Ruthenium(II) complexes derived from substituted cyclobutane and substituted thiazole Schiff base ligands: Synthetic, spectral, catalytic and antimicrobial studies

Article abstract of DOI:10.1081/SIM-200067062

Ruthenium(II) complexes of the type [Ru(CO)(L)₂(B)] (L = novel bidentate Schiff base ligand; B = PPh₃, pyridine (py), piperidine (pip), morpholine (morph) or AsPh₃) have been prepared by reacting [RuHCl(CO)(PPh₃

Full text of DOI:10.1081/SIM-200067062

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Ruthenium(II) Complexes Derived from Substituted
Cyclobutane and Substituted Thiazole Schiff
Base Ligands: Synthetic, Spectral, Catalytic and
Antimicrobial Studies
T. Daniel Thangadurai a & Son-Ki Ihm b
a Laboratory for Chemistry and Biochemistry for Pharmacology and Toxicology , University
Rene Descartes , Paris , France
b Department of Chemical and Biomolecular Engineering , Korea Advanced Institute of
Science and Technology , Republic of Korea
Published online: 31 Jan 2012.
To cite this article: T. Daniel Thangadurai & Son-Ki Ihm (2005) Ruthenium(II) Complexes Derived from Substituted
Cyclobutane and Substituted Thiazole Schiff Base Ligands: Synthetic, Spectral, Catalytic and Antimicrobial Studies, Synthesis
and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 35:6, 499-507, DOI: 10.1081/SIM-200067062
To link to this article: http://dx.doi.org/10.1081/SIM-200067062
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Synthesis and Reactivity in Inorganic, Metal-Organic and Nano-Metal Chemistry, 35:499–507, 2005
Copyright # 2005 Taylor & Francis, Inc.
ISSN: 0094-5714 print/1532-2440 online
DOI: 10.1081/SIM-200067062
Ruthenium(II) Complexes Derived from Substituted
Cyclobutane and Substituted Thiazole Schiff Base Ligands:
Synthetic, Spectral, Catalytic and Antimicrobial Studies
T. Daniel Thangadurai
Laboratory for Chemistry and Biochemistry for Pharmacology and Toxicology, University Rene
Descartes, Paris, France
Son-Ki Ihm
Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science
and Technology, Republic of Korea
It is well known that 3-substituted cyclobutane carboxylic
Ruthenium(II) complexes of the type [Ru(CO)(L)2(B)] acid derivatives exhibit antiinflamatory and antidepressant
(L 5 novel bidentate Schiff base ligand; B 5 PPh3, pyridine
(py), piperidine (pip), morpholine (morph) or AsPh3) have been
prepared by reacting [RuHCl(CO)(PPh3)2(B)] (B 5 PPh3, py,
pip or morph) or [RuHCl(CO)(AsPh3)3] with two novel bidentate
Schiff base ligands derived from 4-(1-methyl-1-mesitylcyclobu-
tane-3-yl)-2-aminothiazole in 1 : 2 molar ratio in benzene. Com- substituted thiazoles and its Schiff base derivatives containing
activities and liquid crystal properties. Various thiazole deriva-
tives showed herbicidal, antiinflamatory, antimicrobial or anti-
parasitic activity (Slip et al., 1974). However, the syntheses and
physicochemical properties of 1,1,3-trisubstituted cyclobutane
plexes have been characterized by analytical, spectroscopic (IR,
UV, H, 13C- and 31P NMR) and magnetic data. An octahedral
structure has been tentatively proposed for all the new complexes.
The thermal properties of the ligands and their complexes have
been studied by TGA. The new complexes have been used as
the mesityl group have not been reported many so far. These
compounds containing cyclobutane, thiazole and Schiff base
1
functions in their chemical modifications may be pharmaco-
logically active and useful as ligands in coordination
catalyst in aryl-aryl coupling and also subjected to antibacterial chemistry.
and antifungal activity studies.
Ruthenium complexes, by virtue of their wide range of
reversible and accessible oxidation states, have proved to be
useful catalysts in many reactions such as hydrogenation, oxi-
dation, carbonylation, hydroformylation, etc. (Sung et al.,
1999; Chatterjee et al., 2000; Goldstein et al., 1994), But
their use as catalyst for aryl-aryl couplings has not been dis-
cussed widely. Mild and efficient aromatic cross-couplings,
catalyzed by various transition metal complexes, have been
developed recently (Bringmann et al., 1990; Watanabe et al.,
1992; Cox et al., 1992). Besides natural product synthesis, con-
struction of large organic receptors in host-guest chemistry
(Kelly et al., 1990), elaboration of dendrimers (Miller et al.,
1992), or one-dimensional polymers (Wallow and Novak,
1991), aromatic couplings can be used to build multi-site
ligands able to incorporate two or several transition metals
(Beley et al., 1993).
Keywords Ruthenium(II), Schiff base, catalyst, aryl–aryl coupling,
antimicrobial
INTRODUCTION
Schiff bases derived from the salicylaldehyde are well
known as polydentate ligands, coordinating as deprotonated
or neutral forms. Several adducts of non-transition, early
transition and f-block metals with such bases acting neutral
ligands (Kawakami et al., 1971; Bullock et al., 1978), have
been studied.
Received 30 December 2004; accepted 8 April 2005.
We gratefully acknowledge financial support from the Brain Korea
21 Project and National Research Laboratory for Environmental
Catalysis.
Address correspondence to T. Daniel Thangadurai, Center for
Superfunctional Materials, Department of Chemistry, Pohang Univer-
sity of Science and Technology, San 31, Hyojo-dong, Nam-gu,
Pohang 790-784, Republic of Korea. E-mail: thanga_durai2000@
yahoo.com
The ligands used in this work have characteristic properties
of cyclobutane, thiazole and Schif bases. The extensive syn-
thetic possibilities of this type of heterocycle, due to the
presence of several reaction sites, hold promise for the prep-
aration of new thiazole derivatives. As part of our systematic
investigations on the reactions of substituted cyclobutane and
499

500
T. D. THANGADURAI AND S.-K. IHM
related ligand with transition metal complexes, we report the Preparation of the Complexes (2–6 and 8–12)
synthesis, spectral studies, catalytic and antimicrobial activites
of mononuclear ruthenium(II) carbonyl complexes of the type
[Ru(CO)(L)2(B)].
All the preparations were carried out under strictly anhy-
drous conditions. To a solution of [RuHCl(CO)(PPh3)2(B)]
(B ¼ PPh3, py, pip or morph) (0.095–0.077 g, 0.01 mmol) or
[RuHCl(CO)(AsPh3)3] (0.108 g, 0.01 mmol) in benzene
(20 mL), the appropriate Schiff base ligands (0.075–0.126 g;
0.02 mmol) were added (molar ratio of the ruthenium
complex : ligand ¼ 1 : 2). The resulting mixture was heated
under reflux for 5 h. The completion of the reaction was
checked by TLC, concentrated on rotavapor to 3 mL and preci-
pitated by addition of petroleum ether (60–808C). The com-
plexes were filtered, washed with petroleum ether and
recrystallized from CH2Cl2/petroleum ether (60–808C)
mixture and dried in vacuo. (color: green, yield: 81–87%)
EXPERIMENTAL
Commercially available RuCl3 3H2O was used without
.
further purification. The solvents were purified and dried
according to the standard procedures (Vogel, 1989). Salicylal-
dehyde, 2-hydroxy-5-bromobenzaldehyde and thiosemicarb-
azide were purchased and were used without further
purification. 1-methyl-1-mesityl-3-(2-chloro-1-oxoethyl)cyclo-
butane was prepared and purified by column chromatography,
1-(2-hydroxybenzylidene)thiosemicarbazide and 1-(2-hydroxy-
5-bromobenzylidene) thiosemicarbazide were prepared by the
reported methods (Daniel Thangadurai and Ihm, 2004;
Cukurovali et al., 2001).
Catalytic Activity
In two necked round-bottom flask with a CaCl2 guard tube,
magnesium turnings (0.320 g; 0.013 g atom) were placed. To
the above, bromobenzene [0.746 g of total 1.884 g
(0.012 mol)] in anhydrous Et2O (5 mL) was added with
stirring. A crystal of iodine was added to activate magnesium
and the mixture was heated under reflux. The appearance of
turbidity after 5 min. indicated initiation of the reaction. The
remaining bromobenzene in Et2O (5 mL) was added
dropwise and the mixture was refluxed for 40 min. To this
mixture, 1.03 mL (0.01 mol) of bromobenzene in anhydrous
Et2O (5 mL) and the ruthenium complex (0.05 mol) chosen
for investigation were added and heated under reflux for 6 h.
The reaction mixture was cooled and hydrolyzed with a satu-
rated solution of aqueous NH4Cl. The Et2O extract, on evapo-
ration of the solvent, gave the crude product, which was
chromatographed on a silica gel column. Petroleum ether
(60–808C) eluted pure biphenyl which compared well with
an authentic sample (TLC plates), (M. p. 69–728C).
Elemental analyses were carried out by using Carlo Erba
1106 analyzer. IR spectra were recorded with Nexus FTIR
spectrophotometer in the range 4000–300 cm21. Electronic
spectra were recorded in CH2Cl2 on Hitachi-Elmer model
20/200 spectrophotometer. Melting points were recorded on
micro heating table and are uncorrected. 1H, 13C and 31P
NMR spectra were recorded on a Brucker 400 MHz instrument
using TMS, TMS and o-phosphoric acid as an internal refer-
ence, respectively. Magnetic susceptibilities were determined
on a Sherwood scientific magnetic susceptibility balance
(Model MK1) at room temperature (258C) using Hg[Co
(SCN)2] as calibrant; diamagnetic corrections were calculated
from Pascal’s constants. Thermal analysis curves were
recorded on a Shimadzu TG-50 thermobalance. The starting
complexes (Daniel Thangadurai and Natarajan, 2001a) and
ligands (Cukurovali et al., 2001) have been prepared by the fol-
lowing literature procedures. The following reaction scheme
will represent the preparation of the Schiff base ligands
[HL1(1), color: pale yellow, m. pt.: 2258C, yield: 84% and
HL2(7), color: pale yellow, m. pt.: 2308C, yield: 87%]
(Scheme 1).
Qualitative Antimicrobial Assay
In this work, Bacillus megaterium (B.m.), Candida albicans
(C.a.), Enterobacter aeroginosa (E.a.), Aspergillus flavus
SCH. 1. Preparation of novel Schiff base ligands.

STUDIES ON RUTHENIUM(II) COMPLEXES
501
(A.f.), Fusarium oxysporium (F.o.) and Rhizoctonia solani
The bidentate Schiff bases react with the ruthenium(II)
(R.s.) were used to investigate the antibacteriological and anti- starting complexes of the type [RuHCl(CO)(PPh3)2(B)] (B ¼
fungal activities of ligands and their appropriate ruthenium(II) PPh3, py, pip or morph) or [RuHCl(CO)(AsPh3)3] to yield com-
complexes. Nutrient agar medium for bacteria and Saburoud plexes of the type [Ru(CO)(L)2(B)] (L ¼ novel bidentate
dextrose agar medium for fungi was poured into the sterilized Schiff base ligand; B ¼ PPh3, py, pip, morph or AsPh3).
Petri plates and allowed to solidify, and the plates were inocu-
In general, reactions of the ligands HL1 and HL2, with
lated with a spore suspension to test micro organisms, respec- starting ruthenium complexes were quick and gave good
tively. The compounds to be tested were dissolved in DMF and yields (81–87%) of mononuclear complexes (2–6 and 8–
soaked in filter paper discs (Whatmann no. 4, 5 mm diameter). 12). The new complexes are air- and light-stable and soluble
The discs were placed on the already seeded plates [incubation in most common organic solvents. Molecular weight determi-
period: 248C for bacteria (24 h); 268C for fungi (36 h)]. After 2 nation (Rast method) and elemental analyses data confirm the
days, the inhibition zone, which appeared around the discs in complexes to be hexa-coordinated. Table 1 lists the analytical
each plate, was measured. To avoid the activity of the data for the ligands and their ruthenium metal complexes.
solvent used in the test solutions, a solvent-only treated plate
was maintained. An untreated control plate was also main-
tained in order to calculate the percentage of inhibition.
Infrared Spectra
The IR spectral data of the ligands and their metal com-
plexes are listed in Table 2. Since there are no C55O, C–Cl
and –NH2 absorptions in the IR spectra of the ligands HL1
and HL2, these peaks indicate the formation of the expected
RESULTS AND DISCUSSION
1-methyl-1-mesityl-3-(2-chloro-1-oxoethyl)cyclobutane is compounds. The strong bands observed at 3130 cm21 for
very soluble in polar organic solvents, such as EtOH, each ligand can be attributed to the –NH-group vibration.
CHCl3, MeOH, and in nonpolar organic solvents, such as This absorption remains unaltered in complexes showing the
Et2O and benzene. The compound is not stable for long non-involvement of this group upon coordination. The
under ordinary laboratory conditions. It is highly affected by ligands exhibit broad medium intensity bands in the 2700–
direct sunlight and decomposed within two months. Hence, 2550 cm21 range, which are assigned to the intramolecular
. . . .
it was used as prepared, without delay. Substituted benzal- hydrogen-bonding vibrations (O-H
N). This situation is
dehyde derivatives of thiosemicarbazide were freshly common for aromatic azomethine compounds containing
prepared in excellent yields according to the well known o-OH groups (Tumer et al. 1999), and in the complexes,
Schiff base methods. The ligands HL1(1) and HL2 (7) were these bands disappear completely. The azomethine group
obtained in excellent yield. The hot solutions of the ligands vibrations of the free ligands occur at 1630 and 1625 cm21
,
were used during complexation. Attempts to crystallize the respectively, and these bands were not observed at the same
complexes in different solvents failed. frequencies in the spectra of all the complexes. They shifted
TABLE 1
Analytical and physical data of Schiff base ligands and ruthenium(II) complexes
Found (calcd.) (%)
S. no.
Compound
(C24H27N3SO)
M.p. ( 8C)
C
H
N
S
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
225
187
176
180
157
163
230
178
153
169
180
171
71.10 (71.07)
66.89 (67.02)
63.89 (63.75)
63.39 (63.44)
62.09 (62.08)
64.90 (64.66)
58.98 (59.49)
59.19 (59.23)
55.19 (55.18)
54.90 (54.95)
53.79 (53.79)
57.29 (57.40)
6.72 (6.70)
5.65 (5.63)
5.65 (5.65)
6.65 (6.12)
6.05 (6.00)
5.45 (5.43)
5.55 (5.41)
4.65 (4.79)
4.69 (4.72)
5.15 (5.13)
4.85 (4.86)
4.65 (4.64)
10.30 (10.36)
7.02 (7.00)
9.22 (9.64)
9.52 (9.59)
9.62 (9.56)
7.02 (6.75)
8.72 (8.70)
6.20 (6.19)
8.02 (8.34)
8.20 (8.31)
8.30 (8.29)
6.02 (6.00)
7.87 (7.90)
5.40 (5.33)
6.40 (6.30)
6.30 (6.27)
6.22 (6.25)
5.20 (5.15)
6.60 (6.60)
4.70 (4.72)
5.40 (5.45)
5.41 (5.43)
5.47 (5.41)
4.51 (4.57)
[Ru(CO)(C24H26N3SO)2(PPh3)]
[Ru(CO)(C24H26N3SO)2(py)]
[Ru(CO)(C24H26N3SO)2(pip)]
[Ru(CO)(C24H26N3SO)2(morph)]
[Ru(CO)(C24H26N3SO)2(AsPh3)]
(C24H26N3SOBr)
[Ru(CO)(C24H25N3SOBr)2(PPh3)]
[Ru(CO)(C24H25N3SOBr)2(py)]
[Ru(CO)(C24H25N3SOBr)2(pip)]
[Ru(CO)(C24H25N3SOBr)2(morph)]
[Ru(CO)(C24H25N3SOBr)2(AsPh3)]
(9)
(10)
(11)
(12)

502
T. D. THANGADURAI AND S.-K. IHM
TABLE 2
IR spectral data of the ligands and ruthenium(II) complexes
n(C55N)a
thiazole
n(C55N)a
azomethine
a
n(OH)a
n(N-H)a
n(CH3)/n(CH2)a
n(C-O)a
;;
n(C O)
S.No.
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
3289
—
3130 s
3130 s
3132 s
3131 s
3130 s
3130 s
3132 s
3130 s
3131 s
3130 s
3132 s
3131 s
2979–2927 m
2979–2927 m
2979–2927 m
2979–2927 m
2979–2927 m
2979–2927 m
2979–2927 m
2979–2927 m
2979–2927 m
2979–2927 m
2979–2927 m
2979–2927 m
1627 s
1626 s
1627 s
1627 s
1625 s
1627 s
1627 s
1626 s
1627 s
1627 s
1625 s
1627 s
1650 vs
1623 vs
1622 vs
1622 vs
1620 vs
1621 vs
1625 vs
1601 vs
1599 vs
1600 vs
1602 vs
1600 vs
1170
1186
1189
1192
1188
1191
1170
1190
1192
1189
1190
1193
—
1950 s
1952 s
1950 s
1950 s
1951 s
—
—
—
—
—
3290
—
1950 s
1954 s
1951 s
1950 s
1952 s
(9)
—
—
(10)
(11)
(12)
—
—
acm21; s ¼ strong, m ¼ medium, vs ¼ very strong.
to lower frequency region, indicating coordination of Schiff electronic spectra of all the complexes indicate an octahedral
bases through azomethine nitrogen. In the free ligands, bands geometry around ruthenium ion in the complexes, and the
at 1170 cm21 can be attributed to the phenolic (C–OH) spectra are very similar to the ones observed for other
group vibration, and in the metal complexes, these bands are
shifted to higher frequencies indicating coordination of
oxygen to the metal atom (Daniel Thangadurai and Natarajan
2001b). The spectra of all the complexes show a very strong
TABLE 3
Electronic spectra and magnetic moment data of ruthenium(II)
absorption at 1950 cm21 due to the coordinated terminal
complexes
a
S.no.
lmax
(1)b
Assignment
carbonyl group (Daniel Thangadurai et al., 2002). In the com-
plexes containing a coordinated nitrogen base, a medium inten-
sity band is observed in the 1000–1020 cm21 region
characteristic of the coordinated pyridine, piperidine and mor-
pholine (Plytazanopoubs et al. 1977). The bands in the 550–
480 and 460–430 cm21 range in the complex spectrum have
been assigned to the n(Ru-N) and n(Ru-O) bands.
1
(2)
586
367
600
375
524
354
510
349
537
357
596
300
561
375
581
344
573
323
559
312
892
7612
991
1A1g ! T1g
charge transfer
1
(3)
(4)
1A1g ! T1g
7540
901
charge transfer
1
1A1g ! T1g
8723
873
charge transfer
1
(5)
1A1g ! T1g
Electronic Spectra
9190
804
charge transfer
All the ruthenium(II) complexes are diamagnetic, indicating
the presence of ruthenium in its þ2 oxidation state. The ground
state of ruthenium(II) in octahedral environment is 1A1g arising
from t62g configuration. The excited states corresponding to the
1
(6)
1A1g ! T1g
8345
798
charge transfer
1
(8)
1A1g ! T1g
7781
865
charge transfer
t52g e1g configuration are T1g, T2g, T1g and T2g. Hence, four
3
3
1
1
1
(9)
1A1g ! T1g
1
3
1
bands corresponding to the transitions A1g ! T1g, A1g
!
8127
917
charge transfer
1
1
1
1
3T2g, A1g ! T1g and A1g ! T2g are possible in the order
of increasing energy. The electronic spectra of all the com-
plexes (Table 3) in dichloromethane showed two bands in the
600–300 nm region. The bands in the 600–510 nm region
1
(10)
(11)
(12)
1A1g ! T1g
9099
832
charge transfer
1
1A1g ! T1g
8993
934
charge transfer
1
have been assigned to the spin-allowed 1A1g ! T1g transition
1
1A1g ! T1g
(Daniel Thangadurai and Natarajan, 2001a). The other high
intensity bands in the 375–300 nm region have been assigned
charge transfer bands on the basis of high extinction coefficient
value (1 ¼ 7,540–9,190 dm3 mol21 cm21). The nature of the
7998
charge transfer
anm.
bdm3 mol21 cm21
.

TABLE 4
1H NMR spectral data of ligands and ruthenium(II) complexes
S.no.
HC55N
. C–H
CH3
Ms-CH3, ortho
Ms-CH3, para
CH2
C–H, thiazole
–NH–
–OH
Aromatics
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
8.11 (s)
8.10 (s)
8.11 (s)
8.12 (s)
8.09 (s)
8.11 (s)
8.01 (s)
8.02 (s)
8.01 (s)
8.00 (s)
8.03 (s)
8.01 (s)
3.69 (q)
3.68 (q)
3.69 (q)
3.69 (q)
3.68 (q)
3.69 (q)
3.29 (q)
3.30 (q)
3.29 (q)
3.30 (q)
3.30 (q)
3.29 (q)
1.48 (s)
1.48 (s)
1.48 (s)
1.48 (s)
1.48 (s)
1.48 (s)
1.49 (s)
1.49 (s)
1.49 (s)
1.49 (s)
1.49 (s)
1.49 (s)
2.16 (s)
2.16 (s)
2.16 (s)
2.16 (s)
2.16 (s)
2.16 (s)
2.15 (s)
2.15 (s)
2.15 (s)
2.15 (s)
2.15 (s)
2.15 (s)
2.42 (s)
2.42 (s)
2.42 (s)
2.42 (s)
2.42 (s)
2.42 (s)
2.40 (s)
2.40 (s)
2.40 (s)
2.40 (s)
2.40 (s)
2.40 (s)
2.56 (d)
2.56 (d)
2.56 (d)
2.56 (d)
2.56 (d)
2.56 (d)
2.55 (d)
2.55 (d)
2.55 (d)
2.55 (d)
2.55 (d)
2.55 (d)
6.06 (s)
6.06 (s)
6.06 (s)
6.06 (s)
6.06 (s)
6.06 (s)
5.98 (s)
5.98 (s)
5.98 (s)
5.98 (s)
5.98 (s)
5.98 (s)
10.02 (s)
10.02 (s)
10.02 (s)
10.02 (s)
10.02 (s)
10.02 (s)
10.10 (s)
10.10 (s)
10.10 (s)
10.10 (s)
10.10 (s)
10.10 (s)
10.12 (s)
6.80–7.39 (m)
6.80–7.39 (m)
6.80–7.39 (m)
6.80–7.39 (m)
6.80–7.39 (m)
6.80–7.39 (m)
6.84–7.38 (m)
6.84–7.38 (m)
6.84–7.38 (m)
6.84–7.38 (m)
6.84–7.38 (m)
6.84–7.38 (m)
—
—
—
—
—
10.26 (s)
—
—
(9)
(10)
(11)
(12)
—
—
—
(s) ¼ singlet, (d) ¼ doublet, (q) ¼ quteret, (m) ¼ multiplet.

504
T. D. THANGADURAI AND S.-K. IHM
ruthenium(II) complexes (Daniel Thangadurai and Natarajan,
2001a).
1H, 13C and 31P NMR Spectra
The 1H NMR spectra assignments are detailed in Table 4. It
1
is important to emphasize that the H resonance of the O–H
group at 10.00–10.89 ppm is due to the presence of intramole-
cular hydrogen bonding (Lindoy et al., 1977). The single
1
proton resonances in the H NMR spectra of these ligands,
which occur at 8.11 ppm for HL1 and 8.01 ppm for HL2, have
been assigned to the azomethine group proton. The aromatic
ring resonances in the ligands and all the complexes are
1
observed as multiplets. The detailed H NMR spectral data
of the ligands and ruthenium(II) complexes are given in
Table 4, and more detailed spectral investigation of cyclobu-
tane compounds can be found in the literature (Daniel Thanga-
durai and Ihm, 2004).
FIG. 1. Suggested structure of the ruthenium(II) Schiff base ligand (R and B
groups are as previously described).
1
The 13C NMR spectral data of the ligands confirm the H
NMR spectral results. Azomethine carbon atoms are
observed at 153.17 and 158.71 ppm, respectively, for HL1
and HL2.
Characteristic 13C NMR peaks for (HL1) (CDCl3, TMS, d
ppm): 120.06 (C1), 132.24 (C2), 121.52 (C3), 132.96 (C4),
118.87 (C5), 159.82 (C6), 153.17 (C7), 171.40 (C8), 101.63
(C9), 148.38 (C10), 32.06 (C11), 42.88 (C12), 45.15 (C13),
26.46 (C14), 145.63 (C15), 135.38 (C16), 132.44 (C17), 137.00
(C18), 22.42 (C19), 23.38 (C20).
Based on elemental analyses, spectral (IR, UV, 1H, 13C and
31P NMR), magnetic moment and thermal studies, the
suggested structure for the complexes is shown in Figure 1.
APPLICATIONS OF NEW RUTHENIUM(II) COMPLEXES
Catalytic Studies
Characteristic 13C NMR peaks for (HL2) (CDCl3, TMS, d
ppm): 121.80 (C1), 152.29 (C2), 121.73 (C3), 136.69 (C4),
113.04 (C5), 135.82 (C6), 158.71 (C7), 171.24 (C8), 101.69
(C9), 148.35 (C10), 32.20 (C11), 42.88 (C12), 45.15 (C13),
26.45 (C14), 145.63 (C15), 135.38 (C16), 132.44 (C17), 137.00
(C18), 22.42 (C19), 23.38 (C20).
31P NMR spectra were recorded in order to confirm whether
the PPh3 group or the heterocyclic base is present in the
complex. A singlet at d 26.74 and 26.54 ppm in the spectrum
of (2) and (8), respectively, confirmed the presence of triphe-
nylphosphine group in these complexes. However, the com-
plexes (3–5 and 9–11) exhibited no such signal confirming
the absence of triphenylphosphine in the complex (Table 4).
This observation revealed the presence of coordinated
pyridine or piperidine or morpholine in the complexes even
after the coordination of bidentate Schiff bases (Daniel
Thangadurai and Natarajan, 2002).
The synthesized ruthenium(II) complexes have been used as
catalysts in aryl-aryl coupling (Table 5). The system chosen for
our study is the coupling of phenylmagnesium bromide with
bromobenzene to give biphenyl as the product (Scheme 2).
Bromobenzene was first converted into the corresponding
Grignard reagent. Then bromobenzene, followed by the
complex chosen for the investigation, were added to the
above reaction medium, and the mixture was heated under
reflux for 7 h. After work up, the mixture yielded biphenyl.
Only a very little amount of biphenyl was formed when
the reaction was carried out without the catalyst. This is
TABLE 5
Yields of biphenyl with different mole ratios of PhMgBr and
ruthenium(II) complex
S. no.
[Ru(CO)(L1)2(PPh3)]
PhMgBra
Yieldb
Thermal Studies
1
2
3
4
5
0.0001
0.0003
0.0005
0.0007
0.0009
0.03
0.03
0.03
0.03
0.03
10.7
26.1
18.4
11.1
13.5
The TGA curves were studied in the 20–5008C range and
the curves showed that the thermal decomposition of the com-
plexes take place in several steps. It is possible that the diffe-
rent groups in ligands lead to a decrease in the stability of all
the complexes. Furthermore, it is known that the electronega-
tivity and the atomic radius of the central metal atom also
affects the thermal stability.
ain mole
bin (%).

STUDIES ON RUTHENIUM(II) COMPLEXES
505
The optimum quantity of catalyst required for the coupling
of phenylmagnesium bromide with bromobenzene has
been investigated by performing a series of experiments
using different mole ratios of phenylmagnesium bromide
and [Ru(CO)(L1)2(PPh3)] (3), and the results are presented in
Table 6. This study revealed the optimum mole ratio of the
Grignard reagent to ruthenium complex 100 : 1 in good agree-
ment with a recent observation (Gnanasoundari and Natarajan,
2004).
SCH. 2. Formation of biphenyl.
The yield of biphenyl obtained from the reactions catalyzed
by the new ruthenium(II) complexes are low when compared to
the yield obtained from the reaction catalyzed by NiCl2(PPh3)2.
(Gnanasoundari and Natarajan, 2004). The couplings catalyzed
by ruthenium complexes containing triphenylphosphine/
triphenylarsine yielded biphenyl in almost equal quantity indi-
cating non-participation of triphenylphosphine/triphenylarsine
in the catalytic cycle.
TABLE 6
Yields of biphenyl with ruthenium(II) complexes
as catalyst
Yield of Ph-Ph
S. no.
Catalyst
(in g)
(%)
1
2
(2)
(3)
(4)
(5)
(6)
(8)
(9)
(10)
(11)
(12)
0.410
0.383
0.376
0.431
0.416
0.503
0.407
0.425
0.404
0.495
26.1
24.4
23.9
27.4
26.5
32.0
25.9
27.1
25.7
31.5
3
Quantitative Antimicrobial Assay
4
The antimicrobial activities of the ligands and their ruthe-
nium(II) complexes have been screened against six different
bacteria and fungal by disc diffusion method (Daniel Thanga-
durai and Ihm, 2004) (Table 7). Different concentrations of the
complex in DMF solution (0.25 and 0.50%) were used for the
studies. The percentage inhibition was calculated as 100(C-T)/
C, where C is the average diameter of bacteria or fungal growth
on the control plate (DMF only) and T is the average diameter
of bacteria or fungal growth on the test plate.
5
6
7
8
9
10
an insignificant amount compared to the yields of biphenyl
obtained from the reactions catalyzed by ruthenium
complexes.
It has also been observed from the antimicrobial screening
studies that the ruthenium chelates have higher activity than
the corresponding free ligands against the same microorganism
TABLE 7
Antimicrobial effects of the ligands and ruthenium(II) complexes
Inhibition (%)
B.M.
0.25
C.a.
0.25
E.a
0.25
A.f.
0.25
F.o.
0.25
R.s.
0.25
Compound
0.50
0.50
0.50
0.50
0.50
0.50
Streptomycin
18
—
5
21
—
7
19
—
8
21
—
9
21
—
6
25
—
10
12
—
13
12
10
13
12
—
11
—
17
7
—
20
9
—
19
8
—
23
11
14
13
—
15
10
12
14
13
13
—
16
9
—
22
10
14
15
13
14
12
15
—
16
16
Bavistin
(1)
(2)
(3)
(5)
(6)
(7)
(8)
(9)
7
8
—
7
—
9
9
9
13
12
14
13
12
14
15
15
13
12
12
—
9
11
11
11
11
10
13
—
13
12
6
9
—
7
15
10
9
7
8
9
11
12
9
7
9
9
8
6
9
7
7
8
7
7
11
11
12
—
—
10
9
—
13
13
13
8
10
10
10
12
9
8
9
11
9
(10)
(12)
8
—
—
8
10
11

506
T. D. THANGADURAI AND S.-K. IHM
Daniel Thangadurai, T.; Son-Ki, Ihm. Novel bidentate ruthenium(III)
Schiff base complexes: synthetic, spectral, electrochemical, cataly-
tic and antimicrobial studies. Trans. Met. Chem. 2004, 29 (2),
189–195.
under identical experimental conditions, which is consistent
with earlier reports (Srivastva, 1980). It has been suggested
that the ligands with the N and O donor system might have
inhibited enzyme production, since enzymes which require a
free hydroxy group for their activity appear to the especially
susceptible to deactivation by the ions of the complexes. Chela-
tion reduces the polarity of the central ion mainly because of
the partial sharing of its positive charge with the donor
groups and possible p-electron delocalization within the
whole chelate ring, this chelation increases the lipophilic
nature of the central atom, which favors its permeation
through lipid layers of the cell membrane (Daniel Thangadurai
et al., 2002; Daniel Thangadurai and Natarajan, 2002;
Maruvada et al., 1994). Furthermore, the mode of action of
the compounds may involve the formation of hydrogen
bonds through the azomethine (.C55N) group of the com-
plexes with the active centers of cell constituents resulting in
the interference with normal cell processes (Singh et al.,
1995). Though the complexes possess activity, it could not
reach the effectiveness of the standard drugs such as Strepto-
mycin and Bavistin. Few compounds were inactive against
different organisms, the variation in the effectiveness of differ-
ent compounds against different organisms depends either on
the imper1eability of the cells of the microbes or differences
in ribosomes of microbial cells (Thangadurai and Ihm, 2003).
The toxic activity of the new compounds increases with
increase in the concentration of the solution.
Daniel Thangadurai, T.; Natarajan, K. Antibacterial activity of ruthe-
nium(II) carbonyl complexes containing tetradentate Schiff bases.
Trans. Met. Chem. 2002, 27 (5), 485–489.
Daniel Thangadurai, T.; Natarajan, K. Mixed ligand complexes of
ruthenium(II) containing a,b-unsaturated-b-ketoaminesand their
antibacterial activity. Trans. Met. Chem. 2001a, 26 (4–5),
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Daniel Thangadurai, T.; Natarajan, K. Synthesis and characterization
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Daniel Thangadurai, T.; Natarajan, K. Tridentate Schiff base
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