Electrophilic substitution of thiophenes with arylpalladium(II) and platinum(II) complexes: Mechanistic studies on palladium-catalyzed CH arylation of thiophenes

Article abstract of DOI:10.1246/bcsj.82.555

Mechanistic studies on palladium-catalyzed CH arylation of thiophenes which has been shown by our group are carried out by a stoichiometric reaction of organometallic complexes. The reaction of arylpalladium(II) halide with 2,3- dibromothiophene in the pr

Full text of DOI:10.1246/bcsj.82.555

© 2009 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 82, No. 5, 555–562 (2009)
555
BCSJ Award Article
Electrophilic Substitution of Thiophenes with Arylpalladium(II)
and Platinum(II) Complexes: Mechanistic Studies on
Palladium-Catalyzed CH Arylation of Thiophenes
Atsushi Sugie,1 Hirotoshi Furukawa,1 Yuji Suzaki,2 Kohtaro Osakada,2
Munetaka Akita,2 Daiki Monguchi,1 and Atsunori Mori*1
1Department of Chemical Science and Engineering, Kobe University, Rokkodai, Nada, Kobe 657-8501
2Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Yokohama 226-8503
Received December 8, 2008; E-mail: amori@kobe-u.ac.jp
Mechanistic studies on palladium-catalyzed CH arylation of thiophenes which has been shown by our group are
carried out by a stoichiometric reaction of organometallic complexes. The reaction of arylpalladium(II) halide with 2,3-
dibromothiophene in the presence of AgNO3/KF as an activator induces electrophilic substitution at the CH bond of the
thiophene to give CH arylated product. The similar reaction of arylplatinum(II) halide with thiophene derivatives affords
the aryl(thienyl)platinum(II) complex which is an analog of a precursor of the product of the CH arylation reaction. These
results suggest that the palladium-catalyzed CH arylation reaction of thiophenes proceeds through electrophilic
substitution.
Transition-metal-catalyzed CH functionalization1,2 attracts
considerable attention as an alternative and more straightfor-
ward pathway to form a carbon-carbon bond compared to
transition-metal-catalyzed coupling of aryl halides with orga-
nometallic reagents.3 In particular, CH substitution reactions of
heteroaromatic compounds increase their significance since
compounds bearing a heteroaromatic moiety are promising for
advanced materials such as organic thin film transistors (TFTs)
and light-emitting devices.4 In order to develop further
practical and efficient catalytic CH substitution reactions,
mechanistic understanding of the reaction is very important.
We have shown that CH arylation of 2-bromothiophene (1a)
with aryl iodide takes place in the presence of a palladium
catalyst and AgF or AgNO3/KF to give aryl(bromo)thiophene.5
It is noteworthy that the catalytic reaction of bromothiophene
proceeds smoothly with the carbon-bromine bond remaining
intact (eq 1).
aryl-PdII-I with 1a gives aryl(thienyl)palladium(II) complex
through electrophilic substitution at the CH bond. (iii)
Reductive elimination of aryl(bromo)thiophene from aryl-
(thienyl)palladium(II) complex takes place accompanied by
the regeneration of palladium(0). Step (i) is well known to
occur with a variety of palladium(0) complexes and aryl
halides and reductive elimination of Aryl1-Aryl2 is also known
(A)
Pd0
I
Aryl
Br
Aryl
S
(iii)
(i)
Aryl
Pd
(ii)
I
Pd Aryl
Br
S
1a
AgF
AgI
HF
Pd cat.
AgF or AgNO3/KF
(B)
+
I
Aryl
Br
DMSO
100 °C
S
PdI
H
Br
Aryl
Br
1a
Aryl
S
S
ð1Þ
Aryl
Br
S
Scheme 1. Plausible reaction mechanisms of palladium-
catalyzed CH arylation of bromothiophene. (A) Electro-
philic substitution followed by reductive elimination and
(B) Mizoroki-Heck type reaction mechanism.
A plausible reaction mechanism for the CH arylation
reaction is shown in Scheme 1A:1d,5 (i) The reaction of
Pd0 with aryl iodide forms aryl-PdII-I. (ii) The reaction of
Published on the web May 13, 2009; doi:10.1246/bcsj.82.555

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Bull. Chem. Soc. Jpn. Vol. 82, No. 5 (2009) BCSJ AWARD ARTICLE
Table 1. The Reaction of Aryl(bpy)halopalladium(II) with 2,3-Dibromothiophene (1b)a)
Br
Br
Br
Br
N
N
Aryl
X
Additive
Pd
+
Aryl
S
S
DMSO
Temp., 5 h
1b
2a: Aryl = -C6H3-Me2-3,5, X = I;
2b: Aryl = -C6H4-COOEt-4, X = I;
2c: Aryl = -C6H3-(CF3)2-3,5, X = I;
3a: Aryl = -C6H3-Me2-3,5, X = Br;
4a: Aryl = -C6H3-Me2-3,5, X = Cl;
5ab: Aryl = -C6H3-Me2-3,5
5bb: Aryl = -C6H4-COOEt-4
5bc: Aryl = -C6H3-(CF3)2-3,5
Product
(yield/%)
Recovered Pd
complex/%
Pd complex
Temp/°C
Additive
2a
2a
2a
2a
2a
2b
2c
3a
4a
50
50
50
50
rt
rt
rt
rt
rt
AgNO3/KF
None
KF
AgNO3
AgNO3/KF
AgNO3/KF
AgNO3/KF
AgNO3/KF
AgNO3/KF
5ab (71)
5ab (0)
5ab (0)
®
51
58
®
®
®
®
®
®
5ab (0)
5ab (67)
5bb (66)
5cb (64)
5ab (55)
5ab (52)
a) The reaction was carried out with aryl(bpy)halopalladium(II) (0.05 mmol) and 2,3-
dibromothiophene (1b) (0.12 mmol) in the presence of additive (0.2 mmol) in DMSO for 5 h.
to proceed from Aryl1-Pd-Aryl2 (iii).6 On the other hand, the
step reaction (ii) has not been well studied and details of this
reaction have not yet been clear. The other plausible mecha-
nism is shown in Scheme 1B which involves insertion of a
C=C bond of thiophene into the Pd-Aryl bond and successive
¢-hydrogen elimination (Mizoroki-Heck type reaction).7 We
have confirmed the formation of AgI through powder XRD
analysis of the silver residue after the catalytic reaction.5a
However, neither isolation nor detection of the important
intermediate aryl(thienyl)palladium(II) complex, which would
be strong evidence to support the mechanism, has been
achieved yet. The reaction mechanism of the palladium-
catalyzed CH arylation would be clear if aryl(thienyl)palla-
dium(II) complex is detected and characterized.
under several conditions with aryl(bpy)halopalladium(II) 2a-
2c, 3a, or 4a and 2.4 equivalents of 2,3-dibromothiophene (1b)
in DMSO for 5 h.5b The results are summarized in Table 1.
Treatment of palladium complex 2a and 1b with AgNO3/KF
at 50 °C afforded the corresponding coupling product 5ab in
71% yield, while the reaction in the absence of AgNO3 and KF
did not proceed but led to recovered complex 2a in 51% yield.
In addition, recovery of complex 2a was observed in 58% yield
in the presence of KF and in the absence of AgNO3. Although
consumption of complex 2a was observed, the reaction with
AgNO3 (in the absence of KF) afforded no coupling product,
but gave unidentified compounds bearing neither thienyl-
palladium nor thienyl-aryl bonds. It is noteworthy that the
reaction proceeded at room temperature although the catalytic
CH arylation of thiophene required 50-100 °C. The reaction
with other aryl(iodo)palladium(II) complexes like (bpy)(4-
ethoxycarbonylphenyl)iodopalladium(II) (2b) and [3,5-bis(tri-
fluoromethyl)phenyl](bpy)iodopalladium(II) (2c) with 1b in the
presence of AgNO3/KF similarly proceeded to give 5bb and
5cb, respectively. When arylpalladium(II) bromide 3a was
treated with 1b and AgNO3/KF at room temperature for 5 h,
arylthiophene 5ab was also obtained in 55% yield. The
reaction of arylpalladium(II) chloride 4a also proceeded to
afford 5ab in 52% yield.
Since the catalytic CH arylation is considered to proceed
through an aryl-PdII-I complex, the reaction of palladium
complexes 2a-2c with 1b should be a part of the catalytic
cycle, which is a class of electrophilic substitution of 1b with
aryl-PdII-I leading to the aryl(thienyl)palladium complex.
However, aryl(thienyl)palladium(II) was not obtained by the
reaction of 2a and 1b at room temperature. Because reductive
elimination of biaryl from diarylpalladium(II) complexes is
known to occur smoothly under mild conditions, the aryl-
(thienyl)palladium complex once formed would be immedi-
Herein, we report studies on a stoichiometric reaction of
palladium and platinum complexes with thiophene derivatives
for the purpose of obtaining intermediate metal complexes of a
step reaction of catalytic CH arylation.8
Results and Discussion
We synthesized aryl(bpy)iodopalladium(II) (bpy = 2,2¤-
bipyridine) 2a-2c by oxidative addition of aryl iodide to
bis(dibenzylideneacetone)palladium(0) in the presence of bi-
dentate nitrogen donor ligand in a manner reported previously.9
Aryl(bpy)bromopalladium(II) 3a (Aryl = -C6H3-Me2-3,5) and
aryl(bpy)chloropalladium(II) 4a (aryl = -C6H3-Me2-3,5) were
also prepared by the reaction of 2a (aryl = -C6H3-Me2-3,5)
with AgNO3 and aqueous solution of KBr or NaCl according to
the literature.10 Since aryl(halo)palladium(II) complexes were
in hand, a stoichiometric reaction of aryl(halo)palladium(II)
complex with thiophene derivatives in the presence of AgNO3/
KF was carried out. As the substrate, 2,3-dibromothiophene
(1b), which resulted in the highest yield in the catalytic CH
arylation reaction, was employed. The reaction was performed

A. Sugie et al.
Bull. Chem. Soc. Jpn. Vol. 82, No. 5 (2009)
557
meta
para
ortho
Br
N
N
N
AgNO3/KF
+
Pt
Br
Pt
S
DMSO
50 °C, 5 h
S
N
Br
I
Ha
7db (91%)
Br
6d
1b
Ha
meta
bipyridyl
ortho
para
J(PtH)
= 52 Hz
J(PtH)
= 55 Hz
Figure 1. Synthesis of platinum(II) complex 7db and its 1H NMR spectrum of platinum(II) complex 7db (300 MHz, DMSO-d6, rt).
ately converted to the product 5ab through reductive elimi-
nation.11 Though the palladium complex was switched to that
bearing an electron-withdrawing group 2b (Aryl = -C6H4-
COOEt-4) or 2c (Aryl = -C6H3-(CF3)2-3,5) and the reaction
temperature was controlled at room temperature in order to
retard reductive elimination, neither isolation nor detection of
the complex was successful. Accordingly, the results suggest
that reductive elimination is inevitable in the electrophilic
substitution of 2,3-dibromothiophene (1b). The results also
indicate that the AgNO3/KF system serves as an effective
activator in electrophilic substitution of aryl-PdII-I, where both
AgNO3 and KF are necessary for the reaction to take place.
Although the role of the AgNO3/KF system as an activator has
not been clear yet, strong affinity between silver and halogen
atoms as well as the effect of fluoride ion would be a key for
the reaction. Although the available aryl halide in the catalytic
CH arylation reaction of thiophene has been limited to the
iodide,5 bromo and chloro palladium complex 3a and 4a
underwent the CH substitution reaction. These findings suggest
that the catalytic CH arylation of a thiophene derivative with an
aryl bromide or chloride would be possible under appropriate
conditions that allow oxidative addition of the aryl halide to
Pd0. Further development of the catalytic CH arylation by the
design of highly active catalysts will be studied in due course.
Since aryl(thienyl)palladium(II) complex was not detected in
the stoichiometric reaction with thiophene derivatives, we
envisaged to synthesize its platinum analog, which would be
more stable toward reductive elimination. The reaction of
(bpy)(iodo)phenylplatinum(II) (6d)12 with 2,3-dibromothio-
phene (1b) was first examined with AgNO3/KF as an activator
under conditions similar to those carried out in the reaction of
the corresponding palladium complex and found to afford
(bpy)(phenyl)thienylplatinum(II) 7db in 91% yield (Figure 1).
The 1H NMR spectrum of 7db showed a doublet signal at
7.28 ppm corresponding to 2H of the ortho-phenyl signal,
which accompanied the coupling by 195Pt nuclei (3J(PtH) =
52 Hz) indicating the existence of a Pt-C(phenyl) bond.12 In
addition, a singlet signal at 6.57 ppm, which corresponds to the
¢-proton of the thiophene ring, was observed along with the
satellite of 195Pt (3J(PtH) = 55 Hz). These results suggest that
7db possesses both Pt-C(phenyl) and Pt-C(thienyl) bonds.
Worthy of note is that this is a new class of reactivity
in platinum(II) complexes13 to construct a Pt-C · bond by
intermolecular electrophilic substitution with a heteroaromatic
compound in the presence of AgNO3/KF without participation
of proximal chelation by a heteroatom.14 It should also be
pointed out that the platinum-carbon bond formation occurred
smoothly at the CH bond when the thiophene derivative had a
carbon-bromine bond. This kind of aryl(thienyl)platinum(II)
complex bearing a carbon-bromine bond on the thiophene ring
has hardly been synthesized by other synthetic pathways, to the
best of our knowledge, such as nucleophilic substitution on the
platinum metal with a thienyl metallic reagent.15
As summarized in Table 2, the reaction with several plati-
num complexes and a variety of thiophene derivatives was
examined. A platinum complex bearing a phenyl or 4-methyl-
phenyl group was employed for the reaction with thiophenes.
The iodo(phenyl)platinum(II) complex 6d reacted with 2,3-
dibromothiophene (1b) even at room temperature to afford the
corresponding aryl(thienyl)platinum complex 7db in a slightly
inferior yield (86%). In addition to 1b, 2-bromo-3-hexylthio-
phene (1c) also afforded the aryl(thienyl)platinum complex 7dc

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Bull. Chem. Soc. Jpn. Vol. 82, No. 5 (2009) BCSJ AWARD ARTICLE
Table 2. The Reaction of [PtX(Aryl)(bpy)] 6d and 6e with Thiophene Derivativesa)
Aryl
S
N
N
Aryl
X
N
N
AgNO3/KF
R2
R1
Pt
Pt
+
1a-1f
DMSO
Temp., 5 h
7db: Aryl = -C6H5, R1 = R2 = Br;
6d: Aryl = -C6H5, X = I;
6e: Aryl = -C6H4-Me-4, X = Cl
7dc: Aryl = -C6H5, R1 = Br, R2 = -nC6H13
7eb: Aryl = -C6H4-Me-4, R1 = R2 = Br;
;
7ea: Aryl = -C6H4-Me-4, R1 = Br, R2 = H;
7ed: Aryl = -C6H4-Me-4, R1 = CHO, R2 = H;
7ee: Aryl = -C6H4-Me-4, R1 = COOEt, R2 = H;
7ef: Aryl = -C6H4-Me-4, R1, R2 = -CH=CH-CH=CH-
Pt complex
Thiophene
Br
Temp/°C
Product
Yield/%
6d
Br
rt
7db
86
S
1b
nC6H13
6d
50
7dc
87
Br
S
1c
6e
6e
1b
50
50
7eb
7ea
74
65
Br
1a
S
CHO
1d
6e
6e
50
50
7ed
7ee
73
74
S
COOEt
1e
S
6e
50
7ef
78
S
1f
a) The reaction was carried out with [PtX(Aryl)(bpy)] (0.05 mmol) and thiophene derivative
(0.12 mmol) for 5 h in the presence of AgNO3 (0.2 mmol) and KF (0.2 mmol) in DMSO.
in 87% yield after stirring at 50 °C for 5 h. The reaction of
(bpy)chloro(4-methylphenyl)platinum(II) (6e) with thiophene
derivative was also found to proceed. The corresponding
platinum complexes were obtained by the reaction with several
thiophene derivatives bearing a bromo group at the 2-position
(1a and 1b) and an electron-withdrawing group (1d and 1e).
The corresponding complexes 7ea-7ee were obtained in good
to excellent yields. Benzothiophene (1f) also underwent the
reaction with platinum complex 6e to afford 7ef in 78% yield.
Aryl(thienyl)platinum(II) complex 7ee was isolated as a
single crystal and characterized by X-ray crystallography.
Figure 2 depicts the molecular structure of 7ee with a square-
planar coordination around the Pt center. The thienyl ligand
bonds to the platinum center through its ¡-carbon (Pt(1)-
C(1) = 1.989(6) ¡).
C(10)
C(16)
C(14)
C(9)
C(8)
C(15)
C(17)
C(11)
C(18)
C(19)
C(20)
C(21)
C(12)
Pt(1)
N(1)
N(2)
C(13)
C(2)
C(3)
C(1)
C(22)
C(4)
C(14)
S(1)
O(2)
C(14)
C(7)
C(5)
O(1)
C(6)
Figure 2. ORTEP drawing of 7ee (50% probability).
Hydrogen atoms were omitted for clarity.

A. Sugie et al.
Bull. Chem. Soc. Jpn. Vol. 82, No. 5 (2009)
559
Table 3. Reaction of [PtX2(bpy)] with Thiophene Derivativesa)
R2
R1
N
N
N
X
X
AgNO3/KF
S
+
1a, 1b, 1d, 1g
R2
Pt
Pt
DMSO,
Temp., 5 h
N
S
R1
8a: R1 = Br, R2 = H;
8b: R1 = Br, R2 = Br;
8d: R1 = CHO, R2 = H;
8g: R1 = Br, R2 = Me;
Pt complex
Thiophene
Temp/°C
Product
Yield/%
Br
Br
S
[PtI2(bpy)]
50
50
50
8b
8b
8g
70
65
79
1b
1b
Me
[PtCl2(bpy)]
[PtI2(bpy)]b)
Br
S
1g
1g
[PtI2(bpy)]b)
rt
8g
8a
10
53
Br
S
[PtCl2(bpy)]
50
1a
CHO
S
[PtCl2(bpy)]
50
8d
69
1d
a) Unless noted, the reaction was carried out with [PtX2(bpy)] (0.1 mmol) and thiophene derivative
(0.3 mmol) for 5 h in the presence of AgNO3 (0.5 mmol) and KF (0.5 mmol) in DMSO. b) The reaction
was carried out with [PtI2(bpy)] (0.05 mmol), 1g (0.24 mmol), AgNO3 (0.4 mmol), and KF (0.4 mmol).
The reductive elimination of the arylthiophene 5db from the
obtained aryl(thienyl)platinum(II) complex 7db was envisaged.
Among several conditions to induce the reductive elimination
step, no reaction was found to proceed by heating the complex
7db at 100 °C for 17 h in DMSO-d6. This finding suggests the
high stability of the platinum complex bearing a thienyl ligand
toward reductive elimination compared with other related
diorganoplatinum(II) complexes.16 Because complex 7db
showed high thermal stability, heating of 7db with an additive
was carried out to accelerate reductive elimination of 5db
according to the literature.17 When a toluene solution of 7ea
and PPh3 was heated at 95 °C for 1.5 h, corresponding
arylthiophene 5ea, which was considered to be generated by
reductive elimination, was obtained in 60% yield (eq 2). By
contrast, reductive elimination of 5db was not observed by
heating the complex 7db with diethyl fumarate18 or with
silver(I) triflate.15a
to the case of the reaction of aryl(halo)platinum(II) complexes
6d and 6e, the reaction of [PtX2(bpy)] (X = Cl and I) with 2,3-
dibromothiophene (1b) in the presence of AgNO3 and KF in
DMSO at 50 °C afforded dithienylplatinum(II) complex 8b in
70% yield (X = I) and 65% yield (X = Cl), respectively.
Though the reaction of [PtI2(bpy)] with 2-bromo-3-methyl-
thiophene (1g) at 50 °C afforded dithienylplatinum(II) complex
8g in 79% yield, the reaction at room temperature gave 8g in
only 10% yield. This result was found to be in contrast to the
reaction of aryl(halo)platinum(II) complexes 6d and 6e. The
corresponding dithienylplatinum(II) complex was also obtained
by the reaction with 2-bromothiophene (1a) and 2-formyl-
thiophene (1d). The dithienylplatinum(II) complex is consid-
ered to be a platinum analog for the proposed intermediate of
the homocoupling reaction catalyzed by palladium,19 which is
also suggested to proceed via electrophilic substitution of the
dihalo complex with two equivalents of thiophene.
PPh3
Conclusion
ð2Þ
Br
Me
7ea
toluene,
95 °C, 1.5 h
S
The reactions using stoichiometric amounts of palladium and
platinum complexes were carried out to study the mechanism
of catalytic CH arylation of thiophenes. When arylpalla-
dium(II) halides 2a-2c were treated with 2,3-dibromothiophene
(1b), silver(I) nitrate, and potassium fluoride, the corresponding
5ea (60%)
The reaction of [PtX2(bpy)] (X = Cl and I)12 was also found
to proceed with thiophene through double electrophilic
substitution.2 The results are summarized in Table 3. Similar

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Bull. Chem. Soc. Jpn. Vol. 82, No. 5 (2009) BCSJ AWARD ARTICLE
to leave a crude solid, which was purified by recrystallization to
afford 30.5 mg of 7db as a yellow solid (91%). 1H NMR (300
MHz, DMSO-d6): ¤ 6.57 (s, 1H), 6.82 (m, 1H), 6.94 (m, 2H), 7.28
(m, 2H), 7.66 (ddd, J = 10.1, 7.5, 1.3 Hz, 1H), 7.79 (ddd, J = 10.1,
7.5, 1.6 Hz, 1H), 8.13 (dd, J = 7.5, 1.3 Hz, 1H), 8.30 (ddd, J =
10.4, 10.4, 2.0 Hz, 1H), 8.35 (ddd, J = 10.4, 10.4, 2.3 Hz, 1H),
8.42 (dd, J = 7.5, 1.6 Hz, 1H), 8.65 (d, J = 8.1 Hz, 2H). Anal.
Calcd for C20H14Br2N2PtS: C, 35.89; H, 2.11; N, 4.19; S, 4.79%.
Found: C, 36.12; H, 2.19; N, 4.07; S, 4.67%.
arylthiophene, the product of CH arylation was obtained while
aryl(thienyl)palladium(II) complex was not detected at all. On
the other hand, aryl(thienyl)platinum(II) complex was synthe-
sized by the similar reaction using arylplatinum(II) halides 6d
and 6e. These findings strongly suggest that CH arylation of
thiophenes with aryl iodide occurs by electrophilic substitution
of the palladium complex promoted by the activating agent
AgNO3/KF. Based on the results of the reaction using
arylpalladium bromide 3a and chloride 4a, aryl bromide and
chloride may be applicable to the CH arylation of thiophene
derivatives when appropriate reaction conditions are applied.
(2,2¤-Bipyridine)[2-(5-bromo-4-hexylthienyl)]phenylplati-
num(II) (7dc):
1H NMR (300 MHz, DMSO-d6): ¤ 0.84 (t,
J = 6.9 Hz, 3H), 1.27 (m, 6H), 1.51 (m, 2H), 2.41 (t, J = 7.8 Hz,
3H), 6.48 (s, 1H), 6.80 (m, 1H), 6.92 (m, 2H), 7.29 (m, 2H), 7.65
(ddd, J = 6.6, 6.5, 0.9 Hz, 1H), 7.73 (ddd, J = 6.6, 6.2, 1.2 Hz,
1H), 8.16 (dd, J = 5.1, 0.9 Hz, 1H), 8.32 (m, 2H), 8.42 (dd,
J = 5.7, 0.9 Hz, 1H), 8.64 (d, J = 8.4 Hz, 2H); Anal. Calcd for
C26H27BrN2PtS: C, 46.29; H, 4.03; N, 4.15; S, 4.75%. Found: C,
45.80; H, 3.83; N, 4.20; S, 4.63%.
(2,2¤-Bipyridine)[2-(5-bromothienyl)](4-methylphenyl)plati-
num(II) (7ea): 1H NMR (500 MHz, DMSO-d6): ¤ 2.17 (s, 3H),
6.51 (d, J = 3.4 Hz, 1H), 6.75 (d, J = 7.5 Hz, 2H), 6.91 (d, J =
3.5 Hz, 1H), 7.16 (d, J = 7.9 Hz, 2H), 7.66 (ddd, J = 5.6, 5.7,
1.1 Hz, 1H), 7.74 (ddd, J = 5.5, 5.5, 1.0 Hz, 1H), 8.23 (dd, J = 5.6,
1.0 Hz, 1H), 8.29-8.34 (m, 2H), 8.44 (dd, J = 5.3, 0.9 Hz, 1H),
8.63 (d, J = 8.1 Hz, 2H); IR(KBr): 3040, 1691, 1602, 1468, 1445,
801, 758, 727 cm¹1; Anal. Calcd for C21H17BrN2PtS: C, 41.73; H,
2.83; N, 4.63; S, 5.31; Br, 13.22%. Found: C, 41.53; H, 3.03; N,
4.52; S, 5.01; Br, 12.95%.
Experimental
General.
Melting points were uncorrected. 1H NMR
(300 MHz, 500 MHz), 13C NMR (75.5 MHz, 125 MHz) spectra
were measured with a Varian Mercury 300 or Bruker Avance 500
spectrometer. Unless specified, measurements of the spectra were
carried out with CDCl3 as a solvent. The chemical shifts were
1
expressed in ppm using CHCl3 (7.26 ppm for H) or DMSO-d6
(2.49 ppm for 1H) or CDCl3 (77.0 ppm for 13C) as an internal
standard. IR spectra were recorded on Shimadzu FTIR-8100A.
Elemental analysis was carried out with a LECO CHNS-932
CHNS or Yanaco MT-5 CHN autorecorder at the Center for
Advanced Materials Analysis, Technical Department, Tokyo
Institute of Technology. High-resolution mass spectra (HRMS,
EI, or FAB) were measured with JEOL MStation.
Materials. DMSO was purchased from Wako Pure Chemical
Industries, Co., Ltd. as an anhydrous grade and stored in a Schlenk
tube under nitrogen atmosphere. Other chemicals were purchased
and used as such. Preparation of palladium complex 2a-2c, 3a, and
4a and platinum complexes 6d and 6e and [PtX2(bpy)] (X = Cl
and I) were performed by methods shown in the literature.9,11-13
General Procedure for the Reaction of Aryl(2,2¤-bipyri-
dine)iodopalladium(II) with 2,3-Dibromothiophene (1b) in the
Presence of AgNO3/KF. To a solution of [PdI(C6H4-COOEt-4)-
(bpy)] (2b, 24.7 mg, 0.05 mmol) in 3 mL of DMSO was added 1b
(0.014 mL, 0.12 mmol) under a nitrogen atmosphere. Potassium
fluoride (11.6 mg, 0.2 mmol) and silver(I) nitrate (34 mg, 0.2
mmol) were then added. The resulting suspension was then stirred
at room temperature for 5 h. The mixture was passed through a
Celite pad, which was washed with dichloromethane repeatedly.
The filtrate was washed with water twice. The organic layer was
concentrated under reduced pressure to leave a crude oil.
Purification by column chromatography on silica gel afforded
12.9 mg of 5bb as light yellow solid (66%).
The reaction of 2a and 2c was carried out in a similar manner as
above. The yield of 5ab was estimated by 1H NMR analysis using
trichloroethene (6.46 ppm) as an internal standard on the basis of
the characteristic signal at 7.08 ppm derived from proton at the 4-
position of the thiophene ring, while that of 5cb was determined by
the proton signal of the 4-position of the phenyl ring (7.82 ppm).
General Procedure for the Reaction of Aryl(halo)platinum
Complexes 6d and 6e with a Thiophene Derivative. To a
mixture of [PtI(Ph)(bpy)] (6d, 27.8 mg, 0.05 mmol), 2,3-dibromo-
thiophene (1b, 0.013 mL, 0.12 mmol), and potassium fluoride
(11.6 mg, 0.2 mmol) was added AgNO3 (34.0 mg, 0.2 mmol) in one
portion under argon atmosphere. The resulting suspension was
stirred at 50 °C for 5 h. After cooling to room temperature, the
mixture was passed through a Celite pad, which was washed with
dichloromethane repeatedly. The filtrate was washed with water
twice. The organic layer was concentrated under reduced pressure
(2,2¤-Bipyridine)[2-(4,5-dibromothienyl)](4-methylphenyl)-
platinum(II) (7eb): 1H NMR (500 MHz, DMSO-d6): ¤ 2.17 (s,
3H), 6.55 (s, 1H), 6.77 (d, J = 7.6 Hz, 2H), 7.15 (d, J = 7.8 Hz,
2H), 7.67 (ddd, J = 5.6, 5.7, 1.2 Hz, 1H), 7.78 (ddd, J = 5.6, 5.6,
1.0 Hz, 1H), 8.19 (dd, J = 5.2, 1.2 Hz, 1H), 8.30-8.36 (m,
2H), 8.43 (dd, J = 5.4, 0.8 Hz, 1H), 8.65 (d, J = 8.2 Hz, 2H); IR
(KBr): 1483, 1467, 1445, 800, 759, 728 cm¹1; Anal. Calcd for
C21H16Br2N2PtS: C, 36.91; H, 2.36; N, 4.10; S, 4.69%. Found: C,
36.15; H, 2.40; N, 3.96; S, 4.83%.
(2,2¤-Bipyridine)[2-(5-formylthienyl)](4-methylphenyl)plati-
num(II) (7ed): 1H NMR (500 MHz, DMSO-d6): ¤ 2.16 (s, 3H),
6.76 (d, J = 7.7 Hz, 2H), 6.99 (d, J = 3.7 Hz, 1H), 7.18 (d, J =
7.8 Hz, 2H), 7.68-7.73 (m, 2H), 7.75 (d, J = 3.7 Hz, 1H), 8.20-
8.24 (m, 2H), 8.33-8.35 (m, 2H), 8.66 (d, J = 8.0 Hz, 2H), 9.52 (s,
1H); IR(KBr): 1640, 1602, 1397, 1372, 759 cm¹1; Anal. Calcd for
C22H18N2OPtS: C, 47.74; H, 3.28; N, 5.06; S, 5.79%. Found: C,
47.12; H, 3.29; N, 4.95; S, 5.51%.
(2,2¤-Bipyridine)[2-(5-ethoxycarbonylthienyl)](4-methylphen-
yl)platinum(II) (7ee): 1H NMR (500 MHz, DMSO-d6): ¤ 1.23 (t,
J = 7.0 Hz, 3H), 2.16 (s, 3H), 4.15 (q, J = 7.0 Hz, 2H), 6.75 (d,
J = 7.6 Hz, 2H), 6.83 (d, J = 3.6 Hz, 1H), 7.18 (d, J = 7.7 Hz,
2H), 7.61 (d, J = 3.6 Hz, 1H), 7.66-7.70 (m, 2H), 8.22 (dd, J =
5.5, 0.9 Hz, 1H), 8.27 (dd, J = 5.4, 0.9 Hz, 1H), 8.29-8.30 (m,
2H), 8.63 (d, J = 8.1 Hz, 2H); IR(KBr): 1640, 1602, 1397, 1372,
759 cm¹1; Anal. Calcd for C24H22N2O2PtS: C, 48.24; H, 3.71; N,
4.69; S, 5.37%. Found: C, 48.02; H, 3.95; N, 4.59; S, 4.95%.
(2,2¤-Bipyridine)(2-benzothienyl)(4-methylphenyl)platinum(II)
(7ef): 1H NMR (500 MHz, DMSO-d6): ¤ 2.14 (s, 3H), 6.73 (d,
J = 7.4 Hz, 2H), 6.93 (s, 1H), 6.96 (t, J = 7.3 Hz, 1H), 7.10 (t,
J = 7.3 Hz, 1H), 7.23 (d, J = 8.0 Hz, 1H), 7.53 (d, J = 7.9 Hz,
1H), 7.63-7.70 (m, 3H), 8.29-8.35 (m, 3H), 8.38 (dd, J = 5.5,
0.9 Hz, 1H), 8.63-8.66 (m, 2H).
The Reductive Elimination of Arylthiophene 5ea from
Aryl(thienyl)platinum Complex 7ea. To a Schlenk tube were

A. Sugie et al.
Bull. Chem. Soc. Jpn. Vol. 82, No. 5 (2009)
561
added aryl(thienyl)platinum complex 7ea (18.1 mg, 0.03 mmol),
triphenylphosphine (78.7 mg, 0.3 mmol) and toluene (4 mL). The
resulting solution was heated at 95 °C for 1.5 h. After cooling to
room temperature, the mixture was washed with water and brine.
The organic layer was concentrated under reduced pressure to leave
a crude solid, which was purified by column chromatography on
silica gel to afford 4.2 mg of 2-bromo-5-(4-methylphenyl)thiophene
(5ea) in 60% yield. Spectroscopic characteristics and physical
properties of the product were identical to the authentic sample.20
General Procedure for the Synthesis of Dithienylplati-
num(II) Complex. To a mixture of [PtI2(bpy)] (30.2 mg, 0.05
mmol), 2,3-dibromothiophene (1b, 0.027 mL, 0.24 mmol) and
potassium fluoride (23.2 mg, 0.4 mmol) in 3 mL of DMSO was
added AgNO3 (68.0 mg, 0.4 mmol) in one portion under argon
atmosphere. The resulting suspension was stirred at 50 °C for 5 h.
After cooling to room temperature, the mixture was passed through
a Celite pad, which was washed with dichloromethane repeatedly.
The filtrate was washed with water twice. The organic layer was
concentrated under reduced pressure to leave a crude solid, which
was purified by recrystallization from dichloromethane/hexane to
afford 27.8 mg of 8b as an orange solid (70%). 1H NMR (500
MHz, DMSO-d6): ¤ 6.60 (s, 2H), 7.81 (t, J = 6.7 Hz, 2H), 8.33 (d,
via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the
Cambridge Crystallographic Data Centre, 12, Union Road,
Cambridge, CB2 1EZ, U.K.; fax: +44 1223 336033; or deposit@
ccdc.cam.ac.uk).
This work was supported by a Grant-in-Aid for Scientific
Research on Priority Areas “Advanced Molecular Transforma-
tions of Carbon Resources” from the Ministry of Education,
Culture, Sports, Science and Technology, Japan.
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J = 4.6 Hz, 2H), 8.38 (ddd, J = 7.7, 7.8, 1.4 Hz, 2H), 8.68 (d, J =
¹1
8.2 Hz, 2H); IR(KBr): 1598, 1445, 1260, 979, 760, 417 cm
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Anal. Calcd for C18H10Br4N2PtS2: C, 25.95; H, 1.21; Br, 38.36; N,
3.36; S, 7.70%. Found: C, 25.74; H, 1.30; Br, 38.30; N, 3.33; S,
7.47%.
(2,2¤-Bipyridine){di[2-(5-bromothienyl)]}platinum(II) (8a):
1H NMR (500 MHz, DMSO-d6): ¤ 6.54 (d, J = 3.5 Hz, 2H), 6.98
(d, J = 3.4 Hz, 2H), 7.77 (ddd, J = 6.6, 6.7, 1.0 Hz, 2H), 8.34-8.37
(m, 4H), 8.67 (d, J = 7.9 Hz, 2H); IR(KBr): 1601, 1446, 1158,
969, 759, 614, 496, 418; HRMS(FAB) Found: 672.8463, Calcd for
C18H12Br2N2PtS2: 672.8456.
(2,2¤-Bipyridine){di[2-(5-formylthienyl)]}platinum(II) (8d):
1H NMR (500 MHz, DMSO-d6): ¤ 7.04 (d, J = 3.8 Hz, 2H), 7.75
(ddd, J = 6.5, 7.0, 0.6 Hz, 2H), 7.82 (d, J = 3.7 Hz, 2H), 8.16 (dd,
J = 4.5, 1.0 Hz, 2H), 8.38 (ddd, J = 8.0, 8.0, 1.0 Hz, 2H), 8.71 (d,
J = 8.5 Hz, 2H), 9.57 (s, 2H); IR(KBr): 1629, 1508, 1445, 1396,
1367, 1272, 1226, 1049, 816, 760, 740, 658, HRMS(FAB) Found:
574.0290, Calcd for C20H15N2O2PtS2 (M + 1): 574.0224.
(2,2¤-Bipyridine){di[2-(5-bromo-4-methylthienyl)]}platinum(II)
(8g): 1H NMR (500 MHz, DMSO-d6): ¤ 2.06 (s, 6H), 6.45 (s,
2H), 7.77 (m, 2H), 8.34-8.39 (m, 4H), 8.65 (d, J = 8.1 Hz, 2H);
Anal. Calcd for C20H16Br2N2PtS2: C, 34.15; H, 2.29; N, 3.98; S,
9.12%. Found: C, 33.54; H, 2.43; N, 4.06; S, 9.08%; HRMS (FAB)
Found: 703.8738, Calcd for C20H1679Br81BrN2S2196Pt: 703.8743.
Crystal Structure Analysis of 7ee. Single crystals of 7ee,
suitable for X-ray diffraction study were obtained by recrystalliza-
tion from CH2Cl2/hexane. Data for 7ee were collected on a Rigaku
Saturn CCD diffractometer equipped with monochromated Mo K¡
radiation (- = 0.71073 ¡). Calculations were carried out using the
program package Crystal Structure, version 3.7, for Windows. A
full-matrix least-squares refinement was used for the non-hydrogen
atoms with anisotropic thermal parameters. 7ee: C24H22N2O2PtS,
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