Versatile formation of Ru(II) hydrazone complexes: Structure, theoretical studies and catalytic activity in α-alkylation

Article abstract of DOI:10.1016/j.poly.2020.114737

New 1-(anthracen-10-yl)methylene)-2-(benzo[d]thiazol-2-yl)hydrazine (BHA) and 1-(anthracen-10-yl)methylene)-2-(quinolin-2-yl)hydrazine (QHA) ligands were reacted with [RuHCl(CO)(E)₃] (E = PPh₃ or AsPh₃) or [RuCl₂(AsPh₃)₃] in a 1:1 mol ratio in chloroform-ethanol medium to synthesis new ruthenium complexes. All the new ruthenium complexes were analyzed by elemental analysis, IR, NMR (¹H, ¹³C and ³¹P) spectroscopy, ESI-Mass spectrometry and single crystal XRD techniques. The single crystal XRD study reveals the octahedral geometry around the ruthenium ion. The study also shows that the ligands coordinate with the Ru metal as monoanionic bidentate N^N donors in complexes 1, 3 and 4 and as a neutral bidentate N^N donor in complex 2 by forming five or four member chelate rings. The intramolecular interactions in the crystal lattices were studied by Hirshfeld surface analysis. The results indicate that π-stacking contacts play an important role in the crystal lattices. DFT calculations were carried out to explain the solid structures of complexes 1–3. Moreover, the synthesized complexes were screened as catalysts for the α-alkylation of ketones with alcohols. The effect of various parameters, such as base, solvent, temperature, time, substituents and also catalyst loading, on the catalytic activity were analyzed. The results depict that the complex 3 was found to be an efficient catalyst for the synthesis of α-alkylation products.

Full text of DOI:10.1016/j.poly.2020.114737

Polyhedron 190 (2020) 114737
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Versatile formation of Ru(II) hydrazone complexes: Structure, theoretical
studies and catalytic activity in a-alkylation
⇑
Kaliyappan Murugan, Subbarayan Vijayapritha, Venkatachalam Kavitha, Periasamy Viswanathamurthi
Department of Chemistry, Periyar University, Salem 636 011, India
a r t i c l e i n f o
a b s t r a c t
Article history:
New 1-(anthracen-10-yl)methylene)-2-(benzo[d]thiazol-2-yl)hydrazine (BHA) and 1-(anthracen-10-yl)
methylene)-2-(quinolin-2-yl)hydrazine (QHA) ligands were reacted with [RuHCl(CO)(E)3] (E = PPh3 or
AsPh3) or [RuCl2(AsPh3)3] in a 1:1 mol ratio in chloroform-ethanol medium to synthesis new ruthenium
complexes. All the new ruthenium complexes were analyzed by elemental analysis, IR, NMR (1H, 13C
and 31P) spectroscopy, ESI-Mass spectrometry and single crystal XRD techniques. The single crystal XRD
study reveals the octahedral geometry around the ruthenium ion. The study also shows that the ligands
coordinate with the Ru metal as monoanionic bidentate N^N donors in complexes 1, 3 and 4 and as a neu-
tral bidentate N^N donor in complex 2 by forming five or four member chelate rings. The intramolecular
Received 19 March 2020
Accepted 1 August 2020
Available online 13 August 2020
Keywords:
Ru(II) hydrazone complexes
Crystal structure
Hirshfeld surface analysis
DFT calculations
interactions in the crystal lattices were studied by Hirshfeld surface analysis. The results indicate that p-
stacking contacts play an important role in the crystal lattices. DFT calculations were carried out to explain
a-Alkylation
the solid structures of complexes 1–3. Moreover, the synthesized complexes were screened as catalysts for
the
ature, time, substituents and also catalyst loading, on the catalytic activity were analyzed. The results
depict that the complex 3 was found to be an efficient catalyst for the synthesis of -alkylation products.
a-alkylation of ketones with alcohols. The effect of various parameters, such as base, solvent, temper-
a
Ó 2020 Elsevier Ltd. All rights reserved.
1. Introduction
In connection with the BH methodology, hitherto Ru and Ir
complexes have been used as the most effective catalysts for the
alkylation of ketones with alcohols [7]. Among the early reports,
The construction of carbon-carbon bonds by the a-alkylation of
ketones with alcohols, catalyzed by transition metal complexes, has
the RuCl2(PPh3)2 catalyst was reported for the a-alkylation of
occupied a special place in synthetic organic chemistry [1]. Conven-
ketones with primary alcohols by Cho et al [8]. In the reported cat-
tionally, a-alkylation reactions were carried out by the reaction of
alytic reaction, 1-dodecene was added as the hydrogen acceptor to
enolates or enamines obtained from ketones with carbon elec-
trophiles, such as alkyl halides [2,3]. However, a pre-functionaliza-
tion step and a stoichiometric excess amount of base, generating an
equivalent amount of salt as waste, were required for above nucle-
ophilic substitution [4]. These drawbacks prompted us to develop
an alternative protocol to achieve the same objective. Borrowing-
hydrogen methodology (BH) is one of the methods has been given
attention in recent years for the alkylation of ketones catalyzed
by transition-metal catalysts [5]. Such reactions release water as
the only by-product and hence are environmentally benign, in addi-
tion to being highly atom economical [6]. In BH methodology, ini-
tially alcohols are converted into the corresponding carbonyl
compounds by oxidation, then unsaturated compounds are formed
by alkylation of the ketones. Finally borrowed hydrogen atoms from
alcohols are used for reduction of the CAC bonds.
arrest the formation of
tion of alkylated ketones. Yus et al proved RuCl2(DMSO)4 was an
efficient catalyst for the -alkylation of ketones with benzylic alco-
hols in the presence of a stoichiometric amount of base [9]. An effi-
cient catalytic system, [Ir(cod)Cl]2/PPh3/KOH, under solvent-free
a-alkylated alcohols via further hydrogena-
a
conditions was developed by Ishii et al to accomplish
[10]. More recently, Ryu’s group developed an efficient RuHCl(CO)
(PPh3)3/Cs2CO3 system for -alkylation of acetophenones [11,12].
a-alkylation
a
The alkylation of ketones with primary alcohols catalyzed by
ruthenium(II)/P,N ligand complexes was reported by Jiang et al.
[13]. Several P, N ligands were screened in this reaction to study
the steric hindrance and electronic effects. Smith et al [14]
described the ruthenium catalyzed
a-alkylation of ketones using
pyridyl methanol, in which there is no need for addition of hydro-
gen receptors or the use of a stoichiometric amount of base. Apart
from the homogeneous catalysts, several recyclable heterogeneous
catalyst systems have been developed and investigated extensively
in recent years [15].
⇑
Corresponding author.
E-mail address: viswanathamurthi@gmail.com (P. Viswanathamurthi).
https://doi.org/10.1016/j.poly.2020.114737
0277-5387/Ó 2020 Elsevier Ltd. All rights reserved.

2
K. Murugan et al. / Polyhedron 190 (2020) 114737
Generally, in development of transition metal catalysts for a
H, 4.34; N, 11.93; S, 9.13%. IR (ATR, cmÀ1): 3032 (
C = N). 1H NMR (400 MHZ, CDCl3, d, ppm): 9.09 (b, 1H, NH),
8.60 (s, 1H, HC = N), 8.31 (s, 1H, Ar-H), 8.10 (d, 2H, Ar-H), 7.98
(d, 2H, 8 Hz, Ar-H), 7.72 (d, 2H, 8 Hz, Ar-H), 7.57–7.55 (m, 5H,
Ar-H), 7.43 (d, 1H, 8 Hz, Ar-H), 7.17 (t, 1H, 8 Hz, Ar-H).
mNH), 1562
specific process, besides choosing the right metal ion, the design
of the ligand is also very important. Since the nature of the ligand
has a profound effect on the coordination chemistry of a metal
complex, the design and ‘‘tailoring” of the ligand properties can
lead to complexes with efficient homogeneous catalytic activities.
In this connection, Schiff-base ligands have gained significant
attention due to their rich coordination chemistry. In particular,
Schiff base ligands possess the main advantages like being easily
accessible under gentle conditions, readily facilitating adjustment
of their structures and chemo-physical properties through the
incorporation of some additional functional groups. On coordina-
tion of Schiff bases with metal ions, the resulting complexes exhi-
bit numerous applications in catalysts [16], pharmaceuticals [17]
and magnetic materials [18].
(m
2.2.2. 2-(2-(Anthracen-9-ylmethylene)hydrazinyl)quinoline (QHA)
This was prepared from 9-anthracenecarboxaldehyde (0.206 g,
1 mmol) and 2-hydrazinylquinoline (0.159 g, 1 mmol). Yield:
77%. Color: Yellow. M.p.: 195 °C. Anal. Calcd. for C24H17N3: C,
82.97; H, 4.93; N, 12.10. Found: C, 83.02; H, 4.98; N, 12.17%. IR
(ATR, cmÀ1): 3039 ( C = N). 1H NMR (400 MHZ, CDCl3,
mNH), 1608 (m
d, ppm): 9.02 (b, 1H, NH), 8.63 (d, 2H, 8.5 Hz Ar-H), 8.48 (s, 1H,
HC = N), 8.02 (d, 3H, Ar-H), 7.67 (d, 2H, Ar-H), 7.56–7.48 (m, 7H),
7.31(s, 1H, Ar-H).
Given such considerations and inspired by the high activity of
Ru(II) complexes in
a-alkylation reactions, in addition to our sys-
2.3. General procedure for the synthesis of the ruthenium complexes
tematic investigation to find effective homogeneous catalysts
[19,20], herein we report the design and synthesis of hydrazone
Schiff base ligands and their ruthenium(II) complexes. The coordi-
nation modes of the ligands with ruthenium metal were investi-
gated using FT-IR, NMR (1H, 13C and 31P) spectroscopy and mass
spectrometry. The solid-state structures of the complexes were
established by single-crystal X-ray diffraction. The catalytic prop-
(1–4)
All the complexes were synthesized by the following general
procedure. [RuHCl(CO)(E)3] (E = PPh3 or AsPh3) or [RuCl2(AsPh3)3]
(0.1 mmol) was reacted under reflux with 1-(anthracen-10-yl)
methylene)-2-(benzo[d]thiazol-2-yl)hydrazine (BHA) (0.1 mmol)
or
1-((anthracen-10-yl)methylene)-2-(quinolin-2-yl)hydrazine
erties of the new complexes were screened for the
of ketones with alcohols.
a-alkylation
(QHA) (0.1 mmol) in a chloroform-ethanol (20 mL, 1:1 v/v) mixture
for 8 h under reflux. Initially an orange color was formed, which
gradually changed to red. The completion of the reaction was con-
firmed by thin layer chromatography (TLC) and the solvent was
evaporated in a rotavapor to obtain the crude product. The crude
product was then purified by column chromatography using the
eluents petroleum ether and ethyl acetate (9:1, v/v).
2. Experimental
2.1. Materials and instrumentation
All the reagents used were of Analar grade. RuCl3ÁxH2O, anthra-
cene 9-carbaldehyde, mercaptobenzothiazole and 2-chloro quino-
line were purchased from Sigma Aldrich. Solvents were dried by
the reported procedures [21]. Elemental analyses were performed
using a Vario EL III elemental analyzer. The IR spectra of the ligands
and the complexes were recorded with a Bruker-alpha instrument
in the 4000–600 cmÀ1 range. NMR (1H, 13C and 31P) spectra were
measured in CDCl3 with a Varian AMX 400 instrument using
tetramethyl silane (1H, 13C) or o-phosphoric acid (31P) as an inter-
nal standard. Electro spray ionization mass spectra were measured
using a liquid chromatography mass spectrometry quadrupole
time-of-flight Micro Analyzer (Shimadzu) at the Indian Institute
of Technology, Chennai. Column chromatography purifications
were performed for the complexes using silica mesh 100–200
mesh. Melting points were recorded on a Lab India melting point
apparatus. The starting precursors [RuHCl(CO)(PPh3)3], [RuHCl
(CO)(AsPh3)3] and [RuCl2(AsPh3)3] were prepared according to
the published literatures [22–24].
2.3.1. [(BHA)RuH(CO)(PPh3)2] (1)
The ligand BHA (0.035 g, 0.1 mmol) was reacted with [RuHCl
(CO)(PPh3)3] (0.095 g, 0.1 mmol) to form complex 1. Yield: 80%.
M.p.: 162 °C. Anal. Calcd for C59H45N3SOP2Ru: C, 70.36; H, 4.50;
N, 4.17; S, 3.18. Found: C, 70.25; H, 4.46; N, 4.12; S, 3.12%. IR
(ATR, cmÀ1): 1900 ( C = N). 1H NMR (400 MHz, CDCl3,
mCO), 1573 (m
d, ppm): À13.44 (t, 1H, Ru-H), 8.61 (s, 1H, HC = N), 8.37–6.91 (m,
43H, Ar-H). 13C NMR (100 MHz, CDCl3, d, ppm): 200.89 (CO),
162.11 (C@N), 148.96 (N@C-N), 133.74–124.85 (Ar-C). 31P NMR
(162 MHz, CDCl3, d, ppm): 48.52. Calcd ESI-mass (m/z) for C59H45
-
N3OP2RuS: 1007.9. Found: 1008.1 [M + H]+. Crystals of complex 1
were grown by the diffusion method with chloroform and ethanol
solvents at room temperature.
2.3.2. [(BHA)RuCl2(AsPh3)2] (2)
The ligand BHA (0.035 g, 0.1 mmol) was reacted with
[RuCl2(AsPh3)3] (0.108 g, 0.1 mmol) to form complex 2. Yield:
75%. M.p.: 192 °C. Anal. Calc for C59H45N3SCl2As2Ru: C, 61.22; H,
3.99; N, 3.69; S, 2.82. Found: C, 61.15; H, 3.79; N, 3.62; S, 2.75%.
IR (ATR, cmÀ1): 3305 (
m NH), 1577 (m
C@N). 1H NMR (400 MHz,
2.2. General procedure for synthesis of the hydrazone ligands
CDCl3, d, ppm): 10.15 (s, 1H, NH), 8.61–6.51 (m, 43H, Ar-H), 8.42
(s, 1H, HC = N). 13C NMR (100 MHz, CDCl3, d, ppm): 162.65
(C@N), 148.03 (NACAN), 134.84–124.85 (Ar-C). Crystals of com-
plex 2 were grown by the diffusion method with chloroform and
ethanol solvents at room temperature.
The ligands were synthesized by the following general proce-
dure. 9-Anthracenecarboxaldehyde (1 mmol) was added to the
hydrazines (1 mmol) in ethanol (20 mL) and the reaction mixture
was subsequently refluxed for 6 h. After completion of the reaction,
a solid compound formed, which was filtered, washed with ether
and dried in air.
2.3.3. [(QHA)RuH(CO)(PPh3)2] (3)
The ligand QHA (0.034 g, 0.1 mmol) was reacted with [RuHCl
(CO)(PPh3)3] (0.095 g, 0.1 mmol) to form complex 3. Yield: 72%.
M.p.: 210 °C. Anal. Calcd for C61H47N3OP2Ru: C, 73.19; H, 4.73; N,
4.20. Found: C, 73.12; H, 4.66; N, 4.13%. IR (ATR, cmÀ1): 1938
2.2.1. 2-(2-(Anthracen-9-ylmethylene)hydrazinyl)benzo[d]thiazole
(BHA)
This was prepared from 9-anthracenecarboxaldehyde (0.206,
1 mmol) and 2-hydrazinyl benzo[d]thiazole (0.165 mg, 1 mmol).
Yield: 77%. Color: Yellow. M.p.: 260 °C. Anal. Calcd. for
(mCO), 1609 (
m
C = N). 1H NMR (400 MHz, CDCl3, d, ppm): À12.41
(t, 1H, Ru-H), 8.33 (s, 1H, HC = N), 8.01–6.59 (m, 45H, Ar-H). 13C
C22H15N3S: C, 74.76; H, 4.28; N, 11.89; S, 9.07. Found: C, 74.82;
NMR (100 MHz, CDCl3, d, ppm): 202.98 (CO), 166.30 (C@N),

K. Murugan et al. / Polyhedron 190 (2020) 114737
3
144.70 (N@C-N), 134.84–124.65 (Ar-C). 31P NMR (162 MHz, CDCl3,
d, ppm): 47.17. Calcd ESI-mass (m/z) for C61H47N3OP2Ru: 1001.3.
Found: 1002.1 [M + H]+. Crystals of complex 3 were grown by
the diffusion method with dichloromethane and petroleum ether
solvents at room temperature.
HOMO, LUMO and electrostatic potential map have been analyzed
from Gaussian03 [28,29], Gauss view [30] and 3D plot software
packages [31].
2.6. General procedure for the a-alkylation of ketones
2.3.4. [(QHA)RuH(CO)(AsPh3)2] (4)
The aromatic ketones (1.5 mmol), aromatic primary alcohols
(1.5 mmol), catalyst (1 mol%), KOH (10 mol%) and toluene (5 mL)
were charged into a round bottom flask and heated at 110 °C for
12 h. The progress of the reaction was monitored by TLC. Upon
completion, the reaction mixture was cooled to room temperature.
The catalyst was separated by the addition of a dichloromethane
and petroleum ether solvent mixture (1:1 v/v, 20 mL), followed
by filtration through celite. The filtrate was concentrated under
reduced pressure and the resulting crude product was purified by
column chromatography over silica gel (100–200 mesh) with a
hexane–ethyl acetate solvent mixture (9.5:0.5, v/v) as the eluent.
The resulting products were identified by a comparison with the
NMR (1H and 13C) and mass spectral data from previous reports.
The ligand QHA (0.034 g, 0.1 mmol) was reacted with [RuHCl
(CO)(AsPh3)3] (1.085 g, 0.1 mmol) to form complex 4. Yield: 60%.
M.p.: 232 °C. Anal. Calcd for C61H47N3OAs2Ru: C, 67.28; H, 4.35;
N, 3.86. Found: C, 67.23; H, 4.30; N, 3.81%. IR (ATR, cmÀ1): 1908
(
m
CO), 1615 (
m
C@N). 1H NMR (400 MHz, CDCl3, d, ppm): À12.78
(s, 1H, Ru-H), 8.33 (s, 1H, HC = N), 8.09–6.80 (m, 45H, Ar-H). 13C
NMR (100 MHz, CDCl3, d, ppm): 203.09 (CO), 166.28 (C@N),
144.15 (N@C-N), 134.84–124.66 (Ar-C). Calcd ESI mass (m/z) for
C
61H47N3OAs2Ru: 1089.9. Found: 1090.0 [M + H]+.
2.4. X-ray crystallography
Crystal data were collected for complexes 1–3 at 296 K using a
Gemini A Ultra Oxford diffraction automatic diffractometer. Gra-
phite monochromated Mo-Ka radiation (k = 0.71073 Å) was used
throughout the analysis. Absorption corrections were performed
by the multi-scan method. Corrections were made for Lorentz
and polarization effects. The structures were solved by the direct
method using the program SHELXS 2018 [25]. Refinement and all
further calculations were carried out using SHELXL. The H atoms
were included in calculated positions and treated as riding atoms
using the SHELXL default parameters. Non-hydrogen atoms were
refined anisotropically using weighted full-matrix least squares
on F2. Atomic scattering factors were incorporated in the computer
programs.
3. Results and discussion
The ruthenium(II) complexes were obtained by the reaction of
the ligands with the ruthenium(II) starting material, [RuHCl(CO)
(E)3] (E = PPh3 or AsPh3) or [RuCl2(AsPh3)3], in chloroform-ethanol
solvent medium under reflux conditions (Scheme 1). The com-
plexes are non-hygroscopic solids for extended periods and are
well soluble in organic solvents like methanol, ethanol, dichloro-
methane, chloroform, 1,4-dioxane, tetrahydrofuran, acetonitrile,
dimethylformamide and dimethyl sulfoxide, as well as in non-
polar solvents like benzene and toluene. The elemental analyses
(C, H, N and S) of the new complexes 1–4 were in good agreement
with the expected structures of the ruthenium hydrazone com-
plexes. The ESI mass spectra of the new complexes reveal that
the calculated molecular masses are in good accord with the
observed molecular masses (Figs. S1–S3 in the supporting informa-
tion). The results confirm the formation of the desired complexes.
2.5. Computational studies
2.5.1. Hirshfeld surface analysis
A necessary complete structural description was carried out by
Hirshfeld Surface Analysis (HSA), which is used to visualize and
quantify the individual types of intermolecular contacts and their
impact on crystal packing in the crystal environment. Furthermore,
HSA helps to define the occupied space by a molecule and parti-
tions the electron density of the crystal into molecular fragments
[26]. The Crystal Explorer 17.5 software was used to calculate the
HSA and the respective fingerprint plots at very high resolution
for the two coordination complexes with the aid of the Crystallo-
graphic Information File (CIF). The dnorm plot clearly shows the dis-
tances from the outside nuclei surface (de) and the inside surface
(di); the fixed color scale dnorm plot for the three coordination com-
plexes were À0.23 to 0.95; À0.12 to 1.70 and À0.08 to À1.86 Å. The
shape index plot was mapped in the color range À1.0 to 1.0 au. In
the dnorm surface, the sum of the vdw radii was indicated by a
white surface, the short contact distances, less than the vdw radii,
were displayed by a blue surface and the close-contact interactions
(hydrogen bond contacts) were shown by a red surface on the
three-dimensional (3D) Hirshfeld surfaces. In the shape index,
3.1. Spectroscopy studies
The IR spectra furnish preliminary information about the metal
ligand bonding. In the spectra of the free ligands, a peak appearing
in the region 3307–3305 cmÀ1 was assigned to the hydrazine NH
stretching frequency. The NH peak was not present in the spectra
of complexes 1, 3 and 4, showing that coordination of the ligands
to the ruthenium metal takes place by deprotonation either via
the hydrazinic nitrogen atom or benzothiazole ring nitrogen atom
by amine imine tautomerism. However, in the spectrum of com-
plex 2, the NH peak did not disappear, revealing the non-participa-
tion of the hydrazinic nitrogen atom in coordination. The strong
band observed in the spectra of the ligands at 1570–1562 cmÀ1
was assigned to the azomethine group. In the spectra of complexes
1 and 2, this band shifted to a higher frequency and appeared in the
region 1577–1573 cmÀ1, indicating the participation of the imine
nitrogen atom in coordination with the metal. However, the
position of the azomethine peak did not change in the spectra of
complexes 3 and 4, depicting the non-participation of the imine
nitrogen atom with the metal center. A strong band was observed
the blue and red colors reflect the cycle stacking (CAHÁ Á Á
p and
pÁ Á Áp
interactions). Moreover, the 2D fingerprint plots help to sum-
marize contact distances to the HSA (di, de), which shows the
range from 0.6 to 2.8 Å, including reciprocal contacts where the
different type of intermolecular interactions of the molecule in
the crystal can be characterized by the shapes of the fingerprint
plots.
in the spectra of complexes 1,
3 and 4 in the region
1938–1900 cmÀ1 which was assigned to a terminally coordinated
carbonyl groups, being observed at a slightly higher frequency than
in the ruthenium precursor complexes. In addition, the coordi-
nated triphenylphosphine and triphenylarsine ligands showed
peaks in the expected regions [32,33].
2.5.2. Density functional theory
The newly synthesized complexes 1–3 were optimized by
B3LYP (DFT) with the 6-311G** basis set [27]. The atomic charges,

4
K. Murugan et al. / Polyhedron 190 (2020) 114737
Scheme 1. Synthesis of the ruthenium(II) complexes 1–4.
The 1H NMR spectra of the ligands and the new complexes con-
firm the coordination of the ligands with the metal (Figs. S4–S9 in
the supporting information). broad singlet appears at
for the aromatic carbon atoms were observed in the region d
133.84–124.65 ppm [34]. The 31P NMR spectra of complexes 1
and 3 were recorded to confirm the presence and configuration
of the triphenylphosphine groups (Figs. S14 and S15 in the
supporting information). The appearance of sharp singlet at d
48.52–47.17 ppm suggests the presence of two magnetically
equivalent triphenylphosphine groups trans to each other [35].
A
d
10.70–10.13 ppm in the spectra of the ligands, which was assigned
to the hydrazine (NH) proton. This peak was absent in the spectra
of metal complexes 1, 3 and 4, confirming that coordination of the
ligands with the ruthenium metal takes place by deprotonation
either via the hydrazinic nitrogen atom or benzothiazole ring
nitrogen atom by amine imine tautomerism. However, in the spec-
trum of complex 2, the NH peak not disappearing reveals the non-
participation of the hydrazinic nitrogen atom in coordination. The
peak appearing at d 8.61–8.34 ppm in the spectra of the ligands is
due to the imine (HC = N) proton, which shifted downfield and
appeared at d 8.60–8.64 ppm in the spectra of complexes 1 and
2, showing the participation of the imine nitrogen atom in coordi-
nation with the metal. In complexes 3 and 4, the position of imine
proton peak did not change, describing non-participation of the
imine nitrogen atom in coordination with the metal. The aromatic
protons appeared in the region d 8.61–6.51 ppm. In addition, for
complexes 1, 3 and 4, a Ru-H signal appeared in the region d
À13.44 to À12.41 ppm. The 13C NMR spectra show the signals
for the coordinated metal complexes in the expected regions
(Figs. S10–S13 in the supporting information). The appearance of
a peak at d 202.98–200.89 ppm reveals the presence of a terminal
carbonyl group. The peak for the azomethine carbon atom was
observed as a singlet at d 162.65–161.11 ppm. The peak due to
the N@C-N carbon atom appeared at d 145 ppm. Moreover, peaks
3.2. Molecular structures of complexes 1–3
The solid-state structures of complexes 1–3 have been deter-
mined by single crystal X-ray diffraction to confirm the exact coor-
dination modes of the ligands and the geometries around the
ruthenium atoms. The crystal data and structure refinement
parameters for complexes 1–3 are summarized in Table 1 and
selected bond lengths and bond angles are depicted in Table 2.
The ORTEP views of complexes 1–3 along with the atomic number-
ing schemes are given in Figs. 1–3. The single-crystal X-ray studies
reveal that complexes 1–3 crystallized in the triclinic system with
the space group Pi. All the Ru(II) complexes describe a distorted
octahedral geometry wherein a bidentate mode is adopted by the
ligand, creating five or four membered chelate rings. The remaining
apical sites are filled up by carbonyl, chloride or hydride ligands
and a pair of PPh3 or AsPh3 co-ligands, giving CN2P2Cl, N2As2Cl2
and CN2P2H coordination environments. Typically, the PPh3 or
AsPh3 co-ligands prefer to occupy cis positions for an enhanced
p-interaction, however the presence of a stronger p-acidic CO

K. Murugan et al. / Polyhedron 190 (2020) 114737
5
Table 1
Crystal data and structural refinement parameters for complexes 1–3.
Complex 1
Complex 2
Complex 3
CCDC
1,990,120
C59H45ClN3OP2RuS
1,990,120
C58H44As2Cl2N3RuS
1136.84
296(2)
0.71073
Triclinic
Pi
1,990,120
C61H47N3OP2Ru
1001.03
296(2)
0.71073
Triclinic
Pi
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
1042.50
296(2)
0.71073
Triclinic
Pi
13.4920(6)
14.1831(7)
15.3520(7)
66.0670(10)
81.460(2)
66.4310(10)
2460.8(2)
2
1.407
0.526
1070
0.22 Â 0.14 Â 0.07
2.747–28.297
À17 ꢀ h ꢀ 17,
À18 ꢀ k ꢀ 18,
À20 ꢀ l ꢀ 20
11,315
12.8355(4)
12.9425(4)
16.0266(5)
92.345(2)
13.0849(3)
18.0296(5)
22.0748(6)
99.8070(10)
92.8880(10)
107.6030(10)
4862.5(2)
b (Å)
c (Å)
a
(°)
b (°)
96.154(2)
c
(°)
106.373(2)
2532.63(14)
2
1.491
1.794
Volume (Å3)
Z
4
Density (calculated, Mg/m3)
Absorption coefficient (mmÀ1
F(000)
1.367
0.435
2064
)
1146
Crystal size (mm3)
0.24 Â 0.17 Â 0.11
1.281–29.113
À17 ꢀ h ꢀ 17,
À17 ꢀ k ꢀ 17,
À21 ꢀ l ꢀ 21
50,726
0.240 Â 0.170 Â 0.070
2.417–20.808
À13 ꢀ h ꢀ 13,
À18 ꢀ k ꢀ 18,
À22 ꢀ l ꢀ 22
17,618
Theta range for data (°) collection
Index ranges
Reflections collected
Independent reflections
11,315 [R(int) = 0.0104]
0.844
13,630 [R(int) = 0.0338]
1.033
10,142 [R(int) = 0.0391]
1.043
Goodness-of-fit on F2
Final R indices [I > 2sigma(I)]
R1 = 0.0426
wR2 = 0.1270
R1 = 0.0499
wR2 = 0.1381
n/a
R1 = 0.0416
wR2 = 0.1185
R1 = 0.0703
wR2 = 0.1417
n/a
R1 = 0.0500
wR2 = 0.1233
R1 = 0.0650
wR2 = 0.1362
n/a
R indices (all data)
Extinction coefficient
Largest diff. peak and hole (e ÅÀ3
)
0.969 and À0.814
1.119 and À1.419
0.597 and À0.330
Table 2
Selected bond lengths and bond angles in complexes 1–3.
Complex 1
Complex 2
Complex 3
Bond lengths (Å)
Ru(1)-C(23)
Ru(1)-N(3)
Ru(1)-N(1)
Ru(1)-P(2)
Ru(1)-P(1)
Ru(1)-H(1A)
1.842(3)
2.120(2)
2.215(2)
2.3625(7)
2.3617(7)
1.439(1)
As(2)-Ru(1)
Ru(1)-N(1)
Ru(1)-N(2)
Ru(1)-Cl(1)
Ru(1)-Cl(2)
Ru(1)-As(1)
2.4723(4)
Ru(1)-C(25)
Ru(1)-N(3)
Ru(1)-N(2)
Ru(1)-P(2)
Ru(1)-P(1)
Ru(1)-H(1)
1.834(8)
2.163(5)
2.180(4)
2.3613(14)
2.3669(15)
1.660
2.099(3)
2.116(3)
2.4176(19)
2.461(2)
2.4887(4)
Bond angles [°]
C(23)-Ru(1)-N(3)
C(23)-Ru(1)-N(1)
N(3)-Ru(1)-N(1)
C(23)-Ru(1)-P(2)
N(3)-Ru(1)-P(2)
N(1)-Ru(1)-P(2)
C(23)-Ru(1)-P(1)
N(3)-Ru(1)-P(1)
N(1)-Ru(1)-P(1)
P(2)-Ru(1)-P(1)
H(1)-Ru(1)-C(23)
N(3)-Ru(1)-H(1A)
N(1)-Ru(1)-H(1)
P(1)-Ru(1)-H(1)
P(2)-Ru(1)-H(1)
178.05(12)
107.21(12)
74.70(9)
90.90(9)
89.48(6)
93.39(6)
89.17(9)
90.11(6)
96.19(6)
169.95(3)
90.03
N(1)-Ru(1)-N(2)
N(1)-Ru(1)-Cl(1)
N(2)-Ru(1)-Cl(1)
N(1)-Ru(1)-Cl(2)
N(2)-Ru(1)-Cl(2)
Cl(1)-Ru(1)-Cl(2)
N(1)-Ru(1)-As(2)
N(2)-Ru(1)-As(2)
Cl(1)-Ru(1)-As(2)
Cl(2)-Ru(1)-As(2)
N(1)-Ru(1)-As(1)
N(2)-Ru(1)-As(1)
Cl(1)-Ru(1)-As(1)
Cl(2)-Ru(1)-As(1)
As(2)-Ru(1)-As(1)
77.14(11)
168.97(8)
91.96(8)
96.42(8)
173.55(8)
94.47(5)
89.49(7)
91.61(7)
92.51(4)
88.60(4)
89.40(7)
88.15(7)
88.58(4)
91.52(4)
178.89(15)
C(25)-Ru(1)-N(3)
C(25)-Ru(1)-N(2)
N(3)-Ru(1)-N(2)
C(25)-Ru(1)-P(2)
N(3)-Ru(1)-P(2)
N(2)-Ru(1)-P(2)
C(25)-Ru(1)-P(1)
N(3)-Ru(1)-P(1)
N(2)-Ru(1)-P(1)
P(2)-Ru(1)-P(1)
N(3)-Ru(1)-H(1)
N(2)-Ru(1)-H(1)
P(1)-Ru(1)-H(1)
P(2)-Ru(1)-H(1)
H(1)-Ru(1)-C(25)
170.2(3)
110.5(3)
60.25(17)
89.7(2)
87.03(12)
89.46 (12)
94.2(2)
89.64(12)
92.41(12)
174.74(6)
95.44
155.65 (1)
88.70
88.11(1)
162.62(1)
86.01(1)
83.94(1)
86.45
85.46
ligand might have forced the bulky PPh3/AsPh3 ligands to take
trans positions for steric reasons [36,37].
small N(1)–Ru(1)–N3(1) bite angle of 74.70(9)°. The ruthenium–li-
gand distances, namely Ru(1)–C(23) 1.842(3) Å, Ru(1)–N(3) 2.120
(2) Å, Ru(1)–N(1) 2.215(2) Å, Ru(1)–H(1A) 1.439(1) Å, Ru(1)–P(2)
2.3625(7) Å and Ru(1)–P(1) 2.3617(7) Å, found in the complexes
agree well with those reported for similar ruthenium complexes
containing triphenylphosphine ligands in trans positions [36].
Complex 2 displays a similar type of coordination environment
In complex 1, the ruthenium atom is in a distorted octahedral
environment with trans angles of [P(1)–Ru(1)–P(2)] 169.96(3)°
and [N(1)–Ru(1)–H(1A)] 162.62(1)°.The carbonyl group trans to
the coordinated N(3) atom [N(3)–Ru(1)–C(23)] gives an angle of
178.05(12). The trans angles deviate from linearity and lead to a

6
K. Murugan et al. / Polyhedron 190 (2020) 114737
Fig. 3. Perspective view (50% probability ellipsoids) of the complex [(QHA)RuH(CO)
(PPh3)2] (3).
Fig. 1. Perspective view (50% probability ellipsoids) of the complex [(BHA)RuH(CO)
(PPh3)2] (1).
Ru(1)–As(2) 2.4723(4) Å, found in the complexes agree well with
those reported for similar ruthenium complexes containing triph-
enylarsine ligands in trans positions [38].
In complex 3, the ligand (QHA) is coordinated to the ruthenium
ion as a monoanionic bidentate N,N-donor ligand, forming a more
strained four-membered chelate ring with an N(2)–Ru(1)–N(3) bite
angle of 60.25(17)° (Fig. 3). A number of reasons have been offered
as being responsible for the versatility in coordination, such as the
bulky quinoline unit restricting rotation about the NAN bond. The
formation of such a four-membered chelate ring by the QHA ligand
and similar ligands is quite normal. The QHA ligand, ruthenium,
carbonyl and hydride constitute one equatorial plane of the octa-
hedron, with the metal at the center, and the two triphenylphos-
phine ligands take up the remaining two axial positions; hence,
they are mutually trans. The carbonyl ligand is trans to the coordi-
nated nitrogen atom of the quinoline moiety and the hydride ion is
trans to the nitrogen N(2) atom. The Ru(1)–H(1A), Ru(1)–C(25), Ru
(1)–P(1) and Ru(1)–P(2) distances are 1.660, 1.834(8), 2.3669(15)
and 2.3613(14) Å respectively. The observed bond distances are
comparable with those found in other reported ruthenium com-
plexes containing PPh3 ligands [39]. The Ru–N(3) length of
2.163 Å is comparable to that found in similar four-membered che-
lates, whereas the Ru–N(2) distance of 2.180 Å is a little longer
than usually observed. The elongation of the Ru–N bond, which
is trans to the Ru–H bond, may be attributed to the trans effect of
the hydride ligand.
Fig. 2. Perspective view (50% probability ellipsoids) of the complex [(BHA)RuCl2(-
AsPh3)2] (2).
3.3. Hirshfeld surface analysis
Hirshfeld surface analysis was completed with the purpose of
reviewing the nature of the intra and intermolecular interactions,
and their contribution to the supramolecular assembly of the com-
plexes. The dnorm and shape index of complexes 1–3 are shown in
Fig. 4. On comparing the coordination complexes 1–3, blue and
white surfaces are more predominant than red surfaces in all three
complexes due to hydrophobic cyclic rings. The dark red and blue
to complex 1, but with the [As(1)–Ru(1)–As(2)] trans angles of
178.89(15)° being higher than the analogous angle in the complex
1. This is due to presence of steric requirements of the chloride and
AsPh3 ligands. The chloride groups trans to the coordinated N(1)
atom, [N(1)–Ru(1)–Cl(1)] and N(2) [N(2)–Ru(1)–Cl(2)], show
angles of 168.97(3) and 173.55(8) °. There is no deviation in the
trans angles from linearity and this leads to an N(2)– Ru(1)–N(1)
bite angle of 77.14(11)°. The ruthenium–ligand distances, namely,
Ru(1)–Cl(1) 2.4176(19) Å, Ru(1)–Cl(2) 2.461(2) Å, Ru(1)–N(1)
2.099(3) Å, Ru(1)–N2(1) 2.116(3) Å, Ru(1)–As(1) 2.4887(4) Å and
surfaces of the shaped index indicate CAHÁ Á Á
p interactions in the
crystals. Fingerprint plots are used to quantify the contribution of
different types of interactions in the solid state (Fig. 5). The finger-
print plots of all three complexes display interactions that are very

K. Murugan et al. / Polyhedron 190 (2020) 114737
7
similar. The HÁ Á ÁH and CÁ Á ÁH types of interactions are highly pre-
HOMO is highly localized on the metal centre and its surroundings
(Ru, As, P, N and S atoms), and the other regions are very low,
whereas in the LUMO, the major contributions are on the phenyl
rings and there is minor contribution for the metal centre and its
surroundings. The positive and negative regions are shown in
green and red colors respectively. In order to understand the
charge injection and transporting properties of the metal coordina-
tion molecules, the global reactivity descriptors were calculated.
The HOMO and LUMO energies rationalise the transfer of charge
in a reaction, [35]. The calculated HOMO energies of the complexes
vary as 1 (À5.46 eV) > 2 (À5.26 eV) > 3 (À4.47 eV) and those of
LUMO exhibit a similar trend: 1 (À1.94 eV) < 2 (À2.29 eV) > 3
sent in the molecules, which also confirm that vdw and CAHÁ Á Á
p
interactions play a major role in the crystal environment. There-
fore, this fingerprint plot clearly confirms weak hydrogen bonding
that gives stability to all three coordination complexes (1–3). The
contribution of the HÁ Á ÁH and CÁ Á ÁH interactions for the molecules
are shown in Fig. 5.
3.4. Density functional theory
The Mulliken atomic charges (MPA) of complexes 1–3 were cal-
culated using the Gaussian09 software [29]. Table S1 shows the
MPA charges of the atoms of the three complexes. An electrostatic
potential map helps to predict the possible reactive sites of the
molecule, where nucleophilic (attracted to regions with positive
potential) and electrophilic (attracted towards regions with nega-
tive potential) regions are present in the molecule. Fig. 6 shows
the isosurface representation of the molecular electrostatic poten-
tial (MSP) of the metal coordination compounds. Large electroneg-
ative regions are found on the surface of the metal coordination
region.
Essential quantum chemical descriptors, such as the HOMO and
LUMO, were calculated for the three metal coordination complexes
(1–3) and these are highly related to the chemical and biological
activities. The molecular surface of the HOMO and LUMO maps
of the three complexes were drawn at 0.2 au and are shown in
Fig. 7, in which the HOMO and LUMO energy surfaces of the mole-
cules were found over the metal and functional group regions. The
(À1.91 eV). The HOMO–LUMO energy gaps in complexes
1
(3.52 eV), 2 (2.96 eV) and 3 (2.57 eV) possess different values,
which is consistent with the experimentally observed values. All
the calculated global reactivity descriptors are shown in Table 3.
3.5. Catalytic studies
Motivated by their prominent presence in a variety of natural
products and pharmaceuticals, as well as in petroleum and bio-
mass feedstocks, considerable research efforts have been focused
on the development of catalytic coupling methods with the utiliza-
tion of ketones and alcohols. Here, the synthesized ruthenium(II)
hydrazone complexes have been used as environmentally
compassionate catalyst for the formation of CAC coupling products
by the
a-alkylation of ketones using alcohols. Initially, the
a-alkylation reaction was started using the benchmark substrates
Fig. 4. Hirshfeld surface analysis mapped with dnorm and shaped index for complexes 1–3.

8
K. Murugan et al. / Polyhedron 190 (2020) 114737
Fig. 5. Fingerprint plot of complexes 1–3, full and resolved into O∙∙∙H, C∙∙∙H and H∙∙∙H contacts, showing the percentages (%) of contacts contributing to the total Hirshfeld
surface area of each molecule.
acetophenone and benzyl alcohol, with catalyst 3. These substrates
were selected in order to optimize various conditions, such as the
presence of base, solvent, time and catalyst loading for the a-alky-
without the metal catalyst in the presence of a catalytic amount
of base showed that the hydrogen borrowing reaction did not
occur completely.
lation. The results of the preliminary reactions are shown in
Table 4. In order to assess the crucial role of the base in promoting
the generation of the metal chalcone intermediate (a, b unsatu-
rated carbonyl) formed in the catalyst cycles, various bases such
as Na2CO3, K2CO3, NaHCO3, KOH, NaOH and KOtBu were employed
to find the best one. Weak bases, such as Na2CO3, K2CO3 and
NaHCO3, were ineffective (Table 4, entries 1–3). The presence of
the strong base NaOH led to a higher yield for this reaction (Table 3,
entry 5, yield 74%). When the reaction was carried out in the pres-
In addition to this, we were interested in exploring the solvent
dependent activities with the most frequently used solvents, such
as toluene, 1,4 dioxane, THF, acetonitrile, benzene, DMF and DMSO
(Table 4, entries 1–15). Aromatic hydrocarbon solvents such as
toluene and benzene (Table 4, entries 10 and 11) were found to
be better reaction media than polar aprotic solvents like DMF
and DMSO (Table 4, entries 12 and 13), whereas ether-like
solvents, such as THF and dioxane, gave moderate yields (Table 4,
entries 7 and 8). The results show that the solvent’s polarity and
ability to dissolve the reactants and catalyst play a vital role in
the efficiency of the catalytic system.
ence of KOH, the a-alkylated product formed in an excellent yield
(Table 4, entry 4, yield 94%), hence which we considered this to be
the choice for the base. Another strong base, KOtBu, was found to
We also explored the significance of catalyst loading and the
results are depicted in Table 5. To study the effect of the amount
of the catalyst, the reactions were carried out with different
be ineffective (Table 4, entry 6). In the absence of a base,
a-alkyla-
tion was not observed (Table 4 entry 14). Moreover, the reaction

K. Murugan et al. / Polyhedron 190 (2020) 114737
9
Fig. 6. Isosurface representation of the molecular electrostatic potential of complexes 1–3. Blue: positive potential, Red: negative potential. The surface values
are + 0.6 and À0.06 eÅÀ1
.
Fig. 7. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the metal coodination compounds. The HOMOs and LUMOs
are drawn at the 0.02 au level.
amounts of catalyst ranging from 0.5 to 1.5 mol %. When the cata-
lyst loading was increased from 0.5 to 1.0 mol % of catalyst 3, the
product yield also increased and reached 94% in 12 h. Increasing
of the catalyst load further to 1.5 mol % led to little difference in
the yield (Table 5, entry 7). Hence, the optimum catalyst loading
was fixed to be 1.0 mol % (Table 5, entry 3). Additionally, catalyst
Table 3
Calculated global reactivity properties of the metal complexes 1–3.
Global Reactivity Descriptor
DFT Energy (eV)
Complex 1
Complex 2
Complex 3
3 was found to be the best catalyst for the
a-alkylation reaction,
Band Gap
HOMO Energy
LUMO Energy
3.52
À5.46
À1.94
5.46
1.94
1.76
2.96
À5.26
À2.29
5.26
2.29
1.48
2.57
À4.47
À1.91
4.47
1.90
1.28
obtaining an excellent yield (Table 5, entry 3). The other catalysts,
1, 2 and 4, showed lower activity than catalyst 3 (Table 4, entries 1,
2 and 4). From the optimization results, it is concluded that 1.0 mol
% of catalyst 3 in toluene was sufficient to push this reaction at
110 °C in presence of KOH.
Ionization Potential I = ÀEHOMO
Electron Affinity A = ÀELUMO
Global Hardness
Electronegativity
g
v
= (IÀA)/2
= (I + A)/2
3.70
3.89
3.78
4.8
3.19
3.96
Electrophilicity
x
=
l
2/2
g
,
l
= À
v
To investigate the substrate scope, we examined the
a-alkylation
for a variety of aromatic acetophenones with different aromatic

10
K. Murugan et al. / Polyhedron 190 (2020) 114737
Table 4
Optimization of catalytic conditions for the
a
-alkylation of acetophenone using benzyl alcohol.a.
Entry
Base
Solvent
T
oC
Time (h)
Yield (%)b
1
2
Na2CO3
K2CO3
NaHCO3
KOH
NaOH
KOtBu
KOH
KOH
KOH
KOH
KOH
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Dioxane
THF
CH3CN
Toluene
Benzene
DMF
110
110
110
110
110
110
100
65
82
110
80
130
140
110
110
12
12
12
12
12
12
12
12
12
14
12
12
12
24
24
40
50
35
94
74
67
75
72
45
90
55
50
45
n.r
18
3
4e
5
6
7
8
9
10
11
12
13
14c
15d
KOH
KOH
_
DMSO
Toluene
Toluene
KOH
a
b
c
Acetophenone (1.5 mmol), benzyl alcohol (1.5 mmol), base (10 mol %), catalyst 3 (1 mol%) in solvent (5 mL).
Isolated yield after column chromatography.
The reaction was carried out without base.
The reaction was carried out without catalyst.
Better optimization conditions.
d
e
Table 5
Influence of substitution and catalyst loading on the
a
-alkylation of acetophenone with benzyl alcohol.a
Entry
Catalyst
Amount of catalyst (Mol %)
Yield (%)b
1
2
3c
4
5
6
7
1
2
3
4
3
3
3
1
1
1
1
0.5
0.8
1.5
85
82
94
79
78
87
96
a
b
c
Acetophenone (1.5 mmol), benzyl alcohol (1.5 mmol), catalyst, KOH (10 mol %) in toluene (5 mL) refluxed at 110 °C for 12 h.
Isolated yield after column chromatography.
Better optimization conditions.
primary alcohols and the results are shown in Table 6. Our Ru cat-
alytic system was tolerant to various functional groups based on
the standard reaction conditions. The reaction of acetophenone with
alcohols such as 2-methyl benzyl alcohol, 4-methoxy benzyl alcohol
and 2-phenyl ethanol afforded the corresponding products in good
yields (Table 6, entries 1–3). Presence of an electron donating group
on benzyl alcohol (Table 6, entries 1 and 2) decreased the yield of the
product when compared to the unsubstituted alcohol (yield 94%).
When o-hydroxy acetophenone was reacted with alcohols, the
yields of the corresponding products was moderate (Table 6, entries
4–7, yield 76–86%). Steric effects due to the presence of the hydroxy
group in the acetophenone plays a role in decreasing the yield
of the products. The reaction of 4-methoxy-2-hydroxy acetophe-
none with alcohols such as benzyl alcohol, 2-methyl benzyl alcohol,
4-methoxy benzyl alcohol and 1-phenyl ethanol afforded the
corresponding CAC coupled products in good yields (Table 6, entries
9–11).
The recyclability of catalyst 3 was studied over 5 runs for the
a-alkylation of acetophenone by benzyl alcohol under the opti-
mized conditions. After each run, the catalyst was recovered by
the addition of a dichloromethane and hexane mixture. The cata-
lyst was then thoroughly washed with hexane and dried in air
before using in the next run. As shown in Fig. 8, the catalyst can
be efficiently reused >5 times without any significant loss of cat-
alytic activity or selectivity, but after that the activity slightly
decreased. This may be due to incomplete catalyst recovery from
the reaction mixture. When compared to previously reported
catalysts [40], the present catalyst for the
a-alkylation of ketones

K. Murugan et al. / Polyhedron 190 (2020) 114737
11
Table 6
a
Evaluations of substrate scope
Entry
1
Ketone
Alcohol
Product
Yield (%)
84
2
91
3
4
87
80
5
6
7
76
86
80
8
9
85
82
(continued on next page)

12
K. Murugan et al. / Polyhedron 190 (2020) 114737
Table 6 (continued)
Entry
10
Ketone
Alcohol
Product
Yield (%)
93
11
86
a
Ketone (1.5 mmol), alcohol (1.5 mmol), catalyst 3 (1 mol %), KOH (10 mol %) in toluene (5 mL) refluxed at 110 °C for 12 h. b Isolated yield after column chromatography.
CRediT authorship contribution statement
Kaliyappan Murugan: Conceptualization, Investigation, Writ-
ing - original draft. Subbarayan Vijayapritha: Validation. Venkat-
achalam Kavitha: Validation. Periasamy Viswanathamurthi:
Methodology, Formal analysis, Writing - review & editing, Visual-
ization, Supervision, Project administration.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
Acknowledgements
We thank the Department of Chemistry, Gandhigram Rural
Institute-Deemed University, Gandhigram (NMR spectra), SAIF,
Gauhati University, Guwahati (single crystal X-Ray) and CIMF,
Periyar University, Salem (single crystal X-Ray) for their help in
characterization studies.
Fig. 8. Recyclability study of catalyst 3 using acetophenone and benzyl alcohol.
Appendix A. Supplementary data
Supplementary data to this article can be found online at
with alcohols is more convenient and more efficient since the com-
https://doi.org/10.1016/j.poly.2020.114737.
plex is easier to prepare, cheaper than others and a less amount of
catalyst gives a better yield.
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and the results show that complex 3 is an efficient catalyst for the
synthesis of the -alkylation products.
a-alkylation of ketones with alcohols
a

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