Synthesis and spectral studies of [RuCl(CO)(L)(PPh3)(B)] (HL = 2′-hydroxychalcones and B = PPh3, pyridine or piperidine) and their catalytic and biological applications

Article abstract of DOI:10.1016/j.saa.2004.11.001

The reactions of [RuHCl(CO)(PPh₃)₂(B)] (B = PPh ₃, pyridine or piperidine) and 2′-hydroxychalcones led to the formation of [RuCl(CO)(PPh₃)(L)(B)] (L = chalconate). The new complexes have been characterized by analytical and spectral (IR, electronic, ¹H NMR and ³¹P NMR) data. They have been assigned an octahedral structure. The complexes have been used as catalysts for the aerial oxidation of cinnamyl alcohol. Some of the complexes have been tested in vitro for growth inhibitory activity against the bacteria E. coli, S. typhi and Pseudomonas sp. and the fungi A. fumigatus.

Full text of DOI:10.1016/j.saa.2004.11.001

Spectrochimica Acta Part A 61 (2005) 2915–2918
Synthesis and spectral studies of [RuCl(CO)(L)(PPh3)(B)]
(HL = 2ꢀ-hydroxychalcones and B = PPh3, pyridine or piperidine)
and their catalytic and biological applications
M.V. Kaveri, R. Prabhakaran, R. Karvembu, K. Natarajan∗
Department of Chemistry, Bharathiar University, Coimbatore 641046, Tamil Nadu, India
Received 27 April 2004; accepted 1 November 2004
Abstract
The reactions of [RuHCl(CO)(PPh3)2(B)] (B = PPh3, pyridine or piperidine) and 2ꢀ-hydroxychalcones led to the formation of
[RuCl(CO)(PPh3)(L)(B)] (L = chalconate). The new complexes have been characterized by analytical and spectral (IR, electronic, 1H NMR
and 31P NMR) data. They have been assigned an octahedral structure. The complexes have been used as catalysts for the aerial oxidation of
cinnamyl alcohol. Some of the complexes have been tested in vitro for growth inhibitory activity against the bacteria E.coli , S.typhi and
Pseudomonas sp. and the fungi A.fumigatus .
© 2004 Elsevier B.V. All rights reserved.
Keywords: Ruthenium(II) complexes; Spectral studies; Catalytic oxidation; Antibacterial activity; Antifungal activity
1. Introduction
here disclose the simple procedure for the synthesis of ruthe-
nium(II) complexes containing triphenylphosphine and chal-
cone and also their catalytic and biological applications.
The selective oxidation of alcohols to carbonyl com-
pounds is a pivotal reaction in organic synthesis and many
stoichiometric oxidants notably chromium and manganese
reagents, producing enormous amounts of heavy metal
wastes, have been utilized to accomplish the reaction [1].
The search for catalytic oxidations with inexpensive green
oxidants, such as molecular oxygen or air, still play a key
role in the development of industrial processes [2]. In this
line, triphenylphosphine complexes of ruthenium have been
found to be efficient catalysts for the aerobic oxidation of
alcohols [3]. Besides, ruthenium triphenylphosphine com-
plexes also exhibited biological activity against pathogenic
microbes [4]. Hence, synthesis and spectral characterization
of new ruthenium complexes containing triphenylphosphine
are of greater importance. Moreover, transition metal com-
plexes of 2ꢀ-hydroxychalcones and related ligands have been
studied extensively due to their interesting behaviour as weak
field or strong field ligands to bivalent metal ions [5]. We
2. Experimental
2.1. Reagents and materials
All the reagents used were of analar or chemically pure
grade. The solvents used were freshly distilled by literature
methods [6]. The ligands 2ꢀ-hydroxychalcones [7] and com-
plexes of the type [RuHCl(CO)(B)(EPh3)2] (where B = PPh3,
pyridine or piperidine) [8] were prepared by the literature
methods.
2.2. Physical measurements
IR spectra of the complexes were recorded in KBr
pellets with a Nicolet FT-IR spectrophotometer in the
400–4000 cm−1 range. Electronic spectra of the complexes
have been recorded in methanol using a Systronics 119 spec-
∗
Corresponding author. Tel.: +91 422 2424655; fax: +91 422 2422387.
E-mail address: k natraj6@yahoo.com (K. Natarajan).
1386-1425/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2004.11.001

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M.V.Kaveri et al./ Spectrochimica Acta Part A 61 (2005) 2915–2918
1
trophotometer in the 200–800 nm range. H NMR and 31P
NMR spectra were recorded in Varian AMX-400 instrument
using TMS and orthophosphoric acid as the standards, re-
spectively. Microanalysis of the complexes was performed
by VarioEL III elemental analyzer.
2.3. Recommended procedures
2.3.1. Synthesis of ruthenium(II) complexes
To
a solution of [RuHCl(CO)(B)(EPh3)2] (where
B = PPh3 or pyridine or piperidine) (0.077–0.11 g; 0.1 mmol)
in benzene (20 cm3), the appropriate chalcone ligands
(0.24–0.284 g; 0.1 mmol) were added in 1:1 molar ratio. The
mixture was heated under reflux for 5 h. The resulting solu-
tion was concentrated to about 3 cm3. The product was sep-
arated by the addition of small amount of petroleum ether
(60–80 ◦C) and recrystallized from CH2Cl2/petroleum ether
mixture and dried under vacuum.
Fig. 1. Structure of 2ꢀ-hydroxychalcones.
ical data (Table 1) of all the complexes are in good agreement
with the proposed formula (Fig. 1).
3.1. Spectroscopic studies
In the IR spectra of the free ligands (Table 2), a strong band
is observed around 1640 cm−1 due to ν(C O). This has been
shifted to a lower wave number by 20–30 cm−1 in the ruthe-
nium complexes indicating the coordination of the ligands to
ruthenium through the carbonyl oxygen atom [5a]. The phe-
nolic C O stretching absorptions of the free ligands occur as
a doublet in the region 1330–1360 cm−1. This band has been
shifted to higher wave number in the spectra of the complexes
due to its coordination to ruthenium ion through the oxygen
atom of the phenolic group and appeared as a singlet or a
doublet. Further, the absorption due to ν(O H) was not ob-
served in the infrared spectra of the complexes in the region
3400–3600 cm−1 suggesting the deprotonation of the ligands
prior to coordination to ruthenium metal. Hence, from the in-
frared spectral data, it is inferred that both the carbonyl and
phenolic oxygen atoms are involved in the coordination of
the chalcones to ruthenium ion in all the complexes. The ab-
sorption due to ν(C C) of the free ligands appeared as a sep-
arate band in their infrared spectra around 1600 cm−1, but the
same could not be identified in the spectra of the ruthenium
complexes because of their possible merging with ν(C O)
[9]. In the complexes, the absorption due to the phenylalkene
vibration appeared in the region 1530–1560 cm−1, which is
slightly lower than that observed in the spectra of the free
2.3.2. Catalytic studies
The catalytic activity of ruthenium(II) complexes in aerial
oxidation of cinnamaldehyde was followed spectrophotomet-
rically by monitoring the increase in the cinnamic acid ab-
sorbance as a function of time. A CH2Cl2 solution of the
ruthenium(II) complexes (2 cm3, 1 × 10−4 M) and freshly
distilled cinnamaldehyde in CH2Cl2 (2 cm3, 1 × 10−4 M)
were mixed in a 1 cm quartz cell at room temperature (26 ◦C)
and the absorbance change at 279 nm was recorded.
3. Results and discussion
All the complexes are in brown colour. Air and light sta-
ble complexes of general formula [RuCl(CO)(L)(PPh3)(B)]
(where L = 2ꢀ-hydroxychalcones and B = PPh3, pyridine (py)
or piperidine (pip)) have been obtained from the reaction of
equimolar amounts of [RuHCl(CO)(PPh3)2(B)] (B = PPh3,
py or pip) and 2ꢀ-hydroxychalcones (HL) in boiling benzene
for 5 h. In all these reactions, it has been observed that the 2ꢀ-
hydroxychalcones behave as uninegative bidentate chelating
ligands by replacing one of the triphenylphosphine groups
and the hydride ion from the starting complexes. The analyt-
Table 1
Analytical data of new ruthenium(II) complexes
Complex
Yield (%)
mp (◦C)
Calculated (found) (%)
C
H
N
[RuCl(CO)(PPh3)2(L1)]
64
61
60
59
63
56
60
58
52
158
138
129
136
118
123
147
150
111
68.94 (69.54)
65.96 (64.32)
67.90 (66.80)
64.64 (64.38)
61.34 (62.06)
63.16 (62.06)
65.73 (64.72)
60.86 (61.50)
62.77 (61.05)
4.68 (5.61)
4.25 (4.10)
4.80 (4.26)
4.47 (4.86)
3.96 (4.28)
4.92 (4.84)
5.24 (5.47)
4.70 (4.92)
4.15 (4.08)
–
–
–
[RuCl(CO)(PPh3)2(L2)]
[RuCl(CO)(PPh3)2(L3)]
[RuCl(CO)(PPh3)(py)(L1)]
[RuCl(CO)(PPh3)(py)(L2)]
[RuCl(CO)(PPh3)2(py)(L3)]
[RuCl(CO)(PPh3)(pip)(L1)]
[RuCl(CO)(PPh3)2(pip)(L2)]
[RuCl(CO)(PPh3)2(pip)(L3)]
1.88 (2.08)
1.83 (1.98)
1.81 (2.21)
1.86 (2.16)
1.82 (2.10)
1.80 (1.92)

M.V.Kaveri et al./ Spectrochimica Acta Part A 61 (2005) 2915–2918
2917
Table 2
IR absorption frequencies (cm−1) and electronic spectral data (nm) of free ligands and their ruthenium(II) complexes
Compound
ν(C≡O)
ν(C=O)
ν(Ph
ν(C=C)
λmax (nm)
C
O)
HL1
–
–
–
1640 s
1635 s
1638 s
1619 s
1905 s
1918 s
1905 s
1605 s
1618 s
1610 s
1618 s
1610 s
1339 m
1341 m
1340 m
1346 m
1358 m
1355 m
1357 m
1357 m
1377 m
1378 m
1376 m
1380 m
1582 s
1577 s
1580 s
1580 s
1548 s
1589 s
1586 s
1546 s
–
–
–
–
340
345, 265
330, 270
340, 270
335, 225
340, 265
330, 270
344, 230
360, 270
HL2
HL3
[RuCl(CO)(PPh3)2(L1)]
[RuCl(CO)(PPh3)2(L2)]
[RuCl(CO)(PPh3)2(L3)]
[RuCl(CO)(PPh3)(py)(L1)]
[RuCl(CO)(PPh3)(py)(L2)]
[RuCl(CO)(PPh3)(py)(L3)]
[RuCl(CO)(PPh3)(pip)(L1)]
[RuCl(CO)(PPh3)(pip)(L2)] [RuCl(CO)(PPh3)(pip)(L3)]
HL1
1946 vs
1945 vs
1960 vs
1945 vs
1948 vs
1952 vs
1944 vs
1943 vs
1949 vs
–
1545 s
1556 s
vs: very strong; s: strong; m: medium intensity.
ligands [7b]. A strong band around 1940 cm−1 indicates the
presence of terminally coordinated carbon monoxide [4b].
The other characteristic absorptions due to triphenylphos-
phine were also found to be present in the expected region
[10]. In the case of the complexes containing coordinated
heterocyclic nitrogen bases, a medium intensity band was
observed in the region 1000–1025 cm−1 [8b].
All the new complexes have been found to be diamagnetic
indicating the presence of ruthenium in +2 oxidation state
arising from t62g configuration. The electronic spectra of all
thecomplexesweretakeninmethanolandtheyshowedtwoto
three bands in the region 380–225 nm (Table 3). The bands
around 380–315 nm have been assigned to charge transfer
transition arising from the excitation of an electron from the
metal t2g level to the unfilled molecular orbitals derived from
the ␲* level of the ligands [3b]. The bands that appeared be-
low 300 nm are characterized by intra-ligand charge transfer.
All the ruthenium complexes exhibit a multiplet at
Fig. 2. Proposed structure of new ruthenium(II) complexes.
31P NMR spectra were recorded in order to confirm the
presence of triphenylphosphine groups and to determine the
geometry of the complexes. In the case of the complexes
containing two triphenylphosphine ligands, a sharp singlet
was observed at 24.49 ppm for the presence of magnetically
equivalent phosphorus atoms suggesting the presence of two
triphenylphosphine groups in a position trans to each other.
The spectrum of all other complexes exhibited a singlet at
24.46 ppm corresponding to the presence of triphenylphos-
phine group in a position trans to heterocyclic nitrogen base.
Based on the analytical and spectral data, an octahedral
structure (Fig. 2) has been tentatively proposed for all the
ruthenium(II) complexes.
1
6.95–7.96 ppm in their H NMR spectra (Table 3), which
has been assigned to the protons of phenyl groups present in
the triphenylphosphine and 2ꢀ-hydroxychalcone ligand. The
signal due to two alkene protons also appeared in the re-
gion 6.9–7.1 ppm and hence, merged with the multiplet of
aromatic protons. This clearly revealed the absence of alkene
coordination to the metal. If alkene carbons were coordinated
to the metal, the resonance due to the protons on the alkene
carbon would have been shifted to lower δ value at least by
2 ppm [11]. In addition, the signal corresponding to CH3 and
piperidine were also observed in the expected region.
3.2. Catalytic oxidation
The catalytic activity of ruthenium(II) complexes in aerial
oxidation of cinnamaldehyde was followed spectrophotomet-
Table 3
1H NMR and 31P NMR data (δ in ppm) of ruthenium(II) complexes
Complex
1H NMR
31P NMR
a
[RuCl(CO)(PPh3)2(L2)]
[RuCl(CO)(PPh3)2(L3)]
6.95–7.96 (m, CH CH and aromatic)
7.06–7.96 (m, CH CH and aromatic)
24.49
[RuCl(CO)(PPh3)(py)(L1)]
[RuCl(CO)(PPh3)(py)(L2)]
[RuCl(CO)(PPh3)(pip)(L1)]
[RuCl(CO)(PPh3)2(pip)(L3)]
7.15–7.7 (m, CH CH and aromatic), 1.28 (s, CH3)
6.6–6.9 (m, CH CH ), 7.0–7.9 (m, aromatic)
7.2–7.9 (m, CH CH and aromatic), 3.1–3.4 (m, piperidine)
7.0–7.9 (m, CH CH and aromatic), 3.1–3.4 (m, piperidine)
24.46
a
24.66
24.66
a
Not recorded.

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MV..Kaveri et al./ Spectrochimica Acta Part A 61 (2005) 2915–2918
Table 4
chelates may be due to the effect of the metal ion on the nor-
malcellprocess. Apossiblemodefortoxicityincreasemaybe
considered in the light of Tweedy’s chelation theory. Chela-
tion reduces the polarity of the metal ion because of partial
sharing of its positive charge with the donor groups and the
␲-electron delocalization over the whole chelate ring. Such
chelation could enhance the lipophilic character of the cen-
tral metal atom, which subsequently favours its permeation
through the lipid layers of the cell membrane. It has been ob-
served that complexes containing heterocyclic nitrogen base
possess more activity than other complexes.
Catalytic activity data of ruthenium(II) complexes
Complex
Rate constant, k (M−1 S−1
)
[RuCl(CO)(PPh3)2(L1)]
[RuCl(CO)(PPh3)2(L2)]
[RuCl(CO)(PPh3)2(L3)]
1.8 × 10−2
2.1 × 10−2
3.0 × 10−2
Table 5
Antibacterial activity data of ruthenium(II) complexes
Compound
Diameter of inhibition
zone (mm)
E.coli
S.typhi
0.25%
0.5%
0.25%
0.5%
HL2
4
6
10
18
6
8
1
5
6
9
8
8
17
11
9
4. Conclusion
[RuCl(CO)(PPh3)2(L2)]
[RuCl(CO)(py)(PPh3)(L2)]
[RuCl(CO)(pip)(PPh3)(L2)]
In conclusion, we have synthesized nine ruthe-
nium(II) complexes containing triphenylphosphine and 2ꢀ-
hydroxychalcones. All the complexes have been character-
ized on the basis of analytical and spectral data. The com-
plexes showed significant catalytic oxidation activity and bi-
ological activity.
20
Table 6
Antifungal activity data of ruthenium(II) complexes
Compound
Diameter inhibition zone (mm)
(A.fumigatus )
0.25%
0.5%
HL1
1.8
3.3
3.9
3.4
3.8
2.9
5.7
6.8
7
References
[RuCl(CO)(PPh3)2(L1)]
[RuCl(CO)(PPh3)(py)(L1)]
[RuCl(CO)(PPh3)(pip)(L1)]
[RuCl(CO)(AsPh3)2(L1)]
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7.9
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