Ladder-type π-conjugated 4-hetero-1,4-dihydrophosphinines: A structure-property study

Article abstract of DOI:10.1002/asia.201000196

π-Conjugated six-membered 1,4-dihydrophosphinines containing a heteroatom (Si, P, S) at the 4 position were synthesized and systematically studied. X-ray crystallographic analyses showed that the central six-membered heterocyclic rings are almost planar.

Full text of DOI:10.1002/asia.201000196

FULL PAPERS
DOI: 10.1002/asia.201000196
Ladder-Type p-Conjugated 4-Hetero-1,4-dihydrophosphinines: A Structure–
Property Study
Yi Ren and Thomas Baumgartner*[a]
Abstract: p-Conjugated six-membered
1,4-dihydrophosphinines containing
between the phosphorus center and the
benzothiophene moiety is enhanced by
the incorporation of a sulfur atom into
the molecular scaffold. The increased
conjugation endows the thiaphosphi-
nines with interesting emission proper-
ties. Theoretical calculations supported
the postulation that the orbital cou-
s* orbital could be enhanced in the
thiaphosphinine system, especially
through a phosphonium center. Cyclic
voltammetry studies revealed that the
thiaphosphinine oxide, thiaphosphoni-
um, and cis-diphosphinine oxide exhib-
it quasi-reversible reduction processes,
which demonstrate that simple changes
in the bridge heteroatoms help to effi-
ciently tune the redox properties of the
ladder-type 4-hetero-1,4-dihydrophos-
phinines.
a
heteroatom (Si, P, S) at the 4 position
were synthesized and systematically
studied. X-ray crystallographic analyses
showed that the central six-membered
heterocyclic rings are almost planar.
The sum of the angles around the phos-
phorus atom increases by 238 from the
trivalent phosphorus to the phosphoni-
um atom in the thiaphosphinine
system, which is consistent with the
NMR spectroscopic studies. UV/Vis
spectroscopy and theoretical calcula-
tions revealed that the communication
pling between the p system and
a
Keywords: organic electronic mate-
rials · p interactions · phosphorus
heterocycles · solid-state structures ·
sulfur heterocycles
Introduction
group atoms, such as boron,[4] silicon,[5] and phosphorus[6]
have recently become desirable targets. The main-group ele-
ments in these materials were found to introduce some intri-
guing photophysical properties, such as high quantum yields,
tunable emission color, and high charge-carrier mobility.
These effects can be attributed to the inherent electronic
structure and chemical versatility of the inorganic centers,
and can generally not be observed in such complexity with
purely carbon-based p-conjugated materials.[1–3] Whereas
boron atoms provide an empty p orbital that can efficiently
interact with p-conjugated systems,[4] silicon and phosphorus
show s–p hyperconjugation between the p* system of the
In recent years, organic p-conjugated compounds have
become an important class of materials owing to their semi-
conducting properties.[1,2] In particular, ladder-type hetero-
ACHTUNGTRENNUNG
acenes[3] have attracted a lot of attention as their rigidified,
planar structure makes them promising candidates for a va-
riety of applications that include, for example, organic field-
effect transistors (OFETs).[1,2] The fusion of ring-systems
generally provides a high degree of p conjugation, which in-
trinsically affords smaller band gaps in the materials; fused
arenes can generally impart quinoid character into the oligo-
mer/polymer and thus lower the band gap relative to, for ex-
ample, simple polyarylenes or polythiophenes, where twist-
ing from planarity can easily disrupt conjugation.[1c,3e] To fur-
ther improve the properties of these materials, ladder-type
oligothiophene and acene analogues that incorporate main-
À
conjugated scaffold and the s* orbital of exocyclic Si/P C
bonds.[5,6] Both of these interactions have a significant
impact on the frontier orbitals of the materials, and thus on
the photophysical properties of the materials as a whole. We
previously observed these beneficial features for the dithie-
no[3,2-b:2’,3’-d]phosphole system (I, Figure 1).[7] Using ex-
tended dithienophosphole heteropentacenes (I, A=C4H4),
we recently reported that the presence of a phosphorus
center also enhances the desirable n-type semiconducting
characteristics in these systems.[8]
[a] Y. Ren, Prof. Dr. T. Baumgartner
Department of Chemistry, University of Calgary
2500 University Drive NW, Calgary, AB T2N 1N4 (Canada)
Fax : (+1)403-289-9488
E-mail: thomas.baumgartner@ucalgary.ca
Importantly, the photophysical properties and solid-state
organization can be efficiently addressed through simple
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201000196.
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Chem. Asian J. 2010, 5, 1918 – 1929

(Scheme 1).[9]
(benzo[b]thiophene)s 1a–1c were obtained from the reac-
The
heteroatom-bridged
bis-
AHCTUNGTRENNUNG
tion between their corresponding heteroatomic reagents
(Me2SiCl2, PhPCl2, (PhSO2)2S) and 2-lithio-3-bromoben-
Figure 1. Dithieno[3,2-b:2’,3’-d]phosphole- and 1,4-dihydro-1,4-phosphasi-
lin-based ladder-type materials. lp=lone pair.
modification at the phosphorus center (E; Figure 1). This is
a staple of organophosphorus p-conjugated materials and
further illustrates the beneficial features of main-group ele-
ment-based electronic materials. In an expansion of our
work on dithienophospholes, we have recently reported our
preliminary studies on ladder-type systems that contain a
central 1,4-dihydro-1,4-phosphasilin ring (II; Figure 1).[9]
Our studies revealed that the incorporation of an additional
silicon center into the scaffold of the dithienophosphole
system significantly changes the photophysics of the scaf-
fold, largely owing to the electronic effect of increasing the
band gap of the system by approximately 1 eV.
To further evaluate the suitability of ladder-type systems
that contain central six-membered rings for p-conjugated or-
ganic electronic materials, we now report our systematic
structure–property studies on a series of extended 1,4-dihy-
drophosphinine-based pentacenes containing a 1,4-P,S or
1,4-P,P substitution pattern. For comparison, we have also
Scheme 1. Synthesis of heteroatomic 1,4-dihydrohosphinines.
zo[b]thiophene, which was generated by monolithiation of
2,3-dibromobenzo[b]thiophene at À788C with nBuLi in
THF or diethyl ether. Subsequent lithiation of compounds
1a–1c with nBuLi at À788C in THF or diethyl ether afford-
ed the 4-heteroatomic 1,4-dihydrophosphinine rings in good
yields after the addition of PhPCl2 with the assistance of
TMEDA; compound 2a could also be obtained without the
addition TMEDA. Owing to the expected occurrence of the
cis- and trans-isomers of the diphosphinine 2b in various
ratios depending on the solvent ratio used (THF/Et2O),[10]
the trivalent phosphorus species was oxidized with hydrogen
peroxide in situ to provide dioxide 3b (Scheme 2). The
latter allowed for the clean separation into cis- and trans-
species by column chromatography, owing to their signifi-
cantly different dipole moments, as recently shown by Ya-
maguchi and co-workers for a p-conjugated ladder bis(phos-
phole).[6f] On the other hand, 4-thia-1,4-dihydrophosphinine
species 2c was isolated and its electronic structure systemat-
ically modified in a series of subsequent reactions at the tri-
À
included the P Si system in our studies. We report that the
tuning of the Highest Occupied Molecular Orbital (HOMO)
and Lowest Unoccupied Molecular Orbital (LUMO) energy
levels, that is, the electronic structure of systems, the solid-
state organization, and the p-conjugation within the molecu-
lar scaffolds can be controlled efficiently by the nature, as
well as the chemical modification of the heteroatoms. This
experimental study is further supported by theoretical calcu-
lations to provide a detailed understanding of these new
classes of ladder-type organophosphorus materials.
Results and Discussion
Synthesis of Extended Ladder-Type 4-Heterophosphinines
Our initial studies involving dithieno[2,3-b:3’,2’-e][1,4-dihy-
dro-1,4]phosphasilins have shown that the corresponding
benzo-extended systems (II, A=C4H4) exhibit a significantly
more planar molecular scaffold than the non-extended core
(II, A=none).[9] To eliminate geometric factors influencing
the electronic structure, that is, those involving bent p-con-
jugated systems, we have focused on the corresponding
benzo-extended heteropentacenes for our study. This focus
should allow us to concentrate on the electronic effects that
come solely from the various heteroatom-functional groups.
The synthesis of the extended molecular scaffolds was
straightforward, and was based on our previously reported
approach towards dithieno-1,4-dihydro-1,4-phosphasilins
Scheme 2. Functionalization of the bis-phosphorus-based system 2b. tht=
tetrahydrothiophene.
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Y. Ren and T. Baumgartner
FULL PAPERS
À
À
À
valent phosphorus center (Scheme 3). These representative
modifications involved oxidation with hydrogen peroxide,
methylation with methyl triflate (MeOTf), and complexa-
with P Si, P P, and P S central rings. Chemical shifts in the
NMR spectra are generally indicative of the delocalization
effect of atoms. According to previous studies, the 31P NMR
shift can give an indication of the electronic shielding at a
phosphorus center, particularly in its trivalent state.[12] The
trivalent phosphorus compounds 2a–c have high-field-shift-
ed 31P NMR resonances, when compared with the bis(benzo-
thieno)phosphole system (I, A=C4H4),[8a] which indicates
the lone pair on the phosphorus atom may not be efficiently
delocalized in the heterocyclic phosphinine systems. It is
worth pointing out that thiaphosphinine compound 2c has
the most highfield-shifted 31P NMR resonance of this series
(d=À60.2 ppm), which is consistent with a strongly pyrami-
dal P-center (see below). Upon oxidation and methylation
of the trivalent phosphorus center, the 31P NMR signal shifts
to lower fields at d=4.1 ppm (3c), or d=À4.1 ppm (4c), as
expected. Notably, the chemical shift difference between the
trivalent, the oxided, and methylated phosphorus species of
tion with [AuACHTUNGTRENNUNG
(tht)Cl] (tht=tetrahydrothiophene),[7–9,11] to af-
forded the corresponding products 3c, 4c, and 5c, respec-
tively, in good yields (Scheme 3).
the thiaphosphinine compounds is much larger (Dd=
+
À
68.4 ppm for P=O, Dd =56.1 ppm for P Me) than for the
dithienophosphole system reported previously (Dd=
Scheme 3. Functionalization of the sulfur-based system 2c.
+
[7,8,11]
À
35.3 ppm for P=O, Dd=33.5 ppm for P Me),
which
indicates a more significant electronic structural change in
the phosphinine system after oxidation/methylation. In the
13C NMR spectrum of compound 4c, the ipso(P)-carbon
atoms of the thieno-units experienced a strong shielding
(d13C=103.6 ppm; cf. 2c d13C=141.7 ppm; 3c d13C=
134.3 ppm; 5c d13C=112.5 ppm; cis-3b d13C=143.3 and
139.7 ppm; trans-3b d13C=143.2 and 139.2 ppm). This indi-
cates that the phosphonium center polarizes the molecule
considerably when compared to the other thiaphosphinine
compounds (see below). As for diphosphinine gold complex
Owing to the intriguing optical properties afforded by po-
À
tential Au Au interactions, the complexation of 1,4-dihydro-
diphosphinine 2b with [Au(tht)Cl] was also carried out
AHCTUNGTRENNUNG
using a mixture of cis/trans-2b containing about 90% cis-
2b.[10] The cis-configured gold complex cis-5b could then be
isolated by washing the product mixture with acetone. These
simple modifications provided us with a family of materials
that were either different in terms of the electronic nature
À
of the phosphorus center, or, in the case of the P P system,
À
in terms of cis/trans-isomerism as well. Differential scanning
calorimetry (DSC) studies on the heteroatomic dihydro-
phosphinines also showed good thermal stability for these
compounds (Tm =230.68C for 3c, 273.98C for 4c, 322.28C
for cis-3b, and 333.68C for trans-3b) with no decomposition
observed at up to 3508C, except for gold complexes 5c and
cis-5b that did not show clear melting transitions in this
range. The obtained materials were then investigated in
detail to elucidate how the degree of p-conjugation within
the molecular scaffold impacts the optical/electronic proper-
ties, as well as their solid-state organization.
cis-5b, the P P coupling constant (J=7.9 Hz) is smaller
than those of the diphosphinine oxides (cis-3b J=36.6 Hz;
trans-3b J=22.8 Hz), which points towards the absence of
À
Au Au intramolecular interactions, owing to a weaker com-
munication between the two P centers (see below).
Molecular Structures and Solid-State Organization Studies
We were able to obtain single crystals of compounds 2c, 3c,
4c, 5c, cis-3b, and trans-3b that were suitable for X-ray
crystallographic studies. As has already been observed in
À
the structure of the oxidized P Si compound 3a (Scheme 1),
the six-membered rings of all new compounds are almost
planar. Thiaphosphinine 2c has a single molecule in the unit
cell (Figure 2). Compared with those of the benzo-extended
system I (A=C4H4),[8a] the endocyclic C7–C8 and C9–C10
bonds (both 1.36 ꢁ) are significantly shorter than the C5–
C6 and C11–C12 bonds (both 1.41 ꢁ) of the benzene rings,
which indicates the conjugation within the molecular frame-
work decreases when an additional sulfur atom is placed in
the phosphole ring. The small sum of the angles around the
phosphorus center (300.18) reveals significant s character on
the phosphorus lone pair, which suggests a reduced commu-
nication with the p system. Sato and co-workers have re-
cently reported the synthesis of somewhat related isomeric
NMR Studies
Our studies involving the phosphasilin system 2a have indi-
cated that its degree of p conjugation is minimal, although
the silicon center should theoretically allow for negative hy-
perconjugation, and as such for delocalization throughout
the whole scaffold; the same is true for the oxidized phos-
phoranyl unit. Even participation of the lone pair of triva-
lent phosphorus species 2a in the p conjugation is limited.
The phosphasilin ring unit was found to essentially isolate
the two benzo[b]thiophene chromophores of the scaffold.[9]
To further investigate this feature in more detail, we ana-
lyzed the 31P NMR shifts of three families of compounds
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Chem. Asian J. 2010, 5, 1918 – 1929

Ladder-Type Conjugated Heterophosphinines
Figure 3. Top: Molecular structure of 3c in the solid state (50% probabil-
ity level); hydrogen atoms and an acetone solvent molecule are omitted
for clarity. Selected bond lengths [ꢁ] and angles [8]: P1–O1 1.485(3), P1–
C7 1.790(4), P1–C10 1.794(3), P1–C21 1.811(4), C5–C6 1.410(5), C6–
C7 1.458(5), C7–C8 1.366(5), C9–C10 1.367(5), C10–C11 1.451(5), C11–
C12 1.413(5), S3–C8 1.730(4), S3–C9 1.732(4); C7-P1-C10 102.74(17), C7-
P1-C21 107.60(16), C10-P1-C21 105.04(16). Bottom: Molecular packing
of 3c.
Figure 2. Top: Molecular structure of 2c in the solid state (50% probabil-
ity level); hydrogen atoms are omitted for clarity. Selected bond lengths
[ꢁ] and angles [8]: P1–C7 1.819(3), P1–C10 1.821(3), P1–C21 1.844(3),
C5–C6: 1.410(5), C6–C7 1.451(4), C7–C8 1.363(4), C9–C10 1.362(4), C10–
C11 1.452(5), C11–C12 1.408(4), S3–C8 1.743(3), S3–C9 1.740(3); C7-P1-
C10: 99.68(14), C7-P1-C21: 100.62(14), C10-P1-C21: 99.86(14). Bottom:
Molecular packing of 2c.
À
C10 1.82 ꢁ); the S C bonds in the central six-membered
bis
atoms in the central ring.[13] Both isomeric bis-
(benzo[b]thieno)-1,4-dithiins show distorted structures, aris-
(benzo[b]thieno)-1,4-dithiins that contain two sulfur
ring also shortened upon oxidation of the phosphorus atom.
The sum of angles around phosphorus center is increased to
315.48 supporting an enhancement of the electronic coupling
between the phosphorus center and the p system by oxida-
tion. In the solid state, 3c shows a herringbone motif, with
molecules showing p–p stacking interaction of 3.5 ꢁ within
each layer (see the Supporting Information).
ACHTUNGTRENNUNG
À
ing from a significantly bent dithiin ring along the S S axis.
The incorporation of a phosphorus center, on the other
hand, planarizes the central six-membered ring, and in turn
should enhance the communication between the heteroa-
À
toms and the p system; Similar S C bond lengths (1.75Æ
The molecular structure of the gold complex 5c in the
solid state shows two independent molecules in the unit cell
(Figure 4). The geometries of the two molecules are very
similar. The gold center shows a relatively linear coordina-
tion (P1-Au1-Cl1 173.38, P1A-Au1A-Cl1A 178.78) in both
molecules with bond lengths of 2.23 ꢁ for Au1-P1, 2.30 ꢁ
for Au1–Cl1, 2.24 ꢁ for Au1A–P1A, and 2.30 ꢁ for Au1A–
Cl1A, which are typical for (phosphanyl)gold(I) chlori-
0.005 ꢁ) also support better conjugation in the scaffold of
2c.
In addition to efficient intramolecular conjugation, strong
p–p intermolecular interactions are also very important for
facilitating the charge transport in the bulk material. Unlike
the 1,4-dihydro-1,4-phosphasilin oxide 3a, which has two
methyl groups on the silicon center that prevent efficient in-
termolecular overlap of the p-conjugated scaffolds,[9] 2c
crystallizes in a “sandwich” herringbone arrangement with
two different kinds of p–p stacking motifs (distance=3.6 ꢁ;
see the Supporting Information).
des.[8c,11b,14] As with 3c, shortened endocyclic P C bonds
À
(P1-C7/C10 both 1.79 ꢁ) are also found in gold complex 5c;
the sum of the angles around the phosphorus atom (313.18)
is similar to that of compound 3c (315.48). Remarkably, in-
À
The oxidation of the phosphorus atom changes the geo-
metric parameters significantly (Figure 3). The endocyclic
stead of aurophilic Au Au interactions, three short intermo-
À
lecular Au S contacts (Au–S 3.72 ꢁ, 3.27 ꢁ, and 3.43 ꢁ)
À
P C bonds (P1–C7/C10 both 1.79 ꢁ) of the thiaphosphinine
induce two different kinds of p–p intermolecular interac-
tions (3.6 ꢁ and 3.8 ꢁ), thereby leading to a dimeric associa-
oxide 3c are shorter than those of 2c (cf. P1–C7/
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Y. Ren and T. Baumgartner
FULL PAPERS
Figure 5. Top: Molecular structure of 4c in the solid state (50% probabil-
ity level); hydrogen atoms are omitted for clarity. Selected bond lengths
[ꢁ] and angles [8]: P1–C1 1.787(3), P1–C8 1.761(3), P1–C11 1.757(3), P1–
C21 1.794(3), C6–C7 1.415(4), C7–C8 1.449(4), C8–C9 1.378(4), C10–
C11 1.370(4), C11–C12 1.456(4), C12–C13 1.414(4), S3–C9 1.734(3); S3–
C10 1.743(3); C8-P1-C11 106.66(14), C8-P1-C21 109.87(14), C11-P1-
C21 107.13(14). Bottom: Molecular packing of 4c.
Figure 4. Top: Molecular structure of 5c in the solid state (50% probabil-
ity level); hydrogen atoms are omitted for clarity. Selected bond lengths
[ꢁ] and angles [8]: P1–Au1 2.2297(12), Au1–Cl1 2.2916(12), P1–
C7 1.365(6), P1–C10 1.793(5), P1–C21 1.816(5), C5–C6 1.393(7), C6–
C7 1.465(6), C7–C8 1.365(6), C9–C10 1.378(6), C10–C11 1.440(6), C11–
C12 1.407(7), S3–C8 1.738(5), S3–C9 1.736(5); C7-P1-C10 103.3(2), C7-
P1-C21 105.1(2), C10-P1-C21 104.7(2), P1-Au1-Cl1: 173.32(4). Bottom:
Molecular packing of 5c.
ring decreases the communication between phosphorus
atoms and the p system, as opposed to the incorporation of
a sulfur atom. The trans-isomer 3b has a structure similar to
cis-3b, but with a bigger sum of angles around P1 (cis-
3b 319.78, trans-3b 314.78). Interestingly, the intermolecular
p–p interactions are also strongly influenced by the small
change in the orientation of the two phosphorus centers. For
cis-3b, two kinds of p–p interactions, with distances of 3.5 ꢁ
and 3.6 ꢁ, can be observed in the solid state (see the Sup-
porting Information). However, in the case of trans-3b the
two bulky phenyl rings on the opposite sides of the planar
molecular scaffold prevent the molecules from efficiently
forming p–p interactions. Here, only short contacts between
two sulfur (3.2 ꢁ), and one sulfur and one oxygen atom
(3.3 ꢁ) of neighboring molecules can be observed.
tion of cis-5c in the solid state (see the Supporting Informa-
tion). The latter is also the reason for different non-linear
geometries around the two gold centers (Au1 and Au1A).
The structure of the phosphonium salt 4c in the solid
state is shown in Figure 5. Notably, the positively charged
phosphorus center further planarizes the central six-mem-
bered ring, which results not only in an increased sum of the
angles around phosphorus (323.78), but also increased endo-
hedral angles around sulfur (4c: C9-S3-C10 102.88; cf.
À
2c 101.48, 3c 101.68, 5c 101.78). The endocyclic P C bonds
(P1-C8/C11 both 1.76 ꢁ) are noticeably even shorter when
compared to the other thiaphosphinines, whilst the carbon
bonds of the central six-membered ring are elongated (C8–
C9 1.38 ꢁ, C10-C11 1.37 ꢁ). The structural information of
4c suggests that the communication between phosphorus
center and the aromatic ring is further enhanced by methyl-
ation of the phosphorus center, which is consistent with the
observation in the NMR studies (see above). Strong p–p
stacking interactions are also observed in 4c (3.5 ꢁ and
3.6 ꢁ; see the Supporting Information).
The very diverse molecular structures of compounds 2c,
3c, 4c, cis/trans-3b, and 5c in the solid state clearly show
that the nature of the central six-membered heterocyclic
ring has a significant impact on the molecular structure and
the solid-state organization, thus highlighting the versatility
that can be introduced by these main group element atoms.
Optical Spectroscopy Studies
On the other hand, the additional phosphorus atom in cis-
3b (Figure 6) and trans-3b (Figure 7) elongates the endocy-
Optical spectroscopy can also be used to determine the
degree of conjugation within a molecular scaffold. In order
À
À
clic P1/P2 C bonds, which indicates that the incorporation
to study the effect of the heteroatoms in these new S P and
À
of a second phosphorus atom in the central six-membered
P P systems, we have systematically investigated their ab-
1922
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Chem. Asian J. 2010, 5, 1918 – 1929

Ladder-Type Conjugated Heterophosphinines
Figure 6. Top: Molecular structure of cis-3b in the solid state (50% prob-
ability level); hydrogen atoms and a dichloromethane solvent molecule
are omitted for clarity. Selected bond lengths [ꢁ] and angles [8]: P1–
O1 1.483(4), P1–C7 1.815(5), P1–C10 1.805(5), P1–C21 1.806(5), P2–
O2 1.487(3), P2–C8 1.781(5), P2–C9 1.792(5), P2–C31 1.793(5), C7–
C8 1.366(7), C9–C10 1.367(7), S1–C8 1.732(5), S2–C9 1.730(5); C7-P1-
Figure 7. Top left: Molecular structure of trans-3b in the solid state (50%
probability level); hydrogen atoms are omitted for clarity. Selected bond
lengths [ꢁ] and angles [8]: P1–O1 1.477(3), P1–C8 1.797(3), P1–
C10 1.805(4), P1–C21 1.797(4), P2–O2 1.486(3), P2–C7 1.794(4), P2–
C9 1.794(4), P2–C31 1.792(4), C7–C8 1.371(5), C9–C10 1.375(5), S1–
C10 104.7(2),
C7-P1-C21 104.9(2),
C21-P1-C10 105.9(2),
C8-P2-
C7 1.742(4),
S2–C9 1.732(4);
C8-P1-C10 105.02(17),
C8-P1-
C9 102.6(2), C9-P2-C31 106.2(2), C31-P2-C8 105.9(2). Bottom: Molecular
packing of 3b.
C21 107.23(18), C21-P1-C10 107.39(17), C7-P2-C9 102.38(17), C9-P2-
C31 105.09(18), C31-P2-C7 107.23(18). Bottom right: Molecular packing
of trans-3b.
sorption and photoluminescence properties. We have further
compared the photophysics of the new heteropentacenes to
those of the phosphasilin system, which has been found to
show only negligible conjugation across the central six-mem-
bered ring.[9] The photophysical properties are summarized
in Table 1. The diphosphinines, cis- and trans-3b, show simi-
lar absorption spectra to that of the phosphasilin system
(2a: lmax =310 nm, 3a: lmax =311 nm)[9] with these lowest
energy absorption at lmax =301 nm and lmax =309 nm, re-
spectively; these absorptions are assigned to p–p* transi-
tions according to the TD-DFT calculations (see below).
The gold complex cis-5b shows a hypsochromic shift (lmax
=
294 nm) compared to the absorption of cis-3b, possibly
owing to the greater electronegativity of oxygen versus gold,
which increases the LUMO energy level and the band gap
Table 1. UV/Vis, fluorescence, and cyclic voltammetry data, and TD-DFT calculations.
Compound
labs [nm][a]
l[nm][c](f[d]
)
Transition[c]
Ered [V][e]
Eox [V][e]
LUMO [eV][f]
HOMO [eV][f]
DE [eV][f]
[b]
(lge MÀ1 cmÀ1
)
2a
3a
cis-3b
trans-3b
cis-5b
289, 310
298.2
306.2
325.1
332.9
N
HOMO–LUMO
HOMO–LUMO
HOMO–LUMO
HOMO–LUMO
nd
nd
nd
À1.07
À1.38
À1.89
À1.90
nd
À5.64
À5.98
À6.23
À6.16
nd
4.57
4.60
4.34
4.26
nd
301 (3.81), 311 (3.71)
277 (4.12), 301 (4.24)
299 (4.56), 309 (4.51)
294 (3.63), 322(sh)
(3.15)
À0.87
À1.15[g]
À1.16
À1.26
1.12
NA
NA
NA
2c
3c
310 (4.47), 336 (4.54)
326 (4.74), 335 (4.69)
361.1
325.0
G
HOMO–LUMO
HOMO–LUMO
NA
1.54
NA
À1.16
À1.46
À4.71
À5.27
À5.89
À9.01
4.11
4.43
N
À1.14[g]
À1.10[g]
À1.65
4c
5c
339 (4.37), 350 (4.29)
333.2
E
HOMO–LUMO
nd
1.34
0.67
4.30
nd
341
N
À1.09
nd
nd
[a] Relevant absorptions, measured in CH2Cl2. [b] Molar absorption coefficient. [c] TD-DFT Calculation level: B3LYP/6-31G(d). [d] Oscillator strength
(f). [e] Measured in CH2Cl2. [f] Calculation level: B3LYP/6-31G(d). [g] Quasi-reversible reduction. NA=not available, nd=not determined.
Chem. Asian J. 2010, 5, 1918 – 1929
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
1923

Y. Ren and T. Baumgartner
FULL PAPERS
of cis-5b. The spectrum of gold complex cis-5b also exhibits
shoulders and broad bands, owing to the presence of multi-
ple conformations of the central six-membered ring in solu-
tion.[14] Compared to the phosphasilin and diphosphinine
systems, the absorptions of the thiaphosphinines are further
Interestingly, the cationic phosphonium compound 4c also
shows yellow fluorescence at lem =535 nm in the solid state,
whereas the other heteroatomic phosphinine compounds do
not show any noticeable solid-state fluorescence. In order to
gain some deeper insight into this different behavior, we
have studied the concentration dependent fluorescence
emission of 4c in solution. At low concentration (c=
1.4·10À6 m), an emission at lem =387 nm was observed. A
lower energy emission (lem =513 nm, fPL =0.023)[15] emerges
as the concentration increases to cꢀ1.0·10À3 m (Figure 9).
bathochromically shifted (2c: lmax =336 nm, 3c: lmax
=
335 nm, 4c: lmax =350 nm, and 5c: lmax =354 nm), thus sup-
porting an increased conjugation in the sulfur-bridged
system. Furthermore, the bathochromic trend (from lmax
=
336 nm for 2c to lmax =354 nm for 5c) of the functionalized
phosphorus center illustrates how the different electronic
nature of phosphorus center can further tune the communi-
cation between the heteroatom center and p-system. Inter-
estingly however, the absorption of the gold complex 5c is
red-shifted from that of the thiaphosphinine oxide 3c, de-
spite the greater electronegativity of oxygen. To investigate
this unusual observation, theoretical calculations have been
performed (see below).
The trivalent thiaphosphinine 2c also shows blue fluores-
cence in dichloromethane with an emission maximum at
lem =476 nm, but with a low quantum yield of fPL =0.03.[15]
A large Stokes shift of Dn=7143 cmÀ1 indicates that its elec-
tronic structure in the ground state is significantly different
from that in the excited state. Similar results have also been
found in triphenylphosphane and phosphane-substituted oli-
gothiophene systems.[16] In MeOH, the emission of 2c shows
a hypsochromic shift of Dl=30 nm (fPL =0.02; Figure 8).
These features indicate the presence of a fast geometrical
conversion of the phosphorus center from a pyramidal
ground state into a more planar excited state in CH2Cl2,
whereas this geometrical conversion could be hindered by
hydrogen bond interactions between the phosphorus center
and protic solvents.[16] By contrast, the oxidized com-
Figure 9. Steady state fluorescence spectra of compound 4c at different
concentrations (arrows indicate increasing concentration; starting c=
1.0·10À6 m, end c=1.4·10À3 m).
However, the absorption features of 4c did not change with
concentration in CH2Cl2 solution. Therefore, the concentra-
tion-dependant emission can be assigned to the formation of
an excimer, which is induced by the polarized electronic
structure of 4c in the excited state.[17] The excimer formation
also explains the solid-state fluorescence of 4c that is not
observed for the other thiaphosphinine derivatives.
pound 3c only shows a weak emission at lem =372 nm (fPL
=
0.001)[15] in CH2Cl2 (378 nm in MeOH), probably owing to
the absence of the geometrical conversion of the oxide
phosphorus center.
Furthermore, cis- and trans-3b did not show any fluores-
cence in solution or in the solid state, presumably owing to
the reduced conjugation in the diphosphinines, as well as
their bulkiness thus preventing an excimer formation. For
gold complexes cis-5b and 5c, low energy emissions origi-
[18]
À
nating from Au Au interactions in the solid state, were
also not observed. This result was supported by the lack of
À
Au Au interactions in the molecular organization of 5b in
the solid-state (see above), and is consistent with the obser-
vations made with the analogous phosphasilin gold com-
plex.[9]
Electrochemical Studies
Recently, we and others were able to show that the incorpo-
ration of phosphorus centers into p-conjugated materials
allows for facile electrochemical reduction, which empha-
Figure 8. Steady state fluorescence spectra of compound 2c: 1) g emis-
sion in CH2Cl2; 2) c emission in CH3OH; 3) b emission in the solid
state.
AHCTUNGTRENNUNG
sizes their n-type characteristics.[6,8] To verify if this is also
true for the series of new materials reported here, the redox
1924
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ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2010, 5, 1918 – 1929

Ladder-Type Conjugated Heterophosphinines
properties of the heteroatomic phosphinine systems were in-
vestigated using cyclic voltammetry. 2,3-Dibromobenzo[c]-
thiophene, which was used as a benchmark compound for
the CV studies, only exhibited an irreversible oxidation at
E=1.22 V. By contrast, an irreversible reduction peak was
observed for the oxidized phosphasilin 3a at relatively low
potential (E=À0.87 V), thus indicating that addition of the
phosphoranyl center endows the scaffold with n-type charac-
teristics. In the thiaphosphinine series, trivalent com-
pound 2c only shows an irreversible oxidation peak at E=
1.54 V, which can be attributed to the electron-rich sulfur
and phosphorus heteroatoms. Modification of the phospho-
rus center, however, changes the redox properties and
switches the character of the material from p-type to n-type.
Both compounds 3c and 4c now show quasi-reversible re-
duction peaks at E=À1.14 V and E=À1.10 V, respectively;
the more positive reduction potential of compound 4c indi-
cates that the cationic phosphonium center can further de-
crease the LUMO energy level of the thiaphosphinine
system. This is in line with the results obtained for the relat-
ed bis(benzothieno)phospholes (I, A=C4H4).[8a] On the
other hand, gold complex 5c not only shows an irreversible
reduction at E=À1.10 V, but also an irreversible oxidation
at E=0.67 V, which can be attributed to the electron rich-
ness of the gold center. Surprisingly, gold complex cis-5b
only shows an irreversible reduction at E=À1.26 V, which is
in contrast to the redox behavior of 5c. This difference
could be rationalized by the different electronic nature of
the heteroatoms (S and P) in the molecular scaffold of cis-
5b and 5c. As for the isomers of 3b, cis-3b has a quasi-re-
versible reduction peak at E=À1.15 V, whilst trans-3b
shows one irreversible reduction peak at E=À1.16 V. The
corresponding oxidation processes were not observed for
these two compounds. These results complement the work
of other groups that have reported similar heteroatom sys-
Figure 10. Schematic molecular orbitals of phospholes and thiaphospho-
nium as derived from theoretical calculations.
culations, B3LYP/6-31G(d) level of theory;[20] see the Sup-
porting Information). The LUMO energy levels (and band
gaps) of the diphosphinines cis/trans-3b, (cis: ELUMO
À1.89 eV, trans: ELUMO =À1.90 eV) are significantly lower
than those of the phosphasilin system (2a: ELUMO
=
=
À1.07 eV and 3a: ELUMO =À1.38 eV) owing to the stronger
electron-withdrawing effect of the two phosphoranyl moiet-
ies and a more pronounced hyperconjugation from the two
phosphoranyl centers, which is consistent with the observed
red-shifted absorption shoulders in the diphosphinine
system.
The trivalent thiaphosphinine 2c exhibits a smaller band
gap (Ebg =4.11 eV) and higher lying LUMO energy level
(ELUMO =À1.16 eV) than those of both the phosphasilin and
diphosphinine systems (3a: Ebg =4.60 eV, cis-3b: Ebg =
4.34 eV, trans-3b: Ebg =4.26 eV). The lone pairs of the phos-
phorus and sulfur centers in the central six-membered rings
largely contribute to the HOMO level, but not to the
LUMO levels. This charge transfer between heteroatoms
and the benzothiophene p-system is consistent with the
large Stokes shift of 2c in dichloromethane (aprotic sol-
vent). The oxidation of the phosphorus center in the thia-
phosphinine oxide 3c brings down both the LUMO and
HOMO levels (DELUMO =0.30 eV; DEHOMO =0.62 eV). The
molecular orbitals reveal that the s* orbital of the exocyclic
tems,
such
as
N-phenylphenothiazine,[19]
bis-
P C bond couples with the p orbitals of the two thiophene
À
T
moieties, thereby lowering the HOMO level significantly,
which is also consistent with the significantly shortened en-
acences[1f,3a–d] that only exhibit reversible oxidation process-
es. Our observations clearly demonstrate that replacing the
N/S heteroatoms with phosphorus centers in a p-conjugated
scaffold affords systems with considerably altered electro-
chemical features.
À
docyclic P C bonds of 3c. The phosphonium center in 4c
further enhances this s*–p interaction (Figure 10, C), thus
lowering both the LUMO and HOMO levels even more;
this enhancement agrees very well with the redox properties
of the thiaphosphinines. Kawashima and co-workers have
recently reported the somewhat related dibenzothiaborins
and TD-DFT calculations have indicated that the HOMO–
LUMO transition in these systems can be attributed to an
intramolecular charge transfer from a sulfur atom to the
boron center that, however, is not the strongest transition.[21]
Both LUMO and HOMO energy levels have a contribution
from the boron center in Kawashimaꢂs system, whereas the
phosphonium center in 4c only contributes to the HOMO
energy level, but not the LUMO level. The different elec-
tronic contribution of the phosphonium center to the
HOMO and LUMO levels can thus explain the enhanced
p–p* transition in the thiaphosphinine system, and conse-
quently also the stronger fluorescence intensity of 4c, com-
pared to its congeners.
Theoretical Studies
The five-membered phosphole is a weak aromatic system,
owing to the pyramidal geometry of the phosphorus center
(A, B, Figure 10). However, the hyperconjugation between
the p* system of the butadiene moiety and the s* orbital of
À
exocyclic P C bond induces a low LUMO energy level in
the phosphole system.[6] Compared with the extended dithie-
nophosphole heteropentacenes (I, A=C4H4, Figure 1),[8a]
the heteroatomic phosphinine systems exhibit larger band
gaps (Table 1) that can be attributed to reduced conjugation
through the additional heteroatoms in the scaffold.
Similar s*–p* hyperconjugation effects are also observed
in the phosphasilin and the diphosphinine systems (DFT cal-
Chem. Asian J. 2010, 5, 1918 – 1929
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
1925

Y. Ren and T. Baumgartner
FULL PAPERS
The calculations also revealed the reasons for the unex-
pected observation in terms of absorption shifts for com-
pounds 2c–5c. In contrast to the phosphasilin and diphos-
quaternization into a phosphonium species, further enhances
the communication between the phosphorus center and the
p system in the thiaphosphinine heteroacene scaffold. This
induces intriguing optical properties that are considerably
distinct from other hetero (Si and P) phosphinines. Chang-
ing the central heteroatoms also dramatically alters the or-
ganization of heteroatomic phosphinines in the solid state.
Even small geometric changes on the phosphorus centers
can provide different packing-motifs, such as p stacking
along the long axis of molecules as observed in cis-3b,
whilst no such packing was observed in trans-3b. More im-
portantly, the redox properties of the p systems can also be
modified with additional heteroatoms. The theoretical stud-
ies have shown that modification of the heteroatoms in the
phosphinine ring helps to decrease the HOMO–LUMO
energy gap. Owing to the increased orbital coupling between
the p orbitals of the two thiophene moieties and the s* orbi-
À
phinine systems, where the s* orbital of the exocyclic P C
bond couples with the p* system (LUMO) of the molecular
scaffold, the opposite is true for the thiaphosphinine oxide
3c and the thiaphosphonium 4c. Here the s* orbital inter-
acts with the p system (HOMO), leading to a lowered
HOMO instead of a lowered LUMO energy level in the
thiaphosphinine system (see Figure 11 and the Supporting
Information). This in turn, increases the band gap of 3c and
is likely the cause of the hypsochromic shift compared to
the gold complex 5c.
À
tal of the exocyclic P C bond in the thiaphosphinine
system, the conjugation within the molecules is enhanced,
which is consistent with the optical properties of these sys-
tems.
Experimental Section
General: All manipulations were carried out under a dry nitrogen atmos-
phere employing standard Schlenk techniques. Solvents were dried using
a MBraun Solvent Purification System. nBuLi (2.5m in n-hexane), bi-
s(phenylsulfonyl)sulfide, methyl triflate, and hydrogen peroxide were
used as received. N,N,N,N-tetramethylethylenediamine (TMEDA),
Figure 11. Frontier orbitals for phosphasilin 3a (top) and thiaphosphoni-
um 4c (bottom), highlighting the interaction of the s* orbital of exocyclic
dichloro
tilled prior to use. 2,3-Dibromobenzo[b]thiophene,[22] [Au
bis
(benzo[b]thieno)phosphasilin oxide (3a)[9] were prepared according to
literature procedures. 31P{1H} NMR, 1H NMR and 13C{1H} NMR spectra
were recorded on Bruker DRX400, DMX300, or Avance(-II,-III) 400
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
À
P C bonds with the p* system (3a) and the p system (4c); B3LYP/6-
AHCTUNGTRENNUNG
31G(d) level of theory.
AHCTUNGTRENNUNG
spectrometers. Chemical shifts were referenced to external 85% H3PO4
(31P), and external TMS (13C, H). Elemental analyses were performed at
1
According to our previous studies, changing the environ-
ment around the phosphorus center in the dithienophos-
ACHTUNGTRENNUNGphole system can control the electronic nature of the whole
the Department of Chemistry at the University of Calgary. Mass spectra
were run on a Finnigan SSQ 7000 spectrometer, or a Bruker Daltonics
AutoFlex III system. Crystal data and details of the data collection are
provided in Table 2. Diffraction data for 2c, 3c, 4c, 5c, cis-3b, and trans-
3b were collected on a Nonius Kappa CCD diffractometer, using Mo Ka
radiation (l) 0.71073 ꢁ (graphite monochromator). The structures were
solved by direct methods (SHELXTL) and refined on F2 by full-matrix
least-squares techniques. Hydrogen atoms were included by using a
riding model. CCDC 769137 (cis-3b), CCDC 769138 (trans-3b),
CCDC 769139 (2c), CCDC 769140 (5c), CCDC 769141 (4c), and
CCDC 769142 (3c) contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge at www.ccdc.cam.
ac.uk/data_request/cif. Melting points were determined on a TA-Q200
DSC instrument. All fluorescence experiments were recorded in a di-
chloromethane solution in a Jasco FP-6600 spectrofluorometer and UV/
Vis/NIR Cary 5000 spectrophotometer. Electrochemical studies were per-
formed on an Autolab PGSTAT302 instrument with a platinum rod as
working electrode, platinum wire as counter electrode, and Ag/AgCl/
KCl3m as reference electrode; the supporting electrolyte was NBu4PF6;
material, particularly through the interaction of the s* orbi-
À
tal of the exocyclic P C bond(s) with the LUMO of the p-
conjugated system.[7,8] This study now confirms that the ad-
ditional heteroatoms in the 4-position (Si, S, P), under the
right conditions (that is, the nature of the phosphorus
center), can enhance this effect as they also have a signifi-
cant influence on the electronic coupling between the s* or-
À
bital of the exocyclic P C bond and the p/p* system.
Conclusions
In conclusion, we have synthesized a series of 4-heteroatom-
ic 1,4-dihydrophophinine heteropentacenes. The electronic
structures of these molecules can be tuned by changing het-
eroatoms (Si, S, and P) in the central six-membered ring, as
supported by multinuclear NMR studies and optical spec-
troscopy. The thiaphosphinine system exhibits a stronger
conjugation than the phosphorus- and silicon-based systems.
Functionalization of the phosphorus center, particularly its
Standard scan rate was 100 mVsÀ1
.
Bis(3-bromobenzo[b]thiophen-2-yl)
(phenyl)phosphane
(1b):
nBuLi
(2.12 mL, 5.29 mmol) was added dropwise at À788C to a solution of 2,3-
dibromobenzo[b]thiophene (1.534 g, 5.29 mmol) in Et2O,. After stirring
for 1 h, PhPCl2 0.474 g, 2.65 mmol) was added dropwise at À788C and
the reaction was gradually warmed to room temperature and stirred over-
night. The mixture was then quenched with water, and extracted three
times with CH2Cl2. The organic layer was collected and dried under
1926
www.chemasianj.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2010, 5, 1918 – 1929

Ladder-Type Conjugated Heterophosphinines
Table 2. Crystal data and structure refinement for 2c, 3c, 4c, 5c, and cis-3b and trans-3b.
Compound
2c
3c
4c
5c
trans-3b
cis-3b
formula
Mr
C22H13PS3
404.51
C22H13OPS3C3H6O
478.58
C24H16F3O3PS4
568.58
C22H13AuClPS3
636.89
C28H18O2P2S2
512.48
C28H18O2P2S2
512.48
T [K]
173(2)
173(2)
173(2)
173(2)
173(2)
173(2)
l [ꢁ]
0.71073
Monoclinic
P21/c
10.074(3)
9.092(4)
20.344(6)
90
103.667(2)
90
1810.6(11)
4
0.71073
Orthorhombic
Pbca
11.209(2)
15.907(3)
24.479(5)
90
0.71073
Triclinic
P-1
0.71073
Triclinic
P-1
0.71073
Monoclinic
C2
20.176(7)
8.198(4)
16.635(5)
90
120.527(2)
90
2370.09
4
0.71073
Monoclinic
P2/c
16.629(4)
11.637(6)
13.826(7)
90
111.006(3)
90
2497.69(19)
4
crystal system
space group
a [ꢀ]
b [ꢀ]
c [ꢀ]
9.0390(4)
10.5370(4)
13.5090(4)
105.106(2)
99.025(2)
99.886(2)
1195.94(8)
2
12.485(2)
13.705(3)
14.006(3)
111.334(1)
104.909(1)
99.238(1)
2069.39(7)
4
a [8]
b [8]
90
90
g [8]
V [ꢁ3]
Z
4364.64(14)
8
1.457
1calcd [Mg/m3]
1.484
0.501
1.579
0.514
2.044
7.624
1.436
0.385
1.476
0.475
m [mmÀ1
]
0.434
F
(000)
832
1984
580
1216
1056
1140
crystal size [mm3]
q range [8]
index ranges
0.47ꢃ0.24ꢃ0.06
2.06–27.48
À13ꢁhꢁ13
À11ꢁkꢁ11
À26ꢁlꢁ26
0.23ꢃ0.21ꢃ0.19
2.46–27.50
À14ꢁhꢁ14
À20ꢁkꢁ20
À31ꢁlꢁ31
9344
0.19ꢃ0.12ꢃ0.10
1.60–27.40
À11ꢁhꢁ11
À13ꢁkꢁ13
À17ꢁlꢁ17
9980
0.25ꢃ0.21ꢃ0.18
1.66–27.55
À16ꢁhꢁ14
À17ꢁkꢁ17
À18ꢁlꢁ18
17332
0.22x 0.21ꢃ0.19
2.34–27.48
À26ꢁhꢁ25
À10ꢁkꢁ10
À21ꢁlꢁ21
5123
0.22ꢃ0.17ꢃ0.16
1.75–27.43
À21ꢁhꢁ21
À13ꢁkꢁ15
À17ꢁlꢁ17
9802
Reflections collected 7464
independent reflec-
tions
4111 [R-
(int)=0.0471]
4993 (R-
5352 (R-
9448 (R-
4292 (R-
5675 (R-
ACHTUNGTREN(NUNG int)=0.0488)
G
(int)=0.0415)
(int)=0.0338)
(int)=0.0226)
(int)=0.0000)
completeness to q [8] 27.48 (99.1%)
absorption correction Empirical
27.50 (99.6%)
Empirical
27.40 (98.1%)
Empirical
27.55 (98.9%)
Empirical
27.48 (99.1%)
Empirical
27.43 (99.5%)
Empirical
max./min. transmis-
sion
0.9108/0.885
0.9220/0.9067
0.9504/0.9086
0.3407/0.2516
0.9304/0.9201
0.9279/0.9027
data/restraints/param- 4111/0/235
eters
4993/0/280
5352/0/316
9448/0/505
5123/1/307
5675/0/321
GoF on F2
1.123
1.152
1.074
1.161
1.176
1.158
final R indices
[I>2s(I)]
R indices (all data)
R1 =0.0529,
wR2 =0.1173
R1 =0.0746,
wR2 =0.1391
R1 =0.0624,
wR2 =0.1705
R1 =0.0868,
wR2 =0.1994
1.306/À0.534
R1 =0.0540,
wR2 =0.1318
R1 =0.0662,
wR2 =0.1504
1.894/À0.504
R1 =0.0279,
wR2 =0.0764
R1 =0.0323,
wR2 =0.0819
0.742/À1.525
R1 =0.0506,
wR2 =0.1307
R1 =0.0581,
wR2 =0.1440
0.524/À0.589
R1 =0.0822,
wR2 =0.1996
R1 =0.1147,
wR2 =0.2263
0.615/À0.889
largest diff. peak/hole 0.390/À0.374
[eꢁ3]
vacuum. The pure white product was obtained after washing the solid
three times with pentane (yield: 1.00 g, 71.1%). 1H NMR (400 MHz,
CDCl3): d=7.87 (ddd, 3JH,H =6.0 Hz, 4JH,H =1.2 Hz, 5JH,H =0.8 Hz, 2H,
benzo), 7.72 (ddd, 3JH,H =6.0 Hz, 4JH,H =2.0 Hz, 5JH,H =1.2 Hz, 2H,
benzo), 7.60–7.55 (m, 4H, Ph), 7.51–7.39 ppm (m, 4H, Ph); 13C{1H} NMR
(100 MHz, CDCl3): d=139.9 (s, thiophene), 138.0 (s, thiophene), 130.5 (s,
thiophene), 126.3 (s, benzo), 125.4 (s, benzo), 123.8 (s, benzo), 122.2 (s,
benzo), 114.5 ppm (s, thiophene); 31P{1H} NMR (162 MHz, CDCl3): d=
À29.8 ppm (s).
Bis
3.77 mmol) was added dropwise at À788C to a solution of bis(3-bromo-
benzo[b]thiophen-2-yl)(phenyl)phosphane 1b (1.002 g, 1.88 mmol) and
ACHTUNGERTN(NUNG benzo[b]thieno)-1,4-diphosphinine-1,4-dioxide 3b: nBuLi (1.51 mL,
AHCTUNGTRENNUNG
TMEDA (0.56 mL, 3.77 mmol) in THF/Et2O (1:1),. After stirring for 1 h
at this temperature, PhPCl2 (0.337 g, 1.88 mmol) was added dropwise. Af-
terwards, the reaction was quickly warmed up to room temperature and
stirred overnight. The mixture was subsequently filtered through neutral
alumina. All volatile materials were removed under vacuum to afford a
yellow solid which was washed several times with pentane and Et2O. The
mixture was dissolved in CHCl3 (20 mL), an excess of H2O2 was added,
and the mixture was stirred overnight at room temperature. After
quenching with water, the organic layer was separated and dried with
MgSO4, and all volatile materials were removed in vacuum. The product
was obtained as light yellow solid. Further purification by column chro-
matography on silica gel (ethyl acetate/hexanes, 1:9 to 9:1) afforded
0.165 g (0.32 mmol) of trans-3b and 0.330 g (0.64 mmol) of cis-3b in
17.1% and 34.3% yields, respectively.
Bis(3-bromobenzo[b]thiophen-2-yl)sulfane
1c:
nBuLi
(1.47 mL,
3.67 mmol) was added dropwise at À788C to the solution of 2,3-dibromo-
benzo[b]thiophene (1.065 g, 3.67 mmol) in THF. After stirring for 1 h at
this temperature, bis(phenylsulfonyl)sulfide (0.578 g 1.84 mmol) in THF
was added dropwise and the reaction was gradually warmed to room
temperature and stirred overnight. The mixture was quenched with
water, and extracted three times with CH2Cl2. The organic layer was col-
lected and dried under vacuum. The pure light yellow product was ob-
tained after washing the solid three times with pentane (yield: 0.61 g,
Cis-isomer: 1H NMR (400 MHz, CDCl3): d=8.61–8.57 (m, 2H, benzo),
8.04–8.00 (m, 2H, benzo), 7.63–7.58 (m, 4H, benzo), 7.56–7.49 (m, 5H,
Ph), 7.45–7.40 (m, 1H, Ph), 7.38–7.33 (m, 2H, Ph), 7.30–7.25 ppm (m,
2H, Ph); 13C{1H} NMR (100 MHz, CDCl3): d=143.3 (dd, 1JC,P =19.6,
2JC,P =6.9 Hz, ipso-thiophene), 140.3 (d, JC,P =7.4 Hz, ipso-Ph), 139.7 (d,
1
3
4
73.3%). H NMR (400 MHz, CDCl3): d=7.80 (ddd, JH,H =6.0 Hz, JH,H
=
5
3
4
1.6 Hz, JH,H =0.8 Hz, 2H, benzo), 7.69 (ddd, JH,H =6.0 Hz, JH,H =0.8 Hz,
5JH,H =0.4 Hz, 2H, benzo), 7.47–7.37 ppm (m, 4H, benzo); 13C{1H} NMR
(100 MHz, CDCl3): d=139.9 (s, thiophene), 138.0 (s, thiophene), 130.5 (s,
thiophene), 126.3 (s, benzo), 125.4 (s, benzo), 123.8 (s, benzo), 122.2 (s,
benzo), 114.5 ppm (s, thiophene).
J
C,P =11.9 Hz, ipso-thiophene), 135.3 (d, JC,P =4.0 Hz, Ar), 134.2 (d, JC,P =
4.1 Hz, Ar), 133.3 (d, JC,P =3.1 Hz, Ar), 132.9 (d, 3JC,P =2.7 Hz, m-Ph),
132.4 (d, 3JC,P =2.6 Hz, m-Ph), 130.9 (s, benzo), 130.8 (d, 2JC,P =9.4 Hz, o-
Ph), 129.0 (s, benzo), 128.8 (s, benzo) 127.4 (s, benzo), 126.2 (s, benzo),
Chem. Asian J. 2010, 5, 1918 – 1929
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
1927

Y. Ren and T. Baumgartner
FULL PAPERS
126.1 (s, benzo), 122.7 ppm (s, benzo); 31P{1H} NMR (162 MHz, CDCl3):
d=5.64 (d, JC,P =36.6 Hz), 5.53 ppm (d, JC,P =36.6 Hz); elemental analy-
sis (%) calcd. for C28H18O2P2S2: C 65.62, H 3.54; found: C 65.46, H 3.79.
Trans-isomer: 1H NMR (400 MHz, CDCl3): d=8.40–8.39 (m, 2H,
benzo), 8.08–8.03 (m, 2H, benzo), 7.94–7.89 (m, 4H, benzo), 7.62–7.58
(m, 1H, Ph), 7.54–7.42 ppm (m, 9H, Ph); 13C{1H} NMR (100 MHz,
CDCl3): d=143.2 (dd, 1JC,P =11.5, 2JC,P =8.7 Hz, ipso-thiophene), 142.4
d=8.25 (d m, JH,H =20.0 Hz, 2H, o-Ph), 7.94–7.90 (m, 2H), 7.74–7.72 (m,
3H), 7.60–7.57 (m, 2H), 7.49–7.44 ppm (m, 4H); 13C{1H} NMR
3
3
2
(100 MHz, CDCl3): d=146.9 (d, 3JC,P =7.4 Hz, Ar), 138.1 (d, JC,P
=
14.5 Hz, Ar), 136.5 (d, 2JC,P =14.0 Hz, Ar), 135.6 (d, 4JC,P =3.0 Hz, p-Ph),
133.3 (d, 2JC,P =13.1 Hz, o-Ph), 130.9 (d, 3JC,P =13.9 Hz, m-Ph), 127.4 (s,
benzo), 127.0 (s, benzo), 122.6 (s, benzo), 122.0 (d, JC,P =9.6 Hz, Ar),
1
1
120.0 (d, JC,P =90.4 Hz, ipso-Ph), 103.6 ppm (d, JC,P =100.3 Hz, ipso-Ar);
31P{1H} NMR (162 MHz, CDCl3): d=À4.1 ppm (s); 19F NMR (282 MHz,
CD2Cl2): d=À78.2 ppm (s); elemental analysis (%) calcd. for
C24H16F3O3PS4: C 50.69, H 2.84; found: C 50.85, H 2.81.
(d, JC,P =7.9 Hz, ipso-Ph), 141.3 (d, JC,P =7.8 Hz, ipso-Ph), 139.2 (d, JC,P
11.9 Hz, ipso-thiophene), 136.6 (d, JC,P =4.6 Hz, Ar), 135.5 (d, JC,P
4.8 Hz, Ar), 133.2 (d, JC,P =1.7 Hz, Ph), 132.4 (d, JC,P =1.5 Hz, Ph), 131.4
(d, JC,P =2.7 Hz, Ph), 131.3 (d, JC,P =2.8 Hz, Ph), 131.2 (d, JC,P =2.9 Hz,
Ph), 131.1 (d, JC,P =3.0 Hz, Ph), 129.1 (d, JC,P =3.3 Hz, Ph), 129.0 (d,
=
=
4
4
Bis(benzothieno)-4-thiaphosphinine gold(I) chloride 5c: [AuACHTUNGTRENNUNG(tht)Cl]
(0.397 g, 1.24 mmol) was added to a solution of 2c (0.500 g, 1.24 mmol)
in CHCl3 (20 mL). The reaction was stirred for 5 h at room temperature.
Then all volatile materials were removed under vacuum, and the remain-
ing solid was washed with pentane and diethyl ether. The product was
obtained as white solid by recrystallization from a concentrated acetone
solution at room temperature (yield: 0.400 g, 50.6%). 1H NMR
(400 MHz, CDCl3): d=8.21–8.16 (m, 2H), 7.90–7.83 (m, 4H), 7.42–
7.38 ppm (m, 3H); 13C{1H} NMR (100 MHz, CDCl3): d=139.3 (s, Ar),
J
C,P =2.4 Hz, Ph), 129.0 (s, benzo), 128.9 (s, benzo) 127.3 (s, benzo), 125.9
(s, benzo), 126.0 (s, benzo), 122.6 ppm (s, benzo); 31P{1H} NMR
(162 MHz, CDCl3): d=5.08 (d, 3JC,P =22.8 Hz), 4.97 ppm (d, JC,P
=
3
22.8 Hz); HRMS: m/z=513.029621 ([M+H]+, calcd. 513.029621).
Bis
G
E
cis-5b:
[Au
ACHTUNGTRENNUNG
2b (89:11) mixture (0.596 g, 1.24 mmol) in CHCl3 (20 mL). The reaction
was stirred for 5 h at room temperature. All volatile materials were re-
moved under vacuum and the remaining solid was washed with diethyl
ether and acetone. The product was obtained as a white solid (yield:
0.590 g, 50.0%). 1H NMR (400 MHz, [D7]DMF): d=8.21–8.16 (m, 2H),
7.90–7.83 (m, 4H), 7.42–7.38 ppm (m, 3H); 31P{1H} NMR (162 MHz,
CDCl3): d=0.6 (d, JP, P =7.9 Hz), 0.5 ppm (d, JP, P =7.9 Hz); HRMS: m/z=
966.89255 ([M+Na]+, calcd. 966.8976).
138.7 (d, JC,P =17.6 Hz, Ar), 138.4 (d, JC,P =13.0 Hz, Ar), 133.9 (d, JC,P
=
17.6 Hz, o-Ph), 132.7 (d, JC,P =2.3 Hz, p-Ph), 130.0 (d, 2JC,P =62.3 Hz,
ipso-Ph), 129.6 (s, benzo), 129.4 (s, benzo), 125.8 (d, J C,P =4.4 Hz, m-Ph),
2
122.2 (d, JC,P =6.9 Hz, benzo), 121.8 (s, benzo), 112.5 ppm (d, JC,P
=
69.0 Hz, ipso-Ar); 31P{1H} NMR (162 MHz, CDCl3): d=À10.0 ppm (s);
MS (ESI, positive ions): m/z=635.92 ([M+H]+, calcd. 636.93).
BisACHTUNGTRENNUNG(benzo[b]thieno)-4-thiaphosphinine 2c: nBuLi (0.65 mL, 1.63 mmol)
was added dropwise at À788C to a solution of bis(3-bromobenzo[b]thio-
phen-2-yl)sulfane 1c (0.372 g, 0.82 mmol) and TMEDA (0.267 mL,
1.79 mmol) in THF/Et2O (1:1),. After stirring for 1 h at this temperature,
PhPCl2 (0.146 g, 0.82 mmol) was added dropwise at À788C and the reac-
tion was quickly warmed to room temperature, and stirred overnight.
The mixture was subsequently filtered through neutral alumina. The pure
product was obtained as white crystals by recrystallization from a concen-
trated CH2Cl2 solution at room temperature (yield: 0.215 g, 65.1%).
1H NMR (400 MHz, CDCl3): d=8.13 (br d, JH,H =8.0 Hz, 2H, benzo),
Acknowledgements
Financial support by the NSERC of Canada and the Canada Foundation
for Innovation (CFI) is gratefully acknowledged. We also thank Alberta
Ingenuity, now part of Alberta Innovates Technology Futures for a grad-
uate scholarship (Y.R.) and a New Faculty Award (T.B.). Thanks to Prof.
Laszlo Nyulaszi (Budapest) for helpful discussions regarding the theoreti-
cal calculations, and Prof. Todd Sutherland (Calgary) for his help with
the electrochemical studies.
7.81 (br d,
JH,H =8.0 Hz, 2H, benzo), 7.46–7.34 (m, 4H, Ph), 7.20–
7.17 ppm (m, 4H, Ph); 13C{1H} NMR (100 MHz, CDCl3): d=141.7 (d,
1JC,P =29.9 Hz, ipso-Ar), 139.6 (d,
JC,P =6.5 Hz, Ar), 138.2 (d, JC,P =
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5.8 Hz, Ar), 136.6 (d, 2JC,P =16.8 Hz, ipso-Ph), 132.0 (d, 2JC,P =19.7 Hz, o-
3
Ph), 128.9 (s, p-Ph), 128.5 (d, JC,P =6.9 Hz, m-Ph), 124.9 (s, benzo), 124.7
(s, benzo), 123.2 (d, JC,P =9.6 Hz, Ar), 121.9 (s, benzo), 122.8 ppm (d,
3JC,P =5.3 Hz, benzo); 31P{1H} NMR (162 MHz, CDCl3): d =À60.2 ppm
(s); Elemental analysis calcd. (%) for C22H13PS3: C 65.32, H 3.24; found:
C 64.79, H 3.30; HRMS (EI): m/z=403.9901 ([M]+, calcd. 403.9917).
BisACHTUNGTRENNUNG(benzo[b]thieno)-4-thiaphosphinine oxide 3c: BisACHTUNGTNER(NUGN benzo[b]thieno)-4-
thiaphosphinine 2c (0.500 g, 1.24 mmol) was dissolved in CHCl3 (20 mL),
an excess of H2O2 (15.5 mL, 30% aqueous solution) was added, and the
mixture was stirred overnight at room temperature. After quenching with
water, the organic layer was separated and dried with MgSO4, and all
volatile materials were removed under vacuum. The product was ob-
tained as a light yellow solid and recrystallized from acetone (yield:
0.445 g, 85.3%). 1H NMR (400 MHz, CDCl3): d=8.15–8.12 (m, 2H),
7.88–7.78 (m, 4H), 7.45–7.41 (m, 3H), 7.37–7.32 ppm (m, 4H);
13C{1H} NMR (100 MHz, CDCl3): d=141.9 (d, JC,P =8.5 Hz, Ar), 139.0
1
(d, JC,P =11.1 Hz, Ar), 138.1 (d, 2JC,P =13.0 Hz; ipso-Ph), 134.3 (d, JC,P
=
4
3
115.6 Hz, ipso-Ar), 133.7 (d, JC,P =2.9 Hz, p-Ph), 131.4 (d, JC,P =11.1 Hz,
m-Ph), 128.7 (d, 2JC,P =13.2 Hz, o-Ph), 125.5 (s; benzo), 125.4 (s, benzo),
123.9 (s, benzo), 121.5 (s, benzo), 120.4 ppm (s, thiophene); 31P{1H} NMR
(162 MHz, CDCl3): d=4.1 ppm (s); elemental analysis (%) calcd. for
C22H13OPS3: C 62.84, H 3.12; found: C 62.90, H 3.24.
BisACHTUNGTRENNUNG(benzo[b]thieno)-4-thiaphosphonium 4c: An excess of methyl triflate
(0.228 g, 1.37 mmol) was added to a solution of 2c (0.500 g, 1.24 mmol)
in CHCl3, and the mixture was stirred overnight at room temperature.
After evaporating all volatile materials in vacuum, the remaining solid
was washed with pentane and diethyl ether. The product was obtained as
yellow crystals by recrystallization from a concentrated CHCl3 solution at
room temperature (yield: 0.460 g, 65.2%). 1H NMR (400 MHz, CDCl3):
1928
www.chemasianj.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2010, 5, 1918 – 1929

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Published online: June 11, 2010
Chem. Asian J. 2010, 5, 1918 – 1929
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
1929