Synthesis, structure, redox behavior, catalytic activity and DFT study of a new family of ruthenium(III)1-(arylazo)naphtholate complexes

Article abstract of DOI:10.1016/j.jorganchem.2016.12.003

Treatment of [RuCl₂(DMSO)₄] with 1-(arylazo)naphthol ligands in benzene under reflux afford the air-stable new ruthenium(III) complexes with general composition [Ru(L-R)₃] (L = bidentate O, N donor; R = H, CH₃, OCH₃, Br, NO₂) in good yield. The 1-(arylazo)naphthol ligands behave as tris-bidentate O, N donors via naphtholic proton and azo nitrogen. The molecular and electronic structure of the complexes have been established by elemental analysis and spectral (FT-IR, UV–vis & EPR) methods. DFT calculations were also carried out on the complexes 1 and 3 along with X-ray crystallized geometry of complex 5. These complexes in dichloromethane solution show intense ligand-to-metal charge transfer (LMCT) transitions in the visible region. The absorption and g-tensor value of these complexes (1, 3 & 5) were also computed and compared along with the available experimental results. The redox behavior of the complexes has been investigated by cyclic voltammetry and the potentials are observed with respect to the electronic nature of substituents (R) in the 1-(arylazo)naphthol ligands. These complexes have shown great promise as catalysts for the conversion of aldehydes to primary amides in good yield.

Full text of DOI:10.1016/j.jorganchem.2016.12.003

Accepted Manuscript
Synthesis, structure, redox behavior, catalytic activity and DFT study of a new family
of ruthenium(III)-1-(arylazo)naphtholate complexes
Madhan Ramesh, Mani Kalidass, Madhavan Jaccob, Dhananjayan Kaleeswaran,
Galmari Venkatachalam
PII:
S0022-328X(16)30554-X
10.1016/j.jorganchem.2016.12.003
JOM 19726
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 30 August 2016
Revised Date: 9 November 2016
Accepted Date: 2 December 2016
Please cite this article as: M. Ramesh, M. Kalidass, M. Jaccob, D. Kaleeswaran, G. Venkatachalam,
Synthesis, structure, redox behavior, catalytic activity and DFT study of a new family of ruthenium(III)-1-
(arylazo)naphtholate complexes, Journal of Organometallic Chemistry (2017), doi: 10.1016/
j.jorganchem.2016.12.003.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT
Graphical Abstract
Synthesis, Structure, Redox Behavior, Catalytic Activity and DFT Study of a
New Family of Ruthenium(III)-1-(arylazo)Naphtholate Complexes
Madhan Ramesha, Mani Kalidassa, Madhavan Jaccob*b, Dhananjayan Kaleeswaranc,
Galmari Venkatachalam*a

ACCEPTED MANUSCRIPT
Synthesis, Structure, Redox Behavior, Catalytic Activity and DFT Study of a
New Family of Ruthenium(III)-1-(arylazo)Naphtholate Complexes
Madhan Ramesha, Mani Kalidassa, Madhavan Jaccob*b, Dhananjayan Kaleeswaranc,
Galmari Venkatachalam*a
aPG & Research Department of Chemistry, Government Arts College, Dharmapuri – 636 705,
Tamil Nadu, India.
bDepartment of Chemistry, Loyola College, Nungambakkam, Chennai –600 034, Tamil Nadu,
India.
cDepartment of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai-400076,
Maharashtra, India.
To whom correspondence should be addressed, e-mail: gvchem@gmail.com [G. Venkatachalam]

ACCEPTED MANUSCRIPT
ABSTRACT
Treatment of [RuCl2(DMSO)4] with 1-(arylazo)naphthol ligands in benzene under reflux
afford the air-stable new ruthenium(III) complexes with general composition [Ru(L-R)3]
(L= bidentate O, N donor; R = H, CH3, OCH3, Br, NO2) in good yield. The 1-(arylazo)naphthol
ligands behave as tris-bidentate O, N donors via naphtholic proton and azo nitrogen. The
molecular and electronic structure of the complexes have been established by elemental analysis
and spectral (FT-IR, UV-vis & EPR) methods. DFT calculations were also carried out on the
complexes 1 and 3 along with X-ray crystallized geometry of complex 5. These complexes in
dichloromethane solution show intense ligand-to-metal charge transfer (LMCT) transitions in the
visible region. The absorption and g-tensor value of these complexes (1, 3 & 5) were also
computed and compared along with the available experimental results. The redox behavior of the
complexes has been investigated by cyclic voltammetry and the potentials are observed with
respect to the electronic nature of substituents (R) in the 1-(arylazo)naphthol ligands. These
complexes have shown great promise as catalysts for the conversion of aldehydes to primary
amides in good yield.
Key words: Ruthenium(III); Arylazo ligands; Crystal structure; Redox properties; Catalytic
activity; DFT study

ACCEPTED MANUSCRIPT
1. INTRODUCTION
The coordination chemistry of the arylazo ligands containing oxygen and nitrogen donors
with transition metal atom is of particular interest with reference to their role in biological [1, 2]
and catalaytic processes [3-6]. The interest for these ligands is mainly based on the following
reasons, i.e., the azo group can stabilize the metal atom in lower oxidation states due to its π-
acidic character and because of this property, the ligands are able to form metal-carbon bonds [7]
and being a hard base, the oxygen donors stabilizes the higher oxidation states of the metal atom.
The arylazo ligands prepared from β-naphthol provide more steric crowd compared to the phenyl
group and these have not been used very often as ligands, only a few reports are available as
co-ligands [4, 6, 8, 9]. The selected ligands (HL1-5) are known bind to metal atom either as mono
anionic O, N donors Fig. 1 (I, II) or O, N, C donors Fig. 1 (III) by cyclometalation.
Fig.1.
Further the complexation of ruthenium by these type ligands is of significant interest,
largely because of their fascinating redox, photophysical, photochemical properties [10] and
catalytic applications [11]. It has been found in the literature that the arylazo phenol/naphthol
ligands are known to coordinate metal ion usually in a bidentate fashion with O, N donor or
tridentate mode with C, N, O donor forming either five or six-membered chelate rings [6, 12].
Furthermore, transition metal complexes of ruthenium have proved to be useful catalysts in many
reactions, such as oxidation, hydrogenation, carbonylation, hydroformylation and isomerization,
by virtue of the accessibility of ruthenium in different oxidation states and ease of coordination
with different ligands.

ACCEPTED MANUSCRIPT
Amides are an important class of chemicals that have widely been used as chemical
intermediates in organic synthesis. The conversion of carbonyl compounds such as aldehydes,
ketones, and oximes is a good candidate for the synthesis of amides. The rearrangement of
aldoximes into amides has been reported using transition metal catalysts containing Ni, Cu, Pd,
Ir and Rh [13]. Crabtree et al reported the ruthenium precursor complex [RuCl2(DMSO)4] was
used as catalyst for the conversion aldehydes to primary amides [14]. As reported in the earlier
literature, ruthenium azo complexes have been extensively used as catalysts for transfer
hydrogenation reactions [2]. To the best of our knowledge, only one report is available on
ruthenium(II) complexes containing thiazolylazo ligands catalyzing aldehyde to amide
conversions. As the source of ruthenium, we have selected the [RuCl2(DMSO)4] precursor
complex, because of its demonstrated ability to accommodate more than one or two bidentate
ligands through the displacement of dimethylsulfoxide and chlorides.
In view of rich interest to understand the coordination mode of arylazo ligands towards
ruthenium, we have synthesized a number of ruthenium(III) complexes containing 1-(arylazo)
naphtholate ligands. The molecular and electronic structure of the ruthenium(III) complexes is
established with help of spectral methods, X-ray diffraction analysis and DFT calculations.
Further, the catalytic efficiency of these ruthenium(III) complexes have been examined for the
conversion of aldehydes to primary amides.
2. EXPERIMENTAL PROCEDURES
2.1. Materials
Commercial RuCl3.3H2O was purchased from Himedia. All the used reagents were
chemically pure or analytical reagent grade. Solvents were purified and dried according to

ACCEPTED MANUSCRIPT
standard procedures. β-naphthol and primary amines were purchased from S.D. Fine-Chem
Limited, India. The supporting electrolyte tetrabutyl ammonium perchlorate (n-Bu4NClO4) was
dried in vacuum prior to use. [RuCl2(DMSO)4] was synthesized by a reported procedure [15].
The azo naphthol ligands were prepared by coupling diazotized aniline and p-substituted aniline
with β-naphthol [16].
The analysis of carbon, hydrogen, and nitrogen were performed in Carlo Erba 1106-
model 240 Perkin Elmer analyzer at Sophisticated Test and Instrumentation Centre (STIC),
Cochin University, Kochi, India. FT-IR spectra were recorded in KBr Pellets with a JASCO 400
plus spectrophotometer. JASCO V- 630 UV–visible Varian spectrophotometer was used to
record the electronic spectra. ESR spectra were recorded in the X-band frequency on a ESR-
JEOL/82 ESR spectrometer with a microwave power of 1 mW and a modulation amplitude of
160.00. Electrochemical measurements were made using an instrument model CHI608E
electrochemical analyzer. A three electrode cell was employed with glassy carbon working
electrode, a platinum wire counter electrode and an Ag/AgCl reference electrode were used in
the cyclic voltammetry experiments. All electrochemical experiments were performed under a
dinitrogen atmosphere. All electrochemical data were collected at 298 K and are uncorrected for
junction potentials.
2.2. Synthesis of ruthenium(III)1-(arylazo)naphtholate complexes
The complexes [Ru(L1–5)3] were synthesized from the reactions of [RuCl2(DMSO)4] with
the ligands L1–L5 by following a general procedure under anhydrous conditions.
1-(arylazo)naphthols (L1-L5) (0.256-0.328g; 1.0 mmol) was dissolved in ethanol (40
mL), and to it was added triethylamine (100 mg, 1.00 mmol). Then, [RuCl2(DMSO)4] (0.1g, 0.20

ACCEPTED MANUSCRIPT
mmol) was added to it. The mixture was then refluxed for 6h to yield a brown solution. The
solvent was evaporated, and the solid mass thus obtained was subjected to purification by thin-
layer chromatography on a silica plate. With benzene as eluant, a brown band separated, which
was extracted with same eluant. On evaporation of an eluant, brown coloured complexes are
obtained as solid form of >80% yield.
2.3. Typical procedure for the conversion of aldehyde to amides
Under an inert atmosphere a mixture containing aldehyde (1 mmol), NH2OH.HCl
(1 mmol), NaHCO3 (1 mmol) and ruthenium catalyst (0.01 mmol) and the mixture was heated to
reflux in toluene for appropriate period of time as mentioned. On completion of the reaction, 2–3
mL methanol was added to the mixture followed by filtration through Celite to remove the
catalyst and NaHCO3. The crude product was then purified by column chromatography
(MeOH/CH2Cl2) and the formation of pure amide was obtained.
2.4. X-ray crystallography
Single crystal of the ruthenium complex 5 (R= NO2) suitable for X–ray diffraction
analysis were obtained by slow diffusion of hexane in to chloroform solution of the complex at
room temperature. The X-ray diffraction data was collected on a Rigaku Saturn 724+ CCD
diffractometer with a Mo-Kα radiation source (l = 0.71075 Å) at 120 K. The data integration and
indexing were performed using Rigaku Crystalclear software [17] and numerical method was
employed to correct for absorption. All the calculations were carried out using the programs in
WinGX module [18] and the structure solution was solved by direct methods using SIR-92 [19].
The final refinement of the structure was carried out using full least-square methods on F2 using

ACCEPTED MANUSCRIPT
SHELX-2014 [20]. All non-hydrogen atoms were refined anisotropically. The hydrogen atoms
were refined isotropically as rigid atoms in their idealized locations.
2.5. Computational modeling and TD-DFT calculations
Quantum chemical calculations were performed using Gaussian 09 program [21]
Unrestricted B3LYP [22, 23] functional with a Los Alamos effective core potential double zeta
valence basis set (LANL2DZ) [24, 25] on Ru was used and 6-31G(d) basis set was used for rest
of the atoms. G-tensor values of all the complexes were obtained from the ORCA package [26]
with B3LYP functional. Time dependent density functional theory (TDDFT) implemented in the
Gaussian 09 program was used for the calculation of excitation energies for first 100 states.
3. RESULTS AND DISCUSSION
A series of ruthenium (III) complexes of the general formula [Ru(Ln)3] (n =1-5)
incorporating 1-(arylazo)naphthol ligands have been synthesized conveniently (scheme 1). These
ruthenium complexes were obtained as brown colored solids with up to 80% yield. The
elemental analysis (CHN) data of the complexes have been found to be in good agreement with
this general formula. All the ruthenium (III) complexes are found to be air-stable in both solid
and liquid states at room temperature is non-hygroscopic. It follows that all ligands act as
bidentate ligands via loss of naphtholic proton and azo nitrogen forming six membered chelate
rings. To observe the influence of the different substituents (R) in phenyl ring on the redox
potentials of the complexes, five 1-(arylazo)naphthols (L1-5) have been used. It is interesting to
note here that during the course of this synthesis, ruthenium undergoes a one-electron oxidation
and aerial oxygen seems to have served as the oxidizing agent.

ACCEPTED MANUSCRIPT
Scheme. 1.
The 1-(arylazo)naphthols usually bind to a metal ion, via dissociation of the naphtholic
proton, as bidentate O, N donors forming either five membered (I) or six-membered (II) chelate
rings [6, 8]. These ligands are also known to coordinate ruthenium metal ion as dianionic
tridentate C, N, O-donors (III) affording interesting cyclometallated complexes [6]. S. Halder et
al reported that in 2-(arylazo)phenol ligands (IV) the carbon-carbon coupling was occurred
between these two ligands linking the two ortho carbon atoms on the two phenyl rings in
ruthenium complexes is very unusual and unprecedented [12].
We were expecting to have similar carbon-carbon coupling may occur between two ortho
carbon atom of phenyl ring in the 1-(arylazo)naphtholate ligand in these ruthenium(III)
complexes, and we end up with tris-bidentate mode of coordination with O, N donors in these
ligands. It may be due to the bulky nature or steric congestion of naphthol group and prevents
from the carbon- carbon coupling between ortho-carbon of phenyl ring in these ligands.
3.1. Characterization
Infrared spectra of all the complexes show multiple bands of varying intensities within
the 4000-400 cm-1. No attempt has been made to assign each individual band to a specific
vibration. However, the infrared spectra of all the ligands exhibit bands around 1427-1438 cm-1
and 1272-1280 cm-1 corresponding to azo υ (N=N–) and phenolic υ(C–O) stretching frequencies
respectively. On complexation υ(N=N–) appears at lower frequency in the range 1386–1395 cm-1
and this red shift supports the coordination of N(azo) to ruthenium ion [27]. This supports the
assumption that the coordination of the nitrogen atom can reduce the electron density in the azo

ACCEPTED MANUSCRIPT
frequency due to the (d-π) Ru(III)-π* (L) back bonding effect [27b]. The band corresponding to
phenolic υ(C–O) stretching is shifted to higher frequency in the range 1279–1293 cm-1 in all the
complexes confirming that the other coordination site is the phenolic oxygen [4, 6]. This was
further supported by disappearance of υ(OH) band in the range 3430-3450 cm-1 in all the
complexes.
Electronic spectra of these complexes have been recorded in dichloromethane solution.
Each complex shows intense absorptions in the ultraviolet and visible region. The absorptions in
the ultraviolet region are believed to be due to transitions within the ligand orbitals. The selected
electronic spectrum is shown in Figs. S1-S5 and spectral data are displaced in Table S6. The
absorption observed in the region 450– 470 nm have been assigned to charge transfer LMCT
transitions taking place from the highest occupied molecular orbital (HOMO) of the ligand to the
singly lowest unoccupied molecular orbital (LOMO) of ruthenium. The bands in the regions at
370–385 nm are due to n–π* transition of non-bonding electrons present on the nitrogen of the
arylazo group in the ruthenium(III) complexes. The band observed around 220–230 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) ion similar
to that of other ruthenium(III) octahedral complexes [28, 30].
The solid state EPR spectra of all the complexes were recorded in X-band frequencies at
room temperature. All the complexes exhibit well-defined single isotropic feature near giso = 2.0
complexes 1-5; = 2.02-2.06). 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 these complexes have been recorded in 1:1
dichloromethane / toluene solution at 77 K. Each complex shows a rhombic spectrum with three

ACCEPTED MANUSCRIPT
distinct ‘g’ values (gx ≠ gy ≠ gz). A selected spectrum is shown in Fig. 2 (Figs. S6-S11) and
spectral data for all the complexes are given in Table 1. The rhombicity of the spectra reflects
asymmetry of the electronic environment around ruthenium in these complexes [31]. These
complexes are significantly distorted from the ideal octahedral geometry.
Fig. 2.
Table 1
3.2. X-ray structure
In order to determine the coordination mode and geometry of the complexes, the
crystallization of the complex [Ru(L5)3] (5) was performed by slow diffusion of hexane into
chloroform. The summary of single crystal X-ray structures and refinement is shown in Table 2
and selected bond lengths and bond angles are given in Table 3. The Ball and Stick model of the
complex(5) is shown in Fig. 3. The molecular structure shows that the 1-(arylazo)naphtholate
ligands are coordinated to ruthenium ion via dissociation of the phenolic proton of the naphthyl
ring in the arylazo fragment as a bidentate O, N donor ligand forming six membered chelating
rings with bite angle of 87.73(3)o O(7)-Ru(1)-N(1), 122.63(16)o Ru(1)-O(7)-C(8) and
124.54(19)o N(1)-Ru(1)-N(2) and bond lengths of 1.9934(2) Å Ru(1)-O(7), 2.0800(3) Å Ru(1)-
N(1) and 1.3054(1) Å O(7)-C(8). The N–N distance is 1.2909(1) Å and is longer than the free
azo bond length (1.25 Å) [32]. The increase in bond length is undoubtedly because of
coordination of N(azo) that can lead to a decrease in the N–N bond order due to both σ- and π-
acceptor character of the ligands, the latter character having a more pronounced effect and may
be the reason for elongation [33]. This is an indication of metal–ligand π-interaction localized in
the M-azo fragment. A six membered ring planar with the naphtholate ligand which is generated

ACCEPTED MANUSCRIPT
by the two carbon atom from the naphtholate group, the two nitrogen atoms from the coordinated
diazo group, the oxygen atom from the phenolic group and ruthenium. Comparing the crystal
data with the one reported by S. Halder et al [12] most of the bond angles of the crystal [Ru(L5)3]
were larger due to the increased congestion around the ruthenium center. This is further supports
why carbon-carbon coupling was not takes place between the phenyl rings of the two ligand
fragment in these complexes. As all the complexes display similar spectral properties, the other
four complexes are assumed to have similar structure to that of complex 5.
Fig. 3.
Table 2
Table 3
3.3. Redox behavior
To get an idea regarding the oxidation and reduction process, the complexes have been
studied by cyclic voltammetry in acetonitrile solution. All the complexes (1x10-3M) are
electroactive with respect to the metal centers and exhibited two redox processes in the potential
range +1.5 V to -1.5 V (0.05 M tetrabutyl ammonium perchlorate as supporting electrolyte at
298 K). Each complex shows an oxidative response on the positive side of SCE and a reductive
response on the negative side. The complexes display a reversible oxidative (RuIV/ RuIII) and
reversible reductive (RuIII/ RuII) responses on the positive and negative side of SCE, respectively
at the scan rate of 100 mVs-1. All the complexes showed well-defined waves E1/2 lies at +0.39 to
+0.67V (RuIV/ RuIII) and -0.65 to -0.22V (RuIII/ RuII). The potentials are summarized in Table 4
and a representative voltammogram is shown in Fig. 4 which remains unchanged upon changing
the scan rate, and the ipa is almost equal to the ipc as is expected for a reversible electron-transfer

ACCEPTED MANUSCRIPT
process. Potential of the RuIII/ RuIV oxidation and RuIII/ RuII reduction in all the complexes has
been found to be sensitive to the nature of the substituent (R) in the phenyl ring of the arylazo
fragment. The potential increases with increasing electron-withdrawing character of the
substituent (R). The half-wave potentials (E1/2) moves to negative value with electron donating
substituent(s) in the aryl ring and reverse movement is observed for electron withdrawing group.
The plot of formal potentials E1/2 versus σ [34] (σ =Hammett para substituent constant of R;
OCH3 = -0.27, CH3 = -0.17, H = 0.00, Br = 0.23, and NO2 = 0.78) is found to be linear for both
the couples Fig. 5. This linear correlation of the redox potentials with the electronic nature (σ) of
the substituents (R) with reasonable slopes (ρ) clearly shows that a single substituent on the
1-(arylazo)naphtholate ligand, which is several bonds away from the electro active metal center,
can still influence the metal-centered redox potentials in a predictable manner. Hence, it is
inferred from the electrochemical data that the present 1-(arylazo)naphtholate ligand system is
suitable for stabilizing higher oxidation state of ruthenium and the electron transfer reaction
takes place without gross changes in the stereo-chemistry of the complexes.
Fig. 4.
Fig. 5.
Table 4
3.4. Electronic Structure of 1, 3 & 5
To probe the influence of different substituents on the phenyl arylazo fragment, detailed
electronic structural calculations were carried out on the ruthenium (III) 1-(arylazo)naphtholate
complex (1) with the substitution of OMe and NO2 on the para position of phenyl ring of arylazo
fragment (3 & 5). Preliminary geometrical information of complex 5 is obtained from X-ray
crystallized coordinates Fig. 3. Ruthenium (III) 1-(arylazo)naphtholate complexes is found to

ACCEPTED MANUSCRIPT
2 0
possess the doublet spin ground state with the fundamental (dxy)2(dxzdyz)3(dz ) (dx2-y2)0 electronic
configuration [35]. This is also consistent with the spin density plot of 1, 3 & 5 Fig. 6 which
shows that the presence of one unpaired electron is strongly delocalized on the ruthenium center
especially on the dyz orbital and slightly on the coordinated nitrogen and oxygen atoms. From the
same values of Mulliken spin density of 1, 3 & 5, these complexes were found to have similar
kind of electronic properties irrespective of the presence of different substituents on the para
position of the phenyl group of arylazo fragments.
Fig. 6.
Notable structural parameters obtained from X-ray crystallographic coordinates of 5
along with DFT optimized geometries of 1, 3 & 5 were collected in Table 5. It is clearly
envisaged from the table, there is a progressive change in the specific structural parameters upon
substituting the electron donating NO2 group in 5 and the electron withdrawing OMe group in 3.
From the Table 5, the bond length of (Ru1-N8, Ru1-O2), and the bond angles (O2-Ru1-O4, N8-
Ru1-O3) of complex 5 is largely deviated from the other two complexes 1 and 3. This shows that
influence of strong electron withdrawing NO2 group on the phenyl group of arylazo fragment.
Further, structural parameters of 5 obtained from the DFT calculations are in close agreement
with the X-ray crystal geometrical parameters are summarized in Table S11. Upon comparison
of both DFT structural parameters of 1, 3 and 5 along with available X-ray structural parameters
of 5, the Ru-N(-O) bond lengths and the bond angles are deviated from the ideal octahedral
geometrical parameters. This is clearly indicates that all the three complexes (1, 3 & 5) possess a
distorted octahedral coordination sphere.

ACCEPTED MANUSCRIPT
Further, we would like to emphasis the bonding nature of three complexes with a view to
understand the stabilization of their metal orbitals with respect to different substituents on the on
the para position of phenyl ring of arylazo fragment. The ground state electronic configuration
2 0
2
of these complexes is found to be (dxy)2 (dxz)2(dyz)1 (dz ) (dx -y2)0 Key metal-ligand orbitals of
3 and 5 along with left and right side of the complex 1 are presented in Fig. 7. The relative eigen-
values are presented in eV with respect to lowest energy dxy orbital. Complex 1 is found to have
energy gap between singly occupied dyz molecular orbital (SOMO) and lowest unoccupied metal
orbital (dz2, LUMO) is about 4.72 eV whereas complexes 3 and 5 possess 4.69 eV and 4.86 eV
respectively. The stabilization of all the metal orbitals with respect to complex is also provided in
the Fig. 7. The stabilization of all the metal orbitals in 5 with respect to 1 is in the range of 0.17
to 0.31 eV whereas complex 3 possess 0.07 to 0.22 eV. From this one can understand the
influence of electron donating nature of substituent OMe which reduces the energy gap between
SOMO and LUMO thereby destabilizing all the metal centered orbitals. Whereas in the case of
5, strong electron withdrawing nature of nitro group stabilizes all the metal center orbitals
eventually increases the energy gap between SOMO and LUMO orbitals. This will dramatically
influence in the reactivity of the particular complexes. Hence complex 3 is found to have better
catalytic ability whereas complex 5 is found to have a moderate reactivity upon conversion of
aldehydes to amides.
Fig. 7.

ACCEPTED MANUSCRIPT
3.5. Spectroscopic Properties of 1, 3 and 5
To facilitate the interpretation of the experimental spectroscopic data and gain further
insight into the electronic structure of 1, 3 & 5, absorption spectra and the spin Hamiltonian
parameters for these complexes were computed.
3.5.1. TD-DFT and g-tensor analysis
In order to rationalize the electronic structure of 5 and also to facilitate the interpretation
of the experimental spectroscopic data, the TD-DFT absorption spectra for 1, 3 and 5 were
computed. TD-DFT computed absorption bands along with oscillator strength (f) and nature of
electronic transitions of all the three complexes Table 5 were found to exhibits a set of
absorption bands ranging from the 420 nm to 521 nm. These most intense computed absorption
bands are largely derives from the ligands to metal charge transfer transition (LMCT). This is in
good agreement with the experimental absorption spectrum of 5 where an intense LMCT band
appears in the region of 450-470 nm. Analysis of Natural Transition Orbitals (NTO) of most
intense transition bands of three complexes in Fig. 8 clearly shows that these transitions
originated from the LMCT.
Fig. 8.
Table 5
The calculated g-tensor values of three complexes are collected in Table 5. Complexes 1,
3 and 5 found to possess a three distinct ‘g’ values. This shows that all the three complexes said
to have a rhombic spectrum. Distorted octahedral geometry of these complexes clearly envisaged

ACCEPTED MANUSCRIPT
from the rhombicity of the g-tensor values. The calculated g-tensor values are in good agreement
with experimental values.
3.6. Catalytic conversion of aldehydes to amides
The scope of our catalytic system is applicable to aromatic, conjugated and heterocyclic
aromatic aldehydes. These aldehydes were converted to their corresponding amides in good yield
at one pot process and the results are summarized in Table 6. On screening different
catalyst/substrate ratios (1:100, 1:500, 1:1000), 1:100 was found to be the optimum ratio of
catalyst/substrate, with the maximum yield of 86%. Benzaldehyde was used as substrate and
complex(1) was used as catalyst for the optimization in the presence of NH2OH.HCl /NaHCO3.
The effect of solvents (toluene, benzene, dichloromethane and methanol etc.,) was studied for the
optimization, and toluene is found to be the best solvent for the conversion of benzaldehyde to
benzamide.
Comparison of the catalysts reveal that catalyst [Ru(L3)3](3) has a better performance for
both benzaldehyde and furan-2-aldehyde, implicating a good yield of 84% and 87%. The
conversion obtained by using catalyst 4 and 5 was lower to the other catalysts indicating that the
substituent (R) in the phenyl ring of arylazo fragment may play a significant role in these
conversions. The catalytic activity of the catalysts 1-3 is similar (81-87%) for the conversion of
furan-2-aldehyde to furan-2-amide. The conjugated aldehyde such as, cinnamaldehyde which
was converted to the corresponding amide in good yield (81-83%).
Table 6

ACCEPTED MANUSCRIPT
All the substrate aldehydes were smoothly converted to the corresponding amides in good
yields. Our observation in this catalytic aldehyde to amide conversion is comparable with that of
a recent observation using [RuCl2(DMSO)4] complex as catalyst [14]. It is interesting to note that
this ruthenium(III) 1-(arylazo)naphtholate complexes efficient by catalyze the aldehyde to amide
up to 87% yield. The obtained results revealed that the naphthol group plays a significant role in
the aldehyde to amide conversion depends on the steric and electronic environment of the
ruthenium. So, the prospective of these complexes as catalysts in the field of aldehydes to amide
conversion can be further improved by fine-tuning of the ligand environment on ruthenium. As
for as we know only few catalytic system on ruthenium [3, 36] have been reported to support the
aldehyde to amide conversion, catalyst like ruthenium(III) 1-(arylazo)naphtholate complexes is
new and novel for its tris-bidentate O, N-donor environment.
4. Conclusion
The present work describes the simple and convenient route to synthesize a new family of
ruthenium(III) complexes incorporating O, N donors of 1-(arylazo)naphtholate ligands. The X-
ray crystal structure of the complex (5) reveals on octahedral environment around ruthenium.
The influence of substituents (R) present in the phenyl ring of 1-(arylazo)naphtholate ligand on
metal center is studied by cyclic voltammetry. The electronic structure and bonding of 1, 3 and
crystallized geometry of complex 5 were investigated by DFT calculations. These ruthenium
complexes have been tested as catalyst for the conversion of aldehyde to amides. The obtained
results imply that the present catalyst system exploring a promising application of new family of
ruthenium(III)1-(arylazo)naphtholate complexes. Based on the computed energy levels of

ACCEPTED MANUSCRIPT
occupied and unoccupied metal orbitals of these three complexes, the effects of different
substituents on the catalytic activity of these complexes were also illustrated.
ACKNOWLEDGEMENTS
The authors are thankful to Professor R. Murugavel for allowing us to use single crystal
X-ray diffraction facility established through a DAE-SRC outstanding investigator award. MJ
thanks the Department of Science and Technology, New Delhi, India, for financial support
through the DST Inspire Faculty Fellowship (Ref. No: IFA3133CH3100) and FAST TRACK
Young Scientist Award (DST SERB Ref. No. CS3353/2013 dated December 11, 2013). MJ
would like to thank Loyola Institute of Frontier Energy (LIFE) for their constant support and
encouragement.
Appendix A. Supplementary material
UV-vis spectra of complexes (Figs. S1-S5), representative EPR spectra of the complexes
(Figs. S7-S11) and optimized structure of complex 5 (Table. S6). CCDC reference number
1438173 for complex 5.

ACCEPTED MANUSCRIPT
REFERENCES
[1] K. N. Kumar, R. Ramesh, Y. Liu, J. Mol. Catal A: Chem. 265 (2007) 218–226.
[2] G. Venkatachalam, R. Ramesh, S. M. Mobin, J. Organomet. Chem. 690 (2005) 3937–3945.
[3] N. Raja, M. U. Raja, R. Ramesh, Inorg. Chem. Commun. 19 (2012) 51–54.
[4] F. Ding, Y. Sun, F. Verpoort, Eur. J. Inorg. Chem. (2010) 1536–1543.
[5] P. Pattanayak, S. P. Parua, D. Patra, C. K. Lai, P. Brandao, V. Felix, S. Chattopadhyay
Inorg. Chim. Acta. 429 (2015) 122–131.
[6] S. Kannan, R. Ramesh, Y. Liu, J. Organomet. Chem.692 (2007) 3380–3391.
[7] I. Omae, Chem. Rev. 79 (1979) 287.
[8] K. Suia, S. M. Peng, S. Bhattacharya, Polyhedron 18 (1999) 631–640.
[9] R. K. Rath, M. Nethaji, A. R. Chakravarty, J. Organomet. Chem. 633 (2001) 79–84.
[10] (a) M. J. Clarke, Coord. Chem. Rev. 232 (2002) 69-93. (b) I. Ando, Coord. Chem. Rev. 248
(2004) 185-203. (c) Y. Saito, T. Azechi, T. kitamura, Y. Hasegawa, Y. Wada, S. Yanagida,
Coord. Chem. Rev. 248 (2004) 1469.
[11] (a) G. Venkatachalam, R. Ramesh, Tetrahedron Lett., 46 (2005) 5215–5218. (b) K. N.
Kumar, G. Venkatachalam, R. Ramesh, Y. Liu. Polyhedron 27 (2008) 157–166. (c) M. U.
Raja, N. Raja and R. Ramesh. The Open Catal.3 (2010) 30-33.
[12] S. Halder, R. Acharyya, S. M. Peng, G. H. Lee, M. G. B. Drew, S. Bhattacharya. Inorg.
Chem. 45 (2006) 9654-9663.
[13] (a) L. Field, P. Barnett, S. H. Shumaker, W. S. Marshall, J. Am. Chem. Soc. 83 (1961)

ACCEPTED MANUSCRIPT
1983-1987. (b) S. K. Sharma, S. D. Bishop, C. L. Allen, R. Lawrence, M. J. Bamford, A. A.
Lapkin, P. Plucinski, R. J. Watson, J. M. J. Williams, Tetrahedron Lett., 52 (2011) 4252.
(c) N. Owston, A. J. Parker, J. M. J. Williams, Org. Lett. 9 (2007) 73-75. (d) S. Park, Y.
Choi, H. Han, S. H. Yang, S. Chang, Chem. Commun. (2003) 1936-1937.
[14] J. F. Hull, S. T. Hilton, R. H. Crabtree, Inorg. Chim. Acta. 363 (2010) 1243-1245.
[15] I. P. Evans, A. Spencer, G. Wilkinson, J. Chem. Soc. Dalton Trans. 204 (1973).
[16] A. I. Vogel, Text Book of Practical Org. Chem. 5th ed., Longman, London 1989.
[17] Crystal Clear, Version-SM Expert 2.0 r4, 2009 and Crystal Structure, Version 4.0, Rigaku,
2010, Rigaku Americas and Rigaku, The Woodlands, Texas, USA and Rigaku Corporation,
Tokyo, Japan.
[18] L. Farrugia, J. Appl. Crystallogr., 45 (2012) 849.
[19] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, J. Appl. Crystallogr, 26 (1993)
343.
[20] G. Sheldrick, ActaCrystallogr., Sect. C: Struct. Chem., 71 (2015) 3.
[21] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb,J. R. Cheeseman, G.
Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P.
Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T.
Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E.
Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A.
Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene,
J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,
O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. Ochterski, R. L. Martin, K. Morokuma,

ACCEPTED MANUSCRIPT
V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels,
O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski and D. J. Fox, GAUSSIAN 09,
(Revision D01) , Gaussian, Inc., Wallingford, CT, 2009.
[22] C. Lee, W. Yang and R. G. Parr, Phys. Rev. 37 (1988) 785–789.
[23] D. Becke, J. Chem. Phys., 98 (1993) 5648 – 5652.
[24] P. J. Hay and W. R. Wadt, J. Chem. Phys., 82 (1985) 299 – 310.
[25] W. R. Wadt and P. J. Hay, J. Chem. Phys., 82 (1985) 284–298.
[26] F. Neese, Density Functional and Semiempirical Program Package, version 2.8, University
of Bonn, Bonn, Germany, 2009.
[27] (a) S. Goswami, R. Mukherjee, A. Chakravorty, Inorg. Chem. 22 (1983) 2825-2832.(b) B.
Mondal, M. G. Walwalker, G. K. Lahiri, J. Chem. Soc. Dalton Trans., (2000) 4209-4217.
[28] A. B. P. Lever, Inorganic Electronic Spectroscopy, second ed., Elsevier, New York, 1984.
[29] M. M. T. Khan, D. Srinivas, R. I. Khureshy, N. H. Khan, Inorg. Chem.29 (1990) 2320-
2326.
[30] S. Pal, S. Pal, Eur. J. Inorg. Chem. (2003) 4244-4252.
[31] N. C. Pramanik, S. Bhattacharya, Polyhedron 16 (1997) 3047-3053.
[32] S. Pal, T. K. Misra, C. Sinha, A. M. Z. Slawin, J. D. Woollins, Polyhedron 19 (2000)
1925-1933.
[33] T. K. Misra, D. Das, C. Sinha, P. Ghosh, C. K. Pal, Inorg. Chem. 37 (1998) 1672-1678.
[34] L. P. Hammett, Physical Organic Chemistry, 2nd ed. McGraw-Hill: New York, 1970.
[35] J. B. Michał, L.-G. Lechosław, Inorg. Chem. 55 (2016) 1758-1769.
[36] G. Prakash, P. Viswanathamurthi, Spectrochim. Acta, Part A. 129 (2014) 352–358.

ACCEPTED MANUSCRIPT
Table 1 EPR data of ruthenium(III) 1-(arylazo)naphtholate complexes.
Complexes
gx
gy
gz
1
2
3
4
5
2.20
2.19
2.23
2.21
2.19
2.08
2.06
2.09
2.04
2.09
1.91
1.92
1.96
1.92
1.93
_______________________________________________________

ACCEPTED MANUSCRIPT
Table 2 Crystal data and structure refinement for complex 5.
____________________________________________________________________________
Empirical formula
Formula weight
C48H30N9O9Ru
977.88
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
120
0.71075
Triclinic
P -1
11.8392(13)
14.199(2)
14.286(2)
85.758(12)
68.297(9)
66.961(8)
2046.3(5)
2
b (Å)
c (Å)
α (˚)
β (˚)
γ (˚)
Volume (Å3)
Z
Density Cacld. (g cm-3)
ꢀ (mm-1)
1.587
0.457
F(000)
994.0
Crystal size (mm3)
θ range (°)
Reflections collected
R indices (all data)
0.12 X 0.16 X 0.28
2.882 to 24.999
7117
R1= 0.0315
wR2 = 0.0355
6568/0/604
1.0201
Data/restraints/parameters
Goodness-of-fit on F2
Largest difference in peak and hole 0.306 and -0.536 (eA˚ -3)
______________________________________________________________________________

ACCEPTED MANUSCRIPT
Table 3 Selected bond length (A˚) and angle (˚) for complex 5.
Bond Length (A˚)
Bond angle (˚)
O7- Ru1- O8
O7- Ru1- O9
O7- Ru1- N1
O7- Ru1- N4
O7- Ru1- N6
O8- Ru1- O9
O8- Ru1- N1
O8- Ru1- N4
O8- Ru1- N6
O9- Ru1- N1
O9- Ru1- N4
O9- Ru1- N6
N1- Ru1- N4
N1- Ru1- N6
N4- Ru1- N6
Ru1- O7- C8
Ru1- O8C-48
Ru1- O9C-32
Ru1- N1- N2
Ru1- N1- C1
N2- N1- C1
91.81
176.12
87.73
93.62
91.99
86.13
81.66
174.57
88.38
95.22
88.44
84.66
98.65
170.03
91.32
122.63
122.88
120.34
124.54
123.78
110.52
Ru1-O7 1.9934(2)
Ru1-O8 2.0136(3)
Ru1-O9 1.9901(2)
Ru1-N1 2.0800(3)
Ru1-N4 2.0164(3)
Ru1-N6 2.0403(3)
O1-N7 1.2309(1)
O2-N7 1.2245(2)
O3-N8 1.2239(2)
O4-N8 1.2249(2)
O5-N9 1.2319(1)
O6-N9 1.2257(1)
O7-C8 1.3054(1)
O8-C48 1.2919(2)
O9-C32 1.3076(1)
N1-N2 1.2909(1)

ACCEPTED MANUSCRIPT
Table 4 Electrochemical data of the ruthenium(III)1-(arylazo)naphtholate complexes.
___________________________________________________________________________
Complexes
RuIV/RuIII
RuIII/RuII
________________________________ _________________________________
Epa (V) Epc (V) E1/2 (V) ∆Ep (mV) Epa (V) Epc (V) E1/2 (V) ∆Ep(mV)
____________________________________________________________________________
1
2
3
4
5
+0.532 +0.453 +0.492
+0.456 +0.374 +0.415
+0.431 +0.359 +0.395
+0.585 +0.500 +0.542
+0.703 +0.637 +0.670
79
82
72
85
66
‒0.633 ‒0.556 ‒0.594
‒0.678 ‒0.585 ‒0.632
‒0.683 ‒0.625 ‒0.654
‒0.495 ‒0.429 ‒0.462
‒0.250 ‒0.192 ‒0.221
77
93
58
66
58
__________________________________________________________________________
Supporting electrolyte: NBu4ClO4 (0.005 M); complex: 0.001 M; solvent: CH3CN; ∆Ep = Epa-
Epc where Epa and Epc are anodic and cathodic potentials respectively; E1/2 = 0.5(Epa + Epc);
scan rate: 100 mV s-1.

ACCEPTED MANUSCRIPT
Table 5 TD-DFT (B3LYP/SCRF-PCM/DCM) Calculated Electronic Transitions for 5.
λ/nm
515.7
f
Transitions
Complex 1
0.025 HOMO-2 (α) ꢀ LUMO+2 (α) (69%)
HOMO-2 (β) ꢀ LUMO+3 (β) (54%)
0.058 HOMO-3 (α) ꢀ LUMO (α) (45%)
HOMO (α) ꢀ LUMO+4 (α) (22%)
0.095 HOMO-1 (α) ꢀ LUMO (α) (23%)
HOMO-3 (α) ꢀ LUMO+2 (α) (19%)
HOMO-1 (β) ꢀ LUMO+2 (β) (17%)
0.050 HOMO-1 (α) ꢀ LUMO (α) (23%)
HOMO-2 (β) ꢀ LUMO+2 (β) (26%)
HOMO-5 (β) ꢀ LUMO+1 (β) (17%)
Complex 3
500.9
487.8
485.3
506.7
486.9
477.9
0.086 HOMO-11 (β) ꢀ LUMO (β) (42%)
HOMO-3 (β) ꢀ LUMO+1 (β) (42%)
0.097 HOMO-2 (α) ꢀ LUMO (α) (34%)
HOMO-3 (β) ꢀ LUMO+1 (β) (37%)
0.056 HOMO (α) ꢀ LUMO+1 (α) (20%)
HOMO-11 (β) ꢀ LUMO (β) (35%)
0.184 HOMO-2 (α) ꢀ LUMO+2 (α) (79%)
0.141 HOMO-2 (β) ꢀ LUMO+3 (β) (95%)
Complex 5
445.8
420.9
520.6
462.1
457.4
447.5
0.198 HOMO-1 (α) ꢀ LUMO+1 (α) (46%)
HOMO-1 (β) ꢀ LUMO+2 (β) (41%)
0.094 HOMO-2 (α) ꢀ LUMO+2 (α) (69%)
HOMO-2 (β) ꢀ LUMO+3 (β) (54%)
0.082 HOMO-3 (α) ꢀ LUMO (α) (44%)
HOMO (α) ꢀ LUMO+4 (α) (22%)
0.075 HOMO-4 (β) ꢀ LUMO+1 (β)
(58%)HOMO-10 (β) ꢀ LUMO (β)
(18%)
443.9
0.096 HOMO-3 (α) ꢀ LUMO+1 (α) (17%)
HOMO-4 (α) ꢀ LUMO+2 (α) (37%)
g-tensor
gxx
gyy
gzz
1
3
5
2.17
2.16
2.07
2.08
1.99
1.99

ACCEPTED MANUSCRIPT
Table 6 One pot conversion of aldehyde to amide using [Ru(Ln)3] (1-5).
Complexes
Aldehydesa
Amides
Yieldsb (%)
1
Benzaldehyde
Furan2-carbaldehyde
Cinnamaldehyde
Benzamide
Furan2-amide
Cinnamide
77
86
81
2
3
4
5
Benzaldehyde
Furan2-carbaldehyde
Cinnamaldehyde
Benzamide
Furan2-amide
Cinnamide
66
81
80
Benzaldehyde
Furan2-carbaldehyde
Cinnamaldehyde
Benzamide
Furan2-amide
Cinnamide
84
87
83
Benzaldehyde
Furan2-carbaldehyde
Cinnamaldehyde
Benzamide
Furan2-amide
Cinnamide
76
65
77
Benzaldehyde
Furan2-carbaldehyde
Cinnamaldehyde
Benzamide
Furan2-amide
Cinnamide
69
78
75
a Aldehyde 1 mmol, NH2OH.HCl (1 mmol) and catalyst (1 mol%) were refluxed
for18 h in toluene.
b Isolated yield after column chromatography.

ACCEPTED MANUSCRIPT
Table and Figure Captions
Table 1 EPR data of ruthenium(III) 1-(arylazo)naphtholate complexes.
Table 2 Crystal data and structure refinement for complex 5.
Table 3 Selected bond length (A˚) and angle (˚) for complex 5.
Table 4 Electrochemical data of the ruthenium(III)1-(arylazo)naphtholate complexes.
Table 5 TD-DFT (B3LYP/SCRF-PCM/DCM) Calculated Electronic Transitions for 5.
Table 6 One pot conversion of aldehyde to amide using [Ru(Ln)3] (1-5).
Fig. 1. Coordination modes of arylazo ligands.
Scheme 1. Preparation of new Ru(III) complexes.
Fig. 2. EPR spectrum of the ruthenium complex (5) in CH2Cl2/ Toluene.
Fig. 3. The ball and stick diagram of the complex [Ru(L5)3] (5).
Fig. 4. Cyclic voltammogram of the complexes (1-5).
Fig. 5. Least-squares plot of (i) E1/2 values of oxidation (RuIV/RuIII) and (ii) E1/2values of
reduction (RuIII/RuII) potentials of complexes.
Fig. 6. X-ray crystallized (Compound 5) and DFT optimized geometry of 1, 3 & 5 along with the
computed spin densities.
Fig. 7. Computed high-lying occupied and low-lying unoccupied Metal orbitals of 1, 3 and 5 and
their relative energies in eV with respect to lowest energy MO.
Fig. 8. Natural Transition Orbitals (NTOs) of intense absorption bands for complexes 1, 3 and 5
shown on occupied (holes) and unoccupied (electrons) NTO pairs.