UiO-66 as an efficient catalyst for N-formylation of amines with CO2 and dimethylamine borane as a reducing agent

Article abstract of DOI:10.1016/j.ica.2019.119274

The most effective way to make the best use of CO₂, is the reductive formylation of amines, as formamides have many applications in industry. A new protocol has been developed for reductive N-formylation of amines with CO₂ as a C1 carbon source and DMAB (Dimethylamine borane) as a reducing agent in the presence of Zr-containing metal–organic framework (MOF) as an efficient, heterogeneous recyclable catalyst. We used UiO-66 and UiO-66-NH₂ as catalysts for N-formylation of amines and observed that both the catalyst performs equally. Therefore, we continued our studies with UiO-66 as a catalyst. The UiO-66 MOF shows good catalytic activity and affording the desired formamides in good to excellent yield. This catalytic system is very efficient for several amines including primary and secondary aliphatic cyclic and aromatic amines. Moreover, the prepared catalyst was recycled up to four recycled without a considerable decrease in catalytic activity.

Full text of DOI:10.1016/j.ica.2019.119274

Journal Pre-proofs
UiO-66 as an efficient catalyst for N-formylation of amines with CO2 and di-
methylamine borane as a reducing agent
Vishal V. Phatake, Ashish A. Mishra, Bhalchandra M. Bhanage
PII:
S0020-1693(19)30792-3
https://doi.org/10.1016/j.ica.2019.119274
ICA 119274
DOI:
Reference:
Inorganica Chimica Acta
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31 May 2019
19 October 2019
8 November 2019
Please cite this article as: V.V. Phatake, A.A. Mishra, B.M. Bhanage, UiO-66 as an efficient catalyst for N-
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doi: https://doi.org/10.1016/j.ica.2019.119274
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UiO-66 as an efficient catalyst for N-formylation of amines with CO2 and
dimethylamine borane as a reducing agent.
Vishal V. Phatake, Ashish A. Mishra and Bhalchandra M. Bhanage*
Department of Chemistry, Institute of Chemical Technology (ICT), Mumbai, India–400019
Email: bm.bhanage@gmail.com, bm.bhanage@ictmumbai.edu.in;
Fax: +91 2233611020; Tel: +91 2233612601
Abstract:
The most effective way to make the best use of CO2, is the reductive formylation of amines, as
formamides have many applications in industry. A new protocol has been developed for
reductive N-formylation of amines with CO2 as a C1 carbon source and DMAB (Dimethylamine
borane) as a reducing agent in the presence of Zr-containing metal-organic framework (MOF) as
an efficient, heterogeneous recyclable catalyst. We used UiO-66 and UiO-66-NH2 as catalysts for
N-formylation of amines and observed that both the catalyst performs equally. Therefore, we
continued our studies with UiO-66 as a catalyst. The UiO-66 MOF shows good catalytic activity
and affording the desired formamides in good to excellent yield. This catalytic system is very
efficient for several amines including primary and secondary aliphatic cyclic and aromatic
amines. Moreover, the prepared catalyst was recycled up to four recycled without a
considerable decrease in catalytic activity.
.
Keyword: One-pot reaction, N-formylation, Amines, CO2 Utilization, UiO-66, Dimethylamine
borane.

1. Introduction
From the last few decades, excessive emission of carbon dioxide is a major contributor gas for the
greenhouse effect. Therefore, many efforts have been developed for capture and utilization of CO2.1-3
Although the CO2 is kinetically and thermodynamically stable molecule, several catalytic systems were
developed for the construction of new C-C, C-O, and C-N bonds by chemical transformation of CO2.4-6 As
CO2 is economical, abundant, non-flammable and renewable carbon source used for the synthesis of
many valuable chemicals like carbonates,7 carbamates,8 formamides,9 benzimidazoles,10 urea,11
methanol,12, etc. However, C-N bond formation reaction is one of the most efficient approach for
transformation of CO2 to formamide by using amines and suitable reductant. Formamides have many
applications in organic synthesis such as solvents, key intermediates in drug molecules and in the
agrochemical industry.13-14
Previous reports showed that the formylation of amines with CO2 is mainly obtained in presence
hydrogen and silanes as compared to boranes as a reductant. Recently, boranes and its derivatives
attracted more attention as they have applications as they are cost-effective, easy to handle, less toxic
and also have high H2 storage capacity with high atom economy as compared to silanes.15-17 Generally,
LiAlH4, NaBH4, amine borane (NH3BH3) have been extensively used as a reducing agent. The
dimethylamine borane (DMAB) is used as a H2 substitute and it was not well explored in the previous
reports. Also, DMAB has high stability, water solubility, and non-flammability. Thus, the DMAB is used as
a greener reducing agent compare to silanes for formylation of amines.18-19 Previous reports showed
that several metals based homogeneous and heterogeneous catalysts had been studied for
dehydrogenation reaction of amine borane.20-22
Conventionally, the formamides are prepared by using toxic CO and phosgene as a C1 reagent,
instead, we use CO2 as a carbon source for N-formylation of amines as CO2 is an attractive and green
approach for the synthesis of formamides.23-24 In this context, expensive metal complexes Ru,25 Pd,26-27
Cu,28-29 Rh,30 Zn,31 Ni32 with respective ligands have been explored for the C-N bond formation, but these
catalytic systems have some environmental issues and having complex catalyst synthesis processes.
However, a metal-free catalytic system such as NHC carbene,33 ionic liquids (ILs),34 organic bases (TBD,35
18
DBU,36 guanidine37), B(C6F5)3 has been proved to be an efficient catalyst for the synthesis of
formamides. Also, basic catalysts like K2WO4, K2CO3,9, and CsCO338 have been used for the N-formylation
of amines. Considering the importance of recyclability and reuse of catalysts, some heterogeneous
catalysts such as a zwitterionic covalent organic framework,39 porous organic polymers with N-
heterocyclic carbenes40 and mesoporous imine-based organic polymer41 have been developed for the
synthesis of formamides, but complicated catalyst synthesis procedure limits its application. They also
have some disadvantages like the requirement of an inert gas atmosphere, difficult catalyst separation,
most of the catalyst requires high pressure (H2 as reductant) and high temperature, use of expensive
metals, less atom economy (Silane as a reductant), tedious work up procedure and difficulty in catalyst
recyclability, etc.
Recently, Metal-Organic Framework (MOF) attracted tremendous attention of chemist as it is porous
material prepared from metal and organic linker through coordination bond.42-45 It is well studied for

adsorption of gases such as for storage of H2 and CH4.46 It has many applications in catalysis,47 gas
storage and capture,46,48-49 drug delivery,50 magnetism51, etc. A various combination of metal and the
organic linker has been used to develop many MOF. For N-formylation reaction system needs both
acidic and basic sites in catalyst as Zirconium based MOF having these sites. Also, zirconium MOFs are
easily prepared having good surface area, excellent chemical resistance for organic solvents and water.
As zirconium-based MOF commonly called as a UiO-66 framework (UiO – University of Oslo) prepared
52
from 1,4benzenedicarboxylate (BDC) linker and Zr6O4(OH)4. The UiO-66 is having good chemical,
hydrolytic and thermal stability over many MOF as it having high coordinated zirconium metal in its
framework. Considering these advantages, we selected UiO-66 and UiO-66-NH2 as a catalyst for N-formylation
reaction using CO2 as a carbon source. The UiO-66 was well explored in literature as an efficient material
for gas storage, transfer hydrogenation and used for CO2 capture.53 In 2011, Chia et. al. reported ZrO2 as
a catalyst for transfer hydrogenation of levulinic acid and its esters.54 Later, catalytic transfer
hydrogenation of ethyl levulinate using zirconium-based MOF was reported by Hwang et. al.55 Recently, Pd
immobilized UiO-66 NH2 as an efficient catalyst used for reduction of nitrobenzene to aniline using formic acid
as a reducing agent.56
Considering these facts, this work is mainly focused on the use of heterogeneous recyclable catalyst
which could effectively catalyze N-formylation reaction of amines with CO2 as a C1 source. To the best of
our knowledge, Metal-Organic Frameworks (MOF) were not used for the formylation of amines with
CO2. Herein, we prepared UiO-66 which could be used as an efficient, cheap, non-toxic catalyst for the
formamides synthesis from CO2 and amines with DMAB as a reducing agent (Scheme 1). Additionally, we
used UiO-66 without immobilized metal or any support.
O
R2
R2
UiO-66
H
C
CO2
N
N
DMAB
H
60 oC, 1.0 MPa CO2
R1
R1
Scheme 1: Formylation of amines by using CO2 and DMAB as a reducing agent.
2. Experimental
2.1 Materials and methods
All chemicals were acquired from TCI chemicals, Alfa Aesar, Sigma Aldrich, and used for the reaction
without purification. CO2 was obtained from Rakhangi Gases Ltd., Mumbai, India, with a purity of 99.99
%.
2.2 Instrumental measurements
The X-ray diffraction images obtained with the use of a Shimadzu XRD-6100 with non-monochromated
Cu Kα radiation (λ=1.5405 Å). The scanning mode within the range of 10 to 80° with a step of 0.02°, with
a scanning rate of 2 deg per min. Thermogravimetric analysis (TGA) curves were performed on a STA-
6000 (Perkin Elmer), under N2 atmosphere (20 mL min–1) between 30 °C to 900 °C, at a heating rate of 20
°C min–1. The morphology of samples was studied by SEM analysis using a TESCAN MIRA 3 model at a 10
kV field-emission scanning electron microscope. FTIR spectra were measured by using a Brucker
PerkinElmer-100 spectrometer from 450 cm-1 to 4000 cm-1. The reaction products were analyzed by the

thin layer chromatography (TLC). The gas chromatography (GC) of PerkinElmer Clarus 400 and GC-MS
(Shimadzu QP 2010 ultra, Rtx- 17, 30 m × 25 mm ID column) were used to calculate yields for the
products as well as for identification of the products. The column chromatography (100-200 mesh silica
gel) was used for the purification of products. NMR spectra were recorded with an Agilent Technologies
(1H NMR at 400 and 500 MHz, 13C NMR at 101 and 126 MHz) spectrometer.
2.3 Experimental procedure for the synthesis of formamides:
N-formylation of amines by CO2 and DMAB in the presence of UiO-66 as a catalyst was carried out in
autoclave. The synthesis of formamides is as follows, Amines (5.0 mmol), UiO-66 (10 mg), DMAB (1.5
equiv.), DMF (7 mL) were added in the reactor at room temperature, reactor was closed, flushed two to
three times by CO2 and 1 MPa CO2 pressure was introduced into reactor, then the reactor was heated to
required temperature with continuous stirring. After the reaction was complete, the reactor was cooled,
and the CO2 pressure was carefully discharged from the autoclave. The UiO-66 MOF was separated by
centrifugation. The resultant mixture was concentrated by rotary evaporator and subjected to the
column chromatography with ethyl acetate-petroleum ether used as an eluent to obtain the product. All
the products are confirmed by GCMS
2.3.1 Recycling test
Piperidine (5.0 mmol), UiO-66 (10 mg), DMAB (1.5 equi.), DMF (7 mL) were added in the reactor at room
temperature, the reactor was closed and 1 MPa CO2 pressure was introduced into the reactor, then the
reactor was heated to required temperature with continuous stirring. After completion of the reaction,
the catalyst was recovered by centrifugation and dried at 60 °C then the catalyst was used for the
further recycle run.
3
Result and discussion
3.1: Synthesis and characterization of UiO-66 and UiO-66-NH2
The UiO-66 and UiO-66-NH2 were prepared by the reported method44,57 and detailed procedure for
the synthesis of UiO-66 and UiO-66-NH2 are shown in the supplementary information (SI). The UiO-66
and UiO-66-NH2 were characterized by IR, XRD, SEM, and TGA.
The structure of samples was confirmed by the powder X-ray diffraction method (Fig. S2, SI). The
2θ peaks at 7.1, 8.3 and 25.54° are observed in the XRD patterns of UiO-66-NH2 and UiO-66 that are in
good accordance with the literature.57 According to experimental, UiO-66-NH2 and UiO-66 are highly
crystalline materials. The average crystalline size of UiO-66 was found by Scherrer’s formula Dhkl =
0.9λ/β cos θ and found to be 23 nm, full-width half maxima (FWHM) is 0.3596, where, θ is the Bragg
angle and β is the line broadening at half the maximum intensity.
The morphology and particle sizes of UiO-66 were investigated by the Scanning electron
microscope. SEM images of the UiO-66 are shown in Fig. S3 (SI). These data point shows that UiO-66
consists of the relatively uniform aggregates with 7-9 µm of the 6.49 µm width and 8.67 µm of the
length.
The Structure of UiO-66 and NH2-UiO-66 also was analyzed by IR spectroscopy. IR spectra of
samples are shown in Fig. S1 (SI). In the spectra of samples, the sharp band at 1662 cm-1 corresponds to
DMF and the two intense peaks at 1585 and 1395 cm-1 assigned to the in/out stretching modes of the

carboxylate group are observed. The peaks observed at 745, 700, 676, 552 and 487 cm-1 assigned to the
-OH and C-H bending peaks are overlapped with Zr-O peaks. The broad band in the region of 3000 to
3500 cm-1 is observed in spectra of samples. This band can point to the existence of the -OH groups in
SBU (secondary bonding unit) of UiO-66 and NH2-UiO-66.
The stability of samples was investigated by thermal gravimetric analysis (TGA). TGA curves of
UiO-66 and NH2-UiO-66 are shown in Fig. S4 (SI). The first weight loss was observed from 38 to 115 °C
and it was about 6.2 wt%. This may be corresponding to the initial loss of solvent. The second weight
loss occurred from 180 to 300 °C and it was about 15.2 wt%. This weight loss related to water
vaporization. The third weight loss observed from 460 to 610 °C and this is major weight loss about 24.4
wt% and corresponds to the decomposition of the organic linker. These data are in agreement with that
reported in literature.58
3.2: Catalytic properties of UiO-66
In the first set of experiments, piperidine is selected as a model substrate for N-formylation of amines
with CO2 as a C1 source to examined catalytic properties of UiO-66.
3.2.1: N-formylation of piperidine with CO2
Table 1: Optimization Tablea
Catalyst
CO2
T, P
N
N
H
O
1a
2a
Entry
Solvent
DMAB
(equiv.)
DMAB (3)
Catalyst (mg)
CO2 Temperature Time (h) Yieldb (%)
(MPa)
(oC)
1
Toluene
UiO-66 (15)
2.0
80
20
10
2
3
4
5
6
7
ACN
THF
1,4-dioxane
DMF
DMAB (3)
DMAB (3)
DMAB (3)
DMAB (3)
DMAB (3)
DMAB (3)
UiO-66 (15)
UiO-66 (15)
UiO-66 (15)
UiO-66 (15)
UiO-66-NH2 (15)
UiO-66-NH2 (15)
2.0
2.0
2.0
2.0
2.0
2.0
80
80
80
80
80
40
20
20
20
20
20
20
45
24
40
90c
92
60
DMF
DMF
Effect of Temperature
8
9
10
DMF
DMF
DMF
DMAB (3)
DMAB (3)
DMAB (3)
UiO-66 (15)
UiO-66 (15)
UiO-66 (15)
2.0
2.0
2.0
60
40
100
20
20
20
88
54
92c
Effect of Pressure
11
12
13
DMF
DMF
DMF
DMAB (3)
DMAB (3)
DMAB (3)
UiO-66 (15)
UiO-66 (15)
UiO-66 (15)
1.5
1.0
0.5
60
60
60
20
20
20
89
86
62

Effect of DMAB loading
14
15
16
DMF
DMF
DMF
DMAB (2)
DMAB (1.5)
DMAB (1)
UiO-66 (15)
UiO-66 (15)
Uio-66 (15)
1.0
1.0
1.0
60
60
60
20
20
20
87
85
58
Effect of Time
17
18
19
DMF
DMF
DMF
DMAB (1.5)
DMAB (1.5)
DMAB (1.5)
UiO-66
UiO-66
UiO-66
1.0
1.0
1.0
60
60
60
16
12
8
90c
85
48
Effect of catalyst/substrate ratio
20
21
22d
23e
24f
DMF
DMF
DMF
DMF
DMF
DMAB (1.5)
DMAB (1.5)
DMAB (1.5)
DMAB (1.5)
DMAB (1.5)
UiO-66 (10)
UiO-66 (5)
UiO-66 (10)
UiO-66 (10)
UiO-66 (10)
1.0
1.0
1.0
1.0
1.0
60
60
60
60
60
12
12
12
12
12
92
72
90
82
58
Effect of other boron adduct
25
26
27
DMF
DMF
DMF
NaBH4 (1.5)
NaBH3CN (1.5)
Na(CH3COO)3BH
(1.5)
UiO-66 (10)
UiO-66 (10)
UiO-66 (10)
1.0
1.0
1.0
60
60
60
12
12
12
67
78
34
Controlled Experiments
28
29
DMF
DMF
1.5
1.5
-
1.0
0.0
60
60
12
12
15
-
UiO-66
Reaction conditions: a) Piperidine (2 mmol), DMAB (1.5 equiv.), CO2 (1 MPa), UiO-66 (10 mg), DMF (7 mL) at 60 °C for 12 h. b)
GC and GC-MS yield. c) isolated yield. d) Piperidine (4 mmol). e) Piperidine (6 mmol) f) Piperidine (10 mmol)
In the first set of experiments, piperidine is selected as a model substrate for N-formylation of amines
with CO2 as a C1 source. Initially, the reaction was performed in the presence of various solvents
(Table 1). When we used non-polar toluene as a solvent, lesser yield of 2a was obtained (Table 1,
entries 1), while weak polar solvents like ACN, THF, 1,4-dioxane are also not appropriate solvents for
the formylation reaction because of the unsatisfactory yield of 2a (Table 1, entries 2 to 4). A 90% yield
of 2a was achieved when we used DMF as a solvent at 80 °C for 20 h (Table 1, entry 5). This is probably
due to the good solubility of CO2 and DMAB in DMF. It is observed that polar solvent has a prominent
effect on the formylation reaction, as the polar solvent can activate N-H bond of secondary amines
through polarization and solvation. Then, we tried the reaction with UiO-66-NH2, also gave the
formylated product in good yield (Table 1, entries 6) but at a lower temperature, the only 60% yield
was obtained (Table 1, entry 7). Therefore, we continued our studies with UiO-66 as a catalyst. After
the solvent study, the effect of temperature was studied. As we decreased the temperature to 60 °C,
88% yield of 2a was observed while at 40 °C low yield was noted (Table 1, entries 8 and 9). The 60 °C
temperature is an optimal temperature used for next set of reaction. Next, the effect of CO2 pressure
was investigated on the reaction system (Table 1, entries 11 and 13). The decrease in pressure from 2
MPa to 1 MPa, slightly decreased in the yield of 1-formylpiperidine (2a) was observed (Table 1, entries
11 and 12). At 5 bar CO2 pressure, less yield of 2a was observed. Next, the effect of DMAB loading was

studied and 1.5 equivalent of DMAB provided 1-formylpiperidine (2a) in very good yield compare to 1
equivalent DMAB (Table 1, entries 14-16). Finally, we focused on the effect of time. The reaction time
was lowered from 20 to 8 h and it was noted that the 12 h reaction time was enough to provide 2a
excellent yield (Table 1, entries 17-19). In the next set of experiments, the effect of substrate/catalyst
ratio was studied. The catalyst loading was decreased from 15 to 5 mg and 10 mg of catalyst loading
gave the good yield of the N-formylated product compared to 5 mg catalyst loading (Table 1, entries
20-21). Then 10 mg catalyst loading was used for further experiments. Next, we increased the
piperidine from 2-10 mmol and it was observed that up to 6 mmol of 1a gave the 1-formylpiperidine
(2a) in good yield, (Table 1, entries 22-24). Effect of other hydrogen sources (boron adducts) was also
studied. When we used NaBH4 and NaBH3CN gave the 67 and 78% yield of 2a respectively, while only
34% yield was obtained in presence Na(CH3COO)3BH as a reducing agent (Table 1, entries 25-27). In a
control experiment we carried out a reaction in the absence of catalyst, only 15% yield of 2a was
obtained (Table 1, entry 28). Also, we examined the reaction in the absence of CO2, 2a was not
observed (Table 1, entry 29). The final optimized reaction condition is Piperidine (6 mmol), DMAB (1.5
equiv.), CO2 (1 MPa), UiO-66 (10 mg), DMF (7 mL) at 60 °C for 12 h.
3.2.2: N-formylation of aromatic and aliphatic amines with CO2
After the optimization study, the substrate scope was also explored. The various primary and
secondary aromatic and aliphatic amines which having different functional groups were tested for the
N-formylation reaction (Scheme 2). Initially, cyclic aliphatic secondary amines namely piperidine,
pyrrolidine, morpholine, piperazine were examined for the formylation of amines and the excellent
yield of the corresponding products were obtained respectively (Scheme 2, 2a to 2d). A primary cyclic
aliphatic amine (cyclohexyl amine), also provided the desired formamide 2e in good yield. The bulkier
secondary aliphatic amines such as di-n-butylamine and di-tert-butylamine furnished the 2f and 2g in
low yields. This is due to the steric hindrance of alkyl substituent (isobutyl) around the nitrogen of
respective amines. The formylation of imidazole and indoline were examined for the optimized
reaction condition and good yield of respective formamide was obtained (Scheme 2, 2h & 2i). Then,
we tested aromatic substrates such as aniline and its derivatives for the formylation reaction. Primary
aromatic amine (aniline) also provided N-formylaniline in excellent yield (Scheme 2, 2j). Then, we
study the electronic effect on the aniline and methoxy and dimethoxy substituted aniline gave a good
yield compared to withdrawing substrates like flouro and OCHF2 substituted aniline (Scheme 2, 2k to
2n). Moreover, the N-methylaniline, N-methylbenzylamine and α-methylbenzyl amine were examined
and the corresponding N-formylated products obtained in excellent yield (Scheme 2, 2o to 2q). Only
34% yield of 2r was observed when we used N-benzyl-2-methylpropan-2-amine as a substrate. The
dibenzyl amine was tested and moderate yield of the desired formamide was noted (scheme 2, 2s).
Then, we utilized o-phenylenediamine as a substrate and cyclized product benzimidazole was
obtained in excellent yield (Scheme 2, 2t).

Scheme 2: Substrate Study
UiO-66
CO2
DMAB, T,P
N
N
H
O
1a
2a
O
N
H
N
O
N
N
N
N
O
O
O
O
O
2e, 88%
H
2d, 88%
2c, 92%
2b, 90%
2a, 92%
O
N
C4H9 C4H9
O
N
N
O
N
N
N
O
O
2g, 30%
2i, 80%
HN
2f, 72%
2h, 86%
2j, 89%
N
H
N
H
N
H
N
O
O
O
O
O
O
O
F
O
O
OCHF2
2o, 92%
N
2m, 76%
N
2n, 70%
2l, 84%
2k, 88%
O
Ph
N
O
Ph
N
NH
N
H
O
2s, 86%
2t, 68%
2r, 34%
2p, 94%
2q, 92%
a) Reaction condition - 1a (5 mmol), CO2 (1.0 MPa), Catalyst (10 mg), DMAB (1.5 equiv.), Solvent
(DMF) at 60 oC for 12 h, Isolated yield.
3.2.3: Stability of UiO-66 in N-formylation of amine with CO2
We also investigated the reusability and recyclability of UiO-66 in N-formylation of piperidine with
CO2. After each catalytic test, the catalyst was recovered by centrifugation, dried (in air), and re-
activated at 60°C for 1 h.44 and then used in the next cycle. It was found that activity of UiO-66
decreases from cycle to cycle (Fig. 1). The catalyst was found to be recyclable up to four recycle
without considerable loss in the yield of the product. UiO-66 sample after the four recycle was
examined by XRD, IR spectroscopy and TGA (Figs S1, S2 and S4, SI). The XRD pattern of the recycled
UiO-66 shows that all peaks were maintained in its existing state with a slight decrease in intensity of

peaks, compared to the fresh catalyst and this result is also confirmed by IR spectra that the there is
no significant changes was observed in the catalyst.
Figure 1: Catalyst recycles study of N-formylation reaction.
3.2.4: Mechanism of formylation of amines
Moreover, the tentative reaction mechanism for the synthesis of formamides catalyzed by UiO-66 as a
heterogeneous recyclable catalyst has been developed based on previously reported methods (Figure
2).18,44 UiO-66 and UiO-66-NH2 possess acid and basic sites which takes part in the reaction
mechanism. Basic sites are sites for the CO2 activation which favour the appearance of the positive
charge on the carbon atom of CO2 molecule. In UiO-66 there is no nitrogen atoms in the structures but
also exhibited basicity, probably by the oxygen atoms in the organic ligands connected to metal
clusters via covalent bonding.55,59-60 Then attack of atom of carbon of CO2 by molecule of amine (NH2-
R) leads to the formation of intermediate 1. Next, Lewis acid sites (Zr atoms) are active sites for the
degradation of dimethylamine borane, activates the B-H bond which leads to form intermediate 2,
Intermediate 2 gave the formylated product and NMe3.H2B–OH as a side product. Both step A and B
(rate of these steps) depend on the amount and strength of active sites and their accessibility. UiO-66
has larger amount of strong acid sites in compared with NH2-UiO-66 that should favour the higher rate
of degradation of dimethylamine borane. In spite the larger number of basic sites in NH2-UiO-66 the
accessibility of acid sites for dimethylamine borane is low.

OH
BH2.NHMe2
R2
O
C
Zr
Zr
Zr
Zr
R1
N
NH
O
H
Zr
R1
R2
O
Or
O
H
O
A
Zr
Zr
Zr
R2
H
O
O
O
O
R
R1
N
Zr
N
H
H
O
R2
1
Me2N.H2B
H
2
Zr
BH2.NMe2
O
Zr
Zr
B
Figure 2: Proposed reaction mechanism for the synthesis of formamides from amines and
dimethylamine borane in the presence of CO2.
3.2.5: Comparison of our method with other approaches
Table 1: Comparison of UiO-66 with other recent catalysts used for N-formylation reaction with CO2
and piperidine
Sr.no Catalyst
.
Base/
Ligand
-
CO2
(bar)
40
30
10
30
30
10
1
H2 source (bar)
Temperature Time Ref
(°C)
130
150
(h)
24
36
20
24
24
4
72
14
1.5
1
2
3
4
5
6
7
8
9
Carpy-CMP@Ru
Co-pincer complex
Pd@HMP-1
Co(ClO4)2. 6H2O, PPh3
Imine-POP@Pd
B(C6F5)3
DBU
FIP-IM@QA
FeN3/KCC1/APTPOSS/
TCT/PVA/Cu(II) MNPs
Ru complex
H2 (40)
H2 (30)
Diphenylmethylsilane 60
H2 (30)
H2 (30)
Me2NH.BH3
PMHS
61
62
64
63
41
18
36
65
68
KtBuO
K2CO3
K3PO4
-
-
-
-
140
100
80
30
35
10
15
PhSiH3
H2 (20)
90
10
11
12
13
14
KtBuO
-
Ph2CyP
-
-
40
30
1
30
10
H2 (40)
H2 (30)
PhSiH3
H2 (40)
90
100
60
130
60
30
20
12
24
12
69
70
66
67
NHC-Ir COD complex
Cu2(OH)2CO3
Pd/NC-800-6.9%
UiO-66
Me2NH.BH3
This

work
The comparisons of the catalytic activity of UiO-66 with other recent catalysts used for N-formylation
amines with utilization of CO2 as a C1 source (Table 1). Although the usage of hydrogen as a clean
energy source has various reports as a reducing agent for N-formylation reaction, but the use of H2 is
problematic because of explosive nature, requirement elevated temperature and pressure and also
used of expensive transition metal complexes.41,61-63,68-70 Although, silanes are well explored in
literature for N-formylation reaction but they are less atom-economical and generally require
expensive catalyst.36,64-67 Also, most of the reported methods are non-recyclable and costly as
compared to boranes. In case of heterogeneous recyclable catalysts, use of silane as a hydrogen
source require tedious work procedure as it generates solid waste. Considering the above
circumstances, use of borane as a reducing agent is ideal compared to H2 and silanes. As borane
having high hydrogen storage capacity, moisture and air stability and easy to handle.
4 Conclusion:
In summary, we have prepared, characterized UiO-66 and UiO-66-NH2 MOFs and its application for the
N-formylation of amines with CO2 to the corresponding formylated product. The DMAB is used as a
greener reducing agent (compare to silane) for the N-formylation of amines. The synthesized catalyst
UiO-66 shows excellent activity for a series of amines including aliphatic, cyclic and aromatic amines to
obtain the formamides in good to excellent yield. Advantageously, the UiO-66 MOF is reused up to
four consecutive cycles without a significant decrease in catalytic activity.
5
6
Acknowledgment
The author Vishal V. Phatake acknowledges to the University grant commission (UGC) India for
providing senior research fellowship (SRF).
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Graphical abstract
Graphical Abstract
O
H
N
UiO-66 MOF
DMAB
R2
CO2
H
N
R2
R1
O
H
R1
UiO-66 MOF
60 oC, DMAB
R2
N
CO2
R
1 = H, Aliphataic, Aromatic
20 examples
H
N
R2
R1
R2 = Aliphatic, Aromaic
Upto 94% yield
R1
R1 = H, Aliphataic, Aromatic
R2 = Aliphatic, Aromaic
20 examples
Upto 94% yield
Highlights
 CO2 was used as an ideal C1 carbon source for N-formylation reaction.
 Zr MOFs (UiO-66 and UiO-66-NH2) were employed for N-formylation of amines.
 First time MOF was used for N-formylation reaction using CO2 as a carbon source.
 Dimethylamine borane (DMAB) used as a reducing agent.
 Good to excellent yields were obtained with Primary and secondary amines.

Conflict of interest
No conflict of interest.