Synthesis, spectral, catalytic, and bioactivity studies of ruthenium(III) complexes containing ONO donor schiff base ligands

Article abstract of DOI:10.1080/15533174.2010.522880

New hexa-coordinated ruthenium(III) complexes of the type [RuX(EPh ₃)₂L] (X= Cl or Br; E = P or As; L = deprotonated dibasic tridentate Schiff base ligand) have been synthesized by the reactions of [RuCl₃(PPh₃)₃], [RuCl₃(AsPh ₃)₃] or [RuBr₃(AsPh₃)₃] with the appropriate Schiff bases. The Schiff bases were synthesized by the condensation of anthranilic acid with acetyl acetone/salicylaldehyde/o-vanillin/ o-hydroxy acetophenone. The complexes were characterized by elemental analyses, spectral (FT-IR, electronic and EPR) electrochemical, and magnetic moment data. Catalytic activity of the complexes in the oxidation of alcohols and the antibacterial activity of the ligands and the complexes have also been studied. Copyright Taylor & Francis Group, LLC.

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Synthesis, Spectral, Catalytic, and Bioactivity Studies
of Ruthenium(III) Complexes Containing ONO Donor
Schiff Base Ligands
N. Thilagavathi a & C. Jayabalakrishnan b
a Department of Chemistry , Surya Engineering College , Tamil Nadu, India
b Post Graduate and Research Department of Chemistry , Sri Ramakrishna Mission
Vidyalaya College of Arts and Science , Tamil Nadu, India
Published online: 02 Feb 2011.
To cite this article: N. Thilagavathi & C. Jayabalakrishnan (2011) Synthesis, Spectral, Catalytic, and Bioactivity Studies of
Ruthenium(III) Complexes Containing ONO Donor Schiff Base Ligands, Synthesis and Reactivity in Inorganic, Metal-Organic,
and Nano-Metal Chemistry, 41:1, 54-64
To link to this article: http://dx.doi.org/10.1080/15533174.2010.522880
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 41:54–64, 2011
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2010.522880
Synthesis, Spectral, Catalytic, and Bioactivity Studies of
Ruthenium(III) Complexes Containing ONO Donor Schiff
Base Ligands
N. Thilagavathi1 and C. Jayabalakrishnan2
1Department of Chemistry, Surya Engineering College, Tamil Nadu, India
2Post Graduate and Research Department of Chemistry, Sri Ramakrishna Mission Vidyalaya College
of Arts and Science, Tamil Nadu, India
of their wide range of chemically accessible oxidation states
have been subject of many recent investigations. Ruthenium
compounds have been extensively investigated as catalysts for
alcohol oxidations using a variety of primary oxidants like io-
dosobenzene, N-methylmorpholine-N-oxide[8,9] tert-butyl hy-
droperoxide, molecular oxygen with ruthenium supported on a
CaO–ZrO2 solid solution.[10] Changes in the electronic, steric,
and geometric properties of the ligand alter the orbitals at the
metal center, and thus affect its properties. In catalytic asym-
metric systems, small changes in the donating ability of the
ligand or the size of its substituents can have a dramatic effect
on the catalyst efficiency and enantioselectivity.[1] The Schiff
base transition metal complexes are attractive oxidation cata-
lysts because of their cheap, easy synthesis and their chemical
and thermal stability.[11] Hence, to explore the effect of the Schiff
base ligands on the catalytic efficiency of ruthenium metal, and
also to investigate the influence of the substituents, we have syn-
thesized a series of ruthenium(III) complexes with four Schiff
base ligands containing ONO donor atoms. Schiff base transi-
tion metal complexes find a variety of applications including
biological, clinical, analytical and industrial, in addition to their
important role in catalysis and organic synthesis.[11] In view of
the promising physiological properties of Schiff bases, we were
interested to study the biological role of metal ions on them. In
connection with such studies and continuation of our research on
synthesis, spectral studies, catalytic and bioactivities of ruthe-
nium complexes with simple and inexpensive ligands,[12−14] we
describe here the synthesis, characterization, and redox prop-
erties of ruthenium(III) complexes containing tridentate Schiff
bases along with their reactivity towards oxidation of alcohols in
the presence of NMO. The antibacterial activity studies of Schiff
bases and their ruthenium complexes were also carried out. The
ligands used in this study were prepared by the condensation of
anthranilic acid with acetyl acetone/salicylaldehyde/o-vanillin/
o-hydroxy acetophenone and they have the following structure
(Figure 1).
New hexa-coordinated ruthenium(III) complexes of the type
[RuX(EPh3)2L] (X = Cl or Br; E = P or As; L = deproto-
nated dibasic tridentate Schiff base ligand) have been synthe-
sized by the reactions of [RuCl3(PPh3)3], [RuCl3(AsPh3)3] or
[RuBr3(AsPh3)3] with the appropriate Schiff bases. The Schiff
bases were synthesized by the condensation of anthranilic acid with
acetyl acetone/salicylaldehyde/o-vanillin/o-hydroxy acetophenone.
The complexes were characterized by elemental analyses, spectral
(FT-IR, electronic and EPR) electrochemical, and magnetic mo-
ment data. Catalytic activity of the complexes in the oxidation of
alcohols and the antibacterial activity of the ligands and the com-
plexes have also been studied.
Keywords antibacterial activity, NMO, oxidation of alcohol, ruthe-
nium(III), Schiff base
INTRODUCTION
Oxidation of organic substrates as catalyzed by coordination
complexes of transition metals in resemblance of enzymatic oxi-
dations is an intriguing area of current research[1] Selective alco-
hol oxidation is a prominent reaction in laboratory and industrial
synthetic chemistry and has attracted substantial recent effort.
Many catalytic systems have been reported for the oxidation of
alcohols. They have some drawbacks, such as instability of the
oxidant at room temperature,[2] not effective for non-activated
alcohols,[3] over oxidation of the alcohol to acid or production
of toxic waste,[4] or not effective for unsaturated alcohols,[5] but
metal nanoparticles and ionic liquids are successively used for
the oxidation of alcohols.[6,7] Ruthenium complexes by virtue
Received 14 November 2009; accepted 18 August 2010.
Address correspondence to C. Jayabalakrishnan, Post Graduate
and Research Department of Chemistry, Sri Ramakrishna Mission
Vidyalaya College of Arts and Science, Coimbatore–641 020, Tamil
Nadu, India. E-mail: cjbsrmvcbe@gmail.com
54

RUTHENIUM(III) SCHIFF BASE OXIDATION OF ALCOHOL
55
resulting solution was concentrated to ca 5 mL and the product
was precipitated by the addition of petroleum ether (60–80◦C).
The precipitate was washed with petroleum ether and recrystal-
lized from petroleum ether-dichloromethane mixture.
Catalytic Oxidation Experiments
To a solution of the alcohol (0.1–0.12 mL, 1 mmol)
in dichloromethane (20 mL), N-methylmorpholine-N-oxide
(NMO) (0.35 g, 3 mmol) and the ruthenium complex (0.009
g, 0.01 mmol) were added and the solution was heated un-
der reflux for 3 h. The mixture was then filtered and the fil-
trate was dried over anhydrous Na2SO4. It was then evapo-
rated to dryness and extracted with diethyl ether. The diethyl
ether extract was filtered and evaporated to give the correspond-
ing carbonyl compound, which was then quantified as its 2,4-
dinitrophenylhydrazone.[15,20]
Biocidal Studies
The ligands and their complexes have been screened for the in
vitro growth inhibitory activity against the gram negative bac-
teria Escherichia coli and the gram positive bacteria Bacillus
subtilis using disc diffusion method. The bacteria were cul-
tured in nutrient agar medium and used as inoculum for the
study. Bacterial cells were swabbed onto nutrient agar medium
in Petri plates. The compounds to be tested were dissolved in
DMSO at a final concentration of 0.5% (0.5 g/100 mL) and 1.0%
(1.0 g/100 mL) and soaked in filter paper discs (5 mm diameter,
1 mm thick). These discs were placed on the already seeded
plates and incubated at 35 2◦C for 24 h. The diameter (mm)
of the inhibition zone around each disc was measured after 24 h
and was taken as a measure of inhibitory activity. Ampicillin
was used as a standard.[21]
FIG. 1. Structure of the Schiff base ligands.
EXPERIMENTAL
Materials and Methods
All the reagents used were analytical reagent grade. Solvents
were purified and dried according to the standard procedures.[15]
RuCl3.3H2O was purchased from Loba Chemie. C H N analy-
sis were performed in Vario EL III CHNS analyzer at Cochin
University, Kerala. IR spectra of the complexes were recorded
in KBr pellets with a Perkin–Elmer 597 infrared spectropho-
tometer in the range 4000–200 cm−1. Electronic spectra were
recorded in dichloromethane with a Systronics double beam UV-
Vis Spectrophotometer 2202. X-band EPR Spectra of powdered
samples at RT and LNT were recorded with Bruker model ER-
200-D Spectrometer using DPPH as g-marker at Indian Institute
of technology, Chennai. Cyclic voltammetric studies were car-
ried out in acetonitrile using a glassy-carbon working electrode
and potentials were referenced to standard calomel electrode us-
ing [N(Bu)4BF4] as supporting electrolyte. Melting points were
recorded on a Raaga heating table and are uncorrected. Mag-
netic susceptibility measurements were made with an EG and
G-PARC vibrating sample magnetometer. Molecular weights
were determined by Rast micro method. Molar conductivities
of freshly prepared solutions were measured using Elico CM
180 conductivity meter. [RuCl3(PPh3)3][16] [RuCl3(AsPh3)3][17]
[RuBr3(AsPh3)3][18] and ligands[19] were prepared by reported
methods.
RESULTS AND DISCUSSION
All the complexes are quite stable in air and light. The analyt-
ical data and the molecular weights (Table 1) for the complexes
are in good agreement with the molecular formula proposed
(Table 2). The molar conductivity values for the complexes in
DMSO solvent (1.0 × 10−3 mol) are in the range 7.9–12.1
ohm−1 cm2 mol−1. It is clear from the conductivity measure-
ment that the complexes are non-electrolytic in nature.
IR Spectra
IR spectrum of the ligand H2Anth-acac shows a band at
1597 cm−1, which is assigned to the νC
of the acetyl ace-
O
tone moiety. Absence of this band and the appearance of a new
band at 1521 cm−1 in the spectrum of the corresponding com-
plexes, which may be assigned to the CH C group, confirms
the enolization of the H2C C O group. But these complexes
do not show any peak around 3000 cm−1, which indicates the
deprotonation of the enolic OH. The above observations con-
firm the coordination of the deprotonated enolic oxygen of the
Preparation of the Complexes
A representative procedure for the preparation of the
ruthenium(III) complexes is detailed here. To a solution of
[RuCl3(PPh3)3] (0.1 g; 0.1 mmol) in benzene (50 mL), 0.02 g
(0.1 mmol) of H2Anth-acac was added and refluxed for 6 h. The

56

RUTHENIUM(III) SCHIFF BASE OXIDATION OF ALCOHOL
57
FIG. 2. Preparation of ruthenium(III) complexes.
which are due to νRu−N and νRu−O, respectively.[24] Thus, in all
the complexes, the Schiff bases behave as dibasic tridentate lig-
ands. ν(Ru−Cl)/ν(Ru−Br) absorption has been found in the 310–320
cm−1 /245–250 cm−1 region and ν(Ru−P)/ν(Ru−As) vibrations dis-
play a band around 514–523 cm−1/470–484 cm−1 in the spectra
of the complexes.[25] Characteristic bands of PPh3/AsPh3 are
observed in the spectra of all the complexes at 1440, 1080, 740,
ligand H2Anth-acac to the ruthenium. Similarly, coordination
of the deprotonated phenolic oxygen of the ligands H2Anth-sal,
H2 Anth-ovan and H2 Anth-ohap to ruthenium is indicated by
the following observations. Disappearance of the band around
3400 cm−1, which is due to phenolic ν(O−H) and the appearance
of ν(C−O) band of the phenolic group at a higher wave number,
from 1292–1299 cm−1 to 1302–1317 cm−1 [22]
.
In all the lig-
ands, the band found around 1560–1577 cm−1 is assigned to
ν(C=N). This band undergoes a negative shift (1521–1550 cm−1
and 680 cm−1
.
)
in the spectrum of the complexes suggesting the azomethine
nitrogen coordination to ruthenium[22] The band due toν(O−H)
of the carboxylic acid group which is present in the spectra
Electronic Spectra
The electronic spectra of the free ligands show two types of
of the ligands disappears in the spectrum of the complexes. A transitions, the first one appears at 255–297 nm (ε = 13820–
band observed around 1687–1732 cm−1 due to the carboxylic 21580 dm3mol−1cm−1), which can be assigned to π → π*
carbonyl group in the ligands is observed at 1643–1700 cm−1 transition of the phenolic chromophore. These peaks are shifted
and at 1433–1456 cm−1 in the complexes arising from νasy to lower wavelength (2–14 nm) in the spectra of the complexes.
and νsym frequencies of the COO− group, respectively. The dif- This may be due to the donation of a lone pair of electrons by
ference between νasy and νsym frequencies has been found to the oxygen of the phenoxy group to the metal atom.[26] The
be ∼250 cm−1. This is a clear indication of the monodentate second type of transition appears at 351–399 nm (ε =15800–
coordination of the carboxyl group with free carbonyl group 24730 dm3mol−1cm−1), which can be assigned to n → π*
after deprotonation[23] Coordination of the Schiff base ligands transition of the C N chromophore. These peaks appear at a
through nitrogen and oxygen to ruthenium is further confirmed lower wavelength (5–29 nm) in the spectra of the complexes.
by the bands present at 440–458 cm−1 and at 413–421 cm−1
,
This indicates that the imine group nitrogen atom is coordi-

58
N. THILAGAVATHI AND C. JAYABALAKRISHNAN
TABLE 2
Electronic spectral data of ruthenium(III) complexes
λmax (nm)
Transition energy
(cm−1
Complex
(ε; dm3mol−1cm−1
)
)
Assignments
ν2/ν1 10Dq
B
C
4
663 (767)
519 (2687)
432 (2380)
639 (876)
520 (2885)
424 (3591)
635 (819)
516 (2854)
428 (2904)
638 (872)
515 (2698)
430(2874)
690 (842)
519 (2753)
417(2954)
665 (704)
520 (2652)
437(3852)
688 (719)
520 (2787)
441(4450)
657 (798)
514 (2851)
428 (4390)
657 (876)
517 (2856)
417 (4298)
15083
19268
23148
15649
19231
23585
15748
19380
23364
15674
19417
23256
14493
19267
23981
15038
19231
22883
14535
19230
22676
15221
19455
23364
15221
19342
23981
2T2g → T1g
4
[RuCl(PPh3)2(Anth-acac)]
2T2g → T2g
1.28
1.23
1.23
1.24
1.33
1.28
1.32
1.28
1.27
26358 523 2165
26678 448 2198
26357 454 2085
26251 468 2059
27740 597 2566
26022 524 2091
2
2T2g → A1g, 2T1g
4
2T2g → T1g
4
[RuCl(PPh3)2(Anth-sal)]
[RuCl(PPh3)2(Anth-ohap)]
[RuCl(AsPh3)2(Anth-acac)]
[RuCl(AsPh3)2(Anth-sal)]
[RuBr(AsPh3)2(Anth-acac)]
[RuBr(AsPh3)2(Anth-sal)]
[RuBr(AsPh3)2(Anth-ovan)]
[RuBr(AsPh3)2(Anth-ohap)]
2T2g → T2g
2
2T2g → A1g, 2T1g
4
2T2g → T1g
4
2T2g → T2g
2
2T2g → A1g, 2T1g
4
2T2g → T1g
4
2T2g → T2g
2
2T2g → A1g, 2T1g
4
2T2g → T1g
4
2T2g → T2g
2
2T2g → A1g, 2T1g
4
2T2g → T1g
4
2T2g → T2g
2
2T2g → A1g, 2T1g
4
2T2g → T1g
25977
4
2T2g → T2g
587 2127
2
2T2g → A1g, 2T1g
4
2T2g → T1g
4
2T2g → T2g
26608 529 2185
27416 515 2405
2
2T2g → A1g, 2T1g
4
2T2g → T1g
4
2T2g → T2g
2
2T2g → A1g, 2T1g
nated to the metal atom.[27] The transitions observed at 417–
520 nm (ε =2380–4450 dm3mol−1cm−1) in the spectra of the
complexes can be assigned to charge transfer transitions. These
bands obscure the weak d-d transitions occurring in this region.
The weak transitions observed at 635–690 nm (ε =704–876
dm3mol−1cm−1) can be attributed to d-d transition in the metal
orbitals. Octahedral low spin d5 complexes have the 2T2g ground
state corresponding to the electronic state t52g and the observed
Magnetic Moment and EPR Spectra
Themagneticsusceptibilitiesofallthecomplexesliebetween
1.73 and 1.94 BM indicating the presence of one unpaired elec-
tron. It is inferred from these values that ruthenium is in the +3
oxidation state.[30] The observed magnetic susceptibilities and
the electronic spectra of the complexes suggest an octahedral
structure for the complexes.
The EPR spectra of powdered samples were recorded
at room temperature. Two representative spectra are shown
in Figures 3 and 4. The complexes showed no indication of any
hyperfine interaction of Ru with N, As, P, Cl and Br. The spec-
tra of all the complexes except complex [RuCl(AsPh3)2(Anth-
ovan)] showed single isotropic resonance with g values of
2.04–2.53 (Table 3). Such isotropic lines are usually observed
either due to intermolecular spin-spin exchange, which can
broaden the lines or due to occupancy of the unpaired elec-
tron in a degenerate orbital[31] corresponding to the electronic
configuration (dxz)2, (dyz)2, (dxy)1. However, the spectra
of complex [RuCl(AsPh3)2(Anth-ovan)] show axial symme-
try with g = 2.01 and g = 2.28. EPR spectra for
4
bands correspond to the transitions 2T2g → T1g (14493–15748
4
2
cm−1), 2T2g → T2g (19230–19455 cm−1), 2T2g → A1g, 2T1g
(22676–23981 cm−1). Values of Racah inter electronic repul-
sion parameters B and C and 10Dq (Table 2) are calculated for
the above transitions, and the values of these ligand field param-
eters are comparable to those reported for other trivalent ruthe-
nium(III) octahedral complexes.[28] Considerable lower value of
the Racah inter electronic repulsion parameter than that of the
free ruthenium ion indicates the covalent nature of the metal lig-
and bond.[29] Higher Dq values are usually associated with con-
siderable electron delocalization. Results of the electronic spec-
tra suggest an octahedral environment around the ruthenium ion.
⊥
||

RUTHENIUM(III) SCHIFF BASE OXIDATION OF ALCOHOL
59
FIG. 3. EPR spectra of [RuBr(AsPh3)2(Anth-ovan)] a. at RT; and b. at LNT.
FIG. 4. EPR spectra of [RuCl(PPh3)2(Anth-sal)] a. at RT; and b. at LNT.
two signals indicates an axial distortion in the complexes. For
an octahedral field with axial distortion gx = gy = gz. The
axial distortion splits the triply degenerate t2 level into a and e.
Thus the energy level order is dxy > dxz, dyz with the unpaired
electron in dxy.[32]
the complexes [RuCl(PPh3)2(Anth-acac)], [RuCl(PPh3)2(Anth-
sal)], [RuCl(PPh3)2(Anth-ohap)], [RuCl(AsPh3)2(Anth-ovan)],
[RuCl(AsPh3)2(Anth-ohap)], [RuBr(AsPh3)2(Anth-sal)] and
[RuBr(AsPh3)2(Anth-ovan)] were recorded at liquid nitrogen
temperature. The LNT epr spectra of [RuCl(PPh3)2(Anth-ohap)]
and [RuBr(AsPh3)2(Anth-ovan)] show no variation from their
corresponding RT epr spectra.
Redox Behavior
However the LNT epr spectra of the complexes
The redox behavior of some of the complexes was studied by
[RuCl(PPh3)2(Anth-acac)], [RuCl(PPh3)2(Anth-sal)], [RuCl cyclic voltammetry (Table 4). A representative cyclic voltam-
(AsPh3)2(Anth-ovan)], [RuCl(AsPh3)2(Anth-ohap)] and mogram is shown in Figure 5. The electrochemical profiles of
[RuBr(AsPh3)2(Anth-sal)] displayed two signals. Presence of the complexes display a quasi-reversible (ꢀEp = 80–400 mV)
TABLE 3
EPR spectral data of ruthenium(III) complexes
Room temperature
Liquid nitrogen temperature
Complex
gx
gz
gy
<g>*
gx
gz
gy
<g>*
[RuCl(PPh3)2(Anth-acac)]
[RuCl(PPh3)2(Anth-sal)]
[RuCl(PPh3)2(Anth-ovan)]
[RuCl(PPh3)2(Anth-ohap)]
[RuCl(AsPh3)2(Anth-acac)]
[RuCl(AsPh3)2(Anth-sal)]
[RuCl(AsPh3)2(Anth-ovan)]
[RuCl(AsPh3)2(Anth-ohap)]
[RuBr(AsPh3)2(Anth-acac)]
[RuBr(AsPh3)2(Anth-sal)]
[RuBr(AsPh3)2(Anth-ovan)]
[RuBr(AsPh3)2(Anth-ohap)]
—
—
—
—
—
—
2.28
—
—
—
—
—
2.31
2.24
2.38
2.10
2.53
2.28
2.01
2.14
2.33
2.27
2.29
2.04
—
—
—
2.60
2.44
2.19
2.05
2.60
2.44
2.47
2.32
—
2.10
—
—
—
2.28
—
—
—
2.10
2.69
2.65
2.22
2.09
2.69
2.69
2.54
2.48
2.39
—
2.04
2.28
2.39
—
2.27
—
<g*>= [1/3 g2x+1/3 g2y+1/3 gz2]1/2

60
N. THILAGAVATHI AND C. JAYABALAKRISHNAN
NMO is shown in Figure 6. NMO behaves as a two electron ox-
idant. Reaction proceeds through the formation of Ru(V)- oxo
species. This is evidenced from the IR spectrum, which shows a
weak band at 805 cm−1 (Figure 7) and the appearance of a peak
at 380 nm in the UV spectrum (Figure 8) that would account for
a loose oxo complex of ruthenium.[35]
Among the ruthenium complexes that have been analyzed,
the order of catalytic activity in terms of yield and turnover num-
ber was [RuBr(AsPh3)2(Anth-acac)] > [RuBr(AsPh3)2(Anth-
ohap)] > [RuCl(PPh3)2(Anth-sal)] > [RuCl(PPh3)2(Anth-
ovan)]. In terms of substituents present in the Schiff base moiety,
the order of activity is 2CH3 > CH3 > H > OCH3. Hence, it
is inferred that inductive effect of the substituents play a ma-
jor role in deciding the catalytic activity of their corresponding
complexes. Presence of two methyl groups in the ligand H2Anth-
acac makes its corresponding complex a better catalyst. Rela-
tively lesser catalytic efficiency was observed for the complex
containing the ligand H2Anth-ohap, which contains one -CH3
group as substituent. The last member in the above order con-
tains -OCH3 group as substituent in its ligand, H2Anth-ovan.
The –I effect of the -OCH3 group makes this complex lesser
active than the other three complexes. It is further inferred from
the results that the AsPh3/ PPh3, Br/Cl ligands may also influ-
ence the catalytic efficiency by their electron donor-acceptor
nature. High donor ability of the triphenylarsine group and the
lesser electronegativity of the bromine might have augumented
the influence of the ligands H2Anth-acac and H2Anth-ohap on
their complexes. Similarly, the lesser donor ability of the triph-
enylarsine group and the higher electronegativity of the chlorine
might have decreased the influence of the ligands H2Anth-sal
and H2Anth-ovan on their complexes. Hence, it is inferred from
the above discussion that electron releasing groups increase the
catalytic activity and electron withdrawing groups decrease the
catalytic activity of their corresponding ruthenium complexes.
This is in line with a previous observation.[36]
FIG. 5. Cyclic voltammogram of [RuCl(AsPh3)2(Anth-ohap)].
redox process. The complexes showed well defined waves in
the range, 0.74 to 1.28 V (RuIII- RuIV) and −0.77 to − 0.90
V (RuIII − RuII). The redox potentials are influenced by the
nature of the ligands. Complexes with ligands having electron
releasing substituents were oxidized and reduced at a lower
potential[33] than the complexes with electron withdrawing
ligands.
Catalytic Oxidation Studies
The oxidation of primary/secondary alcohols was carried
out using the synthesized ruthenium complexes as catalyst and
NMO as an oxidant. Alcohols were converted into their corre-
sponding aldehydes/ketones. Results are shown in Table 5. The
proposed mechanism[34] for the oxidation in the presence of
The relatively higher product yield obtained for oxida-
tion of benzyl alcohol compared to cyclohexanol is due to
the fact that α-CH unit of benzyl alcohol is more acidic
TABLE 4
Cyclic voltammetrya data of ruthenium(III) complexes
Ru (III-IV)
Ru (III- II)
Epc (V) Ef (V)
Complex
Epa (V)
Epc (V)
Ef (V)
ꢀEp (mV)
Epa (V)
ꢀEp (mV)
[RuBr(AsPh3)2(Anth-acac)]
[RuBr(AsPh3)2(Anth-ohap)]
[RuCl(AsPh3)2(Anth-ohap)]
[RuCl(PPh3)2(Anth-sal)]
[RuCl(PPh3)2(Anth-ovan)]
[RuCl(AsPh3)2(Anth-ovan)]
0.78
1.10
1.10
1.32
1.38
1.38
0.70
0.70
0.78
1.14
1.10
1.18
0.74
0.90
0.94
1.23
1.24
1.28
80
400
320
180
280
200
−1.07
−0.99
−0.92
−0.90
−0.9
−0.73
−0.70
−0.75
−0.70
−0.68
−0.64
−0.90
−0.845
−0.835
−0.80
−0.79
−0.77
340
290
170
200
220
260
−0.90
aSupporting electrolyte [N(Bu)4]BF4 (0.1M); all potentials are referenced to SCE; Ef = 0.5 (Epa+ Epc); ꢀEp = (Epa –Epc); where Epa
and Epc are anodic and cathodic potentials respectively; scan rate = 100 mVs−1

RUTHENIUM(III) SCHIFF BASE OXIDATION OF ALCOHOL
61
TABLE 5
Catalytic oxidation of alcohols by ruthenium(III) complexes
Complex
Substrate
Product
Yielda %
Turnover numberb
Benzylalcohol
Cyclohexanol
Cinnamyl alcohol
Benzylalcohol
Cyclohexanol
Cinnamyl alcohol
Benzylalcohol
Cyclohexanol
Cinnamyl alcohol
Benzylalcohol
Cyclohexanol
Benzaldehyde
Cyclohexanone
Cinnamaldehyde
Benzaldehyde
Cyclohexanone
Cinnamaldehyde
Benzaldehyde
Cyclohexanone
Cinnamaldehyde
Benzaldehyde
Cyclohexanone
Cinnamaldehyde
95
76
97
92
72
94
89
68
92
86
65
90
97
78
99
94
74
96
91
70
94
88
68
92
[RuBr(AsPh3)2(Anth-acac)]
[RuBr(AsPh3)2(Anth-ohap)]
[RuCl(PPh3)2(Anth-sal)]
[RuCl(PPh3)2(Anth-ovan)]
Cinnamyl alcohol
ayields based on substrate.
bmoles of product per moles of catalyst.
than cyclohexanol.[37] An important characteristic of the ruthe-
nium/NMO system results in the selective oxidation at the alco-
holic group of unsaturated cinnamyl alcohol to cinnamaldehyde,
tolerating the double bond.[35]
them. The higher the zone of inhibition, the greater the antibac-
terial activity (Table 6). The results of the antimicrobial activity
studies show that the ruthenium chelates are more toxic when
compared with their parent ligands against the same micro-
organisms under the identical experimental conditions. Under
conditions of balanced growth, a bacterium must duplicate ev-
ery cellular constituent during its cell cycle. But in the presence
of ruthenium metal, bacterial DNA loses its replication ability
Biocidal Studies
Inhibition activity of the test compounds were assessed on
the basis of the corresponding zone of inhibition developed by
FIG. 6. Proposed mechanism for the oxidation of alcohols by Ru(III)/NMO.

62
N. THILAGAVATHI AND C. JAYABALAKRISHNAN
FIG. 7. IR spectra of the ruthenium(V)-Oxo active intermediate of [RuCl(PPh3)2(Anth-sal)].
and cellular proteins become inactivated. The mode of action that all four Schiff base ligands had the same activity against
may include induction of filamentous growth in the bacteria as the organisms, and the magnitude of their influence in their cor-
well as induction of phage production from lysogenic strains of responding complexes were also same. The inhibition activity
the bacteria[38] and also the interference in the mitochondnial was reinforced with the increment of concentration. Though
calcium transport.[39] The possible mechanism of action of the
ruthenium complexes is by binding to DNA, which reduces the
synthesis of new DNA.
TABLE 6
A possible mode of toxicity increase may also be considered Antimicrobial activity data of Schiff bases and ruthenium(III)
in the light of Tweedy’s chelation theory. Chelation consider-
ably reduces the polarity of the metal ion because of partial
sharing of its positive charge with the donor groups and possi-
ble p electron delocalization over the whole chelate ring. Such
chelation could enhance the lipophilic character of the central
metal atom, which subsequently favors its permeation through
the lipid layers of the cell membrane. It has been suggested that
the ligands with the N and O donor system might have inhibited
enzyme production, since enzymes that require a free hydroxyl
group for their activity appear to be especially susceptible to de-
activation by the ions of the complexes.[40] It was also inferred
complexes
Diameter of inhibition zone
Bacillus sp. E. Coli
Ligand/Complex
0.5% 1% 0.5% 1%
H2Anth-acac
10
15
18
16
12
16
20
17
10
16
15
17
12
17
18
17
24
14
20
24
21
14
20
25
22
14
22
20
21
17
22
23
22
28
12
16
17
16
10
14
16
15
11
14
15
14
10
15
16
18
26
15
22
24
21
13
18
21
20
16
19
22
20
16
22
22
23
30
[RuCl(PPh3)2(Anth-acac)]
[RuCl(AsPh3)2(Anth-acac)]
[RuBr(AsPh3)2(Anth-acac)]
H2Anth-sal
[RuCl(PPh3)2(Anth-sal)]
[RuCl(AsPh3)2(Anth-sal)]
[RuBr(AsPh3)2(Anth-sal)]
H2Anth-ovan
[RuCl(PPh3)2(Anth-ovan)]
[RuCl(AsPh3)2(Anth-ovan)]
[RuBr(AsPh3)2(Anth-ovan)]
H2Anth-ohap
[RuCl(AsPh3)2(Anth-ohap)]
[RuCl(AsPh3)2(Anth-ohap)]
[RuBr(AsPh3)2(Anth-ohap)]
Ampicillin
0.5% and 1.0% indicate 0.5 g and 1.0 g of the substance in
100 mL of DMSO respectively.
FIG. 8. UV-Vis spectra of the ruthenium(V)-Oxo active intermediate of
[RuBr(AsPh3)2(Anth-ovan)].

RUTHENIUM(III) SCHIFF BASE OXIDATION OF ALCOHOL
63
the complexes possess inhibition activity, it could not reach the
effectiveness of the standard drug, Ampicillin.
New Ruthenium(III) Schiff Base Complexes Containing PPh3 or AsPh3
Co-Ligands. Trans. Met. Chem. 2009, 34, 7–13.
15. Vogel, A.I. Text Book of Practical Organic Chemistry, 5th Edn.; Longmann:
London, 1989, pp 264–279.
16. Chatt, J.; Leigh, G.; Mingos, D.M.P.; Paske, R.J. Complexes of Osmium,
Ruthenium, Rhenium and Indium Halides with Some Tertiary Monophos-
phine and Monoarsines. J. Chem. Soc. (A) 1968, 2636–2641.
17. Viswanathamurthi, P.; Natarajan, K. Mixed Ligand Complexes of Ruthe-
nium(III) Containing N,O/N,S Donor Ligands and Triphenylphosphine and
Triphenylarsine. Indian J. Chem. 1999, 38, 797–801.
18. Natarajan, K.; Poddar, R.K.; Agarwala, U. Mixed Complexes of
Ruthenium(III) and Ruthenium(II) with Triphenylphosphine and Triph-
enylarsine and Other Ligands. J. Inorg. Nucl. Chem. 1977, 39,
431–435.
CONCLUSION
In conclusion, it has been observed that variations in the side
arms of the imine compartment and substituent of the phenyl
ring influence the electrochemical, magnetic and catalytic prop-
erties of the ruthenium(III) complexes. The stability, easy prepa-
ration, mild reaction conditions, and high yields of the products
and the reaction under non-aqueous condition make this reagent
a useful method for the oxidation of alcohols.
19. Asgedom, G.; Sreedhara, A.; Kivikoski, J.; Rao, C.P. Synthesis and Char-
acterization of Vanadyl(IV) Complexes of Schiff Bases Derived from An-
thranilic Acid and Salicylaldehyde (or Its Derivatives) or Acetylacetone.
Single Crystal X-ray Structures of the Oxidized products. Polyhedron 1997,
16, 643–651.
20. Jayabalakrishnan, C.; Karvembu, R.; Natarajan, K. Catalytic and Antimi-
crobial Activities of New Ruthenium(II) Unsymmetrical Schiff Base Com-
plexes. Trans. Met. Chem. 2002, 27, 790–794.
REFERENCES
1. Balsells, J.; Mejorado, L.; Phillips, M.; Ortega, F.; Aguirre, G.; Somanathan,
R.; Walsh, P.J. Synthesis of Chiral Sulfonamide/Schiff Base Ligands. Tetra-
hedron: Asymmetry 1998, 9, 4135–4142.
2. Geraskin, I.M.; Luedtke, M.W.; Neu, H.M.; Nemykin, V.N.; Zhdankin,
V.V. Organic Iodine(V) Compounds as Terminal Oxidants in Iron(III) Ph-
thalocyanine Catalyzed Oxidation of Alcohols. Tetrahedron Lett. 2008, 49, 21. Collins, C.H.; Lyne, P.M. Microbial Methods, University Park Press: Balti-
7410–7412.
more, 1970, p 422.
3. Rong, M.; Liu, C.; Han, J.; Wang, H. Catalytic Oxidation of Alcohols by
a Double Functional Ionic Liquid [bmim]BF4. Catal. Commun. 2009, 10,
362–364.
4. Bagchi, D.; Stohs, S.J.; Downs, B.W.; Bagchi, M.; Preuss, H.G. Cytotoxicity
and Oxidative Mechanisms of Different Forms of Chromium. Toxicology
2002, 180, 5–22.
5. Matsuo, J.; Lida, D.; Yamanaka, H.; Mukaiyama, T. N-Tert-Butylbenzene
Sulfenamide-Catalysed Oxidation of Alcohols to the Corresponding Car-
bonyl Compounds with N-Chlorosuccinimide. Tetrahedron 2003, 59,
6739–6750.
6. Wang, Y.; Yan, R.; Zhang, J.; Zhang, W. Synthesis of Efficient and Reusable
Catalyst of Size-Controlled Au Nanoparticles Within a Porous, Chelating
and Intelligent Hydrogel for Aerobic Alcohol Oxidation. J. Mol. Catal. (A)
Chem. 2010, 317(15), 81–88.
7. Mifsud, M.; Parkhomenko, K.V.; Arends, I.W.C.E.; Sheldon, R.A. Pd
Nanoparticles as Catalysts for Green and Sustainable Oxidation of Func-
tionalized Alcohols in Aqueous Media. Tetrahedron 2010, 66, 1040–1044.
8. Ulaganatha Raja, M.; Gowri, N.; Ramesh, R. Synthesis, Crystal Structure
and Catalytic Activity of Ruthenium(II) Carbonyl Complexes Containing
ONO and ONS Donor Ligands. Polyhedron 2010, 29, 1175–1181.
9. Gunasekaran, N.; Karvembu, R. Synthesis, Characterization,
and Catalytic Applications of Ru(III) Complexes Containing N-
22. Subasi, E.; Kose, P.; Karahan, S.; Ergun, Y. Photochemical Reactions of
M(CO)5THF (M = Cr, Mo, W) with Salen Type (-ONNO-) Schiff Bases.
Synth. React. Inorg. Met-org. Chem. 2009, 39, 139–143.
23. Abd El-Wahab, Z.H. Mononuclear Metal Complexes of Organic Carboxylic
Acid Derivatives: Synthesis, Spectroscopic Characterisation, Thermal In-
vestigation and Antimicrobial Activity. Spectrochim. Acta (A) 2007, 67,
25–38.
24. Refat, M.S.; El-Korashy, S.A.; Nandan Kumar, D.; Ahmed, A.S. Synthe-
ses and Characterisation of Ru(III) with Chelating Containing ONNO
Donor Quadridentate Schiff Bases. Spectrochim. Acta (A) 2008, 70,
898–906.
25. Taqui Khan, M.M.; Vijay Sen Reddy, V. New Tetradentate Ligands Con-
taining Nitrogen, and Phosporous or Arsenic as Donor Atoms and Their
Complexes with Ruthenium(II) and –(III). Inorg. Chem. 1986, 25, 208–
214.
26. Sharma, R.K.; Singh, R.V.; Tandon, J.P. Biscyclopentadienyl Titanium(IV)
Complexes of Monofunctional Bidentate Ketamines. J. Inorg. Nucl. Chem.
1980, 42, 1382–1384.
27. Azza A.A. Abu-Hussen, Linert, W. Synthesis, Spectroscopic and Biological
Activity of New Mononuclear Transition Metal Complexes of Macrocyclic
Schiff Bases Derived from 1,1ꢁ-Diacetylferrocin. Synth. React. Inorg. Met-
org. Chem. 2009, 39, 13–23.
[di(alkyl/aryl)carbamothioyl] Benzamide Derivatives and Triphenylphos- 28. Sharma, V.K.; Srivatsava, S.; Srivatsava, A. Spectroscopic, Thermal
phine/Triphenylarsine. Inorg. Chem. Comm. 2010, 13, 952–955.
10. Yasu-eda, T.; Kitamura, S.; Na-oki Ikenaga, Miyake, T.; Suzuki, T. Selec-
tive Oxidation of Alcohols with Molecular Oxygen Over Ru/CaO–ZrO2
Catalyst. J. Mol. Catal.(A) Chem. 2010, 323, 7–15.
11. Sivagamasundari, M.; Ramesh, R. Luminescent Property and Catalytic Ac-
tivity of Ru(II) Carbonyl Complexes Containing N, O Donor of 2-Hydroxy-
1-Naphthylideneimines. Spectrochim. Acta (A) 2007, 67, 256–262.
and Biological Studies on Some Trivalent Ruthenium and Rhodium
ns Chelating Thiosemicarbazone Complexes Bioinorg. Chem. Appl.
doi:10.1155/2007/68374. 2007, 1–10.
29. El-Sonbati, A.Z.; El-Bindary, A.A.; El-Dssouky, A.; El-Gogary, T.M.;
Hilali, A.S. Substituent Effect on the Spectral Studies on Ruthe-
nium(III) Complexes of 5 (4-Derivatives Phenyldiazo)-3-Phenyl-2-Thioxo-
4-Thiozolidinone. Spectrochim. Acta (A) 2002, 58, 1623–1629.
12. Thilagavathi, N.; Manimaran, A.; Padmapriya, N.; Sathya, N.; Jayabalakr- 30. Jayabalakrishnan, C.; Karvembu, R.; Natarajan, K. Synthesis, Charac-
ishnan, C. Synthesis, Spectroscopic, Redox, Catalytic and Antimicrobial
Properties of some Ruthenium(II) Schiff Base Complexes. Trans. Met.
Chem. 2009, 34, 725–732.
terisation, Catalytic, and Biocidal Studies of Ruthenium(III) Complexes
with Thiosemicarbazones of β-Diketoesters. Synth. React. Inorg. Met-org.
Chem. 2002, 32, 1099–1113.
13. Padma Priya, N.; Arunachalam, S.; Manimaran, A.; Muthupriya, D.; Jaya-
balakrishnan, C. Mononuclear Ru(III) Schiff Base Complexes: Synthesis,
Spectral, Redox, Catalytic, Biological Activity Studies. Spectrochim. Acta
(A) 2009, 72, 670–676.
14. Sathya, N.; Manimaran, A.; Raja, G.; Muthusamy, P.; Deivasigamani, K.;
Jayabalakrishnan, C. Catalytic Oxidation and C C Coupling Reactions of
31. Joseph, M.; Sreekanth, A.; Suni, V.; Prathapachandra Kurup, M.R. Spectral
Characterisation of Iron(III) Complexes of 2-Benzoylpyridine N(4) Substi-
tuted Thiosemicarbazones. Spectrochim. Acta (A) 2006, 64, 637–641.
32. Raveendran, R.; Pal, S. Ruthenium(III) Complexes with N-(actyl)-Nꢁ-(5-R-
Salicylidene) Hydrazines: Synthesis, Structures and Properties. Polyhedron
2008, 27, 655–662.

64
N. THILAGAVATHI AND C. JAYABALAKRISHNAN
33. Basulia, F.; Das, A.K.; Mostafa, G.; Shie-Ming Peng, Bhattacharya,
S. Chemistry of Ruthenium with Some Phenolic Ligands: Synthe-
sis, Structure and Redox Properties. Polyhedron 2000, 19, 1663–
1672.
34. Vijayasri, K.; Rajaram, J.; Kuriacose, J.C. Ruthenium(III)-Catalysed Oxi-
dation of Secondary Alcohols by N-Methylmorpholine-N-Oxide (NMO).
J. Mol. Catal. 1987, 39, 203–217.
35. Kannan, S.; Ramesh, R. Synthesis, Characterisation, Catalytic Oxidation
and Biological Activity of Ruthenium(III) Schiff Base Complexes Derived
from 3-Acetyl-6-Methyl-2H-Pyran-2,4(3H)-Dione. Polyhedron 2006, 25,
3095–3103.
36. Bhattacharya, B.K. Homogeneous Catalysis of Epoxidation of Olefins by
Mono- and Binuclear Schiff Base Complexes. Proc. Indian Acad. Sci.
(Chem. Sci.). 1990, 102, 247–254.
37. Chatterjeea, D.; Mitra, A.; Roy, B.C. Oxidation of Organic Substrates Cat-
alyzed by a Novel Mixed-Ligand Ruthenium(III) Complex. J. Mol. Catal.
2000, 161, 17–21.
38. Durig, J.R.; Danneman, J.; Behnke, W.D.; Mercer, E.E. The Induction
of Filamentous Growth in Escherichia Coli by Ruthenium and Palladium
Complexes. Chem. Biol. Interact. 1976, 13, 287–294
39. Giraldi, T.; Sava, G.; Bertoli, G.; Mestroni, G.; Zassinovich, G. Antitumor
Action of Two Rhodium and Ruthenium Complexes in Comparison with
Cis-Diammine Dichloroplatinum(II). Cancer Research 1977, 37, 2662–
2666.
40. Sindhu Kumari, B.; Rijulal, G.; Mohanan, K. Microwave Assisted Synthe-
sis, Spectroscopic, Thermal and Biological Studies of Some Lanthanide(III)
Chloride Complexes with a Heterocyclic Schiff Base. Synth. React. Inorg.
Met-org. Chem. 2009, 39, 24–30.