Synthesis and properties of ladder-type 1,4-dihydro-1,4-phosphasilins

Article abstract of DOI:10.1139/V09-108

The synthesis and advanced characterization of a series of extended dithieno[2,3-b:3',2'-e][1,4-dihydro-1,4]phosphasilins is reported, and their suitability as new building blocks for organic electronics is evaluated. Synthesis of basic, as well as benzo-

Full text of DOI:10.1139/V09-108

1222
Synthesis and properties of ladder-type
1,4-dihydro-1,4-phosphasilins
Yi Ren, Thomas Linder, and Thomas Baumgartner
Abstract: The synthesis and advanced characterization of a series of extended dithieno[2,3-b:3’,2’-e][1,4-dihydro-1,4]phos-
phasilins is reported, and their suitability as new building blocks for organic electronics is evaluated. Synthesis of basic, as
well as benzo-extended dithienophosphasilins, can be achieved using appropriate 2,3-dibromothiophene precursors in a
two-step protocol introducing the silicon and phosphorus centers subsequently. Both ladder-type materials show the typical
reactivity of trivalent phosphorus species and can quantitatively be converted into the corresponding oxides or gold com-
plexes, the latter exemplified with the basic dithienophosphasilin. Their optoelectronic properties were found to be inferior
to those of related dithieno[3,2-b:2’,3’-d]phospholes, indicating a disruption of the p-conjugation in the molecular scaffold.
X-ray crystallographic studies revealed that the molecular scaffold is planar in the oxidized benzo-extended material,
whereas the basic dithieno materials show some small deviation from planarity. Density functional theory calculations sug-
gest all materials to be planar, with the exception of the benzo-extended trivalent phosphasilin. This structure–property
study illustrates that the disruption of the p-conjugation in the molecular scaffold of the extended phosphasilins is exclu-
sively due to the presence of the silicon center and its electronic effects, rather than structural features.
Key words: phosphorus heterocycles, silicon heterocycles, organic electronics, thiophene, p-conjugation.
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Resume : On a effectue la synthese et la caracterisation avancee d’une serie etendue de dithieno[2,3-b:3’,2’-e][1,4-dihy-
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dro-1,4-]phosphasilines et on a evalue la possibilite de les utiliser dans la synthese de composes organiques electroniques.
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On peut realiser la synthese du produit de base ainsi que de diverses benzodithienophosphasilines en utilisant comme pre-
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curseurs des 2,3-dibromothiophenes appropries dans un protocole en deux etapes au cours desquelles on introduit les cen-
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tres silicies et phosphores ulterieurement. Les deux types de materiaux en echelle presentent la reactivite type des especes
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contenant du phosphore trivalent et ils peuvent etre transformes quantitativement en oxydes correspondants ou en com-
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plexes d’or, un exemple de ce dernier ayant ete prepare avec la dithienophosphasiline basique. On a trouve que leurs pro-
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prietes optoelectroniques sont inferieures a celles des dithieno[2,3-b:3’,2’-d]phospholes, ce qui indique qu’il se produit une
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interruption dans la conjugaison p dans l’echafaudage moleculaire. Les etudes cristallographiques par diffusion des rayons
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X revelent que l’echafaudage moleculaire est plan dans les derives benzo-condenses oxydes alors que les materiaux di-
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thieno de base presentent de faibles deviations par rapport a la planeite. Des calculs a base de la theorie de la fonctionnelle
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de la densite suggerent que tous les materiaux doivent etre plans, a l’exception de la benzophosphasiline trivalente.
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L’etude structure propriete illustre le fait que la disruption de la conjugaison p dans l’echafaudage moleculaire de phos-
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phasilines etendues est exclusivement due a la presence du centre silicium et de ses effets electroniques et n’a rien a voir
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avec ses caracteristiques structurales.
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Mots-cles : heterocycles du phosphore, heterocycles du silicium, electroniques organiques, thiophene, conjugaison p.
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[Traduit par la Redaction]
spite the fact that the incorporation of s3,l3-phosphorus cen-
ters allows for a number of facile, nearly quantitative
chemical modifications to be performed that significantly
impact the materials’ electronic structure.6 The versatile re-
activity of trivalent phosphorus centers allows for the prepa-
ration of entire families of materials from a single precursor,
through oxidation or complexation of the phosphorus cen-
ter.7 Well-defined molecular systems thus allow for the in-
vestigation of important structure–property relationships
through the systematic variation of the model’s chemical
structure that may then be used subsequently to tailor the
materials’ properties towards certain applications.6a
Introduction
Organic p-conjugated materials have received significant
attention in recent years owing to their beneficial photo-
physical and electronic properties that provide intriguing
opportunities for the field of organic electronics. Their
semiconducting properties, in particular, show great poten-
tial for application in electronic devices such as molecular
or polymer-based light-emitting diodes, photovoltaic cells,
field-effect transistors, and sensory materials.1–5
Surprisingly, organophosphorus p-conjugated materials
have received relatively little attention up until recently, de-
Received 19 May 2009. Accepted 16 June 2009. Published on the NRC Research Press Web site at canjchem.nrc.ca on 18 August 2009.
Y. Ren, T. Linder, and T. Baumgartner.1 Department of Chemistry, University of Calgary, 2500 University Drive NW, Calgary, AB
T2N 1N4, Canada.
1Corresponding author (e-mail: thomas.baumgartner@ucalgary.ca).
Can. J. Chem. 87: 1222–1229 (2009)
doi:10.1139/V09-108
Published by NRC Research Press

Ren et al.
1223
Chart 1. Relevant, ring-annelated dithieno- and dibenzo-hetero-
Scheme 1. Synthesis and reactivity of the dithienophosphasilin (3).
cycles reported in the literature.
A few years ago, we introduced the dithieno[3,2-b:2’,3’-
d]phosphole system (Chart 1A) as a new building block for
p-conjugated materials.8 This system conjoins two thio-
phene subunits with a central phosphole moiety via annela-
tion. Fused bithiophene materials are generally promising
candidates for an application in organic electronics, as they
provide a high degree of p-conjugation due to their rigidi-
fied, planar structure that intrinsically affords smaller
HOMO–LUMO (highest occupied molecular obrital – low-
est unoccupied molecular orbital) gaps.9 Our extensive, sys-
tematic investigations to date have revealed that this is also
true for the dithienophosphole system and we were able to
confirm a doping function for the phosphorus center, rather
than it being an integral part of the p-conjugated system.8
Nakayama and co-workers16 have reported somewhat related
phospha-sila-thienotrypticenes in 1993, neither manuscript
focuses on organic electronics. It is noteworthy, however,
that Kawashima and co-workers17 have recently reported a
series of dibenzoborin-based materials (Chart 1D) that show
very promising optoelectronic features for a potential appli-
cation in organic electronics.
This present investigation now explores the synthetic acces-
sibility and properties of dithieno[2,3-b:3’,2’-e][1,4-dihydro-
1,4]phosphasilins, and the chemical versatility of the phos-
phorus center for additional fine-tuning. The study is further
supported by theoretical investigations to gain a deeper
understanding of the properties of this new ladder-type
system.
The materials obtained in the context of our studies display
intriguing photophysical properties with respect to emission
wavelengths, intensity, and tunability that are far superior
over those of related dibenzophospholes;10,11 the parent di-
thienophosphole scaffold is strongly blue-light emitting with
photoluminescence efficiencies of up to 90%. Notably, its
photophysical properties can efficiently be tuned by simple
modifications at either the phosphorus center (E = lone pair)
via oxidation (E = O, S), complexation with main group cen-
Results and discussion
Synthesis and characterization
+
ters (E = BH3, CH3 ) or transition metals (E = [M]), or by
The synthesis of the targeted dithienophosphasilin (3)
(Scheme 1) is straightforward using 2,3-dibromothiophene
as starting material. Due to the ortho-directing effect of the
sulfur atom, the 2-position of the thiophene is favored to-
wards selective lithiation with n-butyllithium at –78 8C.
Subsequent treatment with 0.5 equiv. of Me2SiCl2 affords
the formation of the dithienyldimethylsilane (2) in good
yield (80%). The further addition of 2 equiv. of n-butyl-
lithium at –78 8C allows for the remaining bromo-substitu-
ents of 2 to be lithiated, and the central six-membered ring
is closed by addition of PhPCl2, providing 3 in a similarly
high yield (80%). The dithienophosphasilin (3) shows a 31P
NMR resonance at d = –20.7 ppm that is related to those of
variation of the substitution pattern (R1 on the thieno units or
R2 on the central phosphorus atom; see Chart 1).6f,8,11
Expanding our work on dithienophospholes, in this paper
we now report our initial structure–property investigations on
a new class of ladder-type, p-conjugated materials with a
central 6-membered, 1,4-dihydro-1,4-phosphasilin ring (Chart
1B; E1 = PPh, E2 = SiMe2). We were interested in how the
addition of an additional silylene group within the molecu-
lar scaffold of dithienophospholes would impact the struc-
ture and properties of the resulting class of materials. It
should be mentioned in this context that the number of re-
ported six-membered, heterocyclic fused bithiophene mate-
rials to date is limited to a few thia-silins,12,13 -germins,
and -stannins (Chart 1B),12 as well as dithieno-1,2-disi-
lins14; most of the dithieno materials reported to date
showcase five-membered central heterocycles.9a Although
dibenzophosphasilins (Chart 1C) have been reported by
Skvortsov, Toldov, and co-workers15 in the early 1990s, and
dithienophospholes (cf.: d = –20 3 ppm).8,10
A
29Si NMR
shift of d = –17.7 ppm further supports the successful forma-
1
tion of 3;18 the same is true for the H and 13C NMR data.
As mentioned in the introduction, the trivalent phosphorus
center in 3 is an excellent site for further modification, al-
lowing for the generation of a whole family of new materi-
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Can. J. Chem. Vol. 87, 2009
als. To verify this important tool of organophosphorus p-
conjugated materials6a for this new ladder-type system, we
have performed two representative chemical modifications
converting 3 into the corresponding oxide 4a by treatment
with hydrogen peroxide, and the gold complex 4b by treat-
ment with Au(THT)Cl at room temperature, respectively
(Scheme 1). The distinct lowfield shifted 31P NMR resonan-
ces observed for the modified compounds 4a (d = 11.5 ppm)
and 4b (d = 5.4 ppm) clearly support the successful transfor-
mation, as they again relate fairly well to the values of the
corresponding dithienophosphole oxides and gold com-
Fig. 1. Two views of the molecular structure of 4a in the solid state
(50% probability level; H atoms are omitted for clarity). Selected
˚
bond lengths (A) and angles (8): P1—O1 1.496(4), C1—C2
1.368(9), C2—C3 1.437(8), C3—C4 1.383(8), C5—C6 1.377(8),
C6—C7 1.433(8), C7—C8 1.358(9), P1—C3 1.789(6), P1—C6
1.800(6), P1—C11 1.807(5), Si1—C4 1.863(6), Si1—C5 1.870(6),
Si1—C21 1.855(7), Si1—C22 1.860(6); dihedral angle at P–Si axis:
20.09/17.46.
1
plexes;8,11 the same is true for the H and 13C NMR data.
The 29Si NMR resonances, on the other hand, are less of a
clear indicator, as they remain essentially unchanged at d =
–17.8 ppm (4a) and d = –17.6 ppm (4b).
To our surprise, however, none of the three phosphasilin
materials, 3, 4a, or 4b, showed any notable fluorescence,
which is in stark contrast to strongly emitting dithienophosp-
holes.8,11 This indicates that the incorporation of the silicon
center appears to disrupt the p-conjugation across the sys-
tem by essentially separating the chromophore into two in-
dependent thiophene units. The observation is also
supported by the UV–vis spectroscopic data of the three
compounds that only show narrow absorptions in the deep
UV region of the optical spectrum at lmax = 236 nm for 3,
237 nm for 4a, and 250 nm for 4b (cf. thiophene: lmax
=
230 nm).19
The investigations on the related dibenzophosphasilins
have illustrated that their scaffold is nonplanar at the P–Si
sites, and the central ring generally shows a pronounced
boat conformation. Furthermore, the resulting dihedral angle
between the two halves of the molecule was found to depend
on the chemical nature of the P center.15 To verify whether
the scaffold in the dithienophosphasilin system is also bent
(or planar), we have investigated the solid-state structures of
the two modified species, 4a and 4b. We were able to obtain
single crystals suitable for X-ray diffraction studies of both
compounds at room temperature from acetone solutions. The
structure of 4a shows two independent molecules in the unit
cell, both of which show a somewhat bent molecular scaf-
fold with dihedral angles amounting to approximately 208
and 17.58 (Fig. 1). In contrast to the dibenzo system, the cen-
tral phosphasilin ring in both molecules is fairly planar, with
the silicon center showing a slightly more pronounced devia-
Fig. 2. Two views of the molecular structure of 4b in the solid state
(50% probability level; H atoms are omitted for clarity). Selected
˚
bond lengths (A) and angles (8): Au1—Cl1 2.2861(13), Au1—P1
2.2297(13), C1—C2 1.358(8), C2—C3 1.423(7), C3—C4 1.382(7),
C5—C6 1.371(8), C6—C7 1.433(7), C7—C8 1.355(9), P1—C3
1.802(5), P1—C6 1.810(6), P1—C11 1.813(6), Si1—C4 1.853(6),
Si1—C5 1.865(6), Si1—C21 1.856(6), Si1—C22 1.858(6); P1–
Au1–Cl1 178.24(5); dihedral angle at P–Si axis: 10.94.
˚
˚
tion from planarity (Si: 0.31/0.32 A; P: 0.20/0.13 A). The
bond lengths of the molecular scaffold suggest two isolated
thiophene units without significant conjugation across the
central phosphasiline ring, which is in line with the features
observed for the dibenzophosphasilins.15
The gold complex 4b, on the other hand, exhibits an es-
˚
sentially planar central phosphasiline ring (deviation: 0.17 A
˚
for Si and 0.15 A for P), and the rest of the molecular scaf-
fold shows a significantly smaller deviation from planarity
(*118; Fig. 2). Remarkably, the dithienophosphasilin
scaffold of 4b is bent towards the exocyclic phenyl ring,
whereas in 4a the opposite direction is observed (away from
phenyl group). The bond lengths and angles of the molecular
scaffold of 4b support a comparably more delocalized elec-
tronic structure within the central 1,4-phosphasilin ring.
Whereas endocyclic C–C bonds are significantly elongated
with the peripheral C1–C2 and C7–C8 bonds at 1.358(8)
˚
and 1.355(9) A, respectively, the endocyclic Si–C (1.865(6)
˚
˚
˚
˚
(C3–C4: 1.382(7) A, C5–C6: 1.371(8) A), when compared
and 1.856(6) A) and P–C bonds (1.802(5) and 1.810(6) A)
Published by NRC Research Press

Ren et al.
1225
Scheme 2. Synthesis and chemical modification of the benzoanne-
lated dithienophosphasilin (7).
Fig. 3. Two views of the molecular structure of 8 in the solid state
(50% probability level; H atoms are omitted for clarity). Selected
˚
bond lengths (A) and angles (8): P1—O1 1.4878(18), C5—C6
1.410(4), C6—C7 1.452(3), C7—C8 1.378(4), C9—C10 1.379(4),
C10—C11 1.450(4), C11—C12 1.415(4), P1—C7 1.801(3), P1—
C10 1.803(3), P1—C21 1.810(3), Si1—C8 1.862(3), Si1—C9
1.860(3), Si1—C31 1.860(3), Si1—C32 1.854(3); dihedral angle at
P–Si axis: 4.81/5.83; helical torsion angle: 10.5/12.
are similar in length to the respective exocyclic Si–C/P–C
bonds within the margin of error (Fig. 2).
The bond lengths between the gold center and P1
˚
˚
(2.2297(13) A) or Cl1 (2.2861(13) A) relate well to those
observed for the dithienophosphole system.11b,11e Remark-
ably, 4b exists as a monomer in the solid state and shows
no intermolecular contacts through aurophilic interactions.
Although we have observed this feature with the dithieno-
phosphole system once before,11b related complexes usually
show dimerization through aurophilic interactions in the
solid state.11e,20 The monomeric structure of 4b can, how-
ever, be explained through sterics, as the somewhat bulky
dimethylsilylene group does not easily allow for p-stacking
interactions between two neighboring dithienophosphasilines
brought together in a potential dimer, as observed in the di-
meric dithienophosphole gold complexes.
To potentially reduce the band gap of the dithieno-
phosphasiline scaffold and to increase the degree of deloc-
alization for improved optoelectronic properties of the
materials, we have targeted corresponding benzo-extended
dithienophosphasilins next. We could recently confirm this
feature with the benzo-extended dithienophosphole system
that does indeed show a smaller band gap than the parent
system.21 Synthesis of the corresponding benzoannelated di-
thienophosphasilin is possible in a protocol similar to that
for the parent dithienophosphasilins (vide supra), using 2,3-
dibromobenzo[b]thiophene as starting material. Selective
lithiation with n-butyllithium and treatment with Me2SiCl2
affords the silane (6), which can then be converted into the
extended phosphasilin (7) with another 2 equiv. of n-BuLi
and 1 equiv. of PhPCl2 (Scheme 2).
from that of 6. However, neither of the extended compounds
shows any noteworthy fluorescence emission indicating that
the extension of the p-conjugated system in 7 and 8 is not
sufficient enough to significantly enhance the photophysical
properties of the materials. Again, UV–vis spectroscopic data
suggest that the central phosphasiline ring breaks the system
down into two independent benzothiophene chromophores
without delocalization across the entire scaffold (lmax
=
232 nm for 7, 237 nm for 8). To confirm the planarity of
the system and to support the electronic ‘decoupling effect’
of the central phosphasilin ring, we have also studied the
structure of 8 in the solid state. Suitable single crystals for
an X-ray diffraction study were obtained from a concentrated
acetone solution at room temperature.
The structure of 8 in the solid state shows two independ-
ent molecules in the unit cell that each overlap with parts of
one of their terminal benzene rings (Fig. 3). This overlap
gives rise to some p-stacking type interactions in the typical
˚
range of 3.6–3.7 A. The bond lengths of 8 are similar to
those of a related benzoannelated dithienophosphole oxide21
and reflect a somewhat delocalized electronic system similar
˚
to 4b. The exocyclic Si–C (1.860(7) A by average) and P–C
˚
bonds (1.805(10) A by average) of the central rings relate
well to the other two phosphasiline systems reported herein.
In terms of the molecular geometries, the scaffold of 8 is in-
deed significantly more planar than those of compounds 4a
and 4b; the central phosphasilin ring is perfectly planar. Sur-
prisingly, however, both independent molecules of 8 show
the onset of a helical structure, although the terminal ben-
zene subunits are too far away from each other for claiming
steric issues to be responsible. There are also no distinct in-
termolecular interactions that could cause the twisting from
planarity; electronic factors appear to be intrinsically respon-
sible for the unusual helicity that generates a dihedral torsion
Compared to the non-benzoannelated phosphasilin (3),
compound 7 shows a highfield shifted 31P NMR resonance
at d = –36.5 ppm and a somewhat lowfield shifted 29Si
NMR resonance at d = –16.9 ppm that suggest a significantly
different structure for 7, likely involving a more strongly
bent central phosphasilin ring (vide infra). Oxidation with
hydrogen peroxide affords the oxidized species 8 with a 31P
NMR shift at d = 11.3 ppm that, on the other hand, is very
similar to that of the non-extended oxide 4a. The 29Si NMR
resonance at d = –17.1 ppm is again only slightly shifted
Published by NRC Research Press

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Can. J. Chem. Vol. 87, 2009
angle of 118–128 between the C1(C1A) and C16(C16A)
atoms in each of the two molecules.
Dichlorodimethylsilane and phenyldichlorophosphane were
distilled prior to use. 2,3-Dibromo-benzo[b]thiophene24 and
1
Au(THT)Cl25 were prepared by literature methods. H NMR,
Computational investigations
13C{1H} NMR, 31P{1H} NMR, and 29Si{1H} NMR spectra
were recorded on a Bruker AC200, Bruker DMX-300, or
Bruker DRX-400 spectrometer. Chemical shifts were refer-
enced to external 85% H3PO4 (31P) or tetramethylsilane
To better understand the observed properties of the new
dithienophosphasilin materials, we have optimized the struc-
tures of 3, 4a, 7, and 8 on the B3LYP-6/31G* level of
theory.22 The density functional theory (DFT) calculations
suggest that three of the materials, 3, 4a, and 8, are planar,
whereas 7 is significantly bent at the P–Si axis with a dihe-
dral angle of ca. 308 between the two benzothiophene halves.
These observations relate well to the observed 31P NMR
resonances for the four compounds and the observed molec-
ular structures of 4a (and 4b) and 8 in the solid state. The
planar structures clearly suggest that geometry is not a factor
in the inferior photophysical properties. In fact, the frontier
orbitals for all four compounds extend well over the whole
p-conjugated framework, irrespective of the molecular ge-
ometry. However, the energy of the frontier orbitals can be
used to explain the observed properties. The generally lower
energy levels of the HOMOs as well as the higher energy lev-
els of the LUMOs lead to significantly increased band gaps
1
(TMS) (13C, H, 29Si). Elemental analyses were performed at
the Department of Chemistry at the University of Calgary.
Mass spectrometry (chemical ionization) was performed using
a Finigan SSQ700 and Waters GCTOF Premier instrument.
Optical spectroscopy was performed with dichloromethane
solutions using a Jasco FP-6600 spectrofluorometer and UV-
Vis-NIR Cary 5000 spectrophotometer.
X-ray crystallography
Crystallographic data for 4a, 4b, and 8 are summarized in
Table 1 (also see the Supplementary data). Diffraction data
were collected on a Nonius Kappa CCD diffractometer us-
˚
ing monochromated Mo Ka radiation (l = 0.71073 A) at –
80 8C (4b) and –100 8C (4a, 8). The data sets were cor-
rected for Lorentz and polarization effects, and empirical ab-
sorption correction was applied to the net intensities. The
structures were solved by direct methods and refined using
SHELX.26 After full-matrix least-squares refinement of the
nonhydrogen atoms with anisotropic thermal parameters, the
hydrogen atoms were placed in calculated positions using a
riding model. Refinement of the structure model for 4a re-
sulted in unsatisfactory agreement factors (wR2 = 0.44, R1 =
for the phosphasiline-based materials ranging from Ebg
=
5.06 eV for 3 to Ebg = 4.57 eV for 7 that are basically more
than 1 eV larger than those for related dithienophospho-
les.8b,21 Notably, the band gap of the phosphasilin even in-
creases when the phosphorus center is oxidized (4a: Ebg
=
5.36 eV, 8: Ebg = 4.60 eV), which is contrary to the phosphole
system, where the LUMO can generally be stabilized signifi-
cantly leading to smaller band gaps in the dithienophosphole
oxides.8b,11f,21 These observations support an inherently dif-
ferent electronic structure for the phosphasilin-based materi-
als, although they should theoretically be able to allow for
delocalization of the p-system via hyperconjugative s*–p*
interactions through the Si centers.23
–3
˚
0.13) and high residual electron density (2 e A ). Compari-
son of observed and calculated intensities showed that the
most disagreeable reflections were consistently associated
with much higher observed intensities than expected. This
feature was interpreted as the effect of intensity addition
due to nonmerohedral twinning with the help of PLATON;27
the same twin law was confirmed for a second crystal. Re-
finement of an intensity data set taking into account the
overlap of ca. 80% of the reflections resulted in a batch
scale factor of 0.15 for the smaller individual. Due to in-
complete overlap of reflections, the final agreement factors
Conclusions
In conclusion, we have synthesized a series of di-
thieno[2,3-b:3’,2’-e][1,4-dihydro-1,4]phosphasilins that ex-
tend our studies on the dithieno[3,2-b:2’,3’-d]phosphole
system. Our studies have shown that the phosphasilin frame-
work can efficiently be constructed in two steps and subse-
quent modification of the central phosphorus atom allows
for the formation of a family of derivatives. Investigations
of their properties, however, have revealed that the incorpo-
ration of an additional silylene center within the scaffold of
dithienophospholes significantly impacts the photophysical
properties of the materials, not necessarily due to nonplanar
geometries, but significantly increased band gaps (>4.5 eV).
As a result, no strong fluorescence emission is observed for
the phosphasiline system, which is in stark contrast to the
dithienophosphole system.
are still higher than in the case of the untwinned structures;
–3
˚
the residual electron density dropped to 0.9 e A .
Bis(3-bromothiophen-2-yl)dimethylsilane (2)
To the solution of 2,3-dibromothiophene (1) (0.918 g,
3.79 mmol) in Et2O (20 mL), n-BuLi (1.52 mL, 3.79 mmol)
was added dropwise at –78 8C. After stirring for 40 min,
Me2SiCl2 (0.245 g, 1.897 mmol) was added dropwise at this
temperature. After another 15 min at –78 8C, the reaction
was allowed to warm up, and stirred overnight at room tem-
perature. Subsequently, the mixture was filtered through
neutral alumina and the solvent was removed under vacuum,
1
affording a light yellow oil (yield: 0.580 g, 80%). H NMR
2
(400 MHz, CDCl3, ppm) d: 7.52 (d, JHH = 4.8 Hz, 2H, thi-
Experimental section
2
ophene), 7.13 (d, JHH = 4.8 Hz, 2H, thiophene), 0.81 (s, 6H,
Si(CH3)2). MS (CI) m/z: 383.4 [M + H]+.
General procedures
Reactions were carried out in dry glassware and under inert
atmosphere of purified nitrogen using Schlenk techniques.
Solvents were dried using an MBRAUN solvent purification
system. n-BuLi (2.5 mol/L in hexane), 2,3-dibromothiophene,
and hydrogen peroxide (30% in water) were used as received.
Compound 3
To the solution of bis(3-bromothiophen-2-yl)dimethyl-
silane (0.986 g, 2.58 mmol) in Et2O (200 mL), n-BuLi
(2.06 mL, 5.16 mmol) was added dropwise at –78 8C. After
Published by NRC Research Press

Ren et al.
1227
Table 1. X-ray crystallographic data of compounds 4a, 4b, and 8.
Crystal
4a
4b
8
Empirical formula
Formula weight
Crystal system
Space group
Color
C16H15OPS2Si
346.5
Triclinic
P-1
Colourless
8.7170(4)
9.3890(5)
20.0570(9)
87.147(3)
85.979(3)
89.964(3)
1635.47(14)
4
C16H15AuClPS2Si
562.9
Monoclinic
P21/c
Colourless
12.2520(3)
11.8560(3)
13.0200(3)
90
102.8980(10)
90
1843.56(8)
4
C24H19OPS2Si
446.6
Triclinic
P-1
Colourless
11.6690(4)
14.3750(4)
14.4700(3)
100.554(2)
108.293(2)
104.8340(10)
2133.96(10)
4
˚
a (A)
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
3
˚
V (A )
Z
T (K)
173(2)
0.492
720
193(2)
8.496
1072
173(2)
0.394
928
m (Mo Ka) (mm–1)
F(000)
Crystal size (mm–1)
rcalcd. (g cm–3)
q range (8)
No. of reflections
No. of unique data
Rint
0.21 Â 0.18 Â 0.15
0.23 Â 0.20 Â 0.18
0.21 Â 0.20 Â 0.20
1.407
2.028
1.390
2.04–27.64
12730
7040
1.71–27.47
8063
4200
1.55–27.45
17652
9549
0.0381
0.0253
0.0283
Reflections/parameters ratio
R1, [I > 2s(I)]
wR2 (all data)
GoF on F2
7040/0/380
0.0780
0.2360
4200/0/199
0.0255
0.0935
9549/0/603
0.0464
0.1468
1.106
1.254
1.152
Completeness (%)
Largest diff. peak and hole (e A )
94.3
99.6
98.5
–3
˚
0.912 and –0.576
0.941 and –1.243
0.742 and –0.782
4
stirring at this temperature for 40 min, PhPCl2 (0.462 g,
2.58 mmol) was added dropwise. The reaction was then al-
lowed to warm up quickly and was left stirring overnight at
room temperature. The mixture was subsequently filtered
through neutral alumina and evaporated to dryness. The pure
product 3 was obtained as white solid after recrystallization
4.8 Hz, JHH = 1.6 Hz, 2H, thiophene), 7.61–7.56 (m, 4H,
thiophene and Ph), 7.46–7.35 (m, 3H, Ph). 13C{1H} NMR
(100 MHz, CDCl3, ppm) d: 143.3 (d, JCP = 19.2 Hz, thio-
phene), 142.0 (d, JCP = 109.4 Hz, ipso-thiophene), 135.4
(d, JCP = 108.1 Hz, ipso-Ph), 133.0 (d, JCP = 15.5 Hz, thi-
ophene), 131.4 (d, JCP = 2.8 Hz, p-Ph), 131.1 (d, JCP
15.8 Hz, thiophene), 130.3 (d, JCP = 10.6 Hz, o-Ph), 128.5
3
2
2
2
4
3
=
2
from pentane at room temperature (yield: 0.682 g, 80%).
3
3
1H NMR (400 MHz, CDCl3, ppm) d: 7.66 (dd, JHH
=
(d, JCP = 7.6 Hz, m-Ph), 1.7 (s, Si(CH3)2), 1.1 (s, Si(CH3)2).
4
4.8 Hz, JHP = 2.0 Hz, 2H, thiophene), 7.36–7.32 (m br, 2H,
31P{1H} NMR (162 MHz, CDCl3, ppm) d: 11.5 (s). 29Si{1H}
Ph), 7.28–7.25 (m br, 3H, Ph), 7.14 (dd, 3JHH = 4.8 Hz, 3JHP
=
NMR (80 MHz, CDCl3, ppm) d: –17.8 (d, JSiP = 9.04 Hz).
Elemental anal. calcd. (%) for C16H15OPS2Si (346.48): C
55.46, H 4.36; found: C 55.19, H 4.44.
3
4.0 Hz, 2H, thiophene), 0.56 (d, 4JHP = 6.4 Hz, 6H, Si(CH3)2).
13C{1H} NMR (100 MHz, CDCl3, ppm) d: 145.0 (d, JCP
=
1
1
10.3 Hz, ipso-Ar), 138.9 (d, JCP = 15.9 Hz, ipso-Ph), 135.3
(d, JCP = 1.9 Hz, thiophene), 133.3 (d, JCP = 21.1 Hz,
2
3
Compound 4b
2
thiophene), 132.4 (d, JCP = 34.1 Hz, thiophene), 131.2 (d,
To the solution of dithienophosphasilin (3) (0.984 g,
2.98 mmol) in CH2Cl2 (20 mL), Au(THT)Cl (0.827 g,
2.98 mmol) was added at room temperature. After stirring
overnight, all volatiles were removed under vacuum. The
crude product was washed with acetone and pentane afford-
ing the pure product 4b as a white solid (yield: 1.005 g,
3
2JCP = 10.2 Hz, o-Ph), 128.9 (s, p-Ph), 128.4 (d, JCP
=
7.6 Hz, m-Ph), 1.6 (s, Si(CH3)2), 1.4 (d, JCP = 2.3 Hz,
Si(CH3)2). 31P{1H} NMR (162 MHz, CDCl3, ppm) d: –20.7.
29Si{1H} NMR (80 MHz, CDCl3, ppm) d: –17.7 (s). HR-MS
m/z calcd. for [M + H]+: 330.0122; found: 330.0113.
1
3
60%). H NMR (400 MHz, CDCl3, ppm) d: 7.81 (dd, JHH
=
4
Compound 4a
4.8 Hz, JHH = 2.0 Hz, 2H, thiophene), 7.53–7.47 (m, 2H,
o-Ph), 7.44 (dd, J = 5.6 Hz, J = 4.8 Hz, 2H, thiophene),
7.43–7.35 (m, 3H, Ph), 0.62 (d, JHP = 35.6 Hz, 6H,
Si(CH3)2). 13C{1H} NMR (100 MHz, CDCl3, ppm) d: 141.6
To the solution of dithienophosphasilin (3) (0.800 g,
2.42 mmol) in CHCl3 (20 mL), H2O2 (3 mL, 30% aqueous
solution) was added at room temperature. After stirring
overnight, all volatiles were removed under vacuum. Pure
product 4a was obtained as a white solid after recrystalliza-
2
1
(d, JCP = 10.9 Hz, thiophene), 135.4 (d, JCP = 66.8 Hz,
ipso-thiophene), 131.9 (d, JCP = 62.1 Hz, ipso-Ph), 133.2
(d, JCP = 14.7 Hz, thiophene), 133.0 (d, JCP = 8.4 Hz, thio-
phene), 132.7 (s, p-Ph), 131.7 (d, JCP = 2.6, Hz, o-Ph),
1
2
3
tion from Et2O at room temperature (yield: 0.713 g, 85%).
3
2
1H NMR (400 MHz, CDCl3, ppm) d: 7.76 (dd, JHP
=
Published by NRC Research Press

1228
Can. J. Chem. Vol. 87, 2009
3
129.2 (d, JCP = 12.2 Hz, m-Ph), 1.6 (s, Si(CH3)2), 1.0 (s,
benzo), 125.1 (s, benzo), 122.1 (s, benzo), 1.3 (s, Si(CH3)2),
0.5 (s, Si(CH3)2). 31P{1H} NMR (162 MHz, CDCl3, ppm) d:
11.3 (s). 29Si{1H} NMR (80 MHz, CDCl3, ppm): –17.1 (d,
3JSiP = 11.0 Hz). Elemental anal. calcd. (%) for C24H19OP-
S2Si (446.60): C 64.55, H 4.29; found: C 63.78, H 4.29.
Si(CH3)2). 31P{1H} NMR (162 MHz, CDCl3, ppm) d: 5.4 (s).
29Si{1H} NMR (80 MHz, CDCl3, ppm) d: –17.6 (d, JSiP
=
3
7.74 Hz). Elemental anal. calcd. (%) for C16H15AuClOPS2Si
(562.90): C 34.14, H 2.69; found: C 34.19, H 2.99.
Bis(3-bromobenzo[b]thiophen-2-yl)dimethylsilane (6)
To the solution of 2,3-dibromobenzo[b]thiophene (5)
(1.038 g, 3.56 mmol) in Et2O (30 mL), n-BuLi (1.420 mL,
3.56 mmol) was added dropwise at –78 8C. After stirring
at this temperature for 40 min, Me2SiCl2 (0.2294 g,
3.555 mmol) was added dropwise. After stirring for another
15 min at –78 8C, the reaction was allowed to warm up and
was left stirring overnight at room temperature. The mixture
was subsequently filtered through neutral alumina. Pure
product 6 was obtained as a white solid by recrystallization
from Et2O (yield: 0.520 g, 60%). 1H NMR (400 MHz,
CDCl3, ppm) d: 7.85 (m, 4H, benzo), 7.43 (m, 4H, benzo),
0.88 (s, 6H, Si(CH3)2).
Supplementary data
Supplementary data for this article are available on the
journal Web site (canjchem.nrc.ca) or may be purchased
from the Depository of Unpublished Data, Document Deliv-
ery, CISTI, National Research Council Canada, Ottawa, ON
K1A 0R6, Canada. DUD 3992. For more information on ob-
taining material, refer to cisti-icist.nrc-cnrc.gc.ca/cms/
unpub_e.shtml. CCDC 732433–732435 contain the X-ray
data in CIF format for seven complexes for this manuscript.
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 Union Road, Cambridge
CB2 1EZ, UK; fax +44 1223 336033; or deposit@ccdc.
cam.ac.uk).
Compound 7
To the solution of bis(3-bromobenzo[b]thiophen-2-yl)-
dimethylsilane (6) (0.558 g, 1.16 mmol) in Et2O (200 mL), n-
BuLi (0.930 mL, 2.31 mmol) was added dropwise at –78 8C.
After stirring for 50 min, PhPCl2 (0.207 g, 1.157 mmol) was
added dropwise at –78 8C. The reaction was allowed to
warm up quickly to room temperature and then left stirring
overnight. The mixture was subsequently filtered through
neutral alumina and evaporated to dryness. The pure product
7 was obtained as a white solid by recrystallization from ace-
Acknowledgements
Financial support by the Natural Sciences and Engineer-
ing Research Council of Canada (NSERC) and the Canada
Foundation for Innovation (CFI) is gratefully acknowledged.
We thank Alberta Ingenuity for a graduate scholarship
(Y.R.) and a New Faculty Award (T.B.). We would also
like to thank Ulli Englert (RWTH Aachen University) for
his help with the X-ray diffraction data of 4a.
1
tone at 0 8C (0.300 g, 60%). H NMR (400 MHz, CDCl3,
ppm) d: 8.17–8.14 (m, 2H), 7.97–7.94 (m, 2H), 7.53–7.49
References
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Compound 8
To the solution of the benzanellated dithienophosphasilin
(7) (0.500 g, 1.16 mmol) in CHCl3 (20 mL), H2O2 (3 mL,
30% aqueous solution) was added at room temperature.
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1
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