Synthesis, characterization, redox, catalytic, and antibacterial activities of binuclear ruthenium(III) schiff base complexes containing triphenylphosphine as co-ligand

Article abstract of DOI:10.3109/10799890903555616

New hexa-coordinated binuclear Ru(III) Schiff base complexes of the type [(PPh3)₂X₂Ru]₂L (where, X = Cl or Br; L = binucleating N₂O₂ Schiff bases) have been synthesized and characterized by elemental analysis, magnetic susceptibility measurement, FT-IR, UV-vis, 13C1H-NMR, ESR, cyclic voltammetric, SEM and powder X-ray diffraction pattern. The new complexes have been used as catalyst in C C coupling reaction and the oxidation of alcohols to their corresponding carbonyl compounds by using molecular oxygen atmosphere at ambient temperature. Further, the new Schiff base ligands and their Ru(III) complexes were also screened for their antibacterial activity against K. pneumoniae, Shigella sp., M. luteus, E. coli and S. typhi. From this study, it was found out that the activity of the ruthenium(III) Schiff base complexes almost reaches the effectiveness of the conventional bacteriocide standards. Copyright Taylor & Francis Group, LLC.

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Synthesis, Characterization, Redox, Catalytic,
and Antibacterial Activities of Binuclear
Ruthenium(III) Schiff Base Complexes Containing
Triphenylphosphine as Co-Ligand
Arumugam Manimaran a & Chinnasamy Jayabalakrishnan b
a Department of Physical Sciences , Bannari Amman Institute of Technology ,
Sathyamangalam, Erode, Tamil Nadu, India
b Postgraduate and Research Department of Chemistry , Sri Ramakrishna Mission
Vidyalaya College of Arts and Science , Coimbatore, Tamil Nadu, India
Published online: 16 Feb 2010.
To cite this article: Arumugam Manimaran & Chinnasamy Jayabalakrishnan (2010) Synthesis, Characterization, Redox,
Catalytic, and Antibacterial Activities of Binuclear Ruthenium(III) Schiff Base Complexes Containing Triphenylphosphine as
Co-Ligand, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 40:2, 116-128
To link to this article: http://dx.doi.org/10.3109/10799890903555616
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 40:116–128, 2010
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.3109/10799890903555616
Synthesis, Characterization, Redox, Catalytic, and
Antibacterial Activities of Binuclear Ruthenium(III) Schiff
Base Complexes Containing Triphenylphosphine as
Co-Ligand
Arumugam Manimaran1 and Chinnasamy Jayabalakrishnan2
1Department of Physical Sciences, Bannari Amman Institute of Technology, Sathyamangalam,
Erode, Tamil Nadu, India
2Postgraduate and Research Department of Chemistry, Sri Ramakrishna Mission Vidyalaya
College of Arts and Science, Coimbatore, Tamil Nadu, India
in the development of new chelating ligand systems; partic-
ularly the planarity of the N2O2 ligand provides the means
of creating vacant site, since their binucleating imino ligands
are versatile and they exhibit very rich coordination chemistry,
such species occupy an important position in modern coordina-
tion and inorganic chemistry, but they can also be found at key
points in the development of inorganic biochemistry, catalysis
and optical materials.[6−10] The incorporation of binucleating
Schiff base ligand into ruthenium tertiaryphosphine complexes
was initially aimed at promoting activity of such species to-
wards oxidation of alcohols and aryl-aryl coupling, because
the use of metal-salen derivative Schiff base complexes are
known to react with oxidants like NMO, PhIO, t-BuOOH[11]
and molecular oxygen to form metal oxo-species.[4] The Schiff
base ligands were prepared by condensing 4,4ꢀ-diaminophenyl
and isatin with salicylaldehyde, 2-hydroxy-1-naphthaldehyde,
o-hydroxyacetophenone and o-vanillin. As a part of our contin-
uing efforts[4] to synthesis and characterize ruthenium chelates
using simple and inexpensive Schiff base ligands, we herein de-
scribe the synthesis and characterization of a series of new class
of binuclear ruthenium(III) Schiff base complexes along with
their catalytic activity towards the highly efficient oxidation of
a number of primary and secondary alcohols in the presence of
molecular oxygen atmosphere at ambient temperature and C-C
coupling reactions. Further, the ligands and their Ru(III) Schiff
base complexes were also screened for their antibacterial activ-
ity against K. pneumoniae, Shigella sp., M. luteus, E. coli and
S. typhi.
New hexa-coordinated binuclear Ru(III) Schiff base complexes
of the type {[(PPh3)2X2Ru]2L} (where, X = Cl or Br; L = binucleat-
ing N2O2 Schiff bases) have been synthesized and characterized by
elemental analysis, magnetic susceptibility measurement, FT-IR,
1
UV-vis, 13C{ H}-NMR, ESR, cyclic voltammetric, SEM and pow-
der X-ray diffraction pattern. The new complexes have been used as
catalyst in C C coupling reaction and the oxidation of alcohols to
their corresponding carbonyl compounds by using molecular oxy-
gen atmosphere at ambient temperature. Further, the new Schiff
base ligands and their Ru(III) complexes were also screened for
their antibacterial activity against K. pneumoniae, Shigella sp., M.
luteus, E. coli and S. typhi. From this study, it was found out that the
activity of the ruthenium(III) Schiff base complexes almost reaches
the effectiveness of the conventional bacteriocide standards.
Keywords antibacterial activity, binuclear ruthenium(III), N2O2
donor, phenyl-phenyl coupling, oxidation reactions
INTRODUCTION
The oxidation of alcohols into corresponding aldehydes and
ketones, and aryl-aryl coupling reactions is a crucial reaction in
organic chemistry, both academic and industrial relevance.[1−4]
Moreover, the oxidant used in the reactions generally may lead
to environmental pollution. With the overgrowing environmen-
tal concerns, the development of benign catalytic processes of
highly efficient oxidation of alcohols is becoming increasingly
important.[5] Currently, a considerable effort is being invested
Received 16 September 2009; accepted 11 December 2009.
EXPERIMENTAL
We are thankful to NMR Research Centre, Indian Institute of Sci-
1
ence (IISc), Bangalore, India for providing 13C{ H}-NMR spectra.
Materials and Methods
Address correspondence to Dr. Chinnasamy Jayabalakrishnan,
Postgraduate and Research Department of Chemistry, SRKV Post,
Periyanaickenpalayam, Coimbatore-641020, India. E-mail: drcjbstar@
hotmail.com
All the chemicals and solvents used were purified and dried
by standard methods. IR spectra were recorded as KBr pel-
lets with a Nicolet FT-IR spectrometer in 4000–400 cm−1
116

ACTIVITIES OF BINUCLEAR RUTHENIUM(III) SCHIFF BASE COMPLEXES
117
range. Electronic spectra of the complexes were recorded
Preparation of Schiff Base Ligands
in CHCl2 solutions using Systronics double beam UV-vis
spectrophotometer-2202 in the range 800–200 nm. Microanal-
yses were carried out with a Vario El AMX-400 elemental an-
alyzer at STIC, Cochin University of Science and Technol-
ogy, Kerala, India. EPR spectra of powdered samples were
recorded with a JEOL TEL-100 instrument at X-band fre-
quencies at room temperature. Redox potential studies were
carried out with a BAS CV-27 model electrochemical ana-
lyzer in acetonitrile using glassy carbon working electrode
and the potentials were referenced to Ag-AgCl electrode. Pow-
der XRD were recorded using Shimadzu Model XRD6000 in-
To an ethanolic solution of p-phenylenediamine (1.8 g;
10 mmol), salicylaldehyde/o-hydroxy acetophenone/o-vanillin/
2-hydroxy-1-naphthaldehyde (10 mmol) was added and one
hour for stirring. Then to the above stirring solution about 10
mmol of isatin was added. The mixture was stirred for about half
an hour and then refluxed for about 4 hrs. The resultant product
was washed with ethanol and dried in vacuo (Scheme 1).
Synthesis of Binuclear Ruthenium(III) Schiff Base
Complexes
To a solution of [RuX3(PPh3)3] (where, X = Cl/Br)
(0.20 mmol) in benzene/methanol, an appropriate Schiff base
ligand was ( molar ratio of ruthenium complex to Schiff base
was 2:1) added. The solution was heated under reflux for 6–8
hours (Scheme 2) and then it was concentrated to 5 cm3. The
new complex was separated from it by addition of 10 cm3 of
petroleum ether (60–80◦C). The product was filtered, washed
with petroleum ether and recrystallized from methanol/CH2Cl2
mixture and tried in vacuo (Yield ≈82 %).
˚
strument with CuKα radiation (λ = 1.54060 A) from a Cu
target. Scanning electron micrography associated with energy
dispersive spectrometry (SEM/EDS) was used for morpholog-
ical evaluation. Magnetic moments were measured on an EG
& G PARC vibrating sample magnetometer. Melting points
were recorded with a Veego VMP-DS model heating table and
were uncorrected. The starting complexes [RuCl3(PPh3)3][12]
and [RuBr3(PPh3)3][13] and the Schiff base ligands (Scheme 1)
were prepared by the reported procedure[14] with modification
of the substitutions and the purity of the starting complexes
and the free Schiff base ligands were checked by TLC. The
analytical data, FT-IR, 13C1H-NMR spectral data confirm the
proposed molecular formula and the structure of the Schiff base
ligands.
Catalytic Oxidation Reactions by Binuclear Ru(III) Schiff
Base Complexes
Catalytic oxidation of alcohols to corresponding car-
bonyl compounds by binuclear Ru(III) Schiff base complexes
R2
R2
R1
R1
N
N
O
N
N
HO
HO
R3
HO
R3
HN
N
'keto form'
'enol form'
R1
H
R2
H
R3
H
Abbreviation
H2L1
H
C4H4
H
H
H2L2
H2L3
H2L4
CH3
H
H
H
OCH3
SCH. 1. Structure of Schiff base ligands.

118
A. MANIMARAN AND C. JAYABALAKRISHNAN
RESULTS AND DISCUSSION
R2
All the complexes were isolated in high yields and are stable
both in solid state and in solution. The analytical data (C, H, N)
of all the Schiff base ligands and their Ru(III) complexes are in
good agreement with the calculated values thus confirming the
proposed binuclear composition for all the complexes (Table 1).
The complexes were obtained in powder form. Various attempts
have been made to obtain the single crystals of the complexes,
but it has been unsuccessful. So for all the ligands and their
complexes are stable at room temperature, non-hygroscopic and
insoluble in water, methanol, ethanol and soluble in CH2Cl2,
CHCl3, DMF, DMSO and CH3CN.
R1
N
+
[RuX3(PPh3)3]
N
HO
HO
R3
N
1 : 2 Ratio
Benzene/Methanol
Reflux 6-8 Hrs
R2
Cl
Ru
R1
Cl
O
Ph3P
PPh3
N
N
O
PPh3
R3
Ph3P
Cl
IR Spectra
Ru
Cl
N
The IR spectra of the free Schiff bases were compared with
those of the ruthenium complexes in order to infer the binding
mode of the Schiff base ligands in the complexes. The important
IR absorption frequencies for the synthesized ligands and their
complexes are shown in Table 1. The IR spectral data confirm
the coordination of Schiff bases through azomethine nitrogen
(νC=N) by shifting the νC=N stretching frequency of free Schiff
base ligands to lower frequency in the range 1612–1600 cm−1 in
the complexes and this lowering of this wave number may be at-
tributed to the decrease in electron density on the nitrogen atom
of the azomethine group.[16,17] A medium band corresponding to
phenolic oxygen (νC−O) is observed at 1390–1280 cm−1 for the
free Schiff base ligands. On complexation this band is shifted
to higher frequency in the range 1386–1368 cm−1 for all the
ruthenium complexes.[18,19] This further supported by the dis-
appearance of the νOH band at 3420–3416 cm−1 in all the com-
plexes. Further, appearance of the bands in the region 510–490
and 474–460 cm−1 are probably due to formation of Ru-N and
Ru-O bond, respectively.[20] In addition to other bands observed
near 692, 1091 and 1435 cm−1 is due to triphenylphosphine
fragments.
Where, R1=H/CH3; R2=H/C4H4; R3=H/OCH3; X=Cl/Br
SCH. 2. Formation of binuclear Ru(III) Schiff base complexes.
containing triphenylphosphine/triphenylarsine as co-ligands
were studied in the presence of oxygen atmosphere at am-
bient temperature. A typical reaction using the complexes
{[(PPh3)2(X)2Ru]2L} as a catalyst and alcohols as substrates
at a 1:100 molar ratio is described as follows. A solution of
binuclear Ru(III) Schiff base complex (0.01 mmol) in 20 cm3
CH2Cl2 was added to the solution of alcohol (1 mmol) under
1 atm oxygen atmosphere at ambient temperature. The solution
mixture was stirred at room temperature for 6 hours and the sol-
vent was then evaporated from the mother liquor under reduced
pressure. The resulting carbonyl compounds was then extracted
with petroleum ether (60–80◦C) (20 cm3) and was then quanti-
fied as 2,4-dinitrophenylhydrazone derivative.[15] The oxidation
products are known and are commercially available.
UV-Vis Spectra and Magnetic Susceptibility
The electronic spectra of all the complexes in CH2Cl2 showed
three to six bands in the region 255–644 nm and their assign-
ments are summarized in Table 1 and Figure 1. The ground state
of ruthenium(III) (t25g configuration) is 2T2g, while the first ex-
C-C Coupling Reaction by Binuclear Ruthenium(III) Schiff
Base Complexes
Magnesium turnings (0.320 g) were placed in a flask
equipped with a CaCl2 guard tube. A crystal of iodine was
added. PhBr (0.75 cm3 of total 1.88 cm3) in anhydrous Et2O (5 cited doublet levels in the order of increasing energy are 2A2g and
cm3) was added with stirring and the mixture was heated under 2T1g, which arise from t42ge1g configuration. In most of the ruthe-
reflux. The remaining PhBr in Et2O (5 cm3) was added dropwise nium(III) complexes, the electronic spectra show only charge
and the mixture was refluxed for 40 minutes. To this mixture, transfer bands. Since in a d5 system and specially in ruthe-
1.03 cm3 (0.01 mol) of PhBr in anhydrous Et2O (5 cm3) and nium(III), which has relatively high oxidation properties, the
the Ru(III) Schiff base complex (0.05 mmol) chosen for inves- charge transfer bands of the type Ly → t2g are prominent in the
tigation were added and heated under reflux for 6 hours. The low energy region and obscure the weaker bands due to d-d tran-
reaction mixture was cooled and hydrolyzed with a saturated sition at 502–640 nm. All the binuclear ruthenium complexes
solution of aqueous NH4Cl and the ether extract on evapora- display strong band in the range 466–644 nm followed by a weak
tion gave a crude product which was chromatographed to get shoulder in the range 363–399 nm to be the LMCT transitions.
pure biphenyl and compared well with an authentic sample.[15] Therefore, it becomes difficult to assign conclusively the bands
Melting point: 69–72◦C.
in the visible region. The band observed around 260 nm, which

119

120
A. MANIMARAN AND C. JAYABALAKRISHNAN
FIG. 1. Electronic spectrum of binuclear Ru(III) Schiff base complexes; C1-{[(PPh3)2Cl2Ru]2L1}, C2-{[(PPh3)2Cl2Ru]2L2}, C3-{[(PPh3)2Cl2Ru]2L3}, C4-
{[(PPh3)2Cl2Ru]2L4}, C5-{[(PPh3)2Br2Ru]2L1}, C6-{[(PPh3)2Br2Ru]2L2}, C7-{[(PPh3)2Br2Ru]2L3} and C8-{[(PPh3)2Br2Ru]2L4}.
8.2–9.0 ppm. The phenolic -OH protons of H2L1-H2L4 Schiff
is also present in free ligands, is assigned to π − π* transition
from the benzene ring and the double bond of the azomethine
group. The bands around 300 and 350 nm are due to n-π*
transition of non-bonding electrons present on the nitrogen of
azomethine group in the binuclear ruthenium(III) complexes.
The patterns of the electronic spectra of all the complexes in-
dicate the presence of an octahedral environment around the
ruthenium ion.[4,21−23]
base ligands were observed as a singlet in the region 11.8–13.1
ppm. 1H-NMR spectra exhibit a singlet peak at 1.1 ppm and 3.2
ppm for -CH3 protons for H2L3 and OCH3 protons of H2L4
ligands.
1
13C-NMR spectral data (Table 3) are consistent with H-
NMR spectral data. The methyl carbon of aliphatic substituents,
azomethine (>C N) for all the Schiff base ligands and for
Ph C CH3 of H2L3 and Ph-OCH3 of H2L4 ligand around 20
ppm. The resonance observed at 132.0–168.6 ppm is assigned
to phenyl group of ligands. The N C O and C C N of Indole
derivatives for all the ligands observed around 130 ppm and 125
ppm.
The room temperature magnetic moments show that
the ruthenium(III) complexes are one electron paramagnetic
(Table 2), in the range 1.79–1.89 BM, which corresponds to
the +3 state of ruthenium. It has been observed that the µeff
values indicate a single unpaired electron and is consistent with
non-interacting d5 centers or the absence of any strong magnetic
interactions between the two ruthenium centers of the molecule.
ESR Spectra
The room temperature ESR spectra of powdered samples
were recorded at X-band frequencies (Table 2 and Figure 2).
The solid state ESR spectra of all the complexes exhibit an
anisotropic spectra with rhombic distortion and the ‘g’ values
measured in the range of gx = 2.09–2.02, gy = 2.14–2.06 and
gz = 2.20–2.16 with gav = 2.14–2.09 (Table 2), which derived
from ꢁgꢂ* = [1/3gx2+ 1/3gy2+ 1/3gz2]1/2. The ESR spectra of
the present binuclear ruthenium(III) complexes are similar in
1
13C{ H}-NMR Spectra of Schiff Base Ligands
The formation Schiff base ligands were conveniently moni-
tored by peak ratios in the 1H-NMR spectra. 1H-NMR spectra
of all the ligands (Table 3) were taken in DMSO.d6 solvent.
The aromatic region is a set of multiplets in the range 6.6–7.8
ppm for all the Schiff base ligands, while the azomethine proton
of H2L1, H2L2 and H2L4 ligands were observed in the range

121

122
A. MANIMARAN AND C. JAYABALAKRISHNAN
TABLE 3
1
13C{ H}-NMR spectra of Schiff base ligands
Ligand
H2L1
1H-NMR (δ ppm)
13C-NMR (δ ppm)
phenyl carbons
6.6-7.8
8.2
12.3
m, aromatic (12 H)
s, CH N (1 H)
s, OH (2 H)
156.5–132.0
20.0
130.1
125.6
161.0–139.8
18.7
135.4
126.2
160.9–137.1
19.0
>C N Carbon
N C O (Indole Carbon)
C C N (Indole azomethine)
naphthalene carbons
>C N Carbon
N C O (Indole Carbon)
C C N (Indole azomethine)
phenyl carbons
H2L2
H2L3
6.8-7.4
8.6
13.1
m, aromatic (14 H)
s, CH N (1 H)
s, OH (2 H)
7.0-7.8
12.4
m, aromatic (16 H)
s, OH (2 H)
>C N Carbon
1.1
s, CH3 (3 H)
16.0
-methyl carbon
133.5
124.4
168.6–140.0
19.8
N C O (Indole Carbon)
C C N (Indole azomethine)
Benzene carbons
H2L4
6.8-7.6
9.0
11.8
3.2
m, aromatic (12 H)
s, CH N (1 H)
s, OH (2 H)
>C N Carbon
58.0
-methoxy carbon
s, OCH3 (3 H)
132.8
124.0
N C O (Indole Carbon)
C C N (Indole azomethine)
nature to those of the mononuclear complexes[24−27] and this
indicates that the two paramagnetic centers are equivalent and
there is no super exchange between the two metal centers.[28]
However, these new complexes are dimers with one unpaired
electron on each ruthenium(III) atom, leading to an S-value of
1. The pairing of electrons is prevented by the greater distance
between two ruthenium(III) atoms provided by the bridging bis-
bidentate Schiff base ligands.
and the supporting electrolyte used was [NBu4]ClO4 in CH3CN
solution versus Ag/AgCl at a scan rate of 100 mVs−1. Cyclic
voltammogram Ef of all the ruthenium(III) complexes exhibit in
the range from 0.800 to 1.270 V (RuIII-RuIV) and from −0.113
to −0.250 V (RuIII-RuII), respectively (Table 2 and Figure 3).
All the complexes were electroactive only with respect to the
metal center. In these redox couples, electrons are gained or
lost from the dπ levels orbital of the coordinated metal.[25,29,30]
Complexes showed redox couples with peak-to-peak separation
values (ꢀEp) ranging from 200 to 510 mV, revealing that this
process is at best quasi-reversible. This is attributed to slow
electron transfer and adsorption of the complexes onto the elec-
trode surface. The first oxidation and followed by reduction was
attributed to the oxidation and reduction of one of the ruthe-
nium(III) centers to the corresponding mixed valence complex
and the second to the ruthenium(IV). Hence, it is inferred from
the electrochemical data that the present ligand system is ideally
suitable for stabilizing the higher oxidation state of ruthenium.
Cyclic Voltammogram
The cyclic voltammogram studies of binuclear Ru(III) Schiff
base complexes were carried out using glassy carbon electrode
Powder X-ray Diffraction
X-ray diffraction was performed to obtain further evidence
about the structure of the metal complexes. The diffractograms
obtained for the Schiff base metal complexes are given in Figure
4 and the XRD patterns indicate crystalline nature for the Schiff
base ligands and their Ru(III) complexes. The ‘d’ values, 2θ
angles and (h k l) values are listed in Table 4. The complex
crystallizes in an orthorhombic type of lattice with dimensions
as a = 1.106, b = 1.242 and c =1.204 E. On the basis of above
studies, an octahedral geometry for Ru(III) complexes have been
proposed.[31−33]
FIG. 2. EPR spectrum of binuclear {[(PPh3)2Cl2Ru]2L2} complex.

ACTIVITIES OF BINUCLEAR RUTHENIUM(III) SCHIFF BASE COMPLEXES
123
FIG. 3. Cyclic voltammogram of binuclear {[(PPh3)2Cl2Ru]2L1} and {[(PPh3)2Cl2Ru]2L5} complexes.
Scanning electron micrography (SEM)
trated in Figure 5. From the SEM images, we noted that there
is a uniform matrix of the synthesized complexes, i.e., the com-
plexes are homogeneous phase material. A single phase forma-
tion having layer by layer like morphologies with particle size
10 µm is observed in the free Schiff base ligand and its com-
plex. An ice square like shape is observed in the complex with
the particle size of 10 µm. In general, the SEM photographs of
all the complex show single phase formation withwell-defined
shape and particle size in the range of 10 µm.
Scanning electron micrography is used to evaluate morphol-
ogy and particle size of the Schiff base metal complexes. SEM
images of the synthesized Schiff base ligand (H2L2) and their
corresponding ruthenium complex [(PPh3)2Cl2Ru]2L3 are illus-
TABLE 4
X-ray powder diffraction data of {[(PPh3)2Br2Ru]2L2}
˚
Peak
2θ
Lattice spacing (d) A
h k l
C-C Coupling and Oxidation Reactions
1
2
3
4
5
6
7
8
9
6.235
8.126
24.7412
18.4168
16.5254
15.3754
13.8672
8.9426
4.6847
1.64987
1.0842
1.0128
1.0102
1.0101
2 3 1
The C-C coupling reactions by the synthesized binuclear
ruthenium(III) Schiff base complexes {[(PPh3)2X2-Ru]2L}
were carried out and the results of this study are listed in Table 5.
The system chosen for our study is the coupling of phenylmag-
nesium bromide with bromobenzene was first converted into
the corresponding Grignard reagent. Then bromobenzene, fol-
lowed by the complex chosen for the investigation, was added
to the above reagent and the mixture was heated under re-
flux for 6 hours. After work up, the mixture yielded biphenyl.
Only a very little amount of biphenyl is formed when the re-
action is carried out without the catalyst. This is an insignifi-
cant amount compared to the yields of biphenyl that have been
1 0 6
4 3 2
3 2 4
4 1 2
2 1 4
3 4 6
3 4 5
4 5 6
3 4 6
3 5 4
4 3 4
10.450
11.110
13.960
18.230
20.135
26.468
33.541
40.754
45.349
46.346
10
11
12

124
A. MANIMARAN AND C. JAYABALAKRISHNAN
FIG. 4. Powder X-ray Diffraction pattern of binuclear {[(PPh3)2Cl2Ru]2L2} complex.
obtained from the reactions catalyzed by ruthenium complexes. synthesized binuclear ruthenium(III) Schiff base complexes
The catalytic properties of the new binuclear complexes have {[(PPh3)2X2-Ru]2L} were carried out in the presence of oxy-
also been compared with those already reported binuclear com- gen atmosphere at ambient temperature and the results of this
plexes. It has been observed that the binuclear Ru(III) Schiff study are listed in Table 5. The primary and secondary alco-
base complexes are better catalyst than already reported binu- hols (1 mmol) were effectively oxidized by using 0.01 mmol
clear complexes. The possible mechanism for the coupling of of the catalyst in the coexistence of 1 atm pressure of oxygen
PhMgBr with PhBr catalysed by Ru(III) complexes has already atmosphere at ambient temperature in CH2Cl2. All the com-
reported.[34]
plexes oxidized the primary alcohols and secondary alcohols to
The catalytic oxidation of primary and secondary alco- their corresponding aldehydes and ketones[35,36] with high yield.
hols into their corresponding aldehydes and ketones by the This reaction provides an environmentally friendly route to the
FIG. 5. SEM image of binuclear {[(PPh3)2Cl2Ru]2L3} complex (a) 10.00 µm, (b) 1.00 µm.

ACTIVITIES OF BINUCLEAR RUTHENIUM(III) SCHIFF BASE COMPLEXES
125
TABLE 5
Catalytic activity data of new binuclear Ru(III) complexes
C C coupling
reaction
Catalytic oxidation of alcohols
Yield
Turnover
numbera
Yield
Yield
(%)
Complexes
Substrate
Product
(%)
(mg)
{[(PPh3)2Cl2Ru]2L1}
Cinnamyl alcohol
Benzyl alcohol
Cyclohexanol
Cinnamaldehyde
Benzaldehyde
Cyclohexanone
Propionaldehyde
2-Methyl-propionaldehyde
Cinnamaldehyde
Benzaldehyde
78.32
71.14
90.66
60.10
65.28
75.23
69.00
53.52
51.18
58.56
82.74
73.14
66.53
55.42
60.19
59.48
52.56
40.44
38.09
64.50
92.28
88.44
85.69
59.43
66.72
72.56
67.10
56.60
54.15
67.12
78.21
70.52
48.43
56.56
60.83
76.75
74.63
48.19
50.33
65.20
82
74
94
63
69
78
72
56
54
61
86
76
70
57
62
63
55
44
42
67
96
92
89
63
70
75
69
59
57
70
81
73
51
59
64
80
77
51
53
67
0.382
41.24
28.41
44.10
20.23
35.66
29.50
42.30
36.48
Propan-1-ol
2-methyl propyl alcohol
Cinnamyl alcohol
Benzyl alcohol
Cyclohexanol
{[(PPh3)2Cl2Ru]2L2}
{[(PPh3)2Cl2Ru]2L3}
{[(PPh3)2Cl2Ru]2L4}
0.264
0.402
0.194
0.311
0.258
0.418
0.369
Cyclohexanone
Propan-1-ol
Propionaldehyde
2-Methyl-propionaldehyde
Cinnamaldehyde
Benzaldehyde
2-methyl propyl alcohol
Cinnamyl alcohol
Benzyl alcohol
Cyclohexanol
Cyclohexanone
Propan-1-ol
Propionaldehyde
2-Methyl-propionaldehyde
Cinnamaldehyde
Benzaldehyde
2-methyl propyl alcohol
Cinnamyl alcohol
Benzyl alcohol
Cyclohexanol
Propan-1-ol
2-methyl propyl alcohol
Cyclohexanone
Propionaldehyde
2-Methyl-propionaldehyde
Cinnamaldehyde
Benzaldehyde
{[(PPh3)2Br2Ru]2L1} Cinnamyl alcohol
Benzyl alcohol
Cyclohexanol
Propan-1-ol
2-methyl propyl alcohol
Cyclohexanone
Propionaldehyde
2-Methyl-propionaldehyde
Cinnamaldehyde
Benzaldehyde
{[(PPh3)2Br2Ru]2L2} Cinnamyl alcohol
Benzyl alcohol
Cyclohexanol
Propan-1-ol
2-methyl propyl alcohol
Cyclohexanone
Propionaldehyde
2-Methyl-propionaldehyde
Cinnamaldehyde
Benzaldehyde
{[(PPh3)2Br2Ru]2L3} Cinnamyl alcohol
Benzyl alcohol
Cyclohexanol
Propan-1-ol
2-methyl propyl alcohol
Cyclohexanone
Propionaldehyde
2-Methyl-propionaldehyde
Cinnamaldehyde
Benzaldehyde
Cyclohexanone
Propionaldehyde
2-Methyl-propionaldehyde
{[(PPh3)2Br2Ru]2L4} Cinnamyl alcohol
Benzyl alcohol
Cyclohexanol
Propan-1-ol
2-methyl propyl alcohol
aMoles of product per mole of catalyst.
conversion of alcoholic functions to carbonyl groups and water tified as their 2,4-dinitrophenylhydrazone derivatives.[37] The
is the only by- product during the course of the reaction which relatively higher product yield obtained for the oxidation of cin-
was removed by using molecular sieves. The aldehydes and ke- namyl alcohol is due to the presence of more acidic α-CH unit in
tones formed after 3–6 hours of stirring were isolated and quan- cinnamyl alcohol. Further, the oxidation of cinnamyl alcohol to

126

ACTIVITIES OF BINUCLEAR RUTHENIUM(III) SCHIFF BASE COMPLEXES
127
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