Mechanistic studies on the Pd-Cl cleavage of dichloro-[1-alkyl-2-(naphthylazo)imidazole]palladium(II) complexes by 8-quinolinol

Article abstract of DOI:10.1016/j.poly.2007.01.022

8-Quinolinol (HQ) reacts with [Pd(α-/β-NaiR)Cl₂] [α-/β-NaiR = 1-alkyl-2-(naphthyl-α-/β-azo)imidazole] in acetonitrile (MeCN) solution to give [Pd(α-/β-NaiR)(Q)](ClO₄). The products are characterized by spectroscopic techniques (FT-IR, UV-Vis, NMR). The reaction kinetics show a first order dependence of rate on each of the concentration of the metal complex and HQ. Addition of LiCl to the reaction retarded the rate of reaction and has proved the cleavage of the Pd-Cl bond as the rate-determining step. Thermodynamic parameters (Δ^?H^{{ring operator}} and Δ^?S^{{ring operator}}) are determined from variable temperature kinetic studies. The magnitude of the second order rate constant, k₂, increases as in the order: Pd(NaiEt)Cl₂ < Pd(NaiMe)Cl₂ < Pd(NaiBz)Cl₂ as well as Pd(β-NaiR)Cl₂ < Pd(α-NaiR)Cl₂.

Full text of DOI:10.1016/j.poly.2007.01.022

Polyhedron 26 (2007) 2655–2662
www.elsevier.com/locate/poly
Mechanistic studies on the Pd–Cl cleavage of
dichloro-[1-alkyl-2-(naphthylazo)imidazole]palladium(II)
complexes by 8-quinolinol
*
Pradip Kumar Ghosh, Sushanta Saha, Ambikesh Mahapatra
Department of Chemistry, Jadavpur University, Kolkata 700 032, India
Received 6 December 2006; accepted 10 January 2007
Available online 30 January 2007
Abstract
8-Quinolinol (HQ) reacts with [Pd(a-/b-NaiR)Cl2] [a-/b-NaiR = 1-alkyl-2-(naphthyl-a-/b-azo)imidazole] in acetonitrile (MeCN)
solution to give [Pd(a-/b-NaiR)(Q)](ClO4). The products are characterized by spectroscopic techniques (FT-IR, UV–Vis, NMR).
The reaction kinetics show a first order dependence of rate on each of the concentration of the metal complex and HQ. Addition
of LiCl to the reaction retarded the rate of reaction and has proved the cleavage of the Pd–Cl bond as the rate-determining step.
Thermodynamic parameters (DàHꢀ and DàSꢀ) are determined from variable temperature kinetic studies. The magnitude of the second
order rate constant, k2, increases as in the order: Pd(NaiEt)Cl2 < Pd(NaiMe)Cl2 < Pd(NaiBz)Cl2 as well as Pd(b-NaiR)Cl2 < Pd(a-
NaiR)Cl2.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Keywords: Palladium(II); Substitution; Naphthylazoimidazole; 8-Quinolinol; Pd–Cl cleavage; p-Acidity
1. Introduction
the mechanism of interaction of DNA bases with Pt(II)-
anticancer agents. Arylazoimidazoles are bidentate N,N0-
chelators and form M(N,N0)Cl2 complexes having a
cis-MCl2 configuration. The kinetics and mechanism of
the substitution reactions involving Pd(II) complexes of
aryl-azo heterocycles with adenine [13], cytosine [14],
2-mercapto-pyridine [15], 2-amino-pyrimidine [16], picoli-
nic acid [17] and 8-quinolinol [18] have been reported. We
are intending to incorporate higher steric crowding
around the target metal center by using different ligands
with a basic azoimine chelating mode (–N@N–C@N–),
which will open an avenue to find out mechanistic aspects
of the nucleophilic interaction with the metal center
under different local environments. Naphthylazoimidaz-
oles (ii) are chemical analogues to phenylazoimidazoles
(i), but with a higher degree of steric crowding and elec-
tron donating ability. Herein we present the kinetic and
mechanistic studies of the reaction of 8-quinolinol (HQ)
with Pd(a/b-NaiR)Cl2.
The reaction of DNA bases with platinum/palladium
complexes of chelating N,N0 donors having a cis-MCl2
configuration constitutes a model system which may
allow for exploration of the mechanism of the anti-tumor
activity of cis-platin [1–9]. Both palladium(II) and plati-
num(II) ions form diamagnetic planar complexes and
strongly prefer nitrogen and oxygen donor atoms [10].
Due to very low reacting equilibrium constants for Pt(II)
complexes and their kinetic inertness compared to Pd(II)
complexes (ꢁ105 times slow) [11,12], the reactions are
uncertain in terms of mechanistic studies. Structurally
analogous Pd(II) complexes may be used to find out
*
Corresponding author. Tel.: +91 33 2432 4586; fax: +91 33 2414 6584.
E-mail addresses: ambikesh_ju@yahoo.com, amahapatra@chemistry.
jdvu.ac.in (A. Mahapatra).
0277-5387/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.01.022

2656
P.K. Ghosh et al. / Polyhedron 26 (2007) 2655–2662
1.2
N
N
R
N
N
R
N
N
N
R
1.0
0.8
0.6
0.4
0.2
N
N
N
N
N
α-NaiR
Phenylazoimidazole (i)
β-NaiR
Naphthylazoimidazole (ii)
2. Experimental
500
600
wavelength (nm)
2.1. Reagents/materials
Fig. 1. Spectra of Pd(a-NaiMe)Cl2in MeCN and a reaction mixture of
Pd(a-NaiMe)Cl2 and HQ in MeCN solution at 298 K. The arrows indicate
the decrease and increase of band intensities as the reaction proceeds.
The complexes were prepared by a reported procedure
[19,20]. 8-Quinolinol (SRL, Mumbai) was purified by
recrystallization from a hot ethanol solution. Acetonitrile
(MeCN) was purified by a known procedure [21,22]. All
kinetic and spectroscopic measurements were recorded on
an Agilent 8453E UV–visible Spectroscopy System. Quartz
cells (1.0 cm path length) from Hellma were used. IR spec-
tra (KBr pellet) were recorded on a FT-IR spectrophotom-
first-order rate constants, kobs, were obtained from the
plots of (At ꢂ A ) versus time (s) (Fig. 2) where
1
At = absorbance of the reaction mixture at time t (s) after
mixing of the HQ solution and A = absorbance of same
1
reaction mixture after completion of the reaction.
1
eter Spectrum RX1, Perkin–Elmer. H NMR spectra were
2.2. Synthesis of [Pd(a-/b-NaiR)(Q)](ClO4) (a-NaiR, 3;
b-NaiR, 4)
drawn from a 300 MHz Bruker NMR instrument in
CD3CN using TMS as an internal standard. Microanalyses
were carried out on a Perkin–Elmer 2400 CHN elemental
analyzer. The specific conductance was measured on a
JENCONS 4010 Conductivity Meter. The pH was mea-
sured on a SYSTRONICS 361 Digital pH meter. Rate con-
stants and standard deviations were calculated by linear
regression using a PC-based program, Microcal-origin ver-
sion Origin-6.1.
A representative synthesis of [Pd(a-NaiMe)(Q)](ClO4)
(3a) is given below.
To a MeCN solution of the complex Pd(a-NaiMe)Cl2
(0.025 g, 6.05 · 10ꢂ2 mmol), HQ (0.026 g, 18.15 · 10ꢂ2
mmol) was added and the orange colored solution was stir-
red for about 24 h. It was filtered and allowed to evaporate
to dryness at room temperature. The mass was then dis-
solved in MeOH, and NaClO4 (aq) (1 g) was added to it.
The brown precipitate that formed was filtered and washed
2.1.1. Kinetic measurements
For kinetic measurements, stock solutions of the com-
plexes (ca. 10ꢂ3 mol dmꢂ3) and of 8-quinolinol (HQ) (ca.
10ꢂ2 mol dmꢂ3) were prepared in dry MeCN. Solutions
of different concentrations were prepared by quantitative
dilution of stock solutions using dry MeCN. All experi-
ments were performed at 298 K (unless otherwise men-
tioned) by mixing required volumes of the thermostated
reactants and transferring the mixture to the absorption
cell (1.0 cm length). On addition of 8-quinolinol (HQ) to
the solution of Pd(NaiR)Cl2 in MeCN, the orange solution
changed to yellow-orange. The influence of the addition of
8-quinolinol on the spectra of Pd(a-NaiR)Cl2 is shown in
the Fig. 1. The change proceeds through a single isobestic
point at ca. 472 nm. The decrease in absorbance of the
reaction mixture was recorded automatically at ca.
0.30
Data: Data1_E
Model: ExpDec1
Equation: y = A1*exp(-x/t1) + y0
0.25
0.20
0.15
0.10
0.05
0.00
y0
A1
t1
0.0042 0.00088
0.29008 0.00081
1010.90275
7.79517
500 nm as a function of time (s). A was measured after
0
1000
2000
time (s)
3000
1
ꢁ24 h of mixing, when the absorbance became constant.
In all experiments, the initial molar concentration of HQ,
[HQ]0, was kept at least ten times in excess so as to main-
Fig. 2. Plot of (At ꢂ A
) vs. time (s) for the reaction: [Pd(a-
1
NaiMe)Cl2]0 = 1.09 · 10ꢂ4 mol dmꢂ3
,
[HQ]0 = 3 · 10ꢂ3 mol dmꢂ3 and
tain
a pseudo-first-order kinetic condition. Pseudo-
temperature = 298 K.

P.K. Ghosh et al. / Polyhedron 26 (2007) 2655–2662
2657
with water. The dried product was then chromatographed
over silica gel and MeCN eluted an orange band. Yield:
0.023 g (64.7%).
All other complexes were prepared by the same proce-
dure and the yields varied within 60–70%.
(naphthyl-b-azo)imidazole) [where R = Me (a)/Et (b)/Bz
(c)]. The ligands belong to the unsymmetric bidentate
N,N0-donor type and form dichloropalladium(II) com-
plexes, here after we abbreviate the complexes as
Pd(N,N0)Cl2 (Scheme 1). The reaction kinetics between
Pd(N,N0)Cl2 and 8-quinolinol (HQ) was examined spectro-
photometrically. The reaction is first order in Pd(II) com-
plex as kobs-values are almost constant when all variants
Microanalytical data of the complexes are as follows:
For [Pd(a-NaiMe)(Q)](ClO4) (3a): Anal. Found: C, 47.00;
H, 3.02; N, 11.79%. Calc. for C23H18O5N5PdCl: C,
47.10; H, 3.07; N, 11.95. For [Pd(a-NaiEt)(Q)](ClO4) (3b)
Anal. Found: C, 48.08; H, 3.30; N,11.71%. Calc. for
C24H20O5N5PdCl: C, 48.00; H, 3.33; N, 11.67. For [Pd
(a-NaiBz)(Q)](ClO4)(3c) Anal. Found: C, 52.72; H, 3.35;
N, 11.11%. Calc. for C29H22O5N5PdCl: C, 52.58; H, 3.32;
N, 11.04. For [Pd(b-NaiMe)(Q)](ClO4) (4a) Anal. Found:
C, 47.18; H, 3.12; N, 11.66%. Calc. for C23H18O5N5PdCl:
C, 47.10; H, 3.07; N, 11.95. For [Pd(b-NaiEt)(Q)](ClO4)
(4b) Anal. Found: C, 47.88; H, 3.28; N, 11.78%. Calc. for
C24H20O5N5PdCl: C, 48.00; H, 3.33; N, 11.67. For [Pd(b-
NaiBz)(Q)](ClO4) (4c) Anal. Found: C, 52.50; H, 3.27; N,
10.86%. Calc. for C29H22O5N5PdCl: C, 52.58; H, 3.32; N,
10.58.
are constant except the complex concentration. The kobs
-
values (Table 1) and the linear plots for the kobs versus
[HQ]0 (Figs. 3 and 4) indicate the reaction is first order in
HQ. The slope of the plot is the second order rate constant
(k2) of the reaction. The presence of a defined intercept (k0)
indicates the existence of a minor solvent assisted path to
the overall reaction products (MeCN is a coordinating
solvent).
The rate increases with a rise in temperature, as expected
from the Eyring equation. Activation parameters, standard
enthalpy of activation (DàHꢀ) and standard entropy of acti-
vation (DàSꢀ) were calculated from Eyring plots (Figs. 5
and 6) and are recorded in Table 2. The DàHꢀ value is actu-
ally the sum of the DàHꢀ value for the reaction (for the pre-
equilibrium step) and the DàHꢀ value for the second Clꢂ
displacement. The same is true for the DàSꢀ value also.
The activation parameter values corroborate with the
experimental k2-values. The order for DàHꢀ and DàSꢀ are:
Pd(NaiEt)Cl2 > Pd(NaiMe)Cl2 > Pd(NaiBz)Cl2 and Pd-
(a-NaiR) > Pd(b-NaiR). The iso-kinetic plot (Fig. 7)
supports an identical mechanism for the reaction of
Pd(N,N0)Cl2 with HQ. Kinetic studies in the presence of
3. Results and discussion
3.1. Kinetics and mechanism
Two classes of naphthylazoimidazole complexes of
palladium(II) have been used in this work. They are
Pd(a-NaiR)Cl2 (1) (a-NaiR = 1-alkyl-2-(naphthyl-a-azo)-
imidazole) and Pd(b-NaiR)Cl2 (2) (b-NaiR = 1-alkyl-2-
Cl
Cl
N
N
N
N
Cl
Cl
R
Pd
Pd
R
N
N
Cl
Cl
N
N
N
N
Pd
/
Pd(N,N/)Cl2
Pd(α-NaiR)Cl2 (1)
Pd(β-NaiR)Cl2 (2)
5
4
5
4
f
O
f
e
N
N
O
R
e
N
N
Pd
d
R
Pd
N
N
d
N
N
N
a
c
N
b
8
15
a
10
11
c
9
b
14
13
15
14
10
12
12
11
13
R = Me (a), Et (b), CH2Ph (c)
[Pd(α-NaiR)(Q)](ClO4) (3) [Pd(β- NaiR)(Q)](ClO4) (4)
Scheme 1.

2658
P.K. Ghosh et al. / Polyhedron 26 (2007) 2655–2662
Table 1
6
Pseudo-first-order rate constants (kobs) for reactions of 8-quinolinol with
Pd(R0aiR)Cl2 in MeCN at 298 K
2a
2b
2c
5
4
3
2
1
0
Pd(R0aiR)Cl2
103 [HQ]0
(mol dmꢂ3
103 kobs 10 k2 (dm3
103 k0
(sꢂ1
)
(sꢂ1
)
molꢂ1 sꢂ1
)
)
Pd(a-NaiMe)Cl2 (1a)
1.0
3.0
5.0
7.0
10.0
0.51
0.99
1.45
1.90
2.59
2.30
0.29
0.28
0.23
0.19
0.18
0.14
Pd(a-NaiEt)Cl2 (1b)
Pd(a-NaiBz)Cl2 (1c)
Pd(b-NaiMe)Cl2 (2a)
Pd(b-NaiEt)Cl2 (2b)
Pd(b-NaiBz)Cl2 (2c)
1.0
3.0
5.0
7.0
10.0
0.48
0.86
1.25
1.64
2.22
1.94
3.45
4.27
3.91
5.22
0
2
4
6
8
10
1.0
3.0
5.0
7.0
10.0
0.57
1.27
1.97
2.67
3.70
103[HQ]0 (mol dm-3)
Fig. 4. Plots of kobs vs. [HQ]0 for the reactions: Pd(b-NaiR)Cl2 + HQ in
MeCN. [Pd(b-NaiR)Cl2]0 = 1.00 · 10ꢂ4 mol dmꢂ3 at 298 K.
1.0
3.0
5.0
7.0
10.0
0.62
1.46
2.32
3.20
4.45
1a
1b
1c
6.4
6.8
7.2
7.6
1.0
3.0
5.0
7.0
10.0
0.58
1.36
2.12
2.92
4.10
1.0
3.0
5.0
7.0
10.0
0.67
1.71
2.73
3.80
5.37
[Pd(R0aiR)Cl2]0 = 1.00 · 10ꢂ4 mol dmꢂ3
.
3.24
3.28
3.32
3.36
3.40
1031/T (K-1)
4
Fig. 5. Plots of ln(k/T) vs. (1/T) for the reactions: Pd(a-NaiR)Cl2 + HQ in
1a
1b
MeCN.
1c
3
6.0
2a
2b
2c
2
1
0
6.2
6.4
6.6
6.8
7.0
0
2
4
6
8
10
103[HQ]0 (mol dm-3)
Fig. 3. Plots of kobs vs. [HQ]0 for the reactions: Pd(a-NaiR)Cl2 + HQ in
MeCN. [Pd(a-NaiR)Cl2]0 = 1.00 · 10ꢂ4 mol dmꢂ3 at 298 K.
3.24
3.28
3.32
1031/T (K-1)
3.36
3.40
externally added Clꢂ(LiCl) reveal that the rate as well as
kobs decreases inversely with [Clꢂ]0 (Table 3), which sup-
ports the mechanism given in Scheme 2. The dissociation
Fig. 6. Plots of ln(k/T) vs. (1/T) for the reactions: Pd(b-NaiR)Cl2 + HQ in
MeCN.

P.K. Ghosh et al. / Polyhedron 26 (2007) 2655–2662
2659
Table 2
50
Second order rate constants (k2) at different temperatures and activation
parameters of the reactions
1b
45
40
35
30
25
20
Pd(R0aiR)Cl2
Temperature 10 · k
(K)
(dm3 molꢂ1 (kJ molꢂ1
sꢂ1
DàHꢀ
DàSꢀ
)
(J Kꢂ1
1a
)
molꢂ1
)
Pd(a-NaiMe)Cl2 293
1.70
2.30
3.15
3.98
41( 5)
46( 5)
36( 3)
26( 2)
32( 3)
20( 2)
ꢂ121( 23)
1c
(1a)
298
303
308
2b
2a
Pd(a-NaiEt)Cl2
(1b)
293
298
303
308
1.35
1.42
2.68
3.55
ꢂ105( 21)
ꢂ134( 15)
ꢂ166( 8)
ꢂ145( 12)
ꢂ182( 15)
2c
Pd(a-NaiBz)Cl2 293
2.73
3.58
4.55
5.80
180
160
140
120
100
(1c)
298
303
308
-Δ ‡So (J K-1 mol-1)
Fig. 7. Plot of DàHꢀ vs. DàSꢀ i.e. iso-kinetic plot for the reactions:
Pd(R0aiR)Cl2 + HQ in MeCN.
Pd(b-NaiMe)Cl2 293
3.57
4.37
5.20
6.25
(2a)
298
303
308
phile is a undissociated N,OH donor ligand. It is probable
that the highly negative O donor will coordinate first with
the positively charged metal center, with fast dissociation
Pd(b-NaiEt)Cl2
(2b)
293
298
303
308
3.42
3.95
5.47
6.01
Table 3
Pd(b-NaiBz)Cl2 293
3.71
5.26
6.12
7.05
Effect of externally added LiCl on the pseudo-first-order rate constants
(kobs) for reactions of 8-quinolinol with Pd(R0aiR)Cl2 in MeCN at 298 K
(2c)
298
303
308
Pd(R0aiR)Cl2
103 [LiCl]0 (mol dmꢂ3
)
103 · kobs (sꢂ1
)
Pd(a-NaiMe)Cl2 (1a)
0.2
0.4
0.6
0.8
1.0
1.38
0.75
0.53
0.42
0.34
of the second Pd–Cl bond is the rate controlling process
and the dissociation of the first Pd–Cl bond is affected by
externally added Clꢂ ion. The product was isolated and
characterized as [Pd(N,N0)(Q)]ClO4. The nucleophilic sub-
stitution process involves direct displacement of 2 Clꢂ ions
by 8-quinolinol (Eq. (1)). In the acetonitrile medium, HQ
will exist largely in the undissociated form [23].
Pd(a-NaiEt)Cl2 (1b)
Pd(a-NaiBz)Cl2 (1c)
Pd(b-NaiMe)Cl2 (2a)
Pd(b-NaiEt)Cl2 (2b)
Pd(b-NaiBz)Cl2 (2c)
0.2
0.4
0.6
0.8
1.0
1.19
0.67
0.50
0.41
0.35
0.2
0.4
0.6
0.8
1.0
1.89
0.88
0.60
0.43
0.33
+
O
N
N/
N
Cl
-
HCl
+
Cl
Pd
+
Pd
N/
N
Cl
N
OH
NaClO4
0.2
0.4
0.6
0.8
1.0
2.22
1.09
0.72
0.52
0.39
O
N
-
+
(ClO )
Pd
+ Na Cl
+
N/
4
N
0.2
0.4
0.6
0.8
1.0
2.03
0.93
0.62
0.40
0.27
ð1Þ
The observed rate is
Rate ¼ fk0 þ k2½HQꢃ0g½PdðR0aiRÞCl2ꢃ
0.2
0.4
0.6
0.8
1.0
2.62
1.17
0.73
0.44
0.21
¼ kobs½PdðR0aiRÞCl2ꢃ
kK1
(where k2 ¼
¼ constant at constant ½Clꢂꢃ and kobs
=
½Clꢂꢃ0
0
k0 + k2[HQ]0). The k0 and k2 are the intercept and the slope
[Pd(R0aiR)Cl2]0 = 1.00 · 10ꢂ4 mol dmꢂ3, [HQ]0 = 5.00 · 10ꢂ3 mol dmꢂ3
.
of the plot of kobs versus [HQ]0 respectively. The nucleo-

2660
P.K. Ghosh et al. / Polyhedron 26 (2007) 2655–2662
+
N
(fast)
N
Cl
Cl
N
K
O
N
N
N
O
1
k
+
-
Pd
Pd
+ Cl
N/
Pd
N/
N/
OH
-HCl
(slow)
Cl
(C)
(B)
)
(A
Scheme 2.
of the first Pd–Cl bond, and finally forms a stable four
coordinated square planar intermediate complex (B). Then
quinoline-N (which remains free in B) slowly coordinates
with Pd(II) as a compulsion of chelate stability. Obviously
the latter rate is slower than the former rate. Therefore the
second Pd–Cl bond cleavage is the rate-determining step.
This is also supported by the effect of externally added
Clꢂ ions (LiCl). A plausible mechanism is given in Scheme
2. There are two parallel pathways: one is the existence of a
minor solvent assisted path where MeCN substitutes Clꢂ
initially, then MeCN is displaced by HQ and finally forms
the reaction product (C) (Scheme 3). Although the steric
crowding of the a-/b-naphthyl group in the N,N0 chelating
ligand is significant, its electron withdrawing property, due
to conjugation, stabilizes the Pd(N,N0) chelated species in
preference to de-chelation.
3.2. Product characterization
To a MeCN solution of the complex Pd(N,N0)Cl2, HQ
was added and the orange colored solution was stirred
for about 24 h. It was filtered and allowed to evaporate
almost to dryness at room temperature. The mass so pro-
duced was then dissolved in MeOH and NaClO4 (aq) was
added. A brown precipitate formed which was filtered
and then washed with water and cold MeCN. The dried
product was chromatographed over silica gel and MeCN
eluted an orange-red band. Finally the dried product was
characterized by micro-analytical data (experimental sec-
1
tion), UV–Vis, IR. (Table 4) and H NMR (Table 5) spec-
tral data. The molar conductance data in MeCN solution
(KM = 75–90 S cm2 molꢂ1) show a 1:1 electrolytic nature
of the complexes. The IR spectra of the complexes display
a sharp stretch at 1360–1375 cmꢂ1 which corresponds to
m(N@N) and is red shifted by 5–10 cmꢂ1 from that of
Pd(NaiR)Cl2 [24]. This may be attributed to the charge
delocalization from coordinated Qꢂ to the chelated NaiR
motif. The binding is indirectly established by the disap-
The kinetic data in Table 1 reveal that the magnitude of
k increases in the order Pd(a-NaiEt)Cl2 < Pd(a-Nai-
Me)Cl2 < Pd(a-NaiBz)Cl2. This is because the electron
withdrawing tendency of the Bz group is greater than
Me, which in turn is slightly greater than Et.
+
NCMe
Cl
N
N
Cl
Cl
O
N
N
OH
+N
+
MeCN
Pd
Pd
Pd
N/
N/
N/
-
+
-H
-MeCN
Cl
-Cl
(B)
(A)
-
-Cl
+
O
N
N
Pd
(C)
N/
Scheme 3.
Table 4
Spectral data (FT-IR and UV–Vis) of [Pd(a/b-NaiR)(Q)](ClO4)
Compounds
IR spectral dataa (cmꢂ1
)
UV–Vis spectral datab
max, nm (e, dm3 molꢂ1 cmꢂ1
k
)
m(N@N)
m(C@N)
m(Pd–O)
[Pd(a-NaiMe)(Q)](ClO4) (3a)
[Pd(b-NaiMe)(Q)](ClO4) (4a)
[Pd(a-NaiEt)(Q)](ClO4) (3b)
[Pd(b-NaiEt)(Q)](ClO4) (4b)
[Pd(a-NaiBz)(Q)](ClO4) (3c)
[Pd(b-NaiBz)(Q)](ClO4) (4c)
1560
1558
1560
1558
1559
1559
1651
1651
1651
1651
1652
1652
465
472
468
470
466
469
393 (18730), 482 (9498)
394(18724), 481 (9495)
395 (18720), 485 (9500)
394 (18718), 486 (9499)
395 (18726), 483 (9489)
391 (18728), 483 (9488)
a
KBr disk.
In MeCN solution.
b

P.K. Ghosh et al. / Polyhedron 26 (2007) 2655–2662
2661
Table 5
1H NMR spectral data of [Pd(a/b-NaiR)(Q)](ClO4) in CD3CN
Compound
d, ppm (J, Hz)
4-Hi 5-Hi 8-Hi 9-Hj
10-Hk 11- 13-Hk 14-Hk 15-Hk a-Hj
b-Hk c-Hk d-Hk e-Hk f-Hj
[Pd(a-NaiMe)(Q)]-
(ClO4) (3a)
[Pd(a-NaiEt)(Q)]-
(ClO4) (3b)
[Pd(a-NaiBz)(Q)]-
(ClO4) (3c)
[Pd(b-NaiMe)(Q)]-
(ClO4) (4a)
[Pd(b-NaiEt)(Q)]-
(ClO4) (4b)
[Pd(b-NaiBz)(Q)]-
(ClO4) (4c)
7.02 6.88
7.67 (8.0) 7.52
7.40
7.40
7.42
7.60
7.58
7.64
7.35
7.33
7.38
7.50
7.50
7.50
7.46
7.45
7.50
7.40
7.45
7.45
9.65 (8.0) 9.08
9.60 (8.0) 9.00
9.68 (8.0) 9.10
9.45 (8.0) 8.80
9.40 (8.0) 8.80
9.50 (8.0) 8.85
8.54
8.58
8.60
8.53
8.50
8.55
8.22
8.20
8.25
8.10
8.20
8.22
8.00
8.00
8.05
8.00
8.00
8.05
8.28 (8.0)
8.30 (8.0)
8.34 (8.0)
8.27 (8.0)
8.30 (8.0)
8.35 (8.0)
7.00 6.85
7.65 (8.0) 7.50
7.10 6.95
7.72 (8.0) 7.55
7.07 6.90 7.76
7.04 6.85 7.80
7.10 6.90 7.86
7.96
8.00
8.05
i
Broad singlet.
Doublet.
Multiplet.
j
k
pearance of two m(Pd–Cl) bands corresponding to the cis-
PdCl2 configuration [24–26] and the appearance of new
bands at 1560–1570 and 480–500 cmꢂ1 due to m(C–O)
and m(Pd–O), respectively. All the complexes exhibit a
structureless band at 1090–1100 cmꢂ1 corresponding to
m(ClO4), suggesting the lack of any significant interaction
in the solid state [27].
The solution electronic spectra of the complexes were
recorded in the range 900–200 nm in MeCN. The absorp-
tions below 400 nm are due to intramolecular charge trans-
fer and are not considered further. Two absorptions at
475–485 and 515–525 nm (Fig. 8), absent in the free
ligands, may represent charge transfer transitions localized
on the metallated fragment [28].
The 1H NMR spectra of the complexes were recorded in
CD3CN and the data are collected in Table 5. The proton
numbering pattern is shown in Scheme 1. The data reveal
that the signals in the spectra of the complexes are shifted
downfield relative to the free ligand values [18]. This sup-
ports the coordination of the ligand to Pd(II). An impor-
tant feature of the spectra is the shifting of the imidazole
protons 4-H and 5-H to lower d-values, in general, relative
to the naphthyl protons (6-H–13-H). The imidazole pro-
tons suffer downfield shifting by 0.1-0.2 ppm compared to
the free ligand positions. This supports the strong prefer-
ence of imidazole-N binding to Pd(II). The naphthyl pro-
tons appear as multiplets, except a broad singlet for 6-H
and doublet for 8-H in [Pd(b-NaiR)(Q)](ClO4) and a
40
393nm
394nm
481nm
30
20
10
0
490nm
300
400
500
600
700
800
900
Wave length (nm)
Fig. 8. UV–Vis spectra of [Pd(b-NaiMe)Cl2] (black line) and [Pd(b-NaiMe)(Q)](ClO4) (red line) in MeCN solution. (For interpretation of the references in
color in this figure legend, the reader is referred to the web version of this article.)

2662
P.K. Ghosh et al. / Polyhedron 26 (2007) 2655–2662
[5] M. Kato, J. Takahashi, Y. Sugimoto, C. Kosuge, S. Kishi, S. Yano, J.
Chem. Soc., Dalton Trans. (2001) 747.
[6] J. Li, L.M. Zheng, I. King, T.W. Doyle, S.H. Chan, Curr. Med.
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Valley, CA, 1994, p. 505.
doublet for 15-H in all the complexes. The 1-alkyl group
appears as a singlet for 1-Me in [Pd(a/b-NaiMe)(Q)](ClO4),
a quartet for –N–CH2– and a triplet for the –CH3 group in
[Pd(a/b-NaiEt)(Q)](ClO4) and a singlet for –CH2– and
benzyl protons in the [Pd(a/b-NaiCH2Ph)(Q)](ClO4)
complexes.
[8] P.D. Beer, Acc. Chem. Res. 31 (1998) 71.
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19.
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4. Conclusion
The kinetics of the reactions between Pd(N,N0)Cl2 and
8-quinolinol (HQ) were examined spectrophotometrically
at 500 nm under pseudo-first-order conditions in MeCN.
The reactions are first order with respect to the complex
and HQ. The rate of the reaction is largely influenced by
the p-acidity of the chelating ligand; substitution in the
naphthylazoimidazole backbone influences the rate of the
substitution process significantly. Activation parameters
DàHꢀ and DàSꢀ of the reactions were measured, which cor-
roborates the kinetic rate data. The products isolated from
the reaction between Pd(NaiR)Cl2 and HQ in MeCN have
been characterized by spectral data and support the com-
position [Pd(NaiR)(Q)](ClO4).
Acknowledgements
[21] R. Roy, T.K. Misra, C. Sinha, A. Mahapatra, A. Sanyal, Transition
Met. Chem. 22 (1997) 453.
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[23] T. Suganuma, A. Tanada, H. Tomizawa, M. Tanaka, E. Miki, Inorg.
Chim. Acta 320 (2001) 22.
Financial help from Jadavpur University is gratefully
acknowledged. We thank Dr. C. Sinha, Professor of Chem-
istry, Jadavpur University for his helpful discussions.
[24] J. Dinda, P.K. Santra, C. Sinha, L.R. Falvello, J. Organomet. Chem.
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