Binuclear ruthenium(III) bis(thiosemicarbazone) complexes: Synthesis, spectral, electrochemical studies and catalytic oxidation of alcohol

Article abstract of DOI:10.1016/j.saa.2014.11.039

(Chemical Equation Presented).A new series of binuclear ruthenium(III) thiosemicarbazone complexes of general formula [(EPh₃)₂ (X)₂Ru-L-Ru(X)₂(EPh₃)₂] (where E = P or As; X = Cl or Br; L = NS chelating bis(thiosemicarbazone ligands) has been synthesized and characterized by analytical and spectral (FT-IR, UV-Vis and EPR). IR spectra show that the thiosemicarbazones behave as monoanionic bidentate ligands coordinating through the azomethine nitrogen and thiolate sulphur. The electronic spectra of the complexes indicate that the presence of d-d and intense LMCT transitions in the visible region. The complexes are paramagnetic (low spin d⁵) in nature and all the complexes show rhombic distortion around the ruthenium ion with three different 'g' values (g_x ≠ g_y ≠ g_z) at 77 K. All the complexes are redox active and exhibit an irreversible metal centered redox processes (Ru^III-Ru^III/Ru^IV-Ru^IV; Ru^III-Ru^III/Ru^II-Ru^II) within the potential range of 0.38- 0.86 V and -0.39 to -0.66 V respectively, versus Ag/AgCl. Further, the catalytic efficiency of one of the complexes [Ru₂Cl₂(AsPh₃)₄(L1)] (4) has been investigated in the case of oxidation of primary and secondary alcohols into their corresponding aldehydes and ketones in the presence of N-methylmorpholine- N-oxide(NMO) as co-oxidant. The formation of high valent Ru^V@O species is proposed as catalytic intermediate for the catalytic cycle.

Full text of DOI:10.1016/j.saa.2014.11.039

Accepted Manuscript
Binuclear ruthenium(III) bis(thiosemicarbazone) complexes: synthesis, spec-
tral, electrochemical studies and catalytic oxidation of alcohol
M. Mohamed Subarkhan, R. Ramesh
PII:
S1386-1425(14)01698-9
http://dx.doi.org/10.1016/j.saa.2014.11.039
SAA 12975
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomo-
lecular Spectroscopy
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Revised Date:
Accepted Date:
10 September 2014
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20 November 2014
Please cite this article as: M. Mohamed Subarkhan, R. Ramesh, Binuclear ruthenium(III) bis(thiosemicarbazone)
complexes: synthesis, spectral, electrochemical studies and catalytic oxidation of alcohol, Spectrochimica Acta Part
A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa.2014.11.039
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Binuclear ruthenium(III) bis(thiosemicarbazone) complexes: synthesis,
spectral, electrochemical studies and catalytic oxidation of alcohol
M. Mohamed Subarkhan and R. Ramesh*
School of Chemistry, Bharathidasan University, Tiruchirappalli 620 024, Tamil Nadu, India.
Abstract
A new series of binuclear ruthenium(III) thiosemicarbazone complexes of general formula
[(EPh3)2(X)2Ru-L-Ru(X)2(EPh3)2] (where E = P or As; X = Cl or Br; L = NS chelating
bis(thiosemicarbazone ligands) has been synthesized and characterized by analytical and spectral
(FT-IR, UV-Vis and EPR). IR spectra show that the thiosemicarbazones behave as monoanionic
bidentate ligands coordinating through the azomethine nitrogen and thiolate sulphur. The
electronic spectra of the complexes indicate that the presence of d–d and intense LMCT transitions
in the visible region. The complexes are paramagnetic (low spin d5) in nature and all the
complexes show rhombic distortion around the ruthenium ion with three different ‘g’ values
(gx≠gy≠gz) at 77K. All the complexes are redox active and exhibit an irreversible metal centered
redox processes (RuIII-RuIII/ RuIV-RuIV; RuIII-RuIII/ RuII-RuII) within the potential range of 0.38 to
0.86 V and -0.39to -0.66 V respectively, versus Ag/AgCl. Further, the catalytic efficiency of one
of the complexes [Ru2Cl2(AsPh3)4(L1)] (4) has been investigated in the case of oxidation of
primary and secondary alcohols into their corresponding aldehydes and ketones in the presence of
N- methylmorpholine-N-oxide(NMO) as co-oxidant. The formation of high valent RuV=O species
is proposed as catalytic intermediate for the catalytic cycle.
Keywords: Binucleating thiosemicarbazone ligands; Ruthenium(III) complexes; Synthesis;
spectra; Redox property and Oxidation of alcohol.
*Corresponding author: ramesh_bdu@yahoo.com, Fax: +91 431 2407045/20
1. Introduction

The synthesis and structural investigation of thiosemicarbazones and their transition metal
complexes are considerable centre of attention because of their potentially beneficial variation in
their bonding modes [1-3]. Recently coordination chemistry of mixed hard-soft N and S donor
ligands received much attention due to a most important factor in this objective probably for
designing of ligands with an appropriate structural backbone. They are versatile ligands and
exhibit a wide range of coordination modes in their metal complexes (Scheme 1). They usually
bind to a metal ion, either in the neutral thione form (1a) or in the anionic thiolate form (1b), as
bidentate N, S donor ligands forming five membered chelate ring. The ligand can also bind to the
metal ion via the hydrazinic nitrogen and the thiolate sulphur as monoanionic bidentate N, S
donors forming a four membered chelate ring (1c). However, the binding capacity of
thiosemicarbazones is further increased by condensation of the thiosemicarbazide with an
aldehyde or ketone containing an additional donor atom in a suitable position for chelation [4-6].
In recent years, ruthenium(III) complexes have been proved to be extremely useful catalysts in
organic synthesis such as epoxidation [7, 8], oxidation [9, 10], reduction [11], hydrolysis [12, 13],
transfer hydrogenation [14] and other transformation of organic compounds [15].
Transition metal based catalytic conversion of primary or secondary alcohols into their
corresponding aldehydes or ketones are essential reaction in organic synthesis [16-18]. The
development of effective, green catalytic system that uses clean and inexpensive oxidants such as
molecular oxygen or hydrogen peroxide for converting alcohols on an industrial scale remains an
important challenge [19]. Ruthenium complexes containing triphenylphosphine or triphenylarsine
ligands have been extensively investigated and well established [20] as catalyst for alcohol
oxidation in combination with various oxidants such as dioxygen [21, 22], iodosobenzene [23],
t-BuOOH [24], H2O2 [25], NaIO4 [26] and NMO [27, 28]. Ruthenium based oxidation catalysis
is a powerful and extremely versatile synthetic tool to afford selectively oxygenated products both
in homogeneous and in heterogeneous conversions [29].
Though the oxidation of alcohol has been extensively studied using various ruthenium
complexes, there is no report in the literature where binuclear ruthenium(III)
bis(thiosemicarbazone) complexes was used as a catalyst for this reaction. In continuation of our
research on the synthesis, characterization and catalytic applications of ruthenium and palladium
thiosemicarbazone complexes [30], we herein describe the synthesis and characterization of

binuclear ruthenium(III) complexes of the type [(EPh3)2(X)2Ru-L-Ru(X)2(EPh3)2]. Further, the
catalytic activity of the synthesized complexes was investigated in the case of oxidation of
alcohol in the presence of NMO.
2. Experimental
2.1. Reagents and material
Commercially available RuCl3.3H2O was used as supplied from Loba Chemie Pvt. Ltd.
Triphenylphosphine,
triphenylarsine,
terepthaldehyde,
thiosemicarbazide
and
N-
methylmorpholine–N-Oxide (NMO) derivatives were purchased from Sigma–Aldrich and were
used as received. All the reagents used were chemically pure and analytical grade. The solvents
were freshly distilled prior to use following the standard procedures and degassed before use [31].
The supporting electrolyte, tetra butyl ammonium perchlorate (n-Bu4NClO4), was dried in
vacuum prior to use. The starting precursor ruthenium(III) complexes [RuCl3(PPh3)3],
[RuCl3(AsPh3)3] and [RuBr3(AsPh3)3] [32-34] and terepthaldehyde thiosemicarbazone ligands
[35] were prepared according to the literature procedures.
2.2. Physical measurements
Melting points are uncorrected and were determined in capillary tubes on a Boetius micro
heating apparatus. The analysis of carbon, hydrogen, nitrogen and sulphur was performed at
Sophisticated Test and Instrumentation Centre (STIC), Cochin University of Science And
Technology, Kochi. Infrared spectra of complexes were recorded in KBr pellets with a Perkin–
Elmer 597 spectrophotometer in the range 4000–400 cm-1. Electronic spectra of the complexes
were recorded in DMSO solution with a Cary 300 Bio UV–Vis Varian spectrophotometer in the
range 800–200 nm using cuvettes of 1 cm path length. Magnetic susceptibility measurements of
the complexes in the solid state were determined by using EG and G model 155 vibrating sample
magnetometer. The X-band EPR spectra of the powdered samples were recorded on JEOL JES-
FA200 EPR spectrometer. Electrochemical studies were performed using a Princeton EG and G-
PARC model potentiostat in degassed 0.001M acetonitrile solutions of TBAP as supporting
electrolyte. A three electrode cell was employed with carbon working electrode, a platinum wire
auxiliary electrode and an Ag/AgCl reference electrode. Capillary gas chromatography was

performed on a Bruker GC-436 scion gas chromatography with a BR-1ms FS column (15m
0.25mm * 0.25um).
*
2.3. Synthesis of binuclear ruthenium(III) bis(thiosemicarbazone) complexes
A degassed benzene solution (20 mL) [RuX3(EPh3)3] was taken in a clean 100 ml round
bottom flask. The bis(thiosemicarbazone) ligands (1 mmol) were added to the above solution. The
mixture was heated at reflux for 9 h. The initial dark brown color of the solution gradually
changed to dark green. The solvent was then evaporated under high vacuum at low temperature,
followed by petroleum ether (60–80oC) work up gave a green colored solid. The solid mass thus
obtained was purified using a silica column (60–120 mesh) chromatography. Evaporation of
solvent under reduced pressure afforded 65-70% of the new ruthenium(III)
bis(thiosemicarbazone) complexes.
2.4. Catalytic oxidation
Catalytic oxidation of primary alcohols to the corresponding aldehydes and secondary
alcohols to ketones by binuclear ruthenium(III) complexes was studied in the presence of NMO
as co-oxidant. A typical reaction using the complex [Ru2Cl2(AsPh3)4(L1)] (4) as a catalyst and
primary or secondary alcohol as substrates at a 1:100 molar ratio is described as follows. A
solution of ruthenium complex (4) (0.01 mmol) in 20 cm3 CH2Cl2 was added to the solution of
substrate (1 mmol) and NMO (3 mmol). The solution mixture was refluxed for 3 to 8h. The
filtrate obtained was evaporated under reduced pressure and the residual mass was dissolved in a
mixture of ethyl acetate/hexane (1:4) and then passed through a short column of silica gel using
hexane/ethyl acetate (4:1) as eluent. Removal of solvent and usual workup gave the
corresponding aldehydes or ketones, which were identified by GC and 1H-NMR.
3. Result and Discussion
The thiosemicarbazone ligand derivatives were conveniently prepared in an excellent yield
by the condensation of substituted terepthaldehyde with thiosemicarbazone in 2:1M ratio
respectively. These ligands are react with ruthenium(III) precursors [RuX3(EPh3)3] (where E = P,
X = Cl; E = As, X = Cl or Br) in 1:2 molar ratio respectively in benzene in the presence of
triethylamine as base. The reaction mixture was heated to reflux for 9 h afforded new binuclear

Ru(III) complexes of the general formula [(EPh3)2(X)2Ru-L-Ru(X)2(EPh3)2] (Scheme 2). All the
complexes have been obtained in good yields . The ligands behave as mono anionic bidentate,
replacing one triphenylphosphine/triphenylarsine and one chlorine/bromine from the
ruthenium(III) precursors and the oxidation state of ruthenium remain unchanged during the
formation of the complex. All the complexes are dark green in colour, air stable and are non-
hygroscopic in nature. The synthesized ruthenium(III) complexes are soluble in organic solvents
such as CH2Cl2, DMF, DMSO and CH3CN . Attempts made to grow single crystal were
unsuccessful. The analytical data (C, H, N and S) are listed in (Table 1) are in good agreement
with the calculated values confirming the general molecular formula proposed for all the
complexes.
4. Characterization
4.1. IR Spectra
The coordination mode of the thiosemicarbazone ligand to the ruthenium(III) centre in
complex was investigated using by FT-IR spectroscopy (Table 2). The FT-IR spectra of the free
ligands display a strong band 1602-1620 cm-1 is attributed to the νC=N stretch of the ligand. The
coordination of the ligand to the Ru(III) ion through azomethine nitrogen is expected to reduce
the electron density in the azomethine nitrogen the νC=N absorption and has been observed at a
lower frequency in the complexes (1584-1606 cm-1) [36], which confirms the coordination of
azomethine nitrogen. A sharp band appeared for the ligand at 826–847 cm-1 corresponding to
ν
C=S vibration is disappeared completely in the complexes and a new band is appeared at 1299–
1324 cm-1 corresponding to a possible νC-S vibration, indicating coordination of a thiolate sulphur
after enolisation [37]. The free ligands displayed absorptions due to νC=S and νN-H of N-NH-C=S
group in the region 842-854 cm-1 and 3394-3388 cm-1 respectively and are absent in all the
complexes. In addition, characteristic bands for PPh3 and AsPh3 were also observed in the regions
1440-1448 cm-1 and 1096-1106 cm-1 in all the complexes. The IR spectra of the all complexes
therefore confirm the coordination mode of the ligands to ruthenium(III) ion via the azomethine
nitrogen and the thiolate sulphur along with the presence of coordinated triphenylphosphine /
arsine ligands [38].

4.2. Electronic Spectra
Electronic spectra of all the binuclear Ru(III) complexes showed intense absorptions in the
ultraviolet and visible region. The electronic spectra of all the complexes have been recorded in
DMSO and display four intense absorptions in the region 800–200 nm. The electronic spectral
data of 1–6 are listed in (Table 3) and selected spectrum is shown in Fig. 1. The absorption in the
visible region at 648-660 nm is due to d-d transition and the bands observed in the region 413–
425 nm have been assigned to LMCT transitions. The bands in the regions 352–368 nm are due
to n–π* transition of non-bonding electrons present on the nitrogen of the azomethine group in the
ruthenium(III) complexes. The band observed around 251–260 nm is assigned to π – π*
transitions of the ligand. The pattern of the electronic spectra of all the complexes indicate the
presence of an octahedral environment around ruthenium(III) similar to that of other
ruthenium(III) octahedral complexes [39-41].
4.3. Magnetic moment and EPR Spectra
The room temperature magnetic susceptibility measurements for two of the binuclear
ruthenium(III) bis(thiosemicarbazone) complexes, viz. [Ru2Cl2(AsPh3)4L1] (1) and
[Ru2Cl2(PPh3)4L1] (4) were measured. The room temperature µeff values per ruthenium ion for the
complexes are 1.79 and 1.84 BM respectively. It has been observed that the µeff values indicate a
single unpaired electron present in each ruthenium ion and is consistent with non-interacting d5
metal centers or the absence of any strong magnetic interactions between the two-ruthenium
centres of the molecule [42].
EPR spectra of all the complexes were recorded at X-band frequencies at room
temperature and LNT. The low spin d5 configuration is a good probe of molecular structure and
bonding since the observed ‘g’ values are very sensitive to small changes in structure and to the
metal–ligand covalency. The EPR spectra of all the complexes in the solid state exhibit well
defined single isotropic lines with ‘g’ values in the range 2.40–2.45 at room temperature. Such
isotropic lines are usually the results of either intermolecular spin exchange, which can broaden
the lines or occupancy of the unpaired electron in a degenerate orbital. However, the EPR spectra
of the complexes recorded in toluene solution at 77 K show rhombic spectra with three distinct g
values (gx≠gy≠gz) are (gx = 2.39-2.59, gy = 2.02-2.23, gz= 1.71-1.93) respectively. The EPR data

are summarized in (Table 4) and a representative spectrum is shown in Fig. 2. The rhombicity of
the spectra reflect the asymmetry of electronic environments around ruthenium in the complexes
[43, 44]. The EPR spectra of the present binuclear ruthenium(III) thiosemicarbazone complexes
are similar nature to these of the mononuclear complexes and this indicate that two paramagnetic
centers are equivalent and there is no super exchange interaction between the two metal centers
[45]. However, these new complexes are one unpaired electron each ruthenium(III) atom leading
S-value of 1. The pairing of electron is prevented by the greater distance between two
ruthenium(III) atoms provide by the bidentate thiosemicarbazone ligands [46]. That is a spin-
forbidden transition, characteristic of dinuclear complexes with one unpaired electron on each
ruthenium(III) atom (S = ½). Overall the position of the lines and the nature of the EPR spectra of
the complexes are characteristics of low-spin ruthenium(III) octahedral complexes. Hence, the
results from the EPR spectral analysis indicate that these binuclear ruthenium(III) complexes are
significantly distorted from an octahedral geometry.
4.5. Electrochemical Study
The electrochemical properties of the binuclear ruthenium(III) complexes were studied in
an oxygen free acetonitrile solution by cyclic voltammetry using a glassy carbon electrode and the
potentials are expressed with reference to Ag/AgCl. All the binuclear complexes (1×10-3M) are
electro active and exhibit two successive irreversible oxidations and two reductions waves. The
potentials are summarized in (Table 5) and a representative voltammogram is shown in Fig. 3.
The first reduction process takes place in the potential range -0.39 to -0.51 V and the second
reduction response observed at -0.55 to -0.66 V. Similarly, the irreversibility of first oxidation
process takes place in the potential range +0.38 to +0.51 V and the second oxidation response
observed at +0.76 to +0.86 V. The first oxidation or reduction was attributed to the oxidation or
reduction of one of the ruthenium(III) centres to the corresponding mixed valence complex and
the second to the ruthenium(IV) or ruthenium(II) [14].
RuIII-RuIII
RuIV-RuIV
RuIII-RuII
RuIV-RuIII
RuII-RuII
Irreversible oxidation
Irreversible Reduction

The observed electro chemical behavior supports for the binuclear nature of the
complexes. It has been observed that there is not much variation in the redox potentials due to the
replacement of PPh3 by AsPh3 and nature of bridging ligand present in the complexes [47, 48].
5. Catalytic oxidation of alcohols
Ruthenium mediated oxidations are finding increasing application due to the unique
properties of this extremely versatile transition metal, whose oxidation states can vary from -2
to +8 and this prompted us to carry out this type of reaction. The present work describes the
catalytic oxidation of primary and secondary alcohols by the synthesized ruthenium(III) complex
[Ru2Cl2(AsPh3)4(L1)] (4) in CH2Cl2 in the presence of NMO and the byproduct water was
removed by using about 0.25 g of molecular sieves (Scheme 3). In no case was there any
detectable oxidation of alcohols in the presence of NMO alone or the Ru(III) complexes.
In order to optimize the reaction conditions, various substrate: catalyst ratios in presence
of various co-oxidant were carried out and the results are summarized in (Table 6). For these
initial experiments pentan-2-ol was selected as a test-substrate for oxidation with catalytic
quantity of ruthenium(III) complex (4) in the presence of various co-oxidants. When increasing
the C:S ratio 1:100 and up to 1:500 in dichloromethane, the reaction still proceeds smoothly
accompanied by a moderate drop in conversions. Thus, it was concluded that catalyst: substrate
ratio is 1:100 and co-oxidant NMO is the best compromise between optimal reaction rate in
dichloromethane.
Complex(4) oxidizes primary alcohols to corresponding aldehydes and secondary alcohols
to ketones with moderate to high conversion and the results are listed in (Table 7) (entries 1–10).
The aldehydes or ketones formed after 3 or 8 h of refluxing were determined by GC (Figure
S1–S7, Supplementary data). The results of the present investigation suggest that the complexes
efficiently react with NMO to yield high valent RuV=O species [49], capable of oxygen atom
transfer to alcohols. This was supported by spectral changes that occur on the addition of NMO to
a CH2Cl2 solution of the Ru(III) complexes. The appearance of a peak at 390 nm is attributed to
the formation of RuV=O, which is in conformity with other Ru(V) complexes [49, 50]
(Scheme 4).

In the present study of oxidation, the catalytic oxidation of benzylalcohol to benzaldehyde
results in 74% conversion in 3 h and the maximum conversion 89% was obtained after 8 h. The
complex catalyzes the oxidation of 1-phenyl ethanol into corresponding ketones in 94%
conversion. In the case of diphenylmethanol the oxidation product benzophenone is 96%.
Interestingly, the complex efficiently catalyzes the oxidation of five, six, seven and eight-
membered cyclic alcohols to the corresponding ketones with conversions >86%. Further, the
complex effectively catalyze the aliphatic alcohols like butan-2-ol, pentan-2-ol and pentan-3-ol to
the corresponding ketones with moderate conversions in 3 h and the conversions were improved
to 82%, 99% and 89% respectively after 8 h. It has been observed that the present catalyst (4) has
better catalytic efficiency in the oxidation of alcohols than the previous report on similar
ruthenium complexes [9].
6. Conclusion
Binuclear ruthenium(III) complexes containing bidentate thiosemicarbazone, halides and
triphenylphosphine or triphenylarsine have been synthesized. Analytical and spectral results
confirm the coordination of azomethine nitrogen and thiolate sulphur of the ligand to ruthenium.
The rhombic EPR spectral pattern indicates ruthenium ions are in a distorted octahedral
environment. Further, these complexes were tested as catalyst for the oxidation of variety of
alcohols in the presence of N-methylmorpholine-N-oxide (NMO) and the maximum conversion
was obtained upto 99%.
Acknowledgement
We thank UGC, New Delhi, for financial support in the form of research grant
(Ref. F.39-787/2010 (SR). We also thank SERB- DST, New Delhi for GC instrument facility
through research project.

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M
M
R1
R2
S
R1
R2
R1
R2
M
S
S
N
N
N
N
N
N
NH2
NH2
NH2
H
H
1c
1a
1b
Scheme 1. Various coordination modes of thiosemicarbazone ligands
EPh3
RHN
HN
S
RHN
S
X
Ru
N
X
EPh3
N
N
C6H6
H
H
[RuX3(EPh3)3]
E= P or As ; X= Cl or Br
H
+
H
EPh3
Et3N
9 h reflux
N
S
N
S
X
X
NH
NHR
N
Ru
NHR
EPh3
(R = -H, -CH3, -C6H5)
(R = -H (L1) ; -CH3(L2) ; -C6H5(L3)
E= P or As ; X= Cl or Br)
Scheme 2. Synthesis of new binuclear Ru(III) bis(thiosemicarbazone) complexes

Complex 4
OH
O
NMO/CH2Cl2
+
H2O
reflux, 3h
R1
R1
R
R
R, R' = alkyl (or) aryl
Scheme 3. Catalytic oxidation of alcohols
O
RuIII
NMO
H2O +
R1
R
OH
RuV=0
NM
R1
R
Scheme 4. Proposed catalytic cycle for the oxidation of alcohols by complex (4)

Fig. 1. Absorption spectrum of [Ru2Cl2(PPh3)4(L2)] (1) in DMSO

Fig. 2. EPR spectrum of the complex [Ru2Cl2(PPh2)2(L1)] (3) at 77 K

Fig. 3. Cyclic voltammogram of complex [Ru2Cl2(AsPh ) (L1)] (2)
3 2

Table 1
Analytical data of binuclear Ru(III) (bis)thiosemicarbazone complexes.
* decomposition temperature
S.No.
Complexes
M.P*
(oC)
Calculated (found) %
C
H
N
S
[Ru2Cl2(PPh ) (L1)]
1
2
3
4
5
6
7
8
9
289-291 58.84 (58.81)
294-296 59.28 (59.36)
295-297 61.83 (61.79)
283-285 58.92 (58.87)
281-284 56.47 (56.40)
298-300 59.36 (59.41)
273-275 53.16 (53.09)
280-283 53.68 (53.58)
298-300 56.32 (56.26)
4.13 (4.22) 4.91 (4.87)
4.30 (4.24) 4.81 (4.76)
4.23 (4.18) 4.52 (4.61)
4.22 (4.29) 5.03 (4.96)
3.93 (3.85) 4.20 (4.14)
4.39 (4.46) 4.94 (4.87)
3.74 (3.67) 4.38 (4.54)
3.83 (3.76) 4.35 (4.48)
3.81 (3.93) 4.09 (4.03)
3.68 (3.64)
3 4
[Ru2Cl2(PPh ) (L2)]
3.61 (3.77)
3.43 (3.38)
3.84 (3.78)
3.21 (3.32)
3.77 (3.69)
3.34 (3.47)
3.28 (3.21)
3.06 (3.11)
3 4
[Ru2Cl2(PPh ) (L3)]
3 4
[Ru2Cl2(AsPh ) (L1)]
3 4
[Ru2Cl2(AsPh ) (L2)]
3 4
[Ru2Cl2(AsPh ) (L3)]
3 4
[Ru2Br2(AsPh ) (L1)]
3 4
[Ru2Br2(AsPh ) (L2)]
3 4
[Ru2Br2(AsPh ) (L3)]
3 4

Table 2
IR data of binuclear Ru(III) bis(thiosemicarbazone) complexes.
IR frequencies (ν/cm-1)
Complexes
NHR
3385
C=N
1586
PPh3
1438
C-S
1
2
3
4
5
6
7
8
9
1318
3378
3381
3383
3386
1584
1595
1594
1587
1596
1606
1572
1586
1442
1440
1442
1441
1445
1448
1438
1443
1312
1317
1310
1309
1299
1303
1314
1324
3388
3394
3372
3374

Table 3
Absorption data of binuclear Ru(III) bis(thiosemicarbazone) complexes.
λmax (nm) ε (dm3/mol-1cm-1)
Complexes
1
2
3
4
647(2420)a
651(1861)a
648(2642)a
652(3165)a
425(3290)b
416(2410)b
417(3670)b
415(4330)b
354(6168)c
357(4200)c
361(6167)c
352(7545)c
258(13240)d
251(9260)d
254(14192)d
260(16085)d
5
6
653(3285)a
660(3055)a
414(4587)b
413(4440)b
359(7812)c
368(6270)c
259(11711)d
258(15250)d
ad-d Transition
b LMCT
cn-π*
d π-π*

Table4
EPR data of binuclear Ru(III) bis(thiosemicarbazone) complexes at LNT.
Complexes
gx
gy
gz
<g*>
2.11
2.06
2.22
2.20
2.14
2.15
1
2
3
4
5
6
2.50
2.46
2.55
2.54
2.59
2.39
2.15
2.18
2.23
2.17
2.02
2.06
1.93
1.83
1.89
1.85
1.74
1.71
2
2
<g*> = [1/3 gx + 1/3 gy + 1/3 gz2]1/2

Table 5
Electrochemical data of binuclear ruthenium(III) bis(thiosemicarbazone) complexes
Complexes
Ru(III)-Ru(III)/Ru(II)-Ru(II)
Ru(III)-Ru(III)/Ru( IV)-Ru(IV )
EPc(V)
-0.49
-0.52
-0.43
-0.51
-0.45
-0.39
EPc(V)
-0.61
-0.66
-0.56
-0.66
-0.58
-0.55
EPa(V)
0.42
0.47
0.38
0.51
0.40
0.46
EPa(V)
0.80
1
2
3
4
5
6
0.83
0.76
0.86
0.79
0.84
Supporting electrolyte: [(NBu4)ClO4] (0.001 M); complex: 0.001 M; solvent: acetonitrile;
scan rate: 100 mV s-1. All the potential referenced to Ag/AgCl.

Table 6
Optimization of oxidation of alcohol by pentan-2-ol with [Ru2Cl2(AsPh3)4(L1)] (4).
Entry
C:S ratioa
1:100
1:100
1:100
1:100
1:300
1:500
Conversionb
Co-oxidant
PhIO
1
2
3
4
5
6
80
74
71
91
78
52
tBuOOH
NaIO4
NMO
NMO
NMO
a Substrate (1mmol); complex (0.01mmol); solvent dichloromethane; Temp. 40 0C;Time 3 h.
b Conversion is determined by GC with area normalization; GC conditions: BR-1ms FS column,
60 (15m * 0.25mm * 0.25um), 250 ◦C; FID detector, 280 ◦C; injector, 250 ◦C; carrier gas: N2;
rate: 25 mL/min.

Table 7: Catalytic oxidation of alcoholsby [Ru2Cl2(AsPh3)4(L1)] (4).
Entry
1
Substratea
Products
Time (h)
Conversionb (%)
CHO
OH
3/8
74/88
OH
O
2
3
3
92
OH
O
3
96
O
OH
4
5
3/8
87/96
OH
O
3/8
85/99

O
OH
6
7
3/8
3/8
86/95
O
OH
83/94
58/84
OH
OH
O
O
8
9
3/8
3/8
3/8
60/99
61/83
OH
O
10
a Substrate (1 mmol); NMO (3 mmol); complex (0.01 mmol); solvent dichloromethane;
Temp. 40 0C;
b Conversion is determined by GC with area normalization.

Graphical Abstract
O
OH
Ru - catalyst
NMO/CH2Cl2
reflux, 3h
R
R'
R
R'
R, R' = alkyl (or) aryl

Research Highlights
ꢀ New binuclear Ru(III) complexes containing (bis)thiosemicarbazones were reported.
ꢀ Characterisation of complexes were accomplished by analytical and spectral methods.
ꢀ Electrochemical study supports for the binuclear nature of the complexes.
ꢀ Reported as effective catalyst for the oxidation of alcohols.