Ni(II) and V(IV) Schiff base complexes derived from 2,2′-dimethylpropandiamine: the crystal structure, electrochemical properties and catalytic activities in oxidation of sulfides

Article abstract of DOI:10.1080/00958972.2017.1295306

Tetradentate Schiff base (H₂L) derived from 2,2′-dimethylpropandiamine and its nickel(II) and oxo-vanadium(IV) complexes (NiL, VOL) have been prepared and characterized. The crystal structure of NiL has been determined. The reported structure c

Full text of DOI:10.1080/00958972.2017.1295306

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Ni(II) and V(IV) Schiff base complexes derived from
2,2′-dimethylpropandiamine: The crystal structure,
electrochemical properties and catalytic activities
in oxidation of sulfides
Saeed Rayati, Elham Khodaei, Majid Jafarian, Arezo Bahrami, Andrzej
Wojtczak & Anna Kozakiewicz
To cite this article: Saeed Rayati, Elham Khodaei, Majid Jafarian, Arezo Bahrami, Andrzej
Wojtczak & Anna Kozakiewicz (2017): Ni(II) and V(IV) Schiff base complexes derived from 2,2′-
dimethylpropandiamine: The crystal structure, electrochemical properties and catalytic activities in
oxidation of sulfides, Journal of Coordination Chemistry, DOI: 10.1080/00958972.2017.1295306
To link to this article: http://dx.doi.org/10.1080/00958972.2017.1295306
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Date: 16 February 2017, At: 05:25

Publisher: Taylor & Francis
Journal: Journal of Coordination Chemistry
DOI: http://dx.doi.org/10.1080/00958972.2017.1295306
Ni(II) and V(IV) Schiff base complexes derived from
2,2′-dimethylpropandiamine: The crystal structure, electrochemical
properties and catalytic activities in oxidation of sulfides
SAEED RAYATI*†, ELHAM KHODAEI†, MAJID JAFARIAN†, AREZO BAHRAMI†,
ANDRZEJ WOJTCZAK‡ and ANNA KOZAKIEWICZ‡
†Department of Chemistry, K.N. Toosi University of Technology, P.O. Box 16315-1618, Tehran 15418, Iran
‡Faculty of Chemistry, N. Copernicus University, Gagarina 7, 87-100 Torun, Poland
Tetradentate Schiff base (H2L) derived from 2,2′-dimethylpropandiamine and its nickel(II) and
oxo-vanadium(IV) complexes (NiL, VOL) have been prepared and characterized. The crystal
structure of NiL has been determined. The reported structure contains two molecules of the
complex revealing slightly different conformation and the coordination sphere around nickel is
distorted square planar. The electrochemical properties of the Ni and oxo-vanadium Schiff base
complexes were investigated in CH3CN by cyclic voltammetry. The catalytic activities of the
complexes were studied in the oxidation of sulfides in ethanol. Under the optimized reaction
conditions, in the presence of NiL, 87% and VOL, 100% conversion of methyl phenyl sulfide
with 100% selectivity for sulfoxide were obtained.
Keywords: Green oxidation; Sulfide; Homogeneous catalyst; Nickel; Oxo-vanadium
1. Introduction
Transition metal complexes with Schiff base ligands have been studied because of their
application in electrochemical, biological and catalytic fields [1-4]. Schiff base ligands and their
metal complexes are efficient catalysts under homogeneous and heterogeneous conditions. The
catalytic activity of these catalysts depends on the nature of the substituents as well as the metal
center [5-8]. Therefore, these compounds have been used as catalysts in reactions such as
*Corresponding author. Emails: rayati@kntu.ac.ir; srayati@yahoo.com
1

epoxidation of alkenes [9], ring opening polymerization [10], asymmetric hydrosilylation of
ketones [11], oxidation of alcohols [12] and enantioselective oxidation of sulfides [13-15]. The
selective oxidation of sulfides to sulfoxides is an important transformation in synthesis, biology
and industry because active sulfoxides are effective intermediates in medicinal and
pharmacological fields to prepare therapeutic agents [16]. We report herein the synthesis of a
Schiff base derived from 2-hydroxy-3-methoxybenzaldehyde and 2,2′-
dimethylpropylenediamine (H2L) and its corresponding nickel and oxo-vanadium complexes
(NiL, VOL) and use them as catalysts for oxidation of sulfides with urea hydrogen peroxide
(UHP) and H2O2. Electrochemical properties of the Schiff base complexes were investigated in
CH3CN by cyclic voltammetry.
2. Experimental
2.1. Instruments and reagents
Infrared spectra were recorded as KBr discs using a Unicam Matson 1000 FT-IR. 1H NMR
spectra were obtained in CDCl3 solutions with a Bruker FT NMR 300 (300 MHZ)
spectrophotometer. The residual CHCl3 in conventional 99.8% CDCl3 gives a signal at δ = 7.26
ppm, which was used for calibration of the chemical shifts. A double beam spectrophotometer
(Shimadzu, UV-240) was used for UV-Vis absorption determination. The oxidation products
were analyzed with a HP Agilent 6890 gas chromatograph equipped with a HP-5 capillary
column (phenyl methyl siloxane 30 m × 320 µm × 0.25 µm) and a flame ionization detector.
Electrochemical studies of catalysts were carried out in a conventional three-electrode cell
powered by an electrochemical system consisting of an EG&G model 273
potentiostat/galvanostat and a Solartone model 1255 frequency response analyzer. The system
was run by a pc using the M270 and M398 commercial software packages via a GPIB interface
for impedance measurements. A glassy carbon (GC) disc electrode and graphite electrode were
used as working and counter electrode, respectively. The potentials are relative to aqueous
Ag/AgCl placed in a separate compartment containing 0.1 M tetrabutylammonium perchlorate
(TBAP) in anhydrous acetonitrile.
2,2-Dimethylpropylenediamine, 2-hydroxy-3-methoxybenzaldehyde, nickel(II) acetate,
vanadyl acetylacetonate, hydrogen peroxide and urea hydrogen peroxide (UHP) were used as
2

received from commercial suppliers. Other chemicals were purchased from Merck or Fluka
chemical companies.
2.2. Preparation of the Schiff base (H2L)
H2L was prepared according to the described procedure [17]. To a stirred ethanolic solution
(30 ml) of 2,2-dimethylpropylenediamine (0.102 g, 1 mmol), 2-hydroxy-3-methoxybenzaldehyde
(0.304 g, 2 mmol) was added. The mixture was stirred and heated to reflux for 1 h; the solvent
was evaporated to one-fourth giving a yellow precipitate that was filtered and washed with
ethanol. Yield (92%), Mp 110 °C.
2.3. Preparation of the Ni(II) and VO(IV) Schiff base complexes
Nickel(II) acetate (0.248 g, 1 mmol) or vanadyl acetylacetonate (0.265 g, 1 mmol) dissolved in
30 ml ethanol was added to ethanolic solution of H2L (0.37 g, 1 mmol). The reaction mixture
was refluxed for 1 h and the solvent was evaporated to one-fourth and the precipitates were
filtered and washed with cold ethanol. General structure of NiL and VOL are shown in figure 1.
Analytical and physico-chemical data of H2L, Ni(II) and VO(IV) are presented in table 1.
2.4. X-ray structure of NiL
Crystals of NiL have been obtained from ethanol solution. The diffraction experiment was
performed on a 0.22 × 0.22 × 0.08 mm brown crystal. The X-ray data were collected at 293(2) K
with an Oxford Sapphire CCD diffractometer using MoKα radiation (λ = 0.71073 Å) by ω-2θ
method. Numerical absorption correction was applied [18] with the maximum and minimum
transmissions of 0.9290 and 0.8215. The structure was solved in the triclinic P-1 space group
with direct methods and refined with full-matrix least-squares on F2 with SHELX-97 [19]. The
hydrogens were located from the difference electron density maps and constrained during
refinement. The data collection and refinement processes for the reported structure are
summarized in table 2. Selected bond lengths and angles are presented in table 3.
2.5. General homogeneous oxidation procedure for NiL
Catalytic oxidation was performed in a stirred flask. In a typical experiment, Ni(II) Schiff base
complex (0.0091 mmol) was dissolved in ethanol (1 ml). Then substrate (0.27 mmol) and UHP
3

(0.54 mmol) were added to the reaction mixture. The solution was stirred for 4 h at 45 °C; the
reaction products were monitored by gas chromatography.
2.6. General homogeneous oxidation procedure for VOL
Catalytic oxidation was performed in a stirred flask. In a typical experiment, oxo-vanadium(IV)
complex (0.01 mmol) was dissolved in ethanol (1 ml). Then substrate (2 mmol) and H2O2
(10 mmol) were added to the reaction mixture. The solution was stirred for 10 min at room
temperature and the reaction products were monitored by gas chromatography.
3. Results and discussion
3.1. Spectroscopic studies
Selected IR spectral data are presented in table 4. Comparison of the spectra of the complexes
with the ligand provides evidence for the coordination mode of the ligand. A sharp band at 1623
and 1615 cm-1 due to υ(C=N) (azomethine) indicates involvement of azomethine nitrogen in
coordination to the nickel and vanadium, respectively [20].
Electronic spectral data of the ligand and complexes in chloroform with their assignments
are summarized in table 5. The Ni(II) complex shows a weak broad band at 619 nm, due to
expected d-d transition, which is assigned, to the 1A1-1B1 transition and is typical for the square-
planar nickel(II) complex [21]. More intense band at 434 nm is attributed to either metal to
ligand charge transfer (MLCT) or to the electronic transitions within the ligand. In the vanadium
complex, a lower intensity band at 395 nm and a weak broad band at 590 nm are due to the
ligand to metal charge transfer (LMCT) transition [22] and the d-d transition, respectively.
The proton spectra of the ligand and its nickel(II) complex are reported in table 6. The
absence of OH resonance in the nickel(II) complex with respect to the ligand is a result of
deprotonation upon complexation. The results indicate that the ligand is dibasic [23].
3.1.1. X-ray structure of NiL. The asymmetric unit of NiL contains two molecules of the
complex with slightly different conformation (figure 2). Three water molecules have also been
located in the structure. The electron density maps suggested that O3W has a 50% occupancy
and no hydrogens for water could be located on the electron density maps. Also, ethanol
molecule (occupancy of 50%) was found in the structure, with the crystallographic center of
4

symmetry positioned between its two carbons. As a result, the positional disorder of ethanol
molecule occurs, with methyl and methylene groups occupying two positions averaged by the
center of symmetry and the hydroxyl group bound to each of them with half of the ethanol
occupancy (25%).
In both molecules the coordination sphere has a distorted square geometry. The Ni-N and
Ni-O bond distances are 1.855(2) and 1.880(3) and 1.850(2) and 1.871(3) Å for molecules 1
and 2, respectively (table 2). In both molecules, the bond angles in the coordination sphere
between cis ligands are between 85.13(11) and 94.44(12)°. For trans ligands, the O-Ni-N angles
in molecule 1 of 169.90(12) and 169.96(12) are significantly larger than those of 162.46(12) and
160.99(12)°, found in molecule 2. That deformation can be described with the dihedral angles
between N1-Ni1-O1 and N2-Ni1-O2 best planes being 13.4(2) and 24.8(2)° for molecules 1 and
2, respectively. Besides more pronounced distortion of the coordination sphere in molecule 2 of
the complex, these values indicate the deformation much smaller than that reported for the
analogous copper complex with values of 33.0 reported by Yao et al. [24]. The tetradentate
coordination of the Schiff base ligand results in a slight bend of the ligand, the dihedral angle
between the best planes of two phenyl rings being 17.0(2) and 37.8(1)° for molecules 1 and 2,
respectively, with the difference emphasizing the stronger bend of the second molecule.
Conformation of the central trimethylene bridge is different in two molecules of the
reported structure (figure 3).
The torsion angles in C7-N1-C8-C9-C10-N2-C11 bridging fragment of molecule 1 are
significantly different from the corresponding values found for molecule 2 (table 2). The dihedral
angle between the trimethylene C8-C9-C10 bridge and the best plane of NiN2O2 is 43.3(3) and
48.6(2)° for molecules 1 and 2, respectively. The observed differences in the geometry of two
molecules constituting the asymmetric unit of the reported structure seem to indicate the
flexibility of the Ni(II)-salnptn(3-OMe)2 system, in which the tetradentate coordination could be
achieved with significant differences in the ligand overall conformation. That possibility seems
to be coupled to the sterically demanding 2,2-dimethylpropylenediamine bridge occurring in the
investigated complex.
Two methoxy groups are in the trans conformation described with the torsion angles
C1-C2-O3-C121 and C17-C16-O4-C161, both being 178.8(3)°. For molecule 2 the
5

corresponding torsion angles are 171.0(4) and 172.0(3)°, which indicates slightly larger
displacement of both methoxy groups from the best plane of the phenyl rings.
The structure analysis revealed a network of hydrogen bonds formed between water
molecules and Schiff base ligands. O1W interacts with all oxygens of the ligand of molecule 1,
while O2W forms analogous interactions to the ligand of molecule 2. Details of the hydrogen
bonds are presented in table 7.
3.1.2. Electrochemical studies of NiL. As the potential was scanned from -1 to 3 V, two
overlapping peaks were obtained (figure 4(a) and 4(b)). The first peak is due to oxidation of
Ni(II) to Ni(III) and the second is attributed to the oxidation of ligand [25]. The cyclic
voltammogram for NiL at scan rate of 100 mVs-1 showed a single reduction step characteristic
for a reversible 1 e reaction [26]. The cyclic voltammogram of NiL at different scan rates in
CH3CN (figure 5) was obtained. Also increasing current intensity in the presence of the catalyst
can be seen in figure 6. Cyclic voltammograms of GC/Ni in the presence of 30 mmol methyl
phenyl sulfide at various potential sweep rates and the proportionality of anodic peak currents to
the square root of sweep rates from 50 to 1000 mVs-1 are illustrated in figure 5. The cathodic
peak was not observed at low scan rates, but appeared upon increasing the sweep rate, indicating
that electro-oxidation of nickel species is much faster than catalytic oxidation of sulfide. This
reveals that the oxidation of sulfide on Ni may be a slow process. At higher scan rates, a new
oxidation peak was observed for sulfide oxidation at a potential much more positive than the Ni
oxidation potential. Anodic peak currents that are linearly proportional to the square root of scan
rate suggest that the overall oxidation of sulfide at this electrode is controlled by diffusion of
sulfide to the surface redox sites [27].
3.1.3. Electrochemical studies of VOL. Electrochemical studies of VOL were carried out in
anhydrous acetonitrile by cyclic voltammetry at room temperature. Figure 7 exhibits the cyclic
voltammograms of 1 mmol of VOL in acetonitrile in the presence of methyl phenyl sulfide and
H2O2 between -2 and 2 V. Results show that the current flow is increased in the presence of VOL
complex, indicating the catalytic activity of VOL.
The redox processes were reversible (figure 8), and the cathodic peak current of the
complex increased and the peak shifted to more negative potentials with increasing scan rates.
6

The vanadyl complex exhibits reversible electrochemistry. The number of electrons transferred
in electrode reaction for a reversible couple can be determined from the separation between the
peak potentials [28],
∆EP=Epa-Epc=0.0591/n
where Epa, Epc and n are anodic potential, cathodic potential and the number of electrons
transferred, respectively. The one electron process exhibits a ∆EP approximately 0.059 V.
[V+5OL] + e-
[V+4OL]
The fact that the reduction is reversible indicated that the five-coordinate geometry is stable in
both oxidation states at least on the cyclic voltammetry time scale. Figure 8 shows current flow
is increased in the presence of catalyst, indicating the catalytic activity of oxo-vanadium
complex.
3.1.4. Catalytic oxidation of sulfides in the presence of NiL or VOL. Oxidation of methyl
phenyl sulfide with UHP catalyzed by NiL or VOL gave methyl phenyl sulfoxide as the sole
product. In a search for suitable reaction conditions to achieve maximum conversion, the effects
of amount of oxidant and catalyst, temperature and reaction time were studied.
To optimize the concentration of the catalyst, different amounts of catalyst were used in
oxidation of methyl phenyl sulfide (figure 9). In the absence of catalyst, 13% methyl phenyl
sulfoxide was obtained. The highest conversion were obtained with 0.0091 mmol and 0.01 mmol
of the NiL and VOL catalysts, respectively. Further increments of catalysts slightly decrease the
conversion. This may be due to higher degradation of oxidant at higher concentrations of catalyst
[23]. The effects of UHP and H2O2 concentration on the oxidation of methyl phenyl sulfide have
also been studied (figures 10 and 11). The highest conversion of methyl phenyl sulfide (87% and
100%) were obtained in the 1:2 molar ratio of sulfide/UHP by NiL and 1:5 molar ratio of
sulfide/H2O2 by VOL, respectively. The effect of temperature (0, 25, 45 and 65 °C) on the
homogeneous oxidation of methyl phenyl sulfide by NiL and VOL in ethanol has been studied
(figure 12). The higher oxidation product was achieved at 45 °C and 25 °C for NiL and VOL,
7

respectively. While the rate of oxidation reaction was expected to increase at higher
temperatures, lower conversions were achieved, more pronounced on going from 45 to 65 °C.
This observation seems to be due to the higher degradation of hydrogen peroxide at higher
temperatures. In addition the effect of reaction time in the catalytic oxidation of methyl phenyl
sulfide in the presence of both catalysts is shown in figure 13a and 13b. The highest conversion
(87%) was obtained after 240 min by NiL and (100%) conversion was obtained after 10 min for
oxidation of methyl phenyl sulfide by VOL.
3.1.5. Oxidation of various sulfides by NiL and VOL. In order to demonstrate the efficiency of
these homogeneous catalysts, oxidation of different sulfides under optimized conditions have
also been carried out. As shown in figure 14, sulfides are effectively oxidized to corresponding
sulfoxides in the presence of both catalysts.
The catalytic activities of the Ni and V Schiff bases were compared (figure 14). In
previous studies, we have shown that substituents attached to sulfur have little to moderate
effects on the reactivity of sulfides [29, 30] during oxidation of sulfides catalyzed by
metalloporphyrins; steric and electronic effects of the substituents seem to be involved in the
observed order of reactivity of different sulfides. Due to decreased size of the metal center in the
case of the Ni complex [28], the relative reactivity of the sulfides was more influenced by steric
hindrance around sulfur. The lower conversion of 2-chlorothioanisole (60%) with respect to that
of 4-chlorothioanisole (95%) is probably due to steric hindrance of the chlorine at the ortho
position. Also, the chlorine of the former is closer to the reaction center than the latter and
therefore the electron-withdrawing effect of the chlorine may be involved in the decreased
reactivity of 2-chlorothioanisole. The decreased reactivity of diphenylsulfide relative to the other
sulfides may be also due to steric effects of the bulky phenyl group. No large difference was
observed between the reactivity of 4-chlorothioanisole (95%), thioanisole (89%), para-
methoxythioanisole and 4-cyanothioanisole. Thus introduction of electron-withdrawing or
electron-donating groups at the para position has little effect on the reactivity of the sulfur. In
spite of the fact that vinyl and methyl substituents are of similar size, significantly lower
reactivity was found for phenyl vinyl sulfide in comparison with that of phenyl methyl sulfide.
The sp2 hybridization of the vinyl group in comparison with the sp3 for methyl and the increased
8

group electronegativity [31] of the former may explain this observation. Also, the vinyl group
may be involved in π-π interaction with the sulfur as a π acceptor.
The results of the oxidation of sulfides in the presence of various Schiff base complexes
with H2O2, UHP or TBHP are summarized in table 8. Comparison of this catalytic system with
previously reported systems shows excellent selectivity for sulfoxide product, while conversion
of the thioanisole is significant with respect to the other catalytic systems.
4. Conclusion
The tetradentate Schiff base (N2O2) ligand and NiL and VOL complexes were prepared and
characterized. In the X-ray crystal structure of the nickel complex, the asymmetric unit of the
structure contains two molecules of NiL with slightly different conformation. However, distorted
square planar geometry was observed around nickel. Oxidation of various sulfides with H2O2 or
UHP as a safe oxidant in ethanolic media were enhanced in the presence of NiL or VOL. The
vanadium complex showed better catalytic activity than the nickel complex, perhaps due to
higher oxidation state of the vanadium center. No toxic solvents or byproducts were involved
and no laborious purifications were necessary. This, together with the use of ethanol as standard
“green” solvent as well as wide substrate range, makes this a cost-effective, environmentally
benign methodology. Electrochemical behavior of NiL and VOL complexes in different
conditions by cyclic voltammetry confirm catalytic activity of the prepared complexes.
Appendix A. Supplementary material
Crystallographic data for the structural analysis have been deposited with the Cambridge
Crystallographic Data Centre, CCDC no. 731515. Copy of this information may be obtained free
of charge from the Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK, Fax: (+44)
1223 336 033, or E-mail: deposit@ccdc.cam.ac.uk.
Acknowledgements
The financial support of this work by K.N. Toosi University of Technology research council is
acknowledged.
9

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11

Figure 1. General structure of (a) Ni and (b) VO complexes.
12

Figure 2. Asymmetric unit of NiL·2.5 H2O·0.5 C2H5OH. For clarity the thermal ellipsoids are
displayed at 30% probability; hydrogens omitted.
13

Figure 3. Superposition of two molecules of 1, revealing differences in the ligand conformation.
Molecule 1 is displayed black, molecule 2 gray.
14

200
150
100
50
1200
1200
1000
(a)
1000
(b)
800
600
400
200
0
800
600
400
200
NiL
0
Ligand
N
NiL
-50
Li
Ligand
-100
-150
-200
0
-200
-2
0
2
4
-200
E (V)
-2
0
2
4
-2
0
2
4
(b)
E (V)
E (V)
Figure 4. Cyclic voltammogram of NiL and ligand in 0.1 TBAP/CH3CN between -1 and 3 V at
100 mVs-1.
15

1200
1000
800
600
400
200
0
-200
-400
-600
-800
a
b
c
d
e
f
g
h
i
-3
-2
-1
0
1
2
3
4
E (V)
Figure 5. Cyclic voltammograms of 1 mmol NiL in acetonitrile solution containing 0.1 M TBAP
as supporting electrolyte. Scan rates were in (m V/s): (a) 50, (b) 80, (c) 100, (d) 200, (e) 300,
(f) 400, (g) 500, (h) 600, (i) 1000.
16

3500
3000
2500
2000
1500
1000
500
Cat+sulfide+UHP
UHP+Sulfide
Cat+sulfide
Cat
Ligand
0
-500
-2
-1
0
1
2
3
4
E (V)
Figure 6. Cyclic voltammograms of 1 mmol NiL in acetonitrile solution containing 0.1 M TBAP
as supporting with methyl phenyl sulfide and UHP between -1 and 3 V.
17

1500
1000
500
VOL+methyl phenyl sulfide+H2O2
Blank
0
-2
-1
0
1
2
3
-500
-1000
Figure 7. Cyclic voltammograms of 1 mmol VOL in acetonitrile solution containing 0.1 M
TBAP as supporting with methyl phenyl sulfide and H2O2 between -2 and 2 V.
18

1500
1000
500
a
b
c
d
e
f
0
-2
-1
0
1
2
3
g
h
-500
-1000
V
Figure 8. Cyclic voltammograms of 1 mmol VOL in acetonitrile solution containing 0.1 M
TBAP as supporting electrolyte. Scan rates were in (m V/s): (a) 50, (b) 100, (c) 200, (d) 300, (e)
400, (f) 600, (g) 800, (h) 1000.
19

0.01
0.02
0.0011
100
80
60
40
20
0
0.0091
0.0023
VOL
NiL
0.0067
mmol catalyst
Figure 9. Optimization of catalyst amount on the oxidation of methyl phenyl sulfiide by NiL
(reaction conditions: the molar ratio for catalyst:sulfide:UHP is (X:0.27:0.54) at 45 °C) and VOL
(reaction conditions: the molar ratio for catalyst:sulfide:H2O2 is (X: 2:10) at 25 °C).
20

100
50
0
1:1
1:2
1:3
Sulfide/UHP
Figure 10. The influence of sulfide/oxidant molar ratio on the oxidation of methyl phenyl sulfide
with UHP in the presence of NiL. Reaction conditions: the molar ratio for catalyst:sulfide:UHP
is (0.0091:0.27:X). Reaction time: 4 h.
21

100
80
60
40
20
0
1:1
1:2
1:3
1:4
1:5
1:10
mmol sulfide/mmol H2O2
Figure 11. The influence of sulfide/oxidant molar ratio on the oxidation of methyl phenyl sulfide
with H2O2 in the presence of VOL. Reaction conditions: the molar ratio for catalyst:sulfide:H2O2
is (0.01:2:.10). Reaction time: 10 min.
22

VOL NiL
89
100
80
70
65
23
23
5
0°C
25°C
45°C
65°C
Figure 12. The influence of temperature on the oxidation of methyl phenyl sulfide by NiL
(reaction conditions: the molar ratio for catalyst:sulfide:UHP is (X:0.27:0.54) at 45 °C) and VOL
(reaction conditions: (0.02:2:20) mmol for catalyst:methyl phenyl sulfide and H2O2, respectively,
at 25 °C).
23

100
80
60
40
20
0
100
80
60
40
20
0
(A)
(B)
0
60 120 180 240 300 360
Time(min)
0
5
10
15
Time(min)
Figure 13. The effect of reaction time on the oxidation of methyl phenyl sulfide by (A) NiL
(reaction conditions: the molar ratio for catalyst:sulfide:UHP is (0.0091:0.27:0.54) at 45 °C) and
(B) VOL (reaction conditions: the molar ratio for catalyst:sulfide:H2O2 is (0.01:2:10) at 25 °C).
24

100
80
60
40
20
0
H3
C
H3
C
H3C
S
S
H2C
H3C
S
H3C
H3
C
S
S
S
S
S
S
OCH3
CN
F
Cl
1
2
3
4
5
6
7
88
9
Conversion%NiL
Conversion%VOL
Selectivity% NiL
Selectivity%VOL
89
60
100
80
95
100
100
100
93
21
100
31
100
62
100
90
1000
1000
1000
1000
85
100
97
100
100
100
100
100
100
100
100
90
100
100
100
100
Figure 14. Oxidation of sulfides by NiL (reaction conditions: the molar ratio for
catalyst:sulfide:UHP is (X:0.27:0.54) at 45 °C) and VOL (reaction conditions: (0.02:2:20) mmol
for catalyst:methyl phenyl sulfide and H2O2, respectively, at 25 °C).
25

Table 1. Physical and analytical data of the ligand, Ni and VO complexes.
Formul Yiel
Compound formula
a
d
Color %H
%C
%N
%Metal
-
weight (%)
C21H26N2O4
370.44 92
Yello 7.16(7.0 68.21(68.0 7.49(7.5
7) 8) 6)
Black 5.24(5.6 58.73(59.0 6.14(6.5 13.28(13.7
2) 8) 5) 4)
Brow 6.41(6.2 57.12(57.3 5.87(8.8 10.53(10.7
8) 8) 1) 1)
w
NiC21H24N2O4
426.86 70
481.44 84
VC21H24N2O5·C2H5
OH
n
26

Table 2. Crystal data and structure refinement for NiL.
Formula C43H56Ni2N4O11
Formula weight
T (K) 293(2)
Wavelength (Å)
922.34
0.71073
Crystal systemTriclinic
Space group P-1
Unit cell dimensions
a (Å) 11.1924(8)
b (Å) 12.1286(8)
c (Å) 16.5974(11)
α (°) 80.444(6)
β (°) 85.275(6)
γ (°) 76.560(6)
V (Å3) 2158.7(3)
Z
2
Dcalc (Mg/m3) 1.419
μ (mm-1)
F(000) 972
0.936
Crystal size (mm)
0.22 × 0.22 × 0.08
2.26 to 31.39
θ Range for data collection (°)
Index ranges -13≤h≤15; -17≤k≤17; -23≤ l ≤23
Reflections collected / unique21600 / 12681 [R(int) = 0.0553]
Independent reflections Rint 5530 (0.0663)
Tmax/Tmin
0.9290 and 0.8215
Data / restraints / parameters 12681 / 6 / 551
Goodness-of-fit on F2 0.916
Final R indices [I>2σ(I)]
R1 = 0.0595, wR2 = 0.1093
R indices (all data) R1 = 0.1574, wR2 = 0.1364
Difference peak and hole (eÅ3)
0.627 and -0.416
27

Table 3. Selected bond lengths [Å] and angles [deg] for NiL.
Ni1-O2
Ni1-N1
Ni1-O1
Ni1-N2
O1-C1
1.855(2)
1.860(3)
1.861(2)
1.880(3)
1.301(4)
1.311(4)
Ni2-O22
Ni2-N21
Ni2-O21
Ni2-N22
O21-C21
O22-C37
1.850(2)
1.851(3)
1.859(2)
1.871(3)
1.311(4)
1.317(4)
C17-O2
O2-Ni1-N1
O2-Ni1-O1
N1-Ni1-O1
O2-Ni1-N2
N1-Ni1-N2
O1-Ni1-N2
169.90(12)
85.13(11)
93.34(12)
92.90(12)
90.28(13)
169.96(12)
O22-Ni2-N21
O22-Ni2-O21
N21-Ni2-O21
O22-Ni2-N22
N21-Ni2-N22
O21-Ni2-N22
162.46(12)
86.05(11)
93.47(12)
94.44(12)
91.67(13)
160.99(12)
C7-N1-C8-C9
-113.9(4)
-42.5(4)
-27.4(5)
-114.8(4)
0.7(5)
C27-N21-C28-C29
N21-C28-C29-C30
C28-C29-C30-N22
C29-C30-N22-C31
O21-C21-C22-O23
C21-C22-O23-C221 171.0(4)
O24-C36-C37-O22 -3.6(5)
C37-C36-O24-C236 172.0(3)
-110.3(4)
-32.4(4)
-38.4(4)
-121.9(4)
-2.3(5)
N1-C8-C9-C10
C8-C9-C10-N2
C9-C10-N2-C11
O1-C1-C2-O3
C1-C2-O3-C121
O4-C16-C17-O2
178.8(3)
0.0(5)
C17-C16-O4-C161 178.8(3)
28

Table 4. Selected IR spectral data of the ligand and its NiL and
VOL complexes.
Selected IR bands (cm-1)
Compound
C=N
1638
1623
1615
C=C
1550
1533
1521
C-O
H2L
NiL
1084
1084
1076
VOL
29