Mono-functionalization of porous aromatic frameworks to use as compatible heterogeneous catalysts in one-pot cascade reactions Dedicated to Professor Daniel Brunel on the occasion of his 70th birthday.

Article abstract of DOI:10.1016/j.apcata.2013.09.052

Porous aromatic frameworks (PPAFs) prepared by microwave assisted synthesis can be easily functionalized to obtain solid acid (sulfonic acid) and base (primary amine) catalysts. This porous material demonstrated to be an excellent support of different functional groups. The combination of these functionalized PPAFs was successfully applied as compatible heterogeneous catalysts for cascade reaction of hydrolysis of dimethoxymethylbenzene, acid catalyzed, and Knoevenagel catalyzed by base. The advantages of this catalytic system are its easy synthesis, good catalytic activity, coexistence of incompatible functional groups in homogeneous conditions, with different acid/base ratio, and is recycled up seven times without significant loss of activity. Our concept can be extended to other various one-pot incompatible homogeneous systems and make a contribution toward the creation of environmentally inspired chemical processes through the promotion of multiple reactions in a single reactor.

Full text of DOI:10.1016/j.apcata.2013.09.052

Applied Catalysis A: General 469 (2014) 206–212
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Mono-functionalization of porous aromatic frameworks to use as
compatible heterogeneous catalysts in one-pot cascade reactions
a
b
b
c
Estíbaliz Merino , Ester Verde-Sesto , Eva M. Maya , Avelino Corma ,
d
a,∗
Marta Iglesias , Félix Sánchez
a
Instituto Química Orgánica General, CSIC, SEPCO, c/Juan de la Cierva, 3, 28006 Madrid, Spain
Instituto Ciencia y tecnología de Polímeros, CSIC, c/Juan de la Cierva, 3, 28006 Madrid, Spain
Instituto Tecnología Química, UPV-CSIC, Avda. los Naranjos, s/n, 46022 Valencia, Spain
Instituto Ciencia de Materiales de Madrid, CSIC, c/Sor Juana Inés de la Cruz, 3, 28049 Madrid, Spain
b
c
d
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 July 2013
Received in revised form 4 September 2013
Accepted 27 September 2013
Available online 6 October 2013
Porous aromatic frameworks (PPAFs) prepared by microwave assisted synthesis can be easily func-
tionalized to obtain solid acid (sulfonic acid) and base (primary amine) catalysts. This porous material
demonstrated to be an excellent support of different functional groups. The combination of these func-
tionalized PPAFs was successfully applied as compatible heterogeneous catalysts for cascade reaction of
hydrolysis of dimethoxymethylbenzene, acid catalyzed, and Knoevenagel catalyzed by base. The advan-
tages of this catalytic system are its easy synthesis, good catalytic activity, coexistence of incompatible
functional groups in homogeneous conditions, with different acid/base ratio, and is recycled up seven
times without significant loss of activity. Our concept can be extended to other various one-pot incom-
patible homogeneous systems and make a contribution toward the creation of environmentally inspired
chemical processes through the promotion of multiple reactions in a single reactor.
Dedicated to Professor Daniel Brunel on the
occasion of his 70th birthday.
Keywords:
Porous polymeric aromatic framework
Post-modification
One-pot
© 2013 Elsevier B.V. All rights reserved.
Acid–base catalysts
1
. Introduction
Solid acid and base catalysts have received much attention
surface areas and easy functionalization. These porous materi-
als have ultrahigh surface area and high stability making them
good candidates to develop potential applications in gas stor-
age [16] and gas separation [8–13] and heterogeneous catalysis
[17,20]. Porous aromatic frameworks were previously prepared by
thermal conditions starting from tetrakis-(4-iodophenyl)methane
as a tetrahedral unit and a diboronic acid as a linker [18–20].
Post-synthesis modification of PAFs has been reported to obtain
because of their potential applications for replacing inorganic liquid
acids or alkalis in industry [1–3]. The immobilization of solu-
ble catalysts generally in solid supports, such as zeolites [1–4],
ordered mesoporous materials (MCM-41 and SBA-15) [1–7] has
advantages in comparison with homogeneous counterparts when
applied in organic synthesis. The main advantages are that hand-
ling and separation of the catalyst from the reaction mixture are
easier; catalyst stability is greater and can be recycled to mini-
mize waste production. Most of those soluble catalysts have also
been supported on well-structured micro and mesoporous inor-
ganic and organic–inorganic hybrid materials such as MOFs (metal
organic frameworks) and PMOs (periodic mesoporous organosil-
icas). It has been challenging to have new solids as structured
purely organic materials (POFs) [8–13,19] with pore dimensions
in the micro and mesoporous range, including porous aromatic
frameworks (PPAFs) with diamond-like structure [14,15], to be
used as catalysts supports due to their high stability, high specific
materials for CO -uptake [21–24]. Thus, Zhou and co-workers have
2
prepared sulfonated [22] and chloromethyl [23] PPAFs, the latter
being further modified to amine groups. Recently, we have reported
the first example of bi-functionalized PPAF with acid and base
groups (PPAF-SO H-NH ) and demonstrated that groups that can-
3
2
not coexist in solution can be effectively used in catalytic reactions
by immobilizing them in the same structure [25]. For those reac-
tions in which a cooperative effect between the different active
centers is not necessary, can be very interesting to apply cataly-
sis with different active centers on separate supports to catalyze
one-pot reactions or cascade [26–29]. This paper shows the first
approximation to synthetize monofunctionalized-PPAF and the
study of catalytic behavior of a mixture of acid- and base-PPAF. The
advantages to have the functionality in different physical materials
are that we can design new catalysts and combined to get dif-
ferent active catalytic mixtures, i.e. acid PPAF + strong base-PPAF,
∗ Corresponding author. Tel.: +34 91 2587590; fax: +34 915644853.
E-mail addresses: felix-iqo@iqog.csic.es, FFFFelixxxx@gmail.com (F. Sánchez).
0
926-860X/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2013.09.052

E. Merino et al. / Applied Catalysis A: General 469 (2014) 206–212
207
SO H
NH2
3
NH2
PPAF-NH2
PPAF-SO H
3
Fig. 1. Structure of PPAF-SO3H and PPAF-NH2.
acid + metal–PPAF. In this work, we demonstrate that sulfonic
acid- or amino-mono-functionalized porous aromatic frameworks
otherwise noted. Tetrakis-(4-bromophenyl)methane 1 and tetrakis-
(4-iodophenyl)methane 2 were prepared according to a previously
reported method [30,31]. All reactions were performed under a
purified nitrogen atmosphere. %C, %N, %S and %H contents were
determined in a LECO CHNS-932 analyzer. Thermogravimetric and
differential thermal analyses (TGA–DTA) where conducted in an
air stream with a TA-Q500 instrumental analyzer. The samples
(
PPAF-SO H and PPAF-NH ) (Fig. 1) can be also applied as mixture
3
2
of catalysts for a two steps one pot cascade reactions. Moreover, the
solid mixture consisting of the PPAF-SO H + PPAF-NH catalysts
3
2
was easily recovered by simple filtration and then could be reused
at least seven times with retention of high catalytic activity and
selectivity.
◦
were heated under an air stream from 40 to 850 C with a heating
◦
The novel catalysts were prepared by post-functionalization
of the starting support PPAF-1. This support was prepared from
tetrakis-(4-bromo or 4-iodo)phenylmethane as building block
rate of 10 C/min.
IR spectra were recorded on a Perkin Elmer Spectrum One spec-
trometer and are reported in terms of frequency of absorption
ꢀ
ꢀ
−1
(
Scheme 1) instead of the previously reported 2,2 ,7,7 -tetrabromo
(cm ).
ꢀ
13C solid-state MAS-NMR measurement was recorded with a
or tetraiodo 9,9 -spiro-bisfluorene [25], to facilitate the formation
of a more ordered network.
Bruker AV400 WB spectrometer (Larmor frequencies of 400 and
1
00 MHz, using 4 mm MAS probes spinning at 10 kHz rate).
Nitrogen adsorption isotherms where measured at 77 K using a
2
. Experimental
Micromeritics ASAP 2020. Prior to measurement, the samples were
degassed for 12 h at 200 C. The pore size average was determined
either by BJH method.
◦
All starting materials were purchased from commer-
cial suppliers and used without further purification unless
Scheme 1. Synthesis of PPAF-1 support.

2
08
E. Merino et al. / Applied Catalysis A: General 469 (2014) 206–212
Fig. 2. SEM of PPAF-1-Br and PPAF-1-I.
Table 1
2.1. Catalysts preparation
Elemental analysis of PPAF-1 materials.
Materiala
%a
%Ha
%C
%Brb
%Ib
PPAF-1: 200 mg (0.316 mmol) of 1 or 2, 116 mg (0.692 mmol)
of 1,4-phenylenediboronic acid (3), 41 mg (0.157 mmol) of triph-
enylphosphine, 116 mg (1.384 mmol) of sodium bicarbonate and
PPAF-1-Br
PPAF-1-I
84.07
82.86
5.18
5.14
89.7
92.5
1.7
–
–
1.1
3
.5 mg (0.016 mmol) of palladium acetate are suspended in a mix-
a
Combustion analysis.
EDX analysis.
ture of DMF (2 mL) and water (0.5 mL). The mixture was degassed
by argon bubbling. Microwave heating was performed in a com-
puter controlled CEM Discover microwave with temperature and
pressure control. Initial heating was performed at a power input
of 75 W. After the pressure has reached approx. 12 bar, the heating
b
◦
−1
obtain after drying (120 C, 1 mmHg ) a pale blue solid (157 mg).
Elemental analysis: %C = 71.40, %H = 4.73, %S = 6.04.
◦
PPAF-NO : 250 mg of PPAF-1 were added to trifluoroacetic acid
was stopped until cooled at 60 C and the pressure disappears. Then
the reaction was heated to 145 C for 10 min reaching during this
2
◦
◦
cooled at 0 C. After 10 min, nitric acid (74 ␮L) was slowly added and
the mixture was stirred for 5 h at room temperature. The mixture
was added to ice/water. The solid was filtered, washed with water,
time a pressure of around 7 bar. After cooling to room temperature,
the mixture was filtrated and the crude product was washed with
DMF and water. For removing Pd traces the crude solid was sus-
pended in a mixture of water (100 mL), hydrochloric acid (1 mL) and
nitric acid (2 mL) refluxing until to obtain yellow solid. Finally, the
sample was filtrated, washed with THF and diethyl ether and dried
◦
−1
)
THF and diethyl ether to obtain after drying (120 C, 1 mmHg
a yellow solid (283 mg). Elemental analysis: %C = 72.79, %H = 4.09,
N = 4.58.
PPAF-NH : Tin(II) chloride (2.8 g) was added to a suspension of
%
2
◦ −1
PPAF-NO2 (273 mg) in THF (60 mL) and the mixture was refluxed
overnight. The solid was filtrated and washing with aqueous NaOH
(
120 C, 1 mmHg ) for 2–6 h. The reaction yield was near quanti-
tative based on the molecular weight of the ideal, fully condensed
product.
(
(
%
10%) solution, water, THF and diethyl ether to obtain after drying
120 C, 1 mmHg ) a yellow solid (283 mg). Elemental analysis:
C = 77.88, %H = 5.36, %N = 4.69.
◦
−1
PPAF-SO H: 142 mg of PPAF-1 were suspended in CHCl (5 mL)
3
3
and chlorosulfonic acid (43 ␮L) was slowly added at room tem-
perature. After 10 min, the mixture was refluxed for 5 h. The solid
was filtered, washed with CHCl , water, THF and diethylether to
2.2. Catalyst characterization
3
Chemical composition: %C, %N, %S, and %H contents were deter-
mined in a LECO Model CHNS-932 analyzer (see Tables 1 and 2) and
EDX analysis obtained in a Hitachi SU-8000 microscope operating
at 0.5 kV.
PPAF-1-Br
PPAF-1-I
Thermogravimetric and differential thermal analyses (TGA–DTA)
were conducted in an air atmosphere with a TA-Q500 instrumental
analyzer. The samples were heated under an air stream from 40
◦
◦
to 850 C with a heating rate of 10 C/min. Infrared spectra were
recorded on a Perkin-Elmer Spectrum One spectrometer and are
−
1
13
reported in terms of frequency of absorption (cm ). C solid-state
MAS-NMR measurements were recorded with a Bruker AV400 WB
spectrometer (Larmor frequencies of 400 and 100 MHz, using 4-
mm MAS probes spinning at 10 kHz rate).
Table 2
a
Elemental analysis of functionalized PPAF-1 materials.
Material
%C
%H
%N
%S
2
00
180
160
140
120
100
80
60
PPAF-SO3H
PPAF-NO2
PPAF-NH2
71.40
72.79
77.88
4.73
4.09
5.36
–
4.58
4.69
6.04
–
–
ppm
Fig. 3. 13C-RMN spectra of PPAF-1 obtained from tetrakis-(4-bromo
phenyl)methane or tetrakis-(4-iodophenyl)methane.
a
Combustion analysis.

E. Merino et al. / Applied Catalysis A: General 469 (2014) 206–212
209
PPAF1-Br
100
PPAF-1
PPAF-NH2
100
PPAF1-I
PPAF-SO3H
80
60
40
20
0
80
6
4
2
0
0
0
0
200
400
600
800
200
400
600
800
Temperature(ºC)
Temperature (°C)
Fig. 5. Thermogravimetrical analysis (TGA) in air atmosphere of mono-
functionalized PPAFs compared with the starting support PPAF-1.
PPAF-1-Br
PPAF-1-I
1
,0
,8
,6
,4
,2
,0
◦
◦
diffractometer. Data were collected stepwise over the 1 ≤ 2ꢀ ≤ 65
0
0
0
0
0
angular region, with steps of 0.5 s/step accumulation time and Van-
tec detector and Cu K␣ (ꢁ = 1.542 A˚ ) radiation.
2.3. Catalytic tests
The reactions were carried out in a microreaction vessel of 5 mL.
Benzaldehyde dimethyl acetal 4 (54 ␮L), malononitrile (29 mg) and
dodecane (41 ␮L) were dissolved in 2 mL of toluene and 25 ␮L of
◦
water were stirred at 90 C under argon with 19 mg of PPAF-SO H
3
and 11 mg of PPAF-NH . The samples of the reaction mixture were
2
analyzed by gas chromatography (GC, Konik HCGC 5000B) using a
1
5 m KAP-5 capillary column and a flame ionization detector (FID).
10
20
30
40
50
60
After the completion of the reaction, the mixture of functionalized
materials was separated by filtration and washed with toluene, a
2
θ
Fig. 4. Thermogravimetrical analysis (TGA) in air atmosphere (up) and X-ray diffrac-
tograms (down) of PPAF-1 obtained from tetrakis-(4-bromo phenyl)methane or
tetrakis-(4-iodo phenyl)methane.
buffer AcONa/AcOH, water, THF and Et O. It was then reused for
2
the above one-pot tandem reaction at least seven times.
3. Results and discussion
Textural characterization: Nitrogen adsorption isotherms where
measured at 77 K using a Micromeritics ASAP 2020. Prior to mea-
surement, the samples were degassed for 12 h at 200 C. The pore
3.1. Synthesis and characterization of PPAF-derivatives
◦
size average was determined either by BJH method. WAXS (wide-
angle X-ray scattering) were carried out with a Bruker D8 Advance
We started with the synthesis of PPAF-1 through a Suzuki cou-
pling reaction of tetrakis-(4-bromo or 4-iodophenyl)methane 1
Scheme 2. Synthesis of mono-functionalized PPAFs supports: PPAF-SO3H and PPAF-NH2.

2
10
E. Merino et al. / Applied Catalysis A: General 469 (2014) 206–212
Scheme 3. One-pot-tandem conversion of benzaldehyde catalyzed by PPAF-SO3H and PPAF-NH2.
or 2 [30,31], used as the structure directing monomer, with 1,4-
phenylenediboronic acid 3, with quantitative yields (Scheme 1).
The microwave-assisted synthesis is essential for the successful
quantitative and reproducible synthesis of the networks to give a
porous structure PPAF-1 (a simplified model with diamonded-like
framework is displayed in Scheme 1). Both PPAFs obtained from 1
or 2 were fully characterized by 13C CP–MAS NMR, TGA, WAXS and
SEM images (Fig. 2).
So, this definitely highlights the importance of using a tetraiodo
monomer 2 for the synthesis of PPAFs.
The carbon and nitrogen content determined by elemental
analysis (Table 1) are lower than the theoretical values expected
probably due to poor combustion. This is generally observed for this
type of porous polymers [31]. More accurate data were obtained
using EDX analysis (Table 1).
The aromatic groups forming the backbone of the PPAF-
1 can now be easily post-functionalized, introducing different
groups by aromatic electrophilic substitution reactions. Here we
have introduced sulfonic acid and amino groups by sulfonation
and nitration/reduction of aromatic rings. Sulfonic groups were
introduced by treating PPAF-1 with chlorosulfonic acid in chlo-
The solid-state 13C NMR (Fig. 3) of both supports were similar
which indicated that chemical structure was identical, however, the
TGA (Fig. 4 up) indicated that the support prepared from the more
reactive monomer tetrakis-(4-iodo phenyl)methane 2 has higher
thermal stability. Moreover, this support showed some crystallinity
peaks (Fig. 3 down) which indicated that this structure is slightly
roform to give material PPAF-SO H (Scheme 2). The basic groups
3
more regular network. Besides the PPAF-1 obtained from tetrakis-
were introduced in two steps, first nitration of PPAF-1 with nitric
acid in trifluoroacetic resulted in PPAF-NO2 material and next, the
reduction of nitro groups with hydrated tin(II) chloride yielded
PPAF-NH2 (Scheme 2).
2
(
4-bromo phenyl)methane 1 has a BET surface area of 312 m /g and
3
a total pore volume of 0.53 cm /g whereas starting from tetrakis-(4-
iodo phenyl)methane 2 resulting in a PPAF with higher BET surface
2
3
area of 565 m /g and a total pore volume of 0.88 cm /g. Thus accord-
The presence of the –SO H groups has been confirmed by IR
3
ing with all these results the use of tetrakis-(4-iodophenyl)methane
spectroscopy (Fig. 5 up) which showed the characteristic bands of
−
1
2
1
seem to be more convenient that using the tetrabromo derivative
. This conclusion is in agreement with that previously observed by
the sulfonic group are observed between 1224 and 1124 cm . The
final solid contains about 1.88 mmol/g of sulfonic acid, as deter-
mined by elemental analysis (Table 2) which corresponds to one
sulfonic acid by repeat unit. The presence of the nitro groups has
been proven from the strong IR bands appearing at 1529 and
us in the synthesis of the PPAF from tetraiodo-spirofluorene [13].
3
3
2
2
2
2
2
1
1
1
1
1
20
00
80
60
40
20
00
80
60
40
20
00
−
1
PPAF-SO H
PPAF-NH2
1344 cm . The amount of nitro groups introduced, as measured
by elemental analysis, is 3.3 mmol/g. The course of the nitro groups
reduction was also followed by IR, and the reaction was complete
3
−1
when the bands at 1529 and 1344 cm disappeared. The amount
of nitrogen PPAF-NH (3.35 mmol/g) calculated for elemental anal-
2
ysis was similar to the amount found in the precursor PPAF-NO2
and is equivalent to 1.6 amino groups per each building unit.
The mono-functionalized PPAFs were also characterized by 13C
CP-MAS NMR, TGA, WAXS and SEM images. The 13C-NMR spec-
tra of both polymers were similar to those of the initial support,
not distinguishing between the carbons bonded to acid or basic
groups. However, some differences were found in the TGA ther-
mograms (Fig. 5). The incorporation of sulfonic or amine groups
slightly reduce the thermal stability as it was also observed for the
bi-functionalized PPAF [25].
8
0
0
0
0
6
4
2
0
0
.0
0.2
0.4
0.6
0.8
1.0
After functionalization, both polymers showed amorphous
nature as it was revealed by wide-angle X-ray scattering and
the mesoporous character of the samples was maintained as it
Relative Pressure (P/Po)
Fig. 6. Nitrogen adsorption isotherm of PPAF-SO3H and PPAF-NH2.

E. Merino et al. / Applied Catalysis A: General 469 (2014) 206–212
211
Table 3
Conversion
Yield
Textural properties of functionalized PPAF-1 materials.
(a) 100
Material
Surface area
Pore volume
(cm /g)
Pore diameter
(nm)b
2
a
3
b
(m /g)
90
80
70
60
50
40
30
20
10
0
PPAF-Br
PPAF-I
PPAF-SO3H
PPAF-NH2
312
565
281
148
0.53
0.88
0.22
0.43
6.76
6.00
9.09
16.71
a
BET method.
BJH method.
b
was observed by the N2 adsorption measurements. Thus, both
PPAF-SO H and PPAF-NH showed isotherms characteristics of
mesoporous materials (Fig. 6 but with lower BET surface areas than
3
2
2
the starting support, 281 and 148 m (Table 3).
3
.2. Catalysis
1
2
3
4
5
6
7
Cycle
The synthesis of solid catalysts that combine antagonistic func-
tions is no easy task and examples of solids with, for example, both
acidic and basic functions are limited. The reported examples com-
bine acids such as sulfonic acids, silanols, ureas, and thiols with
amines [32–47]. However, problems such as low catalytic activity
because of weak acidity, difficult preparation, and lack of a continu-
ous range of acidic and basic catalytic sites often significantly limit
their application in organic reactions. We have recently demon-
strated that a PPAF combining basic and acid active sites in the
same structure works very well in cascade reaction without can-
cellation of the active centers [25]. Now, we are expecting that
1
00
Solid
(
b)
Filtrate
9
0
80
7
0
0
6
50
4
3
2
1
0
0
0
0
0
when introducing PPAF-SO H and PPAF-NH2 in a cascade reac-
3
tion no neutralization of the active sites will occur and they will
be able to work independently. To check this assumption one pot-
two steps reaction that requires an acid site to catalyze the first
step and a base site to catalyze the second step, was chosen. This
is the transformation of benzaldehyde dimethylacetal 4 into ben-
zylidenemalononitrile 6 (Scheme 3). In this case the sulfonic acid
groups catalyze the hydrolysis of benzaldehyde dimethylacetal 4
into benzaldehyde 5 that in a second step reacts with malononi-
trile through a Knoevenagel condensation catalyzed by base sites
to obtain the product 6.
0
10 20 30 40 50 60 70 80 90 100 110 120 130
t (min)
Fig. 7. (a) Recycles of mixture of catalysts PPAF-SO3H + PPAF-NH2 (2 h reaction
time). (b) Leaching experiment.
cascade reaction. This fact can also be visualized from the FT-IR
spectra of different functionalized PPAF-materials treated with
either inorganic acids, such as hydrochloric acid or with inor-
ganic bases as sodium hydroxide. It was observed that when
PPAF-SO H is treated with NaOH, the intensity of the bands cor-
responding to the sulfonic group changes and the EDX analysis
also confirms the presence of sodium. In an additional experiment
The combination of PPAF-SO H and PPAF-NH efficiently catal-
3
2
yses (see Table 4) the two step process and no neutralization of the
acid and base sites seems to occur (entry 1). It has to be remarked
that when the reaction was carried out with only PPAF-SO H (entry
3
3
2
), benzaldehyde 5 was observed as main product, while in the
presence of no functionalized PPAF-1 or base functionalized PPAF-
NH2 (entries 3 and 4) no reaction is observed. These results assure
that both acid and basic centers within the catalyst are necessary
for cascade reaction to take place. This catalytic system is remark-
ably superior to that a simple mixture of an acid (Amberlyte IR-120
in acid form, 10 mol%) and a base (Amberlyst A-21 in base form, 10
mol%) polymeric resins, which under the same reaction conditions
only give 7% of conversion at 1 h and 33% after increasing five times
of loading of catalysts (IR-120, 50 mol% + A-21, 50 mol%) (entries 5
and 6) (Table 4).
Table 4
a
Tandem deprotection-aldol reaction.
Entry
Catalyst
Conv. (%)
4
Yield GC (%)
6
5
1
2
3
4
PPAF-SO3H + PPAF-NH2
PPAF-SO3H
100
95
0
0
7
33
100
100
96
13
87
–
–
0
87
8
–
–
7
33
31
6
PPAF-1
PPAF-NH2
In order to study the role of acid and base sites in the PPAF mate-
rials and their compatibility, we carried out a series of experiments
with different acids, bases and both. Thus, when the acid catalyst
b
5
IR-120 + A-21
IR-120 + A-21
PPAF-SO3H + Aniline
PTSA + PPAF-NH2
PTSA + Aniline
6c
0
d
(
PPAF-SO H) was combined with a soluble base, such as aniline,
7
8
9
69
94
77
3
e
we found a low yield of benzylidenemalononitrile 6 (entry 7). Sim-
19
ilar results are obtained when the supported base (PPAF-NH ) was
2
a
Reaction conditions: benzaldehyde dimethyl acetal (0.36 mmol), malononitrile
0.43 mmol), catalyst (10 mol%), toluene (2 mL) + H2O (25 ␮L), 90 C, 1 h.
IR-120 (10 mol%) + A-21 (10 mol%).
IR-120 (50 mol%) + A-21 (50 mol%).
PPAF-SO H (10 mol%) + aniline (12 mol%).
PTSA (12 mol%) + PPAF-NH2 (10 mol%).
mixed with a soluble p-toluenesulfonic acid or when aniline and p-
toluenesulfonic acid were combined, entries 8 and 9, respectively.
These results indicate that when one or both catalysts are in homo-
geneous phase a neutralization of acid and base centers takes place
and as a consequence the catalytic system fells to carry out the
◦
(
b
c
d
e
3

2
12
E. Merino et al. / Applied Catalysis A: General 469 (2014) 206–212
PPAF-SO H + PPAF-NH2 was washed with an aqueous solution
References
3
of HCl (10%). After washing with a ratio HCl solution/PPAF-
[
[
[
1] A. Corma, Chem. Rev. 97 (1997) 2373–2419.
2] M.E. Davis, Nature 417 (2002) 813–821.
3] A. Corma, H. García, Chem. Rev. 103 (2003) 4307–4366.
SO H + PPAF-NH2 of 10 g/g, the sample was washed with distilled
3
water until neutral pH. Then, the final sample was analyzed by
IR and the bands corresponding to the amino group remain and
EDX analysis shows no presence of chlorine. The results indicate
that with our regular treatment no protonation of the amino group
occurs. In any case, we have also carried out the reaction with the
resultant material after washing up to neutral pH and 99% yield
[4] E. Nikolla, Y. Román-Leshkov, M. Moliner, M.E. Davis, ACS Catal. 1 (2011)
08–410.
5] C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuli, J.S. Beck, Nature 359 (1992)
10–712.
[6] D.E. De Vos, M. Dams, B.F. Sels, P.A. Jacobs, Chem. Rev. 102 (2002) 3615–3640.
4
[
7
[
[
[
7] T. Yokoia, Y. Kubota, T. Tatsumi, Appl. Catal., A: Gen. 421–422 (2012) 14–37.
8] A. Thomas, Angew. Chem. Int. Ed. 49 (2010) 8328–8344.
9] N.B. McKeown, P.M. Budd, Macromolecules 43 (2010) 5163–5176.
(
GC) of product 6 was obtained. When the reaction was up scaled
with 1.58 mmol of benzaldehyde dimethyl acetal 4, the product 6
was isolated by column chromatography in 75% yield.
[10] A. Thomas, P. Kuhn, J. Weber, M.M. Titirici, M. Antonietti, Macromol. Rapid
Commun. 30 (2009) 221–236.
11] R. Dawson, A.I. Cooper, D.J. Adams, Prog. Polym. Sci. 37 (2012) 530–563.
12] Y. Zhang, S.N. Riduan, Chem. Soc. Rev. 41 (2012) 2083–2094, References therein
cited.
[13] E. Verde-Sesto, E.M. Maya, A.E. Lozano, J.G. de la Campa, F. Sanchez, M. Iglesias,
J. Mater. Chem. 22 (2012) 24637–24643.
14] T. Ben, H. Ren, S.Q. Ma, D.P. Cao, J.H. Lan, X.F. Jing, W.C. Wang, J. Xu, F.
Deng, J.M. Simmons, S.L. Qiu, G.S. Zhu, Angew. Chem. Int. Ed 48 (2009)
9457–9460.
[
[
The recyclability of the mixture PPAF-SO H + PPAF-NH2 was
3
examined isolating the solid catalysts from the reaction medium
by filtration, and then washing with THF, buffer AcONa/AcOH, for
recovering active centers on the catalysts, water until neutral pH,
[
THF and Et O and drying. The mixture of solid catalysts can be
2
recycled at least seven times without loss in product yield as can
be seen in Fig. 7a. The reaction stopped as soon as the catalyst was
filtered off and separated from reaction medium. This observation
rules out the possibility of leaching of active species and demon-
strates that all the active centers remain in the solid (1 h, 45.3%
yield, filtration of solid and stirring and heating 1 h more, 50.3%)
[
[
15] W.G. Lu, D.Q. Yuan, D. Zhao, C.I. Schilling, O. Plietzsch, T. Muller, S. Brase, J. Guen-
ther, J. Blumel, R. Krishna, Z. Li, H.C. Zhou, Chem. Mater. 22 (2010) 5964–5972.
16] L.J. Murray, M. Dinca, J.R. Long, Chem. Soc. Rev. 38 (2009) 1294–1314.
[17] J.-R. Li, J.K. Ryan, H.-C. Zhou, Chem. Soc. Rev. 38 (2009) 1477–1504.
[
18] J. Lee, O.K. Farha, J. Roberts, K.A. Scheidt, S.T. Nguyen, J.T. Hupp, Chem. Soc. Rev.
8 (2009) 1450–1459.
19] P. Kaur, J.T. Hupp, S.T. Nguyen, ACS Catal. 1 (2011) 819–835.
3
[
(Fig. 7b).
[20] Y. Zhang, S.N. Riduan, Chem. Soc. Rev. 41 (2012) 2083–2094.
[
[
[
[
21] Y. Yuan, F. Sun, H. Ren, X. Jing, W. Wang, H. Ma, H. Zhao, G. Zhu, J. Mater. Chem.
1 (2011) 13498–13502.
22] W. Lu, D. Yuan, J. Sculley, D. Zhao, R. Krishna, H.-C. Zhou, J. Am. Chem. Soc. 133
2011) 18126–18129.
23] W. Lu, D. Yuan, J.P. Sculley, D. Yuan, R. Krishna, Z. Wei, H.-C. Zhou, Angew. Chem.
Int. Ed. 51 (2012) 7480–7484.
2
4
. Conclusion
(
In conclusion we have been able to functionalize PPAF
(
prepared by microwave synthesis) with acid or base groups
24] S.J. Garibay, M.H. Weston, J.E. Mondloch, Y.J. Colón, O.K. Farha, J.T. Hupp, S.B.T.
Nguyen, Cryst. Eng. Commun. 15 (2013) 1515–1519.
by post-functionalization reactions. These isolated catalytically
active centers can be used to catalyze a variety of one pot
acid–base tandem reactions. Specifically, the combination of
[25] E. Merino, E. Verde-Sesto, E.M. Maya, M. Iglesias, F. Sanchez, A. Corma, Chem.
Mater. 25 (2013) 981–988.
[
[27] (a) B. Voit, Angew. Chem. 118 (2006) 4344–4346;
(b) B. Voit, Angew. Chem. Int. Ed. 118 (2006) 4344–4346.
26] F. Gelman, J. Blum, D. Avnir, Angew. Chem. Int. Ed. 40 (2001) 3647–3649.
PPAF-SO H + PPAF-NH2 efficiently catalyzes the conversion of
3
benzaldehyde dimethylacetal 4 in benzylidenemalononitrile 6
demonstrating the possibilities of functionalized PPAFs to act as
heterogeneous acid–base organocatalysts with high catalytic activ-
ity, simple workup and this catalytic combination has been recycled
several times without significant loss of activity. The exceptional
stability of these materials will make them advantageous over their
metal–organic framework (MOF) counterparts. For those reactions
in which it is not necessary that the active centers are close, these
mixtures of catalysts present advantages against bi-functional sys-
tems, such as, their easier preparation, and wider possibilities
for using catalytic systems with different acid/base ratio and/or
different strength. This work shows and opens the possibility to
functionalize porous aromatic frameworks to obtain environmen-
tally catalysts.
[
28] K. Motokura, N. Fujita, K. Mori, T. Mizugaki, K. Ebitani, K. Kaneda, J. Am. Chem.
Soc. 127 (2005) 9674–9675.
29] B. Helms, S.J. Guillaudeu, Y. Xie, M. McMurdo, C.J. Hawker, J.M.J. Frechet, Angew.
Chem. Int. Ed. 44 (2005) 6384–6387.
30] R. Rathore, C.L. Burns, M.I. Deselnicu, Org. Lett. 3 (2001) 2887–2890.
31] J. Weber, A. Thomas, J. Am. Chem. Soc. 130 (2008) 6334–6335.
32] K.K. Sharma, T. Asefa, Angew. Chem. Int. Ed. 46 (2007) 2879–2882.
[
[
[
[
[33] K.K. Sharma, A. Anan, R.P. Buckley, W. Quellette, T. Asefa, J. Am. Chem. Soc. 130
2008) 218–228.
34] S. Shylesh, A. Wagener, A. Seifert, S. Ernst, W.R. Thiel, Angew. Chem. Int. Ed. 49
2010) 3428–3459.
[35] S. Shylesh, A. Wagener, A. Seifert, S. Ernst, W.R. Thiel, Chem. Eur. J. 15 (2009)
052–7062.
(
[
(
7
[
[
36] R.K. Zeidan, S.-J. Hwang, M.E. Davis, Angew. Chem. Int. Ed. 45 (2006) 6332–6335.
37] E.L. Margelefsky, R.K. Zeidan, V. Dufaud, M.E. Davis, J. Am. Chem. Soc. 129 (2007)
13691–13697.
[38] E.L. Margelefsky, A. Bendjeriou, R.K. Zeidan, V. Dufaud, M.E. Davis, J. Am. Chem.
Soc. 130 (2008) 13442–13449.
[
[
[
39] N.T.S. Phan, C.S. Gill, J.V. Nguyen, Z.J. Zhang, C.W. Jones, Angew. Chem. Int. Ed.
45 (2006) 2209–2212.
40] J. Alauzun, A. Mehdi, C. Reye, R.J.P. Corriu, J. Am. Chem. Soc. 128 (2006)
Acknowledgments
8
718–8719.
41] J.D. Bass, A. Solovyov, A.J. Pascall, A. Katz, J. Am. Chem. Soc. 128 (2006)
737–3747.
[42] J.D. Bass, A. Katz, Chem. Mater. 18 (2006) 1611–1620.
We acknowledge to the Dirección General de Investigación Cien-
tífica y Técnica of Spain (Projects MAT2011-29020-C02-02 and
Consolider-Ingenio 2010-CSD-0050-MULTICAT) for financial sup-
port. E.M. thanks CSIC for a contract of “Junta de Ampliación de
Estudios” program.
3
[
[
43] K. Motokura, M. Tada, Y. Iwasawa, J. Am. Chem. Soc. 129 (2007) 9540–9541.
44] K. Motokura, M. Tomita, M. Tada, Y. Iwasawa, Chem. Eur. J. 14 (2008)
4017–4027.
[
[
45] K. Motokura, M. Tada, Y. Iwasawa, J. Am. Chem. Soc. 131 (2009) 7944–7945.
46] Y. Huang, B.G. Trewyn, H.-T. Chen, V.S.-Y. Lin, New J. Chem. 32 (2008)
Appendix A. Supplementary data
1311–1313.
[
47] M.J. Climent, A. Corma, V. Fornés, R. Guil-Lopez, S. Iborra, Adv. Synth. Catal. 344
(2002) 1090–1096.
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.apcata.
2
013.09.052.