Synthesis, characterization, catalytic and antimicrobial studies of ruthenium(III) complexes

Article abstract of DOI:10.2478/s11532-010-0045-8

Ru(III) complexes of the type [RuXB(L)2] have been prepared by the reaction of 3,4-dihydropyrimidin-2(1H)-ones/thiones (HL¹-HL⁴) with the precursors of the type [RuX₃B₃] where X=Cl or Br; B=PPh₃ or AsPh₃ and L is the deprotonated ligand. The synthesized complexes were characterized by physico-chemical methods, electrochemical and magnetic moment data. The catalytic efficiency of the complexes were examined in the oxidation of alcohols and antimicrobial studies were also carried out.

Full text of DOI:10.2478/s11532-010-0045-8

Cent. Eur. J. Chem. • 8(4) • 2010 • 842–851
DOI: 10.2478/s11532-010-0045-8
Central European Journal of Chemistry
Synthesis, characterization, catalytic
and antimicrobial studies of
ruthenium(III) complexes
Research Article
a
b*
Natarajan Thilagavathi , Chinnasamy Jayabalakrishnan
aDepartment of Chemistry, Surya Engineering College,
Erode-638 107, Tamil Nadu, India
bPost Graduate and Research Department of Chemistry,
Sri Ramakrishna Mission Vidyalaya College of Arts and Science,
Coimbatore-641 020, Tamil Nadu, India
Received 7 December 2009; Accepted 8 March 2010
1
4
Abstract:Ru(III) complexes of the type [RuXB(L)2] have been prepared by the reaction of 3,4-dihydropyrimidin-2(1H)-ones/thiones (HL - HL )
with the precursors of the type [RuX B ] where X=Cl or Br; B=PPh or AsPh and L is the deprotonated ligand. The synthesized
3
3
3
3
complexes were characterized by physico-chemical methods, electrochemical and magnetic moment data. The catalytic efficiency of
the complexes were examined in the oxidation of alcohols and antimicrobial studies were also carried out.
Keywords: Ruthenium(III) • NMO • Antimicrobial activity • EPR • Cyclic voltammetry
©
Versita Sp. z o.o.
Chromium based oxidations are effective, but they have
serious drawbacks in terms of green chemistry and
environmental impact. They generate stoichiometric
1
. Introduction
Catalysis has played an important role in the amounts of heavy-metal waste and Cr(VI) is a proven
development of the chemical industry, including new carcinogen [3]. Despite its usefulness as an effective
technologies and solving environmental problems. oxidant, practical applications of iodosylbenzene as an
Homogeneous catalysis by metal complexes have some oxidant are hampered by its low solubility in non-reactive
unique features including high activity and selectivity media, as well as the low thermal stability and the
under milder operating conditions, which has led to explosive properties upon moderate heating [4]. Ionic
major breakthroughs in the reactions of carbonylation, liquids are excellent cleaner solvents, but suffer from the
hydroformylation,
oxidation,
hydrogenation, drawback of reduced activity due to the residual chloride
oligomerization and metathesis [1]. Oxidation is one of ion [5] and are an ineffective oxidate of aliphatic alcohols
the most fundamental reactions in organic synthesis. [6]. Ruthenium and its chloro complexes, particularly
Owing to the current needs to develop forward-looking in the +3 oxidation state, have evinced a great deal
technology that is environmentally friendly with negligible of interest in recent years because of their use in
formation of inorganic salts and efficient highly selective homogeneous catalysis [7]. Ruthenium catalyst is also
formation of products, many aspects must be considered known to be sufficiently selective to avoid over oxidation
in the search for new catalytic oxidation reactions [2]. of aldehydes to acids and are tolerant towards many
Though many catalytic systems have been reported for functional groups that may be present in an alcohol-
the oxidation of alcohols, most of them have limitations. containing molecule. Catalytic oxidation with molecular
*
E-mail: cjbsrmvcbe@gmail.com
8
42

N. Thilagavathi , C. Jayabalakrishnan
oxygen is particularly attractive from an economical and
environmental point of view [8].
H
1R
2RO
N
Y
Over the past decade, dihydropyrimidin-2(1H)-
ones and their derivatives have attracted considerable
attention in organic and medicinal chemistry as
the dihydropyrimidine (or Scaffold), and displays a
fascinating array of pharmacological and therapeutic
properties. Several alkaloids that contain the
dihydropyrimidine core have been isolated from
marine sources, and also exhibit interesting biological
properties [9]. The dihydropyrimidinone ring system is
contained within a number of pharmacologically active
agents, for example, calcium channel blockers; antiviral,
antitumor and anti-inflammatory drugs and they have
been subject of extensive investigations [10]. The
coordination chemistry of the pyrimidine thiolates is of
great interest due to the versatility in their coordinated
forms, the variety of bonding and their relevance to
biological systems. There are two donor atoms in these
types of ligands, soft donor ‘S’ and hard donor ‘N’ which
enable these ligands to coordinate to both hard and soft
metals [11].
NH
CH3
O
Ligand
R1
4-(OCH )-C H
R2
Y
O
S
1
HL
HL
C2H5
C2H5
CH3
3
6
4
2
4-(OCH )-C H
3 6
4
HL3
HL4
4-(OCH )-C H
O
S
3
6
4
4-(OCH
)-C
H
CH
3
3
6
4
Figure 1. The general structure of the ligands.
solvent and tetramethylsilane as the internal standard
at Indian Institute of Science, Bangalore, India. Cyclic
voltammetric studies were carried out in acetonitrile using
a platinum wire counter electrode and a platinum disc
working electrode. All the potentials were referenced
to a Ag/AgCl electrode. The molecular weights were
determined by the Rast micro method. The melting
points were recorded with a Raaga heating table and are
uncorrected. The starting complexes [RuCl (PPh ) ] [14],
3
3 3
[
[
RuCl (AsPh ) ] [15], [RuBr (AsPh ) ] [16] and the ligands
3 3 3 3 3 3
17] were prepared by the reported methods.
In this paper, as a part of continuation of our work [12],
we report the synthesis, structural characterization and
electrochemical properties of a series of ruthenium(III)-
2
.2. Synthesis of the new ruthenium(III)
3,4-dihydropyrimidin-2(1H)-one/thione complexes. In
relevance to the application of the prepared complexes, dihydropyrimidin-2(1H)-one/thione complexes
we have examined the catalytic efficiency of these A representative procedure for the preparation of the
systems in the oxidation of alcohols in the presence of ruthenium(III) complexes is detailed as follows. To a
N-methylmorpholine-N-oxide (NMO)/molecular oxygen solution of [RuCl (PPh ) ] (0.1 g; 0.1 mmol) in benzene
3
3 3
1
as oxidant and the inhibition activity of the complexes (25 mL), 0.06 g (0.2 mmol) of HL was added and
against the growth of the bacteria, Escherichia Coli refluxed for 5 h. The resulting solution was concentrated
and Bacillus Subtilis. Ligands used in this study have to ca 5 mL and the product was precipitated by the
structure presented on Fig. 1.
addition of petroleum ether (60-80 ºC). The precipitate
was washed with petroleum ether and recrystallised from
the petroleum ether-dichloromethane mixture.
2
. Experimental Procedures
2
.3. Procedure for the catalytic oxidation of
alcohols
2
.1. Reagents, materials and instruments
All of the reagents used were of analytical reagent
grade. The solvents were purified and dried according 2.3.1. NMO as oxidant
to the standard procedures [13]. RuCl •3H O was To a solution of alcohol (0.07-0.13 mL, 1 mmol) and
3
2
purchased from Loba chemie. The analysis of carbon, dichloromethane (20 mL), N-methylmorpholine-N-oxide
hydrogen, nitrogen, and sulphur were performed in (NMO) (0.35 g, 3 mmol) and the ruthenium complex
a Vario EL III CHNS analyzer at Cochin University, (0.009 g, 0.01 mmol) were added and the solution was
Kerala, India. The IR spectra of the complexes were heated under reflux for 3 h. The mixture was then filtered
recorded in KBr pellets with a Perkin–Elmer 597 infrared and the filtrate was dried over anhydrous Na SO . It
2
4
−
1
spectrophotometer in the range of 4000–200 cm . The was then evaporated to dryness and extracted with
electronic spectra were recorded in dichloromethane with diethyl ether. The diethyl ether extract was filtered
a Systronics Double beam UV-Vis Spectrophotometer and evaporated to yield the corresponding carbonyl
1
2
202. The H NMR spectra were monitored on a Bruker compound which was then quantified as its 2,4-
AMX-400 NMR spectrophotometer using CDCl3 as dinitrophenylhydrazone [13,18].
8
43

Synthesis, characterization, catalytic and antimicrobial
studies of ruthenium(III) complexes
H
1R
CH3
O
2
.3.2. Molecular oxygen as oxidant
N
Y
To a solution of alcohol (0.07 - 0.13 mL, 1 mmol) and
dichloromethane (20 mL), a mixture of the ruthenium
complex in dichloromethane (0.009 g, 0.01 mmol)
was added and the combination was stirred under
an oxygen atmosphere at ambient temperature for
OR2
2RO
HN
NH
+
[RuX B ]
+
3
3
Y
N
H
1R
O
CH3
Reflux in Benzene
5
h
6
h. The mixture was then evaporated to dryness and
extracted with diethyl ether. The combined extracts
were filtered and evaporated to give the corresponding
carbonyl compound, which was then quantified as its
H
1R
2RO
N
2, 4-dinitrophenylhydrazone [13,19].
Y
Ru
Y
N
X
N
CH
3
2
.4. Procedure for antibacterial activity
O
O
CH
3
B
OR2
The ligands and their complexes have been tested
for the in vitro growth inhibitory activity against the
bacteria Escherichia Coli and Bacillus Subtilis using
a disc diffusion method. The bacteria were cultured in
nutrient agar medium and used as inoculum for this
N
H
1
R
1
2
R = 4-(OCH )-C H ; R = CH3 or C H ; Y = O or S; X=Cl or Br;
3
6
4
2
5
B=PPh or AsPh
3
3
study. Bacterial cells were swabbed onto nutrient agar Scheme 1. Preparation of ruthenium(III) complexes
-1
medium in Petri plates. The compounds to be tested 1539-1548 cm which is due to ν
which indicates the
(C=N),
were dissolved in DMSO at a final concentration of 0.5% enolisation of the HN-C=O part of the ring to N=C-OH.
-
1
(
0.5 g/100 mL) and 1.0% (1.0 g/100 mL) and soaked on Further, the absence of a signal around 3500 cm due
-
1
filter paper discs (5 mm diameter, 1 mm thick). These to ν(O-H) and presence of a signal at 545-593 cm due
discs were placed on previously seeded plates and to ν(Ru-O) [22] confirm the deprotonation and subsequent
incubated at 35±2°C for 24 h. The diameter (mm) of the coordination through the enolic oxygen to ruthenium.
2
4
inhibition zone around each disc was measured after Similarly, in ligands, HL and HL , the ν
2
vibrations
C=S)
(
-1
4 h. Ampicillin was used as a standard [20].
are present at 1200 and 1250 cm respectively. The
absence of the ν(C=S) and ν(N-H) vibrations in the IR
spectrum of the corresponding complexes and presence
of a new band around 1539-1548 cm corresponding to
ν(C=N), confirm the thio-enolisation. The deprotonation of
-1
3
. Results and Discussion
All of the complexes are coloured solids, stable in the thiol group followed by coordination to ruthenium ion
air,light and soluble in common organic solvents such through thiolate sulphur is confirmed by the presence of
-1
as DMSO, dichloromethane and chloroform. The ν(Ru-S) vibrations at 440-465 cm and absence of a band
-
1
microanalytical data and the molecular weights of around 2600 cm due to ν
[23]. A new band present
S-H)
(
-1
the complexes are shown in Table 1. The results are around 689-696 cm corresponding to (Ru-N) vibration
in good agreement with the calculated values, and in the spectra of all the complexes indicates that the
therefore confirms the composition of the mixed ligand other coordinating mode is through nitrogen [22]. The
complexes. The low values of the molar conductance ester carbonyl group vibrations are seen around 1724-
-1
2
-1
-1
(
6.28-13.85 ohm cm mol ) are in agreement with their 1737 cm in the ligand spectra and they show no change
non-electrolytic nature.
in the spectra of the complexes which reflects the non-
involvement of the ester carbonyl group in coordination.
The ν
/ ν(Ru-As) vibrations display a band around 510-
3
.1. IR spectroscopic analysis
(Ru-P)
-1
-1
520 cm / 472-474 cm in the spectra of the complexes.
The mode of ligand bonding to ruthenium is inferred
by comparing the IR spectra of the ligands and the
complexes. In the spectra of all the ligands, the bands
−
1
The ν(Ru-Cl) / ν
absorption is seen in the 310–320 cm
245-250 cm region [24].
(Ru-Br)
−
1
/
-1
-1
present at 3200cm and 1400 cm are due to ν
δ(N-H) vibrations, respectively [21]. The ring ν
and
N-H)
(
1
vibration 3.2. H NMR spectroscopic analysis
-1
1
(C=O)
1
3
of the ligands, HL and HL are observed at 1700 cm . The H NMR spectra of the ligands confirm their structure.
Thesebandsconfirmtheligandsarepresentinketoform. A triplet found at 1.08 ppm and a quartet found at 3.95
1
2
In the spectra of their corresponding complexes, these ppm of ligands, HL and HL , were assigned to the CH
3
bands are absent. A new band is present in the range and CH protons, respectively, of the ethoxy group. The
2
844

N. Thilagavathi , C. Jayabalakrishnan
3
4
ligands, HL and HL , display a singlet at 3.5 ppm for and molar absorption coefficient. The bands which are
the CH protons of the methoxy group. In the spectra present in the lower wavelength region are assigned to
3
of all the ligands, a singlet was found at 3.7 ppm, which the π → π* transitions of the aromatic ring (255 nm) and
was assigned to the OCH protons of the anisaldehyde n → π* transitions of the pyrimidine ring hetero atoms
3
moiety. The methyl protons of the pyrimidine ring gave (296-300 nm) of the ligand moiety. In the electronic
a singlet at 2.2 ppm [25,26]. A singlet present at 5 ppm spectrum of the ligands, the bands corresponding to
was assigned to the proton attached to the asymmetric the π → π* transitions occur in the same position as
carbon of the pyrimidine ring. The aromatic protons of that of their complexes. This reflects that aromatic
the anisaldehyde moiety gave two doublets at 6.8 and group is not involved in the coordination with ruthenium.
7.2 ppm. The NH proton signals were found at 7.65 and There is a bathochromic shift (3-5 nm) in the position
9
.13 ppm [17].
of the bands corresponding to n → π* transitions. This
suggests that the pyrimidine ring hetero atoms (N, O/S)
are involved in coordination with ruthenium [27]. Apart
3
.3. Electronic spectroscopic analysis
The electronic spectra of all the complexes display from these intra ligand transitions, three other sets of
several bands which were assigned to various bands were present in the spectra of all the complexes.
transitions on the basis of their absorption wavelength The bands which are present in the wavelength range
Table 1. Analytical and FT-IR spectroscopic data of the complexes
Analytical data
%
found
IR (cm-1
)
(calculated)
Mol.Wt
calcd)
Complexes
Colour
M.P
°C)
Yield
(%)
(
(
C
H
N
S
ν Ru-N
690
696
694
696
691
691
692
691
694
693
690
689
ν Ru-O/Ru-S
ν C=N
1541
1541
1548
1541
1544
1548
1539
1539
1541
1541
1540
1541
ν Ru-P/Ru-As
[
[
[
[
RuCl(PPh )
60 .02
(58.98)
5.92
(5.73)
3
Brown
Green
Grey
983 (977)
186
190
198
190
173
140
180
190
165
182
189
170
83
92
80
90
92
87
75
95
70
70
88
92
5.11
5.04
4.92
4.97
4.98
4.72
4.42
4.44
4.71
4.23
4.47
4.49
-
574
510
1
(
L ) ]
2
RuCl(PPh )
1003
(1009)
57.97
(57.10)
5.75
(5.55)
6.61
(6.35)
3
440
518
2
(
L ) ]
2
RuCl(PPh )
60.12
(58.19)
6.12
(5.90)
3
951 (949)
985 (981)
-
589
510
3
(
L ) ]
2
6
.98
RuCl(PPh )
56.92
(56.29)
5.54
(5.71)
3
Brown
Green
Grey
(6.53)
465
520
4
(
L ) ]
2
[
[
[
[
RuCl(AsPh )
1025
(1021)
55.32
(56.44)
5.69
(5.48)
3
-
545
474
1
(
L ) ]
2
RuCl(AsPh )
1050
(1053)
55.67
(54.72)
5.52
(5.32)
6.33
(6.09)
3
446
472
2
(
L ) ]
2
RuCl(AsPh )
56.21
(55.62)
5.79
(5.64)
3
Cream
Brown
Brown
Brown
Brown
Green
998 (993)
-
593
472
3
(
L ) ]
2
RuCl(AsPh )
1030
(1025)
52.14
(53.87)
5.64
(5.46)
6.46
(6.25)
3
442
474
4
(
L ) ]
2
[
[
[
[
RuBr(AsPh )
1062
(1065)
54.98
(54.09)
5.12
(5.26)
3
-
575
473
1
(
L ) ]
2
RuBr(AsPh )
1101
(1098)
53.67
(52.50)
5.34
(5.10)
6.01
(5.84)
3
459
473
2
(
L ) ]
2
RuBr(AsPh )
1041
(1037)
54.83
(53.23)
5. 67
(5.40)
3
-
580
474
3
(
L ) ]
2
RuBr(AsPh )
1072
(1070)
51.24
(51.64)
5.51
(5.24)
6.21
(5.99)
3
459
474
4
(
L ) ]
2
8
45

Synthesis, characterization, catalytic and antimicrobial
studies of ruthenium(III) complexes
Table 2. Electronic spectroscopic dataof the complexes
λ max (nm)
Transition
3
-1
Complex
(ε; dm mol
Energy
Assignments
ν2 / ν1
10Dq
B
C
cm-
1
)
-1
(cm )
5
50 (789)
18181
22271
25380
2T → 4T
2
g
1g
1
449 (2890)
394 (3521)
1.22
28291
511
1888
[
[
RuCl(PPh )(L ) ]
3
2
2T → T
4
2
g
2g
2
2T → A , T
2
2
g
1g
1g
6
24 (438)
16025
20391
25706
2
4
T g → T g
2
1
2
490 (1750)
389 (3342)
RuCl(PPh )(L ) ]
1.27
1.16
29479
26809
545
332
2681
2106
3
2
2
4
T g → T g
2
2
2
2
2
T g → A g, T g
2
1
1
2
4
5
98 (593)
16722
19379
24038
T g → T g
2 1
3
516 (2402)
416 (3495)
[
[
RuCl(PPh )(L ) ]
3 2
2
4
T g → T g
2
2
2
2
2
T g → A g, T g
2
1
1
2
2
4
5
21 (631)
19193
22471
25510
T g → T g
2 1
4
445 (2954)
392 (3763)
RuCl(PPh )(L ) ]
1.17
28025
409
1695
3
2
4
T g → T g
2
2
2
2
2
T g → A g, T g
2
1
1
2
2
4
5
50 (773)
18181
22883
25380
T g → T g
2 1
1
437 (2597)
394 (3075)
[
[
[
[
RuCl(AsPh )(L ) ]
3 2
4
1.26
1.23
1.19
28368
29469
27413
587
481
465
1811
2667
1481
T g → T g
2
2
2
2
2
T g → A g, T g
2
1
1
2
2
4
6
10 (421)
16393
20242
25839
T g → T g
2 1
2
494 (2750)
387 (5961)
RuCl(AsPh )(L ) ]
4
3
2
T g → T g
2 2
2
2
2
T g → A g, T g
2
1
1
2
2
4
5
22 (450)
19157
22883
25000
T g → T g
2 1
3
437 (2956)
400 (3333)
RuCl(AsPh )(L ) ]
3
2
4
T g → T g
2
2
2
2
2
T g → A g, T g
2
1
1
2
2
4
5
76 (620)
17361
20920
25510
T g → T g
2 1
4
478 (2534)
392 (3423)
RuCl(AsPh )(L ) ]
3
2
4
1.21
1.24
1.15
28671
28831
28041
444
539
364
2271
2044
1801
T g → T g
2
2
2
2
2
T g → A g, T g
2
1
1
5
57 (500)
17953
22271
25706
1
449 (2243)
389 (5732)
2
T
g
→
4
T
g
[
RuBr(AsPh )(L ) ]
3 2
2
1
2
4
2
2
T g → T g T g → A g,
2
2
2
1
2
4
5
26 (567)
19011
21929
25510
T g → T g
2
1
2
456 (2544)
392 (3466)
[
RuBr(AsPh )(L ) ]
3
2
2
4
T g → T g
2
2
2
2
2
2
2
T g → A g, T g
2
1
1
1
2
7953
2271
2
2
4
5
57 (422)
T g → T g
2 1
3
449 (2100)
389 (3298)
[
[
RuBr(AsPh )(L ) ]
25706
3
2
4
1.24
1.17
28831
27004
539
420
2044
1225
T g → T g
2
2
2
2
T g → A g, T g
2
1
1
5
00 (765)
28 (2171)
401 (3532)
20000
23364
24937
2
2
4
T g → T g
4
2
1
4
RuBr(AsPh )(L ) ]
3
2
4
T g → T g
2
2
2
2
T g → A g, T g
2
1
1
846

N. Thilagavathi , C. Jayabalakrishnan
-
1
~
2
500-600 nm (16025-20000 cm ) are assigned to the the complexes with pyrimidine-thione ligands (sulphur as
4
T2g → T transitions of the metal ‘d’ orbitals. Similarly, the donor atom). This easy oxidation of the pyrimidine-
1g
bands which are present in the wavelength range of one complexes, may be attributed to the presence of
-
1
~
(
400-500 nm (19379 -23364 cm ) and ~380-400 nm more electronegative oxygen [30], makes them better
-1
2
4
24038-25839 cm ) are assigned to the T2g → T
and T2g → A , T g transitions of the metal ‘d’ orbitals,
catalysts for a catalytic oxidation reaction.
2g
2
2
2
1g
1
respectively. The ligand field parameters B, C and
0 Dq were calculated (shown in Table 2) using the
above d-d transition energies and standard equations
23] for ruthenium(III) ion. The values of the ligand
field parameters are comparable to those reported for
other trivalent ruthenium complexes. A considerable
lower value for the Racah inter electronic repulsion
parameter than that of the free ruthenium ion, indicates
the covalent nature of the metal ligand bond [22]. Higher
Dq values are usually associated with considerable
electron delocalization. The results of the electronic
spectra suggest an octahedral environment around the
ruthenium ion [28].
3
.6. Oxidation of alcohols
1
The oxidation of the primary/secondary alcohols was
carried out using the synthesized ruthenium complexes
as the catalyst, NMO / molecular oxygen as the
oxidant and the alcohols were then converted into the
corresponding aldehyde/ketone. The results are shown
in Table 5. The oxidation reaction in the presence of
NMO may proceed through a mechanism which has
been previously reported for a similar type of system
[
[
31]. The proposed mechanism, in the presence of
molecular oxygen, including the oxidation of alcohol by
a Ru complex to form aldehyde and Ru
the oxidation of Ru
n+
(n-2)+
, followed by
(n-2)+
n+
to Ru with O [32]. From these
2
results, it was found that the catalytic activity of the
3
.4. Magnetic moment and EPR spectroscopic
complexes is influenced by the electronegativities of the
1
ligands. [RuCl(PPh )(L ) ] showed the highest catalytic
analysis
3
2
activity. This may be due to the highly electronegative
The effective magnetic moments of the complexes
were measured at room temperature using a vibrating
sample magnetometer. The values are found to be in
the range of 1.72-1.92 BM which indicates the presence
of one unpaired electron. The EPR spectral data of the
ruthenium complexes are presented in Table 3. The
room temperature (RT) EPR spectra of all the complexes
display two signals indicating an axial distortion. In an
axial distortion, the triply degenerate ‘t ’ level (d d d )
chloro ligand and the electronegative oxygen donor
1
atom in the pyrimidin-one ligand. [RuCl(AsPh )(L ) ]
3
2
displayed decreased activity, which may be ascribed
Table 3. EPR spectroscopic data of the complexes
Complex
gx
gy
gz
<g>*
1
[
RuCl(PPh )(L ) ]
2.50
2.50
2.29
2.43
3
2
2
xz yz xy
is split up into a doubly degenerate ‘e’(d d ) and a non-
2
xz yz
[RuCl(PPh )(L ) ]
2.24
2.60
2.39
2.42
2.24
2.60
2.39
2.42
2.02
2.39
2.04
2.19
2.17
2.53
2.27
2.35
3
2
degenerate ‘a’ (dxy) component. However, presence of
three signals (Fig. 2) in the spectra recorded at liquid
nitrogen temperature (LNT) indicates a rhombic distortion
in the complexes. In a rhombic distortion, the doubly
degenerate ‘e’ level is further split into non-degenerate
components and therefore suggests the electronic
3
[
[
RuCl(PPh )(L ) ]
3 2
4
RuCl(PPh )(L ) ]
3
2
RT
[RuCl(AsPh )
3
1
(
L ) ]
2
LNT
2.42
2.42
2.49
2.20
2.42
2.49
2.13
2.14
2.29
2.25
2.33
2.43
2
2
1
configuration is dxz dyz dxy [29]. The RT and LNT (EPR)
spectra of all the complexes indicate no hyperfine
coupling with the active nuclei through Ru, N, As, or P.
2
[
RuCl(AsPh )(L ) ]
3 2
3
[
RuCl(AsPh )(L ) ]
3
2
[RuCl(AsPh
)(L4)
]
2.20
2.42
2.39
2.49
2.44
2.20
2.42
2.39
2.49
2.21
2.03
2.12
2.04
2.28
2.02
2.14
2.32
2.27
2.42
2.23
3
.5. Cyclic voltammetric analysis
3
2
The redox behaviour of some of the complexes was
studied by cyclic voltammetry. The electrochemical
profiles (Table 4, Fig. 3) of the complexes display a
quasi-reversible (∆Ep=100-340 mV) redox process.
The complexes show a well defined wave in the range,
1
[
RuBr(AsPh )(L ) ]
3
2
2
[RuBr(AsPh )(L ) ]
3
2
RT
LNT
3
[
RuBr(AsPh )(L ) ]
3 2
III
IV
III
II
0.85-1.22 V (Ru - Ru ) and 0.40 - 0.75 V( Ru - Ru ).
The redox potentials are influenced by the nature of the
ligands. Complexes with pyrimidin-one ligands (oxygen
4
[RuBr(AsPh
) L
]
2.44
2.44
2.05
2.32
3
2
as the donor atom) were oxidized at a lower potential than <g*>= [1/3 gx2 +1/3 gy2 +1/3 g ]
2
z
1/2
8
47

Synthesis, characterization, catalytic and antimicrobial
studies of ruthenium(III) complexes
a
Table 4. Cyclic voltammetric data of Ru(III) complexes
Ru(III)-Ru(IV)
Ru(III)-Ru(II)
Complex
Epa (V)
Epc (V)
E (V)
ΔEp (mV)
Epa (V)
Epc (V)
E (V)
ΔEp (mV)
f
f
1
[
RuCl(PPh )(L ) ]
0.98
0.76
0.87
230
0.52
0.62
0.57
100
3
2
1
[
RuCl(AsPh )(L ) ]
1.0
1.1
0.78
0.95
0.78
0.76
0.89
1.03
0.85
0.88
220
150
120
240
0.5
0.26
0.35
0.5
0.64
0.6
0.57
0.43
0.75
0.55
140
340
100
100
3
2
1
[
RuBr(AsPh )(L ) ]
3 2
3
[
RuCl(PPh )(L ) ]
0.92
1.0
0.4
3
2
3
[
RuCl(AsPh )(L ) ]
0.6
3
2
2
[
RuCl(PPh )(L ) ]
1.28
1.15
1.22
130
0.3
0.5
0.40
200
3
2
a
supporting electrolyte [NBu ]ClO (0.1 M) ; all potentials are referenced to Ag/AgCl ; E = 0.5(E +E ); ∆E(p) = (E -E ) ; where E and Epc are
4
4
f
pa
pc
pa
pc
pa
anodic and cathodic potentials respectively ; scan rate = 100 mV s 1
-
Table 5. Oxidation of alcohols by ruthenium(III) complexes
Molecular oxygen
oxidant
NMO oxidant
Complex
Substrate
Product
aYield %
bTON
aYield %
bTON
Benzyl alcohol
Cyclohexanol
Cinnamyl alcohol
n-Butanol
Isobutyl alcohol
n-Propanol
Benzaldehyde
94
88
90
75
76
70
96
90
92
77
78
72
47
50
44
41
44
35
48
52
42
42
45
36
Cyclohexanone
Cinnamaldehyde
Butyraldehyde
Ethyl methyl ketone
Propionaldehyde
1
[
[
RuCl(PPh )(L ) ]
3 2
Benzyl alcohol
Cyclohexanol
Cinnamyl alcohol
n-Butanol
Isobutyl alcohol
n-Propanol
Benzaldehyde
86
82
83
70
72
67
88
84
85
72
74
69
47
48
46
41
37
40
48
50
47
42
38
41
Cyclohexanone
Cinnamaldehyde
Butyraldehyde
Ethyl methyl ketone
Propionaldehyde
2
RuCl(PPh )(L ) ]
3
2
Benzyl alcohol
Cyclohexanol
Cinnamyl alcohol
n-Butanol
Isobutyl alcohol
n-Propanol
Benzaldehyde
92
87
89
74
74
70
90
89
91
76
76
72
44
47
40
42
35
37
45
49
42
43
37
38
Cyclohexanone
Cinnamaldehyde
Butyraldehyde
Ethyl methyl ketone
Propionaldehyde
1
[
RuCl(AsPh )(L ) ]
3 2
Benzyl alcohol
Cyclohexanol
Cinnamyl alcohol
n-Butanol
Isobutyl alcohol
n-Propanol
Benzaldehyde
88
85
86
72
74
69
90
87
88
74
76
71
38
41
35
36
33
39
39
42
37
35
34
41
Cyclohexanone
Cinnamaldehyde
Butyraldehyde
Ethyl methyl ketone
Propionaldehyde
1
[
RuBr(AsPh )(L ) ]
3 2
a
b
Yield based on substrate ; Moles of product per mole of catalyst; TON – turn over number
to the presence of a triphenylarsine ligand, which is and that is due to the presence of less electronegative
more electron donating than a triphenylphosphine sulphur donor atom in the pyrimidine-thione ligand. From
ligand. A further decrease in activity was observed for the above results and discussion it may be concluded
1
the complex [RuBr(AsPh )(L ) ], which can be attributed that the electron withdrawing ligands increase the
3
2
to the presence of a less electronegative bromo ligand. catalytic activity of their corresponding complexes and
Among the complexes that were tested for the catalytic this is in line with the literature [33]. This can be also
2
activity, [RuCl(PPh )(L ) ], showed the lowest activity interrupted by saying that the electron withdrawing or
3
2
848

N. Thilagavathi , C. Jayabalakrishnan
a
Table 6. Antibacterial activity of ruthenium(III) complexes
Zone of inhibition (mm)
Bacillus
Subtilis
Escherichia
Coli
Complex /Ligand
0.5%
1.0%
0.5%
1.0%
HL1
11
14
15
19
10
15
15
20
1
[
RuCl(PPh )(L ) ]
3
2
1
[
RuCl(AsPh )(L ) ]
15
18
15
20
3
2
1
Figure 2. The RT and LNT epr spectrum of [RuCl(AsPh )(L ) ]
1
3
2
[RuBr(AsPh )(L ) ]
3 2
14
14
20
20
18
23
16
16
20
21
19
23
HL2
RuCl(PPh )(L ) ]
2
[
3
2
2
[
RuCl(AsPh )(L ) ]
21
20
12
15
25
24
16
20
21
20
12
16
24
24
14
20
3
2
2
[
RuBr(AsPh )(L ) ]
3 2
HL3
3
[
RuCl(PPh )(L ) ]
3 2
3
[
RuCl(AsPh )(L ) ]
16
20
15
21
3
2
3
[
RuBr(AsPh )(L )
15
15
19
19
19
23
16
15
19
22
20
24
3
2
HL4
4
[
RuCl(PPh )(L ) ]
3
2
4
[
RuCl(AsPh )(L ) ]
22
20
24
24
19
22
25
26
3
2
4
[
RuBr(AsPh )(L ) )
3
2
Ampicillin
24
28
26
30
3
Figure 3. The cyclic voltammogram of [RuCl(AsPh )(L ) ]
a
3
2
0.5% and 1.0% indicate 0.5 g and 1.0 g of the compound in 100 mL of
the solvent
electronegative ligands makes the metal centre more
electron deficient thereby facilitating the formation of 3.7. Antibacterial activity
highvalent metal-oxo complex.
The antibacterial activities of ruthenium(III) and the
From an economical and environmental point of view, standard drug, ampicillin, were screened by the disc
we have tested the catalytic efficiency of synthesized diffusion method in DMSO at concentrations of 0.5
ruthenium(III) complexes with molecular oxygen as and 1.0% and were checked against gram positive
oxidant, but the yields and the turnover numbers were bacteria B Subtilis and gram negative bacteria E Coli
moderate when compared with NMO. This is indicated (results shown in Table 6). The results of this study are,
by the low product yield when molecular oxygen is (i) ruthenium complexes are more active in killing the
employed as the oxidant which is in accordance with a bacteria than their ligands, since chelation makes the
previous observation [34].
ligand a powerful bactericidal agent. (The mechanism
the complexes reacts with the bacteria is likely to be
that the complexes disturb the respiration process of
8
49

Synthesis, characterization, catalytic and antimicrobial
studies of ruthenium(III) complexes
the cell and thus block the synthesis of proteins which spectroscopic analysis indicates the N, O/S-bidentate
restricts further growth of the organism.) (ii) the degree coordination of the ligands by replacing the two
of inhibition increases with increasing concentration Cl/Br and the two PPh /AsPh ligands from the metal
3
3
of the complexes from 0.5 to 1.0%. (Beyond that starting complexes. An octahedral structure has been
concentration, there is no change in inhibition.) (iii) the proposed for all the complexes based on the results
sulphur containing ligands exhibit higher inhibition than from electronic spectra, EPR spectra and magnetic
the corresponding oxygen analogues [35]. The variation moment studies. A remarkable catalytic efficiency of the
in the effectiveness of the compounds against different prepared complexes were observed with NMO as the
organisms depends either on the impermeability of the oxidant. However, the efficiency was decreased when
cells of the microbes or the difference in ribosomes of molecular oxygen was used as the oxidant. In the case
microbial cells [36].
of antibacterial analysis, the results revealed that all the
ruthenium(III) complexes have shown higher inhibition
activity than their corresponding ligands.
4
. Conclusions
In conclusion, in this study we have introduced a
new and mild reagent for the oxidation of different types
This paper describes the synthesis, characterization and of alcohols in refluxing dichloromethane. The stability,
application studies of Ru(III) mixed ligand complexes easy preparation, mild reaction conditions, high yields
containing
triphenylphosphine/triphenylarsine
and of the products and non-aqueous reaction conditions
3
,4-dihydropyrimidin-2(1H)-one/thione. The elemental make this pathway a useful method for the oxidation of
analysis and molecular weight determination revealed alcohols. The scope of our catalyst system is illustrated
the proposed stoichiometry of the complexes. The IR by the highly selective oxidation of nonactivated aliphatic
alcohols as well as activated benzyl alcohol and the
secondary alcohols in excellent yields.
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