Synthesis and characterisation of new acetylide-functionalised oligothiophenes and their dinuclear platinum complexes

Article abstract of DOI:10.1039/a704708h

A series of rigid-rod alkynes with extended π conjugation through oligothiophene linkage units in the backbone, 2,5-bis(trimethylsilylethynyl)thiophene Ia, 2,5-diethynylthiophene Ib, 5,5′-bis(trimethylsilylethynyl)-2,2′-bithiophene IIa, 5,5′-diethynyl-2,2

Full text of DOI:10.1039/a704708h

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Synthesis and characterisation of new acetylide-functionalised
oligothiophenes and their dinuclear platinum complexes
Jack Lewis,a Nicholas J. Long,b Paul R. Raithby,*,a Gregory P. Shields,a Wai-Yeung Wong*,a
and Muhammad Younusa
a Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, UK CB2 1EW
b Department of Chemistry, Imperial College of Science, Technology and Medicine,
South Kensington, London, UK SW7 2AY
A series of rigid-rod alkynes with extended π conjugation through oligothiophene linkage units in the backbone,
2,5-bis(trimethylsilylethynyl)thiophene Ia, 2,5-diethynylthiophene Ib, 5,5Ј-bis(trimethylsilylethynyl)-2,2Ј-
bithiophene IIa, 5,5Ј-diethynyl-2,2Ј-bithiophene IIb, 5,5Љ-bis(trimethylsilylethynyl)-2,2Ј:5Ј,2Љ-terthiophene IIIa and
5,5Љ-diethynyl-2,2Ј:5Ј,2Љ-terthiophene IIIb, has been prepared. Treatment of the complex trans-[PtPh(Cl)(PR3)2]
(R = Et or Bun) with half an equivalent of the diterminal alkynyl oligothiophene chromophores Ib–IIIb in
CH2Cl2–NHPri2, in the presence of CuI, at room temperature, afforded the platinum dimers trans-[(Et3P)2PhPt᎐
᎐
᎐
C᎐CRЈC᎐C᎐PtPh(PEt ) ] (RЈ = thiophenediyl 1a, bithiophenediyl 2 or terthiophenediyl 3) and trans-
᎐
᎐
3
2
᎐
n
n
᎐
[(Bu P) PhPt᎐C᎐CRЈC᎐C᎐PtPh(PBu ) ] 1b (RЈ = thiophenediyl) in good yields. All the new compounds have
᎐
᎐
3
2
3 2
been characterised by analytical and spectroscopic methods, and the single-crystal structures of IIa, 1a and 2 have
been established.
᎐
᎐
᎐
The preparation and physical studies of conjugated organo-
metallic complexes and polymers have been the subject of sig-
nificant research interest during the past two decades because
of their possible applications in the materials industry.1,2 In this
respect, α-coupled oligothiophenes are currently attracting a
great deal of attention in the field of electronic and optoelec-
tronic devices such as field-effect transistors (FETs)3–6 and light-
emitting diodes (LEDs),7–9 and even in biological research.10
Moreover, highly organised molecular assemblies based on the
end substitution of thiophene oligomers by the use of trimeth-
ylsilyl,11 alkyl12 or 4,5,6,7-tetrahydrobenzo13 groups have
recently been studied extensively.
With these ideas in mind we set out to prepare a new range of
alkyne-functionalised α-coupled oligothiophenes at their end
positions which can then provide direct access to some bimetal-
lic materials bearing these π-conjugated systems. The introduc-
tion of transition-metal centres, with their large variety of lig-
and environments and oxidation states, is usually expected to
impart interesting physical properties, particularly non-linear
optical properties on the oligothiophene systems.14 Here, we
report the synthesis and characterisation of a series of straight-
chain alkynes with extended π conjugation through thiophene,
bithiophene or terthiophene units in the backbone and their
complexes containing PtPh(PR3)2 groups. The crystal structures
of a selected organic precursor and two diplatinum complexes
are also described.
HC᎐CRЈC᎐CH Ib–IIIb was accomplished by the desilylation
᎐
of Ia–IIIa with K2CO3 in MeOH16 (Scheme 1). The products
were purified by silica column chromatography and character-
ised spectroscopically. All the diterminal acetylenes are quite
unstable in air and under light and give insoluble brown precipi-
tates on standing.
The reaction of the platinum() complex trans-[Pt-
Ph(Cl)(PEt3)2] with half an equivalent of Ib or IIb in CH2Cl2–
NHPri2, in the presence of CuI, at room temperature, readily
᎐
affords the pure platinum dimers trans-[(Et P) PhPt᎐C᎐
CRЈC᎐C᎐PtPh(PEt ) ] (RЈ = thiophenediyl 1a, bithiophenediyl
᎐
3
2
᎐
᎐
3
2
2 or terthiophenediyl 3), in good yields (Scheme 2). The corre-
sponding PBun derivative trans-[(Bu P) PhPt᎐C᎐CRЈC᎐C᎐
᎐
3 3 2
n
᎐
᎐
᎐
PtPh(PBun )2] (RЈ = thiophenediyl) was also prepared in a sim-
3
ilar way. The formulae of these complexes were first established
by positive FAB mass spectrometry and IR and NMR (1H and
31P) spectroscopies, and they all gave satisfactory analytical data.
All the organic ligands and the platinum complexes exhibit
good solubilities in common organic solvents and the solubility
of the complexes increased by changing the auxiliary ligands
from PEt3 to PBun .
3
Spectroscopic properties
The IR spectra of the platinum–σ-acetylide complexes display a
᎐
single strong ν(C᎐C) absorption consistent with a trans con-
᎐
figuration of the acetylenic units around the PtII. As expected,
᎐
the ν(C᎐C) values of the complexes are lower than those of the
᎐
corresponding terminal or Me3Si-substituted acetylide ligands.
This may be attributed to either (i) the metal-to-alkyne π back
bonding or (ii) the Mδϩ᎐CδϪ polarity.17 There was no significant
Results and Discussion
Syntheses
2,5-Bis(trimethylsilylethynyl)thiophene Ia, 5,5Ј-bis(trimethyl-
silylethynyl)-2,2Ј-bithiophene IIa and 5,5Љ-bis(trimethyl-
silylethynyl)-2,2Ј:5Ј,2Љ-terthiophene IIIa were prepared by a
PdII/CuI-catalysed cross-coupling reaction of the dibromides
with trimethylsilylacetylene15 (Scheme 1). These ligands were
isolated as off-white (Ia) and yellow (IIa and IIIa) solids in yields
of 70–85% and have been characterised by elemental analyses
and by IR, NMR (1H and 13C), UV/VIS spectroscopy and mass
spectrometry. They are all stable in air and towards light.
Conversion of Ia–IIIa into their terminal H derivatives
effect of the different phosphine ligands (PEt3 vs. PBun ) on the
3
᎐
C᎐C stretching frequencies of the bimetallic bis(acetylide)
᎐
complexes. The 31P-{1H} NMR spectral data of all the platinum
bis(acetylide) complexes confirm that the phosphines are mutu-
ally trans around the PtII giving a square-planar geometry.
The electronic absorption spectra of the ligands show a
strong, relatively low-energy π–π* transition. A notable feature
is that an increase of the number of thienyl units in the mol-
ecule shifts the position of this band toward longer wave-
lengths. Presumably, a higher degree of conjugation with the
J. Chem. Soc., Dalton Trans., 1997, Pages 4283–4288
4283

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Pd(O2CMe)2 , PPh3 , CuI
'
R
+
Br
R′ Br
Me3Si
H
Me3Si
SiMe3
NHPri2
Ia–IIIa
K2CO3
MeOH
2
2′
R' =
I
S
'
R
H
H
5
2 2′
2 2′
5′
II
Ib–IIIb
S
S
S
5
5′ 2′′
5′′
III
S
S
Scheme 1
PEt3
2 Ph Pt Cl
PEt3
+
H
R′
H
NHPri2
,
CuI
CH2Cl2
PEt3
Ph Pt
PEt3
᎐
᎐
PEt3
Fig.
1
Molecular structure of Me3Si᎐C᎐CRЈC᎐C᎐SiMe3 IIa
᎐ ᎐
(RЈ = bithiophenediyl)
R′
Pt Ph
PEt3
Table 1 Selected bond lengths (Å) and angles (Њ) for compound IIa
m = 1 1a
R′ =
S(1)᎐C(1)
S(1)᎐C(4)
Si(1)᎐C(6)
C(1)᎐C(2)
C(2)᎐C(3)
1.728(5)
1.732(6)
1.825(7)
1.361(8)
1.406(8)
C(3)᎐C(4)
C(4)᎐C(5)
C(5)᎐C(6)
C(1)᎐C(1A)
1.358(8)
1.436(8)
1.204(8)
1.44(1)
S
m
m = 2
m = 3
2
3
Scheme 2
C(1)᎐S(1)᎐C(4)
S(1)᎐C(4)᎐C(3)
C(2)᎐C(3)᎐C(4)
C(5)᎐C(6)᎐Si(1)
91.9(3)
111.5(4)
111.9(5)
176.8(6)
S(1)᎐C(1)᎐C(2)
C(1)᎐C(2)᎐C(3)
C(4)᎐C(5)᎐C(6)
109.8(4)
114.9(5)
179.2(6)
additional thienyl units reduces the energy gap between the
highest occupied and lowest unoccupied molecular orbitals
(HOMO and LUMO). This is consistent with the π–π* transi-
tions observed for the parent oligothiophenes, which vary from
231 nm for thiophene to 350 nm for terthiophene.18 For Me3Si-
substituted acetylides, this transition red-shifts steadily from
331 to 410 nm. The electronic spectra of the diplatinum()
complexes 1–3 are also dominated by the π–π* transitions of
the corresponding bridging ligands (see Experimental section).
The effect of attachment of two platinum fragments is found to
lower the energies of these transitions. It was clearly shown that
the 371 and 353 nm absorptions of free IIa and IIb respectively
move to 406 nm for complex 2, indicating that the platinum
moieties act as net electron acceptors.19 Again, increasing con-
jugation through more thienyl units from complexes 1 to 3 leads
to a decreased transition energy, with λmax for 3 being the larg-
est. It is also noteworthy that no significant difference between
PEt3 and PBun3 as auxiliary ligands in the absorption spectra of
the platinum complexes is observed.
Atoms denoted A are related by the symmetry operation 2 Ϫ x, Ϫy,
2 Ϫ z to the unique atom with the same numbering.
ively], which is consistent with the partial conjugation effect
along the molecule. Common to most planar molecules such as
α-terthienyl and α-hexathienyl, the unit cell of crystals IIa pres-
ents the herringbone packing in space group P21/a.20,21 No sig-
nificant interheteroatom contacts are observed and the dis-
tances between atoms of nearest molecules are all longer than
the sum of the van der Waals radii.
The solid-state structures of complexes 1a and 2 have also
been established by X-ray crystallography. The molecular struc-
tures are illustrated in Figs. 2 and 3, respectively, and selected
bond parameters are collected in Tables 2 and 3. In each case, the
crystal structure consists of discrete dimeric molecules in which
the platinum atoms are surrounded by four ligands in a square-
planar geometry with the two phosphines in a trans arrange-
ment. For 1a there are one and a half molecules in the asym-
metric unit, and only the complete unique molecule is shown in
Fig. 2; the half molecule is disordered about a centre of sym-
metry. For 2 there are two independent half molecules each
possessing crystallographic Ci symmetry with the centre of
symmetry at the midpoint of the C(6)᎐C(6A) bond; only one
molecule is shown in Fig. 3. The metal-to-phosphorus bond
lengths lie in the range of 2.274(5)–2.303(5) (1a) and 2.291(6)–
2.316(6) Å (2). The two PtPh(PEt3)2 units are bridged by a
thiophenediyl- or bithiophenediyl-spaced bis(acetylide) ligand
for 1a and 2, respectively. Like free IIa, the two thiophene
groups in 2 display a trans arrangement in order to minimise the
steric repulsions between the lone pairs on both sulfur atoms. In
Molecular structures
The molecular structure of compound IIa is shown in Fig. 1,
which includes the atom numbering scheme. Selected bond dis-
tances and angles are listed in Table 1. In the solid state two
halves of the molecule are related by a centre of symmetry at
the midpoint of C(1)᎐C(1A) bond. Each molecule is essentially
planar and adopts a trans configuration with respect to the two
thiophene rings. The mean sulfur–carbon bond length is
1.730(6) Å, which is similar to those found in α-terthiophene
and α-sexithiophene.20 The C᎐C bond distances of the thio-
phene ring vary from 1.358(8) to 1.406(8) Å with the average
being 1.375(8) Å. This average is somewhat shorter than that
observed in unsubstituted α-oligothiophenes (range 1.36–1.46
Å).20 The bond C(5)᎐C(6) is longer than that of a typical C᎐C
both cases, the fragment Pt᎐C᎐CRЈC᎐C᎐Pt is nearly planar. The
᎐
᎐
᎐
᎐
᎐
᎐
bond. Moreover, slight shortenings of the bonds C(1)᎐C(1A)
and C(4)᎐C(5) are observed [1.44(1) and 1.436(8) Å, respect-
mean metal-to-carbon (acetylide) bond length is 2.03(2) Å for
1a and 2.01(2) Å for 2, while the average acetylide C᎐C bond
᎐
᎐
4284
J. Chem. Soc., Dalton Trans., 1997, Pages 4283–4288

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᎐
᎐
Fig. 2 Molecular structure of trans-[(Et3P)2PhPt᎐C᎐CRЈC᎐C᎐PtPh(PEt3)2] 1a (RЈ = thiophenediyl)
᎐ ᎐
᎐
᎐
Fig. 3 Molecular structure of trans-[(Et3P)2PhPt᎐C᎐CRЈC᎐C᎐PtPh(PEt3)2] 2 (RЈ = bithiophenediyl)
᎐
᎐
length is 1.20(3) (1a) and 1.25(3) Å (2). The S᎐C bonds of the
bithienyl group in 2 show comparable distances to those in IIa
but the C᎐C distances of the rings are slightly longer in 2
obtained with a Perkin-Elmer Lambda UV/NIR spectrometer.
Preparative thin-layer chromatography (TLC) was carried out
on commercial Merck plates with a 0.25 mm layer of silica, or
on 1 mm silica plates prepared at the University Chemical
Laboratory, Cambridge. Column chromatography was per-
formed on Kieselgel 60 (230–400 mesh) silica gel.
[1.37(3)–1.42(3) Å]. The mean angles of 178(2) (1a) and 177(2)Њ
᎐
(2) for the fragment Pt᎐C᎐C confirm the linear geometry of the
᎐
bis(acetylide) complexes.
Ligand syntheses
Experimental
General
All the ligand precursors were made by following a general
procedure outlined below for IIa and IIb.
Solvents were predried and distilled from appropriate drying
agents.22 All chemicals, except where stated, were from com-
5,5Ј-Bis(trimethylsilylethynyl)-2,2Ј-bithiophene IIa. To an ice-
cooled mixture of 5,5Ј-dibromo-2,2Ј-bithiophene (3.89 g, 12
mmol) in freshly distilled diisopropylamine (70 cm3) under
nitrogen were added CuI (30 mg, 0.16 mmol), Pd(O2CMe)2 (30
᎐
mercial sources and used as received; Me SiC᎐CH was prepared
᎐
3
in this laboratory. The compounds trans-[PtPh(Cl)(PR3)2]
(R = Et or Bun),23 5,5Ј-dibromo-2,2Ј-bithiophene24 and 5,5Љ-
dibromo-2,2Ј:5Ј,2Љ-terthiophene24 were prepared via literature
procedures. The NMR spectra were recorded on a Bruker WM-
250 or AM-400 spectrometer in appropriate solvents, 31P-{1H}
referenced to external trimethyl phosphite and the 1H and 13C-
{1H} to solvent resonances. Infrared spectra were recorded as
CH2Cl2 solutions, in a NaCl cell, on a Perkin-Elmer 1710
Fourier-transform spectrometer and mass spectra on a Kratos
MS890 spectrometer by either the electron impact (EI) or fast
atom bombardment (FAB) technique. Microanalyses were per-
formed in this department. Electronic absorption spectra were
mg, 0.13 mmol) and PPh3 (90 mg, 0.34 mmol). The solution was
᎐
stirred for 20 min, Me SiC᎐CH (2.95 g, 30 mmol) was then added
᎐
3
and the suspension was stirred for 30 min in an ice-bath before
being warmed to room temperature. After reacting for 30 min at
room temperature the mixture was heated to 75 ЊC for 20 h. The
completion of the reaction was verified by IR spectroscopy and
silica TLC. The solution was allowed to cool to room tempera-
ture, Et2O (100 cm3) was added and the precipitate was filtered
off. The brown-yellow filtrate was evaporated to dryness. The
residue was redissolved in Et2O (100 cm3) and washed sequen-
J. Chem. Soc., Dalton Trans., 1997, Pages 4283–4288
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Table 2 Selected bond lengths (Å) and angles (Њ) for complex 1a
Table 3 Selected bond lengths (Å) and angles (Њ) for complex 2
Molecule 1
Molecule 1
Pt(1)᎐P(1)
Pt(1)᎐P(2)
Pt(1)᎐C(1)
Pt(2)᎐P(3)
Pt(2)᎐P(4)
Pt(1)᎐C(19)
Pt(2)᎐C(26)
Pt(2)᎐C(39)
C(19)᎐C(20)
2.290(5)
2.274(5)
2.10(1)
2.292(6)
2.288(6)
2.03(2)
2.02(2)
2.08(1)
1.18(3)
C(20)᎐C(21)
C(21)᎐C(22)
C(22)᎐C(23)
C(23)᎐C(24)
S(1)᎐C(21)
S(1)᎐C(24)
C(24)᎐C(25)
C(25)᎐C(26)
1.42(3)
1.34(3)
1.50(3)
1.33(3)
1.74(2)
1.74(2)
1.40(3)
1.20(2)
Pt(1)᎐P(1)
Pt(1)᎐P(2)
Pt(1)᎐C(1)
Pt(1)᎐C(7)
C(1)᎐C(2)
C(2)᎐C(3)
2.316(6)
2.307(6)
1.96(2)
2.03(2)
1.25(3)
1.42(3)
S(1)᎐C(3)
S(1)᎐C(6)
C(3)᎐C(4)
C(4)᎐C(5)
C(5)᎐C(6)
C(6)᎐C(6A)
1.74(2)
1.74(2)
1.38(3)
1.37(3)
1.37(3)
1.50(4)
P(1)᎐Pt(1)᎐P(2)
P(2)᎐Pt(1)᎐C(1)
Pt(1)᎐C(1)᎐C(2)
C(3)᎐S(1)᎐C(6)
S(1)᎐C(6)᎐C(5)
C(4)᎐C(5)᎐C(6)
178.2(2)
90.0(6)
178(2)
90.7(9)
112(1)
113(2)
P(1)᎐Pt(1)᎐C(1)
C(1)᎐Pt(1)᎐C(7)
C(1)᎐C(2)᎐C(3)
S(1)᎐C(3)᎐C(4)
C(3)᎐C(4)᎐C(5)
90.4(6)
179.0(8)
179(2)
110(1)
115(2)
P(1)᎐Pt(1)᎐P(2)
175.7(2)
89.5(6)
174(2)
177.1(2)
91.5(6)
176(2)
110(2)
112(2)
176(2)
P(1)᎐Pt(1)᎐C(19)
Pt(1)᎐C(19)᎐C(20)
Pt(2)᎐C(26)᎐C(25)
P(3)᎐Pt(2)᎐C(26)
C(26)᎐Pt(2)᎐C(39)
C(21)᎐S(1)᎐C(24)
S(1)᎐C(24)᎐C(23)
C(22)᎐C(23)᎐C(24)
86.7(6)
178(2)
177(2)
88.7(6)
178.3(6)
95(1)
P(2)᎐Pt(1)᎐C(19)
C(1)᎐Pt(1)᎐C(19)
P(3)᎐Pt(2)᎐P(4)
P(4)᎐Pt(2)᎐C(26)
C(19)᎐C(20)᎐C(21)
S(1)᎐C(21)᎐C(22)
C(21)᎐C(22)᎐C(23)
C(24)᎐C(25)᎐C(26)
Molecule 2
Pt(2)᎐P(3)
Pt(2)᎐P(4)
Pt(2)᎐C(37)
Pt(2)᎐C(43)
C(37)᎐C(38)
C(38)᎐C(39)
2.291(6)
2.296(6)
2.05(2)
2.06(2)
1.24(3)
1.35(3)
S(2)᎐C(39)
S(2)᎐C(42)
C(39)᎐C(40)
C(40)᎐C(41)
C(41)᎐C(42)
C(42)᎐C(42A)
1.73(2)
1.74(2)
1.42(3)
1.42(3)
1.40(3)
1.44(4)
109(2)
115(2)
Molecule 2
Pt(3)᎐P(5)
Pt(3)᎐P(6)
Pt(3)᎐C(45)
Pt(3)᎐C(63)
C(63)᎐C(64)
C(64)᎐C(65)
2.293(5)
2.303(5)
2.09(2)
2.03(2)
1.22(2)
1.38(2)
C(65)᎐C(66)
C(66)᎐C(67)
C(67)᎐C(68)
S(2)᎐C(65)
S(2)᎐C(68)
1.30(4)
1.44(7)
1.30(4)
1.73(2)
1.74(2)
P(3)᎐Pt(2)᎐P(4)
174.5(2)
92.3(2)
176(2)
94(1)
109(2)
115(2)
P(3)᎐Pt(2)᎐C(43)
C(37)᎐Pt(2)᎐C(43)
C(37)᎐C(38)᎐C(39)
S(2)᎐C(39)᎐C(40)
C(39)᎐C(40)᎐C(41)
87.5(5)
176.8(7)
167(3)
110(1)
112(2)
P(4)᎐Pt(2)᎐C(43)
Pt(2)᎐C(37)᎐C(38)
C(39)᎐S(2)᎐C(42)
S(2)᎐C(42)᎐C(41)
C(40)᎐C(41)᎐C(42)
P(5)᎐Pt(3)᎐P(6)
176.1(2)
91.4(5)
179.0(7)
95(2)
106(2)
116(2)
P(5)᎐Pt(3)᎐C(63)
Pt(3)᎐C(63)᎐C(64)
C(63)᎐C(64)᎐C(65)
S(2)᎐C(65)᎐C(66)
C(65)᎐C(66)᎐C(67)
87.2(5)
179(2)
163(2)
108(2)
114(2)
The atoms denoted A are generated from the unique atom with the
same number by the symmetry operation Ϫx, 1 Ϫ y, Ϫz.
P(6)᎐Pt(3)᎐C(63)
C(45)᎐Pt(3)᎐C(63)
C(65)᎐S(2)᎐C(68)
S(2)᎐C(68)᎐C(67)
C(66)᎐C(67)᎐C(68)
2,5-Bis(trimethylsilylethynyl)thiophene Ia.25 2,5-Dibromo-
᎐
thiophene (3.00 g, 12.0 mmol), Me SiC᎐CH (4.50 g, 45.0 mmol)
᎐
3
and NHPri2 (100 cm3) were mixed with catalytic amounts of
CuI (30 mg), Pd(O2CMe)2 (30 mg) and PPh3 (90 mg). The crude
product was worked-up, as before, to yield a pale-brown residue
which was then applied to a silica column in hexane (5 cm3) and
eluted with the same solvent. The desired compound Ia was
isolated as an off-white solid (2.80 g, 85%). IR (CH2Cl2): ν /cmϪ1
tially with 10% HCl (3 × 100 cm3), water (3 × 100 cm3),
NaHCO3 (3 × 100 cm3) and water (3 × 100 cm3). The resulting
organic solution was then dried (MgSO4), the solvent removed,
and the brown-yellow residue chromatographed over a silica gel
column by eluting with hexane–CH2Cl2 (9:1 v/v). The product
was eluted as a yellow-orange band and the pure fraction evap-
orated to dryness and recrystallised from hexane–CH2Cl2 to
1
᎐
2146 (C᎐C). H NMR (250 MHz, CDCl ): δ 0.24 (s, 18 H,
᎐
3
SiMe3) and 7.04 (s, 2 H, H3,4). 13C NMR (100.6 MHz, CDCl3):
2,5
᎐
᎐
give IIa as a yellow crystalline solid in 77% yield (3.31 g). IR
δ Ϫ0.20 (SiMe ), 96.89 (C᎐C), 99.93 (C᎐C), 124.50 (C ) and
᎐
3
᎐
(CH2Cl2): ν /cmϪ1 2143 (C᎐C). H NMR (250 MHz, CDCl ): δ
132.32 (C3,4). EI mass spectrum: m/z 276 (Mϩ). UV/VIS
(CH2Cl2): λmax/nm 331 (Found: C, 60.93; H, 7.64. Calc. for
C14H20SSi2: C, 60.81; H, 7.29%).
1
᎐
᎐
0.24 (s, 18 H, SiMe3), 6.99 [d, 2 H, 3J(H3H4) or 3J(H3ЈH4Ј) =33.9,
H3,3Ј] and 7.10 [d, 2 H, J(H4H3) or J(H4ЈH3Ј) = 3.9 Hz, H4,4Ј].
3
3
13C-{1H} NMR (100.6 MHz, CDCl3): δ Ϫ0.16 (SiMe3), 97.18
(C᎐C), 100.54 (C᎐C), 122.41 (C2,2Ј or C5,5Ј), 123.78 (C3,3Ј or C4,4Ј),
2,5-Diethynylthiophene Ib.25 Compound Ia (1.00 g, 3.6
mmol) was desilylated using K2CO3 (0.55 g, 4.0 mmol) in
MeOH (50 cm3). The reaction mixture was covered with alu-
minium foil and left stirring overnight. The solvent was
removed slowly at room temperature using a water pump to
afford a yellow oil which was dissolved in Et2O and washed
with water. The organic layer was dried quickly over MgSO4
and filtered. The solvent was removed to give Ib (0.23 g, 50%) as
a yellow oil which was unstable. Storage overnight under nitro-
gen at 4 ЊC resulted in the oil darkening. Long storage times led
to the formation of a black rubber-like insoluble material which
was presumed to be a polymerisation product. This ligand was
᎐
᎐
᎐
᎐
133.51 (C3,3Ј or C4,4Ј) and 138.13 (C2,2Ј or C5,5Ј). EI mass spec-
trum: m/z 358 (Mϩ). UV/VIS (CH2Cl2): λmax/nm 371 (Found: C,
60.10; H, 6.28. Calc. for C18H22S2Si2: C, 60.28; H, 6.18%).
5,5Ј-Diethynyl-2,2Ј-bithiophene IIb. A mixture of compound
IIa (0.50 g, 1.4 mmol) and K2CO3 (0.19 g, 1.4 mmol) in MeOH
(50 cm3) was stirred at room temperature for 20 h. Infrared
spectroscopy showed that all the starting material had been
consumed. Solvent was removed under reduced pressure to
leave a yellow residue. This residue was dissolved in the min-
imum amount of CH2Cl2 and subjected to column chrom-
atography on silica using hexane–CH2Cl2 (3:2 v/v) as eluent to
therefore freshly prepared for use in any further synthesis. IR
1
(CH2Cl2): ν /cmϪ1 2108 (C᎐C) and 3300 (C᎐CH). H NMR (250
᎐
᎐
afford a major brown-yellow product identified as IIb (0.21 g,
᎐
᎐
70%). IR (CH2Cl2): ν /cmϪ1 2102 (C᎐C) and 3300 (C᎐CH). H
MHz, CDCl ): δ 3.20 (s, 2 H, C᎐CH) and 7.10 (s, 2 H, H ). 13C-
1
3,4
᎐
᎐
᎐
᎐
᎐
᎐
3
1
᎐
᎐
᎐
NMR (250 MHz, CDCl ): δ 3.41 (s, 2 H, C᎐CH), 7.02 [d, 2 H,
{ H} NMR (100.6 MHz, CDCl ): δ 79.04 (C᎐C), 81.02 (C᎐C),
᎐
᎐
᎐
3J(H3H4) or 3J(H3ЈH4Ј) =33.8 H3,3Ј] and 7.16 [d, 2 H, 3J(H4H3) or
124.05 (C2,5) and 132.40 (C3,4). EI mass spectrum: m/z 132 (Mϩ).
3
3J(H4ЈH3Ј) = 3.8 Hz, H4,4Ј]. 13C-{1H} NMR (100.6 MHz, CDCl3):
Microanalytical data are not available due to the instability.
δ 76.66 (C᎐C), 82.68 (C᎐C), 121.44 (C2,2Ј or C5,5Ј), 123.93 (C3,3Ј or
᎐
᎐
᎐
᎐
C4,4Ј), 133.99 (C3,3Ј or C4,4Ј) and 138.10 (C2,2Ј or C5,5Ј). EI mass
spectrum: m/z 214 (Mϩ). UV/VIS (CH2Cl2): λmax/nm 353
(Found: C, 67.02; H, 3.08. Calc. for C12H6S2: C, 67.26; H,
2.82%).
5,5Љ-Bis(trimethylsilylethynyl)-2,2Ј:5Ј2Љ-terthiophene
IIIa.
This compound was prepared as described above for IIa from
5,5Љ-dibromo-2,2Ј:5Ј,2Љ-terthiophene (0.97 g, 2.4 mmol),
᎐
Me SiC᎐CH (0.59 g, 6.0 mmol), CuI (6 mg, 0.03 mmol),
᎐
3
4286
J. Chem. Soc., Dalton Trans., 1997, Pages 4283–4288

View Article Online
Table 4 Summary of crystal structure data for compounds IIa, 1a and 2
IIa
1a
2
Empirical formula
M
C18H22S2Si2
358.66
C44H72P4Pt2S
1147.14
C48H74P4Pt2S2
1229.25
Crystal colour, habit
Crystal dimensions/mm
Crystal system
Space group
Pale yellow
0.42 × 0.28 × 0.13
Monoclinic
P21/a
Pale yellow
0.40 × 0.25 × 0.09
Triclinic
Yellow
0.22 × 0.15 × 0.11
Triclinic
¯
P1
¯
P1
a/Å
b/Å
c/Å
α/Њ
11.534(2)
5.821(1)
16.146(2)
16.804(3)
25.107(5)
9.221(2)
98.40(3)
99.67(3)
83.24(3)
3777(1)
3
15.870(6)
17.460(8)
9.525(4)
97.28(3)
90.80(3)
82.06(3)
2593(2)
2
β/Њ
110.16(2)
γ/Њ
U/Å3
1017.6(3)
2
1.171
Z
Dc/g cmϪ3
1.513
1.574
F(000)
380
0.374
293
1704
5.745
293
1220
5.623
153
µ(Mo-Kα)/mmϪ1
T/K
θ Range/Њ
1.34–25.49
1251
1251
845
0
0.1262, 0
103
0.057, 0.189
0.084, 0.212
1.121
2.50–22.50
10 226
9823
6321
0.0583
0.1364, 8.55
376
0.070, 0.185
0.138, 0.249
1.014
1.19–22.35
17 693
5732
No. reflections collected
No. independent reflections
Observed reflections [I > 2σ(I)]
Rint
5309
0.0948
0.0944, 37.71
502
0.087, 0.199
0.097, 0.207
1.231
x, y
No. refined parameters
R1,a wR2b [I > 2σ(I)]
(all data)
Goodness of fit on F2
Residual electron density/e ÅϪ3
ϩ0.28, Ϫ0.36
ϩ2.24, Ϫ1.98
ϩ1.93, Ϫ3.11
¹
¹
2
a R1 = Σ Fo| Ϫ |Fc /Σ|Fo|. b wR2 = [Σw(Fo2 Ϫ Fc2)2/Σw(Fo )2]². Goodness of fit = [Σw(Fo2 Ϫ Fc2)2/(Nobservns Ϫ Nparams)]², based on all data.
Pd(O2CMe)2 (6 mg, 0.03 mmol) and PPh3 (18 mg, 0.07 mmol)
in NHPri2 (20 cm3). After the usual work-up, the residue was
purified by column chromatography on silica using hexane–
CH2Cl2 (4:1 v/v) to yield crude yellow product IIIa. Recrystal-
mmol, freshly prepared by the reaction of Ia with NBun F) with
2 equivalents of trans-[PtPh(Cl)(PEt3)2] (0.22 g, 0.4 mmol) for
15 h at room temperature, in the presence of CuI (3 mg), in
CH2Cl2–NHPri2 (50 cm3, 1:1 v/v) gave the required complex
as a light yellow solid in 65% yield (0.15 g) after purification
4
lisation from hexane–CH2Cl2 led to bright yellow crystals of
1
IIIa in 71% yield (0.75 g). IR (CH2Cl2): ν /cmϪ1 2142 (C᎐C). H
on a silica column using hexane–CH2Cl2 (1:1) as eluent. IR
᎐
᎐
1
(CH2Cl2): ν /cmϪ1 2083 (C᎐C). H NMR (250 MHz, CDCl ): δ
᎐
NMR (250 MHz, CDCl3): δ 0.24 (s, 18 H, SiMe3), 6.99 [d, 2 H,
᎐
3
3J(H3H4) or 3J(H3ЉH4Љ) = 3.9, H3,3Љ], 7.05 (s, 2 H, H3Ј,4Ј) and 7.12
1.16 (m, 36 H, CH3), 1.71 (m, 24 H, CH2), 6.60 (s, 2 H, H3,4),
6.78 (t, 2 H, Hpara of Ph), 6.94 (t, 4 H, Hmeta of Ph) and 7.31 (br,
4 H, Hortho of Ph). 31P-{1H} NMR (101.3 MHz, CDCl3): δ
Ϫ131.10 [1J(Pt᎐P) = 2677 Hz]. FAB mass spectrum: m/z 1146
(Mϩ). UV/VIS (CH2Cl2): λmax/nm 378 (Found: C, 45.71; H,
6.28. Calc. for C44H72P4Pt2S: C, 46.07; H, 6.33%).
[d, 2 H, 3J(H4H3) or 3J(H4ЉH3Љ) = 3.9 Hz, H4,4Љ]. 13C-{1H} NMR
᎐
(100.6 MHz, CDCl ): δ Ϫ0.15 (SiMe ), 97.28 (C᎐C), 100.48
᎐
᎐
3
3
᎐
(C᎐C), 122.18 (quaternary C, terthienyl), 123.43 (CH, ter-
thienyl), 124.94 (CH, terthienyl), 133.56 (CH, terthienyl),
136.07 (quaternary C, terthienyl) and 138.25 (quaternary C, ter-
thienyl). EI mass spectrum: m/z 440 (Mϩ). UV/VIS (CH2Cl2):
λmax/nm 410 (Found: C, 59.82; H, 5.50. Calc. for C22H24S3Si2: C,
59.95; H, 5.49%).
n
n
᎐
᎐
᎐
trans-[(Bu P) PhPt᎐C᎐CRЈC᎐C᎐PtPh(PBu ) ] 1b (RЈ =
᎐
3
2
3 2
thiophenediyl). This complex was synthesized using the con-
ditions described for 1a but trans-[PtPh(Cl)(PBun )2] (0.28 g, 0.4
3
5,5Љ-Diethynyl-2,2Ј:5Ј,2Љ-terthiophene IIIb. This compound
was synthesized as described above for IIb from IIIa (0.50 g, 1.1
mmol) and K2CO3 (0.15 g, 1.1 mmol) in MeOH (50 cm3). The
residue dissolved in CH2Cl2 was applied to a silica column and
the desired yellow band was collected with the aid of hexane–
CH2Cl2 (7:3 v/v) to afford IIIb (0.25 g, 74%) as a brownish
mmol) was used instead of trans-[PtPh(Cl)(PEt3)2]. Yield: 0.22
1
g (74%). IR (CH2Cl2): ν /cmϪ1 2084 (C᎐C). H NMR (250 MHz,
᎐
᎐
CDCl3): δ 0.97 (m, 36 H, CH3), 1.30 (m, 24 H, CH2), 1.41 (m, 24
H, CH2), 1.66 (m, 24 H, CH2), 6.57 (s, 2 H, H3,4), 6.76 (t, 2 H,
Hpara of Ph), 6.92 (t, 4 H, Hmeta of Ph) and 7.27 [dd, 4 H,
3J(Pt᎐H) = 38 Hz, Hortho of Ph]. 31P-{1H} NMR (101.3 MHz,
CDCl3): δ Ϫ139.28 [1J(Pt᎐P) = 2659 Hz]. FAB mass spectrum:
m/z 1484 (Mϩ). UV/VIS (CH2Cl2): λmax/nm 379 (Found: C,
55.58; H, 8.22. Calc. for C68H120P4Pt2S: C, 55.04; H, 8.15%).
yellow crystalline solid. IR (CH2Cl2): ν /cmϪ1 2102 (C᎐C) and
᎐
᎐
1
᎐
3300 (C᎐CH). H NMR (250 MHz, CDCl ): δ 3.41 (s, 2 H,
᎐
3
C᎐CH), 7.01 [d, 2 H, J(H H ) or J(H H ) = 3.9, H3,3Љ], 7.17
3
3
4
3
3Љ 4Љ
᎐
᎐
[d, 2 H, 3J(H4H3) or 3J(H4ЉH3Љ) = 3.9 Hz, H4,4Љ] and 7.25 (s, 2 H,
H3Ј,4Ј). C-{ H} NMR (100.6 MHz, CDCl ): δ 76.78 (C᎐C),
13
1
᎐
᎐
3
᎐
᎐
᎐
trans-[(Et P) PhPt᎐C᎐CRЈC᎐C᎐PtPh(PEt ) ] 2 (RЈ = bithio-
᎐
3
2
3 2
᎐
82.59 (C᎐C), 121.00 (quaternary C, terthienyl), 123.44 (CH,
᎐
phenediyl). To a mixture of compound IIb (15 mg, 0.07 mmol)
and 2 equivalents of trans-[PtPh(Cl)(PEt3)2] (80 mg, 0.14 mmol)
in CH2Cl2–NHPri2 (30 cm3, 1:1 v/v) was added CuI (2 mg). The
solution was stirred at room temperature over 15 h, after which
all volatile components were removed under reduced pressure.
The product was purified on preparative TLC plates with
hexane–CH2Cl2 (3:2 v/v) as eluent, giving compound 2 as a
terthienyl), 124.83 (CH, terthienyl), 134.03 (CH, terthienyl),
136.01 (quaternary C, terthienyl) and 138.54 (quaternary C, ter-
thienyl). EI mass spectrum: m/z 296 (Mϩ). UV/VIS (CH2Cl2):
λmax/nm 395 (Found: C, 64.94; H, 2.94. Calc. for C16H8S3: C,
64.83; H, 2.72%).
Complex preparations
pale yellow solid in an isolated yield of 55% (47 mg). IR
1
trans-[(Et P) PhPt᎐C᎐CRЈC᎐C᎐PtPh(PEt ) ] 1a (RЈ = thio-
(CH2Cl2): ν /cmϪ1 2082 (C᎐C). H NMR (250 MHz, CDCl ):
᎐
᎐
᎐
᎐
᎐
᎐
3
2
3
2
3
phenediyl). Treatment of the diterminal alkyne Ib (26 mg, 0.2
δ 1.08 (m, 36 H, CH3), 1.72 (m, 24 H, CH2), 6.70 [d, 2 H,
J. Chem. Soc., Dalton Trans., 1997, Pages 4283–4288
4287

View Article Online
3J(H3H4) or 3J(H3ЈH4Ј) = 3.7, H3,3Ј], 6.80 (t, 2 H, Hpara of Ph), 6.84
by the Croucher Foundation. We also thank the Department
3
3
[d, 2 H, J(H4H3) or J(H4ЈH3Ј) = 3.7 Hz, H4,4Ј], 6.96 (t, 4 H,
Hmeta of Ph) and 7.30 (br, 4 H, Hortho of Ph). 31P-{1H} NMR
(101.3 MHz, CDCl3): δ Ϫ131.10 [1J(Pt᎐P) = 2628 Hz]. FAB
mass spectrum: m/z 1229 (Mϩ). UV/VIS (CH2Cl2): λmax/nm 406
(Found: C, 46.20; H, 6.09. Calc. for C48H74P4Pt2S2: C, 46.90; H,
6.07%).
of Chemistry, The University of Hong Kong for the X-ray
data collection of structure IIa during the leave of absence of
W.-Y. W. in Hong Kong.
References
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London, 1992.
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Marder, J. E. John and G. D. Stucky, ACS Symp. Ser., 1991, 455.
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᎐
᎐
᎐
trans-[(Et P) PhPt᎐C᎐CRЈC᎐C᎐PtPh(PEt ) ] 3 (RЈ = terthio-
᎐
3
2
3 2
phenediyl). Similar procedures as for complex 2 were employed
using IIIb (21 mg, 0.07 mmol) to produce bright yellow 3 in
52% yield (48 mg) after TLC purification and recrystallisation.
IR (CH2Cl2): ν /cmϪ1 2081 (C᎐C). 1H NMR (250 MHz,
᎐
᎐
CDCl3): δ 1.09 (m, 36 H, CH3), 1.73 (m, 24 H, CH2), 6.73 [d, 2
H, 3J(H3H4) or 3J(H3ЉH4Љ) = 3.7, H3,3Љ], 6.82 (m, 2 H, Hpara of Ph),
6.91 [d, 2 H, 3J(H4H3) or 3J(H4ЉH3Љ) = 3.7 Hz, H4,4Љ], 6.94 (s, 2 H,
H3Ј,4Ј), 6.96 (t, 4 H, Hmeta of Ph) and 7.30 (m, 4 H, Hortho of Ph).
31P-{1H} NMR (101.3 MHz, CDCl3): δ Ϫ131.08 [1J(Pt᎐P) =
2629 Hz]. FAB mass spectrum: m/z 1311 (Mϩ). UV/VIS
(CH2Cl2): λmax/nm 433 (Found: C, 47.83; H, 5.97. Calc. for
C52H76P4Pt2S2: C, 47.63; H, 5.84%).
6 H. Akimichi, K. Waragai, S. Hotta, H. Kano and H. Sakati, Appl.
Phys. Lett., 1991, 58, 1500; K. Waragai, H. Akimichi, S. Hotta,
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Chem., 1994, 4, 1227 and refs. therein.
16 S. Takahashi, Y. Kuroyama, K. Sonogashira and N. Hagihara,
Synthesis, 1980, 627.
Crystallography
Pale yellow to yellow crystals of compounds IIa, 1a and 2 suit-
able for X-ray diffraction experiments were grown by slow
evaporation of their respective solutions in hexane–CH2Cl2.
Geometric and intensity data were collected using graphite-
monochromated Mo-Kα radiation (λ = 0.710 73 Å) on the fol-
lowing diffractometers: MAR Research image plate scanner
(IIa), Rigaku AFC7R (1a) and Rigaku R-Axis IIc image plate
(2). All pertinent crystallographic data and other experimental
details are summarised in Table 4. For 1a data were collected
using the ω–2θ scan technique with a scan rate of 16.00Њ minϪ1
(in ω). For 2 two data sets were collected; one of them in-
volved 60 × 3Њ oscillation frames with an exposure time of 10
min, and then the crystal was rotated through 90Њ about an axis
45Њ to the vertical and 40 × 3Њ frames with 10 min exposure were
employed for data acquisition. For IIa 65 × 3Њ frames with
an exposure time of 5 min per frame were used. The intensity
data were corrected for Lorentz-polarisation effects. Semi-
empirical absorption corrections based upon ψ scans were
applied (TEXSAN)26 for 1a, interframe scaling for 2, however
no absorption correction was made for IIa.
The structures were solved by direct methods (SHELXTL
PLUS)27 and subsequent Fourier-difference syntheses, and
refined by full-matrix least squares on F2 (SHELXL 93)28 with
anisotropic displacement parameters for the non-H atoms. The
crystal structure of complex 1a contains one and a half mol-
ecules in the asymmetric unit, the half molecule being related to
its symmetry equivalent through a centre of symmetry which
sits at the centre of the thiophene ring, and so the thiophene
atom positions were refined in two sites with 50% occupancy.
Hydrogen atoms were included using a riding model. In the
final cycles of refinement, weighting scheme of the form w =
17 J. Manna, K. D. John and M. D. Hopkins, Adv. Organomet. Chem.,
1995, 38, 79.
18 J. W. Sease and L. Zechmeister, J. Am. Chem. Soc., 1947, 69, 270.
19 J. Hock, A. M. W. Cargill Thompson, J. A. McCleverty and
M. D. Ward, J. Chem. Soc., Dalton Trans., 1996, 4257.
20 T. Siegrist, R. M. Fleming, R. C. Haddon, R. A. Laudise,
A. J. Lovinger, H. E. Katz, P. Bridenbaugh and D. D. Davis,
J. Mater. Res., 1995, 10, 2170.
21 G. Horowitz, B. Bachet, A. Yassar, P. Lang, F. Demanze, J.-L. Fave
and F. Garnier, Chem. Mater., 1995, 7, 1337.
22 W. L. F. Armarego and D. D. Perrin, Purification of Laboratory
Chemicals, Butterworth-Heinemann, 4th edn., 1996.
23 J. Chatt and B. L. Shaw, J. Chem. Soc., 1960, 4020; W. Müller,
G. Schmidtberg and H. Brune, Chem. Ber., 1985, 118, 4653.
24 P. Bäuerle, F. Würthner, G. Götz and F. Effenberger, Synthesis,
1993, 1099.
25 D. Beljonne, M. C. B. Colbert, P. R. Raithby, R. H. Friend and
J. L. Brédas, Synth. Met., 1996, 81, 179; M. C. B. Colbert, Ph.D.
Thesis, Cambridge, 1995.
26 TEXSAN, Single Crystal Structure Analysis Software, Version 1.7,
Molecular Structure Corporation, The Woodlands, TX, 1995.
27 G. M. Sheldrick, SHELXTL PLUS, Siemens Analytical Instru-
ments, Madison, WI, 1990.
2
1/[σ2(Fo ) ϩ (xP)2 ϩ yP], where P = (Fo2 ϩ 2Fc2)/3, was intro-
duced which produced a flat analysis of variance. For 1a and 2
some of the ethyl groups and the phenyl ring showed pos-
itional disorder, and these were refined with partial occupan-
cies, summed to unity and constraints placed on some of the
C᎐C distances.
CCDC reference number 186/700.
Acknowledgements
28 G. M. Sheldrick, SHELXL 93, University of Göttingen, 1993.
We thank the Cambridge Commonwealth Trust and the
Overseas Research Scheme (M. Y.) for financial support and
W.-Y. W. is thankful for a postdoctoral fellowship administered
Received 3rd July 1997; Paper 7/04708H
4288
J. Chem. Soc., Dalton Trans., 1997, Pages 4283–4288