Synthesis, characterization, structure and properties of copper and palladium complexes incorporating azo-amide ligands

Article abstract of DOI:10.1016/j.poly.2014.03.053

The reaction of the multidentate ligand N-(2-(aryldiazenyl)phenyl) picolinamide, HL (3a, 3b and 3c) [HL is ArN = NC₆H ₄NHC(O)Py, where Ar is C₆H₅ for HL¹ (3a), p-MeC₆H₄ for HL² (3b) or p-ClC ₆H₄ for HL³ (3c), and Py stands for pyridyl], with Cu(CH₃COO)₂·H₂O and Na ₂PdCl₄ separately afforded the complexes [(L) ₂Cu] (4a, 4b and 4c) and [(L)PdCl] (5a, 5b and 5c) respectively, where the deprotonated ligand L^- binds copper(II) and palladium(II) in a tridentate (N,N,N) fashion. X-ray structures of [(L³) ₂Cu] (4c) and [(L¹)PdCl] (5a) were determined to confirm the molecular structures. The newly synthesized complex 4a exhibits catalytic activity toward the oxidation of alcohols to the corresponding carbonyl compounds and oxidation of organic thioethers to sulfoxide and sulfone, whereas the complex 5a is an active catalyst for Suzuki and Heck reactions.

Full text of DOI:10.1016/j.poly.2014.03.053

Accepted Manuscript
Synthesis, characterization, structure and properties of copper and palladium
complexes incorporating azo-amide ligands
Poulami Pattanayak, Jahar Lal Pratihar, Debprasad Patra, Paula Brandão, Vitor
Felix, Surajit Chattopadhyay
PII:
S0277-5387(14)00194-6
DOI:
http://dx.doi.org/10.1016/j.poly.2014.03.053
POLY 10635
Reference:
Polyhedron
To appear in:
Received Date:
Accepted Date:
26 December 2013
23 March 2014
Please cite this article as: P. Pattanayak, J.L. Pratihar, D. Patra, P. Brandão, V. Felix, S. Chattopadhyay, Synthesis,
characterization, structure and properties of copper and palladium complexes incorporating azo-amide ligands,
Polyhedron (2014), doi: http://dx.doi.org/10.1016/j.poly.2014.03.053
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Revised Manuscript
Ms. Ref. No.: Poly-D-13-01308
Synthesis, characterization, structure and properties of copper
and palladium complexes incorporating azo-amide ligands
Poulami Pattanayak,a Jahar Lal Pratihar,a,b Debprasad Patra,a,c Paula Brandãod, Vitor
Felixd, Surajit Chattopadhyaya*
aDepartment of Chemistry, University of Kalyani, Kalyani 741235
bDepartment of Chemistry, Kandi Raj College, Murshidabad 742137, India
cDepartment of Chemistry, East Calcutta Girls’ College, Kolkata 700089, India
dDepartment of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal
_______________________________________________________________________
Abstract
The reaction of multidentate ligand N-(2-(aryldiazenyl)phenyl)picolinamide, HL (3a,3b and 3c)
[HL is ArN=NC6H4NHC(O)Py; where Ar is C6H5 (for HL1 i.e. 3a) or p-MeC6H4 (for HL2 i.e.
3b) or p-ClC6H4 (for HL3 i.e. 3c) and Py stands for pyridyl] with Cu(CH3COO)2.H2O and
Na2PdCl4 separately afforded complexes [(L)2Cu] (4a,4b and 4c) and [(L)PdCl] ( 5a,5b and 5c)
respectively, where deprotonated ligand L¯ binds copper(II) and palladium (II) in a tridentate
(N,N,N) fashion. X-ray structures of [(L3)2Cu] (4c) and [(L1)PdCl] (5a) were determined to
confirm the molecular structures. The newly synthesized 4a complex exhibited catalytic activity
toward the oxidation of alcohols to corresponding carbonyl compounds and oxidation of organic
thioethers to sulfoxide and sulfone, whereas 5a complexes were active catalyst for Suzuki and
Heck reactions.
Keywords: N-(2-(aryldiazenyl)phenyl)picolinamide; Cu(II); Pd(II); crystal structure; Oxidation
reaction; Suzuki and Heck reactions
________________________________________________________________________
*To whom corresponding should be addressed E-mail: scha8@rediffmail.com

Synthesis, characterization, structure and properties of copper
and palladium complexes incorporating azo-amide ligands
Poulami Pattanayak,a Jahar Lal Pratihar,a,b Debprasad Patra,a,c Paula Brandãod, Vitor
Felixd, Surajit Chattopadhyaya*
aDepartment of Chemistry, University of Kalyani, Kalyani 741235
cDepartment of Chemistry, East Calcutta Girls’ College, Kolkata 700089, India
dDepartment of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal
_______________________________________________________________________
Abstract
The reaction of the multidentate ligand N-(2-(aryldiazenyl)phenyl)picolinamide, HL (3a, 3b and
3c) [HL is ArN=NC6H4NHC(O)Py, where Ar is C6H5 for HL1 (3a), p-MeC6H4 for HL2 (3b) or p-
ClC6H4 for HL3 (3c), and Py stands for pyridyl], with Cu(CH3COO)2.H2O and Na2PdCl4
separately afforded the complexes [(L)2Cu] (4a, 4b and 4c) and [(L)PdCl] (5a, 5b and 5c)
respectively, where the deprotonated ligand L¯ binds copper(II) and palladium(II) in a tridentate
(N,N,N) fashion. X-ray structures of [(L3)2Cu] (4c) and [(L1)PdCl] (5a) were determined to
confirm the molecular structures. The newly synthesized complex 4a exhibits catalytic activity
toward the oxidation of alcohols to the corresponding carbonyl compounds and oxidation of
organic thioethers to sulfoxide and sulfone, whereas the complex 5a is an active catalyst for
Suzuki and Heck reactions.
Keywords: N-(2-(aryldiazenyl)phenyl)picolinamide; Cu(II); Pd(II); crystal structure; Oxidation
reaction; Suzuki and Heck reactions
________________________________________________________________________
*To whom correspondence should be addressed, e-mail: scha8@rediffmail.com
1. Introduction

This work stems from our interest in the coordination chemistry of transition metals
incorporating 2-(arylazo)aniline and related ligands [1-5]. The synthesis of several ligands
exploiting the reactivity of the free amine function of the 2-(arylazo)aniline backbone (Chart I)
have been reported earlier [1-5]. The ligands 1 and 2 were synthesized
________________________________________________________________________
Please insert Chart I here
________________________________________________________________________
by the reaction of alkyl halides or by the condensation of aldehydes with the free -NH2 group of
2-(arylazo)aniline, respectively (Chart I) [2-5]. In continuation of our endeavor, we contemplated
the use of the amide (CONH) derivative of 2-(arylazo)aniline as a ligand, as shown in 3 [2-5].
The biological relevance of transition metal complexes containing amide nitrogen donors ligands
and the rich catalytic activity of copper complexes in vivo and in vitro encouraged us to prepare
the Cu(II) complexes of the azo-amide ligands, 3 [6-13].
Development of a suitable environmentally benign catalyst for the catalytic oxidation of
organic substrates is a challenge in current chemical research [6-13].
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Please insert Structure 3 here
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Researchers have been using copper(II) complexes as catalysts for oxidative organic
transformations involving the oxidation of alcohols, alkanes, alkenes and thioethers [10-31]. Air,
tertiary butylhydroperoxide (TBHP) and hydrogen peroxide have been used as oxidants in the
presence of Cu(II) catalysts for such catalytic oxidations [10,11,25-30]. However, the advantages
of using H2O2 as the oxidant prompted us to prepare catalysts that are active for oxidations with
H2O2 [32,33]. Thus, the newly synthesized Cu(II) complexes would be screened to search for
such catalytic properties.

In addition to the synthesis and studies on copper complexes, we targeted the preparation
of Pd(II) complexes using the same ligand system, 3, to study the catalytic activity in Heck and
Suzuki reactions, with the purpose of comparing the results with the catalytic activities of the
Cu(II) complexes. C-C coupling reactions catalyzed by Pd(II) complexes have drawn much
attention during the last few decades. Notable examples are Suzuki, Heck and Sonogoshira
coupling reactions [34-46]. C-C coupling reactions catalyzed by Cu(I) complexes, and in a few
cases Cu(II) complexes, have been used for C-C coupling. In the later cases, the initial
conversion of Cu(II) to Cu(I) species were proposed to occur in situ to generate the active
catalyst [47-50]. Therefore, we envisaged that studies on the catalytic properties of the newly
synthesized Pd(II) complexes towards Suzuki and Heck coupling and a comparison with such (if
any) activity of Cu(II) complexes toward these later reactions would be interesting.
Herein, we describe the synthesis of the ligands N-(2-(aryldiazenyl)phenyl)picolinamide,
HL, and the reactions of these ligands with Cu(OAc)2.H2O and Na2PdCl4. Azo-amide chelates of
the compositions [(L)2Cu], 4, and [(L)PdCl], 5, have been isolated and characterized
unequivocally. The catalytic activity of [(L)2Cu] towards the oxidation of benzyl alcohol
derivatives to aldehydes and organic thioethers to sulfoxides and sulfones have been examined.
The catalytic activity of the [(L)PdCl] complexes toward Suzuki and Heck coupling reactions is
also examined.
2. Experimental
2.1. Materials

The solvents used in the reactions were of reagent grade (E. Marck, Kolkata, India) and
were purified and dried by reported procedures [63]. The 2-(arylazo)anilines were prepared
according to the reported procedure [1,52,53]. Picolinoyl chloride was prepared according to the
reported procedure [64]. Palladium chloride and potassium carbonate were purchased from E.
Merck, Kolkata, India. Na2[PdCl4] was prepared following a reported procedure [65].
Phenylboronic acid, iodobenzene, bromobenzene, 1-iodo-3,5-dimethylbenzene, 1-iodo-3,4-
dimethylbenzene, 1-iodo-2-nitrobenzene, 1-iodo-3-nitrobenzene, 1-bromo-3,5-dimethylbenzene,
1-bromo-2-nitrobenzene and styrene were purchased from Aldrich. Copper(II) acetate, benzyl
alcohol and hydrogen peroxide were purchased from E. Merck, Kolkata, India. 4-Iodobenzyl
alcohol, 3-methoxybenzyl alcohol, 4-nitrobenzyl alcohol and phenyl benzyl alcohols were
purchased from Spectrochem, India. Methyl phenyl sulfide, ethyl phenyl sulfide, allyl phenyl
sulfide and benzyl phenyl sulfide were purchased from Sigma Aldrich.
2.2. Physical measurements
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 Perkin-Elmer L120-00A FT-IR
spectrometer with the samples prepared as KBr pellets. Electronic spectra were recorded on a
1
13
Shimadzu UV-1800 PC spectrophotometer. H and C NMR spectra were obtained on Bruker
400 spectrometers in CDCl3.
2.3. Synthesis of the ligands
All the ligands 3a, 3b and 3c were prepared following similar procedures, modifying the
previously reported method for 3a [68]. A representative procedure for 3a is given below.
2.3.1. 3a.

A mixture of 2-(phenylazo)aniline (0.788 g, 4.00 mmol), picolinoyl chloride (0.500 g,
3.98 mmol) and 0.3 g (3 mmol) of triethyl amine in 30 cm3 dry dichloromethane was stirred for
24 h. An orange liquid was obtained after evaporation of the solvent. Column chromatographic
purification of this orange liquid on silica gel (60–120 mesh) using petroleum ether:benzene
(90:10 v/v) mixed solvent as the eluent afforded the desired ligand, 3a. Yield: 60%. C18H14N4O
(302), calcd.: C, 71.52; H, 4.63; N, 18.54; found: C, 71.54; H, 4.60; N, 19.00%. UV/Vis
(CH2Cl2) λmax (ε, M-1cm-1): 376 (18520), 337 (24180), 293 (29520), 242 (25480). IR (KBr
pellets, cm-1) ν: 3275 (Ν−Η), 1692 (C=O), 1533 (N=N). 1H NMR (CDCl3) δ: 12.52 (s, 1H), 8.89
(d, 1H), 8.73 (d, 1H), 8.33 (d, 1H), 8.13 (d, 1H), 8.03 (d, 2H), 7.89-7.94 (m, 2H), 7.49-7.54 (m,
13
2H), 7.37 (d, 2H), 7.21 (t, 1H). C NMR (CDCl3) δ: 162.45 (s, 1C), 152.64 (s, 1C), 150.29 (s,
1C), 148.21 (s, 1C), 139.86 (s, 1C), 137.55 (s, 1C), 136.21 (s, 1C), 132.81 (s, 1C), 131.29 (s,
1C), 129.18 (s, 1C), 126.44 (s, 1C), 123.63 (s, 1C), 123.10 (s, 1C), 122.48 (s, 1C), 120.19 (s,
1C), 119.53 (s, 1C).
2.3.2. HL2 and HL3
The ligands HL2 and HL3 were prepared using 2-(p-tolylazo)aniline and 2-(p-
chlorophenylazo) aniline in place of 2-(phenylazo)aniline, respectively. Yield: HL2, 60% and
HL3, 55%.
HL2, C19H16N4O (316), calcd.: C, 72.15; H, 5.06; N, 17.72; found: C, 72.10; H, 5.10; N,
17.75%. UV/Vis (CH2Cl2) λmax (ε, M-1cm-1): 375 (11867), 335 (14850), 308 (16400), 240
1
(15350). IR (KBr pellets, cm-1) ν: 3288 (Ν−Η), 1686 (C=O), 1522 (N=N). H NMR (CDCl3) δ:
12.45 (s, 1H), 8.86 (d, 1H), 8.61 (d, 1H), 8.33 (d, 1H), 8.00 (d, 2H), 7.90 (s, 1H), 7.50-7.56 (m,
2H), 7.37 (d, 2H), 7.21-7.28 (m, 2H), 2.47 (s, 3H). 13C NMR (CDCl3) 161.19 (s, 1C), 151.89 (s,
1C), 150.79 (s, 1C), 149.06 (s, 1C), 146.14 (s, 1C), 142.06 (s, 1C), 139.95 (s, 1C), 135.70 (s,

1C), 132.49 (s, 1C), 129.89 (s, 1C), 126.56 (s, 1C), 123.95 (s, 1C), 123.16 (s, 1C), 123.04 (s,
1C), 120.19 (s, 1C), 119.46 (s, 1C), 21.60 (s, CH3).
HL3, C18H15N4OCl (338.5), calcd.: C, 63.81; H, 4.43; N, 16.54; found: C, 63.85; H, 4.45;
N, 16.50%. UV/Vis (CH2Cl2) λmax (ε, M-1cm-1): 378 (9550), 333 (15290), 296 (15610), 236
1
(15480). IR (KBr pellets, cm-1) ν: 3290 (Ν−Η), 1695 (C=O), 1522 (N=N). H NMR (CDCl3) δ:
12.49 (s, 1H), 8.90 (d, 1H), 8.71 (d, 1H), 8.34 (d, 1H), 8.07 (d, 2H), 7.89-7.96 (m, 2H), 7.51-7.58
(m, 4H), 7.20-7.24 (m, 1H). 13C NMR (CDCl3) δ: 161.18 (s, 1C), 151.77 (s, 1C), 151.01 (s, 1C),
149.05 (s, 1C), 146.27 (s, 1C), 139.80 (s, 1C), 137.31 (s, 1C), 135.96 (s, 1C), 133.21 (s, 1C),
129.50 (s, 1C), 126.70 (s, 1C), 124.21 (s, 1C), 124.01 (s, 1C), 123.26 (s, 1C), 120.31 (s, 1C),
119.63 (s, 1C).
2.4. Syntheses of the Cu complexes
The complexes [(L1)2Cu], [(L2)2Cu] and [(L3)2Cu] were prepared following similar
procedures. A representative procedure for [(L1)2Cu] is given below.
2.4.1. [(L1)2Cu]
A solution of HL1 (0.100 g, 0.331 mmol) in 15 cm3 methanol was added to a solution of
Cu(CH3COO)2.H2O (0.302 g, 0.100 mmol) in 5 cm3 methanol. The mixture was stirred for 6 h.
The dark brown coloured solid precipitate that formed was separated by filtration and the solid
mass was dissolved in dichloromethane. Upon evaporation of the solvent, a blue-violet solid of
pure [(L1)2Cu] was obtained. Yield: 80%. C36H26N8O2Cu (665.54), calcd.: C, 64.90; H, 3.90; N,
16.82; found: C, 64.94; H, 3.95; N, 16.80%. UV/Vis (CH2Cl2) λmax (ε, M-1cm-1): 478 (6832), 337
(15434), 263 (21770). IR (KBr pellets, cm-1) ν: 1623 (C=O), 1474 (N=N).
2.4.2. [(L2)2Cu] and [(L3)2Cu]

Complexes [(L2)2Cu] and [(L3)2Cu] were prepared using HL2 and HL3 in place of HL1,
respectively. Yield: [(L2)2Cu] 75% and [(L3)2Cu] 70%.
[(L2)2Cu], C38H30N8O2Cu (693.50), calcd.: C, 65.74; H, 3.74; N, 16.14; found: C, 65.80;
H, 3.79; N, 16.20%. UV/Vis (CH2Cl2) λmax (ε, M-1cm-1): 477 (10652), 343 (21330), 260 (25080).
IR (KBr pellets, cm-1) ν: 1621 (C=O), 1470 (N=N).
[(L3)2Cu], C36H24N8O2CuCl2 (734.54), calcd.: C, 58.81; H, 3.25; N, 15.24; found: C,
58.85; H, 3.30; N, 15.30%. UV/Vis (CH2Cl2) λmax (ε, M-1cm-1): 486 (3990), 331 (15400), 263
(15190). IR (KBr pellets, cm-1) ν: 1622 (C=O), 1471 (N=N).
2.5. Syntheses of the Pd Complexes
The complexes [(L1)PdCl], [(L2)PdCl] and [(L3)PdCl] were prepared following similar
procedures. A representative procedure for [(L1)Pd]Cl is given below.
2.5.1. [(L1)PdCl]
A solution of HL1 (0.1 g, 0.329 mmol) in 15 cm3 methanol was added to a solution of
Na2PdCl4 (0.1 g, 0.329 mmol) in 5 cm3 methanol. Immediately the colour of the solution
changed to pink. The solution was stirred for 12 h in the presence of slight heat. The dark
coloured solid precipitate that formed was separated by filtration and the solid mass was
dissolved in dichloromethane. The product was separated by coloumn chromatography using
silica gel (60-120 mesh) using toluene as the eluent. Upon evaporation of the solvent, a dark
solid of pure [(L1)Pd]Cl was obtained. Yield: 70%. C18H13ClN4OPd (443.19), calcd.: C, 48.73;
H, 2.93; N, 12.63; found: C, 48.76; H, 2.90; N, 12.65%. UV/Vis (CH2Cl2) λmax (ε, M-1cm-1): 535
1
(3018), 355 (5284), 263 (13260). IR (KBr pellets, cm-1) ν: 1636 (C=O), 1388 (N=N). H NMR
(CDCl3) δ: 9.17 (d, 1H), 8.98 (d, 1H), 8.08-8.03 (m, 3H), 7.63-7.59 (m, 3H), 7.51 (t, 1H), 7.47
(d, 3H), 7.19 (t, 1H).

2.5.2. [(L2)PdCl] and [(L3)PdCl]
Complexes [(L2)Pd]Cl and [(L3)Pd]Cl were prepared using HL2 and HL3 in place of HL1,
respectively. Yield: [(L2)Pd]Cl 70% and [(L3)Pd]Cl 75% .
[(L2)Pd]Cl, C19H15N4OPdCl (457.19), calcd.: C, 49.86; H, 3.28; N, 12.24; found: C,
49.90; H, 3.25; N, 12.20%. UV/Vis (CH2Cl2) λmax (ε, M-1cm-1): 535 (3300), 355 (6150), 263
(14610). IR (KBr pellets, cm-1) ν: 1637 (C=O), 1384 (N=N). 1H NMR (CDCl3) δ: 9.07 (d, 1H),
8.97 (d, 1H), 8.06-8.00 (m, 3H), 7.1 (t, 1H), 7.56-7.54 (d, 2H), 7.49-7.44 (m, 3H), 7.23 (t, 1H),
2.42 (s, 3H).
[(L3)Pd]Cl, C18H12N4OPdCl2 (477.69), calcd.: C, 45.21; H, 2.51; N, 11.73; found: C,
45.19; H, 2.54; N, 11.70%. UV/Vis (CH2Cl2) λmax (ε, M-1cm-1): 535 (3020), 355 (5150), 263
(11000). IR (KBr pellets, cm-1) ν: 1641 (C=O), 1384 (N=N). 1H NMR (CDCl3) δ: 9.16 (d, 1H),
8.98 (d, 1H), 8.07-7.98 (m, 3H), 7.62-7.58 (m, 3H), 7.52 (t, 1H), 7.40 (d, 2H), 7.19 (t, 1H).
2.6. Crystallography
Single crystals of 4c and 5a were grown by slow evaporation of dichloromethane-
petroleum ether and dichloromethane-hexane solutions at 298 K respectively. Data were
collected by the ω-scan technique on a Bruker Smart CCD diffractometer with Mo-Kα radiation,
monochromated by graphite crystal. Structure solution was done by the direct method with the
SHELXS-97 program [68-69]. Full matrix least square refinements on F2 were performed using
the SHELXL-97 program [68-69]. All non-hydrogen atoms were refined anisotropically using
reflections I > 2σ (I). The C-bound hydrogen atoms were included in calculated positions and
refined using the riding model. Data collection parameters and relevant crystal data are collected
in Table 1.
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Please insert Table 1 here

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2.7. General procedure for the oxidation of alcohols.
A mixture of the aromatic alcohol (0.5 mmol), catalyst 4a (0.002 mmol) and 30 % H2O2
(5 equiv.) was added to a round bottom flask containing 10 mL of acetonitrile. The total mixture
was stirred at 70 °C for 4 h. The reaction was monitored by TLC. After completion of the
reaction, the solvent was removed, the organic phase was separated and dried over Na2SO4, and
the product was purified by column chromatography (hexane/ethyl acetate). Yields were
1
determined by weighing the isolated products, which were characterized by H NMR and IR
spectroscopy (Table 4).
2.8. General procedure for oxidation of organic thioethers.
All the catalytic reactions were performed by a similar procedure. To a solution of 3
mmol of sulfide and 5 mL of 30% H2O2 in methanol-dichloromethane (1:9), 0.0120 mmol of
catalyst 4a was added at 0 °C. The reaction mixture was stirred for 10 h. The solution was
concentrated in a vacuum. The products were separated by preparative TLC using benzene-
acetonitrile (95:5) mixed solvent. Yields were determined by weighing the isolated products,
which were characterized by 1H NMR and IR spectroscopy (Table 5).
2.9. General procedures for the Suzuki cross coupling reaction.
A mixture of aryl halide (2.0 mmol), phenyl boronic acid (0.244 g, 2.0 mmol), the
palladium complex 5a (0.001 mmol) and potassium carbonate (0.232 g, 4.0 mmol) in THF (15
ml)/DMF(15 mL) was refluxed for 1.5 h, as mentioned in Table 3. After 1.5 h, the solvent was
evaporated and the reaction mixture was extracted with diethyl ether. The ether solution was
dried over Na2SO4, filtered and passed through a 12" silica column (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 the products were characterized by
their 1H NMR spectra (Table 6).
2.10. General procedures for the Heck reaction.
A mixture containing aryl halide (5.0 mmol), styrene (5.0 mmol), the palladium complex
5a (0.005 mmol) and potassium carbonate (1.06 g, 10.0 mmol) in methanol (20 ml) was refluxed
for 2 h, as mentioned in Table 4. After the reaction, the solvent was evaporated, the product was
poured into water, extracted with diethyl ether, dried over Na2SO4 and passed through a 12"
silica column (60-120 mesh). Upon evaporation of the ether, solid pure products were obtained.
The yields of the products obtained from all the reactions were determined after isolation and the
products characterized by 1H NMR spectra (Table 7).
3. Results and discussion
3.1. Syntheses
The N-(2-(phenyldiazenyl)phenyl)picolinamide ligand HL1 (3a) was prepared by modifying an
earlier reported method and it was isolated as a yellow solid in reasonable yield by the reaction
of 2-(phenylazo)aniline with picolinoyl chloride in the presence of triethylamine in dry
dichloromethane (Scheme 1) [51]. Moreover, the modified method was utilized to prepare two
other analogues, HL2 (3b) and HL3 (3c).
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Please insert scheme 1 here
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Reactions of the preformed HL ligands with Cu(CH3COO)2.H2O and Na2PdCl4 in 2:1 and
1:1 stoichiometric ratios in methanol afforded solid complexes of the compositions [(L)2Cu] (4)
and [(L)PdCl] (5), respectively (Scheme 1). Although [(L)2Cu] (4) could be synthesized at room
o
temperature, the reaction temperature was elevated to ~50 C during the synthesis of [(L)PdCl].
The neutral [(L)2Cu] and [(L)PdCl] were soluble in common organic solvents, giving brown and

pink solutions respectively. The ligand binds the metal centres in both complexes in a tridentate
(N,N,N) fashion in its anionic form, L¯ , by dissociating the amide proton (see below, crystal
structure).
3.2. Characterization
All the HL ligands displayed characteristic UV-Vis spectra with an absorption maxima
near 330 nm, assigned to the n–π* transition of azo compounds [1,51,52]. The [(L)2Cu] and
[(L)PdCl] complexes exhibited a characteristic low energy absorption near 478 and 560 nm
respectively. Representative UV-Vis spectra of the ligand HL1 (3a), [(L1 )2Cu] (4a) and
[(L1)PdCl] (5a) are shown in Fig. 1. Relevant data are collected in the experimental section.
The νNH stretches of the HL ligands (~3275 cm-1) were absent in the IR spectra of the
complexes [(L )2Cu] and [(L)PdCl], indicating deprotonation of HL upon complexation. The
νN=N frequencies of the HL ligands (~1533 cm-1) shifted to lower frequency (~1384 cm-1) in
[(L)2Cu], and [(L)PdCl], consistent with coordination of the azo nitrogen [1-5]. Coordination of
the deprotonated carboxamido nitrogen to the Cu(II) and Pd(II) centers resulted a shift in the
carbonyl stretching frequency from ~1690 cm-1 in the free ligands (HL) to ~1620 cm-1 for the
[(L)2Cu] complexes and to ~1635 cm-1 for [(L)PdCl] the complexes [54-59].
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Please insert Fig. 1 here
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The ligand HL afforded satisfactory C, H, N analytical data, 1H and 13C NMR spectral data. The
broad resonances near δ 12.52 were assigned to the N-H protons the HL ligands. The methyl
signal of HL2 appeared at δ 2.47, as expected [1-5]. Other aromatic proton resonances appeared
in the region δ 8.89-7.21 and were too complicated for appropriate assignments due to
overlapping of the signals, but the integrations matched with the number of protons.

13
The C NMR spectra of the ligands HL1 and HL3 displayed sixteen aromatic carbon
resonances in the range δ 162.45-119.63, consistent with the structural compositions. The HL2
ligand displayed a resonance for the methyl carbon at δ 21.60 ppm, in addition to sixteen
aromatic carbon resonances that appeared in the range δ 161.19-119.46, matching the structural
composition. The 1H and 13C NMR data are given in Section 2.
In the case of diamagnetic [(L)PdCl] complexes, the N-H resonances were absent in the
1HNMR spectra, signifying the dissociation of this proton upon complexation [1-4]. The
aromatic proton resonances appeared in the region δ 9.08-7.17. The aromatic proton resonances
are complicated due to overlapping of signals, but the integrations matched well with the protons
counts. The methyl signal of [(L2)PdCl] appeared at δ 2.42. Therefore the solution structures of
the ligands and complexes were consistent with the molecular structures in the solid state (see
below, X-ray structure).
3.3. X-ray structure
Crystals of 4c and 5a, suitable for X-ray studies, were grown by slow diffusion of a
dichloromethane solution into petroleum ether. Perspective views of the molecular structures are
shown in Figs. 2 and 3. Selected bond distances and angles are collected in Tables 1 and 2
respectively. In 4a, the geometry about copper is distorted octahedral, where the mono anionic
deprotonated ligand (L) binds meridionally in a tridentate (N,N,N) fashion, forming the bis
chelate. The Cu(II) center is coordinated by two pyridyl nitrogens [N(8) and N(4)], two
deprotonated amide nitrogens [N(3) and N(7)] and two azo nitrogens [N(6) and N(2)]. The
relative orientations within the pairs of pyridyl-N, deprotonated amido-N and azo-N [termed as
N(py), N(am) and N(azo) respectively hereinafter in this manuscript] donors are cis, trans and
cis respectively.

------------------------------------------------------------------------------------------------------------
Please insert Fig. 2 & Tables 2 and 3 here
------------------------------------------------------------------------------------------------------------
Although the averages of the Cu–N(am), and Cu-N(py) lengths (1.967 and 2.13 Å
respectively) are within the normal range [57-61], the Cu–N(azo) distances (2.467 and 2.255 Å)
are longer than the Cu–N(azo) distances in square planar Cu(II) complexes incorporating azo
ligands [62,63]. To the best of our knowledge this is the first X-ray structure of a
hexacoordinated Cu(II) complex incorporating tridentate azo ligands. The two N(py)-Cu-N(azo)
angles (~155.91°) are much less than the ideal octahedral angle (180°), whereas the N(am)-Cu-
N(am) angle (175.16°) is close to 180°.
The geometry about palladium in the molecular structure of 5a is distorted square planar,
where the mono anionic deprotonated ligand (L‾) binds in a tridentate (N,N,N) fashion, with a
chloride ligand which satisfies the tetracoordination (Fig. 3). The Pd(II) center is coordinated by
one pyridyl nitrogen N(4), one deprotonated amide nitrogen N(3) and one azo nitrogen N(1),
forming one five membered and one six membered fused chelate ring, whereas, notably, both the
chelate rings formed by the tridentate L‾ ligand in 4c are five membered. This may be
considered as a good example to demonstrate the advantage of using azo ligands where both the
N donors of the –N=N- function are available for coordination to the metal centre, appropriately
as per requirement. The Pd–N(azo), Pd–N(py), Pd-N(am) and Pd–Cl lengths (1.986(2), 2.011(2),
2.032(2) and 2.3044(7)Å , respectively) are within the normal range [1-5,34].
3.2. Catalytic activity of 4a
3.2.1. Oxidation of aromatic alcohols
The oxidation of primary and secondary alcohols into their corresponding aldehydes and
ketones using Cu(II) compounds as catalysts and H2O2 (30%) as the oxidant in homogenous

media have been utilized in organic chemistry because of academic and industrial relevance
[10,11,14-20]. Herein we report the oxidation of several benzyl (primary) alcohols having
different substitutions in the aromatic ring and one secondary alcohol under atmospheric pressure
with H2O2 (30%) and a catalytic amount of [(L)2Cu] (4a) (Eq. 1). The conversions were
calculated on the basis of isolated yields. Coordination of the peroxide to the copper ion prior to
oxidation during the catalytic cycle was proposed earlier [21]. On the basis of that proposal, in
the case of 4a, dissociation of the relatively longer one or both the Cu-N(azo) linkages and
formation of a coordinatively unsaturated penta or tetra coordinated species within the reaction
mixture was presumed to accommodate the initial coordination of peroxide.
------------------------------------------------------------------------------------------------------------
Please insert Eq. 1 and Table 4 here
------------------------------------------------------------------------------------------------------------
3.2.2.Oxidation of thioethers
Catalytic homogenous oxygenation of organic thioethers to sulfoxides and sulfones has drawn
interest due to their versatile use in current chemical research [10,11,21-25,26,27]. The complex
[(L)2Cu] (4a) exhibited catalytic efficacy towards the oxidation of organic sulfides by H2O2
under ambient conditions (Eq. 2). The best yield was obtained when the reactions were carried
out by stirring the substrate with 3 mol % 4a and 30 % H2O2 for 10 h at 0 °C. The conversion
was calculated on the basis of the isolated yields (Table 4). Oxidations of the organic thioethers
did not occur in absence of [(L)2Cu].
------------------------------------------------------------------------------------------------------------
Please insert Eq. 2 and Table 5 here
------------------------------------------------------------------------------------------------------------
3.3. Catalytic activity of 5a
3.3.1. Suzuki cross-coupling and Heck coupling reactions

Although cross-coupling reactions via C-C bond formation catalyzed by palladium
complexes are ubiquitous, research in this area has been continuing to search for efficient new
generation catalysts and to establish the reaction mechanism unequivocally [34-46]. Complex 5a
exhibited catalytic activity toward Suzuki cross coupling reactions using phenylboronic acid and
aryl halides as substrates. Also, complex 5a displayed its efficacy toward the Heck coupling
reaction where the substrates used were arylhalides (bromoaryls and iodoaryls) and styrene. The
isolated yields and results are collected in Tables 6 and 7. All the reactions were carried out
under an open atmosphere.
-------------------------------------------------------------------------------------------------------
Scheme 1, Eq. 3 and Table 6 and 7 insert here
------------------------------------------------------------------------------------------------------
Complex 4a was ineffective for promoting C-C coupling reactions, whereas 5a was
ineffective for promoting the oxidation of alcohols to aldehydes.
4. Conclusions
The synthesis, characterization and structure of azo amide chelates of Cu(II) and Pd(II) have
been reported. The tridentate ligands L formed hexacoordinated [(L)2Cu] (4) and square planar
[(L)PdCl] (5) complexes. The first X-ray structure of a hexadentate Cu(II) complex
incorporating azo ligands has been reported herein. The effectiveness of 4a as a catalyst toward
the oxidation of primary and secondary alcohols and organic thioethers using H2O2 as the
oxidant has been reported. Complex 4a exhibited catalytic activity for the oxidation of benzyl
alcohol derivatives and organic thioethers in the presence of H2O2 as an oxidant, whereas it was
ineffective for Suzuki and Heck C-C coupling reactions. On the other hand, complex 5a was
active as a catalyst for Suzuki and Heck C-C coupling reactions under atmospheric conditions,
whereas it was ineffective for the oxidation of benzyl alcohol derivatives and organic thioethers
in the presence of H2O2 as an oxidant.

Acknowledgments
PP is thankful to the DST (New Delhi) for funding under the DST-WOS-A scheme (No.
SR/WOS-A/CS-140/2011). The necessary laboratory and infrastructural facilities were provided
by the Department of Chemistry, University of Kalyani. The support of DST under the FIST and
PURSE program to the Department of Chemistry, University of Kalyani is acknowledged.
Supplementary information:
Electronic supplementary materials (ESI) available: Fig.S1-S9 UV-Vis spectra of the
ligands and the complexes, Fig S10-S18 IR spectra of the ligands and the complexes, Fig S19-
1
S27 H and 13CNMR spectra of the ligands and the complexes. CCDC 941846 and 972876
contains the supplementary crystallographic data for 4c and 5a respectively. 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.
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Chart I
R/
N
R/
N
Ar
N CH
N
N
H
N
R
2
1
OH
OH
R= -CH3, -C2H5,
C5H4NCH2,
or
Ar =
CH2CH2N(CH2CH3)2
R/
=H / CH3 / Cl
Chart-I
Structure 3
R
N
N
N
O
H
N
3

Scheme 1
R
N
O
N
N
N
N
Cu
Cu(OAc)2. H2O
MeOH
N
N
R
N
R
N
R
O
N
4
[(L)2Cu]
Cl
N
N
R
N
N
O
N
H
N
NH2
O
Na2PdCl4
MeOH
Cl
3
HL
N
Pd
N
R
= H/CH3/Cl
N
5
O
Compound
R
[(L)PdCl]
3a, 3b,3c
H
CH3
Cl
4a, 4b,4b
5a 5b,5c
Scheme 1. Synthesis of 3, 4 and 5

Eq 1
CHO
CH2OH
H2O2
4a
..
(1)
R
R
Catalyst
R = I, OMe, NO2, Ph
Eq 2
O
S
O
O
H2O2
Catalyst 4a
+
S
S
..
(2)
R1
R2
R1
R2
R1
R2
Eq 3
B(OH)2
THF / DMF
Reflux
MeOH
Reflux
X
.. (3)
K2CO3
Catalyst 5a
R
K2CO3
R
Catalyst
5a
R
X = I or Br
R = H, Me, NO2

Table 1
Crystallographic data for 4c and 5a
4c
5a
C18H13ClN4OPd
443.19
Empirical formula
Formula weight
Crystal system
space group
a/Å
C36H24Cl2N8O2Cu
735.08
Monoclinic
P 2 1/n
13.7262(6)
15.1627(6)
31.0875(14)
90
Monoclinic
P21(No.4)
5.6115(3)
12.7063(7)
11.5717(7)
90
b/Å
c/Å
α/deg
β/deg
γ/deg
λ /Å
91.912(2)
90
97.596(3)
90
0.71073
6466.5(5)
3000
0.71073
817.84(8)
440
V /Å3
F(000)
Z
8
2
T/K
150
180
D/Mg m-3
1.510
1.800
µ/mm-1
0.889
1.312
R1(all data)
0.0768
0.0251
0.2234
0.0547
wR2[I > 2σ(I)]

GOF
1.10
1.03
Table 2
Selected bond distances (Å) and angles (deg) for compound 4c
Distances
Cu(1)-N(2)
Cu(1)-N(3)
2.255(5) Cu(1)-N(8)
1.958(4) Cu(1)-N(4)
2.175(5)
2.092(5)
Cu(1)-N(6)
N(5)-C(19)
N(7)-C(30)
N(8)-C(36)
O(2)-C(31)
N(1)-C(1)
N(3)-C(12)
N(4)-C(14)
N(5)-N(6)
2.467(5) Cu(1)-N(7)
1.439(9) N(6)-C(25)
1.391(7) N(7)-C(31)
1.338(7) N(8)-C(32)
1.230(7) O(1)-C(13)
1.407(8) N(1)-N(2)
1.381(7) N(2)-C(7)
1.338(7) N(3)-C(13)
1.274(7) N(4)-C(18)
Angles
1.976(4)
1.432(8)
1.358(7)
1.335(7)
1.233(7)
1.272(7)
1.430(7)
1.364(7)
1.338(7)
N(2)-Cu(1)-N(3)
N(2)-Cu(1)-N(6)
78.04(17) N(2)-Cu(1)-N(7)
82.08(16) N(2)-Cu(1)-N(4)
106.76(17)
156.21(16)
Cu(1)-N(2)-N(1)
N(2)-Cu(1)-N(8)
N(3)-Cu(1)-N(4)
134.1(4) N(2)-N(1)-C(1)
99.61(18) Cu(1)-N(2)-C(7)
81.52(17) N(1)-N(2)-C(7)
115.5(5)
108.8(3)
114.0(5)
N(3)-Cu(1)-N(6)
N(4)-Cu(1)-N(6)
N(3)-Cu(1)-N(8)
N(3)-Cu(1)-N(7)
N(7)-Cu(1)-N(8)
105.05(18) Cu(1)-N(3)-C(13)
91.68(17) Cu(1)-N(4)-C(14)
99.06(17) Cu(1)-N(3)-C(12)
175.16(18) C(12)-N(3)-C(13)
80.88(17) N(5)-N(6)-C(25)
116.7(3)
111.5(3)
119.7(4)
123.3(4)
112.6(5)
N(6)-Cu(1)-N(8)
N(6)-Cu(1)-N(7)
N(4)-Cu(1)-N(8)
N(4)-Cu(1)-N(7)
Cu(1)-N(6)-N(5)
Cu(1)-N(7)-C(30)
155.61(17) N(6)-N(5)-C(19)
75.41(18) C(14)-N(4)-C(18)
95.49(18) Cu(1)-N(4)-C(18)
93.67(17) Cu(1)-N(7)-C(31)
134.4(4) Cu(1)-N(6)-C(25)
122.5(4)
113.8(5)
118.9(5)
129.5(4)
115.8(4)
105.4(3)

Table 3
Selected bond distances (Å) and angles (deg) for compound 5a
Distances
Pd1-Cl1
Pd1-N1
2.3044(7) N1-C1
1.986(2) C5-C6
1.465(3)
1.387(4)
Pd1-N3
Pd1-N4
O1-C13
N1-N2
2.011(2) C2-C3
2.032(2) C3-C4
1.220(4) C1-C2
1.263(3) N3-C12
1.344(4) N3-C13
1.417(4)
1.392(4)
1.379(5)
1.383(4)
1.381(4)
1.375(4)
N4-C18
C7-C12
Angles
Cl1-Pd1-N1
Cl1-Pd1-N3
92.93(7) Pd1-N1-N2
172.06(7) Pd1-N1-C1
127.63(18)
122.71(17)
Cl1-Pd1-N4
N1-Pd1-N3
N1-Pd1-N4
N3-Pd1-N4
C12-N3-C13
91.73(7) N2-N1-C1
92.98(9) N1-N2-C7
174.99(9) Pd1-N3-C12
82.55(9) Pd1-N3-C13
122.5(2)
109.7(2)
123.4(2)
123.89(18)
113.6(2)

Table 4
Oxidation of sulfides catalyzed by 4a in dichloromethane methanol (9:1) mixed solvent
equiv
Yield (%)
Sulfoxide
Time (h)
Entry
H2O2 (50%)
Sulfone
S
58
55
10
10
10
25
5
5
5
1.
S
30
25
2.
3.
S
52
S
35
5
50
10
4.

Table 5
Oxidation of alcohols catalyzed by 4a in acetonitrile solvent
equiv
H2O2 (50%)
Entry
Yield (%)
88
Time (h)
4
CHO
CHO
OH
OH
OH
5
5
5
MeO
MeO
4
4
82
85
CHO
O
O2N
O2N
OH
78
80
5
4
4
CHO
OH
5
I
I