Efficient epoxidation of electron-deficient alkenes with hydrogen peroxide catalyzed by [γ-PW10O38V2(μ-OH) 2]3-

Article abstract of DOI:10.1002/chem.201101001

A divanadium-substituted phosphotungstate, [γ-PW₁₀O ₃₈V₂(μ-OH)₂]^3- (I), showed the highest catalytic activity for the H₂O₂-based epoxidation of allyl acetate among vanadium and tungsten complexes with a turnover number of 210. In the presence of I, various kinds of electron-deficient alkenes with acetate, ether, carbonyl, and chloro groups at the allylic positions could chemoselectively be oxidized to the corresponding epoxides in high yields with only an equimolar amount of H₂O₂ with respect to the substrates. Even acrylonitrile and methacrylonitrile could be epoxidized without formation of the corresponding amides. In addition, I could rapidly (min) catalyze epoxidation of various kinds of terminal, internal, and cyclic alkenes with H;bsubesubbsubesub& under the stoichiometric conditions. The mechanistic, spectroscopic, and kinetic studies showed that the I-catalyzed epoxidation consists of the following three steps: 1) The reaction of I with H;bsubesubbsubesub& leads to reversible formation of a hydroperoxo species [I;circbsubesubbsubesubbsubesubcirccircbsupesup& (II), 2) the successive dehydration of II forms an active oxygen species with a peroxo group [ ²:²-O₂)]^3- (III), and 3) III reacts with alkene to form the corresponding epoxide. The kinetic studies showed that the present epoxidation proceeds via III. Catalytic activities of divanadium-substituted polyoxotungstates for epoxidation with H ₂O₂ were dependent on the different kinds of the heteroatoms (i.e., Si or P) in the catalyst and I was more active than [γ-SiW₁₀O₃₈V₂(μ-OH)₂] ^4-. On the basis of the kinetic, spectroscopic, and computational results, including those of [γ-SiW₁₀O₃₈V ₂(μ-OH)₂]^4-, the acidity of the hydroperoxo species in II would play an important role in the dehydration reactivity (i.e., k₃). The largest k₃ value of I leads to a significant increase in the catalytic activity of I under the more concentrated conditions. Copyright

Full text of DOI:10.1002/chem.201101001

FULL PAPER
DOI: 10.1002/chem.201101001
Efficient Epoxidation of Electron-Deficient Alkenes with Hydrogen Peroxide
Catalyzed by [g-PW10O38V2ACHTUNGTRNEUNG
(m-OH)2]3ꢀ
Keigo Kamata,[a, b] Kosei Sugahara,[a] Kazuhiro Yonehara,[a] Ryo Ishimoto,[a] and
Noritaka Mizuno*[a, b]
Abstract:
phosphotungstate,
A
divanadium-substituted
[g-PW10O38V2A(m-
ous kinds of terminal, internal, and
cyclic alkenes with H2O2 under the sto-
ichiometric conditions. The mechanis-
tic, spectroscopic, and kinetic studies
showed that the I-catalyzed epoxida-
tion consists of the following three
steps: 1) The reaction of I with H2O2
leads to reversible formation of a hy-
responding epoxide. The kinetic studies
showed that the present epoxidation
proceeds via III. Catalytic activities of
divanadium-substituted polyoxotungs-
tates for epoxidation with H2O2 were
dependent on the different kinds of the
heteroatoms (i.e., Si or P) in the cata-
CTHUNGTRENNUNG
OH)2]3ꢀ (I), showed the highest catalyt-
ic activity for the H2O2-based epoxida-
tion of allyl acetate among vanadium
and tungsten complexes with a turn-
over number of 210. In the presence of
I, various kinds of electron-deficient al-
kenes with acetate, ether, carbonyl,
and chloro groups at the allylic posi-
tions could chemoselectively be oxi-
dized to the corresponding epoxides in
high yields with only an equimolar
amount of H2O2 with respect to the
substrates. Even acrylonitrile and
methacrylonitrile could be epoxidized
without formation of the corresponding
amides. In addition, I could rapidly
lyst and was more active than
I
droperoxo species [g-PW10O38V
N
[g-SiW10O38V2ACTHNGUTERNNUG
(m-OH)2]4ꢀ. On the basis
OH)
A
of the kinetic, spectroscopic, and com-
putational results, including those of
dehydration of II forms an active
oxygen species with a peroxo group [g-
PW10O38V2(m-h2:h2-O2)]3ꢀ (III), and 3)
III reacts with alkene to form the cor-
[g-SiW10O38V2ACTHNUTRGNEUNG
(m-OH)2]4ꢀ, the acidity of
the hydroperoxo species in II would
play an important role in the dehydra-
tion reactivity (i.e., k3). The largest k3
value of I leads to a significant increase
in the catalytic activity of I under the
more concentrated conditions.
Keywords: epoxidation · homoge-
neous catalysis · hydrogen peroxide ·
polyoxometalates · vanadium
(ꢁ10 min) catalyze epoxidation of vari-
Introduction
dation of a,b-unsaturated ketones with organic hydroperox-
ides or H2O2 proceeds under the strong alkaline condi-
tions,[3] these systems cannot be applied to epoxidation of al-
kenes with nitrile groups, due to their hydrolysis to form the
epoxy amides under the basic conditions.[2] While peracetic
acid can also epoxidize electron-deficient alkenes, the high
reaction temperatures and long reaction times often reduce
the selectivities to the corresponding epoxides. In these con-
texts, strong electrophilic oxidants can selectively catalyze
epoxidation of electron-deficient alkenes. While some effi-
cient systems, such as Ru–porphyrin/2,6-dichloropyridine
N-oxide, Mn- or Fe-based complexes/peracetic acid, and di-
Epoxidation of alkenes with environmentally benign H2O2
as an oxidant has received much attention.[1] Especially,
1,2-epoxides with two or more functional groups are valua-
ble intermediates for cosmetics, pharmaceuticals, and poly-
mer materials.[1b] While epoxidation of simple or activated
alkenes proceeds with electrophilic oxidants, epoxidation of
electron-deficient alkenes requires nucleophilic oxidants
such as OOHꢀ.[2,3] Since chemo- and stereoselective epoxi-
ꢀ
oxirane/HSO5 have been developed,[4] those with H2O2
[a] Dr. K. Kamata, K. Sugahara, K. Yonehara, R. Ishimoto,
Prof. Dr. N. Mizuno
under the stoichiometric conditions have scarcely been re-
ported.[5]
Department of Applied Chemistry, School of Engineering
The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku
Tokyo 113-8656 (Japan)
Fax : (+81)3-5841-7220
E-mail: tmizuno@mail.ecc.u-tokyo.ac.jp
Polyoxometalates (POMs) are early transition-metal (M=
V, Nb, Ta, Mo, W, etc.) oxygen cluster anions with discrete
and versatile structures.[6,7] These inorganic compounds have
attracted much attention in the fields of structural chemistry,
biological chemistry, catalysis, molecular magnetism, and ad-
vanced material science.[6,7] The oxidation catalysis by
POMs has received much attention because their chemical
properties can finely be tuned by choosing constituent ele-
ments and counter cations, and their thermal and oxidative
stabilities are high. To date, various kinds of POMs have
[b] Dr. K. Kamata, Prof. Dr. N. Mizuno
Core Research for Evolutional Science and Technology (CREST)
(Japan)
Science and Technology Agency (JST), 4-1-8 Honcho
Kawaguchi, Saitama, 332-0012 (Japan)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201101001.
Chem. Eur. J. 2011, 17, 7549 – 7559
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
7549

Table 1. Effect of catalysts, solvents, and oxidants on epoxidation of 1a
been developed for the H2O2- and O2-based green oxida-
tion.[7]
with H2O2.[a]
We have reported that a bis-m-hydroxo-bridged divanadi-
um-substituted silicotungstate, [g-SiW10O38V2ACHTUNGTRNEUNG
(m-OH)2]4ꢀ, ef-
ficiently catalyzes epoxidation of terminal alkenes with an
equimolar amount of H2O2 with respect to the substrates.[8]
Very recently, we have also reported efficient hydroxylation
of alkanes and oxidative bromination of alkenes, alkynes,
and aromatics with H2O2 catalyzed by a divanadium-substi-
Entry
Catalyst
Solvent
Yield of
2a [%]
1[b]
2
3
4
5
I
I
I
I
I
CH3CN/tBuOH
CH3CN
acetone
84
70
58
22
8
<1
38
82
tuted
phosphotungstate,
[g-PW10O38V
(m-OH)2]3ꢀ
(I,
A
tBuOH
CH3CN/tBuOH
Figure 1).[9] Catalytic activity can significantly be improved
6[b,c]
7[b,d]
8[b,e]
9[b,f]
10[b]
11[b,c]
A
AHCTUNGTRENNUNG
N
A
CH3CN/tBuOH
CH3CN/tBuOH
CH3CN/tBuOH
CH3CN/tBuOH
CH3CN/tBuOH
CH3CN/tBuOH
CH3CN/tBuOH
CH3CN/tBuOH
CH3CN/tBuOH
CH3CN/tBuOH
CH3CN
72
HClO4 (5 mmol)
without
<1
<1
<1
<1
<1
<1
33
<1
<1
8
12[b,c,g] VO
ACTHNUTRGNEN(UG acac)2
13[b,c,g] VOSO4
14[b,c,g] NaVO3
15[b,c,g] V2O5
16[b,c,h]
17[b,c,h]
18[b,c,h]
19[c,h]
20[c,h]
21[b,i]
G
2ACHTUNGTNER(NUNG m-OH)2]
E
AHCTUNGTRENNUNG
G
CHTUNGTRENNUNG
A
U
CH3CN
CH3CN/tBuOH
CH3CN/tBuOH
<1
<1
<1
Figure 1. Molecular structure of I. The {WO6} units and {PO4} unit are
shown as gray octahedra and a black tetrahedron, respectively.
I + TBHP
I + CHP
22[b,j]
[a] Reaction conditions: [TBA]4[g-HPV2W10O40] (5 mmol, TBA=[(n-
C4H9)4N]+), HClO4 (5 mmol), 1a (300 mmol), solvent (3 mL), 30% aque-
ous H2O2 (300 mmol), 333 K, 60 min, under Ar (1 atm). Yields were deter-
mined by GC. Yield (%)=2a (mol)/initial H2O2 (mol)ꢁ100. [b] CH3CN/
tBuOH (1/1, v/v). [c] Without HClO4. [d] HClO4 (2.5 mmol). [e] HClO4
(7.5 mmol). [f] HNO3 (5 mmol). [g] Catalyst (V: 10 mmol). [h] Catalyst
(5 mmol). [i] TBHP (300 mmol). [j] CHP (300 mmol).
by changing the central heteroatom from Si4+ to P5+. In this
paper, we expand the scope of the I-catalyzed efficient oxi-
dation system to epoxidation of electron-deficient alkenes
with stoichiometric amounts of H2O2. Even acrylonitrile and
methacrylonitrile could be epoxidized without formation of
the corresponding amides. In addition, epoxidation of a
wide range of terminal, internal, and cyclic alkenes could be
completed within 10 min under the stoichiometric conditions
(substrate/H2O2 =1:1). The reaction mechanism by I and the
effects of the central heteroatoms in the POMs are investi-
gated on the basis of catalyst effects and kinetic, spectro-
scopic, and computational results.
Results and Discussion
Catalytic epoxidation of alkenes with H2O2: Effects of cata-
lysts, oxidants, and solvents on epoxidation of allyl acetate
(1a) were investigated (Table 1). Under the stoichiometric
conditions using an equimolar amount of H2O2 with respect
to 1a (1a/H2O2/I=60:60:1), 1a could efficiently be oxidized
to the corresponding epoxide (2a). POM I was more active
than [g-SiW10O38V2ACHTUNGTRENNUNG
(m-OH)2]4ꢀ and catalytic activities of di-
vanadium-substituted POMs were dependent on the central
heteroatoms of the POMs (Table 1, entries 1 and 16). The
reaction rate of I was 17.6ꢂ0.7 mmminꢀ1 and much larger
Figure 2. Reaction profiles for epoxidation of 1a with H2O2 catalyzed by
a) I and b) [g-SiW10O38V2ACHTUNGTRNEUNG
(m-OH)2]4ꢀ. Reaction conditions: a) [TBA]4[g-
than
1.1ꢂ0.1 mmminꢀ1
of
[g-SiW10O38V
34A
(H2O)2]4ꢀ,[10] and a
(m-OH)2]4ꢀ
2ACHTUNGTRENNUNG
HPV2W10O40] (5 mmol), HClO4 (5 mmol), 1a (300 mmol), CH3CN/tBuOH
(1.5/1.5 mL), 30% aqueous H2O2 (300 mmol), 333 K, 60 min, under Ar
(1 atm); b) [TBA]4[g-SiW10O38V2ACTHNUGRTENUNG(m-OH)2] (5 mmol), 1a (300 mmol),
CH3CN/tBuOH (1.5/1.5 mL), 30% aqueous H2O2 (300 mmol), 333 K,
60 min, under Ar (1 atm). Yields were determined by GC. Yield (%)=
2a (mol)/initial H2O2 (mol)ꢁ100.
(Figure 2). A divacant POM, [g-SiW10O CHTUNGTRENNUNG
selenium-containing
dinuclear
peroxotungstate,
[SeO4{WO(O2)2}2]2ꢀ,[11] were almost inactive for the present
epoxidation (Table 1, entries 19 and 20). In the absence of I
7550
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Chem. Eur. J. 2011, 17, 7549 – 7559

Epoxidation
FULL PAPER
or presence of the simple vanadium complexes and HClO4,
epoxidation did not proceed (Table 1, entries 10–15). Mono-
(1a–1 f, 1h, and 1k) proceeded chemoselectively to afford
the corresponding epoxides (2a–2 f, 2h, and 2k) (Table 2,
entries 1–12, 14, and 17). Epoxidation of 1a–1 f efficiently
proceeded under the stoichiometric conditions using an
and
PVW11O40]4ꢀ and [a-H2PV3W9O40]4ꢀ, and monoprotonated
[g-HPV2W10O40]4ꢀ with a {OV-(m-O)
(m-OH)-VO} core were
trivanadium-substituted
phosphotungstates,
[a-
AHCTUNGTRENNUNG
inactive (Table 1, entries 6, 17, and 18), suggesting that the
active sites are not the V-O-W and V=O sites, but the bis-m-
hydroxo site of {OV-(m-OH)2-VO} in I. In addition, the reac-
Table 2. Epoxidation of electron-deficient alkenes with H2O2 catalyzed
by I.[a]
Entry
Substrate
Product
Yield
[%]
tion of the bis-m-hydroxo site in [g-SiW10O38V2ACHTUNGTRNEUNG
(m-OH)2]4ꢀ
with small primary alcohols and formic acid smoothly pro-
ceeds to form the corresponding monoesters and monofor-
mate, respectively,[12] supporting the idea. Upon the addition
of 0, 0.5, 1.0, and 1.5 equivalents of HClO4 with respect to
1
84
88
68
86
87
97
70
83
2[b]
3
4[b]
5
[TBA]4[g-HPV2W10O40]
(TBA=tetra-n-butylammonium),
6[b]
7
the 2a yields (reaction rates) were <1% (<0.1 mmminꢀ1),
38% (5.0ꢂ1.0 mmminꢀ1), 84% (17.6ꢂ0.7 mmminꢀ1), and
82% (19.7ꢂ1.2 mmminꢀ1), respectively. The yields and reac-
tion rates linearly increased with an increase in the amounts
of HClO4 and did not much change upon the addition of
ꢃ1.0 equivalents of HClO4 (Table 1, entries 1, 6, 7, and 8).
Therefore, an acid would not be important as a co-catalyst
for epoxidation but as a proton source for the formation of
bis-m-hydroxo site in I. Epoxidation also efficiently proceed-
ed with HNO3 instead of HClO4 (Table 1, entry 9).
8[b]
9
74
89
10[b]
11
73
84
12[b]
13
88
94
Epoxidation did not proceed with organic hydroperoxides,
such as tert-butyl hydroperoxide (TBHP) and cumene hy-
droperoxide (CHP) (Table 1, entries 21 and 22). Thus, H2O2
was the most effective oxidant for the present system. Since
vanadium-catalyzed oxidation of alkanes and aromatic com-
pounds with H2O2 often involves a radical mechanism, elec-
trophilic oxidation of alkenes to the corresponding epoxides
with H2O2 has scarcely been reported because of allylic oxi-
dation, C=C double bond cleavage, and non-productive de-
composition of H2O2.[13] Therefore, effective and selective
epoxidation of alkenes by vanadium-based catalysts general-
ly uses organic hydroperoxides, such as TBHP. The catalytic
performance of the bis-m-hydroxo site of {OV-(m-OH)2-VO}
in I with the organic hydroperoxides was quite different
from those of typical vanadium complexes including vanadi-
um-containing POMs.[13] Reaction of the bis-m-hydroxo site
14
15[c]
16
94
86
17[b]
18[b,d]
19[b]
72
48
56
20
40
59
21[e]
[a] Reaction conditions: [TBA]4[g-HPV2W10O40] (5 mmol), HClO4
(5 mmol), substrate (0.3, 3.0, and 12.0 mmol for entries 1–13, 14–19, and
20 and 21 respectively), CH3CN/tBuOH (1.5/1.5 mL), 30% aqueous
H2O2 (0.3 mmol), 333 K, 60 min, under Ar (1 atm). Yields were deter-
mined by GC. Yield (%)=product (mol)/initial H2O2 (mol)ꢁ100.
[b] 60% aqueous H2O2 (0.3 mmol). [c] 1h (3% yield). [d] 1m (17%
yield). [e] 60% aqueous H2O2 (0.1 mmolꢁ3).
of {OV-(m-OH)2-VO} in [g-SiW10O38V2ACTHNUTRGNEUNG
(m-OH)2]4ꢀ with large
secondary and tertiary alcohols hardly proceeds, because of
the steric crowding between the POM framework and sub-
strates.[12] Therefore, the activation of TBHP and CHP with
the bis-m-hydroxo site of {OV-(m-OH)2-VO} would be sup-
pressed by the steric hindrance of I. Among the solvents
tested, CH3CN/tBuOH (1:1, v/v) was the most effective
(Table 1, entries 1–5). No formation of acetamide was ob-
served, showing that epoxidation does not proceed via a per-
oxycarboximidic acid intermediate generated by the reaction
of acetonitrile with H2O2.[2a] In the absence of tBuOH, the
yield of 2a decreased. Acetone, 1,2-dichloroethane, and
tBuOH were poor solvents.
equimolar amount of 30% aqueous H2O2 with respect to
1a–1 f, and the epoxide yields could be increased to 83–97%
by using 60% aqueous H2O2 (Table 2, entries 1–12). While
various efficient catalytic systems for epoxidation of 1a by
Mn- and Fe-based complexes have been developed, these
systems require an excess amount of peracetic acid with re-
spect to 1a to attain high yields of 2a (Table S1).[4,5,14] In ad-
dition, the yields of 2a were not so high for most H2O2-
based systems. To the best of our knowledge, efficient epoxi-
dation of electron-deficient alkenes with an equimolar
The electron-withdrawing substituents reduce the reactivi-
ties of the alkenes for electrophilic oxidants. Epoxidation of
electron-deficient alkenes with acetate, ether, carbonyl,
chloro, carboxyl, and ester groups at the allylic positions
Chem. Eur. J. 2011, 17, 7549 – 7559
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7551

N. Mizuno et al.
Table 3. Epoxidation of simple alkenes with H2O2 catalyzed by I.[a]
amount of H2O2 with respect to a substrate has never been
achieved. Oxidation of a,b-unsaturated aldehydes 1i and 1l
also gave the corresponding epoxides 2i and 2l as main
products (Table 2, entries 15 and 18). Notably, 1j and 1o
with nitrile groups were chemoselectively epoxidized with-
out changes in the functional groups (Table 2, entries 16 and
21). The formation of the corresponding epoxy amides was
not observed under the present conditions, while the nitrile
groups are generally hydrolyzed under the basic condi-
tions.[2] Thus, the present system based on the strong electro-
philic active oxygen species showed specific chemoselectivi-
ties. The cyclic a,b-unsaturated ketone 1n was also convert-
ed to the corresponding epoxide 2n in moderate yield
(Table 2, entry 20). Epoxidation of R-(ꢀ)-carvone (1g) re-
gioselectively proceeded to give the 8,9-epoxide 2g in 88%
yield without formation of the 1,2-epoxide (Table 2,
entry 13). Such a regioselectivity is observed for electrophil-
ic oxidants.[4b]
Entry Substrate
t
Product
Yield
[%]
[min]
1[b]
2
10
10
90
92
3
10
60
90
85
4[c]
5
6
10
10
88
27
7
8
9
10
5
88
74
95
10
10
10
10
10
87[f]
81
The 2 mmol scale epoxidation of 1a gave the correspond-
ing epoxide 2a in 83% yield [Eq. (1)]. The turnover number
(TON) achieved was 210, which is larger than those of MnII-
bisphen/SBA-15/peracetic acid (198, bisphen/SBA-15=bis-
1,10-phenanthroline ligands covalently attached onto SBA-
11[d]
12[e]
85
15), [Mn
nal-1-phenylethylimine), [((phen)
peracetic acid (40, phen=phenanthroline), MoO3/TiO2/
3ACHTUNGTRENNUNG(ppei)2ACHTUNGTRENNUNG
(OAc)6]/peracetic acid (49, ppei=2-pyridi-
[a] Reaction conditions: [TBA]4[g-HPV2W10O40] (5 mmol), HClO4
(5 mmol), substrate (300 mmol), CH3CN/tBuOH (1.5/1.5 mL), 30% aque-
ous H2O2 (300 mmol), 333 K, under Ar (1 atm). Yields were determined
by GC. Yield (%)=product (mol)/initial H2O2 (mol)ꢁ100. [b] 3a (6 atm).
[c] Reaction conditions: [TBA]4[g-HPV2W10O40] (2.5 mmol), HClO4
(2.5 mmol), 3c (1.0 mmol), CH3CN/tBuOH (1.5/1.5 mL), 30% aqueous
H2O2 (200 mmolꢁ5), 333 K, 60 min, under Ar (1 atm). [d] 4j/total epox-
ideꢃ0.99. [e] 4k/total epoxideꢃ0.99; 2-(4-methyl-3-cyclohexen-1-yl)-
propanal (9% yield). [f] trans/cis=94:6.
2A 2A(m-O)](ClO4)4/
TBHP (13), [(dppe)PtACHTNUGTRENN(UG C6F5)ACHTUTGNERN(NGUN H2O)]OTf/H2O2 (2, dppe=1,2-
bis(diphenylphosphino)ethane) systems.[4,5,14,15]
Table 4. Competitive oxidation with H2O2 catalyzed by I.[a]
Entry
Substrate A
Substrate B
R0(A)/R0(B)
1
2
3
3b
trans-2-hexene
2-methyl-2-pentene
cyclohexane
96/4
98/2
>99/<1
The results for epoxidation of terminal, internal, and
cyclic alkenes are shown in Table 3. Epoxidation of C3–C10
terminal olefins 3a–3d could be completed within 10 min
under stoichiometric conditions (substrate:H2O2 =1:1)
(Table 3, entries 1–5). Epoxidation of 3c efficiently proceed-
ed even with 0.25 mol% I by slow addition of H2O2 (five
portions every 10 min) (Table 3, entry 4). Competitive oxi-
dation of 1-hexene (3b) and cyclohexane with H2O2 cata-
lyzed by I showed that the reaction rate for epoxidation was
by about two orders of magnitude larger than that for hy-
droxylation (Table 4, entry 3).[9a] Not only terminal but also
internal and cyclic olefins were efficiently epoxidized
(Table 3, entries 6–12). For epoxidation of trans- and cis-2-
octenes 3e and 3 f, the configurations around the C=C moi-
eties were retained in the corresponding epoxide, suggesting
that free-radical intermediates are not involved in the pres-
ent epoxidation (Table 3, entries 6 and 7). Cyclohexene 3g
and the corresponding epoxide 4g are sensitive to allylic ox-
idation and acid-catalyzed ring-opening, respectively. Ti-,[16]
Zr-,[17] and Hf-containing[17] POMs also catalyze the H2O2-
based epoxidation of 3g and heterolytic oxidation mecha-
nism has been proposed,[16] while significant amounts of the
2-methyl-1-pentene
3b
[a] Reaction conditions: [TBA]4[g-HPV2W10O40] (3 mmol), HClO4
(3 mmol), substrate (300 mmol), substrate (300 mmol), CH3CN/
tBuOH (1.5/1.5 mL), 30% aqueous H2O2 (300 mmol), 273 K, under Ar
(1 atm). R0 values were determined from the reaction profiles at low con-
version (ꢁ10%) of substrate and H2O2.
A
B
corresponding diol and over-oxidized byproducts are
formed. The present system showed 97% selectivity to 4g
without significant formation of 2-cyclohexen-1-ol, 2-cyclo-
hexen-1-one,
and
trans-1,2-cyclohexanediol
(Table 3,
entry 8), suggesting that the I-catalyzed epoxidation involves
a heterolytic oxidation mechanism in a similar way to those
of Ti-, Zr-, and Hf-containing POMs. On the other hand, al-
lylic oxidation of 3g proceeds in the presence of V-contain-
ing POMs of [PVnMo12ꢀnO40](3+n)ꢀ (n=1 and 2) and selectiv-
ities to 4g are 23–48%.[18] The turnover frequency (TOF) of
I was ꢃ547 hꢀ1, which is much higher than those of
[Ti2(OH)2As2W19O
W11O39)2OH]7ꢀ (2 hꢀ1),[16b] [(b-Ti2SiW10O39)4]24ꢀ (1 hꢀ1),[16b]
and [M6O4(OH)4A(H2O)2A(CH3COO)5A
(AsW9O33)2]11ꢀ (M=Zr:
67A
(11 hꢀ1),[16b]
[(PTi-
G
E
CHTUNGTRENNUNG
7552
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Chem. Eur. J. 2011, 17, 7549 – 7559

Epoxidation
FULL PAPER
33 hꢀ1, M=Hf: 36 hꢀ1).[17] Therefore, I showed high catalytic
activity and selectivity in comparison with the other d0-tran-
sition-metal-substituted POMs.
Such high stereospecificity and diastereo- and regioselectivi-
ties have also been observed for the [g-SiW10O38V2ACHTUNGTRENNUNG(m-
OH)2]4ꢀ-catalyzed epoxidation and explained by the steric
constraints of the active site.[8]
The alkyl substitution increases the pACTHNUGRTENUNG(C=C) HOMO ener-
gies, resulting in increase of the reactivities of the alkenes
with non-sterically hindered electrophilic oxidants, such as
The I-catalyzed epoxidation could be carried out under
the more concentrated conditions. In the presence of I
(0.7 mol%), epoxidation of 3c efficiently proceeded at
333 K to give 4c in 80% yield and the TOF of 11000 hꢀ1
was achieved [Eq. (2)]. The TOF value was larger than
those reported for the transition-metal-catalyzed H2O2-
based epoxidation of terminal aliphatic olefins:[22–24] [FeII-
peroxyacids, peroxides, and peroxo complexes.[19] The p
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
2-butene (ꢀ8.67 eV)>2-methyl-2-pentene (ꢀ8.97 eV)>
trans-2-hexene (ꢀ9.30 eV)ꢄcis-2-hexene (ꢀ9.32 eV)>2-
methyl-1-pentene (ꢀ9.44 eV)>3b (ꢀ9.72 eV). The reactivi-
ty order for epoxidation of a series of C6 alkenes decreased
in the order of 2-methyl-1-pentene (3.18)>cis-2-hexene
(1.46)>3b (1.00 taken as unity)>2-methyl-2-pentene (0.28)
A
[SbF6]2/AcOH (336 hꢀ1, bpmen=N,N’-bis-
ACHUTGTNNERNUG(MeCN)2]ACHTUNGTRENNUGN
A
R
ACHTUNGTRENNUNG
ꢄ2,3-dimethyl-2-butene
(0.24)@trans-2-hexene
(Table 5); this order is not consistent with that of the p
(0.02)
(C=
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
C) HOMO energies of C6 alkenes, but rather with that ob-
ACHTUNGTRENNUNG
CTHUNGTRENNUNG
A
CHTUNGTRENNUNG
Table 5. Initial and relative rates for epoxidation of a series of C6-alkenes
with H2O2 catalyzed by I.[a]
R
G
G
ACHTUNGTRENNUNG
Entry
Olefin
p
(C=C) HOMO
R0
[mmminꢀ1
]
Relative
rate[b]
(11 hꢀ1),[22g] Ti-MCM-68 (205 hꢀ1),[22h] TS-1 (498 hꢀ1),[20] Ti-
MWW (695 hꢀ1),[22i] and Mo- and W-based complexes/
sodium hydrogen carbonate (3200–3960 hꢀ1).[22j–m] In addi-
tion, the present system could be applied to larger-scale pro-
duction of epoxides. The 20 mmol scale epoxidation of 3c
and 3k catalyzed by I (0.5 mol%) with equimolar amounts
of H2O2 with respect to the substrates proceeded with high
selectivities, and the corresponding epoxides 4c and 4k
were isolated in 75 and 73% yields, respectively [Eq. (3)].
energy [eV]
G
1
ꢀ9.44
0.65
3.18
2
3
4
ꢀ9.32
ꢀ9.72
ꢀ8.97
0.30
0.20
0.06
1.46
1.00
0.28
5
6
ꢀ8.67
ꢀ9.30
0.05
0.24
0.02
<0.01
[a] Reaction conditions: [TBA]4[g-HPV2W10O40] (3 mmol), HClO4
(3 mmol), substrate (300 mmol), CH3CN/tBuOH (1.5/1.5 mL), 30% aque-
ous H2O2 (300 mmol), 273 K, under Ar (1 atm). R0 values were deter-
mined from the reaction profiles at low conversion (ꢁ10%) of substrate
and H2O2. [b] The values are ratios of R0/R0 (3b).
served for epoxidation catalyzed by TS-1, in which restricted
transition-state shape selectivity and diffusion effects were
observed.[20] Therefore, the inconsistency of the orders be-
tween the pACHTUNGTRENNUNG(C=C) HOMO energy and the reactivity could
be caused by the steric constraints of the active site of I.
The 3-alkyl-substituted cyclohexenes provide a quantitative
measure of purely steric effects for epoxidation, since elec-
tronic interaction between the C=C double bond and the al-
lylic substituents are not possible.[21] The high trans diaste-
reoselectivity (trans/cis=94:6) for epoxidation of 3-methyl-
1-cyclohexene 3i was observed (Table 3, entry 10). The
more accessible, but less nucleophilic double bonds in non-
conjugated dienes of trans-1,4-hexadiene (3j) and (R)-(+)-li-
monene (3k) were highly regioselectively epoxidized and
the values of [less substituted epoxide]/[total epoxides] were
ꢃ0.99 (Table 3, entries 11 and 12). The results of competi-
tive epoxidation of C6 alkenes with similar alkyl substituents
to the corresponding dienes were in good agreement with
the trends of regioselectivity for I (Table 4, entries 1 and 2).
Reaction mechanism and role of the central heteroatom of
the POM: On the basis of the cold-spray ionization mass
1
(CSI-MS), H NMR, and 51V NMR results, it has been pro-
posed that reaction of I with H2O2 leads to reversible forma-
tion of hydroperoxo species, [g-PW10O38V2ACTHNUTRGENN(UG m-OH)ACHTUNGTRENNUNG(m-
OOH)]3ꢀ (II), and the successive dehydration of II forms an
active oxygen species with a peroxo group, [g-PW10O38V2(m-
h2:h2-O2)]3ꢀ (III) in a similar way to that of [g-SiW10O38V2-
Chem. Eur. J. 2011, 17, 7549 – 7559
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7553

N. Mizuno et al.
A
Si)), show stoichiometric activities for oxidation of l-methio-
tion of 3c with H2O2 catalyzed by I were carried out to in-
vestigate the reaction mechanism and effects of heteroa-
toms. Since epoxidation of 3c with H2O2 catalyzed by I at
2ACTHNGUTERNNUG
nine in water.[25b,c] POM [Zr2(O2) (SiW11O39)2]12ꢀ in combi-
nation with dendritic cations can act as a recoverable cata-
lyst for oxidation of sulfides with H2O2, while the system is
not applicable to epoxidation of alkenes.[25d]
On the basis of the kinetic and spectroscopic results, we
propose a possible reaction mechanism for the I-catalyzed
epoxidation with H2O2 (Scheme 1). First, the bis-m-hydroxo
compound I reversibly reacts with H2O2 to form the m-hy-
droxo-m-hydroperoxo species of II (step 1). Compound II is
reversibly dehydrated to form the active oxygen species III
(step 2). Then, III reacts with alkenes to form the corre-
sponding epoxides (step 3). The overall epoxidation rate is
expressed by Equation (4) (see details in reference [8c]). On
the basis of the kinetic and 51V NMR data, the respective
rate constants k1–k5 for I were calculated to be 6.2ꢁ
101 mꢀ1 sꢀ1, 5.0ꢁ102 mꢀ1 sꢀ1, 6.7 sꢀ1, 2.3ꢁ102 mꢀ1 sꢀ1, and 1.7ꢁ
102 mꢀ1 sꢀ1 (Table 6). The reaction profiles for epoxidation
Table 6. Rate and equilibrium constants for epoxidation of 3c with H2O2
catalyzed by I.[a]
rate and
equilibrium constant
I
CAHUTTGNRENNUG[TBA]4[g-SiW10O38V2ACHTUNGTRENNUNG(m-OH)2]
Scheme 1. Proposed mechanism for epoxidation of alkenes with H2O2
catalyzed by I.
k1 [mꢀ1 sꢀ1
k2 [mꢀ1 sꢀ1
]
]
6.2ꢁ101
3.7ꢁ10ꢀ1
4.9
5.0ꢁ102
k3 [sꢀ1
]
6.7
5.7ꢁ10ꢀ1
2.8ꢁ101
333 K (i.e., under the reaction conditions in Tables 1–3) was
too fast for the rate to be determined, the reaction was car-
ried out at 293 K. The first-order dependences of the reac-
tion rates on concentration of I (0.3–2.0 mm, Figure 3b and
e) and H2O2 (8.5–73.1 mm, Figure 3c and f) were observed.
The dependence of the reaction rate on concentration of 3c
(4.0–1004.7 mm, Figure 3a and c) showed the saturation ki-
netics. This shows the change of the rate-determining step
from the oxygen-transfer step from III to the C=C double
bond (at low concentration of 3c) to the formation of III (at
high concentration of 3c). The kinetic studies at a low con-
centration of 3c (33.3 mm; i.e., in the region of first-order
dependence on concentration of 3c) showed the inversely
second-order dependence of the reaction rate on concentra-
tion of water (62.3–253.3 mm, Figure 4a), whereas the inver-
sely first-order dependence of the reaction rate on concen-
tration of water (97.0–570.0 mm, Figure 4b) was observed at
high concentration of 3c (500.0 mm; i.e., in the region of
zero-order dependence on concentration of 3c). These de-
pendences also support the change of the rate-determining
step. Upon the addition of 3c to a CH3CN/tBuOH (v/v=
1:1) solution of I treated with 30% H2O2, the 51V NMR
signal of II was weakened and that of III almost disap-
peared. All these results suggest that III is the active species
for epoxidation. There are no examples of V-containing
POMs with m-h2:h2-peroxo groups, but a vanadium complex
with a m-h2:h2-peroxo group has been structurally characteri-
zed.[25a] On the other hand, dimeric and trimeric Zr- and Hf-
containing POMs with m-h2:h2-peroxo groups have been syn-
thesized, depending on the lacunary POM precursors used
and it has been reported that dimeric POMs, [M2(O2)2-
k4 [mꢀ1 sꢀ1
]
]
2.3ꢁ102
k5 [mꢀ1 sꢀ1
1.7ꢁ102
2.0ꢁ102
K1 (=k1/k2)
1.2ꢁ10ꢀ1
3.0ꢁ10ꢀ2
6.2ꢁ10ꢀ1 (2.0)
8.3ꢁ10ꢀ1 (19.1)
7.6ꢁ10ꢀ2
2.0ꢁ10ꢀ2
3.1ꢁ10ꢀ1 (1.0)
4.3ꢁ10ꢀ2 (1.0)
K2 (=k3/k4) [m]
k5K1K2 [sꢀ1
]
k3K1 [sꢀ1
]
[a] Rate constants were calculated on the basis of the kinetics and 51V
NMR data. The data for [TBA]4[g-SiW10O38V2A(m-OH)2] were cited from
reference [8c]. The values in the parentheses are the ratios when the
values of [TBA]4[g-SiW10O38V2A(m-OH)2] were taken as unity.
CTHUNGTRENNUNG
CTHUNGTRENNUNG
calculated by the numerical integration of Equation (4)
(shown by the solid lines in Figure 3) fairly well reproduced
the experimental results of concentration of 4c as a function
of time, supporting Scheme 1. The slight deviation of the ob-
served concentrations of 4c from the calculated ones at high
conversions is probably explained by nonproductive decom-
position of H2O2 (Figure 3).
d½epoxideꢅ
dt
k1k3k5½Iꢅ½H2O2ꢅ½olefinꢅ
R0 ¼
¼
2
k2k4½H2Oꢅ þ ðk2½H2Oꢅ þ k3Þk5½olefinꢅ
ð4Þ
The kinetic parameters of I and [g-SiW10O38V
are shown in Table 6. The k1–k3 and k4 values were in the
order of I@[g-SiW10O38V2A
(m-OH)2]4ꢀ and I>[g-SiW10O38V2-
(m-OH)2]4ꢀ, respectively, and the k5, K1, and K2 values did
2ACHTUNGTRENNUNG
CTHUNGTRENNUNG
AHCTUNGTRENNUNG
not much change. At low concentration of 3c, the rate-de-
termining step is reaction of III with 3c, and the reaction
rates of the I-catalyzed epoxidation of 3c are proportional
to k5K1K2. On the other hand, the reaction rates are propor-
tional to k3K1 at high concentration of 3c. The k3 values de-
ACHTUNGTRENNUNG
(XW11O39)2]12ꢀ (M=Zr (X=Si and Ge) and M=Hf (X=
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Chem. Eur. J. 2011, 17, 7549 – 7559

Epoxidation
FULL PAPER
which would result in signifi-
cant increase in the dehydration
reactivity for step 2 (i.e.,
k3).[26,27]
In order to investigate the
steric effect of III, the density
functional theory (DFT) calcu-
lations were carried out. The
transition-state structures and
activation barriers for epoxida-
tion of cis-2-butene and trans-2-
butene with III were calculated
on the assumption that the
olefin double bond directly at-
tacks the peroxo oxygen groups
in
a spiro fashion (i.e., the
CCO plane is almost orthogo-
nal to the VOO plane).[28] The
transition-state structures are
shown in Figure 5. The activa-
tion barrier of cis-2-butene
(TS1, 51 kJmolꢀ1) was much
lower than that of trans-2-
butene (TS2, 64 kJmolꢀ1), while
the HOMO energy (ꢀ6.631 eV)
and NBO charges of the C2
and C3 atoms (ꢀ0.234) of cis-2-
butene were almost the same as
those (ꢀ6.623, ꢀ0.230 eV) of
trans-2-butene. The lengths be-
tween the center of the C=C
double bond and that of the
two vanadium atoms in TS1
and TS2 were 3.270 and
3.295 ꢂ, respectively. Therefore,
cis-alkene is more accessible to
the peroxo oxygen atom than
trans-alkene, resulting in the
low activation barrier.[29]
Figure 3. Dependences of reaction rates on concentrations of a) 3c, b) I, and c) H2O2 and d)–f) reaction pro-
files for epoxidation of 3c with H2O2 catalyzed by I. Conditions: a) and d) [TBA]4[g-HPV2W10O40] (1.0 mm),
HClO4 (1.0 mm), CH3CN/tBuOH (1.5/1.5 mL), 3c (4.0–1004.7 mm and 4.9–1009.0 mm for I and [g-SiW10O38V2-
ACHTUNGTRENNUNG
(m-OH)2]4ꢀ, repsectivelly), H2O2 (33.3 mm), H2O (124.0 mm), 293 K; b) and e) [TBA]4[g-HPV2W10O40] (0.3–
Conclusion
2.0 mm), HClO4 (0.3–2.0 mm), CH3CN/tBuOH (1.5/1.5 mL), 3c (33.3 mm), H2O2 (33.3 mm), H2O (124.0 mm),
293 K; c) and f) [TBA]4[g-HPV2W10O40] (1.0 mm), HClO4 (1.0 mm), CH3CN/tBuOH (1.5/1.5 mL), 3c
(33.3 mm), H2O2 (8.5–73.1 mm), H2O (124.0 mm), 293 K. Solid lines were calculated with Equation (4).
In summary, a divanadium-sub-
stituted phosphotungstate
I
showed high catalytic activity
pended heavily on the different central heteroatoms of the
POMs, while the K1 values were not. The k3K1 value of I
for epoxidation of various kinds of electron-deficient al-
kenes with aqueous H2O2. POM I showed the highest cata-
lytic activity for H2O2-based epoxidation of 1a among vana-
dium and tungsten complexes and a TON of 210 was ach-
ieved. On the basis of the kinetic and spectroscopic results
(19.1) was much larger than that of [g-SiW10O38V2ACTHNUGRTNEUNG(m-
OH)2]4ꢀ (1.0 taken as unity). Thus, the large k3 value of I
leads to significant increase in catalytic activity of I under
the more concentrated conditions [Figure 3a, Tables 1–3,
including those of [g-SiW10O38V2ACHTUNGTRNEUNG
(m-OH)2]4ꢀ, the acidity of
1
and Eqs. (1)–(3)]. The H NMR signal assignable to the hy-
the hydroperoxo species in II would play important roles in
the dehydration reactivity (i.e., k3). The largest k3 value of I
leads to significant increase in catalytic activity of I under
more concentrated conditions.
droperoxo proton of II was observed at 9.49 ppm and the
chemical shift was higher than that of [g-SiW10O38V
(m-OOH)]4ꢀ (9.45 ppm). The appearance of the hydroperoxo
proton of II at the lower field shows the stronger acidity,
2ACHTUNGTRNE(NUNG m-OH)-
ACHTUNGTRENNUNG
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7555

N. Mizuno et al.
Figure 4. Dependence of the reaction rates on the concentration of H2O
for epoxidation of 3c with H2O2 catalyzed by I. Conditions: a) [TBA]4[g-
HPV2W10O40] (1.0 mm), HClO4 (1.0 mm), CH3CN/tBuOH (1.5/1.5 mL),
3c (33.3 mm), H2O2 (33.3 mm), H2O (62.3–253.3 mm), 293 K, slope=
ꢀ1.70 (R2 =0.98); b) [TBA]4[g-HPV2W10O40] (1.0 mm), HClO4 (1.0 mm),
CH3CN/tBuOH (1.5/1.5 mL), 3c (500.0 mm), H2O2 (33.3 mm), H2O (97.0–
570.0 mm), 293 K, slope=ꢀ1.26 (R2 =0.99).
Experimental Section
Figure 5. Transition-state structures and the corresponding activation bar-
riers for epoxidation of a) cis-2-butene and b) trans-2-butene with III in
the gas phase (bond lengths in ꢂ).
Materials: Acetonitrile (Kanto Chemical) and dichloromethane (Kanto
Chemical) were purified by The Ultimate Solvent System (GlassContour
Company) prior to use.[30] Substrates were purified according to the re-
ported procedure.[31] tert-Butyl alcohol was distilled in the presence of
CaH2 and stored over 4 A molecular sieves.[31] The oxidants of H2O2
(30% aqueous solution, Kanto Chemical), tert-butyl hydroperoxide (5.5m
n-decane solution, Aldrich), and cumene hydroperoxide (85% solution,
Alfa Aesar), Na2WO4·2H2O (Nippon Inorganic Colour & Chemical),
H2WO4 (Wako Chemical), Na2SiO3·9H2O (Kanto Chemical), H3PO4
(Kanto Chemical), CsOH (50 wt% aqueous solution, Aldrich), NaVO3
(nacalai tesque), and [(n-C4H9)4]Br (TCI) were used as received. A solu-
tion of 60% aqueous H2O2 was prepared by concentration of 30% aque-
ous H2O2. The commercially-unavailable epoxides were synthesized by
the oxidation with m-chloroperoxybenzoic acid (m-CPBA) (2a, 2c,[32]
2g,[33] 2h,[34] 2j,[35] and 2k[36]), bicarbonate/H2O2 (2e[37]), alkaline H2O2
(2i,[38] 2l,[39] 2m,[39] 2n,[40] 2,3-epoxy-2-methylpropanamide (2p),[2a] and
2,3-epoxypropanamide (2q)[2a]), and sodium hypochlorite (2o[41]) and
[D6]DMSO) were purchased from ACROS or Aldrich and used as re-
ceived.
Instruments: IR spectra were measured on a Jasco FT/IR-460 spectrome-
ter Plus using KBr or KCl disks. NMR spectra were recorded on a JEOL
JNM-EX-270 spectrometer (1H, 270.0; 13C, 67.80; 29Si, 53.45; 31P, 109.25;
1
51V, 70.90; 183W, 11.20 MHz) by using 5 mm tubes (for H, 13C, and 31P) or
10 mm tubes (for 29Si, 51V , and 183W). Chemical shifts (d) were reported
in ppm downfield from SiACHTNUTGRNEUNG
(CH3)4 (solvent, CDCl3) for 1H, 13C, and 29Si
NMR spectra, 85% H3PO4 for 31P NMR spectra, VOCl3 for 51V NMR
spectra, and 2m Na2WO4 (solvent, D2O) for 183W NMR spectra. GC anal-
yses were carried out on Shimadzu GC-2014 with a flame ionization de-
tector equipped with a DB-WAX etr capillary column (internal diame-
ter=0.25 mm, length=30 m). Mass spectra were recorded on a Shimadzu
GCMS-QP2010 equipped with a TC-5HT capillary column at an ioniza-
tion voltage of 70 eV. Cold-spray ionization mass spectra were measured
with a JEOL JMS-T100CS spectrometer in the positive ion mode by
direct infusion with a syringe pump (0.05 mLminꢀ1).
1
identified by comparison of their H and 13C NMR signals with the litera-
ture data (2a,[4d,42] 2c,[32] 2e,[43] 2f,[44] 2g,[4b] 2h,[34] 2i,[45] 2j,[34] 2k,[46] 2l,[47]
2m,[48] 2n,[49] and 2o[50]). Deutrated solvents (CD3CN, CDCl3, D2O, and
7556
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Epoxidation
FULL PAPER
A typical procedure for catalytic epoxidation of alkenes with H2O2: Cata-
lytic reactions were carried out with a glass tube (30 mL) containing a
magnetic stir bar. The catalyst, solvent, and substrate were charged in the
reaction vessel. For the I-catalyzed reactions, diprotonated I was pre-
pared in situ by the reaction of monoprotonated [TBA]4[g-HPV2W10O40]
with one equivalent of perchloric acid (70% aqueous solution). The for-
mation of I was confirmed by 51V NMR (d=ꢀ578 ppm). Reaction was
initiated by the addition of 30% aqueous H2O2. The reaction solution
was periodically analyzed by GC, GC-MS, and NMR spectroscopy. The
Ce3+/4+ titration showed that no H2O2 remained after the reaction.[51] All
products were known compounds and identified by comparison of their
1H and 13C NMR signals with the literature data. The TOF for epoxida-
tion of 3c was determined from the reaction profiles at low conversions
(<20%) of both substrates and H2O2.
119.9, 59.2, 52.6, 39.5, 30.2, 27.3, 24.8, 23.2, 18.6; (4R,8S)-epoxide: d=
134.0, 119.7, 59.1, 53.2, 40.1, 30.0, 27.4, 24.9, 23.4, 17.9.
Synthesis and characterization of [TBA]4[g-HPV2W10O40]: The cesium
salt of a deprotonated divanadium-substituted phosphotungstate Cs5[g-
PV2W10O40] was synthesized according to the published literature proce-
dures[54] and characterized by IR spectroscopy. The TBA salt of a monop-
rotonated derivative [TBA]4[g-HPV2W10O40] was prepared by a cation
exchange reaction. Sodium metavanadate (1.2 mmol) was dissolved in
hot water (120 mL). Upon cooling, the pH of the solution was adjusted
to 2.0 with 3m HCl. Into the solution, Cs5[g-PV2W10O40]·6H2O (3.8 g,
1.1 mmol) was dissolved and the insoluble materials were removed by fil-
tration. Tetra-n-butylammonium bromide (1.8 g, 5.6 mmol) was added
with vigorous stirring. The precipitate was collected by filtration, washed
with water (400 mL), and dried in vacuo. The purity of the crude
[TBA]4[g-HPV2W10O40] (i.e., before the recrystallization from acetone/
ether) was about 90% (confirmed by 51V NMR spctroscopy in CD3CN/
Kinetic studies: A glass tube (15 mL) was used as a reactor for the kinet-
ic studies on epoxidation of 3c with H2O2 catalyzed by I. The reaction
was periodically monitored by GC, and the remaining H2O2 was decom-
posed at 273 K by addition of Ru(OH)x/Al2O3 before the GC analysis.[52]
It was confirmed that epoxidation of 3c did not proceed at all in the
presence of Ru(OH)x/Al2O3 during the decomposition of H2O2. Reaction
conditions are given in the legends of Figures 3 and 4. R0 values were de-
termined from the reaction profiles at low conversions (<10%) of both
3c and H2O2. Solid lines in Figure 3 were calculated with Equation (4).
All the kinetic data were fitted with the Igor Pro version 5.05 program.
The kinetic data fitting was carried out by the least squares method to
minimize the sum of squared residuals [i.e., the difference between the
observed and calculated values using Eq. (4)].
tBuOH (1/1, v/v)), and the b-isomer and VOACTHNUTRGNEN(UG O-tBu)3 species were ob-
served as main by-products. The highly pure [TBA]4[g-HPV2W10O40]
could be obtained according to the following modified procedure. The
crude [TBA]4[g-HPV2W10O40] (1.0 g, ca. 90% purity) was dissolved in
CH3CN (100 mL) and the insoluble materials were removed by filtration.
Acetonitile was removed by evaporation followed by addition of acetone
(10 mL). The resulting yellow precipirate was collected by filtraion (70%
yield). The purity was ꢃ98% (confirmed by 51V NMR spectroscopy).
Further recrystallization from acetone/ether gave analytically pure yel-
lowish orange crystals of [TBA]4[g-HPV2W10O40] with ꢃ99.5% purity
(confirmed by 51V NMR spectroscopy). While the chemical shift was
slightly different from that (ꢀ581 ppm) in the previous report,[9] the 51V
NMR signal at ꢀ578 ppm was observed upon the addtion of one equiva-
lent of HClO4 and the catalytic activity and selectivtity were not affected
by changing the purification procedures, suggesting the formation of I in
the presence of HClO4. 51V NMR (70.90 MHz, CD3CN, 298 K, VOCl3):
d=ꢀ570 ppm; 31P NMR (109.25 MHz, CD3CN, 298 K, H3PO4): d=
ꢀ14.3 ppm; elemental analysis calcd (%) for C64H145N4O40PV2W10
([TBA]4[HPV2W10O40]): C 21.46, H 4.08, N 1.56, P 0.86, V 2.84, W 51.32;
found: C 21.51, H 4.21, N 1.56, P 0.86, V 2.93, W 51.65; IR (KBr): n˜ =
1097, 1062, 1039, 1001, 988, 973, 965, 952, 870, 803, 751, 533, 489, 418,
A larger scale (2mmol scale) epoxidation of 1a: [TBA]4[g-HPV2W10O40]
(0.4 mol% with respect to 1a and H2O2), 70% HClO4 (0.4 mol% with
respect to 1a and H2O2), 1a (2 mmol), and acetonitrile/tert-butyl alcohol
(3/3 mL) were successively placed into a glass reactor. The reaction mix-
ture was stirred at 333 K, and 60% aqueous H2O2 (2 mmol) was added in
five portions (i.e., 0.4 mmolꢁ5) every 10 min. After the addition was
completed, the mixture was stirred at 333 K for additional 20 min (i.e.,
total reaction time was 60 min). The GC yield of 2a was 83%.
A larger scale (20mmol scale) production of 4c and 4k: [TBA]4[g-
HPV2W10O40] (0.5 mol% with respect to substrates and H2O2), 70%
HClO4 (0.5 mol% with respect to substrates and H2O2), 3c or 3k
(20 mmol), and acetonitrile/tert-butyl alcohol (30/30 mL) were successive-
ly placed into a glass reactor. The reaction mixtures were stirred at 333
and 305 K for 3c and 3k, respectively, and 30% aqueous H2O2
(20 mmol) was added in five portions (i.e., 4 mmolꢁ5) every 10 min.
After the addition was completed, the mixture was stirred at 333 and
305 K for 3c and 3k, respectively, for additional 20 min (i.e., total reac-
tion times were 60 min). The GC yields of 4c and 4k were 88 and 86%,
respectively. Then, acetonitrile and tert-butyl alcohol were removed by
evaporation until a yellow precipitate of catalyst was formed. n-Pentane
(60 mL) was added to the resulting solution, followed by the removal of
the precipitate. Then, the residual tert-butyl alcohol was removed by the
extraction with water (20 mLꢁ5). The n-pentane solution was dried with
anhydrous magnesium sulfate followed by the removal of magnesium sul-
fate. The isolation of 4c and 4k was carried out by column chromatogra-
phy on silica gel (Silica Gel 60N, spherical, neutral, 63–210 mm, Kanto,
Cat. No. 37565–79) using n-pentane/diehtyl ether (95:5) as eluent, giving
1.93 g of 4c (75% yield, 99% purity) and 2.21 g of 4k (73% yield
399, 373, 358, 334, 314, 307 cmꢀ1
.
Synthesis and characterization of [TBA]4[g-SiW10O38V2ACHTNUGRTENUNG(m-OH)2]: The
purity of a TBA salt of [g-H2SiV2W10O40]4ꢀ, which was synthesized ac-
cording to the previously reported procedure,[8a] was about 99% (con-
firmed by 51V NMR spectroscopy), and unknown byproducts were ob-
served. Highly pure [TBA]4[g-SiW10O38V2ACTHNUTRGNEUNG(m-OH)2] could be obtained ac-
cording to the following modified procedure. NaVO3 (0.82 g, 6.75 mmol)
was dissolved in water (13.5 mL) by heating at 343 K and the solution
was cooled to room temperature. K8[g-SiW10O36]·12H2O (10 g, 3.3 mmol)
was dissolved in 1m aqueous HCl (35 mL) followed by the quick addition
of 0.5m aqueous solution of NaVO3 (13.5 mL). The mixture was gently
stirred for 5 min and the insoluble materials were removed by filtration.
RbCl (5 g, 41.3 mmol) was added to this solution and the resulting yellow
precipitate was clollected by filtration. The precipietate was dissolved in
water (60 mL) and the insoluble materials were removed by filtraion.
The solution was evaporated to about 5 mL at 303 K. The resulting
yellow precipitate was collected by filtration, washed with small amounts
of cold water, and air-dried for 1 day. Analytically pure Rb2K2[g-
H2SiV2W10O40]·nH2O was obtained. Yield: 6.4 g (ca. 64%); 51V NMR
(70.90 MHz,
D2O,
298 K,
VOCl3):
d=ꢀ586 ppm.
Rb2K2[g-
((4R,8S)-epoxide/ACHTUNGTRENNUNG(4R,8R)-epoxide=2:1), 95% purity, 5% selectivity to
2-(4-methyl-3-cyclohexen-1-yl)-propanal).
H2SiV2W10O40]·nH2O (6.4 g) was dissolved in 0.05m HCl (400 mL) fol-
lowed by the additon of tetra-n-butylammonium bromide (6 g,
18.6 mmol). The resulting yellow precipitate was collected by filtration
and purified by the precipitation method (addition of 1 L of water into a
1
Data for 4c: H NMR (270 MHz, CDCl3, 298 K, TMS): d=2.92–2.89 (m,
1H), 2.74 (t, J=4.9 Hz, 1H), 2.45 (dd, J=5.1, 2.7 Hz, 1H), 1.54–1.30 (m,
12H), 2.65 (dd, J=5.0, 2.6 Hz, 1H), 0.91–0.86 (m, 3H); 13C NMR
(67.8 MHz, CDCl3, 298 K, TMS): d=52.3, 47.0, 32.5, 31.7, 29.1, 25.9,
22.5, 14.0.
Data for 4k:[53] ((4R,8S)- and (4R,8R)-epoxides mixture): 1H NMR
(270 MHz, CDCl3, 298 K, TMS): d=5.37–5.35 (m, 1H), 2.65–2.62 (m,
1H), 2.56–2.52 (m, 1H), 2.10–1.80 (m, 4H), 1.64 (s, 3H), 1.50–1.40 (m,
2H), 1.27 ((4R,8R)-epoxide) and 1.26 ((4R,8S)-epoxide) (s, 3H);
13C NMR (67.8 MHz, CDCl3, 298 K, TMS): (4R,8R)-epoxide: d=133.8,
solution of [TBA]4[g-SiW10O38V2ACTHNUGRTNEG(UN m-OH)2] (ca. 7–8 g) in CH3CN (50 mL))
and evacuated at room temperature for 2 h. Yield: 7.6 g (64%); 29Si
NMR (53.45 MHz, CD3CN, 298 K, TMS): d=ꢀ84.0; 51V NMR
(70.9 MHz, CD3CN, 298 K, VOCl3): d=ꢀ564 ppm; 183W NMR
(11.20 MHz, CD3CN, 298 K, Na2WO4): d=ꢀ82.2, ꢀ95.6, ꢀ129.7 ppm
with the intensity ratio of 4:2:4; 1H NMR (270 MHz, CD3CN, 298 K,
TMS): d=5.07 (2H, V-OH-V) 3.13 (32H, cation), 1.63 (32H, cation),
1.43 (32H, cation), 0.99 ppm (48H, cation); UV/Vis (CH3CN): lmax (e)=
Chem. Eur. J. 2011, 17, 7549 – 7559
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7557

N. Mizuno et al.
240 (36000), 285 (24000), 350 nm (5900 molꢀ1 m3 cmꢀ1); IR (KBr): n˜ =
1151, 1106, 1057, 1004, 995, 966, 915, 904, 875, 840, 790, 691, 550, 519,
482, 457, 405 cmꢀ1; elemental analysis calcd (%) for C64H148SiN4O41V2W10
j) P. Kçgerler, B. Tsukerblat, A. Mꢄller, Dalton Trans. 2010, 39, 21–
36.
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([TBA]4[g-SiW10O38V
2.83, W 51.09; found: C 21.20, H 4.00, N 1.53, Si 1.96, V 2.72, W 50.20.
Quantum chemical calculations: The p(C=C) HOMO energies in Table 5
2ACHTUNGTRENNUNG(m-OH)2]·H2O); C 21.36, H 4.15, N 1.56, Si 0.78, V
AHCTUNGTRENNUNG
were calculated at the HF/6–311G** level with the Gaussian 03 program
package.[55] The calculations of POMs were carried out at the B3LYP
level theory[56] with 6-31+G* basis sets for C, H, and O atoms, 6-31G*
for P atoms, and the double-z quality basis sets with effective core poten-
tials proposed by Hay and Wadt[57] for V and W atoms, respectively. The
geometries were optimized within the following symmetry restrictions:
C2v for [g-PW10O38V
symmetry restrictions for [g-PW10O38V
G
; no
G
G
.
mized geometries and structures are given in Figure 5 and Table S2 and
Figure S2 in the Supporting Information. Transition-state structures were
searched by numerically estimating the matrix of second-order energy
derivatives at every optimization step and by requiring exactly one Ei-
genvalue of this matrix to be negative.
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Acknowledgements
We are grateful to Dr. Y. Nakagawa (The University of Tokyo) for his
help in experiments. This work was supported by the Japan Society for
the Promotion of Science (JSPS) through its “Funding Program for
World-Leading Innovative R&D on Science and Technology (FIRST
Program)”, the Core Research for Evolutional Science and Technology
(CREST) program of the Japan Science and Technology Agency (JST),
the Global COE Program (Chemistry Innovation through Cooperation
of Science and Engineering), the Development in a New Interdisciplinary
Field Based on Nanotechnology and Materials Science Programs, and a
Grant-in-Aid for Scientific Research from the Ministry of Education,
Culture, Science, Sports, and Technology of Japan.
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Received: April 1, 2011
Published online: June 6, 2011
Chem. Eur. J. 2011, 17, 7549 – 7559
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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