Ru(II) with chelating containing N4-type donor quadridentate Pd-oxime metal complexes: Syntheses, spectral characterization, thermal and catalytic properties

Article abstract of DOI:10.1016/j.jorganchem.2008.05.041

Five new metal complexes [Pd(LH)₂] (1), [Pd(L)₂Ru₂(bpy)₄](ClO₄)₂ (2), [Pd(L)₂Ru₂(phen)₄](ClO₄)₂ (3), [Pd(L)₂Ru₂(dafo)₄](ClO₄)₂ (4) and [Pd(L)₂Ru₂(dcbpy)₄](ClO₄)₂ (5), (where, L = ligand, bpy = 2,2′-bipyridine, phen = 1,10-phenantroline, dafo = 4,5-diazafluoren-9-one and dcbpy = 3,3′-dicarboxy-2,2′-bipyridine) have been isolated and characterized by UV-VIS, FT-IR, ¹H NMR, magnetic susceptibility measurements, elemental analysis, molar conductivity, X-ray powder techniques, thermal analyses and their morphology studied by SEM measurements. IR spectra show that the ligand acts in a tetradentate manner and coordinates N₄ donor groups of LH₂ to Pd^II ion. The disappereance of H-bonding (O-H···O) in the trinuclear Ru^II-Pd^II-Ru^II metal complexes, the Ru^II ion centered into the main oxime core by the coordination of the imino groups while the two Ru^II ions coordinate dianionic oxygen donors of the oxime groups and linked to the ligands of bpy, phen, dafo and dbpy. The X-powder results show that 1 metal complex is indicating crystalline nature, not amorphous nature. Whereas, the X-ray powder pattern of the ligand (LH₂) with 2, 3, 4 and 5 exhibited only broad humps, indicating its amorphous nature. The catalytic activity of three different complexes were tested in the Suzuki coupling reaction. The 1, 4 and 5 metal complexes catalyse Suzuki coupling reaction between phenylboronic acid and arylbromides affording biphenyls. Also, the thermal results shown that the most stable complex is 1 compound while the less stable is 4 compound.

Full text of DOI:10.1016/j.jorganchem.2008.05.041

Journal of Organometallic Chemistry 693 (2008) 2835–2842
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Ru(II) with chelating containing N4-type donor quadridentate Pd-oxime metal
complexes: Syntheses, spectral characterization, thermal and catalytic properties
b
b
b
a
Ahmet Kilic a, , Feyyaz Durap , Murat Aydemir , Akin Baysal , Esref Tas
*
a Department of Chemistry, University of Harran, 63190 Sanliurfa, Turkey
b Department of Chemistry, University of Dicle, 21280 Diyarbakir, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Five new metal complexes [Pd(LH)2] (1), [Pd(L)2Ru2(bpy)4](ClO4)2 (2), [Pd(L)2Ru2(phen)4](ClO4)2 (3),
[Pd(L)2Ru2(dafo)4](ClO4)2 (4) and [Pd(L)2Ru2(dcbpy)4](ClO4)2 (5), (where, L = ligand, bpy = 2,20-bipyridine,
phen = 1,10-phenantroline, dafo = 4,5-diazafluoren-9-one and dcbpy = 3,30-dicarboxy-2,20-bipyridine)
have been isolated and characterized by UV–VIS, FT-IR, 1H NMR, magnetic susceptibility measurements,
elemental analysis, molar conductivity, X-ray powder techniques, thermal analyses and their morphology
studied by SEM measurements. IR spectra show that the ligand acts in a tetradentate manner and coor-
dinates N4 donor groups of LH2 to PdII ion. The disappereance of H-bonding (OꢀHꢁꢁꢁO) in the trinuclear
RuII–PdII–RuII metal complexes, the RuII ion centered into the main oxime core by the coordination of
the imino groups while the two RuII ions coordinate dianionic oxygen donors of the oxime groups and
linked to the ligands of bpy, phen, dafo and dbpy. The X-powder results show that 1 metal complex is
indicating crystalline nature, not amorphous nature. Whereas, the X-ray powder pattern of the ligand
(LH2) with 2, 3, 4 and 5 exhibited only broad humps, indicating its amorphous nature. The catalytic activ-
ity of three different complexes were tested in the Suzuki coupling reaction. The 1, 4 and 5 metal com-
plexes catalyse Suzuki coupling reaction between phenylboronic acid and arylbromides affording
biphenyls. Also, the thermal results shown that the most stable complex is 1 compound while the less
stable is 4 compound.
Received 20 March 2008
Received in revised form 27 May 2008
Accepted 29 May 2008
Available online 4 June 2008
Keywords:
Ru(II) complexes
Spectroscopy
X-powder results
Molar conductivity
Suzuki coupling reaction
Thermal properties
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
line (phen), 4,5-diazafluoren-9-one (dafo) and 3,30-dicarboxy-2,20-
bipyridine (dcbpy) ligands notably improved the absorption in the
Considerable attention has focused on the preparation and
properties of ruthenium(II) heterocyclic ligand complexes due to
their stability and photophysical properties. Such metal complexes
ranging from simple monometallic to larger arrays have been re-
viewed by a number of contributors in the area [1]. Also, there is
continuing interest in the chemistry of ruthenium(II) polypyridyl
metal complexes because of their possible use in photochemical
storage of energy or as redox catalysts [2], molecular wires [3], bio-
sensor [4], therapeutic agent applications [5], materials for molec-
ular electronics and photonics [6] and electroluminescent display
devices [7]. Metal-to-ligand charge transfer (MCLT) transitions
dominate photophysical and redox behaviour such complexes.
The metal-to-ligand charge transfer absorption can be extended
to longer wavelengths by appropriate substituent changes on chro-
mophoric ligands [8]. The nature of the ligands around the metal
has been found to dramatically affect the energy conversion
process. Particulary, the introduction of electronic effects via elec-
tron-donor substituents on 2,20-bipyridine (bpy) 1,10-phenanthro-
visible region for efficient sunlight collection [9]. While
(oxime)ruthenium complexes are still relativity rare, we have se-
lected the cis-bis(-bpy)ruthenium(II), cis-bis(-phen)ruthenium(II),
cis-bis(-dafo)ruthenium(II) and cis-bis(-dcbpy)ruthenium(II) moi-
ety as a platform for studies utilizing the symmetric vic-dioxime:
N-(4-amino-1-benzyl piperidine)-phenylglyoxime [10]. These
complexes have enabled us to systematically probe the phenome-
non of proton-coupled electron transfer that occurs when oxime li-
gand is coordinated to a redox active metal center [11].
In this study, we have prepared mononuclear PdII and trinuclear
RuII–PdII–RuII type-metal complexes. Synthesis, characterization,
spectroscopic, and catalytic activities of the new vic-dioxime metal
complexes have been investigated. The metal complexes have been
identified by a combination of 1H NMR spectra, FT-IR spectra, UV–
VIS spectra, magnetic susceptibility measurements, X-ray powder
diffraction measurements, elemental analysis, molar conductivity
measurements and their morphology studied by SEM. The first aim
of this study is to prepare and characterized a new different mono-
nuclear and trinuclear metal complexes. The second aim is to under-
stand catalytic activity of the coordination of different groups
such as H-bond (OꢀHꢁꢁꢁO), 4,5-diazafluoren-9-one (dafo) and
* Corresponding author.
E-mail address: kilica63@harran.edu.tr (A. Kilic).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.05.041

2836
A. Kilic et al. / Journal of Organometallic Chemistry 693 (2008) 2835–2842
3,30-dicarboxy-2,20-bipyridine (dcbpy)tothe oxime moieties through
two oxygen donor atoms. Third aim is to understand their crystalline
or amorphous structures by X-ray powder analysis as well. Fourth
aim is to understand their thermal properties by thermal gravimetric
analyses (TGA) and differential thermal analyses (DTA) as well.
dine, phen = 1,10-phenantroline, dafo = 4,5-diazafluoren-9-one
and dcbpy = 3,30-dicarboxy-2,20-bipyridine) were synthesized.
[RuCl2(bpy)2] ꢁ 2H2O (0.2 g, 0.38 mmol), [RuCl2(phen)2] ꢁ 2H2O
(0.2 g, 0.34 mmol), [RuCl2(dafo)2] ꢁ 2H2O (0.2 g, 0.34 mmol) and
[RuCl2(dcbpy)2] ꢁ 2H2O (0.2 g, 0.28 mmol) were refluxed in etha-
nol–water–DMF mixture (40 ml/10 ml/2 ml) for 45 min. The com-
plex [Pd(LH)2] (0. 15 g, 0.19 mmol for 2, 0.14 g, 0.17 mmol for 3,
0.14 g, 0.17 mmol for 4 and 0.11 g, 0.14 mmol for 5) were then
added and heating were maintained for 36 h. When the solutions
finally turned red-brown, it was cooled to room temperature and
equal volume of saturated aqueous NaClO4 solutions were added
under vigorous stirring. Then, the final products washed three
times with water (10 ml) and diethyl ether (10 ml). The products
were recrystallized from a mixture of CHCl3–EtOH.
2. Experimental
All reagents and solvents were of reagent-grade quality and ob-
tained from commercial suppliers (Fluka). Tetra-n-butylammo-
nium perchlorate (TBAP, Fluka) was used as received. Elemental
analysis was carried out on a LECO CHNS model 932 elemental
analyzer. FT-IR spectra were recorded on a Perkin–Elmer Spectrum
RXI FT-IR Spectrometer as KBr pellets. 1H NMR spectra were re-
corded on a Bruker-Avence 400 MHz spectrometers. Magnetic sus-
ceptibilities were determined on a Sherwood Scientific Magnetic
Susceptibility Balance (Model MK1) at room temperature (25 °C)
using Hg[Co(SCN)4] as a calibrant; diamagnetic corrections were
calculated from Pascal’s constants [12,13]. UV–VIS spectra were re-
corded on a Perkin–Elmer Lambda 25 PC UV–VIS spectrometer.
Molar conductivities (KM) were recorded on a Inolab Terminal
740 WTW Series. X-ray powder was recorded on a Rigaku Ultima
III Series. The thermal analyses measurements (TGA and DTA) were
carried out on a Setaram Labsys TG-16 thermobalance under a
nitrogen atmosphere. The scanning electron microscopy (SEM)
measurements were carried out on a Zeiss Evo 50 Series. The sam-
ples were sputter coated with carbon by Balzers Med 010 to pre-
vent charging when analyzed by the electron beam. GC analyses
were performed on a HP 6890N Gas Chromatograph equipped with
capillary column (5% biphenyl, 95% dimethylsiloxane)
[Pd(L)2Ru2(bpy)4](ClO4)2 (2): Yield: (64%), color: red,
m.p. = 153 °C. Anal. Calc. for C80H76Cl2N16O12PdRu2 (MW: 1833 g/
mol): C, 52.42; H, 4.18; N, 12.23. Found: C, 52.18; H, 3.98; N,
12.54%. KM = 201
cmꢀ1): 3398
(NH), 3090–3031
(C@N), 1358 and 979 (N–O), 1071 and 624
(Ru–N). UV–VIS (kmax, nm, = shoulder peak): 310, 316,
X
ꢀ1cm2 molꢀ1
,
l
t
eff = Dia, IR (KBr pellets, tmax
(Ar–H), 2924–2853 (Aliph-H),
(ClO4) and
/
t
t
t
1604
520
t
t
t
*
420, 460*, 567 (in Acetone) and 268, 294, 317, 380*, 450, 541*
(in DMF). 1H NMR (DMSO-d6, TMS, d ppm): 8.37 (d, 8H, J = 16,
Ar-CH0a;a), 8.60 (d, J = 8, 8H, Ar-CHb0 ;b), 9.14 (d, 8H, J = 5.6, Ar-
CH0c;c), 7.84 (s, 8H, Ar-CHd0 ;d), 7.82–7.80 (m, 20H, Ar-CHothers), 4.62
(s, 2H, NH), 3.18 (s, 2H, N-CH), 2.89 (s, 4H, N-CH2), 2.74 (s, 8H,
N-CH2), 1.22–1.18 (d, J = 16, 8H, Cyc-CH2).
[Pd(L)2Ru2(phen)4](ClO4)2 (3): Yield: (68%), color: red–brown,
m.p. = 224 °C. Anal. Calc. for
1929.1 g/mol): C, 54.79; H, 3.97; N, 11.62. Found: C, 54.47; H,
3.85; N, 11.69%. KM = 198 eff = Dia, IR (KBr pellets,
ꢀ1cm2 molꢀ1
max/cmꢀ1): 3392
(NH), 3061 (Ar–H), 2960–2853 (Aliph-H),
1602 (C@N), 1361 and 971 (N–O), 1088, 623 (ClO4) and 524
C88H76Cl2N16O12PdRu2 (MW:
X
, l
(30 m ꢂ 0.32 mm ꢂ 0.25
lm). Ligand (LH2) (Fig. 1) [14], cis-[Ru
t
t
t
t
(bpy)2Cl2] ꢁ 2H2O cis-[Ru(phen)2Cl2] ꢁ 2H2O, cis-[Ru(dafo)2Cl2] ꢁ
2H2O and cis-[Ru(dcbpy)2Cl2] ꢁ 2H2O [15], 4,5-diazafluoren-9-one
(dafo) [16], 3,30-dicarboxy-2,20-bipyridine (dcbpy) [17] were pre-
pared according to the literature procedures.
t
t
t
t
(Ru–N). UV–VIS (kmax, nm, * = shoulder peak): 293, 309, 324,
457 (in Acetone) and 270, 291 , 462 (in DMF). 1H NMR (DMSO-
*
d6, TMS, d ppm): 8.09 (d, 8H, J = 5.2, Ar-CH0a;a), 8.39 (s, 8H,
Ar-CH0b;b), 8.76 (d, 8H, J = 8, Ar-CHc0 ;c), 7.79 (s, 8H, Ar-CH0d;d), 7.77–
7.75 (m, 20H, Ar-CHothers), 4.55 (s, 2H, NH), 3.58 (s, 2H, N-CH),
2.12 (s, 12H, N-CH2), 1.24 (s, 4H, Cyc-CH2) and 1.15 (s, 4H, Cyc-
CH2).
2.2. Synthesis of the [Pd(LH)2] metal complex 1
A solution of palladium(II) acetate (0.28 g, 1.22 mmol) in abso-
lute ethanol (25 cm3) was added to a solution of ligand (LH2)
(0.86 g, 2.44 mmol), in absolute ethanol (60 cm3) at 55–60 °C. A
distinct change was observed in color from colorless to pale brown
under a N2 atmosphere with continuous stirring. Then, a decrease
in the pH of the solution was observed. The pH of the solution was
ca. 1.5–3.0 and was adjusted to 4.5–5.5 by the addition of a 1% tri-
ethylamine solution in EtOH. After heating the mixture for 5 h in a
water bath, the precipitate was filtered off, washed with H2O and
diethyl ether several times, and dried in vacuo at 35 °C. Yield:
(78%), color: pale brown, m.p. = 204 °C. Anal. Calc. for
[Pd(L)2Ru2(dafo)4](ClO4)2 (4): Yield: (58%), color: red–brown,
m.p. = 276 °C. Anal. Calc. for C84H68Cl2N16O16PdRu2 (MW: 1937 g/
mol): C, 52.09; H, 3.54; N, 11.57. Found: C, 51.93; H, 3.61; N,
11.64%. KM = 208
cmꢀ1): 3386
(NH), 3072
(C@N), 1364 and 947
(Ru–N). UV–VIS (kmax, nm, = shoulder peak):
X
ꢀ1cm2 molꢀ1
(Ar–H), 2954–2847
(N–O), 1077 and 624
,
l
eff = Dia, IR (KBr pellets, tmax
/
t
t
t
(Aliph-H), 1734
t(C@O), 1615
t
t
t(ClO4) and 521
t
*
277, 302, 319, 326, 447 (in Acetone) and 271, 312, 382*, 564*0(in
DMF). 1H NMR (DMSO-d6, TMS, d ppm): 7.53 (s, 8H, Ar-CHa;a),
8.86 (s, 8H, Ar-CH0b;b), 8.24 (d, 8H, Ar-CHc0 ;c), 7.38–7.08 (m, 20H,
Ar-CHothers), 4.46 (s, 2H, NH), 3.52 (s, 2H, N-CH), 2.63 (s, 4H,
N-CH2), 2.31 (s, 8H, N-CH2), 1.23 (s, 4H, Cyc-CH2) and 1.10 (s, 4H,
Cyc-CH2).
C
40H46N8O4Pd (MW: 808.5 g/mol): C, 59.37; H, 5.69; N, 13.85.
Found: C, 59.26; H, 5.56; N, 13.71%. KM = 33
ꢀ1cm2 molꢀ1
Dia, IR (KBr pellets, (NH), 3060–3019 (Ar–H),
max/cmꢀ1): 3392
2949–2752 (Aliph-H), 1692 (C@N), 1334 and
(OꢀHꢁꢁꢁO), 1597
976
X
, leff =
t
t
t
t
t
t
[Pd(L)2Ru2(dcbpy)4](ClO4)2 5: Yield: (63%), color: red–brown,
t
(N–O), 459 t(Pd–N). UV–VIS (kmax, nm, * = shoulder peak):
m.p. = >300 °C. Anal. Calc. for
C88H76Cl2N16O28PdRu2 (MW:
274, 326, 351, 432 (in Acetone) and 266, 311, 434 (in DMF). 1H
*
2185.1 g/mol): C, 48.37; H, 3.51; N, 10.26. Found: C, 48.19; H,
3.46; N, 10.37%. KM = 211
X
ꢀ1cm2 molꢀ1
, l
eff = Dia, IR (KBr pellets,
(Ar-H), 2954-2847
(N–O),
NMR (DMSO-d6, TMS, d ppm) d: 15.28 (s, 2H, OꢀHꢁꢁꢁO), 4.35 (s,
2H, NH), 7.48–7.23 (m, 20H, Ar-CH), 3.61 (s, 2H, N-CH), 2.62 (s,
4H, N-CH2), 2.38 (s, 4H, N-CH2), 1.92 (s, 4H, Cyc-CH2) and 1.24–
1.06 (m, 4H, Cyc-CH2).
t
t
max/cmꢀ1): 3420
(Aliph-H), 1718
t
t
(OH), 3381 (NH), 3078
(C@O), 1616 (C@N), 1381 and 965
(Ru–N). UV–VIS (kmax, nm, = shoulder
t
t
t
t
1077, 624
t
(ClO4) and 526 t
*
peak): 293, 303, 308, 324 (in Acetone) and 301, 395, 597* (in DMF).
1H NMR (DMSO-d6, TMS, d ppm): 10.10 (d, 2H, J = 8, COOH), 7.38 (s,
8H, Ar-CH0a;a), 8.24 (s, 8H, Ar-CHb0 ;b), 7.79 (s, 8H, Ar-CH0c;c), 7.18–7.06
(m, 20H, Ar-CHothers), 4. 64 (s, 2H, NH), 4.21 (s, 2H, N-CH), 2.64 (s,
4H, N-CH2), 2.28 (s, 8H, N-CH2), 2.09 (s, 4H, Cyc-CH2) and 1.22–1.20
(m, 4H, Cyc-CH2) (see Fig. 2).
2.3. Synthesis of the [Pd(L)2Ru2(X)4](ClO4)2 metal complexes
In this study, the complexes [Pd(L)2Ru2(bpy)4](ClO4)2 (2),
[Pd(L)2Ru2(phen)4](ClO4)2 (3), [Pd(L)2Ru2(dafo)4](ClO4)2 (4) and
[Pd(L)2Ru2(dcbpy)4](ClO4)2 5 (where, L = ligand, bpy = 2,20-bipyri-

A. Kilic et al. / Journal of Organometallic Chemistry 693 (2008) 2835–2842
2837
2H2O, RuCl2(dafo)2 ꢁ 2H2O or RuCl2(dcbpy)2 ꢁ 2H2O and then added
NaClO4 in ethanol–water–DMF mixture, as shown in Fig. 2. For the
[Pd(L)2Ru2(X)4](ClO4)2 complexes, the reactions of [Pd(LH)2] with
the system RuCl2(bpy)2 ꢁ 2H2O, RuCl2(phen)2 ꢁ 2H2O, RuCl2(dafo)2 ꢁ
2H2O or RuCl2(dcbpy)2 ꢁ 2H2O/NaClO4 was carried out (Eq. (1)) [18]
3. Results and discussion
The complex of the general formula [Pd(LH)2] was synthesized
by the reactions of ligand (LH2) with the respective Pd(CH3COO)2
in a 1:2 molar ratio in ethanol and the metal complexes of the
general formula [Pd(L)2Ru2(X)4](ClO4)2 (where, L = ligand,
X = 2,20-bipyridine, 1,10-phenantroline, 4,5-diazafluoren-9-one,
3,30-dicarboxy-2,20-bipyridine) were synthesized by the reactions
of [Pd(LH)2] with the respective RuCl2(bpy)2 ꢁ 2H2O, RuCl2(phen)2 ꢁ
2½RuCl2ðXÞ2 ꢁ 2H2Oꢃ þ ½PdðLHÞ2ꢃ þ 2NaClO4
! ½PdðLÞ2Ru2ðXÞ4ꢃðClO4Þ2 þ 2NaCl þ 2HCl
X = 2,20-bipyridine, 1,10-phenanthroline, 4,5-diazafluoren-9-one
ð1Þ
and 3,30-dicarboxy-2,20-bipyridine.
Magnetic susceptibility measurements provide sufficient data
to characterize the structure of the metal complexes. Magnetic mo-
ments measurements of all metal complexes carried out at 25 °C.
The results show that mononuclear 1 with trinuclear 2, 3, 4 and
5 metal complexes are diamagnetic. The morphology and particle
size of the compounds have been illustrated by the scanning elec-
tron micrography (SEM). Fig. 4a and b depicts the SEM images of 1
and 4 metal complexes. We noted that there is a uniform matrix of
the synthesized complexes in the pictograph. This leads us to be-
lieve that we are dealing with homogeneous phase material. The
crystalline shape is observed in the 1 complex and the amorphous
shape is observed in the 4 complex.
OH
C=N
C=N
OH
NH
N
Fig. 1. Structure of ligand (LH2).
H
O
O
R1
R2
R2
R1
C=N
N=C
EtOH, 55-60o
N2 , NEt3
Pd
LH2
Pd(CH3COO)2
(1)
C=N
O
N=C
O
H
(2) [RuCl2(bpy)2].2H2O
(3) [RuCl2(phen)2].2H2O
(4) [RuCl2(dafo)2].2H2O
(5) [RuCl2(dcbpy)2].2H2O
EtOH-H2O-DMF
N2 , reflux
NaClO4
N
NH
R1 =
R2 =
N
N
N
N
Ru
O
O
R1
R2
R1
C=N
N=C
Pd
Ru
(ClO4)2
N=C
C=N
R2
O
N
O
N
N
N
O
HO2C
CO2H
N
,
,
,
=
N
N
N
N
N
N
N
N
N
Fig. 2. The proposed structure for 2, 3, 4 and 5 metal complexes.

2838
A. Kilic et al. / Journal of Organometallic Chemistry 693 (2008) 2835–2842
3.1. NMR Spectra
(phen), 4,5-diazafluoren-9-one (dafo) or 3,30-dicarboxy-2,20-bipyr-
idine (dcbpy) rings of a bpy, phen, dafo or dcbpy ligands are mag-
netically nonequivalent due to the cis-geometry of the complexes
[12,19]. So, multiplets are observed around at 9.14–7.38 ppm in
2, 3, 4 and 5 complexes and have been assigned to the aromatic
protons of 2, 3, 4 and 5 metal complexes.
The data of the 1H NMR spectra (in DMSO-d6) obtained for 1, 2,
3, 4 and 5 metal complexes are given in Section 2. The 1H NMR
spectra of the diamagnetic metal complex 1 was characterized by
the existence of intra-molecular D2O-exchangeable H-bridge
(OꢀHꢁꢁꢁO) protons which were observed by a new signals at low
field, d = 15.25 ppm for 1 complex. The other protons were ob-
served at different field than ligand [14]. In the 1H NMR spectra
of 2, 3, 4 and 5, the D2O-exchangeable hydrogen-bridged protons,
which were evident in 1, disappear after the formation of the
bpy, phen, dafo or dcbpy-bridged metal complexes. In the
1H NMR spectra of 2, 3, 4 and 5 complexes, the proton Ar-CHothers
of phenyl ring is shifted different field compared to those of the
free ligand. The 1H NMR spectra provide information on the cis-
coordination of the bpy, phen, dafo and dcbpy ligands. As reported
previously, each of the 2,20-bipyridine (bpy) 1,10-phenanthroline
3.2. IR spectra
The infrared spectra of 1, 2, 3, 4 and 5 metal complexes have
been studied order to characterize their structures. The IR spectra
of all metal chelates were carried out in the 4000–400 cmꢀ1 range.
The characteristic infrared spectrum data are given in Section 2.
The
and are situated at a frequency significantly different than the free
ligand that the
(C@N) peak observed at 1636 cmꢀ1 for ligand.
Coordination of the vic-dioxime ligands to the metal center
t(C@N) stretching vibrations are affected upon complexation
t
Fig. 3. X-ray powder diffractograms of (a) 1 and (b) 2 complexes.

A. Kilic et al. / Journal of Organometallic Chemistry 693 (2008) 2835–2842
2839
through the four nitrogen atom are expected to reduce the electron
density in the azomethine link and lower the (C@N) absorption
3.4. Solubility and molar conductivity
t
frequency. The peak due to
t
(C@N) are shifted to lower frequencies
The ligand is soluble in common organic solvents such as THF,
C2H5OH, CH2Cl2, and DMSO. Although 1 are soluble in DMSO and
DMF and slightly soluble in CH2Cl2, CHCl3, trinuclear metal com-
plexes 2, 3, 4 and 5 are highly soluble than 1 complex, due to the
presence of Ru(bpy)2, Ru(phen)2, Ru(dafo)2 or Ru(dcbpy)2 bridged
groups in the oxime moities. With a view to studying the electro-
lytic nature of the metal complexes, their molar conductivities
and appears between 1616 and 1597 cmꢀ1, indicating coordination
of the azomethine nitrogen to the Pd metal [20]. However, the dis-
appearance of t(O–H) stretching bands in the IR spectrum of free
ligand together with the existence of H-bridge (OꢀHꢁꢁO) at
1692 cmꢀ1 and the shifting of –C@N and –N–O strectches in the
IR spectra of the 1 metal complexes provide support for MN4-type
coordinations in the metal complexes [21]. In the IR spectra of 2, 3,
4 and 5 metal complexes, the intramolecular hydrogen band was
not observed, as expected. This is because the H-bonded (OꢀHꢁꢁO)
of mononuclear palladium complex disappeared upon an encapsu-
lation of the ruthenium ions on the formation of trinuclear metal
complexes, namely Ru2(bpy)4, Ru2(phen)4, Ru2(dafo)4, and
Ru2(dcbpy)4. The spectra show strong peak at 1734 cmꢀ1 for 4
and 1718 cmꢀ1 for 5 due to carbonyl and carboxylic acid group.
Perchlorate salts show strong antisymmetric stretching band at be-
tween 1088 and 1071 cmꢀ1 and sharp antisymmetric stretching
band at between 624 and 623 cmꢀ1, an indication of uncoordinated
perchlorate anions [22]. The coordination of the bipyridine or phe-
nantroline nitrogen is further supported by the appearance of a
were measured in DMF at 10ꢀ3 M. The molar conductivity (KM
values of 1 metal complex is 33
ꢀ1cm2 molꢀ1 at room tempera-
)
X
ture [27], indicating their almost non-electrolytic nature. Due to
not free ions in 1 complex, the results indicate that this metal com-
plex is very poor in molar conductivity. The molar conductivities
(
KM) values of these trinuclear 2, 3, 4 and 5 metal complexes are
range 208–211
X
-1cm2 molꢀ1 at room temperature, indicating
1:2 electrolytes or three ionic species in solution [28].
3.5. Crystallography
Fig. 3 shows the X-ray powder diffraction data. For more clarity,
a small window, representative of the whole range, restricted to
the 10° < 2h< 40° is presented for the ligand and all metal com-
plexes. We have attempted to prepare single crystals of ligand
(LH2) and 1, 2, 3, 4 and 5 metal complexes in different solvents,
but we could not prepare convenient single crystals of ligand and
peak at 526–520 cmꢀ1, due to
t(Ru–N) stretching vibrations that
are not observed in the infrared spectra of the ligand (LH)2.
3.3. UV–VIS spectra
Electronic spectra of 1, 2, 3, 4 and 5 metal complexes have been
recorded in the 1100–200 nm range in Acetone and DMF solutions
and their corresponding data are given in Section 2. The UV–VIS
spectra of the five metal complexes in Acetone showed 4–5 absorp-
tion bands between 277 and 567 nm and in DMF showed three-six
absorption bands between 266 and 597 nm, respectively. In the
electronic spectra of the five metal complexes, the wide a range
bands seems to be due to both the
p ? p , and n ? p transitions
* *
of C@N and charge-transfer transition arising from
p
electron
interactions between the metal and ligand which involves either
a metal-to-ligand or ligand-to-metal electron transfer [23,24].
The absorption bands below 303 nm in Acetone or DMF are practi-
cally identical and can be attributed to
p ? p
* transitions in the
benzene ring or azomethine (–C@N) groups. Azomethine groups
are a useful tool for the fabrication of the new PdII and RuII–PdII–
RuII metal complexes with specific electronic and structural
properties. The absorption bands observed within the range of
309–351 nm in Acetone and the range of 311–395 nm in DMF
are most probably due to the transition of n ? p
* of imine group
corresponding to the ligand or metal complexes [25]. For mononu-
clear 1 metal complexes, the absorption bands at range 432–
434 nm are assigned to M ? L charge transfer (MLCT) or L ? M
charge transfer (LMCT) [26], respectively. On complex formation,
the electronic spectra of the 1 metal complexes exhibited signifi-
cantly different absorption bands compared to those of the ligand
in Acetone and DMF solutions. As expected, the new bands at range
432–434 nm arising from M ? L charge transfer (MLCT) or L ? M
charge transfer (LMCT) transitions were observed as a result of
coordination of palladium metal through azomethine nitrogen.
These absorption bands are typical for mononuclear 1 metal
complex with a square-planar structure. The complexes 2, 3, 4
and 5 exhibit a shoulder band around 420 with 567 nm and
450 with 597 nm in Acetone and DMF respectively, with the
absorptivity of the former being higher. These spectra are simi-
lar to the other bpy, phen, dafo or dcbpy analogues and are
assigned to the
*
dp p (bpy, phen, dafo or dcbpy)
(RuII) ?
metal-to-ligand charge transfer (MLCT) transition. Examples of
UV–VIS spectra of the ligand and their metal complexes were
presented in Section 2.
Fig. 4. The SEM images of (a) 1 and (b) 4 metal complexes.

2840
A. Kilic et al. / Journal of Organometallic Chemistry 693 (2008) 2835–2842
Fig. 5. The TGA and DTA curves of (a) 1, (b) 4 and (c) 5 metal complexes.
all metal complexes. However, the crystalline nature of 1 complex
and the amorphous nature 2, 3, 4 and 5 metal complexes can be
readily evidenced from their X-ray powder patterns. The 1 metal
complex exhibit sharp reflections and all diffractograms are nearly

A. Kilic et al. / Journal of Organometallic Chemistry 693 (2008) 2835–2842
2841
Table 1
identical, indicating the isostructural nature of this compound.
The Suzuki coupling reaction of arylbromides with phenylboronic acid
Also, the large number of reflections as well as their positions indi-
cates a low crystal symmetry [23b,29]. This results show that 1
metal complex is indicating crystalline nature, not amorphous nat-
ure. Whereas, the X-ray powder pattern of the ligand (LH2) with 2,
3, 4 and 5 exhibited only broad humps, indicating its amorphous
nature.
Entry
R
Cat. (Complex)
Time (h)
Conversion (%)
Yield (%)a
1
2
3
4
5
6
7
8
CHO
CH3CO
CHO
CH3CO
CHO
CH3CO
CHO
CH3CO
CHO
CH3CO
CHO
4
4
1
1
5
5
4
4
1
1
5
5
1
1
1
1
1
1
3
3
3
3
3
3
59.2
21.2
99.2
98.1
23.3
24.9
79.9
34.8
99.5
99.4
69.2
32.2
58.5
18.9
97.9
97.6
21.2
23.7
79.7
33.9
99.3
97.8
68.4
31.6
3.6. Thermal properties
9
The thermal properties of the 1, 4 and 5 metal complexes were
investigated by thermal gravimetric analyses (TGA) and thermal
differential analyses (DTA). Fig. 5a,b and c shows the recorded TGA
and DTA curves of 1, 4 and 5 metal complexes under a nitrogen
atmosphere. The samples were heated up at 1 atm pressure with
a heating rate of 10 °C minꢀ1 a temperature range of 20–1000 °C.
It can be seen that TGA curve of the 1 complex show no mass loss
up to 177 °C (Fig. 5a), indicating the absence of water molecules
and any other adsorptive solvents molecules in coordinate sphere.
As the temperature is increased, the first decomposition stage oc-
curred in the range 177–327 °C which is assigned to loss of
10
11
12
CH3CO
Reaction conditions: 1.0 mmol of aryl bromide; 1.5 mmol of phenylboronic acid;
2.0 mmol Cs2CO3; 1.5% Pd (Cat.) was used; DMF 1.5 ml/H2O 1.5 ml; Temperature
90 °C.
a
GC-yield using diethyleneglycol-di-n-butylether as internal standard.
cant contribution the Suzuki coupling of the arly bromides. In addi-
tion the C@O bond in the 4 complex and the CO2H grup in the 5
complex might be a negative effect on their catalytic activities.
C24H36N2O4 (organic rest) with a weight loss 51.2% and calculated
value is 51.5%, the second decomposition stage occurred in the
range 327–693 °C which is assigned to loss of C12H10 (organic moi-
ety) with a weight loss 69.8% and calculated value is 70.5% (Fig. 5a).
The thermal decomposition of 4 complex occurs at four steps and 5
complex occurs at three steps. The first degradation step take place
in the range of 55–139 °C which is a weight loss 19% for 4 complex
and in the range of 60–119 °C which is a weight loss 1.72% for 5
complex, the second degradation step take place in the range of
139–364 °C which is a weight loss 46% for 4 complex and in the
range of 119–367 °C which is a weight loss 16.42% for 5 complex,
the third degradation step take place in the range of 364–608 °C
which is a weight loss 69% for 4 complex and in the range of
471–827 °C which is a weight loss 16.4% for 5 complex, the fourth
degradation step take place in the range of 608–912 °C which is a
weight loss 91% for 4 complex, respectively (Fig. 5b and c).
4. Conclusions
In this study, the new vic-dioxime ligand and their mononuclear
1, trinuclear 2, 3, 4 and 5 metal complexes were synthesized and
characterized by elemental analyses, FT-IR, UV–VIS, 1H NMR spec-
tra, magnetic susceptibility measurements, molar conductivity,
X-ray powder techniques and their morphology studied by SEM
measurements. Although vic-dioximes complexes have been syn-
thesized for a very long period of time, a few examples of their
heteropolynuclear complexes have studied. This study presents a
series of the mononuclear 1 and the trinuclear vic-dioxime com-
plexes 2, 3, 4 and 5, which were prepared by the coordination of
Ru(bpy)2, Ru(phen)2, Ru(dafo)2 or Ru(dcbpy)2 bridged groups into
the main palladium oxime moities. In the other studies, it is well
known that the biological activities of PdII, Ph2B–PdII–BPh2 and
RuII–PdII–RuII type metal complexes can be improved mixed-ligand
complexes with heterocyclic bases, such as 1,10-phenanthroline,
2,20-bipyridine, 4,40-bipyridine, pyridine, 4,5-diazafluoren-9-one
and 3,30-dicarboxy-2,20-bipyridine. The catalytic tests shown that
1 complex is an active catalyst in the coupling of 4-bromobenzal-
dehyde and 4-bromoacetophenone with phenylboronic acid. But
4 and 5 metal complexes appear to be less efficient as catalyst
for the Suzuki coupling reactions. Also, the thermal results shown
that the most stable complex is 1 compound while the less stable is
compound 4.
3.7. Catalytic tests
Among palladium-catalyzed cross-coupling processes, the Su-
zuki reaction of aryl/vinyl halides with boronic acid is one of the
most efficient methods for C–C bond formation. Following optimi-
zation experiments we found that the reaction performed in mix-
ture of DMF and water, with Cs2CO3 as the base at 90 °C appeared
to be best. We initially tested the catalytic activity of the com-
plexes 1, 4 and 5 for the coupling of p-bromoacetophenone with
phenylboronic acid and the control experiments showed that the
coupling reaction did not occur in the absence of the catalyst. Un-
der these conditions, p-bromoacetophenone and p-bromobenzal-
dehyde react cleanly with phenylboronic acid in good yields
(Table 1). The palladium-catalyzed reaction of aryl halides with
arylboronic acids (the Suzuki coupling reaction) is the most com-
mon method for C–C bond formation [30]. The reactions are usu-
ally carried out homogeneously in the presence of a base under
inert atmosphere. The reactivity of the aryl halide component de-
creases sharply in the order X = I > Br > Cl and electron withdraw-
ing substituents R are required for the chlorides to react [30,31].
The palladium-catalyzed cross-coupling reaction of phenylboronic
acid with aryl bromides has been summarized in Table 1. As a base,
Cs2CO3 [32] was the best choice and as a solvent mixture DMF
(1.5 ml) and H2O (1.5 ml) was found to be better than other sol-
vents. From the results shown in Table 1, it is evident that the 1
complex is more efficient than the other complexes and has the
more selectivity for this coupling reaction. The presence of the
ruthenium metal in the 4 and 5 metal complexes have no signifi-
Acknowledgements
This work has been supported, in part, by the Research Fund of
Harran University (Sanliurfa, Turkey).
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