Effects of heterole spacers on the structural, optical, and electrochemical properties of 2,5-bis(1,5-diphenylphosphol-2-yl)heteroles

Article abstract of DOI:10.1002/hc.20708

2,5-Bis(1,5-diphenylphosphol-2-yl)he-terole derivatives were prepared via Pd-catalyzed Stille-type cross-coupling reactions of α-(tributylstannyl) phosphole or α-iodophosphole with the corresponding 2,5-difunctionalized heteroles (pyrrole, furan, and thio

Full text of DOI:10.1002/hc.20708

Heteroatom Chemistry
Volume 22, Number 3/4, 2011
Effects of Heterole Spacers on the Structural,
Optical, and Electrochemical Properties of
2,5-Bis(1,5-diphenylphosphol-2-yl)heteroles
Yoshihiro Matano,1 Arihiro Saito,1 Masato Fujita,1
and Hiroshi Imahori1−3
1Department of Molecular Engineering, Graduate School of Engineering, Kyoto University,
Nishikyo-ku, Kyoto 615-8510, Japan
2Institute for Integrated Cell-Material Sciences (iCeMS), Kyoto University, Nishikyo-ku,
Kyoto 615-8510, Japan
3Fukui Institute for Fundamental Chemistry, Kyoto University, Sakyo-ku, Kyoto 606-8103, Japan
Received 31 August 2010; revised 21 November 2010
and, as a result, narrows HOMO–LUMO gaps. In
ABSTRACT: 2,5-Bis(1,5-diphenylphosphol-2-yl)he-
each series (σ3-P or σ4-P=O), the lowest π–π* tran-
terole derivatives were prepared via Pd-catalyzed Stille-
sition energies of the phosphole–heterole–phosphole
type cross-coupling reactions of α-(tributylstannyl)
π-systems were found to decrease in the following
phosphole or α-iodophosphole with the correspond-
order: thiophene > furan > pyrrole, and their elec-
ing 2,5-difunctionalized heteroles (pyrrole, furan, and
trochemical oxidation and reduction potentials shift
thiophene). X-ray crystallographic analyses of three
to the negative side in the same order. These results
σ4-P derivatives have elucidated that the coplanar
basically reflect the differences in ionization poten-
phosphole-heterole-phosphole π-networks are con-
tial and electron affinity of the central heterole spac-
structed in both anti–anti and syn–anti conforma-
ers. Density functional theory calculations on the
tions. In the case of the pyrrole-linked σ4-P deriva-
model compounds supported the experimentally ob-
tives, there is a weak hydrogen-bonding interaction
served results. The HOMO of the molecule resides
between NH and P=X (X = O, S) groups. The
on the conjugated polyene network of the π-system,
optical and electrochemical properties of the σ3-P
whereas the LUMO is strongly located on the phosp-
and σ4-P=O derivatives were revealed experimen-
hole subunits. The present comparative study demon-
tally by means of UV–vis absorption/emission spec-
strates, for the first time, that the intriguing electronic
troscopy and cyclic/differential pulse voltammetry. In
structures and the fundamental properties of the 2,5-
all the heterole-linked derivatives, the P-oxidation low-
bis(1,5-diphenylphosphol-2-yl)heteroles can be finely
ers LUMO levels more efficiently than HOMO levels
tuned by simple selection of the appropriate heterole
ꢀ
C
spacer. 2011 Wiley Periodicals, Inc. Heteroatom Chem
22:457–470, 2011; View this article online at wileyonlineli-
Dedicated to Professor Kin-ya Akiba on the occasion of his 75th
brary.com. DOI 10.1002/hc.20708
birthday.
Correspondence to: Yoshihiro Matano; e-mail: matano@scl
.kyoto-u.ac.jp.
Contract grant sponsor: Grants-in-Aid from the Ministry of
Education, Culture, Sports, Science and Technology, Japan.
Contract grant number: 21108511.
INTRODUCTION
Contract grant sponsor: Asahi Glass Foundation.
Contract grant number: 22350016.
2011 Wiley Periodicals, Inc.
Phosphole is now regarded as a promising con-
stituent for making π-conjugated organic materials
c
ꢀ
457

458 Matano et al.
with a low-lying LUMO, a narrow HOMO–LUMO
gap, and a polarizable dienic unit [1]. These char-
acteristic properties of phosphole are derived from
effective σ*–π* orbital interaction between the phos-
phorus center and the adjacent 1,3-diene unit. There-
fore, chemical functionalizations at the phospho-
rus and α-carbon atoms of the phosphole ring are
promising strategies to control the optoelectronic
properties of phosphole-containing π-systems.
of K-1 (E = S) [6]. To our knowledge, however,
optical and electrochemical properties of K-1
and K-2 have not been discussed in the litera-
ture. Re´au and co-workers reported the optical,
electrochemical, and electroluminescent proper-
ties of thiophene- and bithiophene-linked phosp-
hole derivatives K-3, which had been prepared by
the Fagan–Nugent method from the corresponding
thiophene–acetylene precursors [7]. Importantly,
both types A and B phosphole derivatives can be re-
garded as the smallest units of phosphole–heterole
π-conjugated oligomers and polymers, which have
received increasing attention in the search of poten-
tial candidates for the phosphorus-based optoelec-
trochemical materials [8]. In this context, it is of sig-
nificance to understand electronic and steric effects
of the heterole spacers on the fundamental proper-
ties of type B phosphole derivatives. Recently, we
reported the first examples of α,αꢁ-linked terphos-
pholes 1P [9] and 2P [10] (Fig. 1), which ex-
hibited considerably narrow HOMO–LUMO gaps
derived from the phosphole–phosphole–phosphole
linkage. In this study, we aimed to establish a con-
venient method for the construction of phosphole–
heterole–phosphole (heterole: pyrrole, furan, thio-
phene) linkages and to elucidate intrinsic effects
of these heterole spacers on the fundamental prop-
erties of type B phosphole derivatives. We report,
herein, a new synthesis of three classes of 2,5-bis(1,5-
diphenylphosphol-2-yl)heteroles 1X and 2X (X =
N, O, S) based on the Pd-catalyzed cross-coupling
method. With a series of type B compounds avail-
able, we have comparatively elucidated the effects
of the heterole-spacers on the structural, optical,
and electrochemical properties of the phosphole–
heterole–phosphole π-systems.
X
X
X
P
P
P
R
E
R
E
E R
A (X = heteroatom)
B (X = heteroatom)
Heterole–phosphole–heterole hybrid π-systems
of general formula [2,5-bis(2-heterolyl)phos-
A
pholes], especially those bearing 2-thienyl groups,
have been extensively studied, and their fundamen-
tal properties have proven to correlate well with the
character of the α-substituents [2–5]. In these com-
pounds, the central phosphole subunit provides a π-
spacer framework to enable conjugative connectivity
to adjacent heterole moieties. In contrast, the num-
ber of phosphole–heterole–phosphole π-systems of
general formula B [2,5-bis(2-phosphoryl)heteroles]
is rather limited as compared with that of type A
derivatives.
Figure 1 depicts a few examples of type B com-
pounds reported previously. Mathey and co-workers
reported a multistep synthesis of K-1 and K-2 via
Friedel–Crafts C C bond-forming reactions of 3,4-
dimethylphosphole P-metal complexes with the re-
spective heteroles and disclosed a crystal structure
Me
Me
Me
Me
Me
Me
Me
Me
S
O
P
P
E Me
P
P
S Me
X
X
Me E
K-1 (E = lone pair, S)
Me S
Ph
Ph
Ph
Ph
P
P
P
P
K-2
Ph O
O Ph
Ph
Ph
1X
2X
(X = NH, O, S)
S
R
P
R
P
n
Ph E
E Ph
K-3 (n = 1, 2; E = lone pair, S; R = 2-thienyl, 2-pyridyl)
RESULTS AND DISCUSSION
Synthesis of
2,5-Bis(1,5-diphenylphosphol-2-yl)heteroles
Ph O
P
Ph
P
Ph
Ph Ph
Ph
P
P
P
P
Scheme 1 illustrates the synthesis of 2,5-bis(1,5-
diphenylphosphol-2-yl)heterole P-oxide derivatives
2X. The starting materials α-iodophosphole 3 and
α-(tributylstannyl)phosphole 4 were prepared ac-
cording to the reported procedure [10]. Both of
Ph
Ph
Ph O
O Ph
1P
2P
FIGURE 1 Examples of 2,5-bis(phosphoryl)heteroles.
Heteroatom Chemistry DOI 10.1002/hc

Effects of Heterole Spacers on the Properties of 2,5-Bis(1,5-diphenylphosphol-2-yl)heteroles 459
cat. Pd2(dba)3
cat. P(2-furyl)3
O
O
Bu3Sn
SnBu3
+
2 Ph
I
Ph
Ph
P
P
Ph O
P
NMP, 80°C
O
Ph
O Ph
3
5
2O (27%)
cat. Pd2(dba)3
cat. P(2-furyl)3
CuI
X
X
2 Ph
SnBu3
+
Ph
Ph
I
I
P
P
Ph O
P
O Ph
NMP, RT
O
Ph
4
6S (X = S)
2S (X = S; 75%)
6N (X = NBoc)
7N (X = NBoc; ca. 53%)
2N (X = NH; 81%)
180°C
SCHEME 1 Synthesis of σ4-P=O derivatives 2X.
these functionalized phospholes have proven to be
promising synthons in cross-coupling reactions [10].
Treatment of 3 with 2,5-bis(tributylstannyl)furan
5 in the presence of Pd2(dba)3 and P(2-furyl)3 in
NMP for 47 h at 80◦C afforded phosphole–furan–
phosphole P-oxide 2O as the major product. The
low-yield formation of 2O was attributable in a
part to an occurrence of a side reaction, ho-
mocoupling of 5 under the reaction conditions
employed. Phosphole–thiophene–phosphole P-oxide
2S and phosphole–Boc–pyrrole–phosphole P-oxide
7N (Boc = tert-butoxycarbonyl) were prepared by
the Pd-CuI-promoted Stille-type reaction between
α-(tributylstannyl)phosphole 4 and the correspond-
ing 2,5-diiodoheteroles 6X (X = S, N). Under the
Pd-CuI reaction conditions, 4 was consumed within
2 h at room temperature, although the formation of
a small amount of α,α’-biphosphole, namely a ho-
mocoupling product of 4, could not be suppressed
completely. When heated at 180◦C for 30 min with-
out solvent, the Boc group of 7N was successfully
deprotected to afford 2N in 81% yield. Compounds
2O, 2S, 2N, and 7N possess two chiral centers at
phosphorus, and were obtained as a mixture of two
diastereomers. The diastereoselectivity of the cross-
coupling reaction (major/minor) was found to be
62/38 for 2O, 65/35 for 2S, and 62/38 for 7N (de-
termined by 1H and 31P NMR). The diastereomers of
2O and 7N were successfully separated from each
other by a combination of recrystallization and col-
umn chromatography, but those of 2S were difficult
to separate by these methods because of the low sol-
ubility. Compound 2N was obtained as a single di-
astereomer from one of the diastereomers of 7N, by
retention of the stereochemistry at phosphorus.
Reductive deoxygenation at the phosphorus cen-
ters of 2O and 2S (each a mixture of diastereomers)
was achieved with trichlorosilane in chloroform to
give 1O and 1S, respectively (Scheme 2). Compound
1O was isolated in 74% yield by recrystallization,
whereas 1S was isolated in 44% yield by column
chromatography. The σ4-P=O centers of 7N were
also reduced in the same manner, by treatment with
excess trichlorosilane. However, it was found that
the Boc group of the resulting σ3-P product could
not be removed cleanly under our reaction condi-
tions (NaOMe in THF-MeOH, reflux, 21 h). Hence,
we decided to synthesize the pyrrole-linked σ3-P
derivative 1N via P-sulfide 8N. Heating a mixture
of 7N and Lawesson’s reagent in toluene afforded
the phosphole–pyrrole–phosphole P-sulfide 8N ac-
companied by simultaneous deprotection of the
N-Boc group. The reductive desulfurization of 8N
proceeded smoothly by reflux with excess P(NMe2)3
in toluene to produce the target compound 1N in
good yield. In contrast to the σ4-P derivatives 2X,
two diastereomers of the σ3-P derivatives 1X were
HSiCl3
2O
2S
X
Ph
Ph
CHCl3
P
P
Ph
Ph
1O (X = O; 74%)
1S (X = S; 44%)
H
N
Lawesson
toluene
7N
Ph
Ph
P
P
Ph E
E Ph
8N (E = S; 82%)
1N (E = lone pair; 83%)
P(NMe2)3
SCHEME 2 Synthesis of σ3-P derivatives 1X.
Heteroatom Chemistry DOI 10.1002/hc

460 Matano et al.
not separable from each other, suggesting that the
pyramidal inversion occurs at the phosphorus cen-
1
ters for 1X [11]. Indeed, two sets of H peaks due
to the furan-β protons of 1O coalesced at 75◦C in
Cl2CDCDCl2. It should be noted here that the same
diastereomeric mixtures of 1O and 1N were ob-
tained from 2O and 8N, respectively. These results
imply that there is very little difference in the ther-
modynamic stability between two diastereomers of
1X.
Characterization of 2,5-Bis(1,5-diphenylphos-
phol-2-yl)heteroles
Thenewly preparedphosphole-heterole-phosphole π-
systems,2,5-bis(1,5-diphenylphosphol-2-yl)heterole
derivatives 1X, 2X, 7N, and 8N, were characterized
by standard spectroscopic techniques (1H, 31P NMR,
high-resolution MS, IR) and X-ray crystallography
(for 2O, 2N, and 8N). In the 31P NMR spectra of
the diastereomeric mixtures in CDCl3, a set of two
singlet peaks with similar intensity was observed
at δP 29.3–33.7 ppm for 1X and δP 52.5–54.2 ppm
for 2X. The differences in δP values between two
diastereomers of 1X and 2X were found to be very
small (ꢀδP < 0.4 ppm). The 31P chemical shifts ob-
served for a series of the pyrrole-linked derivatives
1N (δP 29.3, 29.6 ppm), 2N (δP 54.2 ppm for one
diastereomer), and 8N (δP 64.5, 65.9 ppm) represent
the intriguing nature of the relevant phosphorus
centers. In the 1H NMR spectra, all the diastere-
omers of 1X and 2X displayed symmetrical spectral
patterns owing to Cs or C2 symmetry, indicating that
the rotation at the interring carbon–carbon bonds
takes place rapidly on the NMR time scale. The
reduction at the phosphorus center from σ4-P=O
(2X) to σ3-P (1X) induces noticeable upfield shifts
of the heterole-β protons by 0.25–0.43 ppm. This
implies that the changes in hybridization mode
and electron density at the phosphorus atoms are
strongly reflected in the electronic character of the
central heterole subunits through the π-network.
FIGURE
2 (a) Top view and (b) side view of 2O
(30% probability ellipsoids). Hydrogen atoms are omit-
˚
ted for clarity. Selected bond lengths (A) and an-
gles (◦): C(1)–C(2), 1.366(6); C(2)–C(3), 1.481(6); C(3)–
C(4), 1.353(6); C(4)–C(5), 1.427(6); C(5)–C(6), 1.364(6);
C(6)–C(7), 1.406(6); C(7)–C(8), 1.377(6); C(8)–C(9),
1.430(6); C(9)–C(10), 1.362(5); C(10)–C(11), 1.470(6);
C(11)–C(12), 1.350(6); P(1)–C(1), 1.835(4); P(1)–C(4),
1.827(4); P(1)–O(1), 1.480(3); P(2)–C(9), 1.812(4); P(2)–
C(12), 1.830(4); P(2)–O(2), 1.492(3); C(1)–P(1)–C(4),
93.68(19); O(1)–P(1)–C(1), 118.84(19); O(1)–P(1)–C(4),
117.87(18); C(9)–P(2)–C(12), 94.13(19); O(2)–P(2)–C(9),
116.37(18); O(2)–P(2)–C(12), 119.26(18).
present phosphole–pyrrole–phosphole π-systems
(ꢀδNH = 1.71–1.79/2.16–2.28 ppm; 2N/8N rel-
ative to 1N) is larger than that reported
for the pyrrole–phosphole–pyrrole π-systems
(ꢀδNH = 1.02/1.70 ppm; σ4-P=O/P=S relative to
σ3-P) [5]. The fact that ꢀδNH values vary depending
on the ratio of NH/P=X groups may support the
above interpretation.
The structures of 2O, 2N, and 8N (each, one
of the diastereomers) were further elucidated by
X-ray crystallography (Figs. 2–4). In the furan-
linked derivative 2O, both of the phosphole rings
adopt S-trans (anti) conformation against the furan
ring, and two P-phenyl groups are nonalternated.
The distortion between the central furan and adja-
cent phosphole rings is very little (dihedral angles,
α = 177.7◦and 175.9◦), which implies that the
phosphole–furan–phosphole π-system is effectively
conjugated. In the pyrrole-linked derivatives 2N and
8N, one phosphole ring adopts S-trans (anti) con-
formation against the pyrrole ring, whereas the
other adopts S-cis (syn) conformation. Based on this
1
In the H NMR spectra of P-oxide 2N and P-sulfide
8N in CDCl3, the NH protons were observed at
δH 9.75 ppm (one diastereomer) and 10.20/10.24
ppm (a mixture of diastereomers), respectively.
The downfield appearances of the NH peaks of 2N
and 8N relative to those of 1N (δH 7.96/8.04 ppm)
indicate that the NH protons of these σ4-P deriva-
tives receive spatial electronic influences from the
neighboring P=O or P=S groups. In other words,
hydrogen-bonding interaction operates between the
NH protons and the oxygen/sulfur atoms bound to
phosphorus in 2N and 8N (vide infra). The degree
of downfield shifts of the NH peaks observed for the
Heteroatom Chemistry DOI 10.1002/hc

Effects of Heterole Spacers on the Properties of 2,5-Bis(1,5-diphenylphosphol-2-yl)heteroles 461
FIGURE 4 (a) Top view and (b) side view of 8N (30%
probability ellipsoids). Hydrogen atoms except for NH are
˚
omitted for clarity. Selected bond lengths (A) and angles
(◦): C(1)–C(2), 1.352(5); C(2)–C(3), 1.461(5); C(3)–C(4),
1.354(4); C(4)–C(5), 1.422(4); C(5)–C(6), 1.375(5); C(6)–
C(7), 1.393(5); C(7)–C(8), 1.384(4); C(8)–C(9), 1.434(4);
C(9)–C(10), 1.350(4); C(10)–C(11), 1.455(4); C(11)–C(12),
1.364(5); P(1)–C(1), 1.828(3); P(1)–C(4), 1.819(3); P(1)–
S(1), 1.9486(13); P(2)–C(9), 1.807(3); P(2)–C(12), 1.822(3);
P(2)–S(2), 1.9580(13); C(1)–P(1)–C(4), 93.99(15); S(1)–
P(1)–C(1), 117.61(11); S(1)–P(1)–C(4), 117.19(11); C(9)–
P(2)–C(12), 94.24(15); S(2)–P(2)–C(9), 114.76(11); S(2)–
P(2)–C(12), 122.46(11).
FIGURE 3 (a) Top view and (b) side view of 2N (30%
probability ellipsoids). Hydrogen atoms except for NH are
˚
omitted for clarity. Selected bond lengths (A) and angles
(◦): C(1)–C(2), 1.351(4); C(2)–C(3), 1.488(4); C(3)–C(4),
1.360(4); C(4)–C(5), 1.440(4); C(5)–C(6), 1.384(4); C(6)–
C(7), 1.403(4); C(7)–C(8), 1.385(4); C(8)–C(9), 1.437(4);
C(9)–C(10), 1.358(4); C(10)–C(11), 1.476(4); C(11)–C(12),
1.360(4); P(1)–C(1), 1.820(3); P(1)–C(4), 1.809(3); P(1)–
O(1), 1.491(2); P(2)–C(9), 1.813(3); P(2)–C(12), 1.826(3);
P(2)–O(2), 1.488(2); C(1)–P(1)–C(4), 93.88(14); O(1)–P(1)–
C(1), 116.24(14); O(1)–P(1)–C(4), 117.66(14); C(9)–P(2)–
C(12), 94.35(14); O(2)–P(2)–C(9), 114.83(14); O(2)–P(2)–
C(12), 121.62(14).
through the phosphole–pyrrole–phosphole linkage is
exhibited as relatively small dihedral angles between
the central pyrrole and adjacent syn/anti phosphole
rings (9.9◦/163.4◦ for 2N, and 16.8◦/175.8◦ for 8N).
The C–C bond length alternation in the phos-
anti–syn π-plane, the relative orientation of two P-
phenyl groups is alternated (alt) for 2N and non-
alternated (non-alt) for 8N (Considering an anti–anti
conformation as the standard π-plane, the observed
orientations of two P-phenyl groups are defined as
non-alt for 2N and alt for 8N). In spite of the differ-
ent orientation of the P-phenyl groups, the structural
features of the π-network observed for 2N are simi-
lar to those observed for 8N. In the crystal structure
of Mathey’s thiophene-linked π-system K-1 (E = S)
[6], one of the phosphole rings (syn conformation)
is almost coplanar (3.3◦) with the thiophene ring,
whereas the other (anti conformation) significantly
deviates from coplanarity (138.9◦). The dissymme-
try observed for alt K-1 was attributed to packing
effects in the crystalline state. In our pyrrole-linked
π-systems 2N and 8N, the effective π-conjugation
˚
phole rings (ꢀl = 0.09–0.13 A; Julg index = 0.55–
0.73) in 2O, 2N, and 8N is obvious as compared
˚
˚
to that of the central furan (ꢀl = 0.03–0.04 A;
Julg index = 0.95) and pyrrole (ꢀl = 0.01–0.02 A;
Julg index = 0.96–0.98), which reflects not only a
marked difference in aromaticity between phosp-
hole and the latter second-row heteroles but also
effective conjugation through the heterole spac-
ers. The interring C–C bond lengths of the P=S
˚
derivative 8N [(1.422(4), 1.434(4) A] are somewhat
shorter than those reported for the thiophene-linked
˚
P=S derivative K-1 [E = S; 1.452(4), 1.461(4) A],
which may indicate that the phosphole–pyrrole–
phosphole π-conjugation is more effective than
the phosphole–thiophene–phosphole π-conjugation.
Heteroatom Chemistry DOI 10.1002/hc

462 Matano et al.
Each phosphorus center forms a tetrahedral ge-
ometry with average C–P–C/C–P–O bond angles of
102.1◦/116.2◦ for 2O and 102.7◦/115.7◦ for 2N, and
average C–P–C/C–P–S bond angles of 101.5◦/116.4◦
for 8N. The N–H group of the pyrrole ring is directed
to the P-oxo (for 2N) or P-thioxo group (for 8N) of
the syn phosphole unit. It seems likely that weak
hydrogen-bonding interaction between the NH pro-
ton and the P-bound chalcogen atom is also present
in the solid state [12].
Optical and Electrochemical Properties of
2,5-Bis(1,5-diphenylphosphol-2-yl)heteroles
To reveal intrinsic effects of the heterole spacers and
the P-substituents on the optical and electrochem-
ical properties of the present phosphole–heterole–
phosphole π-systems, we measured UV–vis absorp-
tion and fluorescence spectra (Fig. 5), as well as the
redox potentials of 1X and 2X in CH2Cl2. The results
are summarized in Table 1 together with the data of
8N and previously reported 1P.
As shown in Fig. 5, the σ3-P derivatives 1X and
the σ4-P=O derivatives 2X displayed intense ab-
sorption bands attributable to π–π* transitions at
around 460–500 nm and 490–520 nm, respectively.
All of 1X are moderately fluorescent, emitting or-
ange fluorescence with quantum yields (ꢁf) of 0.03–
0.26, whereas 2X are weakly fluorescent (ꢁf < 0.01).
The spectral shapes of the pyrrole-linked derivatives
1N/2N are slightly different from those of the furan-
linked derivatives 1O/2O and the thiophene-linked
derivatives 1S/2S, suggesting that the character of
vibronic states of 1N/2N is different from that of
1O/2O and 1S/2S. Both absorption and emission
maxima (λab and λem) vary appreciably depending
on the heterole spacers, and the lowest π–π∗ exci-
tation energies for the σ3-P and σ4-P=O derivatives
decrease in the orders, 1S > 1O > 1N > 1P and
2S > 2O > 2N, respectively. As typically observed
for π-conjugated phosphole derivatives, the oxida-
tion at the phosphorus center from σ3-P to σ4-P=O
induced redshifts of λab and λem values, resulting in
a decreased optical HOMO–LUMO gaps. The differ-
ences in λab/λem values (ꢀλab/ꢀλem) between 1N and
2N (41/63 nm) are larger than those between 1X
and 2X (X = O, 27/34 nm; X = S, 20/30 nm), indi-
cating that the P-oxidation makes more significant
impacts on the polarizability of the pyrrole-linked
π-system than that of the furan- and thiophene-
linked π-systems. Presumably, the charge-transfer
character of the whole π-system is enhanced most
effectively for the pyrrole-linked derivatives, as the
highly electron-donating pyrrole ring and the highly
FIGURE 5 UV–vis absorption (solid line) and fluorescence
(dashed line) spectra of 1X and 2X in CH2Cl2. The fluores-
cence spectra are normalized for comparison.
electron-accepting P-oxo phosphole rings are con-
nected in 2N.
Redox potentials of 1X, 2X, and 8N (mixtures
of diastereomers except for 2N) were measured by
using cyclic voltammetry (CV) and differential pulse
voltammetry (DPV) with 0.1 M nBu4NPF6 as an elec-
trolyte. Both electrochemical reduction and oxida-
tion processes of the σ4-P=O derivatives 2X were ob-
served at more positive potentials than those of the
σ3-P derivatives 1X, indicating that the P-oxidation
lowers HOMO and LUMO levels of the phosphole-
heterole–phosphole π-systems. Compounds 1N, 1O,
and 1S showed reversible voltammograms for the
first oxidation process and irreversible voltammo-
grams for the first reduction process. The first oxida-
tion potentials (Eox) of 1X are shifted to the negative
side in the order 1N > 1O ≈ P > 1S, whereas the
Heteroatom Chemistry DOI 10.1002/hc

Effects of Heterole Spacers on the Properties of 2,5-Bis(1,5-diphenylphosphol-2-yl)heteroles 463
TABLE 1 Optical and Electrochemical Data for 1X, 2X, and 8N in CH2Cl2
Compound
λ
ab(nm)a(log ε)
λ
em(nm)b(ꢀ )
Eox(V)c
Ered(V)c
Eg(V)d
f
1Ne
1Oe
1Pe,f
1Se
2Ng
2Oe
2Se
8Ng
478 (4.55)
472 (4.55)
502 (4.39)
467 (4.57)
519 (4.52)
499 (4.51)
487 (4.45)
517 (4.49)
561 (0.26)
550 (0.03)
634 (<0.01)
542 (0.05)
624 (<0.01)
575 (<0.01)
572 (<0.01)
627 (<0.01)
+0.01 (r)
+0.16 (r)
+0.16 (ir)
+0.24 (r)
+0.32 (ir)
+0.50 (ir)
+0.57 (ir)
+0.31 (r)
−2.36 (ir)
−2.32 (ir)
−2.10 (ir)
−2.25 (ir)
−1.90 (qr)
−1.80 (qr)
−1.78 (qr)
−1.90 (ir)
2.37
2.48
2.26
2.49
2.22
2.30
2.35
2.21
aThe longest absorption maxima. Excited at 440 nm for 1X; 470 nm for 2O and 2S; 510 nm for 2N and 8N.
bFluorescence quantum yield relative to Re´au’s 3,4-C4-bridged 1-phenyl-2,5-dithienylphosphole P–AuCl complex (ꢀf = 0.129).
cThe first oxidation (Eox) and reduction (Ered) potentials (vs. Fc/Fc+) determined by DPV.r: reversible; qr: quasi-reversible; ir: irreversible.
dEg = Eox – Ered
.
eMixture of diastereomers.
f Data from [9].
gSingle diastereomer.
first reduction potentials (Ered) of 1X are shifted to
the positive side in the order, 1P > 1S > 1O > 1N.
These orders are basically the same as the orders
of ionization potential and electron affinity of pyr-
role, furan, phosphole, and thiophene (at B3LYP/6-
31G* level, HOMO/LUMO energies of pyrrole, fu-
ran, phosphole, and thiophene were calculated to
be –5.48/+1.39, –6.11/+0.54, –6.25/–1.01, and –6.33/–
0.21 eV, respectively) [13]. It is now evident that the
electron-donating and electron-accepting ability of
the phosphole–heterole–phosphole π-systems essen-
tially reflects the character of the heterole spacers.
For instance, the pyrrole-linked derivative 1N pos-
sesses the highest electron-donating ability, whereas
the phosphole-linked derivative 1P has the highest
electron-accepting ability. The electrochemical po-
tential gaps (Eg = Eox – Ered) decrease in the order,
1S ≈ O > 1N > 1P. This trend is in good accor-
dance with that observed in the absorption/emission
spectra of 1X. All the σ4-P=O derivatives 2X and
8N displayed irreversible oxidation processes and
quasi-reversible reduction processes in their cyclic
voltammograms. Both Eox and Ered of 2X (as deter-
mined by DPV) shifted to more positive values in the
order, 2S > 2O > 2N, although the differences be-
tween 2S and 2O are small. Similar to a series of 1X,
this order correlates well with the ionization poten-
tials and electron affinity of the respective heteroles
incorporated. The P-functionalizations from σ3 to σ4
(1X to 2X/8N) make more significant impacts on the
reduction processes (ꢀEred = 0.46–0.52 V) than the
oxidation processes (ꢀEox = 0.31–0.34 V). As a re-
sult, the potential gaps of 2X/8N (Eg = 2.21–2.35 V)
become narrower than the respective values of 1X
(Eg = 2.37–2.49 V), which well explains the differ-
ence in the above-mentioned optical HOMO–LUMO
gaps between 1X and 2X/8N.
Theoretical Calculations of
2,5-Bis(1-phenylphosphol-2-yl)heteroles
To get some insights into the intrinsic effects of the
heterole spacers on the electronic structures of the
present phosphole–heterole–phosphole π-systems,
we performed density functional theory (DFT) cal-
culations on model compounds 1Xm (X = N, O,
P, S) and 2Xm (X = N, O, S). In this study, we
calculated only non-alt diastereomers with anti–anti
conformation for all the models (it was found that
there is a negligible difference in total energy (ꢀE =
1.4 kcal mol−1) between alt and non-alt diastere-
omers of 2Om). Selected torsion/bond angles, bond
lengths and HOMO/LUMO energies are summarized
in Table 2. At the optimized structures that have
Cs symmetry, interring distortion between the cen-
tral heterole ring and the adjacent anti phosphole
ꢁ
ꢁ
rings are relatively small (C3–C2–C2 –C3 torsion an-
gle, α = 164.3–169.8◦), suggesting that the three het-
erole rings are effectively π-conjugated. The C3–C2–
ꢁ
C2 bond angles (β) of 1Nm, 1Om, and 2Om are
wider by 3.9–4.2◦ than those of 1Pm, 1Sm, and
2Sm, respectively, which simply reflects the differ-
ent sizes between the second-row heteroles (pyrrole,
furan) and the third-row heteroles (phosphole, thio-
phene). The P-oxidation (from 1Xm to 2Xm) in-
duces coplanarization (ꢀα = 0.5–2.9◦) between the
central heterole and the adjacent phosphole rings,
namely enhancement of conjugation of the heterole-
linked π-network. Indeed, the P-oxidation shortens
˚
the C–C bonds at a and c (ꢀl = 0.002–0.006 A) and
˚
lengthens the C–C bonds at b (ꢀl = 0.002–0.004 A).
In other words, the bond length alternation is di-
minished by the P-oxidation. These effects are most
prominent for the pyrrole-linked derivatives (from
1Nm to 2Nm), probably due to an increase in the
Heteroatom Chemistry DOI 10.1002/hc

464 Matano et al.
TABLE 2 Selected Torsion/Bond Angles, Bond Lengths, and Orbital Energies of 1Xm and 2Xma
α
α
X
a
b
a
b
X
c
Ph
Ph Ph
Ph
P
H
P
H
P
P
β
β
c
H
O
O H
1Xm (anti–anti; non-alt)
2Xm (anti–anti; non-alt)
C2,C2'
H
3'
2'
X
P
X
C3'
E
Ph
P
Ph
C3
P
α
2
H
E
E H
3
α = C3 – C2 – C2' – C3' β = C3 – C2 – C2'
1Nm
NH
1Om
O
1Pm
PH
1Sm
S
2Nm
NH
2Om
O
2Sm
S
X
α/◦◦
164.3
130.2
169.3
132.0
169.4
126.1
165.9
128.1
167.2
129.2
169.8
131.1
166.8
126.9
β/
˚
a/A
1.438
1.399
1.433
1.381
1.439
1.378
1.440
1.386
1.432
1.403
1.427
1.383
1.436
1.389
˚
b/A
˚
c/A
1.406
–1.77
–4.48
1.414
–1.91
–4.60
1.431
–2.11
–4.65
1.410
–1.96
–4.69
1.401
–2.43
–4.90
1.411
–2.54
–5.03
1.408
–2.54
–5.10
ELUMO/eV
EHOMO/eV
aCalculated at B3LYP/6–31G* level.
In both the σ3-P models 1Xm and the σ4-P=O
models 2Xm, HOMO essentially consists of the
conjugated polyene-derived π-networks, whereas
LUMO possesses a significant character of the two
phosphole subunits (Fig. 6). This is reasonable con-
sidering the intrinsic nature of the heterole spacers.
As generally observed for the phosphole-containing
π-systems, the P-oxidation (from 1Xm to 2Xm) low-
ers LUMO levels more significantly than HOMO lev-
els due to the effective σ*–π* orbital interaction at
the phosphole subunits. The heterole spacers play a
crucial role in fine-tuning of the HOMO and LUMO
charge-transfer character of the pyrrole–phosphole
linkage as compared to that of the furan–phosphole
and thiophene–phosphole linkages. In the case of
2Nm, a syn–anti form, which is the same as that ob-
served for 2N in the X-ray single-crystal structural
analysis, was also calculated. The bond parameters
of the π-conjugated units calculated for the syn–
anti diastereomer (see Table 3) are close to those
observed for 2N. The difference in total energy be-
tween the two diastereomers of 2Nm was found to
be 5.2 kcal mol−1, indicating that there is a small
difference in their thermodynamic stability.
TABLE 3 Selected Torsion/Bond angles, Bond Lengths, and Orbital Energies of 2Nm (syn-anti)a
H
P
H
P
Ph
Ph
H
N
H
N
O
α'
O
a'
α
a
b
Ph
Ph
P
P
β'
β
b'
c
O
H
O H
2Nm (syn–anti; non-alt)
α, α’/◦
β, β’/◦
168.0, 18.2
129.3, 133.4
a, a’/A
1.434, 1.432
1.406, 1.403
1.402
ELUMO/eV
EHOMO/eV
–2.35
–4.82
˚
˚
b, b’/A
˚
c/A
aCalculated at B3LYP/6–31G* level.
Heteroatom Chemistry DOI 10.1002/hc

Effects of Heterole Spacers on the Properties of 2,5-Bis(1,5-diphenylphosphol-2-yl)heteroles 465
FIGURE 6 HOMO and LUMO of 1Xm and 2Xm and their orbital energies.
levels. The HOMO levels lower in the following
orders: 1Nm > 1Om > 1Pm > 1Sm for the σ3-P
models and 2Nm > 2Om > 2Sm for the σ4-P=O
models, whereas the LUMO levels lower in the fol-
lowing orders: 1Nm > 1Om > 1Sm > 1Pm for the
σ3-P models and 2Nm > 2Om ≈ Sm for the σ4-P=O
models. In both series, the pyrrole-linked models
possess the highest HOMO and LUMO, whereas the
thiophene- or phosphole-linked models possess the
lowest ones. It is worth noting that these theoretical
results mostly agree with the experimental results of
the redox potentials determined by CV and DPV.
especially those containing phosphole–heterole link-
ages, on the basis of rational design of the π-
components.
EXPERIMENTAL
All melting points were recorded on a Yanagi-
moto micro melting point apparatus and are uncor-
1
rected. H, 13C, and 31P NMR spectra were recorded
on a JEOL JNM-EX400 spectrometer using CDCl3,
CD2Cl2, or Cl2CDCDCl2. Chemical shifts are re-
ported in ppm as relative values versus tetram-
1
ethylsilane (internal reference for H and 13C) and
phosphoric acid (external reference for 31P). High-
resolution mass spectra (HRMS) were obtained on
a JEOL JMS-HS110 spectrometer or a Thermo
Scientific Exactive Spectrometer. IR spectra were
recorded on a JASCO FT/IR-470 Plus spectrom-
eter using KBr pellets. UV–vis absorption spec-
tra were measured on a PerkinElmer Lambda
900 UV/vis/NIR spectrometer. Steady-state fluores-
cence spectra were recorded with a HORIBA SPEX
Fluoromax-3 spectrofluorometer. Electrochemical
measurements were made with an ALS 630a elec-
trochemical analyzer using a glassy carbon work-
ing electrode, a platinum wire counter electrode,
and an Ag/Ag+ [0.01 M AgNO3, 0.1 M nBu4NPF6
CONCLUSION
In summary, we established a convenient method
for the synthesis of 2,5-bis(1,5-diphenylphosphol-2-
yl)heterole derivatives and investigated their struc-
tural, optical, and electrochemical properties com-
paratively. It has been revealed for the first time
that the fundamental properties of the phosphole–
heterole–phosphole π-systems, in both σ3-P and
σ4-P=O forms, are deeply related to the intrinsic
nature of the central heterole spacers. Most impor-
tantly, the present results provide a practical guide-
line to fine-tune the character of HOMO and LUMO
of the phosphole–based π-conjugated materials,
Heteroatom Chemistry DOI 10.1002/hc

466 Matano et al.
(MeCN)] reference electrode. The potentials were
calibrated with ferrocene/ferrocenium [Emid = +0.20
V vs. Ag/Ag+]. Phospholes 3 and 4 were prepared
according to the reported procedures [10]. The sol-
vents used for the reactions were distilled from
sodium benzophenone ketyl (THF and Et2O) or
calcium hydride (CH2Cl2) under inert atmosphere
before use. Other chemicals and solvents were of
reagent-grade quality and used without further pu-
rification. All reactions were performed under an ar-
gon atmosphere.
Ph), 7.29 (t, J = 7.6 Hz, 4H; m-Ph), 7.36–7.40
(m, 4H; m-Ph–P), 7.43–7.47 (m, 2H; p-Ph–P), 7.60
(d, J = 7.6 Hz, 4H; o-Ph), 7.76–7.81 (m, 4H;
o-Ph–P); 13C NMR (100 MHz, CDCl3): δ 26.4, 29.6
(d, J = 9.9 Hz), 30.1 (d, J = 12.4 Hz), 113.1 (d, J =
2.5 Hz), 117.2 (d, J = 101.7 Hz), 126.0 (d, J = 100.0
Hz), 127.6 (d, J = 6.6 Hz), 127.7, 128.8, 128.9 (d,
J = 11.6 Hz), 130.3 (d, J = 91.7 Hz), 130.5 (d, J =
10.7 Hz), 132.1 (d, J = 2.5 Hz), 133.1 (d, J = 9.9 Hz),
149.4 (d, J = 21.5 Hz), 153.2 (d, J = 23.1 Hz), 155.8
(d, J = 24.8 Hz); 31P NMR (162 MHz, CDCl3): δ +52.7;
IR(KBr): νmax 1193 cm−1 (P=O); HRMS (APCI) m/z:
Calcd for C42H35O3P2: 649.2061; Found 649.2048
([M + H]+).
Compound 2O
Pd2(dba)3 (9.2 mg, 0.010 mmol) and tris(2-
furyl)phosphane (9.2 mg, 0.040 mmol) were stirred
in NMP (1.0 mL) for 1 h at room temper-
ature. To this mixture, an NMP solution (1.5
mL) containing 4 (88.1 mg, 0.21 mmol) and 2,5-
bis(tributylstannyl)furan (64.6 mg, 0.10 mmol) was
added. The mixture was stirred for 47 h at 80◦C,
followed by addition of a saturated aqueous NH4Cl
solution. The aqueous phase was extracted with
EtOAc three times, and an organic phase was washed
with brine, dried over Na2SO4, and evaporated un-
der reduced pressure. The residue was subjected
to silica gel column chromatography (CHCl3 to
CHCl3/acetone/MeOH = 70/10/1), and a red frac-
tion was collected and evaporated. Reprecipitation
of the resulting solid from CHCl3/hexane afforded
2O as a purplish red solid (17.5 mg, 27%; a mix-
ture of the two diastereomers). Diastereomers were
separated by silica gel column chromatography
(CHCl3/acetone = 10/1 to 8/1).
Compound 1O
A mixture of 2O (64.6 mg, 0.10 mmol), HSiCl3
(0.50 mL, 4.9 mmol), and CHCl3 (5.0 mL) was
stirred at 80◦C. After 2 h the mixture was concen-
trated under reduced pressure to remove unreacted
HSiCl3, followed by addition of a saturated aqueous
NaHCO3 solution. Insoluble substances were filtered
off through a Celite bed, and the organic phase was
washed with water, dried over Na2SO4, and evapo-
rated under reduced pressure. Reprecipitation of the
resulting solid from CH2Cl2/MeOH afforded 1O as a
reddish orange solid (45.1 mg, 74%).
1O: mp (a mixture of 1:1 diastereomers) 215◦C
1
(dec); H NMR (400 MHz, CDCl3): δ 2.32–2.40 (m,
4H; CH2), 2.55–3.02 (m, 8H; CH2), 6.18 (s, 2H; furan-
β; isomer A), 6.21 (s, 2H; furan-β; isomer B), 7.08–
7.13 (m, 2H; p-Ph), 7.20–7.25 (m, 10H; m-Ph + m-
Ph–P + p-Ph–P), 7.43–7.47 (m, 8H; o-Ph + o-Ph–P);
31P NMR (162 MHz, CDCl3): δ +30.6, +31.0; HRMS
(APCI) m/z: Calcd for C42H34OP2: 616.2085; Found
616.2077 (M+).
1
2O-A: Brownish red solid; mp 250◦C (dec); H
NMR (400 MHz, CDCl3): δ 2.12–2.23 (m, 2H; CH2),
2.31–2.38 (m, 2H; CH2), 2.86–3.01 (m, 6H; CH2),
3.15–3.20 (m, 2H; CH2), 6.47 (s, 2H; furan-β), 7.20
(t, J = 7.4 Hz, 2H; p-Ph), 7.29 (t, J = 7.4 Hz, 4H;
m-Ph), 7.37 (dt, J = 2.4, 7.0 Hz, 4H; m-Ph–P), 7.45
(t, J = 7.2 Hz, 2H; p-Ph–P), 7.61 (d, J = 7.6 Hz,
4H; o-Ph), 7.76 ppm (dd, J = 7.2, 12.0 Hz, 4H; o-
Ph–P); 13C NMR (100 MHz, CDCl3): δ 26.4, 29.7 (d,
J = 10.7 Hz), 30.1 (d, J = 12.3 Hz), 113.4, 117.4 (d,
J = 101.6 Hz), 126.1 (d, J = 100.8 Hz), 127.6 (d, J =
7.4 Hz), 127.7, 128.8, 128.9 (d, J = 12.3 Hz), 130.3
(d, J = 91.7 Hz), 130.4 (d, J = 10.7 Hz), 132.1 (d,
J = 2.5 Hz), 133.1 (d, J = 13.3 Hz), 149.5 (d, J =
24.0 Hz), 152.4 (d, J = 23.1 Hz), 155.8 (d, J = 24.8
Hz); 31P NMR (162 MHz, CDCl3): δ +52.5; IR(KBr);
νmax 1195 cm−1 (P=O).
Compound 2S
Pd2(dba)3 (13.5 mg, 0.015 mmol) and tris(2-
furyl)phosphane (13.6 mg, 0.059 mmol) were stirred
in NMP (1.5 mL) for 1 h at room temperature. To
this mixture, an NMP solution (6.0 mL) containing
3 (368.7 mg, 0.63 mmol) and 2,5-diiodothiophene
(98.9 mg, 0.29 mmol) was added. After Ar bubbling
for 30 min, CuI (127.2 mg, 0.68 mmol) was added
and the resulting mixture was stirred for 1.5 h at the
room temperature. Cold EtOAc (24 mL) was added
to the mixture, and brown precipitates were col-
lected. The crude product was dissolved in CHCl3,
and insoluble substances were filtered off through a
Celite bed. The red solution was evaporated and re-
precipitated from CHCl3/hexane to give analytically
pure 2S as a reddish orange solid (148 mg, 75%).
2O-B: Red solid; mp 252◦C (dec); 1H NMR
(400 MHz, CDCl3): δ 2.11–2.18 (m, 2H; CH2), 2.28–
2.38 (m, 2H; CH2), 2.83–2.97 (m, 8H, CH2), 6.49
(s, 2H; furan-β), 7.20 (t, J = 7.6 Hz, 2H; p-
Heteroatom Chemistry DOI 10.1002/hc

Effects of Heterole Spacers on the Properties of 2,5-Bis(1,5-diphenylphosphol-2-yl)heteroles 467
because of the low solubility, we did not attempt to
chromatography (CH2Cl2 to CH2Cl2/acetone = 1/1)
separate two diastereomers of 2S. mp (a mixture of
6:4 diastereomers) 200◦C (dec); 1H NMR (CDCl3, 400
MHz): δ 2.11–2.22 (m, 2H; CH2), 2.31–2.40 (m, 2H;
CH2), 2.75–3.03 (m, 8H; CH2), 7.16 (s, 2H; Th-β; iso-
mer A), 7.19 (s, 2H; Th-β; isomer B), 7.19 (t, J =
7.3 Hz, 2H; p-Ph), 7.29 (pseudo t, J = 7.8 Hz, 4H;
m-Ph), 7.33–7.39 (m, 4H; m-Ph–P), 7.40–7.46 (m, 2H;
p-Ph–P), 7.61 (d, J = 7.3 Hz. 4H; o-Ph), 7.74–7.79
to give 7N-A (R = 0.45 CH2Cl/acetone = 10/1) and
f
7N-B (R = 0.20 at CH2Cl/acetone = 10/1). After re-
f
precipitation from hexane, 7N-B was obtained as an
orange solid (339 mg, 20%). By contrast, 7N-A (ca.
550 mg, ca. 33%) was obtained as a mixture with a
small amount of the side product, 2,2’-biphosphole
[10].
1
7N-A. Red solid; H NMR (CDCl3, 400 MHz):
1
(m, 4H; o-Ph–P); 31P{ H} NMR (CDCl3, 162 MHz): δ
δ 1.45 (s, 9H; Boc), 1.99–2.09 (m, 2H; CH2), 2.20–2.28
(m, 2H: CH2), 2.62–2.72 (m, 4H; CH2), 2.90–3.00 (m,
4H; CH2), 6.03 (s, 2H; pyrrole-β), 7.20 (t, J = 7.3 Hz,
2H; p-Ph), 7.29 (pseudo t, J = 7.6 Hz, 4H; m-Ph),
7.34–7.38 (m, 4H; m-Ph–P), 7.43–7.46 (m, 2H; p-Ph–
P), 7.61 (d, J = 7.8 Hz, 4H; o-Ph), 7.76 ppm (dd,
+52.8, 53.1; IR (KBr): νmax 1181 (P= O) cm−1; HRMS
(APCI) m/z: Calcd for C42H35O2P2S: 665.1833; Found
665.1812 ([M + H]+).
Compound 1S
1
J = 7.3, 12.2 Hz, 4H; o-Ph–P); 31P{ H} NMR (CDCl3,
A mixture of 2S (68.1 mg, 0.10 mmol), HSiCl3 (0.20
mL, 2.0 mmol), and CHCl3 (35 mL) was stirred for 20
h at 70◦C. After adding additional HSiCl3 (0.40 mL,
4.0 mmol), the resulting mixture was stirred further
for 77 h at 80◦C. A saturated aqueous NH4Cl solu-
tion was added to the mixture, and insoluble sub-
stances were filtered off through a Celite bed. The
aqueous layer was extracted with CHCl3, and the
organic phase was washed with brine, dried over
Na2SO4, and evaporated under reduced pressure.
The residue was subjected to short silica gel column
chromatography (CHCl3), and the orange fraction
was collected, evaporated, and reprecipitated from
CHCl3/MeOH to give 1S as an orange solid (28.4
mg, 44%). mp (a mixture of 1:1 diastereomers) 265◦C
(dec); 1H NMR (Cl2CDCDCl2, 400 MHz): δ 2.31–2.39
(m, 4H; CH2), 2.68–3.01 (m, 8H; CH2), 6.76 (s, 2H;
Th-β; isomer A), 6.77 (s, 2H; Th-β; isomer B), 7.10
(t, J = 7.2 Hz, 2H; p-Ph), 7.19–7.25 (m, 10H; m-Ph
+ m-Ph–P + p-Ph–P), 7.41 (d, J = 7.2 Hz, 4H; o–Ph),
162 MHz): δ +52.8. As the biphosphole could not be
removed completely, only 1H and 31P NMR data are
reported herewith.
7N-B. Orange solid; mp 154–155◦C (dec); 1H
NMR (CDCl3, 400 MHz): δ 1.36 (s, 9H; Boc), 1.87–
1.97 (m, 2H; CH2), 2.23–2.30 (m, 2H; CH2), 2.61–
3.01 (m, 8H; CH2), 6.44 (s, 2H; pyrrole-β), 7.21
(t, J = 7.3 Hz, 2H; p-Ph), 7.26–7.37 (m, 8H; m-Ph
+ m-Ph–P), 7.39 (t, J = 6.8 Hz, 2H; p-Ph–P), 7.69 (d,
J = 7.3 Hz, 4H; o-Ph), 7.70–7.75 (m, 4H; o-Ph–P);
1
31P{ H} NMR (CDCl3, 162 MHz): δ +51.9; IR (KBr):
ν = 1193 (P=O), 1746 (C=O) cm−1; UV–vis (CH2Cl2):
λmax (log ε) 448 nm (4.29); HRMS (FAB) m/z:
Calcd for C47H44NO4P2: 748.2746; Found 748.2746
([M +H ]+).
Synthesis of 8N
To a toluene solution (1 mL) of 7N-A (21 mg, ca.
0.028 mmol), Lawesson’s reagent (11.4 mg, 0.0282
mmol) was added at room temperature. After stir-
ring for 3 h under reflux, CH2Cl2 and aq. NaHCO3
were added into the reaction mixture. The aqueous
phase was extracted with CH2Cl2, and the combined
organic extracts were dried over Na2SO4. After re-
moval of solvents under reduced pressure, the result-
ing mixture was subjected to alumina column chro-
matography (CH2Cl2). The reddish-purple fraction
was collected, evaporated and reprecipitated from
CH2Cl2/hexane to give 8N-A (8.0 mg, 42%). Accord-
ing to a similar procedure, 8N-B was prepared in
82% yield from 7N-B.
1
7.43–7.45 (m, 4H; o-Ph–P); 31P{ H} NMR (CDCl3,
162 MHz): δ +33.5, +33.7; IR (KBr): HRMS (EI)
m/z: Calcd for C42H35P2S: 633.1935; Found 633.1913
([M + H]+).
Compound 7N
Pd2(dba)3 (422 mg, 0.461 mmol) and tris(2-
furyl)phosphane (214 mg, 0.922 mmol) were stirred
in NMP (30 mL) for 2 h at room temperature. An
NMP solution (30 mL) containing 5 (2.95 g, 5.07
mmol), 6 (966 mg, 2.31 mmol), and CuI (878 mg,
4.61 mmol) was added, and the resulting mixture
was stirred for 1 h at the same temperature. The mix-
ture was then added into a mixture of AcOEt and aq.
NH4Cl, and the organic phase was separated, washed
with aq NH4Cl and brine, and dried over Na2SO4. Af-
ter removal of solvents under reduced pressure, the
resulting mixture was subjected to silica gel column
8N-A. Red solid; Mp 180◦C (dec); 1H NMR
(CD2Cl2, 400 MHz): δ 2.24–2.47 (m, 4H), 2.76–3.03
(m, 8H), 6.36 (s, 2H, pyrrole-β), 7.18–7.21 (m, 2H),
7.26–7.30 (m, 4H), 7.31–7.46 (m, 6H), 7.51–7.57
(m, 4H), 7.96–8.01 (m, 4H, o-Ph-P), 10.20 (s, 1H,
1
NH); 13C{ H} NMR (CDCl3, 75 MHz): δ 25.8, 27.6
(d, J = 11.2 Hz), 28.8 (d, J = 11.2 Hz), 110.9 (d,
Heteroatom Chemistry DOI 10.1002/hc

468 Matano et al.
J = 7.4 Hz), 120.2 (d, J = 83.7 Hz), 123.8 (d, J =
60.4 Hz), 125.8 (d, J = 7.4 Hz), 125.8, 126.3 (d, J
= 14.9 Hz), 126.9 (d, J = 70.1 Hz), 127.0, 127.4 (d,
J = 11.8 Hz), 129.0 (d, J = 11.8 Hz), 156. 2 (d, J =
7.48 (m, 2H; p-Ph–P), 7.62 (d, J = 8.1 Hz, 4H; o-
Ph), 7.71–7.78 (m, 4H; o-Ph–P), 9.75 (s, 1H; NH);
1
13C{ H} NMR (CDCl3, 100 MHz): δ 26.3, 28.9 (d,
J = 10.7 Hz), 30.2 (d, J = 12.3 Hz), 112.7 (d, J
= 5.0 Hz), 119.0 (d, J = 99.2 Hz), 127.4, 127.4 (d,
J = 3.3 Hz), 128.5 (d, J = 15.8 Hz), 128.8, 129.0 (d,
J = 12.3 H), 130.4 (d, J = 10.7 Hz), 130.5 (d, J =
90.1 Hz), 132.0, 133.3 (d, J = 14.1 Hz), 148.8 (d, J
= 24.8 Hz), 156.6 (d, J = 26.5 Hz). One of the 13C
NMR peak (ipso-Ph) could not be detected clearly;
1
22.3 Hz); 31P{ H} NMR (CD2Cl2, 162 MHz) δ +64.5;
HRMS (FAB) m/z: Calcd for C42H35NP2S2: 679.1686;
Found 679.1666 (M+). Anal. Calcd for C42H35NP2S2:
C, 74.20; H, 5.19; N 1.97. Found: C, 73.98; H, 5.49;
N, 2.06%.
1
8N-B. Brown solid. mp 205◦C (dec); H NMR
1
(CDCl3, 400 MHz): δ 2.25–2.40 (m, 4H), 2.74–3.00
(m, 8H), 6.39 (d, J = 2.4 Hz, 2H, pyrrole-β), 7.15–
7.20 (m, 2H), 7.24–7.28 (m, 4H), 7.35–7.47 (m, 6H),
7.55–7.58 (m, 4H), 7.85–7.91 (m, 4H, o-Ph–P), 10.24
31P{ H} NMR (CDCl3, 162 MHz) δ +54.2; HRMS (EI)
m/z: Calcd for C42H35NP2: 648.2221; Found 648.2208
([M + H]+).
1
(s, 1H, NH); 31P{ H} NMR (CD2Cl2, 162 MHz) δ
+65.9.
X-ray Crystal Structure Analysis
Single crystals of 2O, 2N, and 8N were grown from
CH2Cl2–MeOH. All measurements were made on a
Rigaku Mercury-8 CCD area detector with graphite
monochromated Mo Kα radiation at 143 K. The
structures were solved by a direct method (SIR92)
[14] and expanded using Fourier techniques [15].
Non-hydrogen atoms were refined anisotropically,
and hydrogen atoms were refined using the rigid
model. All calculations were performed using Crys-
talStructure [16] crystallographic software package
except for refinement, which was performed using
SHELXL-97 [17]. Crystal data and structural refine-
ment parameters are as follows. 2O: C42H34O3P2,
red plate, 0.30 × 0.20 × 0.05 mm, MW = 733.565,
Compound 1N
A toluene solution (5 mL) containing 8N-A (112 mg,
0.164 mmol) and P(NMe2)3 (0.30 mL, 1.6 mmol) was
heated at reflux for 1 h. The reaction mixture was
concentrated under reduced pressure, and a solid
residue was subjected to silica gel column chro-
matography (hexane/CH2Cl2 = 5/1). The orange frac-
tion (R = 0.2) was collected, evaporated, and re-
f
precipitated from CH2Cl2/hexane to give 1N-A as a
brownish red solid (84 mg, 83%). mp (a mixture
of two diastereomers) 213–214◦C; 1H NMR (CD2Cl2,
400 MHz): δ 2.32–2.77 (m, 10H; CH2), 2.94–3.03 (m,
2H; CH2), 6.16 (d, J = 2.4 Hz, 2H, pyrrole-β, isomer
A), 6.20 (d, J = 2.4 Hz, 2H, pyrrole-β, isomer B), 7.10
(t, J = 7.3 Hz, 2H; p-Ph), 7.23–7.33 (m, 10H; m-Ph
+ m-Ph–P + p-Ph–P), 7.42–7.50 (m, 8H; o-Ph + o-
Ph–P), 7.96 (s, 1H; NH, isomer A), 8.04 ppm (s, 1H;
˚
monoclinic, space group = P21/n, a = 12.341(9) A,
◦
˚
3
˚
b = 18.503(14) A, c = 16.000(12) A, β = 95.581(13) ,
−3
˚
V = 3636(5) A , Z = 4, Dc = 1.340 g cm , μ =
3.07 cm−1, 27,060 obsd, 8181 unique, 452 variables,
Rw = 0.2153, R = 0.0945 (I > 2.0 σ(I)), GOF =
1.037. 2N: C42H35NO2P2, red plate, 0.30 × 0.20 ×
0.02 mm, MW = 647.69, monoclinic, space group =
NH, isomer B); 31P{ H} NMR (CDCl3, 162 MHz) δ
1
+29.3, +29.6; HRMS (EI) m/z: Calcd for C42H35NP2:
615.2245; Found: 615.2262 (M+).
˚
˚
˚
P21/c, a = 17.242(9) A, b = 8.028(4) A, c = 26.568(15)
◦
3
˚
A, β = 108.435(6) , V = 3489(3) A , Z = 4, Dc =
1.233 g cm−3, μ = 1.615 cm−1, 25,224 obsd, 7732
unique, 425 variables, Rw = 0.1857, R = 0.0804
(I> 2.0σ(I)), GOF = 1.180. 8N: C42H35NP2S2, red
plate, 0.40 × 0.20 × 0.08 mm, MW = 679.77, mon-
Compound 2N
A solid of 7N (one of the diastereomers; 32.2 mg,
0.044 mmol) was heated at 180◦C without solvent un-
der argon atmosphere. After 30 min, a solid residue
was subjected to silica gel column chromatography
(CH2Cl2 to CH2Cl2/acetone = 10/3) and a red fraction
was collected and evaporated under reduced pres-
sure. Recrystallization of the resulting solid from
CH2Cl2/hexane gave 2N as a brown solid (23.1 mg,
81%). mp (single diastereomer) 284–285◦C (dec); 1H
NMR (CD2Cl2, 300 MHz): δ 2.11–2.18 (m, 2H; CH2),
2.36–2.41 (m, 2H; CH2), 2.78–3.00 (m, 8H; CH2), 6.41
(d, J = 2.6 Hz, 2H; pyrrole-β), 7.20 (t, J = 7.3 Hz,
2H; p-Ph), 7.29–7.38 (m, 8H; m-Ph + m-Ph–P), 7.42–
˚
◦
oclinic, space group = P21/n, a = 12.908(4) A,
˚
˚
b = 18.863(5) A, c = 13.944(4) A, β = 91.488(4) ,
3
−3
˚
V = 3394.1(16) A , Z = 4, Dc = 1.330 g cm ,
μ = 2.84 cm−1, 38,747 obsd, 7547 unique, 425
variables, Rw = 0.1538, R = 0.0834 (I > 2.0σ(I)),
GOF = 1.300. CCDC-788678, CCDC-788679, and
CCDC-788680 contain the supplementary crystal-
lographic data for 2O, 2N, and 8N, respectively.
These data can be obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html (or from
the Cambridge Crystallographic Data Centre, 12,
Heteroatom Chemistry DOI 10.1002/hc

Effects of Heterole Spacers on the Properties of 2,5-Bis(1,5-diphenylphosphol-2-yl)heteroles 469
[5] 2-Pyrrolyl: Matano, Y.; Fujita, M.; Saito, A.; Imahori,
Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223
H. C R Chim 2010, 13, 1035.
[6] Deschamps, E.; Ricard, L.; Mathey, F. Heteroatom
Chem 1991, 2, 377.
336033; or deposit@ccdc.cam.ac.uk).
[7] (a) Hay, C.; Sauthier, M.; Deborde, V.; Hissler, M.;
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[8] (a) Sebastian, M.; Hissler, M.; Fave, C.; Rault-
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Computational Details
The geometry optimization was performed by the
B3LYP method [18] with basis sets of 6-31G* [19].
We carried out vibration analysis with the B3LYP
method to ascertain that each optimized geometry
was not in saddle, but in equilibrium points. All
calculations were carried out with the Gaussian 03
package [20]. The definitions of torsion angle α and
bond angle β are shown in Table 3.
[9] Matano, Y.; Nakashima, M.; Imahori, H. Angew
Chem, Int Ed 2009, 48, 4002.
[10] Saito, A.; Matano, Y.; Imahori, H. Org Lett 2010, 12,
2675.
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