Direct [Formula presented] coupling of indoles with alkylamides via oxidative [Formula presented] functionalization using Fe3O(BDC)3 as a productive heterogeneous catalyst

Article abstract of DOI:10.1016/j.molcata.2016.07.042

A metal-organic framework Fe₃O(BDC)₃ was prepared, and used a recyclable heterogeneous catalyst for the direct [Formula presented] coupling of indoles with alkylamides via oxidative [Formula presented] functionalization. The catalyst

Full text of DOI:10.1016/j.molcata.2016.07.042

Accepted Manuscript
Title: Direct C-C coupling of indoles with alkylamides via
oxidative C-H functionalization using Fe3O(BDC)3 as a
productive heterogeneous catalyst
Author: Son H. Doan Khoa D. Nguyen Phuc T. Huynh Tung
T. Nguyen Nam T.S. Phan
PII:
S1381-1169(16)30292-8
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2016.07.042
MOLCAA 9976
To appear in:
Journal of Molecular Catalysis A: Chemical
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Revised date:
Accepted date:
26-5-2016
21-7-2016
21-7-2016
Please cite thisarticle as: SonH.Doan, Khoa D.Nguyen, Phuc T.Huynh, TungT.Nguyen,
Nam T.S.Phan, Direct C-C coupling of indoles with alkylamides via oxidative C-H
functionalization using Fe3O(BDC)3 as a productive heterogeneous catalyst, Journal
of Molecular Catalysis A: Chemical http://dx.doi.org/10.1016/j.molcata.2016.07.042
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Direct C-C coupling of indoles with alkylamides via oxidative C-H functionalization
using Fe3O(BDC)3 as a productive heterogeneous catalyst
Son H. Doan, Khoa D. Nguyen, Phuc T. Huynh, Tung T. Nguyen, Nam T. S. Phan*
Faculty of Chemical Engineering, HCMC University of Technology, VNU-HCM,
268 Ly Thuong Kiet, District 10, Ho Chi Minh City, Viet Nam
*Email: ptsnam@hcmut.edu.vn
Ph: (+84 8) 38647256 ext. 5681
Fx: (+84 8) 38637504
1

Graphical abstract
O
N
Fe3O(BDC)3
di-tert-butyl peroxide
N
+
O
N
N
Research Highlights
 Fe3O(BDC)3 was used as catalyst for the direct functionalization of indoles.
 High yields of indole derivatives were obtained.
 The catalyst could be recovered and reused.
Abstract
A metal-organic framework Fe3O(BDC)3 was prepared, and used a recyclable
heterogeneous catalyst for the direct C-C coupling of indoles with alkylamides via
oxidative C-H functionalization. The catalyst expressed higher catalytic efficiency for the
direct C-C coupling transformation than that of other MOFs and that of other
homogeneous iron catalysts. The coupling of indoles with alkylamides could only
continued to form indole derivatives in the presence of the solid framework catalyst, and
the donation of leached active iron species, if any, was trivial. The Fe-MOF catalyst
could be reused many times for the synthesis of indole derivatives via the direct C-C
2

coupling without a substantial deterioration in catalytic activity. To the best of our
knowledge, this direct C-C coupling transformation was not previously accomplished
using solid catalysts.
Keywords: Indoles; C-C coupling; C-H functionalization; alkylation; alkylamides.
1. Introduction
Indole derivatives have emerged as privileged scaffolds in a variety of nitrogen-
containing biologically active natural products, pharmaceutical candidates,
agrochemicals, and functional materials [1-8]. The conventional Friedel-Crafts alkylation
using alkyl halides, alcohols, ethers, epoxides, and alkenes in the presence of a Brønsted
or Lewis acid catalyst should be one of the most popular protocols to achieve C-
alkylation of indoles [9-13]. However, the preparation of prefunctionalized starting
materials is required, being a major concern from atom-economical and environmental
aspects [14-16]. The coupling transformation via direct C-H functionalization would
offer shorter and more efficient synthetic schemes to achieve indole derivatives [14, 17,
18]. Li and Li previously demonstrated a CuBr-catalyzed direct C-C coupling of
tetrahydroisoquinolines with indole derivatives [19]. Cai and co-workers developed a
Ni(acac)2-catalyzed direct C-C coupling of cyclic ethers with indole derivatives [20].
Hayashi and co-workers previously reported the first example of a FeCl3-catalyzed
oxidative direct C-C coupling of alkylamides with indole derivatives via the formation of
3

iminium ion followed by conventional Friedel-Crafts alkylation [21]. To polish the green
eligibility for the direct C-C coupling transformation with regard to the simplicity of
reusability, heterogeneous catalysts should be utilized [22]. Additionally, using solid
catalysts would also decrease the contamination of the expected products with hazardous
metals [23, 24].
Metal-organic frameworks (MOFs) have emerged as a new generation of crystalline
materials with permanent porosity, constructed by joining metal ions or metal clusters
with organic bridging ligands [25-29]. The properties of MOFs could be controlled by
combining different metal cations of miscellaneous oxidation states and coordination
geometries with appropriate organic linkers. Although significant efforts are needed for
the commercialization of MOFs, promising applications of these materials in many
disciplines have been extensively explored, extending from gas separation and storage to
catalysis. The application of MOFs as heterogeneous catalysts has recently attracted
significant interests from both academics and industry [30-33]. In principle, it would be
possible to establish the catalytic active site either at each organic linker or each metal
cation in the framework, thus maximizing the dispersion and the loading of useful sites
[34-37]. During the last few years, a plentiful number of organic reactions using MOFs
as heterogeneous catalysts have been reported in the literature [38-42]. Iron-based MOFs
were previously employed as heterogeneous catalysts for a number of organic
transformations, directing at oxidation reactions [43-45]. We recently synthesized
quinazolinones, coumarins, and 1,5-benzodiazepines in the presence of Fe-MOFs as
catalyst [46-48]. In this work, we wish to present the direct C-C coupling of indoles with
4

alkylamides via oxidative C-H functionalization using the iron-based metal-organic
framework Fe3O(BDC)3 as a beneficial heterogeneous catalyst. To the best of our
knowledge, this transformation was not previously accomplished using heterogeneous
catalysts.
2. Experimental
2.1. Synthesis of the metal-organic framework Fe3O(BDC)3
The Fe3O(BDC)3 was synthesized in accordance with a literature method [49, 50]. In a
representative preparation, H2BDC (H2BDC=1,4-benzenedicarboxylic acid; 0.199 g, 1.2
mmol), FeCl3.6H2O (0.325 g, 2.0 mmol) and were added to a mixture of ethanol (60 mL)
and DMF (DMF = N,N’-dimethylformamide; 60 mL). The mixture was magnetically
stirred for 30 min to dissolve the solids completely. The solution was equally added
into eight 20-mL vials. The vials were securely covered and then heated at 85 oC for 48
h, forming the framework as light orange crystals. Subsequent to this period, the vials
were cooled down to room temperature, and the crystals were collected by decantation.
The as-synthesized framework was washed with DMF (3× 10 ml), and immersed in
methanol (3× 10 ml). The framework crystals were then dried in a Shlenkline under
o
vacuum at 140 C for 6 h, producing 0.318g of Fe3O(BDC)3 in the form of brick red
crystals (47 % yield based on H2BDC).
2.2. Catalytic studies
5

In a representative experiment, a mixture of 1-methylindole (0.125 ml, 1 mmol) and
diphenyl ether (0.1 ml), as an internal standard in N,N-dimethylacetamide (4 mL) was
added into a 25 ml round bottom flask. The catalyst (0.014 g, 5 mol%) was then added to
the flask. The catalyst concentration was calculated with regard to the iron/1-
methylindole molar ratio. The reaction mixture was magnetically stirred for 5 min to
scatter the Fe-MOF catalyst in the liquid phase. Subsequently, di-tert-butyl peroxide
(0.62 ml, 3 mmol) were added to the reaction mixture. The solution was magnetically
o
stirred at 120 C for 60 min. Reaction yield was monitored by withdrawing samples at
different time periods, quenching with KOH solution (5% w/w, 1 ml). The organic
constituents were then extracted into ethyl acetate (2 ml), dried over anhydrous Na2SO4,
analyzed by GC concerning diphenylether internal standard. N-Methyl-N-((1-methyl-1H-
indol-3-yl)methyl)acetamide was purified by column chromatography on silica gel. GC-
1
13
MS, H NMR, and C NMR analyses were conducted to confirm the product structure.
To examine the recyclability of the catalyst, the Fe-MOF was separated from the reaction
mixture by centrifugation, washed many times with dichloromethane, activated in a
Shlenkline under vacuum at 140 oC for 3 h, and reused for further experiment.
3. Results and discussion
The Fe3O(BDC)3 was synthesized in accordance with a literature method [49, 50], and
was characterized by several approaches (Fig. S1 – Fig. S7). The Fe-MOF was evaluated
for its catalytic efficiency in the direct C-C coupling of 1-methylindole with N,N-
dimethylacetamide via oxidative C-H functionalization to form N-methyl-N-((1-methyl-
6

1H-indol-3-yl)methyl)acetamide (1) as the major product (Scheme 1). Primary studies
focused on the influence of temperature on the yield of (1). The reaction was carried out
at 5 mol% catalyst for 60 min, using 43 equivalents of N,N-dimethylacetamide, in the
presence of 3 equivalents of di-tert-butyl peroxide as the oxidant, at room temperature,
o
o
o
o
o
60 C, 80 C, 100 C, 120 C and 140 C, respectively. It was noticed that no reaction
occurred at room temperature, with no trace amount of (1) being recorded after 60 min.
As expected, raising the reaction temperature led to a pronounced enhancement in the
o
yield of the indole product. The reaction carried out at 60 C afforded 26% GC yield of
(1) after 60 min, while 37% yield was recorded for the reaction carried out at 80 oC. This
o
value could be dramatically upgraded to 81% for the reaction carried out at 100 C.
o
Performing the transformation at 120 C could afford 96% yield of (1) after 60 min.
o
Increasing the reaction temperature to more than 120 C was found to be unnecessary as
the yield of the indole product was not enhanced any further (Fig. 1).
Comparable to other coupling reactions via the direct functionalization of C-H bonds, an
oxidant should be essential for the C-C coupling reaction using the framework catalyst. It
was therefore determined to investigate the influence of different oxidants on the
formation of (1), having employed di-tert-butyl peroxide, tert-butyl hydroperoxide in
water, cumyl hydroperoxide, tert-butyl hydroperoxide in decane, AgNO3, K2S2O8, and
hydrogen peroxide, as the oxidant for the transformation, respectively. The reaction was
carried out at 120 oC for 60 min, in the presence of 5 mol% catalyst, using 43 equivalents
of N,N-dimethylacetamide, with 3 equivalents of the oxidant. AgNO3, K2S2O8, and
hydrogen peroxide were found to be inappropriate for the coupling reaction, offering
only 21%, 20%, and 29% yields, respectively, 60 min, while 61% yield was observed for
7

that using tert-butyl hydroperoxide in water. It was found that tert-butyl hydroperoxide in
decane was more useful as the oxidant for the reaction than tert-butyl hydroperoxide in
water, producing the indole product in 74% yield after 60 min. Among these oxidants, di-
tert-butyl peroxide demonstrated the best exhibition, with 96% yield of (1) being detected
after 60 min. Indeed, in the first illustration of a FeCl3-catalyzed oxidative direct C-C
coupling of alkylamides with indole derivatives, Hayashi and co-workers employed di-
tert-butyl peroxide as the oxidant for the transformation [21]. Additionally, it was
observed that the amount of di-tert-butyl peroxide also influenced the coupling reaction,
and best result was recorded for the transformation using 3 equivalents of the oxidant
(Fig. 3).
Another point that should be studied for the C-C coupling reaction is the catalyst
concentration. We then decided to explore the impact of catalyst concentration on the
o
yield of (1). The reaction was carried out at 120 C for 60 min, using 43 equivalents of
N,N-dimethylacetamide, with 3 equivalents of di-tert-butyl peroxide as the oxidant, in the
presence of 1 mol%, 3 mol%, 5 mol%, and 7 mol% catalyst, respectively. It should be
noted that less than 5% yield of (1) was detected after 60 min in the absence of the
catalyst, proving the importance of the Fe-MOF for the transformation. As expected, the
presence of the catalyst led to a pronounced enhancement in the yield of the indole
product. The reaction using 1 mol% catalyst could progress to 46% yield of (1) after 60
min, while 63% yield was observed for that using 3 mol% catalyst. As mentioned earlier,
the C-C coupling reaction could produce (1) in 96% yield after 60 min in the presence of
8

5 mol% catalyst. Using more than 5 mol% Fe-MOF catalyst was found to be nonessential
as the yield of the indole product was not upgraded any further (Fig. 4).
As the C-C coupling reaction using the framework catalyst was conducted in liquid
phase, the potentiality that some of catalytically active iron sites on the solid catalyst
could dissolve into the solution should be considered. In several situations, owing to the
leaching phenomenon, the transformation would progress under both heterogeneous and
homogeneous catalysis circumstances. In order to verify if active iron species migrated
from the solid catalyst donated to the formation of (1) in the reaction, a control
o
experiment was performed. The reaction was carried out at 120 C for 60 min, in the
presence of 5 mol% catalyst, using 43 equivalents of N,N-dimethylacetamide, with 3
equivalents of di-tert-butyl peroxide as the oxidant. After the first 10 min reaction time
with 37% yield of (1) being recorded, the catalyst was isolated from the reaction mixture
by centrifugation. The liquid phase was then transported to a new flask, and magnetically
o
stirred for an additional 50 min at 120 C with samples being analyzed by GC at varied
time periods. Experimental results recommended that no additional yield of (1) was
noticed after the solid catalyst was separated from the reaction mixture (Fig. 5). These
observations would support that the C-C coupling reaction could only progress in the
presence of the solid catalyst, and the donation of leached active iron species to the
formation of (1), if any, was trivial.
9

To feature the superiority of using the catalyst for the C-C coupling reaction via
oxidative C-H functionalization to form (1), the catalytic activity of the Fe-MOF was
compared to that of common homogeneous iron catalysts such as FeCl2, FeBr2, FeCl3,
o
Fe(NO3)3, and Fe2(SO4)3. The reaction was carried out at 120 C for 60 min, in the
presence of 5 mol% catalyst, using 43 equivalents of N,N-dimethylacetamide, with 3
equivalents of di-tert-butyl peroxide as the oxidant. In the first example of a FeCl3-
catalyzed oxidative direct C-C coupling of alkylamides with indole derivatives, Hayashi
and co-workers employed 10 mol% FeCl3 as catalyst for the transformation [21]. It was
found that the reaction using FeCl3 catalyst afforded 63% yield of (1) after 60 min. FeCl2
was found to be slightly less active than FeCl3, and 56% yield of the indole product was
detected after 60 min for the reaction using this catalyst. Similarly, the FeBr2-catalyzed
direct C-C coupling reaction could proceed to 55% yield after 60 min. Fe(NO3)3 was also
less active than FeCl3, affording 56% yield after 60 min. Fe2(SO4)3 displayed similar
catalytic activity for the transformation as compared with FeCl3, producing (1) in 63%
yield after 60 min. Interestingly, Fe3O(BDC)3 catalyst presented better exhibition than
these homogeneous iron catalyst, with 96% yield of (1) being achieved after 60 min (Fig.
6).
To underline the considerable aspects of using Fe3O(BDC)3 as catalyst for the C-C
coupling reaction via oxidative C-H functionalization to form (1), the catalytic activity of
the Fe3O(BDC)3 was compared with that of other MOFs such as Co2(BDC)2(DABCO),
10

Ni(HBTC)(BPY),
Ni2(BDC)2(DABCO),
Cu2(BDC)2(DABCO),
Cu(BDC),
Cu2(BPDC)2(DABCO), Cu2(BPDC)2(BPY), Cu3(BTC)2, and Fe3O(BPDC)3. These
MOFs were synthesized by solvothermal method, and characterized in accordance with
o
the literature. The reaction was carried out at 120 C for 60 min, in the presence of 5
mol% catalyst, using 43 equivalents of N,N-dimethylacetamide, with 3 equivalents of di-
tert-butyl peroxide as the oxidant. Co2(BDC)2(DABCO) offered low catalytic activity for
the direct C-C coupling reaction, affording only 31% yield of (1) after 60 min.
Ni(HBTC)(BPY) and Ni2(BDC)2(DABCO) were also noticed to be unacceptable as
catalyst for the transformation, with 19% and 30% yields of the product being detected
after 60 min. It was observed that Cu-MOFs were more active for the reaction than Co-
MOFs and Ni-MOFs. The reaction using Cu3(BTC)2 catalyst could progress to 42% yield
of the indole product after 60 min, while 63% yield was recorded for that using Cu(BDC)
catalyst. Using Cu2(BDC)2(DABCO) and Cu2(BPDC)2(DABCO) as catalyst, the reaction
could produce (1) in 59% yield after 60 min. Fe-MOFs were noticed to be more active
than Cu-MOFs, Co-MOFs, and Ni-MOFs. Indeed, the reaction using Fe3O(BPDC)3
catalyst could offer 76% yield after 60 min. Among these MOFs, Fe3O(BDC)3 displayed
the best exhibition, with 96% yield of (1) being recorded after 60 min (Fig. 7).
To acquire perception into the mechanism of the C-C coupling reaction, further studies
o
were performed. The reaction was carried out at 120 C for 60 min, in the presence of 5
mol% catalyst, using 43 equivalents of N,N-dimethylacetamide, with 3 equivalents of di-
tert-butyl peroxide as the oxidant. In the first experiment series, ascorbic acid or (1E,6E)-
1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione (curcumin) as the
antioxidant was added to the reaction mixture after the first 10 min. The mixture was
11

o
stirred for an additional 50 min at 120 C with samples being analyzed at varied time
periods. Experimental result showed that the yield of (1) was considerably influenced by
the antioxidant (Fig. 8). It could be recommended that the interaction of the intermediate
radicals with the antioxidant would alter the coupling transformation. In the second
experiment series, control reactions were carried out using pyridine as a catalyst poison.
After the first 10 min with 37% yield of (1) being detected, pyridine was added, and the
o
resulting mixture was stirred for an additional 50 min at 120 C. It was found that
pyridine notably affected the catalytic activity of the catalyst in the coupling reaction
(Fig. 9). The feature that pyridine as the catalyst poison expressed a extensive effect on
the formation of (1) would recommend that the adsorption of pyridine on the
Fe3O(BDC)3 destroyed the catalyst activity. Based on these results and the literature
[21], the reaction mechanism was then suggested. Hydrogen abstraction of N,N-
dimethylacetamide assisted by di-tert-butyl peroxide and the catalyst generated the
radical. This radical was then converted to the corresponding iminium ion via a single-
electron transfer process. Consequently, a conventional Friedel-Crafts alkylation occurred
to produce the product, sending the catalyst back to the catalytic cycle (Scheme 2).
As mentioned earlier, the Fe3O(BDC)3 provided better catalytic activity than several
homogeneous and heterogeneous catalysts. To underline the superiority of this catalyst
in the C-C coupling reaction via oxidative C-H functionalization to form (1), one point
that should be beared in mind is the readiness of reusability of the solid catalyst. It is
anticipated that the catalyst can be reused many times in this transformation. The MOF-
based catalyst was therefore explored for reusability in the coupling of 1-methylindole
12

with N,N-dimethylacetamide over 10 consecutive runs. The reaction was carried out at
o
120 C for 60 min, in the presence of 5 mol% catalyst, using 43 equivalents of N,N-
dimethylacetamide, with 3 equivalents of di-tert-butyl peroxide as the oxidant. After the
first run, the Fe-MOF catalyst was isolated from the reaction mixture by centrifugation,
washed many times with dichloromethane, dried in a Shlenkline at 140 oC under vacuum
for 3 h. The recovered catalyst was then reused in further experiment under duplicate
conditions to those of the first run. It was noticed that the catalyst could be reused many
times in the C-C coupling reaction to form (1) without a substantial deterioration in
catalytic efficiency. Indeed, 85% yield of the expected product was still recorded in the
10th run (Fig. 10). Moreover, the structure of the catalyst could be preserved, as shown
by XRD (Fig. 11) and FT-IR (Fig. 12) results of the recovered MOF-based catalyst.
The scope of the work was then developed to direct C-C coupling of different arenes with
alkylamides. In the first reaction series, we conducted the coupling between N,N-
dimethylacetamide and several arenes. The reaction was carried out at 120 oC for 60 min,
in the presence of 5 mol% catalyst, using 43 equivalents of N,N-dimethylacetamide, with
3 equivalents of di-tert-butyl peroxide as the oxidant. The corresponding product was
purified by column chromatography. Under this condition, (1) was obtained in an isolated
yield of 90%. It was noticed that 1H-indole was less reactive than 1-methyl-1H-indole,
producing N-((1H-indol-3-yl)methyl)-N-methylacetamide (2) in 83% yield. The coupling
reaction of N,N-dimethylacetamide with 1-methoxy-4-methylbenzene proceeded to 68%
13

yield of N-(2-methoxy-5-methylbenzyl)-N-methylacetamide (3), while 87% yield of N-
((2-methoxynaphthalen-1-yl)methyl)-N-methylacetamide (4) was recorded for the case of
2-methoxynaphthalene. As expected, anisole expressed less reactivity towards the
coupling reaction than 1-methoxy-4-methylbenzene, though 62% yield of N-(2-
methoxybenzyl)-N-methylacetamide (5) was still obtained. 2-Methylfuran was found to
be more reactive, producing N-methyl-N-((5-methylfuran-2-yl)methyl)acetamide (6) in
93% yield. In the second reaction series, we performed the coupling reaction between 1-
methyl-1H-indole with different amides, including N-ethylacetamide, N-ethyl-N-
methylacetamide, and 3-methyloxazolidin-2-one. It was found that both N-
ethylacetamide and N-ethyl-N-methylacetamide were less reactive than N,N-
dimethylacetamide, though 77% yield of N-(1-(1-methyl-1H-indol-3-yl)ethyl)acetamide
(7) and 72% yield of N-ethyl-N-((1-methyl-1H-indol-3-yl)methyl)acetamide (8) were still
achieved. Moreover, the coupling reaction between 3-methyloxazolidin-2-one and 1-
methyl-1H-indole could progress to 87% yield of 3-methyl-4-(1-methyl-1H-indol-3-
yl)oxazolidin-2-one (9) (Table 1).
4. Conclusions
In summary, the iron-based metal-organic framework Fe3O(BDC)3 was synthesized by a
solvothermal method in accordance with the literature, and was characterized by several
approaches. The Fe-MOF could be used as a productive heterogeneous catalyst for the
direct C-C coupling of indoles with alkylamides via oxidative C-H functionalization. The
Fe3O(BPDC)3 expressed higher catalytic activity for the coupling transformation than
14

that of other MOFs such as Co2(BDC)2(DABCO), Ni(HBTC)(BPY),
Ni2(BDC)2(DABCO), Cu2(BDC)2(DABCO), Cu(BDC), Cu2(BPDC)2(DABCO),
Cu2(BPDC)2(BPY), Cu3(BTC)2, and Fe3O(BPDC)3. The Fe3O(BDC)3 also displayed
better exhibition than other homogeneous iron catalysts such as FeCl2, FeBr2, FeCl3,
Fe(NO3)3, and Fe2(SO4)3. The coupling of indoles with alkylamides via oxidative C-H
functionalization could only progress in the presence of the solid catalyst, and the
contribution of leached active iron species to the formation of the indole product, if any,
was insignificant. The catalyst could be reused many times for the coupling reaction
without a substantial deterioration in catalytic activity.
Acknowledgements
The Viet Nam National Foundation for Science and Technology Development -
NAFOSTED is acknowledged for financial support through project code 104.05-2014.77
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19

100
80
60
40
20
0
RT
60
80
100
120
140
Temperature (oC)
Fig. 1. Yields of (1) at different temperatures.
20

100
80
60
40
20
0
nt
ida
ox
ne
CHP
TBHP/H2O
H2O2
DTBP
AgNO3
K2S2O8
no
TBHP/deca
Oxidant
Fig. 2. Yields of (1) with different oxidants.
21

100
80
60
40
20
0
0
1
2
3
4
Oxidant concentration (eqv.)
Fig. 3. Yields of (1) at different oxidant concentrations.
22

100
80
60
40
20
0
0
1
3
5
7
Catalyst concentration (mol%)
Fig. 4. Yields of (1) at different catalyst concentrations.
23

100
80
60
40
20
0
5 mol% catalyst
Leaching test
0
10
20
30
40
50
60
Time (min)
Fig. 5. Leaching test showed that (1) was not produced in the absence of the solid
catalyst.
24

100
80
60
40
20
0
)3
FeCl2
FeCl3
FeBr2
Fe(NO3)3
Fe2(SO4
Fe3O(BDC)3
Catalyst
Fig. 6. Yields of (1) with different homogeneous iron catalysts.
25

100
80
60
40
20
0
BTC)2
Cu(BDC)
3O(BDC)3
3O(BPDC)3
Fe
Cu3(
BPDC)2(BPY)
Fe
Ni(HBTC)(BPy)
BDC)2(DABCO)
BDC)2(DABCO)
BPDC)2(DABCO)
Cu2(
Ni2(BDC)2(DABCO)
Cu2(
Co2(
Cu2(
Catalyst
Fig. 7. Yields of (1) with different MOFs as catalysts.
26

100
80
60
40
20
0
5 mol% catalyst
Adding ascorbic acid
Adding curcumin
0
10
20
30
40
50
60
Time (min)
Fig. 8. Yields of (1) with antioxidants.
27

100
80
60
40
20
0
5 mol% catalyst
Pyridine test
0
10
20
30
Time (min)
40
50
60
Fig. 9. Yields of (1) with catalyst poison.
28

100
80
60
40
20
0
1
2
3
4
5
6
7
8
9
10
Run
Fig. 10. Catalyst recycling investigation.
29