Catalytic and biological activities of Ru(III) mixed ligand complexes containing N,O donor of 2-hydroxy-1-naphthylideneimines

Article abstract of DOI:10.1016/j.saa.2004.08.008

A series of stable low spin Ru(III) complexes of the type [RuX ₂(EPh₃)₂(L)] (where E = P or As; X = Cl or Br; L = mono basic bidentate Schiff bases) have been synthesized and were characterized by analytical, spectral and

Full text of DOI:10.1016/j.saa.2004.08.008

Spectrochimica Acta Part A 61 (2005) 2081–2087
Catalytic and biological activities of Ru(III) mixed ligand complexes
containing N,O donor of 2-hydroxy-1-naphthylideneimines
G. Venkatachalam, R. Ramesh∗
Department of Chemistry, Bharathidasan University, Tiruchirappalli-620 024, India
Received 19 April 2004; accepted 20 August 2004
Abstract
A series of stable low spin Ru(III) complexes of the type [RuX2(EPh3)2(L)] (where E = P or As; X = Cl or Br; L = mono basic bidentate
Schiff bases) have been synthesized and were characterized by analytical, spectral and electrochemical data. A distorted octahedral geometry
has been proposed for all the complexes. These complexes catalyze oxidation of primary alcohols and secondary alcohol with high yields in
the presence of N-methylmorpholine-N-oxide (NMO). The ruthenium(III) Schiff base complexes show growth inhibitory activity against the
bacteria Staphylococcus aureus (209p) and E. coli ESS (2231).
© 2004 Elsevier B.V. All rights reserved.
Keywords: Ruthenium(III) Schiff base complexes; Spectra; Redox properties; Catalytic oxidation; Antibacterial activity
1. Introduction
N-methylmorpholine-N-oxide and N-N-dimethylaniline-N-
oxide. Furthermore, the catalytic activities of ruthenium
complexes containing tertiaryphosphine or arsine ligands
are well established [18,19]. Chen et al. [20] have proposed
that intercalation, hydrogen bonding and ␲–␲ interaction
are some of the features implicated in the mode of action
of ruthenium complexes as antitumour and antimetastatic
agents. In addition, the presence of ruthenium halogen
bonds in several ruthenium complexes exhibiting anticancer
activity suggesting that these bonds may also play some
important role [21]. In connection with such studies and
continuation of our research on synthesis, spectral studies,
catalytic and bioactivities of ruthenium complexes with
simple and inexpensive ligands [22,23], we describe here
the synthesis, characterization and redox properties of ruthe-
nium(III) complexes containing bidentate Schiff bases along
with their reactivity towards oxidation of organic substrates
in the presence of NMO. The antibacterial activity studies
of Schiff bases and their ruthenium complexes were also
carried out. The Schiff bases were derived from condensation
of 2-hydroxy-1-naphthaldehyde with aniline, o-toluidine,
m-toluidine and p-toluidine. The following Schiff bases
(Fig. 1) were used to prepare the new ruthenium(III)
complexes.
Transition metal complexes containing oxygen and nitro-
gen donor Schiff base ligands have been of research interest
for many years [1–4], because of the versatility of their steric
and electronic properties, which can be fine tuned by choos-
ing the appropriate amine precursors and ring substituents
[5–9]. The accessibility of ruthenium higher oxidation states
[10,11] converts them into excellent candidates as catalyst for
redox reactions. Particularly, metal complexes of ruthenium
have demonstrated to be useful laboratory and industrial
homogenous catalysts in the epoxidation of alkenes and ox-
idation of alcohols using iodosylbenzene, sodiumhypochlo-
rite, hydrogen peroxide and N-methylmorpholine-N-oxide
as oxygen sources [12–15]. Further, the oxidation of organic
substrates mediated by high valent ruthenium-oxo species
evokes much interest in the modelling of cytochrome
P-450 [16]. Sharpless et al. [17] carried out a yield ori-
ented study of oxidation of cholesterol, geranial, etc.,
catalyzed by ruthenium complexes in the presence of
∗
Corresponding author. Tel.: +91 431 2407053;
fax: +91 431 2407045/2407020.
E-mail address: ramesh bdu@yahoo.com (R. Ramesh).
1386-1425/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2004.08.008

2082
G. Venkatachalam, R. Ramesh / Spectrochimica Acta Part A 61 (2005) 2081–2087
under reflux for 6 h. The reaction mixture gradually changed
to deep colour and the solvent was removed under re-
duced pressure. The residue which was precipitated by ad-
dition of pet. ether (60–80 ◦C) and was recrystallized from
CH2Cl2/pet. ether (60–80 ◦C). The compounds were dried
under vacuum (yield: 40–60%) and the purity of the com-
plexes was checked by TLC.
Fig. 1. Schiff base ligands.
2.4. Catalytic oxidation
2. Experimental
Catalytic oxidation of primary alcohols to corresponding
aldehyde and secondary alcohol to ketone by ruthenium(III)
complexes were studied in the presence of NMO as co-
oxidant. A typical reaction using the complex as a catalyst
and benzyl alcohol, cinnamyl alcohol and cyclohexanol as
substrates at 1:100 molar ratio is described as follows. A so-
lution of ruthenium complex (0.01 mmol) in 20 cm3 CH2Cl2
was added to the solution of substrate (1 mmol) and NMO
(3 mmol). The solution mixture was refluxed for 3 h and the
solvent was then evaporated from the mother liquor under
reduced pressure. The solid residue was then extracted with
pet. ether (60–80 ◦C) (20 cm3) and the ether extracts were
evaporated to give corresponding aldehyde which was then
quantified as 2,4-dinitrophenylhydrazone derivative [24].
2.1. Materials
All the reagents used were chemically pure and AR
grade. Solvents were purified and dried according to standard
procedures [24]. RuCl3·3H2O was purchased from Loba-
chemie Pvt. Ltd., and was used without further purification.
2-hydroxy-1-naphthaldehyde and N-methylmorpholine-N-
oxide were purchased from Aldrich.
2.2. Physical measurements
The analysis of carbon, hydrogen and nitrogen were
performed in Carlo-Erba 1106-model 240 perkin-Elmer
analyzer at Central Drug Research Institute (CDRI), Luc-
know, India. FT-IR spectra were recorded in KBr pellets
with a JASCO 400 plus spectrophotmeter in the range
4000–400 cm−1. A Cary 300 Bio UV–vis varian spectropho-
tometer was used to record the electronic spectra. Room tem-
perature solid state magnetic susceptibilities were measured
by using a EG and G model 155 vibrating sample magne-
tometer at IIT, Chennai. EPR spectra were recorded on JEOL
JES-FA200 EPR spectrometer at X-band frequencies for both
powder samples and solution at 278 and 77 K, respectively.
Electrochemical measurements were made using a Princeton
EG and G-PARC model potentiostat using a glassy carbon
working electrode and all the potential were referenced to Ag
/AgCl electrode. The antibacterial activity studies were car-
ried out at Quest Institute of Life sciences, Nicholas Piramal
India Ltd., Mumbai, India. Melting points were recorded with
a Boetius micro-heating table and are uncorrected. The ruthe-
nium(III) complexes [RuCl3(PPh3)3] [25], [RuCl3(AsPh3)3]
[26], [RuBr3(AsPh3)3] [27] and [RuBr3(PPh3)2(CH3OH)]
[28] were prepared according to the literature reports.
2.5. Procedure for antibacterial activity
The in vitro antibacterial activity of the free ligands and
their complexes were tested against the bacteria Staphylococ-
cus aureus (209p) and E. coli ESS (2231) by well diffusion
method using agar nutrient as the medium at 37 ◦C for 18 h.
The Schiff bases and the complexes were stored dry at room
temperature and dissolved in 10% DMSO in methanol. In a
typical procedure [29] a well was made on the agar medium
inoculated with microorganisms. Then the well was filled
with the test solutions using a micropipette and the plates
were incubated at 35 ◦C for 24 h for bacteria. During this pe-
riod, the test solutions were diffused and the growth of the
inoculated microorganisms was affected. The inhibition zone
developed on the plate was measured.
3. Results and discussion
New hexa-coordinated low spin ruthenium(III) Schiff
base complexes [RuX2(EPh3)2(L)] (L = monobasic bidentate
Schiff base ligand; E = P or As; X = Cl or Br) were synthe-
sized in good yields from the reactions of [RuX3(EPh3)] (E =
As; X = Cl or Br, E = P; X = Cl) or [RuBr3(PPh3)2(CH3OH)]
with Schiff base ligands in 1:1 molar ratio in dry benzene is
as shown in Scheme 1.
All the complexes are stable in air at room temperature,
non-hygroscopic in nature and highly soluble in common sol-
vents such as dichloromethane, acetonitrile, chloroform and
DMSO producing intense green solutions. The more solubil-
ity of the complexes is may be due to the presence of chlorides
2.3. Preparation of ruthenium(III) complexes
[RuX2(EPh3)2(L)] (L = monobasic bidentate Schiff base
ligand).
All operations were carried out under strictly anhydrous
conditions and were prepared by the following general pro-
cedure. To a benzene (20 cm3) solution of [RuX3(EPh3)3]
(0.12–0.157 g; 0.125 mmol) (E = P, X = Cl; E = As, X = Cl
or Br) or [RuBr3(PPh3)2(CH3OH)] (0.112 g; 0.125 mmol)
was added to the appropriate Schiff bases (0.030–0.032 g;
0.125 mmol)(HL1–HL4). The solution was allowed to heat

G. Venkatachalam, R. Ramesh / Spectrochimica Acta Part A 61 (2005) 2081–2087
2083
is through the phenolic oxygen atom [30,32]. This fact is
further supported by the disappearance of ␥OH in the range
3350–3450 cm−1 in all the complexes. Bands in the 550–500
and 450–400 cm−1 regions probably due to formation of
M–O and M–N bands, respectively [33]. In addition, the
Schiff base complexes show strong vibrations near 520, 695
and 740 cm−1, which are attributed to the triphenylphosphine
or triphenylarsine fragments [34].
3.2. Electronic spectra
The electronic spectra of ruthenium(III) complexes were
recorded in chloroform in the range 800–200 nm. Most of
the complexes showed two to three bands in the region
748–240 nm and are listed in Table 2. The ground state of
ruthenium(III) is 2T2g and the first excited doublet levels in
the order of increasing energy are 2A2g and 2T1g, arising from
t2g4e1g configuration. The spectral profiles below 400 nm are
very similar and are ligand-centered transitions. These bands
have been designated as ␲–␲* and n–␲* transitions for the
electrons localized on the azomethine group of the Schiff
base ligands [35]. In most of the ruthenium(III) complexes
Scheme 1.
or bromides. The analytical data are listed in Table 1 and are
in good agreement with the general molecular formula pro-
posed for all the complexes.
the charge transfer bands of the type L → T2g are promi-
3.1. IR spectra
␲y
nent in the low energy region, which obscures the weaker
bands due to d–d transitions [30]. It is therefore difficult to
assign conclusively the bands of ruthenium(III) complexes
that appear in the visible region. However, the extinction co-
efficient for the bands in the 748–640 nm region are found
to be very low as compared to that of charge transfer bands.
Hence, the bands around 748–640 nm have been assigned to
The IR spectra displayed high intensity bands in the re-
gion 1620–1626 cm−1 for free ligands (HL1–HL4) are due
to ␥(C
vibration mode. These bands shifted to the lower
N)
frequency in the range 1596–1617 cm−1 on complexation
indicating coordination of the azomethine nitrogen to the
metal atom [30,31] and this lowering may be attributed to
the decrease in electron density at azomethine group. A
strong band observed at ca. 1314–1326 cm−1 in the ligands
(HL1–HL4) has been assigned to phenolic C–O stretching.
On coordination, this band shifts to higher frequency in the
range 1334–1340 cm−1 showing that the other coordination
2
2T2g → A2g transition which is in conformity with assign-
ment made for similar octahedral ruthenium(III) complexes
[36–38]. The pattern of the electronic spectra of all the com-
plexes indicates the presence of an octahedral environment
around ruthenium(III) ion.
Table 1
Analytical data of Ru(III) Schiff base complexes
Complexes
Colour
m.p (◦C)a
Found (calcd.) %
C
H
N
[RuCl2(PPh3)2(L1)]
[RuCl2(AsPh3)2(L1)]
[RuBr2(AsPh3)2(L1)]
[RuBr2(PPh3)2(L1)]
[RuCl2(PPh3)2(L2)]
[RuCl2(AsPh3)2(L2)
[RuBr2(AsPh3)2(L2)]
[RuBr2(PPh3)2(L2)]
[RuCl2(PPh3)2(L3)]
[RuCl2(AsPh3)2(L3)]
[RuBr2(AsPh3)2(L3)]
[RuBr2(PPh3)2(L3)]
[RuCl2(PPh3)2(L4)]
[RuCl2(AsPh3)2(L4)]
[RuBr2(AsPh3)2(L4)]
[RuBr2(PPh3)2(L4)]
Green
Green
Green
Green
Green
Green
Green
Green
Green
Green
Green
Green
Green
Green
Green
Green
149
185
124
188
133
128
139
162
180
122
133
129
136
141
151
178
67.04 (67.64)
61.57 (61.85)
56.84 (56.21)
61.39 (61.69)
67.48 (67.91)
62.77 (62.10)
57.51 (57.19)
62.43 (62.0)
67.47 (67.91)
62.59 (62.17)
57.81 (57.19)
62.56 (62.0)
67.33 (67.91)
62.41 (62.17)
57.63 (57.19)
62.66 (62.08)
4.33 (4.46)
4.21 (4.08)
4.04 (3.75)
4.18 (4.07)
4.01 (4.61)
3.73 (4.22)
3.23 (3.88)
4.73 (4.21)
4.47 (4.61)
4.38 (4.22)
3.23 (3.88)
4.58 (4.21)
4.89 (4.61)
4.71 (4.22)
3.27 (3.88)
4.71 (4.21)
1.31 (1.49)
1.27 (1.36)
1.42 (1.25)
1.61 (1.35)
1.66 (1.46)
1.48 (1.34)
1.56 (1.23)
1.23 (1.33)
1.63 (1.46)
1.27 (1.34)
1.59 (1.23)
1.54 (1.33)
1.31 (1.46)
1.67 (1.34)
1.23 (1.65)
1.57 (1.33)
a
Decomposition point.

2084
G. Venkatachalam, R. Ramesh / Spectrochimica Acta Part A 61 (2005) 2081–2087
Table 2
IR and electronic spectral data of the Ru(III) Schiff base complexes.
Complexes
γC=N (cm−1
)
γC–O (cm−1
)
λmax (␧)dm3 mol−1 cm−1
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
∗
1615
1616
1616
1614
1597
1597
1596
1597
1598
1617
1598
1599
1616
1616
1597
1616
1337
1340
1334
1338
1335
1335
1336
1333
1335
1335
1335
1337
1334
1335
1335
1334
405(2216)a, 320(3764)a
640(400)*, 420(1200)a, 318(1800)c, 242(4900)b
422(1358)a, 312(2283)c, 234(10723)b
440(3852)a, 316(8640)c, 240(13,680)b
418(3644)a, 314(7142)c, 246(15648)b
748(1500)*, 417(2400)a, 312(8130)c, 259(14090)b
742(269)*, 568(262)*, 316(5020)a, 272(8786)b
522(1262)a, 318(5307)c, 263(9048)c
722(1719)*, 410(3556)a, 322(5648)a, 272(16736)b
415(7920)a, 316(18530)c, 288(25070)b
554(2328)a, 320(6276)c, 258(12768)b
732(191)*, 415(6690)a, 314(14400)c, 270(25000)b
540(3760)a, 318(8260)c, 268(16,122)b
740(890)*, 422(2870)a, 312(12320)c, 276(18220)b
560(2680)a, 416(3840)a, 318(11350)c, 264(20760)b
412(4060)a, 316(9265)c, 281(14085)b
d–d transition.
a
b
c
Charge transfer.
␲–␲*.
n–␲*.
3.3. Magnetic moment and EPR spectra
in structure and to metal ligand covalency. The EPR spec-
tra of all the complexes exhibit a characteristic of an axially
symmetric system with g around 2.12–2.46 and g around
1.91–2.27. For an octahedral field with tetragonal distortion
gx = gy = gz and hence two ‘g’ values indicate tetragonal
distortion in these complexes. A representative spectrum of
complex [RuBr2(PPh3)2(L1)] is displayed in Fig. 2. Overall
the position of lines and nature of the EPR spectra of the
The room temperature magnetic moments for some
of the complexes were measured and the values
for [RuBr2(AsPh3)2(L2)], [RuCl2(PPh3)2(L3)] and
[RuBr2(PPh3)2(L4)] are 1.74, 1.76 and 1.66 BM, re-
spectively. These values correspond to one unpaired electron
suggesting a low spin t52g configuration for the ruthenium(III)
ion in an octahedral environment.
⊥
||
The solid state EPR spectra of the complexes were
recorded in X-band frequencies at room temperature and the
‘g’ values are given in Table 3. The low spin d5 configura-
tion is a good probe of molecular structure and bonding since
the observed ‘g’ values are very sensitive to small changes
Table 3
EPR data of Ru(III) Schiff base complexes
*
Complexes
gx
gy
gz
ꢀgꢁ
1
2
3
4
5
6
7
8
9
2.27
2.31
2.46
2.12
2.36
2.26
2.38
2.24
2.46
2.42
2.38
2.26
2.13
2.22
2.24
2.45
2.27
2.31
2.46
2.12
2.36
2.26
2.38
2.24
2.46
2.42
2.38
2.26
2.13
2.22
2.24
2.45
1.96
2.12
2.27
2.00
2.21
1.98
2.02
2.06
2.23
2.16
2.21
2.01
1.91
2.08
2.07
2.20
2.16
2.24
2.36
2.08
2.31
2.16
2.26
2.18
2.38
2.33
2.32
2.17
2.05
2.17
2.18
2.37
10
11
12
13
14
15
16
ꢀ
ꢁ1/2
1
3
1
ꢀgꢁ∗
=
13 g2x + g2y + g2z
.
3
Fig. 2. EPR spectrum of [RuBr2(PPh3)2(L1)].

G. Venkatachalam, R. Ramesh / Spectrochimica Acta Part A 61 (2005) 2081–2087
2085
Table 4
Electrochemical data of Ru(III) Schiff base complexes
Complexes
RuIII/RuIV
RuIII/RuII
Epa (V)
Epc (V)
E1/2 (V)
Ep (mV)
80
Epa (V)
Epc (V)
E1/2 (V)
Ep (mV)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
0.85
0.68
0.73
0.60
0.73
0.70
0.89
0.79
0.66
0.73
0.66
0.54
0.59
0.62
0.56
0.82
0.93
0.61
0.64
0.53
0.65
0.64
0.83
0.68
0.72
0.79
0.78
0.61
0.52
0.56
0.48
0.73
0.89
0.64
0.68
0.56
0.69
0.67
0.86
0.73
0.69
0.65
0.72
0.57
0.55
0.59
0.52
0.77
−0.21
−0.19
−0.16
−0.17
−0.21
−0.16
−0.20
−0.12
−0.28
−0.18
−0.22
−0.13
−0.43
−0.20
−0.34
−0.11
−0.27
−0.27
−0.23
−0.25
−0.25
−0.25
−0.27
−0.20
−0.40
−0.27
−0.30
−0.20
−0.49
−0.26
−0.43
−0.19
−0.24
−0.23
−0.19
−0.21
−0.25
−0.20
−0.23
−0.16
−0.34
−0.22
−0.26
−0.16
−0.46
−0.23
−0.38
−0.15
60
70
90
70
80
60
60
110
60
70
120
70
70
60
80
90
80
70
80
80
90
70
80
120
90
80
70
60
60
90
80
Supporting electrolyte: [NBu4](ClO4) (0.05M); concentration of the complex: 0.001 M; scan rate: 100 mV s−1
.
complexes are characteristic of low spin ruthenium(III) oc-
tahedral complexes [30,38,39].
indicates that the electron transfer is reversible and the mass
transfer is limited. It has been observed that some of the
complexes show quasireversible ( EP = 90–120 mV) redox
processes which did not change with change in scan rates,
supporting reversibility [42]. The electron donating group
(–CH3) ability of the substituent on the phenyl ring of the
Schiff base favored oxidation of RuIII to RuIV [43].
3.4. Electrochemical study
The redox properties of all the complexes were inves-
tigated in acetonitrile solution by cyclic voltammetry and
the redox processes are metal centered only (Table 4).
Cyclic voltammogram of all the complexes (1 × 10−3 M)
exhibit a reversible oxidation and reversible reduction
peaks at the scan rate 100 mV s−1. A representative cyclic
votammogram of [RuBr2(PPh3)2(L1)] is shown in Fig. 3.
All the complexes showed well-defined waves in the
range (E1/2) +0.52 to +0.89 V (RuIV/RuIII) and −0.15 to
−0.46 V (RuIII/RuII) versus Ag/AgCl. The redox processes
are reversible with peak-to-peak separation ( Ep) values
ranging from 60–80 mV corresponding to one-electron
process [40,41]. For scan rate 100 mV s−1, the ratio ip/SR
(ip = peak current; SR = scan rate) was approximately one,
the peak separation being independent of the scan rate. This
[RuIIIX2(EPh3)2(L)] ꢀ [RuIVX2(EPh3)2(L)]+ + e−
There is not much variation due to replacement of chlo-
rides by bromides and triphenylphosphine by arsine. Hence,
from the electrochemical data it is clear that the present ligand
system is ideally suitable for stabilizing the higher oxidation
state of ruthenium ion [30].
4. Catalytic activity
Catalytic oxidation of primary alcohols and secondary al-
cohol by some of the synthesized ruthenium(III) Schiff base
complexes were carried out in CH2Cl2 in the presence of
NMO and the results are summarized in Table 5. The oxi-
dation was performed at room temperature in CH2Cl2 from
which water was removed using powdered molecular sieves.
All complexes oxidize primary alcohol to the corresponding
aldehyde and secondary alcohol to ketone with high yield.
The aldehyde or ketone formed after 3 h of reflux were quanti-
fied as their 2,4-dinitrophenylhydrazone derivatives and there
was no detectable oxidation in the absence of ruthenium com-
plexes. Results of present investigation suggest that the com-
plexes are able to react efficiently with NMO to yield a high
valent ruthenium-oxo species [44], capable of oxygen atom
transfer to alcohols. This was further supported by spectral
changes that occur by addition of NMO to a dichloromethane
solution of the ruthenium(III) complexes. The appearance
Fig. 3. Cyclic voltammogram of [RuBr2(PPh3)2(L1)].

2086
G. Venkatachalam, R. Ramesh / Spectrochimica Acta Part A 61 (2005) 2081–2087
Table 5
Table 6
Catalytic oxidation of alcohols by ruthenium complexes/NMO
Antibacterial data of Ru(III) Schiff base complexes
Complex
1
Substrate
Product
Yielda (%)
Complex
Diameter of inhibition zone (mm)
Benzyl alcohol
Cinnamyl alcohol
Cyclohexanol
Benzyl alcohol
Cinnamyl alcohol
Cyclohexanol
Benzyl alcohol
Cinnamyl alcohol
Cyclohexanol
Benzyl alcohol
Cinnamyl alcohol
Cyclohexanol
Benzyl alcohol
Cinnamyl alcohol
Cyclohexanol
Benzyl alcohol
Cinnamyl alcohol
Cyclohexanol
Benzyl alcohol
Cinnamyl alcohol
Cyclohexanol
A
A
K
A
A
K
A
A
K
A
A
K
A
A
K
A
A
K
A
A
K
65.0
88.4
24.4
95.5
98.0
8.6
Stap. aureus (209p) (50 ␮l)
E. Coli ESS (2231) (50 ␮l)
HL1
1
3
4
HL2
6
7
HL3
9
11
HL4
13
16
–
–
14
14
15
–
15
16
17
–
2
3
61.9
84.8
22.8
63.0
79.6
28.0
61.5
95.5
22.2
82.6
89.3
28.3
90.3
92.0
32.8
16
18
–
15
17
–
4
15
17
–
15
18
–
7
11
13
15
17
– denotes no activity.
8
13
coli ESS (2231) at minimum concentration and the results
are shown in Table 6. The results indicate that the complexes
show more activity and the ligands do not have any activity
against same microbes under identical experimental condi-
tions. This would suggest that the chelation could facilitate
the ability of a complex to cross a cell membrane [48] and can
be explained by Tweedy’s chelation theory [49]. Chelation
considerably reduces the polarity of the metal ion because
of partial sharing of its positive charge with donor groups
and possible ␲-electron delocalization over the whole chelate
ring. Such a chelation could enhance the lipophilic charac-
ter of the central metal atom, which subsequently favors its
permeation through the lipid layer of the cell membrane. The
variation in the effectiveness of different compounds against
different organisms depends either on the impermeability of
the cells of the microbes or on differences in ribosome of mi-
crobial cells. Though the complexes of this type were found
to have potential antibacterial activity against the bacterial
microbes, it could not reach the effectiveness of the conven-
tional bacterial control Ampicillin.
A or K = corresponding aldehyde or ketone.
a
Yield based on substrate; alcohol (1 mmol); NMO (3 mmol); catalyst
(0.01 mmol).
of the peak at 390 nm is attributed to the formation of high
Ru(V)-oxo species which is in conformity with other oxo-
ruthenim(V) complexes [44,45]. Further, support in favor of
the formation of such species identified from the IR spectrum
of solid mass (obtained by evaporation of resultant solution
to dryness), which showed a band at 860 cm−1, characteristic
of ruthenium(V)-oxo species [43,44,46].
The relatively higher yield for oxidation of cinnamyl alco-
hol than benzyl alcohol or cyclohexanol is due to the presence
of ␣-CH unit in cinnamyl alcohol, which is more acidic than
benzyl alcohol or cyclohexanol. Unsaturated alcohol like cin-
namyl alcohol is selectively oxidized at the alcoholic group
with high yield without competing double bond. This is an
important characteristic of ruthenium/NMO system. It has
been observed that these ruthenium(III) Schiff base com-
plexes have better catalytic efficiency in the case of oxida-
tion of benzyl alcohol, cinnamyl alcohol and cyclohexanol
when compared to the earlier report [43,45–47] on similar
ruthenium complexes as catalysts in the presence of NMO/t-
BuOOH. Hence, it is relevant from the cyclic voltammetric
data that the oxidation effected by catalysts is likely to occur
via ruthenium higher oxidation states, which is easily acces-
sible through chemical oxidation with co-oxidants like NMO,
t-BuOOH, PhIO, etc. [18,47].
Acknowledgement
The authors express their sincere thanks to Council of
Scientific and Industrial Research (CSIR), New Delhi [Grant
No. 01(1725)/02/EMR-II] for financial support. One of the
authors (G.V.) thanks CSIR for the award of Senior Research
Fellowship (SRF).
References
5. Antibacterial activity
[1] R.D. Archu, B. Wang, Inorg. Chem. 29 (1990) 39.
[2] S. Chang, L. Jones, C.M. Henling, R.H. Grubbs, Organometallics 17
(1998) 3460.
[3] S. Yamada, Coord. Chem. Rev. 190 (1999) 537.
[4] B. De Clereq, F. Verpoort, Macromolecules 35 (2002) 8943.
The in vitro cytotoxicity of ligands and the complexes
were screened in vitro in order to evaluate activity against
two microbes namely bacteria Stap. aureus (209p) and E.

G. Venkatachalam, R. Ramesh / Spectrochimica Acta Part A 61 (2005) 2081–2087
2087
[5] A. Berkessel, M. Franvenkon, T. Schwenkreis, J. Steinmetz, J. Mol.
Catal. A: Chem. 117 (1997) 39.
[27] K. Natarajan, R.K. Poddar, U. Agarwala, J. Inorg. Nucl. Chem. 39
(1977) 431.
[6] B. De Clereq, F. Verpoort, Adv. Synth. Catal. 34 (2002) 639.
[7] T. Opstal, F. Verpoort, Synlett 6 (2002) 935.
[8] T. Opstal, F. Verpoort, Angew Chem. Int. Ed. 42 (2003) 2876.
[9] B. De Clereq, F. Lefebvre, F. Verpoort, Appl. Catal. A 247 (2003)
345.
[10] A. Llobet, D.J. Hodgson, T.J. Meyer, Inorg. Chem. 29 (1990)
3760.
[11] A. Llobet, Inorg. Chim. Acta 221 (1994) 125.
[12] J.R. Thronback, G. Wilkinson, J. Chem. Soc., Dalton Trans. (1978)
110.
[28] T.A. Stephenson, G. Wilkinson, J. Inorg. Nucl. Chem. 28 (1966)
954.
[29] M.J. Pelczar, E.C.S. Chan, N.R. Krieg, Microbiology, 5th ed.,
Mcgraw-Hill, New York, 1998.
[30] R. Ramesh, S. Maheswaran, J. Inorg. Biochem. 96 (2003) 457.
[31] S.N. Pal, S. Pal, J. Chem. Soc., Dalton Trans. (2002) 2102.
[32] B. Khera, A.K. Sharma, N.K. Kaushik, Polyhedron 2 (1983) 1177.
[33] K. Nakamato, Infrared and Raman Spectra of Inorganic and Coor-
dination Compounds, Wiley Interscience, New York, 1971.
[34] A.K. Das, S.M. Peng, S. Bhattacharya, J. Chem. Soc., Dalton Trans.
(2000) 181.
[13] T. Katsuki, Coord. Chem. Rev. 140 (1995) 189.
[14] I. Claustro, G. Abali, E. Sanchez, J.H. Acquaye, Inorg. Chim. Acta
342 (2003) 29.
[35] K. Chichak, U. Jacquemard, N.R. Brande, Eur. J. Inorg. Chem.
(2002) 357.
[15] A.R. Silva, C. Freire, B. Castro, New J. Chem. 28 (2004) 253.
[16] B. Meunier, Chem. Rev. 92 (1992) 1411.
[17] K.B. Sharpless, K. Akashi, K. Oshima, Tetrahedron Lett. 29 (1976)
2503.
[18] W.H. Leung, C.M. Che, Inorg. Chem. 28 (1989) 4619.
[19] W.K. Wong, X.P. Chen, J.P. Gao, Y.G. Chi, W.X. Pan, W.Y. Wang,
J. Chem. Soc., Dalton Trans. (2002) 113.
[20] H. Chen, J.A. Parkinson, S. Parsons, R.A. Coxall, R.O. Gould, P.J.
Sadler, J. Am. Chem. Soc. 124 (2002) 3064.
[21] P.M.T. Piggot, L.A. Hall, A.J.P. White, D.J. Williams, Inorg. Chim.
Acta 357 (2004) 207.
[22] R. Ramesh, Inorg. Chem. Comm. 7 (2004) 274.
[23] R. Ramesh, M. Sivagamasundari, Synth. Reac. Inorg. Met. Org.
Chem. 33 (2003) 899.
[24] A.I. Vogel, Test Book of Practical Organic Chemistry, 5th ed., Long-
man, London, 1989.
[25] J. Chatt, G.J. Leigh, D.M.P. Mingos, R.J. Paske, J. Chem. Soc. A
(1968) 2636.
[26] R.K. Poddar, I.P. Khullar, U. Agarwala, J. Inorg. Nucl. Chem. Lett.
10 (1974) 221.
[36] K. Natarajan, U. Agarwala, Bull. Chem. Soc., Jpn. 49 (1976) 2877.
[37] A.B.P. Lever, Inorganic Electronic Spectroscopy, 2nd ed., Elsevier,
New York, 1984.
[38] M.M.T. Khan, D. Srinivas, R.I. Khureshy, N.H. Khan, Inorg. Chem.
29 (1990) 2320.
[39] O.K. Medhi, U. Agarwala, Inorg. Chem. 19 (1980) 1381.
[40] A.M. El-Hendawy, M.S. El-shahawi, Polyhedron 8 (1989) 2813.
[41] Z. Shirin, R.N. Mukhergee, Polyhedron 11 (1992) 2625.
[42] J. Chakravarthy, S. Bhatacharya, Polyhedron 13 (1994) 2671.
[43] M.S. El-Shahawi, A.F. Shoair, Spectrochim. Acta A 60 (2004) 121.
[44] M.M.T. Khan, C. Sreelatha, S.A. Mirza, G. Ramachandriah, S.H.R.
Abdi, Inorg. Chim. Acta 154 (1988) 102.
[45] A.S. Goldstein, R.S. Drago, J. Chem. Soc. Chem. Comm. (1991) 21.
[46] D. Chattergee, A. Mitra, B.C. Roy, J. Mol. Catal. A: Chem. 161
(2000) 17.
[47] A.M. El-Hendawy, A.H. Alkubaisi, A.E. Kourashy, M.M. Shanab,
Polyhedron 12 (1993) 2343.
[48] C.S. Allardyce, P.J. Dyson, D.J. Ellis, P.A. Salter, J. Organomet.
Chem. 668 (2003) 35.
[49] B.G. Tweedy, Phytopathalogy 55 (1964) 910.