A novel binuclear iron(III)-salicylaldazine complex; synthesis, X-ray structure and catalytic activity in sulfide oxidation

Article abstract of DOI:10.1016/j.poly.2020.114531

A novel binuclear iron(III)-salicylaldazine complex has been synthesized and characterized by various techniques such as IR and UV–Vis spectroscopy and X-ray crystallography. The catalytic oxidation of sulfides in the presence of the aforementioned complex was explored at room temperature using urea hydrogen peroxide (UHP) as an oxidant. Effects of different reaction conditions consisting catalyst and oxidant amount, solvent effect and reaction time on the catalytic activity and selectivity in the reaction of methylphenylsulfide oxidation has been surveyed. Perfect selectivity toward sulfoxide was achieved after 15 min in CH₃CN by choice of a properly optimized reaction condition.

Full text of DOI:10.1016/j.poly.2020.114531

Polyhedron 183 (2020) 114531
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
A novel binuclear iron(III)-salicylaldazine complex; synthesis, X-ray
structure and catalytic activity in sulfide oxidation
Elnaz Mesbahi , Mojtaba Bagherzadeh , Mojtaba Amini b, , Ali Akbari , Arkady Ellern , L. Keith Woo
a
a,
⇑
⇑
c
d
d
a
Chemistry Department, Sharif University of Technology, P.O. Box 11155-3615, Tehran, Iran
Department of Chemistry, Faculty of Science, University of Maragheh, Maragheh, Iran
Solid Tumor Research Center, Cellular and Molecular Medicine Institute, Urmia University of Medical Sciences, Urmia, Iran
Chemistry Department, Iowa State University, Ames, IA 50011-3111, USA
b
c
d
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel binuclear iron(III)-salicylaldazine complex has been synthesized and characterized by various
techniques such as IR and UV–Vis spectroscopy and X-ray crystallography. The catalytic oxidation of sul-
fides in the presence of the aforementioned complex was explored at room temperature using urea
hydrogen peroxide (UHP) as an oxidant. Effects of different reaction conditions consisting catalyst and
oxidant amount, solvent effect and reaction time on the catalytic activity and selectivity in the reaction
of methylphenylsulfide oxidation has been surveyed. Perfect selectivity toward sulfoxide was achieved
Received 31 January 2020
Accepted 25 March 2020
Available online 30 March 2020
Keywords:
Catalyst
Binuclear
Iron
after 15 min in CH
3
CN by choice of a properly optimized reaction condition.
Ó 2020 Elsevier Ltd. All rights reserved.
Oxidation
Sulfide
1
. Introduction
employed in the sulfoxidation process due to their availability,
low cost and environmental benignity [12–15].
With regard to the presence of diiron centers in a variety of bio-
logical systems, such as ( -oxo) bis( -carboxylato) diiron(III) core
in methemerythrin and a ( -oxo)( -carboxylato)diiron(III) core in
In this paper, the synthesis and x-ray crystallography of a novel
l
l
2 2
binuclear iron(III) complex using N O -donor Schiff base salicylal-
l
l
dazine (H salcyn) as a ligand is reported. Moreover, the catalytic
2
E. coli ribonucleotide reductase, synthesis and characterization of
novel binuclear iron complexes have been paid attention consider-
ably in the field of inorganic chemistry. These complexes could be
considered as a synthetic model mimicking the actual biological
systems closely as possible [1–5]. Transition metal complexes con-
sisting of various ligands such as phthalocyanines, porphyrins, and
azines have been widely studied in this case. Azines are potential
ligands capable of forming metal chelates with transition metal
ions. Salicylaldazine, as a member of azine compounds, has also
the tendency to form a chelate with different transition metals.
Although there have been a lot of studies investigating the crystal
structure of the salicylaldazine, there has been fewer surveys
reporting the structure of its metal complexes so far [6].
activity of the mentioned complex in the presence of urea hydro-
gen peroxide (UHP) as an oxidant during selective oxidation of sul-
fides to corresponding sulfoxides under mild reaction condition is
explored (Scheme 1).
2
. Experimental section
All chemicals and solvents were purchased from Fluka and
2
Merck companies. Salicylaldazine (H salcyn) was synthesized
according to a published procedure [16].
The selective oxidation of sulfides to sulfoxides is one of the
chemical transformations in chemistry [7–11]. Variety of catalytic
systems constructed from iron complexes have been successfully
2 3 2 5
2.1. Synthesis of the complex [Fe (salcyn) ]∙C H OH
The complex was synthesized through the addition of an
ethanolic solution (15 ml) containing ligand H salcyn (3 mmol)
to an ethanol solution (10 ml) of FeCl O (2 mmol). The mixture
2
3
Á6H
2
was refluxed for 24 h. After cooling the reaction solution, the dark
brownish microcrystalline particles were filtered, washed with
cool ethanol and then dried in the air at room temperature.
⇑
Corresponding authors.
E-mail addresses: bagherzadeh@sharif.edu (M. Bagherzadeh), mamini@mara-
gheh.ac.ir (M. Amini).
https://doi.org/10.1016/j.poly.2020.114531
0
277-5387/Ó 2020 Elsevier Ltd. All rights reserved.

2
E. Mesbahi et al. / Polyhedron 183 (2020) 114531
Table 1
Crystal data and structure refinement for the complex [Fe
2
(salcyn)
3 2 5
]∙C H OH.
[
Fe
2
(salcyn)
]∙C H OH
3 2 5
Empirical formula
C
43
H32Fe N O
2 6 6.50
Scheme 1. Oxidation of sulfides in the presence of a binuclear iron(III)-salicylal-
dazine complex.
Formula weight
Temperature
Wavelength
Crystal system
Space group
Unit cell dimensions
848.44 g/mol
173(2) K
0.71073 Å
triclinic
PÀ1
2.2. X-ray structure analysis for complex
a = 11.6354(10) Å, a = 67.0810(12)°
b = 12.2637(10) Å, b = 87.0400(13)°
A black prism-like specimen of C43
H
32Fe
2
N
6
O
6.50, approximate
c = 15.4676(13) Å, c = 69.5260(13)°
dimensions 0.100 mm  0.100 mm  0.260 mm, was used for
the X-ray crystallographic analysis. The X-ray intensity data were
measured. The total exposure time was 2.35 h. The frames were
integrated with the Bruker SAINT Software package using a nar-
row-frame algorithm. The integration of the data using a triclinic
unit cell yielded a total of 13,420 reflections to a maximum h angle
of 26.37° (0.80 Å resolution), of which 7555 were independent (av-
Volume
Z
Density (calculated)
Absorption coefficient
F(0 0 0)
1895.3(3) Å3
2
3
1.487 Mg/m
0.826 mm
À1
872
Crystal size
0.100 Â 0.100 Â 0.260 mm
Theta range for data collection 1.44–26.37
Index ranges
Reflections collected
Independent reflections
À14 ꢀ h ꢀ 11, À15 ꢀ k ꢀ 15, À19 ꢀ l ꢀ 19
13,420
erage redundancy 1.776, completeness = 97.4%, Rint = 1.88%) and
7555 [R(int) = 0.0188]
2
6
436 (85.19%) were greater than 2
r
(F ). The final cell constants
Completeness to theta = 25.00° 97.4%
of a = 11.6354(10) Å, b = 12.2637(10) Å, c = 15.4676(13) Å,
= 67.0810(12)°, b = 87.0400(13)°, = 69.5260(13)°, vol-
ume = 1895.3(3) Å , are based upon the refinement of the XYZ-cen-
troids of 5635 reflections above 20 (I) with 4.315° < 2h < 57.42°.
Absorption correction
Max. and min. transmission
Refinement method
Multi-scan
0.9220 and 0.8140
Full-matrix least-squares on F2
7555/0/532
a
c
3
Data/restraints/parameters
r
Goodness-of-fit on F2
1.025
Data were corrected for absorption effects using the multi-scan
method (SADABS). The ratio of minimum to the maximum appar-
ent transmission was 0.892. The calculated minimum and maxi-
mum transmission coefficients (based on crystal size) are 0.8140
and 0.9220.
Final R indices [I > 2sigma(I)]
R indices (all data)
Largest diff. peak and hole
R1 = 0.0321, wR2 = 0.0814
R1 = 0.0400, wR2 = 0.0864
0.890 and À0.300 e.Å
À3
The final anisotropic full-matrix least-squares refinement on F2
with 532 variables converged at R1 = 3.21%, for the observed data
and wR2 = 8.64% for all data. The goodness-of-fit was 1.025. The
largest peak in the final difference electron density synthesis was
2.3. Catalytic sulfoxidation
0
.2 mmol UHP as an oxidant was added slowly to a stirring
solution of 1 ml of CH CN containing the complex [Fe (salcyn) ],
3
2
3
3
3
a substrate (0.2 mmol) and chlorobenzene (0.2 mmol) as an inter-
nal standard. Stirring was continued for 15 min at room tempera-
ture in a closed system. The reaction progress was monitored by
0
.890 e-/Å and the largest hole was À0.300 e-/Å with an RMS
3
deviation of 0.055 e-/Å . On the basis of the final model, the calcu-
3
À
lated density was 1.487 g/cm and F(0 0 0), 872 e .
Fig. 1. ORTEP diagram of complex [Fe
2
(salcyn)
3
]∙C
H
2 5
OH with thermal ellipsoids drawn at a 50% probability limit.

E. Mesbahi et al. / Polyhedron 183 (2020) 114531
3
Table 2
The molecular structure of the complex [Fe
is shown in Fig. 1. Crystal data, selected bond lengths, and angles
(salcyn)
]∙C
H
OH
2
3
2
5
2 3
Significant Bond lengths [Å] and angles [°] for the complex [Fe (salcyn) ].
Bond lengths (Å)
Bond angles (°)
(Å, °) are listed in Tables 1 and 2. As shown in Fig. 1, each of the
three H
to two iron ions by the two phenolate-O and the two imine-N
atoms to form a facial O coordination sphere which is con-
nected via three diaza (@N–N@) bridges. Complex [Fe (salcyn)
2
salcyn ligands loses one hydrogen atom and coordinates
Fe1–O1
Fe1–O3
Fe1–O4
Fe1–N1
Fe1–N3
Fe1–N4
1.9090(14)
1.8942(14)
1.9401(14)
2.1857(16)
2.1742(17)
2.1590(16)
O3–Fe1–O1
O3–Fe1–O4
O3–Fe1–N4
O1–Fe1–N1
N4–Fe1–N1
N3–Fe1–N1
95.08(6)
101.10(6)
90.90(6)
85.19(6)
88.10(6)
85.47(6)
3 3
N
2
3
]
∙
C
2
H
5
OH crystallizes in the space group PÀ1 with one full complex
molecule in the asymmetric unit. One cluster and a half of disor-
dered by two positions EtOH solvent were found in the asymmetric
unit of the triclinic cell. The FeÁ Á ÁFe distance of the complex is
GC. Assignments of the products were made by comparison with
authentic samples.
3
.901(4) Å.
2
The iron-oxygen and iron-nitrogen bond distances of the H sal-
cyn groups are in the 1.894–1.940(14) and 1.159–1.186(16) Å
ranges, respectively.
3
. Results and discussion
2 3 2 5
In the crystal lattice of the complex [Fe (salcyn) ]∙C H OH, the
intermolecular hydrogen bonds C–HÁ Á ÁO (2.715 Å) between a ben-
zene ring C–H group and phenolate-O belonging to the two neigh-
boring complexes, form an infinite 1-D polymeric array along the
3.1. Complex characterization
The complex [Fe
tion of three equivalent of H
Á5H O in the presence of triethylamine in ethanol. The complex is
2
(salcyn)
3
] has been synthesized by the reac-
axis (Fig. 2). Also, a p–p interaction with the benzene ring of the
salcyn with two equivalents of FeCl
3
-
adjacent chain is observed with interplanar distance about 3.345 Å.
In order to optimize the reaction conditions in the sulfide oxida-
tion, oxidation of methylphenylsulfide (MPS) in the presence of the
2
2
stable under air and moisture and is fully soluble in polar solvents
such as ethanol, methanol, dichloromethane, and acetonitrile. The
complex is characterized by spectroscopic methods like FT-IR and
UV–Vis spectroscopy and X-ray crystallography.
2 3
complex [Fe (salcyn) ] using UHP as an oxidant was carried out
initially (Table 3). Note that the reaction in the absence of catalyst
resulted in only a trace amount of sulfoxide (entry 1). The solvent
effect on the oxidation reaction of MPS has been surveyed using
The IR spectrum of the complex (Fig. S1) shows strong absorp-
À1
tions in the 1686 cm corresponding to the
m(C@N) stretching fre-
various solvents viz CH
tries 2–5). The lower conversion was observed in (1:1) mixture of
CH Cl /CH OH as a solvent (entry 4). A trace amount of product
was achieved in the case of CH Cl (entry 5). Excellent conversions
were observed considering CH CN and CH OH as reaction media
(entries 2, 3). Overall CH CN was considered as the optimized sol-
3 3 2 2 3 2 2
CN, CH OH, CH Cl /CH OH and CH Cl (en-
quency of the H
2
salcyn ligands [17]. Because coordinated H
2
salcyn
ligands are dianionic, thus the bands due to phenolic OH stretch of
ligands are absent.
2
2
3
2
2
The UV–Vis spectra of the complex [Fe
bands in the 220, 295 and 362 nm regions, which are respectively
attributed to intraligand *, phenolate (p ) ? iron(III) (d
and a charge transfer (CT) transitions (Fig. S1) [18–20].
2
3
(salcyn) ] shows intense
3
3
3
p
?
p
p
r
*
)
vent with regard to the high selectivity of the current reaction
achieved. Reducing the amount of complex from 0.0048 mmol to
2 3 2 5
Fig. 2. Crystal packing diagram of the complex [Fe (salcyn) ]∙C H OH along a axis.

4
E. Mesbahi et al. / Polyhedron 183 (2020) 114531
Table 3
a
Oxidation of methylphenylsulfide in different conditions.
Entry
Solvent
Catalyst loading (mmol)
Amount of UHP (mmol)
Reaction time (h)
Conversion (%)b
Selectivity (%)c
1
2
3
4
5
6
7
8
9
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
3
3
3
2
2
3
3
3
3
3
CN
CN
OH
–
0.4
0.4
0.4
0.4
0.4
0.4
0.5
0.1
0.2
0.3
30
30
30
30
30
15
15
15
15
15
trace
>99
>99
81
trace
>99
–
0.0048
0.0048
0.0048
0.0048
0.0012
0.0024
0.0024
0.0024
0.0024
99
87
89
–
99
100
100
Cl
Cl
2
:CH
3
OH
2
CN
CN
CN
CN
CN
>99
73
>99 (51)d
>99
100 (83)
99
d
1
0
a
b
c
Reaction conditions: 1 ml of solvent; 0.2 mmol of methylphenylsulfide.
Determined by GC on the crude reaction mixture.
Selectivity to sulfoxide = (sulfoxide%/(sulfoxide% + sulfone%)) Â 100.
d
In the presence of FeCl
3
Á6H
2
O as a catalyst.
0
.0012 mmol, gave rise to the high conversion of MPS and product
selectivity. Therefore optimized amount (0.0024 mmol) of the
complex [Fe (salcyn) ] was used for the other oxidation reactions.
2
3
Moreover, it is worth mentioning that MPS is totally converted to
the corresponding sulfoxide with selectivity (100%) after 15 min
using a low amount of oxidant (0.2 mmol) (entry 8).
The complex [Fe
alyst. The catalytic efficiency of the complex [Fe
2
(salcyn)
3
] behaved as a good sulfoxidation cat-
(salcyn) ] in the
2
3
presence of various sulfide substrates is recorded in Table 4. A
comparative catalytic study has been performed taking
methylphenylsulfide, dibenzylsulfide, benzyl phenyl sulfide, divi-
nyl sulfide, diethyl sulfide, and dioctyl sulfide as substrates using
UHP as an oxidant. Good to excellent conversions (75–99%) and
selectivities (95–99%) were obtained depending on the nature of
the sulfide substrates for all the cases mentioned above. No over
oxidation was observed for the substrates containing C@C bonds
and benzylic C–H bonds, (entries 2–4). Oxidation of dioctyl sulfide
as an aliphatic substrate showed the lowest conversion (75%) as
compared to other substrates (entry 6).
Scheme 2. Proposed reaction mechanism in the presence of the complex
Fe (salcyn) ].
[
2
3
According to the previous reports [21,22], in the presence of
UHP oxidant (H
2
O
2
Á Á ÁH
2 2 2 2
NCONH ), interaction of H O with one
Fe center results in the formation of an intermediate with Fe@O
bond following by the reaction of organic sulfide with the men-
tioned Fe@O bond, and giving rise to the production of sulfoxides
(Scheme 2).
In conclusion, the complex [Fe
2
(salcyn)
Á5H O in 2:3 mol ratio. The as-
prepared complex was used as an efficient catalyst for the oxida-
tion of sulfides. In the presence of complex [Fe (salcyn) ], all of
3
] was synthesized by
Table 4
Oxidation of sulfides with UHP catalyzed by the complex [Fe
2
(salcyn)
3
].a
the reaction of H
salcyn and FeCl
2
3
2
Entry substrate
Conversion
Selectivity
b
(%)c
(
%)
2
3
the substrates show satisfactory reactivity and corresponding sul-
foxides could be furnished in relatively high yields. To the best of
our knowledge, this work is the first study of a binuclear iron(III)
complex catalyzed oxidation of sulfides.
1
99
99
2
3
92
91
96
96
CRediT authorship contribution statement
Elnaz Mesbahi: Conceptualization, Methodology. Mojtaba
Bagherzadeh: Supervision. Mojtaba Amini: Supervision. Ali
Akbari: Writing - original draft. Arkady Ellern: Software. L. Keith
Woo: Software.
4
S
67
95
5
6
90
75
99
97
S
Declaration of Competing Interest
a
Reaction conditions: 1 ml of CH
3
CN; 0.2 mmol of substrate; 0.2 mmol UHP;
].
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.
0
.0024 mmol the complex [Fe (salcyn)
2
3
b
Determined by GC on the crude reaction mixture.
Selectivity to sulfoxide = (sulfoxide%/(sulfoxide% + sulfone%)) Â 100.
c

E. Mesbahi et al. / Polyhedron 183 (2020) 114531
5
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Many thanks to the Research Council of the Sharif University of
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