Ruthenium and palladium complexes incorporating amino-azo-phenol ligands: Synthesis, characterization, structure and reactivity

Article abstract of DOI:10.1016/j.ica.2015.02.002

The ligands 2-((2-aminophenyl)diazenyl)phenol, HOL¹-NH₂, 1a; 2-((2-aminophenyl)diazenyl)-5-methylphenol, HOL²-NH₂, 1b; and 2-((2-aminophenyl) diazenyl)-5-chlorophenol, HOL³-NH₂, 1c, which are abbreviated as HOL-NH₂, 1, afforded the complexes of compositions [(OL-NH)Pd(PPh₃)], 2, and [(OL-NH)Ru(CO)(PPh₃)₂], 3, upon reaction with Na₂PdCl₄ and Ru(CO)₃(PPh₃)₃ respectively. In all the complexes the metals ions, Pd(II) or Ru(II), are coordinated by deprotonated ligand (OL-NH)^2- in tridentate (N, N, O) fashion. X-ray structures of [(OL²-NH)Pd(PPh₃)], 2b, and [(OL¹-NH)Ru(CO)(PPh₃)₂], 3a, were determined to confirm the molecular structures. The cyclic voltammograms of [(OL-NH)Ru(CO)(PPh₃)₂] exhibited two quasi reversible oxidative response near 0.25 and 1.12 V vs. SCE. The nature of HOMO as obtained by DFT calculations has been inspected to have an insight into the redox orbitals. The newly synthesized [(OL-NH)Pd(PPh₃)], 2a, complexes exhibited catalytic activity toward the Suzuki, Heck, Cyanation and amination reactions. Catalytic activity of complex [(OL¹-NH)Ru(CO)(PPh₃)₂], 3a, was examined for the conversion of ketones to corresponding alcohols by transfer hydrogen reactions.

Full text of DOI:10.1016/j.ica.2015.02.002

Inorganica Chimica Acta 429 (2015) 122–131
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Ruthenium and palladium complexes incorporating amino-azo-phenol
ligands: Synthesis, characterization, structure and reactivity
Poulami Pattanayak a, Sankar Prasad Parua a, Debprasad Patra b, C.-K. Lai c, Paula Brandão d, Vitor Felix d,
Surajit Chattopadhyay a,
⇑
a Department of Chemistry, University of Kalyani, Kalyani 741235, India
b Department of Chemistry, East Calcutta Girls’ College, Kolkata 700089, India
c Department of Chemistry, Central National University, Jhong-Li 32001,Taiwan
d Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal
a r t i c l e i n f o
a b s t r a c t
The ligands 2-((2-aminophenyl)diazenyl)phenol, HOL1-NH2, 1a; 2-((2-aminophenyl)diazenyl)-5-
methylphenol, HOL2-NH2, 1b; and 2-((2-aminophenyl) diazenyl)-5-chlorophenol, HOL3-NH2, 1c, which
are abbreviated as HOL-NH2, 1, afforded the complexes of compositions [(OL-NH)Pd(PPh3)], 2, and
[(OL-NH)Ru(CO)(PPh3)2], 3, upon reaction with Na2PdCl4 and Ru(CO)3(PPh3)3 respectively. In all the com-
plexes the metals ions, Pd(II) or Ru(II), are coordinated by deprotonated ligand (OL-NH)2ꢀ in tridentate
(N, N, O) fashion. X-ray structures of [(OL2-NH)Pd(PPh3)], 2b, and [(OL1-NH)Ru(CO)(PPh3)2], 3a, were
determined to confirm the molecular structures. The cyclic voltammograms of [(OL-NH)Ru(CO)(PPh3)2]
exhibited two quasi reversible oxidative response near 0.25 and 1.12 V vs. SCE. The nature of HOMO as
obtained by DFT calculations has been inspected to have an insight into the redox orbitals. The newly
synthesized [(OL-NH)Pd(PPh3)], 2a, complexes exhibited catalytic activity toward the Suzuki, Heck, Cya-
nation and amination reactions. Catalytic activity of complex [(OL1-NH)Ru(CO)(PPh3)2], 3a, was exam-
ined for the conversion of ketones to corresponding alcohols by transfer hydrogen reactions.
Ó 2015 Elsevier B.V. All rights reserved.
Article history:
Received 14 November 2014
Received in revised form 31 January 2015
Accepted 2 February 2015
Available online 14 February 2015
Keywords:
2-((2-Aminophenyl)azo)phenol
Pd(II) Ru(II)
Crystal structure
C–C coupling reaction
C–N coupling reactions
Hydrogen transfer reaction
1. Introduction
Also, the tridentate (C, N, N or N, N, N) coordination of aryla-
zoaniline and related ligands (C–G in Chart 1) to the transition
Chemistry of platinum metal complexes with azo ligands has
been continuing and has drawn considerable interest [1–15]. Sev-
eral notable results concerning electron transfer reactions [1–8],
metal–carbon bond formation [11–13], CH activation [11–13],
aromatic ring amination [4], aromatic hydroxylation [11], iso-
merism [5], cytotoxic properties toward cancer cells and catalytic
transformations have been reported [9,10]. The fascinating
chemistry of ruthenium and palladium complexes of the ligands,
as shown in Chart 1, have been reported. [5,16–22]. Viewing the
intriguing chemistry of platinum metals incorporating bidentate
phenyl azopyridine (N, N) and azobenzene (N, C) ligands, research-
ers designed and synthesized several azobenzene based tridentate
ligands, such as, arylazophenol (C, N, N) and pyridylazonapthol (N,
N, O) ligands, AB (Chart 1) [5,7,14,15,17,23,24].
metal ions have been reported [5,10,12,19,20]. Under this milieu,
we contemplated to study the chemistry of palladium and rutheni-
um of amino-azo-phenol ligand, HOL-NH2, 1, for the first time
where the azo ligands are expected to bind the metal ions in tri-
dentate (N, N, O donor) mode. The complexes of platinum metals
of second transition series, Rh, Ru and Pd in particular, have drawn
much attention to the chemical researchers because of their cat-
alytic efficiency [25–27]. Since, Ru and Pd substrates are less
expensive compared to other higher platinum metals so we con-
templated to study the coordination chemistry and catalytic activ-
ities of newly synthesized Ru and Pd complexes. In General, Pd(0)
and Pd(II) complexes have utilized as catalyst for several kinds of
catalytic transformations, e.g., C–C coupling, amination and cyana-
tion [28–37]. Whereas Ru(II) catalysts are well known since the
discovery of homogenous hydrogenation [38]. Homogenous reduc-
tion of ketones to 2° alcohols by transfer hydrogen catalysis has
been considered as one of the convenient processes [39–43].
Therefore we expected interesting results in terms of catalytic
activity of newly synthesized platinum metal complexes.
⇑
Corresponding author.
E-mail address: scha8@rediffmail.com (S. Chattopadhyay).
http://dx.doi.org/10.1016/j.ica.2015.02.002
0020-1693/Ó 2015 Elsevier B.V. All rights reserved.

P. Pattanayak et al. / Inorganica Chimica Acta 429 (2015) 122–131
123
chromatography using silica gel (60–120 mesh) and product was
separated as a pink band by petroleum ether/ toluene (1:1v/v)
mixed solvent as eluent. Upon evaporation of the solvent, the pure
[(OL1-NH)Pd(PPh3)] complex was obtained as dark solid. Yield:
60%. C30H23N3OPPd (565): Anal. Calc. for C, 62.07; H, 4.13; N,
7.24.; Found: C, 62.00; H, 4.10; N, 7.30%. UV–Vis spectrum (CH2Cl2)
R
OH
N
N
1
NH2
kmax (e
, Mꢀ1 cmꢀ1) = 554 (7460), 525 (6020), 445 (4690), 335
(3530), 269 (15560), 225(67200). IR data (KBr, cmꢀ1):
m = 3346
(NH), 1339 (N@N), 1610 (C@N). 1H NMR CDCl3 (d, ppm): 8.43 (d,
1H, J = 12.0), 7.98 (d, 1H, J = 8.0), 7.88–7.83 (m, 5H), 7.58–7.48
(m, 10H), 7.31 (d, 2H, J = 2.0), 7.22–7.21 (d, 1H, J = 1.6), 7.06 (t,
1H), 6.67 (t, 1H, J = 8.0), 6.37 (d,1H, J = 8.4) 4.32 (d,1H,NH, J = 8.0).
Herein we describe the syntheses, characterizations and struc-
tures of new palladium (II) and ruthenium (II) complexes incorpo-
rating tridentate (N, N, O) amino-azo-phenolato ligands, HOL-NH2,
1. Catalytic properties of newly prepared palladium complexes
toward C–C coupling, cyanation and C–N coupling reactions have
been examined and described in this paper. The transfer hydrogen
catalysis by newly synthesized ruthenium complexes have been
reported in this paper.
2.3.2. [(OL2-NH)Pd(PPh3)], 2b and [(OL3-NH)Pd(PPh3)], 2c
Complexes [(OL2-NH)Pd(PPh3)] and [(OL3-NH)Pd(PPh3)] were
prepared using H2L2-OH and H2L3-OH in place of H2L1-OH, respec-
tively. Yield: [(OL2-NH)Pd(PPh3)] 55% and [(OL3-NH)Pd(PPh3)] 50%.
C31H26N3OPPd (593.94): Anal. Calc. for C, 62.63; H, 4.37; N, 7.07.
Found: C, 62.65; H, 4.40; N, 7.02%. UV–Vis spectrum (CH2Cl2) kmax
(e
, Mꢀ1 cmꢀ1) = 554 (12000), 525 (10600), 445 (6515), 335 (6740),
2. Experimental
269 (23240), 225 (54000). IR data (KBr, cmꢀ1):
m = 3345 (NH),
1348 (N@N), 1611 (C@N). 1H NMR CDCl3 (d, ppm): 8.26 (d, 1H,
J = 8.0), 7.96 (d, 1H, J = 12.0), 7.87–7.82 (m, 5H), 7.57–7.48 (m,
10H), 7.04 (t, 2H, J = 8.0), 6.66–6.61 (m, 3H), 6.36 (d, 1H, J = 8.0),
4.73 (d,1H, J = 12.0), 2.36 (s, 3H).
2.1. Materials
The solvents used in the reactions were of reagent grade
(E. Marck, Kolkata, India) and were purified and dried by reported
procedure [44]. 2-((2-aminophenyl)azo)phenol, HOL-NH2 were
prepared according to the reported procedure [9,12] Palladium
chloride was purchased from E. Merck, Kolkata, India. Na2[PdCl4]
C30H22N3OPPdCl (593.5): Anal. Calc. for C, 58.58; H, 3.74; N,
6.83. Found: C, 58.60; H, 3.70; N, 6.89%. UV–Vis spectrum (CH2Cl2)
kmax (e
, Mꢀ1 cmꢀ1) = 554 (10000), 525 (8700), 445 (6920), 335
(4980), 269 (21300), 225 (95700). IR data (KBr, cmꢀ1):
m = 3341
was prepared following
a reported procedure [45]. Ru(CO)3
(NH), 1344 (N@N), 1611 (C@N). 1H NMR CDCl3 (d, ppm): 8.29 (d,
1H, J = 8.0), 7.94 (d, 1H, J = 8.0), 7.84–7.79 (m, 5H), 7.69–7.46 (m,
9H), 7.19 (d, 1H, J = 4.0), 7.07 (t, 1H, J = 8.0), 6.76 (d, 1H), 6.67 (t,
1H), 6.37 (d, 1H, J = 8.0), 4.90 (d,1H, J = 12.0).
(PPh3)2 was prepared was prepared following the reported
procedure [46]. Phenylboronic acid, 4-chloro phenyl boronic
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,
styrene were purchased from Aldrich. K4Fe(CN)6, triethyl amine,
acetophenone, benzophenone, 2-chloro acetophenone, 4-chloro
acetophenone, 4-methyl acetophenone were purchased from E.
Merck, Kolkata, India. Potassium tertiary butoxide were purchased
from Spectrochem, India.
2.4. Synthesis of [(OL-NH)Ru(CO)(PPh3)2], 3
2.4.1. [(OL1-NH)Ru(CO)(PPh3)2], 3a
To a solution of Ru(CO)3(PPh3)2 (0.0156 g, 0.469 mmol) in
toluene (40 mL), HOL1-NH2 ligand (0.100 g, 0.469 mmol) was
added. The mixture was refluxed for 6 h and a dark solution was
obtained. The dark solid, obtained upon evaporation of the solvent,
was loaded on preparative silica TLC plate. Pure [(OL1-
NH)Ru(CO)(PPh3)2] complex was separated as green band using
toluene/acetonitrile (95:5 v/v) mixed solvent as the eluent. The
compound was recrystallised from dichloromethane-petroleum
ether mixed solvent. Yield: 50%. C49H38N3O2P2Ru (863.83): Anal.
Calc. for C, 68.06; H, 4.39; N, 4.86. Found: C, 68.10; H, 4.42; N,
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 Parkin-Elmer L120-00A FT-IR spectrometer with the
samples prepared as KBr pellets. Electronic spectra were recorded
on a Shimadzu UV-1800 PC spectrophotometer. 1H NMR spectra
were obtained on Bruker 400 spectrometers in CDCl3.
4.80%. UV–Vis spectrum (CH2Cl2) kmax
(8270), 599 (15100), 489 (25000), 256 (93100). IR (KBr):
= 3363 (NH) 1925 (C@O), 1608 (C@N), 1352 (N@N) cmꢀ1 1H
(e,
Mꢀ1 cmꢀ1) = 660
2.3. Synthesis of [(OL-NH)Pd(PPh3)], 2
m
.
NMR CDCl3 (d, ppm): 7.67 (d, 1H, J = 8.0), 7.51 (t, 1H), 7.46–7.44
(m, 1H), 7.32–7.13 (m, 15H), 6.78 (d, 1H, J = 8.0), 6.68 (t, 1H,
J = 8.0), 6.47 (t, 1H, J = 8.0), 6.14 (m, 2H), 5.95(d, 1H, J = 8.0), 4.58
(s, NH). E1/2 [V]: 0.28, 1.17.
All the complexes, [(OL1-NH)Pd(PPh3)], [(OL2-NH)Pd(PPh3)] and
[(OL3-NH)Pd(PPh3)] were prepared following similar procedures. A
representative procedure for [(OL1-NH)Pd(PPh3)] is given below.
2.3.1. [(OL1-NH)Pd(PPh3)], 2a
2.4.2. [(OL2-NH)Ru(CO)(PPh3)2], 3b and O(L3-NH)Ru(CO)(PPh3)2], 3c
Complex [(OL2-NH)Ru(CO)(PPh3)2] and [(OL3-NH)Ru(CO)(PPh3)2]
were prepared and purified following a similar procedure as
described for [(OL1-NH)Ru(CO)(PPh3)2] using ligand HL2-NH2 and
HL3-NH2 in place of HL1-NH2. Yield: 0.114 g, (60%) and 0.101 g
(55%) respectively.
A solution of HOL1-NH2 (0.100 g, 0.469 mmol) in 15 mL metha-
nol was added dropwise to a solution of Na2PdCl4 (0.138 g,
0.469 mmol) in 5 mL methanol. Immediately the color of the solu-
tion changed to brown. The mixture was stirred for 8 h at 50 °C.
The solvent was evaporated to obtain dark brown gummy mass.
The mass was collected and dried under vacuum. This gummy
mass was dissolved in dichloromethane (20 ml) and solid triphenyl
phosphine (0.120 g, 0.469 mmol) was added. The mixture was
stirred for 30 min. Resulting solution was subjected to column
C50H40N3O2P2Ru (877.83): Anal. Calc. for C, 68.35; H, 4.55; N,
4.78. Found: C, 68.38; H, 4.59; N, 4.70%. UV–Vis spectrum (CH2Cl2)
kmax
(e
, Mꢀ1 cmꢀ1) = 660 (5500), 599 (10000), 489 (21000), 319
(26000), 256 (60000). IR (KBr):
m
= 3361 (NH) 1927 (C@O), 1608

124
P. Pattanayak et al. / Inorganica Chimica Acta 429 (2015) 122–131
(C@N), 1354 (N@N) cmꢀ1
J = 20.0), 7.51 (t, 1H), 7.46–7.15 (m, 1H), 6.78 (d, 1H, J = 8.0), 6.68
(d, 1H, J = 8.0), 6.48 (t, 1H), 6.16 (t, 2H), 5.98(d, 1H, J = 8.0), 4.58
(s, NH), 2.35(s, CH3). E1/2 [V]: 0.24, 1.09.
.
1H NMR CDCl3 (d, ppm): 7.64 (d, 1H,
2.7. General procedure for the Heck reaction
mixture containing aryl halide (5.0 mmol), styrene
A
(5.0 mmol), the palladium complex 2a (0.005 mmol) and potassi-
um carbonate (1.06 g, 10.0 mmol) in methanol (20 mL) were
refluxed for 2 h. After reaction the solvent was evaporated and
the product was poured into water and extracted with diethyl
ether, dried over Na2SO4 and passed through 12// silica column
(60–120 mesh). Upon evaporation of the ether, solid of pure prod-
ucts were obtained. The isolated yields of the products for all the
reactions were determined after isolation. Few products were
characterized by 1H NMR spectroscopy (Fig. S-20) and others were
identified by matching the IR spectra and melting point.
C49H37N3O2P2RuCl (898.33): Anal. Calc. for C, 68.45, H, 4.11, N,
4.67. Found: C, 68.49, H, 4.15, N, 4.70%. UV–Vis spectrum (CH2Cl2)
kmax
(75000). IR (KBr):
(N@N) cmꢀ1 1H NMR CDCl3 (d, ppm): 7.67 (d, 1H, J = 8.0), 7.53 (t,
(e
, Mꢀ1 cmꢀ1) = 660 (7700), 599 (11500), 489 (23925), 256
m
= 3359 (NH), 1936 (C@O), 1610 (C@N), 1347
.
1H), 7.46 (d, 1H, J = 8.0), 7.32–7.13 (m, 15H), 6.77 (d, 1H, J = 8.0),
6.44 (t, 1H), 6.13 (t, 1H), 5.92(d, 1H, J = 8.0), 4.67(s, NH). E1/2 [V]:
0.30, 1.19.
2.5. Crystallography
2.8. General procedures for the cyanation reaction
Single crystals of 2b and 3a were grown by slow evaporation of
dichloromethane-petroleum ether and dichloromethane-hexane
IIn a round bottom flask a mixture of aryl halides (5.5 mmol),
K4Fe(CN)6 (5.5 mmol), palladium catalyst, 2a (0.02 mmol), triethyl
amine (10 mmol) and 10 mL DMF was taken and the mixture was
stirred for 24 h under air at100 °C. After reaction was over the solvent
was evaporated and the product was poured into water and extracted
with diethyl ether, dried over Na2SO4 and passed through 12// silica
column (60–120 mesh). Upon evaporation of the ether, pure products
were obtained. The isolated yields of the products obtained from
all the reactions were determined after isolation and character-
ized by IR spectroscopy (Fig. S-21) since cyano substituent
solutions at 298 K respectively. Data were collected by
technique on a Bruker Smart CCD diffractometer with Mo K
x
-scan
a
radia-
tion monochromated by graphite crystal. Structure solution was
done by direct method with SHELXS-97 program [47,48]. Full matrix
least square refinements on F2 were performed using SHELXL-97 pro-
gram [47,48]. All non-hydrogen atoms were refined anisotropically
using reflections I > 2r (I). The C-bound hydrogen atoms were
included in calculated positions and refined as riding model. Data
collection parameters and relevant crystal data are collected in
Table 1.
(
mCN ꢁ 2230 cmꢀ1) exhibit very characteristic stretching band.
2.6. General procedures for the Suzuki cross coupling reaction
2.9. General procedures for the amination reaction
A mixture of aryl halide (5.0 mmol), phenyl boronic acid
(0.244 g, 5.0 mmol), potassium carbonate (0.232 g, 4.0 mmol) and
the complex 2a (0.001 mmol,) in THF (15 mL)/DMF (15 mL) was
taken in a round bottom flask. The mixture was refluxed for 1 h.
After 1 h the solvent was evaporated and the mixture was extract-
ed with diethyl ether. The ether solution was dried over Na2SO4
and filtered and passed through 12// silica column (60–120 mesh).
After evaporation of the ether, solid pure products were obtained.
The isolated yields of the products for all the reactions were deter-
mined after isolation. Few products were characterized by 1H NMR
spectroscopy (Fig. S-19) and others were identified by matching
the IR spectra and melting point.
In a round bottom flask a mixture of aryl halides (5 mmol),
amine (5 mmol), palladium catalyst, 2a (0.05 mmol), potassium
tertiary butoxide (10 mmol) and 20 mL toluene was taken and
the mixture was stirred for 24 h under air at 120 °C under N2 atmo-
sphere. After reaction was over the solvent was evaporated and the
product was poured into water and extracted with diethyl ether,
dried over Na2SO4 and passed through 12// silica column (60–120
mesh). Upon evaporation of the ether, solid of pure products were
obtained. The isolated yields of the products for all the reactions
were determined after isolation. Few products were characterized
by 1H NMR spectroscopy (Fig. S-22) and others were identified by
matching the IR spectra and melting point.
2.10. Transformation of ketones to 2°-alcohols via hydrogen transfer
reactions
Table 1
Crystallographic data for [(OL2-NH)Pd(PPh3)], 2b and [(OL1-NH)Ru(CO)(PPh3)2], 3a.
Chemical formula
C31H26N3OPPd
C49H38N3O2P2Ru
In a round bottom flask (0.071 g, 3.9 mmol) ketones, the ruthe-
nium complex, 3a (0.0013 mmol) and (0.0036 g, 0.0625 mmol) of
KOH was heated to reflux in 10 mL of i-PrOH for appropriate time.
The complex was removed as precipitate from the reaction mixture
by the addition of diethyl ether followed by filtration and subse-
quent neutralization with 5 mL of 1 (M) HCl. Then the ether layer
was dried over Na2SO4 and passed through 12// silica column
(60–120 mesh). Upon evaporation of the ether, solid of pure prod-
ucts were obtained. The isolated yields of the products for all the
reactions were determined after isolation. Few products were
characterized by 1H NMR spectroscopy (Fig. S-23) and others were
identified by matching the IR spectra and melting point.
Crystal size (mm)
Formula weight
Crystal system
Space group
a (Å)
0.03 ꢂ 0.16 ꢂ 0.02
593.94
monoclinic
P21/c (No. 14)
13.8683(5)
20.5065(8)
9.3521(3)
90
96.760(2)
90
0.71073
2641.16(16)
1208
0.50 ꢂ 0.20 ꢂ 0.05
864.84
triclinic
ꢀ
P1 (No. 2)
10.5935(4)
12.7897(4)
17.6155(5)
74.4650(10)
73.1780(10)
71.1570(10)
0.71073
2121.69(12)
888
b (Å)
c (Å)
a
(°)
b (°)
(°)
c
k (Å)
V (Å3)
F(000)
Z
4
2
T (K)
Nref
293
6610
150
9390
2.11. DFT calculations
Npar
335
1.494
0.793
0.0437
0.0876
1.01
514
1.354
0.488
0.0288
0.0841
1.13
Dcalc (mg/mꢀ3
)
Using the X-ray coordinates of the 3a, ground state electronic
structure calculations have been carried out using DFT [49] meth-
ods with the Orca 2.7 program [50] Becke’s hybrid function [51]
with the Lee–Yang–Parr (LYP) correlation function [51] was used
throughout the study. LANL2DZ valence and effective core potential
l
(mmꢀ1
)
R1 (all data)
wR2 [I > 2 (I)]
Goodness-of-fit (GOF)
r

P. Pattanayak et al. / Inorganica Chimica Acta 429 (2015) 122–131
125
functions were used. All energy calculations were performed using
the self-consistent field ‘‘tight’’ option of the Orca 2.7 program to
ensure sufficiently well converged values for the state energies.
3. Results and discussion
3.1. Syntheses
Reaction of HOL-NH2, 1, with equivalent amount of Na2PdCl4 in
presence of triphenyl phosphine at elevated temperature (ꢃ50 °C)
afforded the solid complexes of composition [(OL-NH)Pd(PPh3)], 2
(Scheme 1). Reaction of HOL-NH2 with Ru(CO)3(PPh3)2 in refluxing
toluene afforded the green complex [(OL-NH)Ru(CO)(PPh3)2], 3
(Scheme 1). Dissociation of an amino proton and phenolic proton
of HOL-NH2 in both the occasions (see below) implied the coordi-
nation of anionic (OL-NH)2ꢀ to the metal centers. Interestingly,
Ru(II) complexes incorporating tridentate (OL-NH)2ꢀ could not be
isolated when Ru(II) substrates, such as [Ru(PPh3)3Cl2] or
[Ru(H)(CO)(PPh3)3Cl], were treated with HOL-NH2. Therefore,
oxidative addition of HOL-NH2 along with concomitant loss of H2
has been assumed to occur during the formation of 3.
Fig. 1. UV–Vis spectra of (ꢀ) HOL1-NH2, (ꢀ) [(OL1-NH)Pd(PPh3)] and (ꢀ) [(OL1-
NH)Ru(CO)(PPh3)2].
supplementary materials (Figs. S7–S14) and data are collected in
Experimental Section.
The phenolic proton of HOL-NH2 (appeared near d 12.90) was
absent in the 1H NMR spectra of complexes [(OL-NH)Pd(PPh3)],
3.2. Characterization
2
and [(OL-NH)Ru(CO)(PPh3)2], 3 indicating coordination of
phenolato oxygen [14,20,21]. The N-H resonance for [(OL-NH)
Ru(CO)(PPh3)2] complex was observed near d 4.60 as broad singlet
for one equivalent proton whereas the [(OL-NH)Pd(PPh3)] com-
plexes displayed N-H resonance within the range d 4.7 4–4.9 1
for one equivalent proton as doublet (may be due to long range
coupling) signifying the dissociation of one of the amino protons
of HOL-NH2 during complexation [10,11,13,21]. The aromatic pro-
tons of coordinated (OL-NH)2ꢀ appeared as overlapped multiplets
within d 8.2 8ꢀd 6.3 6 for both, palladium and ruthenium, com-
plexes. Three sets of multiplets for [(OL-NH)Pd(PPh3)] appeared
in the ranges of d 7.8 7ꢀd 7.8 2, d 7.5 7–d 7.5 4 and d 7.5 1ꢀd 7.4
8 for six protons, three protons and six protons respectively due
to coordinated PPh3 ligands [22] whereas in case of [(OL-NH)
Ru(CO)(PPh3)2], the multiplets characteristic to trans PPh3 ligands
appeared within the range d 7.3 6–7.1 3 [22].
The UV–Vis spectra of [(OL-NH)Pd(PPh3)], 2, and [(OL-
NH)Ru(CO)(PPh3)2], 3, exhibited low energy absorption band near
554 nm and 649 nm respectively. The low energy absorptions in
metal complexes were assigned to electronic transition within
the orbitals containing substantial ligand character [10,11,13,21].
The other absorption bands appeared within 445–225 nm for
[(OL-NH)Pd(PPh3)] and 599–256 nm for [(OL-NH)Ru(CO)(PPh3)2].
The representative UV–Vis spectra of complexes are shown in
Fig. 1. The UV–Vis spectra of all the complexes are given in supple-
mentary materials (Figs. S1–S6) and data are collected in
Experimental Section.
The complexes, 2 and 3, exhibited sharp singlet for mNH stretch-
es within 3346–3361 cmꢀ1 whereas the mNH2 of the ligands
appeared as a twin band near 3407 and 3284 cmꢀ1 [10,11,13,21].
This is consistent with the dissociation of an amino proton of
HOL-NH2 upon coordination. The mN
@
(1333–1352 cmꢀ1) for the
N
3.3. Crystal and molecular structures
complexes shifted to lower energy than the mN
@ of free ligands
N
(1468–1460 cmꢀ1) indicating the coordination of azo nitrogen
[10,11,13,21]. The mCO of 3 appeared within the range 1925–
1936 cmꢀ1 [22]. The IR spectra of all the complexes are given in
3.3.1. [(OL2-NH)Pd(PPh3)]
Suitable X-ray quality crystals of [(OL2-NH)Pd(PPh3)] were
grown by slow diffusion of dichloromethane solution into hexane.
A perspective view of the molecule has been shown in Fig. 2 and
selected bond distances and angles are collected in Table 2. The
geometry of the coordination sphere of [(OL2-NH)Pd(PPh3)] is dis-
torted square planar (mean deviation 0.00256) consistent with for-
mal +2 oxidation state [13]. The dianionic (OL2-NH)2ꢀ ligands
(dissociating the phenolic and amino protons) bind to the metal
in tridentate (N, N, O) fashion along with one PPh3 ligand to com-
plete the tetra coordination. Two adjacent chelate rings formed by
the (OL2-NH)2ꢀ ligand are of the sizes five and six member. The six
member diazoketiminato (–HN–C@C–N@N–) chelate formation is
a characteristic of the coordination behavior of 2-arylazoaniline
ligands [23,24]. The C(aryl)-O distance (1.327(4) Å) is close to C–
O distances (ꢃ1.344 Å) in coordinated catechols [52] signifying
phenolato binding rather than phenoxyl. On the other hand, N3–
C12 distance (1.333(4) Å) is closer to the same distance
(ꢃ1.315 Å) in amido coordinated arylamines rather than semidine
or quinone forms [53] indicating coordination of dianionic (OL-
NH)2ꢀ. The Pd–O distance (2.019(2) Å) is longer than the Pd–O
lengths (ꢃ1.968 Å) in catecholato complexes whereas the Pd1–
N3 distance (1.945(3) Å) is shorter than that of amido complexes
(ꢃ2.011 Å) [54] possibly due to diverse trans effects.
R
O
Pd
N
N
Na2PdCl4
Methanol
PPh3
R
N
NH
2
OH
N
R
NH2
PPh
O
3
N
N
Ru
CO
Ru(CO)3(PPh3)2
Toluene
NH
PPh3
3
[(OL-NH)Ru(CO)(PPh3)2]3
[(OL1)Ru(CO)(PPh3)2] 3a
HOL-NH21 [(OL-NH)Pd(PPh3)] 2
R
H
HOL1-NH2 1a
CH3 HOL2-NH2
[(OL1)PdCl] 2a
[(OL2)PdCl] 2b
[(OL2)Ru(CO)(PPh3)2] 3b
1b
1c
3
3
Cl
HOL3-NH2
[(OL )PdCl]
[(OL )Ru(CO)(PPh3)2]
2c
3c
Scheme 1. Synthesis of complexes.

126
P. Pattanayak et al. / Inorganica Chimica Acta 429 (2015) 122–131
Table 2
Selected bond distances (Å) and angles (deg) for compound [(OL2-NH)Pd(PPh3)], 2b.
Distances
Pd1–P1
Pd1–O1
N1–N2
N1–C6
N2–C7
N3–C12
C1–C6
2.2935(9)
2.019(2)
1.274(4)
1.425(4)
1.370(4)
1.333(4)
1.399(4)
1.399(4)
1.378(5)
1.512(5)
Pd1–N1
Pd1–N3
O1–C1
C3–C4
C4–C5
C5–C6
C7–C8
C7–C12
C8–C9
2.003(3)
1.945(3)
1.327(4)
1.395(5
1.365(5)
1.386(4)
1.414(5)
1.423(4)
1.359(5)
C1–C2
C2–C3
C3–C13
Angles
P1–Pd1–O1
P1–Pd1–N1
P1–Pd1–N3
O1–Pd1–N1
O1–Pd1–N3
N1–Pd1–N3
Pd1–O1–C1
Pd1–N1–N2
Pd1–N1–C6
95(2)
176.62(8)
N2–N1–C6
N1–N2–C7
Pd1–N3–C12
N1–C6–C5
N1–C6–C1
N2–C7–C8
N2–C7–C12
N3–C12–C11
N3–C12–C7
117.7(3)
120.4(3)
126.8(2)
124.5(3)
114.2(3)
113.8(3)
127.6(3)
119.4(3)
123.8(3)
93.93(9)
83.52(10)
172.94(10)
89.44(11)
110.22(17)
131.6(2)
110.69(19)
Fig. 2. Molecular structure of 2b with atom numbering scheme. Hydrogen atoms
are omitted for clarity.
3.3.2. [(OL1-NH)Ru(CO)(PPh3)2]
Suitable crystals of [(OL1-NH)Ru(CO)(PPh3)2] were grown by
slow diffusion of dichloromethane solution into petroleum ether.
A perspective view of the molecule has been shown in Fig. 3 and
selected bond distances and angles are collected in Table 3.
The dianionic (OL1-NH)2ꢀ ligand is coordinated to the Ru(II) in a
tridentate (O, N, N) fashion along with two mutually trans PPh3
ligands. The CO ligand completed hexacoordination in distorted
octahedral geometry. Like [(OL2-NH)Pd(PPh3)] in [(OL1-NH)
Ru(CO)(PPh3)2] two adjacent chelate rings formed by the
(OL1-NH)2ꢀ ligand are of the sizes five and six member. C(aryl)-O
(1.328(3) Å) and C12–N3 (1.334(3) Å) distances are close to the
same distances in O-coordinated phenolato (ꢃ1.313 Å) [55] and
N-coordinated anilido (ꢃ1.445 Å) ligands respectively [54] signify-
ing the character of the coordinated dianionic ligand (OL1-NH)2ꢀ
.
3.4. Electrochemical properties of [(OL-NH)Ru(CO)(PPh3)2], 3
The [(OL-NH)Ru(CO)(PPh3)2], 3, complexes exhibited two one
electron quasi reversible oxidative responses within the ranges
0.24–0.30 and 1.17–1.19V versus SCE Eq. (1).
Fig. 3. Molecular structure of 3a with atom numbering scheme. Hydrogen atoms
are omitted for clarity.
+
[(OL-NH)Ru(CO)(PPh3)2]
e
ð1Þ
[(OL-NH)Ru(CO)(PPh3)2]
A representative cyclic voltammogram of [(OL1-NH)Ru(CO)
(PPh3)2] has been shown in Fig. 4 and the half wave potentials
are given in To have an insight into the redox process, composition
of the HOMO has been evaluated carrying out single point DFT
calculations. Orbital diagrams of HOMO and LUMO are shown in
Fig. 5. HOMO is delocalized within the (OL-NH) fragment signifying
the participation of ligand orbital in electron transfer process. The
major contribution of ligand orbitals in HOMO and LUMO is also
consistent with the structured intense low energy (575–650 nm)
absorptions for [(OL-NH)Ru(CO)(PPh3)2] complexes.
Table 3
Selected bond distances (Å) and angles (deg) for [(OL1-NH)Ru(CO)(PPh3)2], 3a.
Ru1–P1
Ru1–P2
N1–N2
O2–C49
Ru1–C49
N1–C6
2.3929(5)
2.3928(5)
1.276(3)
1.151(3)
1.872(2)
1.434(3)
1.328(3)
Ru1–O1
Ru1–N1
Ru1–N3
C4–C5
N2–C7
N3–C12
C3–C4
2.0827(17)
2.0640(17)
2.0272(19)
1.380(5)
1.369(3)
1.334(3)
1.401(5)
O1–C1
P1–Ru1–P2
P1–Ru1–O1
P1–Ru1–N1
P1–Ru1–N3
P1–Ru1–C49
P2–Ru1–O1
178.42(2)
91.47(4)
92.04(5)
88.60(5)
91.14(6)
90.11(4)
N1–Ru1–N3
Ru1–O1–C1
P2 –Ru1–C49
N3 –Ru1–C49
O1–Ru1–N1
O1–Ru1–N3
88.26(7)
112.43(14)
91.14(6)
96.52(8)
80.41(7)
168.66(6)
3.5. Catalytic activity of [(OL1-NH)Pd(PPh3)]
3.5.1. Suzuki cross-coupling and Heck coupling reactions
Suzuki and Heck coupling (Eqs. (2) and (3)) reactions are
well known for aromatic C–C coupling and are useful synthetic

P. Pattanayak et al. / Inorganica Chimica Acta 429 (2015) 122–131
127
protocols in organic chemistry [28–30]. Several compounds of
palladium have been used as catalyst for such C–C coupling
reactions with different degrees of efficacy. The bulky phosphine
ligand are expected to be more labile compared to halides in
[(OL-NH)Pd(PPh3)] complexes and may have better catalytic effi-
ciency. Suzuki cross coupling and Heck reactions were carried
out using [(OL1-NH)Pd(PPh3)] as catalyst and the results have
been summarized in Tables 4 and 5. The isolated yields of prod-
ucts for coupling of phenyl group or p-chlorophenyl group,
using phenyl boronic acid or p-chlorophenyl boronic acid as
substrates respectively, with different aryl halides have been
given in Table 4. Herein it is worthwhile to mention that chlor-
oaryls undergo coupling in addition to bromo and iodo aryls.
Earlier, the coupling of aryl boronic acid with chloroaryls did
not take place using palladium complexes incorporating mono
Fig. 4. Cyclic Voltammogram of [(OL1-NH)Ru(CO)(PPh3)2].
Fig. 5. (a) HOMO and (b) LUMO of 3a.
Table 4
Suzuki cross coupling reaction with catalyst 2a.
Boronic acid
Aryl halide
Product
Isolated yield
75
Cl
B(OH)2
B(OH)2
B(OH)2
85
78
Br
Br
75
Br
NO2
B(OH)2
NO2
98
95
I
B(OH)2
B(OH)2
I
95
85
I
B(OH)2
B(OH)2
NO2
NO2
I
O2N
O2N
(continued on next page)

128
P. Pattanayak et al. / Inorganica Chimica Acta 429 (2015) 122–131
Table 4 (continued)
Boronic acid
Aryl halide
Product
Isolated yield
80
I
Cl
Cl
Cl
B(OH)2
B(OH)2
NO2
NO2
90
I
Cl
O2N
O2N
82
75
Cl
Br
Cl
Cl
B(OH)2
B(OH)2
Cl
Cl
Br
75
Br
NO2
Cl
B(OH)2
NO2
90
92
I
Cl
Cl
B(OH)2
B(OH)2
Cl
Cl
I
Solvent = THF/DMF, Base = K2CO3, Time = 1 h.
Table 5
Heck reaction with catalyst 2a.
Styrene
Aryl halide
Product
Isolated yield
82
Br
Br
80
82
Br
NO2
NO2
90
90
I
I
92
I
NO2
NO2
82
70
I
O2N
O2N
Cl
Solvent = MeOH, Base = K2CO3, Time = 2 h.

P. Pattanayak et al. / Inorganica Chimica Acta 429 (2015) 122–131
129
THF / DMF
Reflux
anionic tridentate azo ligands [20,21,23] and a chloride ligand
within the coordination sphere. So coordination of PPh3 as an
alternative of chloride ligand along with dianionic tridentae
azo ligand has been detected to be suitable for chloryl sub-
strates. Possibly the prior dissociation of bulky PPh3 ligand of
palladium complexes enhanced its ability to C–Cl activation.
Although the catalyst concentration after the reactions could
not be determined quantitatively but it was believed that the
catalytic cycle followed Pd(II)/Pd(IV) mechanism [30].
X
B(OH)2
+
/
/
K2CO3
0.001mmol, 2a
R
R
R
R
R=H, Cl
R/= H,NO2, Me
X=Br, I
ð2Þ
MeOH
Reflux
+
/
K2CO3
/
2a
Table 6
0.005 mmol,
X=Br, I
Cyanation reaction of aryl halides and K4Fe(CN)6 with catalyst 2a.
ð3Þ
Aryl halide
Br
Product
Isolated yield
80
CN
CN
3.5.2. Cyanation reaction
78
Syntheses of cyanoarenes by cyanation of aryl halides, is useful
transformation in organic chemistry, since, cyanoarenes are the
Br
75
Table 8
Br
NO2
CN
Transformation of ketones to 2°-alcohols via hydrogen transfer reactions for 3a.
NO2
Substrate
Product
Isolated yield (%)
90
98
95
O
OH
I
CN
CN
82
75
O
OH
I
O
OH
96
I
CN
MeO
Me
MeO
Me
80
O
OH
NO2
NO2
Solvent = DMF, Base = Et3N, Time = 24 h.
73
68
Cl
OH
Cl
O
O
OH
Table 7
Cl
OH
Amination reaction of aryl halides with catalyst 2a.
Cl
O
60
Amine Aryl halide Product
Isolated yield
80
NH2
NH2
H
N
Br
Solvent = Isopropanol, Base = KOH, Time = 2 h.
75
H
N
Br
NO2
R
H
R2
PPh3
HO
O
H
H
OH
NO2
R1
N
R
u
CO
N
98
95
NH2
NH2
H
N
N
PPh3
I
I
H
R
N
H
R1
R
H
O
R2
I
PPh3
O
PPh3
HO
N
HO
N
N
N
Ru
Ru
CO
PPh3
CO
PPh3
H
N
H
N
96
98
NH2
NH2
H
N
R
NO2
NO2
H
PPh3
H
HO
N
Ru
PPh3
N
I
CO
N
O
H
N
O
R2
R1
Solvent = DMF, Base = K2CO3, Et3N, Time = 24 h.
Scheme 2. Probable mechanism for transfer hydrogenation reaction.

130
P. Pattanayak et al. / Inorganica Chimica Acta 429 (2015) 122–131
R
R
R
R
N
N
OH
N
N
N
N
N
N
N
N
N
H
N
N
C
H
N
OH
R/
NH2
E
R/
A
B
D
R
N
R
HO
OH
N
N
N
N
I
N
N
N
N
OH
H
N
H
N
O
H
G
F
Chart 1.
building blocks for the synthesis of fine chemicals, herbicides, dyes,
agrochemicals and pharmaceuticals [31–33]. There are reports
where the cyanations were carried out using KCN, NaCN, CuCN
and Zn(CN)2 as cyanide sources [31–33]. Recently K4Fe(CN)6 has
been used as cyanide source for catalytic aromatic cyanation
[31–33]. Herein, the cyanation of various aryl halides using
K4[Fe(CN)6] as the cyanide source and [(OL1-NH)Pd(PPh3)], 2a,
complex as catalyst have been carried out (Eq. (4)). The yields of
isolated products are collected in Table 6.
the sacrificial hydrogen donor and solvent [39–42]. These results
prompted us to investigate the catalytic activity [(OL1-
NH)Ru(CO)(PPh3)2], 3a toward transfer hydrogenation (Eq. (6)).
The results are given in Table 8. Since the compositions of HOMO
and LUMO consist of considerable ligand contribution (DFT results,
see above), so well defined metal centered redox responses were
unexpected to rationalize the catalytic behavior. On the other
hand, taking the reported proposal of such catalytic pathway into
account [43], the plausible pathway of catalytic process may be
assumed to proceed as shown in Scheme 2, presuming the proto-
nation of phenolato oxygen is more probable compared to the pro-
tonation of amido nitrogen.
0.02mmol, 2a
CN
/
K4Fe(CN)6
Et3N, DMF
/
ð4Þ
OH
0.0013 mmol
O
R/= H,NO2, Me
X=Br, I
3a, KOH
2-propanol
ð6Þ
/
/
3.5.3. Amination reaction
4. Conclusions
Aromatic amines and their derivatives are useful compounds in
the pharmaceutical, agrochemical and polymer industries [34–37].
Recently, the palladium-catalyzed amination of aryl halides in pres-
ence of K2CO3, Et3N, Cs2CO3 bases has gained attention [34–37].
Herein, the reaction of aniline with aryl halides in presence of KOt-
Bu base and [(OL1-NH)Pd(PPh3)], 2a, complex as catalyst in toluene
solvent was carried out to obtain the C–N coupled products (Eq.
(5)). The yields of isolated products are collected in Table 7.
New complexes of Pd(II) and Ru(II) incorporating tridentate
N,N,O donor ligand, 2-((2-aminoaryl) diazenyl) phenol, have been
synthesized and characterized unequivocally. The palladium and
ruthenium complexes contain PPh3 co-ligand. Suitability of phos-
phine containing complexes as catalyst encouraged us to study
the catalytic activity of newly synthesized complexes. Palladium
complexes have exhibited efficiency toward C–C and C–N coupling
and cyanation reactions. On the other hand the ruthenium com-
plexes exhibited efficiency toward transfer hydrogen catalysis.
Redox property of ruthenium complexes has been discussed.
H
N
NH2
0.05mmol 2a
+
/
/
KOtBu, Toluene
R/= H,NO2, Me
X=Br, I
Acknowledgments
We are thankful to the DST (New Delhi) for funding and fellow-
ship to PP under DST-WOS-A project (No. SR/WOS-A/CS-140/
2011). The necessary laboratory and infrastructural facility are pro-
vided by the Dept. of Chemistry, University of Kalyani. The support
of DST under FIST program to the Department of Chemistry, and
PURSE to the University of Kalyani is acknowledged.
ð5Þ
3.6. Catalytic activity of [(OL1-NH)Ru(CO)(PPh3)2]
3.6.1. Transformation of ketones to 2°-alcohols via hydrogen transfer
reactions
Appendix A. Supplementary material
The homogenous catalytic hydrogenation of ketones for prepar-
ing the 2°-alcohols is often utilized in fine chemical, pharmaceuti-
cal and agrochemical industries [39–42]. Several ruthenium
complexes have exhibited catalytic activity towards transfer
hydrogenation reactions of ketones using 2-propanol (i-PrOH) as
CCDC 010802–1010803 contain the supplementary crystallo-
graphic data for 2b–3a. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif. Supplementary data associated

P. Pattanayak et al. / Inorganica Chimica Acta 429 (2015) 122–131
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