Novel dioxomolybdenum complexes containing ONO-tridentate Schiff base ligands derived from 4-aminobenzohydrazide: synthesis, spectral characterization, and application as efficient homogeneous catalysts for selective sulfoxidation

Article abstract of DOI:10.1007/s13738-021-02282-0

Novel dioxomolybdenum Schiff base complexes, [MoO₂(Lⁿ)(CH₃OH)], were synthesized by the reaction of MoO₂(acac)₂ and ONO donor Schiff base ligands (H₂Lⁿ) derived by the condensati

Full text of DOI:10.1007/s13738-021-02282-0

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-021-02282-0
ORIGINAL PAPER
Novel dioxomolybdenum complexes containing ONO‑tridentate Schif
base ligands derived from 4‑aminobenzohydrazide: synthesis, spectral
characterization, and application as efcient homogeneous catalysts
for selective sulfoxidation
Hadi Kargar1 · Mehdi Fallah‑Mehrjardi2
Received: 27 February 2021 / Accepted: 10 May 2021
© Iranian Chemical Society 2021
Abstract
Novel dioxomolybdenum Schif base complexes, [MoO2(Ln)(CH3OH)], were synthesized by the reaction of MoO2(acac)2
and ONO donor Schif base ligands (H2Ln) derived by the condensation of 4-aminobenzohydrazide and substituted salicyla-
ldehydes. The synthesized ligands and their complexes were characterized by various spectroscopic techniques like FT-IR,
1H NMR, 13C NMR, and elemental analysis (CHN). The geometries around the central metal atom in the complexes were
suggested distorted octahedral. Moreover, the catalytic efciency of the complexes was investigated by oxidizing the aryl
and alkyl sulfdes in the presence of tert-butyl hydroperoxide in 1,2-dichloroethane under refux conditions. This method has
numerous ascendancies, such as high yield, short reaction time, and excellent selectivity to produce corresponding sulfoxides
without overoxidation to sulfones.
Keywords Dioxomolybdenum · ONO-tridentate Schif base · Homogeneous catalyst · Selective sulfoxidation
Introduction
because of the presence of N–H moiety in close vicinity to
the azomethine group [12].
Schif bases are very fascinating kinds of ligands in devel-
oping the chemistry of coordination compounds due to the
presence of azomethine chromophore [1–5]. Hydrazones
are a unique category of Schif bases because of their wide
applications in various optical, biological, catalytic, and
analytical felds [6, 7]. These compounds are efective anti-
viral, antifungal, antibacterial, antineoplastic, and DNA
photocleaving agents [8–10]. Hydrazones can adopt difer-
ent modes of coordination according to the requirements
of geometries and oxidation states of various metal ions to
form coordination complexes [11]. Furthermore, hydrazones
can redesign themselves in the form of self-assembly due
to hydrogen bonding, both in free and coordinated form
There are large numbers of metal complexes with imine-
based Schif bases, which are commonly used as oxidation
catalysts in various types of important organic reactions,
due to their commercially cheap, easy mode of preparation,
and outstanding chemical and thermal strength in both, solid
and liquid states [13–16]. Among the second row of transi-
tion metal series, molybdenum is a very important, versatile,
and trace biometal, which is capable of making a diverse
type of complexes with numerous organic ligands [17, 18].
The pliability of molybdenum in holding various kinds of
stable and manageable oxidation states made it very popu-
lar in biological and catalytic reactions [18–20]. Oxo and
dioxomolybdenum(VI) complexes with nitrogen, sulfur, and
oxygen donor ligands made them useful models for numer-
ous molybdenum-based enzymes [20–22]. In addition to
their bioactive potential, these are also signifcantly impor-
tant in reversible oxotransferase reaction in aqueous aerobic
media [23] because of the presence of metal in MoO22+ form
[24]. Dioxomolybdenum complexes have remarkable cata-
lytic properties which lead to their application as a catalyst
in various oxidation reactions like, epoxidation of olefns,
* Hadi Kargar
h.kargar@ardakan.ac.ir; hadi_kargar@yahoo.com
1
Department of Chemical Engineering, Faculty
of Engineering, Ardakan University, P.O. Box 184, Ardakan,
Iran
2
Department of Chemistry, Payame Noor University,
19395-3697 Tehran, Iran
Vol.:(0123456789)
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Journal of the Iranian Chemical Society
oxidation of sulfdes to sulfoxides, oxidation of alcohols, and
hydroxylation of phenols [25–38].
Sulfoxides are important building blocks due to their
involvement in biological as well as chemical processes.
These are used in asymmetric synthesis, as intermediates
in drug development, Swern oxidation [39, 40], carbon to
carbon bond formation [41, 42], and in Diels–Alder reac-
tion [43]. Sulfoxidation is carried out by various kinds of
transition metals like manganese, cobalt, iron, titanium [44,
45], etc. Sulfoxidation by dioxomolybdenum complexes is
fascinating due to their lenient and particular behavior with
sensitive functional groups [46–50].
In continuation to our efort on the synthesis of novel
Schif base complexes [51–59], we are hereby describing the
synthesis, spectroscopic characterization, crystal structure,
and catalytic potential of four novel dioxomolybdenum(VI)
complexes derived from 4-aminobenzohydrazide in selec-
tive sulfoxidation of various aliphatic and aromatic sulfdes.
Experimental
Materials and physical methods
All the chemicals employed in the current work were of
99.9% pure and purchased from well renowned suppliers
like Sigma-Aldrich and Merck. Microanalyses of the synthe-
sized compounds were done by a Heraeus CHN-O-FLASH
EA 1112 elemental analyzer. Infrared spectra were taken
by making KBr disks on a Shimadzu FT-IR IRPrestige-21
spectrophotometer from 4000 to 400 cm−1. 1H & 13C NMR
spectra were measured at ambient temperature by using
BRUKER AVANCE 400 MHz spectrometer by employing
tetramethylsilane (TMS) as an internal reference and dime-
thyl sulfoxide (DMSO-d6) as a solvent.
Scheme 1 The synthetic pathways for H2Ln ligands and MoO2(Ln)
(CH3OH) complexes
N 14.57%. FT-IR (KBr, cm−1): 3625 (ꢀ N–H); 3440 & 3362
(ꢀ H–N–H); 1640 (ꢀ C=O); 1603 (ꢀ C=N); 1556 (ꢀ C=C); 1287 (ꢀ
C–O(phenolic)); 1086 (ꢀ N–N). 1H NMR (400 MHz, DMSO-d6,
ppm): 5.86 [2 H, s, (–NH2)], 6.61 [2 H, (H–C11, H–C13),
d, 3J=8.4 Hz], 6.94 [1 H, (H–C2), d, 3J=8.8 Hz], 7.29 [1
H, (H–C3), dd, 3J=8.8 Hz, 4J=2.4 Hz], 7.61 [1 H, (H–C5),
d, 4J=2.4 Hz], 7.68 [2 H, (H–C10, H–C14), d, 3J=8.4 Hz],
8.53 [1 H, s, (–CH=N)], 11.54 [1 H, s, (–NH)], 11.85 [1 H,
s, (–OH)]. 13C NMR (100 MHz, DMSO-d6, ppm): 112.6
(C11, C13), 118.1 (C2), 118.5 (C6), 120.7 (C9), 122.8 (C4),
127.8 (C5), 129.4 (C10, C14), 130.3 (C3), 144.5 (C7), 152.6
(C12), 155.9 (C1), 162.8 (C8).
Synthesis of ONO‑tridentate Schif base ligands
For the preparation of ONO-tridentate Schif base ligands,
H2Ln, a mixture of 4-aminobenzohydrazide and the respec-
tive salicylaldehyde (5-chlorosalicylaldehyde=HL1, 5-bro-
mosalicylaldehyde=HL2, 5-methylsalicylaldehyde=HL3,
and 5-methoxysalicylaldehyde=HL4) with 1:1 stoichiomet-
ric ratio was dissolved in MeOH. The mixture was stirred
for about 3 h under refux conditions to give a clear yellow
solution. After that, the solvent was allowed to slowly evapo-
rate for a period of 6 days to give the products in pure form
(H2L1-H2L4). The elemental analyses, 1H NMR, 13C NMR,
and FT-IR data, clearly confrmed their composition. The
synthesis of the ligands is depicted in Scheme 1.
H2L2; (E)-4-amino-N’-(5-bromo-2-hydroxybenzylidene)
benzohydrazide, Yield: 84%. Calculated for C14H12BrN3O2:
C 50.32, H 3.62, N 12.57%. Analysis found: C 50.45, H 3.66,
N 12.48%. FT-IR (KBr, cm−1): 3624 (ꢀ N–H); 3441 & 3360
(ꢀ H–N–H); 1639 (ꢀ C=O); 1602 (ꢀ C=N); 1556 (ꢀ C=C); 1286 (ꢀ
C–O(phenolic)); 1085 (ꢀ N–N). 1H NMR (400 MHz, DMSO-d6,
ppm): 5.87 [2 H, s, (–NH2)], 6.61 [2 H, (H–C11, H–C13),
d, 3J=8.8 Hz], 6.89 [1 H, (H–C2), d, 3J=8.4 Hz], 7.40 [1
H, (H–C3), dd, 3J=8.8 Hz, 4J=2.4 Hz], 7.69 [2 H, (H–C10,
H–C14), d, 3J=8.8 Hz], 7.74 [1 H, (H–C5), d, 4J=2.4 Hz],
8.53 [1 H, s, (–CH=N)], 11.55 [1 H, s, (–NH)], 11.85 [1 H,
s, (–OH)]. 13C NMR (100 MHz, DMSO-d6, ppm): 110.3
(C11, C13), 112.6 (C2), 118.5 (C6), 118.6 (C9), 121.3 (C4),
H2L1; (E)-4-amino-N’-(5-chloro-2-hydroxybenzylidene)
benzohydrazide, Yield: 87%. Calculated for C14H12ClN3O2:
C 58.04, H 4.18, N 14.50%. Analysis found: C 57.76, H 4.23,
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Journal of the Iranian Chemical Society
129.4 (C5), 130.7 (C10, C14), 133.1 (C3), 144.3 (C7), 152.6
(C12), 156.3 (C1), 162.8 (C8).
C=N–N=C); 1367 (ꢀ C–O(phenolic)); 1261 (ꢀ C–O); 1080 (ꢀ N–N);
935 (ꢀ O=Mo=O) asym; 899 (ꢀ O=Mo=O) sym; 590 (ꢀ Mo–O);
H2L3; (E)-4-amino-N’-(5-methyl-2-hydroxybenzylidene)
benzohydrazide, Yield: 78%. Calculated for C15H15N3O2: C
66.90, H 5.61, N 15.60%. Analysis found: C 67.03, H 5.68,
N 15.47%. FT-IR (KBr, cm−1): 3439 (ꢀ N–H); 3368 & 3221
(ꢀ H–N–H); 1622 (ꢀ C=O); 1604 (ꢀ C=N); 1579 (ꢀ C=C); 1286 (ꢀ
C–O(phenolic)); 1082 (ꢀ N–N). 1H NMR (400 MHz, DMSO-d6,
ppm): 2.26 [3 H, s, (–CH3)], 5.85 [2 H, s, (–NH2)], 6.60 [2
467 (ꢀ Mo–N). H NMR (400 MHz, DMSO-d6, ppm): 3.18
1
3
[3 H, –CH3 (Methanol), d, J = 5.2 Hz], 4.13 [1 H, –OH
(Methanol), q, 3J=5.2 Hz], 6.00 [2 H, s, (–NH2)], 6.60 [2
H, (H–C11, H-C13), d, 3J=7.2 Hz], 6.95 [1 H, (H–C2), d,
3J=8.8 Hz], 7.49 [1 H, (H–C3), d, 3J=8.8 Hz], 7.68 [2 H,
(H–C10, H–C14), d, 3J=7.2 Hz], 7.80 [1 H, s, (H–C5)], 8.76
[1 H, s, (–CH=N)]. 13C NMR (100 MHz, DMSO-d6, ppm):
67.4 (C (Methanol)), 113.1 (C11, C13), 115.2 (C2), 120.3
(C6), 122.0 (C9), 124.6 (C4), 130.0 (C5), 132.2 (C10, C14),
133.3 (C3), 151.8 (C7), 152.9 (C12), 157.7 (C1), 169.9 (C8).
[MoO2(L2)(CH3OH)]: Yield 68%. Calculated for
C15H14BrMoN3O5: C 36.61, H 2.87, N 8.54%. Analysis
found: C 36.48, H 2.93, N 8.45%. FT-IR (KBr, cm−1):
3466 & 3361 (ꢀ H–N–H); 1604 (ꢀ C=N); 1544 (ꢀ C=C); 1490 (ꢀ
C=N–N=C); 1367 (ꢀ C–O(phenolic)); 1261 (ꢀ C–O); 1080 (ꢀ N–N);
935 (ꢀ O=Mo=O) asym; 898 (ꢀ O=Mo=O) sym; 590 (ꢀ Mo–O);
3
H, (H–C11, H–C13), d, J = 8.4 Hz], 6.82 [1 H, (H–C2),
d, 3J=8.0 Hz], 7.09 [1 H, (H–C3), d, 3J=8.0 Hz], 7.28 [1
H, (H–C5), d, 4J=2.4 Hz], 7.68 [2 H, (H–C10, H–C14), d,
3J=8.4 Hz], 8.51 [1 H, s, (–CH=N)], 11.29 [1 H, s, (–NH)],
11.72 [1 H, s, (–OH)]. 13C NMR (100 MHz, DMSO-d6,
ppm): 19.9 (C15), 112.6 (C11, C13), 116.2 (C2), 118.4 (C6),
118.7 (C9), 127.7 (C4), 129.4 (C5), 129.5 (C10, C14), 131.5
(C3), 146.7 (C7), 152.5 (C12), 155.2 (C1), 162.6 (C8).
H2L4; (E)-4-amino-N’-(5-methoxy-2-hydroxyben-
zylidene)benzohydrazide, Yield: 81%. Calculated for
C15H15N3O3: C 63.15, H 5.30, N 14.73%. Analysis found:
C 63.33, H 5.23, N 14.64%. FT-IR (KBr, cm−1): 3440 (ꢀ
N–H); 3360 & 3263 (ꢀ H–N–H); 1666 (ꢀ C=O); 1608 (ꢀ C=N);
1566 (ꢀ C=C); 1288 (ꢀ C–O(phenolic)); 1087 (ꢀ N–N). 1H NMR
(400 MHz, DMSO-d6, ppm): 3.73 [3 H, s, (-OCH3)], 5.85
[2 H, s, (-NH2)], 6.61 [2 H, (H-C11, H-C13), d, 3J=8.4 Hz],
6.85 [1 H, (H–C2), d, 3J=8.8 Hz], 6.89 [1 H, (H–C3), dd,
3J=8.8 Hz, 4J=2.4 Hz], 7.07 [1 H, (H–C5), d, 4J=2.4 Hz],
7.69 [2 H, (H–C10, H–C14), d, 3J=8.4 Hz], 8.55 [1 H, s,
(–CH=N)], 10.95 [1 H, s, (–NH)], 11.76 [1 H, s, (–OH)].
13C NMR (100 MHz, DMSO-d6, ppm): 55.4 (C15), 112.6
(C11, C13), 117.1 (C2), 117.6 (C6), 118.7 (C9), 119.0 (C4),
129.4 (C5), 129.7 (C10, C14), 146.2 (C3), 151.3 (C7), 152.0
(C12), 152.5 (C1), 162.7 (C8).
1
466 (ꢀ Mo–N). H NMR (400 MHz, DMSO-d6, ppm): 3.18
3
[3 H, –CH3 (Methanol), d, J = 5.2 Hz], 4.13 [1 H, –OH
(Methanol), q, 3J=5.2 Hz], 6.00 [2 H, s, (–NH2)], 6.60 [2
H, (H–C11, H-C13), d, 3J=7.2 Hz], 6.90 [1 H, (H–C2), d,
3J=8.8 Hz], 7.60 [1 H, (H–C3), d, 3J=8.8 Hz], 7.69 [2 H,
(H–C10, H–C14), d, 3J=7.2 Hz], 7.72 [1 H, s, (H–C5)], 8.76
[1 H, s, (–CH=N)]. 13C NMR (100 MHz, DMSO-d6, ppm):
66.3 (C (Methanol)), 112.1 (C11, C13), 113.1 (C2), 115.2
(C6), 120.7 (C9), 122.6 (C4), 130.0 (C5), 135.2 (C10, C14),
136.1 (C3), 151.7 (C7), 152.9 (C12), 158.2 (C1), 169.9 (C8).
[MoO2(L3)(CH3OH)]: Yield 64%. Calculated for
C16H17MoN3O5: C 44.98, H 4.01, N 9.83%. Analysis found:
C 45.14, H 4.06, N 9.75%. FT-IR (KBr, cm−1): 3369 & 3244
(ꢀ H–N–H); 1604 (ꢀ C=N); 1562 (ꢀ C=C); 1446 (ꢀ C=N–N=C);
1330 (ꢀ C–O(phenolic)); 1251 (ꢀ C–O); 1087 (ꢀ N–N); 923 (ꢀ
O=Mo=O) asym; 893 (ꢀ O=Mo=O) sym; 603 (ꢀ Mo–O); 462 (ꢀ
Mo–N). 1H NMR (400 MHz, DMSO-d6, ppm): 2.29 [3H, s,
-CH3], 3.18 [3 H, –CH3 (Methanol), d, 3J=5.2 Hz], 4.23 [1
H, –OH (Methanol), q, 3J=5.2 Hz], 5.95 [2 H, s, (–NH2)],
General procedure for the synthesis
of the complexes
3
For the synthesis of dioxomolybdenum complexes,
MoO2(Ln)(CH3OH), equimolar amounts of H2Ln (1 mmol)
and MoO2(acac)2 (1 mmol, 0.330 g) were suspended in
methanol (100 mL) in a round bottom fask equipped with
a magnetic bar for steady stirring to attain the uniformity.
The suspension was refuxed for approximately 3 h and then
2/3rd of the solvent was evaporated to concentrate the mix-
ture and the remaining solution was cooled over an ice bath
to get the orange-colored crystals. The crystals were col-
lected by fltration and then washed thoroughly with water,
methanol, and diethyl ether, separately, and fnally dried in
vacuo.
6.59 [2 H, (H–C11, H–C13), d, J = 8.4 Hz], 6.82 [1 H,
(H–C2), d, 3J=8.0 Hz], 7.29 [1 H, (H–C3), d, 3J=8.0 Hz],
4
7.54 [1 H, d, J = 1.6 Hz, (H–C5)], 7.68 [2 H, (H–C10,
H-C14), d, 3J=8.4 Hz], 8.71 [1 H, s, (–CH=N)]. 13C NMR
(100 MHz, DMSO-d6, ppm): 19.8 (C15), 66.3 (C (Metha-
nol)), 113.0 (C11, C13), 117.1 (C2), 118.1 (C6), 120.3 (C9),
129.8 (C4), 130.3 (C5), 133.3 (C10, C14), 152.7 (C3), 153.0
(C7), 153.4 (C12), 153.5 (C1), 169.8 (C8).
[MoO2(L4)(CH3OH)]: Yield 71%. Calculated for
C16H17MoN3O6: C 43.35, H 3.87, N 9.48%. Analysis found:
C 43.54, H 3.93, N 9.35%. FT-IR (KBr, cm−1): 3460 & 3410
(ꢀ H–N–H); 1604 (ꢀ C=N); 1558 (ꢀ C=C); 1489 (ꢀ C=N–N=C);
1373 (ꢀ C–O(phenolic)); 1276 (ꢀ C–O); 1037 (ꢀ N–N); 929 (ꢀ
O=Mo=O) asym; 898 (ꢀ O=Mo=O) sym; 617 (ꢀ Mo–O); 474 (ꢀ
[MoO2(L1)(CH3OH)]: Yield 73%. Calculated for
C15H14ClMoN3O5: C 40.24, H 3.15, N 9.39%. Analysis
found: C 40.38, H 3.19, N 9.28%. FT-IR (KBr, cm−1):
3466 & 3362 (ꢀ H–N–H); 1604 (ꢀ C=N); 1545 (ꢀ C=C); 1490 (ꢀ
1
Mo–N). H NMR (400 MHz, DMSO-d6, ppm): 3.18 [3 H,
–CH3 (Methanol), d, 3J=5.2 Hz], 3.77 [3H, s, –OCH3], 4.13
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Journal of the Iranian Chemical Society
[1 H, –OH (Methanol), q, 3J=5.2 Hz], 5.95 [2 H, s, (–NH2)],
Results and discussion
3
6.60 [2 H, (H–C11, H–C13), dd, J=8.4 Hz, 4J=2.4 Hz],
6.86 [1 H, (H–C2), dd, 3J=8.8 Hz, 4J=2.8 Hz], 7.09 [1 H,
(H–C3), dd, 3J=8.8 Hz, 4J=2.8 Hz], 7.29 [1 H, s, (H–C5)],
Synthesis
3
7.68 [2 H, (H–C10, H–C14), dd, J=8.4 Hz, 4J=2.4 Hz],
Hydrazone-based ONO-tridentate Schif base ligands, H2Ln,
were prepared by treating 4-aminobenzohydrazide with the
corresponding salicylaldehyde in nearly 78–87% yield in
methanol. The reaction of H2Ln with MoO2(acac)2 in a 1:1
ratio under refux conditions directed to the formation of
molybdenum(VI) complexes. The fndings from spectro-
scopic characterization are in compliance with the proposed
molecular formula of the synthesized compounds. Scheme 1
gives a comprehensive view of the synthetic procedure
adopted for the preparation of novel compounds.
8.73 [1 H, s, (–CH=N)]. 13C NMR (100 MHz, DMSO-d6,
ppm): 55.6 (C15), 65.5 (C (Methanol)), 113.0 (C11, C13),
115.7 (C2), 116.3 (C6), 119.0 (C9), 120.6 (C4), 120.7 (C5),
129.9 (C10, C14), 152.6 (C3), 152.7 (C7), 153.3 (C12),
153.4 (C1), 169.6 (C8).
General procedure for selective oxidation of sulfdes
with t‑BuOOH catalyzed by MoO2(Ln)(CH3OH)
complexes
1H NMR and 13C NMR spectra
To a solution of sulfde (1 mmol) and t-BuOOH (2 mmol) in
DCE (5 mL), Mo complex (0.01 mmol) was added and the
contents were refuxed with continuous stirring for the speci-
fed intervals of times as listed in Table 8. The continuation
of the catalytic conversion was scrutinized by thin-layer
chromatography by employing n-hexane and ethyl acetate
in 5:2 ratio. On the accomplishment of sulfoxidation, the
product was separated by column chromatography using
over silica gel with n-hexane and ethyl acetate (70:30) as an
eluent. All of the products were known compounds and were
also further confrmed by comparing their physicochemical
characteristics with those of authentic samples.
1
The H and 13C NMR data of the H2L1 ligand and its
Mo complex in DMSO-d6 is presented in the experimen-
tal section and the spectra are shown in Figs. 1, 2 and
3. Two signals appearing at δ = 11.85 and 11.54 ppm
1
in the H NMR spectrum of the ligand correspond to
OH (phenolic) and NH protons, respectively, disap-
pear on treatment with Mo salt, demonstrate about the
sites of coordination of the ligand with the molybde-
num. This also ascertains the occurrence of keto-imine
tautomerism upon complexation. Moreover, a singlet of
azomethine proton (–HC=N) at δ = 8.53 ppm observed
Fig. 1 1H NMR spectrum of the
H2L1 ligand in DMSO-d6
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Journal of the Iranian Chemical Society
Fig. 2 1H NMR spectrum of the
MoO2(L1)(CH3OH) complex in
DMSO-d6
in the spectrum of the ligand was shifted downfield at
δ = 8.76 ppm showing the deshielding due to the decrease
in the electronic density upon the coordination of azome-
thine nitrogen with the metal atom. There is a slight shift
in the positions of aromatic protons in the NMR spectra
of the ligand upon complex formation. A singlet of amino
proton (–NH2) at δ = 5.86 ppm observed in the spectrum
of the ligand was shifted downfield at δ = 5.99 ppm
showing the deshielding upon complex formation. These
protons are failed to exhibit any noticeable shifts in their
positions upon complexation.
FT‑IR spectra
FT-IR spectra of the H2L1 ligand and its Mo complex are
presented in Fig. 4. The two most important absorption
peaks visible in the vibrational spectra of ligand at 3625
and 1640 cm−1 are attributed to the stretching vibration of
ν(NH) and ν(C=O). These characteristic peaks were disap-
peared on complexation with molybdenum, intimating the
dianionic nature as well as the sites of coordination of the
ligand with metal. The azomethine chromophore (HC=N)
vibrational band for the H2L1 ligand and its complex was
appeared at 1603 and 1604 cm−1, respectively. The phenolic
oxygen of H2L1 ligand in complex formation was supported
by the shifting of its peculiar peak from 1286 to 1367 cm−1
as evident from the stacked FT-IR spectrum [60–63]. The
distinctive peaks of primary amine (NH2) were observed
at 3362 & 3440 cm−1 in the spectrum of the ligand and at
3362 and 3466 cm−1 in the MoO2(L1)(CH3OH) complex.
Cis-Mo(O)2 fraction also gives its symmetric and asymmet-
ric stretching vibration bands at 899 and 935 cm−1, respec-
tively, which are in accordance with the literature [62, 63].
Moreover, some new Mo–O and Mo–N peaks are also vis-
ible at 590 and 467 cm−1, respectively, for the Mo com-
plex, which is also in agreement with the similar complexes
reported earlier [64–66]. The important absorption peaks
of the ligands and Mo complexes are listed in Table 3. The
spectra of H2L2–H2L4 and their Mo complexes are also given
in Figures S13-S18.
The 13C NMR spectra of the H2L1 ligand and its Mo
complex are shown in Fig. 3. The signals for the car-
bonyl, phenolic, and methine carbons were observed at
162.8, 155.9, and 152.6 ppm, respectively. The chemi-
cal shift values of the carbons present in the vicinity of
the coordinating atoms (i.e., C8, C1, and C7) showed
an appreciable change in their position due to coordina-
tion-induced shifts confirming the association of these
functionalities in coordination. The other aromatic car-
bons of the ligand and Mo complex appeared in their
respective regions according to the literature. Hence,
13C NMR spectra also support the conclusions made
1
1
from H NMR spectral data. The H and 13C NMR
chemical shifts of all ligands and their Mo complexes
are given in Tables 1 and 2. Also, the NMR spectra of
H2L2–H2L4 ligands and their Mo complexes are shown
in Figures S1-S12.
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Fig. 3 13C NMR spectra of the ligand H2L1 (Top) and its MoO2(L1)(CH3OH) complex (Bottom) in DMSO-d6
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1
Table 1 Characteristic H NMR chemical shift values (ppm), peak multiplicity and coupling constant J (Hz) for the synthesized ligands and
complexes recorded in DMSO-d6
Protons
Ligands
H2L1 (X = Cl)
H2L2 (X = Br)
H2L3 (X = Me)
H2L4 (X = OMe)
–CH3
–NH2
H11 & H13
H2
–
–
2.26 (s, 3H)
5.85 (s, 2H)
3.73 (s, 3H)
5.85 (s, 2H)
5.86 (s, 2H)
5.87 (s, 2H)
6.61 (d, 2H), [3J=8.4 Hz] 6.61 (d, 2H), [3J=8.8 Hz] 6.60 (d, 2H), [3J=8.4 Hz] 6.61 (d, 2H), [3J=8.4 Hz]
6.94 (d, 1H), [3J=8.8 Hz] 6.89 (d, 1H), [3J=8.4 Hz] 6.82 (d, 1H), [3 =8.0 Hz]
6.85 (d, 1H), [3J=8.8 Hz]
H3
7.29 [dd, 1H), [3J=8.8 Hz, 7.40 [dd, 1H), [3J=8.8 Hz, 7.09 [d, 1H), [3J=8.0 Hz] 6.89 [dd, 1H), [3J=8.8 Hz, 4J=2.4 Hz]
4J=2.4 Hz]
4J=2.4 Hz]
H5
H10 & H14
H7
–NH
–OH
7.61 (d, 2H), [4J=2.4 Hz] 7.74 (d, 2H), [4J=2.4 Hz] 7.28 (d, 2H), [4J=2.4 Hz] 7.07 (d, 2H), [4J=2.4 Hz]
7.68 (d, 2H), [3J=8.4 Hz] 7.69 (d, 2H), [3J=8.8 Hz] 7.68 (d, 2H), [3J=8.4 Hz] 7.69 (d, 2H), [3J=8.4 Hz]
8.53 (s, 1H)
11.54 (s, 1H)
11.85 (s, 1H)
8.53 (s, 1H)
11.55 (s, 1H)
11.85 (s, 1H)
8.51 (s, 1H)
11.29 (s, 1H)
11.72 (s, 1H)
8.55 (s, 1H)
10.95 (s, 1H)
11.76 (s, 1H)
Protons
Complexes
MoO2L1 (X = Cl)
MoO2L2 (X = Br)
–
MoO2L3 (X = Me)
2.29 (s, 3H)
MoO2L4 (X = OMe)
3.77 (s, 3H)
–CH3
–
–CH3 (MeOH) 3.18 (d, 3H), [3J=5.2 Hz] 3.18 (d, 3H), [3J=5.2 Hz] 3.18 (d, 3H), [3J=5.2 Hz] 3.18 (d, 3H), [3J=5.2 Hz]
–OH (MeOH)
–NH2
H11 & H13
H2
H3
H10 & H14
H5
4.13 (q, 1H), [3 =5.2 Hz]
6.00 (s, 2H)
4.13 (q, 1H), [3J=5.2 Hz] 4.23 (q, 1H), [3J=5.2 Hz] 4.13 (q, 1H), [3J=5.2 Hz]
6.00 (s, 2H) 5.95 (s, 2H) 5.95 (s, 2H)
6.60 (d, 2H), [3J=7.2 Hz] 6.60 (d, 2H), [3J=7.2 Hz] 6.59 (d, 2H), [3J=8.4 Hz] 6.60 (dd, 2H), [3J=8.4 Hz, 4J=2.4 Hz]
6.95 (d, 1H), [3J=8.8 Hz] 6.90 (d, 1H), [3J=8.8 Hz] 6.82 (d, 1H), [3J=8.0 Hz] 6.86 (dd, 1H), [3J=8.8 Hz, 4J=2.8 Hz]
7.49 (d, 1H), [3J=8.8 Hz] 7.60 (d, 1H), [3J=8.8 Hz] 7.29 (d, 1H), [3J=8.0 Hz] 7.09 (dd, 1H), [3J=8.8 Hz, 4J=2.8 Hz]
7.68 (d, 2H), [3J=7.2 Hz] 7.69 (d, 2H), [3J=7.2 Hz] 7.68 (d, 2H), [3J=8.4 Hz] 7.68 (dd, 2H), [3J=8.4 Hz, 4J=2.4 Hz]
7.80 (s, 1H)
8.76 (s, 1H)
7.72 (s, 1H)
8.76 (s, 1H)
7.54 (d, 1H), [4J=1.6 Hz] 7.29 (s, 1H)
8.71 (s, 1H) 8.73 (s, 1H)
H7
The efect of diferent oxidants like NaIO4, H2O2, urea
H2O2 (UHP), (Bu)4NIO4, and t-BuOOH was investigated for
the oxidation of diphenyl sulfde in the presence of Mo cata-
lyst. The results showed that t-BuOOH is the best source of
oxygen in sulfoxidation and it was also proved the reaction
could not be performed in the absence of oxidant (Table 5).
The efect of diferent amounts of oxidant was studied
and the results are shown in Table 6. The conversion did
not complete in the presence of amounts less than 2 mmol
of oxidant. The best amount of oxidant was 2 mmol, which
completed the reaction and produced sulfoxide as the only
product. The greater amount of oxidant converted some of
the sulfoxides to sulfone and produced a mixture of the two
products.
Catalytic activity
Dioxomolybdenum complexes often show interesting cat-
alytic properties, especially in oxidation reactions [67].
Compared to previously reported species, the present com-
plexes have excellent activity and selectivity. The catalytic
efciency of Mo(VI) complexes was investigated by the
selective sulfoxidation reaction. To optimize the reaction
conditions, the oxidation of diphenyl sulfde (1 mmol) using
t-BuOOH (2 mmol) in the presence of MoO2(L1)(CH3OH)
complex was selected as a model reaction, and the infu-
ence of diferent factors, that may afect the reaction, were
studied.
To fnd the most suitable solvent for this reaction, various
solvents, such as toluene, acetonitrile, acetone, 1,2-dichlo-
roethane (DCE), chloroform, dichloromethane, ethanol, and
n-hexane were examined in the presence of t-BuOOH as oxi-
dant and MoO2(L1)(CH3OH) complex as catalyst (Table 4).
DCE was found to be the best solvent for the reaction due to
its higher reactivity and selectivity.
The effect of different amounts of catalyst was also
investigated and the outcomes are listed in Table 7. It was
observed that in the absence of the catalyst the reaction
failed to proceed. The rate of conversion was increased
with the increase in the amount of catalyst and complete
1 3

Journal of the Iranian Chemical Society
Table 2 Characteristic 13C NMR chemical shift values (ppm) for the synthesized ligands and complexes recorded in DMSO-d6
Carbons
Ligands
H2L1 (X = Cl)
H2L2 (X = Br)
H2L3 (X = Me)
H2L4 (X = OMe)
–CH3
C11 & C13
C2
C6
C9
C4
C5
C10 & C14
C3
–
–
19.9
55.4
112.6
118.1
118.5
120.7
122.8
127.8
129.4
130.3
144.5
152.6
155.9
162.8
110.3
112.6
118.5
118.6
121.3
129.4
130.7
133.1
144.3
152.6
156.3
162.8
112.6
116.2
118.4
118.7
127.7
129.4
129.5
131.5
146.7
152.5
155.2
162.6
112.6
117.1
117.6
118.7
119.0
129.4
129.7
146.2
151.3
152.0
152.5
162.7
C7
C12
C1
C8
Carbons
Complexes
MoO2L1 (X = Cl)
MoO2L2 (X = Br)
MoO2L3 (X = Me)
MoO2L4 (X =
OMe)
–CH3
-CH3 (MeOH)
–
67.4
–
66.3
19.8
66.3
55.6
65.5
C11 & C13
C2
C6
C9
C4
C5
C10 & C14
C3
C7
113.1
115.2
120.3
122.0
124.6
130.0
132.2
133.3
151.8
152.9
157.7
169.9
112.1
113.1
115.2
120.7
122.6
130.0
135.2
136.1
151.7
152.9
158.2
169.9
113.0
117.1
118.1
120.3
129.8
130.3
133.3
152.7
153.0
153.4
153.5
169.8
113.0
115.7
116.3
119.0
120.6
120.7
129.9
152.6
152.7
153.3
153.4
169.6
C12
C1
C8
transformation was cropped up when 0.01 mmol of the cata-
lyst was used in the oxidation of 1 mmol diphenyl sulfde.
After optimizing the reaction conditions, oxidation of
diferent aliphatic and aromatic sulfdes in the presence of
MoO2(Ln)(CH3OH) complexes was evaluated under the
optimized reaction conditions (Table 8). It is obvious from
Table 8 that all studied sulfdes were completely converted
into their sulfoxides. The chemoselectivity of the procedure
was remarkable. The sulfdes were oxidized under the afec-
tion of this catalytic system and the desired sulfoxides were
obtained in 100% selectivity. The most important advantage
of this method is that there is no evidence of overoxidation
to the production of sulfone in all substrates.
Based on previously reported mechanisms [68], a plausi-
ble mechanism for the oxidation of sulfdes using t-BuOOH
catalyzed by [MoO2(Ln)(CH3OH)] complexes is pro-
posed and depicted in Scheme 2. The catalyst, which is a
dioxomolybdenum(VI) complex, is inactive as such in the
oxidation process. The complex reacts with the peroxide to
form the peroxomolybdenum species as intermediate, which
is active in the oxidation reaction. It seems that the oxidation
of sulfdes to sulfoxides in the presence of peroxides pro-
ceeds through a one-step oxygen-transfer mechanism with
the simultaneous electrophilic attack of the sulfur on one
of the oxygens of peroxide and breaking the O–O bond and
formation of the S=O bond.
1 3

Journal of the Iranian Chemical Society
Fig. 4 FT-IR spectra of the
H2L1 ligand and MoO2(L1)
(CH3OH) complex
H2L1
C=N
NH
MoO2L1
NH2
C=O
NH2
C=N
Table 3 FT-IR spectral data of
Assignment
H2L1
MoO2L1
–
H2L2
3624
MoO2L2
–
H2L3
3439
MoO2L3
H2L4
3440
MoO2L4
–
the ligands and their Mo(IV)
complexes (cm−1
)
ꢀ
ꢀ
3625
–
N–H
3440
3466
3441
3466
3368
3369
3360
3460
H–N–H
3362
3362
3360
3361
3221
3244
3263
3410
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
1640
1603
1556
-
1287
–
1086
–
–
–
–
–
1639
1602
1556
-
1286
–
1085
–
–
–
–
–
1622
1604
1579
-
1286
–
1082
–
–
–
–
–
1666
1608
1566
-
1288
–
1087
–
–
–
–
–
C=O
1604
1545
1490
1367
1261
1080
935
899
590
467
1604
1544
1490
1367
1261
1080
935
898
590
466
1604
1562
1446
1330
1251
1087
923
893
603
462
1604
1558
1489
1373
1276
1037
929
898
617
474
C=N
C=C
C=N–N=C
C–O(phenolic)
C–O
N–N
O=Mo=O(asym)
O=Mo=O(sym)
Mo–O
Mo–N
1 3

Journal of the Iranian Chemical Society
Table 4 The efect of solvent on the oxidation of diphenyl sulfde
with t-BuOOH catalyzed by MoO2(L1)(CH3OH)a
Table 6 The efect of diferent amounts of oxidant on the oxidation of
diphenyl sulfde catalyzed by MoO2(L1)(CH3OH)a
Entry
Solvent
Conver-
sion
Entry
Oxidant amount
(mmol)
Conversion (%)b Selectivity
to sulfoxide
(%)b
(%)c
1
2
3
4
5
6
7
8
Toluene
n-Hexane
75
80
90
50
100
90
50
80
1
2
3
4
5
6
1
40
55
65
80
100
100
100
100
100
100
100
78
1.2
1.5
1.8
2
Acetonitrile
Acetone
1,2-Dichloroethane
Chloroform
Dichloromethane
Ethanol
3
aReaction conditions: diphenyl sulfde (1 mmol), t-BuOOH, catalyst
(1 mol%), DCE (5 mL), refux, 1 h
bGC yields
aReaction conditions: diphenyl sulfde (1 mmol), t-BuOOH (2 mmol),
catalyst (1 mol%), solvent (5 mL), refux, 1 h
cSelectivity to sulfoxide=(sulfoxide%/(sulfoxide%+sulfone%))×100
bGC yields
Table 5 The efect of oxidant
Table 7 The efect of amounts
Entry Oxidant
Conver-
sion
Entry Catalyst
amount
Conver-
sion
on the oxidation of diphenyl
sulfde catalyzed by MoO2(L1)
(CH3OH)a
of catalyst on the oxidation of
diphenyl sulfde catalyzed by
MoO2(L1)(CH3OH)a
(%)b
(mmol)
(%)b
1
2
3
4
5
6
No oxidant
NaIO4
H2O2
UHP
Bu4NIO4
t-BuOOH
0
1
2
3
4
5
No catalyst
0
90
80
70
10
100
0.002
0.005
0.008
0.010
50
70
90
100
aReaction conditions: diphenyl
sulfde (1 mmol), t-BuOOH
(2 mmol), DCE (5 mL), refux,
1 h
aReaction conditions: diphe-
nyl sulfde (1 mmol), oxidant
(2 mmol), catalyst (1 mol%),
DCE (5 mL), refux, 1 h
bGC yields
bGC yields
Conclusion
To demonstrate the capability and efficiency of
[MoO2(Ln)(CH3OH)] complexes as homogeneous catalysts
over the reported catalysts in the literature for oxidation of
sulfdes, the oxidation reaction of methylphenyl sulfde was
considered as a representative example and conducted in
the presence of diferent catalysts (Table 9). The results of
this comparison study revealed that [MoO2(Ln)(CH3OH)]
catalysts accelerate the rate of reaction and provide a high
yield of the desired product.
We have synthesized a series of [MoO2(Ln)(CH3OH)] com-
plexes with hydrazone-type Schif bases derived by the
condensation of substituted salicylaldehydes and 4-amin-
obenzohydrazide in methanol. The synthesized ligands and
their Mo(VI) complexes were characterized by FT-IR, 1H
NMR, 13C NMR, and elemental analysis (CHN). The coor-
dination sites are azomethine nitrogen, enolic and phenolic
1 3

Journal of the Iranian Chemical Society
Table 8 Selective oxidation of sulfdes with t-BuOOH catalyzed by MoO2(Ln)(CH3OH) complexesa
Time (min.)/Yield (%) c
Entry
Sulfide
Sulfoxideb
MoO2L1
15/89
MoO2L2
MoO2L3
15/90
MoO2L4
15/89
O
S
S
1
2
3
15/88
15/89
10/88
S
O
S
15/91
10/89
15/90
10/90
15/90
10/87
O
S
S
O
4
5
6
S
S
S
S
CH3
20/93
60/92
30/90
20/94
60/93
30/92
20/91
60/91
30/90
20/93
60/89
30/93
S
CH3
O
S
O
S
CH2
CH2
CH2
CH2
O
S
7
40/91
40/90
40/91
40/88
Cl
Cl
O
S
S
S
CH2
CH2
S
NO2
CH3
8
30/88
20/93
15/89
20/90
30/89
20/92
15/90
20/87
30/85
20/90
15/87
20/89
30/85
20/89
15/91
20/90
CH2
CH2
NO2
CH3
O
S
9
O
S
CH3
CH3
CH2
CH3
Br
10
11
CH3
CH3
CH2
CH3
Br
O
S
S
CH2
CH2
aReaction conditions: sulfde (1 mmol), t-BuOOH (2 mmol), catalyst (1 mol%), DCE (5 mL), refux conditions
bAll products were identifed by the comparison of their physical and spectral data with those of authentic samples
c Isolated yield
1
oxygens as evident from H NMR and FT-IR. Moreover,
the catalytic activities of the complexes were evaluated for
the selective oxidation of sulfdes to sulfoxides by the use
of t-BuOOH in 1,2-dichloroethane under refux conditions.
This procedure ofers several advantages, including high
yield, short reaction time, and excellent selectivity to pro-
duce corresponding sulfoxides without overoxidation to
sulfones.
1 3

Journal of the Iranian Chemical Society
Scheme 2 Plausible mechanism for the oxidation of sulfdes with t-BuOOH catalyzed by MoO2Ln(CH3OH) complexes
Table 9 Comparison of the
efciency of [MoO2(Ln)
(CH3OH)] complexes
Entry
Catalyst
Conditions
Time (min)
Yield (%)
Ref
1
2
3
4
5
6
7
8
[PZnMo2W9O39]5−
IL(R=t-Bu)-V(IV)
IL(R=NO2)-V(IV)
VO2F(dmpz)2
V(IV)O-MCM-41
VO(acac)@Sb@SMNPs
Fe3O4/salen of Cu(II)
PMo12 ⊂Mo72Fe30
SiMo12 ⊂Mo72Fe30
MoO2(L1)(CH3OH)
MoO2(L2)(CH3OH)
MoO2(L3)(CH3OH)
MoO2(L4)(CH3OH)
H2O2, CH3CN, r.t
30
92
85
76
95
95
100
83
85
93
93
94
91
93
[69]
[70]
[70]
[71]
[72]
[73]
[74]
[75]
with some other reported
catalysts for the oxidation of
methylphenyl sulfde
H2O2, CH2Cl2, 20 °C
H2O2, CH2Cl2, 20 °C
H2O2, MeCN, 0–5 °C
UHP, EtOH, r.t
TBHP, DCE, 85 °C
H2O2, EtOH, 60 °C
H2O2, CH2Cl2/EtOH, r.t
H2O2, CH2Cl2/EtOH, r.t
t-BuOOH, DCE, refux
t-BuOOH, DCE, refux
t-BuOOH, DCE, refux
t-BuOOH, DCE, refux
240
240
300
480
60
180
75
75
20
20
20
9
[75]
10
11
12
13
This work
This work
This work
This work
20
1 3

Journal of the Iranian Chemical Society
26. T.A. Alsalim, J.S. Hadi, E.A. Al-Nasir, H.S. Abbo, S.J.J. Titinchi,
Catal. Lett. 136, 228 (2010)
Supplementary Information The online version contains supplemen-
tary material available at https://doi.org/10.1007/s13738-021-02282-0.
27. A.P. de Azevedo Marques, E.R. Dockal, F.C. Skrobot, I.L.V. Rosa,
Inorg. Chem. Commun. 10, 255 (2007)
Acknowledgements We gratefully acknowledge practical support of
28. S. Bunce, R.J. Cross, L.J. Farrugia, S. Kunchandy, L.L. Meason,
K.W. Muir, M. O’Donnel, R.D. Peacock, D. Stirling, S.J. Teat,
Polyhedron 17, 4179 (1998)
this study by Ardakan University and Payame Noor University.
Declarations
29. K.S. Munawar, S. Ali, M.N. Tahir, N. Khalid, Q. Abbas, I.
Qureshi, S. Shahzadi, Russ. J. Gen. Chem. 85, 2183 (2015)
30. R.S. Walmsley, Z.R. Tshentu, S. Afr, J. Chem. 63, 95 (2010)
31. S. Mohebbi, F. Nikpour, S. Raiati, J. Mol. Catal. A: Chem. 256,
265 (2006)
Conflict of interest No potential confict of interest was reported by
the authors.
32. M.M. Cecchini, F. De Angelis, C. Iacobucci, S. Reale, M. Cruci-
anelli, Appl. Catal. A: Gen. 599, 117622 (2020)
References
33. M. Mancka, W. Plass, Inorg. Chem. Commun. 10, 677 (2007)
34. M. Salavati-Niasari, M. Bazarganipour, J. Mol. Catal. A: Chem.
278, 173 (2007)
1. J. Devi, N. Batra, R. Malhotra, Spectrochim. Acta Part A 97, 397
(2012)
35. Y.D. Li, X.K. Fu, B.W. Gong, X.C. Zou, X.B. Tu, J.X. Chen, J.
Mol. Catal. A: Chem. 322, 55 (2010)
2. M. Gupta, S. Sihag, A.K. Varshney, S. Varshney, J. Chem. 745101
(2013)
36. Y. Yang, Y. Zhang, S.J. Hao, Q.B. Kan, J. Colloid Interface Sci.
362, 157 (2011)
3. E. Yousif, A. Majeed, K. Al-Sammarrae, N. Salih, J. Salimon, B.
Abdullah, Arab. J. Chem. 10, S1639 (2017)
37. S.M. Bruno, J.A. Fernandes, L.S. Martins, I.S. Goncalves, M.
Pillinger, P. Ribeiro-Claro, J. Rocha, A.A. Valente, Catal. Today
114, 263 (2006)
4. H. Kargar, R. Behjatmanesh-Ardakani, V. Torabi, M. Kashani, Z.
Chavoshpour-Natanzi, Z. Kazemi, V. Mirkhani, A. Sahraei, M.N.
Tahir, M. Ashfaq, K.S. Munawar, Polyhedron 195, 114988 (2021)
5. H. Kargar, R. Behjatmanesh-Ardakani, V. Torabi, A. Sarvian, Z.
Kazemi, Z. Chavoshpour-Natanzi, V. Mirkhani, A. Sahraei, M.N.
Tahir, M. Ashfaq, Inorg. Chim. Acta 514, 120004 (2021)
6. R. Sudheer, M. Sithambaresan, N.R. Sajitha, E. Manoj, M.P.
Kurup, Acta Crystallogr. E71, 702 (2015)
38. C.Y. Lorber, S.P. Smidt, J.A. Osborn, Eur. J. Inorg. Chem. 655
(2000)
39. I. Fernandez, N. Khiar, Chem. Rev. 103, 3651 (2003)
40. A.M. Khenkin, R. Neumann, J. Am. Chem. Soc. 124, 4198 (2002)
41. N. Baig, V.K. Madduluri, A.K. Sah, RSC Adv. 6, 28015 (2016)
42. D.H. Hua, in Advances in Carbanion Chemistry, ed. by V.
Snieckus (JAI Press, London, 1992)
7. P.B. Sreeja, M.R.P. Kurup, A. Kishore, C. Jasmin, Polyhedron 23,
575 (2004)
43. P. Renaud, M. Gerster, Angew. Chem. Int. Ed. 37, 2562 (1998)
44. Y.Z. Wang, P. Wang, C. Li, Y.Q. Su, Synth. React. Inorg. Met.-
Org. Nano-Met. Chem. 46, 927 (2016)
8. R.S. Nair, M. Kuriakose, V. Somasundaram, V. Shenoi, M.R.P.
Kurup, P. Srinivas, Life Sci. 116, 90 (2014)
45. P. Suresh, S. Srimurugan, B. Babu, H.N. Pati, Tetrahedron Asym-
metry 18, 2820 (2007)
9. E.N. Nfor, A. Husian, F. Majoumo-Mbe, I.N. Njah, O.E. Ofong,
S.A. Bourne, Polyhedron 63, 207 (2013)
46. R.D. Chakravarthy, K. Suresh, V. Ramkumar, D.K. Chand, Inorg.
Chim. Acta 376, 57 (2011)
10. R. Pal, V. Kumar, A.K. Gupta, V. Beniwal, Med. Chem. Res. 23,
3327 (2014)
47. M.M. Javadi, M. Moghadam, I. Mohammadpoor-Baltork, S. Tang-
estaninejad, V. Mirkhani, J. Iran. Chem. Soc. 12, 477 (2015)
48. V. Mirkhani, S. Tangestaninejad, M. Moghadam, I. Mohammad-
poor-Baltork, H. Kargar, J. Mol. Catal. A: Chem. 242, 251 (2005)
49. M.M. Javadi, M. Moghadam, I. Mohammadpoor-Baltork, S. Tang-
estaninejad, V. Mirkhani, H. Kargar, M.N. Tahir, Polyhedron 72,
19 (2014)
11. M. Wu, D.D. Yang, H.W. Zheng, Q.F. Liang, J.B. Li, Y. Kang, S.
Li, C. Jiao, X.J. Zheng, L.P. Jin, Dalton Trans. 50, 1507 (2021)
12. R.P. Bakale, G.N. Naik, C.V. Mangannavar, I.S. Muchchandi, I.N.
Shcherbakov, C. Frampton, K.B. Gudasi, Eur. J. Med. Chem. 73,
38 (2014)
13. B. Türkkan, B. Sarıboğa, N. Sarıboğa, Transit. Met. Chem. 36,
679 (2011)
50. W. Sheng, J.-L. Shi, H. Hao, X. Li, X. Lang, J. Colloid Interface
Sci. 565, 614 (2020)
14. D.M. Boghaei, S. Mohebi, J. Mol. Catal. A: Chem. 179, 41 (2002)
15. P.G. Cozzi, Chem. Soc. Rev. 33, 410 (2004)
16. K.S. Munawar, S. Ali, M.N. Tahir, N. Khalid, Q. Abbas, I.Z.
Qureshi, S. Hussain, M. Ashfaq, J. Coord. Chem. 73, 2275 (2020)
17. R. Ramnauth, S. Al-Juaid, M. Motevalli, B.C. Parkin, A.C. Sul-
livan, Inorg. Chem. 43, 4072 (2004)
51. H. Kargar, Transit. Met. Chem. 39, 811 (2014)
52. R. Kia, H. Kargar, J. Coord. Chem. 68, 1441 (2015)
53. A. Sahraei, H. Kargar, M. Hakimi, M.N. Tahir, J. Mol. Struct.
1149, 576 (2017)
54. A.A. Ardakani, H. Kargar, N. Feizi, M.N. Tahir, J. Iran. Chem.
Soc. 15, 1495 (2018)
18. H. Li, J. Wu, X. Huang, G. Lu, J. Yang, X. Lu, Q. Xiong, H.
Zhang, ACS Nano 7, 10344 (2013)
55. H. Kargar, V. Torabi, A. Akbari, R. Behjatmanesh-Ardakani, M.N.
Tahir, J. Iran. Chem. Soc. 16, 1081 (2019)
19. C. Wang, M. Yu, A.F. Kyle, P. Jakubec, D.J. Dixon, R.R. Schrock,
A.H. Hoveyda, Chem. Eur. J. 19, 2726 (2013)
56. H. Kargar, V. Torabi, A. Akbari, R. Behjatmanesh-Ardakani, A.
Sahraei, M.N. Tahir, J. Mol. Struct. 1205, 127642 (2020)
57. H. Kargar, F. Aghaei-Meybodi, R. Behjatmanesh-Ardakani, M.R.
Elahifard, V. Torabi, M. Fallah-Mehrjardi, M.N. Tahir, M. Ashfaq,
K.S. Munawar, J. Mol. Struct. 1230, 129908 (2021)
58. H. Kargar, A.A. Ardakani, M.N. Tahir, M. Ashfaq, K.S. Munawar,
J. Mol. Struct. 1229, 129842 (2021)
20. K.C. MacLeod, P.L. Holland, Nat. Chem. 5, 559 (2013)
21. H. Sugimoto, S. Tatemoto, K. Toyota, K. Ashikari, M. Kubo, T.
Ogura, S. Itoh, Chem. Commun. 49, 4358 (2013)
22. H. Sugimoto, M. Sato, L.J. Giles, K. Asano, T. Suzuki, M.L. Kirk,
S. Itoh, Dalton Trans. 42, 15927 (2013)
23. M.E. Judmaier, C.H. Sala, F. Belaj, M. Volpe, N.C. Mösch-Zan-
etti, New J. Chem. 37, 2139 (2013)
59. H. Kargar, A.A. Ardakani, K.S. Munawar, M. Ashfaq, M.N.
Tahir, J. Iran. Chem. Soc. (2021). https://doi.org/10.1007/
s13738-021-02207-x
24. M. Bagherzadeh, L. Tahsini, R. Latif, A. Ellern, L.K. Woo, Inorg.
Chim. Acta 361, 2019 (2008)
25. M.R. Maurya, M. Kumar, S.J.J. Titinchi, H.S. Abbo, S. Chand,
Catal. Lett. 86, 97 (2003)
1 3

Journal of the Iranian Chemical Society
60. A.K. Singh, O.P. Pandey, S.K. Sengupta, Spectrochim. Acta Part
A 85, 1 (2012)
68. F. Ruf, A. Fabian, O. Farkas, A. Kucsman, Eur. J. Org. Chem.
2102 (2009)
61. S. Durmus, A. Atahan, M. Zengin, Spectrochim. Acta Part A 84,
1 (2011)
69. B. Yadollahi, Chem. Lett. 32, 1066 (2003)
70. R. Tan, C. Li, Z. Peng, D. Yin, D. Yin, Catal. Commun. 12, 1488
(2011)
62. A.H. Kianfar, M. Paliz, M. Roushani, M. Shamsipur, Spectrochim.
Acta Part A 127, 422 (2014)
71. S. Hussain, D. Talukdar, S.K. Bharadwaj, M.K. Chaudhuri, Tet-
rahedron Lett. 53, 6512 (2012)
63. M. Shebl, Spectrochim. Acta Part A 70, 850 (2008)
64. S. Gao, X.-F. Zhang, L.-H. Huo, H. Zhao, Acta Crystallogr. E60,
m1731 (2004)
72. M. Nikoorazm, A. Ghorbani-Choghamarani, N. Noori, Appl.
Organomet. Chem. 29, 328 (2015)
65. A. Rana, R. Dinda, P. Sengupta, S. Ghosh, L.R. Falvello, Polyhe-
dron 21, 1023 (2002)
73. M. Bagherzadeh, M. Bahjati, A. Mortazavi-Manesh, J. Orga-
nomet. Chem. 897, 200 (2019)
66. V. Vrdoljak, M. Cindric, D. Milic, D. Matkovic-Calogovic, P.
Novak, B. Kamenar, Polyhedron 24, 1717 (2005)
67. T.M. Asha, M.R.P. Kurup, J. Chem. Crystallogr. 49, 219 (2019)
74. A. Ghorbani-Choghamarani, B. Ghasemi, Z. Safari, G. Azadi,
Catal. Commun. 60, 70 (2015)
75. H. Taghiyar, B. Yadollahi, Sci. Total Environ. 708, 134860 (2020)
1 3