Copper(I) Iodide Accelerates Catalytic Activation in Rhodium Complex-catalyzed
Helix-sense-selective Polymerization of Achiral Phenylacetylene Monomers
1

Hiroo Katagiri,1 Takashi Kaneko,2 Masahiro Teraguchi,2;3 and Toshiki Aoki1;2;3
Graduate School of Science and Technology, Niigata University, Ikarashi 2-8050, Niigata 950-2181
2
Center for Transdisciplinary Research, Niigata University, Ikarashi 2-8050, Niigata 950-2181
3
Department of Chemistry and Chemical Engineering, Faculty of Engineering, Niigata University,Ikarashi 2-8050, Niigata 950-2181(Received August 20, 2007; CL-070880; E-mail: kanetaka@gs.niigata-u.ac.jp)

PEA
H

R HCl PEACuI
PEA =HIPEACu

12

PEAClRh

Rh
ClRH
NH

orCuCl
PEA

PEA

PEARh

Rh
ClH

H
N
H

R

R

Rh
R
R

R

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Vol.37 No.4 2008 p:390{391
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April 5, 2008

The Chemical Society of Japan
Published on the web (Advance View) February 27, 2008; doi:10.1246/cl.2008.390

390

Chemistry Letters Vol.37, No.4 (2008)

Copper(I) Iodide Accelerates Catalytic Activation in Rhodium Complex-catalyzed
Helix-sense-selective Polymerization of Achiral Phenylacetylene Monomers
1Hiroo Katagiri,1 Takashi Kaneko,2 Masahiro Teraguchi,2;3 and Toshiki Aoki1;2;3
Graduate School of Science and Technology, Niigata University, Ikarashi 2-8050, Niigata 950-2181
2Center for Transdisciplinary Research, Niigata University, Ikarashi 2-8050, Niigata 950-2181
3Department of Chemistry and Chemical Engineering, Faculty of Engineering, Niigata University,Ikarashi 2-8050, Niigata 950-2181(Received August 20, 2007; CL-070880; E-mail: kanetaka@gs.niigata-u.ac.jp)

Achiral phenylacetylene monomers were polymerizedusing a rhodium (Rh) complex catalyst in the presence of (S)1-phenylethylamine. Addition of copper(I) iodide (CuI) into
the catalytic system improved the polymer yield. The monomer,
which had two hydroxy groups and a hydrogalvinoxyl unit, gave
the corresponding polymer with an optically active helical conformation stabilized by intramolecular hydrogen bonding. The
chemical oxidation of the polymer yielded the corresponding optically active helical polyradical with high spin concentration.

Rh cat, CuIn(R )- or (S )-PEA

RROO

R=OHOH

OC12H25OOH

1OH

2OH

3

OH

Scheme 1.
Substituted polyacetylenes have attracted attention as one of
the most interesting -conjugated functional polymers since it
was found that group 5-, 6-, and 9-transition metals eﬀectivelycatalyzed the polymerization of substituted acetylenes.1 In
particular, some rhodium complex catalysts provide eﬃcient
polymerization of monosubstituted acetylenes since thesecatalysts polymerize bulky monomers such as dendrimers2–4
and monomers containing functional groups (including stableradicals),5 and polymerization proceeds even in aqueous media.6
In addition, the polymers obtained often have high degrees
of polymerization and stereoregularities, i.e., cis-transoidal andhelical structures.7–9 Recently, we succeeded in helix-senseselective polymerization of achiral monomers 1 and 2 using achiral catalyst system, i.e., polymerization using [Rh(nbd)Cl]2
catalyst in the presence of (R)-1-phenylethylamine ((R)-PEA)or (S)-1-phenylethylamine ((S)-PEA) to give the corresponding
poly(phenylacetylene)s poly110,11 and poly2 (Scheme 1).12,13
These products exhibited optically active helical conformation
in solution, with an excess of one-handed helix kineticallystabilized by intramolecular hydrogen bonds (poly1) and thebulkiness of the side groups (poly2). In this study, we synthesized the new achiral monomer 3 and found that the helixsense-selective polymerization of the monomers improved polymer yield by addition of CuI to the catalyst system. Moreover,
we succeeded in synthesizing the optically active helical polyradical with high spin concentration via chemical oxidation of
the poly3 with rigid and one-handed helical conformation in
THF solution, which is kinetically stabilized by intramolecularhydrogen bonds.
The monomer 3 was polymerized in the presence of several
Rh complex catalysts, chiral PEA cocatalyst, and an achiral solvent. The red solid polymer poly3 was obtained by precipitationfrom the polymerization mixtures into methanol. The polymerization data for these resultant polymers are summarized inTable 1. Under polymerization conditions without CuI, polymer
yields were lower than those in the presence of CuI. Gel permeation chromatography indicated that the polymerization mixture

contained little oligomer; instead it consisted mostly of unreacted monomers. Therefore, GPC results suggest that the low polymer yield resulted from the slow reaction rate of complexation tothe polymerization active species. This improvement in polymer
yields by addition of CuI also was observed during thepolymerization of 1. In a previously proposed polymerization
mechanism,14–17 the polymerization active species are generated
by end-on coordination of acetylide to Rh. The monomers 1 and
3 are relatively bulky and contain hydroxy groups. Thus, itappears that the low polymerization activity was caused byinhibition of acetylide formation due to active protons of themonomer hydroxy groups and by the bulkiness of the monomers.
In contrast, addition of CuI to the catalytic system improved
polymer yield. Cross-coupling reactions of halogenoaryls
with acetylene derivatives using Pd complex catalysts, i.e.,
Sonogashira coupling,18 proceeds via end-on coordination ofacetylide to Pd, where CuI accelerates acetylide coordination
due to formation of copper acetylide. The eﬀect of CuI additionin the polymerization of 1 and 3 is analogous to this coupling
reaction, i.e., the transmetalation of copper acetylide to Rh
accelerated complexation to polymerization active species as
Table 1. Polymerizationa of 3 in toluene using Rh complexes inthe presence of (S)-(–)-phenylethylamine
No.

Rhbcomplex

Temp/ C[CuI]/[Rh]

Yieldc/%Mw d/105

Mw =Mn d

12345Rh IRh I
Rh I
Rh IIRh II

25250000120151592772278.3
7.8
4.23.530148.7
4.73.6a[M]0 = 0.05 M; [M]0 /[Rh]0 = 20; [PEA]0 /[Rh]0 = 100; 1 h(No. 1–3), 4 h (No. 4), and 2 h (No. 5); PEA: phenylethylamine.
b
Rh I: [Rh(nbd)Cl]2 ; Rh II: Rhþ (nbd)[(6 -C6 H5 )B (C6 H5 )3 ].
cMethanol insoluble fraction. d Measured by GPC calibrated with
polystyrene standard.

Copyright Ó 2008 The Chemical Society of Japan

Chemistry Letters Vol.37, No.4 (2008)391
was achieved even after the oxidation reaction, and successful
synthesis of an optically active polyradical with high spin concentration occurred, i.e., with high radical contents compared
to previously reported optically active helical copolymer-polyradical.22 The magnetic and magneto-optical properties of the
optically active helical polyradicals will be discussed in greater
detail in a subsequent paper.

20

poly3

polyradical−1321−2250300

350400450Wavelength / nm

5005500600

ε /104.dm3.mol−1cm−1[θ ] / 104.deg.cm2.dmol−11Figure 1. CD (top) and UV–vis (bottom) absorption spectra ofpoly3 (No. 5 in Table 1) and its polyradical with spin concentration of 0.8 spin/unit in THF (0.5 mmol/dm3 ).
shown in the Graphical Abstract. Moreover, replacement of[Rh(nbd)Cl]2 by Rhþ (nbd)[(6 -C6 H5 )B (C6 H5 )3 ]19 in the polymerization catalytic system appeared to enhance the reactivity
remarkably, probably because elimination of tetraphenyl borateanion proceeded more readily compared to chloride anion.20
Of all polymers obtained, poly3 possessed optical activity,and split-type induced CD signals were observed for the THF
solution of 3 at 300 nm as shown in Figure 1, indicating an
excess of one-handed helical polyacetylene backbone.21 It isclear that the helix-sense-selective polymerization occurred in
the presence of chiral PEA because monomer 3 has no chiralmoieties and the CD signal at 300 nm was similar to that of previously reported poly1. The polymer obtained by polymerization
at low temperature (0  C) showed a larger Cotton eﬀect compared to the polymers obtained by polymerization at room temperature. These results indicate improvement of the helix-senseselectivity for the polymerization. The CD intensity of poly3
was nearly constant, even when the solution was heated to60  C, because the rigid and one-handed helical conformation
was stabilized by intramolecular hydrogen bonds. Thisbehavior is in contrast to previous results reported for poly2,
whose CD signal intensity was dependent on temperature overthe experimental range and decreased reversibly with increasing
temperature for the CD spectra of poly2 in solution used immediately after preparation.13
The hydrogalvinoxyl units of poly3 were converted to thecorresponding galvinoxyl radicals after treatment with fresh
PbO2 under an oxygen-free atmosphere, and the color of theTHF solution turned from orange to brown. The absorption
maximum at 420 nm due to the hydrogalvinoxyl chromophoredecreased, and a new absorption peak due to the galvinoxyl
radical chromophore appeared at 470 nm. The ESR spectrumof the polyradical showed a broad signal at g ¼ 2:0047, indicating formation of the phenoxyl radical. The spin concentration of
the polyradical was determined by doubly integrating the ESR
signal in comparison with that of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) solution as a standard. Spin concentration of
the polyradical reached ca. 0.6–0.8 spin/unit by adjusting oxidative conditions. The polyradical was stable enough to maintaininitial spin concentration under ESR and CD measurement
conditions. In the CD spectra of the polyradical, the Cotton
eﬀect was still observed at 300 nm, as shown in Figure 1. This
indicates that maintenance of the excess of the one-handed helix

This work was partially supported by a Grant-in-Aid forExploratory Research (No. 18651046) for Science Researchin a Priority Area ‘‘Super-Hierarchical Structures’’ (Nos.
19022009 and 19022010) and for Young Scientists (A) (No.
17681010) from MEXT, by a Grant-in-Aid for Scientiﬁc Research (No. 19350054) from JSPS, and by the Iketani Scienceand Technology Foundation, the Mukai Science and Technology
Foundation, and the Asahi Glass Foundation.
References and Notes
1

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Sci., Part A: Polym. Chem. 2007, 45, 165.
2 T. Kaneko, T. Horie, M. Asano, T. Aoki, E. Oikawa, Macromolecules 1997, 30, 3118.
3 T. Kaneko, M. Asano, K. Yamamoto, T. Aoki, Polym. J. 2001,33, 879.
4 T. Kaneko, K. Yamamoto, M. Asano, M. Teraguchi, T. Aoki,J. Membr. Sci. 2006, 278, 365.
5 A. Fujii, T. Ishida, N. Koga, H. Iwamura, Macromolecules 1991,24, 1077.
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2004, 45, 8109.
12 Y. Umeda, T. Kaneko, M. Teraguchi, T. Aoki, Chem. Lett. 2005,34, 854.
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Macromolecules 2005, 38, 9420.
14 R. J. Kern, J. Polym. Sci., Part A-1: Polym. Chem. 1969, 7, 621.
15 Y. Kishimoto, P. Eckerle, T. Miyatake, T. Ikariya, R. Noyori,J. Am. Chem. Soc. 1994, 116, 12131.
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20 The polydispersity ratio was also improved probably by theaccelerated complexation to polymerization active species.
21 Poly3 was also obtained by the polymerization in the presenceof (R)-PEA, and its CD spectra almost showed the mirror imageof poly3 in Figure 3.
22 T. Kaneko, T. Yamamoto, T. Aoki, E. Oikawa, Chem. Lett.
1999, 623.

Published on the web (Advance View) February 27, 2008; doi:10.1246/cl.2008.390