Synthesis and spectral characterization of 2′-hydroxy chalconate complexes of ruthenium(II) and their catalytic and biological applications

Article abstract of DOI:10.1016/j.saa.2007.10.043

The reactions of [RuHCl(CO)(B)(EPh₃)₂] (B = EPh₃ or pyridine; E = P or As) and 2′-hydroxychalcones in 1:2 ratio led to the formation of [Ru(CO)(B)(L)₂] (B = PPh₃, AsPh₃ or Py; L = 2′-hydrox

Full text of DOI:10.1016/j.saa.2007.10.043

Available online at www.sciencedirect.com
Spectrochimica Acta Part A 70 (2008) 1222–1226
Synthesis and spectral characterization of 2ꢀ-hydroxy chalconate
complexes of ruthenium(II) and their catalytic and
biological applications
M. Muthukumara, P. Viswanathamurthia,∗, K. Natarajanb
a Department of Chemistry, Periyar University, Salem 636011, India
b Department of Chemistry, Bharathiar University, Coimbatore 641046, India
Received 4 October 2007; received in revised form 25 October 2007; accepted 31 October 2007
Abstract
The reactions of [RuHCl(CO)(B)(EPh3)2] (B = EPh3 or pyridine; E = P or As) and 2ꢀ-hydroxychalcones in 1:2 ratio led to the formation of
[Ru(CO)(B)(L)2] (B = PPh3, AsPh3 or Py; L = 2ꢀ-hydroxychalcones). The new complexes have been characterized by analytical and spectral (IR,
1
electronic and H NMR) data. They have been assigned an octahedral structure. The new complexes were found to catalyze the oxidation of
alcohols to aldehydes using N-methylmorpholine-N-oxide as co-oxidant. All the new complexes were found to be active against bacteria such as
E. coli, Salmonella typhi and fungi Aspergillus niger. The activity was compared with standard Streptomycin or Bavistin.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Ruthenium(II) complexes; Spectral studies; Catalytic oxidation; Antibacterial activity; Antifungal activity
1. Introduction
[15]. In this line, triphenylphosphine complexes of ruthenium
have been found to be efficient catalyst for the aerobic oxida-
tion of alcohols [16]. Besides, ruthenium triphenylphosphine
complexes also exhibited biological activity against pathogenic
microbes [17]. Hence, synthesis of new ruthenium complexes
containing triphenylphoshine is of greater importance. More-
over, transition metal complexes of 2ꢀ-hydroxychalcones and
related ligands have been studied extensively due to their inter-
esting behaviour as weak field or strong field ligands to bivalent
metal ions [18].
Chalcones and their analogues are well known for having
variable bactericidal [1], fungicidal [2] and carcinogenic activ-
ity [3]. Moreover, 2ꢀ-hydroxychalcones have been employed as
analytical reagents for some metal ions [4,5]. The most com-
mon and widespread compounds of the chalconoid group are
the chalcones, which possess a 1,3-diaryl-2-propen-1-one car-
bon frame work [6–8]. Unsubstituted and substituted chalcones
had higher activity in tissue culture. A wide range of pharma-
cological activities have been identified for various chalcones,
these include antioxidant, antitumor [9], antimalarial [10] and
anticancer activities [11]. 2ꢀ-Hydroxychalcone was the most
effective in enzyme activities and gene expressions [12]. Stud-
ies on 2ꢀ-hydroxychalcone complexation with some transition
metal ions (CoII, NiII, CuII, PtII and PdII) led to stable com-
plexes, with a square planar configuration, in a 1:2 metal:ligand
stoichiometry [13,14]. The search for catalytic oxidations with
inexpensive green oxidants, such as molecular oxygen or air,
still plays a key role in the development of industrial processes
We here disclose the simple procedure for the synthesis of
ruthenium(II) complexes containing triphenylphosphine, triph-
enylarsine and chalcones and examined their catalytic and
biological applications.
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
[19]. The ligands 2ꢀ-hydroxychalcones [20], and the starting
complexes [RuHCl(CO)(PPh3)3] [21], [RuHCl(CO)(AsPh3)3]
[22], [RuHCl(CO)(Py)(PPh3)2] [23] were prepared according
∗
Corresponding author. Tel.: +91 427 2345766; fax: +91 427 2345124.
E-mail address: viswanathamurthi@yahoo.com (P. Viswanathamurthi).
1386-1425/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2007.10.043

M. Muthukumar et al. / Spectrochimica Acta Part A 70 (2008) 1222–1226
1223
molar ratios is described as follows. A solution of ruthenium
complex (0.01 mmol) in 20 cm3 CH2Cl2 was added to the solu-
tion of substrate (1 mmol) and NMO (3 mmol) and molecular
sieves. The solution mixture was stirred for 3 h at room tem-
perature and the solvent was then evaporated to dryness. The
solidresiduewasthenextractedwithpetroleumether(60–80 ◦C)
(3 × 10 cm3) and the combined extracts were filtered and evapo-
rated to give corresponding aldehyde, which was then quantified
as 2,4-dinitrophenylhydrazone derivative [19].
3. Results and discussion
All the complexes are in brown colour. Air and light sta-
ble complexes of general formula [Ru(CO)(B)(L)2] (where
L = 2ꢀ-hydroxychalcones and B = PPh3, AsPh3 or Py) have
been obtained from the reaction of [RuHCl(CO)(B)(EPh3)2]
(B = EPh3 or pyridine; E = P or As) and 2ꢀ-hydroxychalcones
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 two of the triph-
enylphosphine groups, a hydride and a chloride ion from the
starting complexes. The analytical data (Table 1) of all the
complexes are in good agreement with the proposed molecular
formula.
Fig. 1. Structure of 2ꢀ-hydroxychalcones
Ligand
X
L1
L2
L3
L4
H
OCH3
Cl
CH3
to the literature methods. The general structure of the chalcone
ligands used in this study is given in Fig. 1.
2.2. Physical measurements
3.1. Infrared spectral analysis
IR spectra of the complexes were recorded in KBr pel-
lets with a Nicolet FT-IR spectrophotometer in 400–4000 cm−1
range. Electronic spectra of the complexes have been recorded
in CH2Cl2 using a Shimadzu UV-1650 PC spectrophotometer in
200–800 nm range. 1H NMR spectra were recorded in Jeol GSX-
400instrumentusingCDCl3 assolvent. Elementalanalyseswere
performed at Central Drug Research Institute, Lucknow, India.
Melting points were recorded on a Technico microheating table
and are uncorrected.
In the IR spectra of the free ligands (Table 2), a strong band
is observed around 1640 cm−1 due to υC O. This band has been
shifted to a lower wave number by 20–30 cm−1 in the ruthenium
complexes indicating the coordination of the ligands to ruthe-
nium through the carbonyl oxygen atom [20]. The phenolic υC–O
stretching absorptions of the free ligands occur in the region
1339–1343 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
[24]. Further, the absorption due to υO–H was not observed 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 infrared 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 absorption due to υC–C of the free lig-
ands appeared as a separate 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 υC–O [25]. In the complexes, the absorption due to the
2.3. Recommended procedures
2.3.1. Synthesis of new ruthenium(II) chalconato complexes
To a solution of [RuHCl(CO)(B)(EPh3)2] where B = EPh3 or
pyridine; E = P or As (0.1 mmol) in benzene (20 cm3), the appro-
priate chalcone (0.2 mmol) were added in a 1:2 molar ratio. The
mixture was heated under reflux for 5 h. The resulting solution
was concentrated to about 3 cm3. The product was separated by
the addition of small amount of petroleum ether (60–80 ◦C) and
recrystallized from CH2Cl2/petroleum ether mixture and dried
under vacuum.
phenylalkene vibration appeared in the region 1542–1551 cm−1
,
which is slightly lower than that observed in the spectra of the
free ligands [20]. A strong band around 1945–1959 cm−1 indi-
cates the presence of terminally coordinated carbon monoxide
[26]. In the complexes containing coordinated pyridine, a weak
band is observed at 1027–1029 cm−1 [27]. In addition, the other
characteristic absorption due to triphenylphosphine were also
found to be present in the expected region [28].
2.4. Catalytic studies
Catalytic oxidation of primary alcohols to corresponding
aldehyde and secondary alcohol to ketone by ruthenium(II)
chalconato complexes were studied in the presence of NMO
as co-oxidant. A typical reaction using the complex as a cat-
alyst and benzyl alcohol, cyclohexanol as substrates at 1:100

1224
M. Muthukumar et al. / Spectrochimica Acta Part A 70 (2008) 1222–1226
Table 1
Analytical data of ruthenium(II) chalconato complexes
Complexes
Yield (%)
m.p. (◦C)
Calculated (found)(%)
C
H
N
[Ru(CO)(PPh3)(L1)2]
[Ru(CO)(PPh3)(L2)2]
[Ru(CO)(PPh3)(L3)2]
[Ru(CO)(PPh3)(L4)2]
[Ru(CO)(Py)(L1)2]
61
68
72
58
56
60
69
63
74
69
56
65
100
146
112
164
085
100
110
105
125
133
128
130
70.24 (70.34)
68.22 (68.12)
64.91 (64.51)
70.74 (70.54)
66.05 (66.35)
63.86 (63.56)
59.76 (59.86)
66.85 (66.75)
66.74 (66.94)
65.05 (65.25)
61.90 (61.80)
67.32 (67.42)
4.45 (4.35)
4.60 (4.70)
3.89 (3.79)
4.77 (4.87)
4.16 (4.36)
4.37 (4.27)
3.48 (4.68)
4.58 (4.48)
4.23 (4.13)
4.39 (4.59)
3.70 (3.66)
4.54 (4.64)
–
–
–
–
2.14 (2.24)
1.96 (1.98)
1.94 (1.90)
2.05 (2.10)
–
–
–
–
[Ru(CO)(Py)(L2)2]
[Ru(CO)(Py)(L3)2]
[Ru(CO)(Py)(L4)2]
[Ru(CO)(AsPh3)(L1)2]
[Ru(CO)(AsPh3)(L2)2]
[Ru(CO)(AsPh3)(L3)2]
[Ru(CO)(AsPh3)(L4)2]
Table 3
1H NMR data (δ in ppm) of ruthenium(II) chalconato complexes
3.2. Electronic spectral analysis
All the new complexes have been found to be diamagnetic
indicating the presence of ruthenium in +2 oxidation state arising
from t26g configuration. The electronic spectra of all the com-
plexes were taken in CH2Cl2 and they showed two bands in the
region 359–225 nm (Table 2). The bands around 359–312 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 [29].
The bands that appeared below 300 nm are characterized by
intra-ligand charge transfer.
Complexes
1H NMR (ppm)
[Ru(CO)(PPh3)(L1)2]
[Ru(CO)(PPh3)(L3)2]
[Ru(CO)(Py)(L3)2]
[Ru(CO)(AsPh3)(L1)2]
[Ru(CO)(AsPh3)(L4)2]
7.05–7.67 (m, –CH CH– and aromatic)
7.21–7.25 (m, –CH CH– and aromatic)
7.74–8.20 (m, –CH CH– and aromatic)
7.01–7.69 (m, –CH CH– and aromatic)
7.25–7.78 (m, –CH CH– and aromatic),
1.28 (s, CH3)
[Ru(CO)(AsPh3)(L3)2]
7.20–7.90 (m, –CH CH– and 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 [30]. In
addition, the signal corresponding to CH3 was also observed in
the expected region.
Based on the analytical and spectral data, an octahedral
structure (Fig. 2) has been tentatively proposed for all the ruthe-
nium(II) chalconato complexes.
3.3. 1H NMR spectral analysis
All the ruthenium complexes exhibit a multiplet in the region
1
7.05–8.20 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 ligands [24]. The
signal due to two alkene protons also appeared in the region
6.9–7.1 ppm and hence, merged with the multiplet of aromatic
Table 2
IR absorption frequencies (cm−1) and electronic spectral data (nm) of free ligands and their ruthenium(II) chalconato complexes
Compound
νC
νC
νC–O
νC
C
λmax (ε)(dm3 mol−1 cm−1
)
O
O
L1
–
–
–
–
1639
1639
1640
1634
1625
1623
1606
1622
1606
1604
1605
1605
1617
1619
1623
1618
1340
1343
1339
1341
1384
1363
1350
1400
1359
1359
1357
1400
1401
1400
1401
1400
1572
1564
1585
1562
1548
1544
1545
1542
1549
1544
1551
1543
1548
1544
1545
1543
–
–
–
–
L2
L3
L4
[Ru(CO)(PPh3)(L1)2]
[Ru(CO)(PPh3)(L2)2]
[Ru(CO)(PPh3)(L3)2]
[Ru(CO)(PPh3)(L4)2]
[Ru(CO)(Py)(L1)2]
[Ru(CO)(Py)(L2)2]
[Ru(CO)(Py)(L3)2]
[Ru(CO)(Py)(L4)2]
[Ru(CO)(AsPh3)(L1)2]
[Ru(CO)(AsPh3)(L2)2]
[Ru(CO)(AsPh3)(L3)2]
[Ru(CO)(AsPh3)(L4)2]
1949
1946
1951
1957
1946
1945
1945
1945
1958
1959
1959
1959
323(26,580), 232(31,040)
359(22,360), 232(31,040)
312(28,190), 233(31,160)
339(24,270), 232(31,040)
321(27,890), 235(32,320)
355(21,840), 234(31,370)
316(30,120), 242(35,480)
340(23,960), 245(36,530)
329(25,370), 243(35,640)
341(23,750), 244(35,890)
329(25,370), 237(33,170)
330(25,580), 225(30,460)

M. Muthukumar et al. / Spectrochimica Acta Part A 70 (2008) 1222–1226
1225
Table 4
formed after stirring for about 3 h, which was then quantified as
their 2,4-dinitrophenylhydrazone derivatives [19]. The results
obtained are given in Table 4. The relatively higher product
yield obtained for the oxidation of benzylalcohol as compared
to cyclohexanol is due to the fact that the ␣-CH unit of benzy-
lalcohol is more acidic than cyclohexanol [31].
Catalytic activity data of ruthenium(II) chalconato complexes
Complex
Substrate
Product
Yield (%)
[Ru(CO)(PPh3)(L1)2]
Benzyl alcohol
Cyclohexanol
Benzyl alcohol
Cyclohexanol
Benzyl alcohol
Cyclohexanol
Benzyl alcohol
Cyclohexanol
Benzyl alcohol
Cyclohexanol
Benzyl alcohol
Cyclohexanol
Benzyl alcohol
Cyclohexanol
Benzyl alcohol
Cyclohexanol
Benzyl alcohol
Cyclohexanol
Benzyl alcohol
Cyclohexanol
Benzyl alcohol
Cyclohexanol
Benzyl alcohol
Cyclohexanol
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
38.5
07.0
26.5
05.9
39.0
08.9
28.2
06.7
32.0
06.8
18.3
05.6
22.4
05.4
22.4
06.8
23.6
07.3
26.1
07.9
45.5
09.8
29.2
06.6
[Ru(CO)(PPh3)(L2)2]
[Ru(CO)(PPh3)(L3)2]
[Ru(CO)(PPh3)(L4)2]
[Ru(CO)(Py)(L1)2]
3.5. Biocidal study
The results (Tables 5 and 6) showed that the ruthenium com-
plexes are more toxic than their parent ligands against the same
microorganisms and under identical experimental conditions
[32]. Theincreaseinbiologicalactivityofthemetalchelatesmay
be due to the effect of the metal ion on the normal cell process.
A possible mode for toxicity increase may be considered in the
light of Tweedy’s chelation theory [33]. Chelation reduces the
polarity of the metal ion because of partial sharing of its positive
chargewiththedonorgroupsandpossible␲-electrondelocaliza-
tion over the whole chelate ring. Such chelation could enhance
the lipophilic character of the central metal atom, which subse-
quently favours its permeation through the lipid layers of the cell
membrane [34]. Further, the toxicity of the compounds increases
with increase in concentration. Though the complexes possess
activity, it could not reach the effectiveness of the standard drug
StreptomycinorBavistin. Thevariationintheeffectivenessofthe
different compounds against different organisms depends either
on the impermeability of the cells of the microbes or differences
in ribosomes of microbial cells [35,36].
[Ru(CO)(Py)(L2)2]
[Ru(CO)(Py)(L3)2]
[Ru(CO)(Py)(L4)2]
[Ru(CO)(AsPh3)(L1)2]
[Ru(CO)(AsPh3)(L2)2]
[Ru(CO)(AsPh3)(L3)2]
[Ru(CO)(AsPh3)(L4)2]
A, benzaldehyde; B, cyclohexanone.
3.4. Catalytic activity
The oxidation of benzylalcohol and cyclohexanol was car-
ried out with the new ruthenium(II) chalconato complexes as
catalysts in the presence of N-methylmorpholine-N-oxide as
co-oxidant and CH2Cl2 as solvent. All the complexes oxidize
primary alcohols to corresponding aldehydes and secondary
alcohols to corresponding ketones with low to moderate yield
(Table 4). This reaction provides an efficient route to the con-
version of alcoholic functions to carbonyl groups and water is
the only by product during the course of the reaction which was
removed by using molecular sieves. The aldehydes and ketones
Table 5
Antibacterial activity data of ruthenium(II) chalconato complexes
Compound
Diameter of inhibition zone (mm)
E. coli
Salmonella typhi
0.25%
0.5%
0.25%
0.5%
L2
3
6
11
14
19
5
7
13
18
24
4
5
9
11
17
7
9
13
14
21
[Ru(CO)(PPh3)(L2)2]
[Ru(CO)(Py)(L2)2]
[Ru(CO)(AsPh3)(L2)2]
Streptomycin
Table 6
Antifungal activity data of ruthenium(II) chalconato complexes
Compound
Diameter of inhibition zone (mm)
Aspergillus niger
0.25%
0.5%
L1
2
3
3.5
3.8
11
3
5
6
8
16
[Ru(CO)(PPh3)(L1)2]
[Ru(CO)(Py)(L1)2]
[Ru(CO)(AsPh3)(L1)2]
Bavistin
Fig. 2. Proposed structure of new ruthenium(II) chalconato complexes.

1226
M. Muthukumar et al. / Spectrochimica Acta Part A 70 (2008) 1222–1226
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Some new ruthenium(II) chalconato complexes have been
synthesized using chalcones formed from derivatives of ben-
zaldehyde and 2-hydroxyacetophenone. The new complexes
have been characterized by analytical and spectral data. An
octahedral structure has been tentatively proposed for all the
complexes. The complexes showed significant catalytic and bio-
logical activity.
Acknowledgements
The authors express their sincere thanks to Council of Sci-
entific and Industrial Research (CSIR), New Delhi [Grant No.
01(2065)/06/EMR-II] for financial support. One of the authors
(M.M.) thanks CSIR for the award of Senior Research Fellow-
ship.
[24] M.V. Kaveri, R. Prabhakaran, R. Karvembu, K. Natarajan, Specrtrochim.
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