Bithiophene-fused benzo[c]phospholes: Novel P,S-containing hybrid π-conjugated systems with small HOMO-LUMO energy gaps

Article abstract of DOI:10.1002/ejoc.200701008

Bithiophene-fused benzo[c]phospholes were successfully prepared by a Ti^II-mediated cyclization of dialkynylated bithiophene derivatives. It was revealed that the optical and electrochemical properties of the bithiophene-fused benzo[c]phospholes are deeply related to the π-conjugation modes at the fused bithiophene subunits. Both experimental and theoretical results demonstrate that the appropriately ringannulated systems are potential emitters with small HOMOLUMO energy gaps covering the orange-to-red region due to the efficient π-electron derealization over the three conjugated heterole rings. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejoc.200701008

SHORT COMMUNICATION
DOI: 10.1002/ejoc.200701008
Bithiophene-Fused Benzo[c]phospholes: Novel P,S-Containing Hybrid
π-Conjugated Systems with Small HOMO–LUMO Energy Gaps
Tooru Miyajima,[a] Yoshihiro Matano,*[a] and Hiroshi Imahori[a,b]
Keywords: Phospholes / Thiophenes / Fused-ring systems / Conjugation / Pi interactions
Bithiophene-fused benzo[c]phospholes were successfully
prepared by a TiII-mediated cyclization of dialkynylated bi-
thiophene derivatives. It was revealed that the optical and
electrochemical properties of the bithiophene-fused benzo-
[c]phospholes are deeply related to the π-conjugation modes
at the fused bithiophene subunits. Both experimental and
theoretical results demonstrate that the appropriately ring-
annulated systems are potential emitters with small HOMO–
LUMO energy gaps covering the orange-to-red region due
to the efficient π-electron delocalization over the three conju-
gated heterole rings.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
we designed a new class of ring-annulated benzo[c]phos-
pholes that would possess a small o-quinonoid character.
Herein, we report the first systematic study of the synthesis,
structure, and optical and electrochemical properties of
three types of bithiophene-fused benzo[c]phospholes. We
experimentally demonstrated that changing the bithiophene
skeleton dramatically affects the HOMO and LUMO ener-
gies as well as the intrinsic emitting properties of the hybrid
phosphole–bithiophene-fused π systems.
Introduction
Phosphole is known as a poorly aromatic heterocyclo-
pentadiene having a low-lying LUMO and a narrow
HOMO–LUMO energy gap due to the effective σ*–π* con-
jugation.[1,2] The optical and electrochemical properties of
phospholes, which are derived from the phosphane-linked
cis-1,3-diene functionality, can be varied widely by chemical
modifications at the dienic backbone and at the phosphorus
center. In this context, the phosphole-based π-conjugated
systems[3–5] are promising candidates for use in optoelec-
tronic applications.[6,7] In particular, the ring-annulated
polycyclic π-conjugated systems such as dibenzo[b,d]phos-
pholes and dithieno[b,d]phospholes have attracted growing
interest, as they possess rigid and elongated π networks that
are beneficial for designing efficient light-emitting and elec-
tron-conducting materials.[8,9] A recent theoretical study on
the electronic structures and reactivities of a series of
benzo[c]heteroles predicted that benzo[c]phosphole would
also be an attractive skeleton for developing novel phos-
phole-based π-conjugated systems with relatively small
HOMO–LUMO energy gaps.[10] However, the chemistry of
benzo[c]phospholes still remains unveiled due to the lack
of a general method for the synthesis of thermally stable
derivatives. Namely, the highly reactive o-quinonoid charac-
ter of unsubstituted benzo[c]phosphole has precluded its
isolation under ambient conditions.[11] With this in mind,
Results and Discussion
Bithiophene-fused benzo[c]phospholes 4–9 were success-
fully prepared by the TiII-mediated cyclization[12] of di-
alkynylated bithiophene derivatives 1–3 (Scheme 1). Reac-
tion of 1a[13] with (η2-propene)Ti(OiPr)2 generated in situ
from Ti(OiPr)4 and 2 equiv. of iPrMgCl,[14] followed by
treatment with dichloro(phenyl)phosphane, gave a mixture
containing target compound 4a and unreacted 1a, which
were not separable by column chromatography. Therefore,
the mixture was subsequently treated with AuCl(SMe2) to
afford AuI–phosphole complex 7a, which could be easily
isolated as a red solid in 57% yield. Treatment of 7a with
an excess amount of P(NMe2)3 in toluene, followed by re-
precipitation from MeOH reproduced σ3-phosphole 4a in
91% yield in high purity. The 2-thienyl-substituted deriva-
tives (4b and 7b) and the other types of bithiophene-fused
benzo[c]phospholes (5, 6, 8, and 9) were prepared from the
corresponding bithiophene derivatives (1b, 2, and 3) accord-
ing to a similar procedure.
[a] Department of Molecular Engineering, Graduate School of
Engineering, Kyoto University,
Nishikyo-ku, Kyoto 615-8510, Japan
Fax: +81-75-383-2571
Compounds 4–9 are air- and thermally stable solids solu-
ble in common organic solvents such as CHCl3, CH2Cl2,
THF, and toluene, and they were fully characterized by
standard spectroscopic techniques. The 31P NMR peaks of
E-mail: matano@scl.kyoto-u.ac.jp
[b] Institute for Integrated Cell-Material Sciences, Kyoto University
Nishikyo-ku, Kyoto 615-8510, Japan
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
Eur. J. Org. Chem. 2008, 255–259
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
255

T. Miyajima, Y. Matano, H. Imahori
SHORT COMMUNICATION
phosphole ring in 7a [1.353(6)–1.374(5) Å and 1.502(7) Å]
are close to those in 11a [1.346(9)–1.350(9) Å and
1.484(9) Å],[6b] and the Au–P bond length [2.2283(10) Å]
and the P–Au–Cl bond angle [177.27(4)°] are within the
range of typical values reported for AuI–phosphole com-
plexes.[17] In both 4a and 7a, the two α-phenyl groups are
twisted from the phosphole ring with dihedral angles of
53.1–54.7° and 51.8–88.0°, respectively.
Scheme 1. Synthesis of bithiophene-fused benzo[c]phospholes 4–9.
σ3-derivatives 4–6 appeared at δ = 24.2–29.6 ppm, whereas
those of Au complexes 7–9 appeared at δ = 46.5–51.4 ppm.
The observed downfield shifts (Δδ = 19.0–23.9 ppm for 7,
8, 9 vs. 4, 5, 6) clearly support that the gold is coordinated
to the phosphorus center. The downfield appearances of the
31P NMR peaks of 4–6 relative to those (δ = 12.7–
13.6 ppm) of Réau’s 3,4-C4-bridged σ3-phospholes 10a,b
(Figure 1)[3c] are presumably due to π conjugation along the
benzo[c]-backbone of the present fused π system.
Figure 2. ORTEP diagram of 4a (50% probability ellipsoids). Hy-
drogen atoms are omitted for clarity. Selected bond lengths [Å] and
angles [°]: P1–C1 1.7934(14), P1–C4 1.7958(16), P1–C13
1.8272(15), C1–C2 1.374(2), C2–C3 1.486(2), C3–C4 1.374(2); C1–
P1–C4 92.22(7), C1–P1–C13 104.97(6), C4–P1–C13 106.00(7).
To disclose the optical and electrochemical properties of
the bithiophene-fused benzo[c]phospholes, we measured
UV/Vis absorption and fluorescence spectra and redox po-
tentials of 4–9, and the results are summarized in Table 1.
The UV/Vis absorption spectra of 4a and 5a display broad
absorption bands attributable to the π–π* transition in the
visible region (Figure 3). In the fluorescence spectra, 4a and
5a show single emission bands in the orange region with
relatively high quantum yields (4a, ΦF = 17.6%; 5a, ΦF
= 9.7%). The absorption and fluorescence maxima of 4a
(462 nm; 600 nm) and 5a (472 nm; 609 nm) are remarkably
Table 1. Optical and electrochemical data for 4–9.
Compd. Absorption[a]
Fluorescence[a]
Redox potentials[b]
λabs / nm[c] logε λem / nm[d] ΦF / %[e] Eox / V[f] Ered / V[f]
4a
4b
5a
5b
6a
6b
7a
7b
8a
8b
9a
9b
462
483
472
491
395 (sh)
409 (sh)
502
535
503
3.89
3.94
3.66
3.69
3.36
3.51
3.73
3.79
3.46
3.67
3.15
3.45
600
646
609
656
548
582
661
710
675
720
596
606
17.6
2.9
9.7
0.45
0.36
0.47
0.39
0.66
0.56
0.83
0.66
0.86
0.70
1.12
0.88
–2.14
–2.00
–2.09
–1.97
–2.35
–2.18
–1.63
–1.55
–1.62
–1.50
–1.86
–1.76
Figure 1. 2,5-Diarylphospholes 10 and 11, dithieno[b,d]phosphole
12, and bithiophene-fused benzo[c]phosphole models 4m–6m.
2.6
0.64
1.10
0.30
0.05
0.10
0.02
0.47
0.67
The structures of 4a and 7a were further elucidated by
X-ray crystallography.[15] As shown in Figure 2, the π-con-
jugated phosphole and bithiophene rings in 4a are nearly
coplanar with moderate C–C/C=C bond length alternations
(Δd = 0.04–0.13 Å).[16] The phosphorus atom is pyra-
midalized with the sum of the C–P–C bond angles of
303.2°. The planar, fused π structure was also observed for
7a (Supporting Information, Figure S1), in which the phos-
phorus atom adopts a distorted tetrahedral geometry
539
420 (sh)
435 (sh)
[a] Measured in CH2Cl2. [b] Determined by DPV in CH2Cl2 with
0.1 m nBu4NPF6. [c] The longest absorption maxima. [d] Excited
at 440 nm for 4, 5, 7, and 8 and at 420 nm for 6 and 9. [e] Fluores-
cence quantum yields relative to 11b (ΦF = 12.9%; ref.[6b]). [f] Re-
(ΣC–P–C = 310.9°). The Cα–Cβ and Cβ–Cβ bond lengths of the dox potentials vs. Fc/Fc+ couple.
256
www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 255–259

Bithiophene-Fused Benzo[c]phospholes
redshifted relative to those of 10a (354 nm; 466 nm)[3c] (0.66 V) and more negative Ered (–2.35 V) relative to those
and Baumgartner’s dithieno[b,d]phosphole 12 (338 nm; of 4a and 5a, showing that the HOMO–LUMO energy gaps
415 nm),[9a] exhibiting the effective π-extension in the pres- of 4a and 5a (ΔE = 2.56–2.59 V) are much smaller than
ent fused π systems. In marked contrast, 6a exhibits a weak that of 6a (ΔE = 3.01 V). This is in good agreement with
absorption peak (sh) at 395 nm and is far less emissive (ΦF the results obtained from the absorption and fluorescence
= 0.64%). The Stokes shift of 6a (7070 cm–1) is considerably spectra (vide supra).
larger relative to those of 4a (4980 cm–1) and 5a
(4770 cm–1). The observed large redshifts in 4a and 5a rela- redox potentials to the positive direction (7, 8, 9 vs. 4, 5, 6).
tive to that of 6a are attributable to the difference in their Noticeably, the shifts of the reduction potentials (ΔEred
The complexation at the phosphorus center shifted the
=
π-conjugation modes. That is, the π electrons are less ef- 0.42–0.51 V) are somewhat larger than those of the oxi-
ficiently spread over the fused rings for 6a than for 4a and dation potentials (ΔEox = 0.30–0.46 V), indicating that the
5a, as all three heterole rings are linked at the respective LUMO is lowered more largely than the HOMO by the
β-positions in 6a. Moreover, the small ΦF value of 6a in complexation. On the other hand, the replacement of the α-
comparison with those of 4a and 5a may result from the substituents at the phosphole ring from phenyl to 2-thienyl
large Stokes shift of 6a, which accelerates nonradiative de- shifted the oxidation and reduction potentials to the nega-
cay of the S1 state of 6a. The above results demonstrate for tive and positive directions, respectively, thereby narrowing
the first time that the optical properties of benzo[c]phos- the HOMO–LUMO energy gaps by 0.20–0.34 V.
pholes are tunable by chemical modifications at the fused π
backbone.
To gain more insight into the electronic structures of bi-
thiophene-fused benzo[c]phospholes, we carried out DFT
calculations at the B3LYP/6-31G* level on α-unsubstituted
model compounds 4m, 5m, and 6m.[18] As visualized in Fig-
ure 4, the frontier orbitals of 4m and 5m are derived from
the typical frontier orbitals of both the phosphole and bi-
thiophene moieties, and they are spread over the entire π-
conjugated plane. The HOMOs hold antibonding charac-
ters between the adjacent heterole subunits, whereas the
LUMOs represent interring bonding interactions. On the
other hand, the frontier orbitals of 6m differ from those of
4m and 5m. For instance, the LUMO of 6m represents al-
most no bonding interactions among the three heterole
rings. As a consequence, the calculated HOMO–LUMO
separations of 4m (3.21 eV) and 5m (3.20 eV) are much
smaller than that of 6m (3.95 eV).[19] This agrees well with
the experimentally observed results. As illustrated in Fig-
Figure 3. UV/Vis absorption (solid line) and fluorescence (dashed
line) spectra of 4a, 5a, and 6a in CH2Cl2.
It is well known that the chemical functionalizations at ure 4, the σ*(P–CPh) orbital contributes to the LUMO to
the α-carbon atoms and the phosphorus atom affect optical some degree, which explains the more pronounced effects of
and electrochemical properties of the phosphole ring.[2] The the complexation on the LUMOs relative to their HOMOs.
α-2-thienyl-substituted derivatives 4b, 5b, and 6b exhibit ab-
sorption and emission maxima at longer wavelengths than
do the corresponding α-phenyl derivatives, although the ba-
thochromic shifts (Δλabs = 14–21 nm; Δλem = 34–47 nm: 2-
thienyl vs. phenyl) are smaller than those reported for 10b
versus 10a (Supporting Information, Figure S2a).[3c] The P
coordination to the AuCl salt induces more pronounced ef-
fects on the optical properties, that is, the larger batho-
chromic shifts in absorption and emission spectra (Δλabs
=
25–52 nm; Δλem = 24–66 nm) and the considerable decrease
in emission efficiency (Supporting Information, Fig-
ure S2b). Note that the fluorescence of chromophores 4 and
5 covers the orange-to-red region (λem = 600–656 nm).
The electrochemical redox processes of 4–9 were found
to be irreversible, and the redox potentials listed in Table 1
were determined by means of differential pulse voltamme-
try (DPV). The first oxidation potentials (Eox) and the first
reduction potentials (Ered) of 4a are 0.45 and –2.14 V (vs.
ferrocene/ferrocenium), respectively, both of which are com-
parable to the respective potentials of 5a (Eox = 0.47 V; Ered
Figure 4. HOMO (lower) and LUMO (upper) of 4m (a), 5m (b),
and 6m (c).
Conclusions
We successfully applied the TiII-mediated cyclization pro-
= –2.09 V). By contrast, 6a showed more positive Eox tocol to the preparation of three types of bithiophene-fused
Eur. J. Org. Chem. 2008, 255–259
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
257

T. Miyajima, Y. Matano, H. Imahori
SHORT COMMUNICATION
benzo[c]phospholes, which are the first examples of ther-
mally and chemically stable benzo[c]phospholes. It was re-
vealed that the optical and electrochemical properties of the
bithiophene-fused benzo[c]phospholes strongly depend on
the π-conjugation modes of the fused rings. Both experi-
mental and theoretical results demonstrate that the appro-
priately fused π systems are potential emitters with small
HOMO–LUMO energy gaps reaching into the near-infra-
red region. The chemical functionalization at the annulated
bithiophene moieties will allow us to further extend the
two-dimensional π networks. In this regard, the bithio-
phene-fused benzo[c]phospholes are highly promising
building blocks for tailoring P,S-containing hybrid π-conju-
gated materials toward optoelectronic applications.
[1]
For reviews, see: a) L. D. Quin, The Heterocyclic Chemistry of
Phosphorus, Wiley, New York, 1981; b) F. Mathey, Chem. Rev.
1988, 88, 429; c) L. D. Quin in Comprehensive Heterocyclic
Chemistry (Eds.: A. R. Katritzky, C. W. Rees, E. F. V. Scriven),
Elsevier, Oxford, 1996, vol. 2; d) F. Mathey, Phosphorus–Car-
bon Heterocyclic Chemistry: The Rise of a New Domain, Elsev-
ier, Oxford, 2001; e) F. Mathey, Angew. Chem. 2003, 115, 1616;
Angew. Chem. Int. Ed. 2003, 42, 1578.
[2]
[3]
For reviews, see: a) M. Hissler, P. W. Dyer, R. Réau, Coord.
Chem. Rev. 2003, 244, 1; b) T. Baumgartner, R. Réau, Chem.
Rev. 2006, 106, 4681 (Correction: 2007, 107, 303); c) P. W. Dyer,
R. Réau in Functional Organic Materials (Eds.: T. J. J. Müller,
U. H. F. Bunz), Wiley-VCH, Weinheim, 2007, pp. 119–177; d)
M. G. Hobbs, T. Baumgartner, Eur. J. Inorg. Chem. 2007, 3611.
a) C. Hay, D. L. Vilain, V. Deborde, L. Toupet, R. Réau, Chem.
Commun. 1999, 345; b) C. Hay, C. Fischmeister, M. Hissler, L.
Toupet, R. Réau, Angew. Chem. 2000, 112, 1882; Angew. Chem.
Int. Ed. 2000, 39, 1812; c) C. Hay, M. Hissler, C. Fischmeister,
J. Rault-Berthelot, L. Toupet, L. Nyulászi, R. Réau, Chem.
Eur. J. 2001, 7, 4222; d) C. Hay, C. Fave, M. Hissler, J. Rault-
Berthelot, R. Réau, Org. Lett. 2003, 5, 3467; e) C. Fave, M.
Hissler, T. Kárpáti, J. Rault-Berthelot, V. Deborde, L. Toupet,
L. Nyulászi, R. Réau, J. Am. Chem. Soc. 2004, 126, 6058.
a) E. Deschamps, L. Ricard, F. Mathey, Angew. Chem. 1994,
106, 1214; Angew. Chem. Int. Ed. Engl. 1994, 33, 1158; b)
S. S. H. Mao, T. D. Tilley, Macromolecules 1997, 30, 5566; c)
Y. Morisaki, Y. Aiki, Y. Chujo, Macromolecules 2003, 36, 2594;
d) T. Sanji, K. Shiraishi, M. Tanaka, Org. Lett. 2007, 9, 3611.
a) D. Delaere, M. T. Nguyen, L. G. Vanquickenborne, Phys.
Chem. Chem. Phys. 2002, 4, 1522; b) D. Delaere, M. T. Nguyen,
L. G. Vanquickenborne, J. Phys. Chem. A 2003, 107, 838; c) Y.-
L. Liu, J.-K. Feng, A.-M. Ren, J. Comput. Chem. 2007, 28,
2500.
a) C. Fave, T.-Y. Cho, M. Hissler, C.-W. Chen, T.-Y. Luh, C.-
C. Wu, R. Réau, J. Am. Chem. Soc. 2003, 125, 9254; b) H.-C.
Su, O. Fedhel, C.-J. Yang, T.-Y. Cho, C. Fave, M. Hissler, C.-
C. Wu, R. Réau, J. Am. Chem. Soc. 2006, 128, 983.
a) C. Fave, M. Hissler, K. Sénéchal, I. Ledoux, J. Zyss, R.
Réau, Chem. Commun. 2002, 1674; b) Y. Matano, T. Miyajima,
H. Imahori, Y. Kimura, J. Org. Chem. 2007, 72, 6200.
a) S. Kobayashi, M. Noguchi, Y. Tsubata, M. Kitano, H. Doi,
T. Kamioka, A. Nakazono, Jpn. Pat. 2003231741, 2003; b) Y.
Makioka, T. Hayashi, M. Tanaka, Chem. Lett. 2004, 33, 44.
See also ref.[6b]
Experimental Section
7a: To a mixture of 1a (110 mg, 0.30 mmol), Ti(OiPr)4 (0.088 mL,
0.30 mmol), and Et2O (9 mL) was added a solution of iPrMgCl
(2.0 m in ether, 0.30 mL, 0.60 mmol) at –60 °C. The resulting mix-
ture was stirred for 3 h at –40 °C, followed by the addition of
PhPCl2 (0.041 mL, 0.30 mmol) at this temperature. The resulting
suspension was warmed to 0 °C and stirred for 1 h. After stirring
for an additional 3 h at room temperature, the mixture was sub-
jected to short silica gel column chromatography (CH2Cl2). The
orange fraction was then collected and treated with AuCl(SMe2)
(90 mg, 0.30 mmol). The color of the solution turned to red in a
few seconds, and the mixture was concentrated under reduced pres-
sure. The solid residue was subjected to silica gel column
chromatography (CH2Cl2/hexane). The red fraction was collected,
evaporated, and washed with MeOH to give 7a as a red solid
[4]
[5]
[6]
1
(120 mg, 57%). M.p. 215 °C (dec). H NMR (400 MHz, CD2Cl2):
δ = 6.56 (d, J = 5.2 Hz, 2 H), 7.01 (d, J = 5.2 Hz, 2 H), 7.05 (br.,
2 H), 7.27 (br., 2 H), 7.32–7.42 (m, 4 H), 7.42–7.60 (m, 5 H), 7.79
(br., 2 H) ppm. 31P{1H} NMR (162 MHz, CD2Cl2): δ = +46.5
ppm. MS (MALDI-TOF): m/z = 707 [M]+. HRMS (FAB): calcd.
for C30H19AuClPS2 [M]+ 706.0020; found 706.0016.
[7]
[8]
4a: P(NMe2)3 (32 μL, 0.18 mmol) was added to a toluene solution
(5 mL) containing 7a (42 mg, 0.060 mmol). After stirring at room
temperature for 10 min, the mixture was concentrated under re-
duced pressure. The residue was washed with MeOH to give 4a as
an orange solid (26 mg, 91%). M.p. 175 °C (dec). 1H NMR
(400 MHz, CD2Cl2): δ = 6.85 (d, J = 5.2 Hz, 2 H), 7.02 (d, J =
5.2 Hz, 2 H), 7.10–7.24 (m, 5 H), 7.25–7.40 (m, 10 H) ppm.
13C{1H} NMR (100 MHz, CD2Cl2): δ = 122.8, 126.3, 127.4, 128.5
[9]
a) T. Baumgartner, T. Neumann, B. Wirges, Angew. Chem.
2004, 116, 6323; Angew. Chem. Int. Ed. 2004, 43, 6197; b) T.
Baumgartner, W. Bergmans, T. Kárpáti, T. Neumann, M. Ni-
eger, L. Nyulázi, Chem. Eur. J. 2005, 11, 4687; c) Y. Dienes, S.
Durben, T. Kárpáti, T. Neumann, U. Englert, L. Nyulázi, T.
Baumgartner, Chem. Eur. J. 2007, 13, 7487; d) A. Acharya, Y.
Koizumi, S. Seki, A. Saeki, S. Tagawa, Y. Ie, Y. Aso, J. Pho-
tochem. Photobiol. A 2005, 173, 161.
(d, JP,C = 9.9 Hz), 128.8, 128.9 (d, JP,C = 9.1 Hz), 129.9 (d, JP,C
=
[10]
[11]
T. C. Dinadayalane, G. N. Sastry, J. Chem. Soc. Perkin Trans.
2 2002, 1902.
7.4 Hz), 130.3 (d, JP,C = 1.7 Hz), 132.6 (d, JP,C = 3.3 Hz), 134.7 (d,
JP,C = 1.6 Hz), 134.9 (d, JP,C = 19.0 Hz), 136.2 (J = 14.9 Hz), 138.0
(d, JP,C = 14.9 Hz), 146.1 (d, JP,C = 3.3 Hz) ppm. 31P{1H} NMR
(162 MHz, CD2Cl2): δ = +24.6 ppm. MS (MALDI-TOF): m/z =
474 [M]+. HRMS (FAB): calcd. for C30H19PS2 [M]+ 474.0666;
found 474.0672.
Most of the benzo[c]phospholes reported have no substituent
at the benzo backbone and readily undergo Diels–Alder reac-
tions. The isolated benzo[c]phospholes bearing phosphonio
groups at the α-positions were reported to be highly moisture-
sensitive solids. See: a) J. M. Holland, D. W. Jones, J. Chem.
Soc., C 1970, 122; b) J. M. Holland, D. W. Jones, J. Chem. Soc.
Perkin Trans. 1 1973, 927; c) T. H. Chan, K. T. Nwe, Tetrahe-
dron Lett. 1973, 48, 4815; d) T. H. Chan, K. T. Nwe, Tetrahe-
dron 1975, 31, 2537; e) A. Schmidpeter, M. Thiele, Angew.
Chem. 1991, 103, 333; Angew. Chem. Int. Ed. Engl. 1991, 30,
308; f) A. Decken, F. Bottomley, B. E. Wilkins, E. D. Gill, Or-
ganometallics 2004, 23, 3683; g) R. A. Aitken in Science of Syn-
thesis (Eds.: D. Bellus, S. V. Ley, R. Noyori, M. Regitz, P. J.
Reider, E. Schaumann, I. Shinkai, E. J. Thomas, B. M. Trost),
Thieme, New York, 2000, vol. 10, pp. 809–815.
Supporting Information (see footnote on the first page of this arti-
cle): Experimental details, characterization data, and DFT compu-
tational results.
Acknowledgments
This work was partly supported by Japan Science and Technology
Agency in Research for Promoting Technological Seeds (No. 10-034).
258
www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 255–259

Bithiophene-Fused Benzo[c]phospholes
[12] For the syntheses of phospholes by titanacyclopentadienes, see:
a) I. Tomita, M. Ueda, Macromol. Symp. 2004, 209, 217; b) I.
Tomita, Polym. Prepr. 2004, 45, 415; c) Y. Matano, T. Miya-
jima, T. Nakabuchi, Y. Matsutani, H. Imahori, J. Org. Chem.
2006, 71, 5792. See also refs.[4d,7b]
[13] U. Dahlmann, R. Neidlein, Helv. Chim. Acta 1996, 79, 755.
[14] a) H. Urabe, T. Hata, F. Sato, Tetrahedron Lett. 1995, 36, 4261;
b) H. Urabe, F. Sato, J. Org. Chem. 1996, 61, 6756; c) F. Sato,
H. Urabe, S. Okamoto, Chem. Rev. 2000, 100, 2835 and refer-
ences cited therein.
These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
The dihedral angles between the phosphole ring and the two
thiophene rings are 6.0–8.8° for 4a and 3.3–7.7° for 7a. The
phosphorus atom is slightly deviated from the mean plane of
the benzo[c]phosphole skeleton by 0.14 Å for 4a and 0.06 Å for
7a.
a) S. Attar, W. H. Bearden, N. W. Alcock, E. C. Alyea, J. H.
Nelson, Inorg. Chem. 1990, 29, 425. Au–P, 2.220(9)–2.227(2) Å;
P–Au–Cl, 172.4(1)–178.8(1)°; b) see ref.[6b] Au–P, 2.2290(16)–
2.2300(16) Å; P–Au–Cl, 171.64(7)–174.63(8)°; c) Y. Dienes, M.
Eggenstein, T. Neumann, U. Englert, T. Baumgartner, Dalton
Trans. 2006, 1424. Au–P, 2.2249(12) Å; P–Au–Cl, 177.
The calculated structural parameters of 4m are in good accord-
ance with the experimentally determined parameters of 4a, sug-
gesting that 4m is a good model for discussing the electronic
structure of 4a. The structural parameters of 4m, 5m, and 6m
are summarized in Figure S4 in the Supporting Information.
[16]
[17]
[15] Crystal data for 4a: formula C30H19PS2, monoclinic, crystal
size 0.45ϫ0.20ϫ0.15 mm, space group P21/n (#14), a =
6.2062(2) Å,
b = 21.4229(9) Å, c = 17.4039(8) Å, β =
97.372(3)°, V = 2294.80(16) Å3, Z = 4, ρcalcd. = 1.374 gcm–3, μ
= 3.19 cm–1, collected 18067, independent 5203, parameters
299, Rw = 0.0728, R = 0.0383 [IϾ2.00σ(I)], GOF = 1.015.
Crystal data for 7a: formula C31H21PAuCl3PS2, triclinic, crystal
[18]
[19]
¯
size 0.20ϫ0.15ϫ0.05 mm, space group P1, a = 9.888(3) Å, b
=
12.243(4) Å,
c
=
12.481(4) Å,
α
=
100.709(4)°,
β
=
=
102.781(4)°, γ = 95.077(4)°, V = 1434.5(8) Å3, Z = 2, ρcalcd.
1.833 gcm–3, μ = 26.29 cm–1, collected 11613, independent
6302, parameters 344, Rw = 0.0648, R = 0.0329 [IϾ2.00σ(I)],
GOF = 1.012. CCDC-660029 (for 4a) and -660028 (for 7a)
contain the supplementary crystallographic data for this paper.
The HOMO and LUMO energies (in eV) are as follows: 4m
(–5.10, –1.89), 5m (–5.16, –1.96), 6m (–5.55, –1.60).
Received: October 24, 2007
Published Online: November 27, 2007
Eur. J. Org. Chem. 2008, 255–259
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
259