Homogeneous catalytic oxidation of olefins with hydrogen peroxide in the presence of a manganese-substituted polyoxomolybdate

Article abstract of DOI:10.1007/s10562-013-1101-8

[PMo₁₁Mn(H₂O)O₃₉]^5- is used as catalyst in the homogeneous oxidation of cis-cyclooctene, cyclohexene, styrene, and geraniol with H₂O₂ in acetonitrile. Oxidation of cis-cyclooctene gives only cyclooctene oxide; cyclohexene-1,2-diol is the main product for cyclohexene; styrene is preferentially oxidized to benzaldehyde; a TOF almost as high as 28800 h^-1 is reached for geraniol oxidation.

Full text of DOI:10.1007/s10562-013-1101-8

Catal Lett (2014) 144:104–111
DOI 10.1007/s10562-013-1101-8
Homogeneous Catalytic Oxidation of Olefins with Hydrogen
Peroxide in the Presence of a Manganese-Substituted
Polyoxomolybdate
•
Tiago A. G. Duarte Isabel C. M. S. Santos
•
•
•
´
Mario M. Q. Simo˜es M. Grac¸a P. M. S. Neves
•
Ana M. V. Cavaleiro Jose A. S. Cavaleiro
´
Received: 17 June 2013 / Accepted: 3 September 2013 / Published online: 25 September 2013
Ó Springer Science+Business Media New York 2013
Abstract [PMo11Mn(H2O)O39]5- is used as catalyst in
the homogeneous oxidation of cis-cyclooctene, cyclohex-
ene, styrene, and geraniol with H2O2 in acetonitrile. Oxi-
dation of cis-cyclooctene gives only cyclooctene oxide;
cyclohexene-1,2-diol is the main product for cyclohexene;
styrene is preferentially oxidized to benzaldehyde; a TOF
almost as high as 28800 h-1 is reached for geraniol
oxidation.
oxidation states, possible activation of various oxidants and
inherent acidity [1]. POMs have been considered as soluble
analogues of metal oxides and have found applications in
oxidative and acid catalysis, both in homogeneous and
heterogeneous systems [7–12].
The oxidation chemistry of organic compounds aims to
create value-added functionalized derivatives starting from
different types of substrates, from hydrocarbons to phar-
maceuticals, or from terpenes to PAHs, for instance [13,
14]. Nowadays, green and sustainable chemistry has a great
impact both in the laboratory and in industry. Aqueous
hydrogen peroxide is considered as one of the most
attractive oxidants both from the environmental and the
economical perspective, triggering the search for efficient
catalysts able to activate hydrogen peroxide, since oxidants
such as manganese dioxide, chromic acid, potassium
dichromate or selenium dioxide are known to produce large
amounts of toxic wastes, particularly when applied on an
industrial scale [14, 15].
Keywords Polyoxomolybdate Á Homogeneous
catalysis Á Oxidation Á Hydrogen peroxide Á Olefins
1 Introduction
Throughout the last decades, polyoxometalates (POMs)
have received much attention, since POMs represent an
important family of inorganic materials with a variety of
structures and composition, with unique properties for
potential applications in various fields from materials sci-
ence to biology and medicine [1–6]. In particular, one of
the most significant domains of interest is catalysis, owing
to POMs properties such as oxidative stability, adjustable
In this context, most reported work on the oxidation of
organic compounds like hydrocarbons and alcohols in the
presence of polyoxometalates concern studies with Keggin-
type lacunary and transition metal-substituted polyoxo-
tungstates (TMSP) or mixed vanadomolybdates [PMo12-x
VxO40]n- [7, 9, 16]. TMSP may be viewed as complexes of
transition metal ions with lacunary Keggin or Dawson
anions as ligands. The mono-substituted Keggin- and
Dawson-type polyoxometalates have been compared with
metalloporphyrins [7]. Other related species, like tri-
substituted or sandwich-type anions, have the possibility of
incorporating several transition metals in their structure.
Despite the known differences in redox properties of
polyoxotungstates versus polyoxomolybdates, the transi-
tion metal-substituted polyoxomolybdates and their cata-
lytic properties have been scarcely investigated [16–26]. In
T. A. G. Duarte Á I. C. M. S. Santos (&) Á
M. M. Q. Simo˜es (&) Á M. G. P. M. S. Neves Á
J. A. S. Cavaleiro
´
QOPNA, Departamento de Quımica, Universidade de Aveiro,
3810-193 Aveiro, Portugal
e-mail: ivieira@ua.pt
M. M. Q. Simo
˜es
e-mail: msimoes@ua.pt
A. M. V. Cavaleiro
CICECO, Departamento de Quımica, Universidade de Aveiro,
3810-193 Aveiro, Portugal
´
123

Homogeneous Catalytic Oxidation of Olefins
105
these reports, substituted polyoxomolybdates with, namely,
CoII, MnII, NiII, CuII, ZnII, FeIII, RuIII, SbIII, were used
together with several oxidants, such as, oxygen, iodobenzene
diacetate and hydrogen peroxide. To the best of our knowl-
edge, there is only one report in homogeneous oxidation with
hydrogen peroxide, using [PMo11Mn(Br)O39]5-, as catalyst
for the isobutyraldehyde oxidation [20]. This same anion was
used in the oxidation of cumene, oct-1-ene and cyclohexene
but using oxygen as oxidant [17]. Recently, the use of
Cs5[PMo11M(H2O)O39]Á6H2O (Co, Mn, Ni) was reported as
heterogeneous catalyst in solvent-free, liquid-phase oxida-
tion of styrene, also with hydrogen peroxide [24, 25]. The
same authors studied the oxidation of alcohols catalyzed by
transition metal (Co, Mn, Ni) mono-substituted Keggin-
phosphomolybdates under the same conditions [26].
reflectance spectra were registered on a Jasco V-560
spectrometer, using MgO as reference for diffuse reflec-
tance. Magnetic susceptibilities were measured by the
Evans method, at room temperature (r.t.), with a Sherwood
Scientific Magnetic Susceptibility Balance MSB-MK I,
calibrated with [HgCo(NCS)4] [33]. Diamagnetic correc-
tions were taken from Meites [34].
The GC–MS analyses were performed on a Finnigan
Trace GC–MS (Thermo Quest CE instruments) using helium
as the carrier gas (35 cm/s) and a quartz liner injector; GC–
FID analysis were performed using a Varian Star 3900
chromatograph and helium as the carrier gas (35 cm/s) and a
quartz liner injector. Fused silica capillary columns of the
DB-5 type (30 m; 0.25 mm i.d.; 25 lm film thickness) were
used in both cases. The chromatographic conditions were as
follows: for styrene, initial temperature (90 °C); temperature
rate (5 °C/min until 140 °C, then 50 °C/min); final temper-
ature (250 °C); injector temperature (250 °C); detector
temperature (270 °C); for cis-cyclooctene, initial tempera-
ture (80 °C); temperature rate (20 °C/min); final tempera-
ture (220 °C); injector temperature (250 °C); detector
temperature (250 °C); for cyclohexene, initial temperature
(70 °C); temperature rate (15 °C/min); final temperature
(220 °C); injector temperature (250 °C) detector tempera-
ture (270 °C); for geraniol, initial temperature (100 °C);
temperature rate (5 °C/min until 150 °C, then 15 °C/min);
final temperature (220 °C); injector temperature (250 °C);
detector temperature (250 °C).
Following our previous work on the use of manga-
nese(III) substituted polyoxotungstates [27–31], in the
present paper we report the oxidation of several model
substrates with carbon–carbon double bonds in their
structure, namely cis-cyclooctene (1), cyclohexene (2),
styrene (3) and geraniol (4), with 30 % (w/w) aqueous
H2O2 in acetonitrile, using the tetrabutylammonium (TBA)
salt of a manganese(II) substituted Keggin-type POM,
TBA4H[PMo11Mn(H2O)O39]Á2H2O (TBAPMo11Mn), as
homogeneous catalyst. As far as one can tell, with one
exception [17], there are no references concerning the use
of this catalyst in the oxidation of such substrates.
2 Experimental
2.2 Synthesis of TBA4H[PMo11Mn(H2O)O39]Á2H2O
(TBAPMo11Mn)
2.1 Reagents and Methods
The compound was prepared by an adaptation of a described
procedure for TBA4[PW11Mn(H2O)O39] [35]. Firstly,
Na2MoO4Á2H2OÁ(41 mmol, 10 g) and Na2HPO4 (3 mmol, 0
39 g) were dissolved in 20 mL of water, and heated for
10 min at 80–90 °C. After cooling, the pH was adjusted to
4.8 by adding, slowly and with stirring, HCl 6 M [35]. To this
solution were added (at 90 °C with vigorous stirring) two
aqueous solutions prepared with MnSO4ÁH2O (3 mmol,
0.51 g, in 4 mL) and K2S2O8 (2 mmol, 0.41 g, in 4 mL),
respectively. The resulting solution was maintained at the
same temperature (90 °C) for approximately 2 h and then an
aqueous solution of TBABr (20 mmol, 5 mL) was added.
The immediate formation of a solid was observed, which was
filtered, washed with water, ethanol and ethyl ether, and
dried in a vacuum desiccator. Anal. found (%): Mo, 38.9; P,
1.17; Mn, 1.95; C, 28.0; H, 5.35, N, 2.10. Calcd. for
C64H151MnMo11N4PO42 (%): Mo, 37.8; P, 1.11; Mn, 1.97;
C, 27.6; H, 5.20, N, 2.01. Total weight loss found: 37.9 %;
calcd: 36.0 %. FT-IR (cm-1): 1059(m), 1039(m), 938(s),
874(m), 821(s), 755 (s), 499(w). FT-Raman (cm-1): 958,
940, 885, 597, 234. Magnetic moment at r.t.: 5.36 lB.
Acetonitrile (Panreac), 30 % (w/w) aqueous hydrogen
¨
peroxide (Riedel de-Haen), and cis-cyclooctene, cyclo-
hexene, geraniol and styrene (Aldrich) were used as
received. All other solvents used herein were obtained from
commercial sources and used as received or distilled and
dried using standard procedures. Compound TBA3P-
Mo12O40 (TBAPMo12) was prepared as described else-
where [20, 32].
Elemental analysis for P, Mo and Mn were performed
by ICP spectrometry (Central Laboratory of Analysis,
University of Aveiro) and C, H, N elemental analysis were
performed on a Leco CHNS-932 apparatus. Weight loss
was determined by thermogravimetric analysis performed
between 30 and 700 °C at 5 °C/min on a TGA-50 Shi-
madzu thermobalance. Infrared absorption spectra were
recorded on a Mattson 7000 FTIR spectrometer, using KBr
pellets. Powder X-ray diffraction (XRD) was performed on
powders deposited on silicon substrates, using a Philips
X’Pert instrument operating with Cu-Ka radiation
˚
(k = 1.54178 A) at 40 kV/50 mA. UV–Vis and diffuse
123

106
T. A. G. Duarte et al.
2.3 General Oxidation Procedure
vessel equipped with a magnetic stirrer, using H2O2
(30 wt. % aqueous solution) as oxidant. The oxidation
reactions of 1, 2 and 3 were performed at 80 °C whereas
the oxidation reactions of 4 were done at r.t. and pro-
tected from light.
The oxidation reactions of cis-cyclooctene (1), cyclo-
hexene (2), styrene (3) and geraniol (4) (Table 1) were
carried out in acetonitrile, in a closed 5 mL reaction
Table 1 Results obtained for the oxidation of olefins with H2O2 catalysed by PMo11Mn
Substrate
TONa Conversion (%)
Selectivity (%)
O
1
–
426
252
–
71
42
1a
100
100
PMo11Mnb
b
PMo12
Without catalyst
–
7
100
H
O
O
H
H
H
O
O
O
O
O
2
–
–
2a
2b
2c
2d
2e
PMo11Mnc
142
71
6
0
15
0
16
0
15
25
48
75
c
PMo12
22
–
11
2
Without catalyst
100
0
0
0
0
H
O
O
O
O
O
H
O
O
3
–
–
3a
3b
3c
3d
3e
PMo11Mnd
220
66
75
5
7
9
4
d
PMo12
13
–
4
0
100
0
0
0
0
0
0
0
0
0
Without catalyst
O
O
O
H H
C 2O
H H
C 2O
H H
C 2O
4
–
–
4a
95
96
100
100
4b
PMo11Mne
PMo11Mnf
183
652
133
–
91
65
13
1
5
4
0
0
f
PMo12
Without catalyst
a
b
c
d
e
Turnover number (mol of products per mol of catalyst)
Reaction conditions: catalyst (5.0 lmol), CH3CN (1.5 mL), substrate (3.0 mmol), 30 wt % H2O2 (3.3 mmol), 6 h at 80 °C
Reaction conditions: catalyst (5.0 lmol), CH3CN (1.5 mL), substrate (1.0 mmol), 30 wt % H2O2 (3.0 mmol), 6 h at 80 °C
Reaction conditions: catalyst (3.0 lmol), CH3CN (3.0 mL), substrate (1.0 mmol), 30 wt % H2O2 (4.0 mmol), 6 h at 80 °C
Reaction conditions: catalyst (5.0 lmol), CH3CN (1.5 mL), substrate (1.0 mmol), 30 wt % H2O2 (1.0 mmol), 2 h at r.t. and in the absence of
light
f
Reaction conditions: catalyst (1.0 lmol), CH3CN (1.5 mL), substrate (1.0 mmol), 30 wt % H2O2 (1.0 mmol), 2 h at r.t. and in the absence of
light
123

Homogeneous Catalytic Oxidation of Olefins
107
Fig. 1 I FTIR spectra of (a)
TBAPMo11Mn; (b)
(II)
(I)
TBAPMo11Mn-ac, material
recovered at the end of the
reaction, after catalysis (a drop
of the reaction mixture was
dried on a KBr pellet). Reaction
conditions: substrate, 1.0 mmol;
catalyst, 1.0 lmol; acetonitrile,
1.0 mL; aqueous 30 % (w/w)
H2O2, 1.0 mmol; r.t.; II FT-
Raman spectrum of
(b)
(a)
TBAPMo11Mn; III XRD of
TBAPMo11Mn
4000
3000
2000
1000
0
1600
1350
1100
850
600
350
Wavenumbers (cm-1)
Wavenumber (cm-1)
(III)
The typical procedure was as follows: to the substrate (1.0
or 3.0 mmol) and the catalyst (1.0, 3.0 or 5.0 lmol) in ace-
tonitrile (1.0 or 3.0 mL), aqueous 30 % (w/w) H2O2 (1.0,
3.0, 3.3 or 4.0 mmol of H2O2) was added and the resulting
solution stirred for the allotted time. Aliquots were taken
directly from the reaction mixture and injected into the GC-
FID or GC-MS equipments, using helium as the carrier gas
and a quartz liner injector, for analysis of the starting mate-
rials and products. The triphenylphosphine test [36] was also
used to verify the potential formation of cyclohexene
hydroperoxide. However, this hydroperoxide was not
detected during cyclohexene oxidation under the present
conditions. The oxidation of cyclohexene was also tested i)
under an argon atmosphere in a closed reactor, and ii) using
1 mmol of iodine as a radical trap. Blank reactions were
performed for all the substrates in all the conditions tested.
The prepared salt was characterized by chemical analysis,
thermogravimetry, infrared, Raman and Uv/Vis spectros-
copy, powder DRX and r.t. magnetic moment determination.
The method used in this work for the synthesis of TBAP-
Mo11Mn was different from those reported for TBA salts of
the [PMo11Mn(L)O39]n- anions (L = CH3CN, Br- or H2O
[20, 37, 38]), but the characterization data (Sect. 2) agrees
well with what has been published and are in agreement with
the proposed formula. FT-IR spectra (Fig. 1-I) and FT-
Raman spectra (Fig. 1-II) show the characteristic patterns of
metal-substituted heteropolyanions with the Keggin struc-
ture in the region between 600 and 1,100 cm-1 [39]. The
former is identical to that reported by Combs-Walker and
Hill for [PMo11Mn(CH3CN)O39]5- in the same region [38].
The Raman spectrum presents strong bands at 958 and
940 cm-1 and compares well with that reported for potas-
sium salts [39]. The compound used in this work was found
to be crystalline by powder X-ray diffraction (Fig. 1-III),
crystallizing with a cubic lattice, as reported by Coronado
et al. [37]. TBAPMo11Mn is isostructural with related
3 Results and Discussion
The oxidative reactions of compounds 1–4 with H2O2 were
performed in acetonitrile in the presence of catalytic amounts
of TBAPMo11Mn. The use of tetra-alkylammonium salts
guarantees the adequate solubility in organic solvents [7, 8].
TBA4H[PM11M’(H2O)O39] salts, M = Mo,
W
and
M’ = 1st row transition metal [37, 40].
The presence of MnII in the compound was confirmed
by the value of its magnetic moment at r.t. (5.36 lB) [34]
123

108
T. A. G. Duarte et al.
and by the absence of d–d bands in the electronic spectra.
The diffuse reflectance spectrum showed only the bands
characteristic of the Keggin-type polyoxomolybdates, at
213 and 278 cm-1, attributed to Mo/O charge transfer
between atoms in O-Mo-O bridges [38]. When dissolved in
acetonitrile, the TBAPMo11Mn visible spectrum (identical
to that reported in [38]) is very similar to that obtained in
the solid state, and no d–d band is observed.
the epoxide group is retarded by the steric hindrance of the
cyclooctane ring [41]. Some allylic oxidation was also
observed with the formation of cyclohex-2-en-1-ol and the
cyclohex-2-en-1-one. These two products are usually
obtained when a radical mechanism is involved, typically
2a 2b 2c 2d 2e
60
The
polyoxometalate
[PMo11Mn(H2O)O39]5-
50
40
30
20
10
0
(PMo11Mn) was found to be catalytically active in the
oxidation of all the substrates 1–4 in the conditions used in
this work (Table 1). For comparison, TBAPMo12 was also
tested in the oxidation of all the substrates (Table 1),
showing much less activity than PMo11Mn, except in the
epoxidation of cis-cyclooctene, for which the yield
observed when PMo11Mn was replaced by PMo12 was
about 42 % after 6 h. In the presence of PMo11Mn, cis-
cyclooctene was selectively oxidized to the corresponding
epoxide, without the production of any by-product, at
80 °C, for a substrate/catalyst molar ratio (S/C) of 600 and
H2O2/substrate near 1. The reaction has a rapid evolution
reaching 44 % of conversion after 1 h, and 71 % of con-
version after 6 h of reaction (TON = 426) (Fig. 2).
1
2
3
4
5
6
Time (h)
Fig. 3 Selectivity profile for the oxidation of cyclohexene in the
presence of PMo11Mn. Products and reaction conditions indicated in
Table 1
100
3a 3b 3c 3d 3e
The oxidation of cyclohexene was performed with an
excess of H2O2 because when a stoichiometric H2O2/sub-
strate molar ratio was used low conversion values (less
than 10 % after 6 h of reaction) were obtained. For H2O2/
substrate = 3 the conversion was 65 % after 3 h and 71 %
after 6 h (Fig. 2). The major product was 1,2-cyclohex-
anediol (Table 1; Fig. 3), which is probably due to the
epoxide ring opening; the corresponding hydroxyketone
was also formed, possibly due to overoxidation of the diol.
The epoxide was always a minor product. It is known that
cyclohexene oxide is a very reactive epoxide, since the
steric influence of the cyclohexane ring promotes ring
opening of the epoxide, whereas cyclooctene oxide is one
of the most stable epoxides known, since every reaction of
80
60
40
20
0
1
2
3
4
5
6
Time (h)
Fig. 4 Selectivity profile for the oxidation of styrene in the presence
of PMo11Mn. Products and reaction conditions indicated in Table 1
100
80
80
70
60
50
40
60
40
Sub/cat = 1000
30
20
Cyclooctene
Sub/cat = 200
20
Cyclohexene
0
10
Styrene
0
10
20
30
40
50
60
0
Time (min)
0
1
2
3
4
5
6
Time (h)
Fig. 5 Time course for the oxidation of geraniol in the presence of
PMo11Mn using 1.0 mmol of H2O2; substrate: 1.0 mmol; acetoni-
trile: 1.5 mL; at r.t. and in the absence of light; catalyst: 5.0 lmol
(filled triangle) or catalyst: 1.0 lmol (filled circle)
Fig. 2 Conversion vs time profile for the oxidation of olefins in the
presence of PMo11Mn. Reaction conditions indicated in Table 1
123

Homogeneous Catalytic Oxidation of Olefins
109
0.3
behaviour was already observed for tungsten polyoxo-
metalates during our previous works [27, 29, 30, 42].
Styrene is preferentially oxidized to benzaldehyde
(75 % selectivity), through the cleavage of the vinylic
double bond, although minor products were also observed
(Table 1). The oxidation of styrene in the presence of other
transition metal-substituted POMs was already reported,
benzaldehyde being commonly obtained [43], but this is
the first report for this PMo11Mn catalyst. In this case the
major product is also benzaldehyde (Fig. 4). The conver-
sion profile for styrene is similar to those of cis-cyclooc-
tene and cyclohexene, reaching almost the same conversion
after 6 h; however, styrene oxidation shows the slowest
kinetic profile (Fig. 2).
t = 0 min
t = 20 min
t = 40 min
t = 60 min
t = 80 min
t = 100 min
t = 120 min
0.2
0.1
0
450
550
650
750
850
Wavenumber (nm)
Fig. 6 Visible spectra of TBAPMo11Mn at the beginning (without
H2O2) (t = 0 min) and during the reaction (t = 20–120 min). Reac-
tion conditions: geraniol, 1.0 mmol; catalyst, 1.0 lmol; acetonitrile,
1.0 mL; aqueous 30 % (w/w) H2O2, 1.0 mmol; r.t.
Geraniol is an allylic alcohol that offers several places
of potential oxidative attack, namely at the two double
bonds, at the allylic carbon centres, and at the carbon
bonded to the hydroxyl group. In the presence of catalytic
amounts of PMo11Mn the oxidation of geraniol with H2O2,
at r.t., affords the 2,3-epoxide as the main product with
high selectivity (Table 1). The diepoxide was found as the
only minor product. When using a S/C = 200 the reaction
is very fast and 88 % of conversion is achieved after
15 min of reaction (Fig. 5). This corresponds to a TON of
176 and a TOF of 705 h-1. At S/C = 1000, conversion
after 15 min is 60 % (TON = 605 and TOF = 2420 h-1).
from an autoxidation pathway [17]. In order to confirm
this, reactions in the presence of I2, a well-known radical
scavenger, were done and no cyclohex-2-en-1-ol and cy-
clohex-2-en-1-one were obtained. Moreover, the major
product was again 1,2-cyclohexanediol with 69 % selec-
tivity. Additional tests, carried out under an argon atmo-
sphere, provided the same results as in air, suggesting that
the oxygen needed for the autoxidation pathway was pro-
vided by the H2O2 and nor by atmospheric O2. This type of
H
H
2O
O
O
nII
M
H
H
2O2
H
O
O
nII
M
nII
M
H
O
2
H
H
O
O
O
nII
M
H
Scheme 1 Major pathway for the formation of the epoxidation products
123

110
T. A. G. Duarte et al.
In both cases, leaving the reaction for 2 h has almost no
influence on the obtained conversion and selectivity
(Table 1). Moreover, when S/C = 1000 was used, as can
be observed in Fig. 5, after only 1 min of reaction 48 % of
geraniol conversion was reached, which corresponds to 480
TON and 28755 h-1 TOF.
high as 28800 h-1 for this reaction. High selectivity (95 %)
for 2,3-epoxygeraniol was found in the case of geraniol.
ˆ
Acknowledgments Thanks are due to Fundac¸a˜o para a Ciencia e a
Tecnologia (FCT, Portugal), European Union, QREN, FEDER and
COMPETE for funding the QOPNA research unit (project PEst-C/
QUI/UI0062/2011) and CICECO (PEst-C/CTM/LA0011/2011).
When preferential epoxidation of geraniol at the C2–C3
position occurs, this has been explained by the formation of
a complex involving the metal centre, the oxidant and the
substrate, that may coordinate through the OH group [44,
45] or by the possible association of the substrate to the
anion by hydrogen bonding in the close proximity of any
metal centre [28]. Selective formation of the 2,3-epoxide in
the oxidation of geraniol with H2O2 was observed before in
the presence of some metal substituted polyoxotungstates
[46, 47].
References
1. Pope MT, Mu¨ller A (eds) (2001) Polyoxometalate chemistry:
From topology via self-assembly to applications. Kluwer,
Dordrecht
2. Coronado E, Gimenez-Saiz C, Gomez-Garcia CJ (2005) Coord
Chem Rev 249:1776
3. Yamase T (2005) J Mater Chem 15:4773
4. Proust A, Thouvenot R, Gouzerh P (2008) Chem Commun 1837
5. Wang MS, Xu G, Zhang ZJ, Guo GC (2010) Chem Commun
46:361
The visible spectra of PMo11Mn at the beginning,
throughout, and at the end of the reactions were compared
in solution (Fig. 6). No alterations were seen in the visible
region of the spectra, indicating that Mn(II) is present
during all the reaction time as the major species. At the end
of the reaction, a drop of the reaction mixture was dried on
a KBr pellet and the infrared spectrum measured in order to
assess the stability of the catalyst. This FTIR spectrum
(Fig. 1-Ib) of PMo11Mn has the same pattern as the
starting material. This and the absence of an induction
period on the course of the reactions seem to indicate that
the degradation of the present heteropolyanion is not likely.
The PMo11Mn catalyst as was possible to see during
this work, led to several kinds of products, through radical
and non-radical mechanisms. Using all the information
obtained with the stability studies of the catalyst and the
products obtained with the several substrates we propose a
major pathway for the formation of the epoxidation pro-
ducts (Scheme 1), in accordance to Fig. 6, thus centred on
Mn(II) and involving a ligand exchange [48, 49].
6. Cronin L, Muller A (2012) Chem Soc Rev 41:7333
7. Hill CL, Prosser-McCartha CM (1995) Coord Chem Rev 143:407
8. Kozhevnikov IV (1998) Chem Rev 98:171
¨
9. Neumann R (2004) In: Backvall JE (ed) Modern oxidative
methods. Wiley–VCH, Weinheim
10. Hill CL (2007) J Mol Catal A 262:2
11. Mizuno N, Yamaguchi K, Kamata K (2011) Catal Surv Asia
15:68
12. Streb C (2012) Dalton Trans 41:1651
13. Sheldon RA, Arends I, Hanefeld U (2007) Green chemistry and
catalysis. Wiley–VCH, Weinheim
14. Monteiro JLF, Veloso CO (2004) Top Catal 27:169
15. Noyori R, Aoki M, Sato K (2003) Chem Commun 1977
16. Khenkin AM, Shimon LJW, Neumann R (2001) Eur J Inorg
Chem 789
17. Neumann R, Dahan M (1995) J Chem Soc Chem Commun 171
18. Neumann R, Dahan M (1998) Polyhedron 17:3557
19. Knapp C, Ui T, Nagai K, Mizuno N (2001) Catal Today 71:111
20. Hu J, Burns RC (2002) J Mol Catal A 184:451
21. Mizuno N, Min JS, Taguchi A (2004) Chem Mater 16:2819
22. Karcz R, Pamin K, Poltowicz J, Haber J (2009) Catal Lett
132:159
23. Mazari T, Marchal CR, Hocine S, Salhi N, Rabia C (2009) J Nat
Gas Chem 18:319
24. Patel A, Pathan S (2012) J Coord Chem 65:3122
25. Pathan S, Patel A (2013) Ind Eng Chem Res 52:7
26. Pathan S, Patel A (2013) Appl. Catal. A 459:59
27. Santos ICMS, Balula MSS, Simo˜es MMQ, Neves MGPMS,
Cavaleiro JAS, Cavaleiro AMV (2003) Synlett 11:1643
28. Santos ICMS, Simo˜es MMQ, Pereira MMMS, Martins RRL,
Neves MGPMS, Cavaleiro JAS, Cavaleiro AMV (2003) J Mol
Catal A 195:253
29. Balula MSS, Santos ICMS, Simo˜es MMQ, Neves MGPMS,
Cavaleiro JAS, Cavaleiro AMV (2004) J Mol Catal A 222:159
30. Estrada AC, Santos ICMS, Simo˜es MMQ, Neves MGPMS,
Cavaleiro JAS, Cavaleiro AMV (2011) Appl Catal A 392:28
31. Estrada AC, Simo˜es MMQ, Santos ICMS, Neves MGPMS,
Cavaleiro JAS, Cavaleiro AMV (2011) ChemCatChem 3:771
32. Rocchiccioli-Deltcheff C, Fournier M, Franck R, Thouvenot R
(1983) Inorg Chem 22:207
4 Conclusions
This paper presents the first utilization of the Keggin-type
PMo11Mn in oxidative catalysis of unsaturated organic
compounds using hydrogen peroxide as oxidant. The TBA
salt of this POM was synthesized by a procedure adapted
from the literature. PMo11Mn was tested as homogeneous
catalysts in the oxidation of cis-cyclooctene, cyclohexene,
styrene, and geraniol with aqueous 30 % (w/w) H2O2.
Globally, this catalyst shows a good performance for the
oxidation of these substrates, reaching reasonable TON. In
particular, PMo11Mn shows excellent activity for geraniol
oxidation, reaching 48 % of conversion, after 1 min of
reaction, for S/C = 1000, giving rise to a TOF almost as
33. Figgis BN, Lewis J (1965) Tech Inorg Chem 4:137
34. Mulay LN (1963) In: Meites L (ed) Handbook of analytical
chemistry. McGraw-Hill, New York
123

Homogeneous Catalytic Oxidation of Olefins
111
35. Balula MSS, Santos ICMS, Gamelas JAF, Cavaleiro AMV,
Binsted N, Schlindwein W (2007) Eur J Inorg Chem 1027
36. Shulpin GB, Guerreiro MC, Schuchardt U (1996) Tetrahedron
52:13051
37. Coronado E, Galan-Mascaros JR, Gimenez-Saiz C, Gomez-Gar-
cia CJ, Triki S (1998) J Am Chem Soc 120:4671
38. Combs-Walker LA, Hill CL (1991) Inorg Chem 30:4016
39. Rocchiccioli-Deltcheff C, Thouvenot R (1977) J. Chem. Res.
(S) 2:46
40. Gamelas JAF, Soares MR, Ferreira A, Cavaleiro AMV (2003)
Inorg Chim Acta 342:16
41. Arends IWCE, Sheldon RA (2002) Top Catal 19:133
42. Estrada AC, Simo˜es MMQ, Santos ICMS, Neves MGPMS,
Cavaleiro JAS, Cavaleiro AMV (2010) Monatsh Chem 141:1223
43. Punniyamurthy T, Velusamy S, Iqbal J (2005) Chem Rev
105:2329
44. Sakaguchi S, Nishiyama Y, Ishii Y (1996) J Org Chem 61:5307
45. Adam W, Alsters PL, Neumann R, Saha-Moller CR, Sloboda-
Rozner D, Zhang R (2003) J Org Chem 68:1721
46. Sousa JLC, Santos ICMS, Simo˜es MMQ, Cavaleiro JAS,
Nogueira HIS, Cavaleiro AMV (2011) Catal Commun 12:459
47. Balula SS, Santos ICMS, Cunha-Silva L, Carvalho AP, Pires J,
Freire C, Cavaleiro JAS, de Castro B, Cavaleiro AMV (2013)
Catal Today 203:95
48. Oyama ST (ed) (2008) Mechanisms in homogeneous and heter-
ogeneous epoxidation catalysis. Elsevier, Amsterdam
49. Saisaha P, de Boer JW, Browne WR (2013) Chem Soc Rev
42:2059
123