Synthesis and characterization of two binuclear nickel(II) complexes of thiophenol-based "end-off" compartmental ligands and their application as catalysts for selective oxidation of sulfides

Article abstract of DOI:10.1080/00958972.2015.1107723

Reaction of the binucleating S-protected ligand precursors 2-(N,N-dimethylthiocarbamato)-5-methylisophthalaldehyde di-2′-hydroxy anil (I) and 2-(N,N-dimethylthiocarbamato)-5-methylisophthalaldehyde di-2′-hydroxy 5′-methyl anil (II) with nickel(II) acetate tetrahydrate in the presence of pyrazole afforded the binuclear nickel(II) complexes [L^INi2(pz)] (1) and [L^IINi2(pz)] (2), respectively. The complexes have been characterized by routine physicochemical studies as well as by X-ray single crystal structure analysis. In both complexes, Ni(II) ions are doubly bridged by the thiophenolic sulfur of the pentadentate Schiff base ligand and a pyrazolate group. Efficient protocols for the oxidation of sulfides to sulfoxides with high selectivities, catalyzed by binuclear -thiophenolato - pyrazolatonickel(II) in the presence of urea hydrogen peroxide (UHP) were explored. We obtained predominantly the monooxygenated product. The resulting products are obtained in good to excellent yields within a reasonable time.

Full text of DOI:10.1080/00958972.2015.1107723

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Synthesis and characterization of two binuclear
nickel(II) complexes of thiophenol-based “end-off”
compartmental ligands and their application as
catalysts for selective oxidation of sulfides
Narjes Khadir, Mojtaba Amini, Abdeljalil Assoud, Mojtaba Bagherzadeh &
Davar M. Boghaei
To cite this article: Narjes Khadir, Mojtaba Amini, Abdeljalil Assoud, Mojtaba Bagherzadeh
&
Davar M. Boghaei (2015): Synthesis and characterization of two binuclear nickel(II)
complexes of thiophenol-based “end-off” compartmental ligands and their application
as catalysts for selective oxidation of sulfides, Journal of Coordination Chemistry, DOI:
10.1080/00958972.2015.1107723
To link to this article: http://dx.doi.org/10.1080/00958972.2015.1107723
Accepted author version posted online: 05
Nov 2015.
Published online: 30 Nov 2015.
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Date: 01 December 2015, At: 10:02

Journal of Coordination Chemistry, 2015
ꢁꢁp://ꢂx.ꢂꢃꢄ.ꢃꢅg/10.1080/00958972.2015.1107723
ꢀ
Synthesis and characterization of two binuclear nickel(II)
complexes of thiophenol-based “end-off” compartmental ligands
and their application as catalysts for selective oxidation of
sulfides
a
b
c
a
Narjes Khadir , Mojtaba Amini , Abdeljalil Assoud , Mojtaba Bagherzadeh and
a
Davar M. Boghaei
ꢆ
b
Cꢀꢇꢈꢄꢉꢁꢅꢊ dꢇpꢆꢅꢁꢈꢇꢋꢁ, sꢀꢆꢅꢄꢌ uꢋꢄvꢇꢅꢉꢄꢁꢊ ꢃꢌ tꢇcꢀꢋꢃꢍꢃgꢊ, tꢇꢀꢅꢆꢋ, iꢅꢆꢋ; fꢆcꢎꢍꢁꢊ ꢃꢌ scꢄꢇꢋcꢇ, dꢇpꢆꢅꢁꢈꢇꢋꢁ ꢃꢌ Cꢀꢇꢈꢄꢉꢁꢅꢊ,
c
uꢋꢄvꢇꢅꢉꢄꢁꢊ ꢃꢌ mꢆꢅꢆgꢀꢇꢀ, mꢆꢅꢆgꢀꢇꢀ, iꢅꢆꢋ; dꢇpꢆꢅꢁꢈꢇꢋꢁ ꢃꢌ Cꢀꢇꢈꢄꢉꢁꢅꢊ, uꢋꢄvꢇꢅꢉꢄꢁꢊ ꢃꢌ Wꢆꢁꢇꢅꢍꢃꢃ, Wꢆꢁꢇꢅꢍꢃꢃ, Cꢆꢋꢆꢂꢆ
ABSTRACT
ARTICLE HISTORY
rꢇcꢇꢄvꢇꢂ 11 aꢎgꢎꢉꢁ 2015
accꢇpꢁꢇꢂ 25 sꢇpꢁꢇꢈbꢇꢅ 2015
Reaction of the binucleating S-protected ligand precursors 2-(N,N-
dimethylthiocarbamato)-5-methylisophthalaldehyde di-2′-hydroxy anil (I)
and 2-(N,N-dimethylthiocarbamato)-5-methylisophthalaldehyde di-2′-
hydroxy 5′-methyl anil (II) with nickel(II) acetate tetrahydrate in the presence
KEYWORDS
Bꢄꢋꢎcꢍꢇꢆꢅ nꢄ(ii) cꢃꢈpꢍꢇxꢇꢉ;
ꢉꢄꢋgꢍꢇ cꢅꢊꢉꢁꢆꢍ X-ꢅꢆꢊ
ꢂꢄffꢅꢆcꢁꢄꢃꢋ ꢉꢁꢎꢂꢊ; ꢉꢎꢍfiꢂꢇ;
ꢃxꢄꢂꢆꢁꢄꢃꢋ
I
of pyrazole afforded the binuclear nickel(II) complexes [L Ni (pz)] (1) and
2
II
[
L Ni (pz)] (2), respectively. The complexes have been characterized by
2
routine physicochemical studies as well as by X-ray single crystal structure
analysis. In both complexes, Ni(II) ions are doubly bridged by the thiophenolic
sulfur of the pentadentate Schiff base ligand and a pyrazolate group. Efficient
protocols for the oxidation of sulfides to sulfoxides with high selectivities,
catalyzed by binuclear μ-thiophenolato-μ-pyrazolatonickel(II) in the
presence of urea hydrogen peroxide (UHP) were explored. We obtained
predominantly the monooxygenated product. The resulting products are
obtained in good to excellent yields within a reasonable time.
CONTACT mꢃjꢁꢆbꢆ aꢈꢄꢋꢄ
ꢈꢆꢈꢄꢋꢄ@ꢈꢆꢅꢆgꢀꢇꢀ.ꢆc.ꢄꢅ; dꢆvꢆꢅ m. Bꢃgꢀꢆꢇꢄ
ꢂbꢃgꢀꢆꢇꢄ@ꢉꢀꢆꢅꢄꢌ.ꢇꢂꢎ
sꢎppꢍꢇꢈꢇꢋꢁꢆꢍ ꢂꢆꢁꢆ ꢌꢃꢅ ꢁꢀꢄꢉ ꢆꢅꢁꢄcꢍꢇ cꢆꢋ bꢇ ꢆccꢇꢉꢉꢇꢂ ꢆꢁ ꢀꢁꢁp://ꢂx.ꢂꢃꢄ.ꢃꢅg/10.1080/00958972.2015.1112004
©
2015 tꢆꢊꢍꢃꢅ & fꢅꢆꢋcꢄꢉ

2
N. KHADIR ET AL.
1. Introduction
Selective oxidation of sulfides to sulfoxides as key intermediates in the synthesis of biologically impor-
tant compounds has been of growing interest owing to the increasing environmental, ecological, and
economic concerns [1–10]. Transition metal-catalyzed oxidation of sulfides has been developed to selec-
tively oxidize sulfides to sulfoxides, because sulfoxides have enormous applications in the preparation
of significant molecules such as drugs, flavors, germicides, catabolism regulators, ligands in asymmetric
catalysis, and oxo-transfer reagents [11–15]. As a result, valuable procedures have been developed for
sulfide oxidation with aqueous hydrogen peroxide in combination with a variety of transition metal
compounds, in particular titanium, vanadium, molybdenum, tungsten, and rhenium as catalysts [16–25].
However, nickel-containing compounds have been little studied in catalytic oxidation processes [26, 27].
As part of our ongoing study on the selective and green synthesis of sulfoxides [28–36], herein
we report the synthesis, spectroscopic characterization, and crystal structures of two new binuclear
nickel(II) complexes, [LPd (pz)] {pz = the exogenous pyrazolyl ligand; L = 2,6-bis[(2-phenoxy)imi-
2
I
nomethyl]-4-methylthiophenolate (L ), 2,6-bis{[(2-hydroxy-5methylphenyl)imino]methyl}-4-methylth-
II
iophenolate (L )}. These new complexes were evaluated as catalysts for the selective oxidation of a
series of sulfides to the corresponding sulfoxides in excellent yield and selectivity under mild reaction
conditions with the aid of urea hydrogen peroxide (UHP) as an oxidant (Scheme 1).
2. Experimental
2
.1. Materials
All chemicals were obtained from commercial sources and used as received. Solvents were dried
according to standard procedures and distilled prior to use. 2-(N,N-dimethylthiocarbamato)-5-
methylisophthalaldehyde di-2′-hydroxy anil (I) was prepared according to the literature method [37].
2
.2. Physical measurements
Elemental analyses were performed on Fison equipment, model EA 1108. UV–Vis spectra were recorded
with a CARY 100 Bio VARIAN UV–Vis spectrophotometer using quartz cells having a 1.0 cm path length.
−1
Infrared spectra (4000–400 cm ) of solid samples were obtained in KBr pellets using a Unicam Matson
O
N
O
N
N N
Ni
Ni
R
S
R
CH3
Complex
R
H
1
2
Me
Scheme 1. mꢃꢍꢇcꢎꢍꢆꢅ ꢉꢁꢅꢎcꢁꢎꢅꢇ ꢃꢌ bꢄꢋꢎcꢍꢇꢆꢅ ꢋꢄckꢇꢍ(ii) cꢃꢈpꢍꢇxꢇꢉ [lnꢄ (pz)].
2

JꢀURNAL ꢀF CꢀꢀRDINATIꢀN CHEMISTRY
3
1
1
000 FT-IR spectrophotometer. H NMR spectra were recorded on a Bruker 500-DRX Avance spec-
trometer. Chemical shifts for NMR spectra are referenced to TMS. Melting points of the products were
monitored on a BUCHI Melting Point Model B-540 apparatus and are uncorrected. Gas chromatography
(GC) analyses were performed on an Agilent Technologies 6890 N, equipped with a 19019 J-413 HP-5,
5
% phenyl methyl siloxane, capillary column (60.0 m × 250 μm × 1.00 μm).
2
.3. Crystal structure determination
The crystal structures of 1 and 2 were established using X-ray diffraction. Diffraction data were col-
lected on a Bruker Kappa APEX II diffractometer using graphite-monochromated Mo-Kα radiation
(
λ = 0.71073 Å). Data were collected using ω- and ϕ-scans of 0.3° in groups of frames at different ω and
ϕ with exposure times of 10–30 s per frame depending on the crystal scattering. They were corrected
for Lorentz and polarization effects using the Bruker SAINT software package [38]. Absorption correc-
tions were based on fitting a function to the empirical transmission surface as sampled by multiple
equivalent measurements using SADA BS [39]. All structures were solved using the direct method and
refined using the least squares method with the Bruker SHELXTL software package [40]. All hydrogens
in geometrically idealized positions were refined using a rigid model with C–H = 0.93–1 Å and isotropic
displacement parameters Uiso(H) = 1.2 Ueq(C)–1.5 Ueq(C).
Figure 1. (ꢆ) orteP ꢂꢅꢆwꢄꢋg ꢃꢌ 1 ꢉꢀꢃwꢄꢋg ꢁꢀꢇ ꢆꢁꢃꢈ-ꢍꢆbꢇꢍꢄꢋg ꢉꢊꢉꢁꢇꢈ ꢆꢋꢂ 50% ꢁꢀꢇꢅꢈꢆꢍ ꢇꢍꢍꢄpꢉꢃꢄꢂꢉ. (b) Pꢇꢅꢉpꢇcꢁꢄvꢇ vꢄꢇw ꢃꢌ ꢁꢀꢇ ꢌꢃꢅꢈꢆꢁꢄꢃꢋ
ꢃꢌ ꢆ 1-d cꢀꢆꢄꢋ ꢄꢋ 1 ꢌꢃꢅꢈꢇꢂ ꢁꢀꢅꢃꢎgꢀ π–π ꢉꢁꢆckꢄꢋg ꢄꢋꢁꢇꢅꢆcꢁꢄꢃꢋꢉ ꢆꢍꢃꢋg ꢁꢀꢇ a-ꢆxꢄꢉ. hꢊꢂꢅꢃgꢇꢋꢉ ꢆꢅꢇ ꢃꢈꢄꢁꢁꢇꢂ ꢌꢃꢅ cꢍꢆꢅꢄꢁꢊ.

4
N. KHADIR ET AL.
Figure 2. (ꢆ) orteP ꢂꢅꢆwꢄꢋg ꢃꢌ 2 ꢉꢀꢃwꢄꢋg ꢁꢀꢇ ꢆꢁꢃꢈ-ꢍꢆbꢇꢍꢄꢋg ꢉꢊꢉꢁꢇꢈ ꢆꢋꢂ 50% ꢁꢀꢇꢅꢈꢆꢍ ꢇꢍꢍꢄpꢉꢃꢄꢂꢉ. (b) Pꢇꢅꢉpꢇcꢁꢄvꢇ vꢄꢇw ꢃꢌ ꢁꢀꢇ ꢌꢃꢅꢈꢆꢁꢄꢃꢋ
ꢃꢌ ꢆ 1-d cꢀꢆꢄꢋ ꢄꢋ 2 ꢌꢃꢅꢈꢇꢂ ꢁꢀꢅꢃꢎgꢀ π–π ꢉꢁꢆckꢄꢋg ꢄꢋꢁꢇꢅꢆcꢁꢄꢃꢋꢉ ꢆꢍꢃꢋg ꢁꢀꢇ a-ꢆxꢄꢉ. hꢊꢂꢅꢃgꢇꢋꢉ ꢆꢅꢇ ꢃꢈꢄꢁꢁꢇꢂ ꢌꢃꢅ cꢍꢆꢅꢄꢁꢊ.
2
.4. Synthesis of II
2
.4.1. 2-(N,N-dimethylthiocarbamato)-5-methylisophthalaldehyde di-2′-hydroxy 5′-methyl
anil (II)
3
To a solution of 2-amino-4-methylphenol (1.08 g, 8.8 mmol) in methanol (10 cm ) was added 2-(N,N-
dimethylthiocarbamato-S)-5-methylisophthalaldehyde (1 g, 4 mmol) in boiling methanol (20 cm ).The result-
3
ing red solution was heated under reflux for 10 min; then, allowed to cool to room temperature.The product
separated as yellow precipitate of the dimethylcarbamoyl-sulfur-protected ligand was collected by filtration,
washed with methanol, and air dried. m.p. = 203–206 °C, yield: 93.27%. Anal. Calcd for C H N ꢀ S:C, 67.66;
2
6
27
3
3
−1
H, 5.90; N, 9.10; S, 6.95. Found: C, 67.53; H, 5.80; N, 9.13; S, 6.90%. IR (KBr, cm ): 3408 ν(ꢀH), 3026 ν(C–H ),
920 and 2862 ν(C–H ), 1664 ν(C=ꢀ), 1616 ν(C=N), 1488 ν(C=C). UV–vis (MeꢀH), [λ , nm (ε, L mol cm )]:
63.47 (1664.97), 266.80 (3455.74), 204.00 (7476.35). H-NMR (δppm in CDCl ): 9.22 (s, 2H, imine), 8.19 (s, 2H,
ar
−1
−1
2
3
al
max
1
3
protons of central aromatic ring), 6.96–7.1 (m, 8H, 2-imino-4-methylphenolic and ꢀHphenolic protons), 3.26
and 3.04 (b, 6H, N(CH ) ), 2.5 (s, 3H, CH ), 2.33 (s, 6H, CH ).
3
2
3
3
2
.5. Synthesis of binuclear nickel(II) complexes
[LINi (pz)] (1). A solution containing 0.20 g of the S-protected ligand precursor I (0.42 mmol) and 0.04 g
2
3
of pyrazole (0.64 mmol) in 15 cm of boiling CH CN was added to a hot solution of 0.19 g of nickel(II)
3

JꢀURNAL ꢀF CꢀꢀRDINATIꢀN CHEMISTRY
5
Table 1. Cꢅꢊꢉꢁꢆꢍ ꢂꢆꢁꢆ ꢆꢋꢂ ꢉꢁꢅꢎcꢁꢎꢅꢇ ꢅꢇfiꢋꢇꢈꢇꢋꢁ ꢌꢃꢅ 1 ꢆꢋꢂ 2.
Empirical formula
C H N ꢀ Ni S (1)
C H N ꢀ Ni S (2)
26 22 4 2 2
2
4
18
4
2
2
fꢃꢅꢈꢎꢍꢆ wꢇꢄgꢀꢁ
tꢇꢈpꢇꢅꢆꢁꢎꢅꢇ (K)
Wꢆvꢇꢍꢇꢋgꢁꢀ (Å)
Cꢅꢊꢉꢁꢆꢍ ꢉꢊꢉꢁꢇꢈ
spꢆcꢇ gꢅꢃꢎp
Cꢅꢊꢉꢁꢆꢍ cꢃꢍꢃꢅ, ꢉꢀꢆpꢇ
Cꢅꢊꢉꢁꢆꢍ ꢉꢄzꢇ (ꢈꢈ)
a (Å)
b (Å)
c (Å)
α (°)
β (°)
543.90
296 (2)
0.71073
571.95
296 (2)
0.71073
mꢃꢋꢃcꢍꢄꢋꢄc
mꢃꢋꢃcꢍꢄꢋꢄc
P2 /c
P2 /c
1
1
Bꢍꢆck, ꢅꢃꢂ
Bꢍꢆck, ꢅꢃꢂ
0.02 × 0.70 × 0.36
8.0865 (2)
21.1312 (5)
14.2806 (2)
90
108.644 (10)
90
0.02 × 0.12 × 0.32
9.0391 (10)
18.9100 (2)
12.5261 (10)
90
103.6411 (4)
90
γ (°)
3
V (Å )
2080.68 (4)
1.942
1.736
2312.18 (9)
1.653
1.643
μ, ꢈꢈ−
1
−3
dꢂCꢆꢍcꢂ (g cꢈ )
Z
4
4
F (0 0 0)
tꢀꢇꢁꢆ ꢅꢆꢋgꢇ ꢌꢃꢅ ꢂꢆꢁꢆ cꢃꢍꢍꢇcꢁꢄꢃꢋ
iꢋꢂꢇx ꢅꢆꢋgꢇꢉ
1112
2.154–28°
−11 ≤ h ≤11
1176
2.446–26°
−9 ≤ h ≤6
−
−
24 ≤ k ≤15
15 ≤ l ≤16
−19 ≤ k ≤26
−17 ≤ l ≤17
0.7460 ꢆꢋꢂ 0.6320
fꢎꢍꢍ-ꢈꢆꢁꢅꢄx ꢍꢇꢆꢉꢁ-ꢉqꢎꢆꢅꢇꢉ ꢃꢋ F
1.041
mꢆxꢄꢈꢎꢈ ꢆꢋꢂ ꢈꢄꢋꢄꢈꢎꢈ ꢁꢅꢆꢋꢉꢈꢄꢉꢉꢄꢃꢋ
rꢇfiꢋꢇꢈꢇꢋꢁ ꢈꢇꢁꢀꢃꢂ
Gꢃꢃꢂꢋꢇꢉꢉ-ꢃꢌ-fiꢁ ꢃꢋ F
0.7460 ꢆꢋꢂ 0.6972
fꢎꢍꢍ-ꢈꢆꢁꢅꢄx ꢍꢇꢆꢉꢁ-ꢉqꢎꢆꢅꢇꢉ ꢃꢋ F
1.024
2
2
2
R ꢆꢋꢂ wR ꢄꢋꢂꢄcꢇꢉ [I > 2σ(I)]
R = 0.0264, wR = 0.0684
R = 0.0397, wR = 0.0990
1
2
1
2
1
2
R ꢆꢋꢂ wR ꢄꢋꢂꢄcꢇꢉ (ꢆꢍꢍ ꢂꢆꢁꢆ)
R = 0.0359, wR = 0.0750
R = 0.0599, wR = 0.1139
1
2
1
2
1
2
−3
lꢆꢅgꢇꢉꢁ ꢂꢄff. pꢇꢆk ꢆꢋꢂ ꢀꢃꢍꢇ (ꢇ Å )
0.419 ꢆꢋꢂ −0.364
0.776 ꢆꢋꢂ −0.301
3
acetate tetrahydrate (1.07 mmol) in 15 cm of DMSꢀ. The intense brown solution was ꢁltered and then
remained at room temperature for two days. Crystals of 1 were collected by ꢁltration, washed with ace-
tonitrile, and dried at 80 °C under vacuum. Yield: 0.19 g (81%). Anal. Calcd for C H N ꢀ Ni S:C, 53.00;
2
4
18
4
2
2
−1
H, 3.34; N, 10.30; S, 5.90. Found: C, 52.64; H, 3.11; N, 9.86; S, 5.20%.IR (KBr, cm ): 2922 ν(C–H ), 1637 and
619 br ν(C=N ), 1594 ν(C=N(L )), 1474 ν(C=C), 545 ν(Ni–N). UV–vis (CH ꢀH), [λmax, nm (ε, L mol cm )]:
15.92 (1134.43), 422.57 (5236.66), 266.66 (36763.33), 233.14 (51956.66), 217.95 (56710.00).
al
I
−1
−1
1
7
p
z
3
II
II
[
L Ni (pz)] (2). [L Ni (pz)] was prepared in a similar method to that of 1 except that II was used in
2 2
the preparation instead of I. Yield: 80%. Anal. Calcd for C H N ꢀ Ni S:C, 54.60; H, 3.88; N, 9.80; S, 5.61.
2
6
22
4
2
2
−1
Found: C, 54.30; H, 3.43; N, 9.50; S, 5.30%.IR (KBr, cm ): 2920 ν(C–H ), 1638 and 1618 br ν(C=N ), 1591
ν(C=N (L )), 1485 ν(C=C), 546 ν(Ni–N). UV–vis (CH ꢀH), [λmax, nm (ε, L mol cm )]: 713.91 (1260.00),
20.91 (9033.33), 268.32 (42070.00), 234.79 (59723.30), 219.90 (60833.33).
al
pz
II
−1
−1
3
4
3. Results and discussion
3
.1. Description of the structures
Figures 1a and 2a display the structure of 1 and 2, respectively. Crystallographic data for 1 and 2 are
given in Table 1. Selected bond lengths and angles are listed in Table 2. In both complexes, the nickel(II)
ions Ni1 and Ni2 are bridged on one side by a μ -thiophenolate sulfur as an endogenous bridging com-
2
ponent and on the other side by a μ-N,N′-bridging pyrazolate as an exogenous bridging component.
The intramolecular Ni(1)⋯Ni(2) separation is 3.4832(5) Å in 1 and 3.4767(6) Å in 2. These internuclear
Ni⋯Ni distances are significantly shorter than the Cu⋯Cu internuclear distance of 3.5926(3) Å observed
in [Cu L(pz)(DMSꢀ)] having the same binucleating ligand [41]. Each nickel ion is bonded to one phe-
2
noxo ꢀ, one imine N, and one μ-thiophenolate S of the end-off compartmental ligand and one N of the
bridging pyrazolate in a distorted square plane. The maximum deviations from the least-squares planes
defined by Ni(1), N(1), N(3), S(1), ꢀ(1) and Ni(2), N(2), N(4), S(1), ꢀ(2) in 1 are 0.0041 and 0.0169 Å and in

6
N. KHADIR ET AL.
Table 2. sꢇꢍꢇcꢁꢇꢂ ꢄꢋꢁꢇꢅꢆꢁꢃꢈꢄc bꢃꢋꢂ ꢂꢄꢉꢁꢆꢋcꢇꢉ (Å) ꢆꢋꢂ ꢆꢋgꢍꢇꢉ (°) ꢌꢃꢅ 1 ꢆꢋꢂ 2.
Compound
1
2
nꢄ1–o1
nꢄ1–n3
nꢄ1–s1
nꢄ1–n1
nꢄ2–o2
nꢄ2–n4
nꢄ2–s1
nꢄ2–n2
o1–nꢄ1–s1
n1–nꢄ1–n3
nꢄ1–s1–nꢄ2
C1–s1–nꢄ1
n4–nꢄ2–n2
s1–nꢄ2–o2
C1–s1–nꢄ2
1.8534(14)
1.8748(17)
2.1081(5)
1.8863(16)
1.8487(14)
1.8746(17)
2.1048(5)
1.8848(16)
173.20(5)
178.37(7)
111.54(2)
113.11(6)
176.72(7)
170.93(5)
113.82(7)
1.849(2)
1.868(3)
2.1084(10)
1.883(3)
1.859(2)
1.877(2)
2.1084(9)
1.880(3)
171.50(9)
177.58(12)
111.03(4)
113.31(12)
178.34(13)
172.85(13)
112.45(11)
Table 3. oxꢄꢂꢆꢁꢄꢃꢋ ꢃꢌ ꢈꢇꢁꢀꢊꢍpꢀꢇꢋꢊꢍ ꢉꢎꢍfiꢂꢇ ꢄꢋ ꢂꢄffꢇꢅꢇꢋꢁ ꢉꢃꢍvꢇꢋꢁꢉ.ꢆ
Entry
Solvent
Conversion (%)b
Selectivity (%)c
1
2
3
4
5
6
7
8
9
h2o
eꢁoh
18
63
59
51
15
8
11
23
76
100
97
98
mꢇoh
mꢇCn
Ch Cꢍ
98
100
100
100
100
98
2
2
hꢇxꢆꢋꢇ
tꢃꢍꢎꢇꢋꢇ
eꢁoac
mꢇoh/Ch Cꢍ
2
2
ꢆ
rꢇꢆcꢁꢄꢃꢋ cꢃꢋꢂꢄꢁꢄꢃꢋꢉ: 1 ꢈl ꢃꢌ ꢉꢃꢍvꢇꢋꢁ; 1 ꢈꢈꢃꢍ ꢃꢌ ꢈꢇꢁꢀꢊꢍpꢀꢇꢋꢊꢍ ꢉꢎꢍfiꢂꢇ; 1 ꢈꢈꢃꢍ uhP; 0.01 ꢈꢈꢃꢍ 1; ꢅꢇꢆcꢁꢄꢃꢋ ꢁꢄꢈꢇ: 60 ꢈꢄꢋ.
dꢇꢁꢇꢅꢈꢄꢋꢇꢂ bꢊ GC ꢃꢋ ꢁꢀꢇ cꢅꢎꢂꢇ ꢅꢇꢆcꢁꢄꢃꢋ ꢈꢄxꢁꢎꢅꢇ.
b
c
sꢇꢍꢇcꢁꢄvꢄꢁꢊ ꢁꢃ ꢉꢎꢍꢌꢃxꢄꢂꢇ = (ꢉꢎꢍꢌꢃxꢄꢂꢇ %/(ꢉꢎꢍꢌꢃxꢄꢂꢇ % + ꢉꢎꢍꢌꢃꢋꢇ %)) × 100.
Figure 3. iꢋflꢎꢇꢋcꢇ ꢃꢌ ꢁꢀꢇ ꢅꢆꢁꢄꢃ ꢃꢌ ꢁꢀꢇ ꢉꢎbꢉꢁꢅꢆꢁꢇ ꢁꢃ ꢁꢀꢇ ꢃxꢄꢂꢆꢋꢁ. rꢇꢆcꢁꢄꢃꢋ cꢃꢋꢂꢄꢁꢄꢃꢋꢉ: 1 ꢈl ꢃꢌ mꢇoh/Ch Cꢍ ; 0.01 ꢈꢈꢃꢍ 1; ꢅꢇꢆcꢁꢄꢃꢋ
2
2
ꢁ
ꢄꢈꢇ: 60 ꢈꢄꢋ.
2
are 0.0081 and 0.0070 Å, respectively. The Ni–ꢀ, Ni–N, and Ni–S bonds are within the normal ranges
and are comparable to those observed in similar bridged nickel(II) dimers [42–44].
In the crystal packing of 1, it is obvious that adjacent binuclear units are linked through π–π stack-
ing interactions involving metal chelate–central phenyl and central phenyl–terminal phenyl rings to
form an infinite 1-D chain along the a-axis (Figure 1b). In the crystal packing structure of 2, as shown in
Figure 2b, the orientation of the binuclear molecules in the crystal lattice is in such that π⋯π stacking

JꢀURNAL ꢀF CꢀꢀRDINATIꢀN CHEMISTRY
7
Table 4. oxꢄꢂꢆꢁꢄꢃꢋ ꢃꢌ ꢉꢎꢍfiꢂꢇꢉ wꢄꢁꢀ uhP ꢄꢋ pꢅꢇꢉꢇꢋcꢇ ꢃꢌ 1 ꢆꢋꢂ 2.ꢆ
Conversion (%) (TꢀN)c
b
Selectivity (%)d
Entry
Substrate
1
2
1
2
S
1
97 (19.4)
98 (19.6)
93
91
CH
3
S
2
99 (19.8)
98 (19.6)
91
93
2 3
CH CH
S
3
4
95 (19.0)
93 (18.6)
93 (18.6)
94 (18.8)
95
94
96
95
S
5
6
95 (19.0)
98 (19.6)
95 (19.0)
92 (18.4)
91
90
88
91
S
S
7
8
S
85 (17.0)
96 (19.2)
76 (15.2)
94 (18.8)
90
92
89
95
S
OH
9
S
S
S
71 (14.2)
75 (15.0)
56 (11.2)
69 (13.8)
78 (15.6)
49 (9.8)
99
99
100
98
H
3
C
CH
3
1
0
1
H
3
CH
2
C
2 3
CH CH
1
100
100
C H
C H
8 17
8
17
ꢆ
b
c
rꢇꢆcꢁꢄꢃꢋ cꢃꢋꢂꢄꢁꢄꢃꢋꢉ: 0.2 ꢈꢈꢃꢍ ꢃꢌ ꢉꢎꢍfiꢂꢇ; 0.4 ꢈꢈꢃꢍ uhP; 0.01 ꢈꢈꢃꢍ cꢆꢁꢆꢍꢊꢉꢁ; 1 ꢈl ꢃꢌ mꢇoh/Ch Cꢍ .
dꢇꢁꢇꢅꢈꢄꢋꢇꢂ bꢊ GC ꢎꢉꢄꢋg ꢆꢋ ꢄꢋꢁꢇꢅꢋꢆꢍ ꢉꢁꢆꢋꢂꢆꢅꢂ ꢁꢇcꢀꢋꢄqꢎꢇ ꢃꢋ ꢁꢀꢇ cꢅꢎꢂꢇ ꢅꢇꢆcꢁꢄꢃꢋ ꢈꢄxꢁꢎꢅꢇ.
ton = (ꢈꢈꢃꢍ ꢃꢌ ꢉꢎꢍꢌꢃxꢄꢂꢇ + ꢈꢈꢃꢍ ꢃꢌ ꢉꢎꢍꢌꢃꢋꢇ)/ꢈꢈꢃꢍ ꢃꢌ cꢆꢁꢆꢍꢊꢉꢁ.
2
2
ꢂ
sꢇꢍꢇcꢁꢄvꢄꢁꢊ ꢁꢃ ꢉꢎꢍꢌꢃxꢄꢂꢇ = (ꢉꢎꢍꢌꢃxꢄꢂꢇ % / (ꢉꢎꢍꢌꢃxꢄꢂꢇ % + ꢉꢎꢍꢌꢃꢋꢇ%)) × 100.
interactions involving metal chelate, pyrazolate, terminal phenyl, and central phenyl rings reinforce
the packing. These interactions propagate, leading to a 1-D chain along the a-axis. The π–π stacking
interaction parameters are given in Table S1 of ESI.
3
.2. Catalytic reactivity
The reaction was first carried out using 1 as a catalyst and methylphenyl sulfide (MPS) as a standard
substrate in different solvents and different ratios of the substrate to the catalyst. H ꢀ, CH Cl , toluene,
2
2
2
ethylacetate, and hexane only afforded low yields of the oxidized product after 2 h of reaction at room
temperature, possibly due to the insufficient solubility of the various reaction components (Table 3).
Among the solvents examined, 1:1 mixture of CH ꢀH/CH Cl was found to be the best for this catalytic
3
2
2
system.
Because 1 showed good catalytic activity and efficiency in the oxidation of MPS, we investigated
the influence of the ratio of the substrate to the oxidant (Figure 3). When the ratio of the substrate to
the oxidant was increased from 2:1 to 1:2, the conversion of MPS increased from 53 to 97%. With a
further increase in the ratio of the substrate to the oxidant to 1:3, the selectivity of MPS decreases
from 93 to 70%.
1
and 2 were examined as catalysts for oxidation of various sulfides including dialkyl sulfides, cyclic
sulfide, benzylalkyl sulfide, substituted arylalkyl, and dialkyl sulfides bearing different functional groups

8
N. KHADIR ET AL.
with UHP as oxidant; the results are given in Table 4. Just like the oxidation of MPS, excellent catalytic
activities and selectivities were obtained for all tested sulfides. The very good conversions of substrates
of 49–99%, depending on the nature of the sulfide, were obtained for all cases. In the oxidation of benzyl
phenyl sulfide and dibenzyl sulfide, no oxidation was observed at the benzylic C–H bonds (entries 4
and 5). In particular, in the oxidation of sulfides bearing other active functional groups, such as hydroxyl
and C=C bonds, the otherwise easily oxidized functional groups were tolerated (entries 7 and 8). As
illustrated in Table 4, the catalytic activity of 1 and 2 appear to be equal.
4. Conclusion
Two new binuclear nickel(II) complexes [LNi (pz)] have been synthesized and structurally characterized.
2
In both complexes, the nickel ions are doubly bridged by an endogenous thiophenolate-sulfur and an
exogenous pyrazolate group with Ni⋯Ni distance of 3.5926(3) Å. Also we have explored a new method
for selective oxidation of various aromatic and aliphatic sulfides to the corresponding sulfoxides with
UHP as the oxidant catalyzed by binuclear nickel complexes. The described method in this article clearly
indicates that the methodology involves mild and selective synthesis of sulfoxides from both aromatic
and aliphatic sulfides. The resulting products were obtained in good yields.
Supplementary material
CCDC 1413106 and CCDC 1413107 contain the supplementary crystallographic data for this paper. This data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre,
1
2 Union Road, Cambridge CB2 1EZ, UK; Fax: (+44) 1223-336-033; or E-mail: deposit@ccdc.cam.ac.uk.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
Partial funding support was provided by the Research Council of University of Maragheh (M.A.) and Sharif University of
Technology (D.M.B.).
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