Synthesis of Stereoregular Telechelic Poly(phenylacetylene)s: Facile Terminal Chain-End Functionalization of Poly(phenylacetylene)s by Terminative Coupling with Acrylates and Acrylamides in Rhodium-Catalyzed Living Polymerization of Phenylacetylenes

Article abstract of DOI:10.1021/jacs.1c00150

Various α,β-unsaturated carbonyl compounds, such as acrylates and acrylamides, were quantitatively introduced to the terminal chain end of poly(phenylacetylene)s by C-C bond formation with terminal organorhodium(I) species formed in the living polymerization of phenylacetylenes with a rhodium-based multicomponent catalytic system that we have recently developed, when these carbonyl compounds were used as terminating reagents. This enables the facile and versatile synthesis of stereoregular telechelic poly(phenylacetylene)s with various functional groups at both the initial and terminal chain ends because the components of aryl boronic acid derivatives used as initiators in our multicomponent catalytic system are quantitatively introduced to the initiating end of the resulting polymer.

Full text of DOI:10.1021/jacs.1c00150

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Synthesis of Stereoregular Telechelic Poly(phenylacetylene)s: Facile
Terminal Chain-End Functionalization of Poly(phenylacetylene)s by
Terminative Coupling with Acrylates and Acrylamides in Rhodium-
Catalyzed Living Polymerization of Phenylacetylenes
Kensuke Echizen, Tsuyoshi Taniguchi,* Tatsuya Nishimura, and Katsuhiro Maeda*
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ABSTRACT: Various α,β-unsaturated carbonyl compounds, such as acrylates and acrylamides, were quantitatively introduced to
the terminal chain end of poly(phenylacetylene)s by C−C bond formation with terminal organorhodium(I) species formed in the
living polymerization of phenylacetylenes with a rhodium-based multicomponent catalytic system that we have recently developed,
when these carbonyl compounds were used as terminating reagents. This enables the facile and versatile synthesis of stereoregular
telechelic poly(phenylacetylene)s with various functional groups at both the initial and terminal chain ends because the components
of aryl boronic acid derivatives used as initiators in our multicomponent catalytic system are quantitatively introduced to the
initiating end of the resulting polymer.
polymers with a cis geometry,3c which has been reported to be
INTRODUCTION
■
a prerequisite for the formation of a helical conformation of the
Poly(phenylacetylene)s are important π-conjugated polymers
as promising candidates of new functional materials because of
polyacetylene backbone.4 Furthermore, well-controlled living
polymerization of phenylacetylenes by rhodium catalysis has
been developed.5 In representative seminal works, Noyori6 and
Masuda7 independently reported well-controlled living poly-
merization of phenylacetylenes by well-defined rhodium(I)
complexes derived from the commercially available
bicyclo[2.2.1]hepta-2,5-diene rhodium(I) chloride dimer [Rh-
(nbd)Cl]2. In the polymerization of phenylacetylenes using
Noyori’s system consisting of the rhodium(I) complex
Rh(CCPh)(nbd)(PPh3)2 and 4-(dimethylamino)pyridine
(DMAP), an initiating end functionalization of poly-
(phenylacetylene)s is virtually impossible because it is
the properties of their rigid π-conjugated polyene backbones,
including optoelectronic properties, high gas permeability, and
liquid crystallinity.1 Moreover, many polyacetylenes including
poly(phenylacetylene)s form a helical conformation, for which
the helix sense can be controlled by introducing chiral groups
into the pendants, using noncovalent interactions with chiral
compounds, or using a chiral catalyst during the polymer-
ization reaction. These helical polyacetylenes with a controlled
helix sense have potential applications to functional chiral
materials such as chiral recognition materials, asymmetric
catalysts, nonlinear optical materials, and ferroelectric liquid
crystals.2
Poly(phenylacetylene)s are usually synthesized by transition-
metal-catalyzed polymerization of the corresponding phenyl-
acetylene monomers.3 Coordination−insertion polymerization
of phenylacetylenes by rhodium(I) catalysts is widely used as a
reliable method for synthesis of poly(phenylacetylene)s
because the catalysts are highly tolerant toward various
functional groups and usually produce highly stereoregular
Received: January 6, 2021
Published: February 18, 2021
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© 2021 American Chemical Society
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Figure 1. Living polymerization of phenylacetylenes by our multicomponent catalytic system and the controlled termination reaction (a) and
rhodium(I)-catalyzed conjugate addition of aryl boronic acid derivatives to α,β-unsaturated carbonyl compounds (b).
presumed that a hydrogen atom is introduced to an initiating
end of the polymer from a rhodium hydride species formed in
situ.6c In contrast, in Masuda’s system consisting of the
rhodium(I) complex [(nbd)Rh{C(Ph)CPh2}(PAr3)] and
PPh3, the triphenylvinyl group on the Rh complex is
introduced to the initiating end of poly(phenylacetylene)s.8
However, versatile functionalization of an initiating end of the
polymer by this catalytic system seems to be difficult because
functionalized triphenylvinyl lithium reagents, which are
precursors of the active rhodium complex, are not easily
accessible reagents.7c,9,10
Very recently, we developed a new method for well-
controlled living polymerization of phenylacetylenes using a
multicomponent catalytic system composed of [Rh(nbd)Cl]2,
aryl boronic acid derivatives, diphenylacetylene, 50% aqueous
KOH and PPh3 (Figure 1a).11 This method enables a facile
and versatile initiating end functionalization of poly-
(phenylacetylene)s because the aromatic residues of the aryl
boronic acids used are introduced to an initiating end of
poly(phenylacetylene)s along with at least two molecules of
diphenylacetylene. The isolated polymer has a hydrogen atom
at the terminal chain end, as depicted as structure 2 in Figure
1a when the terminal rhodium(I) species 1 is protonated by
acetic acid added as a quenching reagent after the polymer-
ization. If another phenylacetylene monomer is added instead
of acetic acid after consumption of the first monomer, block
copolymers are synthesized because the rhodium(I) species 1
at a polymer terminal chain end retains polymerization activity.
However, to the best of our knowledge, effective terminal chain
end functionalization of poly(phenylacetylene)s by end-
capping reagents (terminators), except for a proton, of living
polymerization has not been reported.
In organic synthesis, organoboronic acid derivatives are
widely used as building blocks in rhodium-catalyzed C−C
bond formation reactions.12 Rhodium-catalyzed conjugate
addition reactions between organoboronic acid derivatives
and α,β-unsaturated carbonyl compounds are some of the
most powerful tools (Figure 1b).13 Mechanistically, organo-
boronic acid derivatives can work as nucleophiles through
transformation to the corresponding organorhodium(I) species
7 by transmetalation with a hydroxy (R3 = H) or alkoxy (R3 =
alkyl) rhodium(I) catalyst 6. The formed organorhodium(I)
species 7 add to α,β-unsaturated carbonyl compounds 3 by a
coordination−insertion mechanism to form rhodium(I)
enolate intermediates 8. Water or alcohols are typically
added to the catalytic system to close the catalytic cycle by
protonation of enolates 8, which are converted to the
corresponding saturated carbonyl products 9 with regeneration
of the rhodium(I) catalyst 6.
We envisioned the application of this conjugate addition
reaction to the living rhodium(I) species 1 at the terminal end
of poly(phenylacetylene)s formed in the polymerization of
phenylacetylenes using our multicomponent catalytic system. If
the rhodium(I) species 1 causes an addition reaction to various
α,β-unsaturated carbonyl compounds 3, the corresponding
rhodium(I) enolates 4 would be produced by C−C bond
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Table 1. Results of Terminal Chain End Functionalization of Poly(phenylacetylene) Using Acrylates and Acrylamides as
a
Terminators
b
c
c
d
entry
1
2
3
4
5
6
7
8
15
yield (%)
Mn
Mw/Mn
degree of chain end functionalization (%)
15a
15a
15b
15c
15d
15e
15f
15g
15h
15i
>95
>95
>95
>95
>95
>95
86
>95
87
>95
90
5100
9100
4900
5000
4900
4800
6000
5200
4800
5800
5200
34600
5300
6000
4700
5500
4800
5800
4900
5100
5200
5700
1.04
1.04
1.03
1.03
1.03
1.04
1.04
1.02
1.04
1.04
1.04
>95
>95
>95
>95
>95
>95
>95
75
>95
>95
>95
>95
>95
>95
>95
>95
>95
>95
>95
90
e
9
10
11
12
15j
15k
15l
f
g
g
92
1.38
13
14
15
16
17
18
19
>95
>95
85
1.04
1.03
1.05
1.04
1.04
1.04
1.04
1.08
1.05
1.02
15m
15n
15o
15p
15q
15r
15s
15t
15u
86
>95
>95
90
>95
>95
>95
h
20
21
22
>95
>95
a
Typical conditions: [Rh(nbd)Cl]2 (0.02 mmol), 10a (0.06 mmol), 11 (0.12 mmol), 12 (0.10 mmol), 13 (0.12 mmol) in THF (0.4 mL) for 5 min
b
at 0 °C, then 14a (2.0 mmol) in THF (3.6 mL) for 1 h at 30 °C, and then 15a−u (0.16 or 0.32 mmol) for 24 h at 30 °C. Methanol-insoluble part.
c
Determined by SEC using TSKgel G4000HXL + G3000HXL + G3000HXL as columns on the basis of polystyrene standards (THF, 40 °C).
d
e
f
g
Determined by 1H NMR analysis. 14a/[Rh] = 100. 14a/[Rh] = 500/1. Determined by SEC using Shodex KF-805L as a column on the basis of
h
polystyrene standards (THF, 40 °C). 15s/[Rh] = 16/1.
formation (Figure 1a). Finally, the rhodium species is
eliminated by β-hydride elimination in situ (Mizoroki−Heck
type reaction) or protonation by quenching the reaction
mixture (conjugate addition type reaction).14 In any case, the
α,β-unsaturated carbonyl compounds 3 are introduced to the
terminal end of the polymer to provide telechelic poly-
(phenylacetylene)s 5 having functional groups at both ends.15
Herein we report a facile method for terminal chain end
functionalization of poly(phenylacetylene)s using α,β-unsatu-
rated carbonyl compounds such as acrylates and acrylamides as
terminators of the rhodium-catalyzed living polymerization of
phenylacetylenes. This terminal chain end functionalization
method allows, for the first time, the synthesis of stereoregular
telechelic poly(phenylacetylene)s because the substituents of
the aryl boronic acids used as initiators are introduced into the
initiating chain end of the resulting polymer in our rhodium-
based multicomponent catalytic system.11
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RESULTS AND DISCUSSION
■
We designed a model system of living polymerization of
phenylacetylene (14a) with a multicomponent catalytic system
composed of [Rh(nbd)Cl]2, 4-methylphenylboronic acid
(10a), diphenylacetylene (11), a 50% (w/v) aqueous solution
of KOH (12), and PPh3 (13) (14a/[Rh] = 50/1, [Rh]/10a/
11/12/13 = 1/1.5/3/2.5/3) to test terminal end functional-
ization using α,β-unsaturated carbonyl compounds.11 To the
polymerization mixture was directly added 4 equiv of ethyl
acrylate (15a) to the rhodium catalyst after the living
polymerization had been conducted for 1 h at 30 °C in
THF, and the resultant mixture was further stirred for 24 h at
30 °C. A 50-mer polymer having a narrow molecular weight
distribution (Mw/Mn = 1.04) was quantitatively obtained as a
methanol-insoluble part (entry 1 in Table 1).
1
The H NMR spectrum of the obtained polymer showed
sharp signals based on poly(phenylacetylene), indicating that
high cis stereoregularity (>95%) is kept even after the
termination reaction for 24 h (Figure 2).1a,3b,4a Moreover,
Figure 3. High-resolution APCI-TOF-MS spectrum of 16a (Mn =
2900, Mw/Mn = 1.03) (a), the expanded spectrum of 16a (n = 25)
(b), and the calculated spectrum of 16a (n = 25) (c).
based on the polymer was detected up to m/z 4000 in the
HRMS spectrum, and each peak has a difference of m/z 102
corresponding to a phenylacetylene repeating unit. For
instance, a peak at m/z 3098.4396 corresponds to
C
240H185O2 [M + H]+ (calcd 3098.4369), which can be
+
assigned as a structure composed of 25-mer poly-
(phenylacetylene) (n = 25, C200H150), one 4-methylphenyl
group (C7H7), two diphenylacetylene units (C14H10 × 2), and
a terminal ethyl acrylate moiety (C5H7O2) (Figure 3b,c).
Molecular ions based on a polymer having a hydrogen atom
instead of an ethyl acrylate moiety were not detected in the
spectrum, strongly supporting full introduction of ethyl
acrylate to the terminal end of the polymer. We tried to
reduce the amount of ethyl acrylate (15a) used to 2 equiv to
Figure 2. 1H NMR spectrum of 16a (entry 1 in Table 1) in CDCl3 at
room temperature.
1
the rhodium catalyst, but H NMR analysis of the obtained
polymer indicated incomplete introduction (83% chain end
functionalization) of 15a to the polymer terminal end in 24 h.
This termination reaction using 15a was hardly affected by the
degree of polymerization of the polymer (entry 2 in Table 1).
Next, we focused on terminal end functionalization of
poly(phenylacetylene)s using various terminators under the
same living polymerization conditions. Typically, the intro-
duction rate of terminators was estimated from integral values
clear signals assignable to an ethyl ester were observed at 1.13
and 4.05 ppm, for which the integration values were 3H and
2H, respectively, in comparison with 3H of a methyl group of a
4-methylphenyl group at the initiating end of the polymer.
This means that 15a was quantitatively introduced to the
terminal end of the polymer. On the other hand, signals of
methylene groups were absent, suggesting that the polymer
16a having an α,β-unsaturated ester was produced by β-
hydride elimination of a rhodium species in situ (Mizoroki−
Heck type reaction). This structure was confirmed by APCI-
TOF-MS of 16a having a low molecular weight (Mn = 2900,
Mw/Mn = 1.03), which was synthesized by living polymer-
ization at a low feed ratio of the monomer to the initiator
(14a/[Rh] = 25/1). As shown in Figure 3a, a series of peaks
1
of characteristic signals in H NMR spectra of the isolated
polymers. tert-Butyl, 2-trimethylsilylethyl, and 2,2,2-trichlor-
oethyl acrylates (15b−d) were quantitatively introduced to the
terminal end of the polymer as in the case of ethyl acrylate
(15a) (entries 3−5 in Table 1), and they are beneficial for
further functionalization of the polymer because different
conditions can be used in hydrolysis depending on the
situation. Characteristic functional groups such as epoxide and
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Scheme 1. Termination Reaction of the Living Polymerization of Phenylacetylene (14a) with α,β-Unsaturated Ketone 15v,
a
Methacrylate 15w, and Acrylate 15x Having a Methacrylate Moiety
a
The yield was calculated from the methanol-insoluble part. Mn and Mw/Mn values were determined by SEC using TSKgel G4000HXL + G3000HXL
+ G3000HXL as columns on the basis of polystyrene standards (THF, 40 °C). The degree of chain end functionalization (%) was determined by 1H
NMR analysis.
fluorous groups could be readily introduced using acrylates 15e
and 15f (entries 6 and 7 in Table 1). Acrylate 15g, having a
free hydroxyl group, was incompletely introduced (75% chain
end functionalization) (entry 8 in Table 1), while acrylate 15h
having a TBS-protected hydroxyl group was quantitatively
introduced to the polymer terminal end (entry 9 in Table 1).
These results clearly indicate that a free hydroxyl group
inhibits rhodium-mediated addition to acrylates, but the reason
is unclear. Tosyl-protected acrylate 15i was also introduced to
the polymer terminal end, and it would be useful for further
transformation by SN2 substitution reactions (entry 10 in
Table 1). A useful alkyne moiety could be introduced to the
polymer terminal end using acrylate 15j (entry 11 in Table 1).
Acrylate 15k having a polyethylene glycol chain (40-mer) was
quantitatively introduced to the polymer terminal end,
indicating that the synthesis of a heteroblock copolymer is
possible by the present method (entry 12 in Table 1). The
broadened molecular weight distribution of the obtained
polymer is probably due to tailing in the SEC chromatogram,
and this was caused by the introduced polyethylene glycol
chain because an aliquot of the polymerization solution before
addition of 15k provided a polymer having a narrow molecular
weight distribution (Mn = 49000, Mw/Mn = 1.12).
philicity of acrylamides is lower than that of acrylates.
However, quantitative introduction of 15l to the polymer
terminal end was achieved by increasing the amount of 15l to 8
equiv (entry 13 in Table 1). The N-methylated analogue 15m
was also quantitatively introduced to the polymer terminal end,
indicating that tertiary acrylamides can be used for terminal
chain end functionalization (entry 14 in Table 1). The
electronic nature of the aromatic ring of acrylamides seems to
have little effect on the reactivity in the present termination
reaction, because acrylamides 15n and 15o having a methoxy
group and a chlorine atom, respectively, readily reacted with a
living species (entries 15 and 16 in Table 1). An iodine atom of
acrylamide 15p was intact under the present reaction
conditions, and this is useful for further functionalization by
cross-coupling reactions (entry 17 in Table 1). Since
characteristic signals were overlapped with signals of the
1
polymer component in H NMR spectra of the polymers
obtained by reactions with 15o and 15p, estimation of the
chain end functionalization was complemented by HRMS
analysis (see the Supporting Information). It is notable that
pyrene and crown ether moieties were successfully introduced
to the polymer terminal chain end using acrylamides 15q and
15r, respectively, because such functional groups are often
important for the development of functional materials (entries
18 and 19 in Table 1). The secondary aliphatic acrylamide 15s
showed a relatively low reactivity, and 90% chain end
functionalization was achieved using an increased amount of
15s (16 equiv) (entry 20 in Table 1). However, tertiary
aliphatic acrylamides 15t and 15u worked as good terminators
as was the case for aromatic acrylamides to give 16t and 16u,
Our interest turned to end functionalization using
acrylamides instead of acrylates because various acrylamides
are also easily accessible by condensation between acryloyl
chloride and functionalized amines. When 4 equiv of N-(4-n-
propylphenyl)acrylamide (15l) to the rhodium catalyst was
used as a model terminator, 15l was introduced to the polymer
terminal end in only 60% chain end functionalization, unlike
the case for acrylates. This is probably because the electro-
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Figure 4. Synthesis of telechelic poly(phenylacetylene)s having functional pendants. The same conditions as those shown in footnote a in Table 1
were used unless otherwise noted (see the Supporting Information). The yield was calculated from the methanol-insoluble part. Mn and Mw/Mn
values were determined by SEC using TSKgel G4000HXL + G3000HXL + G3000HXL as columns on the basis of polystyrene standards (THF, 40
°C).
respectively, with nearly quantitative chain end functionaliza-
tion (entries 21 and 22 in Table 1).
intact methacrylate moiety at the terminal end, which would be
useful for further functionalization (Scheme 1, eq 3).
Figure 4 shows examples of the synthesis of telechelic
polymers from other functionalized phenylacetylene mono-
mers using a combination of various aryl boronic acid
derivatives and terminators. Aryl boronic acid derivatives
having protected phenol (10b, R = OH), protected alkynyl
(10c, R = OH), hydroxymethyl (10d, R2 = pin), and protected
amino (10e, R = OH) substituents were chosen as initiators
because these functional groups are useful for further
functionalization of the corresponding polymers. Acrylates
(15e, 15f, 15j) and acrylamides (15p, 15r) were used as
representative terminators from the viewpoint of usefulness.
Telechelic polymers 17−21 were synthesized from monomer
14b having a methoxy group, monomer 14c having an ester
group, and monomers 14d,16 14e,17 and 14f18 having stimuli-
responsive functional groups. These representative examples
show the potentially broad scope of monomers in the present
method.19
We found that α,β-unsaturated ketone 15v was also
introduced to the polymer terminal end, though a larger
amount (12 equiv to a rhodium catalyst) of 15v was required
for quantitative introduction (Scheme 1, eq 1). Interestingly,
the 1H NMR spectrum of polymer 16v obtained by this
reaction indicated that 15v was introduced as an α,β-saturated
ketone, unlike the cases of acrylates and acrylamides (see the
Supporting Information). This indicates that the β-hydride
elimination of an intermediary rhodium(I) enolate was
suppressed in situ probably because an enol form having an
O−Rh bond is preferred over a keto form having a C−Rh
bond in the isomerization equilibrium of rhodium(I) enolate.14
When methyl methacrylate (15w) was used as a terminator
instead of acrylates under the standard conditions, 15w was
not introduced to the polymer terminal end at all (Scheme 1,
eq 2). The contrasting results indicate that the effect of the
steric factor of alkenes is significant in the present termination
reaction.
Finally, we performed postfunctionalization of the telechelic
poly(phenylacetylene)s synthesized by the present method
(Scheme 2). For instance, we examined introduction of a
cyclodextrin residue into the polymer terminal end by
postfunctionalization because its direct introduction to the
polymer terminal end by the present termination reaction
Since 15w did not react with the living species, we tested a
chemoselective reaction using the terminator 15x having both
acrylate and methacrylate moieties. As expected, the reaction
resulted in perfect chemoselectivity and gave 16x having an
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a
Scheme 2. Postfunctionalization of Telechelic Poly(phenylacetylene)s
a
Mn and Mw/Mn values were determined by SEC using TSKgel G4000HXL + G3000HXL + G3000HXL as columns on the basis of polystyrene
standards (THF, 40 °C).
seems to be very difficult due to multiple hydroxy groups. After
basic hydrolysis of the terminal ethyl ester of 16a, the resultant
polymer having a terminal carboxy group was reacted with
commercially available 3A-amino-3A-deoxy-(2AS,3AS)-α-cy-
clodextrin (22) using 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-
methylmorpholinium chloride (DMT-MM) as a condensing
reagent to afford 23 having a cyclodextrin moiety at the
terminal end in good yield (Scheme 2a).20
Furthermore, postfunctionalization of the telechelic polymer
19 at both chain ends was demonstrated (Scheme 2b). As the
first step, an iodine atom at the terminal end of 19 was
converted to a protected alkynyl group, which would be useful
for further functionalization, by a Sonogashira reaction to give
polymer 24. As the second step, biotin (25) was introduced to
a hydroxy group at the initiating end of 24 by a condensation
reaction using 1-(3-dimethylaminopropyl)-3-ethylcarbodii-
mide hydrochloride (EDC•HCl) to give 26 in good yield.11
lene, 50% aqueous KOH, and PPh3. A variety of easily available
acrylates and acrylamides having functionalized groups were
quantitatively introduced to the terminal chain end of
poly(phenylacetylene)s having high cis stereoregularity and a
narrow molecular weight distribution. Since the initiating end
of poly(phenylacetylene)s is readily functionalized by the
component of aryl boronic acid derivatives, the present
controlled termination reaction consequently offers a method
for the facile synthesis of unprecedented telechelic poly-
(phenylacetylene)s. The method was applicable to other
phenylacetylene monomers having functional groups, and we
therefore anticipate that the broad scope of this method will
spark the development of novel functional materials based on
telechelic poly(phenylacetylene)s.
ASSOCIATED CONTENT
■
CONCLUSION
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/jacs.1c00150.
We have developed a method for versatile terminal end
functionalization of poly(phenylacetylene)s by collaborating
rhodium-catalyzed conjugate addition to α,β-unsaturated
carbonyl compounds with living polymerization of phenyl-
acetylenes using a multicomponent catalytic system composed
of [Rh(nbd)Cl]2, aryl boronic acid derivatives, diphenylacety-
Experimental details, characterizations of polymers,
supporting data, and NMR spectra (PDF)
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monosubstituted polyacetylenes using Rh complex catalysts. Control
of solid structure and π-conjugation length. Macromol. Chem. Phys.
1999, 200, 265−282. (d) Mayershofer, M. G.; Nuyken, O. Living
polymerization of substituted acetylenes. J. Polym. Sci., Part A: Polym.
Chem. 2005, 43, 5723−5747. (e) Shiotsuki, M.; Sanda, F.; Masuda, T.
Polymerization of substituted acetylenes and features of the formed
polymers. Polym. Chem. 2011, 2, 1044−1058.
(4) (a) Simionescu, C. I.; Percec, V.; Dumitrescu, S. Polymerization
of acetylenic derivatives. XXX. Isomers of polyphenylacetylene. J.
Polym. Sci., Polym. Chem. Ed. 1977, 15, 2497−2509. (b) Yashima, E.;
Huang, S.; Okamoto, Y. An optically active stereoregular poly-
phenylacetylene derivative as a novel chiral stationary phase for
HPLC. J. Chem. Soc., Chem. Commun. 1994, 1811−1812. (c) Percec,
V.; Rudick, J. G.; Peterca, M.; Wagner, M.; Obata, M.; Mitchell, C.
M.; Cho, W.-D.; Balagurusamy, V. S. K.; Heiney, P. A.
Thermoreversible cis-cisoidal to cis-transoidal isomerization of helical
dendronized polyphenylacetylenes. J. Am. Chem. Soc. 2005, 127,
15257−15264. (d) Percec, V.; Rudick, J. G.; Peterca, M.; Heiney, P.
A. Nanomechanical function from self-organizable dendronized
helical polyphenylacetylenes. J. Am. Chem. Soc. 2008, 130, 7503−
7508.
AUTHOR INFORMATION
Corresponding Authors
■
Tsuyoshi Taniguchi − Graduate School of Natural Science
and Technology, Kanazawa University, Kanazawa 920-
1192, Japan; orcid.org/0000-0002-4945-480X;
Email: tsuyoshi@p.kanazawa-u.ac.jp
Katsuhiro Maeda − Graduate School of Natural Science and
Technology and Nano Life Science Institute (WPI-NanoLSI),
Kanazawa University, Kanazawa 920-1192, Japan;
orcid.org/0000-0002-5341-8799; Email: maeda@
se.kanazawa-u.ac.jp
Authors
Kensuke Echizen − Graduate School of Frontier Science
Initiative, Kanazawa University, Kanazawa 920-1192, Japan
Tatsuya Nishimura − Graduate School of Natural Science and
Technology, Kanazawa University, Kanazawa 920-1192,
Japan; orcid.org/0000-0002-8416-4007
Complete contact information is available at:
https://pubs.acs.org/10.1021/jacs.1c00150
(5) Seminal reports of living polymerization of acetylenes:
(a) Kunzler, J. F.; Percec, V. Living non-conjugated polyacetylenes.
Polym. Bull. 1987, 18, 303−309. (b) Kunzler, J.; Percec, V. Living
polymerization of aryl substituted acetylenes by MoCl5 and WCl6
based initiators: The ortho phenyl substituent effect. J. Polym. Sci.,
Part A: Polym. Chem. 1990, 28, 1221−1236. Recent review: (c) Tan,
N. S. L.; Lowe, A. B. Polymerizations mediated by well-defined
rhodium complexes. Angew. Chem., Int. Ed. 2020, 59, 5008−5021.
(6) (a) Kishimoto, Y.; Eckerle, P.; Miyatake, T.; Ikariya, T.; Noyori,
R. Living polymerization of phenylacetylenes initiated by Rh-
(C≡CC6H5)(2,5-norbornadiene)[P(C6H5)3]2. J. Am. Chem. Soc.
1994, 116, 12131−12132. (b) Kishimoto, Y.; Miyatake, T.; Ikariya,
T.; Noyori, R. An efficient rhodium (I) initiator for stereospecific
living polymerization of phenylacetylenes. Macromolecules 1996, 29,
5054−5055. (c) Kishimoto, Y.; Eckerle, P.; Miyatake, T.; Kainosho,
M.; Ono, A.; Ikariya, T.; Noyori, R. Well-controlled polymerization of
phenylacetylenes with organorhodium (I) complexes: Mechanism and
structure of the polyenes. J. Am. Chem. Soc. 1999, 121, 12035−12044.
(7) (a) Misumi, Y.; Masuda, T. Living polymerization of
phenylacetylene by novel rhodium catalysts. Quantitative initiation
and introduction of functional groups at the initiating chain end.
Macromolecules 1998, 31, 7572−7573. (b) Misumi, Y.; Kanki, K.;
Miyake, M.; Masuda, T. Living polymerization of phenylacetylene by
rhodium-based ternary catalysts, (diene)Rh(I) complex/vinyllithium/
phosphorus ligand. Effects of catalyst components. Macromol. Chem.
Phys. 2000, 201, 2239−2244. (c) Miyake, M.; Misumi, Y.; Masuda, T.
Living polymerization of phenylacetylene by isolated rhodium
complexes, Rh[C(C6H5)=C(C6H5)2](nbd)(4-XC6H4)3P (X = F,
Cl). Macromolecules 2000, 33, 6636−6639. (d) Saeed, I.; Shiotsuki,
M.; Masuda, T. Living polymerization of phenylacetylene with
tetrafluorobenzobarrelene ligand-containing rhodium catalyst systems
featuring the synthesis of high molecular weight polymer. Macro-
molecules 2006, 39, 8567−8573. (e) Shiotsuki, M.; Kumazawa, S.;
Onishi, N.; Sanda, F. Molecular weight dependence of helical
conformation of amino acid-based polyphenylacetylenes. J. Polym.
Sci., Part A: Polym. Chem. 2011, 49, 4921−4925. (f) Kumazawa, S.;
Castanon, J. R.; Shiotsuki, M.; Sato, T.; Sanda, F. Chirality
amplification in helical block copolymers. Synthesis and chiroptical
properties of block copolymers of chiral/achiral acetylene monomers.
Polym. Chem. 2015, 6, 5931−5939.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was partially supported by the JSPS KAKENHI
(Grant-in-Aid for Specially Promoted Research, No.
18H05209 (K.M.), Grants-in-Aid for Scientific Research (C)
Nos. 19K06972 (T.T.) and No. 18K04723 (T.N.) and the
World Premier International Research Center Initiative (WPI),
MEXT, Japan.
REFERENCES
■
(1) (a) Simionescu, C.; Percec, V. Progress in polyacetylene
chemistry. Prog. Polym. Sci. 1982, 8, 133−214. (b) Lam, J. W.; Tang,
B. Z. Functional polyacetylenes. Acc. Chem. Res. 2005, 38, 745−754.
(c) Aoki, T.; Kaneko, T.; Teraguchi, M. Synthesis of functional π-
conjugated polymers from aromatic acetylenes. Polymer 2006, 47,
4867−4892. (d) Masuda, T. Substituted polyacetylenes. J. Polym. Sci.,
Part A: Polym. Chem. 2007, 45, 165−180. (e) Liu, J.; Lam, J. W.;
Tang, B. Z. Acetylenic polymers: syntheses, structures, and functions.
Chem. Rev. 2009, 109, 5799−5867. (f) Jin, Y.-J.; Kwak, G. Properties,
functions, chemical transformation, nano-, and hybrid materials of
poly(diphenylacetylene)s toward sensor and actuator applications.
Polym. Rev. 2017, 57, 175−199.
(2) (a) Rudick, J. G.; Percec, V. Induced helical backbone
conformations of self-organizable dendronized polymers. Acc. Chem.
Res. 2008, 41, 1641−1652. (b) Akagi, K. Helical polyacetylene:
asymmetric polymerization in a chiral liquid-crystal field. Chem. Rev.
2009, 109, 5354−5401. (c) Yashima, E.; Maeda, K.; Iida, H.;
Furusho, Y.; Nagai, K. Helical polymers: synthesis, structures, and
functions. Chem. Rev. 2009, 109, 6102−6211. (d) Freire, F.; Quinoa,
E.; Riguera, R. Supramolecular assemblies from poly-
(phenylacetylene)s. Chem. Rev. 2016, 116, 1242−1271. (e) Yashima,
E.; Ousaka, N.; Taura, D.; Shimomura, K.; Ikai, T.; Maeda, K.
Supramolecular helical systems: helical assemblies of small molecules,
foldamers, and polymers with chiral amplification and their functions.
Chem. Rev. 2016, 116, 13752−13990. (f) Maeda, K.; Yashima, E.
Helical polyacetylenes induced via noncovalent chiral interactions and
their applications as chiral materials. Top. Curr. Chem. 2017, 375, 72.
(3) (a) Simionescu, C. I.; Percec, V. Thermal cis-trans isomerization
of cis-transoidal polyphenylacetylene. J. Polym. Sci., Polym. Chem. Ed.
1980, 18, 147−155. (b) Furlani, A.; Napoletano, C.; Russo, M. V.;
Feast, W. J. Stereoregular polyphenylacetylene. Polym. Bull. 1986, 16,
311−317. (c) Tabata, M.; Sone, T.; Sadahiro, Y. Precise synthesis of
(8) Kumazawa, S.; Castanon, J. R.; Onishi, N.; Kuwata, K.;
Shiotsuki, M.; Sanda, F. Characterization of the polymerization
catalyst [(2,5-norbornadiene)Rh{C(Ph)=CPh2}(PPh3)] and identi-
fication of the end structures of poly(phenylacetylenes) obtained by
polymerization using this catalyst. Organometallics 2012, 31, 6834−
6842.
(9) Kanki, K.; Misumi, Y.; Masuda, T. Synthesis of poly-
(phenylacetylene)-block-poly(β-propiolactone) by use of Rh-cata-
3611
https://dx.doi.org/10.1021/jacs.1c00150
J. Am. Chem. Soc. 2021, 143, 3604−3612

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
lyzed living polymerization of phenylacetylene. Inorg. Chim. Acta
2002, 336, 101−104.
rhodium-catalyzed living polymerization are often insoluble in most
solvents, which makes their NMR and SEC analysis difficult.6c,11
(20) Kunishima, M.; Kawachi, C.; Monta, J.; Terao, K.; Iwasaki, F.;
Tani, S. 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methyl-morpholinium
chloride: an efficient condensing agent leading to the formation of
amides and esters. Tetrahedron 1999, 55, 13159−13170.
(10) Loong Tan, N. S.; Nealon, G. L.; Turner, G. F.; Moggach, S. A.;
Ogden, M. I.; Massi, M.; Lowe, A. B. Rh(I)(2,5-norbornadiene)-
(biphenyl)(tris(4-fluorophenyl)phosphine): Synthesis, characteriza-
tion, and application as an initiator in the stereoregular (co)
polymerization of phenylacetylenes. ACS Macro Lett. 2020, 9, 56−60.
(11) Taniguchi, T.; Yoshida, T.; Echizen, K.; Takayama, K.;
Nishimura, T.; Maeda, K. Facile and versatile synthesis of end-
functionalized poly(phenylacetylene)s: A multicomponent catalytic
system for well-controlled living polymerization of phenylacetylenes.
Angew. Chem., Int. Ed. 2020, 59, 8670−8680.
(12) Yoshida, K.; Hayashi, T. In Modern Rhodium-Catalyzed Organic
Reactions; Evans, P. A., Ed.; Wiley-VCH: Weinheim, Germany, 2005;
pp 55−77.
(13) (a) Fagnou, K.; Lautens, M. Rhodium-catalyzed carbon-carbon
bond forming reactions of organometallic compounds. Chem. Rev.
2003, 103, 169−196. (b) Hayashi, T.; Yamasaki, K. Rhodium-
catalyzed asymmetric 1,4-addition and its related asymmetric
reactions. Chem. Rev. 2003, 103, 2829−2844. (c) Edwards, H. J.;
Hargrave, J. D.; Penrose, S. D.; Frost, C. G. Synthetic applications of
rhodium catalysed conjugate addition. Chem. Soc. Rev. 2010, 39,
2093−2105.
(14) (a) Zou, G.; Wang, Z.; Zhu, J.; Tang, J. Rhodium-catalyzed
Heck-type reaction of arylboronic acids with α,β-unsaturated esters:
tuning β-hydrogen elimination vs. hydrolysis of alkylrhodium species.
Chem. Commun. 2003, 2438−2439. (b) Zou, G.; Guo, J.; Wang, Z.;
Huang, W.; Tang, J. Heck-type coupling vs. conjugate addition in
phosphine-rhodium catalyzed reactions of aryl boronic acids with α,β-
unsaturated carbonyl compounds: a systematic investigation. Dalton
Trans. 2007, 3055−3064.
(15) Tasdelen, M. A.; Kahveci, M. U.; Yagci, Y. Telechelic polymers
by living and controlled/living polymerization methods. Prog. Polym.
Sci. 2011, 36, 455−567.
(16) (a) Okoshi, K.; Sakurai, S.-i.; Ohsawa, S.; Kumaki, J.; Yashima,
E. Control of main-chain stiffness of a helical poly(phenylacetylene)
by switching on and off the intramolecular hydrogen bonding through
macromolecular helicity inversion. Angew. Chem., Int. Ed. 2006, 45,
8173−8176. (b) Sakurai, S.-i.; Okoshi, K.; Kumaki, J.; Yashima, E.
Two-dimensional surface chirality control by solvent-induced helicity
inversion of a helical polyacetylene on graphite. J. Am. Chem. Soc.
2006, 128, 5650−5651. (c) Okoshi, K.; Kajitani, T.; Nagai, K.;
Yashima, E. Uniaxial orientation of a rodlike helical poly-
(phenylacetylene) in an electric field. Macromolecules 2008, 41,
258−261.
́
(17) (a) Freire, F.; Seco, J. M.; Quinoa, E.; Riguera, R. Chiral
̃
amplification and helical-sense tuning by mono-and divalent metals
on dynamic helical polymers. Angew. Chem., Int. Ed. 2011, 50, 11692−
́
11696. (b) Freire, F.; Seco, J. M.; Quinnoa, E.; Riguera, R.
̃
Nanospheres with tunable size and chirality from helical polymer-
metal complexes. J. Am. Chem. Soc. 2012, 134, 19374−19383.
́
̃
(c) Hirose, D.; Isobe, A.; Quinoa, E.; Freire, F.; Maeda, K. Three-state
switchable chiral stationary phase based on helicity control of an
optically active poly(phenylacetylene) derivative by using metal
cations in the solid state. J. Am. Chem. Soc. 2019, 141, 8592−8598.
(18) (a) Shimomura, K.; Ikai, T.; Kanoh, S.; Yashima, E.; Maeda, K.
Switchable enantioseparation based on macromolecular memory of a
helical polyacetylene in the solid state. Nat. Chem. 2014, 6, 429−434.
(b) Ishidate, R.; Shimomura, K.; Ikai, T.; Kanoh, S.; Maeda, K.
Macromolecular helicity induction and memory in a poly-
(biphenylylacetylene) bearing an ester group and its application to
a chiral stationary phase for high-performance liquid chromatography.
Chem. Lett. 2015, 44, 946−948. (c) Ishidate, R.; Sato, T.; Ikai, T.;
Kanoh, S.; Yashima, E.; Maeda, K. Helicity induction and memory
effect in poly(biphenylylacetylene)s bearing various functional groups
and their use as switchable chiral stationary phases for HPLC. Polym.
Chem. 2019, 10, 6260−6268.
(19) We did not use ortho-substituted phenylacetylenes as
monomers because the corresponding polymers obtained by
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