interaction. More importantly, the electron-accepting abil-
ity of the phosphole-based π-systems can be largely en-
hanced by the oxidation of the phosphorus center from PIII
to PV. Indeed, precisely designed arene-fused phosphole
P-oxides and P-sulfides have evolved as a new class of low-
molecular-weight n-type semiconductors.5,6 The solubility
and polarity of phosphole-based π-systems can also be
tuned by the substituents at P-sites.
Scheme 1. Synthesis of Phosphole Monomers 5aꢀd, 6b, and 9aꢀc.
Figure 1. Tuning sites of σ4-P polyphospholes 1 and 2.
give the corresponding 2,5-bis(tributylstannyl)phosphole
P-sulfonimides 5aꢀd accompanied by the evolution of nitro-
gen gas. Iodolysis of the CꢀSn bonds of 5b with I2 afforded
2,5-diiodophosphole P-imide 6b. To obtain the polyphosp-
hole, we conducted a Stille coupling reaction between 5b and
6b in the presence of a palladium catalyst and CuI;9 how-
ever, the expected polymerization did not proceed smoothly
even after prolonged heating. This may be partly attribu-
table to the steric congestion induced by the P- and
β-substituents on the phosphole ring. We therefore decided
to use β-unsubstituted phospholes as a part of monomers.
Reaction of 2,5-bis(trimethylsilyl)phosphole 710 with 4aꢀc
afforded β-unsubstituted phosphole P-sulfonimides 8aꢀc,
which were subsequently transformed to 2,5-dibromophosp-
holes 9aꢀc by treatment with N-bromosuccinimide (NBS).
As expected, Stille coupling between 5b and 9b under the
PdꢀCuI catalysis conditions proceeded smoothly at rt to
give the target poly(phosphole P-octylsulfonimide) 2b with-
in a few hours (Scheme 2). The polymer 2b was isolated as a
deep blue solid by repeated precipitations from CH2Cl2ꢀ
MeOH and CH2Cl2ꢀhexane. The number-average molecu-
lar weight (Mn) and polydispersity index (PDI) of 2b were
determined by gel permeation chromatography as 24 000
and 1.8, respectively, relative to polystyrene standards
(Figure S1 in the Supporting Information, SI). With the
same catalysis system, poly(phosphole P-imide)s 2a (Mn =
24 000, PDI = 1.6) and 2c (Mn = 24 000, PDI = 1.9)
were prepared from the corresponding monomers 5a/9a and
5c/9c (Scheme 2). The polymers 2aꢀc showed two branches
of broad 31P NMR peaks at δP 2ꢀ6 and 23ꢀ28 ppm
in CD2Cl2, which were assignable to the 31P nuclei of
β-unsubstituted and β-substituted phosphole units, respec-
tively. In the IR spectra, 2aꢀc displayed PdN stretching
The electronic features of phosphole could be useful in
the π-networks of conjugated polymers (Figure 1), and
there have been some theoretical studies on unsubstituted
polyphosphole.7 However, the experimental research on
polyphosphole derivatives has been left untouched until
recently.8 In 2010, we reported the first example of poly-
(phosphole P-oxide) (1, R = p-C12H25OC6H4; Figure 1),
which has been proven to possess a high electron affinity
and a narrow HOMOꢀLUMO gap compared with
P3HT.9 These findings motivated us to develop poly-
phospholes bearing σ4-phosphorus(V) centers as a new
class of polymer-based n-type semiconductors. We report
herein the first synthesis and charge-carrier transport proper-
ties of poly(phosphole P-alkanesulfonylimide)s 2 (Figure 1).
Scheme 1 depicts the syntheses of phosphole monomers
bearing iminophosphoryl (σ4-PVdN) moieties, which in-
clude the Staudinger reaction as a key step for the intro-
duction of solubilizing alkyl chains onto the phosphorus
centers. One of the advantages of this protocol is that a series
of monomers with different alkyl chains are available from
the common phosphole synthons. 2,5-Bis(tributylstannyl)-
phosphole 3, generated in situ from 1,7-bis(tributylstannyl)-
hepta-1,6-diyne according to the reported procedure,9 re-
acted with four kinds of alkane-1-sulfonyl azides 4aꢀd to
(5) (a) Tsuji, H.; Sato, K.; Ilies, L.; Itoh, Y.; Sato, Y.; Nakamura, E.
Org. Lett. 2008, 10, 2263. (b) Tsuji, H.; Sato, K.; Sato, Y.; Nakamura, E.
J. Mater. Chem. 2009, 19, 3364. (c) Tsuji, H.; Sato, K.; Sato, Y.;
Nakamura, E. Chem.;Asian J. 2010, 5, 1294.
(6) (a) Matano, Y.; Miyajima, T.; Fukushima, T.; Kaji, H.; Kimura,
Y.; Imahori, H. Chem.;Eur. J. 2008, 14, 8102. (b) Saito, A; Miyajima,
T.; Nakashima, M.; Fukushima, T.; Kaji, H.; Matano, Y.; Imahori, H.
Chem.;Eur. J. 2009, 15, 10000. (c) Matano, Y.; Saito, A.; Fukushima,
T.; Tokudome, Y.; Suzuki, F.; Sakamaki, D.; Kaji, H.; Ito, A.; Tanaka,
K.; Imahori, H. Angew. Chem., Int. Ed. 2011, 50, 8016. (d) Matano, Y.;
Saito, A.; Suzuki, Y.; Miyajima, T.; Akiyama, S.; Otsubo, S.; Nakamoto,
E.; Aramaki, S.; Imahori, H. Chem.;Asian J. 2012, 7, 2305.
vibration bands at νmax 1261ꢀ1266 cmꢀ1
.
The P-imide monomer 10 (Figure 2) was prepared by
Stille coupling of 5a with iodobenzene, and its structure
(7) (a) Salzner, U.; Lagowski, J. B.; Pickup, P. G.; Poirier, R. A.
Synth. Met. 1998, 96, 177. (b) Ma, J.; Li, S.; Jiang, Y. Macromolecules
ꢀ
2002, 35, 1109. (c) Casanovas, J.; Aleman, C. J. Phys. Chem. C 2007, 111,
(10) Nief, F.; de Borms, T. B.; Ricard, L.; Carmichael, D. Eur. J.
Inorg. Chem. 2005, 637.
4823. (d) Zhang, G.; Ma, J.; Wen, J. J. Phys. Chem. B 2007, 111, 11670.
(8) Chain-type R,R0-conjugated quaterphospholes and terphosp-
holes: (a) Deschamps, E.; Ricard, L.; Mathey, F. Angew. Chem., Int.
Ed. Engl. 1994, 33, 1158. (b) Matano, Y.; Nakashima, M.; Imahori, H.
Angew. Chem., Int. Ed. 2009, 48, 4002.
(11) C26H24NO2PS, MW = 445.49, 0.40 ꢁ 0.15 ꢁ 0.10 mm3,
˚
˚
orthorhombic, Pbca, a = 11.060(3) A, b = 18.268(5) A, c = 21.576ꢀ(61)
3
A, V = 4359.1(19) A , Z = 8, Fcalcd = 1.358 g cmꢀ3, μ = 2.46 cm
,
˚
˚
collected 30 161, independent 4912, parameters 280, Rw = 0.1424, R =
0.0568 (I > 2.0σ(I)), GOF = 1.044.
(9) Saito, A.; Matano, Y.; Imahori, H. Org. Lett. 2010, 12, 2675.
Org. Lett., Vol. 15, No. 4, 2013
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