Design, synthesis and properties of orthopalladated complexes: Proheterogeneous catalyst

Article abstract of DOI:10.1016/j.poly.2016.02.024

The reaction of multidentate ligand, 3-((E)-(2-((E)-4-aryldiazenyl)phenylimino)methyl)benzene-1,2-diol, H₂L (H₂L¹, 1a; H₂L², 1b and H₂L³, 1c) and (E)-2-((2-(aryldiazenyl)phenylamino)methyl)phenol, HA (HA¹, 3a; HA², 3b and HA³, 3c) [where H represents the dissociable protons upon complexation, and aryl groups of H₂L and HA are phenyl for H₂L¹ and HA¹, p-methylphenyl for H₂L² and HA², and p-chlorophenyl for H₂L³ and HA³], with Na₂PdCl₄ separately afforded orthometallated complexes [(L)Pd], (2a, 2b and 2c) and [(A)PdCl] (4a, 4b and 4c) respectively. In the case of [(L)Pd], the deprotonated L^2- ligands bind palladium (II) in a tetradentate (C,N,N,O) fashion whereas in the case of [(A)PdCl], the deprotonated A^- ligands bind Pd(II) in tridentate (C,N,N) manner. X-ray structures of [(L¹)Pd], (2a) and [(A¹)PdCl] (4a) were determined to confirm the molecular structures. Both the complexes 4a and 5a exhibited catalytic activity toward Suzuki and Heck reactions. Conversion of [(A)PdCl] to its oxidized form upon ligand oxidation is reported.

Full text of DOI:10.1016/j.poly.2016.02.024

Polyhedron 110 (2016) 165–171
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Polyhedron
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Design, synthesis and properties of orthopalladated complexes:
Proheterogeneous catalyst
Uttam Das a,b, Poulami Pattanayak a, Debprasad Patra a,c, Paula Brandão d, Vitor Felix d,
Surajit Chattopadhyay a,
⇑
a Department of Chemistry, University of Kalyani, Kalyani 741235, India
b Department of Chemistry, Kalyani Govt. Engg. College, Kalyani 741235, India
c Department of Chemistry, East Calcutta Girls’ College, Kolkata 700089, India
d Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of multidentate ligand, 3-((E)-(2-((E)-4-aryldiazenyl)phenylimino)methyl)benzene-1,2-diol,
H2L (H2L1, 1a; H2L2, 1b and H2L3, 1c) and (E)-2-((2-(aryldiazenyl)phenylamino)methyl)phenol, HA (HA1,
3a; HA2, 3b and HA3, 3c) [where H represents the dissociable protons upon complexation, and aryl groups
of H2L and HA are phenyl for H2L1 and HA1, p-methylphenyl for H2L2 and HA2, and p-chlorophenyl for
H2L3 and HA3], with Na2PdCl4 separately afforded orthometallated complexes [(L)Pd], (2a, 2b and 2c)
and [(A)PdCl] (4a, 4b and 4c) respectively. In the case of [(L)Pd], the deprotonated L2ꢀ ligands bind pal-
ladium (II) in a tetradentate (C,N,N,O) fashion whereas in the case of [(A)PdCl], the deprotonated Aꢀ
ligands bind Pd(II) in tridentate (C,N,N) manner. X-ray structures of [(L1)Pd], (2a) and [(A1)PdCl] (4a) were
determined to confirm the molecular structures. Both the complexes 4a and 5a exhibited catalytic activ-
ity toward Suzuki and Heck reactions. Conversion of [(A)PdCl] to its oxidized form upon ligand oxidation
is reported.
Received 15 January 2016
Accepted 5 February 2016
Available online 4 March 2016
Keywords:
Orthopalladation
Crystal structure
Oxidation reaction
Suzuki and Heck reactions
Proheterogeneous catalyst
Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction
one of the interesting area in current chemical research [1–4].
The notable example involving the condensation of free phenolic
Catalytic activities of organometallic palladium (II) complexes,
incorporating azo ligands, in homogenous media have been
reported [1–4]. Immobilization of such complexes on solid support
is scarce in the chemical literature [5]. Immobilization of potential
catalysts on solid support provides the scope to carry out the cat-
alytic process in heterogeneous media. Several strategies have
been adopted to anchor the catalyst on solid support [6–18].
Anchoring the catalyst on solid support through covalent linkage
is one of the strategies to develop heterogeneous catalysts [6–18].
Synthesis of appropriately designed new palladium complexes
possessing catalytic activity in homogenous media and suitable
for anchoring on polymer support through covalent linkage is
–OH, a spectator functional group in the ligand backbone, with
the C–Cl fragment on the solid support is one among several strate-
gies employed for affixing the metal complexes on solid polymer
support (Scheme 1) [19]. Thus synthesis of metal complexes with
free spectator –OH functional group in the ligand backbone and
examination of catalytic properties of the complexes in homoge-
nous media are of interest before anchoring. Therefore, we contem-
plated to design ligands where one free spectator phenolic –OH
functional group would be present. Thus we designed the ligand
system 1 with the expectation to obtain palladium complexes, 2.
Further, the ligands 3 were used for the synthesis of palladium
complexes with a free phenolic –OH functional group.
⇑
Corresponding author.
E-mail address: scha8@rediffmail.com (S. Chattopadhyay).
http://dx.doi.org/10.1016/j.poly.2016.02.024
0277-5387/Ó 2016 Elsevier Ltd. All rights reserved.

166
U. Das et al. / Polyhedron 110 (2016) 165–171
OH
n
M
+
H2C
O
CH2 H2C
O
O
CH2Cl CH2Cl CH2Cl
M
M
M
Metal Complex
Chloromethyl polystyrene
Polymer anchored complex
Scheme 1.
R
R
R
HO
HO
O
HO
HO
Pd
N
N
N
N
N
N
N
N
HN
H
H
1
2
3
Herein, we report synthesis of two types of palladium com-
obtained after evaporation of the solvent. Isolated yield: 2.54 g
(80%). Anal. calc. C19H15N3O2 (317): C, 71.92; H, 4.73; N, 13.25.
Found: C, 71.63; H, 4.82; N, 13.35%. UV–Vis spectrum (CH2Cl2) kmax
plexes with free phenolic –OH function. Suitability and catalytic
activities of the newly synthesized complexes in homogeneous
media have been described.
(e
, Mꢀ1 cmꢀ1) = 340 (15869), 300 (28668). IR (KBr pellets, cmꢀ1):
m
= 1461 (N@N), 1626 (C@N), 3468 (O–H). 1H NMR CDCl3: d
14.61 (s, OH), 8.64 (s, CH@N), 8.04 (d, 2H), 7.84 (d, 1H), 7.58–
7.46 (m, 5H), 7.02 (d, 1H), 6.94 (d, 1H), 6.76 (t, 1H), 6.06 (s, 1H).
2. Experimental
2.1. Materials
2.3.2. H2L2, 1b and H2L3, 1c
Ligands 1b and 1c were prepared using 2-(p-tolylazo)aniline
and 2-(p-chlorophenylazo) aniline in place of 2-(phenylazo)ani-
line, respectively. Yield: 1b, 82% and 1c, 78%.
2-(Arylazo)anilines were prepared according to the reported
procedure [20–22]. The solvents used in the reactions were of
reagent grade (E. Merck, Kolkata, India) and were purified and
dried by reported procedure [23]. 2,3-Dihydroxybenzaldehyde
was purchased from Sigma Aldrich and used without further
purification. Palladium chloride, sodium borohydride, potassium
carbonate, NaBH4 and silica for thin layer chromatography were
purchased from E. Merck, Kolkata, India. Na2[PdCl4] was prepared
following a reported procedure [24]. Phenylboronic acid, iodoben-
zene, Styrene, 3-chloro per benzoic acid were purchased from
Aldrich.
Anal. calc. C20H18N3O2 (331): Isolated yield: 2.71 g (82%). C,
72.50; H, 5.44; N, 12.69. Found: C, 72.53; H, 5.42; N, 12.75%. UV–
Vis spectrum (CH2Cl2) kmax
(e
, Mꢀ1 cmꢀ1) = 327 (14629), 299
(28305). IR (KBr pellets, cmꢀ1):
m
= 1454 (N@N), 1616 (C@N),
3407 (O–H). 1H NMR CDCl3: d 14.7 (s, OH), 8.59 (s, CH@N), 7.93
(d, 2H), 7.81 (d, 1H), 7.50 (t, 1H), 7.44 (d, 1H), 7.37–7.31 (m, 3H),
7.00 (d, 1H), 6.90 (d, 1H), 6.73 (t, 1H), 6.16 (s, 1H), 2.43 (t, 3H).
C
19H14N3O2Cl (351.5): Isolated yield: 2.74 g (78%). Anal Calc. C,
64.86; H, 3.98; N, 11.95. Found: C, 64.79; H, 3.95; N, 11.99%. UV–
Vis spectrum (CH2Cl2) kmax
, Mꢀ1 cmꢀ1) = 356 (18825), 304
(32650). IR (KBr pellets, cmꢀ1):
= 1454 (N@N), 1626 (C@N),
(e
2.2. Physical measurements
m
3411 (O–H). 1H NMR CDCl3: d 14.65 (s, OH), 8.60 (s, CH@N), 7.96
(d, 2H), 7.80 (d, 1H), 7.56 (t, 1H), 7.49–7.44 (m, 3H), 7.34 (t, 1H),
7.03 (d, 1H), 6.92 (d, 1H), 6.75 (t, 1H), 6.16 (s, 1H).
Microanalysis (C, H, N) was performed using a Perkin-Elmer
2400 C, H, N, S/O series II elemental analyzer. Infrared spectra were
recorded on a Parkin-Elmer L120-00A FT-IR spectrometer with the
samples prepared as KBr pellets. Electronic spectra were recorded
on a Shimadzu UV-1800 PC spectrophotometer. 1H NMR spectra
were obtained on Bruker 400 spectrometers in CDCl3 and
[D6]-DMSO. Mass spectra were obtained on Waters XEVO G2-S
QTOf mass spectrometer.
2.4. Synthesis of ligands HA, 3
The ligands HA2, 3b and HA3, 3c were prepared following same
procedure as reported earlier for 3a [25] using 2-(p-tolylazo)ani-
line and 2-(p-chlorophenylazo) aniline in place of 2-(phenylazo)
aniline respectively.
2.3. Synthesis of ligands H2L, 1
2.4.1. HA2, 3b and HA3, 3c
All the ligands, 1a, 1b and 1c were prepared following similar
procedures. A representative procedure for 1a is given below.
Anal. Calc. C20H19N3O (317): Isolated yield: 0.448 g (85%). C,
75.71; H, 5.99; N, 13.25. Found: C, 75.68; H, 5.95; N, 31.31%. UV–
2.3.1. 1a
Vis spectrum (CH2Cl2) kmax (e,
Mꢀ1 cmꢀ1) = 450 (2930), 326
A mixture of 2-(phenylazo)aniline (1.97 g, 10 mmol) and 2,3-
dihydroxybenzaldehyde (1.38 g, 10 mmol) in 100 cm3 dry diethyl
ether was refluxed for 12 h. A red crystalline solid of 1a was
(6500), 229 (6745). IR (KBr pellets, cmꢀ1):
m = 1453 (N@N), 3400
(OH). 1H NMR CDCl3: d 7.88 (s, NH), 7.75 (d, 1H), 7.63 (d, 2H),
7.24–7.13 (m, 4H), 7.00–6.81 (m, 3H), 4.50 (d, 2H), 2.34 (s, 3H).

U. Das et al. / Polyhedron 110 (2016) 165–171
167
Anal. Calc. C19H16N3OCl (337.5): Isolated yield: 0.448 g (80%). C,
of the product is 0.073 g (50%). Anal. Calc. C19H17N3OPd (444.25): C,
67.56; H, 4.74; N, 12.44. Found: C, 67.54; H, 4.76; N, 12.51%. UV–
51.37; H, 3.64; N, 9.46. Found: C, 51.34; H, 3.67; N, 9.51%. UV–Vis
Vis spectrum (CH2Cl2) kmax
(
e
,
Mꢀ1 cmꢀ1) = 451 (2553), 325
spectrum (CH2Cl2) kmax
372 (55344), 358 (56638), 282 (348111), 250 (59190). IR (KBr pel-
lets, cmꢀ1): = 1393 (N@N), 3116 (N–H), 3330 (O–H). 1H NMR
(e
, Mꢀ1 cmꢀ1) = 484 (13911), 405 (35766),
(5468), 223 (5876). IR (KBr pellets, cmꢀ1):
m = 1453 (N@N), 3410
(O–H). 1H NMR CDCl3: d 78.16 (s, NH), 7.77 (d, 1H), 7.72 (d, 2H),
7.45–7.37 (m, 2H), 7.28–7.22 (m, 1H), 7.23–7.13 (m, 2H), 6.89–
6.80 (m, 4H).
m
CDCl3: 7.62 (d, 2H), 7.27 (t, 2H), 7.16 (d, 1H), 7.11 (t, 1H), 7.04 (t,
1H), 6.99–6.91 (m, 3H), 6.80 (d, 1H), 6.68 (t, 1H), 6.11 (broad s,
NH), 4.21 (broad, CH2).
2.5. Syntheses of [(L)Pd], 2
2.6.2. [(A2)PdCl], 4b and [(A3)PdCl], 4c
All the complexes, [(L1)Pd], 2a, [(L2)Pd], 2b, and [(L3)Pd], 2c,
were prepared following similar procedures. A representative pro-
cedure for 2a is given below.
Complexes [(A2)PdCl], 4b and [(A3)PdCl], 4c were prepared
using HA2 and HA3 in place of HA1, respectively. Yield: [(HL2)Pd]
55% and [(HL3)Pd] 45%.
Anal. Calc. C20H18N3OPd (458.28): Yield of the product is 0.082 g
(70%), C, 52.41; H, 3.97; N, 9.17. Found: C, 52.39; H, 3.99; N, 9.20%.
2.5.1. [(L1)Pd], 2a
To a solution of Na2PdCl4 (0.06 g, 0.02 mmol) in 5 cm3 metha-
nol, (0.065 g, 0.2 mmol) H2L1 in 15 cm3 methanol, was added drop-
wise. Immediately the color of the solution changed to brown. This
solution was stirred for 8 h constantly at 60 °C. The dark colored
solid precipitate was separated by filtration. And the solid mass
was dissolved in dichloromethane. The pure product was separated
by preparative thin layer chromatography on silica gel one brown
band separated using benzene as solvent. Upon evaporation of the
solvent, a dark solid of pure [(L1)Pd] was obtained. Single crystal
was obtained from slow evaporation of the solvent from dichloro-
methane. Isolated yield is 37 mg (45%), Anal. Calc. C19H14N3O2Pd
(421.74): C, 54.06; H, 3.32; N, 9.96. Found: C, 53.94; H, 3.29; N,
UV–Vis spectrum (CH2Cl2) kmax
(7666), 374 (8466), 350 (14660), 282 (11266), 255 (24533). IR
(KBr pellets, cmꢀ1): = 1390 (N@N), 3143 (N–H), 3325 (O–H). 1H
(e
, Mꢀ1 cmꢀ1) = 480 (8900), 410
m
NMR CDCl3: 7.63 (d, 1H), 7.43 (d, 1H), 7.40–7.28 (m, 2H), 7.6–
7.24 (m, 1H), 7.20 (t, 1H), 7.15–7.00 (m, 3H), 6.98 (t, 2H), 6.73 (t,
1H), 6.20 (broad s, N–H), 4.22 (broad, CH2).
Anal. Calc. C19H16N3OPdCl (478.69): Yield of the product is
0.071 g (45%), C, 47.67; H, 3.16; N, 8.78. Found: C, 47.70; H, 3.18;
N, 8.82%. UV–Vis spectrum (CH2Cl2) kmax
(8882), 403 (15764), 375 (24058), 360 (24411), 283 (17294),
(e
, Mꢀ1 cmꢀ1) = 480
259 (25000). IR (KBr pellets, cmꢀ1):
m = 1395 (N@N), 3139 (N–H),
3334 (O–H). 1H NMR CDCl3: 7.43 (d, 1H), 7.36 (t, 2H), 7.19–7.15
(m, 2H), 7.13–7.07 (m, 2H), 6.95–6.92 (m, 1H), 6.87 (d, 1H), 6.81
(d, 1H), 6.72 (d, 1H), 6.68 (t, 1H), 6.58 (broad s, N–H), 4.25 (broad,
CH2).
9.98%. UV–Vis spectrum (CH2Cl2) kmax
(3952), 362 (24035), 344 (22402), 307 (19366), 292.6 (19501)
(e,
Mꢀ1 cmꢀ1) = 518.5
247.5 (26699). IR (KBr pellets, cmꢀ1):
m = 1426 (N@N), 1606
(C@N), 3373 (O–H). 1H NMR d6-DMSO: 9.150 (s, 1H), 8.105 (d,
1H), 8.071 (s, 1H), [7.839 (d, 2H), or 7.854–7.827 (m, 2H)], 7.744
(d, 1H), 7.656 (t, 1H), [7.36 (q, 2H), or 7.387–7.334 (m, 2H)],
7.234 (t, 1H), 6.967 (d, 1H), 6.866 (d, 1H), 6.476 (t, 1H).
2.7. Crystallography
Single crystals of 2a & 4a were grown by slow evaporation of
dichloromethane- and methanol solutions at 298 K respectively.
2.5.2. [(L2)Pd], 2b and [(L3)Pd], 2c
Data were collected by
diffractometer with Mo K
x
a
-scan technique on a Bruker Smart CCD
radiation monochromated by graphite
Complexes [(L2)Pd], 2b and [(L3)Pd], 2c were prepared using
H2L2 and H2L3 in place of H2L1, respectively. Yield: [(L2)Pd] 50%
and [(L3)Pd] 40%.
crystal. Structure solution was done by direct method with
SHELXS–97 program [26,27]. Full matrix least square refinements
on F2 were performed using SHELXL–97 program [26,27]. All non-
hydrogen atoms were refined anisotropically using reflections
I > 2r (I). The C-bound hydrogen atoms were included in calculated
positions and refined as riding model. Data collection parameters
Anal. Calc. C19H14N3O2Pd (435.74): Isolated yield is 43 mg (50%),
C, 52.32; H, 3.21; N, 9.64. Found: C, 52.38; H, 3.24; N, 9.72%. UV–
Vis spectrum (CH2Cl2) kmax
(16746), 364.7 (20097), 310 (16313), 294.4 (17008) 248.3
(e,
Mꢀ1 cmꢀ1) = 514 (4676), 387
(21750). IR (KBr pellets, cmꢀ1):
m = 1431 (N@N) , 1607 (C@N),
and relevant crystal data are collected in Table 1.
3373 (O–H). 1H NMR d6-DMSO: 9.112 (s, 1H), 8.082 (d, 1H),
8.006 (s, 1H), 7.70 (d, 1H), 7.616 (t, 1H), 7.554 (s, 1H), 7.348 (t,
1H), 7.027 (d, 1H), 6.961 (d, 1H), 6.868 (d, 1H), 6.470 (t, 1H),
2.348 (t, 3H).
2.8. General procedures for the Suzuki cross coupling reaction
A mixture of phenyl boronic acid (0.28 g, 2.5 mmol), aryl halide
(2.5 mmol), potassium carbonate (5 mmol) and the palladium
complex (0.002 mmol) in THF (20 ml) was refluxed for 3 h as writ-
ten in Table 4. After completion of the reaction the solvent was
evaporated and washed with water and extracted in diethyl ether
and dried over anhydrous Na2SO4, passed through 12// silica col-
umn (60–120 mesh). Upon evaporation of the solvent, solid pure
product was isolated; yields of the products were determined
and characterized by H1 NMR spectroscopy (Table 4).
Anal. Calc. C19H13N3O2ClPd (456.24): Isolated yield is 32 mg
(40%), C, 49.97; H, 2.85; N, 9.21. Found: C, 46.03; H, 2.83; N,
9.25%. UV–Vis spectrum (CH2Cl2) kmax
(5707), 385.6 (21314.7), 262 (26728.7), 316 (21181), 309
(e,
Mꢀ1 cmꢀ1) = 514.9
(20662), 260.5 (26474). IR (KBr pellets, cmꢀ1):
m = 1430 (N@N),
1607 (C@N), 3385 (O–H). 1H NMR d6-DMSO: 9.03 (s, 1H), 8.19 (s,
1H), 8.00 (d, 1H), 7.79 (d, 1H), 7.73 (d, 1H), 7.57 (t, 1H), 7.27 (t,
1H), 7.18 (d, 1H), 6.87 (d, 1H), 6.77 (d, 1H), 6.40 (t, 1H).
2.6. Syntheses of [(A)PdCl], 4
2.9. General procedures for the Heck reaction
2.6.1. [(A1)PdCl], 4a
A methanolic solution (5 cm3) of Na2PdCl4 (0.1 g, 0.33 m mol)
was added to a solution (15 cm3) of HA1 (0.1 g, 0.33 mmol) in
methanol dropwise. The color of the solution turned reddish
brown. The resulting solution was refluxed for 12 h. Solvent was
evaporated and solid mass obtained. Finally the pure product
was washed by petroleum ether to remove the excess ligand. Yield
Styrene (5.0 mmol), aryl halide (5.0 mmol), potassium carbon-
ate (10.0 mmol) and the palladium complex (0.003 mmol) were
mixed in methanol (20 ml) and refluxed for 2 h as mentioned in
Table 5. At the end of the reaction solvent was evaporated and
the residue was poured into water and extracted in diethyl ether,
dried over anhydrous Na2SO4 and pass through 12// silica column

168
U. Das et al. / Polyhedron 110 (2016) 165–171
Table 1
Table 4
Crystallographic Data for 2a and 4a.
Suzuki cross coupling reaction with catalyst 2a and 4a.
2a
4a
Aryl halide
Product
Isolated yield
Isolated yield
with 2a
with 4a
Formula
C
19H14N3O2Pd
C19H15ClN3OPd
443.21
monoclinic
P 2 1/n
11.8643(6)
16.4117(10)
18.5363(10)
90
99.4800(10)
90
0.71073
3560.0(3)
1768
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
412.54
monoclinic
P21/n (No.14)
6.6459(4)
12.4235(7)
18.8547(10)
90
97.064(2)
90
0.71073
1544.93(15)
822
87
85
I
O2N
O2N
95
96
I
I
a
(°)
b (°)
(°)
c
NO2
NO2
k (Å)
97
96
98
95
V (Å3)
F(000)
Z
4
149
1.774
1.132
8
150
1.510
0.889
T (K)
D (mg mꢀ3
)
I
l
(Mo Ka) (mmꢀ1
)
R1 (all data)
wR2 [I > 2 (I)]
Goodness-of-fit (GOF) on F2
0.0251
0.0547
1.03
0.0328
0.0792
0.98
r
82
80
I
82
77
80
75
Table 2
Br
Br
Selected bond distances (Å) and angles (°) for compound 2a.
Distances
Pd(1)–O(1)
Pd(1)–N(2)
Pd(1)–N(3)
Pd(1)–C(1)
O(1)–C(19)
2.001(6)
1.916(6)
2.035(7)
2.008(9)
1.321(12)
O(2)–C(18)
N(1)–N(2)
N(1)–C(6)
N(2)–C(7)
N(3)–C(12)
1.370(13)
1.277(10)
1.413(11)
1.411(10)
1.428(11)
NO2
NO2
77
78
Br
Angles
O1–Pd1–N2
O1–Pd1–N3
O1–Pd1–C1
N2–Pd1–N3
N2–Pd1–C1
N3–Pd1–C1
Pd1–O1–C19
Pd1–N3–C12
Pd1–N3–C13
177.5(3)
94.8(3)
101.6(3)
83.2(3)
N3–C12–C7
N3–C12–C11
Pd1–C1–C6
Pd1–N2–N1
Pd1–N2–C7
N1–N2–C7
N2–N1–C6
C12–N3–C13
Pd1–C1–C2
114.9(7)
126.2(8)
107.8(6)
123.2(5)
115.4(6)
121.4(6)
108.6(7)
124.4(8)
133.7(7)
Solvent = THF/DMF, base = K2CO3, time = 3 h.
80.3(3)
chloropalladate in methanol afforded the orthometallated com-
plexes, 2, (hereinafter, abbreviated as [(L)Pd] in this paper). The
compound was crystalised from dichloromethane solution by slow
evaporation. Interestingly, reaction of ligands 3 (abbreviated as
HA) with sodium tetrachloropalladate afforded the orthometal-
lated complexes 4 (abbreviated as [(A)PdCl]), where the dangling
phenolic –OH did not participate in coordination and remained
free (Scheme 3). The compound crystallized from the reaction
mixture.
163.5(3)
121.6(5)
111.1(5)
124.5(6)
Table 3
Selected bond distances (Å) and angles (°) for compound 4a.
Distances
Pd(1)–Cl(1)
Pd(1)–N(2)
Pd(1)–N(3)
Pd(1)–C(1)
2.3307(8)
1.942(2)
2.159(2)
1.967(3)
N1–N2
1.273(3)
1.520(4)
1.458(4)
1.365(4)
3.2. Characterization
N3–C13
N3–C12
O(1)–C(19)
All the H2L, 1, exhibit a broad absorption maxima near 310 nm
whereas HA, 3, ligands displayed characteristic two clear absorp-
tion maxima near 430 nm and 320 nm in UV–Vis spectra (Fig. 1).
The orthopalladated complexes, [(L)Pd], 2, showed low energy
absorption near 520 nm, whereas [(A)PdCl], 4, exhibited low
energy twin absorptions near 520 and 480 nm along with several
other absorption bands within the 450–250 nm [28,29]. Relevant
data are collected in experimental section.
Angles
Cl1–Pd1–N2
Cl1–Pd1–N3
N2–Pd1–N3
N2–Pd1–C1
N3–Pd1–C1
177.47(7)
99.69(6)
82.72(9)
80.04(12)
162.56(11)
Pd1–C1–C2
N1–C6–C1
N1–C6–C5
N2–C7–C12
N2–C7–C8
133.0(2)
118.8(3)
119.2(3)
114.7(3)
123.7(3)
(60–120 mesh). After evaporation of the ether, solid pure products
were obtained. The yields of the products obtained from all the
reactions were determined after isolation and characterized by
1H NMR spectra (Table 5).
The
m
N=C stretches of H2L, 1, ligands (ꢁ1626 cmꢀ1) were shifted
to lower frequency (1607 cmꢀ1) in the IR spectra of [(L)Pd], 2, com-
plexes indicating the coordination of the aldimine nitrogen [28,30].
The mN=N frequencies of H2L (ꢁ1452 cmꢀ1) shifted to lower fre-
quency (ꢁ1430 cmꢀ1) in [(L)Pd] indicating coordination of the
azo nitrogen [28–30,31]. The mOH of the H2L, 1, ligands appeared
within the range 3410–3470 cmꢀ1 which shifted to ꢁ3375 cmꢀ1
in the [(L)Pd] complexes after coordination [28,30,31]. The mNH
stretch of the ligands HA2, 3b and HA3, 3c, appeared near
3400 cmꢀ1 which did not disappear upon complexation consistent
with the structural formula as shown in 4 of Scheme 3. Relevant
data are collected in experimental section.
3. Results and discussion
3.1. Syntheses
New ligands 1, (hereinafter, abbreviated as H2L), were success-
fully synthesized by the condensation of 2-arylazo aniline A, with
vanillin (Scheme 2). Further reaction of 1 with sodium tetra-

U. Das et al. / Polyhedron 110 (2016) 165–171
169
Table 5
hydroxy functions and the singlet for CH@N proton appeared near
d 8.6 for H2L [28,31]. The pattern and proton counts of aromatic
protons for H2L1 three doublets, each for one equivalent proton,
appeared at d 6.94, 7.03 and 7.84 and one doublet for two equiva-
lent proton was visible at d 8.03; two triplet for one equivalent pro-
ton at d 6.77, d 7.39 and a multiplet (d 7.37–d 7.59) for five protons
accounted for the total number of twelve protons, H2L2 and H2L3
matched well with the structural formula. One of the phenolic
OH resonances of H2L, 1, disappeared in the 1H NMR spectra of
[(L)Pd], complexes 2, and the broad singlet near d 9.1 for one equiv-
alent proton was consistent with a free OH [28,31]. The aldimino
proton of [(L)Pd], 2, complexes (ꢁd 8.0) shifted to upfield region
compared to that of the ligands (ꢁd 8.6). The pattern and proton
counts of aromatic region matched well with the structural formu-
lae of [(L1)Pd], [(L2)Pd] and [(L3)Pd] [e.g. for [(L1)Pd]; eleven proton
resonances appeared as six doublets and five triplets each for one
equivalent proton], the singlets [For [(L2)Pd] at d 7.55 and for [(L3)
Pd] at d 7.79 were are consistent with orthopalladation]. Thus for
all the [(L)Pd] complexes, retention of structures in solution could
be established. The 1H NMR spectrum of HA1, 3a, was reported
elsewhere [25]. The 1H NMR spectra of HA2, 3b, and HA3, 3c, have
been recorded and matched well with the structures. The NH pro-
tons of the ligands (near d 8.0) appeared as broad triplet due to
coupling with methylene protons. The same NH protons were
observed within d 6.1–6.5 as broad triplet indicating existence of
NH protons in the complexes. Methylene protons of HA2 and
HA3, adjacent to the amino group appeared near d 4.5 as doublet
due to coupling with the amino proton. The doublet of methylene
protons split into two apparent singlets due to nonequivalence in
the corresponding complexes, [(A)PdCl], 4 [29]. All other data are
collected in experimental section.
Heck reaction with catalyst 2a and 4a.
Aryl halide
Product
Isolated
yield with
2a
Isolated
yield with
4a
84
82
Br
Br
85
82
NO2
NO2
81
91
80
92
Br
I
NO2
NO2
84
86
82
85
I
O2N
O2N
I
91
93
90
90
I
3.3. X-ray structure
Suitable Crystals of [(L1)Pd], 2a and [(A1)PdCl], 4a, were picked
for X-ray studies. Perspective views of the molecular structures
have been shown in Figs. 2 and 3. Selected bond distances and
angles are collected in Tables 2 and 3 respectively. In 2a the geom-
etry about palladium(II) is distorted square planar, where the dian-
ionic deprotonated ligand (L1)2ꢀ binds in tetradentate (C,N,N,O)
fashion forming the orthometallated chelate.
I
Solvent = MeOH, base = K2CO3, time = 2 h.
The compositions of ligands H2L, 1, and HA, 3, matched well
with the C, H, N analytical data and 1H NMR spectral data. The
broad singlets near d 14.65 and d 6.1 for two phenolic OH of two
In the molecular structure of 4a the geometry about palladium
is distorted square planar where the mono anionic deprotonated
O
R
HO
R
HO
R
OH
OH
O
N
HO
N
Na2PdCl4
Pd
N
N
N N
N
500C
Stirr
Et2O
Reflux
N
NH2
1
2
A
Compound
Abbreviation
R
H
1a
H2L1
1b
1c
H2L2
H2L3
CH3
Cl
H
2a
[(L1)Pd]
CH3
Cl
2b
2c
[(L2)Pd]
[(L3)Pd]
Scheme 2.

170
U. Das et al. / Polyhedron 110 (2016) 165–171
R
R
Na2PdCl4
HO
Cl
HO
HN
Reflux
Pd
N
N
N
N
N
H
H
H
3
4
Abbreviation
R
H
Compound
3a
HA1
CH3
Cl
3b
3c
HA2
HA3
4a
[(A1)PdCl]
H
CH3
Cl
4b
4c
[(A2)PdCl]
[(A3)PdCl]
Scheme 3.
Fig. 3. Molecular structure of 3a with atom numbering scheme. Hydrogen atoms
are omitted for clarity.
Fig. 1. UV–Vis spectra of H2L2
(
), HA2
(
), [(L2)Pd] ( ) and [(A2)PdCl] (ꢀ).
ligand (Lꢀ) binds in a tridentate (C,N,N) fashion with a chloride
ligand which satisfies the tetra coordination (Fig. 3).
3.4. Catalytic activity of 2a and 4a
3.4.1. Suzuki cross-coupling and Heck coupling reactions
Both the complex 2a and 4a exhibited catalytic activity
toward Suzuki cross coupling using phenylboronic acid and aryl
halides as substrates, whereas arylhalides (bromoaryls and
iodoaryls) and styrene were used as substrates for Heck reac-
tions Eq. (1).
B(OH)2
THF/ DMF
Reflux
MeOH
Reflux
X
K2CO3
Catalyst 2a, 4a
R
K2CO3
ð1Þ
R
Catalyst
2a, 4a
R
X = I or Br
R = H, Me, NO2
Fig. 2. Molecular structure of 2a with atom numbering scheme. Hydrogen atoms
are omitted for clarity.

U. Das et al. / Polyhedron 110 (2016) 165–171
171
O
HO
Cl
Pd
Cl
N
HCl
Pd
2e, -2H
Pd
N
N
N
N
N
N
N
N
OH
H
I
4
Scheme 4.
The isolated yields, reaction time are collected in Tables 4 and 5.
All the reactions were carried out under open atmosphere and
without addition of any other ligand.
After one set of catalytic reaction, we could recover the catalyst,
[(L1)Pd], 2a, from homogenous mixture up to the extent of 57% as
determined spectrophotometrically. On the other hand, [(A1)PdCl],
4a, complex converted to compound I after the catalytic reactions
as shown in Scheme 4.
Appendix A. Supplementary data
CCDC 763730 and 1445628 contains the supplementary crystal-
lographic data for 2a and 4a. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at http://dx.doi.org/10.
1016/j.poly.2016.02.024.
As a result, we contemplated to study the status of [(A1)PdCl] in
solution in presence of air. Gradual change in absorption spectrum
of [(A1)PdCl] was monitored spectrophotometrically in dichloro-
methane or methanol solution at different time interval for 3 days
at room temperature (Fig. S34). The complex, [(A1)PdCl] trans-
formed to I in dichloromethane solution but not in methanol solu-
tion. Therefore the oxidation of alkyl amine (–NH–CH2–) of [(A1)
PdCl] to imine (–N@CH–) of compound I occurred in dichloro-
methane solution with concomitant coordination of phenolato –
O. Although the compound I, was reported earlier but the catalytic
property of I toward Suzuki coupling was not examined and
reported [28]. Nevertheless, compound I exhibited catalytic effi-
cacy for one substrate under identical conditions as that of [(A1)
PdCl]. Since I exhibited catalytic property toward Suzuki coupling
and [(A1)PdCl] gets converted to I in solution so we could not
determine the real form of the catalyst when coupling was carried
out using [(A1)PdCl] catalyst. Herein the Pd(II)–Pd(IV) catalytic
cycle may be proposed to be operative [32] in case of 2a whereas
in the case of 4a it was difficult to propose any putative mechanism
because this gets converted to I during the catalytic reaction.
References
[1] P. Pattanayak, J.L. Pratihar, D. Patra, C.-H. Lin, S. Chattopadhyay, Polyhedron 63
(2013) 133.
[2] J.L. Pratihar, P. Pattanayak, D. Patra, C.-H. Lin, S. Chattopadhyay, Polyhedron 33
(2012) 67.
[3] P. Pattanayak, J.L. Pratihar, D. Patra, P. Brandão, V. Felix, S. Chattopadhyay,
Polyhedron 79 (2014) 43.
[4] P. Pattanayak, S.P. Parua, D. Patra, C.K. Lai, P. Brandão, V. Felix, S.
Chattopadhyay, Inorg. Chim. Acta 429 (2015) 122.
[5] S.M. Islam, P. Mondal, A. Singha Roy, S. Mondal, D. Hossain, Tetrahedron Lett.
51 (2010) 2067.
[6] C. Baleizão, B. Gigante, H. Garcia, A. Corma, J. Catal. 215 (2003) 199.
[7] C. Baleizão, A. Corma, H. García, A. Leyva, J. Org. Chem. 69 (2004) 439.
[8] A. Corma, Chem. Rev. 95 (1995) 559.
[9] W.M. Rhinj Van, D. De-Vos, P.A. Jacobs, Fine Chemicals through Heterogeneous
Catalysis, Wiley-VCH, Weinheim, 2001. Vol. 106.
[10] A. Corma, H. Garcia, Chem. Rev. 102 (2002) 3837.
[11] N.E. Leadbeater, M. Marco, Chem. Rev. 102 (2002) 3217.
[12] C.A. McNamara, M.J. Dixon, M. Bradley, Chem. Rev. 102 (2002) 3275.
ˇ
ˇ
ˇ
[13] M. Opanasenko, P. Štepnicka, J. Cejka, RSC Adv. 4 (2014) 65137–65162.
[14] C. Baleizao, A. Corma, H. Garcia, A. Leyva, Chem. Commun. (2003) 606.
[15] V. Polshettiwar, C. Lenb, A. Fihri, Coord. Chem. Rev. 253 (2009) 2599.
[16] A. Biffis, M. Zecca, M. Basato, J. Mol. Catal. A: Chem. 173 (2001) 249.
[17] N. Kann, Molecules 15 (2010) 6306.
4. Conclusions
[18] Y. Uozumi, H. Danjo, T. Hayashi, Tetrahedron Lett. 39 (1998) 8303.
[19] A.K. Sutar, T. Maharana, Y. Das, P. Rath, J. Chem. Sci. 126 (2014) 1695.
[20] N. Maiti, S. Pal, S. Chattopadhyay, Inorg. Chem. 40 (2001). 2204-2005.
[21] N. Maiti, B.K. Dirghangi, S. Chattopadhyay, Polyhedron 22 (2003) 3109.
[22] N. Maiti, S. Chattopadhyay, Indian J. Chem. 42A (2003) 2327.
[23] D.D. Perrin, W.L.F. Armarego, Purification of Laboratory Chemicals, third ed.,
Pergamon, New York, 1988.
[24] A.I. Vogel, A.R. Tatchell, B.S. Furnis, A.J. Hannaford, Vogel’s Textbook of
Practical Organic Chemistry, fifth ed., 1996.
[25] P. Pattanayak, D. Patra, J.L. Pratihar, A. Burrows, M.F. Mahon, S. Chattopadhyay,
Inorg. Chim. Acta 363 (2010) 2865.
Several new ligands and two types of new orthopalladated Pd
(II) complexes, [(L1)Pd], 2a, and [(A1)PdCl], 4a, where the coordina-
tion modes are (C,N,N,O) and (C,N,N,Cl), respectively, have been
reported. Both types of complexes were catalytically active toward
Suzuki and Heck coupling reactions. The [(A1)PdCl], 4a, complexes
underwent oxidative conversion in presence of air to form the
orthometallated complexes, I. Therefore, [(A1)PdCl], 4a complexes
can be considered as the precatalyst. However, immobilisation of
the [(L1)Pd], 2a, catalyst to the appropriate solid support for the
preparation of heterogeneous catalyst is yet to be successfully car-
ried out. Further, work is on progress in this regard.
[26] G.M. Sheldrick, Acta Crystallogr. A 64 (2008) 112.
[27] G.M. Sheldrick, SHELXL-97, University of Göttingen, Göttingen, Germany,
Program for the Refinement of Crystals Structures from Diffraction Data, 1997.
[28] P. Pattanayak, J.L. Pratihar, D. Patra, V.G. Puranik, S. Chattopadhyay,
Polyhedron 27 (2008) 2209.
[29] D. Patra, P. Pattanayak, J.L. Pratihar, S. Chattopadhyay, Polyhedron 26 (2007)
5484.
Acknowledgments
[30] P. Pattanayak, J.L. Pratihar, D. Patra, A. Burrows, M. Mohan, S. Chattopadhyay,
Eur. J. Inorg. Chem. (2007) 4263.
[31] P. Pattanayak, J.L. Pratihar, D. Patra, S. Mitra, A. Bhattacharyya, H.M. Lee, S.
Chattopadhyay, Dalton Trans. (2009) 6220.
[32] F.E. Hahn, M.C. Jahnke, V. Gomez-Benitez, D. Morales-Morales, T. Pape,
Organometallics 24 (2005) 6458.
The necessary laboratory and infrastructural facility are pro-
vided by the Department of Chemistry, University of Kalyani. The
support of DST under FIST and PURSE program to the Department
of Chemistry, University of Kalyani is acknowledged.