Coordination behavior of ligand based on NNS and NNO donors with ruthenium(III) complexes and their catalytic and DNA interaction studies

Article abstract of DOI:10.1016/j.saa.2012.07.028

Reactions of 2-acetylpyridine-thiosemicarbazone HL¹, 2-acetylpyridine-4-methyl-thiosemicarbazone HL², 2-acetylpyridine-4- phenyl-thiosemicarbazone HL³ and 2-acetylpyridine-semicarbazone HL⁴ with ruthenium(III) precursor complexes were studied and the products were characterized by analytical and spectral (FT-IR, electronic, EPR and EI-MS) methods. The ligands coordinated with the ruthenium(III) ion via pyridine nitrogen, azomethine nitrogen and thiolate sulfur/enolate oxygen. An octahedral geometry has been proposed for all the complexes based on the studies. All the complexes are redox active and display an irreversible and quasireversible metal centered redox processes. Further, the catalytic activity of the new complexes has been investigated for the transfer hydrogenation of ketones in the presence of isopropanol/KOH and the Kumada-Corriu coupling of aryl halides with aryl Grignard reagents. The DNA cleavage efficiency of new complexes has also been tested.

Full text of DOI:10.1016/j.saa.2012.07.028

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 864–870
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Coordination behavior of ligand based on NNS and NNO donors with
ruthenium(III) complexes and their catalytic and DNA interaction studies
⇑
R. Manikandan, P. Viswnathamurthi
Department of Chemistry, Periyar University, Salem 636011, Tamilnadu, India
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
Ruthenium(III) Schiff base complexes containing 2-acetylpyridine thiosemicarbazone/semicarbazone
were synthesized and characterized. They have been assigned an octahedral structure. The new com-
plexes were found to be efficient catalyst for transfer hydrogenation and Kumada–Corriu coupling reac-
tions. The complexes also successfully cleaved the DNA.
"
A new series of ruthenium(III) Schiff
base complexes were synthesized.
Spectral studies have proved the
binding modes of ligand with central
metal ion.
"
"
"
The complexes have used as
catalysts in the transfer
hydrogenation and coupling
reaction.
The synthesized complexes cleaved
DNA even at lower concentrations.
Mg
Dry ether
Ru(III) Complex
Dry ether
Br
+
MgBr H3CO
Br
H3CO
a r t i c l e i n f o
a b s t r a c t
Reactions of 2-acetylpyridine-thiosemicarbazone HL1, 2-acetylpyridine-4-methyl-thiosemicarbazone
HL2, 2-acetylpyridine-4-phenyl-thiosemicarbazone HL3 and 2-acetylpyridine-semicarbazone HL4 with
ruthenium(III) precursor complexes were studied and the products were characterized by analytical
and spectral (FT-IR, electronic, EPR and EI-MS) methods. The ligands coordinated with the ruthenium(III)
ion via pyridine nitrogen, azomethine nitrogen and thiolate sulfur/enolate oxygen. An octahedral geom-
etry has been proposed for all the complexes based on the studies. All the complexes are redox active and
display an irreversible and quasireversible metal centered redox processes. Further, the catalytic activity
of the new complexes has been investigated for the transfer hydrogenation of ketones in the presence of
isopropanol/KOH and the Kumada–Corriu coupling of aryl halides with aryl Grignard reagents. The DNA
cleavage efficiency of new complexes has also been tested.
Article history:
Received 1 May 2012
Received in revised form 26 June 2012
Accepted 9 July 2012
Available online 27 July 2012
Keywords:
Ruthenium(III) complexes
Spectral studies
Catalytic transfer hydrogenation
Kumada–Corriu coupling
DNA cleavage
Ó 2012 Elsevier B.V. All rights reserved.
Introduction
acidic thiol proton, resulting in the formation of a five-membered
chelate ring. Thiosemicarbazones and semicarbazones of aromatic
Derivatives of semicarbazones and thiosemicarbazones are
amongst the most widely studied nitrogen and oxygen/sulfur do-
nor ligands [1,2]. In particular, transition metal complexes of thio-
semicarbazones have been receiving considerable interest largely
because of their biological activities [3,4]. Thiosemicarbazones
usually react as chelating ligands with transition metal ions by
bonding through the sulfur and the azomethine nitrogen atoms
and in some cases they behave as tridentate ligands and bond
through the sulfur and two nitrogen atoms [5–7]. Complexation
of the thiosemicarbazone usually occurs via dissociation of the
aldehydes or ketones are known to act as tridentate ligands can
yield cyclometallated complexes having two fused five-membered
chelate rings at the metal center [8,9].
Among transition metal complexes ruthenium complexes have
been widely used as catalysts in various catalytic reactions such as
hydrogenation, oxidation, isomerization, polymerization, nucleo-
philic addition to multiple bonds and carbon–carbon bond forma-
tion [10,11]. The ability of ruthenium to assume a wide range of
oxidation states and coordination geometries provides unique
opportunities for catalysis. Reduction of carbonyl compounds is
an important transformation in organic synthesis from both aca-
demic and industrial points of view [12]. Transfer hydrogenation
of ketones by using an alcohol, preferably isopropyl alcohol, is an
⇑
Corresponding author. Fax: +91 427 2345124.
E-mail address: viswanathamurthi@rediffmail.com (P. Viswnathamurthi).
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.07.028

R. Manikandan, P. Viswnathamurthi / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 864–870
865
interesting alternative to the classical hydrogenation process
requiring the use of dihydrogen gas [13,14]. Ruthenium(II) com-
plexes containing diphosphine and 1,2 diamine ligands, in the
presence of a base and isopropanol, are excellent catalysts for the
hydrogenation of ketones under mild conditions [15]. Pincer type
ruthenium(II) complexes containing the monoanionic terdentate
NCN/PCP ligands as active catalysts for the transfer hydrogenation
of ketones [16].
N
C
N
D
N
H3C
N
C
H
H
R
Carbon–carbon bond formation in the presence of a transition
metal catalyst is a key step in many synthetic protocols of organic
chemicals, natural products, as well as in a variety of industrial
processes. One important example of such a catalytic transforma-
tion is the Grignard cross-coupling reaction that has been used in
a wide range of synthetic and industrial applications. For example,
the coupling of aromatic Grignard compounds with aryl halides of-
fers a convenient synthetic access to biaryls, terphenyls and olig-
oaryls that have become important building blocks for the
synthesis of natural products, liquid crystals, polymers and ligands
in transition metal complexes [17,18]. A number of nickel and pal-
ladium complexes have been reported to catalyze the coupling of
Grignard reagents with aryl bromides and iodides [19,20].
Metallopharmaceuticals are known to act on DNA by inhibiting
DNA replication and transcription. Thus, studies on the interaction
of metal complexes with DNA may reveal useful information on
the rational drug design and development of sensitive chemical
probe for DNA [21]. Various transition metal complexes derived
from pyrimidine [22], polyamines [23], 1,10-phenanthroline [24],
N-methyl-2-aminomethylpyrrolidine [25], aminoacid derivatives
[26], macrocycles [27], diamines [28] and Schiff bases [29] have
been reported as good candidates for DNA structural probes, DNA
cleavage studies, DNA molecular light switches and new therapeu-
tics. Recently, the DNA cleavage properties of ruthenium com-
plexes have been investigated extensively [30]. Even though, few
reports are available about the catalytic properties of ruthenium
[31–34], it is still interesting for further investigation with new li-
gand system. Hence, we describe here the synthesis and character-
ization of ruthenium(III) complexes containing 2-acetylpyridine
thiosemicarbazone/semicarbazone. Further the redox behavior,
catalytic and DNA cleavage property of the synthesized complexes
have been investigated.
Ligand
HL1
HL2
HL3
HL4
D
S
R
H
S
CH3
S
C6H5
H
O
Fig. 1. Structure of Schiff base ligands.
a JEOL JES-FA200 X-band frequencies at room temperature using 2,
2-diphenyl-1-picrylhydrazyl radical (DPPH) as internal standard at
Pondicherry University, Pondicherry, India. The EI-MS spectra were
recorded by the EI technique at using JEOL JMS600H instrument in
the HRMS facility NIIST, Thiruvananthapuram. Cyclic voltammetric
measurements were carried out with a BAS CV-27 electrochemical
analyzer in acetonitrile and [(n-C4H9)4N](ClO4)(TBAP) used as sup-
porting electrolyte under nitrogen atmosphere. Three electrode
cells was employed with glassy carbon working electrode, a plati-
num wire as counter electrode and an Ag/AgCl as reference elec-
trode. Melting points were recorded on a Technico micro heating
table and are uncorrected. The catalytic yields were determined
using ACME 6000 series GC-FID with DP-5 column of 30 m length,
0.53 mm diameter and 5.00 lm film thickness.
2.3. Synthesis of ruthenium(III) Schiff base complexes
The general procedure for the preparation of the complexes is as
follows. To a solution of 0.1 mmol [RuX3(EPh3)3] (E = P or As; X = Cl
or Br) in benzene was added 0.1 mmol ligand (mole ratio of ruthe-
nium complex and ligand is 1:1, respectively) and the mixture was
refluxed for 5 h. The product was separated by the addition of
small amount of petroleum ether (60–80 °C). The resulting com-
plexes were recrystallized from CH2Cl2/petroleum ether and dried
under vacuum. The overall yield obtained for all the complexes
were 67–78%.
2. Experimental
2.1. Materials and reagents
All the reagents used were chemically pure and AR grade. The
solvents were purified and dried according to standard procedures.
RuCl3ꢀH2O was purchased from Loba Chemie Pvt. Ltd. The starting
complexes [RuCl3(PPh3)3], [RuCl3(AsPh3)3] and [RuBr3(AsPh3)3]
[35–37] and 2-acetylpyridine thiosemicrabazone/semicarbzone
Schiff base ligands (Fig. 1) were prepared according to the litera-
ture procedures [38,39]. DNA cleavage studies were carried out
according to reported procedure [40].
2.4. Typical procedures for transfer hydrogenation of ketones
The catalytic transfer hydrogenation reactions were also studied
using ruthenium(III) Schiff base complexes as a catalyst, ketone as
substrate and KOH as base at 1:500:2.5 molar ratios. The procedure
was described as follows. A mixture containing ketone (5.0 mmol),
the ruthenium complex (0.01 mmol) and KOH (0.025 mmol) was
heated to reflux in 10 ml of i-PrOH for 2 h. After completion of reac-
tion the catalyst was removed from the reaction mixture by the
addition of petroleum 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.
2.2. Physical measurements
Microanalysis of carbon, hydrogen and nitrogen was carried out
using Vario EL III Elemental analyzer at SAIF – Cochin India. The IR
spectra of the ligand and their complexes were recorded as KBr pel-
lets on a Nicolet Avatar model in 400–4000 cmꢁ1 range. Electronic
spectra of the ligand and their complexes have been recorded in
dichloromethane using a Shimadzu UV – 1650 PC spectrophotome-
ter in 200–800 nm range. 1H NMR spectra were recorded in Jeol GSX
– 400 instrument using DMSO as the solvent. Electron paramagnetic
resonance spectra (EPR) of the powder samples were recorded with
2.5. Typical procedures for Kumada–Corriu reactions
Magnesium turnings (320 mg) were placed in a two-neck-
round-bottomed flask with a calcium chloride guard tube. A crystal

866
R. Manikandan, P. Viswnathamurthi / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 864–870
Table 2
IR absorption frequencies (cmꢁ1) and electronic spectral data (nm) of free ligands and
ruthenium(III) Schiff base complexes.
X
N
N
EPh3
D
Benzene
[RuX3(EPh3)3]
+
Ru
X
Compound
mNH
mCN
mCO
mCS
kmax
5 h / reflux
C
N
D
N
C N
HL1
3183
3187
3194
3174
–
–
–
–
–
–
–
–
–
–
–
–
1609
1580
1598
1585
1574
1560
1565
1583
1573
1565
1562
1579
1574
1569
1560
1580
–
–
–
836
834
801
–
747
745
743
–
741
740
741
–
737
741
745
–
297, 234
360, 341, 241
329, 279, 238
336, 310, 260
492, 364, 331, 283, 237
496, 367, 268, 238, 236
487, 350, 260, 254
460, 354, 238
490, 314, 309
480, 343, 310
496, 350, 308, 253
459, 340, 256
488, 332, 324, 307
491, 352
498, 360, 334, 269, 212
462, 346, 313, 243
H3C
N
C
H
H3C
N
C
HL2
H
R
N R
HL3
H
HL4
1686
–
–
–
1332
–
–
–
1336
–
–
–
[RuCl2(PPh3)L1]
[RuCl2(PPh3)L2]
[RuCl2(PPh3)L3]
[RuCl2(PPh3)L4]
[RuCl2(AsPh3)L1]
[RuCl2(AsPh3)L2]
[RuCl2(AsPh3)L3]
[RuCl2(AsPh3)L4]
[RuBr2(AsPh3)L1]
[RuBr2(AsPh3)L2]
[RuBr2(AsPh3)L3]
[RuBr2(AsPh3)L4]
(E = P or As; X = Cl or Br; D = S or O; R = H, CH3 or C6 H5)
Scheme 1. Synthesis of ruthenium(III) Schiff base complexes.
of iodine was added to activate the surface of the magnesium. Bro-
mobenzene (0.5 ml of a total of 1.3 ml, 12 mmol) in 5 ml of anhy-
drous diethyl ether was added with stirring and heated under
reflux. Turbidity after 5 min indicated the initiation of the reaction.
The remaining bromobenzene in 5 ml of ether was added drop
wise and the reaction mixture was refluxed for 40 min. To this
reaction mixture, 1.03 ml (10 mmol) of 4-bromoanisole in 5 ml of
anhydrous diethyl ether and the ruthenium complex (0.03 mmol)
was added and the mixture was stirred for 6 h. The reaction mix-
ture was quenched with 10 ml of H2O, and the mixture was diluted
with diethyl ether. After separation of organic and aqueous phases,
the organic phase was washed with 50 ml of H2O, and then dried
over MgSO4, filtered and evaporation of solvent. The crude product
was purified by column chromatography on silica gel to afford of 4-
phenyl anisole.
1336
3. Result and discussion
The reactions of [RuX3(EPh3)3] (E = P or As; X = Cl or Br) with 2-
acetylpyridine thiosemicarbazone/semicarbazone in 1:1 molar ra-
tio in dry benzene afforded new hexa-coordinated low-spin ruthe-
nium(III) Schiff base complexes (Scheme 1). The analytical data
(Table 1) are in good agreement with the general molecular for-
mula proposed. In all the reactions, the Schiff base ligand behaves
as mono negative tridentate ligands by replacing two molecules of
triphenylphosphine or triphenylarsine and one molecule of chlo-
ride or bromide ion from the precursors. All the complexes are
air-stable, non-hygroscopic in nature, insoluble in water and
highly soluble in common solvents such as chloroform, dichloro-
methane, acetonitrile and dimethyl sulphoxide. Attempts made
to grow single crystals of the complexes went unsuccessful.
Fig. 2. EPR spectrum of [RuCl2(PPh3)L1].
The free ligands showed a strong band in the region 1580–
1609 cmꢁ1 due to tC=N. This band has been shifted to lower fre-
quencies 1560–1583 cmꢁ1 in the metal complexes indicating the
coordination of the ligands to metal through the azomethine nitro-
gen atom [41]. The bands due to tN–H and tC=S appeared around
3174–3194 cmꢁ1 and 801–836 cmꢁ1 in the free ligands has disap-
peared on complexation and a new band appeared around 737–
747 cmꢁ1. These observation attributed to thioenolization of the
ANHAC@S group and subsequent coordination through the depro-
tonated sulfur [42,43]. The semicarbazone ligand (HL4) tC=O
3.1. Infrared spectroscopic analysis
The important IR absorption frequencies of the ligands and their
metal complexes along with their assignment are listed in Table 2.
Table 1
Analytical data of free ligands and ruthenium(III) Schiff base complexes.
Compound
Colour
M. Pt (°C)
Calculated (found) (%)
C
H
N
S
HL1
Yellow
Yellow
Yellow
Yellow
Brown
Brown
Brown
Brown
Brown
Brown
Brown
Brown
Brown
Brown
Brown
Brown
180
170
185
210
235
160
170
230
160
258
158
160
261
250
160
180
49.46(49.32)
51.90(51.78)
62.20(62.46)
53.92(53.45)
49.76(49.58)
50.54(50.43)
54.62(54.73)
51.07(51.53)
46.50(46.56)
47.30(41.39)
51.41(51.57)
47.64(47.45)
41.07(41.38)
41.87(41.56)
45.94(45.94)
41.95(41.94)
5.18(5.26)
5.80(5.72)
5.21(5.56)
5.65(5.43)
3.85(3.62)
4.08(4.43)
4.61(4.99)
3.95(3.99)
3.60(3.38)
3.82(3.52)
3.77(3.54)
3.69(3.86)
3.18(3.53)
3.38(3.56)
3.37(3.79)
3.24(3.79)
28.84(28.69)
26.90(26.29)
26.72(26.54)
31.44(31.65)
8.92(8.43)
8.73(8.54)
7.96(7.35)
9.16(9.35)
8.34(7.59)
8.17(8.52)
7.49(7.35)
8.54(8.67)
7.36(7.58)
7.23(7.45)
6.60(6.12)
7.52(7.12)
16.50(16.32)
15.39(15.78)
11.85(11.63)
–
5.10(5.58)
4.99(4.68)
4.55(3.56)
–
4.77(4.71)
4.67(4.68)
4.28(4.67)
–
4.21(4.61)
4.14(4.23)
3.83(3.68)
–
HL2
HL3
HL4
[RuCl2(PPh3)L1]
[RuCl2(PPh3)L2]
[RuCl2(PPh3)L3]
[RuCl2(PPh3)L4]
[RuCl2(AsPh3)L1]
[RuCl2(AsPh3)L2]
[RuCl2(AsPh3)L3]
[RuCl2(AsPh3)L4]
[RuBr2(AsPh3)L1]
[RuBr2(AsPh3)L2]
[RuBr2(AsPh3)L3]
[RuBr2(AsPh3)L4]

R. Manikandan, P. Viswnathamurthi / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 864–870
867
Table 3
EPR spectral data of the ruthenium(III) Schiff base complexes.
O
O
OH
OH
Ru(III) Complex
KOH / iprOH
reflux 2 h
+
+
Complex
gx
gy
gz
hg⁄i
[RuCl2(PPh3)L1]
[RuCl2(PPh3)L2]
[RuCl2(PPh3)L3]
[RuCl2(AsPh3)L1]
[RuCl2(AsPh3)L2]
[RuBr2(AsPh3)L3]
–
–
–
–
–
–
2.30
2.71
2.21
2.62
2.22
2.23
–
–
–
–
–
–
–
–
–
–
–
–
Scheme 2. Transfer hydrogenation of ketones.
h
i
1=2
hgꢂi ¼ 1=3gx2 þ 1=3gy2 þ 1=3g2z
.
appeared around 1686 cmꢁ1 in free ligands has disappeared on
complexation and new band appeared around 1332–1336 cmꢁ1
which due to ketoenolization [44]. The band at 3380–3427 cmꢁ1
in the spectra has been assigned to terminal ANHAR group [45].
All the ruthenium(III) complexes show strong vibrations near
530, 690, 745 and 1550 cmꢁ1 which are attributed to PPh3/AsPh3
[46].
3.2. Electronic spectroscopic analysis
The electronic spectra of the complexes were recorded in
dichloromethane solution in the region 200–800 nm (Table 2). All
the ruthenium(III) Schiff base complexes display strong band in
the visible region in the range 459–498 nm due to charge transfer
transition. The bands in the 307–367 nm regions are due to n–p⁄
Fig. 4. Catalytic transfer hydrogenation of cyclohexanone (A), acetophenone (B)
and isobutylmethyl ketone (C) in different time intervals.
Fig. 3. EI-Mass spectrum of [RuCl2(PPh3)L1].
Table 4
Electrochemical spectral data of the ruthenium(III) Schiff base complexes.a
Complex
RuIII/RuIV Epa(V)
Epa(V)
RuIII/RuII Epc(V)
Ef(V)
DEp(mV)
[RuCl2(PPh3)L2]
[RuCl2(AsPh3)L2]
[RuCl2(AsPh3)L3]
[RuBr2(AsPh3)L1]
[RuBr2(AsPh3)L3]
[RuBr2(AsPh3)L4]
0.50
0.55
0.60
0.65
0.70
0.60
ꢁ0.80
ꢁ0.90
ꢁ0.95
ꢁ0.90
ꢁ0.96
ꢁ0.98
ꢁ0.65
ꢁ0.60
ꢁ0.55
ꢁ0.53
ꢁ0.52
ꢁ0.75
ꢁ0.73
ꢁ0.75
ꢁ0.75
ꢁ0.71
ꢁ0.74
ꢁ0.86
150
300
400
370
440
230
a
Working electrode, glassy carbon electrode; reference electrode, Ag–AgCl electrode; supporting electrolyte [NBu4]ClO4 (0.01 M); concentration of the complex, 0.001 M;
scan rate, 100 mV sꢁ1; Ef = 0.5(Epa + Epc),
Ep = Epa–Epc
D
.

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R. Manikandan, P. Viswnathamurthi / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 864–870
Table 5
Table 6
Catalytic transfer hydrogenation of cyclohexanone by [RuBr2(AsPh3)L2]/i-PrOH/KOH.
Catalytic transfer hydrogenation of ketones by ruthenium(III) Schiuff base
complexes.a
Entry
Reaction time (h)
% Conversion*
Complex
Substrate
Product
Conversion
(%)b
1
2
3
4
2
2
2
2
99a
58b
Not detectedc
Not detectedd
[RuCl2(PPh3)(L3)]
89
O
OH
*
The conversion of product determined by GC and comparing with authentic
sample.
a
Reactions were carried out at 90 °C using substrate (5 mmol), catalyst
OH
O
86
(0.01 mmol) in isopropanol, KOH (0.025 mmol).
b
Reactions were carried out at 90 °C using substrate (5 mmol), catalyst
(0.005 mmol) in isopropanol, KOH (0.025 mmol).
c
The reaction was carried out without catalyst.
The reaction was carried out without KOH.
d
OH
85
92
O
O
O
O
transition of non-bonding electrons present in the nitrogen of the
azomethine group in the ruthenium(III) Schiff base complexes.
The bands observed around 212–297 nm is as assigned to
p–
p⁄
[RuCl2(PPh3)(L4)]
[RuBr2(AsPh3)(L1)]
[RuBr2(AsPh3)(L2)]
O
O
O
OH
OH
OH
transitions of the ligands. The pattern of the electronic spectra of
all the complexes indicates the presence of an octahedral environ-
ment around the ruthenium(III) ion [47].
OH
O
O
O
90
3.3. EPR spectroscopic analysis
The EPR spectra of powdered samples were recorded at room
temperature. The representative spectra are shown in Fig. 2. The
complexes showed no indication of any hyperfine interaction of
Ru with N, As, P, Cl and Br. The spectra of all the complexes showed
single isotropic resonance with g values of 2.21–2.71 (Table 3).
Such isotropic lines are usually observed either due to intermolec-
ular spin–spin exchange, which can broaden the lines or due to
occupancy of the unpaired electron in a degenerate orbital [48]
corresponding to the electronic configuration (dxz)2, (dyz)2, (dxy)1.
OH
89
96
OH
94
3.4. Mass spectroscopic analysis
The electron impact mass spectra of complexes are recorded
and investigated at 70 eV of electron energy. The representative
mass spectrum of complex [RuCl2(PPh3)L1] are given in Fig. 3.
The complex is characterized by moderate to high relative inten-
sity molecular ion peaks. It is obvious that, the molecular ion peaks
are in good agreement with the suggested empirical formula as
indicated from elemental analyses. The spectrum showed a molec-
ular ion peak M+ at M/Z 627, which is equivalent to its molecular
weight of the complex. The molecular ion peak fragmentation with
the loss of two chlorine molecules, gave a peak at M/Z 592 and 557
due to fragment ion [RuCl(PPh3)L1]+ and [Ru(PPh3)L1]+. Further, the
fragments leading to the formation of the species [RuL1]+ which
undergo demetalation to form the species [L+H]+ gave fragment
ion at M/Z 193.
OH
93
99
OH
98
96
OH
3.5. Redox properties
a
Conditions: reactions were carried out at 90 °C using 5 mmol of ketone (10 ml
isopropanol) and catalyst/substrate/KOH ratio 1:500:2.5.
The conversion of product determined by GC and comparing with analyses of
authentic samples.
The electron transfer properties of the Ru(III) Schiff base com-
plexes were studied by cyclic voltammetry. Voltammograms of
these complexes recorded from 0 to 2.0 V for RuIII/RuIV and from
0 to ꢁ2.0 V for RuIII/RuII vs Ag–AgCl (Table 4). The voltammograms
reveal a pair of redox waves for these complexes, which corre-
sponds to +0.50 to +0.70 RuIII/RuIV (oxidation) and ꢁ0.52 to
ꢁ0.98 RuIII/RuII (reduction) at the positive and negative potentials,
respectively. The redox process of the complexes exhibits an irre-
b
RuIII/RuII is due to slow electron transfer and absorption of the
complexes on to the electrode surface. The potentials of both the
oxidation (RuIII/RuIV) and reduction (RuIII/RuII) have been found
to be sensitive to the nature of the substituent (R) in the 2-acetyl-
pyridine thiosemicarbazone ligands and replacement of chlorides
by bromides and triphenyl phosphine by arsine. Hence from the
electrochemical data it is clear that the present ligand system is
ideally suitable for stabilizing the higher oxidation state of ruthe-
nium ion.
versible oxidation and quasi-reversible reduction (The
DEp values
for the above reduction process ranging from 150 to 440 mV).
The irreversible redox processes RuIII/RuIV observed for these
complexes may be due to short-lived oxidation state of metal ion
where as a quasi-reversible process observed for the reduction

R. Manikandan, P. Viswnathamurthi / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 864–870
869
Mg
Dry ether
Ru(III) Complex
Dry ether
Br
+
MgBr H3CO
Br
H3CO
Scheme 3. Kumada–Corriu reaction of aryl bromide with Grignard reagent.
Table 7
Kumada–Corriu reaction of 4-bromoanisole with phenylmegnesium bromide by ruthenium(III) Schiff base complexes at room temperature in diethyl ether (6 h).a
Complex
Coupling partner
Aryl halide
Product
Yield (%)b
[RuCl2(PPh3)L1]
35
28
48
36
OCH3
OCH3
OCH3
OCH3
MgBr
Br
OCH3
OCH3
OCH3
OCH3
[RuCl2(AsPh3)L3]
[RuBr2(AsPh3)L2]
[RuBr2(AsPh3)L4]
MgBr
MgBr
MgBr
Br
Br
Br
a
Based on phenylmegnisium bromide (12 mmol), 4-bromoanisole (10 mmol) and ruthenium(III) Schiff base complex (0.03 mmol).
The yield of product was determined using a 1H NMR.
b
3.6. Catalytic transfer hydrogenation of ketones
a
Transfer hydrogenation of ketones in the presence of newly
synthesized Ru(III) Schiff base complexes has been studied in iso-
propanol/KOH medium (Scheme 2). The reaction was conducted
at a catalyst, substrate and base in molar ratio 1:500:2.5, respec-
tively. [RuBr2(AsPh3)L2] was selected as a model catalyst for opti-
mization of the reaction conditions. In order to study the effect
of time on the activity, the product analysis was done at regular
intervals of time under similar reaction conditions (Fig. 4) and opti-
mized as 2 h.
Form II
Form I
To evaluate the catalytic efficiency of [RuBr2(AsPh3)L2], the
reduction of cyclohexanone was carried out under similar reaction
conditions in the absence of catalyst and found that no reasonable
conversion was observed (Table 5, entry 2). The reduction of cyclo-
hexanone was carried out with lower amount of [RuBr2(AsPh3)L2],
the yield was low (Table 5, entry 3). Also the reaction was carried
out in the absence of base, no transfer hydrogenation of cyclohexa-
none was observed (Table 5, entry 4). The role of KOH is to generate
the catalyst from chloro precursor and the reaction mediates
through the hydride species. The base facilitated the formation of
the ruthenium alkoxide by abstracting the proton of alcohol and
subsequently, the alkoxide underwent b-elimination to give a ruthe-
nium hydride which is the active species in this reaction. The trans-
fer hydrogenation of other aliphatic and aromatic ketones was then
examined using the optimized reaction conditions. Among the
ruthenium(III) Schiff base complexes that have been analyzed, the
order of catalytic activity in terms of yield was [RuBr2(AsPh3)L2] >
[RuBr2(AsPh3)L1] > [RuCl2(PPh3)L4] > [RuCl2(PPh3)L3] (Table 6). In
terms of substituents present in the Schiff base moiety, the order
of activity is CH3 > H > C6H5. Hence, it is inferred that inductive effect
of the substituent plays a major role in deciding the catalytic activity
of their corresponding complexes. It is further inferred from the re-
sults that the AsPh3/PPh3, Br/Cl ligands may also influence the cata-
lytic efficiency by their electron donor–acceptor nature.
b
Form II
Form I
Fig. 5. Agarose gel electrophoresis diagram showing the cleavage DNA of Esche-
richia coli by Ru(III) Schiff base complex in TAE Buffer (4.84 g Tris base, pH = 8,
0.5 M EDTA/1 L). Lane M, DNA alone; Lane C, Control DNA (untreated complex). (a)
Lane 1, [RuBr2(PPh3)L2] 10
4, [RuCl2(PPh3)L3] 10 and 50
[RuBr2(AsPh3)L1] 100 and 200 g/ml and Lane 3 and 4 [RuCl2(PPh3)L3] 100 and
200 g/ml concentrations.
l
g/ml; Lane 2, [RuBr2(AsPh3)L1] 10
l
g/ml and Lane 3 and
lg/ml concentrations. (b) Lane
1
and
2
l
l
mixture was stirred for 6 h (Scheme 3). After work up, the crude
product was purified by column chromatography on silica gel to af-
ford 28–48% yield of 4-phenylanisole (Table 7). The product was
characterized by 1H NMR and comparison with literature data
[49]. The present catalyst systems are able to couple aryl bromides
with aryl Grignard reagents at room temperature in a low catalyst
loading for good yields.
3.7. Catalytic Kumada–Corriu reactions
3.8. DNA cleavage studies by gel electrophoresis
The system chosen for the study is the coupling of phenyl mag-
nesium bromide with 4-bromoanisole to give 4-phenylanisole as
the product. Bromobenzene was first converted into the corre-
sponding Grignard reagent. Then 4-bromoanisole, followed by
the ruthenium(III) Schiff base complex, were added and the
The potential of the present complexes to cleavage DNA was
studied by gel electrophoresis using supercoiled DNA of Esche-
richia coli in TAE buffer (pH 8). When circular plasmid DNA is sub-
jected to gel electrophoresis, relatively fast migration will be

870
R. Manikandan, P. Viswnathamurthi / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 864–870
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observed for the intact supercoil form (Form I). If scission occurs on
one strand (nicking), the supercoil will relax to generate a slower-
moving open circular form (Form II). If both strands are cleaved, a
linear form (Form III) that migrates between Forms I and II will be
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cleaved DNA at 10
same concentration (lanes
l
g/ml and [RuBr2(AsPh3)L1] was inactive at
1
and 2). For the complex
[RuCl2(PPh3)L3], the amount of Form I of DNA diminished gradu-
ally, whereas that of Form II increased when concentration of the
complex increased. This shows that the complex is inactive at
10 lg/ml concentration and displayed partial cleavage at 50 lg/
ml concentration (lanes 3 and 4). At higher concentration, the com-
plexes [RuBr2(AsPh3)L1] and [RuCl2(PPh3)L3] (Fig. 5b lanes 1–4)
completely cleave the DNA.
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In this work we have synthesized series of new ruthenium(III)
2-acetylpyridine thiosemicarbazone/semicarbazone complexes
bearing triphenylphosphine/arsine. The characterization of all the
complexes was accomplished by analytical and spectral (FT-IR,
electronic, EPR and EI-MS) methods. Spectral studies are confirmed
the coordination mode of the ligand to the metal through NNS/
NNO donors and reveal the presence of an octahedral geometry
around the ruthenium center. The catalytic efficiency of the
complexes was determined for transfer hydrogenation and
Kumada–Corriu coupling reactions. The complexes also efficiently
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Acknowledgements
We are thankful to, Department of Chemistry, Pondicherry Uni-
versity, Pondicherry, SAIF, Cochin, HRMS facility NIIST, Thiruva-
nanthapuram for providing instrumental facilities and Biogenics,
Research and training center in Biotechnology, Hubli, Karnataka
for DNA studies.
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