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N. Khadir et al. / Inorganica Chimica Acta 440 (2016) 107–117
of boiling acetonitrile (CH3CN) was added to a hot solution of
0.012 g of palladium(II) chloride (0.064 mmol) in 3 mL of DMSO.
The intense red solution was filtered and then remained at room
temperature for two days. Crystals of [L1aPd2(pz)] (1) were col-
lected by filtration, washed with acetonitrile and dried at 80 °C
under vacuum. Yield: 0.012 g (60%). Anal. Calc. for C24H18N4O2Pd2S:
C, 45.09; H, 2.84; N, 8.76; S, 5.02. Found: C, 44.08; H, 2.76; N, 8.59;
2-imino-4-methylphenolic protons), 6.22 (t, J = 2.0 Hz, 1H,
pyrazolic protons), 2.25 (s, 6H, CH3), 1.38 (s, 9H, tert-butyl).
2.6. General procedure for the Heck cross-coupling reaction
In a round-bottom flask equipped with a magnetic stir bar, aryl
halide (1.5 mmol), olefine (1 mmol), potassium carbonate
(1 mmol), catalysts 1–4 (0.02 mmol) and DMF (2 mL) were added
and heated at 100 °C. The mixture was vigorously stirred under
these reaction conditions and completion of the reaction was mon-
itored by TLC (Ethyl acetate: n-hexane, 25:75).
In each case, after completion of the reaction, the reaction mix-
ture was cooled to room temperature. Then, Ethyl acetate (5 mL)
and water (10 mL) were added. The aqueous layer was further
extracted by ethyl acetate (2 * 5 mL). The combined organic layers
were washed with saturated brine for two times, dried over
MgSO4, filtered, and concentrated to give the desired product.
All of compounds have been characterized by comparing their
melting point, IR and 1H NMR spectra with the values found in
the literatures [47–51].
S, 5.20%. IR (KBr, cmꢀ1): 3029
m(C–Har), 2921
m(C–Hal), 1666–1590
br
m
(C@Npz) and
m
(C@N ðL1aÞ), 1463
m
(C@C), 540 (Pd–N). UV–Vis
m
(DMF), [kmax, nm (
e
, L molꢀ1 cmꢀ1)]: 518 (1258), 365 (1957), 308
(2193), 234 (3257). 1H NMR (d ppm in DMSO-d6): 8.99 (s, 2H,
imine), 8.11 (s, 2H, protons of central aromatic ring), 7.84 (d,
J = 7.5 Hz, 2H, o-iminophenolic protons) 7.59 (d, J = 0.7 Hz, 2H,
pyrazolic protons), 7.16 (t, J = 7.0 Hz, 2H, o-iminophenolic protons),
6.84 (d, J = 8.5 Hz, 2H, o-iminophenolic protons), 6.57 (t, J = 7.5 Hz,
2H, o-iminophenolic protons), 6.22 (bs, 1H, pyrazolic protons), sol-
vent peak obscures the signal arising from protons of methyl group
attached to central aromatic ring.
2.5.2. [L1bPd2(pz)] (2)
The complex [L1bPd2(pz)] was prepared in a similar method to
that of complex [L1aPd2(pz)] (1) except that 1b was used in the
preparation instead of 1a. Yield: 70%. Anal. Calc. for
3. Results and discussion
C
26H22N4O2Pd2S: C, 46.79; H, 3.32; N, 8.40; S, 4.80. Found: C,
46.69; H, 3.36; N, 8.47; S, 4.72%. IR (KBr, cmꢀ1): 3056
m(C–Har),
3.1. Syntheses and spectroscopic characterizations
2920
(C@C), 542
m
(C–Hal), 1663–1610 br
m
(C@Npz) and
m
(C@N ðL1bÞ), 1477
m
The Schiff base condensation reaction of
2 equiv. of o-
m
(Pd–N). UV–Vis (DMF), [kmax, nm (e
, L molꢀ1 cmꢀ1)]:
aminophenol or 2-amino-4-methylphenol with 1 equiv. of the 2-
(N,N-dimethylthiocarbamato)-isophthalaldehyde of 5-tBu or 5-Me
lead to the formation of compartmental S-protected ligand precur-
sors 1a–2b having two available adjacent, similar coordination
compartments (Scheme 1). The binuclear palladium(II) complexes
1–4 were synthesized by reacting the ligand precursors 1a–2b
with PdCl2 in the presence of pyrazole at room temperature in
DMSO and acetonitrile mixed solvent. The free thiophenolate
ligands being liberated, via a PdII-promoted S-deprotection reac-
tion of corresponding ligand precursors, during the formation of
the complexes. These ligand precursors and binuclear palladium
(II) complexes were characterized by elemental analysis, IR, 1H
NMR and UV–Vis spectroscopies. Infrared spectra of the ligand pre-
cursors show a band around 3366–3420 cmꢀ1, which can be
ascribed to the stretching of phenolic OH group. This band has dis-
appeared in the spectra of all the complexes, indicating the depro-
tonation of phenolic OH followed by coordination to the metal ion.
A broad band around 1470–1600 cmꢀ1 in spectra of complexes
may be attributed to the stretching of C@N functional groups of
Schiff-base ligands and pyrazolyl group. In 1H NMR spectra of
ligands, the azomethine proton (–CH@N) signal was observed at
9.22–9.27 ppm. This signal was shifted up field in the spectra of
the binuclear complexes (9.00 ppm), suggesting shielding of the
514 (1363), 369 (1773), 300 (2987), 244 (3211). 1H NMR (d ppm in
DMSO-d6): 8.98 (s, 2H, imine), 8.12 (s, 2H, protons of central
aromatic ring), 7.66 (s, 2H, 2-imino-4-methylphenolic protons),
7.58 (s, 2H, pyrazolic protons), 6.99 (dd, J = 8.0, J = 1.5 Hz, 2H,
2-imino-4-methylphenolic protons), 6.73 (d, J = 8.0 Hz, 2H, 2-imino-
4-methylphenolicprotons), 6.22 (bs, 1H, pyrazolic protons), 2.33
(s, 6H, CH3), solvent peak obscures the signal arising from protons of
methyl group attached to central aromatic ring.
2.5.3. [L2aPd2(pz)] (3)
The complex [L2aPd2(pz)] was prepared in a similar method to
that of complex [L1aPd2(pz)] (1) except that 2a was used in the
preparation instead of 1a. Yield: 80%. Anal. Calc. for
C
27H24N4O2Pd2S: C, 47.59; H, 3.55; N, 8.22; S, 4.71. Found: C,
47.47; H, 3.43; N, 8.00; S, 4.8%. IR (KBr, cmꢀ1): 3053
m(C–Har),
2956
(C@C), 541
m
(C–Hal), 1669–1606 br
m
(C@Npz) and
m
(C@N ðL2aÞ), 1463
m
m
(Pd–N). UV–Vis (DMF), [kmax, nm (e
, L molꢀ1 cmꢀ1)]:
514 (1794), 364 (2235), 316 (3222), 241 (3251). 1H NMR (d ppm
in DMSO-d6): 9.08 (s, 2H, imine), 8.37 (s, 2H, protons of central
aromatic ring), 7.85 (d, J = 8.5 Hz, 2H, o-iminophenolic protons)
7.56 (d, J = 1.75 Hz, 2H, pyrazolic protons),7.16 (t, J = 7.5 Hz, 2H,
o-iminophenolic protons), 6.82 (d, J = 8.0 Hz, 2H, o-iminophenolic
protons), 6.58 (t, J = 7.5 Hz, 2H, o-iminophenolic protons), 6.22
(t, J = 2.0 Hz, 1H, pyrazolic protons), 1.38 (s, 9H, tert-butyl).
azomethine group in the complexes due to
p-back bonding from
Pd(II) [52]. The UV–Vis absorption spectra of the ligand precursors
and their binuclear Pd(II) complexes were recorded in methanol
and DMF solution, respectively. The precursor ligands show
2.5.4. [L2bPd2(pz)] (4)
The complex [L2bPd2(pz)] was prepared in a similar method to
that of complex [L1aPd2(pz)] (1) except that 2b was used in the
preparation instead of 1a. Yield: 75%. Anal. Calc. for
intense absorption bands (
in the ranges 220–300 and 358–364 nm characteristic of, respec-
tively, the
p⁄ and n ? p⁄ transitions [53–55]. The spectra of
the complexes show intense absorption bands in the range 230–
370 nm
= 104–103 Lꢀ1 molꢀ1 cmꢀ1), which are attributed to
intraligand transitions. In addition, the complexes exhibit a non-
ligand band around 515 nm (
> 103 Lꢀ1 molꢀ1 cmꢀ1) which are
attributed to the MLCT transition [56–59]. For square planar
e
= 104–103 Lꢀ1 molꢀ1 cmꢀ1) with kmax
p
?
C
29H23N4O2Pd2S:C, 49.45; H, 3.29; N, 7.95; S, 4.55. Found: C,
49.32; H, 3.20; N, 8.09; S, 4.248%.IR (KBr, cmꢀ1): 3014
m(C–Har),
(
e
2958 and 2920
1481 (C@C), 547
m
(C–Hal), 1663–1598br
m
(C@Npz) and
m
(C@N ðL2bÞ),
m
m(Pd–N). UV–Vis (DMF), [kmax, nm (
e
, L molꢀ1
e
cmꢀ1)]: 515 (1802), 365 (2611), 312 (3290), 240 (3937). 1H NMR
(d ppm in DMSO-d6): 9.04 (s, 2H, imine), 8.37 (s, 2H, protons of cen-
tral aromatic ring), 7.66 (s, 2H, 2-imino-4-methylphenolic protons)
7.56 (d, J = 2.0 Hz, 2H, pyrazolic protons), 6.99 (dd, J = 8.5, J = 1.2 Hz,
2H, 2-imino-4-methylphenolic protons), 6.72 (d, J = 8.5 Hz, 2H,
Pd(II) complexes, three spin-allowed d–d transitions 1A1g ? 1A2g
,
1A1g ? 1B1g and 1A1g ? 1Eg are expected in the visible region. In
the present binulear complexes these transitions were obscured
by either charge transfer or ligand bands [60,61].