Dimeric cyclopalladated azobenzenes: Structural differences between 2-hydroxypyridine and 2-mercaptopyridine bridged complexes

Article abstract of DOI:10.1016/S0022-328X(02)01229-9

Binuclear chloro-bridged cyclopalladated azobenzenes [Pd(A)Cl]₂ (A = ortho-metallated azobenzene or its derivatives) have been reacted with aqueous (aq.) AgNO₃ followed by the addition of 2-hydroxypyridine (2-PyOH: donor centres of deprotonated form abbreviated N.O)/2-mercaptopyridine (2-PySH; donor centres of deprotonated form abbreviated N,S) in presence of Et₃N to synthesis bridged dinuclear compound [Pd(A)(μ-N,O)]₂-[Pd(A)(μ-N,S)]₂. The compositions of the complexes have been established by elemental analyses, IR, UV-vis, ¹H and ¹³C-NMR spectral data. The structural confirmation has been carried out by X-ray crystallography. The structures show anti-sysmmetric metallacycle in the dimer and N,O/N,S bridging arrangement. The dimer [Pd(A₁)(μ-N,X)]₂ shows strong Pd?Pd interaction (A₁ = 2-(phenylazo)benzene). The coordination mode in [Pd(A₁)(μ-N,O)]₂ shows trans pyridine-N to Pd-N(azo) bond while in [Pd(A₁)(μ-N,S)]₂ pyridine-N is trans to the Pd-C bond. The square planes are convergent towards heterocyclic bridging side.

Full text of DOI:10.1016/S0022-328X(02)01229-9

Journal of Organometallic Chemistry 650 (2002) 202ꢁ209
/
www.elsevier.com/locate/jorganchem
Dimeric cyclopalladated azobenzenes: structural differences between
2-hydroxypyridine and 2-mercaptopyridine bridged complexes
Subrata Maity a, Ramkrishna Roy a, Chittaranjan Sinha a,*, Wen-Jyh Sheen b,
Kaliyamoorthy Panneerselvam b, Tian-Huey Lu b
a Department of Chemistry, The University of Burdwan, Burdwan 713104, India
b Department of Physics, National Tsing-Hua University, Hsinchu 300, Taiwan, ROC
Received 4 October 2001; received in revised form 23 January 2002; accepted 23 January 2002
Abstract
Binuclear chloro-bridged cyclopalladated azobenzenes [Pd(A)Cl]2 (Aꢀortho-metallated azobenzene or its derivatives) have been
/
reacted with aqueous (aq.) AgNO3 followed by the addition of 2-hydroxypyridine (2-PyOH; donor centres of deprotonated form
abbreviated N,O)/2-mercaptopyridine (2-PySH; donor centres of deprotonated form abbreviated N,S) in presence of Et3N to
synthesise bridged dinuclear compound [Pd(A)(m-N,O)]2ꢁ
/
[Pd(A)(m-N,S)]2. The compositions of the complexes have been established
vis, H and 13C-NMR spectral data. The structural confirmation has been carried out by X-ray
crystallography. The structures show anti-symmetric metallacycle in the dimer and N,O/N,S bridging arrangement. The dimer
[Pd(A1)(m-N,X)]2 shows strong PdÁ Á ÁPd interaction (A1ꢀ2-(phenylazo)benzene). The coordination mode in [Pd(A1)(m-N,O)]2 shows
trans pyridine-N to PdꢀN(azo) bond while in [Pd(A1)(m-N,S)]2 pyridine-N is trans to the PdꢀC bond. The square planes are
convergent towards heterocyclic bridging side. # 2002 Published by Elsevier Science B.V.
1
by elemental analyses, IR, UVꢁ
/
/
/
/
/
/
Keywords: Cyclopalladated azobenzenes; 2-Hydroxypyridine; 2-Mercaptopyridine; Bridged binuclear; X-ray structure; Electrochemistry
1. Introduction
mixed cyclopalladated complexes [5ꢁ
the reaction [7] of [Pd(A)Cl]2 with monoanionic N,O
and S,S-chelators (Aꢀazobenzenes; N,Oꢀ8-quinoli-
nolato, 2-picolinato, 2-quinaldato); (S,Sꢀdithiocarba-
mate, xanthate) gives monocyclopalladated mixed
complex [Pd(A)(N,O)]ꢁ[Pd(A)](S,S)] [7]. In the present
/
8]. For example,
Azobenzenes are C, N donor ligands and are good
candidates to synthesise cyclometallated compounds of
/
/
/
transition [1ꢁ
majority of the reaction has been reported with palla-
dium(II) [1ꢁ16]. Many reviews concerning their synth-
/19] and non-transition metals [20,21]. A
/
/
paper we report, further new type of mixed dinuclear
cyclopalladeted complexes of azobenzenes with 2-hydro-
eses and reactivities appear in literature [1,11].
Cyclopalladated compounds have found numerous
xypyridineꢁ
/
2-mercaptopyridine having Pd
/
Á Á Á
/
Pd interac-
applications in organic syntheses [9ꢁ11], material
/
tion. 2-Hydroxypyridine (2-PyOH) and 2-mercapto-
pyridine (2-PySH) are versatile monoanionic bridging
agent and forms large number of complexes with
science [12], biology [13] and metallomesogenic field
[14]. Azobenzenes yield chloro/acetato bridged dinuclear
cyclopalladated compounds [1,2] upon reaction with
[PdCl4]2ꢂ or Pd(OAc)2, respectively. Acetato bridged
cyclopalladated dimers exist in a folded anti-symmetric
form with C2-symmetry [3]. The bridge splitting reac-
tions of the dimer with neutral and anionic ligands give
unusual M
[22ꢁ26]. Donor centres are abbreviated in deprotonated,
2-PyOH as N, O and in deprotonated, 2-PySH as N,S.
Bridged dimer [Pd(A)(m-N,O)]2 exhibits stronger Pd
/
Á Á Á
/
M interaction in platinum metal chemistry
/
/
Á Á Á
/
Pd interaction than [Pd(A)(m-N,S)]2. The binding mode
and atom numbering pattern is shown in Scheme 1. The
coordination mode in [Pd(A)(m-N,O)]2 exhibits trans
* Corresponding author. Tel.: ꢃ91-342-557683; fax: ꢃ91-342-
530452.
E-mail address: c_r_sinha@yahoo.com (C. Sinha).
pyridine-N to Pdꢀ
/
N(azo) bond while in [Pd(A)(m-N,S)]2
pyridine-N is trans to the Pdꢀ
/C bond. Single crystal X-
0022-328X/02/$ - see front matter # 2002 Published by Elsevier Science B.V.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 1 2 2 9 - 9

S. Maity et al. / Journal of Organometallic Chemistry 650 (2002) 202ꢁ
/209
203
Found: C, 53.40; H, 3.30; N, 11.09. C34H26N6O2Pd2 (2a)
1
Calc.: C, 53.49; H, 3.41; N, 11.01%. H-NMR (CDCl3):
3
6.05 (d, 1H, H(3), JHH
ꢀ7.5 Hz), 6.55 (t, 1H, H(4),
/
3
3JHH
7.0 Hz), 6.90 (t, 1H, H(5), JHH
(m, 2H, H(10,14)), 7.22 (t, 2H, H(15,16), JHH
ꢀ
/
ꢀ7.5 Hz), 7.04
/
3
ꢀ/7.5
3
Hz), 7.71 (d, 1H, H(6), JHH
ꢀ
/
9.0 Hz), 7.74 (d, 2H,
3
3
H(8,12), JHH
ꢀ
/
6.9 Hz), 8.00 (d, 1H, H(17), JHH
ꢀ7.0
/
Hz). 13C{1H}-NMR (CDCl3): four pairs of quaternary
C-centres at 170.443, 161.266, 148.541, 142.546; 13 pairs
of CH centres at 148.582, 137.625, 134.910, 129.687,
128.291, 128.291, 127.637, 127.637, 130.343, 123.708,
117.496 and 110.536.
Scheme 1. A1: RꢀR?ꢀH (1a/2a/3a); A2: Rꢀ4-Me, R?ꢀH (1b/2b/
3b); A3: RꢀH, R?ꢀ10-Me (1b?/2b?/3b?); A4: Rꢀ4-Me, R?ꢀ10-Me
(1c/2c/3c); A5: RꢀR?ꢀ4-Cl (1d/2d/3d).
2.1.2. [Pd(A2/A3)(m-N,O)]2 (2b/2b?)
The reaction between [Pd(A2/A3)Cl]2 (1b/1b?) (0.2 g,
0.30 mM) and 2-PyOH (0.06g, 0.63 mM) as before has
synthesised [Pd(A2/A3)(m-N,O)]2 (2b/2b?) and isolated in
75% yield. Anal. Found: C, 54.55; H, 3.70; N, 10.50.
C36H30N6O2Pd2 (2b/2b?). Calc.: C, 54.63; H, 3.79; N,
10.60%. 1H-NMR (CDCl3) spectra give complicated
ray structure studies of the complexes confirm their
structural differences.
2. Experimental
spectral pattern in the range 6.0ꢁ8.0 ppm, which may be
/
due to isomer mixing and have not been assigned.
2-Hydroxypyridine was obtained from Aldrich and
used as received. Palladium chloride was received from
Arora Matthey, Calcutta, India. Azobenzenes and
chlorobridged cyclopalladated azobenzenes were synthe-
sised as reported earlier [7]. Dichloromethane, chloro-
form and acetonitrile for spectroscopic and
electrochemical work were purified and dried by known
procedures [18]. All other chemicals and solvents were
reagent grade and were used as received.
2.1.3. [Pd(A4)(m-N,O)]2 (2c)
The reaction between [Pd(A4)Cl]2 (0.2 g, 0.28 mM)
and 2-PyOH (0.06 g, 0.63 mM) as before has synthesised
[Pd(A4)(m-N,O)]2 (2c) and isolated in 68% yield. Anal.
Found:. C, 55.60; H, 4.10; N, 10.20. C38H34N6O2Pd2
(2c). Calc.: C, 55.69; H, 4.15; N, 10.25% 1H-NMR
3
(CDCl3): 5.75 (s, 1H, H(3)), 6.84 (d, 1H, H(5), JHH
ꢀ
/
IR spectra (KBr disk) were recorded on JASCO
vis spectra
3
6.9 Hz), 6.88 (d, 2H, H(9,11), JHH
ꢀ
/
9.0 Hz), 6.95
model 420 FT-IR spectrophotometer. UVꢁ
/
3
(d,1H, H(14), JHH
3JHH
6.9 Hz), 7.55 (d, 1H, H(6), JHH
(d, 2H, H(8,12), JHH
3JHH 6.9 Hz). 13C{1H}-NMR (CDCl3): six pairs of
ꢀ
/
8.1 Hz), 7.23 (t, 2H, H(15,16),
were obtained using JASCO UVꢁ
/
visꢁ
/
NIR model V-570
3
ꢀ
/
ꢀ
/8.1 Hz), 7.60
spectrophotometer. 1H and 13C{1H}-NMR spectra were
collected from Bruker 300 MHz FT-NMR spectrometer
in CDCl3 using tetramethylsilane as internal reference.
3
ꢀ/8.1 Hz), 8.03 (d, 1H, H(17),
ꢀ
/
quaternary C-centres at 170.348, 161.266, 156.212,
149.589, 141.969, 129.415; 11 pairs of CH centres at
148.198, 137.579, 134.875, 128.673, 128.363, 128.363,
126.242, 123.579, 123.579, 117.476 and 110.460. -Me
signals at 22.295 and 21.309 ppm.
Elemental analyses were performed using PerkinꢁElmer
/
2400 CHN elemental analyser.
2.1. Preparation of complexes
2.1.1. [Pd(A1)(m-N,O)]2 (2a)
To an acetone solution (15 ml) of [Pd(A1)Cl]2 (0.2 g,
0.31 mM) was added aq. AgNO3 (0.11 g, 0.65 mM)
solution. The mixture was refluxed for 2 h. The
precipitated AgCl was filtered at hot condition through
G-4 sintered crucible. To this orange solution 2-hydro-
xypyridine in acetone solution (10 ml) in presence of
Et3N (0.06 g, 0.63 mM) was added dropwise with
continuous stirring (1 h) under nitrogen atmosphere.
2.1.4. [Pd(A5)(m-N,O)]2 (2d)
The reaction between [Pd(A5)Cl]2 (0.2 g, 0.26 mM)
and 2-PyOH (0.06 g, 0.63 mM) as before has synthesised
[Pd(A5)(m-N,O)]2 (2d) and isolated in 72% yield. Anal.
Found: C, 45.20; H, 2.40; N, 9.25. C34H22N6O2Cl4Pd2
(2d). Calc.: C, 45.29; H, 2.44; N, 9.32%.1H-NMR
3
(CDCl3): 5.88 (s, 1H, H(3)), 6.96 (d, 1H, H(5), JHH
ꢀ
/
6.9 Hz), 7.05 (d, 1H, H(14), 3JHH
ꢀ8.1 Hz), 7.14 (d, 2H,
/
3
H(9,11), JHH
3
6.9 Hz), 7.28 (t, 2H, H(15,16), JHH
The colour of the solution turned to brownꢁ/red and the
ꢀ
/
ꢀ
/
3
6.9 Hz), 7.60 (d, 1H, H(6), JHH
precipitate appeared slowly on bubbling nitrogen gas.
The precipitate was filtered, washed with water, and
ꢀ8.1 Hz), 7.72 (d, 2H,
/
3
H(8,12), JHH
3
8.1 Hz), 7.96 (d, 1H, H(17), JHH
ꢀ
/
ꢀ6.9
/
crystallised from chloroformꢁ
product was dried over CaCl2, yield, 0.165 g, 70%. Anal.
/
hexane via diffusion. The
Hz). The compound is not sufficiently soluble to run
13C{1H}-NMR (CDCl3) spectrum.

204
S. Maity et al. / Journal of Organometallic Chemistry 650 (2002) 202ꢁ209
/
3
7.63 (d, 1H, H(6), JHH
2.1.5. [Pd(A1)(m-N,S)]2 (3a)
ꢀ7.5 Hz), 8.41 (d, 1H, H(17),
/
3JHH
ꢀ6.0 Hz). The compound is not sufficiently
/
The reaction between [Pd(A1)Cl]2 (1a) (0.2 g, 0.29
mM) and 2-PySH (0.06g, 0.54 mM) as before has
synthesised [Pd(A1)(m-N,S)]2 (3a) and isolated in 67%
yield. Anal. Found: C, 51.50; H, 3.07; N, 10.50.
C34H26N6S2Pd2 (3a). Calc.: C, 51.33; H, 3.27; N,
soluble to run 13C{1H}-NMR (CDCl3) spectrum.
2.2. X-ray diffraction studies
1
3
10.57%. H-NMR (CDCl3): 6.08 (d, 1H, H(3), JHH
3
7.5 Hz), 6.56 (t, 1H, H(4), JHH
ꢀ
/
ꢀ9.0 Hz), 6.88 (t, 1H,
/
Crystal suitable for X-ray work was grown by slow
diffusion of dichloromethane solution into hexane at
3
H(5), JHH
3
9.0 Hz), 7.00 (d,1H, H(14), JHH
ꢀ
/
ꢀ7.5
/
3
Hz), 7.06 (t, 2H, H(9,11), JHH
ꢀ7.5 Hz), 7.03 (t, 1H,
/
H(10), 3JHH
Hz), 7.37 (d, 2H, H(8,12), JHH
ꢀ
/
9.0 Hz), 7.20 (t, 2H, H(15,16), 3JHH
ꢀ9.0
/
298 K. The crystal size are 0.20ꢄ
/
0.14ꢄ0.11 and
/
0.08 mm3 for 2a and 3a, respectively. X-
Ray diffraction data was collected at 295(2) K with the
3
0.55ꢄ0.40ꢄ
/
/
ꢀ9.0 Hz), 7.60 (d, 1H,
/
3
3
H(6), JHH
ꢀ
/
7.5 Hz), 8.36 (d, 1H, H(17), JHH
ꢀ6.0
/
Hz). 13C{1H}-NMR (CDCl3): four pairs of quaternary
C-centres at 168.541, 156.283, 147.081, 131.846; 13 pairs
of CH centres at 145.192, 133.618, 132.841, 130.140,
128.840, 128.840, 126.038, 126.038, 129.378, 117.789,
114.548, 103.889 and 110.460.
Siemens SMART CCD using graphite-monochromatised
˚
Moꢁ
/
Ka radiation (lꢀ0.71073 A). A summary of the
/
crystallography data and structure refinement para-
meters are given in Table 1. The collected reflections
were 6478 and 38 879 for 2a and 3a, respectively. Of
them, the reflections recorded using v-scan technique
were 5491 for 2a and 7763 for 3a. Intensities were
corrected for Lorentz and polarisation factors. Semi-
empirical corrections based on c-scan were applied. The
structure was solved by heavy atom methods using
SHELXS-97 and successive difference Fourier syntheses.
All non-hydrogen atoms were refined anisotropically.
The hydrogen atoms were fixed geometrically and
refined using riding model. In the final difference
Fourier map the residual maxima and minima were
2.1.6. [Pd(A2/A3)(m-N,S)]2 (3b/3b?)
The reaction between [Pd(A2/A3)Cl]2 (1b/1b?) (0.2 g,
0.30 mM) and 2-PySH (0.06 g, 0.54 mM) as before has
synthesised [Pd(A2/A3)(m-N,S)]2 (3b/3b?) and isolated in
70% yield. Anal. Found: C, 52.38; H, 3.57; N, 10.30.
C36H30N6S2Pd2 (3b/3b?). Calc.: C, 52.50; H, 3.65; N,
10.21%. 1H-NMR (CDCl3) spectra give complicated
spectral pattern in the range 6.0ꢁ8.0 ppm, which may be
due to isomer mixing and have not been assigned.
/
ꢂ3
˚
0.295 and 0.640 e A
˚
for 2a and 0.480 and ꢂ0.891 e
/
2.1.7. [Pd(A4)(m-N,S)]2 (3c)
A
97.
ꢂ3. All calculations were carried out using the SHELX
-
The reaction between [Pd(A4)Cl]2 (1c) (0.2 g, 0.28
mM) and 2-PySH (0.06g, 0.54 mM) as before has
synthesised [Pd(A4)(m-N,S)]2 (3c) and isolated in 72%
yield. Anal. Found: C, 53.48; H, 3.87; N, 9.72.
C38H34N6S2Pd2 (3c). Calc.: C, 53.60; H, 4.00; N,
Table 1
Summarised crystallographic data for [Pd(A1)(N,X)]2
1
9.87%. H-NMR (CDCl3): 5.85 (s, 1H, H(3)), 6.83 (m,
3
3H, H(5,9,11), 7.02 (d, 1H, H(14), JHH
ꢀ7.5 Hz), 7.15
/
3
Crystal parameters
2a
3a
(t, 2H, H(15,16), JHH
3JHH
9.0 Hz), 7.55 (d, 1H, H(6), JHH
(d, 1H, H(17), 3JHH 6.0 Hz). 13C{1H}-NMR (CDCl3):
ꢀ
/
9.0 Hz), 7.25 (d, 2H, H(8, 12),
3
ꢀ
/
ꢀ7.5 Hz), 8.30
/
Empirical formula
Formula weight
Crystal system
Space group
C34H26N6O2Pd2 C34H26N6S2Pd
ꢀ
/
763.41
Monoclinic
P21/c
795.53
Orthorhombic
Pbca
six pairs of quaternary C-centres at 169.045, 158.830,
154.742, 146.521, 138.019, 125.518; 11 pairs of CH
centres at 144.849, 136.059, 133.521, 127.849, 125.591,
125.591, 121.432, 121.432, 120.492, 113.678, 104.077. -
Me signals at 20.843 and 19.789 ppm.
˚
a (A)
10.3900(6)
14.1283(8)
20.3941(12)
90.619(1)
2993.5(3)
4
17.949(7)
16.084(7)
22.181(7)
90
˚
b (A)
˚
c (A)
b (8)
3
V (A )
˚
6403(4)
8
1.650
Z
2.1.8. [Pd(A5)(m-N,S)]2 (3d)
Dcalc (g cmꢂ3
)
1.694
12.44
The reaction between [Pd(A5)Cl]2 (1d) (0.2 g, 0.26
mM) and 2-PySH (0.06g, 0.54 mM) as before has
synthesised [Pd(A5)(m-N,S)]2 (3d) and isolated in 75%
yield. Anal. Found: C, 43.58; H, 2.27; N, 9.12.
C34H22N6S2Pd2 (3d). Calc.: C, 43.74; H, 2.36; N,
m (Moꢁ
/
Ka) (cmꢂ1
)
12.88
55
2u max (8)
Number of unique reflections
Number of observed data
55
6478
38 879
7763
5491
(I ꢀ2s(I))
Parameters refined
398
397
1
9.01%. H-NMR (CDCl3): 6.13 (s, 1H, H(3)), 6.91 (d,
R
Rw
0.0227
0.0545
1.058
0.050
0.0977
1.041
1H, H(5), 3JHH
Hz), 7.27 (m, 2H, H(15,16)), 7.30 (d, 2H, H(9,11),
ꢀ
/
9.0 Hz), 7.06 (d, 1H, H(14), 3JHH
ꢀ
/
7.5
Goodness-of-fit
3
7.5 Hz), 7.42 (d, 2H, H(8,12), JHH
3JHH
ꢀ
/
ꢀ9.0 Hz),
/

S. Maity et al. / Journal of Organometallic Chemistry 650 (2002) 202ꢁ
/209
205
3. Results and discussion
3.1. Synthesis
Binuclear chloro-bridged cyclopalladeted azoben-
zenes [Pd(A)Cl]2 used as starting compound for the
synthesis of the compounds in the present report.
Treatment of [Pd(A)Cl]2 in CH2Cl2 solution with 2-
hydroxypyridine (deprotonated form is abbreviated
N,O)/2-mercaptopyridine (deprotonated form is abbre-
viated N,S) in the presence of sodium methoxide
(NaOMe) give a new product in the yield of 20ꢁ30%.
/
The reaction of [Pd(A)Cl]2 with AgNO3 (aq.) in boiling
acetone solution and the subsequent treatment of 2-
hydroxypyridineꢁ
Et3N synthesised the same product in 65ꢁ
/
2-mercaptopyridine in presence of
70% yield.
/
The second method has been used for the synthesis of
the complexes. The complexes were characterised by
microanalyses, IR, 1H, and 13C-NMR spectral data. The
complexes are fairly soluble in organic solvents and non-
conducting in nature. The azobenzenes and the products
obtained are shown in Scheme 1.
Fig. 2. Single crystal X-ray structure of [Pd(A1)(m-N,S)]2 (3a).
Table 2
Selected bond lengths and angles
(i) or
[Pd(A)Cl]2 ꢃ N; X 0 [Pd(A)(m À N; X)]2
˚
Distance (A)
Angle (8)
(ii)
1
2=3
[Pd(A1)(m-N,O)]2 (2a)
(i) 2-Hydroxypyridine (2-PyOH)ꢁ
(2-PySH) in CH2Cl2ꢃNaOMe; (ii) AgNO3 (aq.) solu-
tion in acetoneꢃ2-PyOHꢁ2-PySH in presence of Et3N.
/
2-mercaptopyridine
Pd(1)ꢀC(41)
Pd(1)ꢀN(4)
Pd(1)ꢀN(1)
Pd(1)ꢀO(2)
Pd(2)ꢀC(31)
Pd(2)ꢀN(3)
Pd(2)ꢀN(2)
Pd(2)ꢀO(1)
N(4)ꢀN(6)
N(3)ꢀN(5)
1.955(2)
C(41)ꢀPd(1)ꢀN(4)
N(1)ꢀPd(1)ꢀO(2)
N(1)ꢀPd(1)ꢀN(4)
C(41)ꢀPd(1)ꢀO(2)
C(31)ꢀPd(2)ꢀN(3)
N(2)ꢀPd(2)ꢀO(1)
N(2)ꢀPd(2)ꢀN(3)
C(31)ꢀPd(2)ꢀO(1)
79.21(9)
/
2.037(2)
2.042(2)
2.113(16)
1.959(2)
2.043(2)
2.043(2)
2.111(2)
1.268(3)
1.276(2)
2.840(3)
88.57(7)
171.70(8)
178.34(8)
94.28(8)
/
/
3.2. X-Ray structure study
87.26(7)
173.23(7)
178.46(8)
The X-ray structure of [Pd(A1)(m-N,O)]2 (2a) and
[Pd(A1)(m-N,S)]2 (3a) have been determined. Perspective
molecular views are shown in Figs. 1 and 2 and the
selected bond parameters are listed in Table 2.
Pd(1)
/
Á Á Á
/
Pd(2)
[Pd(A1)(m-N,S)]2 (3a)
Pd(1)ꢀC(8)
Pd(1)ꢀN(1)
Pd(1)ꢀN(3)
Pd(1)ꢀS(1)
Pd(2)ꢀC(30)
Pd(2)ꢀS(2)
N(1)ꢀN(2)
N(5)ꢀN(6)
1.981(4)
N(1)ꢀPd(1)ꢀC(8)
N(3)ꢀPd(1)ꢀS(1)
N(1)ꢀPd(1)ꢀS(1)
C(8)ꢀPd(1)ꢀN(3)
N(4)ꢀPd(2)ꢀS(2)
C(30)ꢀPd(2)ꢀN(4)
N(5)ꢀPd(2)ꢀS(2)
N(5)ꢀPd(2)ꢀC(30)
78.7(2)
91.3(1)
2.067(4)
2.119(4)
2.299(1)
1.965(4)
2.298(1)
1.272(5)
1.274(5)
2.878(1)
3.2.1. Geometrical features
Azobenzene binds as bidentate chelating C,N-fashion
171.2(1)
174.6(2)
91.1(1)
about palladium(II) and 2-pyridone (m-N,O)ꢁ
/
2-mercap-
topyridone (m-N,S) act as bidentate bridging ligand.
176.6(2)
170.0(1)
78.4(2)
Pd(1)
/
Á Á Á
/
Pd(2)
Molecular unit consists of a C,N-cyclopalladated dimer
in a folded arrangement with C2-symmetry bridged by
N,O/N,S group. The chelate ring, Pd(C,N), is planar
˚
N,
(deviationB
/
0.03 A) and the chelate angle, Cꢀ
/
Pdꢀ
/
lies 79.390.18 in [Pd(A1)(m-N,O)]2 (2a) and 78.59
/
/
0.28
in [Pd(A1)(m-N,S)]2 (3a). The pendant phenyl ring to
cyclopalladated fragment is no longer planar with the
chelate fragment. It is twisted by av. 35 and 458 from the
Pd(C,N) plane for 2a and 3a, respectively. In [Pd(A1)(m-
N,O)]2 (2a) the atomic arrangements N(1), C(41), N(4),
Fig. 1. Single crystal X-ray structure of [Pd(A1)(m-N,O)]2 (2a).

206
S. Maity et al. / Journal of Organometallic Chemistry 650 (2002) 202ꢁ209
/
˚
O(2), Pd(1) and N(2), C(31), N(3), O(1), Pd(2) constitute
˚
0.05 A). In
2.119(4); Pd(2)ꢀ
than PdꢀN(azo) bond lengths: Pd(1)ꢀ
Pd(2)ꢀN(5), 2.082(4) A. Elongation of Pdꢀ
distances in [Pd(A1)(m-N,S)]2 (3a) compared with
/
N(4), 2.129(4) A and they are longer
N(1), 2.067(4);
N(py) bond
two independent square planes (deviationB
/
/
/
˚
[Pd(A1)(m-N,S)]2 (3a) the square planes are N(1), C(8),
/
/
N(3), S(1), Pd(1) and N(5), C(30), N(4), S(2), Pd(2) are
˚
˚
planar with mean deviation is B/0.05 A. These two
[Pd(A1)(m-N,O)]2 (2a) by ꢀ
due to strong trans influence of the Pdꢀ
former whereas in [Pd(A1)(m-N,O)]2 (2a) the Pdꢀ
is trans to PdꢀO bond. The PdꢀO and PdꢀS distances
are found to be longest in 2a and 3a, respectively. The
/
0.08 A and that may be
C bond in
C bond
square planes in 2a/3a are convergent towards hetero-
cyclic-binding site. Viewed down the Pd Pd axis
/
/
Á Á Á
/
/
projects the molecule in a distorted ‘gauche’ conforma-
tion (Fig. 3) with following interplanar angles:
/
/
/
O(1)ꢀPd(2)
O(2)ꢀPd(1)Á Á Á
C(31)ꢀPd(2)
C(41)ꢀPd(1)Á Á Á
/
Á Á Á
/
Pd(1)ꢀN(1)
17.458
18.898
23.178
23.168
S(2)ꢀPd(2)
S(1)ꢀPd(1)Á Á Á
C(8)ꢀPd(1)Á Á Á
C(30)ꢀPd(2)Á Á Á
/
Á Á Á
/
Pd(1)ꢀN(3)
38.448
38.848
34.278
35.148
/
/
Pd(2)ꢀN(2)
/
/
Pd(2)ꢀN(4)
/
Á Á Á
/
Pd(1)ꢀN(4)
/
/
Pd(2)ꢀN(5)
Pd(1)ꢀN(1)
/
/
Pd(2)ꢀN(3)
/
/
˚
N distance is av. 1.27 A and slightly elongated than
Angular deviation is higher in [Pd(A1)(m-N,S)]2 (3a)
than that of [Pd(A1)(m-N,O)]2 (2a) and may be due to
larger strain provided by thiolato-S in 3a compared with
phenolato-O in 2a. This strain is originated undoubtedly
from bulkier size of S than O. The angles extended by
Nꢁ
free ligand values (1.25 A) [27]. This is an indication of
metalꢁ
/
˚
/
ligand p-interaction localised in the M-azo frag-
ment [28].
It is observed that O(m-N,O) prefers to bind Pd(II)
Nꢀ
/
Pdꢀ
/
S in 3a is contracted by ꢀ
/
28 compared with that
trans to the PdꢀC bond in 2a while pyridine-N(m-N,S) is
/
of Nꢀ
/
Pdꢀ
/O in 2a which may be due to larger atomic
bonded trans to the Pdꢀ
is not directly perpendicular to the square planes and the
/C bond in 3a. The Pd/Á Á Á/Pd axis
size of coordinated-S (m-N,S) than that of coordinated-
O (m-N,O). Trans angles are deviated from linearity and
may be due to angular strain provided by cyclopalla-
dated ring.
deviation supports convergence of the square planes
towards heterocyclic bridging unit. In 2a, the intera-
˚
O(1) (2.295 A)/
tomic contacts of 2-pyridone, N(1)/
Á Á Á
/
˚
N(2)/
Á Á Á
/
O(2) (2.298 A) are shorter than distances of
Á Á ÁC(41)
N(3) (4.079 A). Similarly in 3a the
3.2.2. Bond parameters
azobenzene fragment of Pd(C,N) unit, C(31)
/
/
˚
C bond lengths are av. 1.96 A in 2a and 1.97
˚
˚
The Pdꢀ
/
(4.681 A)/N(4)
/
Á Á Á
/
˚
˚
S(1) (2.690 A)/
˚
S(2) (2.695 A) are shorter than distances in
A in 3a. There are two types of Pdꢀ
and PdꢀN(azo). In [Pd(A1)(m-N,O)]2 (2a) the Pdꢀ
distances are closely spaced: PdꢀN(py): Pd(1)ꢀN(1),
2.042(2); Pd(2)ꢀN(2), 2.043(2) and PdꢀN(azo): Pd(1)ꢀ
N(4), 2.037(2); Pd(2)ꢀ
N,S)]2 (3a) the PdꢀN(py) bond lengths are Pd(1)ꢀ
/
N bonds: Pdꢀ
/
N(py)
contacts of 2-mercaptopyridone, N(4)
/
Á Á Á
/
/
/
N
N(3)/
Á Á Á
/
˚
C(30) (3.606 A)/N(1)
/
/
cyclopalladaed unit, C(8)
/
Á Á Á
/
/
Á Á Á
/
˚
/
/
/
N(5) (5.153 A). The conformation of the bridged square
planes is also accounted from the torsion angle data
(Table 3, Fig. 3).
˚
/
N(3), 2.043(2) A. In [Pd(A1)(m-
/
/
N(3),
Fig. 3. Comparison of conformation angles for (i) 2a and (ii) 3a. For (i): (2a) m, ꢂ18.90; n, ꢂ17.45; o, ꢂ23.16; p, 23.178. For (ii): (3a) m?, ꢂ38.84;
n?, ꢂ38.44; o?, ꢂ35.14; p?, ꢂ34.278.

S. Maity et al. / Journal of Organometallic Chemistry 650 (2002) 202ꢁ
/209
207
Table 3
Some selective conformational and torsion angles
[Pd(A1)(m-N,O)]2 (2a)
[Pd(A1)(m-N,S)]2 (3a)
N(1)ꢀPd(1)
O(2)ꢀPd(1)Á Á Á
C(41)ꢀPd(1)Á Á Á
N(4)ꢀPd(1)Á Á ÁPd(2)
/
Á Á Á
Pd(2)
Pd(2)
/
Pd(2)
87.07(5)
78.92(4)
N(3)ꢀPd(1)
S(1)ꢀPd(1)Á Á Á
C(8)ꢀPd(1)Á Á Á
N(1)ꢀPd(1)Á Á Á
/
Á Á Á
Pd(2)
Pd(2)
Pd(2)
/
Pd(2)
83.6(1)
79.9(1)
96.7(1)
105.6(1)
/
/
/
/
/
/
100.73(6)
101.06(5)
/
/
/
/
/
/
Torsion angles
Pd(1)ꢀO(2)ꢀC(21)ꢀN(2)
Pd(1)ꢀN(1)ꢀC(11)ꢀO(1)
Pd(2)ꢀO(1)ꢀC(11)ꢀN(1)
Pd(2)ꢀN(2)ꢀC(21)ꢀO(2)
N(2)ꢀPd(2)ꢀPd(1)ꢀO(2)
N(3)ꢀPd(2)ꢀPd(1)ꢀC(41)
N(1)ꢀPd(1)ꢀPd(2)ꢀO(1)
N(4)ꢂPd(1)ꢀPd(2)ꢀC(31)
ꢂ29.8(3)
ꢂ6.9(3)
ꢂ19.3(3)
1.6(3)
Pd(1)ꢀS(1)ꢀC(13)ꢀN(4)
Pd(1)ꢀN(3)ꢀC(18)ꢀS(2)
Pd(2)ꢀN(4)ꢀC(13)ꢀS(1)
Pd(2)ꢀS(2)ꢀC(18)ꢀN(3)
N(3)ꢀPd(1)ꢀPd(2)ꢀS(2)
N(5)ꢀPd(2)ꢀPd(1)ꢀC(8)
N(4)ꢀPd(2)ꢀPd(1)ꢀS(1)
N(1)ꢀPd(1)ꢀPd(2)ꢀC(30)
ꢂ40.42
ꢂ15.94
ꢂ2.90
ꢂ28.56
ꢂ38.44
ꢂ34.27
ꢂ38.84
ꢂ35.14
ꢂ18.90(7)
ꢂ23.16(9)
ꢂ17.45(7)
ꢂ23.17(9)
3.3. Spectral studies
the reported results [7]. Symmetric azobenzenes (A1, A4,
A5) yield single mixed dimer and is supported by two -
Me signals of equal intensity in [Pd(A4)(m-N,X)]2.
Azobenzene protons perturb significantly by the sub-
stituents in the usual manner [27] and heterocyclic
The complexes display IR spectra characteristic to
N) at 1380ꢁ
1385 cmꢂ1 [7]. The assignment of all
bands has not been attempted. However, a comparison
n(Nꢁ
/
/
of the spectra with those of the respective chloro-
protons (13-Hꢂ16-H) are distinctly different and hardly
/
bridged dimers and of free 2-hydroxypyridineꢁ
/
2-mer-
affected by the substituents in the azobenzene ring. The
13C-NMR spectra of the complexes are in agreement
with the proposed structure.
captopyridine affords useful information. Heterocyclic
ring stretching in free ligand at 1608, 1420, 1240, 1155
cmꢂ1 are shifted to higher energy region by 5ꢂ
/
15
cmꢂ1. [Pd(A)(m-N,O)]2 (2) exhibit stretching at 440ꢂ
470 and 330ꢂ O)
360 cmꢂ1 corresponding to n(Pdꢀ
and n(PdꢀN), respectively [Pd(A)(m-N,S)]2 (3) exhibit
n(PdꢀS) and n(PdꢀN) at 300ꢁ330 and 360ꢁ
380 cmꢂ1
respectively. The solution spectra were recorded in
900ꢂ200 nm in chloroform and assigned on the basis
/
3.4. Electrochemistry
/
/
/
The electrochemical studies of the complexes were
carried out by cyclic voltammetry under N2 environment
using glassy carbon working electrode in acetonitrile
solution. The redox potentials are expressed with
reference to saturated calomel electrode (SCE) in pre-
/
/
/
/
,
/
of literature data [7]. Absorptions below 400 nm are due
to intramolecular charge transfer transition and are not
considered further. Out of two transitions in the visible
sence
of
n-tetrabutylammoniumperchlorate
[n-
Bu4N][ClO4]. The IR compensation was applied intern-
ally in the instrument. All the complexes display two
redox responses (Fig. 4). The peak potentials are nearly
region in 450ꢂ
may be assigned to charge transfer in the metallated azo
fragment, dp(Pd)0azo(A) [9]. The second transition
/
480 and 540ꢂ580 nm the first transition
/
/
invariant with scan rate (50ꢂ
appears at ꢂ0.6 to ꢂ0.8 V for [Pd(A)(m-N,O)]2 (2) and
0.7 to ꢂ0.9 V for [Pd(A)(m-N,S)]2 (3) and is quasir-
eversible as it evident from peak-to-peak separation
(DEpꢀ70ꢁ90 mV). The second redox response is
irreversible in nature (DEpꢀ120 mV) and appears at
more negative value (ꢀ 1.1 V). The cathodic peak
current (ipc) is proportional to v1/2 and ipa/ipc lies at
0.93ꢂ1.04 suggesting reversibility of the redox process.
/
500 mV sꢂ1). First couple
(longer wave length) is new and may be associated with
charge transition in the bridged palladium(II)-hetero-
cyclic unit.
The complexes display well resolved 1H-NMR spectra
in CDCl3 which have been assigned on the basis of
/
/
ꢂ
/
/
/
/
/
chemical shifts, spinꢁ
/spin structure and the effect of
/
ꢂ
/
1
substituents. The H-NMR spectra of cyclopalladated
complexes [7], serve as guide to the assignment of
azobenzene protons in the present series of complexes.
The atom numbering pattern is shown in Scheme 1. In
case of unsymmetrical azobenzene (A2/A3), where the
metallation of both substituted and unsubstituted rings
occurs, the population of isomer having metallation in
the substituted ring is higher in line with the electrophilic
nature of the palladation reaction [29]. The intensity
ratio of two -Me signals of [Pd(A2)(m-N,X)]2 (2b/3b):
[Pd(A3)(m-N,X)]2 (2b?/3b?) is 2:1 and is in agreement with
/
The current height measurement exhibits one-electron
redox process. The reduction is believed to be the
accommodation of electron at LUMO characterised by
azo group [7]. The half wave potential (E1/2) moves to
negative value with electron donating substituent(s) in
the aryl ring and reverse movement is observed for
electron withdrawing group. The second response is
irreversible and does not conform to the second step
reduction of azo function [17]. The reduction of hetero-

208
S. Maity et al. / Journal of Organometallic Chemistry 650 (2002) 202ꢁ209
/
Fig. 4. Cyclic voltammogram of Pd(A2)(m-N,O)]2 in MeCN using Pt-millielectrode and [n-Bu4N][ClO4] as supporting electrolyte at 298 K.
[4] E.C. Constable, A.M.W.T. Cargill, T.A. Leese, D.G.F. Reese,
cyclic coligand is not ruled out which may need
comparatively higher energy to accommodate electrons
at the antibonding orbital. There may be a certain
degree of involvement of coligand p-orbital in conjunc-
tion with azo-anti bonding orbital.
D.A. Tocher, Inorg. Chim. Acta 182 (1991) 93.
[5] (a) J.M. Vila, M. Gayoso, M. Pereira, A. Rommer, J.J.
Fernandez, M. Thornton Pett, J. Organomet. Chem. 401 (1991)
385;
(b) M. Ghedini, S. Morrone, F. Neve, D. Pucci, Gazz. Chem. Ital.
126 (1996) 511;
(c) J. Albert, J.M. Cadena, J.M. Vila, J. Granell. Tetrahedron
Asymm. 8 (1997) 991.
4. Supplementary materials
[6] J. Vicente, A. Arcas, D. Bautista, M.C. Ramirez-de-Arellano,
Organometallics 17 (1998) 4544.
Atomic coordinates H-atom coordinates, thermal
parameters, a complete list of bond distances and angles,
and lists of structure factors are available from the
CCDC, 12, Union Road, Cambridge CB 2 1EZ, UK on
request and the deposition numbers are 147256 for 2a
and 156639 for 3a.
[7] (a) K. Bag, T.K. Misra, C. Sinha, Polyhedron 17 (1998) 4109;
(b) R. Roy, K. Bag, P.K. Santra, C. Sinha, Transition Met. Chem.
24 (1999) 302.
[8] B.J. O’Keefe, P.J. Steel, Organometallics 17 (1998) 3621.
[9] (a) A.K. Mahaptra, D. Bondyopadhyay, P. Bondyopadhyay, A.
Chakravorty, Inorg. Chem. 25 (1986) 2214;
(b) A.K. Mahaptra, D. Bondyopadhyay, P. Bondyopadhyay, A.
Chakravorty, J. Chem. Soc. Chem. Commun. (1984) 999.;
(c) R. Bhowmick, H. Biswas, P. Bondyopadhyay, J. Organomet.
Chem. 498 (1995) 81;
Acknowledgements
(d) K. Kamraj, D. Bondyopadhyay, Organometallics 18 (1999)
438.
Financial support from the Department of Science
and Technology and the University Grants Commission
(under DSA-II scheme), New Delhi are gratefully
acknowledged. Authors, T.H.L., K.P. and W.J.S. thank
National Science Council, ROC, for support under
grant NSC89-2112-M-007-083. We thank to Dr. K.
Bag, Garbeta College, Midnapore, India for his initial
contribution in this work.
[10] (a) C. Sinha, D. Bondyopadhyay, A. Chakravorty, Inorg. Chem.
27 (1988) 1173;
(b) C.K. Pal, S. Chattopadhyay, C. Sinha, A. Chakravorty, J.
Organomet. Chem. 439 (1992) 91;
(c) S. Chattopadhyay, C. Sinha, S.B. Choudhury, A. Chakra-
vorty, J. Organomet. Chem. 427 (1992) 111;
(d) C. Sinha, Transition Met. Chem. 19 (1994) 41.
[11] (a) A.D. Ryabov, Synthesis (1985) 233;
(b) J. Vicente, J.A. Abad, B. Rink, R. Fernandez-de-Bolladilla,
P.G. Jones, M.C. Ramirezde-Arelland, Organometallics 16 (1997)
24.
[12] (a) J. Buey, P. Espinet, J. Organomet. Chem. 507 (1996) 137;
(b) D.P. Lydon, G.N.V. Cave, J.P. Rourke, J. Mater. Chem. 7
(1997) 403.
References
[13] C. Navarro-Ranniger, I. Lopez-Solera, J. Rodriguez, J.L. Garica-
Ruanno, P.R. Raithby, J.R. Masaguer, C. Alonso, J. Med. Chem.
36 (1993) 3795.
[1] (a) G. Wilkinson, F.G.A. Stone, E.W. Abel (Eds.), Comprehen-
sive Organometallic Chemistry, Pergamon Press, New York,
1982;
[14] (a) M. Ghedini, D. Pucci, F. Neve, Chem. Commun. (1996) 137.;
(b) A. Crispini, M. Ghedini, D. Pucci, E. Cesarotti, O. Frances-
cangeli, R. Bartolino, Liq. Cryst. 16 (1994) 373.
[15] G. Sanchez, J.L. Serrano, M.A. Moral, J. Perez, E. Molins, G.
Lopez, Polyhedron 18 (1999) 3057.
(b) V.V. Dunina, C.A. Zelevskaya, V.M. Potatov, Russ. Chem.
Rev. 57 (1988) 250.
[2] A.C. Cope, R.W. Siekman, J. Am. Chem. Soc. 87 (1965) 3272.
[3] (a) A. Suarez, J.M. Vila, M.T. Pereira, E. Gayoso, M. Gayoso, J.
Organomet. Chem. 335 (1987) 359;
(b) M. Gomez, J. Granell, M. Martinez, J. Chem. Soc. Dalton
Trans. (1998) 37.
[16] P.G. Jones, M.C. de Arellano, J. Chem. Soc. Dalton Trans. (1996)
2713.

S. Maity et al. / Journal of Organometallic Chemistry 650 (2002) 202ꢁ
/209
209
[17] (a) A.K. Mahapatra, S. Dutta, S.N. Goswami, M. Mukharjee,
A.K. Mukherjee, A. Chakravorty, Inorg. Chem. 25 (1986) 1715;
(b) G.K. Lahiri, S. Bhattacharya, M. Mukherjee, A.K. Mukher-
jee, A. Chakravorty, Inorg. Chem. 26 (1987) 3359.
[18] (a) S. Chattopadhyay, C. Sinha, P. Basu, A. Chakravorty,
Organometallics 10 (1991) 1135;
(b) J.A.R. Navarro, M.A. Romero, J.M. Salas, J. Chem. Soc.
Dalton Trans. (1997) 1001.
[24] M. Krumm, I. Mutikainen, B. Lippert, Inorg. Chem. 30 (1991)
884.
[25] (a) M. Ghedini, A. Crispini, Comments Inorg. Chem. 21 (1999)
53;
(b) S. Chattopadhyay, C. Sinha, P. Basu, A. Chakravorty, J.
Organomet. Chem. 414 (1991) 421;
(c) C. Sinha, Polyhedron 12 (1993) 2363.
(b) M. Ghedini, D. Pucci, A. Crispni, I. Aiello, F. Barigelletti, A.
Gessi, O. Francescangeli, Appl. Organomet. Chem. 13 (1999) 565.
[26] (a) T.S. Lobana, R. Verma, Indian J. Chem. 38A (1999) 592];
(b) G. Will, E. Waghorue, D. Fitzmourice, D. Guha, A. Mondal,
S. Mukherjee, Indian J. Chem. 38 (1999) 753;
(c) V. Martinezmerino, M.J. Gil, J. Chem. Soc. Perkin Trans. 2
(1999) 33.
[19] (a) J. Albert, A. Gonzalez, J. Granell, R. Moragas, X. Solans, M.
Font-Bandia, Comp. Organomet. Chem. 2 (1982) 765;
(b) J. Vicente, M.D. Bermudez, J. Escribano, M.P. Carrillo, P.G.
Jones, J. Chem. Soc. Dalton Trans. (1990) 3083.
[20] J. Vicente, M.T. Chicote, M.C. Ramirez-de-Arellano, G. Pelizzi,
E. Vitali, J. Chem. Soc. Dalton Trans. (1990) 279.
[21] N. Sudha, H.B. Singh, Coord. Chem. Rev. 135/136 (1994) 469.
[22] (a) J.M. Rawson, R.E.P. Winpenny, Coord. Chem. Rev. 139
(1995) 313;
[27] (a) D. Das, Ph.D. Thesis, Burdwan University, Burdwan, 1998.;
(b) A. Crispni, M. Ghedini, D. Pucci, Acta Crystallogr. Sect. C-
Cryst. Struct. Commun. 54 (1998) 1869;
(c) D.C. Zhange, L.Q. Ge, Z.H. Fei, Y.O. Zhange, K.B. Yu, Acta
Crystallogr. Sect. C-Cryst. Struct. Commun. 54 (1998) 1909.
[28] (a) T.K. Misra, D. Das, C. Sinha, P. Ghosh, C.K. Pal, Inorg.
Chem. 37 (1998) 1672;
(b) K. Mashima, M. Tanaka, K. Tani, H. Nakano, A. Nakamura,
Inorg. Chem. 35 (1996) 5244;
(c) K. Tani, S. Nakamura, T. Yamagata, Y. Kataoka, Inorg.
Chem. 32 (1993) 5398.
(b) P.K. Santra, T.K. Misra, D. Das, C. Sinha, A.M.Z. Slawin,
J.D. Woollins, Polyhedron 18 (1999) 2869.
[23] (a) J.V. Cuevas, G. Garcia-Herbosa, A. Munoz, S. Garcia-
Granda, D. Miguel, Organometallics 16 (1997) 2220;
[29] F. Basuli, P. Chattopadhyay, C. Sinha, Polyhedron 15 (1996)
2439.