', trace
1 mmol
1 mmol
3a, 19%
1
2
3
4
5
6
TFE
DMF
MeOH
TFE
TFE
–
1:3
1:3
1:3
1:2
1:2
1:2
–
5
5
5
5
5
120
120
120
120
90
25
50
50
25
40
50
<30
78
Scheme 1 Chemoselectivity of the ZIF-8/TFE adduct in an N-formyla-
tion reaction
84
>92
>99
88
In summary, crystalline ZIF-8 was successfully synthe-
sized and, in the presence of TFE, was found to be an effi-
cient and recyclable catalyst for N-formylation and N-
acetylation reactions. The catalyst could be separated from
the reaction mixture by filtration and reused in subsequent
runs without a significant loss of its catalytic activity.
150
a Reaction conditions: PhNH2 (1 mmol), HCO2H, ZIF-9, solvent (3 mL).
b Substrate ratio: aniline/formic acid.
c Isolated yield.
Table 2 Reactions of Various Amines and Carboxylic Acids in the Pres-
ence of ZIF-8/TFEa
Supporting Information
Supporting information for this article is available online at
O
ZIF-8/TFE
5 mg/3 mL
R1
R1
https://doi.org/10.1055/s-0037-1610159.
S
u
p
p
ortiInfogrmoaitn
S
u
p
p
o
nrtogI
f
rmoaitn
NH
R2
1a
HOH
+
+
RCO2H
N
R2
R
40 °C
2a
3a
References and Notes
Entry R1
R2
R3
Product Time (min) Yield (%)
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a Reaction conditions: amine (1 mmol), carboxylic acid (2 mmol), ZIF-8 (5
mg), TFE (3 mL), 40 °C.
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model reaction under solvent-free conditions in the pres-
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yield decreased slightly over eight runs, and more sharply
over the ninth and tenth runs (Figure S3).
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stirred at 40 °C for the appropriate time (Table 2). When the
reaction was complete (TLC), the catalyst was recovered by cen-
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N-Phenylformamide (3a)
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White solid; yield: 120 mg (>99%); mp 45 °C. 1H NMR (300
MHz, CDCl3): δ = 7.28 (m, 3 H, CH of Ar), 7.57 (d, 3JHH = 8.4 Hz, 2
H), 8.33 (s, 1 H, H of CHO), 9.15 (br s, 1 H, NH).
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© Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–D