MOFs come up to scratch: An environmentally benign route to oxidative [4 + 2] cycloaddition on maleimides solely: Via MOFs in water

Article abstract of DOI:10.1039/d0gc00619j

The first Diels-Alder reaction of vinyl arenes with ene systems catalyzed by MOFs is reported. Maleimides and maleic anhydride were annulated/dehydrogenated on styrenes in the presence of a mixed-metal (FeNi)MIL-88A catalyst. Neither an additional oxidant nor a source of halogen is needed to drive this oxidative [4 + 2] cyclization reaction. Kinetic evidence such as activation entropy corroborates the proposed concerted mechanism. The reaction proceeds merely through a cost-effective catalyst in water as the greenest solvent. The product of annulation of styrene with maleic anhydride was used for the first L-selective annulative π-extension on naphthalene.

Full text of DOI:10.1039/d0gc00619j

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DOI: 10.1039/D0GC00619J
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ARTICLE
MOFs Come up to Scratch: An Environmentally Benign Route to
Oxidative [4+2] Cycloaddition on Maleimides Solely via MOF in
Water
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Masoumeh Abbasnia, Mehdi Sheykhan*, Mona Bahmani, Parvaneh Taghizadeh
www.rsc.org/
The first Diels-Alder reaction of vinyl arenes with ene systems catalyzed by MOFs is reported. Maleimides and maleic
anhydride were annulated/dehydrogenated on styrenes in the presence of a mixed-metal (FeNi)MIL-88A catalyst. Neither
additional oxidant nor a source of halogen is needed to drive this oxidative [4+2] cyclization reaction. Kinetic evidence such
as activation entropy corroborates the proposed concerted mechanism. The reaction proceeds merely through a cost-
effective catalyst in water as the greenest solvent. The product of annulation of styrene with maleic anhydride was used
for the first L-selective annulative π-extension on naphthalene.
reaction with another coupling partner, thus suppressing side-
reactions of styrenes, are considered as notable achievements.
In this context, Liang et al. managed to couple two styrenes in
Introduction
Fusion of a ring segment through formation of two new bonds
at the expense of two other bonds is a transformation which
has always appealed to organic chemists. Given the fact that
maleimides have a high aspiration for involvement of both
their olefinic carbons in their reactions, myriads of reactions
have been emerged concerning maleimides as one of coupling
a
metal-free reaction without observing considerable
8
polymerization (Scheme 1a). Having followed their lead, two
years later Lei used yne systems, which are far more active
than double bonds, to trap styrenes with the aid of a metal
9
catalyst (Scheme 1b). Also lately, a report on electrochemical
[
4+2] annulation of styrenes has been published which led to
1
partners in cyclization reactions. However, in most cases the
naphthalenes after going through a rearrangement (Scheme
double bond of maleimides cannot be preserved thus usually
succinimides, rather than maleimides, are present in the
structure of the products formed. In our previous work, we
succeeded in retaining the maleimide core in annulation with
1
0
1
c). All the foregoing research work had a feature in
common: “using two or more halogenated reagents in their
reactions”.
2
styrenes via a Pd-catalyzed consecutive C-H activation.
+
Acr - Mes ClO4- (1%)
Subsequent to our work, Antonchick et al. reported a novel
dehydrogenative Diels-Alder (D-A) reaction of alkylarenes on
benzoquinone which could successfully be extended to
styrenes.3 But, when it was applied to maleimides, as
2-Phenyl malononitrile (20%)
Adv. Synth. Catal. 2016
Nat. Commun. 2018
a)
b)
+
Ph
Selectfluor (0.5 equiv.)
blue LED
MeCN, N2, 12 h
Ph
R1
R1
+
Acr - Mes ClO4- (3%)
Co(dmgH)2Py2PF6 (8%)
mentioned earlier, the double bond of maleimide converted to
a single bond even using a twofold excess of an oxidant
oxidant. Diels-Alder (D-A) reaction is known as a robust
transformation for the synthesis of six-membered rings in
+
R2
blue LED
DCE, 24 h
R2
R1
R1
Angew. Chem. Int. Ed. 2019
CF(+)Ni(-) 10 mA
N(4-BrC6H4)3
R2
R2
HFIP
Et4NOTs
MeCN
4
R1
organic chemistry. Therefore, when construction of an arene
R2
R1
R1
ring is demanded,5 D-A reactions have always been a sought-
c) R2
after method. Among dienes used in D-A reactions, styrenes
are of the most challenging cases. This is mainly due to the
competitive unwanted reactions of styrenes, i.e. [2+2]
CF(+)Ni(-) 5 mA
R4
n
Bu4NBF4
R2
R3
HFIP
MeCN/THF
R3
R4
6
7
cycloaddition, and polymerization. It is for this reason that all
reports concerning engagement of styrene in an annulation
R
This work
R
[MOF]
+
EWG
EWG
Halogen-free
Oxidant-free
Additive-free
EWG
a. Chemistry Department, University of Guilan, P.O. Box 41335-1914, Rasht, Iran, Fax:
R= H, alkyl, aryl
EWG
H2O
+981333367262, Email: sheykhan@guilan.ac.ir
Scheme 1. [4+2] reactions of styrenes
Electronic Supplementary Information (ESI) available: See DOI: 10.1039/x0xx00000x
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It is worth mentioning that despite all efforts in this field, D-A being porous. As a solution, proper “mixed-metalVMiewOAFrtsic”lewOnelirnee
reaction on styrenes (as a diene system rather than an ene designed which introduced porosity inDtoOI:t1h0e.10f3r9a/mD0eGwCo0r0k61b9yJ
system) has still remained challenging. To give a better insight neutralization of structure and therefore the need for the
into this, a comparison between a styrenyl system and a dienyl presence of counterions within the pores was obviated.19
system in terms of their reactivity in D-A reaction was made in Given the powerful catalytic activities of Ni(II) complexes in
2
0
Verma’s work. In this study, when Pd-catalyzed reaction of 5- various D-A annulations
and since the preparation of
vinyl substituted indoles A with acrylates was studied, the trimeric mixed-metal acetate of Fe(III) and Ni(II) has been
2
1
reaction led to 5-substituted carbazoles B instead of previously reported, in this paper, we focused on the
benzoindoles C confirming that it was diene systems which synthesis of hypothetical neutral/porous (FeNi)MIL-88A,
won this competition over styrenes in D-A reaction (Scheme (Fe
2
NiO(O
2 2 3 2
CCH=CHCO ) .nH O) as the catalyst of choice. As the
1
1c
2
).
first step toward this end (and according to reference 18), 2.8
Metal-organic frameworks have been shown to be powerful mmol of iron(III) chloride hexahydrate, 1.4 mmol of nickel
catalysts in a vast area of chemistry. They owe their catalytic nitrate hexahydrate and 4.2 mmol fumaric acid were dissolved
properties to coordinatively unsaturated sites (CUS) around in 30 mL of water and stirred for 15 minutes. The mixture was
their metal-nodes.1 Catalysis of both oxidation
2
13
and transferred into a Teflon-lined autoclave and heated at 100 °C
reduction reactions 14 is the most common reactivity patterns for 15 h. After filtration and washing with water, the product
reported for MOFs. As well as these reactions, there have been was analyzed by various spectroscopic methods. Then,
2
2
copious examples of MOF-catalyzed organic coupling regarding literature reports about Ag(I), we chose it as
reactions.15 Recently, inspired by Mukherjee et al. a few another candidate to check its efficiency/synergistic effect in
reports on D-A annulations catalyzed by MOFs have been the D-A reaction when deposited on the structure of MIL-88A.
reported. However, all are either hetero-D-A or D-A by using Therefore, Ag-deposited MIL-88A nanoparticles were prepared
simple/real dienes.16 Herein, we will describe the first D-A by a post-synthetic exchange (PSE) of Ag(I) source with the
reaction of styrenes with ene systems catalyzed by an MOF, prepared MIL-88A. XRD, FTIR, SEM, TEM, EDAX-elemental
2
which preserved the ene’s double bond. The reaction is free mapping, N adsorption/desorption isotherm, BET and BJH
from any toxic additive and can be conducted in water as the were used to characterize the synthesized compounds (Figures
greenest solvent. Use of water as a non-toxic medium is the 1-4 and S1-4). In addition, the thermal stability of the
most preferred option among chemists. Preference for this synthesized
material
was
analyzed
by
solvent over others also rises from its low cost and widespread Thermogravimetry/Differential Thermal Analyzer (Figure 5).
availability. Yet, despite its advantageous features since most XRD patterns of the Ag-deposited MIL-88A and (FeNi)MIL-88A
of organic compounds show poor solubility in water, use of in Co anode have been shown in Figure S1. In the case of MIL-
this environmentally benign solvent is limited in organic 88A and (FeNi)MIL-88A, diffraction patterns can be clearly
o
reactions. Plus, water is infamous for deactivating most metal seen at 2Ɵ: 12.6ᵒ, 14.0 which are related to the pure MIL-88A
1
8b,23
catalysts due to which transition-metal catalysts often work structure regarding literature reports on Cu anode.
No
inefficiently in this solvent. Given all the afformentioned, detectable difference was observed between XRD of Ni
contriving reactions which are feasible in water as the sole modified structure and that of the parent compound
1
7
medium of the reaction is of great value.
confirming that the structure of MIL-88A remained intact
(
Figure S1a-b). When Ag was deposited on MIL-88A, a different
CO2R
CO2R
-
scenario happened due to the presence of Cl anions in the
pores of MIL-88A which was consistent with Liu’s report. In
its XRD, there were three additional diffractions at 32.4 , 37.6
and 54.2 related to 111, 200 and 220 patterns of AgCl (JCPDS
no. 31-1238) confirming the precipitation of AgCl in the pores
of MIL-88A (Figure S1c).
RO2C
CO2R
24
o
o
N
H
CO2R
o
[
Pd]
B
RO2C
N
H
CO2R
Figure S2 depicts the FTIR spectra of the prepared compounds.
A
RO2C
CO2R
-1
-1
The bands at 1394 cm and 1601 cm are generated by the
symmetric and asymmetric stretching of the C=O bonds of
carboxylate groups of the fumarate linkers. The bands at 1219
cm- can be assigned to the C-O vibration of the fumarate
N
H
CO2R
[
Pd]
C
1
Scheme 2. A dienyl system eclipsing a styrenyl system
-1
groups. Broad band at around 3000-3600 cm indicates O-H
stretching mode of adsorbed water which overlaps with
stretching of C-H bonds. In addition, forming Fe-Oxo clusters
Results and Discussion
-1
The MOF MIL-88A was prepared according to the literature.18
can be proved by the band at around 577 cm , the
-1
characteristic band of Fe-O bonds. The bands at 644 cm and
Because of the key role of metal nodes in MOF structures,
catalytic property as well as chemical stability of MOFs can be
tuned by the synthesis of “mixed-metal MOFs”. It is
noteworthy that in conventional (single-metal) MIL-88 MOFs,
anions fill the pores, thereby preventing the structure from
1
23,25
6
77 cm- are related to the carbonyl group
and C-H
bending mode, respectively. As is clear, no detectable changes
were found in the FTIR spectrum of mixed-metal FeNi nor in
that of the Ag-deposited MIL-88A proving that the structures
2
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did not change considerably after introducing Ag(I) and Ni(II) hexagonal spindle-like morphology and the surface of the
View Article Online
DOI: 10.1039/D0GC00619J
samples was not smooth due to the porous structure.
into the parent compound.
Porosity and morphology of the prepared MOFs have been The results of TEM (Figure 2) are accurately in agreement with
outlined in Figure 1. SEM images recorded by a Zeiss the SEM ones showing uniform sizes of spindles in both the
instrument ensured the porous structures of the prepared prepared materials.
MOFs. As was expected, both of the prepared samples showed
a
b
c
d
Figure 1. SEM images of (FeNi)MIL-88A (a-b) and Ag-deposited MIL-88A (c-d)
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a
b
c
d
Figure 2. TEM images of (FeNi)MIL-88A (a-b) and Ag-deposited MIL-88A (c-d)
The quantitative amounts of the metal content were elemental contents were shown to be 2.59 mmol/g Fe and
measured by the energy dispersive X-ray spectroscopy (EDAX) 0.22 mmol/g Ag. Thus, the molar ratio of Fe/Ag is about 12. As
elemental mapping (Figure S3-S4). Analyses indicated the a result, it can be noted as Fe2.77Ag0.23O(O
2 2 3
CCH=CHCO ) . For
presence of Fe, C, Ni and Cl for the (FeNi)MIL-88A; and Fe, C, the (FeNi)MIL-88A the analysis confirmed the content of Fe
-
-4
Ag, and Cl and for Ag-deposited MIL-88A; the presence of Cl in and Ni about 2.97 mmol/g and 8.8×10 mmol/g, respectively.
the structure of (FeNi)MIL-88A confirmed the partial This indicates that the molar ratio of Fe/Ni is about 3300/1.
exchanging of Ni in the structure. Elemental mapping Therefore,
demonstrates the uniform distribution of all elements (O, Cl, Fe NiO(O CCH=CHCO
Fe and Ni in the case of (FeNi)MIL-88A and O, Cl, Fe and Ag in (FeNi)MIL-88A. On the basis of such low exchanging value of Ni
the case of Ag-deposited MIL-88A) within the MOF structures. (about 0.03%), it can be inferred that as opposed to our initial
despite
the
hypothesized
formula
2
2
2 3
) , it had better be denoted as
To give more precise information, the structures were intent for the synthesis of neutral-porous (FeNi)MIL-88A, the
analyzed by ICP. In the case of Ag-deposited MIL-88A, the
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prepared mixed-metal compound is not neutral and must have deposited MIL-88A (Figure 3a) confirmed a combination of
View Article Online
-
DOI: 10.1039/D0GC00619J
contained counterion (Cl ) in its pores (as can be seen in EDAX). type II and III isotherms, mostly like type II, in agreement with
1
8b
Due to the low Ni uptake (as confirmed by ICP about <0.001 the literature. In contrast, (FeNi)MIL-88A showed a type III
mmol/g) and insufficient accuracy of EDAX, the amount of Ni isotherm (Figure 3b). It can be deduced that together with
cannot be measured, whereas for Ag-deposited MIL-88A, EDAX mesopores, some micropores are present in the former
showed 3.8 wt.% Ag (equal to 0.35 mmol Ag/g of catalyst). structure which are filled at very low pressures. To determine
Higher Ag impregnation on the structure is due to deposition the pore diameters of the materials, the structures were
of AgCl in the pores which was also confirmed by XRD.
Specific surface areas of the catalysts and properties of their volume was increased from 0.05 cm /g for Ag-deposited MIL-
analyzed by the BJH analysis (Figure 4). Based on findings, pore
3
3
pores were investigated by the N
2
adsorb-desorb isotherm, 88A to 0.11 cm /g for (FeNi)MIL-88A. This is maybe due to
BET and BJH (Figures 3-4). It was previously reported that the what is explained as the partial neutralization and therefore
2
26
19
specific surface area of MIL-88A was below 30 m /g;
removal of counterions from the pores of MIL-88 which is in
adsorb/desorb isotherm.
therefore we expected to obtain a lower value than those of agreement with its type III N
other MOFs.27 This low surface area of MIL-88A was explained It is notable that while (FeNi)MIL-88A includes only mesopores
by its flexible structure and probably closed pores during the over 18 nm, in Ag-deposited MOF together with these
2
pre-treatment
degassing
for
N
2
adsorb/desorb mesopores, there are also micro scale pores with diameters of
measurement.28 As was envisaged, specific surface areas of about 1.8 nm. The observation confirms that the precipitation
the prepared (FeNi)MIL-88A and Ag-deposited MIL-88A were of AgCl within the pores of the structure reduces some pore
2
calculated to be about 7.5 and 6.7 m /g, respectively. N
2
diameters to the micropores scale (consequently leads to a
adsorption/desorption isotherms of the prepared Ag- reduction in the total pore volume).
35
30
25
20
15
10
5
0
1
1
20
00
a
b
8
6
4
2
0
0
0
0
0
Saturation point
type III
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
p/po
p/po
2
Figure 3. N Adsorption/desorption isotherm of (a) Ag-deposited MIL-88A and (b) (FeNi)MIL-88A
0.0025
0.0020
0.0015
0.0010
0.0005
1
.8 nm micropores
0.020
no micropores found
a
b
0.015
0.010
0.005
0.000
0
5
10 15 20 25 30 35 40 45 50 55
0
5
10
15
20
25
dV /drp
r /nm
p
p
Figure 4. BJH analysis of (a) Ag-deposited MIL-88A and (b) (Fe-Ni)MIL-88A
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Figure 5. TGA-DTA analysis of (Fe-Ni)MIL-88A
TGA results are also in agreement with that of MIL-88A in the oxidized when exposed to TBHP and generation of undesirable
literature 29 (see Figure 5). As can be seen, the as-prepared by-products resulting from the foregoing side reaction. Using
31
o
(
Fe-Ni)MIL-88A is fully stable under 250 C and experiences NaClO and NaClO
4
gave the similar results (entries 5,6). With
only one weight loss of about 30% due to evaporation of this result, CuCl seemed to be the best choice as an external
o
water. Above 250 C, a three step weight-loss of exothermic oxidant, so optimization of catalyst loading was then taken
processes occurs each of which is overlapping with one into consideration. As expected, decreasing the amount of the
another and consecutive. An exothermic process takes place at catalyst had a destructive effect on the yield, whereas
o
about 270-360 C together with about 50% weight loss related increasing it to 15 mg built up the yield, albeit rather
to sublimation of fumarate and the collapse of the inconsiderably (entries 7,8). As the next step, we replaced MIL-
framework.30 There are also two other exothermic processes 88A with our prepared mixed-metal MOFs. This time in the
o
at 383 and 468 C. According to the study of XRD of MIL-88A presence of Ag-deposited MIL-88A and (FeNi)MIL-88A the
2
9
framework at different temperatures in Yang’s work
at reaction proceeds smoothly and led to the similar yields
o
around 400 C, MIL-88A is converted to γ-Fe
O
2 3
. Upon (entries 9,10). Next, we went further and executed the
increasing the temperature to 450-500 C, in situ conversion of reaction merely by use of mixed-metal MOFs and eliminated
o
2 3 2 3
γ-Fe O into α-Fe O occurs and finally MIL-88A is converted to the oxidant from the reaction (entries 11,12). To our delight,
carbon-coated α-Fe
2
O
3
nanospindles. Therefore, it can be even in the absence of additional oxidant, the reactions led to
o
concluded that the peaks at 383 and 468 C may be related to the desired D-A/aromatization product in 41 and 46% yields,
the formation of γ-Fe
O
2 3
2 3
and α-Fe O , respectively.
respectively. Compared with the entry 1 in which used
Having characterized our prepared catalysts, we then set out unmodified MIL-88A, it can be concluded that silver and nickel
to put their efficiency in promoting organic reactions into test. must have a synergistic effect when added into the
For this purpose, the reaction of styrene 1, as diene, and N- framework. Therefore, (FeNi)MIL-88A (10 mg, about 0.017
methyl malemide 2 in the presence of the synthesized MIL-88A mol% according to ICP) was chosen as the best catalyst in the
as catalyst in acetonitrile was chosen as the model reaction. absence of any oxidant. In continuation, the effect of various
The reaction led to a trace amount of benzo[e]isoindole-1,3- solvents in the reaction was studied (entries 13-17). Among all
dione 3 (<5% by GC) (Table 1, entry 1). Since we sought out the solvents used, best yield was obtained in water. No product
construction of a naphthalene ring, an oxidation step seemed was formed in the presence of acetic acid as an additive
to be essential, thus the reaction was tested in the presence of confirming that the only requirement to promote the reaction
3
additional oxidants (entries 2-4). AgNO as a metal oxidizing is our prepared catalyst (entry 18). Accomplishing the reaction
agent increased the yield to 38% (entry 2), by the same token, in water as a safe solvent apart from exclusion of the oxidant is
CuCl gave a relatively high yield (entry 3). However, use of quite an achievement meeting Green Chemistry postulates.
TBHP, as a non-metallic oxidant, totally suppressed the Lowering the reaction time to 6 h led to a drop in the yield
reaction and only a trace amount of the product was obtained (entry 19).
(entry 4). This may be due to the tendency of styrenes to be
6
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Table 1. Screening the reaction conditions a
Table 2. (FeNi)MIL-88A catalyzed annulation of styrenes on maleimideVsiew Article Online
a
DOI: 10.1039/D0GC00619J
R2
O
catalyst
R2
+
N
additive
solvent
O
O
[
(FeNi)MIL-88A]
R1
O
Me
R1
+
N
N
2
H O
1
2
3
O
O
Me
O
R
N
1
2
3a-r
O
R
entry
catalyst
additive
-
solvent
yield%
trace
38
Me
Ph
1
2
3
4
5
6
7
8
9
MIL-88A(10 mg)
MIL-88A(10 mg)
MIL-88A(10 mg)
MIL-88A(10 mg)
MIL-88A(10 mg)
MIL-88A(10 mg)
MIL-88A(5 mg)
MIL-88A(15 mg)
acetonitrile
acetonitrile
acetonitrile
acetonitrile
acetonitrile
acetonitrile
acetonitrile
acetonitrile
acetonitrile
acetonitrile
acetonitrile
acetonitrile
toluene
AgNO
CuCl
3
O
Me
O
N
Me
O
O
43
N
N
N
O
O
O
O
TBHP
NaClO
trace
trace
trace
13
48
45
52
41
46
55
Me
Me
, 83% (4882)
Br
Me
b
3a, 80%
(
4705)
3b, 77% (4529)
3c
3d, 81% (4764)
b
NaClO
4
CuCl
CuCl
CuCl
CuCl
-
-
-
-
-
-
-
O2N
MeO
O
Cl
O
Me
O
O
Ag-MIL-88A (10 mg)
(FeNi)MIL-88A(10 mg)
Ag-MIL-88A(10 mg)
N
Me
N
O
N
Me
N
Me
O
O
O
1
1
1
1
1
1
1
1
1
1
2
2
0
1
2
3
4
5
6
7
8
9
0
1
3e, 77% (4529)
3f, 65% (3823)
3g, 81% (4764)
3h, 0%
(FeNi)MIL-88A(10 mg)
(FeNi)MIL-88A(10 mg)
(FeNi)MIL-88A(10 mg)
(FeNi)MIL-88A(10 mg)
(FeNi)MIL-88A(10 mg)
(FeNi)MIL-88A(10 mg)
(FeNi)MIL-88A(10 mg)
(FeNi)MIL-88A(10 mg)
Me
Me
Ethyl acetate
DCE
ethanol
53
trace
60
O
Me
O
O
O
N
N
O
N
N
O
O
O
H
H
Ph
Ph
2
H O
2
H O
2
H O
2
H O
2
H O
80
trace
45d
3i, 74% (4352)
3j, 75% (4411)
3k, 60% (3529)
3l, 74% (4352)
c
Me
AcOH
-
-
Ni(NO
3
)
2
.6H
2
O(10 mg)
no rxn
78(79,76,
O
O
N
O
N
e
recovered from #17
N
O
O
O
7,75) f
Ph
7
Ph
a
Reaction conditions: styrene (3 equiv), N-methyl maleimide (0.05 mmol),
3m, 70% (4117)
3n, 71% (4176)
3o, 71% (4176)
o
b
c
additive (1 equiv), solvent (0.3 mL), 100 C, 20 h. as a 2M solution. 0.05 mL
AcOH. Quenched after 6 h. The reaction of entry 15 was repeated in a twofold
scale. Reusing of the catalyst in 2 , 3 , 4 and 5 runs.
Me
d
e
f
nd rd th
th
O
O
Me
O
O
O
O
O
O
When the reaction was tested in the presence of
homogeneous nickel source, no reaction occurred after 20 h
O
p, 68% b (4000)
, 64% b (3764)
3q
, 66% b (3882)
3r
3
(
entry 20). The experiment illustrates the heterogeneous type
a
Reactions were run under the following conditions: Styrene (3 mmol),
of catalysis and the role of single-site Ni-Fe catalytic centers
inside the pores of the prepared MOF (see also supporting
information S4; the catalyst hot filtration test). Recoverability
of the prepared MOF was also tested which showed it could be
o
maleimide (1 mmol), (FeNi)MIL-88A (200 mg, 0.017 mol%), water (5 mL), 100 C,
2
of the products. 5 equiv of maleic anhydride in acetonitrile as solvent was used.
0 h. The numbers in parentheses are the turnover numbers based on the yield
b
recovered and reused in successive runs with a slight loss of The reaction was also tested for N-H-, N-phenyl-, N-benzyl-, N-
activity (entry 21, Figure S5). Also, no leaching of Ni or Fe was phenethyl and N-cyclohexyl maleimides which resulted in
detected by evaluation of reaction solution using ICP.
corresponding benzo[e]isoindole-1,3-diones in good yields (3i-
Eventually, we found 0.017 mol% (FeNi)MIL-88A in water as 3o). Maleic anhydride was also used as the dienophile instead
the best condition to the desired benzo[e]isoindole-1,3-dione. of maleimide, generating naphtho[1,2-c]furan-1,3-dione
With the optimized conditions in hand, we then investigated derivatives in 64-68% yields (3p-r). In comparison with our
the scope of the reaction (Table 2).
previous report which took advantage of homogeneous Pd,
Therefore, miscellaneous styrenes were reacted with N-methyl the present report is based on a heterogeneous cost-effective
maleimide. p-Methyl styrene readily gave the D-A product catalyst. As an additional benefit, the reaction is also
albeit in a slightly lower yield than styrene (3a,b). However, environmentally benign due to the following privileges: (a) no
when styrenes possessing substituents at α-position were leaching was observed by the catalyst according to ICP; (b) the
used, an increase in the yields of the corresponding products reaction proceeds in water as the greenest solvent without any
was observed (3c,d). Appending an electron-releasing methoxy need for an organic co-solvent; (c) it works under oxidant-free
group at C4 position furnished the desired product in a 77% conditions; and (d) the TON by the (FeNi)MIL-88A is between
isolated yield (3e). Gratifyingly, halogen-containing styrenes 3500 to 4800 for various derivatives. According to the
that can be potential substrates for subsequent reactions were recoverability test of the catalyst (Table 1, entry 19), a TON
also reacted effectively with their halide segment being over 27000 was obtained for 3a during 6 consecutive runs.
remained intact (3f-3g).
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ARTICLE
Journal Name
To confirm whether the reaction proceeded through a chain Table 3. 1/[maleimide] vs time in the reaction of styrene with N-beVnizeywl mAratilceliemOidnelinaet
radical pathway or a D-A mechanism, the reaction of styrene 1 80, 100 and 120 oC
DOI: 10.1039/D0GC00619J
and N-benzyl maleimide 2 was tested in the presence of BHT
as a radical inhibitor which did not bring about a marked
change in the yield of the desired product (Scheme 3a).
Control experiment proved that a chain radical mechanism
might be unlikely. Additionally, the competition reaction
between two different styrenes was conducted (Scheme 3b).
Evaluation showed that electron-rich p-methoxystyrene reacts
more efficiently, verifying that electrons must have been
released from vinyl arene during the reaction.
1
/[maleimide] (L/mol)
t (sec)
5400
Reaction temperature (K)
353
373
393
42.6949
48.7527
52.9852
33.0999
51.7598
64.6616
22.2135
60.2159
110.482
1
1
0800
6200
1
20
00
80
a) Reaction in the presence of a radical inhibitor
Intercept
Slope
R-Square (COD)
-23.9647 ± 7.6476
0.00817 ± 6.5558
8E-4
O
catalyst
1
+
O
70%
water
0.99361
N
Ph BHT (1 equiv)
N
O
O
Intercept
Slope
18.27874 ±
0.00292 ± 3
Ph
1
2
.07822E-4
R-Square (C
0.98903
b) Competition reaction two different styrenes
60
H
O
27%
O
catalyst
water
H
N
N
Intercept
37.85393 ± 1.13
9.52809E-4 ± 9.7
+
O
O
40
20
0
.075 mmol
Ph
N
Slope
5
725E-5
O
Ph
R-Square (COD)
0.98962
0
.05 mmol
5
1%
MeO
O
MeO
0.075 mmol
Ph
4000
6000
8000
10000
12000
14000
16000
18000
Scheme 3. Control experiments
t (sec)
Mechanistic studies: To determine the order of reaction and Figure 6. Plot of 1/[maleimide] vs time in the reaction of styrene with N-benzyl
gain more insight into its mechanism, the changes in maleimide at 80, 100 and 120 oC
concentration of maleimide over time (d[maleimide]/dt) in the
reaction of N-benzyl maleimide with styrene under the Also, the kinetic reaction parameters (activation entropy,
standard conditions were studied by HPLC. In this reaction, activation enthalpy, activation Gibbs energy and activation
aliquots (0.05 mL) were removed every 90 minutes and this energy) were measured using Eyring- and Arrhenius plots to
was continued for 6 hours. HPLC was used to determine the check whether the reaction proceeded through a Diels-Alder
concentration of N-benzyl maleimide at each time by using a reaction or not. To this end, the concentrations of N-benzyl
calibration plot. Two plots were recorded. The first one was maleimide in reaction coordination were determined at three
o
recorded to check the fist-order kinetic and the other for the different temperatures (80, 100 and 120 C) and the plots of
second-order kinetic reaction. The ln[maleimide] and lnk versus 1/T and ln(k/T) versus 1/T were recorded (Figure 7,
1
/[maleimide] were plotted versus time (Figure S6a-b). The Table 4).
second plot shows a straighter line with a correlation value of
.989, which is indicative of a second-order reaction. From the
0
-3
-1
-1
slope of the line, a rate constant of 2.9×10 L.mol sec is
obtained at 100 C. In contrast, when the data is plotted in a
o
first-order manner a much lower correlation value (= 0.964) is
obtained. From the plot of Figure S6b it is easily seen that the
reaction demonstrates simple second-order reaction kinetics.
To determine kinetic parameters of the reaction by Eyring plot
and Arrhenius plot, the reaction rate constants were measured
at three different temperatures.
o
The related reaction rate constants k at 80 and 120 C were
-3
-3
measured as 1.0×10 and 8.2×10 L/mol.sec, respectively
Table 3, Figure 6).
(
8
| J. Name., 2012, 00, 1-3
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Journal Name
ARTICLE
Table 5. Solvent effect in the reaction of N-benzyl maleimide witVhieswtyArretniceleoOnnltinhee
-
-
-
-
-
-
4.5
5.0
5.5
6.0
6.5
7.0
optimal conditions
DOI: 10.1039/D0GC00619J
Intercept
Slope
Pearson's r
R-Square (COD)
Adj. R-Square
13.70157 ± 0.4500
-7279.74782 ± 167
-0.99974
a
3
entry
solvent
10 × second-order rate
0.99947
0.99894
constant k, L/mol.sec
1
2
3
4
5
H
2
O
2.9
2.4
2.1
1.9
1.6
EtOH
toluene
EtOAc
MeCN
Based on the data acquired it was found that the reaction
constant changed only slightly over the change of solvent. The
slight acceleration of the reaction in the protic solvents may
results from hydrogen-bonding of water and/or EtOH to the
polarized activated T.S.34 Thus, considering that no
0.0025
0.0026
0.0027
0.0028
intermediate was observed in the reaction and on the basis of
experimentally found large negative value of activation
1
/T
-
-
-
-
-
-
10.5
11.0
11.5
12.0
12.5
3
5
entropy
it can be proposed that the reaction proceeded
b
through a D-A mechanism. Therefore, in line with the recently
published work by Bickelhaupt’s group demonstrating that
Lewis acids catalyze D-A reactions by reduction of repulsion
Intercept
Slope
Pearson's r
R-Square (COD)
Adj. R-Square
6.78142 ± 0.43454
-6907.63947 ± 16
-0.99973
0.99945
0.99891
3
6
between the π-systems of diene and incoming dienophile, it
can be presumed that in this reaction the MOF catalyst acts as
a Lewis acid to promote D-A cyclization within its mesopores.
Although the number of publications concerning the reaction
of styrene with triple bonds has been more prevalent than
those reporting its reaction with double bonds, it still falls into
the category of the least developed reactions. Among the few
examples that have been released so far, only α-substituted
styrenes in which the active α position was blocked by a
substituent furnished the expected aromatic D-A products
13.0
0
.0025
0.0026
0.0027
0.0028
1
/T
3
7
(
Scheme 4a). However, when styrene with accessible double
Figure 7. Arrhenius (a) and Eyring (b) plots of the reaction of styrene with N-benzyl
maleimide in water
bond position was utilized, two molecules of alkynes got
involved and dihydronaphthalene was obtained (Scheme
3
7b,38
Table 4. The kinetic parameters of the reaction of styrene and N-benzyl maleimidea
4b).
Here, to further expand the versatility of this
approach, maleimide was replaced with dimethyl acetylene
dicarboxylate 4 (DMAD) the reaction of which gave rise to
dimethyl naphthalene-1,2-dicarboxylate 5 in 66% yield through
an annulation/oxidative aromatization process (Scheme 4c).
Satisfyingly, as opposed to prior reports we managed to gain
naphthalene without occupying the active α-site of styrene
substantiating the efficiency of this approach. This procedure
can be a suitable alternative to the prevailing methods which
need either as high a temperature as 180 ˚C or commercially
‡
‡
∆
S‡ (J/mol.K)
∆H (kJ/mol)
∆G (kJ/mol)
E
a
(kJ/mol)
110.0a
-141.1
57.4
60.5
a
‡
‡
‡
o
The activation free energy ΔG was estimated from ΔH and ΔS at 100 C.
According to Eyring plot, the activation entropy of the reaction
is about -141.1 e.u, in the range of that typical of D-A reactions
from -120 to -175 e.u)
stepwise organic reactions. Furthermore, to rule out the
probable ionic/polar transition states, reaction constant k of
the reaction was measured in various solvents (Table 5).
3
2
(
and more negative than that of
3
9
unavailable starting materials to yield similar product.
3
3
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ARTICLE
Journal Name
Conclusion
View Article Online
DOI: 10.1039/D0GC00619J
R
R
CO2Me
CO2Me
In conclusion, the first MOF-catalyzed D-A type annulation of
vinyl arenes as diene on maleimides has been introduced. The
reaction is also applicable to the electron-poor triple bonds
leading to naphthalenes bearing electron-withdrawing
substituents. Also, the synthetic utility of the product
successfully led to a PAH target molecule, ensuring that simple
styrenes can be a parent molecule of PAHs. To the best of our
knowledge this is the first example of π-extension of styrene to
PAH families.
a)
+
CO2Me
CO2Me
CO2Me
CO2Me
R = Me, Ph
H
CO2Me
b)
c)
+
CO2Me
CO2Me
CO2Me
CO2Me
This work:
H
H
[
(FeNi)MIL-88A]
+
MeCN, 100 o
C
CO2Me
CO2Me
5
Experimental section
CO2Me
4
1
The synthesis of nickel-exchanged MIL-88A ((FeNi)MIL-88A)
Scheme 4. Annulation of styrenes on DMAD
FeCl
3 2 3 2 2
.6H O (2.8 mmol, 0.757 g) and Ni(NO ) .6H O (1.4 mmol,
0
.4 g) were added to a vessel and 30 mL deionized water was
PAHs, main component of OLEDs and TFTs, are classically
synthesized using pre-functionalized molecules during
added. Then fumaric acid (4.2 mmol, 0.487 g) was added and
the resulted mixture was stirred for 15 minutes. The mixture
was transferred into a Teflon-lined autoclave and heated at
1
0
analyzed by various spectroscopic methods.
The synthesis of silver-deposited on MIL-88A
MIL-88A was prepared according to the literature. Fumaric
acid (4.2 mmol, 0.487 g) and FeCl .6H O (4.2 mmol, 1.13 g)
3 2
4
0
stepwise methods. As an alternative way to the synthesis of
PAHs, newly one-shot APEX reactions have received significant
attention by use of a ‘template arene’ and a ‘π-extending
reagent’.41 Recently, Itami et al. reported the first K-selective
π-extension on phenanthrene for the synthesis of
nanographene.42 However, despite all efforts, APEX reactions
00 °C for 15 h. After filtration and washing with hot water,
.35 g mustard color powder was obtained. The product was
4
1
on naphthalene have been rarely studied. The only report on
this front was disclosed by Cramer et al. in which annulation
were added to a vessel containing 21 mL deionized water. The
mixture was stirred for 1 h at room temperature and then
transferred into a 70 mL Teflon-lined autoclave. The autoclave
4
3
took place in the K-region of naphthalene. Having said that,
L-selective π-extension on naphthalene has not been explored
so far. Previously, it was shown that phthalic anhydrides can
o
was placed in an oven and heated to 70 C for 8 h. After
4
4
be used as precursors of PAHs. Yet, the number of
phenanthrenes possessing aryl substituents at peripheral rings,
due to unavailability of cyclic anhydride as its starting material,
was only limited. Hence, the products of our reaction can be
used as starting materials for further functionalization. To
showcase the indirect broad application of our products both
in the organic synthesis and nanotubes, we reacted cyclic
anhydride 3p with diphenyl acetylene 6 with manipulation of
the previous report which successfully led to the synthesis of
cooling to room temperature and centrifugation, the resulted
solid was washed thoroughly with hot water and ethanol and
o
dried at 100 C to yield MIL-88A. AgNO
3
(0.25 mmol, 37 mg)
was dissolved in a 35 mL 1:1 solution of deionized water and
ethanol. 0.25 g of the as-prepared MIL-88A was added to the
o
resulting solution and heated to 85 C for 1 day. The solid was
washed with water and ethanol and dried at room
temperature which finally resulted in a yellowish-orange
powder (0.2 g).
General procedure for the synthesis of Benzo[e]isoindole-1,3-
diones
1
,2,3,4-tetraphenylphenanthrene 7, a readily convertible
compound to other PAHs, in 41% isolated yield (Scheme 5).
In a vial equipped with a stir bar, vinyl arene (3 mmol),
maleimide (1 mmol) and (FeNi)MIL-88A (0.2 g, 0.017 mol%)
were dissolved in water (5 mL) and capped. The resulting
standard
condition
PdCl2 (20%)
Diphenylacetylene 6
I
II
I
II
Ph
Ph
I
O
o
TBAI (40%)
III
mixture was heated in an oil bath at 100 C for 20 h. After
O
K CO (2 equiv.)
Ph
2
3
O
PPh3 (20%), DMF, 140 oC
extraction with dichloromethane and drying the organic layer
over sodium sulfate, the solution was evaporated under
reduced pressure. The organic residue was purified by column
chromatography. Pure benzo[e]isoindole-1,3-dione was
obtained after recrystallization of the product from n-hexane.
General procedure for the synthesis of Naphtho[1,2-c]furan-1,3-
diones
Ph
1
3p
7
Scheme 5. The three Rings: Synthetic utility of product 3p in the synthesis of
unsymmetrical highly-substituted phenanthrene
Vinyl arene (1 mmol), maleic anhydride (5 mmol, 0.49 g) and
(
FeNi)MIL-88A (0.2 g, 0.017 mol%) in acetonitrile (5 mL), was
o
stirred at 100 C for 20 h in a capped vessel. After extraction
with dichloromethane and drying over sodium sulfate, the
organic layer evaporated under reduced pressure. The organic
1
0 | J. Name., 2012, 00, 1-3
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Journal Name
residue was purified by
chromatography. Recrystallization of the product using n-
hexane gave pure products.
ARTICLE
Abele, Angew. Chem. Int. Ed. 2013, 52, 3822V;iew(l)ArtRic.leAO.nliAne.
a
silica loaded column
Foster and M. C. Willis, Chem. Soc. Rev. 2013, 42, 63; (m) J. L.
DOI: 10.1039/D0GC00619J
Li, T. Y. Liu and Y. C. Chen, Acc. Chem. Res. 2012, 45, 1491;
(
n) B. S. Bodnar and M. J. Miller, Angew. Chem. Int. Ed. 2011,
The synthesis of 1,2,3,4-tetraphenylphenanthrene (7)
5
0, 5630; (o) S. Reymond and J. Cossy, Chem. Rev. 2008, 108,
5
359; (p) K. C. Nicolaou, S. A. Snyder, T. Montagnon and G.
Naphtho[1,2-c]furan-1,3-dione 3p (1mmol), diphenyl acetylene
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Q. Xiong, L. Lin, X. Zhao, J. Lang, X. Liu and X. Feng, J. Org.
Chem. 2018, 83, 12527.
6
(2 equiv), PdCl
2
(20 mol%), tetra-n-butylammonium iodide
CO (2 equiv)
(40 mol%), triphenylphosphine (20 mol%) and K
2
3
were dissolved in DMF (5 mL) and capped. The mixture was
5
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o
heated at 140 C for 20 h. The resulted mixture was extracted
with dichloromethane and the organic layer was dried over
sodium sulfate. The solution was evaporated under reduced
pressure and the organic residue was purified by column
chromatography.
(
4
d) K. M. Brummond and L.S. Kocsis, Acc. Chem. Res. 2015,
8, 2320.
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Hot filtration test of the catalyst
To study the homogeneous or heterogeneous type of the
catalyst, the reaction of styrene 1 and N-benzyl maleimide 2 in
the optimal condition was quenched after 6 h when it resulted
in 32% yield of 3a. The catalyst (FeNi)MIL-88A was filtered
from the hot reaction solution and the reaction was allowed to
continue for further 14 h by the filtrate. The reaction led to
(
2
b) L.S. Kocsis, E. Benedetti and K. M. Brummond, Org. Lett.
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Wei and J. Ye, Angew. Chem. Int. Ed. 2019, 58, 6756.
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heterogeneous catalyst not by the homogeneous solution.
a
1
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There are no conflicts to declare.
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Acknowledgements
We are grateful to the research council of the University of
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