Economical oxygenation of olefins and sulfides catalyzed by new molybdenum(VI) tridentate schiff base complexes: Synthesis and crystal structure

Article abstract of DOI:10.1002/zaac.201200079

New cis-dioxomolybdenum(VI) complexes (MoO₂Y^xCH ₃OH) were synthesized using MoO₂(acac)₂ and 2[(1-hydroxy-2-methylpropane-2-ylimino)methyl]phenol derivatives as tridentate ONO donor Schiff base ligands (H₂Y^x). MoY¹ was crystallized in orthorhombic space group Pbca. The epoxidation of olefins using tert-butyl hydroperoxide and oxidation of sulfides to the sulfoxides by hydrogen peroxide were efficiently enhanced by the catalytic activity of title Mo ^VI complexes with excellent selectivity. The high efficiency and relative stability of the catalysts was observed by turnover number and UV/Vis investigations. The electron-rich and bulky ligands promoted the effectiveness of the catalysts. Copyright

Full text of DOI:10.1002/zaac.201200079

ARTICLE
DOI: 10.1002/zaac.201200079
Economical Oxygenation of Olefins and Sulfides Catalyzed by New
Molybdenum(VI) Tridentate Schiff Base Complexes: Synthesis and Crystal
Structure
Abdolreza Rezaeifard,*[a] Maasoumeh Jafarpour,*[a] Heidar Raissi,[a]
Mahboubeh Alipour,[a] and Helen Stoeckli-Evans[b]
Keywords: Molybdenum; Schiff base; Peroxides; Oxygenation; Catalysis
Abstract. New cis-dioxomolybdenum(VI) complexes (MoO2YxCH3OH)
were synthesized using MoO2(acac)2 and 2[(1-hydroxy-2-methylpro-
were efficiently enhanced by the catalytic activity of title MoVI com-
plexes with excellent selectivity. The high efficiency and relative stability
pane-2-ylimino)methyl]phenol derivatives as tridentate ONO donor of the catalysts was observed by turnover number and UV/Vis investi-
Schiff base ligands (H2Yx). MoY1 was crystallized in orthorhombic gations. The electron-rich and bulky ligands promoted the effectiveness
space group Pbca. The epoxidation of olefins using tert-butyl hydroper- of the catalysts.
oxide and oxidation of sulfides to the sulfoxides by hydrogen peroxide
in the selective oxidation of olefins and sulfides.[6] The steric
Introduction
hindrance and electron attracting capacities of ligands strongly
The enthusiasm shown in the coordination chemistry of mo-
influenced the oxidation activity of molybdenum complexes.
lybdenum followed the discovery of molybdenum in a number
Herein, we would like to introduce new dioxomolybden-
of redox enzymes, such as aldehyde oxidase, sulfite oxidase,
um(VI) Schiff base complexes containing simple and easy pre-
xanthine oxidase, nitrate reductase, and nitrogenase.[1] Diox-
pared asymmetric ONO tridentate ligands based on 2[(1-hy-
omolybdenum(VI) complexes are important catalysts as well
droxy-2-methylpropane-2-ylimino)methyl]phenol as efficient
as catalyst-precursors for oxygen-transfer-reactions in chemi-
cal transformations.[2] Special interest in MoVI-oxo complexes
catalysts in the oxygenation of olefins to epoxides and sulfides
to sulfoxides using tert-butyl hydroperoxide (TBHP) and hy-
arose particularly in the late 1960’s, when ARCO and Halcon
drogen peroxide respectively (Scheme 1). We also report the
published patents on the olefin-epoxidation using tert-butylhy-
droperoxide (TBHP) as an oxidant through MoVI complexes
in homogeneous phase.[3] The ability of molybdenum to form
stable complexes with oxygen-, nitrogen-, and sulfur-contain-
ing ligands led to development of molybdenum Schiff base
complexes, which are efficient catalysts both in homogeneous
and heterogeneous reactions.[4] The activity of these com-
plexes varied markedly with the type of ligands and coordina-
tion sites.[5]
Very recently, we reported the synthesis and catalytic ac-
tivity of dioxomolybdenum(VI) complexes of tridentate Schiff
base ligands derived from salicylaldehydes and amino alcohols
* Dr. A. Rezaeifard, Dr. M. Jafarpour
Fax: 98-0561-2502515
E-Mail: rrezaeifard@birjand.ac.ir; rrezaeifard@gmail.com
[a] Catalysis Research Laboratory
Department of Chemistry, Faculty of Science
University of Birjand
Birjand, 97179–414, Iran
[b] Institute of Physics
University of Neuchâtel
Rue Emile-Argand 11
2009 Neuchâtel, Switzerland
Supporting information for this article is available on the WWW
Scheme 1. Oxygenation of olefins and sulfides catalyzed by different
under http://dx.doi.org/10.1002/zaac.201200079 or from the au-
thor.
MoVI-Schiff base complexes utilized in this study.
Z. Anorg. Allg. Chem. 2012, 638, (᭿), 1–9
© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1

A. Rezaeifard, M. Jafarpour et al.
ARTICLE
crystal structure of a sample of these molybdenum complexes Table 2. Crystal data and structure refinement for the complex MoY1.
(MoY1) determined by single-crystal X-ray diffraction.
MoO2(Y1)(CH3OH)
Empirical formula
Formula weight
C16H19MoNO5
401.26
Results and Discussion
Temperature /K
173
Wavelength /
Crystal system
Space group
0.71073
orthorhombic
Pbca
Structural Discussion of Dioxo-MoVI Complexes
The dioxomolybdenum complexes (MoY1–MoY5) were
prepared by reaction of 2[(1-hydroxy-2-methylpropane-2-yli-
mino)methyl]phenol derivatives (Scheme 1) and dioxomolyb-
denum(VI) acetylacetonate, which were characterized by ele-
mental analysis, IR, NMR, and UV/Vis spectroscopy as well
as mass spectrometry. The analytical and selected spectro-
scopic data of the ligands and molybdenum complexes are
given in Table 1. The synthesis, characterization, and crystal
structure of MoY2 have been reported previously.[7] In addition
to the crystal data for MoY1 (Table 2) and MoY2,[7] spectro-
scopic and elemental analyses are in agreement with a mono-
meric complex with a ligand:Mo ratio of 1:1. When the reac-
tions were performed using two equivalents of the ligands, the
same products were formed as observed with one equivalent
of the ligand.
The Schiff base ligand is bonded to the MoO2+2 ion through
deprotonated naphthol and and alcohol oxygen atoms and one
imine nitrogen atom, which is trans to an oxo group. For ex-
ample, the IR spectra of MoY1 in KBr matrix confirm the
presence of imine bond (C=N) mode at 1615 cm–1, C=C vi-
bration bands of the aromatic ring at 1542 cm–1, and Mo–O
vibration bands at 889 and 921 cm–1. Crystallographic data and
details of the structure refinements are summarized in Table 2.
The ORTEP plot of the MoY1 complex accompanied with the
relevant bond lengths and angles are given in Figure 1. The –
C(CH3)2CH2– part of the ligand (atoms C13, C14, and C15)
is disordered and these atoms have final refined occupancies
A:B of 0.780(4):0.220(4) (see CIF for details). The O=Mo=O
angles are 105.67° and the Mo=O distances are 1.718 Å and
Unit cell dimensions
a /Å
b /Å
c /Å
α /°
β /°
9.7635(5)
15.2538(10)
20.8861(10)
90.00
96.918(10)
90.00
3110.6(3)
8
1.714
0.869
γ /°
V /Å3
Z
Dcal /Mg·m–3
Absorption coefficient /mm–1
F(000)
1632
Crystal size /mm3
θ range for data collection /°
Index ranges
0.15ϫ0.3ϫ0.31
2.0 to 29.3
–13 Յ h Յ 13
–20 Յ k Յ 20
–27 Յ l Յ 28
35498
4212 [R(int) = 0.051]
99
Multi-scan
0.9532 and 1.0536
Full-matrix least-squares on
F2
Reflections collected
Independent reflections
Completeness to θ = 29° /%
Absorption correction
Max. and min. transmission
Refinement method
Data / restraints / parameters
Goodness-of-fit on F2
Final R indices [IϾ2sigma (I)]
R indices (all data)
4212 / 2 / 246
1.068
a)
b)
R1 = 0.0326, wR2 = 0.0648
a)
b)
R1 = 0.0498, wR2 = 0.0689
Largest diff. peak and hole
0.44, –0.59
a) R1 = Σ||Fο|–|Fc||/Σ|Fο|. b) wR2 = Σw[(Fο2–Fc ) / Σw[(Fο2)2]}1/2
2 2
.
Catalytic Epoxidation of Olefins
The oxidation of cyclooctene using H2O2 and TBHP, which
1.698 Å. The appearance of signals at δ = 3.14 and 3.13 ppm did not proceed in the absence of catalyst under mild and re-
in the 1H NMR spectra of MoY1 and MoY5, respectively, dem- flux conditions was used as a model reaction. It was observed
onstrate the coordination of a methanol molecule to the central that only TBHP has ability to trigger the reaction in the pres-
MoVI atoms.[6] The Mo–O–C angle and Mo–O distance for ence of MoY1 catalyst. To find optimum reaction conditions,
Mo–OHCH3 in MoY1 are 121.71° and 2.534 Å, respectively. the influence of different factors that may affect the conversion
The crystal packing diagram (Figure 2) shows the formation and selectivity of the reaction was investigated. A systematic
of the O–H···O hydrogen bonded centrosymmetric dimer. The examination of cyclooctene oxidation in various solvents was
electronic spectra of the MoY1 complex revealed a high inten- performed in the presence of a minute amount (0.1 mol-%) of
sity charge-transfer band (LMCT) in 308 nm[8] (Figure 3).
MoY1 in different temperatures (Table 3). Considering the
Table 1. Selected spectroscopic data of tridentate Schiff base ligands and MoVI complexes.
Compound
δppm (CH=N)
IR /cm–1
νCH=N
1H
13C
νMo=O
νaromatic
H2Y1
MoY1
H2Y3
MoY3
H2Y4
MoY4
H2Y5
MoY5
8.66
9.42
8.26
8.70
8.23
8.60
8.41
8.62
154.5
161.0
167.7
165.7
162.0
162.5
163.6
163.6
1622
1615
1644
1628
1626
1628
1624
1628
–
1540
1542
1539
1555
1487
1558
1462
1555
889, 921
–
826, 929
–
899, 922
–
813, 932
2
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© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Economical Oxygenation of Olefins and Sulfides Catalyzed by New Molybdenum(VI) Tridentate Schiff Base Complexes
Figure 3. Electronic spectra of the H2Y1 (a) and MoY1 (b) in meth-
anol.
Figure 1. A view of the molecular structure of MoY1, showing the
Table 3. The influence of solvent nature and temperature on the epox-
idation of cyclooctene using TBHP catalyzed by MoY1.a).
numbering scheme and displacement ellipsoids drawn at the 50%
probability level. Selected bond lengths /Å and angles /°: Mo(1)–O(1)
1.9437(17), Mo(1)–O(2) 1.9487(16), Mo(1)–O(3) 1.6980(19), Mo(1)–
O(4) 1.718(17), Mo(1)–O(5) 2.3538(17), Mo(1)–N(1) 2.2786(17),
N(1)–C(11) 1.286(3), N(1)–C(12) 1.504(3), O(1)–C(1) 1.334(3), O(1)–
Mo(1)–O(2) 150.45(6), O(3)–Mo(1)–O(4) 105.68(9), O(4)–Mo(1)–
O(5) 82.10(7), O(1)–Mo(1)–O(3) 98.73(8), O(1)–Mo(1)–O(4)
101.44(7), O(2)–Mo(1)–O(3) 97.65(8), O(2)–Mo(1)–O(4) 97.57(8),
O(1)–Mo(1)–N(1) 79.94(6), O(2)–Mo(1)–N(1) 74.78 (6), Mo(1)–
O(5)–C(16) 121.71(15), O(2)–Mo(1)–O(1)–C(1) 36.82(3), O(3)–
Mo(1)–O(1)–C(1) –86.12 (2), O(4)–Mo(1)–O(1)–C(1) 165.83(2),
O(5)–Mo(1)–O(1)–C(1) 86.2 (2), N(1)–Mo(1)–O(1)–C(1) 5.4(2).
Entry
Solvent
Epoxide yieldb) /% (T /°C)c Time /min
1
2
3
4
5
CH3CN
(CH3)2CO
C2H5OH
CH2Cl2
CHCl3
0
0
0
15
60
60
60
60
60
82
5(40), 13 (50), 49 (60), 99
(80)
6
DCE
25
a) The molar ratio of cyclooctene/TBHP/catalyst was 1000:1500:1. b)
GC yield based on mesitylene as internal standard. c) The reactions
were run in air at reflux condition except for DCE which was per-
formed at different temperatures.
Figure 4. Effect of catalyst loading on the reaction rate and yield of
cyclooctene oxide.
The examination of various molar ratios of TBHP/olefin in
the catalytic oxidation of cyclooctene in DCE showed that for
full oxidation of the cyclooctene the use of 1.5 equivalents of
TBHP is sufficient (Figure 5). Under the optimized conditions
(1000:1500:1 molar ratio for olefin/TBHP/catalyst in DCE at
Figure 2. Crystal packing of MoY1 viewed down the c axis, showing
the formation of the O–H···O hydrogen bonded centrosymmetric dimer
(hydrogen bonds are shown as dashed lines).
yield and reaction time, DCE was found to be the best reaction 80 °C), cyclooctene converted completely within 25 min and
solvent; nevertheless, a temperature of 80 °C was required for 94% of epoxide product was secured as sole product.
the completion of the reaction in desired time (entry 6). The
In order to establish the general applicability of the method,
poorer yields obtained with CH2Cl2 and CHCl3 is probably various olefins were subjected to the oxidation protocol under
caused by the lower reaction temperature at their reflux condi- the influence of the MoY1 catalyst (Table 4). As summarized in
tions.
Table 4, different olefins are generally excellent substrates for
The use of further amount of catalyst concentrations in the this catalyst. It led to complete conversion of cyclohexenes, cy-
oxidation of cyclooctene confirmed a very low catalyst loading clooctene, and norbornene with the formation of the correspond-
(0.1 mol-%) for complete conversion of cyclooctene in desired ing epoxides as sole products (entries 1–4). The chemoselectiv-
time (25 min) (Figure 4).
ity of the procedure was prominent. The oxidative hydroxyl
Z. Anorg. Allg. Chem. 2012, 1–9
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A. Rezaeifard, M. Jafarpour et al.
ARTICLE
group was completely tolerated under the influence of this cata-
lytic system and the corresponding epoxide was obtained in
100% selectivity (entries 5–7). Also, the promising results were
achieved for the stereoselectivity of this simple oxidation
method. The complete retention of configuration in the epoxid-
ation of trans-stilbene and high stereoselectivity in the oxidation
of cis-stilbene (90%) were obtained (entries 8, 9). A notable
feature of the present oxidation system compared with our pre-
vious reports,[6b,c] was its oxidation activity towards electron-
poor styrenes (entries 11–14). It led to moderate yields of the
corresponding epoxides with excellent selectivity (Ͼ97%).
Catalytic Oxidation of Sulfides to Sulfoxides
Figure 5. Effect of TBHP/olefin molar ratio on the reaction rate and
yield of cyclooctene oxide.
The sulfoxidation activity of MoY1 catalyst in the oxidation
of thioanisole using H2O2 as oxidant in ethanol providing envi-
ronmentally friendly conditions was examined. Performing the
reaction in the presence of 0.1 mol-% of MoY1 using equi-
molar ratio of H2O2 and thioanisole under mild conditions,
afforded the related sulfoxide as sole product in low yield
(36%) within 80 min. To achieve the desired yield and selec-
tivity of sulfoxide product, 1 mol-% of catalyst and 1.5 equiva-
lent of TBHP should be employed in this oxidation system
(Table 5). Nevertheless, further increase in these amounts de-
creased the sulfoxide selectivity (entries 6–8). The efficiency
of sulfide oxidation crucially affected by the nature of solvent.
From the evaluation of seven reaction solvents, ethanol was
found to be the solvent of choice in terms of conversion yield
and particularly environmentally problems (Figure 6). The ef-
fective solvation of the polar sulfoxide by protic solvents such
as methanol and ethanol, increases the conversion of the sul-
fide to sulfoxide, nevertheless, prevents the over-oxidation of
sulfoxide to sulfone.[9]
Table 4. Epoxidation of olefins using TBHP catalyzed by MoY1 in
DCE.a)
Encouraged by the excellent catalytic performance for the
thioanisole oxidation, different sulfides were subjected to the
reaction system in the presence of MoY1 and the results are
listed in Table 6. All substrates could be smoothly converted
to sulfoxides with high to excellent conversion rates, and ex-
cellent selectivities were obtained under mild conditions. The
highest yields were obtained for dialkyl and diallyl sulfide
(98–100%) after 25 min. The replacement of one or both alkyl
or allyl groups with phenyl or benzyl group increased the reac-
tion times (60 and 80 min versus 25 min); however, no regular
trends in electronic and steric requirements were observed. A
salient feature of the present sulfoxidation system is its excel-
lent selectivity. Sulfoxides could be nearly stoichiometrically
produced and the generation of the corresponding sulfones was
well controlled, which makes this process a good alternative
for sulfoxide production. Also, a sulfide with a carbon–carbon
double bond (entry 2, 6), was cleanly transformed into the cor-
responding sulfoxide in excellent yield. In addition, benzyl
phenyl sulfide (entry 8) was selectively oxidized to their corre-
sponding sulfoxide without formation of any benzylic oxi-
dation by-products.
a) The reactions were run for 25 min under air in DCE at 80 °C and the
molar ratio of olefin/ TBHP/catalyst was 1000:1500:1. b) Conversions
and selectivity were determined by GC based on mesitylene as internal
Green conditions used for oxidation of sulfides in the pres-
ent strategy by using an easy-made catalyst offered ready scal-
ability. The performing of the oxidation reaction under a semi
1
standard. c) Yield of isolated product. d) Determined by H NMR spec-
troscopy. e) All products were identified by comparison with authentic
samples[8c]. f) The remainder is the related benzaldehyde.
4
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© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Economical Oxygenation of Olefins and Sulfides Catalyzed by New Molybdenum(VI) Tridentate Schiff Base Complexes
Table 5. Effect of catalyst and oxidant content on the oxidation of thioanisole in the presence of MoY1 in ethanol.a).
Entry
Catalyst /mol-%
H2O2 equivalent
Sulfoxide yieldb) /%
Selectivityb) /%
Time /min
1
2
3
4
5
6
7
8
0.1
0.2
0.5
1
1
1
1
36
50
80
82
100
90
97
92
100
100
100
100
100
90
80
80
80
80
60
60
60
60
1.5
1.5
1
1.5
2
2
5
1.5
1.5
97
92
a) The reactions were run in air at 25 °C using 0.1 mmol of thioanisole. b) GC yield based on mesitylene as internal standard.
Stability and Activity of Mo-Catalysts
The good/excellent yields of epoxides (46–100%) and sulf-
oxides (65–100%) obtained using these new catalytic methods
in desired times displays the superior catalytic activity of the
present dioxo-MoVI complexes.[4] More evidences in this mat-
ter were obtained by determining the turnover numbers (TON)
of MoY1 catalyst in the oxidation of cyclooctene by TBHP
and thioanisole by H2O2. The impressive turnover frequencies
(TOF = 8800 h–1 for epoxidation and 2000 h–1 for sulfoxid-
ation) and turnover numbers (TON = 10000/24h for epoxid-
ation and 9000/24h for sulfoxidation) obtained in this oxi-
dation system indicate well the high efficiency and relative
stability of the catalyst. This was further supported by the
Figure 6. Effects of solvent nature on the reaction rate and yield of
study of the electronic spectra of the catalyst during the oxi-
dation of cyclooctene and thioanisole using the intensity of the
characteristic absorption band at 308 nm (Figures S1 and S2,
Supporting Information). The durability of 80 and 93% with
MoY1 for epoxidation and sulfoxidation reactions respectively,
indicates clearly the high stability of the Mo-catalyst under
oxidation conditions. Encouraged by these results, the recycl-
ing of oxidation system by addition of new samples of the
cyclooctene (65 μL) and TBHP (75 μL) to the reaction mixture
was investigated. The cyclooctene conversion was quantitative
and can be reused in at least three catalytic cycles leading to
relatively equivalent results (100, 97, and 98% for runs 1–3).
We also investigated the influence of electronic and steric
requirements of ligands upon the catalytic activity of molybde-
num complexes in this oxidation system. Based on the TOFs
obtained in the epoxidaion of cyclooctene (Figure 7), the li-
gands influence the catalytic activity according to their rigidity,
the steric hindrance and electron properties.[10] The order of
catalytic activities of different molybdenum complexes was
found to be MoY4ϾMoY5ϾMoY1ϾMoY2ϾMoY3. This de-
gree of activity can be explained with respect to epoxidation
mechanism summarized in Scheme 2. At the initial stage of
the epoxidation reaction, its rate is limited by the known
monomer-dimer equilibrium,[11] and subsequently by the at-
tachment of the t-BuOOH molecule to the molybdenum(VI)
ion and the formation of an intermediate complex [MoO2(Y1)
(t-BuOOH)] (II). The higher catalytic activity of electron-rich
MoY4, hindered MoY5, and rigid MoY1 is very probably
caused by their resistance to formation of catalytically inactive
cyclooctene oxide.
Table 6. Oxidation of various sulfides by H2O2 catalyzed by MoY1 in
ethanol.a).
a) The reactions were run in air at 25 °C and the molar ratio of sulfide/
H2O2/catalyst was 100:150:1. b) Conversions, yields, and selectivity
were measured by GC based on mesitylene as internal standard. c) All
products were identified by authentic samples. d) Yield of isolated
product. e) The remainder is the related sulfone.
scale-up condition using 25 mmol of thioanisole as substrate
gave 92% of the related sulfoxide after purification with silica species (I) enhancing the oxidation activity of the catalyst. In
chromatography eluting with n-hexane/ethyl acetate (10/3).
accord with this argument, electron-deficient MoY3 that facili-
Z. Anorg. Allg. Chem. 2012, 1–9
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5

A. Rezaeifard, M. Jafarpour et al.
ARTICLE
Scheme 2. Summarized mechanism suggested for olefin epoxidation with TBHP catalyzed by cis-dioxomolybdenum complexes.
tates the formation of inactive species (I), lapses the formation stability of Mo-catalysts towards oxidative degradation. The
of active intermediate and consequently the epoxidation reac- applicability of these easily prepared molybdenum Schiff base
tion. Nevertheless, as outlined in Figure 7, different electroni- complexes both in the epoxidation and sulfoxidation reactions
cally and structurally molybdenum complexes displayed no- with high efficiency and stability in combination with TBHP
table resistance towards oxidative degradation (TONs ≈ 10000/ and H2O2 as desired oxygen sources highlight the novelty of
24h), which is a salient feature of these new Mo-catalysts.
these new MoVI-catalysts and make the present catalytic meth-
ods more attractive for applied goals.
Experimental Section
General Remarks: All reagents were used as received. Solvents were
purified by standard methods and dried if necessary. Methanol was
distilled from magnesium methoxid. Acetylacetate and ammoniumhep-
tamolybdate were purchased from Fluka and were used as received.
All reactions and workups were carried out in air.
Instrumentation: X-ray data collections were recorded with a Stoe
Image Plate Diffraction System. Purity determinations of the products
were accomplished by GC with a Shimadzu GC-16A instrument using
a 25 m CBP1–S25 (0.32 mm ID, 0.5 μm coating) capillary column. IR
spectra were recorded with a Perkin–Elmer 780 instrument. UV/Vis
spectra were recorded with a 160 Shimadzu spectrophotometer. NMR
spectra were recorded with a Bruker Avance DPX 500 MHz instru-
ment. Mass spectra were recorded with a Shimadzu GC-MS-QP5050A.
Figure 7. Influence of electronic and structural requirements on the
catalytic activity of Mo-catalysts in the epoxidation of cyclooctene
using TBHP in DCE at 80 °C with the molar ratio of 10000:15000:1
for cyclooctene/TBHP/Mo complex.
Synthesis of H2Y1 Ligand: The asymmetric tridentate Schiff base
(H2Y1) was obtained by addition of a solution of 2-amino-2-meth-
ylpropan-1-ol (0.89 g, 0.01 mol) in methanol (10 mL) to a solution of
2-hydroxy-1-naphthaldehyde (1.72 g, 0.01 mol) in methanol (10 mL),
and the reaction mixture was stirred in air at reflux for 1 h. The solu-
tion was kept one day giving a yellow precipitate. The crude product
was recrystallized from CHCl3. Yield 92% (2.3 g). M.p.: 120 °C.
C15H17NO2 (243.13): calcd. C 74.05, H 7.04, N 5.76%; found: C
Conclusions
The syntheses of five new MoVI complexes
[MoO2Yx(CH3OH)] based on 2[(1-hydroxy-2-methylpropane-
2-ylimino)methyl]phenol as ONO tridentate Schiff base ligand
were described. The crystal structure of a sample of these com-
plexes showed an orthorhombic space group Pbca. A highly
74.11, H 6.98, N 5.74%. IR (KBr): ν˜ = 3171 (νOH), 1622 (νC=N), 1540
1
efficient epoxidation method using TBHP activated by these (νC=C) cm–1. H NMR (250 MHz, CDCl3): δ = 1.46 (s, 6 H, –CH3),
simple MoVI complexes in desired times with excellent chemo-
and stereoselectivity was developed. Also green oxidation of
sulfides using H2O2 was efficiently enhanced with excellent
selectivity in ethanol under the influence of these Mo-catalysts.
3.66 (s, 2 H, –CH2), 4.8 (s, 1 H, OHalkyl), 6.21–7.69 (m, 6 H, ArH),
8.66 (s, 1 H, CH=N), 14.1 (s, 1 H, OHphenol) ppm. 13C NMR (75 MHz,
CDCl3): δ = 23.8, 58.7, 70.0, 105.6, 117.5, 122.3, 125.0, 125.7, 127.9,
129.2, 134.0, 138.0, 154.5 ppm. MS: m/z 243 (M+).
The electron-rich and bulky groups on the salicylidene ring of
ligand promoted the effectiveness of the catalyst. The relative
high TOF and TON obtained in the oxidation of sulfides and
Synthesis of MoY1 Complex: To the ligand H2Y1 (2.43 g) was added
dioxidomolybdenum(VI) acetylacetonate,[12] (3.28 g, 0.01 mol) in
methanol (10 mL). The reaction mixture was stirred under reflux for
olefins confirmed clearly the high activity and also relative 1 h. The yellow precipitate was filtered and washed with cooled meth-
6
www.zaac.wiley-vch.de © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Z. Anorg. Allg. Chem. 2012, 1–9

Economical Oxygenation of Olefins and Sulfides Catalyzed by New Molybdenum(VI) Tridentate Schiff Base Complexes
anol. Suitable single crystal was obtained in acetonitril-methanol solu- (H2Y3–H2Y5) and dioxo-molybdenum (VI) complexes (MoY3–
˚
tion. Yield 97% (3.9 g). M.p.Ͼ250 C. C16H19MoNO5 (401.26): calcd.
C 47.89, H 4.77, N 3.49%; found: C 47.85, H 4.80, N 3.50%. IR
(KBr): ν˜ = 3171 (νOH), 1615 (νC=N), 1542 (νC=C), 921,889 (νMo=O) cm–
1. 1H NMR (250 MHz, [D6]DMSO): δ = 1.46 (s, 6 H, –CH3), 3.14 (d,
3 H, CH3OH), 4.29 (s, 2 H, –CH2), 7.14–8.04 (m, 6 H, ArH), 9.42 (s,
1 H, CH=N) ppm. 13C NMR (75 MHz, [D6]DMSO): δ = 25.9, 49.0,
68.8, 84.8, 111.6, 121.1, 122.1, 124.2, 128.3, 128.5, 129.3, 133.4,
136.2, 157.6, 161.0 ppm.
MoY5). UV/Vis spectral changes of the MoY1 complex during the
oxidation reactions.
Acknowledgements
Support for this work by Research Council of University of Birjand is
highly appreciated.
Note: The synthesis and spectroscopic data of other ligands and molyb-
denum complexes are given in the Supporting Information.
References
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in this paper have been deposited with the Cambridge Crystallo-
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UK. Copies of the data can be obtained free of charge on quoting the
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deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk).
Supporting Information (see footnote on the first page of this article):
Synthesis and characterization of other tridentate Schiff base ligands
Z. Anorg. Allg. Chem. 2012, 1–9
© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
7

A. Rezaeifard, M. Jafarpour et al.
ARTICLE
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Received: February 22, 2012
Published Online: ᭿
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© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2012, 1–9

Economical Oxygenation of Olefins and Sulfides Catalyzed by New Molybdenum(VI) Tridentate Schiff Base Complexes
A. Rezaeifard,* M. Jafarpour,* H. Raissi, M. Alipour,
H. Stoeckli-Evans .............................................................. 1–9
Economical Oxygenation of Olefins and Sulfides Catalyzed by
New Molybdenum(VI) Tridentate Schiff Base Complexes:
Synthesis and Crystal Structure
Z. Anorg. Allg. Chem. 2012, 1–9
© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
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