Binuclear ruthenium(II) carbonyl schiff base complexes containing N 2O2 donors and their catalytic and biological activities

Article abstract of DOI:10.1080/15533174.2010.522883

An interesting series of binuclear ruthenium(II) Schiff base complexes of the type [RuCl(CO)(EPh₃)₂(B)]₂L (where E=P/As; B=PPh₃/AsPh₃/Py; L=binucleating monobasic bidendate Schiff base ligand) have been synthesized by reacting [RuCl(CO)(EPh₃) ₂(B)]₂ with Schiff bases derived from acetoacetanilide and salicylaldehyde/o-hydroxyacetophenone/o-vanillin/2-hydroxy-1-naphthaldehyde with benzene. The complexes were characterized by analytical, spectroscopic, and electrochemical measurements. The new diamagnetic ruthenium(II) complexes have N₂O₂ metal binding sites, which are linked to each other with a biphenyl bridge and act as potential catalyst for the oxidation of wide range of primary and secondary alcohols to corresponding aldehydes and ketones in the presence of molecular oxygen and also in C-C coupling reactions. Further, the antibacterial properties of the free ligands and their metal complexes were evaluated against certain bacteria such as Escherichia Coli and Staphylococcus aureus. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/15533174.2010.522883

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Binuclear Ruthenium(II) Carbonyl Schiff Base
Complexes Containing N2O2 Donors and their
Catalytic and Biological Activities
Nagarajan Sathya a , Gunasekaran Raja a & Chinnasamy Jayabalakrishnan a
a Post Graduate and Research Department of Chemistry, Sri Ramakrishna Mission
Vidyalaya College of Arts and Science, Coimbatore, Tamil Nadu, India
Available online: 02 Feb 2011
To cite this article: Nagarajan Sathya, Gunasekaran Raja & Chinnasamy Jayabalakrishnan (2011): Binuclear Ruthenium(II)
Carbonyl Schiff Base Complexes Containing N2O2 Donors and their Catalytic and Biological Activities, Synthesis and
Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 41:1, 81-90
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 41:81–90, 2011
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2010.522883
Binuclear Ruthenium(II) Carbonyl Schiff Base Complexes
Containing N2O2 Donors and their Catalytic and Biological
Activities
Nagarajan Sathya, Gunasekaran Raja, and Chinnasamy Jayabalakrishnan
Post Graduate and Research Department of Chemistry, Sri Ramakrishna Mission Vidyalaya College
of Arts and Science, Coimbatore, Tamil Nadu, India
coordination chemistry. Such species occupy an important po-
sition in modern inorganic chemistry.[5,6] Much research works
have been published concerning the use of Schiff base ligands,
which incorporate nitrogen imine, and phenolate donors seems
appropriate synthesizing ruthenium complexes capable of ox-
idizing organic substrates.[7,8] Schiff base complexes of tran-
sition metals[9] having O and N donor atoms have shown an
exponential increase as inorganic catalysts for various organic
transformations. Furthermore, binuclear complexes have been
found to be better catalysts than mononuclear complexes.[10]
Also, transition metalphosphine/arsine complexes, especially
ruthenium complexes, find application in classical catalytic pro-
cesses such as hydrogenation, isomerization, decarboxylation,
reductive elimination, oxidative addition, and in making C C
bonds.[11] The incorporation of binucleating Schiff base ligand
into ruthenium tertiary phosphine/arsine complexes was initially
aimed at promoting activity of such species towards oxidation
of alcohols. Selective oxidation of alcohols to aldehydes and
ketones is a key reaction in organic synthesis. The development
of new products that can use air or molecular oxygen as oxidant
is certainly more attractive than other traditional methods that
are environmentally damaging.[12]
Metal ions in ligand-bridged binuclear complexes have
gained an importance due to the intramolecular electron transfer
processes that find utility in the design of photochemical molec-
ular devices[10] or as bio-mimetic model of the photosynthetic
systems in biology.[13] Bimetallic coordination complexes have
numerous applications, such as in the treatment of cancer,[14] as
antibacteriocide agents,[15] as antiviral agents,[16] and for other
biological properties.[17] Chelation causes drastic changes in the
biological properties of a ligand and also the metal moiety.
As part of our systematic study on ligand-bridged binuclear
ruthenium complexes, we describe the synthesis and characteri-
zation of a series of new class of binuclear ruthenium(II) Schiff
base complexes along with their catalytic and biological activ-
ity. The following binucleating Schiff base ligands (Scheme 1)
containing N2O2 type bidentate compartments were used to
synthesize a new series of binuclear ruthenium(II) Schiff base
complexes.
An interesting series of binuclear ruthenium(II) Schiff
base complexes of the type [RuCl(CO)(EPh3)2(B)]2L (where
E P/As; B PPh3/AsPh3/Py; L binucleating monobasic biden-
date Schiff base ligand) have been synthesized by reacting
[RuCl(CO)(EPh3)2(B)]2 with Schiff bases derived from acetoac-
etanilide and salicylaldehyde/o-hydroxyacetophenone/o-vanillin/2-
hydroxy-1-naphthaldehyde with benzene. The complexes were
characterized by analytical, spectroscopic, and electrochemical
measurements. The new diamagnetic ruthenium(II) complexes
have N2O2 metal binding sites, which are linked to each other with
a biphenyl bridge and act as potential catalyst for the oxidation of
wide range of primary and secondary alcohols to corresponding
aldehydes and ketones in the presence of molecular oxygen and also
in C C coupling reactions. Further, the antibacterial properties of
the free ligands and their metal complexes were evaluated against
certain bacteria such as Escherichia Coli and Staphylococcus
aureus.
Keywords antibacterial activity, binucleating ligand, binuclear ruthe-
nium(II) complex, catalytic activity, electrochemistry
INTRODUCTION
The coordination chemistry of binuclear transition metal
complexes has received much attention in recent years.[1,2] Tran-
sition metal complexes, with bidentate ligands containing both
the hard and soft donor groups, have been used extensively
in coordination and organometallic chemistry. The majority of
such ligands are functionalized phosphines where the phospho-
rus is a soft donor and either oxygen or nitrogen is the hard
donor.[3,4] Currently, a considerable effort is being invested in
the development of new chelating ligands; particularly, the bin-
ucleating imino ligands are versatile and they exhibit very rich
Received 21 July 2010; accepted 18 August 2010.
One of the authors, N. Sathya, expresses her sincere thanks to
University Grants Commission (UGC), New Delhi [RGN-SRF No. F.
16-740 (SC)/2007 (SA-III)] for financial support.
Address correspondence to Chinnasamy Jayabalakrishnan, Post
Graduate and Research Department of Chemistry, Sri Ramakrishna
Mission Vidyalaya College of Arts and Science, Coimbatore – 641020,
Tamil Nadu, India. E-mail: drcjbstar@gmail.com
81

82
N. SATHYA ET AL.
an hour and then refluxed for about 6 hrs. The resultant product
was washed with methanol and the purity of the ligands was
checked by TLC.
Synthesis of Binuclear Ruthenium(II) Schiff Base
Complexes
All the reactions were carried out under the strictly anhydrous
condition. The monobasic bidentate Schiff bases (0.04–0.05 g;
0.1 mmol) were added to a solution of [RuHCl(CO)(EPh3)2(B)],
(E P/As; B PPh3/AsPh3/Py) in 2:1 molar ratio in ben-
zene/chloroform (50 mL) mixture, and then refluxed for 6 hrs.
The resulting compound was precipitated by the addition of
small quantity of petroleum ether (60–80◦C). The complexes
were then filtered off, washed with petroleum ether, and recrys-
tallized from CH2Cl2/petroleum ether and dried under vacuo.
SCH. 1. Keto-enol tautomerism of the Schiff base ligands.
RESULTS AND DISCUSSION
A new series of binuclear ruthenium(II) Schiff base
complexes of the type [RuCl(CO)(EPh3)2(B)]2L (E P/As;
B PPh3/AsPh3/Py; L monobasic bidentate Schiff base lig-
ands) were achieved by reacting binuclear ruthenium(II) pre-
cursors [RuHCl(CO)(EPh3)2(B)] with monobasic bidentate
Schiff base ligands in 2:1molar ratio, respectively, in ben-
zene/chloroform mixture (Scheme 2).
The synthesized binuclear ruthenium(II) Schiff base com-
plexes are stable in air at room temperature, non-hygroscopic
in nature, and soluble in common solvents such as
dichloromethane, chloroform, acetonitrile, benzene, and THF.
The analytical data of the complexes are in good agreement
with the calculated values thus confirming the proposed binu-
clear composition for all the complexes (Table 1).
EXPERIMENTAL
Materials and Physical Measurements
All the chemicals used were chemically pure and AR grade.
Solvents were purified and dried according to the standard
procedure.[18] RuCl3.3H2O was purchased from Loba Chemie
and was used without any further purification. The carbon, hy-
drogen, nitrogen, and sulphur analyses were performed on a
Vario EL III CHNS analyzer at Cochin University of Science
and Technology, Kerala, India. IR spectra were recorded as KBr
pellets in the 400–4000 cm−1 region using a Perkin Elmer FT-
IR 8000 spectrophotometer. Electronic spectra were recorded
in dichloromethane solution with a Systronics double beam
1
UV-Vis spectrophotometer 2202 in the range 200–800 nm. H
NMR and 13C NMR spectra were recorded on a Bruker 400
MHZ instrument using TMS as an internal reference. 31P NMR
spectra were recorded on a Bruker 400 MHZ instrument using
ortho phosphoric acid as an internal reference. Electrochemi-
cal studies were carried out on a BAS CV-50 electrochemical
analyzer in dichloromethane solution by using a glassy carbon
working electrode and [NBu4]ClO4 was used as a supporting
electrolyte. Melting points were recorded on a Veego VMP-DS
model heating table and were uncorrected. The starting com-
plexes [RuHCl(CO)(PPh3)3],[19] [RuHCl(CO)(AsPh3)3],[20] and
[RuHCl(CO)(PPh3)2(Py)][21] were prepared according to the
reported procedures. Catalytic oxidation,[22] aryl-aryl coupling
experiments,[23] and antibacterial activities[24] were carried out
by using reported literature methods.
IR Spectroscopy
The important IR absorption bands for the synthesized
complexes are shown in Table 2. The observed bands may
be classified into those originating from the ligands and
those arising from the bands formed between ruthenium(II)
metal ion and the coordinating sites. A strong band observed
around 1700 cm−1 in the free Schiff base ligands due to νC
O
completely disappeared on complexation. This may be due to
the enolization and subsequent coordination through the de-
protonated enolised oxygen atom.[25] The azomethine nitrogen
νC
stretching frequency of the free ligands (H2L1-H2L4)
N
appears at 1618–1621 cm−1, which has been shifted to lower
frequency in the range 1592–1606 cm−1 in accordance with
the coordination of the azomethine function to the metal ion for
all complexes.[26,27] This lowering frequency may be attributed
to the decrease in electron density on the nitrogen atom of the
Preparation of Binucleating Mono Basic Bidentate Schiff
Base Ligands
To
a methanolic solution of benzidine (10 mmol) azomethine group. In all the complexes, the bands in the region
salicylaldehyde/o-hydroxyacetophenone/o-vanillin/2-hydroxy- 1460–1531 cm−1 have been assigned to the mixed vibrational
[28]
1-naphthaldehyde (10 mmol) was added and kept for stirring. mode arising from νC
and νC
.
C
A medium band corre-
N
Then to the above stirring solution of acetoacetanilide sponding to phenolic oxygen νC−O is observed at 1250–1283
(10 mmol) was added. The mixture was stirred for about half cm−1 for the free ligands, respectively. On complexation, this

BINUCLEAR RUTHENIUM(II) SCHIFF BASE COMPLEXES
83
SCH. 2. Structure of binuclear ruthenium(II) Schiff base complexes.
1938–1957 cm−1 due to terminally coordinated free carbonyl
band is shifted to higher frequency in the range 1309–1322
cm−1 for all the ruthenium(II) Schiff base complexes.[29] This
is further supported by the disappearance of the νOH in the
range 3027–3412 cm−1 in all the complexes. For all the new
complexes, the IR spectra showed a strong band in the region
group. For the complexes {[RuCl(CO)(PPh3)(Py)]2L1},
{[RuCl(CO)(PPh3)(Py)]2L2},
{[RuCl(CO)(PPh3)(Py)]2L3}
and {[RuCl(CO)(PPh3)(Py)]2L4}, the IR spectra showed
a medium intensity band in the region 1027–1028 cm−1
,
TABLE 1
Analytical data for binuclear ruthenium(II) Schiff base complexes
Calculated (found) (%)
Ligands and complexes
Color
Melting point (◦C)
C
H
N
H2L1
Yellow
Yellow
Orange
Orange
Black
Green
Green
Black
128
130
125
126
136
134
144
172
138
164
154
137
164
142
139
155
77.83 (77.86)
78.09 (78.02)
75.45 (75.40)
79.65 (79.67)
67.84 (67.86)
61.87 (61.83)
63.46 (63.41)
67.97 (67.93)
62.04 (62.01)
63.67 (63.63)
67.39 (67.34)
61.55 (61.51)
63.03 (63.06)
68.59 (68.54)
62.70 (62.73)
64.54 (64.52)
5.63 (5.60)
5.89 (5.83)
5.69 (5.64)
5.46 (5.42)
4.59 (4.54)
4.18 (4.16)
4.36 (4.31)
4.66 (4.63)
4.26 (4.28)
4.45 (4.47)
4.62 (4.65)
4.22 (4.20)
4.34 (4.37)
4.57 (4.59)
4.18 (4.17)
4.35 (4.39)
9.39 (9.37)
9.10 (9.13)
8.79 (8.75)
8.44 (8.40)
2.30 (2.31)
2.10 (2.14)
4.81 (4.82)
2.29 (2.32)
2.09 (2.07)
4.76 (4.73)
2.27 (2.24)
2.07 (2.05)
4.71 (4.74)
2.24 (2.21)
2.05 (2.03)
4.65 (4.63)
H2L2
H2L3
H2L4
{[RuCl(CO)(PPh3)2]2L1}
{[RuCl(CO)(AsPh3)2]2L1}
{[RuCl(CO)(Py)(PPh3)]2L1}
{[RuCl(CO)(PPh3)2]2L2}
{[RuCl(CO)(AsPh3)2]2L2}
{[RuCl(CO)(Py)(PPh3)]2L2}
{[RuCl(CO)(PPh3)2]2L3}
{[RuCl(CO)(AsPh3)2]2L3}
{[RuCl(CO)(Py)(PPh3)]2L3}
{[RuCl(CO)(PPh3)2]2L4}
{[RuCl(CO)(AsPh3)2]2L4}
{[RuCl(CO)(Py)(PPh3)]2L4}
Brown
Black
Green
Brown
Green
Green
Orange
Green

84
N. SATHYA ET AL.
TABLE 2
IR and electronic data of binuclear ruthenium(II) Schiff base complexes
FT-IR cm−1
Ligands and complexes
ν(C=N)
ν(Ph−C−O)
ν(C=N+C=CH)
ν(CꢀO)
ν(Py)
UV-Vis λmax (nm)
H2L1
1618
1620
1621
1621
1605
1606
1604
1600
1603
1592
1600
1594
1602
1601
1600
1601
1283
1273
1280
1250
1322
1322
1312
1312
1310
1311
1312
1309
1312
1310
1309
1310
—
—
—
—
—
—
—
—
—
—
—
—
—
—
1028
—
—
1028
—
—
1028
—
—
1027
304, 368, 411
302, 369, 390, 411
304, 368, 414
305, 368, 412, 444, 483
256, 291, 442
256,292, 366, 389
256, 293, 366, 390
256, 296, 363, 389
254, 294, 358,
H2L2
H2L3
H2L4
{[RuCl(CO)(PPh3)2]2L1}
{[RuCl(CO)(AsPh3)2]2L1}
{[RuCl(CO)(Py)(PPh3)]2L1}
{[RuCl(CO)(PPh3)2]2L2}
{[RuCl(CO)(AsPh3)2]2L2}
{[RuCl(CO)(Py)(PPh3)]2L2}
{[RuCl(CO)(PPh3)2]2L3}
{[RuCl(CO)(AsPh3)2]2L3}
{[RuCl(CO)(Py)(PPh3)]2L3}
{[RuCl(CO)(PPh3)2]2L4}
{[RuCl(CO)(AsPh3)2]2L4}
{[RuCl(CO)(Py)(PPh3)]2L4}
1514
1517
1531
1513
1484
1512
1513
1460
1514
1510
1513
1510
1954
1957
1940
1947
1952
1938
1948
1950
1940
1949
1949
1944
254, 360, 390
254, 294, 344, 389, 467
254, 296, 364, 389, 456
254, 296, 350, 387, 467
254, 293, 357, 389, 466
251, 338, 390
256, 296, 356, 394, 438
regions were due to n-π∗ transition of non-bonding electrons
present on the nitrogen of the azomethine group in the binuclear
ruthenium(II) complexes. The pattern of the electronic spectra
for the complexes indicated the presence of an octahedral
environment around the binuclear ruthenium(II) ion similar to
that of the other ruthenium octahedral complexes.[32,33]
which has the characteristic of coordinated nitrogen base.[21]
Characteristic bands for triphenylphosphine/arsine were also
present in the expected region 1433–1437 cm−1 [30]
.
Electronic Spectra
The electronic absorption spectra of the free ligands and their
complexes in CH2Cl2 were recorded and the values are listed in
Table 2. The spectra of the free ligands showed that two types
of transitions appearing in the range 302–305 and 368–483 nm
were due to π − π∗ and n-π∗ transitions involving molecular
orbital of the C N, phenolic–OH and enolic-OH chromophore.
These bands were shifted in the spectra of the complexes,
indicating the involvement of imine group nitrogen, phenolic
oxygen, and enolic oxygen in coordination with central metal
atom. The spectra of the complexes showed three to five bands
in the region 251–467 nm. All the Schiff base ruthenium
complexes were diamagnetic, indicating the presence of ruthe-
nium in +2 oxidation state. The ground state of ruthenium(II)
1H, 31P, and 13C NMR Spectra
1
The H-NMR spectra of ligands and the binuclear ruthe-
nium(II) complexes were recorded in DMSO-d6 solution to
confirm the binding mode of the Schiff base to ruthenium ion
and the values are given in Table 3. The aromatic protons for all
the ligands appeared as a multiplet at 6.6–7.9 ppm. The acetoac-
etanilide moiety of NH, CH, CH3 and enolic-OH protons appear
as a singlet at 3.5–3.9, 2.3–3.7, 1.6–2.8, and 12.2–15.5 ppm, re-
spectively. The azomethine proton of H2L1, H2L3, and H2L4
ligands appear as singlet at 8.1–8.3 ppm. For the ligand H2L2,
the methyl protons appear as singlet at 2.3 ppm. The methoxy
protons for H2L3 ligand appears as singlet at 2.4 ppm. For all
the ligands the phenolic-OH protons appear as singlet in the
range 9.0–9.4 ppm. On complexation, multiplets are observed
in an octahedral environment is A1g, arising from the t26g
1
configuration, and the excited states corresponding to the t52ge1g
configuration are 3T1g, 3T2g, 1T1g and 1T2g. Hence, four bands around 6.6–7.9 ppm have been assigned for aromatic protons
1
3
1
3
corresponding to the transitions A1g → T1g, A1g → T2g, and triphenylphosphine/arsine/pyridine protons. The NH, CH
1
1
1
1A1g → T1g and A1g → T2g are possible in order of the and CH3 protons in all the complexes appears as singlet at 3.3–
increasing energy. The binuclear ruthenium(II) complexes in 3.4, 2.3–3.8, and 1.4–2.9 ppm. The complexes containing the
the visible region display the high intensity band in the range azomethine protons appear as singlet in the range 7.8–8.6 ppm.
438–467 nm was assigned to be the LMCT transitions.[31−33] The N C CH3 protons appear as singlet at 2.2 ppm in the com-
The band observed in the range 251–296 nm were assigned plexes {[RuCl(CO)(PPh3)2]2L2}, {[RuCl(CO)(AsPh3)2]2L2}
to π − π* transition from the benzene ring and the double and {[RuCl(CO)(PPh3)(Py)]2L2}. The methoxy protons in the
bond of the azomethine group. The bands in the 338–394 nm complexes {[RuCl(CO)(PPh3)2]2L3}, [RuCl(CO)(AsPh3)2]2L3

BINUCLEAR RUTHENIUM(II) SCHIFF BASE COMPLEXES
85
TABLE 3
1H NMR spectra of binuclear ruthenium(II) Schiff base complexes
Ligands and complexes
H2L1
1H NMR spectra
6.9–7.8 (m, Ar), 3.95 (s, NH), 12.2 (s, enolic-OH), 2.65 (s, CH), 2.19 (s, CH3), 8.34 (s, HC N),
9.05 (Ph-OH)
6.6–7.6 (m, Ar), 3.57 (s, NH), 12.3 (s, enolic-OH), 2.63 (s, CH), 2.31 (s, CH3), 2.13 (s, CH3-C N),
9.05 (Ph-OH)
6.6–7.9 (m, Ar), 3.84 (s, NH), 13.3 (s, enolic-OH), 3.74 (s, CH), 2.88 (s, CH3), 8.20 (s, HC N),
9.45 (Ph-OH), 2.48 (s, OCH3)
6.7–7.8 (m, Ar), 3.63 (s, NH), 15.5 (s, enolic-OH), 2.33 (s, CH), 1.60 (s, CH3), 8.13 (s, HC N),
9.40 (Ph-OH)
H2L2
H2L3
H2L4
{[RuCl(CO)(PPh3)2]2L1}
7.0–7.7 (m, Ar), 3.4 (s, NH), 2.65 (s, CH), 2.3 (s, CH3), 7.85 (s, HC N)
{[RuCl(CO)(AsPh3)2]2L1} 7.3–7.9 (m, Ar), 3.43 (s, NH), 2.64 (s, CH), 2.3 (s, CH3), 8.34 (s, HC N)
{[RuCl(CO)(Py)(PPh3)]2L1} 7.2–7.8 (m, Ar), 3.4 (s, NH), 2.65 (s, CH), 2.2 (s, CH3), 8.40 (s, HC N)
{[RuCl(CO)(PPh3)2]2L2}
6.9–7.7 (m, Ar), 3.4 (s, NH), 2.60 (s, CH), 2.2 (s, CH3), 2.2 (s, CH3-C N)
{[RuCl(CO)(AsPh3)2]2L2} 7.3–7.7 (m, Ar), 3.35 (s, NH), 2.65 (s, CH), 2.2 (s, CH3), 2.2 (s, CH3-C N)
{[RuCl(CO)(Py)(PPh3)]2L2} 7.2–7.7 (m, Ar), 3.4 (s, NH), 2.5 (s, CH), 2.2 (s, CH3), 2.2 (s, CH3-C N)
{[RuCl(CO)(PPh3)2]2L3}
7.2–7.7 (m, Ar), 3.3 (s, NH), 3.8 (s, CH), 2.9 (s, CH3), 7.85 (s,HC N), 2.3 (s, OCH3)
{[RuCl(CO)(AsPh3)2]2L3} 7.3–7.4 (m, Ar), 3.37 (s, NH), 3.8 (s, CH), 2.8 (s, CH3), 8.2 (s,HC N), 2.2 (s, OCH3)
{[RuCl(CO)(Py)(PPh3)]2L3} 7.2–7.6 (m, Ar), 3.34 (s, NH), 3.8 (s, CH), 2.8 (s, CH3), 8.4 (s,HC N), 2.5 (s, OCH3)
{[RuCl(CO)(PPh3)2]2L4}
6.6–7.7 (m, Ar), 3.3 (s, NH), 2.3 (s, CH), 1.4 (s, CH3), 7.85 (s, HC N)
{[RuCl(CO)(AsPh3)2]2L4} 7.3–7.7 (m, Ar), 3.4 (s, NH), 2.5 (s, CH), 2.2 (s, CH3), 8.4 (s, HC N)
{[RuCl(CO)(Py)(PPh3)]2L4} 7.2–7.7 (m, Ar), 3.34 (s, NH), 2.5 (s, CH), 2.2 (s, CH3), 8.6 (s, HC N)
and {[RuCl(CO)(PPh3)(Py)]2L3} appears as singlet in the range
The 13C NMR data were recorded in DMSO d6 solution
2.2–2.5 ppm. The signals for phenolic-OH and enolic-OH pro- and the assignments of ligands and the complexes are listed in
ton disappeared in all the complexes, which indicate the coor- Table 4 (Figure 1). For all the ligands, the aromatic carbons ap-
dination of ruthenium through the oxygen atoms. The presence peared in the range 113–144 ppm. The acetoacetanilide moiety
of other signals in the complexes indicates that these groups do of enolic, CH, C N and CH3 carbon appeared at 86–89 ppm,
not coordinate with the ruthenium atom.
48–56 ppm, 150–160 ppm, and 15–21 ppm. For all the ligands
31P NMR spectra were recorded for a complex in order displayed a single resonance at 162–169 ppm, which shows that
to confirm the presence of triphenylphosphine groups and the azomethine carbon atoms, which also confirms the structure
to determine the geometry of the complex. The observation of ligands. For H2L2 ligand, the methyl carbon appeared
of two sharp singlets at 28.4 and 30.3 ppm in the spec- at 19 ppm and H2L3 ligand, the methoxy carbon appeared
trum of {[RuCl(CO)(PPh3)2]2L2} revealed that the presence at 30 ppm. For the complexes {[RuCl(CO)(PPh3)2]2L1},
of two magnetically equivalent phosphorus atoms, suggesting {[RuCl(CO)(PPh3)2]2L2}, {[RuCl(CO)(PPh3)2]2L3} and
that the two PPh3 groups in each nuclei are trans to each {[RuCl(CO)(PPh3)2]2L4}, the aromatic carbon appeared at
other.[30]
120–134 ppm. For the above complexes, the acetoacetanilide
TABLE 4
13C NMR spectra of binuclear ruthenium(II) Schiff base complexes
13C NMR spectra
Ligands and complexes
H2L1
H2L2
H2L3
H2L4
116–138 (Ar, C), 86 (enolic C), 48 (CH), 160 (C N), 18 (CH3), 163 (HC N)
113–144 (Ar, C), 88 (enolic C), 48 (CH), 156 (C N), 15 (CH3), 163 (C N), 19.0 (CH3)
118–129 (Ar, C), 86 (enolic C), 56 (CH), 150 (C N), 20 (CH3), 162 (HC N), 30.7 (OCH3)
116–130 (Ar, C), 89 (enolic C), 50 (CH), 158 (C N), 21 (CH3), 169 (HC N)
{[RuCl(CO)(PPh3)2]2L1} 120–134 (Ar, C), 84 (enolic C), 46 (CH), 158 (C N), 18 (CH3), 161 (HC N), 178 (C≡O)
{[RuCl(CO)(PPh3)2]2L2} 127–134 (Ar, C), 85 (enolic C), 48 (CH), 154 (C N), 16 (CH3), 160 (C N), 19 (CH3), 180 (C≡O)
{[RuCl(CO)(PPh3)2]2L3} 129–133 (Ar, C), 84 (enolic C), 54 (CH), 152 (C N), 18 (CH3), 162 (HC N), 182 (C≡O), 30 (OCH3)
{[RuCl(CO)(PPh3)2]2L4} 128–134 (Ar, C), 88 (enolic C), 50 (CH), 156 (C N), 20 (CH3), 166 (HC N), 176 (C≡O)

86
N. SATHYA ET AL.
FIG. 1. 13C NMR spectra of {[RuCl(CO)(PPh3)2]2L1}.
moiety of enolic, CH, C N and CH3 carbons appeared tials, but showed two successive quasi-reversible or irreversible
at 84–88 ppm, 46–54 ppm, 152–158 ppm, and 16–20 oxidative couples at positive potentials. The oxidation in the
ppm. For the complexes {[RuCl(CO)(PPh3)2]2L2} and complexes corresponds to:
{[RuCl(CO)(PPh3)2]2L3}, the methyl and methoxy carbons
−e−
−e−
appeared at 19 ppm and 30 ppm. For all the complexes, the
azomethine carbon and terminal carbonyl group C≡O appeared
in the range 160–166 ppm and 176–182 ppm.
II
II
II
III
III
III
—ꢁ
ꢂ—
—ꢁ
ꢂ—
Ru − Ru
Ru − Ru
Ru − Ru
+e−
+e−
The quasireversible oxidation process occurs with peak-to-
peak separations (ꢃEP) of 120–750 mV, suggesting two, single
step, one electron transfer process[34] The oxidation of each
complexes were characterized by well- defined waves with Ef
values in the range 0.16–0.34 V corresponding to first oxida-
tion couple and the second oxidation couple in the range 0.49–
1.24 V. The first oxidation was attributed to the oxidation of
one of the ruthenium(II) centers to the corresponding mixed va-
lence complex[35,36] and the second to the ruthenium(III). The
irreversible oxidation observed in the complex is presumably
due to oxidative dissociation of the ligands that occurs at the
ruthenium(III) center.[37] All these facts are indicative of sig-
nificant electronic interactions between the two metal centers.
The low difference of 200–700 mV observed for our complexes
as compared to other complexes[38] is due to the fact that the
distance between the two metal centers is long due to lengthy
bridging ligands.
Electrochemical Studies
Electrochemical study was carried out for all the binuclear
ruthenium(II) Schiff base complexes in dichloromethane solu-
tion at a glassy carbon working electrode, and all the potentials
were expressed with reference to Ag-AgCl. The values are given
in Table 5 (Figure 2). All the binuclear ruthenium(II) Schiff base
complexes do not show any reduction wave at negative poten-
CATALYTIC ACTIVITIES
Catalytic Oxidations
Catalytic oxidation of primary and secondary alcohols by free
ligands, metal precursors, and binuclear ruthenium(II) Schiff
base complexes were carried out in CH2Cl2 and stirred for
about 6 hrs under an oxygen atmosphere at room tempera-
ture. The resulting carbonyl compounds were quantified as
2, 4-dinitrophenylhydrazone derivatives, and the results are
summarized in Table 6. Only a very little amount of carbonyl
FIG. 2. Cyclic voltammogram of {[RuCl(CO)(AsPh3)2]2L1}.

BINUCLEAR RUTHENIUM(II) SCHIFF BASE COMPLEXES
87
TABLE 5
Cyclic voltammetrya data of binuclear ruthenium(II) Schiff base complexes
RuI2II,III – Ru2II,II
Complexes
Epa (v) EpC (v) Ef (v) ꢃEp (mV) Epa (v) EpC (v) Ef (v) ꢃEp (mV)
{[RuCl(CO)(PPh3)2]2L1}
{[RuCl(CO)(AsPh3)2]2L1}
{[RuCl(CO)(Py)(PPh3)]2L1}
{[RuCl(CO)(PPh3)2]2L2}
{[RuCl(CO)(AsPh3)2]2L2}
{[RuCl(CO)(Py)(PPh3)]2L2}
{[RuCl(CO)(PPh3)2]2L3}
{[RuCl(CO)(AsPh3)2]2L3}
{[RuCl(CO)(Py)(PPh3)]2L3}
{[RuCl(CO)(PPh3)2]2L4}
{[RuCl(CO)(AsPh3)2]2L4}
{[RuCl(CO)(Py)(PPh3)]2L4}
0.23
0.28
0.39
—
0.48
0.35
0.52
0.46
0.56
0.52
0.48
0.50
0.35
0.03
0.08
—
0.03
0.12
0.04
0.06
0.10
0.15
0.09
0.08
0.29
0.16
0.24
—
0.26
0.24
0.28
0.26
0.33
0.34
0.29
0.29
120
250
310
—
450
230
480
400
460
370
390
420
0.93
0.90
1.27
—
1.52
1.25
1.33
1.37
1.32
1.26
1.41
1.40
1.11
0.64
0.79
—
0.77
0.98
0.65
0.84
1.01
1.05
1.02
1.07
1.02
0.77
1.03
—
1.15
1.11
0.49
1.10
1.17
1.15
1.21
1.24
180
260
480
—
750
270
330
530
310
210
390
330
aSupporting electrolyte [NBu4]ClO4 (0.1 M); scan rate, all potentials are referenced to Ag/AgCl; Ef = 0.5(Epa + Epc);
Where, Epa and Epc are anodic and cathodic peak potentials, respectively; scan rate,100 mVs−1
.
TABLE 6
Catalytic activity data of binuclear ruthenium(II) Schiff base complexes
Oxidation of alcohols
Aryl-Aryl coupling Benzyl alcohol → Cyclohexanol → Propane-1-ol → Isobutyl alcohol → 2-
reaction Biphenyl Benzaldehyde Cyclohexanone Propionaldehyde Methyl-propionaldehyde
Metal percursors,
ligands and
complexes
Yield
(mg)
Yield Yield Turnover Yield Turnover Yield Turnover Yield
(%)
(%) numbera (%) numbera (%) numbera (%)
Turnover
numbera
[RuHCl(CO)(PPh3)3]
[RuHCl(CO)(AsPh3)3]
[RuHCl(CO)(Py)(PPh3)2]
H2L1
0.108
0.105
0.100
0.0382
0.066
0.053
0.044
0.280
0.253
11.22 21.9
10.91 21.2
10.39 20.2
22.7
22.0
20.9
19.2
18.2
17.5
8.0
14.0
11.0
9.0
69
62
51
71
70
69
72
71
68
67
65
64
20.0
18.9
18.2
7.9
14.3
11.5
16.1
15.1
14.1
5.0
9.1
8.3
6.7
52
48
44
66
61
57
62
58
56
50
48
44
21.4
20.1
18.7
6.7
12.1
11.1
8.9
69.2
63.5
58.5
87.4
81.1
76.1
82.4
77.3
74.2
66.0
63.5
58.5
18.4
16.9
15.8
7.0
9.6
9.1
6.1
53
49
43
67
61
57
62
59
57
52
49
47
19.8
18.2
17.0
5.3
7.3
6.9
3.96
6.85 15.0
5.5 12.0
4.57 10.0
9.0
9.08
H2L2
15.7
12.6
10.1
76.7
69.7
59.3
87.2
76.7
66.3
81.6
75.4
62.1
74.3
70.0
58.3
H2L3
H2L4
8.95
4.6
{[RuCl(CO)(PPh3)2]2L1}
29.09
26.28
19.95
50.39
48.10
46.96
48.10
46.44
45.51
26.91
25.45
24.10
75
69
58
86
75
65
80
74
61
73
66
57
71.6
64.5
53.7
74.5
73.1
71.6
75.2
74.1
70.9
70.2
68.4
66.6
40.5
36.8
32.6
50.8
46.7
43.2
47.2
44.5
43.1
39.1
36.9
35.6
{[RuCl(CO)(AsPh3)2]2L1}
{[RuCl(CO)(Py)(PPh3)]2L1} 0.192
{[RuCl(CO)(PPh3)2]2L2}
{[RuCl(CO)(AsPh3)2]2L2}
0.485
0.463
{[RuCl(CO)(Py)(PPh3)]2L2} 0.452
{[RuCl(CO)(PPh3)2]2L3}
0.463
0.447
{[RuCl(CO)(AsPh3)2]2L3}
{[RuCl(CO)(Py)(PPh3)]2L3} 0.438
{[RuCl(CO)(PPh3)2]2L4}
{[RuCl(CO)(AsPh3)2]2L4}
0.259
0.245
{[RuCl(CO)(Py)(PPh3)]2L4} 0.232
aMoles of product per mole of catalyst.

88
N. SATHYA ET AL.
TABLE 7
Antibacterial activity of binuclear ruthenium(II) Schiff base complexes
Diameter of inhibition zone (mm)
S. aereus
E. coli
Metal percursors,
ligands, and complexes
0.5%
1.0%
1.5%
2.0%
0.5%
1.0%
1.5%
2.0%
[RuHCl(CO)(PPh3)3]
[RuHCl(CO)(AsPh3)3]
[RuHCl(CO)(Py)(PPh3)2]
H2L1
—
3
5
—
—
2
—
5
—
—
8
5
3
5
5
6
—
3
4
—
8
6
7
9
7
3
5
6
2
12
11
9
18
16
14
19
17
18
13
11
10
9
9
10
5
8
9
2
4
5
—
3
—
—
8
—
5
5
3
7
5
7
7
—
5
3
2
15
6
8
10
7
6
7
9
2
8
6
8
11
3
10
8
6
23
21
24
25
22
26
24
20
25
—
23
27
H2L2
H2L3
5
4
H2L4
5
{[RuCl(CO)(PPh3)2]2L1}
{[RuCl(CO)(AsPh3)2]2L1}
{[RuCl(CO)(Py)(PPh3)]2L1}
{[RuCl(CO)(PPh3)2]2L2}
{[RuCl(CO)(AsPh3)2]2L2}
{[RuCl(CO)(Py)(PPh3)]2L2}
{[RuCl(CO)(PPh3)2]2L3}
{[RuCl(CO)(AsPh3)2]2L3}
{[RuCl(CO)(Py)(PPh3)]2L3}
{[RuCl(CO)(PPh3)2]2L4}
{[RuCl(CO)(AsPh3)2]2L4}
{[RuCl(CO)(Py)(PPh3)]2L4}
Amikacin
19
17
12
25
20
19
23
20
22
19
15
13
19
12
13
13
11
18
13
16
20
—
18
16
5
12
10
8
12
12
11
11
9
12
8
8
10
7
6
5
3
6
7
—
7
12
14
—
12
13
—
7
8
20–26
19–26
DMSO-Solvent
No Activity
One of the complexes {[RuCl(CO)(PPh3)2]2L2} has been
tested for its reusability (Figure 3). The catalyst was recycled
four times and the yield of the product was compared during the
oxidation of benzyl alcohol to benzaldehyde. There is no appre-
ciable change in the yield of the product when the catalyst was
recycled. This confirms the catalytic activity of the complex.
The heterogeneous nature of the catalyst has also been exam-
ined. The oxidation was completely stopped by the removal of
{[RuCl(CO)(PPh3)2]2L2} from the reaction solution.
compound is formed when the reaction is carried out without
the catalyst. This is an insignificant amount compared with the
yields of carbonyl compounds that have been obtained from
the reaction catalyzed by free ligands, metal precursors, and
binuclear ruthenium(II) complexes. In the catalytic oxidation,
all the complexes did not show much activity for the conver-
sion of aliphatic alcohols such as propane-1-ol (66–44%) and
isopropyl alcohol (70–43%) to the corresponding aldehydes.
Whereas this catalytic system works well for the oxidation of
aromatic alcohols such as benzyl alcohol (86–57%) and cyclo-
hexanol (72–51%) to corresponding aldehyde and ketone, inthe
case of the catalytic efficiency of the complexes containg L1
and L4 was lower than that of L2 and L3. The essential dif-
ference between these complexes is that the hydrogen atom
of the L1 and L4 is replaced by the methyl group of L2 and
the methoxy group of L3. Hence, it seems that the presence
of electron donating methyl and methoxy group enhances the
catalytic activity of L2 and L3 containing complexes over the
L1 and L4 containing complexes.[39,40] The catalytic oxidation
of binuclear ruthenium(II) complexes has been found to show
better catalytic activities compared with similar mono nuclear
complexes.[41]
FIG. 3. Recycling of [RuCl(CO)(PPh3)2]2L2 catalyst for the oxidation of
Benzyl alcohol.

BINUCLEAR RUTHENIUM(II) SCHIFF BASE COMPLEXES
89
CONCLUSION
Aryl-aryl Coupling Reaction
The potential binucleating monobasic bidentate Schiff base
ligands had been prepared and were employed to synthesize
a new class of binuclear ruthenium(II) Schiff base complexes
incorporating PPh3/AsPh3 as ancillary ligands. The spectral in-
vestigation suggests the presence of an octahedral geometry
around ruthenium metal. All the complexes were tested as cat-
alyst for the oxidation of variety of alcohols in the presence of
molecular oxygen. In these complexes, the complexes contain-
ing electron donating group shows more efficiency. Moreover,
the reusability of the catalyst has also been proved. Finally, the
antimicrobial properties of the complexes were studied and the
mode of action of these complexes against the microbes was
also explained.
The free ligands, metal precursors, and the ruthenium(II)
binuclear complexes have been used as catalysts in the aryl-aryl
coupling reactions (Table 6). The system chosen for the study is
the coupling of phenyl magnesium bromide with bromobenzene
to give biphenyl as the product. Bromobenzene was first con-
verted into the corresponding Grignard reagent. The bromoben-
zene, followed by the ligands and the complex chosen for the
investigation, was added to the above reagent and the mixture
was heated under reflux for 6 hrs. After work up, the mixture,
yielded biphenyl. Only a very little amount of Ph2 is formed
when the reaction is carried out with the catalyst. This is an in-
significant amount compared to the yields of Ph2 obtained from
the reactions catalysed by the ligands, metal precursors, and the
binuclear ruthenium(II) complexes.[10] Ruthenium(II) binuclear
complexes are better catalysts than the respective mononuclear
complexes. This could be because of bicentered catalysis in bin-
uclear complexes.[42] The yield of biphenyl obtained from the re-
action catalyzed by the new binuclear ruthenium(II) complexes
are low when compared to the yield obtained from the reaction
catalyzed by [NiCl2(PPh3)2].[23] This may be due to the fact that
the active species derived from ruthenium complexes are less
stable compared with the active species from [NiCl2(PPh3)2],
as the effectiveness of the catalysts is directly related to their
ability to generate the corresponding active species.[43] The cou-
plings catalysed by ruthenium complexes containing PPh3 and
AsPh3 yielded biphenyl in almost equal quantity indicating non-
participation of PPh3 or AsPh3 in the catalytic cycle.
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Antibacterial Activities
The antibacterial activities of the free ligands, metal precur-
sors, and binuclear ruthenium(II) Schiff base complexes were
tested against certain pathogenic bacteria using disc diffusion
method.[24] The zone of inhibition against the growth of bacteria
for the ligands, metal precursors, and binuclear ruthenium(II)
complexes is given in Table 7. It has been suggested that the lig-
ands with N and O donor system might have inhibited enzyme
production, since enzymes that require free hydroxyl groups
for their activity appear to the especially susceptible to deacti-
vation by the ions of the complexes. The complexes facilitate
their diffusion through the lipid layer of spore membranes to
the site of action ultimately killing them by combining with
–OH groups of certain cell enzymes. The variation in the effec-
tiveness of different biocidal agents against different organisms
depends on the impermeability of the cell. Chelation reduces
the polarity of the central metal atom, mainly because of partial
sharing of its positive charge with the ligand. Also, the nor-
mal cell process may be affected by the formation of hydrogen
bond, through the azomethine nitrogen atom with the active
centers of cell constituents.[17] From the results, it is clear that
binuclear ruthenium(II) carbonyl Schiff base complexes exhibit
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