Ruthenium(II) carbonyl complexes containing chalconates and triphenylphosphine/arsine

Article abstract of DOI:10.1007/s12039-011-0125-0

A series of new hexa-coordinated ruthenium(II) carbonyl complexes of the type [RuCl(CO)(EPh₃)(B)(L^1-4)] (4-15) (E = P or As; B = PPh₃, AsPh₃ or Py; L = 2-hydroxychalcone) were synthesized from the reaction of [RuHCl(CO)(EPh₃)₂(B)] (1-3) (E = P or As; B = PPh3, AsPh3 or Py) with equimolar chalcone in benzene under reflux. The new complexes have been characterized by analytical and spectroscopic (IR, electronic, ¹H, ³¹P{¹H}, and ¹³C NMR) methods. On the basis of data obtained, an octahedral structure has been assigned for all the complexes. The 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 were also found to be efficient transfer hydrogenation catalysts. The antifungal properties of the ligands and their complexes have also been examined and compared with standard Bavistin. Indian Academy of Sciences.

Full text of DOI:10.1007/s12039-011-0125-0

c
J. Chem. Sci. Vol. 123, No. 5, September 2011, pp. 567–576. ꢀ Indian Academy of Sciences.
Ruthenium(II) carbonyl complexes containing chalconates
and triphenylphosphine/arsine
P VISWANATHAMURTHI∗ and M MUTHUKUMAR
Department of Chemistry, Periyar University, Salem 636 011, India
e-mail: viswanathamurthi@rediffmail.com
MS received 1 October 2010; revised 25 March 2011; accepted 19 May 2011
Abstract.
A series of new hexa-coordinated ruthenium(II) carbonyl complexes of the type
[RuCl(CO)(EPh3)(B)(L1−4)] (4–15) (E = P or As; B = PPh3, AsPh3 or Py; L = 2ꢁ-hydroxychalcone) were
synthesized from the reaction of [RuHCl(CO)(EPh3)2(B)] (1–3) (E = P or As; B = PPh3, AsPh3 or Py)
with equimolar chalcone in benzene under reflux. The new complexes have been characterized by analytical
and spectroscopic (IR, electronic, H, 31P{1H}, and 13C NMR) methods. On the basis of data obtained, an
1
octahedral structure has been assigned for all the complexes. The 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 were also found to be efficient transfer hydro-
genation catalysts. The antifungal properties of the ligands and their complexes have also been examined and
compared with standard Bavistin.
Keywords. Ruthenium(II) complexes; spectroscopic studies; catalytic oxidation; catalytic transfer
hydrogenation, antifungal study.
1. Introduction
and its operational simplicity, transition-metal catalysed
hydrogenation, either with isopropyl alcohol or with a
formic acid/triethylamine mixture as a hydride source,
has emerged as an attractive alternative to asymmet-
ric hydrogenation with H2. One of the most efficient
systems has been reported by the group of Noyori.19
Utilizing a ruthenium(II) catalyst, isopropyl alcohol as
a donor and potassium hydroxide as a promoter, Noyori
and co-workers have demonstrated that transfer hydro-
genation reactions of aromatic ketones can occur at
room temperature.
The preparation of a new ligand was perhaps the
most important step in the development of metal com-
plexes which exhibit unique properties and novel reac-
tivity. Chalcones, an important class of compounds that
are widely distributed in nature, have attracted a great
deal of interest due to their applications as antibac-
terial, antiinflammatory and anticancer pharmaco-
logical agents.20–22 Several chalcones are intensively
studied, modified and synthesized in order to develop
more potential biological and catalytic activities. 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. In
this line triphenylphosphine/arsine complexes of ruthe-
nium have been found to be efficient catalyst for the
Among the platinum group metals, ruthenium has been
extensively studied in terms of its coordination and
organometallic chemistry due to their stability, struc-
tural novelty1,2 and catalytic applications.3,4 As the
coordination environment around the central metal
ion imparts the properties of complexes, complexa-
tion of ruthenium by diverse ligands is of significant
importance.5,6 Organometallic compounds containing
phosphine ligands are extensively synthesized due to
their structural importance and catalytic applications in
both small-scale organic synthesis and bulk industrial
production.7–9
Oxidation using transition metal complexes is one of
the most important and basic reactions in organic syn-
thesis and is being developed as a topic of much current
interest.10–15 Catalytic oxidations may be considered
to be one of the more environmentally friendly reac-
tions16 and most important transformations in industrial
chemistry.17
Catalytic reduction of ketones to produce secondary
alcohols can be carried out using transfer hydrogena-
tion.18 In view of the low cost of the reducing agent
∗For correspondence
567

568
P Viswanathamurthi and M Muthukumar
oxidation of alcohols. In addition, ruthenium complexes 2.2 Instrumentation
have long pedigree as catalysts for transfer hydro-
genation reactions in the presence of isopropanol as
hydrogen source.
Analyses of carbon, hydrogen and nitrogen were per-
formed in Carlo Erba 1108 analyzer at Central Drug
Research Institute (CDRI), Lucknow, India. FT-IR
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 on a Shimadzu UV-visible 1650 PC spec-
trophotometer in 200–800 nm range. The NMR spectra
(1H, 31P{1H} and 13C) were recorded in Jeol GSX- 400
instrument. The samples were dissolved in CDCl3 and
1H NMR and 13C NMR spectra were obtained using
TMS as the internal standard. 31P{1H} NMR spectra
of the complexes were obtained using ortho phospho-
ric acid as a reference. The catalytic yields were deter-
mined using ACME 6000 series Gas chromatography
instrument equipped with a flame ionization detector
(FID) using a DP-5 column of 30 m length, 0.53 mm
diameter and 5.00 μm film thickness. Melting points
were recorded on a Technico micro heating table and
are uncorrected.
In continuation of our effort to synthesize new cata-
lyst system, we report here the synthesis of a series of
hexa-coordinated ruthenium(II) complexes with chal-
cone and other co-ligands. The characterization of the
complexes was accomplished by analytical and spectral
methods. The synthesized complexes have been effec-
tively used as catalyst in the oxidation of alcohols in
the presence of NMO and transfer hydrogenation of
ketones in isopropanol with KOH as base. Further, anti-
fungal properties of the synthesized complexes have
also been tested.
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 procedures.23 RuCl3.3H2O was pur-
chased from Loba Chemie Pvt. Ltd., and was used
without further purification. The starting complexes
[RuHCl(CO)(PPh3)3] (1),24 [RuHCl(CO)(AsPh3)3]
(2)25 and [RuHCl(CO)(Py)(PPh3)2] (3)26 were pre-
pared according to the literature methods. The general
structure of the chalcone ligands used in this study is
given below (figure 1).
2.3 Synthesis of chalcone ligands
Chalcone ligands were synthesized by stirring 2-
hydroxy-4-methoxy acetophenone (0.8309 g, 5 mmol)
with corresponding substituted benzaldehyde (0.6007–
0.8309 g, 5 mmol) in the presence of 50 mL alcoholic
sodium hydroxide solution (20%). After 24 h stirring,
the reaction mixture was treated with conc. HCl (5 mL,
5 M), resulting in the formation of precipitate. The pre-
cipitate was filtered, dried under vacuum. Yield = 80%
(0.6601 g, 5 mmol, L1), 75% (0.6200 g, 5 mmol, L2),
88% (0.7302 g, 5 mmol, L3), 78% (0.6503 g, 5 mmol,
L4). The compounds are purified by crystallization from
ethanol solution.
H3CO
OH
O
C
2.4 Synthesis of new ruthenium(II) chalconate
complexes (4–15)
R
All complexes were synthesized by the following com-
mon procedure. To a solution of [RuHCl(CO)(EPh3)2
(B)](1-3) (E = P or As; B = PPh3, AsPh3 or Py) (0.1 g)
in benzene (20 mL), the appropriate chalcone (0.0247–
0.0409 g) were added in 1:1 molar ratio. The mixture
was heated under reflux for 6 h. After the reaction time,
the reaction mixture was concentrated to around 3 mL.
The reaction mixture was cooled and then treated with
10 mL of petroleum ether (60–80◦C), resulting in the
formation of new ruthenium chalconate complex. The
complex was filtered, dried under vacuum. Yield = 76%
Ligand
R
L1
L2
L3
L4
4-(CH3)C6H4
4-(OCH3)C6H4
4-(Cl)C6H4
3, 4-(OCH3)2C6H3
Figure 1. Structure of chalcone.

Ruthenium(II) carbonyl complexes
569
(4), 65% (5), 72% (6), 68% (7), 67% (8), 79% (9), a catalyst, ketone as substrate and KOH as pro-
81% (10), 72% (11), 74% (12), 82% (13), 76% (14), moter at 1:300:2.5 molar ratios. The procedure was
79% (15). The complexes were purified by crystalliza- described as follows. A mixture containing ketone
tion from CH2Cl2/petroleum ether mixture. The purity (3.75 mmol), the ruthenium complex (0.0125 mmol)
of the complexes was checked by NMR.
and KOH (0.03 mmol) in 10 mL of isopropyl alcohol
was reacted under reflux in water bath for different time
period. After completion of reaction the catalyst was
removed from the reaction mixture by the addition of
diethyl ether followed by filtration and subsequent neu-
tralization with 1 M HCl. The ether layer was filtered
through a short path of silica gel by column chromatog-
raphy. The filtrate was concentrated to ≈1 mL and sub-
jected to GC analysis and the hydrogenated product was
identified and determined with authentic samples.
2.5 Procedure for catalytic oxidation of alcohols
Catalytic oxidation of primary alcohols to correspond-
ing aldehydes 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 sec-
ondary alcohol, as substrate at 1:100 molar ratio was
described as follows. A solution of ruthenium complex
(0.01 mmol) in CH2Cl2 (20 mL) was added to the mix-
ture containing substrate (1 mmol), NMO (3 mmol) and
molecular sieves. The reaction mixture was refluxed
for 1 h, and the solvent was then evaporated from the
mother liquor under reduced pressure. The solid residue
was then extracted with diethyl ether (20 mL), concen-
trated to ≈1 mL and was analysed by GC. The oxida-
tion products were identified by GC co-injection with
authentic samples.
3. Results and discussions
Diamagnetic, hexa-coordinated low spin ruthe-
nium(II) complexes of general formula [Ru(CO)-
(EPh3)(B)(L1−4)] (4–15) (E = P or As; B = PPh3,
AsPh3 or Py; L = chalcone) were synthesized in good
yields from the reaction of [RuHCl(CO)(EPh3)2(B)]
(1–3) (E = P or As; B = PPh3, AsPh3 or Py) with
chalcone ligands in dry benzene in equal molar ratio
(scheme 1).
In all these reactions, it has been observed that the
chalcones behave as monoanionic bidentate chelating
ligands by replacing a triphenylphosphine/arsine and a
hydride ion from the starting complexes.
2.6 Procedure for catalytic transfer hydrogenation
of ketone
The catalytic transfer hydrogenation reactions were
All the complexes are stable in air at room
studied using ruthenium(II) chalconate complex as temperature, brown in colour, non-hygroscopic and
H3CO
OH
C
[RuHCl(CO)(EPh3)2(B)]
(1-3)
+
O
(L1-4
)
R
Benzene/
Reflux 6h
EPh3
O
CO
Cl
H3CO
Ru
O
C
B
(4-15)
R
(E = P or As; B = PPh3, AsPh3 or Py; L1 = R = 4-(CH3)C6H4, L2 = R = 4-(OCH3)C6H4, L3 = R = 4-(Cl)C6H4,
L4 = R = 3, 4-(OCH3)2C6H3)
Scheme 1. Formation of ruthenium(II) chalconate complexes.

570
P Viswanathamurthi and M Muthukumar
Table 1. Analytical data of ruthenium(II) chalconate complexes.
Complex
Yield (%)
D.Pt (◦C)
Calculated (found) (%)
H
C
N
[RuCl(CO)(PPh3)2(L1)] (4)
[RuCl(CO)(PPh3)2(L2)] (5)
[RuCl(CO)(PPh3)2(L3)] (6)
[RuCl(CO)(PPh3)2(L4)] (7)
[RuCl(CO)(AsPh3)2(L1)](8)
[RuCl(CO)(AsPh3)2(L2)] (9)
[RuCl(CO)(AsPh3)2(L3)] (10)
[RuCl(CO)(AsPh3)2(L4)] (11)
[RuCl(CO)(Py)(PPh3)(L1)] (12)
[RuCl(CO)(Py)(PPh3)(L2)] (13)
[RuCl(CO)(Py)(PPh3)(L3)] (14)
[RuCl(CO)(Py)(PPh3)(L4)] (15)
76
65
72
68
67
79
81
72
74
82
76
79
171
138
178
143
144
115
138
134
195
142
136
132
67.82(67.68)
66.70(66.58)
65.17(64.98)
65.90(66.02)
62.11(62.16)
61.17(61.18)
59.79(59.72)
60.59(60.61)
63.69(63.54)
62.39(62.33)
60.54(60.56)
61.58(61.46)
4.74(4.76)
4.66(4.63)
4.33(4.35)
4.73(4.72)
4.34(4.32)
4.28(4.26)
3.98(4.02)
4.34(4.37)
4.56(4.58)
4.47(4.51)
4.06(4.10)
4.55(4.57)
–
–
–
–
–
–
–
–
1.81(1.89)
1.77(1.72)
1.76(1.73)
1.71(1.67)
highly soluble in common organic solvents such as of the ligands to ruthenium through the carbonyl oxy-
dichloromethane, acetonitrile, chloroform, benzene and gen atom.27 A strong band observed at 1358–1365 cm−1
DMSO. The analytical data are listed in table 1 and are in the free chalcone ligands has been assigned to phe-
in good agreement with the general molecular formula nolic υC−O stretching. This band has been shifted to
proposed for all the complexes.
higher wave number 1372–1384 cm−1 in the spectra of
the complexes due to its coordination to ruthenium ion
through the oxygen atom of the phenolic group.28 This
has been further supported by the disappearance of the
broad υOH band around 3400–3600 cm−1 in the com-
plexes, indicating deprotonation of the phenolic pro-
ton prior to coordination to ruthenium metal. Hence,
from the infrared spectroscopic data, it is inferred
that both the carbonyl and phenolic oxygen atoms are
involved in the coordination of the chalcone to ruthe-
nium ion in all the complexes. The absorption due to
3.1 Infrared spectroscopic analysis
The important IR absorption bands for the synthesized
ligands and complexes are shown in table 2. The free
chalcone ligands showed a strong band in the region
1631–1642 cm−1 due to υC−O. This band has been
shifted to a lower wave number 1603–1623 cm−1 in
the ruthenium complexes indicating the coordination
Table 2. IR absorption frequencies (cm−1) of free ligands and their ruthenium(II) chalconate complexes.
Compound
νC≡O
νC=O
νC=C
νc–o
PPh3/AsPh3
L1
L2
L3
L4
4
5
6
7
8
-
-
-
-
1631
1634
1642
1636
1606
1603
1603
1605
1618
1612
1623
1623
1605
1603
1606
1604
1568
1574
1582
1565
1543
1542
1542
1542
1549
1549
1545
1548
1541
1542
1544
1543
1358
1363
1361
1365
1380
1382
1382
1384
1373
1382
1372
1381
1380
1382
1380
1381
-
-
-
-
1955
1952
1952
1950
1960
1959
1960
1959
1945
1943
1944
1945
1435, 1093, 696
1434, 1093, 695
1434, 1093, 695
1436, 1094, 696
1434, 1075, 692
1435, 1076, 692
1434, 1076, 692
1435, 1076, 693
1446, 1095, 694
1438, 1094, 695
1438, 1092, 694
1437, 1092, 696
9
10
11
12
13
14
15

Ruthenium(II) carbonyl complexes
571
υC−C of the free ligands 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 ruthe-
Table 3. Electronic spectroscopic data (nm) of free ligands
and their ruthenium(II) chalconate complexes.
Compound
λmax
Assignments
nium complexes because of their possible merging with
29
L1
L2
L3
L4
4
5
6
7
8
301, 246, 204
307, 247, 206
298, 245, 205
289, 245, 209
n - π*, π- π*
n - π*, π- π*
n - π*, π- π*
n - π*, π- π*
υC−O
.
In the complexes, the absorption due to the
phenyl alkene vibration appeared in the region 1565–
1582 cm−1, which is slightly lower than that observed in
the spectra of the free ligands.30 A strong band around
1943–1960 cm−1 indicates the presence of terminally
coordinated carbon monoxide31 in all the complexes.
In the IR spectra of the complexes containing pyri-
dine, a medium intensity band is observed in the region
of 1017–1023 cm−1 which is characteristic of coordi-
nated nitrogen bases.32 In addition, the other character-
istic bands due to triphenylphosphine or triphenylarsine
(around 1440, 1090 and 700 cm−1) were also present
in the spectra of all the complexes.33 The observed
bands in the regions 454–476 cm−1 in the mononu-
clear complexes are tentatively assigned to the υRu−Cl
vibrations.34
358, 234, 205
n - π*, π- π*, C.T
n - π*, π- π*, C.T
n - π*, π- π*, C.T
n - π*, π- π*, C.T
n - π*, π- π*, C.T
n - π*, π- π*, C.T
n - π*, π- π*, C.T
n - π*, π- π*, C.T
n - π*, π- π*, C.T
n - π*, π- π*, C.T
n - π*, π- π*, C.T
n - π*, π- π*, C.T
371, 338, 240, 204
362, 334, 238, 208
401, 373, 246, 207
332, 244, 209
368, 336, 246, 207
334, 249, 208
334, 258, 248, 218
365, 240, 209
368, 243, 208
9
10
11
12
13
14
15
338, 239, 209
389, 374, 236, 209
nature of the observed electronic spectra and the posi-
tion of absorption bands are consistent with those of
other similar ruthenium(II) octahedral complexes.37
3.2 Electronic spectroscopic analysis
All the chalconate ruthenium complexes are diamag-
netic, indicating the presence of ruthenium in the +2
oxidation state. The ground state of ruthenium(II) in an
octahedral environment is 1A1g, arising from the t26g con-
figuration, and the excited states corresponding to the
3.3 1H NMR Spectroscopic analysis
The 1H NMR spectra of the ruthenium(II) chal-
conate complexes were recorded in CDCl3 to con-
firm the binding of chalcone to ruthenium ion. All
the complexes exhibit series of overlapping multiplet
3
2
1
t52g e1g configuration are T1g, T12g, T1g and T2g. Hence,
3
four bands corresponding to the transitions 1A1 → T1g,
3
1
1
1A1g → T2g, 1A1g → T1g and 1A1g → T2g are possible
1
in the region 6.54–7.75 ppm in their H NMR spec-
in the order of increasing energy.
tra (table 4), which have been assigned to the pro-
tons of phenyl groups present in the PPh3 or AsPh3
or Py and chalcone.30 The signal for alkene protons
also appeared in the region 6.5–7.5 ppm and hence,
merged with the multiplet of aromatic protons. The sig-
nal for (−OCH3)C6H4 methoxy proton was observed as
a singlet at 3.90–4.07 ppm region and (−OCH3)C6H3
methoxy protons appeared as a singlet at 3.53–3.62 ppm
region.
Further, the signal for methyl protons appeared as a
singlet at 1.25–1.26 ppm region. No peak was observed
for the OH protons, supporting the assumption that the
phenolic hydroxyl group is deprotonated and coordi-
nated through the oxygen of chalcone to the ruthenium.
The electronic spectral data of the free ligands and
their complexes in dichloromethane are listed in table 3.
The spectra of all the free ligands showed two types
of transitions. The peak appeared at 204–247 nm range
was assigned to π – π* transitions involving molec-
ular orbital located on the phenolic chromophore.
These peaks have been shifted in the spectra of the
complexes; this may be due to the donation of a lone
pair of electrons by the oxygen of the phenoxy group to
the central metal atom.35 The second type of transitions
appeared at 289–307 nm range assigned to n – π* tran-
sitions involving molecular orbital of the −C=O chro-
mophore and the benzene ring. These bands have also
been shifted upon complexation indicated that, the car-
bonyl group oxygen atom appears to be coordinated to
the metal ion.36 The spectra of all the complexes show
another type of transition different from the free lig-
3.4 31P{1H} NMR spectroscopic analysis
ands. The bands appeared at range 332–401 nm, which 31P{1H} NMR spectra of some of the complexes were
can be assigned to charge transfer transitions.37 The recorded to confirm the presence of triphenylphosphine

572
P Viswanathamurthi and M Muthukumar
Table 4. 1H NMR data (δ in ppm) of free ligands and their ruthenium(II) chalconate
complexes.
Complex
δ(ppm)
4
7
9
10
12
14
6.92–7.56 (m, aromatic and -CH=CH-), 3.54 (OCH3), 1.26 (s,CH3)
7.07–7.66 (m, aromatic and -CH=CH-), 4.07, 3.96, 3.58 (OCH3)
6.99–7.74 (m, aromatic and -CH=CH-), 3.90, 3.62 (OCH3)
6.89–7.65 (m, aromatic and -CH=CH-), 3.59 (OCH3)
7.21–7.68 (m, aromatic and -CH=CH-), 3.53 (OCH3), 1.25 (s,CH3)
6.54–7.75 (m, aromatic and -CH=CH-), 3.62 (OCH3)
groups and to determine the geometry of the com- 3.6 Catalytic oxidation
plexes (table 5). In the case of the complexes con-
Catalytic oxidation of primary alcohols and secondary
taining two triphenylphosphine ligands, a sharp singlet
was observed around 30.05–30.12 ppm due to presence
of magnetically equivalent phosphorus atoms suggest-
ing the presence of two triphenylphosphine groups in a
position trans to each other.35 The spectrum of all other
complexes exhibited a singlet around 30.05 ppm corre-
sponding to the presence of triphenylphosphine group
in a position trans to heterocyclic nitrogen base.14
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 with high yields
and the results are listed in table 6. The aldehydes
or ketones formed after 1 h of reflux were determined
by GC and there was no detectable oxidation in the
absence of ruthenium complex. The catalytic activity of
new ruthenium(II) chalconate complexes is compara-
ble with that of corresponding starting complexes in the
case of oxidation of benzyl alcohol. The new complexes
exhibit greater catalytic activities for the oxidation of
cyclohexanol.
Results of the present investigations suggest that the
complexes are able to react efficiently with NMO to
yield a high valent ruthenium-oxo species,39 which is
capable of oxygen atom transfer to alcohols. This was
further supported by spectroscopic changes that occur
by addition of NMO to a dichloromethane solution of
the ruthenium(II) complexes. The appearance of a peak
at 390 nm in UV-Vis spectra is attributed to the forma-
tion of RuIV = O species, which was also found for
other oxo ruthenium(IV) complexes.40,41 Further sup-
port in favour of the formation of such species was iden-
tified from the IR spectra of the solid mass (obtained by
3.5 13C NMR Spectroscopic analysis
The 13C NMR spectra of ruthenium(II) chalconate
complexes (table 5) exhibit a resonance at 208.25–
204.98 ppm region and are assigned to CO carbon. A
sharp singlet appeared at 179.26–177.83 ppm region.
This band was assigned to phenolic –C–O carbon. The
appearance of a peak at 167.58–163.73 ppm region
in the spectra is due to coordinated carbonyl carbon.
Multiplets appeared around 135.52–124.27 ppm region
have been assigned to aromatic carbons. The alkene
carbons appeared in the region 134.58–125.45 ppm,
and hence merged with the aromatic carbons. The two
singlet appeared around 55.38 and 54.96–54.86 ppm
region assigned to methoxy carbon of (−OCH3)C6H4
and (−OCH3)C6H3 groups. In addition, methyl carbon
appeared at 20.34 ppm region.
Table 5. 13C NMR and 31P{1H} NMR data (δ in ppm) of ruthenium(II) chalconate complexes.
Complex
13C NMR (ppm)
31P{1H} NMR (ppm)
4
6
13
14
206.34(s), 178.68(s), 167.49(s), 124.27–132.73(m), 54.93(s), 20.34(s)
205.92(s), 177.83(s), 163.73(s), 127.75–134.36(m), 54.89(s)
208.25(s), 179.26(s), 167.58(s), 127.76–134.51(m), 55.36(s), 54.86(s)
204.98(s), 178.18(s), 165.74(s), 127.13–135.52(m), 54.96(s)
30.12
30.05
30.05
30.05

Ruthenium(II) carbonyl complexes
573
Cyclohexanone was converted into cyclohexanol in
excellent yield (99%) for all the catalyst. Acetophe-
none was converted into corresponding alcohol in
moderate yield (62–77%). Similarly, isobutyl methyl
ketone underwent transfer hydrogenation to afford the
corresponding alcohol in moderate yield (65–79%).
It has been found that complexes containing triph-
enylphosphine or pyridine as ligands possess higher cat-
alytic activity than triphenylarsine as ligands for the
substances acetophenone and isobutyl methyl ketone.
The catalytic efficiency of new ruthenium(II) chal-
conate complexes is moderately increased for conver-
sion of cyclohexanone to cyclohexanol whereas the
activity is tremendously improved for reduction of ace-
tophenone and isobutyl methyl ketone when compared
to corresponding starting complexes.
We were also interested in mechanism of the above
transfer hydrogenation processes. Although no studies
have been carried out to determine the mechanism for
these particular catalytic processes, it is gener-
ally assumed that transition-metal-catalysed hydrogen
transfer involves metal hydrides as key intermediates.
An essential component for this reaction is potas-
sium hydroxide, which facilitates the formation of the
ruthenium alkoxide by abstracting the proton of the
alcohol and subsequently, the alkoxide underwent β-
elimination to give a ruthenium hydride intermediate
and release of acetone. Formation of Ru–H complexes
from Ru–Cl precursors has been well-documented,10
and such in situ formed Ru–H species can act as
the active catalysts for transfer hydrogenation of
ketones.42,43 Coordination of a ketone substrate to
Ru–H intermediate produces a new compound and is
followed by insertion of the coordinated ketone car-
bonyl into the Ru–H bond to form new Ru-alkoxide
which is then reacted with isopropyl alcohol to afford
Table 6. Catalytic oxidation data of ruthenium(II) chal-
conate complexes.
Complex
Substrate
Product
Yield (%)a
5
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
98
89
86
81
99
80
97
76
94
74
99
53
94
51
93
54
81
37
87
52
81
46
6
9
10
11
12
13
15
1
2
3
A: Benzaldehyde; B: Cyclohexanone
aYields were determined by GC and comparing with the
analyses of authentic samples38 (Benzaldehyde, Cyclohex-
anone).
evaporation of the resultant solution to dryness), which
showed a band at 860 cm−1, characteristic of RuIV = O
species.39,41
3.7 Catalytic transfer hydrogenation
Ruthenium mediated transfer hydrogenation reactions the alcohol product.
are found to be effective catalytic systems in which
hydrogen is transferred from one organic molecule to
another and this made us interested to carry out this type
of reactions.
3.8 Antifungal activity
The complexes [RuCl(CO)(PPh3)2(L4)] (7),
[RuCl(CO)(AsPh3)2(L1)] (8) and [RuCl(CO)(Py)-
(PPh3)(L3)] (14) are taken as model catalyst and the
catalytic activity in the transfer hydrogenation of var-
ious aliphatic and aromatic ketones in the presence
of isopropyl alcohol and KOH as promoter has been
explored. The complexes catalyse the reduction of
ketones to corresponding alcohols in excellent yields
and in relatively short reaction times and the results
of these organic transformations are presented in
table 7.
One of the chalcone ligands and their ruthenium
chelates were screened in vitro in order to evaluate their
antifungal activity against Aspergillus niger and Mucor
Species at two different concentrations by disc diffu-
sion method.44 The results (table 8) showed that the
ruthenium chelates are more toxic as compared with
their parent ligand against the same microorganisms
under identical experimental conditions. The increase
in the antifungal activity of metal chelates may be due
to the effect of the metal ion on the normal cell pro-
cess. A possible mode for toxicity increase may be

574
P Viswanathamurthi and M Muthukumar
Table 7. Catalytic transfer hydrogenation of ketones by ruthenium(II) chalconate
complexes.a
considered in the light of Tweedy’s chelation theory.45 metal atom, which subsequently favours its permeation
‘Chelation considerably reduces the polarity of the through the lipid layers of cell membrane’.46 Further,
metal ion because of partial sharing of its positive the toxicity of the compounds increases with increase
charge with the donor groups and possible π-electron in concentration. Though the complexes possess activ-
delocalization over the whole chelate ring. Such chela- ity, it could not reach the effectiveness of the standard
tion could enhance the lipophilic character of the central drug Bavistin.

Ruthenium(II) carbonyl complexes
575
Table 7. (continued).
aConditions: reactions were carried out under heated to reflux. 3.75 mmol of ketone
(10 mL isopropyl alcohol); catalyst/ketone/KOH ratio 1:300:2.5
bYields were determined by GC and comparison with authentic samples
4. Conclusions
Table 8. Fungicidal activity data for some ruthenium(II)
chalconate complexes.
Several new ruthenium(II) chalconate complexes were
synthesized using chalcone ligands synthesized from
the reaction between benzaldehyde and 2-hydroxy-4-
methoxyacetophenone. The new complexes have been
characterized by analytical and spectroscopic methods.
An octahedral structure has been tentatively proposed
for all the complexes. The complexes showed efficient
catalytic activity for the oxidation of both primary and
secondary alcohols with excellent yields in short reac-
tion time and also for transfer hydrogenation of ketones
Compound
Diameter of inhibition zone (mm)
Aspergillus niger Mucor Species
50 ppm
100 ppm
50 ppm
100 ppm
L4
7
11
15
6
18
23
21
38
10
42
45
41
56
8
21
24
20
42
13
36
47
43
53
Bavistin

576
P Viswanathamurthi and M Muthukumar
with high conversions. The complexes also exhibit con-
siderable amount of antifungal activity at the time of
screening.
Fache F, Sautet P, Lemaire M 1998 J. Am. Chem. Soc.
120 1441
19. Hashiguchi S, Fujii A, Takehara J, Ikariya T, Noyori R
1995 J. Am. Chem. Soc. 117 7562
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Supplementary material
1
Representative Uv-Vis, H NMR, 31P{1H} NMR and
13C NMR spectrum of ruthenium(II) chalconate com-
plexes have been provided as figures S1–S4 in supple-
mentary materials (see www.ias.ac.in/chemsci).
25. Sanchez-Delgado R A, Lee W Y, Choi S R, Cho Y, Jun
M J 1991 Trans. Met. Chem. 16 241
Acknowledgements
26. Gopinathan S, Unny I R, Deshpande S S, Gopinathan C
1986 Ind. J. Chem. A 25 1015
The authors express their sincere thanks to Council of
Scientific and Industrial Research (CSIR), New Delhi
[Grant No. 01(2065)/06/EMR-II] for financial support.
27. Muthukumar
M,
Viswanathamurthi
P
2008
Specrtrochim. Acta A 70 1222
One of the authors (MM) thanks CSIR for the award of 28. Kannan S, Sivagamasundari M, Ramesh R, Liu Y 2008
J. Organomet. Chem. 693 2251
29. Fuson N, Josien M L, Shelton E M 1954 J. Am. Chem.
Soc. 76 2526
Senior Research Fellowship.
30. Kaveri M V, Prabhakaran R, Karvembu R, Natarajan K
2005 Specrtrochim. Acta A 61 2915
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