Chiral schiff base ruthenium(II) carbonyl complexes: Synthesis, characterization, catalytic and antibacterial studies

Article abstract of DOI:10.1080/15533170600732767

Chiral Schiff base ruthenium(II) carbonyl complexes of the type [Ru(CO)(L′)(B)] (L′= tetradentate Schiff bases; B=PPh 3 , pyridine (py), piperidine (pip) or morpholine (morph)) has been synthesised by the reactions of [RuHCl(CO)(PPh 3 ) 2 (B)] (B=PPh 3 or

Full text of DOI:10.1080/15533170600732767

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Chiral Schiff Base Ruthenium(II) Carbonyl Complexes:
Synthesis, Characterization, Catalytic and Antibacterial
Studies
T. Daniel Thangadurai a & Son‐Ki Ihm b
a Laboratory for Chemistry and Biochemistry for Pharmacology and Toxicology, CNRS UMR
8601 , University Rene Descartes , Paris, France
b Department of Chemical and Biomolecular Engineering , Korea Advanced Institute of
Science and Technology , Daejeon, Republic of Korea
Published online: 15 Feb 2007.
To cite this article: T. Daniel Thangadurai & Son‐Ki Ihm (2006) Chiral Schiff Base Ruthenium(II) Carbonyl Complexes:
Synthesis, Characterization, Catalytic and Antibacterial Studies, Synthesis and Reactivity in Inorganic, Metal-Organic, and
Nano-Metal Chemistry, 36:5, 435-440
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Synthesis and Reactivity in Inorganic, Metal-Organic and Nano-Metal Chemistry, 36:435–440, 2006
Copyright # 2006 Taylor & Francis Group, LLC
ISSN: 0094-5714 print/1532-2440 online
DOI: 10.1080/15533170600732767
Chiral Schiff Base Ruthenium(II) Carbonyl Complexes:
Synthesis, Characterization, Catalytic and Antibacterial Studies
T. Daniel Thangadurai
Laboratory for Chemistry and Biochemistry for Pharmacology and Toxicology, CNRS UMR 8601,
University Rene Descartes, Paris, France
Son-Ki Ihm
Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science
and Technology, Daejeon, Republic of Korea
designing metal complexes related to synthetic and natural
Chiral Schiff base ruthenium(II) carbonyl complexes of the oxygen carriers.[6] Extensive information is available on the
type [Ru(CO)(L0)(B)] (L05 tetradentate Schiff bases; B 5 PPh3,
pyridine (py), piperidine (pip) or morpholine (morph)) has been
chemistry of transition metal complexes containing Schiff
bases, related mostly to first row transition metals, relatively
synthesised by the reactions of [RuHCl(CO)(PPh3)2(B)]
(B 5 PPh3 or py or pip or morph) with appropriate Schiff bases
little work has been done on ruthenium complexes containing
Schiff bases.[7] Ruthenium complexes, by virtue of their wide
having the donor groups (O,N) viz., bis[3(10-naphthyl)salicylidene-
cyclohexanediimine] (L1) or bis[3(10-naphthyl)salicylidenepropy- range of reversible and accessible oxidation states, have
lenediimine] (L2) or bis[3(10-naphthyl)salicylidenediphenyldii
mine] (L3) in 1 : 1 molar ratio. Complexes have been characterized
proved to be useful catalysts in many reactions such as
hydrogenation, oxidation, carbonylation, hydroformylation,
etc.[8–10] In addition, some ruthenium carbonyl complexes
by elemental analyses and spectral (IR, electronic, 1H- and
31P-NMR) data. An octahedral structure has been tentatively
proposed for all the new complexes. The catalytic and anti-
play an important role in homogeneous catalysis.[11] In view
bacterial activities have also been carried out for these new of not only to investigate the coordination behavior of chiral
complexes.
Schiff bases containing N2O2 chromophores, but also to
assess the catalytic and biological activity of new complexes,
we report the synthesis, spectral, catalytic and antibacterial
studies of ruthenium(II) carbonyl complexes of the type
[Ru(CO)(L0)(B)] (L0 ¼ chiral Schiff bases; B ¼ PPh3,
pyridine (py), piperidine (pip) or morpholine (morph)). The
general structure of chiral Schiff base ligands used in this
study is shown in Figure 1.
Keywords chiral ligand, ruthenium(II), deprotonation, steric effect,
chelation
INTRODUCTION
During the past decades, there has been a great deal of
interest in the synthesis and characterization of transition
metal Schiff base chelates because of their importance as cata-
lysts in many reactions.[1–4] Recently, Kureshy et al. reported,
enantioselective epoxidation of non functionalised olefins, viz.
cis-stilbene, trans-3-nonene and trans-4-octene with iodosyl
benzene as oxidant was demonstrated in the presence of cata-
lytic amounts of chiral Schiff base metal complexes.[5] Further-
more, tetradentate Schiff base complexes are important in
EXPERIMENTAL
Commercially available RuCl3.3H2O was used without
further purification. The solvents were purified and dried
according to the standard procedures.[12] Elemental analyses
were carried out by using Carlo Erba 1106 elemental
analyzer. IR spectra were recorded with Nexus FTIR spectro-
photometer in the range 4000–500 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-NMR and 31P-NMR
spectra were recorded on a Brucker 400 MHz instrument
using TMS and o-phosphoric acid as an internal reference,
respectively. The starting complexes[13] and Schiff base
Received 23 January 2006; accepted 29 March 2006.
Address correspondence to Center for Superfunctional Materials,
Department of Chemistry, Pohang University of Science and Technol-
ogy, San 31, Hyojo-dong, Nam-gu, Pohang 790-784, Republic of
Korea. Eail: thanga_durai2000@yahoo.com
435

436
T. D. THANGADURAI AND S.-K. IHM
suspensions of pathogenic bacteriocides. By using the steri-
lized cork borer, wells were dug in the center of the culture
plates. The test complex solution (0.5 mL) in DMSO was
added to these wells, and the plates were incubated at
26 + 28C for 24 h. Then the inhibition zone appeared around
the wells in each plate was measured and recorded as the cyto-
toxic effect of the appropriate complexes. The solvent only
treated plate was maintained separately in order to avoid the
activity due to solvent, if any. Streptomycin sulfate was used
as a standard.
RESULTS AND DISCUSSION
Chiral Schiff base ligands react with [RuHCl(CO)(PPh3)2
(B)] (B ¼ PPh3 or py or pip or morph) in 1 : 1 molar ratio in
benzene to afford stable chelated ruthenium(II) carbonyl com-
plexes as shown below (Scheme 1). The new complexes are
soluble in most of the common organic solvents. Molecular
weight determination (Rast method) and elemental analysis
FIG. 1. Structure of chiral Schiff base ligands.
ligands[14] have been prepared by the procedures available in data (Table 1) confirm the complexes to be a hexa-coordinated.
literature.
Infrared Spectra
The IR spectra of the Schiff base ligands were compared
General Procedure for Preparation of [Ru(CO)(L’)(B)]
(L’ 5dibasic chiral Schiff base ligand; B 5 PPh3 or py or
pip or morph)
with that of the ruthenium complexes to obtain the information
about the binding mode of the ligands to ruthenium metal in the
To a benzene (20 mL) solution of [RuHCl(CO)(PPh3)3] or
[RuHCl(CO)(PPh3)2(B)] (B ¼ py or pip or morph) (0.077–
0.095 g, 0.01 mmol), added the appropriate Schiff base
ligands (0.060–0.087 g, 0.01 mmol) (molar ratio of the ruthe-
nium complex : ligand ¼ 1 : 1). 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
precipitated by petroleum ether (60–808C). The complexes
were filtered, washed with petroleum ether and recrystallised
from CH2Cl2/petroleum ether (60–808C) and its purity was
checked by TLC (yield: 75–85%).
complexes (Table 2). A strong band was observed at 1640–
1620 cm21 in the spectra of the free Schiff bases, which is
the characteristic of the azomethine (2HC55N) group. It is
expected that coordination of the nitrogen to the metal atom
would reduce the electron density in the azomethine group
and thus lower the 2HC55N absorption. In the IR spectra of
the complexes, this band is shifted to the region at 1615–
1595 cm21, indicating the coordination of the Schiff bases
Catalytic Studies
The catalytic activity of ruthenium(II) carbonyl complexes
in aerial oxidation of cinnamaldehyde was followed by spec-
trometrically monitoring the increase in the cinnamic acid
absorbance as a function of time. A chloroform solution of
the ruthenium(II) complex (2 mL, 1 ꢀ 1024 M) and 2 mL of
1 ꢀ 1023 M freshly distilled cinnamaldehyde in chloroform
was mixed in 1 cm quartz cell at room temperature (248C)
and the absorbance change at 280 nm was recorded.
Antibacterial Studies
Two pathogenic microbials were used to test the biological
activity of the ligands and their ruthenium(II) carbonyl com-
plexes, namely, S. aureus and S. typhi. The nutrient agar (NA)
medium was prepared[15] and a quantity of 10 mL of the
medium was poured into the sterilized Petri plates and
allowed to solidify. The plates were inoculated with spore
SCH. 1. Preparation of chiral Schiff base Ruthenium(II) complexes.

CHIRAL SCHIFF BASE RUTHENIUM(II) CARBONYL COMPLEXES
437
TABLE 1
Analytical data of Schiff base ruthenium(II) carbonyl complexes
Found (Calcd.) %
S. No
Complex
Color
M. Pt. 8C
C
H
N
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
[Ru(CO)(L1)(PPh3)]
[Ru(CO)(L1)(py)]
[Ru(CO)(L1)(pip)]
[Ru(CO)(L1)(morph)]
[Ru(CO)(L2)(PPh3)]
[Ru(CO)(L2)(py)]
[Ru(CO)(L2)(pip)]
[Ru(CO)(L2)(morph)]
[Ru(CO)(L3)(PPh3)]
[Ru(CO)(L3)(py)]
[Ru(CO)(L3)(pip)]
[Ru(CO)(L3)(morph)]
Green
Green
Green
Green
Green
Green
Green
Green
Green
Green
Green
Green
135
120
125
130
127
140
155
135
155
151
130
140
76.10(76.48)
80.92(81.89)
80.70(81.08)
79.00(78.57)
72.80(72.78)
68.20(68.76)
65.90(65.70)
67.30(67.35)
75.80(75.75)
73.73(73.77)
73.20(73.23)
70.95(71.78)
5.70(5.61)
5.75(6.09)
6.70(6.76)
6.40(6.46)
4.60(4.69)
5.90(5.78)
5.03(4.88)
4.97(4.98)
4.79(4.65)
4.60(4.48)
5.10(5.02)
5.01(4.96)
2.79(2.83)
5.61(5.62)
5.59(5.68)
6.29(6.41)
3.10(3.03)
5.68(5.60)
5.36(5.35)
5.60(5.61)
2.60(2.64)
4.90(4.78)
4.91(4.85)
4.81(4.74)
(9)
(10)
(11)
(12)
through azomethine nitrogen.[16] A strong band was obtained at assigned to the charge transfer transitions.[20] The nature of
1290–1270 cm21 in the free Schiff bases, which has been the electronic spectra of all the complexes indicates that an
assigned to phenolic C–O absorption. On complexation, this octahedral geometry around ruthenium ion in the complexes
band was shifted to a higher frequency range 1320– and the spectra are very similar to the ones observed for the
1300 cm21, indicating the other coordination of Schiff bases other ruthenium(II) complexes.[21]
through the phenolic oxygen atom.[17] This has been further
supported by the disappearence of the broad band at
1H and 31P-NMR Spectra
ꢀ3000 cm21 n(OH) in the complexes indicating the deprotona-
1
The H-NMR spectra of the complexes were recorded to
confirm the presence of coordinated chiral Schiff bases in the
ruthenium(II) complexes and are presented in Table 2. In com-
plexes (1–4), mutiplets observed in the regions d 1.86–2.06
and 2.60–2.75 ppm has been assigned to methylene group
protons and methine proton, respectively. The presence of
doublets and a multiplet in the regions d 1.20–1.23, 2.10–
2.13 and 2.35–2.40 ppm in complexes (5–8), has been
assigned to methyl protons, methylene protons and methine
proton, respectively. The presence of a sharp singlet at d
2.55–2.60 ppm in the spectra of complexes (9–12), has been
assigned as due to the methine proton. In all the complexes,
tion occurs prior to coordination. The spectra of all the com-
plexes showed a very strong absorption around ꢀ1950 cm21
due to the coordinated carbonyl group. The complexes
contain coordinated nitrogen bases, a medium intensity band
was observed in the 1020–1000 cm21 region, corresponding
to the coordinated pyridine, piperidine and morpholine.[18]
Thus, the IR spectral data reveal the dibasic tetradentate
behavior of chiral Schiff base moiety in all the ruthenium
complexes.
Electronic Spectra
All the ruthenium(II) complexes are diamagnetic, indicating a multiplet observed in the region d 7.20–8.20 ppm has
the presence of ruthenium in þ2 oxidation state. The ground assigned to the protons in triphenyl phosphine, heterocyclic
state of ruthenium(II) (t62 g configuration) in an octahedral nitrogen bases and naphthyl. A sharp singlet at d 8.90–
1
environment is A1 g and the excited states corresponding 10.00 ppm in the spectra of all the complexes has assigned to
3
3
1
1
to the t52 g e1g configuration are T1 g, T2 g, T1 g and T2 g
Hence, four bands corresponding to the transitions are in good agreement with the values reported for similar
.
azomethine proton signal. The above spectral observations
1A1 g! T1 g, A1 g! T2 g, A1 g! T1 g and A1 g! T2 g are chiral Schiff base complexes.[14]
3
1
3
1
1
1
1
possible in the order of increasing energy. The electronic
The 31P-NMR spectra were recorded for few complexes to
spectra of all these complexes in dichloromethane showed confirm the presence of triphenylphosphine group or hetero-
one or two bands in the 550–320 nm region. The bands in cyclic nitrogen base in the complexes. The signal appeared at
the 550–495 nm range were assigned to the spin-allowed d 26.05, 26.10 and 25.99 ppm in the spectrum of (1), (5) and
1
1A1 g! T1 g transition based on the low extinction coefficient (9) respectively, confirmed the presence of triphenylphosphine
values ([) as compared to charge transfer bands.[19] The group in these complexes. However, complexes (2), (7)
other high intensity bands in the 375–320 nm region were and (10) exhibited no such signal confirming the absence of

TABLE 2
IR, Electronic and NMR spectral data of ruthenium (II) carbonyl complexes
Cpx. No
n(C O)a
;;
n
(C–O)a
n
(C55N)a
l
maxb
([)
1H-NMR
31P-NMR
26.05
(1)
1940 vs
1945 vs
1945 vs
1950 vs
1950 vs
1310 s
1310 s
1300 s
1310 s
1315 s
1595 vs
1600 vs
1600 vs
1615 vs
1595 vs
500
340
495
325
320
(878)
(3099)
(729)
1.86–2.01 (m, 4(CH2)), 2.60–2.69 (m, CH),
7.20–8.00 (m, aromatic), 8.90 (s, N55CH)
1.88–2.05 (m, 4(CH2)), 2.63–2.74 (m, CH),
7.22–8.03 (m, aromatic), 9.00 (s, N55CH)
1.89–2.04 (m, 4(CH2)), 2.63–2.75 (m, CH),
7.23–8.10 (m, aromatic), 8.90 (s, N55CH)
1.86–2.06 (m, 4(CH2)), 264–2.72 (m, CH),
7.21–8.00 (m, aromatic), 9.00 (s. N55CH)
1.20–1.22 (d, CH3), 210–211 (d, CH2),
2.35–2.39 (m, CH), 7.20–8.00
(2)
(3)
(4)
(5)
no signal
(4294)
(4038)
a
550
375
340
(979)
(5415)
(4312)
a
26.10
(m, aromatic), 8.90 (s, N55CH)
(6)
(7)
(8)
1960 vs
1955 vs
1940 vs
1310 s
1320 s
1315 s
1610 vs
1605 vs
1600 vs
500
360
(747)
(4011)
1.20–1.23 (d, CH3), 2.10–2.13 (d, CH2),
2.35–2.40 (m, CH), 7.20–8.20
(m, aromatic), 8.93 (s, N55CH)
1.20–1.23 (d, CH3), 2.10–2.12 (d, CH2),
2.35–2.39 (m, CH), 7.20–8.00
(m, aromatic), 9.00 (s, N55CH)
1.20–1.23 (d, CH3), 2.10–2.11 (d, CH2),
2.35–2.39 (m, CH), 7.20–8.00
(m, aromatic), 8.96 (s, N55CH)
a
365
(5067)
no signal
a
495
370
(887)
(5567)
(9)
(10)
(11)
(12)
1945 vs
1960 vs
1950 vs
1960 vs
1310 s
1300 s
1300 s
1320 s
1595 vs
1610 vs
1615 vs
1610 vs
330
(4987)
2.55 (s, CH), 7.20–7.90 (m, aromatic),
9.97 (s, N55CH)
2.58 (s, CH), 7.20–8.00 (m, aromatic),
9.99 (s, N55CH)
2.55 (s, CH), 7.20–7.90 (m, aromatic),
9.98 (s, N55CH)
2.60 (s, CH), 7.20–8.00 (m, aromatic),
9.97 (s, N55CH)
25.99
505
325
370
(937)
(4576)
(4847)
no signal
a
a
320
(5978)
a ¼ cm21; b ¼ nm; s-strong; vs- very strong; [ -dm3 mol21 cm21; s-singlet; d-doublet; m-multiplet; a-not recorded.

CHIRAL SCHIFF BASE RUTHENIUM(II) CARBONYL COMPLEXES
439
triphenylphosphine group. This observation indicates the reten-
TABLE 4
Antibacterial activity data of Schiff base ligands and
ruthenium(II) carbonyl complexes
tion of coordinated pyridine or piperidine or morpholine in the
complexes even after the coordination of tetradentate Schiff
bases. The 31P-NMR spectral studies clearly indicate a more
labile Ru-P bond compared to Ru-N bond in these com-
plexes, which is a reflection of better s-donating ability
of the nitrogen bases compared to that of phosphorus in
triphenylphosphine.[19]
Diameter of inhibition zone (mm)a
S. aureus S. typhi
1%
Compound
1%
2%
9
2%
9
Streptomycin sulfate
(standard antibiotic)
7
6
Catalytic Studies
The catalytic activitiy of complexes (1), (3), (5), (7), (9) and
(11) was investigated for aerial oxidation of cinnamaldehyde to
cinnamic acid. The course of the reaction was followed spec-
trometrically by monitoring the increase in benzoic acid absor-
bance at 280 nm as a function of time. Plots of the absorbance
versus time were linear. The slope of the line is equal to the
reaction rate constant K, the observed K values are given in
Table 3. There is no change in absorbance at 280 nm in the
absence of complex, indicating the catalytic activity of new
complexes. The catalytic activity was found to decrease with
increase in size of the diamino group.[22] This may be due to
possibility of steric effect which hindered the formation of acti-
vated complex and thus reduced the rate of oxidation.[23] Based
on the low extinction coefficient values ([ ¼ 24,987) as
compared to trans-isomer, the product was assigned to be a
cis- isomer (Table 4).
(L1)
(1)
(2)
(L2)
(5)
(6)
(L3)
(10)
(12)
3
7
5
1
3
3
2
4
3
5
8
6
2
5
5
5
6
7
1
4
4
1
2
3
3
5
4
4
7
6
2
4
5
5
7
8
a1% and 2% indicate 1 g and 2 g of the compound in 100 mL of test
solution.
identical experimental conditions, which is consistent with
earlier reports.[25] This can be attributed to the Tweedy’s chela-
tion theory, according to which the chelation reduces the
polarity of the metal atom mainly because of the partial
sharing of its positive charge with donor group and possible
p-electron delocalisation over the whole ring.[26,27] This
increases the lipophilic character of the metal chelate which
favours its permeation through lipid layers of the bacterial
membranes. Furthermore, the mode of action of the com-
pounds may involve the hydrogen bond through the .C55N
group with active centres of cell constituents resulting in the
interference with normal cell process.[28] Though the com-
plexes possess activity, it could not reach the effectiveness of
the standard drug (Streptomycin sulfate). The variation in the
Antibacterial Studies
The antibacterial activities of the complexes were studied
by Agar-Well diffusion method.[24] Seven days old cultures
of S. aureus and S. typhi were used as a test organisms which
were grown on nutrient agar (NA) medium. Then, 1% and
2% solutions of the complexes in DMSO were used for the
studies. From the results it is concluded that the ruthenium(II)
carbonyl complexes possess more activity than their parent
ligand and the toxicity increases with increase in concentration
of the test solution containing new complexes (Table 4). It has
also been observed from the antibacterial screening studies that
the ruthenium chelates have higher activity than the corre-
sponding free ligands against the same microorganism under
TABLE 3
Catalytic activity of ruthenium(II)
carbonyl complexes
Cpx. No.
K (M21 s21
)
(1)
(3)
(5)
(7)
(9)
(11)
1.316 ꢀ 1023
1.161 ꢀ 1023
2.718 ꢀ 1023
3.008 ꢀ 1024
3.871 ꢀ 1025
4.113 ꢀ 1025
FIG. 2. General structure of the ruthenium(II) carbonyl complexes.

440
T. D. THANGADURAI AND S.-K. IHM
14. Kureshy, R. I.; Khan, N. H.; Abdi, S. H. R.; Bhatt, A. K.; Iyer, P.
Synthesis, physicochemical studies and aerobic enantioselective
epoxidation of non-functionalized olefins catalyzed by new
Co(II) chiral salen complexes. J. Mol. Cat. 1997, 121, 25–31.
15. DanielThangadurai, T.;Natarajan, K. Synthesisandcharacterisation
of new ruthenium(III) complexes containing tetradentate Schiff
bases. Synth. Recat. Inrog. Met.-Org. Chem. 2001, 31, 549–568.
16. Daniel Thangadurai, T.; Natarajan, K. Tridentate Schiff base
complexes of ruthenium(III) containing ONS/ONO donor
atoms and their biocidal activities. Trans. Met. Chem. 2001, 26,
717–722.
effectiveness of different compounds against different organ-
isms depends either on the impermeability of the cells of the
microbes or differences in ribosomes of microbial cells.[29]
The following octahedral structure has been tentatively
proposed for all the new ruthenium(II) carbonyl complexes
1
based on the analytical and spectral (IR, electronic, H- and
31P-NMR) data (Figure 2).
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