Preparation of platinum complexes containing a thioamide-based SCS pincer ligand and their light emitting properties

Article abstract of DOI:10.1016/j.jorganchem.2004.03.003

Reaction of 1,3-bis(1-pyrrolidinothiocarbonyl)benzene with PtCl₂(PhCN)₂ afforded a platinum complex with η³-S,C,S type coordination. The molecular structure of the SCS-pincer platinum(II) complex was determined by X-ray an

Full text of DOI:10.1016/j.jorganchem.2004.03.003

Journal of Organometallic Chemistry 689 (2004) 1860–1864
www.elsevier.com/locate/jorganchem
Preparation of platinum complexes containing a thioamide-based
SCS pincer ligand and their light emitting properties
a,
a
a,
b
Takaki Kanbara *, Keisuke Okada , Takakazu Yamamoto *, Hiromitsu Ogawa ,
b
Tetsuji Inoue
a
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
b
TDK Corporation, Technical Center, 2-15-7 Higashi-Ohwada, Ichikawa-shi, Chiba 272-8558, Japan
Received 1 December 2003; accepted 2 March 2004
Abstract
Reaction of 1,3-bis(1-pyrrolidinothiocarbonyl)benzene with PtCl2(PhCN)2 afforded a platinum complex with g3-S,C,S type
coordination. The molecular structure of the SCS-pincer platinum(II) complex was determined by X-ray analysis. Substitution of
chloro ligand with anionic ligands such as iodo and acetylide was carried out. The complexes exhibit strong emission in a glassy
frozen state as well as in the solid state. Light-emitting diodes based on the complexes displayed red electroluminescence.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Thioamide; Pincer ligand; Platinum; Luminescence; Light-emitting diode
1. Introduction
gands comparable to the 1,3-bis[(thioether)meth-
yl]benzene and its derivatives, which have been recently
investigated for a number of catalytic reactions exten-
sively [1,3]. Nonoyama and coworkers [2] have inves-
tigated cyclopalladation of a series of thioamide-based
aromatic ligands, and ortho ortho-cyclopalladation of
1,3-bis(thiocarbamoyl)benzenes has also been reported.
On the other hand, tridentate cyclometalated plati-
num(II) complexes have also attracted considerable
attention in recent years, mainly because of their in-
teresting photoluminescence properties and their utili-
zation [4]. We thus have prepared a thioamide-based
new pincer platinum(II) complex with 1,3-bis(1-pyrro-
lidinothiocarbonyl)benzene (Hbptb). The molecular
structure, substitution reactions, photoluminescence
properties of the complexes, and its preliminary
application in light-emitting diodes (LEDs) are also
reported.
Recently, pincer ligands play an increasing role in
coordination chemistry and catalysis [1]. One of their
advantages comes from the possibility to finely tune the
reactivity of the metal center by adjusting the electronic
properties of the different pincer ligands. For example,
NCN-pincer ligand (NCN ¼ [2,6-(CH2NMe2)2C6H3]ꢀ)
stabilizes unusual oxidation states of the metals such as
Ni(III) intermediate in the Kharasch addition. These
have led to the continuous interest that has been de-
voted to the synthesis of pincer ligands with various
mixed systems incorporating different heteroatoms such
as O, S, N, and P. However, much less attention has
been paid to SCS-pincer ligands constituted of thio-
amide group (e.g. 1,3-bis(thiocarbamoyl)benzene) and
their cyclometalated transition–metal complexes [2].
The thioamide-based SCS-pincer ligands also consist of
mixed donor sets (g3-S,C,S coordination mode), and
the thioamide group could exist as zwitterionic form.
Therefore, they could be prospective anionic pincer li-
4
3
2
5
6
S
S
N
N
+
PtCl2(PhCN)2
1
- HCl,
- 2 PhCN
N
N
S
Pt
S
Cl
Hbptb
1
* Corresponding authors. Tel.: +81459245222; fax: +81459245276.
E-mail address: tkanbara@res.titech.ac.jp (T. Kanbara).
ð1Þ
0022-328X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.03.003

T. Kanbara et al. / Journal of Organometallic Chemistry 689 (2004) 1860–1864
1861
2. Results and discussion
the range observed for the pincer Pt complexes [1a,1b,4,5].
The C@S bond lengths are longer than those of free
Hbptb, whereas the C–N bond lengths of thioamide
group are not significantly altered upon coordination of
the thioamide groups. The C@S and C–N bond lengths lie
in the range of lengths found in [PdCl(bptb)] [2b].
The SCS-pincer platinum complex (PtCl(bptb), 1) was
obtained in moderate yield (67%) from the reaction of
Hbptb and an equimolar amount of dichlorobis(benzo-
nitrile)platinum(II) (PtCl2(PhCN)2). Complex 1 is fairly
stable to air and water. In the IR spectrum of 1, a higher
frequency shift of m(C–N) for the thioamide group (1503
cmꢀ1) is observed (1481 cmꢀ1 for Hbptb), indicating the
S-coordination of the thioamide group and an increase in
double bond character of the C–N bond in the coordi-
nation form. In the 1H NMR spectrum of 1, the ratios of
peaks area of the aromatic proton signals are reduced by
1H and the methylene signals assignable to the pyrroli-
dino group is deshielded on complexation. In the 13C-
spectrum of 1, the ortho ortho-platinated carbon (C(1)) is
deshielded by 37 ppm (d 128.3 for Hbptb). 195Pt NMR
spectrum of 1 shows a signal at d )5281.
Reaction of 1 with phenylacetylene in the presence of
CuI and triethylamine easily led to a transmetalation to
form a phenylacetylide complex (Pt(CBCPh)(bptb), 2)
in good yield. Treatment of 1 and 2 with an excess of
1
CH3I gave iodo complex (PtI(bptb), 3), respectively. H
NMR spectra of 1 and 2 after the reaction with an ex-
cess of CH3I showed the signals assigned to 3 and
chloromethane (for the reaction of 1), and 1-phenyl-1-
propyne (for the reaction of 2). Several arenium–plati-
num complexes have been prepared and isolated from
reactions of the pincer-type platinum complexes with
CH3I, which would be formed via SN2-type nucleophilic
substitution of the halide by the metal nucleophile fol-
lowed by a 1,2-methyl migration between Pt and the
ortho,ortho-platinated carbon of the aryl ligand
[1a,1c,5,6]. The iodo complex 3 was also obtained from
the reaction of 1 with AgBF4 and NaI.
The molecular structures of Hbptb and 1 were con-
firmed by X-ray crystallography (Fig. 1). Complex 1 has a
distorted square-planar geometry similar to [PdCl(bptb)]
[2b]. The Pt(1)–C(1) and Pt(1)–Cl(1) bond lengths lie in
CuI, Et3N
N
N
N
N
+
S
Pt
S
S
Pt
Cl
1
S
2
ð2Þ
ð3Þ
- MeX
N
N
N
N
+
MeI
S
Pt
I
S
S
Pt
S
X
1, X = Cl
2, X = ≡-Ph
3
The complexes 1 and 2 are not light-emissive in solu-
tion at room temperature, whereas strong photolumi-
nescence was observed in the glassy frozen state as well as
in the solid state. The iodo complex 3 is not light-emissive
in solution and in the solid state. The absorption spectral
data and emission data of the complexes 1 and 2 are
summarized in Table 1. The lifetime of the complexes in
the frozen state is about 10 ls, indicating phosphorescent
emission. Fig. 2 shows emission spectra of 1 and 2 in the
solid state and in the glassy frozen state. Not large dif-
ference in energy between the solid state and the glassy
emission suggests the same electronic origins of the
emitting states. Solid state d8–d8 and ligand–ligand in-
teractions of the photoluminescent cyclometalated plat-
inum(II) complexes have been investigated [4a–4d]. In
the present case, however, X-ray diffraction analysis of 1
confirms that the Ptꢁ ꢁ ꢁPt distance between adjacent
Fig. 1. X-ray crystal structure of Hbptb (a) and 1 (b) with thermal
ellipsoids drawn at the 50% probability level. One of the two crystal-
lographically independent molecules of 1 is shown. Hydrogen atoms
ꢀ
are omitted for clarity. Selected bond lengths (A) and angles (°): (a)
S(1)–C(7), 1.678(4); S(2)–C(12), 1.676(5); N(1)–C(7), 1.316(5); N(2)–
C(12), 1.319(5); S(1)–C(7)–C(2), 118.5(3); S(1)–C(7)–N(1), 122.4(3);
S(2)–C(12)–C(6), 119.6(3); S(2)–C(12)–N(2), 123.0(3). (b): Pt(1)–C(1),
1.945(7); Pt(1)–Cl(1), 2.388(2); Pt(1)–S(1), 2.265(3); Pt(1)–S(2),
2.255(2); S(1)–C(7), 1.716(8); S(2)–C(12), 1.721(7); N(1)–C(7), 1.31(1);
N(2)–C(12), 1.32(1); S(1)–Pt(1)–S(2), 172.56(7); Cl(1)–Pt(1)–C(1),
179.2(2); S(1)–C(7)–C(2), 116.5(6); S(1)–C(7)–N(1), 118.0(6); S(2)–
C(12)–C(6), 116.9(6); S(2)–C(12)–N(2), 116.5(5).

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T. Kanbara et al. / Journal of Organometallic Chemistry 689 (2004) 1860–1864
Table 1
Photophysical properties of 1 and 2
kmax (nm) (ꢀb, Mꢀ1 cmꢀ1
)
kem (nm)
kem (nm)
/
sf (ls)
a
c
d
e
f
1
2
255 (33 000), 345 (10 400), 440 (4500)
247 (32 000), 340 (10 300), 445 (1400)
630
640
595
600
0.11
0.24
11.0
8.3
a Absorption maxima in CH2Cl2 at room temperature.
b Molecular absorption coefficient.
c Emission maximum of a microcrystalline sample.
d Emission maximum in a mixture of CH2Cl2, ethanol, and methanol matrix at 77 K.
e Fluorescence quantum yield compared with that of fac-tris(2-phenylpyridine)iridium (/f ¼ 0:4 ꢂ 0:1) [9].
f Emission decay lifetime.
Fig. 2. Emission spectra of 1 (–––) and 2 (- - -): (a) microcrystalline
sample at room temperature, (b) in frozen CH2Cl2–MeOH–EtOH
matrix (77 K).
Fig. 3. Electroluminescence spectra of the LEDs for 1 (–––) and 2 (- - -)
(inset: multilayer configuration of LED).
8
8
180 cd mꢀ2 (0.20% efficiency) and 422 cd mꢀ2 (0.20%) at
100 mA cmꢀ2, respectively. In order to make practicable
LEDs, further optimization should be required.
ꢀ
complexes is 6.59 A, indicating there is no d –d inter-
action, while the intermolecular plane separation be-
ꢀ
tween the two ligand planes (about 7.2 A) would not
As described above, new platinum complexes having
the thioamide-based SCS-pincer ligand have been pre-
pared. The pincer complexes exhibit interesting photo-
luminescent properties and stability in air, making them
good prospects for use in optoelectronic devices and
sensors. Substitution of the chloro ligand of 1 with
various neutral and anionic ligands was possible. At-
tempts to tune their photoluminescent properties of the
platinum complexes and to prepare other transition-
metal complexes with the thioamide-based SCS-pincer
ligands are being undertaken.
allow overlap of the p orbitals. We tentatively assigned
that the emissive excited state of the complexes is related
to MLCT formed by intersystem crossing between sin-
3
glet and triplet states. A similar photoluminescent feature
was recently observed with a platinum complex con-
taining phosphine sulfide-based SCS pincer ligand [4e].
Based on the photoluminescence properties, pre-
liminary application of 1 and 2 as light-emitting mate-
rials in the LEDs has been examined. Fig. 3 shows
electroluminescence spectra of the LEDs (the LEDs
fabricated in the present study were illustrated in the
inset of Fig. 3). Red (1) or reddish orange (2) electro-
luminescence was observed. The electroluminescence
spectra of the LEDs essentially agreed with the photo-
luminescence spectra of the complexes, revealing that
the electroluminescence emission occurred at the com-
plexes. The sub-peak at about 430 nm was attributable
to the emission from poly(9-vinylcarbazole) matrix. The
present LEDs using 1 and 2 have emission intensities of
3. Experimental
3.1. General procedures
All solvents were dried and distilled prior to use.
PtCl2(PhCN)2 was prepared as described previously [7].

T. Kanbara et al. / Journal of Organometallic Chemistry 689 (2004) 1860–1864
1863
Hbptb was prepared by the Willgerodt–Kindler reaction
according to the literatures [2,8].
evaporated, and the crude product was washed with
CH3CN and died under vacuum to give 3 as a red solid
(12 mg, 65% yield).
IR and NMR spectra were recorded on a JASCO
FTIR-460Plus spectrometer, and JEOL JNM-EX-400
and La-500 NMR spectrometer, respectively. Elemental
analyses were carried out with a Yanaco CHN Corder
MT-5 and a Yanaco SX-Elements Micro Analyzer YS-
10. UV–Vis. absorption spectra and emission spectra
were recorded on a Shimadzu UV-3100PC spectropho-
tometer and a Hitachi F-4500 fluorescence spectropho-
tometer, respectively. Emission lifetime measurements
were performed with a Hamamatsu Photonics C4780
picosecond fluorescence lifetime measurement system.
3.4.2. Procedure B
1 (16 mg, 0.03 mmol) was suspended in acetone (5
ml), and AgBF4 (6 mg, 0.03 mmol) was added. After the
dissolution of the starting complex, water (1 ml) was
added. The precipitated silver chloride was filtered off.
The addition of NaI (15 mg, 0.1 mmol) and water (5 ml)
to the filtrate gave a red precipitate. The precipitate was
filtered and washed with water and methanol and dried
under vacuum to give 3 as a red solid (7 mg, 39% yield).
1H NMR (400 MHz, DMSO-d6): d 7.85 (d, 2H,
J ¼ 8:4 Hz), 7.24 (t, 1H, J ¼ 8:2 Hz), 4.29 (t-br, 4H),
3.97 (t-br, 4H), 2.08 (m-br, 8H). Anal. Found: C, 31.00;
H, 3.05; N, 4.91; I, 20.09; S, 9.34. Calc. for
C16H19N2IPtS2: C, 30.73; H, 3.06; N, 4.48; I, 20.29; S,
10.25%.
3.2. PtCl(bptb) (1)
An CH3CN solution (25 ml) of Hbptb (30 mg, 0.1
mmol) was added to a chloroform solution (5 ml) of
PtCl2(PhCN)2 (47 mg, 0.1 mmol), and the reaction
mixture was stirred at 65 °C for 15 h. The resulting
precipitate was filtered and washed with CH3CN and
dried in vacuo to give 1 as an orange solid (36 mg, 67%
yield).
1H NMR (400 MHz, DMSO-d6): d 7.76 (d, 2H,
J ¼ 8:3 Hz), 7.16 (t, 1H, J ¼ 7:9 Hz), 4.29 (t-br, 4H),
3.97 (t-br, 4H), 2.08 (m-br, 8H). 13C NMR (100 MHz,
DMSO-d6): d 198.2, 165.3 (1J(Pt) was not resolved),
143.0 (2J(Pt) ¼ 76.8 Hz), 129.8 (3J(Pt) ¼ 54.9 Hz), 119.1,
55.8, 54.8, 25.9, 22.9. 195Pt NMR (107 MHz, DMSO-d6,
referenced to H2PtCl6): d )5281. Anal. Found C, 35.53;
H, 3.83; N, 5.49; Cl, 6.74; S, 11.85. Calc. for
C16H19ClN2PtS2: C, 35.99; H, 3.59; N, 5.25; Cl, 6.64; S,
12.01%.
3.5. Crystal data for Hbptb and 1
The diffraction data were collected with a Rigaku
AFC5R diffractometer with graphite monochromated
ꢀ
Mo Ka (k ¼ 0:71070 A) at room temperature. The data
were corrected for Lorentz and polarization effects, and
an empirical absorption correction was applied. The
structure was solved by direct methods (SIR 92) or hea-
vy-atom Patterson methods, and expanded using Fourier
techniques. The non-hydrogen atoms were refined an-
isotropically. Hydrogen atoms were located by assuming
the ideal geometry and included in the structure calcu-
lation without further refinement of the parameters.
Hbptb: C16H20N2S2, M ¼ 304:47, orthorhombic,
space group P212121, a ¼ 12:012ð9Þ, b ¼ 17:707ð9Þ,
3.3. Pt(CBCPh)(bptb) (2)
c ¼ 7:492ð7Þ A, Z ¼ 4, Dcalc ¼ 1:269 g cmꢀ3, l(Mo
ꢀ
To a DMF solution (1 ml) of 1 (27 mg, 0.05 mmol)
was added phenylacetylene (92 mg, 0.9 mmol) and CuI
(4 mg, 0.02 mmol) and triethylamine (1 ml). The reac-
tion mixture was stirred at room temperature for 5 days.
The resulting precipitate was filtered and washed with
DMF and dried under vacuum to give 2 as an orange
solid (25 mg, 82% yield).
1H NMR (400 MHz, DMSO-d6): d 7.86 (d, 2H,
J ¼ 7:3 Hz), 7.16 (m, 5H), 7.06 (t, 1H, J ¼ 7:2 Hz), 4.32
(t-br, 4H), 4.03 (t-br, 4H), 2.09 (m-br, 8H). 195Pt NMR
(107 MHz, DMSO-d6, referenced to H2PtCl6): d )5521.
Anal. Found: C, 47.78; H, 4.63; N, 4.44; S, 9.83. Calc.
for C24H24N2PtS2: C, 48.07; H, 4.03; N, 4.67; S, 10.69%.
Ka) ¼ 3.26 cmꢀ1, T ¼ 296 K, F ð000Þ ¼ 648. A total of
2126 reflections were measured, 2103 unique. The final
cycle of full-matrix least squares refinement on F was
based on 1306 observed reflections (I > 2rðIÞ, 181
valuable parameters) with factors of R1 ¼ 0:037,
Rw ¼ 0:048, GOF ¼ 0.85.
1: C16H19ClN2PtS2, M ¼ 534:00, triclinic, space
ꢁ
group P1, a ¼ 12:327ð4Þ, b ¼ 12:559ð7Þ, c ¼ 12:085ð5Þ
ꢀ
A, a ¼ 101:81ð3Þ, b ¼ 105:45ð3Þ, c ¼ 102:30ð4Þ°, Z ¼ 4,
Dcalc ¼ 2:095 g cmꢀ3, l(Mo Ka) ¼ 86.57 cmꢀ1, T ¼ 296
K, F ð000Þ ¼ 1024. A total of 8128 reflections were
measured, 7771 unique. The final cycle of full-matrix
least squares refinement on F was based on 4983 ob-
served reflections (I > 3rðIÞ, 397 valuable parameters)
with factors of R1 ¼ 0:030, Rw ¼ 0:042, GOF ¼ 0.93.
3.4. PtI(bptb) (3)
3.4.1. Procedure A
3.6. Preparation and measurement of LEDs
To a CH2Cl2 solution (15 ml) of 1 (16 mg, 0.03 mmol)
was added an excess MeI (0.1 ml). The solution was
stirred at room temperature for 8 days. The solvent was
LEDs consisted of the ITO electrode, the hole
injection layer of poly[3,4-(ethylenedioxy)thiophene]-

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T. Kanbara et al. / Journal of Organometallic Chemistry 689 (2004) 1860–1864
poly(styrenesulfonic acid) (PEDOT-PSS), the emitting
layer, the electron transporting layer of 4,7-diphenyl-
1,10-phenanthroline (Bathophenanthroline, VPT), the
electron injection layer of LiF, and the Al electrode.
In all cases, the ITO anode was overcoated with
PEDOT-PSS (about 50 nm). Thin films of the emit-
ting materials (about 100 nm) were prepared by spin-
casting from a mixture of chloroform–toluene (1:2)
solution of a mixture of poly(9-vinylcarbazole), 2-(4-
biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole, and
the platinum complex (PVK-tert-BuPBD-1 or 2). The
thin layers of VPT (about 30 nm) and LiF (about 0.5
nm), and the Al cathode (about 150 nm) were prepared
by vacuum deposition. Electroluminescence spectra and
light-intensity characteristics of the LEDs were measured
by using a monochromator with photodiode-array and
luminance meter (light meter). All the measurements
were done under vacuum (about 10ꢀ1 Pa) or argon
atmosphere at room temperature.
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