Luminescent digold ethynyl thienothiophene and dithienothiophene complexes; their synthesis and structural characterisation

Article abstract of DOI:10.1039/b415965a

A series of protected and terminal dialkynes with extended π-conjugation through the fused oligothienyl linker unit in the backbone, 2,5-bis(trimethylsilylethynyl)thieno[3,2-b]thiophene 1a, 5,5′- bis(trimethylsilylethynyl)dithieno[3,2-b: 2′,3′-d]thiophene

Full text of DOI:10.1039/b415965a

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F U L L P A P E R
Luminescent digold ethynyl thienothiophene and dithienothiophene
complexes; their synthesis and structural characterisation
Peiyi Li,a Birte Ahrens,a,b Neil Feeder,a Paul R. Raithby,*b,c Simon J. Teatc and
Muhammad S. Khan*d
a Department of Chemistry, University of Cambridge, Cambridge, UK CB2 1EW
b Department of Chemistry, University of Bath, Bath, UK BA2 7AY.
E-mail: p.r.raithby@bath.ac.uk; Fax: 01225 386231; Tel: 01225 383183
c CCLRC Daresbury Laboratory, Daresbury, Warrington, WA4 4AD, UK
d Department of Chemistry, College of Science, Sultan Qaboos University, P.O. Box 36,
Al Khod 123, Sultanate of Oman
Received 15th October 2004, Accepted 12th January 2005
First published as an Advance Article on the web 31st January 2005
A series of protected and terminal dialkynes with extended p-conjugation through the fused oligothienyl linker unit
in the backbone, 2,5-bis(trimethylsilylethynyl)thieno[3,2-b]thiophene 1a, 5,5ꢀ-bis(trimethylsilylethynyl)dithieno[3,2-b:
2ꢀ,3ꢀ-d]thiophene 1b, 2,5-bis(ethynyl)thieno[3,2-b]thiophene 2a, 5,5ꢀ-bis(ethynyl)dithieno[3,2-b:2ꢀ,3ꢀ-d]thiophene 2b,
has been synthesized and characterised. The digold alkynyl complexes [(Ph3P)Au(C≡C)(C6H2S2)(C≡C)Au(PPh3)] 3a
and [(Ph3P)Au(C≡C)(C8H2S3)(C≡C)Au(PPh3)] 3b have then been prepared by the reaction of two equivalents of
Ph3PAuCl and a methanolic KOH solution of 1a and 1b, respectively. The complexes have been characterised
spectroscopically. The crystal structures show that the gold centres adopt a linear two-coordinate geometry
appropriate for Au(I) complexes. Within the crystals adjacent molecules are linked by Au · · · S intermolecular
˚
interactions in the range 3.48–3.89 A, but there are no short Au · · · Au contacts. The absence of Au · · · Au
interactions in solution is confirmed by UV/visible absorption and emission spectroscopy, the spectra being
dominated by ligand-centred p–p* interactions.
advantages in our investigations of the physical and electronic
Introduction
properties of the platinum-containing diyne dimers and poly-yne
Oligomers and polymers containing thiophene rings have
polymers of the types illustrated in Fig. 1.9 In these complexes
attracted considerable attention as new functional materials
and polymers the electronic properties of the materials can be
for use in molecular devices because of their near-metallic
tuned by altering the nature of the aromatic or heteroaromatic
conductivity.1 Among the thiophene derivatives, fused ring
spacer group, X. The more electron withdrawing the spacer
systems such as thienothiopene and dithienothiophene have
group is the lower is the band gap between the S0 ground state
emerged as excellent building blocks in the synthesis of a
and the first singlet excited state, S1. In all the systems studied
variety of opto-electronic materials. The self-rigidification of
the S1 level is ca. 0.7 eV above the first triplet excited state, T1.10
these materials due to the fused ring system and the delocalised
p-systems that extend over the fused ring units give them novel
opto-electronic properties.2 Thus, dithienothiophene derivatives
have been used in photo- and electro-luminescent devices, two-
photon absorption and excited fluorescence, non-linear opti-
cal chromophores, and photochromic materials.3 While these
materials have exhibited considerable potential in applications
such as LEDs, LEPs and photoswitches,4 there are a number of
ways in which the electronic properties of these materials can
be optimised further. The solubility of oligomeric thienophenes
and dithienothiophenes in organic solvents is limited and, more
importantly, in the organic systems it is only possible to excite
into the excited singlet states of the materials using optical
methods, which limits the luminescent efficiency to 25% (because
there are three excited triplet states for each singlet state).5 The
inclusion of transition metal-containing units into the purely
organic materials can help to overcome these problems. For
example, the inclusion of metal–phosphine units, where the
phosphines are long chain alkyl phosphines, such as n-butyl
phosphine, improve the solubility of the materials in a range of
organic solvents.6 Secondly, heavy transition metals have, among
their properties, high levels of spin–orbit coupling, one of the
Fig. 1 Platinum-containing “rigid rod” dimers and poly-yne polymers.
consequences of which is that quantum mechanical selection
rules are modified, and spin crossover into the excited triplet
states becomes possible, improving the luminescent efficiency of
the materials.7 Further, the presence of the metals may afford
additional luminescent properties to the materials as well as
those resulting purely from the ligands.8 We have exploited these
Of particular interest are our studies on platinum11 and gold
poly-yne complexes and oligomers12 that contain one, two or
three thiophene rings (Fig. 2), and their relationship to the
purely organic polythiophene oligomers and polymers.3 As the
8 7 4
D a l t o n T r a n s . , 2 0 0 5 , 8 7 4 – 8 8 3
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
©

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Fig. 3
Fig. 2 Platinum or gold-containing polythiophine poly-yne complexes.
conditions led to the formation of dark insoluble material that
was presumed to be a polymerisation product. Because of this
instability the digold complexes 3a and 3b were obtained in
good yield by adding two equivalents of triphenylphosphine
gold chloride directly to solutions of 1a and 1b in methanolic
KOH, respectively (Scheme 1). Additional methoxide ions, as
the sodium or potassium salt, were added to each reaction, as
the methoxide acts both as a base and as a halide abstractor.
The products were purified by passing them through a short
alumina column using THF as eluent, and recrystallised from a
dichloromethane–hexane mixture.
number of thiophene rings in the system increases, the optical
band gap is reduced, as is the intersystem crossing from the
singlet to triplet excited state.10 We have recently extended
our studies to the related platinum-containing thienothiophene
and dithienothiophene dimers and polymers, and compared
the results to the studies on the non-fused poly-thiophene
platinum poly-ynes.13 We find that the band gap is related to
the conjugation length through the polythiophene, and whether
the thiophene is fused or not is of secondary importance.
We now describe a related series of systematic studies on gold-
containing ethynyl thienothiophene and dithienothiophene
complexes, [(Ph3P)Au(C≡C)(C6H2S2)(C≡C)Au(PPh3)] 3a and
[(Ph3P)Au(C≡C)(C8H2S3)(C≡C)Au(PPh3)] 3b. Here, we report
their synthesis, characterisation and solution luminescent prop-
erties, and compare the results with those found for the related
dithiophene 4a and terthiophene gold complexes 4b (Fig. 3).12
Results and discussion
Synthesis and spectroscopic characterisation
The trimethylsilyl-protected diynes 1a and 1b were prepared as
described previously by the palladium(II)/copper(I)-catalysed
cross-coupling reaction of trimethylsilylethyne with 2,5-
dibromothieno[3,2-b]thiophene and 5,5ꢀ-dibromodithieno[3,2-
i
b:2ꢀ,3ꢀ-d]thiophene in Pr2NH–THF.14–16 The protected alkynes
Scheme 1
are indefinitely stable towards light and air at ambient temper-
ature and were fully characterised by IR, NMR (1H and 13C)
spectroscopy, EI mass spectrometry, as well as by satisfactory
elemental analyses. The desilylation reaction to produce the
deprotected diynes 2a17 and 2b was achieved by treating 1a and
1b with methanolic KOH (Scheme 1). The products were purified
by silica gel column chromatography and characterised spec-
troscopically. The diterminal alkynes 2a and 2b are somewhat
unstable; storage at ambient temperature and under aerobic
The initial characterisation of 3a and 3b as [(Ph3P)Au(C≡
C)(C6H2S2)(C≡C)Au(PPh3)] and [(Ph3P)Au(C≡C)(C8H2S3)-
(C≡C)Au(PPh3)], respectively, was carried out spectroscopically
(see Experimental section). The IR spectrum of each of the two
complexes exhibited a single absorption at 2105 cm−1(3a) and
2104 cm−1 (3b) that can be assigned to m(C≡C) stretches, and are
typical of the values found in other gold–alkynyl complexes.12
While this IR fingerprint is useful for confirming the presence
D a l t o n T r a n s . , 2 0 0 5 , 8 7 4 – 8 8 3
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◦
˚
of the acetylenic unit in the complexes, there is little change in
its position over a wide range of metals or X groups attached
to the acetylene and, therefore, it does not provide information
as to the electronic properties of the coordinating groups. The
1H and 13C NMR confirm the presence of the phosphine ligands
and of the thienothiophene and dithienothiophene groups in 3a
and 3b, respectively. In the 13C NMR spectrum two signals at d
96.67 and 96.85 for 3a, and a broad signal at d 96.84 for 3b, can
be assigned to the alkynylic carbons. The 31P NMR spectra of 3a
and 3b show only one signal at d 42.77 for 3a, and at d 42.75 3b,
which indicates that the two phosphorus nuclei in each complex
are equivalent. LSIMS mass spectra exhibit the molecular ions
for the complexes at m/z 1105 (3a) and 1161 (3b).
Table 1 Bond lengths (A) and angles ( ) for 3a
Au(1)–C(1)
Au(1)–P(1)
Au(2)–C(10)
Au(2)–P(2)
C(1)–C(2)
C(2)–C(3)
1.979(19)
2.271(4)
1.992(14)
2.279(4)
1.23(3)
C(3)–S(1)
C(5)–S(2)
C(6)–S(1)
S(2)–C(8)
C(8)–C(9)
C(9)–C(10)
1.763(17)
1.729(14)
1.721(15)
1.768(17)
1.43(2)
1.42(2)
1.18(2)
C(1)–Au(1)–P(1)
C(10)–Au(2)–P(2)
C(2)–C(1)–Au(1)
C(1)–C(2)–C(3)
176.4(5)
174.7(4)
173.1(13)
176.2(19)
C(10)–C(9)–C(8)
C(9)–C(10)–Au(2)
C(6)–S(1)–C(3)
C(5)–S(2)–C(8)
172.0(16)
174.3(12)
89.9(8)
92.1(7)
X-Ray structure determinations
Single crystals suitable for X-ray analyses were grown from
layering dichloromethane and hexane solutions, although crys-
tals of 3a were so small and weakly diffracting that the data
was collected using synchrotron X-ray radiation, on Station
9.8, at the CCLRC Daresbury Laboratory. The structures were
determined in order to establish the molecular conformations
of the two complexes and to investigate the possibility of
polymer formation through Au · · · Au interactions in the solid
state. Previously, it has been found that many gold–alkynyl
complexes do form oligomers or polymers through d10 · · · d10
Au · · · Au interactions, and that these interactions contribute to
the luminescent properties of these materials.8,12 Recently, it has
been suggested that the formation of intermolecular Au · · · Au
interactions in digold alkynyl complexes, or the absence of them,
may be influenced by the separation between the Au atoms in
the molecular dimers.12,18
The molecular structure of [(Ph3P)Au(C≡C)(C6H2S2)(C≡C)-
Au(PPh3)] 3a is shown in Fig. 4 while selected bond parameters
are listed in Table 1. As expected for Au(I) complexes, the
two gold centres adopt the linear two-coordinate geometry
with an average (C≡)C–Au–P angle of 176.3(5)◦, and the
alkynylic units also adopt a◦linear geometry with an average
Fig. 5 The packing diagram of [(Ph3P)Au(C≡C)(C6H2S2)(C≡C)-
Au(PPh3)] 3a viewed down the {100} direction.
cular contacts involving gold atoms are with the thiophene sulfur
˚
˚
atoms: Au(1) · · · S(1a) 3.484 A and Au(2) · · · S(2b) 3.520 A, and
through this weak interaction molecular sheets in the (110) plane
are formed. The Au · · · S distances can be compared with the
˚
C≡C–Au angle of 173.1(12) . The average Au–P (2.278(4) A)
˚
and Au–C(≡C) (1.98(2) A) are similar to those observed in
a range of alkynyl–gold phosphine complexes.11,12 The average
value of 3.841 A found in [(Ph3P)Au(C≡C)(C4H2S)(C4H3S)].
˚
˚
C≡C bond length of 1.22(2) A is also close to the idealised value.
There are no other short intermolecular contacts within the
crystal structure.
The bond parameters within the thienothiophene ligand not
deviate significantly from those observed in the free trimethylsilyl
protected diethynyl compound15 and from those in related metal
complexes.19 The thienothiophene group is essentially planar
The molecular structure of [(Ph3P)Au(C≡C)(C8H2S3)(C≡C)-
Au(PPh3)] 3b (Fig. 6) and its molecular parameters (Table 2)
are generally similar to those of 3a but with the fused three-
ring dithienothiophene ring replacing the two-ring thienothio-
phene linker group. The two gold centres are again linear two
˚
with a maximum deviation of 0.02 A for C(4) from the least-
squares plane through the C6S2 unit.
˚
From the structural viewpoint, the intermolecular interac-
tions within the crystal are the most interesting. A packing dia-
gram for 3a is shown in Fig. 5, and what is immediately apparent
is that there are no intermolecular Au · · · Au contacts under
coordinate, and the average Au–P (2.273(4) A) and Au–C(≡C)
˚
(2.05(2) A) distances are similar to those in 3a and within the
range found in related alkynyl gold phosphine complexes.11,12
˚
The average C≡C distance of 1.20(1) A is not significantly
˚
4 A. In fact, in 3a the shortest intermolecular Au · · · Au distance
different from that in 3a either. The bond parameters within the
dithienothiophene unit are similar to those in the trimethylsilyl-
substituted diethynyl precursor compound,16 and from those
˚
is 7.177 A while the intramolecular Au(1) · · · Au(2) separation
˚
along the molecular chain is 13.733 A. The shortest intermole-
Fig. 4 The molecular structure of [(Ph3P)Au(C≡C)(C6H2S2)(C≡C)Au(PPh3)] 3a showing the atom numbering scheme adopted.
8 7 6
D a l t o n T r a n s . , 2 0 0 5 , 8 7 4 – 8 8 3

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Fig. 6 The molecular structure of [(Ph3P)Au(C≡C)(C8H2S3)(C≡C)Au(PPh3)] 3b showing the atom numbering scheme adopted.
◦
˚
of contacts gives AuS2Au diamonds linking three adjacent
molecules through the structure (Fig. 6). As in 3a there are
no short Au · · · Au intermolecular contacts, the shortest being
Table 2 Bond lengths (A) and angles ( ) for 3b
Au(1)–C(1)
Au(1)–P(1)
Au(2)–C(12)
Au(2)–P(2)
C(1)–C(2)
C(2)–C(3)
C(3)–S(1)
2.010(6)
2.2758(16) C(5)–S(2)
2.000(6) S(2)–C(8)
2.2700(16) C(7)–S(3)
S(1)–C(6)
1.733(6)
1.733(6)
1.737(6)
1.716(6)
1.761(6)
1.436(9)
1.187(9)
˚
5.483 A, between Au(2) and the Au(2) atom related by the
symmetry operation −2 − x, −1 − y, 1 − z. This intermolecular
distance may be compared to the intermolecular Au · · · Au
1.206(9)
1.409(8)
1.760(6)
S(3)–C(10)
C(10)–C(11)
C(11)–C(12)
˚
distance of 7.177 A in 3a. This intramolecular Au(1) · · · Au(2)
˚
distance in 3a, along the molecular chain, is of 15.365(1) A
which, as expected from the dimensions of the spacer group, is
longer than in 3a (13.733 A).
C(1)–Au(1)–P(1)
C(12)–Au(2)–P(2)
C(2)–C(1)–Au(1)
C(1)–C(2)–C(3)
171.65(18) C(11)–C(12)–Au(2)
174.01(19) C(6)–S(1)–C(3)
169.6(6)
91.8(3)
90.6(3)
91.5(3)
˚
165.9(6)
170.1(6)
178.1(7)
C(5)–S(2)–C(8)
C(7)–S(3)–C(10)
Absorption and emission spectra
C(12)–C(11)–C(10)
The absorption and emission spectral data for 3a and 3b is
presented in Table 3 as is the data for the terminal diethynyl lig-
ands HC≡C(C6H2S2)C≡CH 2a and HC≡C(C8H2S3)C≡CH 2b.
The data was recorded at room temperature in dichloromethane
solution.
in related compounds.20 The whole dithienothiophene unit is
essentially planar with a maximum deviation of 0.025 A for S(3)
from the least squares plane through all the atoms.
˚
Both the digold complexes and the organic precursors exhibit
absorptions in the range 300–400 nm, and the general shape of
the absorption spectra for the complexes is similar to that of
the free ligands, but shifted to longer wavelengths. This strong
dependence of the absorption spectra on the alkynyls suggests
that the absorptions are ligand-centred, but the red-shift upon
coordination of the gold phosphine units is consistent with there
being an increase in conjugation length over the molecule. In
related systems it has been suggested that there is some mixing
of the ligand p–p* transitions with a r(Au–C) contribution in the
HOMO and possibly some Au 6pp contribution in the LUMO.21
This may also be the case here. However, the red shift observed
between the free ligand and the complex could be explained,
alternatively, in terms of the existence of a higher lying, ligand
centred HOMO caused by the inductive effect of the Au–C≡C
bond, and is thus unrelated to the conjugation length of the
spacer group, but this ambiguity cannot be resolved with the
available data.
There is a significant difference between 3a and 3b in terms
of the intermolecular packing as can be seen in Fig. 7. In
3b only the central sulfur atom of the dithienothiophene unit
is involved in Au · · · S interactions. This sulfur atom displays
˚
contact distances of 3.820 A with Au(1) related by the symmetry
˚
operation −x, −y − 1, −z, and 3.892 A with Au(1) related by
the symmetry operation x − 1, y, z. These Au · · · S distances are
comparable to those in [(Ph3P)Au(C≡C)(C4H2S)(C4H3S)], but
significantly longer than those found in 3a. This arrangement
The value of the red-shift upon complexation to the Au centre
decreases as the size of the central spacer group increases:
ca. 52 nm for 3a vs. 2a compared to ca. 30 nm for 3b
vs. 2b. This is understandable as the percentage contribution
Table 3 Absorption and emission data for the free ligands [H(C≡C)-
(C6H2S2)(C≡C)H] 2a, [H(C≡C)(C8H2S3)(C≡C)H] 2b, and the com-
plexes [(Ph3P)Au(C≡C)(C6H2S2)(C≡C)Au(PPh3)] 3a and [(Ph3P)Au-
(C≡C)(C8H2S3)(C≡C)Au(PPh3)] 3b at room temperature, in CH2Cl2
Absorption. k/nm
Emission (k/nm)
excited at kmax
(e/104 dm3 mol−1 cm−1
)
2a
2b
3a
3b
304 (sh, 3.0), 317 (3.6), 332 (3.5)
327 (2.8), 342 (3.9), 359 (3.9)
356 (6.6), 376 (8.2)
355, 380 (sh)
370 (sh), 387
390, 406
Fig. 7 The packing diagram of [(Ph3P)Au(C≡C)(C8H2S3)(C≡C)-
Au(PPh3)] 3b viewed down the {100} direction showing the intermolec-
ular interactions.
357 (sh, 4.3), 376 (7.8), 397 (8.9)
411, 431
D a l t o n T r a n s . , 2 0 0 5 , 8 7 4 – 8 8 3
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of the gold-centred orbitals in the HOMO and LUMO
decrease as the conjugation length in the spacer group in-
creases. The absorption maxima can also be compared to those
observed in [(Ph3P)Au(C≡C)(C4H2S)2(C≡C)Au(PPh3)] 4a and
[(Ph3P)Au(C≡C)(C4H2S)3(C≡C)Au(PPh3)] 4b,12 which showed
transitions at 373, 391 and 415 nm and 401, 421 and 451 nm,
respectively. There is a general shift to shorter wavelength in the
fused systems, and the most informative comparison is between
the absorption maxima for 3b and 4a since both these systems
have the same number of “formal” conjugated double bonds.
On average the absorptions in 3b are shifted by ca. 15 nm to
shorter wavelength compared to those for 4a consistent with
higher energy transitions in the fused ring system.
the length of and the volume occupied by the spacer groups.
However, there are no discernable trends in the lengths of the
intermolecular Au · · · Au interactions. It is apparent, however,
from Table 4 that for the complexes with Au · · · Au bonding
interactions, where both solid-state and solution state emission
data is available, there is a significant red shift in the emission
position in the solid state compared to the solution. This is
consistent with a contribution from the Au · · · Au bond to the
emission process in the solid state, and indicates that short
Au · · · Au contacts do not occur in solution. For the systems
with the longer spacer groups, where there are no Au · · · Au
interactions in the solid state, there is little difference between
the solid state and solution emission spectra.
The emission behaviour of 2a and 3a and 2b and 3b
in solution, at room temperature, mirrors their absorption
behaviour, in that the emission maxima are a function of
the spacer group. The excitation spectra have similar profiles
to the absorption spectra, suggesting that the emission arises
from the lowest-energy absorption band. The variation in
the excitation wavelength has little influence on the emission
spectrum, indicating a single emissive state or multiple states
that are in equilibrium. The Stokes shifts for 3a and 3b of
ca. 30 and 52 nm, respectively, are relatively small and are
consistent with the lowest emission state being a singlet. Related
Au(I) complexes have also been reported as having lowest
emission states with lifetimes in the order of nanoseconds.22,23
Also, the observed Stokes shifts here are somewhat smaller
than those reported for the related non-fused polythiophene
complexes [(Ph3P)Au(C≡C)(C4H2S)2(C≡C)Au(PPh3)] 4a and
[(Ph3P)Au(C≡C)(C4H2S)3(C≡C)Au(PPh3)] 4b,12 which may re-
flect the fact that the rigid fused thiophene ring systems allow
limited geometric rearrangements in the excited state.
In a more detailed comparison, it is found that the com-
plex [(Ph3P)Au(C≡C)(C8H2S3)(C≡C)Au(PPh3)] 3b has a similar
˚
intramolecular Au · · · Au separation (15.365(1) A) to those in
the related non-fused dithiophene systems [(Ph3P)Au(C≡C)-
˚
(C4H2S)2(C≡C)Au(PPh3)] 4a (15.382(1) A) and [(Cy3P)Au(C≡
C)(C4H2S)2(C≡C)Au(PCy3)] (15.376(1) A).12 The shortest inter-
˚
˚
molecular Au · · · Au separation in 3a is ca. 1.5 A shorter than
˚
in 4a and ca. 2.0 A shorter than in [(Cy3P)Au(C≡C)(C4H2S)2-
(C≡C)Au(PCy3)]. These differences may reflect differences
in crystal packing in the three structures. Both 4a and
[(Cy3P)Au(C≡C)(C4H2S)2(C≡C)Au(PCy3)] have solvent mole-
cules present in the lattice that are involved in hydrogen bonding,
and do not exhibit any Au · · · S interactions, whereas 3b is free
of solvent in the crystal and the central sulfur atom of the
dithieno[3,2-b:2ꢀ,3ꢀ-d]thiophene ring is involved in Au · · · S non-
covalent interactions (vide supra).
Conclusions
The absence of Au · · · Au interactions in the solid state, as
confirmed by the crystal structure analyses, and, therefore,
presumably in solution is entirely consistent with the observed
solution absorption and emission spectra where ligand p–p*
transitions dominate.
The thienothiophene and dithienothiophene alkynyl digold
derivatives [(Ph3P)Au(C≡C)(C6H2S2)(C≡C)Au(PPh3)] 3a and
[(Ph3P)Au(C≡C)(C8H2S3)(C≡C)Au(PPh3)] 3b can be prepared
readily from the trimethylsilyl-protected dialkynyl derivatives,
in methanolic KOH, by the reaction with two equivalents
of (Ph3P)AuCl. The crystal structures of 3a and 3b show
that, in both cases, adjacent molecules are linked by Au · · · S
interactions, and that Au · · · Au interactions, that are common
in related systems where the spacer groups between the two
alkynyl groups are shorter in length, are absent. The UV/visible
absorption and emission spectra are both dominated by ligand-
centred p–p* transitions, and there is only a small mixing
contribution from the gold centres, consistent with the small
observable red-shift of the signals when the spectra for the metal
complexes are compared to those from the free ligand.
Comparison of structural and emission data with that in other
digold alkynyl complexes
The inter- and intramolecular Au · · · Au separations, together
with phosphine cone angles,24 the volume occupied by the C≡C–
X–C≡C spacer groups, and the significant peaks in the emission
spectra for 3a and 3b are compared with equivalent data for other
known digold alkynyl complexes in Table 4. It is interesting to
note that in the structures of the simple digold alkynyl complexes
that have been reported, where the alkynyls are linked by a spacer
group that consists of a single aromatic ring, and in which the
central unit is close to linear, molecules are linked by Au · · · Au
Experimental
˚
interactions in the range 3.122–3.235 A. However, as the spacer
General
groups and, therefore, the intramolecular Au · · · Au separations
increase in length the Au · · · Au contacts are replaced by other
types of intermolecular interactions such as Au · · · S contacts
or p–p stacking. In Table 4 the structures are listed in order of
increasing intramolecular Au · · · Au separation, which can be
used as a measure of the length of the linker group. Although
the number of structural examples in Table 4 is limited, and
only tentative suggestions can be made, it appears that bonding
Au · · · Au intermolecular interactions occur only in systems
where the intermolecular Au · · · Au distances are short (ca.
All reactions were carried out under an atmosphere of dry
nitrogen using standard Schlenk techniques. Solvents were
freshly distilled, dried and degassed before use by standard
procedures.30 Infrared spectra were recorded using a NaCl cell
on a PERKIN ELMER PARAGON 1000 FT-IR spectrometer.
UV/vis spectra were recorded on Perkin-Elmer Lambda-12
1
spectrometer and Cary 100 Bio UV-visible spectrometer. H,
13C and 31P NMR spectra were recorded on Bruker28 DRX-
400/500 spectrometers. Chemical shifts in ppm are relative to
the residue solvent resonance (1H and 13C) and external 85%
H3PO4 (31P). Mass spectra were recorded on KRATOS CON-
CEPT/MSI CONCEPT IH/MICROMASS PLATFORM-LC
mass spectrometers. Elementary analyses were performed at
Department of Chemistry, University of Cambridge. Solution
emission spectra were recorded at 293 K on AMINCO Bowman
Series 2 Luminescence Spectrometer. Au(PPh3)Cl,31 thieno[3,2-
b]thiophene32 and dithieno[3,2-b:2ꢀ,3ꢀ-d]thiophene32 were pre-
pared by a literature methods.
˚
3.2 A), and where the phosphine groups or the spacer groups are
not bulky. For instance, it appears that when PCy3 groups (cone
angle 170◦) are present intermolecular Au · · · Au bonding does
not occur regardless of the size of the spacer group present. For
example, there is no Au · · · Au bonding interaction in (Cy3P)Au–
C≡C–C≡C–Au(PCy3)25 although the intramolecular Au · · · Au
˚
separation, at 7.785 A, and the volume of the spacer group, at
3
˚
53.1 A , are the shortest and smallest, respectively, in Table 4.
Not surprisingly, there is an approximate correlation between
8 7 8
D a l t o n T r a n s . , 2 0 0 5 , 8 7 4 – 8 8 3

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D a l t o n T r a n s . , 2 0 0 5 , 8 7 4 – 8 8 3
8 7 9

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8 8 0
D a l t o n T r a n s . , 2 0 0 5 , 8 7 4 – 8 8 3

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Syntheses
(ipso-C) (aromatic C of thiophenes). LSIMS (m/z): 388.03
(Calc. Mr = 388.71). Anal. Calc. for C18H20S3Si2: C, 55.62; H,
5.19. Found: C, 55.85; H, 5.29%.
2,5-Dibromothieno[3,2-b]thiophene33. A solution of NBS
(21.34 g, 0.12 mol) in DMF (150 mL) was added to a
stirred and ice-cooled solution of thieno[3,2-b]thiophene (8.35 g,
59.58 mmol) in DMF (70 mL). After the mixture was stirred for
3 h under ice cooling, crushed ice was added and the resulting
mixture was extracted with CH2Cl2. The extracts were washed
with water, dried over MgSO4, and evaporated. The residue was
5,5ꢀ-Bis(ethynyl)dithieno[3,2-b:2ꢀ,3ꢀ-d]thiophene (2b). Com-
pound 1b was proto-desilylated as in 1a and the crude product
was worked up, as before, to yield a red solid. Silica column
chromatography with CH2Cl2–hexane (1 : 1 v/v) gave a red solid
identified as 2b in 76% yield. The purified diterminal alkyne
was used immediately to prepare the Pt(II) di-ynes and poly-
ynes or, if necessary, was stored as dilute solution in pentane at
1
subjected to alumina column chromatography. H NMR ((d,
500 MHz, CDCl3)): 7.62 (s, 2H, thienothiophene). 13C NMR
(d, 500 MHz, CDCl3): 124.48, 126.53, (ipso-C), 138.67 (ipso-C),
(thienothiophene). EIMS (m/z): 298 (Calc. Mr = 298.03 for
C6H2Br2S2).
◦
0 C. Decomposition of the pentane solution was apparent by
an orange color after storage of more than a few days at room
temperature. IR (CH2Cl2): m/cm−1 2101 (–C≡C–), 3298 (C≡C–
H). 1H NMR (d, 500 MHz, CDCl3): 3.50 (s, 2H, C≡CH), 7.31
(s, 2H, dithienothiophene). 13C NMR (d, 100.6 MHz, CDCl3):
79.50, 80.16 (C≡C), 120.73 (ipso-C), 126.76, 131.17 (ipso-C),
141.61 (ipso-C) (dithienothiophene). EIMS (m/z): 244. (Calc.
Mr = 244.34).
5,5ꢀ -Dibromodithieno[3,2-b:2ꢀ,3ꢀ -d]thiophene. Dithieno[3,2-
b:2ꢀ,3ꢀ-d]thiophene was prepared according to a literature
preparation.34 0.98 g (5.0 mmol) dithieno[3,2-b:2ꢀ,3ꢀ-d]thiophene
in DMF (20 cm3) was reacted with 2 g (11.2 mmol) NBS at room
temperature overnight. The light yellow suspension was treated
with water and filtered off. After silica column chromatography
with hexane, 1.7 g (88%) pale greenish fine needle crystals
[(Ph3P)Au(–C≡C–C6H2S2–C≡C–)Au(PPh3)] (3a). To
a
freshly prepared sample of alkyne, 43 mg (0.13 mmol) 2,5-
bis(trimethylsilylethynyl)thieno[3,2-b]thiophene (1a), obtained
from the reaction of trimethylsilyl-protected alkyne with
KOH/CH3OH) in CH2Cl2 (30 cm3), was added gold(I)
phosphine chloride 125 mg (0.25 mmol), followed by CH3OH/
NaOCH3 (20 cm3, containing 20–30 mg Na). The mixture
was stirred under N2 at room temperature overnight and then
filtered through cellulose. The filtrate was evaporated to dryness
under reduced pressure. CH2Cl2 was added to the residue. The
resulting suspension was stirred for about 15 min and filtered
off. The filtrate was reduced in volume and loaded on a short
alumina column, and then eluted with mixed solvents of THF
(or ethyl acetate)–hexane. Solvents were removed in vacuo to
yield a yellow power. Pure product was obtained either by
layering concentrated CH2Cl2 solution with hexane, or by ether
vapour diffusion into the concentrated CH2Cl2 solution. Yield:
109 mg (72%) yellow crystalline solid. IR (CH2Cl2): m/cm−1
2105vw (–C≡C–). 1H NMR (d, 500 MHz, CDCl3): 7.17 (s, 2H,
H of thiophene), 7.42–7.56 (m, 30H, H of PPh3). 13C NMR
(d, 500 MHz, CDCl3): 96.67, 96.85 (–C≡C–); 123.16, 127.61
(ipso-C), 137.60 (ipso-C) (aromatic C of thiophenes); 129.08,
129.17, 129.37 (ipso-C), 129.82 (ipso-C), 131.55, 134.21, 134.32
1
was obtained. H NMR (d, 500 MHz, CDCl3): 7.27 (s, 2H,
H of thiophenes). 13C NMR (d, 500 MHz, CDCl3): 112.32
(ipso-C), 123.17, 130.82 (ipso-C), 139.05 (ipso-C) (aromatic
C of thiophenes). EI (m/z): 353.8 (Calc. Mr = 354.092 for
C8H2Br2S3).
2,5-Bis(trimethylsilylethynyl)thieno[3,2-b]thiophene (1a). To
solution of 2,5-dibromothieno[3,2-b]thiophene (2.0 g,
a
6.71 mmol) in iPr2NH–THF (70 cm3, 1 : 1 v/v) under nitrogen
was added a catalytic mixture of CuI (20 mg), Pd(OAc)2 (20 mg)
and PPh3 (60 mg). The solution was stirred for 20 min. at 50 ◦C
and then trimethylsilylethyne (1.64 g, 16.7 mmol) was added.
The reaction mixture was left with stirring for 20 h at 75 ◦C. The
completion of the reaction was determined by silica TLC and IR
spectroscopy. The solution was allowed to cool down to room
temperature, filtered and the solvent mixture removed under
reduced pressure. The residue was subjected to silica column
chromatography using hexane to afford 1a as a colourless solid
in 85% yield (1.78 g). IR (CH2Cl2): m/cm−1 2141 (–C≡C–). H
1
NMR (d, 250 MHz, CDCl3): 0.26 (s, 18H, SiMe3), 7.26 (s, 2H,
fused bithienyl). 13C NMR (d, 100 MHz, CDCl3): 0.04 (s, SiMe3),
97.68, 101.68 (C≡C), 124.60, 126.71, 138.75 (fused bithienyl).
EI MS: m/z: 332 (M+). Calc. for C16H20Si2S2: C, 57.80; H, 6.06.
Found C, 57.68; H, 6.01%.
1
(C of PPh3). 31P{ H} NMR (d, 400 MHz, CDCl3): 42.77.
LSIMS (m/z): 1105 (Calc. Mr = 1104.764). Anal. Calc. for
Au2C46H32P2S2: C, 50.01; H, 2.92. Found: C, 49.48; H, 3.00%.
2,5-Bis(ethynyl)thieno[3,2b]thiophene (2a). The bis-trimethyl-
silylethynyl derivative 1a (1.0 g, 3.01 mmol) was proto-
desilylated in THF–methanol (50 cm3, 4 : 1 v/v) using aqueous
KOH (0.38 g, 6.86 mmol in 1 cm3 H2O). The reaction mixture
was stirred at room temperature for 2 h, solvent removed and
the crude product was purified by silica column chromatography
using hexane. 2a was isolated as a yellow solid in 95% yield
(0.54 g). This material slowly darkened upon standing at
atmospheric and reduced pressure. IR (CH2Cl2): m/cm−1 2105
(–C≡C–), 3297 (C≡C–H). 1H NMR (d, 500 MHz, CDCl3): 3.50
(s, 2H, C≡CH), 7.25 (s, 2H, thienothiophene). 13C NMR (d,
500 MHz, CDCl3): 79.81, 82.56 (C≡C), 123.88, 133.92 (ipso-
C), 138.06 (ipso-C), (thienothiophene). EIMS (m/z): 188 (Calc.
Mr = 188.26).
[(Ph3P)Au(–C≡C–C8H2S3–C≡C–)Au(PPh3)] (3b). The com-
plex 3b was synthesised using the same general procedure as
for 3a using 50 mg (0.13 mmol) 5,5ꢀ-bis(trimethylsilylenthynyl)-
dithieno[3,2-b:2ꢀ,3ꢀ-d]thiophene (1b) and 130 mg (0.26 mmol)
Au(PPh3)Cl. Yield: 42 mg (28%) brownish crystalline solid. IR
1
(CH2Cl2): m/cm−1 2104vw (–C≡C–). H NMR (d, 500 MHz,
CDCl3): 7.29 (s, 2H, H of thiophene), 7.43–7.56 (m, 30H, H
of PPh3). 13C NMR (d, 500 MHz, CDCl3): 96.84 (br, –C≡C–);
124.37, 125.60 (ipso-C), 130.14 (ipso-C), 140.77 (ipso-C) (aro-
matic C of thiophenes); 129.10, 129.19, 129.34 (ipso-C), 129.78
1
(ipso-C), 131.57, 131.58, 134.21, 134.32 (C of PPh3). 31P{ H}
NMR (d, 400 MHz, CDCl3): 42.75. LSIMS (m/z): 1161 (Calc.
Mr = 1160.846). Anal. Calc. for Au2C48H32P2S3: C, 49.66; H,
2.78. Found: C, 48.86; H, 2.88%.
5,5ꢀ-Bis(trimethylsilylenthynyl)dithieno[3,2-b:2ꢀ,3ꢀ-d]thiophene
(1b). This compound was synthesised by the same method as
for 1a using 1.56 g (4.4 mmol) 5,5ꢀ-dibromodithieno[3,2-b:2ꢀ,3ꢀ-
d]thiophene. The product was purified by alumina column
chromatography with hexane and subsequent recrystallisation
from methanol. Yield: 0.91 g (52%) light yellow crystalline solid.
X-Ray crystallography
For crystal data, see Table 5.
Data collection and reduction. The crystals of 3a and 3b were
mounted in inert oil on a glass fibre. Data were measured using
1
IR (CH2Cl2): m/cm−1 2141 (–C≡C–). H NMR (d, 500 MHz,
Mo-Ka radiation (k = 0.71073 A) with a Nonius Kappa area
˚
CDCl3): 0.26 (s, 18H, H of TMS), 7.37 (s, 2H, H of thiophenes).
13C NMR (d, 500 MHz, CDCl3): −0.25 (s, SiMe3); 97.54, 101.14
(–C≡C–); 124.13(ipso-C), 125.82, 131.15 (ipso-C), 141.58
detector (3b), or a Bruker AXS SMART CCD area detector on
Station 9.8 of the CLRC Daresbury Laboratory (3a), both fitted
with an Oxford Cryostream low-temperature attachment.
D a l t o n T r a n s . , 2 0 0 5 , 8 7 4 – 8 8 3
8 8 1

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Table 5 Crystallographic data for [(Ph3P)Au(C≡C)(C6H2S2)(C≡C)Au(PPh3)] 3a and [(Ph3P)Au(C≡C)(C8H2S3)(C≡C)Au(PPh3)] 3b
3a
3b
Empirical formula
C46H32Au2P2S2
1104.71
150(2)
0.68870
Monoclinic
Pc
C48H32Au2P2S3
1160.79
180(2)
0.71070
Triclinic
¯
P1
Mr
T/K
˚
k/A
Crystal system
Space group
Unit cell dimensions:
˚
a/A
7.1766(17)
15.917(4)
17.041(4)
90
92.13(2)
90
1945.2(7)
2
8.9500(2)
12.8200(2)
18.6550(4)
73.760(1)
84.726(1)
85.198(1)
2042.58(7)
2
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
V/A
Z
Dc/Mg m−3
1.886
7.756
1.887
7.440
l/mm−1
F(000)
1056
1112
Crystal size/mm
h Range for data collection/◦
Index ranges, hkl
Reflections collected
0.08 × 0.08 × 0.04
0.15 × 0.15 × 0.02
3.66–25.49
1.14–27.50
−4 to 7, −3 to 19, −20 to 17
3875
−11 to 11, −16 to 16, −24 to 24
49223
Independent reflections (Rint
Absorption correction
Max., min. transmission
Data/restraints/parameters
Goodness-of-fit on F2
)
3865 (0.0295)
Semi-empirical
0.7467, 0.5758
3865/20/469
1.042
R1 = 0.0428, wR2 = 0.1091
R1 = 0.0439, wR2 = 0.1103
0.003(11)
9354 (0.0966)
Semi-empirical
0.8654, 0.4016
9354/0/496
1.043
Final R indices [I > 2r(I)]
R Indices (all data)
R1 = 0.0460, wR2 = 0.1168
R1 = 0.0653, wR2 = 0.1327
—
2.713, −3.307
Absolute structure parameter
−3
˚
Largest diff. peak, hole/e A
1.302, −0.956
Structure solution and refinement. Structures were solved by
direct methods (SHELXS-86)35 and subjected to full-matrix
least-squares refinement on F2 (program SHELXL-97).36 All
non-hydrogen atoms were refined anisotropically. Hydrogen
atoms were included using rigid methyl groups or a riding model.
CCDC reference numbers 252933 and 252934.
4 (a) C. D. Dimitrakopoulos and P. R. L. Malenfant, Adv. Mater., 2002,
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5 J. S. Wilson, A. Ko¨hler, R. H. Friend, M. K. Al-Suti, M. R. A. Al-
Mandhary, M. S. Khan and P. R. Raithby, J. Chem. Phys., 2000, 113,
7627.
6 (a) B. F. G. Johnson, A. K. Kakkar, M. S. Khan, J. Lewis, A. E.
Dray, R. H. Friend and F. Wittmann, J. Mater. Chem., 1991, 1, 485;
(b) M. S. Khan, A. K. Kakkar, N. J. Long, J. Lewis, P. R. Raithby,
P. Guyen, T. B. Marder, F. Wittmann and R. H. Friend, J. Mater.
Chem., 1994, 4, 1227.
7 (a) D. Beljonne, H. F. Wittmann, A. Ko¨hler, S. Graham, M. Younus,
J. Lewis, P. R. Raithby, M. S. Khan, R. H. Friend and J. L. Bre´das,
J. Chem. Phys., 1996, 105, 3868; (b) M. Younus, A. Ko¨hler, S. Cron,
N. Chawdhury, M. R. A. Al-Mandhary, M. S. Khan, J. Lewis, N. J.
Long, R. H. Friend and P. R. Raithby, Angew. Chem., Int. Ed., 1998,
37, 3036; (c) N. Chawdhury, A. Ko¨hler, R. H. Friend, M. Younus,
N. J. Long, P. R. Raithby and J. Lewis, Macromolecules, 1998, 31,
722.
8 (a) V. W.-W. Yam and K. K.-W. Lo, Chem. Soc. Rev., 1999, 28, 323;
(b) V. W.-W. Yam, K. K.-W. Lo and K. M.-C. Wong, J. Organomet.
Chem., 1999, 578, 3; (c) R. J. Puddephatt, Chem. Commun., 1998,
1055.
9 (a) W.-Y. Wong, W.-K. Wong and P. R. Raithby, J. Chem. Soc., Dalton
Trans., 1998, 2761; (b) M. S. Khan, M. R. A. Al-Mandhary, M. K.
Al-Suti, A. K. Hisham, P. R. Raithby, B. Ahrens, M. F. Mahon,
L. Male, E. A. Marseglia, E. Tedesco, R. H. Friend, A. Ko¨hler,
N. Feeder and S. J. Teat, J. Chem. Soc., Dalton Trans., 2002, 1358;
(c) M. S. Khan, M. R. A. Al-Mandhary, M. K. Al-Suti, N. Feeder,
S. Nahar, P. R. Raithby, A. Ko¨hler, R. H. Friend, P. J. Wilson and
P. R. Raithby, J. Chem. Soc., Dalton Trans., 2002, 2441; (d) M. S.
Khan, M. K. Al-Suti, M. R. A. Al-Mandhary, B. Ahrens, J. K.
Bjernemose, M. F. Mahon, L. Male, P. R. Raithby, R. H. Friend, A.
Ko¨hler and J. S. Wilson, Dalton Trans., 2003, 65; (e) M. S. Khan,
M. R. A. Al-Mandhary, M. K. Al-Suti, B. Ahrens, M. F. Mahon,
L. Male, P. R. Raithby, C. E. Boothby and A. Ko¨hler, Dalton
Trans., 2003, 74; (f) M. S. Khan, M. R. A. Al-Mandhary, M. K.
Al-Suti, F. R. Al-Battashi, S. Al-Saadi, B. Ahrens, J. K. Bjernemose,
M. F. Mahon, P. R. Raithby, M. Younus, N. Chawdhury, A. Ko¨hler,
See http://www.rsc.org/suppdata/dt/b4/b415965a/ for cry-
stallographic data in CIF or other electronic format.
Acknowledgements
We are grateful to the EPSRC for financial support and for a
grant to purchase the Enraf Nonius Kappa CCD diffractometer.
We are also grateful for financial support from the European
Commission project SANEME (under the framework of the
5th IST programme, contract number IST-1999-10323). P. L.
thanks the Cambridge Overseas Trust and the Overseas Re-
search Scheme for financial support. The award of a DAAD
grant (Gemeinsames Hochschulsonder-programm III von Bund
und La¨ndern) (to B. A.) is gratefully acknowledged. We grate-
fully acknowledge Sultan Qaboos University (SQU) Research
Grant No. IG/SCI/CHEM/02/01. M. S. K. acknowledges the
receipt of a Royal Society of Chemistry Journals Grant.
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