Chiral teleinduction in asymmetric polymerization of 3,5-bis(hydroxymethyl) phenylacetylene having a chiral group via a very long and rigid spacer at 4-position

Article abstract of DOI:10.1246/cl.2012.244

A new polymer prepared by polymerization of 3,5-bis-(hydroxymethyl) phenylacetylene having a chiral menthyl group via a very long and rigid spacer by an achiral rhodium complex with triethylamine as an initiator showed strong CD absorptions assigned to th

Full text of DOI:10.1246/cl.2012.244

doi:10.1246/cl.2012.244
244
Published on the web February 25, 2012
Chiral Teleinduction in Asymmetric Polymerization of 3,5-Bis(hydroxymethyl)phenylacetylene
Having a Chiral Group via a Very Long and Rigid Spacer at 4-Position
Yunosuke Abe,1 Toshiki Aoki,*1 Hongge Jia,2 Shingo Hadano,3 Takeshi Namikoshi,4
Yuriko Kakihana,1 Lijia Liu,1 Yu Zang,1 Masahiro Teraguchi,1 and Takashi Kaneko1
1Graduate School of Science and Technology, Niigata University, 2-8050 Ikarashi, Nishi-ku, Niigata 950-2181
2Department of Polymeric Material and Engineering, Qiqihar University, Wenhua street 42, Qiqihar, P. R. China
3Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, Kanagawa 226-8503
4Material Science and Engineering, Kitami Institute of Technology, 165 Koen-cho, Kitami, Hokkaido 090-8507
(Received December 9, 2011; CL-111180; E-mail: toshaoki@eng.niigata-u.ac.jp)
A new polymer prepared by polymerization of 3,5-bis-
(hydroxymethyl)phenylacetylene having a chiral menthyl group
via a very long and rigid spacer by an achiral rhodium complex
with triethylamine as an initiator showed strong CD absorptions
assigned to the main chain in spite of the long distance (23 ¡)
between the chiral group and the polymerizing group in the
monomer. This distance is the longest to the best of our
knowledge. In addition, switching between the two chiralities of
the resulting polymer was realized in the CD spectrum.
OH
R
H
OH
R
[Rh(nbd)Cl]2
Et3N
Toluene
n
OH
OH
1a, Poly(1a): R=
OCH2
O
O
1b, Poly(1b): R=
OCH2
O
O
Many kinds of chiral poly(substituted acetylene)s have been
reported because they have unique properties such as enantio-
selective recognition.1 There are two methods for synthesizing
them. One is polymerization of chiral monomers by achiral
initiators, asymmetric-induced polymerization (AIP)2 that we
reported for the first time and then many other chemists have
reported,3 and the other is polymerization of achiral monomers
by chiral initiators, helix-sense-selective polymerization
(HSSP)4 we reported first. The AIP was simple and many kinds
of chiral monomers were suitable for AIP, while the HSSP
needed two hydroxy groups in the monomers and, therefore,
structures of monomers suitable for HSSP are limited. Many
AIP’s of many kinds of chiral monomers were reported which
were not only substituted acetylenes but also other types of
chiral monomers.5 However, to realize AIP effectively, the
distance between the chiral group and the polymerizing group in
the monomers for AIP should be small. For example, in chiral
arylisocyanates (S1 in Supporting Information),6 propiolic esters
(S2),7 and bulky vinyl monomers (S3),8 the longest values for
their distances in the monomers which were suitable for AIP
were 9, 11, and 12 ¡ respectively (See Table S1 in SI15). Since
the distances must be small, variation of structures of monomers
for AIP was limited.
1c, Poly(1c): R=
OC12H25
Scheme 1. Synthesis of poly(1a) and poly(1b) having hy-
droxymethyl groups at 3,5-positions.
H
[Rh(nbd)Cl]2
Et3N
R
R
Toluene or Et3N
n
2a, Poly(2a): R=
OCH2
O
O
2b, Poly(2b): R=
O
Si
Si
Scheme 2. Synthesis of poly(2a) and poly(2b) without
hydroxymethyl groups at 3,5-positions.
realize chiral teleinduction, we selected 3,5-bis(hydroxymeth-
yl)phenylacetylene (1a in Scheme 1) having a chiral menthyl
group11 via a very long (23 ¡)12 and rigid spacer as a chiral
monomer for AIP (Scheme 1). The two hydroxy groups are
expected to make the backbone of the resulting polymer more
rigid. In addition, switching between the two chiralities will be
reported in CD spectra. To investigate effect of the length of the
spacers on AIP, 1b which has a shorter spacer (16 ¡) than 1a was
synthesized (Scheme 1). To investigate the effect of the two
hydroxy groups on AIP, 2a (Scheme 2) which has the same
spacer as 1a but no hydroxy groups was synthesized. In
addition, to compare the effect of rigidity of the spacers on AIP,
2b was used which has a very flexible spacer. The distances
between the chiral group and the polymerizing group of 1a, 1b,
2a, and 2b were 23, 16, 23, and 10 ¡, respectively (Table 1 and
Scheme 2).12
Amabilino et al.9 reported AIP of a chiral isocyanide (S4)
where the distance between the chiral group and the polymer-
izing group was 21 ¡ and [ª] for the resulting polymers was only
990. They called it chiral teleinduction. Percec et al.10 reported
AIP of chiral phenylacetylenes having dendron structure as a
spacer (S5). The distance between the chiral group and the
polymerizing group was 21 ¡ and [ª] for the resulting polymers
was less than 2500. Therefore, to our knowledge, 21 ¡ is the
longest distance between the chiral group and the polymerizing
group in monomers suitable for AIP. Here in this paper we call
asymmetric induction in polymerization of chiral monomers
where the distance between the chiral group and the polymer-
izing group are more than 21 ¡, chiral teleinduction. In order to
Chem. Lett. 2012, 41, 244-246
© 2012 The Chemical Society of Japan
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245
Table 1. Chiral teleinduction in asymmetric-induced polymerization of chiral phenylacetylenesa
Monomer Polymer
20
20
b
e
b
f
½¡ꢀD
/°
Distancec
Yieldd
/%
Mw
½¡ꢀD
/°
[ª]435
/©103 deg cm2 dmol
g435
e
Code
Mw/Mn
¹1
¹8
/¡
/©105
/©10
1a
1b
2a
2bg
¹61.9
¹58.2
¹63.1
¹2.6
23
16
23
10
90.4
98.6
91.4
87.5
21
44
11
3.8
6.5
8.2
2.3
¹188
¹291
¹88.5
¹0.39
8.17
22.7
0.206
0
191
768
2.1
0
8.6
aMonomers 1a, 1b, and 2a: at room temperature for 6 h in toluene. [monomer] = 0.1 mol L¹1, [monomer]/[[Rh(nbd)Cl]2] = 100, 2b: at
c
room temperature for 4 h in Et3N; [2b] = 0.2 mol L¹1, [2b]/[[Rh(nbd)Cl]2] = 200. bIn CHCl3. Distances between an asymmetric
d
e
f
g
carbon and an ethynyl group were calculated by MMFF. Methanol insoluble part. By GPC. g = ([ª]/3300)/¾. From ref. 3n.
θ
θ
ε
ε
Wavelength/nm
Wavelength/nm
Figure 2. CD and UV-vis spectra of (A) 1a in CHCl3, and
poly(1a) in (B) CHCl3, (C) CHCl3/DMSO = 45/55 (v/v) and
(D) CHCl3/DMSO = 95/5 ((D) was the solution prepared by
addition of CHCl3 to the solution C).
Figure 1. CD and UV-vis spectra of poly(1a), poly(1b), and
poly(2a) in CHCl3.
These chiral monomers were polymerized by an achiral
rhodium complex ([Rh(nbd)Cl]2) to yield high MW (=106)
polymers in high yields as shown in Table 1. Since specific
rotation values for poly(1a) and poly(1b) were much higher than
those of the corresponding monomers, chiral inductions to the
main chains were suggested. In addition, since CD signals
assigned to their main chain were observed for poly(1a) and
poly(1b), chiral induction to the main chains was confirmed
(Figure 1). Therefore, AIP of 1a where the distance between the
chiral group and the polymerizing group is 23 ¡ was realized,
i.e., chiral teleinduction in AIP of 1a was achieved. In addition,
the [ª] value was large (=8170) and much larger than those of
poly(S4) and poly(S5).
poly(1c) (Figure S115), the backbone of poly(1a) was main-
tained by intramolecular hydrogen bonds.4 Rigid backbones can
accept chiral information more effectively from the pendant
chiral groups.14 Therefore, poly(1a) showed much higher g
values than poly(2a) (Table 1). Poly(2b) having a short spacer
(10 ¡) showed no CD although poly(2a) having a longer spacer
(23 ¡) showed CD. It was thought that 2b was not suitable for
AIP because the spacer in 2b was so flexible that chiral
induction was difficult. In summary, 1a was suitable for AIP in
spite of the long distance of the spacer because of rigidity of
the spacer and the main chain. Chiral teleinduction in AIP was
achieved.
The value of g for poly(1a) was 100 times higher than that
for poly(2a), although they had the same spacers and chiral
groups. The difference between the two monomers was that 1a
has two hydroxy groups and 2a does not. The two hydroxy
groups in the monomer unit can make the backbone of the
resulting polymer more rigid by making intramolecular hydro-
gen bonds, judging from our previous results that phenyl-
acetylene monomers having two hydroxy groups (1c) yielded
very rigid polymers having one-handed helical backbone
maintained by intramolecular hydrogen bonds.4,13 Judging from
similarity of the CD and UV spectra for poly(1a) (Figure 1) and
When DMSO as a polar solvent was added to a chloroform
solution of poly(1a) and poly(1b) showing CD around 435 nm
assigned to the main chain (Figures 2B and S2A,15 respective-
ly), the CD disappeared and the UV band shifted to longer
wavelengths (Figures 2C and S2B,15 respectively), because the
intramolecular hydrogen bonds were broken, the helical con-
jugated conformation was extended, and the one-handed
conformation was racemized (Similar phenomenon in poly(1c)
was reported by our group (Figure S115)).4 This was supported
by the fact that poly(2a) having no hydroxy groups showed no
change when DMSO was added (Figure S315).
Chem. Lett. 2012, 41, 244-246
© 2012 The Chemical Society of Japan
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246
Polymer 1995, 36, 2403. i) T. Aoki, K.-i. Shinohara, T. Kaneko, E.
Oikawa, Macromolecules 1996, 29, 4192. j) T. Aoki, Y. Kobayashi, T.
Kaneko, E. Oikawa, Y. Yamamura, Y. Fujita, M. Teraguchi, R.
Nomura, T. Masuda, Macromolecules 1999, 32, 79. k) T. Kaneko, T.
Yamamoto, T. Aoki, E. Oikawa, Chem. Lett. 1999, 623. l) K.-i.
Shinohara, T. Aoki, T. Kaneko, J. Polym. Sci., Part A: Polym. Chem.
2002, 40, 1689. m) M. Teraguchi, J.-i. Suzuki, T. Kaneko, T. Aoki, T.
Masuda, Macromolecules 2003, 36, 9694. n) T. Aoki, T. Fukuda, K.-i.
Shinohara, T. Kaneko, M. Teraguchi, M. Yagi, J. Polym. Sci., Part A:
Polym. Chem. 2004, 42, 4502. o) M. Teraguchi, K. Mottate, S.-Y. Kim,
T. Aoki, T. Kaneko, S. Hadano, T. Masuda, Macromolecules 2005, 38,
6367.
a) T. Aoki, T. Kaneko, N. Maruyama, A. Sumi, M. Takahashi, T. Sato,
M. Teraguchi, J. Am. Chem. Soc. 2003, 125, 6346. b) T. Sato, T. Aoki,
M. Teraguchi, T. Kaneko, S.-Y. Kim, Polymer 2004, 45, 8109. c) S.
Hadano, M. Teraguchi, T. Kaneko, T. Aoki, Chem. Lett. 2007, 36, 220.
d) H. Katagiri, T. Kaneko, M. Teraguchi, T. Aoki, Chem. Lett. 2008,
37, 390. e) Y. Umeda, T. Kaneko, M. Teraguchi, T. Aoki, Chem. Lett.
2005, 34, 854. f) T. Kaneko, Y. Umeda, T. Yamamoto, M. Teraguchi, T.
Aoki, Macromolecules 2005, 38, 9420. g) T. Kaneko, Y. Umeda, H.
Jia, S. Hadano, M. Teraguchi, T. Aoki, Macromolecules 2007, 40,
7098. h) S. Hadano, T. Kishimoto, T. Hattori, D. Tanioka, M.
Teraguchi, T. Aoki, T. Kaneko, T. Namikoshi, E. Marwanta, Macro-
mol. Chem. Phys. 2009, 210, 717. i) H. Jia, M. Teraguchi, T. Aoki, Y.
Abe, T. Kaneko, S. Hadano, T. Namikoshi, E. Marwanta, Macro-
molecules 2009, 42, 17. j) L. Liu, Y. Zang, S. Hadano, T. Aoki, M.
Teraguchi, T. Kaneko, T. Namikoshi, Macromolecules 2010, 43, 9268.
k) L. Liu, Y. Oniyama, Y. Zang, S. Hadano, T. Aoki, M. Teraguchi, T.
Kaneko, T. Namikoshi, E. Marwanta, Polymer 2010, 51, 2460.
a) S.-J. Su, N. Kuramoto, Chem. Mater. 2001, 13, 4787. b) T. Oishi, K.
Kagawa, H. Nagata, Polymer 1997, 38, 1461. c) T. Nakano, D.
Tamada, J.-i. Miyazaki, K. Kakiuchi, Y. Okamoto, Macromolecules
2000, 33, 1489. d) T. Sakaguchi, G. Kwak, T. Masuda, Polymer 2002,
43, 3937. e) T. Nakano, O. Nakagawa, M. Tsuji, M. Tanikawa, T. Yade,
Y. Okamoto, Chem. Commun. 2004, 144. f) G. Wulff, Angew. Chem.,
Int. Ed. Engl. 1989, 28, 21. g) G. Wulff, P. K. Dhal, Macromolecules
1990, 23, 4525. h) G. Wulff, H. Schmidt, H. Witt, R. Zentel, Angew.
Chem., Int. Ed. Engl. 1994, 33, 188. i) T. Kakuchi, A. Narumi, H.
Kaga, T. Ishibashi, M. Obata, K. Yokota, Macromolecules 2000, 33,
3964. j) T. Kakuchi, A. Narumi, H. Kaga, Y. Yamauchi, M. Obata, T.
Uesaka, K. Yokota, Macromolecules 2001, 34, 38.
In the case of poly(1a), when the CD around 435 nm
assigned to the main chain disappeared (Figure 2C), a new CD
signal appeared at 300 nm. Since this signal was identical to that
for the corresponding monomer, 1a (Figure 2A), this was
assigned to a chiral structure of the monomer unit. When to the
solution of chloroform/DMSO (45/55 (v/v)) (Figure 2C)
chloroform was added, the resulting solution of chloroform/
DMSO (95/5 (v/v)) showed almost the same CD signals
(Figure 2D) as the original solution of chloroform (Figure 2B).
Therefore, change in CD by changing polarity of solvents
was reversible (Figure S415). In conclusion, chiral switching
between two kinds of chiral structures, one handed helical
backbone and chiral pendant groups has been realized for the
first time. On the other hand, in the case of poly(1b) having the
same chiral groups and shorter spacers, when the CD around
435 nm assigned to the main chain disappeared, no new CD
signals appeared (Figure S2B15). When to the solution of
chloroform/DMSO (55/45 (v/v)) chloroform was added, the
resulting solution of chloroform/DMSO (95/5 (v/v)) showed
almost the same CD signals (Figure S2C15) as the original
solution in chloroform (Figure S2A15). Therefore, the change
in CD by changing polarity of solvents was reversible
(Figure S515). In summary, chiral switching between on and
off in CD signals for one handed helical backbone was observed
(Figure S215) similarly to the findings we reported for poly(1c)
before (Figure S115).4 In the case of poly(2a) having no hydroxy
groups, no response by changing polarity of the solvent was
observed (Figure S315). Therefore, only in poly(1a) reversible
response of their CD between two kinds of chiralities by
changing polarity of the solvents was observed because the one-
handed helicity was kept by their intramolecular hydrogen bonds
and the chiral phenylethynylphenyl group absorbed at a more
than 250 nm where 1b did not have any absorbance.
4
5
In conclusion, a new polymer prepared by polymerization of
a chiral phenylacetylene having two hydroxy groups and a chiral
menthyl group via a very long and rigid spacer by an achiral
rhodium complex with triethylamine as an initiator showed
strong CD absorptions assigned to the main chain in spite of the
long distance (23 ¡) between the chiral group and the polymer-
izing group in the monomer. Therefore, chiral teleinduction was
achieved. This distance is the longest in AIP to the best of our
knowledge. In addition, reversible switching in CD between
one-handed helical backbone and chiral pendant groups by
changing polarity of the solvent has been realized for the first
time.
6
7
K. Maeda, Y. Okamoto, Macromolecules 1998, 31, 5164.
H. Nakako, Y. Mayahara, R. Nomura, M. Tabata, T. Masuda,
Macromolecules 2000, 33, 3978.
J. Cui, X. Lu, A. Liu, X. Wan, Q. Zhou, Macromolecules 2009, 42,
7678.
a) D. B. Amabilino, E. Ramos, J.-L. Serrano, T. Sierra, J. Veciana,
Polymer 2005, 46, 1507. b) D. B. Amabilino, J.-L. Serrano, T. Sierra,
J. Veciana, Mendeleev Commun. 2004, 14, 256. c) E. Gomar-Nadal,
J. Veciana, C. Rovira, D. B. Amabilino, Adv. Mater. 2005, 17, 2095.
d) D. B. Amabilino, E. Ramos, J.-L. Serrano, T. Sierra, J. Veciana,
J. Am. Chem. Soc. 1998, 120, 9126.
8
9
10 V. Percec, J. G. Rudick, M. Peterca, M. Wagner, M. Obata, C. M.
Mitchell, W.-D. Cho, V. S. K. Balagurusamy, P. A. Heiney, J. Am.
Chem. Soc. 2005, 127, 15257.
11 In our previous reports on the AIP, we found polymers having menthyl
groups2 had tendency to show stronger CD peaks than others such as
pinanyl groups.3l,3n
12 Distances between a polymerizable group and an asymmetric carbon of
all the compounds in this report were calculated by MMFF.
13 When we attempted the HSSP of phenylacetylenes having two
methoxymethyl,4a hydroxy, hydroxyethyl, or hydroxybutyl groups
instead of the two hydroxymethyl groups, the resulting polymers had
no CD. Therefore, the two hydroxymethyl groups were found to be
very important.
14 Since the CD spectra for 1a (Figure 2A) and the pendant groups
(Figure 2C) in poly(1a) were the same, the effect of interaction
between the chiral pendant groups on the chiral teleinduction to the
main chain was thought to be small.
References and Notes
1
a) T. Aoki, T. Kaneko, M. Teraguchi, Polymer 2006, 47, 4867. b) E.
Yashima, K. Maeda, H. Iida, Y. Furusho, K. Nagai, Chem. Rev. 2009,
109, 6102. c) S. Ito, K. Nozaki, in Catalytic Asymmetric Synthesis, 3rd
ed., ed. by I. Ojima, Wiley, Hoboken, 2010, Chap. 13, pp. 931-985.
T. Aoki, M. Kokai, K.-i. Shinohara, E. Oikawa, Chem. Lett. 1993,
2009.
a) Y. Shirakawa, Y. Suzuki, K. Terada, M. Shiotsuki, T. Masuda, F.
Sanda, Macromolecules 2010, 43, 5575. b) J. Qu, F. Sanda, T. Masuda,
Eur. Polym. J. 2009, 45, 448. c) J. Qu, F. Jiang, H. Chen, F. Sanda, T.
Masuda, J. Polym. Sci., Part A: Polym. Chem. 2009, 47, 4749. d) K.
Terada, T. Masuda, F. Sanda, Macromolecules 2009, 42, 913. e) Y.
Suzuki, M. Shiotsuki, F. Sanda, T. Masuda, Chem.®Asian J. 2008, 3,
2075. f) T. Masuda, J. Polym. Sci., Part A: Polym. Chem. 2007, 45,
165. g) E. Yashima, S. Huang, T. Matsushima, Y. Okamoto, Macro-
molecules 1995, 28, 4184. h) K.-i. Shinohara, T. Aoki, E. Oikawa,
2
3
15 Supporting Information is available electronically on the CSJ-Journal
Web site, http://www.csj.jp/journals/chem-lett/index.html.
Chem. Lett. 2012, 41, 244-246
© 2012 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/