Troeger's base-functionalised organic nanoporous polymer for heterogeneous catalysis

Article abstract of DOI:10.1039/b920113k

An organic nanoporous polymer (BET surface area of 750 m² g ^-1) containing bicovalently-bonded Troeger's base as functional moieties in the network was synthesized, characterised, and further applied as a promising heterogeneous catalyst in the addition reaction of diethylzinc to aromatic aldehyde. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/b920113k

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¨
Troger’s base-functionalised organic nanoporous polymer
for heterogeneous catalysisw
Xin Du,a Yalei Sun,a Bien Tan,b Qingfeng Teng,a Xiaojun Yao,a
Chengyong Suc and Wei Wang*a
Received (in Cambridge, UK) 28th September 2009, Accepted 25th November 2009
First published as an Advance Article on the web 14th December 2009
DOI: 10.1039/b920113k
An organic nanoporous polymer (BET surface area of 750 m2 gꢀ1
¨
containing bicovalently-bonded Troger’s base as functional
)
moieties in the network was synthesized, characterised, and
further applied as a promising heterogeneous catalyst in the
addition reaction of diethylzinc to aromatic aldehyde.
Micro- and mesoporous materials with large specific surface
areas are potentially of great practical value in the fields of
catalysis, adsorption, chromatography, sensor technology,
and gas storage.1–4 For potential applications as efficient
heterogeneous catalysts, appropriate chemical functionalisation
of these nanoporous solids is a vital challenge. Considering the
stable performance and recycle use of the catalysts, attachment
of catalytic moieties via covalent bonds is preferential in
chemical functionalisation.5 The classical strategy for this
purpose is to anchor the functional groups (catalytic moieties)
onto the pore surface of the synthesized nanoporous materials
via grafting method (post-synthesis, route A in Fig. 1). In this
case, the organic functional groups are inhomogeneously
distributed and pendent into the pore volume, which may
cause the pore-blocking and eventually deactivate the catalytic
system.6 A preferable strategy is, therefore, the ‘‘bottom-up’’
approach by which the functional groups can be homoge-
neously distributed and embedded into the pore wall (routes B
and C in Fig. 1). For example, periodic mesoporous organo-
silicas (PMOs)7,8 could be prepared as functional inorganic–
organic hybrid materials via self-condensation of bridged
organosilanes (R0O)3Si–R–Si(OR0)3 (route B). Another
prominent example is the synthesis of 2D9 and 3D10 covalent
organic frameworks (COFs) in which organic building blocks
are linked entirely by strong covalent bonds (similar to route C).
Although hydrothermal and mechanical stabilities of the
synthesized materials could be improved by the ‘‘bottom-up’’
strategy, scarce examples has been successful so far in
constructing well-ordered nanoporous materials as hetero-
geneous catalysts. The reason lies in that it is normally difficult
to maintain material structures, such as the long-range order
Fig. 1 Schematic representation of general strategies for functional-
ising nanoporous materials via covalent bonding. The classical
strategy shown in route A is the grafting method (post-synthesis).
The ‘‘bottom-up’’ approaches are depicted in route B (self-condensation)
and route C (one-pot), respectively. Using route C, an organic
nanoporous polymer 3 was constructed in this work by using Troger’s
¨
base derivative (one enantiomer 1 is depicted) as the functional groups
(catalytic moieties) and 1,3,5-triethynylbenzene 2 as the linkers.
(crystallinity in the case of COFs) and even the porosity,
when catalytic moieties are intended to be introduced into
the framework.11
The recently developed nanoporous organic polymers, e.g.,
polymers of intrinsic microporosity (PIMs)12 and conjugated
microporous polymers (CMPs),13 may be new candidates for
efficient and robust heterogeneous catalysts constructed by the
‘‘bottom-up’’ approach. Albeit being amorphous in nature,
these nanoporous polymers offer much freedom for rational
designs of catalytic building blocks to be covalently embedded
in the polymeric network. Moreover, as implied in the
pioneering work14 of Cooper and co-workers, the pore size
and surface area of nanoporous polymers may be fine-tuned
for diverse catalytic reactions by varying the molecular length
of the building blocks. Indeed, several pioneering reports on
the application of covalent microporous polymers in catalysis
have appeared very recently.15 We report herein for the
first time an organic nanoporous polymer 3 containing
a State Key Laboratory of Applied Organic Chemistry, College of
Chemistry and Chemical Engineering, Lanzhou University,
Lanzhou 730000, P. R. China. E-mail: wang_wei@lzu.edu.cn;
Fax: +86 931 8915557; Tel: +86 931 8912282
b School of Chemistry and Chemical Engineering, Huazhong
University of Science and Technology, Wuhan 430074, P. R. China
c School of Chemistry and Chemical Engineering, Sun Yat-Sen
University, Guangzhou 510275, P. R. China
bicovalently-bonded Troger’s base in the network constructed
¨
by the Sonogashira–Hagihara cross-coupling reaction
w Electronic supplementary information (ESI) available: Additional
experimental and characterization details, thermal analysis, FTIR, TEM,
EDX, and atomistic simulation profiles. See DOI: 10.1039/b920113k
(route C in Fig. 1). Moreover, the nanoporous polymer 3
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shows reasonable catalytic activity in the addition reaction of
diethylzinc to 4-chlorobenzaldehyde.
Troger’s base and its derivatives (e.g., 2,8-diiodo-6H,12H-
¨
5,11-methanodibenzo[b,f][1,5]diazocine, 1) are chiral diamines
with two stereogenic nitrogen centers. A unique set of structural
features (C2 symmetry, rigidity, and V-shape geometry) render
this class of compounds very attractive for applications in
molecular recognition, bioorganic chemistry, supramolecular
chemistry, drug development, and specifically, asymmetric
catalysis.16 Using palladium-catalyzed Sonogashira–Hagihara
cross-coupling reaction to form the covalent bonds and using
1,3,5-triethynylbenzene 2 as the linkers (Fig. 1), we accordingly
synthesized the Troger’s-base-functionalised polymer 3 in one
¨
step (see experimental details in ESIw) with a yield of 72%.
After the reaction, the synthesized polymer 3 was readily
precipitated from solution as a brown-colored powder. The
powder is totally insoluble in all organic solvents tested
(calc. for C23H14N2: C 86.79, H 4.40, N 8.81; found: C 81.42,
H 4.70, N 7.21). This polymer is amorphous as evidenced
by powder X-ray diffraction (not shown). The results of
thermogravimetric analysis (TGA) and differential scanning
calorimetry (DSC) (Fig. S9, ESIw) indicate that decomposition
of polymer 3 starts from 350 1C and is completed by 620 1C
when heated at a rate of 10 1C minꢀ1, and the polymer
exhibited a one-step weight loss. Fig. 2 shows SEM images
of polymer 3; the material spheres are fairly uniform in size
and the average sphere size is ca. 350 nm.
Fig. 3 13C CP/MAS NMR spectrum for nanoporous polymer 3,
which was recorded at an MAS rate of 10 kHz. Asterisks denote
spinning sidebands.
mesopores. The micropore surface area, derived from the
t-plot method, is 313 m2gꢀ1. The inset in Fig. 4(b) shows the
pore volume for polymer 3 as calculated by NLDFT. The total
pore volume, estimated from the amount adsorbed at p/p0 =
0.98, is 0.74 cm3 gꢀ1. The micropore volume for polymer 3 is
0.14 cm3 gꢀ1 using the t-plot method.
The catalytic activity of polymer 3 was examined in the
addition reaction of diethylzinc 4 to 4-chlorobenzaldehyde 5,
which gives 1-(4-chlorophenyl)propan-1-ol 6 as the product.
The results obtained are summarized in Table 1. It was
The polymer 3 was further characterized by 13C cross-
polarization magic-angle spinning (CP/MAS) NMR spectroscopy
(Fig. 3). The signals at ca. 59, 67, 125, 129 and 149 ppm confirm
reported that, in the presence of Troger’s base 7a, the above-
¨
mentioned reaction gave product 6 in the yield of 74%19 under
homogeneous conditions (entry 1). We performed this reaction
that the skeleton of Troger’s base is well distributed in the
¨
under same reaction conditions with Troger’s base derivative
¨
polymeric network. The peak at ca. 119 ppm and the shoulder
at ca. 135 ppm correspond to carbon atoms of CAr–C and CAr–H
on 1,3,5-trisubstituted benzene, respectively. The peak at
ca. 90 ppm is ascribed to sp-hybridised –Car–CRC–Car– sites.
There are no evident peaks at ca. 76 and 82 ppm, which indicates
the complete condensation of –CRCH groups.
The porosity of polymer 3 was investigated by sorption
analysis using nitrogen (Fig. 4). In Fig. 4(a) is shown the N2
volume adsorbed, Vads, vs. relative pressure, p/p0, for polymer 3.
BET analysis gave a surface area of 750 m2 gꢀ1. According to
the IUPAC classification,17 polymer 3 gave rise to Type I
nitrogen gas sorption isotherms with H3 hysteresis loops,
indicating that polymer 3 consists of micro- and mesopores.
As calculated by using non-local density functional theory
(NLDFT),18 Fig. 4(b) shows a semilogarithmic for the pore
size distribution (PSD) curves for polymer 3, in which two
comparable peaks are located at ca. 0.6 and 1.3 nm. The broad
PSD curves suggest the presence of both micropores and
Fig. 4 (a) N2 adsorption–desorption isotherms measured at 77 K
(the adsorption branch is labeled with open symbols). (b) The pore size
distribution calculated by NLDFT. The inset shows cumulative pore
volume calculated by NLDFT.
Fig. 2 SEM images for the synthesized nanoporous polymer 3.
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Table
1
Catalytic performance for the addition reaction of
knowledge, this is the first report of a Troger’s-base-
¨
diethylzinc (Et2Zn) 4 to 4-chlorobenzaldehyde 5. Each reaction was
conducted at 40 1C
functionalised organic nanoporous polymer for catalytic
applications.21 The catalytic results imply that, the Troger’s-
¨
base-functionalized nanoporous polymers may act as promising
heterogeneous catalysts applicable to a variety of reactions
catalyzed by Troger’s-base and its derivates.22,23 Furthermore,
¨
the strategy applied herein may provide new possibilities in
connecting nanoporous polymer networks and asymmetric
catalysts, especially the so-called ‘‘organocatalysts’’24 being
developed recently. Efforts towards these approaches are
actively underway in this lab.
Entry
Catalyst
x (mol%)a
Time/d
Yield of 6 (%)b
1
2
3
4
5
6
7
7a
7b
5
20
20
40
40
40
40
2
2
2
1
2
2
2
74c
65
47
60
56
55
56
The authors gratefully acknowledge the National Natural
Science Foundation of China (No. 20602016), the 111 Project,
and the Program for New Century Excellent Talents in
University (NCET-06-0904) for financial support.
3, fresh
3, fresh
3, 1st run
3, 2nd run
3, 3rd run
a
b
Molar ratio of Troger’s-base relative to 5. Isolated yield. Result
c
¨
Notes and references
from ref. 19.
1 F. Hoffmann, M. Cornelius, J. Morell and M. Froba, Angew.
¨
Chem., Int. Ed., 2006, 45, 3216.
2 Handbook of Porous Solids, ed. F. Schuth, K. Sing and
J. Weitkamp, Wiley-VCH, Berlin, 2002.
3 A. I. Cooper, Adv. Mater., 2009, 21, 1291.
4 K. E. Maly, J. Mater. Chem., 2009, 19, 1781.
5 A. F. Trindade, P. M. P. Gois and C. A. M. Afonso, Chem. Rev.,
2009, 109, 418.
6 M. Gruttadauria, F. Giacalone and R. Noto, Chem. Soc. Rev.,
2008, 37, 1666.
7 A. Kuschel, H. Sievers and S. Polarz, Angew. Chem., Int. Ed., 2008,
47, 9513.
¨
7b (20 mol%) as the homogenous catalyst, which gave product
6 in the yield of 65% (entry 2). To our delight, polymer 3
(entries 3–7) shows comparable activities in catalyzing the
addition reaction. When polymer 3 containing Troger’s-base
¨
units (entries 3 and 4, 20 and 40 mol% relative to 5) was
applied as a heterogeneous catalyst to the reaction, yields of 47
and 60% were obtained, respectively. Moreover, the reaction
was still efficient after at least three cycles (entries 5–7). The
13C CP/MAS NMR spectrum of the catalyst recorded after the
third run (entry 7) is almost identical to that of the fresh
polymer 3 (see Fig. S5, ESIw). We are currently carrying
out following-up experiments to investigate the activity and
stability of the catalysts in further catalytic cycles.
8 Q. H. Yang, J. Liu, L. Zhang and C. Li, J. Mater. Chem., 2009, 19,
1945.
´
9 A. P. Cote, A. I. Benin, N. W. Ockwig, M. O’Keeffe, A. J. Matzger
and O. M. Yaghi, Science, 2005, 310, 1166.
10 H. M. El-Kaderi, J. R. Hunt, J. L. Mendoza, A. P. Cote
R. E. Taylor, M. O’Keeffe and O. M. Yaghi, Science, 2007, 316, 268.
11 P. M. Budd, Science, 2007, 316, 210.
´
,
In summary, with the use of 1,3,5-triethynylbenzene 2 as the
12 N. B. McKeown and P. M. Budd, Chem. Soc. Rev., 2006, 35, 675.
13 J. X. Jiang, F. Su, A. Trewin, C. D. Wood, N. L. Campbell, H. Niu,
C. Dickinson, A. Y. Ganin, M. J. Rosseinsky, Y. Z. Khimyak and
A. I. Cooper, Angew. Chem., Int. Ed., 2007, 46, 8574.
14 J. X. Jiang, F. Su, A. Trewin, C. D. Wood, H. Niu, J. T. A. Jones,
Y. Z. Khimyak and A. I. Cooper, J. Am. Chem. Soc., 2008, 130,
7710.
linkers and Troger’s base 1 as the functional moieties, a novel
¨
organic nanoporous polymer 3 exhibiting moderate surface
area (750 m2
g
ꢀ1) was successfully prepared in one step
(route C in Fig. 1). In comparison to those of PIMs12 which
consist of spirocyclic groups as linkers, the porosity of polymer 3
may arise from 1,3,5-triethynylbenzene 2 and from the rigid
and contorted structure of functional moieties, i.e., the
15 (a) J. Schmidt, J. Weber, J. D. Epping, M. Antonietti and
A. Thomas, Adv. Mater., 2009, 21, 702; (b) R. Palkovits,
M. Antonietti, P. Kuhn, A. Thomas and F. Schuth, Angew. Chem.,
Int. Ed., 2009, 48, 6909.
16 S. Sergeyev, Helv. Chim. Acta, 2009, 92, 415.
¨
V-shape geometry of Troger’s base 1 (see the atomistic simulation
¨
in Fig. S8, ESIw). Troger’s base 1 was bicovalently connected
¨
17 K. S. W. Sing, D. H. Everett, R. A. W. Haul, L. Moscou, R. A. Pierotti,
J. Rouquerol and T. Siemieniewska, Pure Appl. Chem., 1985, 57, 603.
18 Other techniques such as small-angle X-ray scattering (SAXS)
and wide-angle X-ray scattering (WAXS) may provide further
information on the inner interface of the nanoporous systems.
For detailed discussion, see: (a) J. Schmidt, M. Werner and
A. Thomas, Macromolecules, 2009, 42, 4426; (b) J. Weber,
M. Antonietti and A. Thomas, Macromolecules, 2008, 41, 2880.
19 M. Harmata and M. Kahraman, Tetrahedron: Asymmetry, 2000,
11, 2875.
with the linkers 2 via the palladium-catalyzed Sonogashira–
Hagihara cross-coupling reaction which was successfully
applied in the synthesis of CMPs.13,14 It is important to
mention that, compared to the post-synthesis method, a high
loading of functional moieties could be achieved (2.58 mmol gꢀ1
in the case of Troger’s base) via the ‘‘bottom-up’’ approach.
¨
A similar strategy was recently realized by Weber and
Thomas,20 who synthesized microporous conjugated polymer
consisting of 9,90-spirobifluorene as the functional moieties for
potential applications in organic electronics.
20 J. Weber and A. Thomas, J. Am. Chem. Soc., 2008, 130, 6334.
21 Mirkin and co-workers recently reported the only example in
exploiting Troger’s base as ligands in the synthesis of infinite
¨
co-ordination polymers (ICPs). The catalytic application of
Troger’s-base-derived ICP was, however, not attempted: Y. Jeon,
¨
G. S. Armatas, D. Kim, M. G. Kanatzidis and C. A. Mirkin,
Small, 2009, 5, 46.
By contrast with Troger’s-base derivates as homogeneous
¨
catalysts, the nanoporous polymer 3 shows comparable activity
in catalyzing the addition reaction of diethylzinc to 4-chloro-
benzaldehyde. Moreover, the catalytic activity did not show
appreciable decrease after, at least, three cycles. These results
indicate that, as an effective heterogeneous catalyst, polymer 3
has also the great advantage of reusability. To the best of our
22 Y. M. Shen, M. X. Zhao, J. Xu and Y. Shi, Angew. Chem., Int. Ed.,
2006, 45, 8005.
23 H. Wu, X. M. Chen, Y. Wan, L. Ye, H. Q. Xin and D. Q. Shi,
Tetrahedron Lett., 2009, 50, 1062.
24 D. W. C. MacMillan, Nature, 2008, 455, 304.
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972 | Chem. Commun., 2010, 46, 970–972