Two palladium(II) complexes based on Schiff base ligands: Synthesis, characterization, luminescence, and catalytic activity

Article abstract of DOI:10.1007/s11243-013-9691-y

Two Pd(II) complexes involving Schiff base ligands, namely, [Pd(L1) ₂] (1), [Pd₂(L₂)Cl₂] (2) [HL1 = 2-((2,6-diisopropylphenylimino)methyl)-4,6-dibromophenol, L2 = N-(4-isopropylbenzylidene)-2,6-diisopropylbenzenamine] have been synthesized using solvothermal methods and characterized by elemental analysis, IR-spectroscopy, thermogravimetric analysis, powder X-ray diffraction, UV-vis absorption spectra, and single-crystal X-ray diffraction. Complex 1 is a mononuclear cyclometalated Pd(II) complex, whereas complex 2 is a μ-chloro-bridged dinuclear. Both 1 and 2 display photoluminescence in the solid state at 298 K and possess fluorescence lifetimes (τ ₁ = 86.40 ns, τ ₂ = 196.21 ns, τ ₃ = 1,923.31 ns at 768 nm for 1, τ ₁ = 69.92 ns, τ ₂ = 136.40 ns, τ ₃ = 1,714.26 ns at 570 nm for 2). The Suzuki reactions of 4-bromotoluene with phenylboronic acid by complexes 1-2 have also been studied.

Full text of DOI:10.1007/s11243-013-9691-y

Transition Met Chem (2013) 38:299–305
DOI 10.1007/s11243-013-9691-y
Two palladium(II) complexes based on Schiff base ligands:
synthesis, characterization, luminescence, and catalytic activity
•
Hai-Fu Guo Xin Zhao De-Yun Ma
•
•
•
Ai-Ping Xie Wei-Bo Shen
Received: 20 December 2012 / Accepted: 4 January 2013 / Published online: 19 January 2013
Ó Springer Science+Business Media Dordrecht 2013
Abstract Two Pd(II) complexes involving Schiff base
ligands, namely, [Pd(L1)2] (1), [Pd2(L2)Cl2] (2) [HL1 =
2-((2,6-diisopropylphenylimino)methyl)-4,6-dibromophenol,
L2 = N-(4-isopropylbenzylidene)-2,6-diisopropylbenzen-
amine] have been synthesized using solvothermal methods
and characterized by elemental analysis, IR-spectroscopy,
thermogravimetric analysis, powder X-ray diffraction, UV–
vis absorption spectra, and single-crystal X-ray diffraction.
Complex 1 is a mononuclear cyclometalated Pd(II) complex,
whereas complex 2 is a l-chloro-bridged dinuclear. Both 1
and 2 display photoluminescence in the solid state at 298 K
and possess fluorescence lifetimes (s1 = 86.40 ns, s2 =
196.21 ns, s3 = 1,923.31 ns at 768 nm for 1, s1 = 69.92 ns,
s2 = 136.40 ns, s3 = 1,714.26 ns at 570 nm for 2). The
Suzuki reactions of 4-bromotoluene with phenylboronic acid
by complexes 1–2 have also been studied.
instances exhibits interesting reactivities and photolumines-
cence [1–6]. However, compared with platinum(II) complexes
involving Schiff base ligands, whose applications as lumines-
cent sensors are of considerable interest in inorganic photo-
chemistry [7, 8], relatively scant attention has been focused
upon the luminescent characteristics of palladium(II) com-
plexes [2]. In general, luminescent cyclopaladated complexes
show low efficiency emissions detected only at low tempera-
tures [9] due to the presence of thermally accessible low-lying
metal centered states (MC) that allow excited states to expe-
rience non-radiative decay [10]. Moreover, the palladium-
catalyzed formation of biaryls from arylhalides with arylbo-
ronic acids (the Suzuki reaction) has become one of the
mainstays of modern synthetic organic chemistry for the for-
mation of carbon–carbon bonds [11, 12]. Compared with
homogeneous catalysis for such coupling reactions, heteroge-
neous catalysis involving supported metal complexes offers
several advantages, such as robustness and increased air and
moisture stability [13, 14]. Various supports, including silica,
sepiolites, zeolites and polymers, have been used to heteroge-
nize the homogeneous catalysts [15–18]. Palladium(II) com-
plexes derived from Schiff base ligands have been extensively
studied over the past few decades in the light of their applica-
tions as heterogeneous catalysts in organic reactions [19]. As
part of our ongoing investigation into the palladium complexes
involving Schiff base ligands [19], we here report the synthesis,
characterization, luminescent properties, and catalytic activi-
ties of two new Pd(II) complexes based on Schiff base ligands.
Introduction
Schiff bases continue to be of considerable interest as ligands
that are used in conjunction with palladium metals. This class
of compounds displays diverse structural features and in some
Electronic supplementary material The online version of this
article (doi:10.1007/s11243-013-9691-y) contains supplementary
material, which is available to authorized users.
H.-F. Guo (&) ꢀ X. Zhao ꢀ D.-Y. Ma ꢀ A.-P. Xie ꢀ W.-B. Shen
School of Chemistry and Chemical Engineering, Zhaoqing
University, Zhaoqing 526061, People’s Republic of China
e-mail: guohaifu@zqu.edu.cn
Experimental
X. Zhao
All chemicals were commercially available and used as
received without further purification. Elemental analyses for
C, H, and N were carried out using a Vario EL III Elemental
College of Chemical Engineering, Inner Mongolia
University of Technology, Inner Mongolia 010051,
People’s Republic of China
123

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Transition Met Chem (2013) 38:299–305
Analyzer. Infrared spectra were recorded (4,000–400 cm-1)as
KBr disks on a Shimadzu IR-440 spectrometer. Thermo-
gravimetric analyses (TGA) were performed on an automatic
simultaneous thermal analyzer (DTG-60, Shimadzu) under a
flow of N2 at a heating rate of 10 °C/min between ambient
temperature and 800 °C. Powder XRD investigations were
carried out on a Bruker AXS D8-Advanced diffractometer at
931(m), 873(m), 837(s), 796(m), 759(s), 731(m), 667(w),
599(w), 557(m), 459(w). MP: 84–85 °C.
Preparation of [Pd(L1)2] (1)
Na2PdCl4 (0.0887 g, 0.5 mmol) was dissolved in methanol
(10 mL). HL1 (0.426 g, 1 mmol) was added and the mixture
stirred at room temperature for 5 h under an anhydrous
atmosphere. The resulting mixture was filtered under
reduced pressure. The collected solid was washed with ethyl
ether and dried in air to give yellow crystals that were puri-
fied by recrystallization from methylene chloride (15 mL)
and hexane (10 mL). Yield 0.382 g (78 %). Anal. For
C38H40Br4N2O2Pd (%): Calcd. C 46.40, H 4.07, N 2.85;
Found C: 46.45, H 4.05, N 2.83. FTIR (KBr, cm-1): 3,450(s),
2,962(s), 2,931(w), 2,875(w), 1,608(vs), 1,504(m), 1,433(s),
1,402(w), 1,384(w), 1,311(s), 1,218(w), 1,155(s), 1,101(w),
1,058(w), 945(w), 889(w), 856(w), 806(w), 769(m), 748(w),
723(m), 671(w), 640(w), 538(m).
˚
40 kV and 40 mA with Cu-Ka(k = 1.5406A) radiation. UV–
vis absorption spectra were measured using a Shimadzu UV-
160A spectrophotometer. Luminescence spectra and lifetimes
for crystalline samples were recorded at room temperature on
an Edinburgh FLS920 phosphorimeter. Nuclear magnetic
resonance spectra were recorded on a Bruker Avance
400 MHz spectrometer. 1H-NMR chemical shifts are reported
in ppm from tetramethylsilane with the solvent resonance as
the internal standard (CDCl3, d = 7.26). Data are reported as
follows: chemical shift (d ppm), multiplicity (s = singlet,
d = doublet, t = triplet, m = multiplet), coupling constants
(Hz), integration, and assignment. 13C-NMR spectra were
collected on a 100 MHz spectrometer with complete proton
decoupling. Chemical shifts are reported in ppm from the tet-
ramethylsilane (TMS) with the solvent resonance as internal
standard (CDCl3, d = 77.23). Melting points were measured
uncorrected with a Mel-Temp apparatus.
Preparation of [Pd2(L2)Cl2] (2)
Complex 2 was prepared by the same procedure as 1 except
that HL1 was replaced with L2. Yield 0.182 g (81 %); Anal
for C44H56Cl2N2Pd2 (%): Calcd. C 58.89, H 6.25, N 3.12;
Found C 58.94, H 6.28; N 3.08. FTIR (KBr, cm-1): 3,467(s),
2,962(s), 2,871(w), 1,597(s), 1,583(vs), 1,456(s), 1,409(w),
1,398(w), 1,380(w), 1,328(m), 1,282(m), 1,226(m),
1,178(m), 1,135(m), 1,056(m), 1,037(w), 983(w), 935(w),
892(w), 819(m), 800(m), 763(m), 757(w), 611(w), 535(w),
420(m).
Preparation of HL1
The preparation of HL1 was carried out according to the
reported procedures [20].Yield 4.75 g (52 %). IR (KBr,
cm-1): 3,473(s), 2,962(s), 2,883(w), 1,622(vs), 1,444(s),
1,382(w), 1,352 (m), 1,323(w), 1,290(m), 1,217(w),
1,161(s), 1,101(w), 1,056(w), 991(w), 945(w), 867(w),
804(m), 759(m), 717(m), 684(s), 570(w), 505(w).
Catalytic reactions
Preparation of L2 (L2)
A mixtureof4-bromotoluene(1.0 mmol), phenylboronicacid
(1.2 mmol), organic solvents (6 mL), base (2.0 mmol), and
0.5 mol % of catalyst was stirred at 80 °C under air. After the
reaction, the catalyst was separated by filtration. The filtrate
was dried over Na2SO4 and again filtered. The products were
quantified by GC–MS analysis (Shimadzu GCMS-QP5050A
equipped with a 0.25 mm 9 30 m DB-WAX capillary col-
umn). The typical GC–MS analysis program was as follows:
initial column temperature 100 °C, hold 2 min, ramp tem-
perature to 280 °C at 15 °C/min, and hold for 5 min.
L2 was prepared by the condensation of cuminaldehyde
(2.96 g, 20 mmol) with 2,6-diisopropylaniline (3.55 g,
20 mmol) in ethanol (20 mL) as the reaction medium. The
solution was refluxed for 4 h and then allowed to cool at
room temperature. The yellow precipitate was recrystal-
lized from ethanol to give L2 as straw yellow crystals.
1
Yield 4.29 g (66 %). H NMR (400 MHz, CDCl3) d: 8.16
(s, 1H, CHN), 7.09–7.85 (m, 6H, Ar–H), 2.98 [t,
J = 4.56 Hz, 3H, CH(CH3)2], 1.23 (q, J = 4.68 Hz, 18H,
CH3); 13C NMR (100 MHz, CDCl3) d: 161.8, 152.8, 149.4,
137.7, 133.9, 128.7, 126.9, 124.0, 123.0, 77.2, 77.0, 76.8,
34.3, 27.9, 23.9, 23.5. Anal. Calcd for C22H28N: C, 86.27;
H, 9.15; N, 4.58. Found: C, 86.32; H, 9.12; N, 4.56. IR
(KBr, cm-1): 3,456(s), 2,966(s), 2,871(m), 1,641(vs),
1,606(m), 1,573(w), 1,508(m), 1,461(m), 1,438(w),
1,380(w), 1,363(m), 1,325(w), 1,307(s), 1,255(w),
1,240(w), 1,176(s), 1,097(s), 1,054(s), 1,018(w), 993(w),
X-ray crystallographic determination
Single-crystal X-ray diffraction analyses of complexes 1–2
were performed on a Bruker Apex II CCD diffractometer
operating at 50 kV and 30 mA using MoKa radiation
˚
(k = 0.71,073 A). Data collection and reduction were
123

Transition Met Chem (2013) 38:299–305
301
Table 1 Crystallographic data for compounds 1–2
Compound
1
2
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
C
38H40Br4N2O2Pd
C44H56Cl2N2Pd2
896.61
982.76
296 (2)
296 (2)
Triclinic
Monoclinic
P21/n
P-1
˚
a (A)
8.7889(10)
12.1647(7)
10.0977(6)
17.9704(10)
90.00
˚
b (A)
11.1925(12)
˚
c (A)
11.2702(12)
a (°)
b (°)
c (°)
62.534(2)
82.656(2)
102.4890(10)
90.00
86.042(2)
3
˚
V (A )
975.55(18)
2,155.2(2)
2
Z
1
D (Mg m3)
1.673
1.382
Limiting indices
Reflections collected/unique
Rint
-10 B h B 10, -13 B k B 12, -13 B l B 11
-14 B h B 14, -12 B k B 9, -11 B l B 21
10,260/3,465
0.0405
12,139/3,850
0.0229
F(000)
484
920
h (°)
2.05–25.20
1.048
3.04–25.20
1.110
Goodness-of-fit on F2
R(I [ 2r)
R1 = 0.0411
wR2 = 0.0988
R1 = 0.0659
wR2 = 0.1117
1.022, -0.970
R1 = 0.0216
wR2 = 0.0616
R1 = 0.0251
wR2 = 0.0642
0.309, -0.316
R (all data)
-3
˚
Largest diff. peak and hole (A
)
P
P
R = (||Fo| - |Fc||)/ |Fo|
P
P
wR = [ w(F2o - Fc2)2/ w(Fo)2]1/2
˚
performed using the APEX II software [21]. Multiscan
absorption corrections were applied for all the data sets
using SADABS, as included in the APEX II program [21].
Small residual absorption effects were treated with XABS2
[22]. The structures were solved by direct methods and
refined by least squares on F2 using the SHELXTL pro-
gram package [23]. All non-hydrogen atoms were refined
with anisotropic displacement parameters. Hydrogen atoms
attached to carbon and oxygen were placed in geometri-
cally idealized positions and refined using a riding model.
Crystallographic data are listed in Table 1. Selected bond
lengths and angles are given in Table 2.
Table 2 Selected bond lengths (A) and angles (°)
Complex 1
Pd–O1i
O1i–Pd1–O1
O1–Pd1–N1i
Complex 2
Pd1–C2
1.991(3)
180
Pd–N1i
O1i–Pd1–N1i
N1i–Pd1–N1
2.031(4)
92.05(14)
180
87.95(14)
1.979(2)
2.4538(6)
81.40(8)
176.08(5)
97.17(5)
Pd1–Cl1
2.3271(6)
2.0344(17)
94.83(6)
Pd1–Cl1i
Pd1–N1
C2–Pd1–N1
N1–Pd1–Cl1
N1–Pd1–Cl1i
C2–Pd1–Cl1
C2–Pd1–Cl1i
Cl1–Pd1–Cl1i
177.62(7)
86.569(19)
Symmetry codes: for 1 i = 1 - x, -y, -z; for 2 i = 1 - x, 1 - y, -z
The structure of complex 1 is shown in Fig. 1. The
molecule structure is trans-[Pd(L1)2], and the palladium
atom lies on a crystallographic inversion center and
assumes a square planar configuration. The Pd–O and
Results and discussion
To prepare complexes 1–2, the Schiff base ligands were
treated with Na2PdCl4 in equimolar amounts at room
temperature in methanol. The reactions proceeded without
reflux under mild conditions, thus preventing oxidation of
Pd(II) to Pd(IV) [24].
˚
Pd–N distances of 1.991(2) and 2.031(4) A, respectively,
are similar to those seen in related complexes [4, 25]. For
˚
instance, distances of 1.966(8) and 2.067(10) A for the
123

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Transition Met Chem (2013) 38:299–305
Fig. 2 The molecular structure of compound 2 with numbering
scheme. All H atoms were omitted for clarity. Symmetry code:
(i) 1 - x, -y, -z
Fig. 1 The molecular structure of compound 1 with numbering
scheme. All H atoms were omitted for clarity. Symmetry code:
(i) 1 - x, -y, -z
Powder X-ray diffraction analysis
In order to check the purity of complexes 1–2, bulk sam-
ples were measured by X-ray powder diffraction at room
temperature. As shown in Fig. 3, the peak positions of the
experimental patterns are in a good agreement with the
simulated patterns, which clearly indicates the high purity
of the complexes.
Pd–O and Pd–N bonds are found in a related bis(salicylide-
neaminato) palladium complex derived from 2-hydroxy-4-
(n-hexyloxy)benzaldehyde and 4-n-hexylaniline [26]. The
planes of the two phenyl rings are inclined by 3.98(2) and
88.31(4)°to the PdN2O2 coordination plane, respectively. In
the six-membered chelate rings, the six atoms (Pd1, O1, C1,
C6, C7, and N1) are essentially planar. The bite angle [N1–
Pd1–O1 = 92.04(2)°] is in good agreement with those found
in a structurally related mononuclear complex [5, 27].
The molecular structure of complex 2 is shown in Fig. 2.
Selected bond distances and angles are given in Table 2. In
this complex, each Schiff base ligand (L2) is bonded to the
di-l-chloro-bridged unit through nitrogen atoms and an
aromatic carbon atom, providing two equivalent five-
membered N–C–Pd–C-chelate rings. The geometry at the
Pd(II) center in 2 is square planar, with the two cyclo-
metalated ligands in a trans arrangement with respect to
˚
the PdꢀꢀꢀPd axis. The Pd1–C2 bond [1.979(3) A] is shorter
˚
than the expected value of 2.08 A based on the sum of the
covalent radii of carbon and palladium, but consistent with
those found for related complexes where partial multiple-
bond character of the Pd–C was assumed [28, 29]. The
˚
Pd1–N1 bond distance [2.034(2) A] is in agreement with
the sum of covalent radii for nitrogen and palladium [30],
and similar to values reported earlier [28, 29]. The lengths
˚
of the Pd–Cl bond trans to C [2.454(2) A] and the Pd–Cl
˚
bonds trans to N [2.327(5) A] reflect the different trans
influences exerted by the phenyl carbon and nitrogen
atoms. In the five-membered chelate rings, the five atoms
(Pd1, N1, C7, C1, and C2) are essentially planar. The bite
angle [C2–Pd1–N1 = 81.40(6)°] is in good agreement with
those found in a structurally related l-Cl dimer [29].
Fig. 3 PXRD patterns in complexes 1–2, a for 1 and b for 2
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Transition Met Chem (2013) 38:299–305
303
step occurs below 250 °C. The weight-loss step above
250 °C corresponds to decomposition of the structure.
Complex 2 shows a weight loss of 8.2 % (150–200 °C),
corresponding to the escape of two chlorine atoms (Calcd
7.9 %). Then, a sharp weight loss occurs above 250 °C due
to decomposition of the structure.
Electronic absorption and emission properties
of complexes 1–2
The UV–visible absorption spectra of 1 and 2 depicted in this
work have been obtained. The UV–vis spectral data in DMF
are listed in Table 3, and the absorption spectra are shown in
Fig. 5. The intense absorptions at kmax = 279 nm for 1,
kmax = 253, 273 nm for 2 (e = *104 dm3 mol-1 cm-1
)
are assigned to intraligand transitions of the cyclometalated
ligand. The e value at 361 for 1 and 345 for 2 is 4,800 and
4,200 dm3 mol-1 cm-1, respectively, and we tentatively
assign this band to a spin-allowed 4d(Pd) ? p*(L1)
(1MLCT) transition [2]. Absorption bands at
kmax = 340–400 nm in the related complexes [Pd(C,N)2]
(HC,N = 2-phenylpyridine, 2-(20-thienyl)pyridine, 7,8-
benzoquinoline) have also been ascribed to MLCT
Fig. 4 Thermogravimetric curves (DTA and TG) for complexes
1 (a) and 2 (b)
IR spectra analysis
FT-IR spectra of ligands HL1, L2, 1 and 2 were recorded
as KBr pellets (Fig. S1–S2). In the IR spectrum, strong,
broad bands at 3,473 cm-1 for HL1, 3,456 cm-1 for L2,
3,450 cm-1 for 1 and 3,467 cm-1 for 2 may be assigned to
the m(O–H) stretching vibrations of water molecules
(impurity). Features at 2,962, 2,883, and 1,622 cm-1 for
HL1, 2,966, 2,871, and 1,641 cm-1 for L2, 2,962, 2,931,
2,875, and 1,608 cm-1 for 1, 2,962, 2,871, and 1,597 cm-1
for 2 are associated with the methyl, methylene, and
–CH=N– groups, respectively. The absorption peaks of the
–CH=N– group in 1 and 2 are obviously blue-shifted
against the related ligands, perhaps due to the conjugative
effect between Pd2? ions and the ligands.
Thermogravimetric analyses of complexes 1–2
The TG and DTA curves of 1 and 2 are shown in Fig. 4.
Complex 1 has thermal stability as no clean weight-loss
Fig. 5 UV–vis absorption spectra of 1 and 2 in DMF at 298 K
Table 3 Photophysical data
Compounds
Medium (T/K)
k/nm (e/dm3 mol-1 cm-1
)
Emission k/nm
1
DMF (298)
Solid (298)
DMF (298)
Solid (298)
279 (34,200), 361 (4,800)
Non-tested
Non-emission
512, 644, 695, 716, 768
non-emission
2
253 (sh, 36,200), (273 (22,700), 345 (4,200)
Non-tested
525, 570, 622, 690, 714, 765
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Transition Met Chem (2013) 38:299–305
transitions [31]. Ligand-field d–d transitions have been
invoked for absorptions in the 340–400 nm range for ortho-
metalated azobenzene Pd(II) complexes [32], but unrea-
sonably high e values (ca. 8 9 103 dm3 mol-1 cm-1) are
reported. We reason that the e values at 361 nm for 1 and
345 nm for 2 are also larger than would be expected for d–d
transitions in Pd(II) derivatives.
luminescent lifetimes of solid 1 and 2 using an Edinburgh
FLS S920 phosphorimeter with a 450-W xenon lamp as
excitation source show lifetimes for 1 of s1 = 87.20 ns,
s2 = 190.45 nm, and s3 = 1,805.10 nm at 616 nm, for 2
of s1 = 69.92 ns, s2 = 136.40 nm, s3 = 1,714.26 nm at
570 nm (Fig. 7).
As part of a continuing program dedicated to lumines-
cent d8 systems, the spectroscopic behavior of complexes
1–2 is presented. Both structures are non-emissive in DMF
at room temperature, which is similar to previous reports
[2, 3]. Solid-state emission luminescence spectra of 1–2 at
room temperature are shown in Fig. 6. For 1, the emission
spectrum shows a shoulder at kmax = 512 nm and four
structureless bands at kmax = 644, 695, 716, and 768 nm,
respectively. For 2, the emission spectrum shows two sharp
bands at kmax = 525, 570 nm, and four structureless bands
at kmax = 622, 690, 714, and 765 nm, respectively. Both
the absorption and solid-state excitation spectra for 1–2
reveal the presence of low-energy ligand-field states in the
330–400 nm spectral region. The high-energy structures of
Suzuki reaction catalysis
The results reveal that the base and solvent for the Suzuki
reaction greatly influence catalytic activity (Table 4). The
reaction temperature has less effect on the catalytic activity.
Toluene is the best solvent for this catalytic system. In other
organic solvents, for example, ethanol/water, ethylene
glycol or DMF, relatively low yields of coupling products
were obtained. Among five different bases investigated for
these reactions, K2CO3 was found to be the most effective
(Table 4, entry 1); Na2CO3, CH3ONa, NaOAc, and NaOH
were substantially less effective. KF failed to promote the
reaction (Table 4, entry 10). Compared with other Pd(II)
complexes containing Schiff bases, the catalytic activities
of the present complexes for the Suzuki reaction proved to
be highly effective [14].
3
1 and 2 are assigned to a IL excited state [2]. The broad
structureless emission in the range of 600–800 nm is ten-
3
tatively assigned to an excimeric IL transition [2]. The
Fig. 6 Solid-state excitation and emission spectra of a 1 and b 2 at
298 K
Fig. 7 Luminescent lifetimes of a 1 and b 2 in the solid state at
298 K
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Transition Met Chem (2013) 38:299–305
305
Table 4 The effect of base and solvent on the complexes 1–2 catalyzed Suzuki reaction of 4-bromotoluene with phenylboronic acid
Entry
Base
Solvent
Temp.(°C)
Atm.
Time (min)
Yields (%) 1/2
1
2
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Na2CO3
CH3ONa
NaOH
NaOAc
KF
Toluene
80
25
Air
Air
Air
Air
Air
Air
Air
Air
Air
Air
50
50
50
50
50
50
50
50
50
50
92/95
78/80
73/76
76/77
65/69
56/59
51/53
40/44
Trace
–/–
Toluene
3
Ethanol/water = 2:2
Ethylene glycol
DMF
80
4
80
5
100
80
6
Toluene
7
Toluene
80
8
Toluene
80
9
Toluene
80
10
Toluene
80
4. Zhang H, Norman DW, Wentzell TM, Irving AM, Edwards JP,
Wheaton SL, Vogels CM, Westcott SA (2005) Transit Met Chem
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B, Roviello A, Tuzi A (2004) Inorg Chim Acta 357:548
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Chim Acta 357:913
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253:2599
Conclusion
In summary, we have described in this paper that the synthesis
of two new Schiff base ligands and their Pd(II) complexes.
Both 1 and 2 show good thermal stability and exhibit photo-
luminescence in the solid state at room temperature
(s1 = 86.40 ns, s2 = 196.21 ns, s3 = 1,923.31 ns at 768 nm
for 1, s1 = 69.92 ns, s2 = 136.40 ns, s3 = 1,714.26 ns at
570 nm for 2). Moreover, complexes 1 and 2 exhibit highly
catalytic activities in the Suzuki coupling reaction of 4-bro-
motoluene with phenylboronic acid, which are also very
sensitive to the choice of base and solvent.
14. Isiam SM, Mondal P, Tuhina K, Roy AS, Mondal S, Hossain D
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Supporting information available
16. Mukherjee S, Samanta S, Roy BC, Bhaumik A (2006) Appl Catal
A Gen 301:79
Fig. S1–S2 including the FT-IR spectrum of the ligands
(HL1 and L2) and the complexes 1–2. Crystallographic data
for the structures reported in this article have been deposited
with the Cambridge Crystallographic Data Centre, CCDC
910681-910682 for 1 and 2. Copies of this information may
be obtained free of charge from the Director, CCDC, 12
Union Road, Cambridge, CB21EZ, UK (fax: ?44 1223 336
033; e-mail: deposit@ccdc.cam.ac.uk or (http://www.ccdc.
cam.ac.uk) or also available from the author on request.
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Kodama T, Kitayama Y (2004) J Catal 228:141
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Acknowledgments We are thankful for financial support of this work
provided by Science and Technology Planning Project of Zhaoqing City
(2012G030), Science and Technology Innovation Planning Project of
Zhaoqing City (2012G013), and Distinguished Young Talents in
Higher Education of Guangdong Province (2012LYM_0134).
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