Diacetylene-Based C 2h-Symmetric Monomers for Two-Dimensional-Polymer Synthesis

Article abstract of DOI:10.1055/s-0036-1588664

Two linear monomers with two terminal photoreactive groups (anthracene or maleimide) embedded in a diacetylene skeleton were synthesized for two-dimensional-polymer synthesis. Both of them were crystallized and their single-crystal structures were solved. It was found that the size of terminal groups can be critical for diacetylene's arrangement. The crystal structure of dimaleimide monomer revealed that maleimide groups strongly stacking in antiparallel and the photo-induced [2+2] cycloaddition of stacked maleimides was preliminary studied.

Full text of DOI:10.1055/s-0036-1588664

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Georg Thieme Verlag Stuttgart · New York
2016, 27, A–F
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letter
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M. Song et al.
Letter
Diacetylene-Based C -Symmetric Monomers for Two-Dimensional-
2h
Polymer Synthesis
Mengyao Song
Hanbing Ma
Minghan Ren
Zhaoquan Ai
Ming Li*
Polymerization
Hubei Collaborative Innovation Center for Advanced Organic
Chemical Materials & Laboratory for the Synthesis and Application
of Organic Functional Molecules, Ministry of Education & College
of Chemistry and Chemical Engineering, Hubei University,
O
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y
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N
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430062, Wuhan, P. R. of China
limingljy@163.com
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Received: 20.09.2016
Accepted after revision: 06.11.2016
Published online: 30.11.2016
ate linear parallel fashion, which is feasible for topopoly-
merization to form polydiacetylenes along x axis (Figure 1,
7,8
9,10
DOI: 10.1055/s-0036-1588664; Art ID: st-2016-w0622-l
b). The resulting polydiacetylene is stable over 300 °C.
On another hand, terminal groups face to face (ftf) stack,
which is feasbile for the topodimerization to form polymers
along y axis. Anthracene is topochemically reactive while it
ftf stacks (Figure 1, d), but the resulting dimer generally de-
composes over 100 °C.11 In order to achieve high thermal
stability, we further utilized maleimide as terminal groups
Abstract Two linear monomers with two terminal photoreactive
groups (anthracene or maleimide) embedded in a diacetylene skeleton
were synthesized for two-dimensional-polymer synthesis. Both of them
were crystallized and their single-crystal structures were solved. It was
found that the size of terminal groups can be critical for diacetylene’s
arrangement. The crystal structure of dimaleimide monomer revealed
that maleimide groups strongly stacking in antiparallel and the photo-
induced [2+2] cycloaddition of stacked maleimides was preliminary
studied.
owing to the high thermal stability of the maleimide di-
mer.1
2,13
Schmidt demonstrated that when a couple of ole-
fins in single crystals ftf pack with a distance of 3.5–4.2 Å,
14,15
Key words two-dimensional polymer, single crystal, topochemistry,
diacetylene, maleimide
photoinduced [2+2] cyclization can be carried out.
Eventhough it is still no reported topodimerization be-
tween maleimides, we expected that toporeaction is possi-
ble (Figure 1, e) since [2+2] cyclization of maleimides in
solution have been well documented.1
A two-dimensional (2D) polymer is a free-standing and
covalently bonded polymer sheet with a few atoms thick
6,17
1
and long-range internal order, which may have potential
Monomer 1 was simply synthesized from propargyl al-
cohol and anthracene-9-carboxylic acid in two steps
(Scheme 1, a). Hexa-2,4-diyne-1,6-diol (3) was prepared by
CuCl/tetramethyl ethylenediamine (TMEDA) catalyzed air-
applications in nanoseperators and electronics. Since this
concept was promoted in 2009, tens of cyclic monomers
were synthesized and very few of them were successfully
2
18
applied in 2D-polymer synthesis in single crystals. These
oxidization of propargyl alcohol. Double Steglich esterifi-
monomers always have three photoreactive (anthracene)
cation19 between 3 and anthracene-9-carboxylic acid af-
3
20
units embedded in a C skeleton and in this case, resulting
2
forded monomer 1. Single crystals were grown from ethyl
3v
D polymers bearing rigid hexgon pores (Figure 1, a).4–6
acetate by slow evaporation in a glass vessel, however, irra-
diating (λ = 365 or 254 nm) or heating these crystals led to
no reactions. X-ray crystallography analysis disclosed the
reason of its nonreactivity. There are neither linear parallel
stacking between diacetylenes, nor feasible ftf stacking be-
tween anthracenes. In a layer, neighboring anthracenes are
partially off-set stacking with a distance of 3.485 Å, while
diacetylenes are arranged in parallel with distance further
than 10 Å (Scheme 1, b). Such far distance may be due to
the large steric hindrance of anthrance, which repels di-
acetylene’s stacking.
Synthesis of such monomers are generally not simple, that
is, the final cyclization reaction needs to be performed in
diluted solution and always generates side products such as
oligomers. In order to explore 2D polymers with different
topologies from simple monomers, we designed C -sym-
2h
metric monomers with two terminal topochemically reac-
tive groups (anthracene or maleimide) embedded in a di-
acetylene skeleton (Figure 1, c) and expected to utilize them
to synthesize 2D polymers in single crystals (Figure 1, b).
The resulting 2D polymers from them have flexible square
pores. In single crystals, diacetylenes stack in an appropri-
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M. Song et al.
Letter
Figure 1 (a) Reported monomers having three anthracene units embedded in a C3v skeleton for the synthesis of 2D polymer (bond black squares
represent anthracene units; reproduced from ref. 3). (b) Synthesis of 2D polymer in single crystals from C2h-symmetric monomers (black spots repre-
sent terminal photoreactive groups). (c) Molecular structure of monomer 1 and 2. (d) Dimerization of anthracene. (e) Dimerization of maleimide via
[
2+2] cyclization.
In order to confirm the packing of maleimide in single
of furan under thermal treatment of 4.25 The second proce-
dure has three steps. Propargyl maleimide 8 was synthe-
sized by dehydration condensation between propargyl
amine and maleic anhydride in two steps.26 Compound 8
was further atmospherically oxidized yielding monomer 2.
By slow evaporation at ambient temperature, colorless
plane crystals can be obtained from the solution of mono-
mer 2 in THF and toluene (v/v = 1:1). These crystals are
quite thin with a large lateral size (ca. 1 cm; see Figure 3, a).
X-ray crystallography analysis demonstrated that maleim-
ides stacking in antiparallel. Olefinic groups between
neighboring monomers are aligned with strong interac-
tions, as indicated by a distance of 3.923 Å (Figure 2, a). This
distance is in the range for topochemical [2+2] cyclization
crystals, a known compound 9 embedded with two ma-
leimide groups was firstly synthesized (Scheme 2, a). Com-
pound 9 was synthesized from 4,4′-oxydianiline and maleic
21
anhydride by dehydration–condensation. Crystals were
obtained from chloroform. X-ray crystallography analysis
reveals that both terminal maleimides are off-set antiparal-
lel arranged with their neighbors (Scheme 2, b). Even
though distances are not in the range of Schmidt [2+2] cy-
clization (irradiation of this crystal at 365 or 254 nm led to
no reaction), this crystal structure indicates that maleimide
has a tendency to stack in an antiparallel fashion in single
crystals.
Monomer 2 was synthesized with two synthetic proce-
22
14
dures (Scheme 3). The first procedure has five steps. A
Diels–Alder reaction between maleic anhydride and furan
followed by ammoniation gave the known compound 6.23
Nucleophilic substitution of propargyl bromide with 6 pro-
suggested by Schmidt. Another pair of olefinic groups be-
tween neighboring monomers are also aligned in parallel,
but the distance is too far (4.826 Å) for the [2+2] cyclization.
Moreover, diacetylenes arrange in a linear fashion but the
distance of potential polymerizing carbons are 4.791 Å,
24
duced the compound 5, which was atmospherically oxi-
7,8
dized with CuCl–TMEDA catalyst to yield the key interme-
which is still not suitable for the topopolymerization but
18
diate 4. The monomer 2 was finally obtained by removal
much closer than that in single crystals of monomer 1. This
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M. Song et al.
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Scheme 1 (a) Synthetic procedure of monomer 1 (numbers in the chemical structure of monomer 1 are used to label its NMR data). (b) Crystal
structure of monomer 1. Hydrogens are omitted for clarity. Distance unit: Å.
Scheme 2 (a) Synthetic procedure of bismaleimide 9. (b) Crystal structure of bismaleimide 9. Hydrogen atoms are omitted for clarity. Distance unit: Å.
closer distance may be due to the smaller size of maleimide.
It should be noted that the precursor 4 has a similar inter-
nal packing in its single crystal (Figure 2, b). Neighboring
furanmaleimide groups are off-set aligned with strong in-
teractions, as indicated by a distance of ca. 3.9 Å, while di-
acetylenes arrange in a linear fashion but the distance
(6.627 Å) of potential polymerizing carbons is much further
than that in the single crystal of monomer 2. Such far distance
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M. Song et al.
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O
Br
O
O
O
O
furan
NH3 (aq)
reflux
O
Et2O, rt
O
O
HN
DMF, K CO
2
3
7
6
60 °C
O
O
O
O
O
CuCl
TMEDA
O
O
N
N
acetone
N
O
40 °C
O
O
O
5
4
xylene
reflux
1
2
, maleic anhydride
acetone
reflux
O
O
O
CuCl
TMEDA
N
NH2
N
N
, xylene, reflux
acetone
40 °C
O
O
O
8
2
Scheme 3 Synthetic procedures of monomer 2
may be due to the steric hindrance of furanmaleimide, as
the similar effect of anthracenes in single crystals of mono-
mer 1.
with crystals and then irradiated by an UV lamp (λ = 365
nm) for 15 hours. After irradiation, colorless crystals me-
chanically disintegrated, so as to lose X-ray quality (Figure
3, b). In order to demonstrate the chemical structure of the
irradiated material, two model compounds (N-ethyl ma-
leimide dimer and maleimide dimer) were synthesized
(Supporting Information, compounds 10 and 11). It was
found that in IR spectra characteristic vibrations of cyclobu-
tane ring are at ca. 748 and 647 cm–1 (Supporting Informa-
tion, Figures S9, S10). In Raman spectra, absorptions of ma-
leimide are at ca. 304, 1052, 1588 cm and cyclobutane
ring are at ca. 978 and 1186 cm–1 (Supporting Information,
Figures S11, S12). Through comparing IR and Raman spec-
tra with model compounds, a cyclobutane structure was
preliminarily established in the irradiated material (Figure
As in the crystal of monomer 2, olefinic groups of ma-
leimide between neighbors are aligned in the range for to-
14
pochemical [2+2] cyclization, topochemical reaction was
attempted by light irradiation. A glass slide was charged
–1
6
, c and d). In IR spectra, stretching vibrations of HC= (3165,
–1
3101 cm ) and out-of-plane bending vibration of cis-
–1
HC=CH (696 cm ) totally disappeared while characteristic
–1
vibrations of cyclobutane ring at 732 and 614 cm in-
creased. In Raman spectra, absorptions of maleimide at
3
00, 1042, 1584 cm–1 was completely vanished while ab-
–1
sorptions of cyclobutane ring at 980 and 1181 cm ap-
peared. It should be noted that after irradiation the diacety-
lene (diacetylene and polydiacetylene are Raman active but
not IR active) absorption at ca. 2270 cm–1 retained and
there are no characteristic absorptions of polydiacetylene
–1 27
at ca. 1470 and 2050 cm , which reveals that diacetylene
is nonreactive in this crystal at all. Unfortunately, this irra-
diated product is insoluble in any common solvents so it is
impossible to measure it by liquid NMR spectroscopy or de-
termine its molecular weight by GPC. What even more
tough is that the growth of feasible single crystals is very
difficult. Only a small amount of crystals was obtained at
one time. We attempted a lot of times, but most of time,
monomer 2 was easy to form needles, whose crystal struc-
ture cannot be solved. So it is hard to get enough materials
for further characterization such as solid-state NMR spec-
Figure 2 Crystal structure of monomer 2 (a) and compound 4 (b). Hy-
drogen atoms are omitted for clarity. Distance unit: Å.
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Figure 3 Optical microscope (OM) images of monomer 2 crystals (a) before and (b) after irradiation; (c) IR and (d) Raman spectra of monomer 2
before and after irradiation; (e) proposed structure of the irradiated product.
troscopy and powder X-ray diffraction. Further demonstra-
tion of its structure is possible only when enough crystal
material can be obtained. Anyway, from above Raman and
IR measurements, we propose a possible structure of the
insoluble product as shown in Figure 3 (e).
Differential scanning calorimetry (DSC) and thermo-
gravimetric analysis (TGA) measurements were used to
evaluate the thermal behavior of the irradiated product
thesized. Single crystals of them have been obtained and X-
ray structures were solved. They all show layered struc-
tures but are still infeasible for 2D-polymer synthesis. We
found that terminal groups all have some tight stacking and
sizes of terminal groups can be critical for diacetylene’s
stacking. When terminal groups are larger, diacetylenes are
arranged further to each other. Within these crystals, we
found maleimides can be arranged in antiparallel with their
olefin groups strongly stacking, and their Schmidt to-
pochemical dimerization was preliminary studied. Even
though these monomers are still not feasible for 2D polym-
erization, we believe our studies will give a clue for the fur-
ther monomer design for 2D-polymer synthesis and what is
more, an interesting solid-state approach for polyimide
synthesis.
(Supporting Information, Figures S13, 14). The DSC curve
shows there is no sharp endotherm peak at 147 °C (melting
point of monomer 2) but a quite broad, smooth, and weak
endotherm area from 30–250 °C (21.922 kJ per mol repeat-
ing unit), which means the irradiated product is not mono-
mer 2 anymore and it is stable and does not have a glass
transition temperature (Tg) lower than 250 °C. The TGA
measurement shows a similar stability pattern because the
weight loss below 6% up to 250 °C. This minor weight loss
may result from the removal of moisture.
Acknowledgment
In summary, two monomers (1, 2) with two terminal
photoreactive groups (anthracene or maleimide) embed-
ded in a diacetylene skeleton have been successfully syn-
Support of this work by the Science and Technology Foundation of
Hubei Provincial Department of Education (Q2015003) is gratefully
acknowledged. We thank Dr. Yuhong Zhang (at Hubei University) for
her support in Raman spectroscopical matters.
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M. Song et al.
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Supporting Information
hexylcarbodimide (1128 mg, 5 mmol), and 4-dimethylamino-
pyridine (28 mg, 0.2 mmol) in 1-methyl-2-pyrrolidone (10 mL)
under argon atmosphere. The mixture was stirred at 40 °C for 5
d. The yellow mixture was washed with water and passed a
silicon chromatographic column affording monomer 1 as a
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0036-15886.
S
u
p
p
ortioIgnfrm oaitn
S
u
p
p
ortioIgnfrm oaitn
1
yellow solid (820 mg, 1.6 mmol, 79%); mp >250 °C. H NMR (400
References and Notes
MHz, CDCl ): δ = 8.56 (s, 2 H, H-6), 8.08 (d, J = 8 Hz, 4 H, H-2 or
3
H-5), 8.03 (d, J = 8 Hz, 4 H, H-2 or H-5), 7.57 (m, 4 H, H-3 or H-
4
(
(
(
(
1) Sakamoto, J.; Heijst van, J.; Lukin, O.; Schlüter, A. D. Angew.
Chem. Int. Ed. 2009, 48, 1030.
2) Servalli, M.; Trapp, N.; Wörle, M.; Klärner, F.-G. J. Org. Chem.
), 7.48 (m, 4 H, H-3 or H-4), 5.29 (s, 4 H, H-1) ppm. 13C NMR
(
150 MHz, CDCl ): δ = 168.81, 131.03, 130.16, 128.78, 127.49,
3
1
26.24, 125.69, 124.91, 73.86, 71.17, 53.36 ppm. HRMS (LC-MS
2
016, 81, 2572.
3) Kissel, P.; Schlüter, A. D.; Sakamoto, J. Chem. Eur. J. 2009, 15,
955.
+
TOF, formic acid): m/z calcd for C36H22O4 [MH] : 519.1591;
found: 519.1587.
8
(
21) Grigoras, M.; Sava, M.; Colotin, G.; Simionescu, C. I. J. Appl.
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22) Synthesis of Monomer 2
4) Kissel, P.; Erni, R.; Schweizer, W. B.; Rossell, M. D.; King, B. T.;
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(a) A solution of compound 4 (0.383 g, 0.95 mmol) in xylene
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(200 mL) was refluxed for 3 h under an argon atmosphere. After
reaction, the hot solution was quickly filtered to remove insolu-
ble byproducts and then concentrated by rotary vacuum.
Monomer 2 was obtained as white solid from the cooling solu-
tion (0.168 g, 0.63 mmol, 66.3%). (b) An open beak was charged
with CuCl (0.102 g, 1 mmol) and TMEDA (0.121 g, 1 mmol) in
acetone (2 mL). After stirring for 3 min, compound 8 (0.654 g,
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4
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(
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1
(
0.131 g, 0.49 mmol, 20.4%); mp 147 °C. H NMR (400 MHz,
(
13
CDCl ): δ = 6.75 (s, 2 H, CH), 4.33 (s, 2 H, CH ) ppm. C NMR
3
2
11721.
(
150 MHz, CDCl ): δ = 169.18, 134.72, 72.13, 67.52, 27.58 ppm.
3
(
(
(
(
(
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8
2
4
269.0562; found: 269.0567.
(
23) Kötteritzsch, J.; Stumpf, S.; Hoeppener, S. J.; Vitz, M. D.; Hager,
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(
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20) Synthesis of Monomer 1
5
A sealed tube was charged with compound 3 (221 mg, 2 mmol),
9-anthracene carboxylic acid (1115 mg, 5 mmol), N,N-dicyclo-
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, A–F