Ruthenium carbonyl complex of a redox non-innocent ONS donor azophenol ligand: Electrochemistry, photophysical property, electronic structure and catalytic activity towards oxidation of alcohols

Article abstract of DOI:10.1016/j.jorganchem.2016.11.012

A ruthenium carbonyl complex, [Ru(CO)₂(L)(Cl)₂] (1) with a redox non-innocent thioether-containing azo-phenol ligand has been synthesized and characterized by various spectroscopic techniques, along with X-ray structure determination. Cyclic voltammogram of 1 exhibits Ru(II)/Ru(III) quasireversible oxidation (E_1/2= 1.22 V) along with ligand based two successive reductions. Theoretical calculations using DFT/B3LYP method have been used to interpret the electronic structure of the complex. Synthesized ruthenium(II) complex efficiently catalyzed the oxidation of alcohols in presence of N-methylmorpholine-N-oxide.

Full text of DOI:10.1016/j.jorganchem.2016.11.012

Accepted Manuscript
Ruthenium carbonyl complex of a redox non-innocent ONS donor azophenol ligand:
Electrochemistry, photophysical property, electronic structure and catalytic activity
towards oxidation of alcohols
Puspendu Roy, Apurba Sau Mondal, Ajoy Kumar Pramanik, Tapan Kumar Mondal
PII:
S0022-328X(16)30516-2
10.1016/j.jorganchem.2016.11.012
JOM 19697
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 8 August 2016
Revised Date: 1 November 2016
Accepted Date: 4 November 2016
Please cite this article as: P. Roy, A.S. Mondal, A.K. Pramanik, T.K. Mondal, Ruthenium carbonyl
complex of a redox non-innocent ONS donor azophenol ligand: Electrochemistry, photophysical
property, electronic structure and catalytic activity towards oxidation of alcohols, Journal of
Organometallic Chemistry (2016), doi: 10.1016/j.jorganchem.2016.11.012.
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GRAPHICAL ABSTRACT
Ruthenium carbonyl complex of a redox non-innocent ONS donor azophenol
ligand: Electrochemistry, photophysical property, electronic structure and
catalytic activity towards oxidation of alcohols
Puspendu Roy, Apurba Sau Mondal, Ajoy Kumar Pramanik and Tapan Kumar Mondal*
A ruthenium carbonyl complex, [Ru(CO)2(L)(Cl)2] (1) of a redox non-innocent thioether-
containing azo-phenol ligand has been synthesized and characterized. Cyclic voltammogram of 1
exhibits Ru(II)/Ru(III) quasireversible oxidation (E1/2 = 1.22 V) along with ligand based
reductions. DFT calculations have been used to interpret the electronic structure of the complex.
Catalytic activities towards oxidation of alcohols have been studied.

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Ruthenium carbonyl complex of a redox non-innocent ONS donor azophenol
ligand: Electrochemistry, photophysical property, electronic structure and
catalytic activity towards oxidation of alcohols
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Puspendu Roy, Apurba Sau Mondal, Ajoy Kumar Pramanik and Tapan Kumar Mondal*
Inorganic Chemistry Section, Department of Chemistry, Jadavpur University, Kolkata-700032,
India
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Abstract
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A ruthenium carbonyl complex, [Ru(CO)2(L)(Cl)2] (1) with a redox non-innocent thioether-
containing azo-phenol ligand has been synthesized and characterized by various spectroscopic
techniques, along with X-ray structure determination. Cyclic voltammogram of 1 exhibits
Ru(II)/Ru(III) quasireversible oxidation (E1/2 = 1.22 V) along with ligand based two successive
reductions. Theoretical calculations using DFT/B3LYP method have been used to interpret the
electronic structure of the complex. Synthesized ruthenium(II) complex efficiently catalyzed the
oxidation of alcohols in presence of N-methylmorpholine-N-oxide.
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Key words: Ruthenium carbonyl complex; ONS donor azophenol ligand; X-ray structure;
Electronic structure; Electrochemistry; Catalytic activity.
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Corresponding author: Email: tkmondal@chemistry.jdvu.ac.in
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23 1. Introduction
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Chelating behavior of ONS donor ligands with transition metals has been studied with the aim of
gaining more information about their nature of coordination, structural and spectral features [1-
5]. They can stabilize metal ion in uncommon oxidation states [6, 7], to generate uncommon
coordination numbers in the resultant complexes [6-8] and to participate in a variety of
interesting redox reactions. The chemistry of azo-ligands has been widely explored due to their
interesting physical, chemical, photophysical and photochemical, catalytic properties especially
in the low valent transition metal coordination and organometallic compounds [9-16]. Besides,
the study of compounds containing S and N atoms is interesting due to their significant
antifungal, antibacterial and anticancer activities [17-24].
There has been considerable interest in transition metal ions catalyzed biological
oxidation events including hydroxylation, epoxidation, dehalogenation, sulfoxidation,
dehydrogenation, alcohol and aldehyde oxidation reactions [25-29]. The oxidation of alcohols
plays an important role in organic synthesis and the efforts are continuing for the development of
new oxidative processes to avoid the traditional methods for oxidation using stoichiometric
amount of inorganic oxidants [30-32]. Inspite of several proposed mechanism, the formation of
metal oxo moieties (Mn+=O) have been well accepted for late transition metal complexes as
active intermediates in most of the oxidation reactions [27-29, 33]. Ruthenium carbonyl
complexes have been widely used as catalysts for oxidation of organic compounds [34-36]. In
the past few decades there has been a growing interest in transition metal-catalyzed oxidation of
alcohols, which take place at milder conditions using oxidants such as molecular oxygen,
hydrogen peroxide, tert-butyl hydroperoxide and N-methylmorpholine-N-oxide (NMO) [37-42].

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Herein, we have synthesized a new ONS donor thioether containing azophenol ligand, 4-
chloro-2-((2-(ethylthio)phenyl)diazenyl)phenol (HL) and its ruthenium carbonyl complex,
[Ru(CO)2(L)(Cl)2] (1). An array of tools including X-ray diffractometry, electrochemistry, and
electronic absorption and emission spectroscopy abetted with DFT calculations were used to
characterize the compounds. The catalytic activity of the ruthenium(II) complex for the oxidation
of primary and secondary alcohols to the respective aldehyde and ketones were studied using N-
methylmorpholine-N-oxide (NMO) as oxidizing agent.
52 2. Experimental
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2.1. Materials and methods
RuCl3.3H2O was purchased from Arrora Matthey, Kolkata, India. [Ru(CO)2(Cl)2]n was prepared
following the reported method [43]. 2-(Ethylthio)benzenamine was synthesized by published
procedure [44]. All other chemicals and solvents were of reagent grade and were used without
further purification.
Microanalyses (C, H, N and S) were performed using a PerkinElmer 2400 CHNS/O
elemental analyzer. HRMS mass spectra were obtained on a Waters (Xevo G2 Q-TOF) mass
spectrometer. The electronic spectra were taken on a Lambda 750 PerkinElmer
spectrophotometer. IR spectra were recorded on RX-1 PerkinElmer spectrophotometer in the
spectral range 4000-400 cm-1 with the samples in the form of KBr pellets. Luminescence
property was measured using LS-55 PerkinElmer fluorescence spectrophotometer at room
temperature (298 K) in acetonitrile by 1 cm path length quartz cell. Fluorescence lifetimes were
measured using a time-resolved spectrofluorometer from IBH, UK. The instrument uses a
picoseconds diode laser (NanoLed-03, 370 nm) as the excitation source and works on the
principle of time-correlated single photon counting [45]. The goodness of fit was evaluated by χ2

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criterion and visual inspection of the residuals of the fitted function to the data. NMR spectra
were recorded in CDCl3 on a Bruker (AC) 300 MHz FT-NMR spectrometer in the presence of
TMS as internal standard. Cyclic voltammetric measurements were carried out using a CHI
Electrochemical workstation. A platinum wire working electrode, a platinum wire auxiliary
electrode and Ag/AgCl reference electrode were used in a standard three-electrode configuration.
Bu4NPF6 was used as the supporting electrolyte in acetonitrile and the scan rate used was 50 mV
s−1 under nitrogen atmosphere.
Luminescence quantum yield was determined using carbazole as reference with a known
φR of 0.42 in MeCN. The complex and the reference dye were excited at the same wavelength,
maintaining nearly equal absorbance (~0.1), and the emission spectra were recorded. The area of
the emission spectrum was integrated using the software available in the instrument and the
quantum yield is calculated according to the following equation:
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φS/φR = [AS / AR ] x [(Abs)R /(Abs)S ] x [ηS /ηR ]
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Here, φS and φR are the luminescence quantum yield of the sample and reference, respectively.
AS and AR are the area under the emission spectra of the sample and the reference respectively,
(Abs)S and (Abs)R are the respective optical densities of the sample and the reference solution at
the wavelength of excitation, and ηS and ηR are the values of refractive index for the respective
solvent used for the sample and reference.
2.2. Synthesis
2.2.1. Synthesis of 4-chloro-2-((2-(ethylthio)phenyl)diazenyl)phenol (HL)
A solution of 2-(ethylthio)benzenamine (3.06 g, 0.02 mol) in 1:1 HCl (10 mL) was cooled in an
ice bath and an ice cold solution of NaNO2 (2.0 g in 10 mL water) was added to it under stirring.
Then it was added to an ice cold solution of Na2CO3 (6 g in 25 mL) and 4-chlorophenol (2.56 g,

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0.02 mol) with vigorous stirring and an orange-red precipitate was obtained. The precipitate was
filtered and washed with cold water, then dried over CaCl2. The product was purified by using a
silica gel (mesh 60-120) column. An orange-red band of HL was eluted by 30% (v/v) ethyl
acetate-petroleum ether mixture. Evaporation of solvent under reduced pressure yielded the pure
HL. Yield, 3.7 g (72%).
Anal. Calc.C14H13ClN2OS (HL): C, 57.43; H, 4.48; N, 9.57; S, 10.95%. Found: C, 57.24;
H, 4.43; N, 9.48; S, 10.83%. IR data (KBr, cm-1): 3434 υ(O-H), 1421 υ(N=N). 1H NMR (CDCl3,
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300 MHz): δ (ppm): 12.67 (1H, s), 7.95 (1H, s), 7.85 (1H, d, J = 8.0 Hz), 7.28-7.45 (4H, m),
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7.02 (1H, d, J = 8.8 Hz), 3.04 (2H, q, J = 7.2 Hz), 1.40 (3H, t, J = 7.3). C NMR (CDCl3, 75
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MHz): δ (ppm): 14.02 (-S-CH2-CH3), 26.79 (-S-CH2-CH3), 116.49 (Ar-C), 119.75 (Ar-C),
124.36 (Ar-C), 125.97 (Ar-C), 127.95 (Ar-C), 131.99 (Ar-C), 132.09 (Ar-C), 132.87 (Ar-C),
137.72 (Ar-C), 138.62 (Ar-C), 147.75 (Ar-C), 150.98 (Ar-C). HRMS m/z, 293.6234 (calculated
for [C14H13ClN2OS + H]+: 293.8053).
2.2.2. Synthesis of ruthenium complex (1)
To a suspension of [Ru(CO)2Cl2]n (0.228 g, 1.0 mmol) in acetonitrile (30 mL), HL (0.257 g, 1.0
mmol) was added and the reaction mixture was refluxed for 8 h under N2 atmosphere to yield a
dark red solution. The solvent was then removed under reduced pressure. The dried crude
product was purified by using a silica gel (mesh 60-120) column. The red band of 1 was eluted
by 50% (v/v) ethyl acetate-petroleum ether mixture. On removal of the solvent under reduced
pressure the pure complex 1 was obtained as a red solid which was further dried under vacuum.
Yield, 0.305 g (63%).
Anal. Calc. for C16H12Cl2N2O3RuS: C, 39.68; H, 2.50; N, 5.78; S, 6.62%. Found: C,
39.36; H, 2.42; N, 5.70; S, 6.52%. IR data (KBr, cm-1): 2061, 1997 υ(CO); 1387 υ(N=N).1H

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NMR data (CDCl3, ppm): 8.51 (1H, d, J = 7.2), 7.95 (1H, s), 7.46-7.57 (4H, m), 7.05 (1H, d, J =
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8.4 Hz), 3.32 (2H, q, J = 7.3 Hz), 1.45 (3H, t, J = 7.4). C NMR (CDCl3, 75 MHz): δ (ppm):
14.37 (-S-CH2-CH3), 26.59 (-S-CH2-CH3), 115.27 (Ar-C), 122.72 (Ar-C), 126.41 (Ar-C), 128.36
(Ar-C), 129.63 (Ar-C), 132.53 (Ar-C), 134.65 (Ar-C), 137.22 (Ar-C), 138.62 (Ar-C), 143.13
(Ar-C), 146.65 (Ar-C), 150.67 (Ar-C), 197.45 (CO), 203.21 (CO). HRMS m/z, 507.4636 (M-
Na+: 507.3360). E1/2 (RuII/RuIII): 1.22 V (∆E = 110 mV); E1/2(L/L•−
E1/2(L•−/L2- : -1.18 V (∆E = 120 mV).
): -0.47 V (∆E = 50 mV) and
)
2.3. Crystal structure determination and refinement
Single crystals of 1 were obtained by slow diffusion of n-hexane into dichloromethane solution
of the complex. X-ray data were collected using an automated Bruker AXS Kappa smart Apex-II
diffractometer equipped with an Apex-II CCD area detector using a fine focus sealed tube as the
radiation source of graphite monochromated Mo Kα radiation (λ = 0.71073 Å). Details of crystal
analyses, data collection and structure refinement are summarized in Table 1. Reflection data
were recorded using the ω scan technique. The structure was solved and refined by full-matrix
least-squares techniques on F2 using the SHELX-97 [46]. The absorption corrections were done
by multi-scan (SHELXTL program package) and all the data were corrected for Lorentz,
polarization effect. Hydrogen atoms were included in the refinement process as per the riding
model.
2.4. Computational method
Full geometry optimization was carried out by density functional theory (DFT) method using
B3LYP hybrid exchange correlation functional for the complex [47, 48]. All elements except
ruthenium were assigned the 6-31G(d) basis set, whilst the LanL2DZ basis set with effective
core potential was employed for ruthenium atom [49-51]. Vibrational frequency calculations

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were performed to ensure that the optimized geometries were local minima on the potential
energy surface and only positive Eigen values were obtained. All calculations were performed
with Gaussian09 program package [52] with the aid of the GaussView, Version 5 visualization
program [53]. Natural bond orbital analyses were performed using the NBO 3.1 module of
Gaussian09 [54, 55]. Vertical electronic excitations based on B3LYP optimized geometry were
computed using the time-dependent density functional theory (TDDFT) formalism [56-58] using
conductor-like polarizable continuum model (CPCM) [59-61] in acetonitrile to simulate the
solvent. GaussSum [62] was used to calculate the fractional contributions of various groups to
each molecular orbital.
2.5. Procedure for catalytic oxidation of alcohols
Catalytic oxidation of primary alcohols to corresponding aldehydes and secondary alcohols to
ketones by ruthenium(II) complexes were studied in the presence of NMO as oxidant. A typical
reaction using the complex as a catalyst and primary or secondary alcohol, as substrate at 1:100
molar ratio was described as follows. A solution of complex 1 (0.01 mmol) in CH2Cl2 (25 mL)
was added to the mixture containing PhCH2OH (1 mmol), NMO (3 mmol) and molecular sieves.
The reaction mixture was refluxed and conversion of PhCH2OH to PhCHO was monitored
taking the reaction mixture at 10 minutes time interval. The solvent of the reaction mixture was
evaporated under reduced pressure. The residue was then extracted with diethyl ether,
concentrated to ≈ 1 mL. Conversions were determined by GC instrument equipped with a flame
ionization detector (FID) using a HP–5 column of 30 m length, 0.53 mm diameter and 5.00 µm
film thickness. The column, injector and detector temperatures were 200, 250 and 2500C
respectively. The carrier gas was N2 (UHP grade) at a flow rate of 30 mL/min. The injection
volume of sample was 2 µL. The oxidation products were identified by GC co-injection with

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authentic samples. No significant conversion was observed after 50 minutes. All other alcohols
were oxidized by refluxing the reaction mixture for 1 h and conversions were monitored
following the identical protocol.
163 3. Results and discussion
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3.1. Synthesis and formulation
The thioether-containing ONS donor azo-phenol ligand (HL) was synthesized by diazo-coupling
reaction between 2-(ethylthio)benzenamine and 4-chlorophenol. It was characterized by
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elemental analysis along with various spectroscopic techniques. H NMR spectrum of HL in
CDCl3 showed a singlet peak at 12.67 ppm corresponding to the phenolic-OH proton. The
aromatic protons are appeared at 7.02-7.95 ppm. The S-CH2CH3 protons are observed as triplet
and quartet at 1.40 and 3.04 ppm (Fig. S1). IR spectrum of HL exhibits characteristic υ(N=N)
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peaks at 1421 cm-1 along with broad υ(O-H) peak at 3434 cm-1 (Fig. S3). The ruthenium
carbonyl complex, [Ru(CO)2(L)(Cl)2] (1) was synthesized by the reaction of HL and
[Ru(CO)2Cl2]n in acetonitrile under reflux (Scheme 1). Both HL and complex 1 exhibit
satisfactory microanalytical and mass spectral data in CH3CN (see the Experimental Section).
The IR spectrum of 1 exhibits stretching at 1387 cm-1 correspond to υ(N=N). It is appeared at
lower frequency region compared to free ligand, which is supported the coordination of azo-N.
In addition, two sharp peaks are observed at 1997 and 2061 cm-1 correspond to υ(CO) with cis
configuration in the complex (Fig. S5). 1H NMR spectrum of 1 exhibits slight downfield shifting
of aromatic protons. A sharp downfield shift of the quartet signal is observed for S-CH2CH3
protons (3.32 ppm), which is indicated the coordination of S atom to ruthenium in the complex
(Fig. S6).

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S
[Ru(CO)2Cl2]n
S
CO
Reflux in acetonitrile
N
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CO
Cl
Cl
Cl
[Ru(CO)2(L)(Cl)2]
HL
Scheme 1. Synthesis of ruthenium carbonyl complex, [Ru(CO)2(L)(Cl)2] (1)
3.2. Crystal structure
The X-ray crystallographic data collection and refinement parameters of 1 are given in Table 1.
Selected bond lengths and bond angles are given in Table 2. ORTEP plot of the molecular
structure with the atomic numbering scheme for 1 is shown in Fig. 1. The ruthenium atom adopts
a distorted octahedral geometry and is coordinated by two carbonyl ligands in a cis arrangement,
along with the coordination of azo-N and O atoms of the ligand, while the trans positions are
occupied by thiether-S and chlorine atoms. The deviation of the ruthenium coordination sphere
from the ideal octahedron is because of the small bite angles of the chelate rings (Ru1-O1-C1-
C6-N2-N1) [80.76(14)°] and (Ru1-N1-C7-C12-S1) (80.08(11)°). The Ru-C(CO) (Ru1-C13,
1.936(3) and Ru1-C14, 1.942(4) Å) and C-O (C13-O2, 1.145(5) and C14-O3, 1.161(6) Å) bond
distances are found as expected for similar ruthenium carbonyl complexes [63, 64]. The N1-N2
bond length, 1.315(4) Å is quite elongated as compared to the expected free ligand azo distance
[65], supporting the strong dπ(Ru)→π*(N=N) back donation in the complex.
3.3. Absorption and emission spectra

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The solution spectrum of HL in acetonitrile exhibits two sharp intense peaks at 413 (ε = 22539
M-1 cm-1) and 321 nm (ε = 35442 M-1 cm-1), along with a shoulder at 446 nm. In ruthenium
complex, the high energy intense band appears at 370 nm (ε = 24246 M-1 cm-1) along with a
shoulder at 342 nm, while the low energy band is red shifted compared to free ligand and
observed at 555 nm (ε = 11535 M-1 cm-1) (Fig. 2).
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The free ligand (HL) does not exhibit any emission upon excitation in both the absorption
bands at 413 nm and 321 nm. However, upon excitation at 370 nm for complex 1, emission is
observed with emission maxima at 480 nm along with a shoulder at 440 nm (Fig. 3). The
emission quantum yields (φ) of the complex is 0.018. Lifetime data of the emission decay curve
was deconvoluted with respect to the lamp profile. The observed emission decay fits with bi-
exponential profile with χ2 = 1.123 (Fig. 4). We have used mean fluorescence lifetime (τf = a1τ +
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a2τ2, where a1 and a2 are relative amplitude of decay process) to study the excited state stability
of the complex. The emission lifetime of the complex is found to be 3.66 ns.
3.4. DFT computation and electronic structure
The geometry of HL and complex 1 were optimized by DFT method in singlet ground state using
the B3LYP correlation functional. The optimized bond parameters for complex 1 are given in
Table 2. The calculated bond distances and angles are well correlated with the X-ray crystal
structure data.
The contour plots of selected molecular orbitals of HL are given in Fig. 5. The HOMO is
concentrated on phenol moiety and is π character; the HOMO-1 and HOMO-2 are non-bonding
in character and concentrated on S atom and azo moiety respectively. The LUMO has π*(L)
character with major contribution of π*(N=N) orbital. The energy and compositions of some
selected molecular orbitals of complex 1 are summarized in Table 3. Contour plots of some

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selected molecular orbitals of 1 are given in Fig. 6. The HOMO is 85% π(L) character along with
reduced contribution of dπ(Ru) in the complex. The HOMO-1 and HOMO-2 are mixed dπ(Ru)
(22-26%) and pπ(Cl) (62-67%) character. Other high energy occupied molecular orbitals
(HOMO-3 to HOMO-10) have mixed dπ(Ru) and π(L) character. The low energy unoccupied
molecular orbital (LUMO) has 97% π*(L) character with major contribution of π*(N=N) orbital.
The significant contribution of dπ(Ru) orbitals along with π*(L) and π*(CO) in LUMO+1 to
LUMO+5, indicative of the mixing of metal d-orbitals with ligand group of orbitals in the
complex.
To understand the nature of Ru-CO bonding, natural bond orbitals (NBOs) calculations
were performed on the optimized geometry of the complex. The occupancies and hybridizations
of the calculated Ru–C and C–O natural bond orbitals (NBOs) are summarized in Table 4. For
each carbonyl group three natural bond orbitals are detected for the C–O bond, and one orbital
for the Ru–C bond. The NBOs of Ru–C bonds have ~31% Ru and ~69% C character (bond order
Ru1-C13, 1.1990 and Ru1-C14, 1.0115). The sp2 hybridized NBOs of C–O bonds have ~30% C
and ~70% O character, while the NBOs, mostly having p-character, have reduced contribution
(~25%) of C and 75% character of O in the complex (bond order C13-O2, 2.1683 and C14-O3,
2.2056).
The bonding between CO ligands and Ru atom is supported by the resonance structure
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from the calculated atomic charges (Table 4). The calculated natural charges
on the carbon atoms of the carbonyl ligands are positive, whereas the oxygen atoms are
negatively charged. The calculated charge on the ruthenium atom (-0.726 a.u.) is considerably
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lower than the formal charge (+2). The populations of the 4dxy, 4dxz, 4dyz, 4dx2-y and 4dz2 of the
ruthenium atom are 1.7273, 1.8137, 1.7497, 1.1309 and 1.0913.

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3.4. TDDFT calculation and electronic spectra
To interpret the electronic spectra singlet-singlet vertical electronic excitations were carried out
by TDDFT/CPCM method in acetonitrile. The sharp intense peaks of HL at 413 and 321 nm
correspond to HOMO → LUMO and HOMO-3 → LUMO transitions and have π → π* character.
The HOMO-3 → LUMO transition (n → π*) corresponds to the shoulder peak at 446 nm (Table
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5). In complex 1, the low energy band at 555 nm corresponds to HOMO → LUMO transition
having intra-ligand charge transfer (ILCT) character along with minor contribution of metal to
ligand charge transfer (MLCT) transition. The band at 370 nm has mixed halogen to ligand
charge transfer (XLCT) and MLCT character. In addition, ligand centered transition (HOMO-3
→ LUMO) is observed at 344 nm.
3.5. Electrochemistry
The electrochemical behavior of the complex was investigated by cyclic voltammetry (CV) in
presence of Bu4NPF6 in MeCN at scan rate 50 mV S-1. Complex 1 exhibits one quasireversible
oxidation couple at 1.22 V (∆E = 110 mV) along with one reversible reduction couple at -0.47 V
(∆E = 50 mV) and a quasireversible reduction with E1/2, -1.18 V (∆E = 120 mV), positive and
negative to reference electrode respectively (Ag/AgCl) in the potential range 2.0 to −2.0 V (Fig.
7). The oxidation is assigned as Ru(II) to Ru(III) oxidation, while the two successive reduction
couples correspond to the reduction of azo ligand with the formation of L•− and L2- respectively.
3.6. Catalytic oxidation
The catalytic activities of our synthesized ruthenium complex (1) towards the oxidation of
primary and secondary alcohols were tested in dichloromethane in the presence of NMO oxidant.
In order to optimize the reaction conditions, different substrate:catalyst ratios in presence of
NMO were carried out and the results are summarized in Table 6. For these initial experiments

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benazyl alcohol was selected as a test-substrate and allowed it to react with catalytic quantities of
complex in dichloromethane in presence of NMO. In the C:S ratio 1:50 and 1:100 the conversion
of benzyl alcohol to benzaldehyde is almost same but with increasing the C:S ratio to 1:200 or
1:300, the reaction still proceeds smoothly accompanied by a moderate drop in conversions
while in C:S ratio 1:500 sharp drop in conversion is observed. Thus, it was concluded that
catalyst:substrate ratio is 1:100 in presence of NMO is the best compromise between optimal
conversion in dichloromethane. Other alcohols like, 2-butanol, 1-phenylethanol, cyclopentanol,
cyclohexanol, cycloheptanol and cycloctanol selectively converted into corresponding carbonyl
compounds with 1 mol% of catalyst in presence of NMO. A series of reactions were carried out
with either the ruthenium complex or NMO only under identical condition but there was no
detectable oxidation in absence ruthenium complex or NMO.
Complex (1) oxidizes primary alcohols to corresponding aldehydes and secondary
alcohols to ketones with moderate to high conversion (77-88%) (Table 7). The isolated yield for
the oxidation of 2-butanol to 2-butanone is reduced to 45% may be due to the loss of volatitle 2-
butanone. Results of the investigations suggest that the ruthenium complex efficiently reacts with
NMO to yield a high valent ruthenium−oxo species [66, 67], which is capable of oxygen atom
transfer to alcohols. This is further supported by the appearance of a new stretching band at 858
cm−1 (Fig. S9), characteristic of Ru(IV)=O species in the IR spectrum of the solid mass of the
reaction mixture obtained by evaporation of the resultant solution to dryness [68-70]. Further
support in favour of the formation such species identified by the appearance of a new peak at 398
nm corresponds to the formation of Ru(IV)=O [71] in the UV-Vis spectrum of a
dichloromethane solution of the complex in presence of NMO (Fig. 8). The appearance of a new
peak at 398 nm corresponds to the formation of Ru(IV)=O species [71]. The complex catalyzes

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297
298
299
300
301
302
the oxidation of benzyl alcohol to benzaldehyde with 77% conversion. In case of cyclohexanol
the oxidation product cyclohexanone is 88%. The catalytic efficiency of our synthesized
complex is less when we compared to the catalytic efficiency of some reported ruthenium
complexes reported earlier [72-74]. However, the present complex shows catalytic activity
comparable to our previously reported ruthenium complexes [16, 27, 28] and even shows better
catalytic activity than the other ruthenium(II) complexes reported earlier [75].
303 4. Conclusion
304
305
306
307
308
309
We have synthesized and characterized a ruthenium carbonyl complex (1) of ONS donor
thioether ligand (HL). X-ray structure of 1 confirmed the pseudo-octahedral geometry around
ruthenium centre. The metal based oxidation and ligand based reduction processes were studied
by cyclic voltammetric studies. The electronic structure of the complex was interpreted by DFT
calculations. The ruthenium(II) catalyzed oxidation of alcohols was studied and showed
moderate to high yield.
310 Acknowledgement
311
312
313
314
315
316
317
318
319
Financial support received from the Department of Science and Technology, New Delhi, India is
gratefully acknowledged. P. Roy and A. Sau Mondal thankful to UGC, New Delhi, India for
fellowships.
Supplementary materials
Crystallographic data for the structure 1 was deposited with the Cambridge Crystallographic
Data center with the CCDC No. 1478954. Copies of this information may be obtained free of
charge from the Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (e-mail:
deposit@ccdc.cam.ac.uk or www:htpp://www.ccdc.cam.ac.uk).

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439
Table 1. Crystallographic data and refinement parameters of [Ru(CO)2(L)(Cl)2] (1)
440
Formula
C16H12Cl2N2O3RuS
484.31
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
Formula Weight
Crystal System
Space group
Triclinic
P1
a, b, c [Å]
10.155(5), 10.431(5), 11.691(5)
85.132(5)
67.245(5)
65.176(6)
1003.6(8)
2
α
β
γ
V [ Å3]
Z
D(calc) [g/cm3]
Mu(MoKa) [ /mm]
F(000)
1.603
1.167
480
Absorption Correction
Temperature (K)
Radiation [Å]
θ(Min-Max) [°]
Dataset (h; k; l)
Total, Unique Data, R(int)
Observed data [I > 2σ(I)]
Nref, Npar
multi-scan
293(2)
0.71073
1.92-26.37
-12 to 12; -12 to 12; -14 to 14
14616, 4061, 0.0262
3815
4061, 217
0.0707, 0.1791
0.245 and -0.124
1.088
R, wR2
ꢀq(max) and ꢀq(min) [e/Å3]
Goodness of fit(S)
461
462
463

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464
Table 2. Selected X-ray and calculated bond distances and angles of [Ru(CO)2(L)(Cl)2] (1)
465
Bonds(Å)
X-ray
Calc.
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
Ru1-Cl2
Ru1-S1
Ru1-O1
Ru1-N1
Ru1-C13
Ru1-C14
O2-C13
O3-C14
N1- N2
2.3900(17)
2.3965(17)
2.125(4)
2.081(2)
1.936(3)
1.942(4)
1.145(5)
1.161(6)
1.315(4)
2.422
2.431
2.112
2.130
1.927
1.919
1.149
1.152
1.296
Angles(o )
X-ray
Calc.
O1-Ru1-C13
O1-Ru1-C14
O1-Ru1-Cl2
O1-Ru1-S1
O1-Ru1-N1
O2-C13-Ru1
O3-C14-Ru1
N1-Ru1-C13
N1-Ru1-C14
N1-Ru1-Cl2
N1-Ru1-S1
S1-Ru1-C13
S1-Ru1-C14
S1-Ru1-Cl2
Cl2-Ru1-C13
Cl2-Ru1-C14
C13-Ru1-C14
94.51(12)
172.55(11)
91.36(11)
92.92(11)
80.76(14)
178.6(4)
91.67
173.55
89.57
94.88
80.46
177.82
176.67
171.75
94.85
93.02
78.71
96.63
90.30
169.85
90.12
86.66
91.21
175.7(4)
171.77(18)
92.24(16)
94.95(10)
80.08(11)
93.53(15)
88.35(15)
172.83(4)
91.88(15)
86.68(15)
92.7(2)

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489
Table 3. Energy and compositions of some selected molecular orbitals of 1
MO
Energy
% Composition
Ru
17
25
24
18
53
02
11
26
22
04
30
09
36
22
19
19
50
Cl
0
CO
59
37
70
08
10
01
01
03
03
01
06
03
05
03
08
05
12
L
LUMO+5
LUMO+4
LUMO+3
LUMO+2
LUMO+1
LUMO
-0.44
-0.77
-0.90
-1.16
-1.41
-2.59
-5.47
-6.31
-6.37
-6.60
-6.84
-7.31
-7.63
-7.70
-7.70
-7.89
-8.27
24
35
05
74
20
97
85
09
08
90
60
84
39
69
34
60
28
03
01
0
07
0
HOMO
03
62
67
05
04
04
20
06
39
16
10
HOMO-1
HOMO-2
HOMO-3
HOMO-4
HOMO-5
HOMO-6
HOMO-7
HOMO-8
HOMO-9
HOMO-10
490
491
492
493

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494
495
Table 4. Hybridization and Occupancy of M‒C(CO), C‒O(CO) and N=N(azo) bonds and NBO
atomic charges of 1 obtained from NBO analysis
Bond
order
NBO charges
Bonds
Occupancy
Contribution
Hybridization
atoms
Ru1
Cl2
S1
charge
Ru1-C13 1.8929(0.0912) 1.1990 31.32%Ru + 68.68%C
Ru1-C14 1.8905(0.0970) 1.0115 29.32%Ru + 70.68%C
Ru(sp2.16d1.48) + C(sp0.53
Ru(sp2.48d1.44) + C(sp0.52
)
)
-0.7258
-0.3923
0.5824
-0.1530
-0.1417
0.7913
0.8096
-0.4259
-0.4177
Ru1-N1
C13-O2
1.9052(0.1618) 0.5420 19.07%Ru + 80.93%N
1.9973(0.1364) 2.1683 25.54%C + 74.46%O
Ru(sp3.36d2.58) + N(sp1.80
)
C(sp52.26) + O(sp39.95
C(sp99.99) + O(sp99.99
)
)
N1
1.9974(0.1497)
1.9955(0.0168)
25.23%C + 74.77%O
30.42%C + 69.58%O
N2
C(sp1.99) + O(sp1.27
)
C13
C14
O2
C14-O3
N1-N2
1.9977(0.1183) 2.2056 25.24%C + 74.76%O
C(sp99.99) + O(sp99.99
C(sp42.71) + O(sp30.52
)
)
1.9970(0.1090)
1.9906(0.0153)
25.59%C + 74.41%O
30.07%C + 69.93%O
C(sp2.04) + O(sp1.29
N1(sp2.24) + N2(sp2.27
N1(sp99.99) + N2(sp99.99
)
O3
1.9861(0.0162) 1.0975 51.48%N1 + 48.52%N2
1.9045(0.4742) 59.54%N1 + 40.46%N2
)
)
496
497
498
499
500
501
502
503
504
505
506

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507
508
Table 5. Vertical electronic transition calculated by TDDFT/CPCM method of HL and complex
1
Compd.
E (eV)
Osc.
Key excitations
Character
λ (nm)
λexpt. (nm)
(ε, M-1cm-1)
446 (sh.)
Strength (f)
(71%)HOMO-1→LUMO
(72%)HOMO→LUMO
n→π*
π→π*
486.63
424.93
2.5478
2.9178
0.0030
0.1656
HL
413 (22539)
330.06
3.7564
0.4865
321 (35442)
555 (11535)
(69%)HOMO-3→LUMO
π→π*
547.2
401.6
367.4
2.2658
3.0873
3.3744
0.1002
0.0064
0.2355
(95%)HOMO→LUMO
π(L)/dπ(Ru)→π*(L)
π(L)→ dπ(Ru)
(84%)HOMO→LUMO+1
1
370 (24246)
342 (sh.)
(49%)HOMO-2→LUMO
(45%)HOMO-1→LUMO
(69%)HOMO-3→LUMO
dπ(Ru)/pπ(Cl)→π*(L)
π(L)→π*(L)
343.7
3.6073
0.0863
509
510
511
512
513
514
515
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520

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Table 6. Optimization of oxidation reaction by PhCH2OH with 1a
Entry
C:S ratio
1:50
Conversion (%)b
1
2
3
4
5
77
77
73
65
52
1:100
1:200
1:300
1:500
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
a Substrate (1 mmol); NMO (3 mmol); complex (0.01 mmol); solvent dichloromethane; temp.
40°C.
b Conversions determined by GC

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Table 7. Catalytic oxidation of alcohols by Ru(II) complex 1 using NMO as oxidanta
Substrate
Product
Conversion (%)
Isolated yield (%)
Benzyl alcohol
2-Butanol
Benzaldehyde
2-Butanone
77
79
83
81
88
85
79
71
45
76
68
75
80
75
1-Phenylethanol
Cyclopentanol
Cyclohexanol
Cycloheptanol
Cycloctanol
Acetophenone
Cyclopentanone
Cyclohexanone
Cycloheptanone
Cycloctanone
539
540
a Substrate (1 mmol); NMO (3 mmol); complex (0.01 mmol); solvent dichloromethane;Temp.
40°C; Conversions determined by GC instrument equipped with a flame ionization detector
(FID) using a HP-5 column of 30 m length, 0.53 mm diameter and 5.00 µm film thickness.
541
542
543
544
545
546
547
548
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550
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553

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577
578
Figure captions
Fig. 1. ORTEP plot of 1 with 35% ellipsoidal probability
Fig. 2. UV-Vis spectra of HL (─) and 1 (─) in acetonitrile
Fig. 3. Emission spectrum of 1 in acetonitrile (λexcitation = 370 nm)
Fig. 4. Exponential decay profiles of prompt (■■■) and 1 (•••)in acetonitrile (λexcitation = 370 nm)
Fig. 5. Contour plots of selected molecular orbitals of HL
Fig. 6. Contour plots of selected molecular orbitals of 1
Fig. 7. Cyclic voltammogram of 1 in acetonitrile
Fig. 8. UV-Vis spectra of 1 (─) and [1 + NMO] (─) in dichloromethane

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Fig. 1