New cycloplatinated complexes with 2-arylimidazolines: Synthesis, crystal structures and photophysical properties

Article abstract of DOI:10.1016/j.jorganchem.2007.01.033

The synthesis, crystal structures and photophysical properties of a series of cycloplatinated complexes are presented. The complexes have the general formula (C^∧N)Pt(O^∧O), where O^∧O is acetylacetonate and C^∧N re

Full text of DOI:10.1016/j.jorganchem.2007.01.033

Journal of Organometallic Chemistry 692 (2007) 2006–2013
www.elsevier.com/locate/jorganchem
New cycloplatinated complexes with 2-arylimidazolines:
Synthesis, crystal structures and photophysical properties
*
*
Jun-Fang Gong , Xin-Heng Fan, Chen Xu, Jin-Lei Li, Yang-Jie Wu , Mao-Ping Song
Department of Chemistry, Henan Key Laboratory of Chemical Biology and Organic Chemistry, Key Laboratory of Applied Chemistry
of Henan Universities, Zhengzhou University, Zhengzhou 450052, PR China
Received 8 December 2006; received in revised form 30 December 2006; accepted 9 January 2007
Available online 30 January 2007
Abstract
The synthesis, crystal structures and photophysical properties of a series of cycloplatinated complexes are presented. The complexes
have the general formula (CꢀN)Pt(OꢀO), where OꢀO is acetylacetonate and CꢀN represents 2-arylimidazoline ligands. All of them are
luminescent in CH2Cl2 solution at room temperature. Different aryl group on N-1 of the ligand has no significant effect on the emission
properties of the platinum complexes. While introducing alkyl group on N-1 or electron-donating group on 2-aryl ring does result in a
blue shift of emission maxima or even an increase in emission intensity.
ꢁ 2007 Elsevier B.V. All rights reserved.
Keywords: Cycloplatinated; 2-Arylimidazolines; Crystal structures; Photoluminescent
1. Introduction
100%. Furthermore, the emission color of cyclometalated
platinum complexes can be tuned through rational modifi-
cation of the cyclometalating ligand or ancillary ligand [2].
In search of new LED emitters, we synthesized a series of
cycloplatinated complexes with 2-arylimidazolines (Scheme
1). The reason for the choice of 2-arylimidazoline as cyclo-
metalating ligand is that it can be easily modified by chang-
ing the substituent on N-1 or 2-aryl group. Some related
palladacyclic complexes and a chloro-bridged platinacyclic
dimer derived from 2-phenylimidazoline (1c) have been
previously reported and their in vitro antileukaemic activity
has been investigated [6]. Herein we wish to present our
results on the synthesis, crystal structures and photophysi-
cal properties of new platinacyclic complexes 3a–3e.
Square-planar platinum complexes have received con-
siderable attention due to their intriguing photophysi-
cal and photochemical properties [1]. In particular,
cyclometalated platinum complexes with pyridines such
as 2-arylpyridine [2], 6-phenyl-2,20-bipyridine [3], 1,3-di(2-
pyridyl)benzene [4] and other cyclometalating ligands [5]
have been extensively investigated over the past years.
These luminescent complexes are an attractive class of mol-
ecules as potential phosphorescent emitters in organic
light-emitting devices (OLEDs) because the strong spin–
orbit coupling of the heavy platinum atom allows for effi-
cient intersystem crossing (ISC) from the singlet (S1) to
the triplet (Tn) as well as the enhancement of the T1–S0
transition. Thus, OLEDs based on these phosphors can uti-
lize all of the electrogenerated singlet and triplet excitons,
theoretically attaining an internal quantum efficiency of
2. Results and discussion
2.1. Synthesis and characterization
The synthesis of 2-arylimidazolines 2a–2e and the corre-
sponding cyclometalated platinum (II) complexes 3a–3e is
shown in Scheme 1. Ligands 2a–2d were prepared from
benzoyl chloride or p-methoxybenzoyl chloride in two steps
*
Corresponding authors. Tel.: +86 371 67763207; fax: +86 371
67766667 (Jun-Fang Gong).
E-mail addresses: gongjf@zzu.edu.cn (J.-F. Gong), wyj@zzu.edu.cn
(Y.-J. Wu).
0022-328X/$ - see front matter ꢁ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.01.033

J.-F. Gong et al. / Journal of Organometallic Chemistry 692 (2007) 2006–2013
2007
R3
N
R2
R3
N
R1
R2
1) K2PtCl4/HOAc
1)
2)
N
O
H2N
OH
R1
COCl
R1
Pt
2) acetylacetone/Na2CO3
2-ethoxyethanol
SOCl2, R3NH2
R2
N
O
1a-1b
2a-2d
3a-3d
R1 = R2 = H, R3 = p-Tol (a), R1 = R2 = H, R3 = Ph (b),
R1 = R2 = H,
R
1 = H (a), OCH3 (b)
R3 = p-OCH3C6H4 (c), R1 = OCH3, R2 = i-Pr, R3 = p-OCH3C6H4 (d)
Ph
Ph
N
N
H
N
1) K2PtCl4/HOAc
N
N
DMF, NaH
PhCH2Cl
Pt
2) acetylacetone/Na2CO3
2-ethoxyethanol
N
O
O
1c
2e
3e
Scheme 1.
according to the published procedure [7]. The reaction of
1a or 1b with aminoethanol or valinol in the presence of
Et3N in THF at room temperature afforded the amido
alcohols, which were treated with excess thionyl chloride,
followed by arylamines such as p-toluidine or phenylamine
or p-methoxyaniline. After basic workup with 10% NaOH
and purification by preparative TLC on silica gel plates
eluting with ethyl acetate, 2-arylimidazolines 2a–2d were
obtained. Ligand 2e was synthesized from the reaction of
2-phenylimidazoline (1c) with benzylchloride in the pres-
ence of NaH base. Then treatment of K2PtCl4 with 2 equiv
of ligand 2 produced the proposed chloro-bridged dimer
[2a,2b], which was subsequently converted into the
expected cycloplatinated complexes 3 upon reaction with
acetylacetone (acac) in the presence of Na2CO3 in 2-eth-
oxyethanol. Complexes 3 were isolated as air-stable yellow
solids in 20–33% yields. All the new compounds were well
elemental analysis. Furthermore, the molecular structures
of both 3c and 3d were determined by X-ray single crystal
analysis.
The molecular structures of complexes 3c and 3d are
shown in Figs. 1 and 3 (displacement ellipsoids are drawn
at the 30% probability level). Crystallographic and data
collection parameters are summarized in Table 1. Selected
˚
bond lengths (A) and angles (ꢂ) are given in Table 2. The Pt
atom in each complex is in a slightly distorted square-pla-
nar environment bonded to the nitrogen and the C1(C6)
atoms of 2-arylimidazoline ligand, the two oxygen atoms
of acac. The deviations of the Pt atoms from the planes
˚
˚
for complexes 3c and 3d are 0.0376 A and 0.0149 A, respec-
tively. In two complexes, the arylimidazoline metallacycle
is essentially flat. While the N-aryl ring is not coplanar with
the plane of the (arylimidazoline)Pt(acac) fragment and the
dihedral angles between them are 88.1ꢂ and 87.0ꢂ for com-
plexes 3c and 3d, respectively. These characters are similar
1
characterized by H NMR, 13C NMR, ESI–MS, IR and
Fig. 1. Molecular structure of complex 3c. Hydrogen atoms are omitted for clarity.

2008
J.-F. Gong et al. / Journal of Organometallic Chemistry 692 (2007) 2006–2013
Table 1
Crystallographic and data collection parameters for 3c and 3d
Empirical formula
Formula weight
Temperature (K)
Wavelength (A)
Crystal system
Space group
C21H22N2O3Pt
545.50
291(2)
0.71073
Monoclinic
P2(1)/n
C25H30N2O4Pt
617.60
293(2)
0.71073
Monoclinic
P2(1)/n
˚
Unit cell dimensions
˚
a (A)
8.777(8)
18.944(16)
10.016(2)
24.022(5)
˚
b (A)
˚
c (A)
12.726(11)
10.334(2)
a (ꢂ)
b (ꢂ)
c (ꢂ)
90
90
90.17(3)
90
2486.5(9)
106.349(10)
90
2030.5(3)
3
˚
Volume (A )
Z
4
4
Calculated density (Mg/m3)
Absorption coefficient (mmꢁ1
F(000)
1.784
6.933
1056
1.650
5.675
1216
)
Crystal size (mm)
Theta range for data collection
Index ranges
Reflections collected/unique (Rint
Completeness to 2h
0.41 · 0.15 · 0.07
2.65–27.50ꢂ
ꢁ11 6 h 6 11, ꢁ24 6 k 6 24, ꢁ16 6 l 6 16
17771/4664 (0.0285)
99.8%
0.20 · 0.18 · 0.14
2.15–25.50ꢂ
ꢁ11 6 h 6 11, ꢁ29 6 k 6 29, ꢁ12 6 l6 0
7695/4349 (0.0749)
93.9%
)
Maximum and minimum transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
0.6280 and 0.1647
Full-matrix least-squares on F2
4664/0/247
0.5038 and 0.3965
Full-matrix least-squares on F2
4349/0/290
1.030
1.072
Final R indices [I > 2r(I)]
R indices (all data)
Largest difference in peak and hole (e A
R1 = 0.0226, wR2 = 0.0487
R1 = 0.0323, wR2 = 0.0526
0.302 and ꢁ1.196
R1 = 0.0588, wR2 = 0.1557
R1 = 0.0715, wR2 = 0.1645
1.046 and ꢁ1.031
ꢁ3
˚
)
˚
Table 2
Selected bond lengths (A) and angles (ꢂ) for 3c and 3d
found that the Pt–C bond lengths (1.976(3) A for 3c and
˚
˚
1.989(11) A for 3d) are slightly longer, while the Pt–N bond
˚
˚
Compound
3c
3d
lengths (1.980(3) A for 3c and 1.980(10) A for 3d) are
slightly shorter in comparison with the corresponding bond
lengths for the bis(imidazoline) pincer Pt(II) complex
Pt(1)–N(1)
1.980(3)
1.976(3)
2.095(2)
2.018(2)
1.980(10)
1.989(11)
2.093(8)
2.018(8)
Pt(1)–C(1)/Pt(1)–C(6)
Pt(1)–O(2)/ Pt(1)–O(1)
Pt(1)–O(3)/Pt(1)–O(2)
˚
(1.910(11) or 1.957(13) A for Pt–C, and 2.008–2.043 for
Pt–N) [8].
C(1)–Pt(1)–N(1)/C(6)–Pt(1)–N (1)
C(1)–Pt(1)–O(3)/C(6)–Pt(1)–O(2)
N(1)–Pt(1)–O(3)/N(1)–Pt(1)–O(2)
C (1)–Pt(1)–O(2)/C(6)–Pt(1)–O(1)
N(1)–Pt(1)–O(2)/ N(1)–Pt(1)–O(1)
O(3)–Pt(1)–O(2)/O(2)–Pt(1)–O(1)
C(17)–O(2)–Pt(1)/C(2)–O(1)–Pt(1)
C(19)–O(3)–Pt(1)/C(4)–O(2)–Pt(1)
C(7)–N(1)–Pt(1)/C(12)–N(1)–Pt(1)
C(8)–N(1)–Pt(1)/C(20)–N(1)–Pt(1)
C(2)–C(1)–Pt(1)/C(7)–C(6)–Pt(1)
C(6)–C(1)–Pt(1)/C(11)–C(6)–Pt(1)
80.59(11)
93.03(11)
173.61(9)
173.02(10)
94.00(9)
92.38(9)
122.4(2)
123.5(2)
117.0(2)
133.2(2)
128.5(2)
115.1(2)
80.6(4)
94.3(4)
174.8(3)
173.9(4)
93.4(3)
91.7 (3)
122.9(7)
124.1(8)
116.9(7)
131.5(6)
127.0(8)
114.6(7)
Fig. 2 shows that in the crystal of 3c there exist three
types of intermolecular Pt ꢀ ꢀ ꢀ H hydrogen bonds (PtA
˚
˚
ꢀ ꢀ ꢀ H20Z = 3.216 A, Pt1Z ꢀ ꢀ ꢀ H9A = 3.011 A, Pt1Z ꢀ ꢀ ꢀ
˚
H11A = 3.121 A), which are attributed to construct the
1D chain structure of complex 3c. In addition, hydrogen
bonds between oxygen atom and the adjacent C–H group
of benzene ring are present in the crystal (the distance is
˚
2.532 A), which lead to the generation of the 2D supermo-
lecular architecture. Fig. 4 shows that complex 3d has a
one-dimensional zigzag chain structure formed by Pt ꢀ ꢀ ꢀ H
˚
˚
(Pt1C ꢀ ꢀ ꢀ H14 = 3.133 A, Pt ꢀ ꢀ ꢀ H17 = 3.176 A) hydrogen
bonds. Molecules of 3c are found to pack in a head-to-head
fashion. While those of 3d are in a head-to-tail fashion. The
˚
Pt ꢀ ꢀ ꢀ Pt distances between adjacent complexes are 6.647 A
to those in the chiral pincer Pt(II) complexes with 1,3-
bis(20-imidazolinyl)phenyl which have been previously
reported by us [8]. All the bond lengths and angles around
Pt(II) in 3c and 3d are essentially identical and the data are
also comparable to those found in the related cycloplati-
nated complexes [2a,2b]. The two Pt–O bond lengths in
3c or 3d are different with the longer distances correspond-
ing to oxygen trans to the cyclometalating carbon. It is
8
8
˚
˚
in 3c, 8.215 A and 9.905 A in 3d, indicating a lack of d –d
interaction [2a,5b,9]. The two adjacent ligand planes in 3c
are not parallel (dihedral angle of 25.5ꢂ) with an interpla-
˚
nar distance of 4.2314 A, which is too long for a p–p stack-
ing interaction [2b,10]. While those in 3d are parallel with
˚
corresponding interplanar distances of ca. 4.4451 A and
˚
5.2156 A, respectively.

J.-F. Gong et al. / Journal of Organometallic Chemistry 692 (2007) 2006–2013
2009
Fig. 2. Two-dimensional lamellar structure of complex 3c showing the hydrogen bonds. Non-hydrogen bonding H atoms are omitted for clarity.
Fig. 3. Molecular structure of complex 3d. Hydrogen atoms are omitted for clarity.
2.2. Photophysical properties of the cyclometalated
complexes
ilar features. The intense absorption bands at wavelengths
below 300 nm are attributed to p–p* transitions of the
ligands. In addition, all of the complexes have a broad, less
intense absorption band at kmax 347–364 nm, which tails
beyond 400 nm. It can tentatively be assigned to MLCT
transition resulting from the promotion of an electron from
The absorption spectra data and emission data of the
ligands 2 and complexes 3 are summarized in Table 3.
All the UV–vis spectra of complexes 3 in CH2Cl2 have sim-

2010
J.-F. Gong et al. / Journal of Organometallic Chemistry 692 (2007) 2006–2013
Fig. 4. One-dimensional zigzag chain structure of complex 3d showing the hydrogen bonds. Non-hydrogen bonding H atoms are omitted for clarity.
Table 3
Photophysical properties of 2 and 3
kmaxa/nm (eb (Mꢁ1 cmꢁ1
)
kex (nm)
kem (nm)
Ue (%)
c
d
Compounds
2a
2b
2c
2d
2e
3a
3b
3c
3d
3e
a
229 (14490)
228 (12160)
230 (19302)
228 (13066), 279 (12215)
230 (10356)
229 (18603), 244 sh (17082), 363 (7556)
229 (17277), 244 (16398), 364 (7188)
228 (28957), 243 sh (23787), 363 (10060)
228 (24243), 248 (22968), 347 (9827)
230 (20236), 244 (19782), 362 (6530)
289
299
330
324
292
409
411
418
411
398
368
370
482
465
344, 406
562, 594
560, 599
564, 588
539, 560
538, 574
1.67
2.62
2.30
3.49
3.03
Absorption maxima in CH2Cl2 solution at room temperature.
Molecular absorption coefficient.
b
c
Excitation maximum in 5 · 10ꢁ4M CH2Cl2 solution at room temperature.
d
e
Emission maximum in 5 · 10ꢁ4M CH2Cl2 solution at room temperature.
Quantum yield obtained from measurements using quinine sulfate in 1 M H2SO4 (U = 0.546) as standard [11].
Pt(d) HOMO to the p* LUMO on the 2-arylimidazoline
ligand. The change of the substituent on N-1 of the ligand
from C6H5 (3b) to p-CH3C6H4 (3a) or p-OCH3C6H4 (3c) or
even CH2C6H5 (3e) has very little effect on the position of
this band (kmax around 363 nm), if any. However, this
absorption is slightly blue-shifted for complex 3d (kmax
347 nm) with electron-donating group (OMe) on 2-aryl
ring. Compared with those for the bis(imidazoline) pincer
Pt(II) complexes (kmax around 390 nm), all the lowest
energy MLCT absorption bands for complexes 3 are
blue-shifted [8].
It is found that the substituents on N-1 greatly influence
the fluorescent emission properties of ligands 2 in CH2Cl2
solution at room temperature. Thus, changing the substitu-
ent from p-CH3C6H4 (2a) or C6H5 (2b) to more electron-
donating aryl group such as p-OCH3C6H4 (2c or 2d) leads
to an obvious red shift of the emission maximum (368 nm
and 370 nm vs 482 and 465 nm) and a significant increase in
emission intensity. For ligand 2e with CH2Ph on N-1, it
displays emissions at 344 and 406 nm with similar intensity
to that of 2a and 2b. Upon photoexcitation, all the
platinum complexes studied also show emission in CH2Cl2

J.-F. Gong et al. / Journal of Organometallic Chemistry 692 (2007) 2006–2013
2011
3. Experimental
3a
3b
3.1. General
3c
3d
All reactions were carried out under a dry nitrogen
atmosphere using standard Schlenk techniques. Com-
pounds 1b [12] and 1c [13] were prepared according to lit-
erature methods. All the other reagents were used as
commercial sources. Melting points were measured using
a WC-1 microscopic apparatus and were uncorrected. Ele-
mental analysis was determined with a Thermo Flash EA
1112 elemental analyzer. IR spectra were collected on a
Bruker VECTOR22 spectrophotometer in KBr pellets.
1H and 13C NMR spectra were recorded on a Bruker
DPX-400 spectrometer in CDCl3 with TMS as an internal
standard. Mass spectra were performed on the Agilent LC/
MSD Trap XCT instrument. UV–Vis absorption spectra
were recorded using a Perkin Elmer Lamda 35 spectrome-
ter at room temperature. The photoluminescence spectra
were measured on a HORIBA Jobin Yvon FluoroMax-P
spectrofluorimeter at room temperature.
3e
450
600
750
Fig. 5. Emission spectra of complexes 3 in 5 · 10ꢁ4M CH2Cl2 solution at
room temperature.
3.2. Synthesis of ligands 2a–2e
solution at room temperature. Different from the substitu-
ent effects in ligands 2, the change of the substituent on N-1
from p-CH3C6H4 (3a) or C6H5 (3b) to p-OCH3C6H4 (3c)
has no significant effect on the room-temperature emission
properties of the complexes and these three compounds
show very similar spectra to one another, with emission
maxima around 560 and 590 nm (Fig. 5). A possible reason
for the result is that the N-aryl is unconjugated with the
other parts of the complex which is confirmed by X-ray sin-
gle crystal analysis of 3c and 3d. The related pincer Pt (II)
complexes display broad structureless emissions with kmax
at 575–577 nm [8]. On the other hand, the emission peaks
of complex 3d with a methoxy group on 2-aryl ring and
3e with CH2Ph on N-1 are subject to a small blue shift.
For 3d, the emission intensity also increases. The above
results give some useful information on further ligand
modification for tuning the emission properties of the
related platinum complexes. Finally, it is found that the
emission maxima of these complexes are significantly red-
shifted compared with the value of 486 nm reported for
[(2-phenylpyridine)Pt (acac)] at room temperature in 2-
MeTHF [2a].
In summary, a series of cycloplatinated complexes with
2-arylimidazolines have been synthesized and character-
ized. All the complexes display photoluminescence in
CH2Cl2 solution at room temperature. Although the sub-
stituents on N-1 greatly influence the fluorescent emission
properties of 2-arylimidazoline ligands, the different aryl
group on N-1 has no significant effect on the emission
properties of the platinum complexes. Introducing alkyl
group on N-1 or electron-donating group on 2-aryl ring
does result in a blue shift of emission maxima or even an
increase in emission intensity. Further studies are in
progress.
3.2.1. General procedure for the synthesis of ligands 2a–2d
To a stirred solution of amino alcohol (7.5 mmol) and
Et3N (2.10 mL, 15 mmol) in THF (10 mL) was added
dropwise a solution of benzoyl chloride (0.58 mL, 5 mmol)
or p-methoxy-benzoyl chloride (0.68 mL, 5 mmol) in
60 mL THF at room temperature. After stirring for 16 h,
the reaction mixture was filtered and evaporated. The res-
idue was purified by passing through a short silica gel col-
umn with acetone/petroleum ether (1:1) as eluent, giving
white solids of the corresponding amido alcohol. Then
the obtained amido alcohol (2.4 mmol) reacted with thio-
nyl chloride (0.71 mL, 9.7 mmol) at reflux for 6 h. Excess
thionyl chloride was evaporated. The residue was dissolved
in dry diethyl ether (5 mL) and filtered to remove insoluble
impurities. To this solution was added dry triethylamine
(1 mL, 7.2 mmol), followed by p-toluidine, or phenylamine
orp-methoxyaniline (2.64 mmol). After stirring for 5 h at
room temperature, 10% NaOH (10 mL) was added and
stirred for 24 h. The aqueous was extracted with
dichloro-methane and the organic layer was dried over
MgSO4 and evaporated. The crude was purified by pre-
parative TLC on silica gel plates eluting with ethyl acetate
to afford ligands 2a–2d as pale yellow oil (which will solid-
ify during preservation). 2a–2c are known compounds.
Characterization data for 2d: 56.5% yield. IR (KBr,
1
cmꢁ1): 1613 (mC@N). H NMR (400 MHz, CDCl3): d 0.95
(d, J = 6.7 Hz, 3H, CH(CH3)2), 1.03 (d, J = 6.7 Hz, 3H,
CH(CH3)2), 1.89–1.93 (m, 1H, CHMe2), 3.51–3.58 (m,
1H, CH2), 3.73 (s, 3H, OCH3), 3.76 (s, 3H, OCH3), 3.98–
4.04 (m, 2H, CH2 + NCH), 6.70–6.78 (m, 6H, ArH), 7.43
(d, J = 8.6 Hz, 2H, ArH); 13C NMR (100 MHz, CDCl3):
d 17.8, 18.9, 33.2, 55.2, 55.4, 57.2, 69.9, 113.3, 114.0,
123.5, 125.0, 130.4, 137.2, 156.0, 160.6, 161.6. ESI–MS

2012
J.-F. Gong et al. / Journal of Organometallic Chemistry 692 (2007) 2006–2013
(M+H)+ Calc. for C20H25N2O2: 325.2, found: 325.1. Anal.
Calc. for C20H24N2O2: C, 74.04; H, 7.46; N, 8.64. Found:
C, 74.19; H, 7.54; N, 8.53%.
1H, ArH), 7.28–7.36 (m, 3H, PhH), 7.41–7.44 (m, 2H,
PhH), 7.58 (d, J = 7.5 Hz, 1H, ArH);13C NMR
(100 MHz, CDCl3): d 27.3, 27.9, 48.8, 55.4, 102.2, 121.9,
126.1, 126.2, 127.4, 129.7, 130.1, 130.6, 134.8, 140.2,
141.2, 175.5, 183.2, 184.9. ESI–MS (M+H)+ Calc. for
C20H21N2O2Pt: 516.1, found: 516.1. Anal. Calc. for
C20H20N2O2Pt: C, 46.60; H, 3.91; N, 5.43. Found: C,
46.86; H, 4.02; N, 5.28%.
3.2.2. Synthesis of 2e
A 50 mL three neck round-bottom flask was equipped
with a 10 mL addition funnel and a nitrogen inlet. To a
stirring solution of sodium hydride (72 mg, 3 mmol) in
DMF (5.0 mL) was added dropwise a solution of 2-pheny-
limidazoline (300 mg, 2 mmol) in DMF (5.0 mL) at 0 ꢂC.
After 30 min, the resulting solution was added dropwise a
solution of benzyl chloride (0.36 mL, 3 mmol) in DMF
(5.0 mL) at room temperature. After stirring for 24 h at
room temperature, the reaction was poured into 300 mL
of water and exacted with chloroform. The combined
organic phases were washed with brine, and then dried over
magnesium sulfate. After filtering and concentrating, the
residue was applied to a column of silica gel with chloro-
form/methanol (5:1) as eluent to give 2e as an oil. 2e is also
a known compound.
3c: Yellow solid, 33.2% yield. m.p.: 199–200 ꢂC. IR
(KBr, cmꢁ1): 1567 (mC=N and
m
C=O). 1H NMR
(400 MHz, CDCl3): d 1.90 (s, 3H, CH3), 1.94 (s, 3H,
CH3), 3.85 (s, 3H, OCH3), 3.95–4.00 (m, 2H, CH2), 4.06–
4.11 (m, 2H, CH2), 5.43 (s, 1H, CH), 6.37 (d, J = 7.8 Hz,
1H, ArH), 6.66–6.70 (m, 1H, ArH), 6.94 (d, J = 8.8 Hz,
2H, ArH), 7.05–7.08 (m, 1H, ArH), 7.22 (d, J = 8.8 Hz,
2H, ArH), 7.57 (d, J = 7.6 Hz, 1H, ArH); 13C NMR
(100 MHz, CDCl3): d 27.3, 27.9, 48.7, 55.5, 55.8, 102.2,
114.9, 122.0, 126.0, 128.1, 130.0, 130.6, 133.8, 134.9,
140.1, 158.9, 175.8, 183.1, 184.9. ESI–MS: (M + H)+ Calc.
for C21H23N2O3Pt: 546.1, found: 546.3. Anal. Calc. for
C21H22N2O3Pt: C, 46.24; H, 4.07; N, 5.14%. Found: C,
46.52; H, 4.10; N, 5.05%.
3.3. General procedure for the synthesis of cycloplatinated
complexes 3a–3e
3d: Yellow solid, 20.3% yield. m.p: 186–188 ꢂC. IR
1
(KBr, cmꢁ1):1575 (mC=N and mC=O). H NMR (400 MHz,
A mixture of 2-arylimidazoline ligand (0.4 mmol) and
K2PtCl4 (83 mg, 0.2 mmol) in HOAc (4 mL) were refluxed
for 30 h. The reaction mixture was allowed to cool down to
room temperature and filtered. The obtained yellow precip-
itate was thought to be the chloro-bridged dimer which was
washed with HOAc, H2O and acetone, respectively, then
dried in vacuum. Without further purification and charac-
terization, the dimer was treated with 3 equiv of acetyl-
acetone in the presence of 10 equiv of Na2CO3 in
2-ethoxyethanol at 100 ꢂC under nitrogen for 24 h. After
the removal of the solvent, the residue was purified by pre-
parative TLC on silica gel plates using CH2Cl2 as the eluent
to afford 3.
CDCl3): d 0.90–0.92 (m, 6H, CH(CH3)2), 1.87 (s, 3H,
CH3), 1.92 (s, 3H, CH3), 2.61–2.65 (m, 1H, CHMe2),
3.79–3.82 (m, 1H, CH2), 3.80 (s, overlapped with CH2,
3H, OCH3), 3.84 (s, 3H, OCH3), 4.05–4.10 (m, 1H, CH2),
4.12–4.17 (m, 1H, NCH), 5.41 (s, 1H, CH), 6.25 (dd,
J = 2.6, 8.6 Hz, 1H, ArH), 6.33 (d, J = 8.6 Hz, 1H, ArH),
6.92–6.95 (m, 2H, ArH), 7.12 (d, J = 2.6 Hz, 1H, ArH),
7.15–7.19 (m, 2H, ArH); 13C NMR (100 MHz, CDCl3): d
14.3, 18.5, 27.3, 27.9, 29.3, 55.0, 55.1, 55.5, 64.8, 102.0,
108.4, 114.2, 114.8, 127.2, 127.4, 127.9, 133.8, 142.4,
158.7, 160.5, 173.6, 183.1, 184.6. ESI–MS: (M+H)+ Calc.
for C25H31N2O4Pt: 618.2, found: 618.7. Anal. Calc. for
C25H30N2O4Pt: C, 48.62; H, 4.90; N, 4.54. Found: C,
48.84; H, 5.01; N, 4.49%.
3a: Yellow solid, 20.5% yield. m.p.: 212–214 ꢂC. IR
(KBr, cmꢁ1): 1567 (mC=N and
m
C=O). 1H NMR
3e: Yellow solid, 20.6% yield. m.p.: 155–157 ꢂC. IR
(400 MHz, CDCl3): d 1.90 (s, 3H, CH3), 1.94 (s, 3H,
CH3), 2.41 (s, 3H, CH3), 3.96–4.01 (m, 2H, CH2), 4.09–
4.14 (m, 2H, CH2), 5.43 (s, 1H, CH), 6.45 (d, J = 7.7 Hz,
1H, ArH), 6.69 (app t, 1H, J = 7.5 Hz, ArH), 7.07 (app t,
J = 7.5 Hz, 1H, ArH), 7.17 (d, J = 8.3 Hz, 2H, ArH),
7.22 (d, J = 8.3 Hz, 2H, ArH), 7.58 (d, J = 7.5 Hz, 1H,
ArH); 13C NMR (100 MHz, CDCl3): d 21.2, 27.3, 27.9,
48.7, 55.6, 102.2, 121.9, 126.1, 126.3, 130.1, 130.3, 130.6,
134.9, 137.5, 138.5, 140.1, 175.6, 183.1, 184.9. ESI–MS:
(M+H)+ Calc. for C21H23N2O2Pt: 530.1, found: 530.3.
Anal. Calc. for C21H22N2O2Pt: C, 47.64; H, 4.19; N,
5.29. Found: C, 47.93; H, 4.29; N, 5.19%.
(KBr, cmꢁ1): 1569 (mC=N and
m
C=O). 1H NMR
(400 MHz, CDCl3): d 1.88 (s, 3H, CH3), 1.94 (s, 3H,
CH3), 3.73–3.78 (m, 2H,CH2), 3.83–3.89 (m, 2H, CH2),
4.92 (s, 2H, CH2Ph), 5.41 (s, 1H, CH), 6.91 (t,
J = 7.5 Hz, 1H, ArH), 7.15 (t, J = 7.5 Hz, 1H, ArH),
7.25–7.38 (m, 6H, PhH + ArH), 7.65 (d, J = 7.6 Hz, 1H,
ArH); 13C NMR (100 MHz, CDCl3): d 27.3, 27.9, 29.7,
48.3, 51.6, 102.2, 122.5, 124.8, 126.9, 127.9, 129.0, 130.2,
131.2, 135.0, 136.4, 140.5, 183.2, 184.9. ESI–MS:
(M+H)+Calc. for C21H23N2O2Pt: 530.1, found: 530.2.
Anal. Calc. for C21H22N2O2Pt: C, 47.64; H, 4.19; N,
5.29. Found: C, 47.84; H, 4.27; N, 5.19%.
3b: Yellow solid, 21.4% yield. m.p.: 179–181 ꢂC. IR
(KBr, cmꢁ1): 1570 (mC=N and
m
C=O). 1H NMR
3.4. Structure determination
(400 MHz, CDCl3): d 1.91 (s, 3H, CH3), 1.95 (s, 3H,
CH3), 3.98–4.03 (m, 2H, CH2), 4.13–4.18 (m, 2H, CH2),
5.43 (s, 1H, CH), 6.47 (d, J = 7.4 Hz, 1H, ArH), 6.69
(app t, 1H, J = 7.5 Hz, ArH), 7.07 (app t, J = 7.5 Hz,
Crystals of 3c and 3d were obtained by recrystallization
from CH2Cl2-methanol at room temperature. Crystallo-
graphic data for 3c were collected at 291(2) K on a Bruker

J.-F. Gong et al. / Journal of Organometallic Chemistry 692 (2007) 2006–2013
2013
[2] (a) J. Brooks, Y. Babayan, S. Lamansky, P.I. Djurovich, I. Tsyba,
R. Bau, M.E. Thompson, Inorg. Chem. 41 (2002) 3055;
(b) B. Yin, F. Niemeyer, J.A.G. Williams, J. Jiang, A. Boucekkine,
L. Toupet, H. Le Bozec, V. Guerchais, Inorg. Chem. 45 (2006) 8584;
(c) N.M. Shavaleev, H. Adams, J. Best, R. Edge, S. Navaratnam,
J.A. Weinstein, Inorg. Chem. 45 (2006) 9410;
(d) J. Liu, Y. Liu, C. Luo, E. Liu, Y. Yang, Q. Gan, M. Zhu, W.
Zhu, Chem. J. Chin. Univ. 10 (2006) 1873.
[3] (a) W. Lu, B.X. Mi, M.C.W. Chan, Z. Hui, N. Zhu, S.T. Lee, C.M.
Che, Chem. Commun. (2002) 206;
APEX-II area-detector diffractometer with Mo Ka radia-
tion (k = 0.71073 A). Absorption corrections were applied
˚
by using SADABS. The hydrogen atoms were assigned with
common isotropic displacement factors and included in
the final refinement by using geometrical restrains. Crystal-
lographic data for 3d were measured on a Rigaku-Raxis-IV
X-ray diffractometer using graphite-monochromated Mo
˚
Ka radiation (k = 0.71073 A) at 293(2) K. The hydrogen
atoms were included but not refined. The full-matrix
least-squares calculations on F2 were applied on the final
refinement. The two structures were solved by direct meth-
ods. All non-hydrogen atoms were described anisotropi-
cally. Their raw data were corrected and the structures
were solved using the SHELX-97 program.
(b) W. Lu, M.C.W. Chan, N. Zhu, C.M. Che, C. Li, Z. Hui, J. Am.
Chem. Soc. 126 (2004) 7639;
(c) W. Lu, B.X. Mi, M.C.W. Chan, Z. Hui, C.M. Che, N. Zhu, S.T.
Lee, J. Am. Chem. Soc. 126 (2004) 4958.
[4] (a) J.A.G. Williams, A. Beeby, E.S. Davies, J.A. Weinstein, C.
Wilson, Inorg. Chem. 42 (2003) 8609;
(b) W. Sotoyama, T. Satoh, N. Sawatari, H. Inoue, Appl. Phys. Lett.
86 (2005) 153505/1;
(c) S.J. Farley, D.L. Rochester, A.L. Thompson, J.A.K. Howard,
J.A.G. Williams, Inorg. Chem. 44 (2005) 9690.
Acknowledgements
[5] (a) Selected examples: B.K.W. Chiu, M.H.W. Lam, D.Y.K. Lee,
W.Y. Wong, J. Organomet. Chem. 689 (2004) 2888;
(b) T. Kanbara, K. Okada, T. Yamamoto, H. Ogawa, T. Inoue, J.
Organomet. Chem. 689 (2004) 1860;
We are grateful to the Innovation Fund for Outstanding
Scholar of Henan Province (0621001100) and the Natural
Science Foundation of Henan Province (0611012100) for
financial support of this work.
(c) G.L. Zhang, Y.T. Chuai, H.Q. Guo, D.C. Zou, Acta Phys. Chim.
Sin. 21 (2005) 1407;
(d) L. Mao, T. Moriuchi, H. Sakurai, H. Fujii, T. Hirao, Tetrahedron
Lett. 46 (2005) 8419;
Appendix A. Supplementary data
(e) K. Okamoto, T. Kanbara, T. Yamamoto, A. Wada, Organomet-
allics 25 (2006) 4026.
CCDC 627418 and 627419 contain the supplementary
crystallographic data for 3c and 3d. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail: depos-
it@ccdc.cam.ac.uk. Supplementary data associated with
this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2007.01.033.
´
[6] (a) C. Navarro-Ranninger, F. Zamora, I. Lopez-Solera, A. Monge,
J.R. Masaguer, J. Organomet. Chem. 506 (1996) 149;
´
´
(b) F. Zamora, V.M. Gonzalez, J.M. Perez, J.R. Masaguer, C.
Alonso, C. Navarro-Ranninger, Appl. Organomet. Chem. 11 (1997)
659.
[7] N.A . Boland, M. Casey, S.J. Hynes, J.W. Matthews, M.P. Smyth, J.
Org. Chem. 67 (2002) 3919.
[8] X.Q. Hao, J.F. Gong, C.X. Du, L.Y. Wu, Y.J. Wu, M.P. Song,
Tetrahedron Lett. 47 (2006) 5033.
[9] T. Kanbara, T. Yamamoto, J. Organomet. Chem. 688 (2003) 15.
[10] C. Janiak, J. Chem. Soc., Dalton Trans. (2000) 3885.
[11] S.R. Meech, D. Phillips, J. Photochem. 23 (1983) 193.
[12] X.C. Liao, X.L. Wu, W.Z. Wang, Zhengzhou Daxue Xuebao,
Lixueban 34 (2002) 92.
References
[1] B. Ma, P.I. Djurovich, M.E. Thompson, Coord. Chem. Rev. 249
(2005) 1501, and references cited therein.
[13] P. Dash, D.P. Kudav, J.A. Parihar, J. Chem. Res. (2004) 490.