Arsole-Containing π-Conjugated Polymer by the Post-Element-Transformation Technique

Article abstract of DOI:10.1002/anie.201608404

A synthetic method to obtain an arsole-containing π-conjugated polymer by the post-transformation of the organotitanium polymer titanacyclopentadiene-2,5-diyl unit with an arsenic-containing building block is described. The UV/Vis absorption maximum and onset of the polymer were observed at 517 nm and 612 nm, respectively. The polymer exhibits orange photoluminescence with an emission maximum (E_max) of 600 nm and the quantum yield (Φ) of 0.05. The polymer proved to exhibit a quasi-reversible redox behavior in its cyclic voltammetric (CV) analysis. The energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were estimated to be ?5.43 and ?3.24 eV, respectively, from the onsets for oxidation and reduction signals in the CV analysis. Further chemical modification of the arsole unit in the π-conjugated polymer by complexation of gold(I) chloride occurred smoothly resulting in the bathochromic shift of the UV/Vis absorption and lowering of the LUMO energy level.

Full text of DOI:10.1002/anie.201608404

Angewandte
Communications
Chemie
International Edition: DOI: 10.1002/anie.201608404
German Edition: DOI: 10.1002/ange.201608404
Organometallic Polymers Hot Paper
Arsole-Containing p-Conjugated Polymer by the Post-Element-
Transformation Technique
Yoshimasa Matsumura, Makoto Ishidoshiro, Yasuyuki Irie, Hiroaki Imoto, Kensuke Naka,
Kazuyoshi Tanaka, Shinsuke Inagi, and Ikuyoshi Tomita*
Abstract: A synthetic method to obtain an arsole-containing
p-conjugated polymer by the post-transformation of the
organotitanium polymer titanacyclopentadiene-2,5-diyl unit
with an arsenic-containing building block is described. The
UV/Vis absorption maximum and onset of the polymer were
observed at 517 nm and 612 nm, respectively. The polymer
exhibits orange photoluminescence with an emission maxi-
mum (Emax) of 600 nm and the quantum yield (F) of 0.05. The
polymer proved to exhibit a quasi-reversible redox behavior in
its cyclic voltammetric (CV) analysis. The energy levels of the
highest occupied molecular orbital (HOMO) and lowest
unoccupied molecular orbital (LUMO) were estimated to be
À5.43 and À3.24 eV, respectively, from the onsets for oxidation
and reduction signals in the CV analysis. Further chemical
modification of the arsole unit in the p-conjugated polymer by
complexation of gold(I) chloride occurred smoothly resulting
in the bathochromic shift of the UV/Vis absorption and
lowering of the LUMO energy level.
weaker s-donation of arsines compared to that of phosphines
accelerates various transition-metal-catalyzed cross-coupling
[
3]
reactions. Also, some arsenic–metal complexes exhibit
interesting optical features that cannot be attained by use of
[
4]
the corresponding phosphines.
In recent years, element-block-containing polymers have
attracted increasing attentions as advanced functional mate-
[
5]
rials. Especially, p-conjugated polymers having element-
blocks are expected to reveal advanced optoelectronic
features suitable for solar cell applications, light-emitting
diodes, and chemosensors. Although the optoelectronic
features of the p-conjugated polymers are most probably
affected largely by the element-blocks, the synthesis of
p-conjugated polymers possessing diverse element-blocks
have scarcely been attained by the established polyconden-
sation processes owing to the high reactivity of the carbon-
element bonds under the polymerization conditions.
Previously, we have reported the synthesis of p-conju-
gated polymers having phosphole units by the reaction of
[6]
T
he heavier Group 15 elements are attractive components
regioregular titanacyclopentadiene-containing polymers,
for construction of functional organic molecules. For example,
phosphines and arsines possessing trivalent Group 15 ele-
ments (PR and AsR , respectively) are known to serve as
generated in situ from aromatic diynes and a low-valent
titanium complex through the regiospecific metallacycliza-
[
7]
tion, with dichlorophosphine derivatives. The resulting
phosphole-containing polymers exhibit attractive electronic
features of low LUMO energy levels owing to the s*Àp*
3
3
ligands of transition metals which play very important roles to
exhibit excellent catalytic activity and optoelectronic features.
Although both phosphines and arsines are known to have
similar trigonal pyramidal structures with very close steric
parameters, such as bond angles and bond length of the
orbital interaction that cannot be observed in the correspond-
[
8]
ing pyrrole-containing polymers.
Based on the fact that arsines are attractive Group 15
element-containing building blocks which often reveal supe-
rior functions compared to phosphines as mentioned above,
the incorporation of arsole units, the arsenic analogue of
phospholes, into p-conjugated polymers is an attractive
approach to create advanced functional materials. Very
recently, Heeney and co-workers reported the synthesis of
[1]
element–carbon (AsÀC and PÀC) moieties, their transition
metal complexes often exhibit totally different catalytic
activities and functions, which are ascribable to the different
ability of both the s-donation of the lone pair in the pnictogen
atoms to the metals and the back-donation from the metals to
[
2]
the unoccupied d-orbitals of the pnictogens. That is, the
[
9]
a p-conjugated polymer possessing dithienoarsole unit. It
was also described that the field effect transistor device
fabricated from the dithienoarsole-containing polymer exhib-
its excellent stability in air. This report encouraged the
authors to carry out the synthetic study of arsole-containing
p-conjugated polymers.
[
*] Dr. Y. Matsumura, Prof. Dr. S. Inagi, Prof. Dr. I. Tomita
School of Materials and Chemical Technology
Tokyo Institute of Technology
Nagatsuta-cho 4259-G1-9, Midori-ku, Yokohama 226-8502 (Japan)
E-mail: tomita@echem.titech.ac.jp
M. Ishidoshiro, Dr. Y. Irie, Dr. H. Imoto, Prof. Dr. K. Naka
Graduate School of Science and Technology
Kyoto Institute of Technology
Concerning the synthesis of arsole derivatives, the reac-
tion of dichlorophenylarsine with dicarboanion equivalents of
[10]
butadienes such as zirconacyclopentadiene
and 1,4-dili-
Goshokaido-cho, Matsugasaki, Sakyo-ku, Kyoto 606-8585 (Japan)
[
11]
thiobutadiene derivatives was reported by Fagan et al. and
Ashe III et al., respectively, in the 1980s. However, most
probably due to the highly toxic and volatile nature of
dichlorophenylarsine, which was in fact misused in the First
World War as the chemical weapons, no further progress of
Prof. Dr. K. Tanaka
Fukui Institute for Fundamental Chemistry
Kyoto University
34-4 Nishihiraki-cho, Takano, Sakyo-ku, Kyoto 606-8103 (Japan)
Supporting information for this article can be found under:
http://dx.doi.org/10.1002/anie.201608404.
Angew. Chem. Int. Ed. 2016, 55, 1 – 5
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!

Angewandte
Communications
Chemie
the related chemistry was achieved after these synthetic
studies.
peak intensity ratio of the aromatic protons and the lateral
alkoxy protons in the H-NMR spectrum of 6 (Figure S1,
1
Recently, Naka et al. reported a safer way to generate
diiodoarsines in situ from less volatile cyclo-oligoarsines with
iodine, which were successfully employed in the synthesis of
phosphorescence-active dibenzoarsoles by the reaction with
observed: 4.00:8.98, expected: 4:9).
The absorption maximum (lmax) and absorption onset
(lonset) of 6 were observed at 517 nm and 612 nm (Figure 1,
respectively, in the UV/Vis absorption spectra taken in CHCl3
which were bathochromically shifted by more than 120 nm
[12]
2
,2’-dilithiobiphenyl.
We have also described the transformation of the
titanacyclopentadiene derivative into 2,5-diaryl-1-phenylar-
[13]
compared to those of 6’ (lmax = 395 nm, lonset = 446 nm;
[
13]
soles in high yields by use of diiodophenylarsine. Because
the attempt to functionalize the 2,5-bis(p-bromoaryl)-1-
phenylarsoles by the transition-metal-catalyzed cross-cou-
pling reactions resulted in the lower yields of the objective
products, probably due to the suppression of the catalytic
[
13b]
activity by the arsoles,
it would be difficult to approach the
arsole-containing polymers by the transition-metal-catalyzed
polycondensation of arsole-containing monomers. On the
basis of the fact that the reactivity of the titanacyclopenta-
diene units is high enough for the smooth transformation into
arsole derivatives and that the obtained arsole derivatives are
much more stable towards oxidation than the phosphole
[
13]
analogues,
we describe the synthesis of unprecedented
arsole-containing p-conjugated polymers by the reaction of
the organometallic polymer possessing titanacyclopentadiene
with diiodoarsine. The unique optical and electronic proper-
ties of the arsole-containing p-conjugated polymers are also
discussed.
The reaction of the organotitanium polymer (5), which
was prepared from 1,4-bis(2-ethylhexyloxy)-2,5-diethynyl-
benzene (3) and the titanium(II) complex (4) generated
in situ from titanium(IV) isopropoxide and isopropylmagne-
sium chloride from À788C to À508C, with diiodophenylarsine
(2) was carried out under the conditions for the transforma-
tion of titanacyclopentadiene derivatives into arsoles
Scheme 1). By this polymer reaction, the polymer (6) was
(
Figure 1. UV/Vis absorption spectra (a) and photoluminescence spec-
tra (b) of 6 and 6’ in CHCl solution or film.
isolated in 88% yield as a dark red solid after precipitation
into methanol. The number-average molecular weight (Mn)
and molecular weight distribution (M /M ) of 6 were
3
w
n
estimated to be 5500 and 2.5, respectively, by SEC (chloro-
form as eluent, polystyrene standards). The polymer (6) is
stable enough under ambient conditions. It is soluble in
common organic solvents such as chloroform, dichlorome-
thane, tetrahydrofuran, and toluene. The structure of 6 was
supported by its H NMR and C NMR spectra (Supporting
Information, Figures S1, S2, and S5). The efficiency of this
transformation was found to be quantitative judging from the
Figure 2, Table S1). The extension of the effective p-con-
jugation was supported by the observed clear bathochromic
shifts. In the case of film, the lonset of 6 was bathochromically
shifted approximately by 10 nm compared to that measured in
CHCl . The polymer (6) exhibited an orange photolumines-
3
1
13
cence (PL) in CHCl with an emission maximum (Emax) and
3
the quantum yield (F) of 600 nm and 0.05, respectively. The
optical properties of 6 are very close to those of a phosphole-
containing polymer (lmax = 522 nm, lonset = 620 nm,
Emax = 594 nm, F = 0.10), which was prepared by
reaction of the same organotitanium polymer
[6a]
(
5).
This result indicates that the electronic
character of the arsole ring is almost comparable
to that of the phosphole ring.
In the CV analysis of 6, the quasi-reversible
oxidation and reduction peaks were observed at
0
.53 eV and À1.66 eV, respectively (Figure S8).
The energy levels of the highest occupied molec-
ular orbital (HOMO) and lowest unoccupied
molecular orbital (LUMO) were estimated to be
À5.43 and À3.24 eV, respectively, from the onsets
Scheme 1. Synthesis of arsole-containing polymer (6).
2
www.angewandte.org
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1 – 5
These are not the final page numbers!

Angewandte
Communications
Chemie
durability of 6 for electronic
oxidation would be attrac-
tive for the electronic appli-
cations of this unique mate-
rial.
The chemical modifica-
tion of 6 was further per-
formed to tune up the opto-
electronic properties of the
polymer. Because the triva-
lent arsenic atom can coor-
dinate with transition metals
[
13]
such as gold(I) chloride,
6
was subjected to the reac-
tion with gold(I) chloride
(
1.2 equiv) in CH Cl at
2 2
Figure 2. Cyclic voltammograms of 6 (a) and a phosphole-containing polymer (b) in film on a Pt wire
ambient temperature for
1 h (Scheme 2). A polymer
immersed in the acetonitrile solution of tetra-n-butylammonium hexafluorophosphate (0.10m), at a sweep
À1
rate of 100 mVs
.
for oxidation and reduction signals in the CV analysis. The
HOMO and LUMO energy levels of 6 were very close to
those of the phosphole-containing polymer (HOMO =
[
6a]
À5.35 eV, LUMO = À3.28 eV).
taining polymer (6) also exhibits both electron-donating and
accepting-properties. Especially, the remarkably low LUMO
Namely, the arsole-con-
-
energy level of 6 would be due to the s*Àp* orbital
interaction (see below). The polymer (6) was found to exhibit
the quasi-reversible oxidation under the CV measurement
conditions, where the oxidation peak was constantly observed
throughout several sweeps (Figure 3a). To the contrary, the
corresponding phosphole-containing polymer undergoes the
irreversible structural change under the analogous measure-
ment conditions, resulting in a significant decrease in the
oxidation peak after the first sweep (Figure 3b). The higher
reversibility of oxidation of 6 is most probably due to the high
stability of the doped form of 6. The good reversibility and
Scheme 2. Chemical modification of 6 with gold(I) chloride.
possessing the coordinated structure (7) was isolated in 87%
yield as a purple solid after precipitation into hexane. From
the SEC analysis, M and M /M of 7 were estimated to be
n
w
n
6100 and 2.3, respectively. Similar to the case of 6, the
polymer (7) was stable enough under ambient conditions.
The structure of the polymer was supported by its
1
13
H NMR and C NMR spectra (Figure S6). Especially, in
1
H NMR spectrum of 7, the entire lower magnetic field shift
of the peaks of the aromatic
protons in comparison with
those of 6 strongly sup-
ported the quantitative
nature of the chemical
modification. The UV/Vis
absorption spectrum of 7
was taken in CHCl3 (Fig-
ure S7 and Table S1), where
lmax and lonset of 7 were
observed at 549 nm and
6
47 nm, respectively, which
were bathochromically
shifted by about 30 nm com-
pared to those of the poly-
mer (6). This bathochromic
shift, namely, narrowing of
the band gap of the polymer
(7) by the coordination with
gold(I) chloride, was found
to be due to the lowering of
the LUMO energy level of
Figure 3. Orbital correlation diagrams for arsole derivatives based on the DFT calculations.
Angew. Chem. Int. Ed. 2016, 55, 1 – 5
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
3
These are not the final page numbers!

Angewandte
Communications
Chemie
7
. The LUMO energy level of 7 (À3.56 eV, estimated from its
[2] a) A. P. M. Robertson, P. A. Gray, N. Burford, Angew. Chem. Int.
Ed. 2014, 53, 6050 – 6069; Angew. Chem. 2014, 126, 6162 – 6182;
b) J. W. Dube, Y. Zheng, W. Thiel, M. Alcarazo, J. Am. Chem.
Soc. 2016, 138, 6869 – 6877.
CV analysis; Figure S9 and Table S2) was significantly lower
than that of 6 (LUMO = À3.24 eV), indicating that the arsole-
gold complex exhibits a stronger electron-accepting property
compared to the uncoordinated arsole unit.
The density functional theory (DFT) calculation at the
B3LYP/6-31G(d) and LanL2DZ ECP set combination (ECP
for the Au atom only) using the Gaussian09 program
[
3] a) V. Farina, B. Krishnan, J. Am. Chem. Soc. 1991, 113, 9585 –
595; b) Y. Obora, Y. Tsuji, M. Kobayashi, T. Kawamura, J. Org.
Chem. 1995, 60, 4647 – 4649.
9
[4] a) K. Naka, T. Kato, S. Watase, K. Matsukawa, Inorg. Chem.
2012, 51, 4420 – 4422; b) H. Unesaki, T. Kato, S. Watase, K.
Matsukawa, K. Naka, Inorg. Chem. 2014, 53, 8270 – 8277; c) H.
Imoto, S. Tanaka, T. Kato, S. Watase, K. Matsukawa, T. Yumura,
K. Naka, Organometallics 2016, 35, 364 – 369.
[
14]
package suggested that the low-lying LUMO energy level
of the arsole unit comes from the s*Àp* orbital interaction
between the p* molecular orbital (MO) of the butadiene
moiety and the s* MO of the AsÀPh bond, as proposed in the
[
[
5] Y. Chujo, K. Tanaka, Bull. Chem. Soc. Jpn. 2015, 88, 633 – 643.
6] a) Y. Matsumura, M. Ueda, K. Fukuda, K. Fukui, I. Takase, H.
Nishiyama, S. Inagi, I. Tomita, ACS Macro Lett. 2015, 4, 124 –
127; b) Y. Matsumura, K. Fukuda, S. Inagi, I. Tomita, Macromol.
Rapid Commun. 2015, 36, 660 – 664.
[
15]
[8]
silole, germole, stannole, and phosphole units. In the case
of the gold complex (arsoleÀAuCl), the energy level of the s*
MO of AsÀPh (phenylarsineÀAuCl) is lower than that of
AsÀPh (free phenylarsine), which could bring about the
stronger s*Àp* orbital interaction with the energetically
[
[
7] a) S. Yamaguchi, R. Z. Jin, K. Tamao, F. Sato, J. Org. Chem.
1998, 63, 10060 – 10062; b) T. Hamada, D. Suzuki, H. Urabe, F.
Sato, J. Am. Chem. Soc. 1999, 121, 7342 – 7344.
similar p* MO of the butadiene moiety. The result obtained in
the present study indicates that the LUMO energy level of
arsole unit could be tunable by the facile complexation and/or
chemical reactions on the arsenic atom.
8] a) T. Baumgartner, R. Rꢀau, Chem. Rev. 2006, 106, 4681 – 4727;
b) S. S. H. Mao, T. D. Tilley, Macromolecules 1997, 30, 5566 –
5569; c) Y. Morisaki, Y. Aiki, Y. Chujo, Macromolecules 2003,
36, 2594 – 2597; d) H. S. Na, Y. Morisaki, Y. Aiki, Y. Chujo,
Polym. Bull. 2007, 58, 645 – 652; e) A. Saito, Y. Matano, H.
Imahori, Org. Lett. 2010, 12, 2675 – 2677; f) V. Lemau de Ta-
lancꢀ, M. Hissler, L. Z. Zhang, T. Kꢁrpꢁti, L. Nyulꢁszi, D. C.
Quintero, P. Bꢂuerle, R. Rꢀau, Chem. Commun. 2008, 2200 –
In summary, an arsole-containing p-conjugated polymer
was prepared by the reaction of a regioregular organo-
titanium polymer with a derivative of diiodoarsine as an
arsinating reagent, which was generated in situ from less
volatile hexaphenylcyclohexaarsine. The arsole-containing
polymer was found to have both high HOMO and low
LUMO energy levels. This polymer also exhibited quasi-
reversible oxidation peak in CV measurements. The chemical
modification of the arsole-containing polymer with gold(I)
chloride proceeded smoothly, resulting in remarkable
changes in the optical and electronic properties of the
polymer. To our knowledge, this is the first example of the
synthesis of arsole-containing polymers. On the basis of the
unique features of the arsole-containing polymers, further
macromolecular design would provide interesting materials
that exhibit advanced functions. Thus, the designed synthesis
of a series of the polymers and their applications, such as
sensor, recovery, storage, and optoelectronic devices, are
currently being investigated.
2202.
[
9] J. P. Green, Y. Han, R. Kilmurray, M. A. McLachlan, T. D.
Anthopoulos, M. Heeney, Angew. Chem. Int. Ed. 2016, 55, 7148 –
7151; Angew. Chem. 2016, 128, 7264 – 7267.
[
[
[
[
10] P. Fagan, W. Nugent, J. Am. Chem. Soc. 1988, 110, 2310 – 2312.
11] A. J. Ashe III, F. J. Drone, Organometallics 1985, 4, 1478 – 1480.
12] T. Kato, S. Tanaka, K. Naka, Chem. Lett. 2015, 44, 1476 – 1478.
13] a) M. Ishidoshiro, Y. Matsumura, H. Imoto, Y. Irie, T. Kato, S.
Watase, K. Matsukawa, S. Inagi, I. Tomita, K. Naka, Org. Lett.
2015, 17, 4854 – 4857; b) M. Ishidoshiro, H. Imoto, S. Tanaka, K.
Naka, Dalton Trans. 2016, 45, 8717 – 8723.
14] Gaussian09, RevisionC.01, M. J. Frisch, G. W. Trucks, H. B.
Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G.
Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakat-
suji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J.
Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y.
Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery, Jr.,
J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers,
K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K.
Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi,
M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B.
Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A.
Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels,
ꢃ. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, and D. J. Fox,
Gaussian, Inc., Wallingford CT, 2009.
[
Acknowledgements
This work was supported by a Grant-in-Aid for Scientific
Research on Innovative Areas “New Polymeric Materials
Based on Element-Blocks (No.2401)” (JP24102007) of The
Ministry of Education, Culture, Sports, Science, and Tech-
nology, Japan.
[
15] a) S. Yamaguchi, K. Tamao, Bull. Chem. Soc. Jpn. 1996, 69,
2
327 – 2334; b) S. Yamaguchi, Y. Itami, K. Tamao, Organo-
Keywords: arsination · arsoles · organometallic polymers ·
polymer reactions · p-conjugated polymers
metallics 1998, 17, 4910 – 4916.
Received: August 28, 2016
[
1] S. Sasaki, K. Sutoh, F. Murakami, M. Yoshifuji, J. Am. Chem.
Soc. 2002, 124, 14830 – 14831.
Revised: October 3, 2016
Published online: && &&, &&&&
4
www.angewandte.org
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1 – 5
These are not the final page numbers!

Angewandte
Communications
Chemie
Communications
Organometallic Polymers
Y. Matsumura, M. Ishidoshiro, Y. Irie,
H. Imoto, K. Naka, K. Tanaka, S. Inagi,
I. Tomita*
&&&& — &&&&
Arsole-Containing p-Conjugated Polymer
by the Post-Element-Transformation
Technique
Colorful polymer: An arsole-containing p-
conjugated polymer was prepared by
reacting the titanacyclopentadiene unit of
an organometallic polymer with an
resulting polymer exhibits a low LUMO
energy level, quasi-reversible redox
behavior, and an excellent ability to
coordinate gold(I) chloride.
arsenic-containing building block. The
Angew. Chem. Int. Ed. 2016, 55, 1 – 5
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!