Coupling of arylamine with coordinated arylazopyrimidine in platinum(II) complexes. Single crystal X-ray structure, spectra and electrochemistry

Article abstract of DOI:10.1016/j.poly.2005.10.035

2-(Arylazo)pyrimidine (p-R-C₆H₄-N{double bond, long}N-C₄H₃N₂, aapm, R = H (papm, 3a), Me (tapm, 3b), Cl (Clpapm, 3c)) are N,N′-chelating ligands. Platinum(II) complexes, Pt(aapm)Cl₂ (4) have been synthesized by the reaction of K₂PtCl₄ and aapm in MeCN-water under refluxing condition. The reaction of Pt(aapm)Cl₂ with ArNH₂ in MeCN has synthesized C-N coupled product, Pt(aapm-N-Ar)Cl (5-10). The single crystal X-ray structure determination of one of the compounds has suggested the coupling of ArNH₂ at ortho-C-H of the pendant aryl part of aapm in the chelated complex. The stereochemistry and the bonding are described by ¹H NMR data. The solution electronic spectra of Pt(aapm-N-Ar)Cl exhibit multiple transition at Vis-NIR region (500-1250 nm) which are absent in Pt(aapm)Cl₂. Cyclic voltammograms show two quasireversible azo reductions of Pt(aapm)Cl₂; Pt(aapm-N-Ar)Cl exhibit four successive redox couples, one of them (positive to SCE) is oxidative in nature and other (negative to SCE) are ligand reductions.

Full text of DOI:10.1016/j.poly.2005.10.035

Polyhedron 25 (2006) 1571–1578
www.elsevier.com/locate/poly
Coupling of arylamine with coordinated arylazopyrimidine
in platinum(II) complexes. Single crystal X-ray structure,
spectra and electrochemistry
a
a
b
c
a,
*
S. Senapoti , Sk. Jasimuddin , G. Mostafa , T.-H. Lu , C. Sinha
a
Department of Chemistry, Inorganic Section, Jadavpur University, Kolkata 700 032, West Bengal, India
b
Department of Physics, Jadavpur University, Kolkata 700 032, India
Department of Physics, National Tsing Hua University, Hsinchu, Taiwan 300, Taiwan, ROC
c
Received 1 October 2005; accepted 21 October 2005
Available online 20 December 2005
Abstract
2-(Arylazo)pyrimidine (p-R-C6H4–N@N–C4H3N2, aapm, R = H (papm, 3a), Me (tapm, 3b), Cl (Clpapm, 3c)) are N,N0-chelating
ligands. Platinum(II) complexes, Pt(aapm)Cl2 (4) have been synthesized by the reaction of K2PtCl4 and aapm in MeCN–water under
refluxing condition. The reaction of Pt(aapm)Cl2 with ArNH2 in MeCN has synthesized C–N coupled product, Pt(aapm-N–Ar)Cl
(5–10). The single crystal X-ray structure determination of one of the compounds has suggested the coupling of ArNH2 at ortho-
1
C–H of the pendant aryl part of aapm in the chelated complex. The stereochemistry and the bonding are described by H NMR data.
The solution electronic spectra of Pt(aapm-N–Ar)Cl exhibit multiple transition at Vis–NIR region (500–1250 nm) which are absent in
Pt(aapm)Cl2. Cyclic voltammograms show two quasireversible azo reductions of Pt(aapm)Cl2; Pt(aapm-N–Ar)Cl exhibit four successive
redox couples, one of them (positive to SCE) is oxidative in nature and other (negative to SCE) are ligand reductions.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Keywords: Arylazopyrimidine; Platinum(II); C–N coupling reaction; Crystal structure; Electrochemistry
1. Introduction
arylazopyrimidines are most efficient. p-acidic azoimine
chelating substance. This property has been utilized to sta-
bilize low valent metal oxidation state [10]. Besides, we
have been able to use Pd(aapm)Cl2 to bring the C–N cou-
pling reaction with ArNH2 [5] at ambient condition. In this
work, we will report hitherto unknown platinum(II) com-
plexes of aapm (3) and their coupling reaction with
ArNH2. The complexes have been characterized by the
spectral and electrochemical data. The structure of the cou-
pled product has been characterized in one case by single
crystal X-ray diffraction study.
The coordination of ligand to metal center changes the
electronic property of them and the ligand itself may
undergo reaction with nucleophiles at enhanced rate on
comparing with free ligand case. This is a growing field
in the metal assisted organic transformation [1,2]. The
p-acidity of the coordinating ligand plays a vital role in
regulating the reaction. Arylazoheterocycles are potent p-
acidic ligands and undergo varieties of metal assisted organic
transformation those are otherwise impossible [3–7]. We
have been designing different series of azoheterocycles such
as azoimidazoles [8], azopyridines, [9] and azopyrimidines
[10]. Being a strongest p-acidic N-heterocycle, pyrimidine
in the series of imidazole, pyridine and pyrimidine, the
2. Experimental
2.1. Measurements
*
Microanalytical data (C, H, N) were collected on Perkin–
Elmer 2400 CHNS/O elemental analyzer. Spectroscopic
Corresponding author. Fax: +91 033 2413 7121.
E-mail address: c_r_sinha@yahoo.com (C. Sinha).
0277-5387/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.10.035

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S. Senapoti et al. / Polyhedron 25 (2006) 1571–1578
data were obtained using the following instruments: UV–
Vis spectra, JASCO UV–Vis–NIR model V 570; IR spectra
our of the solution changed gradually from orange-red to
brown. The solution was evaporated in air, and the residue
was washed thoroughly first with water (2 · 5 ml) and then
with 50% aqueous-ethanol (3 · 5 ml). The residue was dis-
solved in dichloromethane (10 ml) and the solution was
chromatographed over silica gel column (60–120 mesh).
An orange-brown band was eluted by C7H9–MeCN (9:1)
mixture. The eluted solution on evaporation in vacuo gave
pure compound. Orange-brown compound was isolated in
45% yield.
1
(KBr disk, 4000–200 cmꢀ1), FTIR JASCO model 420; H
NMR spectra, Bruker (AC) 300 MHz FTNMR spectrom-
eter. Electrochemical measurements were performed using
computer-controlled PAR model 270 VERSASTAT elec-
trochemical instruments with Pt-disk electrodes. All mea-
surements were carried out under a nitrogen environment
at 298 K with reference to saturated calomel electrode
(SCE) in acetonitrile using [nBu4N][ClO4] as supporting
electrolyte. The reported potentials are uncorrected for
junction potential.
The greenish-brown product is the coupled product,
Pt(papm-N-C6H5)Cl. All other complexes were prepared
similarly; yield, 40–55%. Calc. for C16H12N5ClPt (5a): C,
38.05; H, 2.38; N, 13.87. Found: C, 38.12; H, 2.31; N,
13.73%. Calc. for C17H14N5ClPt (6a): C, 39.34; H, 2.70;
N, 13.50. Found: C, 39.23; H, 2.61; N, 13.41%. Calc. for
C17H14N5ClPt (7a): C, 39.34; H, 2.70; N, 13.50. Found:
C, 39.24; H, 2.62; N, 13.40%. Calc. for C17H14N5ClPt
(8a): C, 39.34; H, 2.70; N, 13.50. Found: C, 39.20; H,
2.60; N, 13.39%. Calc. for C17H14N5OClPt (9a): C, 38.16;
H, 2.62; N, 13.09. Found: C, 38.00; H, 2.56; N, 13.20%.
Calc. for C16H11N5Cl2Pt (10a): C, 35.62; H, 2.04; N,
12.98. Found: C, 35.48; H, 2.11; N, 12.86%. Calc. for
C17H14N5ClPt (5b): C, 39.34; H, 2.70; N, 13.50. Found:
C, 39.22; H, 2.66; N, 13.42%. Calc. for C18H16N5ClPt
(6b): C, 40.56; H, 3.00; N, 13.14. Found: C, 40.43; H,
2.94; N, 13.02%. Calc. for C18H16N5ClPt (7b): C, 40.56;
H, 3.00; N, 13.14. Found: C, 40.37; H, 2.84; N, 13.05%.
Calc. for C18H16N5ClPt (8b): C, 40.56; H, 3.00; N, 13.14.
Found: C, 40.41; H, 2.89; N, 13.00%. Calc. for
C18H16N5OClPt (9b): C, 39.38; H, 2.91; N, 12.76. Found:
C, 39.15; H, 2.82; N, 12.64%. Calc. for C17H13N5Cl2Pt
(10b): C, 36.88; H, 2.35; N, 12.65. Found: C, 36.74; H,
2.28; N, 12.54%. Calc. for C16H11N5Cl2Pt (5c): C, 35.62;
H, 2.04; N, 12.98. Found: C, 35.53; H, 2.10; N, 12.77%.
Calc. for C17H13N5Cl2Pt (6c): C, 36.88; H, 2.35; N,
12.65. Found: C, 36.75; H, 2.31; N, 12.53%. Calc. for
C17H13N5Cl2Pt (7c): C, 36.88; H, 2.35; N, 12.65. Found:
C, 36.69; H, 2.28; N, 12.54%. Calc. for C17H13N5Cl2Pt
(8c): C, 36.88; H, 2.35; N, 12.65. Found: C, 36.74; H,
2.29; N, 12.52%. Calc. for C17H13N5OCl2Pt (9c): C,
35.85; H, 2.28; N, 12.30. Found: C, 35.71; H, 2.20; N,
12.19%. Calc. for C16H10N5Cl3Pt (10c): C, 36.47; H, 1.74;
N, 12.20. Found: C, 36.55; H, 1.81; N, 12.23%.
2.2. Materials
2-(Arylazo)pyrimidines were prepared by the reported
procedure [10]. H2PtCl6 Æ xH2O was purchased from
Arrora Matthey, Kolkata, India. K2PtCl4 was prepared
from the reported method [8]. Aniline, o-toluidine, m-tolu-
idine, p-toluidine, p-chloroaniline were received from Sisco
Research Lab (SRL). The purification of acetonitrile and
preparation of n-tetra butylammonium perchlorate
[nBu4N][ClO4] for electrochemical work were done as
before [10]. Dinitrogen was purified by bubbling through
an alkaline pyrogallol solution. All other chemicals and
solvents were of reagent grade and were used without fur-
ther purification. Commercially available SRL silica gel
(60–120 mesh) was used for column chromatography.
2.3. Preparation of complexes
2.3.1. Dichloro[2-(phenylazo)pyrimidine]platinum(II),
Pt(papm)Cl2 (4a)
2-(Phenylazo)pyrimidine (papm) (0.2 g, 1.09 mmol) in
MeCN–H2O (15 ml) was added to an MeCN–H2O (1:1,
v/v, 40 ml) solution of K2PtCl4 (0.4 g, 0.96 mmol) and
the mixture was refluxed for 24 h. On slow evaporation, a
brown precipitate gradually appeared; it was filtered and
washed with cold MeCN–H2O (1:1, v/v, 3 · 5 ml). The
dried mass was dissolved in a minimum volume of CH2Cl2
and chromatographed over a silica gel column. The desired
compound was eluted by C7H9–MeCN (2:1, v/v) as an
orange-red band; yield, 0.3 g (50%). Other complexes were
prepared under identical conditions and yield varied in the
range 45–50%. Calc. for C10H8N4Cl2Pt (4a): C, 26.66; H,
1.77; N, 12.44. Found: C, 26.55; H, 1.69; N, 12.35%. Calc.
for C11H10N4Cl2Pt (4b): C, 28.44; H, 2.15; N, 12.07.
Found: C, 28.55; H, 2.08; N, 11.99%. Calc. for
C10H7N4Cl2Pt (4c): C, 24.76; H, 1.44; N, 11.56. Found:
C, 24.62; H, 1.37; N, 11.42%.
2.4. X-ray structure determination
The X-ray quality single crystal of Pt(papm-N–C6H4–
Me-m)Cl (7a) was grown by slow diffusion of hexane into
dichloromethane solution of the complex at 298 K. The
crystal size was 0.25 · 0.11 · 0.08 mm3. X-ray diffraction
data were collected at 293(2) K with the Siemens SMART
CCD using graphite-monochromatized Mo Ka radiation
2.3.2. Chloro[(2-(8-imidophenyl)phenylazo)pyrimidine-
N,N0,N00]platinum(II), Pt(papm-N–C6H5)Cl, (5a)
To an acetonitrile solution (15 ml) of Pt(papm)Cl2
(90.3 mg, 0.67 mmol) was added slowly aniline (0.1 g,
1.08 mmol) in the same solvent (10 ml). The reaction mix-
ture was stirred and refluxed continuously for 4 h. The col-
˚
(k = 0.71073 A). Unit cell parameters were determined
from least-squares refinement of setting angles with 2h in
the range 4–57ꢁ. A summary of the crystallographic data
and structure refinement parameters are given in Table 1.

S. Senapoti et al. / Polyhedron 25 (2006) 1571–1578
1573
Table 1
yielded greenish brown product (Eq. (1)). This has been
identified as amine coupled product abbreviated Pt(aapm-
N–C6H4-R0Cl) [where, R0 = H (5), o-Me (6) m-Me (7), p-
Me (8), p-OMe (9), p-Cl (10)].
Crystallographic data of Pt(papm-N–C6H4–Me-m)Cl (7a)
Chemical formula
Formula weight
Crystal size (mm3)
Crystal system
Space group
C17H14ClN5Pt
517.88
0.25 · 0.11 · 0.08
monoclinic
P21/n
7.459(1)
16.899(2)
13.117(18)
92.497(3)
1652.0(4)
4
295(2)
0.71073
4–57
9981
5
5
4
6
NH2
6
4
˚
C
a (A)
3
N
Cl
N
1
C
N
3
N
˚
Cl
Cl
N
b (A)
2
1
Pt
+
2
Pt
˚
c (A)
N
14
A
N
7
N
13
b (ꢁ)
R/
N
3
˚
15
16
V (A )
7
12
11
8
12
11
8
B
Z
18
B
9
17
9
T (K)
R
10
10
˚
k (A)
R
R
2h Range (ꢁ)
Reflection collected
Unique reflections
-R/
Pt(aapm-N-C6H4 )Cl
4
a
2522
5-10
hkl Range
ꢀ9 6 h 6 9, ꢀ21 6 k 6 20, 20 6 l 6 ꢀ15
ð1Þ
qcalc (g cmꢀ3
)
2.082
8.662
0.0303
0.0569
0.904
l (Mo Ka) (mmꢀ1
)
Rb
wRc
The arylamination takes place at the ortho position (at the
C(8)–H bond) to azo function in the pendant aryl ring (B-
ring) of aapm and forms platinum(II) complex of tridentate
N,N0,N00-chelating ligand (N,N0,N00 refer to N(pyrimidine),
N(azo) and N(arylamine), respectively). Microanalytical
data support the composition of the complexes (see
Section 2).
Goodness-of-fitd
a
I > 2r(I)%.
P
P
b
R = |F ꢀ F |/ Fo.
h
i
o
c
1=2
P
P
2
c
wR ¼
ðF 2o ꢀ F 2c Þ = wðF 4oÞ
, w = 1/[r2(Fo)2 + (0.0283P)2], where
P ¼ ðF o þ 2F 2c Þ=3.
d
Goodness-of-fit is defined as [w|Fo ꢀ Fc|/(no ꢀ nv)]1/2, where no and nv
denotes the numbers of data and variables, respectively.
3.2. Molecular structure of Pt(papm-N–C6H4–Me-m)Cl
(7a)
Of 9981 collected reflections 2522 unique reflections were
recorded using x-scan technique. Data were corrected for
Lp effects and for linear decay. Semi-empirical absorption
corrections based on w-scans were applied. The structure
was solved by direct method using SHELX-97 and successive
difference Fourier syntheses [11]. All non-hydrogen atoms
were refined anisotropically. The hydrogen atoms were
fixed geometrically and refined using riding model. In the
final difference Fourier maps the residual maximum and
A molecular view of Pt(papm-N–C6H4–Me-m)Cl is
shown in Fig. 1 and the selected bond parameters are listed
in Table 2. The crystallographic asymmetry unit contains
24 non-hydrogen atoms of which 17 lie in a plane nearly
perpendicular to crystallographic c-axis. These atoms com-
prise the two chelate rings, the aromatic groups fused to
them and the Pt and Cl-atoms. The atomic groups Pt,
N(1), C(4), N(3), N(4), and Pt, N(4), C(5), C(10), N(5) con-
minimum were 1.312 and ꢀ0.627 e Aꢀ3. All calculations
˚
˚
were carried out using the SHELX-97.
stitute two chelate planes (mean deviation <0.04 A) and
they are nearly planar (dihedral angle 1.8ꢁ). The chelate
bite angles are N(1)–Pt–N(4), N(4)–Pt–N(5), 79.3ꢁ(4) and
81.8ꢁ(8). The Pt atom lies within the square plane defined
by N3Cl donor centers (deviation, <0.01). The pendant
m-tolyl ring is inclined at an angles of 64.35ꢁ with the prin-
cipal plane of 17 atoms. There are three types of Pt–N
2.5. Molecular orbital calculations
Extended Huckel molecular orbital calculation [12,13]
was performed using the ICON software package originally
developed by Hoffmann. The atomic parameters were
taken from the crystallographic data (Table 1). For draw-
ing figures and graphic package ‘cacao’ was used.
˚
bonds: Pt–N(pyrimidine) [Pt–N(1)], 2.013(3) A; Pt–N(azo)
˚
[Pt–N(4)], 1.919(9) A and longest Pt–N(arylamine) [Pt–
˚
N(5)], 2.014(9) A. The shortest Pt–N bond length is Pt–
3. Results and discussion
N(1) and longest Pt–N distance is Pt–N(5). The N@N bond
length is 1.312(1) A. The free ligand value of N@N bond is
˚
3.1. Synthesis and formulation
not available but the literature data available in some free
arylazoheterocycles suggest that it is nearly 1.25(1) A [14].
˚
2-(Arylazo)pyrimidines (aapm, 3) are N,N0-chelators.
The reaction of aapm with K2PtCl4 in MeCN–H2O (1:1,
v/v) has yielded orange-red crystalline product,
Pt(aapm)Cl2 (4), in the yield of 45–50%.
The reaction between Pt(aapm)Cl2 and ArNH2 in 1:1
ratio in MeCN suspension under refluxing condition has
The elongation of N@N azo distance is consistent with
electron delocalization from metal to ligand fragment
[5,6]. A significant back-bone conjugation is also observed
in the coordinated anionic ligand. This is viewed from
the difference in N(azo)–C(phenyl-B/pyrimidine-C), distan-
˚
ces. The N(azo)–C(pyrimidine-C) (N(3)–C(4)), 1.381(4) A;

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S. Senapoti et al. / Polyhedron 25 (2006) 1571–1578
Fig. 1. Molecular structure of [Pt(papm-N–C6H4–Me-o)Cl] (7a).
A hydrogen bonded cyclic dimmer is observed through
Table 2
˚
˚
Selected bond lengths (A) and angles (ꢁ) of Pt(papm-N–C6H4–Me-m)Cl
(7a)
C(12)–H(12)ꢁ ꢁ ꢁN(3) C(12)–H, 0.93 A; H(12)ꢁ ꢁ ꢁN(3),
˚
˚
2.598(7) A; C(12)ꢁ ꢁ ꢁN(3), 2.598(7) A and \C(12)–H(12)–
N(3), 165.53ꢁ. Dimers are then arranged compactly to pro-
vide a platform for p–p interaction between pyrimidine
(acceptor) of one unit with azophenyl ring (donor) of adja-
cent unit (distance between Cg(4) of pyrimidineꢁ ꢁ ꢁCg(3) of
˚
Bonds
Distances (A)
Angles
Value (ꢁ)
Pt–N(1)
Pt–N(4)
Pt–N(5)
N(3)–N(4)
C(4)–N(1)
C(4)–N(3)
Pt–Cl(1)
C(5)–N(4)
C(10)–N(5)
C(11)–N(5)
N(1)–C(1)
N(2)–C(4)
N(2)–C(3)
C(2)–C(3)
C(1)–C(2)
C(5)–C(6)
C(6)–C(7)
C(7)–C(8)
C(8)–C(9)
C(9)–C(10)
2.013(3)
1.919(9)
2.014(9)
1.381(6)
1.381(6)
1.381(6)
2.291(2)
1.346(6)
1.332(8)
1.441(1)
1.332(8)
1.322(1)
1.333(3)
1.361(9)
1.353(8)
1.411(7)
1.350(8)
1.419(9)
1.367(6)
1.435(1)
N(1)–Pt–N(4)
N(4)–Pt–N(5)
N(1)–Pt–Cl(1)
N(5)–Pt–Cl(1)
N(1)–Pt–N(5)
N(4)–Pt–Cl(1)
Pt–N(1)–C(4)
Pt–N(5)–C(10)
Pt–N(4)–C(5)
79.3(4)
81.8(8)
97.0(4)
101.7(4)
161.1(8)
176.3(8)
110.2(6)
111.3(50)
116.4(1)
˚
azophenyl equals to 3.735(5) A) and a supramolecular lad-
der is formed (Fig. 2).
˚
N(azo)–C(phenyl-B) (N(4)–C(5)), 1.346(6) A are noticeably
shorter than that of N(imino)–C(phenyl-A) (N(5)–C(11)),
˚
1.441(1) A. More interesting feature is the ring C–C dis-
tance in B-ring C(5)–C(10); they have been elongated by
˚
0.02–0.1 A from that of ring-A and ring-C parameters.
This leads us to conclude that the ring-B is more efficiently
involve in back bone conjugation than that of other rings
(A and C) with the coordinated Pt(II). This is also sup-
˚
ported by the shortening of Pt–N(4) distance (1.919(9) A)
with reference to Pt–N(1), 2.013(3) and Pt–N(5),
˚
2.014(9) A. The bond parameters and backbone conjuga-
Fig. 2. Supramolecular ladder constituted via pꢁ ꢁ ꢁp interaction between
tion are also comparable with the literature data [5,6].
pyrimidine and azoaryl in hydrogen-bonded cyclic dimers.

S. Senapoti et al. / Polyhedron 25 (2006) 1571–1578
1575
3.3. Spectra and bonding
In chloroform solution of Pt(aapm)Cl2 the absorption
bands are observed at 250–550 nm. On comparison with
free ligand data we may conclude that the transitions
<400 nm are intraligand charge transfer transitions [10].
The spectral pattern have changed abruptly in Pt(aapm-
N–Ar)Cl (5–10) and exhibit multiple transitions in the vis-
ible to NIR region (500–1250 nm). The spectral data are
collected in Table 3 and a representative figure is shown
in Fig. 3. The low energy spectral band in Pt(aapm-N–
Ar)Cl, is associated with HOMO ! LUMO (62a ! 63a)
charge transfer [5,6]. The MOs are calculated by EHMO
approximation using X-ray crystallographic parameter of
Pt(papm-N–C6H4–Me-m)Cl (7a). The HOMO (62a)
receives 68% azoaryl group and 26% metal orbitals and
The presence of two m(Pt–Cl) stretches at 340 and
300 cmꢀ1 in Pt(aapm)Cl2 is in agreement with cis-PtCl2
configuration [15] while a single transmission at 300–
320 cmꢀ1 is observed in the amine coupled products (5–
10). The sharp single band at 1400–1415 cmꢀ1 in free ligand
is referred to m(N@N) [5]. This has been shifted to lower
frequency, 1360–1375 cmꢀ1 in Pt(aapm)Cl2 and supports
the coordination of azo-N to Pt(II). In Pt(aapm-N–Ar)Cl
(5–10) the m(N@N) appears at 1260–1290 cmꢀ1; this signif-
icant reduction in azo frequency may be due to charge
delocalization from N–Ar fragment (ring A) to the azo
function intramolecularly (vide infra).
Table 3
a
b
Solution spectral and cyclic voltammetric data
Compounds
UV–Vis–NIR spectra kmax/nm(10ꢀ3e/dm3 molꢀ1 cmꢀ1
)
Cyclic voltammetric datab E1/2/V (DEp/mV)
E11=2
ꢀE21=2
ꢀE31=2
ꢀE41=2
Pt(papm)Cl2 (4a)
Pt(p-tapm)Cl2 (4b)
Pt(p-Clpapm)Cl2 (4c)
Pt(papm-N-C6H5)Cl (5a)
541(1.10), 408(4.40), 324(2.97)
528(1.42), 405(4.82), 328(3.08)
546(0.97), 415(3.82), 335(4.52)
1222(0.86)c, 1046(1.93), 902(2.11) 806(1.58)c, 736(0.88)c,
550(1.18)c, 472(4.39), 412(6.03), 358(8.91)
1216(1.08)c, 1038(2.46), 900(2.74), 804(2.66), 758(2.06)c,
688(1.15)c, 474(5.02)c, 418(7.46), 358(11.66)
1224(1.40)c, 1050(2.90), 906(3.44), 808(2.50)c, 738(1.25)c,
470(6.16)c, 414(8.68), 356(13.15)
0.12(100)
0.17(120)
0.09(100)
1.14(180)
1.20(200)
1.05(200)
1.113(100) 0.314(70)
1.047(150) 0.375(105) 0.898(140) 1.264(190)
1.018(100) 0.388(95) 0.935(160) 1.269(160)
0.778(170) 1.085(180)
Pt(papm-N-C6H4-Me-o)Cl (6a)
Pt(papm-N-C6H4-Me-m)Cl (7a)
Pt(papm-N-C6H4-Me-p)Cl (8a)
Pt(papm-N-C6H4-OMe-p)Cl (9a)
Pt(papm-N-C6H4-Cl-p)Cl (10a)
Pt(p-tapm-N-C6H5)Cl (5b)
1220(1.55), 1052(3.49), 918(3.84), 807(2.79), 740(1.45),
474(6.99)c, 420(10.06), 358(15.05)
1.052(76)
1.009(95)
0.325(140) 0.870(100) 1.294(170)
0.413(100) 0.945(170) 1.448d
1216(1.08)c, 1054(3.18), 914(3.47), 811(2.55)c, 734(1.24)c,
510(3.80)c, 456(7.98), 428(8.38), 356(12.85)
1220(1.08)c, 1060(3.05), 892(3.29), 800(2.50)c, 732(1.20)c,
540(1.10)c, 470(4.21), 410(5.96), 356(10.43)
1160(0.92)c, 1050(2.05), 928(1.23)c, 840(2.60)c, 738(1.89),
556(1.23)c
1.127(100) 0.304(120) 0.746(160) 1.018(180)
1.018(90)
1.011(90)
1.010(95)
1.007(80)
0.968(90)
0.409(110) 0.904(140) 1.236(175)
0.438(100) 0.930(120) 1.227(190)
0.430(100) 0.925(130) 1.240(190)
0.450(100) 0.923(120) 1.253(170)
0.474(110) 0.938(140) 1.532d
Pt(p-tapm-N-C6H4-Me-o)Cl (6b)
Pt(p-tapm-N-C6H4-Me-m)Cl (7b)
Pt(p-tapm-N-C6H4-Me-p)Cl (8b)
Pt(p-tapm-N-C6H4-OMe-p)Cl (9b)
Pt(p-tapm-N-C6H4-Cl-p)Cl (10b)
Pt(p-Clpapm-N-C6H5)Cl (5c)
1164(1.07)c, 1020(2.15), 920(1.35)c, 830(2.22), 730(1.42),
520(5.62)
1156(1.22), 1018(2.24), 906(1.56), 828(2.19)c, 732(1.40),
518(5.08)c
1166(0.97), 1055(1.88), 933(2.39)c, 852(1.70), 746(0.91),
560(1.50), 485(4.61)
1154(0.94)c, 1016(1.53), 912(1.69)c, 872(2.45)c, 736(1.09),
442(6.39)
1174(1.08), 1032(2.10), 910(1.45)c, 830(2.45), 755(1.57),
530(5.36),
1.086(100) 0.383(100) 0.801(95)
1.208(160)
1198(0.62)c, 1028(1.32)c, 908(1.46), 729(1.40), 740(1.51),
768(1.99)c, 482(4.53)c
1.117(85)
1.026(90)
1.031(80)
0.405(100) 0.749(120) 1.159(150)
0.375(110) 1.040(100) 1.136(190)
Pt(p-Clpapm-N-C6H4-Me-o)Cl (6c)
Pt(p-Clpapm-N-C6H4-Me-m)Cl (7c)
Pt(p-Clpapm-N-C6H4-Me-p)Cl (8c)
1198(0.64), 1044(1.19), 930(1.45), 745(1.40), 568(1.95),
500(3.64), 445(8.95)
1200(0.79), 1048(1.35), 935(1.55), 740(1.50), 570(2.00),
500(3.50), 440(9.05)
1208(0.71)c, 1040(1.40), 920(1.66), 740(1.50), 572(2.03),
490(4.85)
0.368(120) 1.048(90)
1.127(170)
1.026(100) 0.375(100) 1.040(130) 1.136(160)
Pt(p-Clpapm-N-C6H4-OMe-p)Cl (9c) 1200(0.68), 1060(2.04), 950(2.89), 805(2.83), 745(1.65c),
0.938(90)
1.122(90)
0.394(110) 0.823(130) 1.359d
565(1.34), 475(5.32)
Pt(p-Clpapm-N-C6H4-Cl-o)Cl (10c)
1224(1.06), 1066(2.10), 910(3.05), 810(2.42), 740(1.22)c,
560(1.26), 480(5.42)
0.300(100) 0.728(110) 1.048(140)
a
Solvent CHCl3.
b
Solvent MeCN, supporting electrolyte [nBu4N][ClO4], Pt-disk milli working electrode, Pt-wire auxiliary electrode, reference electrode SCE, at 298 K.
Shoulder.
c
d
Epc
.

1576
S. Senapoti et al. / Polyhedron 25 (2006) 1571–1578
substituent R (at B-ring) influences more prominently to
the LUMOs and the band maxima (kmax) follow the
sequence p-Clpapm < papm < p-tapm. This is expected in
view of the electronic property of p-Me and p-Cl groups.
In the 1H NMR spectra the signals were assigned on the
basis of chemical shifts, spin–spin interaction and their
effect on substitution and on comparison with the spectra
of Pd(aapm)Cl2 [5]. The spectral data are given in Table
4. The downfield portion of the spectra corresponds to
pyrimidine-H (4-H–6-H, C-ring) [10] and upperfield por-
tion refers to azo–aryl-protons, 8-H–12-H (B-ring). The
binding of aapm with Pt(II) is supported by the appearance
1
of spin–spin coupling [16] of H (4-H) and 195Pt (33.1%)
3
and the coupling constant is JPt–H is 20–24 Hz.
The NMR spectra of 5–10 resemble those of their Pd-
containing analogues, Pd(aapm-N–Ar)Cl, [5] and are con-
sistent with their proposed structures. A strong 195Pt–1H
(J = 21–27 Hz) was observed to the pyrimidine 4H reso-
nance (Fig. 4). The effect of substituents R0 (R0-C6H4–N–)
on the signal movement is in accordance with the electronic
effect of the group [16,17]. A significant observation is that
azo–aryl protons (B-ring) (9-H–12-H) in Pt(aapm-N–
C6H4-R0Cl) are up field shifted by 0.5–1.2 ppm relative to
Pt(aapm)Cl2 while pyrimidine protons (C-ring protons,
4-H–6-H) are shifted to up field side by 0.2–0.5 ppm com-
pared to the parent complex, Pt(aapm)Cl2. Azopyrimidine
function is electron deficient while N-aryl ring (ring A) is
r-donor and may support intramolecular charge transfer
transition. This may be reason for up field shifting of
arylazopyrimidine protons (4-H–12-H) in the fused
compound.
Fig. 3. Electronic spectra of Pt(p-tapm)Cl2 (4b) (. . .. . .) and Pt(p-tapm–
N–C6H4–Me-m) (7b) (—) in CHCl3.
the LUMO (63a) shares 33% azo and 31% azoaryl charac-
ter. Other transitions may be characterized to HOMO ꢀ 1
(61a) ! LUMO (63a), HOMO ꢀ 2 (60a) ! LUMO (63a),
HOMO (62a) ! LUMO + 1 (64a) etc. The effect of substi-
tuent R (at B-ring of arylazopyrimidine) and R0 (at A-ring
of N–Ar) are also observed. Both steric and electronic
effects of X influence the energy of HOMOs. The electron
donating substituents destabilize the MOs and thus energy
of HOMO is increased. The o-Me provides greater steric
effect compared to other and influences the HOMO. The
Table 4
1H NMR spectral data of Pt(aapm)Cl2 (4) and Pt(aapm-N–Ar)Cl (5–10) in CDCl3
Compound d/ppm (J/Hz)
4-Ha
5-Hb
6-Ha
8-Ha
9-H
10-H 11-H
7.12c 7.12c
12-Ha
7.26c
14-Ha
15-H
16-H 17-H
6.62c 6.62c
18-Ha
R
R0
4a
4b
4c
5a
6a
7a
8a
9a
10a
5b
6b
7b
8b
9b
10b
5c
6c
7c
8c
9c
10c
a
8.41(6.0) 7.63(7.0) 8.19(7.0) 7.26(7.0) 7.12c
8.36(6.0) 7.60(7.0) 8.17(7.0) 7.11(7.0) 6.86a(7.0)
8.44(6.0) 7.60(7.0) 8.28(7.0) 7.34(7.0) 7.44a(8.0)
6.86a(7.0) 7.11(7.0)
7.44a(8.0) 7.34(7.0)
2.44
8.04(6.0) 6.80(7.0) 8.29(6.0)
8.02(6.0) 6.74(7.0) 8.26(6.0)
8.04(6.0) 6.74(7.0) 8.27(6.0)
8.00(6.0) 6.72(7.0) 8.25(6.0)
8.00(6.0) 6.73(6.0) 8.24(6.0)
8.07(6.0) 6.81(7.0) 8.33(6.0)
8.03(6.0) 6.77(7.0) 8.20(6.0)
8.04(6.0) 6.76(7.0) 8.18(6.0)
8.05(6.0) 6.75(7.0) 8.16(6.0)
8.04(6.0) 6.70(7.0) 8.22(7.0)
8.00(6.0) 6.71(7.0) 8.20(7.0)
8.05(6.0) 6.80(6.0) 8.35(6.0)
8.08(6.0) 6.88(7.0) 8.35(6.0)
8.06(6.0) 6.86(7.0) 8.33(6.0)
8.06(6.0) 6.87(7.0) 8.32(6.0)
8.09(6.0) 6.82(6.0) 8.31(6.0)
8.05(6.0) 6.80(7.0) 8.36(6.0)
8.10(6.0) 6.84(7.0) 8.35(6.0)
6.21a(7.0) 6.99c 6.99c
6.69(8.0) 7.28(8.0) 6.62c
7.28(8.0)
7.22(8.0)
7.20(7.0)
6.18a(7.0) 6.93c 6.93c
6.19a(7.0) 6.90c 6.90c
6.17a(7.0) 6.88c 6.88c
6.14a(7.0) 6.86c 6.86c
6.30a(7.0) 7.06c 7.06c
6.67(8.0)
6.67(8.0) 6.92d
6.65(8.0) 7.20(9.0) 6.39a(8.0)
6.63(8.0) 7.15(9.0) 6.34a(9.0)
6.77(7.0) 7.38(8.0) 6.82a(7.0)
6.40a(7.0) 6.58c 6.58c
6.39c 6.39c
2.67
2.56
2.31
3.81
6.39a(8.0) 7.20(9.0)
6.34a(9.0) 7.15(9.0)
6.82a(7.0) 7.38(8.0)
6.04a
6.02d
6.04d
6.00d
6.03d
6.08d
6.42d
6.40d
6.40d
6.39d
6.33d
6.37d
6.71a(9.0) 6.60(7.0) 7.35(8.0) 6.60c
6.60c 6.60c
6.37a(7.0) 6.60c 6.60c
6.38c 6.38c
7.35(8.0)
7.20(8.0)
7.18(7.0)
2.42
6.69a(7.0) 6.58(7.0)
2.44 2.60
2.42 2.50
2.42 2.33
6.70a(7.0) 6.60(7.0) 6.90d
6.68a(7.0) 6.60(7.0) 7.24(7.0) 6.42a(7.0)
6.70a(7.0) 6.62(7.0) 7.19(8.0) 6.35a(9.0)
6.66a(7.0) 6.60(7.0) 7.42(8.0) 6.35a(9.0)
7.20a(8.0) 7.07(7.0) 6.88(7.0) 6.54c
6.42a(7.0) 7.24(7.0)
6.35a(9.0) 7.19a(8.0) 2.44 3.84
6.78a(7.0) 7.42a(8.0) 2.45
6.54
6.54c
6.60c
6.46c
6.88(7.0)
7.38(8.0)
7.34(8.0)
7.17a(8.0) 7.09(7.0)
7.79a(7.0) 7.06(7.0) 7.23d
7.16a(7.0) 7.09(7.0) 6.69(7.0) 6.17a(7.0)
7.13a(7.0) 7.01(7.0) 6.65(7.0) 6.12a(7.0)
6.44a(7.0) 6.60
6.46
2.69
2.58
2.33
3.82
6.17a(7.0) 6.69(7.0)
6.12a(7.0) 6.65(7.0)
6.80a(7.0) 7.22(7.0)
7.16(7.0)
7.05(7.0) 7.22(7.0) 6.80a(7.0)
Doublet.
Triplet.
b
c
Multiplet.

S. Senapoti et al. / Polyhedron 25 (2006) 1571–1578
1577
Fig. 4. 1H NMR spectrum of Pt(p-Clpapm–N–C6H4–Me-p)Cl (8c) in CDCl3 at 298 K.
3.4. Electrochemistry
The electrochemical properties of Pt(aapm)Cl2 (4) and
Pt(aapm-N–Ar)Cl (5–10) have been investigated by cyclic
voltammetry. The results are given in Table 3 and a repre-
sentative voltammogram is shown in Fig. 5. Pt(aapm)Cl2
exhibit two quasireversible (DEp > 100 mV) reduction cou-
ples at negative to SCE and have assigned to reduction of
azo group [13,18,19]. Pt(aapm-N–Ar)Cl show four succes-
sive redox couples. One redox couple appears at positive
side to SCE in the potential range 0.8–1.1 V and oxidative
in nature. This redox response is quasireversible in nature
which is supported from DEp P 80 mV (DEp = [Epa ꢀ Epc],
peak-to-peak separation). One electron nature of the redox
couple is supported from ipa/ipc (ꢂ1.0) and differential
pulse voltammetry (DPV). Platinum(II) unlike palladium
Fig. 5. Cyclic voltammogram of Pt(p-tapm–N–C6H4–Me-m)Cl (7b) in
MeCN.

1578
S. Senapoti et al. / Polyhedron 25 (2006) 1571–1578
is irreversibly oxidized to platinum(IV) by 2e stoichiometry
[6,18]. The redox responses at positive potential to SCE
may be corresponding to electron extraction from HOMO
(62a), which has major share from N–Ar group (68%).
Thus Eq. (2) is justified.
bridge Crystallographic Data center, CCDC No. 184679.
Copies of this information may be obtained free of charge
from the Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK, e-mail: deposit@ccdc.cam.ac.uk or www:
htpp://www.ccdc.cam.ac.uk.
Three redox responses at negative to SCE are reductive
in nature. The reductions correspond to sequential electron
feeding at LUMOs. There are four successive redox acces-
sible levels in –N@N–C@N– group (Eqs. (3)–(6)). The
LUMO (63a) shares 33% azo (–N@N–) contribution and
thus electron may be localized at azo center. So the reduc-
tions may be ascribed by Eqs. (3)–(6).
Acknowledgments
Financial support from the University Grants Commis-
sion and Department of Science and Technology, New
Delhi are gratefully acknowledged.
C
References
C
Cl
N
N
Cl
N
N
- e
+ e
Pt
1
Pt
1
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+
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R/
A
R/
A
B
B
R
R
ð2Þ
ð3Þ
ð4Þ
ð5Þ
ð6Þ
þe
ꢀ
*
½–N@N–C@N–ꢃ )
½–N@N–C'N–ꢃꢀ )
½–N@N–C'N–ꢃ
þe
2ꢀ
3ꢀ
*
½–N'N–C'N–ꢃ
þe
þe
2ꢀ
*
½–N'N–C'N–ꢃ
½–N–N–C'N–ꢃ3ꢀ1 )
)
½–N–N–C'N–ꢃ
4ꢀ
*
½–N–N–C–N–ꢃ
[10] P.K. Santra, D. Das, T.K. Misra, R. Roy, C. Sinha, S.-M. Peng,
Polyhedron 18 (1999) 1909.
4. Conclusion
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H. Lu, Polyhedron 19 (2000) 1263.
Pt(arylazopyrimidinie)Cl2 have been reacted with aryl-
amine (ArNH2). The coupled products have been character-
ized by spectroscopic and electrochemical studies. In one
case the structural confirmation has been carried out by
X-ray diffraction study. Crystallographic parameters have
been used to EHMO calculation. The spectral and electro-
chemical results have been correlated with MO calculation
and compared with the results of palladium complexes.
[16] L.M. Jackman, S. Sternhell, Applications of Nuclear Magnetic
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5. Supplementary materials
[17] C. Sinha, Polyhedron 12 (1993) 2363.
[18] S. Chattopadhyay, C. Sinha, P. Basu, A. Chakravorty, Organomet-
allics 10 (1991) 1135.
Crystallographic data for the structure Pt(papm-N–
C6H4–Me-m)Cl (7a) have been deposited with the Cam-
[19] P. Santra, Ph.D. thesis, Burdwan University, Burrdwan, 2001.