Catalytic oxidation of organosulfides to sulfoxides using two novel Cu(II) and Ni(II) complexes with aqueous H2O2: Effect of TMAO promoter on oxidation of organosulfides

Article abstract of DOI:10.1016/j.molcata.2010.10.002

Two new copper(II) and nickel(II) complexes [Cu(MeOH)(O-NO ₂)(L)](NO₃)·CH₃OH (1) and [Ni(L) ₂(NO₃)₂]·H₂O (2) derived from the 4′-(2-thienyl)-2,2′,6′,2″-terpyridine (L) were synthesized. The ligand and complexes were characterized with elemental analysis, ¹H and ¹³C NMR, IR spectroscopy and finally the solid structure of complexes were determined by X-ray crystallography. Complexes (1) and (2) were tested as homogenous catalysts for sulfoxidation of a variety of organosulfide substrates utilizing hydrogen peroxide in the presence of a catalytic amount of trimethylamine N-oxide (TMAO). Addition of TMAO to the reaction mixture enhanced the conversion and selectivity.

Full text of DOI:10.1016/j.molcata.2010.10.002

Journal of Molecular Catalysis A: Chemical 333 (2010) 94–99
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Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Catalytic oxidation of organosulfides to sulfoxides using two novel Cu(II)
and Ni(II) complexes with aqueous H O : Effect of TMAO promoter on oxidation
2
2
of organosulfides
∗
Ali Nemati Kharat , Abolghasem Bakhoda, Taraneh Hajiashrafi
School of Chemistry, University college of Science, University of Tehran, PO Box 13145-1357, Tehran, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 June 2010
Received in revised form
Two new copper(II) and nickel(II) complexes [Cu(MeOH)(O–NO )(L)](NO )·CH OH (1) and
2
3
3
ꢀ
ꢀ
ꢀ
ꢀꢀ
[
Ni(L)2(NO3)2]·H2O (2) derived from the 4 -(2-thienyl)-2,2 ,6 ,2 -terpyridine (L) were synthesized.
1 13
The ligand and complexes were characterized with elemental analysis, H and C NMR, IR spectroscopy
and finally the solid structure of complexes were determined by X-ray crystallography. Complexes (1)
and (2) were tested as homogenous catalysts for sulfoxidation of a variety of organosulfide substrates
utilizing hydrogen peroxide in the presence of a catalytic amount of trimethylamine N-oxide (TMAO).
Addition of TMAO to the reaction mixture enhanced the conversion and selectivity.
© 2010 Elsevier B.V. All rights reserved.
2
0 September 2010
Accepted 3 October 2010
Available online 28 October 2010
Keywords:
ꢀ
ꢀ ꢀ ꢀꢀ
4
-(2-Thienyl)-2,2 ,6 ,2 -terpyridine
Sulfoxidation
Trimethylamine N-oxide
X-ray crystallography
1
. Introduction
Chemical building blocks containing sulfoxide functional groups
the ideal combination of simplicity of method, good rate, selectivity
and high yields of desired sulfoxides. For this reason, the chemistry
of the several transition metal complexes with O, N, S and P donor
ligands are subject of current interests [12–14]. Recently, many cat-
alytic oxidation of thioethers to the proper sulfoxide catalyzed by
Ni(II) and Cu(II) complexes were reported [15–19].
are particularly useful for the construction of various important
compounds in both bulk and fine chemicals [1–3]. The exten-
sive chemistry of sulfoxides and sulfones makes them very useful
reagents in organic synthesis in general and useful synthetic inter-
mediates for the construction of various chemically and biologically
significant molecules in particular [4–7]. In this manner metal cat-
alyzed asymmetric oxidation of sulfides, a powerful strategy for the
rapid preparation of enantiopure sulfoxides, has garnered exten-
sive attention from the synthetic community [2]. The sulfoxides
are usually produced by oxidation of sulfides with several oxidative
procedures and a variety of oxidants like molecular oxygen, hydro-
gen peroxide, urea hydrogen peroxide, tert-butylhydroproxide,
iodosyl benzene and sodium hypochlorite [8–11]. Unfortunately
most of these reagents are not satisfactory for large-scale synthesis
due to the formation of environmentally unfavorable by-products,
the low content of effective oxygen, and high cost. Among various
terminal oxidants used, hydrogen peroxide has relatively high oxy-
gen content, leaves only water as waste product and has low cost in
price than other oxidants. Generally, it is important that to stop the
reaction at the sulfoxide step but the reported methods rarely offer
With this background, we describe here the synthesis, spec-
troscopy and X-ray crystallographic structure determination
ꢀ
ꢀ
ꢀ
ꢀꢀ
of Ni(II) and Cu(II) complexes with 4 -(2-thienyl)-2,2 ,6 ,2 -
terpyridine ligand and the catalytic activity of these novel
complexes. Also improvements of the catalytic oxidation of sulfides
were investigated in presence of catalytic amount of trimethy-
lamine N-oxide.
2. Experimental
2.1. Materials and instruments
The ligand was synthesized according to the previously pub-
lished procedures with slightly modification [20]. All solvents
were obtained from commercial sources and used without fur-
ther purification unless stated otherwise. If required, solvents
were further purified by standard methods. 2-Acetylpyridine,
thiophene-2-carboxaldehyde, 28.0–30.0% aqueous ammonia and
potassium tert-butoxide were purchased from Merck chemicals
and were used as received. The hydrated metal salts and TMAO
were obtained from Fluka. Melting points are uncorrected and
∗ Corresponding author. Tel.: +98 21 61112499; fax: +98 21 66495291.
E-mail address: alnema@khayam.ut.ac.ir (A.N. Kharat).
1
381-1169/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2010.10.002

A.N. Kharat et al. / Journal of Molecular Catalysis A: Chemical 333 (2010) 94–99
95
Table 1
were obtained with Electrothermal 9200 melting point appara-
−
1
Crystallographic and structure refinements data for complexes (1) and (2).
tus. Infrared spectrums from 250 to 4000 cm
of solid samples
were taken as 1% dispersion in CsI pellets using a Shimadzu-470
spectrometer. H and C NMR spectra were recorded at room
temperature on a Bruker AVANCE 300 MHz. The NMR spectra
(1)
(2)
1
13
Formula
C20.5H19CuN5O7.5S
551.01
150(1)
0.71073
Triclinic
P1¯
0.10 × 0.08 × 0.08
8.5024(3)
9.4502(3)
15.5274(6)
93.6050 (19)
101.8820 (17)
107.6250 (18)
1153.04(7)
2
1.587
2.6–27.5
564
1.09
C38H28N8NiO7S2
831.51
150(1)
0.71073
Triclinic
P1¯
0.20 × 0.16 × 0.12
12.6736 (7)
13.2558 (8)
14.6113 (5)
67.122 (3)
79.437 (3)
63.110 (2)
2016.97 (18)
2
1.369
2.6–27.5
856
0.64
Formula weight
Temperature/K
Wavelength ꢀ/Å
Crystal system
Space group
Crystal size/mm
a/Å
b/Å
are referenced to Me Si as external standards. Elemental analy-
4
sis was performed using a Heraeus CHN–O Rapid analyzer. The
course of the reactions was monitored by gas chromatography (Agi-
lent Technologies 6890N Instrument), equipped with a capillary
column (19019 J-413 HP-5, 5% phenyl methyl siloxane, capillary
3
6
0.0 mm × 250 mm × 1.00 mm), and a flame ionization detector.
c/Å
◦
˛
/
2.2. Synthesis of ligand (L)
◦
◦
ˇ/
/
ꢁ
3
Volume/Å
Z
Density (calc.)/g cm
ꢂ ranges for data collection
F(0 0 0)
To a solution of 2-acetylpyridine (2.42 g, 20 mmol) in 75 ml
absolute ethanol, were added thiophene-2-carboxaldehyde (1.12 g,
0 mmol), potassium tert-butoxide (3.09 g, 27.5 mmol) and ammo-
−
1
1
nia solution (30 ml). The reaction mixture was stirred at ambient
Temperature for 18 h. After this time, the precipitated impure prod-
uct was filtered off and successively washed with cold water and
cold ethanol–water (50:50) solution and finally with minimum
amount of cold diethyl ether. The bright yellow product was dried
−
1
Absorption coefficient/mm
Index ranges
−11 ≤ h ≤ 10
−16 ≤ h ≤ 16
−15 ≤ k ≤ 17
−19 ≤ l ≤ 19
18,777
−
12 ≤ k ≤ 12
19 ≤ l ≤ 20
−
Data collected
13,523
for 2 days in vaccuo over P O5. The yield was 1.36 g (43%). Physical
and spectroscopic properties were consistent with those reported
in the literature [21].
Unique data (Rint)
Parameters, restrains
5227, (0.0712)
327, 10
0.0649, 0.1578
0.1191, 0.1923
1.05
9141, (0.066)
514, 27
0.0699, 0.1748
0.1349, 0.2039
0.98
2
a
Final R1, wR2 (Obs. data)
a
Final R1, wR2 (All data)
2
Goodness of fit on F (S)
A˚ 3
2.3. Synthesis of complex (1)
Largest diff peak and hole/e
0.76, −0.91
0.93, −0.86
ꢀ
ꢀ
ꢀ
ꢀꢀ
To
a
solution of 4 -(2-thienyl)-2,2 ,6 ,2 -terpyridine (L)
the reactions were run at least twice and the found values were
averaged.
(
0.1 g,0.32 mmol) in CHCl3 (5 ml) was added a solution of
Cu(NO ) ·3H O (0.039 g, 0.16 mmol) in methanol (10 ml). The
3
2
2
color of the reaction mixture was turned to deep green immedi-
ately. After stirring for 30 min at ambient temperature, the green
solution was left to evaporate slowly at room temperature. After
2.6. Crystal structure determination and refinement
The crystallographic data was collected with a Nonius Kappa
1
7
1
1
3
week, greenish-blue blocks of (1) were isolated (yield 0.07 g,
CCD diffractometer, using graphite-monochromated Mo K␣ radi-
ation of 0.71073 A˚ . For [Cu(MeOH)(O–NO )(L)](NO )·CH OH,
◦
−1
9.5%, decompose >298 C). IR (CsI, cm ): 3431b, 3062w, 1761w,
609s, 1560m, 1480m, 1426m, 1374s, 1292w, 1238w, 1156w,
096w, 1019m, 843w, 788m, 724m, 644w, 562w, 502w, 415w,
52w. Anal. Calc C, 43.44; H, 3.46; N, 12.66. Found C, 43.47; H, 3.49;
2
3
3
(1),
a
greenish-blue
block
with
a
dimension
of
0
.10 mm × 0.08 mm × 0.08 mm and for [Ni(L) ](NO ) ·H O,
2
3
2
2
(2), a brownish-orange block crystal with a dimension of
N, 12.61.
0
.20 mm × 0.16 mm × 0.12 mm was mounted. Cell constants
and an orientation matrix for data collection were obtained by
2
.4. Synthesis of complex (2)
least-squares refinement of diffraction data from 5227 for (1) and
9
141 for (2) unique reflections. Data were collected at a temper-
ꢀ
ꢀ
ꢀ
ꢀꢀ
To a solution of 4 -(2-thienyl)-2,2 ,6 ,2 -terpyridine (L) (0.1 g,
.32 mmol) in CHCl (5 ml) was added a solution of Ni(NO ) ·6H O
◦
ature of 150(1) K to a maximum 2ꢂ value of 55 for both (1) and
(2). The numerical absorption coefficients, ꢃ, for Mo K␣ radiation
are 1.038 and 0.642 mm for 1 and 2, respectively. The structures
0
(
3
3
2
2
0.047 g, 0.16 mmol) in acetonitrile (10 ml). The color of the reaction
−1
solution was turned to brownish green. The mixture was stirred
for 20 min at room temperature and then was left to evaporate
slowly at room temperature. After 5 days, brownish-orange blocks
of (2) were obtained (yield 0.113 g, 84.9%, decompose >322 C). IR
CsI, cm ): 3417b, 3057w, 1607 s, 1557m, 1470m, 1425m, 1365b,
248m, 1157w, 1088w, 1017m, 895w, 844w, 790m, 707w, 637w,
59w, 416w, 215s. Anal. Calc. C, 54.89; H, 3.39; N, 13.48. Found C,
4.92; H, 3.41; N, 13.43.
were solved by direct methods [21] and subsequent differences
Fourier map and then refined on F2 by a full-matrix least-squares
procedure using anisotropic displacement parameters [21]. All of
hydrogen atoms were located in a difference Fourier map and then
refined isotropically. Cell refinements were performed using the
Denzo-SMN crystallographic software package [22]. A summary
of the crystal data, experimental details and refinement results is
given in Table 1.
◦
−1
(
1
5
5
2.5. General procedure for catalytic oxidation reactions
3. Results and discussion
In a typical experiment, a mixture of 1 mmol of sulfide, 2 mmol
3.1. Synthesis of complexes
of hydrogen peroxide,0.04 mmol of catalyst and 0.05 mol of TMAO
ꢀ
were added to a vessel containing 2 ml CH CN at room tempera-
Two new complexes were synthesized with 4 -(2-thienyl)-
3
ꢀ
ꢀ
ꢀꢀ
ture while the progress of the reaction was monitored by TLC. After
2,2 ,6 ,2 -terpyridine ligand as depicted in Scheme 1. The ligand
was prepared in one pot synthesis from condensation of 2-
acetylpyridine, thiophene-2-carboxaldehyde and ammonia in the
presence of t-BuOK [20]. For preparation of complex (1) and (2),
hydrated copper nitrate and nickel nitrate were reacted with lig-
1
h, the reaction mixture was analyzed directly by gas chromatog-
raphy. In some cases reaction products were identified by injection
of pure chemicals, but in other cases confirmed by GC–mass spec-
troscopy. The yields were calculated from standard curves. Most of

9
6
A.N. Kharat et al. / Journal of Molecular Catalysis A: Chemical 333 (2010) 94–99
Scheme 1. Reagents and condition for the synthesis of complex (1) and (2) at room temperature.
ꢀ
ꢀ
ꢀ
ꢀꢀ
and in methanol–chloroform and acetonitrile–chloroform mixture,
respectively.
environment consists of nitrate ion, one 4 -(2-thienyl)-2,2 ,6 ,2 -
terpyridineligand and one methanol molecule giving a distorted
square based pyramidal geometry. The Cu–N and Cu–O average
bond distances are 1.990(4) and 2.095(3) A˚ , respectively, both con-
3.2. Description of the molecular structure of
sistent with the range observed for similar copper mixed ligand
compouds [23,24]. The unit cell-packing diagram of the complex
is presented in Fig. 2. Different hydrogen bonds exist in the struc-
ture. One between free nitrate ion and the OH group of coordinated
[
[
Cu(MeOH)(O–NO )(L)](NO )·CH OH (1), and
2
3
3
Ni(L) ](NO ) ·H O (2)
2
3
2
2
Recrystallization of micro crystals of complex (1) in methanol
◦
methanol (O4· · ·O5 = 2.648(6) A˚ and O4–H4–O5 angle of 150.6 ) and
and acetonitrile yield greenish-blue and brownish-orange block
crystals correspond to (1) and (2), respectively. Crystallographic
data for (1) and (2) are given in Table 1. The structure of (1)
another one exists between the coordinated nitrate and the free
methanol molecule (O9· · ·O3 = 3.285(13) A˚ and O9–H9–O3 angle of
consists of [Cu(MeOH)(O–NO )(L)] cation and nitrate anion accom-
2
panying with one methanol molecule (Fig. 1). The copper(II)
Fig. 1. The labeled diagram of [Cu(MeOH)(O–NO2)(L)](NO3)·CH3OH (1). Thermal
ellipsoids are at 30% probability level and hydrogen atoms were omitted for more
clarity.
Fig. 2. Crystal packing diagram for [Cu(MeOH)(O–NO2)(L)](NO3)·CH3OH (1). Hydro-
gen bonds are shown as dashed lines.

A.N. Kharat et al. / Journal of Molecular Catalysis A: Chemical 333 (2010) 94–99
97
Fig. 3. The labeled diagram of [Ni(L)2](NO3)2·H2O (2). Thermal ellipsoids are at 30% probability level.
◦
1
79.4 ). The Cu1–O4 bond distance is longer than the others, due to
3.3. Catalytic sulfoxidation and effect of TMAO
hydrogen bonding with nitrate counter ion, making it more labile
than the others for substitution.
In order to find the optimum conditions for oxidation reactions,
an attempt was made to investigate the effects of solvent and TMAO
as promoter on the oxidation of organosulfides. At first, oxidation of
methylphenylsulfide as a model substrate was carried out in vari-
ous solvents such as acetone, methanol, ethanol, dichloromethane,
chloroform, dichloroethane and acetonitrile. The reactions were
run with molar ratio of 1:25:50 for catalyst:substrate:oxidant that
was found as optimum conditions. The polar solvents, i.e. methanol,
ethanol and acetonitrile were more effective than less polar sol-
ꢀ
Complex (2) consists of two tridentate chelating 4 -(2-thienyl)-
ꢀ ꢀ ꢀꢀ
2
,2 ,6 ,2 -terpyridine ligand. The molecular structure and atom
numbering scheme and also the crystal packing are shown in
Figs. 3 and 4, respectively. The complex has a distorted octahedral
ꢀ
geometry. The two rigid tridentate chelating 4 -(2-thienyl)-
ꢀ ꢀ ꢀꢀ
2
,2 ,6 ,2 -terpyridine ligands are the main factors accounting for
this distortion. The average Ni–N distance for (2) is 2.067(4) A˚ that
is in agreement with the values reported for similar structures
[
25–27].
There are also different hydrogen bonds in complex (2),
vents (see Table 2). Since H O2 is not completely soluble in less
2
polar organic solvents such as dichloromethane, dichloroethane
and chloroform, the oxidation yields are low in these solvents.
Furthermore, to investigate the effect of oxidant in the catalytic
systems, oxidation of methylphenylsulfide was carried out using
various molar ratios of oxidant to sulfide (see Fig. 5). The oxidation
which are between the nitrate ion and free water molecules,
◦
O1W· · ·O6 = 2.837(5) A˚ and O1W–H1WA–O6 angle of 179.4 , and
also O1W· · ·O3A = 2.769(14) A˚ with O1W–H1W–O3Ai angle of
i
◦
1
79.0 (symmetry code: (i) x, y + 1, z − 1).
reactions with 2 equiv. H O2 afforded 88% and 80% conversions for
2
[
Cu(MeOH)(O–NO )(L)](NO )·H O and[Ni(L) ](NO ) ·H O, respec-
2
3
2
2
3
2
2
tively. Higher amounts of H O up to 3 and 4 equiv. led to
2
2
growth in the conversions, but decreased the selectivity to
sulfoxide in both catalytic systems. The decrease in selectiv-
ity is faster in [Cu(MeOH)(O–NO )(L)(NO )]·H O compared to
2
3
2
[
Ni(L) (NO ) ]·H O, so the highest selectivity to sulfoxide as well as
2
3
2
2
reasonably high conversions were obtained with 2 equiv. of H O
2
2
(see Fig. 5).
Table 2
Effect of solvent on the oxidation of methylphenylsulfide catalyzed by (1) and (2).a
Solvent
Conversion (%)b
Conversion (%)c
Acetone
Methanol
Ethanol
Dichloromethane
Chloroform
Dichloroethane
Acetonitrile
16
44
59
11
9
10
49
56
9
5
13
70
15
73
a
Condition of reaction: the molar ratio for catalyst:substrate:oxidant are 1:25:50.
The reactions were run for 60 min at room temperature.
b
GC yields based on the starting sulfides with catalyst (1).
GC yields based on the starting sulfides with catalyst (2).
Fig. 4. Crystal packing diagram for [Ni(L)2](NO3)2·H2O (2). Hydrogen bonds are
c
shown as dashed lines.

9
8
A.N. Kharat et al. / Journal of Molecular Catalysis A: Chemical 333 (2010) 94–99
in 99% conversion. The selectivity and conversion of the sulfoxide
were further increased to >99% when the amount of TMAO was
increased to 5 mol% for catalyst. A control experiment without com-
plex (1) provided the sulfoxide in only 5% yields and no sulfone
was observed. These studies suggest that complex (1) together with
TMAO catalyzed the oxidation of sulfide to the sulfoxide in the pres-
ence of 30% hydrogen peroxide. Also, the same procedures were
performed with complex (2), as it shown in Fig. 6 and the results
were presented in Table 3.
To study the applicability of this catalyst for oxidation of
other sulfides,
dialkyl sulfides, were oxidized to the corresponding sulfoxides
see Table 4). The reactivity and conversions were depen-
a series of aryl alkyl, aryl allyl, diaryl and
(
dent on the nature of the substituents. In the case of allyl
sulfides, no oxidation was observed at the carbon–carbon dou-
ble bond. Similarly, benzylic sulfides could be oxidized to the
corresponding sulfoxides without affecting the benzylic C–H
bond [14]. Dialkyl sulfides were moderately reactive providing
the corresponding sulfoxide. These oxidations could usually be
stopped at the sulfoxide stage without over oxidation to the
sulfone.
The higher activity of complex (1) can be explained by the pres-
ence of labile methanol ligand. The presence of this weak and
labile ligand, have a key role in the formation of active “metal-
oxo” species. This was confirmed by the longer Cu–O bond distance
than normal condition. Also the vacant site in complex (1) affect the
formation of “metal-oxo” species than the other eight coordinated
complex (2). Moreover, the conversion average of oxidation reac-
tions catalyzed by complex (1) and (2), increased from 76.75% and
7
4.1% to 91.6% and 88%, respectively. These figures show that the
catalytic amount of TMAO enhance the conversion and selectivity
of the oxidation of organosulfides. This happened because TMAO
facilitated the formation of “metal-oxo” species in metal complexes
especially in copper complex. Based on our knowledge; it is the
first report for catalytic oxidation of organosulfides co-catalyzed
by TMAO. Finally, we think that TMAO facilitate the reaction by
changing the oxygen source from hydrogen peroxide to TMAO and
the latter is more controllable than H2O2. It means that the TMAO
oxidize the organosulfides to corresponding sulfoxides and then is
recycled by hydrogen peroxide. The oxidation was stopped at sul-
foxide step for the selectivity of TMAO for formation of sulfoxide.
Fig. 5. The effect of amount oxidant on the oxidation of methylphenylsulfide by (a)
complex (1) and (b) complex (2).
We found that under experimental conditions in this work, the
oxidation occurred to a 3:1 mixture of sulfoxide and sulfone in 73%
conversion in the presence of 4 mol% of the complex (1) in ace-
tonitrile. Addition of 3 mol% TMAO to the reaction mixture led the
oxidation to a 15:1 mixture of sulfoxide and sulfone (94% sulfoxide)
Fig. 6. Catalytic sulfoxidation ofmethylphenylsulfide by complex (1) or complex (2) in the presence of TMAO.
Table 3
Oxidation of methylphenylsulfide using complex (1) and (2) as catalyst and effect of TMAO as promoter.
a
Entry
Complex (1)
Complex (2)
TMAO
Conversion (%)b
Sulfoxide(%)
Sulfone (%)
Selectivity (%)c
1
2
3
4
5
6
7
8
4 mol%
–
–
–
None
81
5
99
>99
80
5
73
∼5
8
–
5.5
1
9
–
6
3
90
100
94
99
89
100
94
97
–
5 mol%
3 mol%
5 mol%
None
5 mol%
3 mol%
5 mol%
4 mol%
4 mol%
93.5
∼99
71
–
–
–
–
–
4 mol%
–
4 mol%
4 mol%
∼5
95
95
89
92
a
Substrate (1 mmol), complex (1) or (2) (4 mol%), TMAO (5 mol%) and 30% H2O2 (2 mmol) were stirred for 1 h at RT in CH3CN (2 mL).
Analyzed by GC.
Selectivity(%) = sulfoxide(%)/[sulfoxide(%) + sulfone(%)].
b
c

A.N. Kharat et al. / Journal of Molecular Catalysis A: Chemical 333 (2010) 94–99
99
Table 4
Oxidation of organosulfides using complex (1) and (2) as catalyst in the presence and absence of TMAO as promoter.
a
Entry
Substrate
Complex (1),
conv.(%)/select.(%)
Complex (1), without
TMAO conv.(%)/select.(%)
Complex (2),
conv.(%)/select.(%)
Complex (2), without
TMAO conv.(%)/select.(%)
b,d
c,d
b,d
c,d
1
2
3
4
5
6
7
8
Dimethylsulfide
Dipropylsulfide
Diphenylsulfide
Benzylphenylsulfide
Dibenzylsulfide
Methylphenylsulfide
Ethylphenylsulfide
Diallylsulfide
89/97
93/97
95/97
89/96
91/97
99/94
94/96
83/97
73/92
78/90
76/92
74/93
79/90
81/90
80/92
73/86
82/97
89/94
90/95
87/97
86/96
95/94
89/96
86/97
71/89
76/88
71/85
70/86
76/88
80/89
78/92
71/81
a
Substrate (1 mmol), complex (1) or (2) (4 mol%), TMAO (5 mol%) and 30% H2O2 (2 mmol) were stirred in acetonitrile (2 mL) at room temperature.
Yields and conversions in the presence of TMAO. The yield was calculated based on starting substrate, by using GC and with comparison of authentic samples.
Yields and conversions in the absence of TMAO. The yield was calculated based on starting substrate, by using GC and with comparison of authentic samples.
Selectivity(%) = sulfoxide(%)/[sulfoxide(%) + sulfone(%)].
b
c
d
The more experimental and theoretical studies can help us to find
out how the TMAO stop the reaction at sulfoxide step.
[4] G.H. Posner, M. Weitzberg, T.G. Hamill, E. Asirvatham, H. Cun-Heng, J. Clardy,
Tetrahedron 42 (1986) 2919.
[
5] A.G. Renwick, in: L.A. De Damani (Ed.), Sulfur-Containing Drugs and Related
Organic Compounds, Part B, vol. 1, Ellis Horwood, Chichester, UK, 1989, p. 133.
4
. Conclusion
[6] J.M. Shin, Y.M. Cho, G. Sachs, J. Am. Chem. Soc. 126 (2004) 7800.
[
[
[
7] M.C. Carreno, M. Ribagorda, G.H. Ponser, Angew. Chem. Int. Ed. 41 (2002) 2753.
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