Ruthenium(II) chalconate complexes: Synthesis, characterization, catalytic, and biological studies

Article abstract of DOI:10.1016/j.saa.2009.06.041

A series of new hexa-coordinated ruthenium(II) carbonyl complexes of the type [RuCl(CO)(EPh₃)(B)(L)] (E = P or As; B = PPh₃, AsPh₃ or Py; L = 2′-hydroxychalcones) have been prepared by reacting [RuHCl(CO)(EPh₃)₂(B)] (E = P or As; B = PPh₃, AsPh₃ or Py) with 2′-hydroxychalcones in benzene under reflux. The new complexes have been characterized by analytical and spectral (IR, electronic, ¹H, ³¹P and ¹³C NMR) data. Based on the above data, an octahedral structure has been assigned for all the complexes. The new complexes exhibit catalytic activity for the oxidation of primary and secondary alcohols into their corresponding aldehydes and ketones in the presence of N-methylmorpholine-N-oxide (NMO) as co-oxidant and also found efficient catalyst in the transfer hydrogenation of ketones. The antifungal properties of the complexes have also been examined and compared with standard Bavistin.

Full text of DOI:10.1016/j.saa.2009.06.041

Spectrochimica Acta Part A 74 (2009) 454–462
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
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Ruthenium(II) chalconate complexes: Synthesis, characterization, catalytic, and
biological studies
M. Muthukumar, P. Viswanathamurthi∗
Department of Chemistry, Periyar University, Salem 636011, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of new hexa-coordinated ruthenium(II) carbonyl complexes of the type [RuCl(CO)(EPh3)(B)(L)]
(E = P or As; B = PPh3, AsPh3 or Py; L = 2ꢀ-hydroxychalcones) have been prepared by reacting
[RuHCl(CO)(EPh3)2(B)] (E = P or As; B = PPh3, AsPh3 or Py) with 2ꢀ-hydroxychalcones in benzene under
reflux. The new complexes have been characterized by analytical and spectral (IR, electronic, 1H, 31P
and 13 C NMR) data. Based on the above data, an octahedral structure has been assigned for all the com-
plexes. The new complexes exhibit catalytic activity for the oxidation of primary and secondary alcohols
into their corresponding aldehydes and ketones in the presence of N-methylmorpholine-N-oxide (NMO)
as co-oxidant and also found efficient catalyst in the transfer hydrogenation of ketones. The antifungal
properties of the complexes have also been examined and compared with standard Bavistin.
© 2009 Elsevier B.V. All rights reserved.
Received 30 January 2009
Received in revised form 15 June 2009
Accepted 17 June 2009
Keywords:
Ruthenium(II) complexes
Spectral studies
Catalytic oxidation
Catalytic transfer hydrogenation
Antifungal study
1. Introduction
and Ru(BINAP)(diamine) [19] have become the most prominent
members for the reduction of ketones in high yields. Pincer-type
Chalcones bearing non-natural substituents have been synthe-
sized during the recent years in order to develop drugs active
against cancer [1,2], malaria [3], leishmaniase [4], tuberculosis
[5] and cardiovascular diseases [6]. Apart from its use in medi-
cal science, some chalcone derivatives [7] exhibit second harmonic
generation (SHG), and hence they are also used in non-linear optical
(NLO) applications. 2ꢀ-Hydroxychalconate complexes of ruthe-
nium(II) containing triphenylphosphine have been found to show
significant catalytic oxidation and biological activities [8]. Many
research groups are developing the synthetic chemistry related
to ruthenium complexes because of their multiple applications in
many different scientific fields [9]. Ruthenium complexes have been
used as catalysts or catalyst precursors for a variety of purposes
including hydrogenation, oxidation, isomerisation, polymerization,
nucleophilic addition to multiple bonds and carbon–carbon bond
formation [10].
The oxidation of alcohols into their corresponding aldehydes
and ketones is of greater importance in synthetic organic chem-
istry [11]. Ruthenium complexes have a long pedigree as catalysts
for transfer hydrogenation reactions in the presence of isopropanol
as hydrogen source [12,13]. Several recent examples of ruthenium
N-heterocyclic carbene complexes [14–16], Ru(arene)-(diamine)
[17], ruthenium(III) amine-bis(phenolate) tripodal complexes [18]
arylruthenium(II) complexes containing the monoanionic terden-
tate NCN and PCP ligands have been reported by van Koten as active
catalysts for the transfer hydrogenation of ketones in the pres-
ence of isopropanol and KOH [20]. Even though there are number
of reports available on the transfer hydrogenation of ketones by
ruthenium complexes, only limited reports are available for cat-
alytic transfer hydrogenation of ketones by ruthenium chalconate
complexes.
We, herein report the synthesis of a series of hexa-coordinated
ruthenium(II) chalconate complexes containing PPh3/AsPh3. The
characterization of the complexes was accomplished by analytical
and spectral (IR, electronic, 1H, 31P and 13C NMR) methods. Further,
some of the synthesized complexes have been effectively used as
catalyst in oxidation of alcohols in the presence of NMO and transfer
hydrogenation of ketones in the presence of isopropanol and KOH
as base. The antifungal properties of the complexes have also been
examined and compared with standard Bavistin.
2. Experimental
2.1. Reagents and materials
All the reagents used were chemically pure and AR grade.
The solvents were purified and dried according to standard pro-
cedures [21]. RuCl3·3H2O was purchased from Loba Chemie Pvt.
Ltd., and was used without further purification. The starting com-
plexes [RuHCl(CO)(PPh3)3] [22], [RuHCl(CO)(AsPh3)3] [23] and
∗
Corresponding author. Fax: +91 427 2345124.
E-mail address: viswanathamurthi@rediffmail.com (P. Viswanathamurthi).
1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2009.06.041

M. Muthukumar, P. Viswanathamurthi / Spectrochimica Acta Part A 74 (2009) 454–462
455
L
4 is prepared from 1-acetyl-2-naphthol (0.9311 g, 5 mmol) and
3, 4-dimethoxy benzaldehyde (0.8309 g, 5 mmol). m.p. 95 ◦C (81%
yield). Found: C 75.43, H 5.42. C21H18 O4 requires C 75.41, H 5.38%.
IR: ꢀ(C
1629 s cm−1, ꢀ(C
1556 w cm−1, ꢀ(C–O) 1340 m cm−1
.
O)
C)
2.4. Synthesis of new ruthenium(II) chalconate complexes
All reactions were carried out under strict anhydrous condi-
tions and were prepared by the following common procedure. To
a solution of [RuHCl(CO)(EPh3)2(B)] (E = P or As; B = PPh3, AsPh3
or Py) (0.1 g, 0.1 mmol) in benzene (20 cm3), the appropriate 2ꢀ-
hydroxychalcone (0.0266–0.0435 g, 0.1 mmol) were added in 1:1
molar ratio. The mixture was heated under reflux for 6 h. The reac-
tion mixture gradually changed to deep color and the solvent was
removed under reduced pressure. The product was separated by the
addition of small amount of petroleum ether (60–80 ◦C) and recrys-
tallized from CH2Cl2/petroleum ether mixture. The compounds
were dried under vacuum and the purity of the complexes was
checked by TLC.
Fig. 1. Structure of 2ꢀ-hydroxychalcones.
2.5. Catalytic oxidation
Catalytic oxidation of primary alcohols to corresponding aldehy-
des and secondary alcohols to ketones by ruthenium(II) chalconate
complexes were studied in the presence of NMO as co-oxidant.
A typical reaction using the complex as a catalyst and primary
or secondary alcohol, as substrates at 1:100 molar ratio was
described as follows. A solution of ruthenium complex (0.01 mmol)
in CH2Cl2 (20 cm3) was added to the mixture containing substrate
(1 mmol), NMO (3 mmol) and molecular sieves. The solution mix-
ture was refluxed for 3 h and the solvent was then evaporated
from the mother liquor under reduced pressure. The solid residue
was extracted with petroleum ether (60–80 ◦C) (20 cm3) and was
analyzed by GC. The oxidation products were identified by GC co-
injection with authentic samples.
[RuHCl(CO)(Py)(PPh3)2] [24] were prepared according to the lit-
erature methods. The general structure of the 2ꢀ-hydroxychalcone
ligands used in this study is given below (Fig. 1).
2.2. Physical measurements
The analysis of carbon, hydrogen and nitrogen were performed
on Carlo Erba 1108 model analyzer at the Central Drug Research
Institute, Lucknow, India. Infrared spectra were recorded in KBr
pellets 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-visible 1650 PC spectrophotometer
in 200–800 nm range. 1H, 31P and 13C NMR spectra were recorded
in Jeol GSX-400 instrument using CDCl3 as solvent. 1H NMR and
13C NMR spectra were obtained at room temperature using TMS
as the internal standard. 31P NMR spectra of the complexes were
obtained at room temperature using ortho phosphoric acid as a
reference. Melting points were recorded on a Technico micro heat-
ing table and are uncorrected. The catalytic yields were determined
using ACME 6000 series GC-FID with a DP-5 column of 30 m length,
0.53 mm diameter and 5.00 ␮m film thickness.
2.6. Catalytic transfer hydrogenation of ketones
The catalytic transfer hydrogenation reactions were also studied
using ruthenium(II) chalconate complexes as a catalyst, ketone as
substrate and KOH as base at 1:300:2.5 molar ratios. The procedure
was described as follows. A mixture containing ketone (3.75 mmol),
the ruthenium complex (0.0125 mmol) and KOH (0.03 mmol) was
heated to reflux in 10 cm3 of i-prOH for 30 min. After completion
of reaction the catalyst was removed from the reaction mixture by
the addition of diethyl ether followed by filtration and subsequent
neutralization with 1 M HCl. The ether layer was filtered through
a short path of silica gel by column chromatography. The filtrate
was subjected to GC analysis and the hydrogenated product was
identified and determined with authentic samples.
2.3. Synthesis of chalconate ligands
Chalconate ligands were prepared by condensing 4-substituted
benzaldehyde (0.6007–0.8309 g, 5 mmol) with 1-acetyl-2-
naphthol (0.9311 g, 5 mmol) in presence of 50 cm3 alcoholic
sodium hydroxide solution (20%). After 24 h stirring, the product
was precipitated by addition of concentrated hydrochloric acid.
Then the product was filtered and recrystallized from ethanol [25].
L1 is prepared from 1-acetyl-2-naphthol (0.9311 g, 5 mmol) and
4-methyl benzaldehyde (0.6 cm3, 5 mmol). m.p. 87 ◦C (73% yield).
Found: C 83.31, H 5.59. C20H16O2 requires C 83.26, H 5.54%. IR: ꢀ(C O)
3. Results and discussions
Diamagnetic, hexa-coordinated low spin ruthenium(II) com-
plexes of general formula [RuCl(CO)(EPh3)(B)(L)] (E = P or As;
B = PPh3, AsPh3 or Py; L = 2ꢀ-hydroxychalcone) were synthesized in
good yields from the reaction of [RuHCl(CO)(EPh3)2(B)] (E = P or
As; B = PPh3, AsPh3 or Py) with 2ꢀ-hydroxychalcone ligands in dry
benzene in equal molar ratio (Scheme 1).
1632 s cm−1, ꢀ(C
1565 w cm−1, ꢀ(C–O) 1335 m cm−1
.
C)
L2 is prepared from 1-acetyl-2-naphthol (0.9311 g, 5 mmol) and
4-methoxy benzaldehyde (0.61 cm3, 5 mmol). m.p. 125 ◦C (78%
yield). Found: C 78.93, H 5.29. C20H16O3 requires C 78.91, H 5.24%.
In all these reactions, it has been observed that the 2ꢀ-
hydroxychalcones behave as uninegative bidentate chelating
ligands by replacing a triphenylphosphine/arsine and a hydride ion
from the starting complexes.
All the complexes are stable in air at room temperature, brown in
color, non-hygroscopic and highly soluble in common organic sol-
IR: ꢀ(C
1630 s cm−1, ꢀ(C
1555 w cm−1, ꢀ(C–O) 1332 m cm−1
.
O)
C)
L3 is prepared from 1-acetyl-2-naphthol (0.9311 g, 5 mmol) and
4-chloro benzaldehyde (0.7029 g, 5 mmol). m.p. 82 ◦C (68% yield).
Found: C 73.91, H 4.24. C19H13O2Cl requires C 73.81, H 4.21%. IR:
ꢀ(C
1633 s cm−1, ꢀ(C
1565 w cm−1, ꢀ(C–O) 1339 m cm−1
.
O)
C)

456
M. Muthukumar, P. Viswanathamurthi / Spectrochimica Acta Part A 74 (2009) 454–462
Scheme 1. Formation of Ru(II) chalconate complexes.
vents such as dichloromethane, acetonitrile, chloroform and DMSO.
The analytical data are listed in Table 1 and are in good agreement
with the general molecular formula proposed for all the complexes.
the complexes, indicating deprotonation of the phenolic proton
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 absence of ꢀRu–H vibra-
tion around 2010–2020 cm−1 in the new complexes indicated that
the hydride ion in the starting complexes replaced by chalcone
ligands during coordination. The absorption due to ꢀC–C of the
free ligands appeared as a separate band in their infrared spec-
tra around 1600 cm−1, but the same could not be identified in the
spectra of the ruthenium complexes because of their possible merg-
3.1. Infrared spectral analysis
The important IR absorption bands for the synthesized ligands
and complexes are shown in Table 2. The observed bands may be
classified into those originating from the ligands and those aris-
ing from the bands formed between ruthenium(II) metal ion and
the coordinating sites. The free chalconate ligands showed a strong
band in the region 1629–1633 cm−1 due to ꢀC O. This band has been
shifted to a lower wave number 1605–1623 cm−1 in the ruthenium
complexes indicating the coordination of the ligands to ruthenium
through the carbonyl oxygen atom [26]. A strong band observed at
1332–1340 cm−1 in the free chalconate ligands has been assigned
to phenolic ꢀC–O stretching. This band has been shifted to higher
wave number 1378–1384 cm−1 in the spectra of the complexes due
to its coordination to ruthenium ion through the oxygen atom of
the phenolic group [27]. This has been further supported by the
disappearance of the broad ꢀOH band around 3400–3600 cm−1 in
ing with ꢀC
[28]. In the complexes, the absorption due to the
O
phenyl alkene vibration appeared in the region 1555–1565 cm−1
,
which is slightly lower than that observed in the spectra of the free
ligands [8]. A strong band around 1943–1959 cm−1 indicates the
presence of terminally coordinated carbon monoxide [29]. In the IR
spectra of the complexes, a medium intensity band is observed in
the region 1024–1028 cm−1 which is characteristic of coordinated
nitrogen bases [30]. In addition, the other characteristic bands due
to triphenylphosphine or triphenylarsine (around 1440, 1090 and
700 cm−1) were also present in the spectra of all the complexes [31].
Table 1
Analytical data of ruthenium(II) chalconate complexes.
Complex
Formula
Yield (%)
m.p. (◦C)
Calculated (found) (%)
C
H
N
[RuCl(CO)(PPh3)2(L1)]
[RuCl(CO)(PPh3)2(L2)]
[RuCl(CO)(PPh3)2(L3)]
[RuCl(CO)(PPh3)2(L4)]
[RuCl(CO)(AsPh3)2(L1)]
[RuCl(CO)(AsPh3)2(L2)]
[RuCl(CO)(AsPh3)2(L3)]
[RuCl(CO)(AsPh3)2(L4)]
[RuCl(CO)(Py)(PPh3)(L1)]
[RuCl(CO)(Py)(PPh3)(L2)]
[RuCl(CO)(Py)(PPh3)(L3)]
[RuCl(CO)(Py)(PPh3)(L4)]
C57H45O3P2ClRu
C57H45O4P2ClRu
C56H42O3P2Cl2Ru
C58H47 O5P2ClRu
C57H45O3As2ClRu
C57H45O4As2ClRu
C56H42O3As2Cl2Ru
C58H47 O5As2ClRu
C44H35O3PNClRu
C44H35O4PNClRu
C43H32O3PNCl2Ru
C45H37O5PNClRu
53
61
58
62
56
49
52
55
48
51
63
68
153
133
167
152
151
143
142
139
160
121
155
141
70.11(69.92)
68.98(67.88)
66.25(65.96)
66.97(66.92)
63.07(63.12)
62.11(62.08)
60.70(60.68)
61.49(61.50)
65.03(65.24)
63.69(63.58)
61.78(61.86)
65.41(65.22)
4.64(4.68)
4.57(4.68)
4.41(4.39)
4.80(4.72)
4.41(4.43)
4.34(4.28)
4.07(3.97)
4.41(4.39)
4.66(4.46)
4.56(4.58)
4.15(4.11)
4.83(4.79)
–
–
–
–
–
–
–
–
1.85(1.79)
1.81(1.92)
1.80(1.84)
1.82(1.78)

M. Muthukumar, P. Viswanathamurthi / Spectrochimica Acta Part A 74 (2009) 454–462
457
Table 2
IR absorption frequencies (cm−1) and electronic spectral data (nm) of ruthenium(II) chalconate complexes.
Compound
ꢀC≡O
ꢀC
ꢀC–O
ꢀC
ꢁmax (ε) (dm3 mol−1 cm−1
)
O
C
L1
–
–
–
1632
1630
1633
1629
1618
1605
1617
1617
1618
1621
1619
1623
1614
1606
1615
1615
1335
1332
1339
1340
1384
1383
1383
1384
1382
1383
1380
1378
1381
1383
1382
1383
1565
1555
1565
1556
1555
1550
1555
1551
1560
1549
1542
1548
1553
1550
1553
1553
–
–
–
–
L2
L3
L4
–
[RuCl(CO)(PPh3)2(L1)]
[RuCl(CO)(PPh3)2(L2)]
[RuCl(CO)(PPh3)2(L3)]
[RuCl(CO)(PPh3)2(L4)]
[RuCl(CO)(AsPh3)2(L1)]
[RuCl(CO)(AsPh3)2(L2)]
[RuCl(CO)(AsPh3)2(L3)]
[RuCl(CO)(AsPh3)2(L4)]
[RuCl(CO)(Py)(PPh3)(L1)]
[RuCl(CO)(Py)(PPh3)(L2)]
[RuCl(CO)(Py)(PPh3)(L3)]
[RuCl(CO)(Py)(PPh3)(L4)]
1954
1943
1955
1954
1959
1959
1958
1959
1945
1945
1947
1945
326(19,523), 212(31,648)
672(548), 323(19,638), 236(22,523), 202(33,425)
670(542), 210(31,256),
328(19,916), 235(27,141), 213(32,040), 205(34,374)
678(476), 239(28,498)
676(512), 237(27,980), 210(31,256)
677(493), 238(28,252), 203(33,625)
682(442), 236(27,523)
638(592), 278(25,916), 271(26,328), 236(27,523)
672(548), 618(708), 330(19,142), 238(28,252)
668(562), 278(28,920), 236(27,523), 210(31,256)
675(532), 278(28,920), 271(29,563), 236(27,523)
and 2ꢀ-hydroxychalcone ligands [36]. 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 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 ı value at least
by 2 ppm [37]. The signal for methyl protons appear as a singlet in
the region 1.52–1.58 ppm. In addition, a singlet around 3.8 ppm was
assigned to methoxy proton. No peak was observed for the OH pro-
ton, supporting the fact that the phenolic group is deprotonated,
suggesting coordination through the phenolic oxygen of chalcone
to the ruthenium. The new complexes did not show any signal in
the up-field region (−5 to −12 ppm) for the hydride ligand, thus
proving its substitution by the chalcone ligands.
The observed bands in the regions 460–475 cm−1 in the mononu-
clear complexes are tentatively assigned to the ꢀRu–Cl vibrations
[32].
3.2. Electronic spectral analysis
All the chalconate ruthenium complexes are diamagnetic, indi-
cating the presence of ruthenium in the +2 oxidation state. The
ground state of ruthenium(II) in an octahedral environment is
1A1g, arising from the t6 configuration, and the excited states cor-
2g
responding to the t52g eg1 configuration are T1g
,
3T2g and T1g
1
.
,
3
1
3
Hence, four bands corresponding to the transitions A1g → T1g
1A1g → T2g
,
1A1g → T1g and A1g → T2g are possible in order of
3
1
1
1
increasing energy.
The electronic spectra of all the complexes in dichloromethane
showed two to four bands in the region 682–202 nm (Table 2).
The bands around 682–618 nm have been assigned to spin allowed
3.4. 31P NMR spectral analysis
31P NMR spectra of some of the complexes were recorded to
confirm the presence of triphenylphosphine groups and to deter-
mine the geometry of the complexes (Table 4, Fig. 2). In the case of
the complexes containing two triphenylphosphine ligands, a sharp
singlet was observed around 29.03–29.13 ppm due to presence of
magnetically equivalent phosphorus atoms suggesting the pres-
ence of two triphenylphosphine groups in a position trans to each
other [36]. The spectrum of all other complexes exhibited a singlet
around 28.53–28.65 ppm corresponding to the presence of triph-
enylphosphine group in a position trans to heterocyclic nitrogen
base [15].
1
1A1g → T1g transition [33] and the other high intensity bands
in the visible region around 330–323 nm have been assigned to
charge transfer transition based on their extinction coefficient val-
ues (Table 2) [34]. The bands that appeared below 300 nm are
characterized by intra-ligand charge transfer. The nature of the
observed electronic spectra and the position of absorption bands
are consistent with those of other similar ruthenium(II) octahedral
complexes [35].
3.3. 1H NMR spectral analysis
The 1H NMR spectra of the ruthenium(II) complexes were
recorded in CDCl3 to conform the binding of chalcone to ruthenium
ion. All the complexes exhibit multiplet in the region 6.73–7.99 ppm
in their 1H NMR spectra (Table 3), which has been assigned to the
protons of phenyl groups present in the PPh3 or AsPh3 or pyridine
3.5. 13C NMR spectral analysis
The 13C NMR spectra of some of the complexes were
recorded to confirm the formation of new ruthenium(II) chal-
conate complexes (Table 4). The spectrum shows multiplets around
113.69–135.72 ppmregionassignedtoaromaticcarbons. Thealkene
carbons appeared in the region 115.45–130.58 ppm, and hence
merged with the aromatic carbons. The appearance of a peak
at 160.84–168.52 ppm region in the spectrum is due to carbonyl
Table 3
1H NMR data (ı in ppm) of ruthenium(II) chalconate complexes.
Complex
1H NMR (ppm)
[RuCl(CO)(PPh3)2(L3)]
7.03–7.48 (m, –CH CH– and aromatic)
7.05–7.91 (m, –CH CH– and aromatic),
3.83 (s, OCH3)
6.73–7.99 (m, –CH CH– and aromatic),
3.86, 3.83 (s, OCH3)
6.86–7.69 (m, –CH CH– and aromatic),
1.58 (s, CH3)
6.95–7.37 (m, –CH CH– and aromatic)
7.14–7.82 (m, –CH CH– and aromatic),
1.52 (s, CH3)
[RuCl(CO)(Py)(PPh3)(L2)]
Table 4
13 C NMR and 31 P NMR data (ı in ppm) of ruthenium(II) chalconate complexes.
[RuCl(CO)(Py)(PPh3)(L4)]
[RuCl(CO)(AsPh3)2(L1)]
Complex
13 C NMR (ppm)
31 P NMR
(ppm)
[RuCl(CO)(PPh3)2(L1)]
[RuCl(CO)(PPh3)2(L2)]
[RuCl(CO)(Py)(PPh3)(L2)]
[RuCl(CO)(Py)(PPh3)(L4)]
127.60–134.61(m), 165.96(s), 20.71(s)
120.69–134.66(m), 160.84(s), 55.43(s)
113.79–134.54(m), 168.52(s), 55.43(s)
115.13–135.72(m), 162.89(s), 55.96(s)
29.13
29.03
28.53
28.65
[RuCl(CO)(Py)(PPh3)(L3)]
[RuCl(CO)(Py)(PPh3)(L1)]

458
M. Muthukumar, P. Viswanathamurthi / Spectrochimica Acta Part A 74 (2009) 454–462
Fig. 2. 31 P NMR spectra of [RuCl(CO)(PPh3)2(L2)].
Fig. 3. Proposed structure of new ruthenium(II) chalconate complexes.
carbon. In addition, sharp singlets appeared at 55.43–55.96 and
20.71 ppm region assigned to methoxy and methyl carbon, respec-
tively.
The oxidation of benzylalcohol to benzaldehyde resulted in
73–99% yield and cyclohexanol to cyclohexanone resulted in
50–98% yield. 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 benzylalcohol is more acidic than
cyclohexanol [38]. It has been observed that the triphenylarsine
ruthenium(II) chalconate complexes possess greater catalytic activ-
ity than triphenylphosphine complexes. The catalytic activity of
new ruthenium(II) chalconate complexes is comparable with that
of corresponding starting complexes for the oxidation of benzyl
alcohol whereas the activity is tremendously improved to the new
complexes for the oxidation of cyclohexanol. The conversion of
primary and secondary alcohols to corresponding aldehydes and
ketones increases with increase in reaction time up to 3 h (Fig. 4).
It has also been observed that the ruthenium(II) chalconate com-
plexes have better catalytic efficiency in the case of oxidation of
primaryandsecondaryalcoholswhencomparedtoanearlierreport
[26] on similar ruthenium complexes as catalysts in the presence
of NMO.
Based on the analytical and spectral (IR, electronic, 1H, 31P and
13C NMR) data, an octahedral structure (Fig. 3) has been tentatively
proposed for all the ruthenium(II) chalconate complexes.
3.6. Catalytic oxidation
Catalytic oxidation of primary alcohols and secondary alcohols
by the synthesized ruthenium(II) carbonyl chalconate complexes
were carried out in CH2Cl2 in the presence of NMO, and the by-
product water was removed by using molecular sieves. All the
complexes oxidize primary alcohols to the corresponding aldehy-
des and secondary alcohols to ketones (Scheme 2) with high yields
and the results are listed in Table 5. The aldehydes or ketones
formed after 3 h of reflux were determined by GC and there was
no detectable oxidation in the absence of ruthenium complex.
Results of the present investigations suggest that the com-
plexes are able to react efficiently with NMO to yield a high
valent ruthenium-oxo species [39] capable of oxygen atom trans-
fer to alcohols. This was further supported by spectral changes
that occur by addition of NMO to a dichloromethane solution
of the ruthenium(II) complexes. The appearance of a peak at
390 nm is attributed to the formation of RuIV O species, which
is in conformity with other oxo ruthenium(IV) complexes [40,41].
Further support in favor of the formation of such species was
Scheme 2. Catalytic oxidation of alcohols.

M. Muthukumar, P. Viswanathamurthi / Spectrochimica Acta Part A 74 (2009) 454–462
459
Table 5
Catalytic oxidation data of ruthenium(II) chalconate complexes.
Complex
Substrate
Product
Yield (%)a
TONb
[RuCl(CO)(PPh3)2(L1)]
Benzyl alcohol
Cyclohexanol
A
B
81
79
81
79
[RuCl(CO)(PPh3)2(L2)]
[RuCl(CO)(PPh3)2(L4)]
[RuCl(CO)(AsPh3)2(L1)]
[RuCl(CO)(AsPh3)2(L2)]
[RuCl(CO)(AsPh3)2(L3)]
[RuCl(CO)(AsPh3)2(L4)]
[RuCl(CO)(Py)(PPh3)(L2)]
[RuCl(CO)(Py)(PPh3)(L3)]
[RuCl(CO)(Py)(PPh3)(L4)]
[RuHCl(CO)(PPh3)3]
Benzyl alcohol
Cyclohexanol
A
B
93
90
93
90
Benzyl alcohol
Cyclohexanol
A
B
92
71
92
71
Benzyl alcohol
Cyclohexanol
A
B
89
85
89
85
Benzyl alcohol
Cyclohexanol
A
B
90
88
90
88
Scheme 3. Proposed catalytic cycle for the oxidation of alcohols by the Ru(II) chal-
conate complexes.
Benzyl alcohol
Cyclohexanol
A
B
99
98
99
98
Benzyl alcohol
Cyclohexanol
A
B
85
79
85
79
Benzyl alcohol
Cyclohexanol
A
B
84
75
84
75
Benzyl alcohol
Cyclohexanol
A
B
73
70
73
70
Scheme 4. Catalytic transfer hydrogenation of ketones.
Benzyl alcohol
Cyclohexanol
A
B
93
71
93
71
Benzyl alcohol
Cyclohexanol
A
B
81
37
81
37
isopropanol–KOH medium using a molar ratio 1:2.5:300 for the
catalyst, KOH and the ketone in 10 cm3 of isopropanol (Scheme 4).
Typical results are shown in Table 6 . The catalyst performed
efficientlyforbothaliphaticandaromaticketoneswithhighconver-
sion and turnover. Cyclohexanone was converted into cyclohexanol
in 96–99% yield. Acetophenone was converted into corresponding
alcohol in 73–89% yield. Similarly, isobutyl methyl ketone under-
went transfer hydrogenation to afford the corresponding alcohol in
75–78% yield, and found that all type of the catalysts performed
efficiently for reduction of cyclohexanone to cyclohexanol. The
catalytic efficiency of new ruthenium(II) chalconate complexes is
moderately increased for conversion of cyclohexanone to cyclohex-
anol whereas the activity is tremendously improved for reduction
of acetophenone and isobutyl methyl ketone when compared to
corresponding starting complexes. In the absence of base no trans-
fer hydrogenation of ketones was observed. The role of KOH is to
generate the catalyst from the chloro precursor and the reaction
mediates through the hydride species. The base facilitated the for-
mation of the ruthenium alkoxide by abstracting the proton of the
alcohol and subsequently, the alkoxide underwent ␤-elimination to
give a ruthenium hydride which is the active species in this reaction.
Addition of bases like NaOH or Na-(iOPr) also leads to similar
final conversion, but the highest rate was observed when KOH was
employed [42]. Pamies and Backvall [43] studied the mechanism
for a number of bisphosphineruthenium(II) complexes by monitor-
ing the racemization of monodeuterated S-phenylethylalcohol with
acetophenone and found that the catalysts under study in most of
the cases followed the monohydride pathway. Since our catalysts
are similar to those studied by Pamies and Backvall we assumed
that the reactions followed the monohydride pathway.
[RuHCl(CO)(AsPh3)3]
[RuHCl(CO)(Py)(PPh3)2]
Benzyl alcohol
Cyclohexanol
A
B
87
52
87
52
Benzyl alcohol
Cyclohexanol
A
B
81
46
81
46
A: benzaldehyde; B: cyclohexanone.
a
Yield determined by GC and comparing with the analyses of authentic samples.
Ratio of moles of product obtained to the moles of the catalyst used.
b
identified from the IR spectrum of the solid mass (obtained by
evaporation of the resultant solution to dryness), which showed
a band at 860 cm−1, characteristic of RuIV O species [39,41]
(Scheme 3).
3.7. Catalytic transfer hydrogenation
The catalytic transfer hydrogenation of ketones in the pres-
ence of ruthenium chalconate complexes has been studied in
3.8. Antifungal activity
The in vitro antifungal screening against Aspergillus niger and
Mucor Sp. for the ligands and some of their ruthenium(II) complexes
have been carried out by disc diffusion method [44]. The results
(Table 7) showed that the new ruthenium(II) chalconate complexes
are more toxic than their parent ligands and starting complexes
against the same microorganisms and under identical experimen-
tal conditions. The increase in the antifungal activity of the metal
chelates may be due to the effect of the metal ion on the normal cell
Fig. 4. Catalytic oxidation of benzylalcohol (A) and cyclohexanol (B) in different time
intervals.

460
M. Muthukumar, P. Viswanathamurthi / Spectrochimica Acta Part A 74 (2009) 454–462
process. A possible mode for toxicity increase may be considered in
the light of Tweedy’s chelation theory [45]. ‘Chelation reduces the
polarity of the metal ion because of partial sharing of its positive
charge with the donor groups and possible ␲-electron delocaliza-
tion over the whole chelate ring. Such chelation could enhance the
lipophilic character of the central metal atom, which subsequently
favors its permeation through the lipid layers of the cell mem-
brane’ [46]. 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 Bavistin. The
Table 6
Catalytic transfer hydrogenation of ketones by ruthenium(II) chalconate complexesa.
Complex
Substrate
Product
Conversion (%)
89
TONb (TOF)c
267(534)
[RuCl(CO)(PPh3)2(L2)]
78
99
234(468)
297(594)
[RuCl(CO)(AsPh3)2(L3)]
73
75
96
219(438)
225(450)
288(576)
[RuCl(CO)(Py)(PPh3)(L4)]
77
76
99
231(462)
228(456)
297(594)
[RuHCl(CO)(PPh3)3]
18
16
88
54(108)
48(96)
264(528)
[RuHCl(CO)(AsPh3)3]
38
26
87
114(228)
78(156)
261(522)

M. Muthukumar, P. Viswanathamurthi / Spectrochimica Acta Part A 74 (2009) 454–462
461
Table 6 (Continued )
Complex
Substrate
Product
Conversion (%)
18
TONb (TOF)c
54(108)
[RuHCl(CO)(Py)(PPh3)2]
26
89
78(156)
267(534)
a
Conditions: reactions were carried out at 80 ◦C using 3.75 mmol of ketone (10 cm3 isopropanol); catalyst/ketone/KOH ratio 1:300:2.5.
Yield of product was determined using a ACME 6000 series GC-FID with a DP-5 column of 30 m length, 0.53 mm diameter and 5.00 ␮m film thickness and by comparison
b
with authentic samples. TON = ratio of moles of product obtained to the moles of the catalyst used.
c
TOF (TON h−1).
Table 7
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Aspergillus niger Mucor Sp.
50 ppm
100 ppm
50 ppm
100 ppm
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[RuHCl(CO)(PPh3)3]
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[RuHCl(CO)(Py)(PPh3)2]
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[RuCl(CO)(Py)(PPh3)(L2)]
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38
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Acknowledgements
The authors express their sincere thanks to Council of Sci-
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