Micro-Cu4I4-MOF: Reversible iodine adsorption and catalytic properties for tandem reaction of Friedel-Crafts alkylation of indoles with acetals

Article abstract of DOI:10.1039/c6cc07027b

We report a convenient approach, the first of its kind, to construct a microscale non-metal@MOF composite catalytic host-guest system for an organic tandem reaction. The reported porous Cu₄I₄-MOF is able to reversibly adsorb molecula

Full text of DOI:10.1039/c6cc07027b

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Micro-Cu4I4-MOF: reversible iodine adsorption and catalytic
properties for tandem reaction of Friedel–Crafts alkylation of
indoles with acetals
Received 00th January 20xx,
Accepted 00th January 20xx
Neng-Xiu Zhu,† Chao-Wei Zhao,† Jian-Cheng Wang, Yan-An Li, and Yu-Bin Dong∗
DOI: 10.1039/x0xx00000x
www.rsc.org/
We report a convenient approach, the first of kind, to construct
microscale non-metal@MOF composite catalystic host-guest
system for organic tandem reaction. The reported porous Cu4I4-
MOF is able to reversibly adsorb molecular iodine at room
temperature. The obatined I2@Cu4I4-MOF host-guest system can
be a highly heterogeneous catalyst to promote the Friedel–Crafts
alkylation of indoles with acetals in a one-pot two-step fashion
under solvent-free conditions at room temperature.
The design and fabrication of active catalytic species loaded
MOFs has been become a very useful approach to access
highly heterogeneous catalytic materials for sustainable
organic reactions. In the context of catalyst support, MOFs are
proven to be a promising class of carriers for stabilizing active
catalytic species.1 Thus far, the encapsulation of metals,
especially precious nano metal species, such as Pt, Pd, Rh, Ru,
Au, Ag and so on, in MOF hosts are the main theme in this
field.2 In contrast, the loading of other kinds of guest species,
such as inorganic non-metal and organic species, with active
catalytic properties has received considerably less attention.3
Very recently, the study of MOF-supported heterogeneous
catalytic system trends to expand from single-step catalysed
reaction to multistep catalysed tandem reactions due to the
more and more serious sustainable and environmental issues.
In principle, tandem reactions feature lower cost, fewer
chemicals and less energy consumptions. Although the
Fig. 1 a) Synthesis of Cu4I4-MOF (
1
) and 0.75I2@Cu4I4-MOF (
and regenerated
in iodine vapour for 10 min and
. d) XPS spectrum of
2
). b) Photographs
significant progress in metal@MOF catalysed cascade showing the iodine adsorption process of
1
1 by heating, and
corresponding SEM images. c) TGA traces of
20 min, and the regenerated
1, 1
reactions has been made,4 the tandem reactions based on
non-metal@MOF heterogeneous catalytic systems, however,
are unprecedented.
1
2.
have been well demonstrated to be very useful for a variety of
organic transformation.5 In principle, metal-free homogeneous
catalytic species can also be incorporated into the MOFs and
translate their heterogeneous counterparts. In this
contribution, we report a Cu4I4-MOF which is able to reversibly
upload molecular iodine. Furthermore, the resulted I2@Cu4I4-
As the counterpart of metal catalysts, metal-free catalysts
MOF (2) can be a highly heterogeneous catalyst to promote
acetals deprotection and Friedel–Crafts alkylation in a tandem
way.
The desolvated Cu4I4-MOF (1) was prepared by a modified
method previously reported by us (ESI).6 As shown in Fig. 1a,
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the CH3CN solution of the tri-armed ligand
L
and CuI was
Molecular I2 is generally known to be a homogeneous catalyst
refluxed for 1h, and the obtained crystalline solid was further and widely applied to promote various organic
heated at 90°
C for additional 1 h to generate light yellow transformations.8 Iodine, however, is very scarce in natural
micro-sized crystalline solids (Fig. 1b). The size of Cu4I4-MOF world. On the other hand, 129I is one of important radioisotope
particles is basically less than 20 µm based on SEM image (Fig. and very harmful to human health.9 So the development of
1b). The XRPD patterns of micro-sized
bulk crystals (Fig. S1).
1
identical to that of iodine cyclic utilized heterogeneous catalysts for eco-friendly
demands is an urgent issue. Inspired by this, iodine loaded
As described before,
interpenetrating framework containing 1D oval channels along benzaldehyde dimethyl acetal deprotection of benzaldehyde.
the crystallographic c axis with a dimension of ca. 19 17 Å.
Interestingly, when the crystalline solids of was exposed to
1 possesses a 4-connected sra 2-fold compound 2 was firstly used to test the catalytic property for
×
2 (I2, 1 mol %)
OCH3
OCH3
1
CHO
the iodine vapour (p(I2) is ca. 0.3 mm Hg) in a sealed vial, and
the colour of the sample changed rapidly from light yellow to
dark brown as the elapse of time (Fig. 1b). The iodine
adsorption process was monitored by thermogravimetric
analysis (TGA), and the saturated iodine loading was reached
Solvent-free, r.t., 10 h
in ca. 30 min to generate I2-loaded host-guest system of
0.75I2 Cu4I4L, an iodine content of up to 12.5 %, Fig. 1c).
Although we tried many times to get the single crystals of , it
2
(
⊂
2
did not work. We believe that the I2 species was stabilized in
pores by the weak host-guest interactions, which is commonly
observed in other I2@MOF system.3 The encapsulated
molecular iodine was unambiguously confirmed by the X-ray
photoelectron spectroscopy (XPS) measurement (Fig. 1d). The
Fig. 3 2 catalysed solvent-free benzaldehyde dimethyl acetal deprotection, and
corresponding 1H NMR spectrum for the product (300 MHz, 25
C, CDCl3).
°
XPS indicates that the valences of 2 included iodine species are
0 and -1, which further supports the I2 (guest) and I-
(framework) existence.7 Notably, above iodine loading is
When benzaldehyde dimethyl acetal was treated by
2 (1 mol %
I2) under solvent-free condition at room temperature,
reversible. When
encapsulated iodine was completely removed and
regenerated based on TGA analysis (Fig. 1c). XDPR patterns
indicated that the crystallinity and structural integrity of are
maintained during this reversible I2 loading process (Fig. S1).
2 was heated at 120°C for 3 h, the quantitative yield (Yield, >99 %, ESI) of benzaldehyde based on
1H NMR spectrum was obtained in 10 h (monitored by TLC). As
shown in Fig. 3, no any peaks related to benzaldehyde
dimethyl acetal can be detected in the 1H NMR spectrum after
1
was
1
reaction, indicating the
2 catalysed benzaldehyde dimethyl
acetal deprotection is clean and highly efficient.
H
N
H
2 (I2, 1 mol %)
N
+
CHO
Solvent-free, r.t., 10 h
N
H
Fig. 2 Left: CO2 adsorption isotherm for
centred at 1.3 nm.
2 at 195 K. Right: The pore width of 2 is
The porosity of iodine loaded
adsorption–desorption experiment. As shown in Fig. 2, the CO2
adsorption capacity of
at 1 atm is 100.50cm3 g-1 (195 K) and
the calculated Brunauer–Emmett–Teller (BET) surface area is
2 was confirmed by the gas
2
Fig.
4 2 catalysed solvent-free Friedel-Crafts alkylation of indole with
benzaldehyde and corresponding 1H NMR spectrum for the product (300 MHz,
DMSO-d6).
275.56 m2 g-1. Compared to
is 173.2 cm3 g-1 (195 K) and the (BET) surface area of
1
(the CO2 adsorption capacity of
1
1
is 641
In addition to that,
2 also exhibits highly active catalyst for
m2 g-1),6 the decrease of CO2 adsorption capacity and
corresponding surface area is clearly resulted from the
molecular iodine species loading. The pore size distribution
curve, calculated from Barrett-Joyner-Halenda analysis, shows
the synthesis of bis(indolyl)methanes, which is an important
class of compounds with a range of biological activities,10 via
indole Friedel-Crafts alkylation under solvent-free condition
(Fig. 4). The treatment of benzaldehyde (1 mmol) with indole
a narrow pore diameter distribution at ca. 1.30 nm for
2), which is slightly smaller than that of 1
(1.45 nm).6
2 (Fig.
(2 mmol) in the presence of
2 (1.0 mol % I2) at room
temperature (10 h) afforded the corresponding Friedel-Crafts
2 | J. Name., 2012, 00, 1-3
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alkylation product in high yield (93 %) after column silica gel using CH2Cl2/ petroleum ether (1 : 3) as an eluent to
chromatography purification (ESI). In contrast, the synthesis of afford the expected product as white solid in 93 % yield (Fig. 5,
bis(indolyl)methane catalysed by
resulted in a very low isolated yield (~9 %) under the same
reaction conditions, suggesting that the encapsulated I2 in the behaviour under the reaction conditions. After each catalytic
host framework is the main active catalytic species for this cycle, could be easily recovered by centrifugation and
reaction. For the solid benzaldehyde substrates, the Friedel- filtration after adding ethyl acetate, and then directly reused in
Crafts alkylation can be carried out in xylene or by solid phase the next run. As a heterogeneous catalyst, can be reused five
grinding method. For example the alkylation of solid indole times without significantly loss its catalytic activity (Yields, 86-
with solid 4-nitrobenzaldehyde can be performed in xylene (10 93 %, Fig. 5a). The heterogeneity of was further
h) or solid phase grinding (grinded 10 min every other 2 h, 5 demonstrated by a leaching test. As shown in Fig. 5b, the
times) in the presence of (I2, 1 mol %) at room temperature, reaction solution was removed quickly from and transferred
1
without iodine species ESI).
Notably,
2
herein exhibits a typical heterogeneous catalytic
2
2
2
2
2
the corresponding yields are 90 and 89 %, respectively (ESI).
to another reaction vial under the same conditions after 4 h.
No further increase in the product conversion was detected
H
N
during the next 6 h without 2. The I and Cu concentrations in
H
2 (I2, 1 mol %)
the filtrate are 3.250 and 0.165 µg/mL (based on ICP),
corresponding to 3.0 % I and 0.2 % Cu losses, respectively. The
comparison of the XRPD patterns before and after the fifth
catalytic cycle demonstrated that the crystallinity, structural
integrity of Cu4I4-MOF were well maintained (Fig. 5c). TGA
OCH3
OCH3
N
+
Solvent free, r.t., 10 h
N
H
measurement (Fig. 5d) showed that the iodine amount in
2
after the five catalytic cycles of this tandem reaction is 11.5 %,
indicating that molecular iodine guest can be mostly stabilized
in the MOF pores and only tiny amount of iodine species
leaching (ca. 8.0 %) occurred during the reaction process. The
small amount I2 leaching could be the reason for the slight
decrease in catalysis efficiency of
2 during the recycling
catalytic runs. The SEM image shows that the morphology of
was well preserved even after five catalytic runs (Fig. 5e).
2
To our knowledge, there are only two examples related to
heterogeneous catalytic benzaldehyde dimethyl acetal
deprotection and indole Friedel-Crafts alkylation tandem
reaction are reported.11 The reported tandem reaction was
catalysed by porous aluminosilicate (60°
C, CH3CN)11a and
triphenylphosphine-m-sulfonate/CBr4 (r.t., CH3CN)11b to
generate corresponding Friedel-Crafts alkylation product in 91
and 75 % yields, respectively. In our case, the use of
2 has the
experimentally advantage of avoiding highly toxic CBr4 species
and that no higher temperature is needed. More importantly,
the 2-catalysed reaction needed no additional organic solvents
except the reaction substrates. Thus as the reaction is easy to
manipulate and avoids the use of toxic and volatile solvents, it
could be considered as a clean catalytic synthesis approach.
The scope of this I2-loaded host-guest catalytic system was
explored by performing the acetals deprotection-Friedel–
Crafts alkylation tandem reactions of various other substituted
Fig. 5 a)
activity. b) Reaction time examination (black line) and leaching test (red line) for
the tandem reaction. c) XRPD patterns of after the second catalytic run and
after the fifth catalytic run, respectively. d) TGA traces of desolved and
after five catalytic cycles, respectively. e) SEM image of after five catalyti runs.
2 can be resued for five catalytic cycles without loss of its catalytic
2, 2
2
1
,
2
2
2
aromatic and aliphatic acetals with indoles. Table
1
As shown above, I2-loaded
2 herein is able to respectively
summarized the results of these reactions. We found that the
substituted benzaldehyde acetals with either electron-
donating or electron-withdrawing groups gave satisfied overall
isolated yields (87-90 %), but are slightly lower than that of
pristine benzaldehyde acetal. On the other hand, the
combination of benzaldehyde acetal with bromo-substituted
indole also resulted in slightly lower isolated yield (86 %, entry
9). In addition, reaction of aliphatic acetal (entry 8) proceeded
efficiently, giving good isolated yield (89 %). Reaction of cyclic
acetal (entry 7), however, gave relatively lower isolated yield
facilitate benzaldehyde dimethyl acetal deprotection and
indole Friedel-Crafts alkylation under solvent-free conditions
at room temperature. So it is plausible to suppose that these
two types of reactions could be integrated into a one-pot two-
step reaction. Inspired by this, we performed the following
experiment.
A mixture of benzaldehyde dimethyl acetal (1 mmol) and
indole (2 mmol) in the presence of
2 (1 mol % I2) was stirred at
room temperature for 10 h (monitored by TLC), and the
reaction residue was purified by column chromatography on
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1
2
(a) A. Corma, H. García and F. X. Llabrés i Xamena, Chem.
Rev., 2010, 110, 4606–4655. (b) M. Yoon, R. Srirambalaji, K.
Kim, Chem. Rev., 2012, 112, 1196–1231. (c) A. H. Chughtai,
N. Ahmad, H. A. Younus, A. Laypkov, F. Verpoort, Chem. Soc.
Rev., 2015, 44, 6804-6849.
(a) A. Dhakshinamoorthy, H. Garcia, Chem. Soc. Rev., 2012,
41, 5262-5284. (b) H. R. Moon, D.-W. Lim, M, P. Suh, Chem.
Soc. Rev., 2013, 42, 1807-1824.
X.-M. Zhang, C.-W. Zhao, J.-P. Ma, Y. Yu, Q.-K. Liu, Y.-B. Dong,
Chem. Commun., 2015, 51, 839-842.
(a) K. Manna, T. Zhang, F. X. Greene, W. Lin, J. Am. Chem.
Soc., 2015, 137, 2665–2673. (b) E. Verde-Sesto, E. Merino, E.
Rangel-Rangel, A. Corma, M. Iglesias, F. Sánchez, ACS
(85 %), which might be resulted from the better stability of the
reagent.12
In addition to that, larger sized 1-pyrenecarboxaldehyde
acetal was also used as the substrate to perform the tandem
reaction catalysed by
2 under the same reaction conditions
(ESI). The corresponding Friedel–Crafts alkylated product was
obtained in much lower isolated yield (ca. 28 %), suggesting
the internal surface catalysis might be the predominant
3
4
process, and the high catalytic activity exhibited by 2 should be
a synergy effect of both outside and internal surface catalytic
processes.
Sustainable Chem. Eng., 2016,
4, 1078–1084. (c) M. H.
Beyzavi, N. A. Vermeulen, A. J. Howarth, S. Tussupbayev, A.
B. League, N. M. Schweitzer, J. R. Gallagher, A. E. Platero-
Prats, N. Hafezi, A. A. Sarjeant, J. T. Miller, K. W. Chapman, J.
F. Stoddart, C. J. Cramer, J. T. Hupp, O. K. Farha, J. Am. Chem.
Soc., 2015, 137, 13624–13631. (d) P. V. Dau, S. M. Cohen,
Inorg. Chem., 2015, 54, 3134–3138. (e) J.-S. Wang, F.-Z. Jin,
H.-C. Ma, X.-B. Li, M.-Y. Liu, J.-L. Kan, G.-J. Chen, Y.-B. Dong,
Inorg. Chem., 2016, 55, 6685-6691. (f) Y.-A. Li, S. Yang, Q.-K.
Liu, G.-J. Chen, J.-P. Ma, Y.-B. Dong, Chem. Commun., 2016,
52, 6517- 6520. (g) Q. Yang, Y.-Z. Chen, Z. U. Wang, Q. Xu, H.-
L. Jiang, Chem. Commun., 2015, 51, 10419-10422. (h) Q.
Yang, Q. Xu, S.-H. Yu, H.-L. Jiang, Angew. Chem., Int. Ed.,
2016, 55, 3685-3689. (i) Y.-Z. Chen, Y.-X. Zhou, H. Wang, J.
Table 1. Synthesis of bis(indolyl)methanes from substituted acetals and indoles
catalysed by 2.a
Entry
1
acetals
indoles
Yield (%)a
93
OCH3
H
N
OCH3
OCH3
OCH3
H
N
2
3
4
5
90
88
87
89
F
OCH3
OCH3
H
N
H3C
Lu, T. Uchida, Q. Xu, S.-H. Yu, H.-L. Jiang, ACS Catal., 2015, 5,
2062-2069.
OCH3
OCH3
H
N
5
(a) W. Adam, C. R. Saha-Möller, P. A. Ganeshpure, Chem.
Rev., 2001, 101, 3499–3548. (b) C.-L. Sun, Z.-J. Shi, Chem.
Rev., 2014, 114, 9219–9280. (c) L. Dai, Y. Xue, L. Qu, H.-J.
Choi, J.-B. Baek, Chem. Rev., 2015, 115, 4823–4892. (d) C.
Allais, J.-M. Grassot, J. Rodriguez, T. Constantieux, Chem.
Rev., 2014, 114, 10829–10868.
C.-W. Zhao, J.-P. Ma, Q.-K. Liu, X.-R. Wang, Y. Liu, J. Yang, J.-S.
Yang, Y.-B. Dong, Chem. Commun., 2016, 52, 5238 – 5241.
(a) B. C. Bravo, S. L. Michelhaugh, M. P. Soriaga, J. Phys.
Chem., 1991, 95, 5245 - 5249. (b) Q.-K. Liu, J.-P. Ma, Y.-B.
Dong, Chem. Commun., 2011, 47, 7185–7187.
H3CO
O2N
Br
OCH3
OCH3
H
N
OCH3
OCH3
H
N
6
7
6
90
O
H
N
7
85
89
O
8
(a) B. Das, P. Balasubramanyam, M. Krishnaiah, B.
OCH3
OCH3
H
N
Veeranjaneyulu, G. C. Reddy, J. Org. Chem., 2009, 74, 4393.
(b) K. Žmitek, M. Zupan, S. Stavber, J. Iskra, J. Org. Chem.,
2007, 72, 6534. (c) N. Deka, D. J. Kalita, R. Borah, J. C. Sarma,
J. Org. Chem., 1997, 62, 1563. (d) J. S. Yadav, B. V. S. Reddy,
M. S. Reddy, A. R. Prasad, Tetrahedron Lett., 2002, 43, 9703.
8
H
N
OCH3
OCH3
9
86
Br
9
(a) P. Yi, A. Aldahan, V. Hansen, G. Possnert, X. L. Hou,
Environ. Sci. Technol., 2011, 45, 903–909. (b) R. Chance, A. R.
Baker, L. Carpenter, T. D. Jickells, Environ. Sci.: Processes
Impacts, 2014, 16, 1841-1859. (c) X. Hou, H. Dahlgaard, B.
Rietz, U. Jacobsen, S. P. Nielsen, A. Aarkrog, Analyst, 1999,
124, 1109-1114.
a Conditions: solvent-free, 2 (1 mol % I2), r.t., 10 h. b Isolated yield.
In conclusion, we report a practical way to fabricate non-
metal@MOF catalytic host-guest system. The porous Cu4I4-
MOF herein is able to incorporate with molecular iodine into
an I2@Cu4I4-MOF host-guest system which is a highly effective
heterogeneous catalyst for acetals deprotection-Friedel–Crafts
alkylation tandem reaction under solvent-free conditions at
room temperature.
10 M. Shiri, M. A. Zolfigol, H. G. Kruger, Z. Tanbakouchian, Chem.
Rev., 2010, 110, 2250-2293.
11 (a) T. M. Kubezyk, S. M. Williams, J. R. Kean, T. E. Davies, S. H.
Taylor, A. E. Graham, Green Chem., 2011, 13, 2320–2325. (b)
C. Huo, C. Sun, C. Wang, X. Jia, W. Chang, ACS Sustainable
Chem. Eng., 2013, 1, 549-553.
We are grateful for financial support from NSFC (Grant Nos.
21671122, 21475078 and 21271120), 973 Program (Grant Nos.
2012CB821705 and 2013CB933800) and the Taishan Scholar’s
Construction Project.
12 D. B. G. Williams, A. Cullen, A. Fourie, H. Henning, M. Lawton,
W. Mommsen, P. Nangu, J. Parker, A. Renison, Green Chem.,
2010, 12, 1919-1921.
Notes and references
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I2@Cu4I4-MOF can be a highly heterogeneous catalyst to promote tandem reaction of Friedel–Crafts alkylation of indoles with
acetals under solvent-free conditions at room temperature.
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