High turnover numbers for the catalytic selective epoxidation of alkenes with 1 atm of molecular oxygen

Article abstract of DOI:10.1002/1521-3773(20011001)40:19<3639::AID-ANIE3639>3.0.CO;2-0

The diiron-substituted silicotungstate γ-SiW₁₀{Fe³⁺(OH₂}₂O ₃₈^6- (schematically shown) is an effective catalyst for the oxygenation of alkenes in homogeneous reaction media with 1 atm of molecular oxygen. For example, a selectivity for cyclooctene oxide of 98% and a turnover number of 10000 were achieved in the epoxidation of cyclooctene. The catalyst is stable under the reaction conditions, and its ability to use molecular oxygen raises the prospect of using it in industrial epoxidation processes.

Full text of DOI:10.1002/1521-3773(20011001)40:19<3639::AID-ANIE3639>3.0.CO;2-0

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Figure 2 shows the time course of the oxygenation of
cyclooctene with 1 atm of molecular oxygen catalyzed by 1 at
356 K. The average carbon balance for six runs was (100 Æ
8)%. Cyclooctene oxide was selectively produced together
High Turnover Numbers for the Catalytic
Selective Epoxidation of Alkenes with 1 atm of
Molecular Oxygen**
Yoshiyuki Nishiyama, Yoshinao Nakagawa, and
Noritaka Mizuno*
Catalytic epoxidation of alkenes has attracted much
attention both in industrial processes and in organic syntheses,
because epoxides are among the most useful synthetic
intermediates. Epoxidation of alkenes can be carried out by
various techniques with various oxidants. However, stoichio-
metric (noncatalytic) epoxidation is still widely used, and
large amounts of byproducts, particularly salts, are formed.
For example, propylene oxide has been produced commer-
cially by alkaline dehydrochlorination of propylene chloro-
hydrin with formation of large amounts of metal salts.[1±3] The
utilization of molecular oxygen for a catalytic epoxidation
without reducing reagents or radical initiators is a rewarding
goal, because molecular oxygen has the highest content of
active oxygen, and no byproducts are formed from it, in
contrast to various other oxidants.[4±13] However, only a few
ideal homogeneous epoxidations of alkenes with molecular
oxygen at 1 atm without reducing reagents or radical initiators
have been achieved, because organic ligands of the catalysts
are degraded or the catalysts act as stoichiometric oxidants.
Therefore, a high catalyst turnover number (TON) is a key.
The catalytic activity of polyoxometalates has attracted much
attention, because their acidic and redox properties can be
controlled at the atomic or molecular level. The strong acidity
and oxidizing power of polyoxometalates have led to many
studies on homogeneous and heterogeneous catalysis.[13±16]
The additional attractive and technologically significant
aspect of polyoxometalates in
Figure 2. Oxygenation of cyclooctene with molecular oxygen catalyzed by
~
&
*
1 at 356 K. , conversion of cyclooctene; , TON; , selectivity for
~
*
cyclooctene oxide; , selectivity for 2-cycloocten-1-ol; , selectivity for
2-cycloocten-1-one. Catalyst, 1.5 mmol; solvent, 1,2-dichloroethane/aceto-
nitrile 1.5/0.1 mL; substrate, 18.5 mmol; pO ˆ 1 atm. C ˆ conversion, S ˆ
2
selectivity.
with small amounts of 2-cycloocten-1-ol and 2-cycloocten-1-
one. After 385 h, the conversion and selectivity for cyclo-
octene oxide reached 82 and 98%, respectively, and the TON
was 10000. The value is more than 100 times higher than those
so far reported for the epoxidation of cyclooctene with 1 atm
of molecular oxygen alone.[20]
Oxygenation of various alkenes with 1 atm of molecular
oxygen was carried out in the presence of 1 at 356 K. Similarly
to the oxygenation of cyclooctene, longer reaction periods
increased the TON for each alkene. The results are summar-
ized in Table 1. The main products were the corresponding
catalysis is their inherent stabil-
ity towards oxygen donors.[17±19]
We used the Keggin-type diiron-
substituted silicotungstate
1
(Figure 1) as a catalyst precursor
for the selective epoxidation of
alkenes with molecular oxygen
at 1 atm and found that this
epoxidation can be catalyzed
with high TONs. The catalyst is
thus able to use molecular oxy-
gen as an oxidant, and raises the
prospect of using this type of
inorganic catalyst for industrial
epoxidation processes.
Table 1. Oxygenation of various alkenes with molecular oxygen catalyzed
by 1 at 356 K.[a]
Substrate
TON C [%] Products
S [%]
cyclododecene
9600 74
10000 82
2200 17
2500 20
cyclododecene oxide 64[b]
Figure 1. Polyhedral repre-
2-cyclododecen-1-ol
2-cyclododecen-1-one
cyclooctene oxide
2-cycloocten-1-ol
2-cycloocten-1-one
1,2-octene oxide
1-octen-3-ol
31
5
98
1
1
93
5
sentation
of
g-
(1).
6
SiW10{Fe3‡(OH2)}2O38
cyclooctene
The two iron atoms are rep-
resented by shaded octahe-
dra. The WO6 moieties occu-
py the white octahedra, and
an SiO4 group is shown as the
internal black tetrahedron.
1-octene
1-octen-3-one
2
2-octene (cis/trans ˆ 8/2)
2,3-octene oxide
2-octen-4-ol
94
5
2-octen-4-one
2,3-heptene oxide
2-hepten-4-ol
2-hepten-4-one
2,3-hexene oxide
2-hexen-4-ol
1
91
8
[*] Prof. Dr. N. Mizuno, Y. Nishiyama, Y. Nakagawa
Department of Applied Chemistry, School of Engineering
The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656
(Japan)
2-heptene (cis/trans ˆ 8/2) 2900 24
2-hexene (cis/trans ˆ 4/6) 1300 11
1
79
19
2
Fax : (‡81)3-5841-7220
E-mail: tmizuno@mail.ecc.u-tokyo.ac.jp
2-hexen-4-one
[**] We acknowledge T. Hayashi (The University of Tokyo), M. Wada
(Nippon Shokubai Co., Ltd.), and Y. Sumita (Nippon Shokubai Co.,
Ltd.) for their help with experiments. This work was supported in part
by a Grant-in-Aid for Scientific Research from the Ministry of
Education, Science, Sports and Culture of Japan.
[a] Reaction conditions: catalyst, 1.5 mmol; solvent, 1,2-dichloroethane/
acetonitrile, 1.5/0.1 mL; substrate, 18.5 mmol; pO ˆ 1 atm; reaction time,
2
385 h. The substrate/O2 ratio in the gas phase may lie within the explosion
limit. [b] Includes the selectivity for 1,2-cyclododecanediol (6%).
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epoxides in all oxygenation reactions. This fact and the
obtained TONs show that 1 can efficiently catalyze the
epoxidation of various kinds of alkenes.
Figure 3 shows IR spectra of 1 after oxygenation of
cyclooctene with 16O2 and 18O2 at 356 K. As-prepared 1 shows
ˆ
bands at 960 [n(W Oterminal)], 902, 884 [n(SiO)], 800 (n(W-O-
1
Keggin-type polyoxometalates show characteristic UV/Vis
bands, and therefore their structures have often been charac-
terized by UV/Vis spectroscopy. The UV/Vis spectrum of as-
prepared 1 showed bands at 275 (e ˆ 22600), 334 (10000), and
W) for corner-sharing octahedra), and 753 cm (n(W-O-W)
1
470 nm (68m 1 cm ), and after being used for the oxygenation
of cyclooctene 1 showed the original absorption bands with
almost the same intensities. The IR bands of the original
skeletal vibration of 1 changed only slightly (see below).
Magnetic susceptibility measurements and recording of
Mössbauer and 183W NMR spectra on the reaction solution
to investigate the structure of 1 were thwarted by insufficient
sensitivity at the low concentration (0.38 mm). After 1 (0.15m)
was treated with 1 atm of molecular oxygen in [D3]acetonitrile
for 96 h at 356 K, the 183W NMR spectrum showed two broad
signals at d ˆ 1330 and 1840 with an integral ratio of 2:1,
characteristic of the C2v symmetry of the original g-Keggin
structure. This indicates that the two iron atoms occupy the
same positions as shown in Figure 1 under the reaction
conditions and that the structure of 1 is retained during the
reaction. In addition, the fact that 1 is even stable in the
presence of hydrogen peroxide,[21] as demonstrated by 183W
NMR spectrocopy, supports this conclusion.
The oxygenation of cyclooctene was not inhibited by the
presence of 1 ± 3 equiv (relative to 1) of alkyl-radical scav-
engers such as p-tert-butylcatechol. For example, the con-
version and selectivity for cyclooctene oxide after 96 h in the
presence of 1 equiv of p-tert-butylcatechol were 20 and 92%,
respectively. These values are in good agreement with those of
18 and 92%, respectively, in the absence of the radical
scavenger. For epoxidation of trans- and cis-2-octenes, the
trans/cis-oxide ratios were 10 and 0.2, respectively, that is, the
reaction was rather stereospecific. Similarly, epoxidation of
cis-2-hexene proceeded rather stereospecifically. In contrast,
epoxidation via a radical intermediate proceeds nonstereo-
specifically. In fact, addition of a radical initiator, N-hydroxy-
phthalimide, mainly produced trans-2-octene oxide (trans/
cis ˆ 4) in the epoxidation of cis-2-octene. In addition,
epoxidations of cis-2-octene and cis-2-hexene were faster
than those of the corresponding trans-2-alkenes, as has been
observed for epoxidation catalyzed by oxo iron porphyrins,
which proceeds differently from epoxidation via a radical
pathway.[22]
Figure 3. IR spectra of 1 after oxygenation of cyclooctene with 16O2 (a) and
18O2 (b and dotted line in a) for 96 h at 356 K. The spectra were measured
by quickly evaporating the reaction solution, washing the resulting solid
with diethyl ether, drying and then pressing it into a KBr pellet. A ˆ ab-
sorbance.
for edge-sharing octahedra). After 1 being used for the
oxygenation of cyclooctene with 16O2, a new band was
1
ˆ
observed at 832 cm (Figure 3a). It is reported that Fe O
bands appear in the range of 810 ± 860 cm 1.[22] After oxygen-
ation with 18O2 a new band was observed at 776 cm
(Figure 3b). The shift of 56 cm is in fair agreement with
the expected shift of 48 cm . The band disappeared after the
1
1
1
reaction with cyclooctene under Ar, and cyclooctene oxide
(1.9 equiv) was formed; this shows that the iron ± oxygen
species is reactive. The amount of H218O produced was 2 Â
10 4 mol, close to that of 2-cycloocten-1-one, and much less
than that of cyclooctene oxide. In addition, the amount of
cyclooctene oxide produced was about two times larger than
the amount of O2 consumed.[25] The above results show that
the epoxidation proceeds without co-formation of water, and
an intermediate iron ± oxygen species is formed.
In conclusion, we have demonstrated that 1 efficiently
catalyzes the epoxidation of alkenes with molecular oxygen
alone, a green route to epoxides. Detailed investigations on
the reaction mechanism are in progress.
Experimental Section
The kinetic studies showed zero-order dependence of
reaction rates on the concentration of cyclooctene ([cyclo-
octene]), and first-order dependence on the concentration of
The catalyst precursor 1 was synthesized as its tetrabutylammonium salt by
the reported procedure:[26] A solution of K8[g-SiW10O36] ´ 12H2O (3.0 g,
1.0 mmol) in deionized water (30 mL) was quickly adjusted to pH 3.90 with
concentrated nitric acid. Then, an aqueous solution of Fe(NO3)3 ´ 9H2O
(0.82 g, 2.0 mmol) in water (5 mL) was added. The color of the solution
turned to pale yellow. After the solution had been stirred for 5 min, the
addition of an excess of tetra-n-butylammonium nitrate (3.1 g, 10 mmol)
resulted in a yellow-white precipitate. The precipitate was collected by
filtration and purified by twice dissolving it in acetonitrile (15 mL) and
adding water (300 mL) to reprecipitate the product. The yield of the
purified compound was about 1.5 g (50%). The polyoxometalate g-
1 ([1]) and the partial pressure of molecular oxygen (pO ).
2
These results indicate that the rate of decrease in [cyclo-
octene] is expressed by
d[cyclooctene]/dt ˆ k[1]pO [cy-
2
clooctene]0. Moreover, a maximum rate was obtained for
pO ˆ 1 ± 2 atm. The oxygenation of adamantane showed that
2
the ratio of tertiary/secondary C H bond selectivity on a per
bond basis was 11.[23] Under free-radical conditions, the value
is normally three, that is, different from that in the present
system. All these results demonstrate that nonradical proc-
esses prevail to a major degree in the present system,[24]
although some contribution of free radicals is still a possibility.
6
SiW10{Fe3‡(OH2)}2O38 (1) has a g-Keggin structure with C2v symmetry,
and the two iron centers occupy adjacent, edge-shared octahedra, as shown
in Figure 1. UV/Vis, Mössbauer, EPR, and magnetic susceptibility data
show that two high-spin Fe3‡ centers are equivalent and antiferromagneti-
cally coupled.[26]
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Alkenes were distilled and treated with activated alumina to remove
impurities and alkyl hydroperoxide. The reaction was carried out in a glass
vial or a round-bottomed flask containing a magnetic stir bar under 1 atm
of molecular oxygen as described previously.[21] 2-Cyclohexen-1-one was
usually used as an internal standard. The homogeneous reaction solution
was periodically sampled and analyzed by gas chromatography on a TC-
WAX capillary column and by NMR spectroscopy. The amounts of oxygen
consumed were measured with a gas burette. It was confirmed for the
oxygenation of cyclooctene that no reaction proceeded without catalysts.
Turnover numbers were calculated as moles of products per mole of 1.
Cleavage of the Calkyl Caryl Bond of
[Pd CH2CMe2Ph] Complexes**
Â
Â
Juan Campora,* Enrique Gutierrez-Puebla,
Â
Jorge A. Lopez, Angeles Monge, Pilar Palma,*
Diego del Río, and Ernesto Carmona*
The cleavage and functionalization of strong C C single
bonds[1] by transition metal compounds is an important
transformation,[2±6] which is relevant to Ziegler± Natta catal-
ysis[7] and to other organometallic processes.[8, 9] Aryl elimi-
nation by activation of a b-Calkyl Caryl bond[5] is the micro-
scopic reverse of the migratory insertion of an alkene into a
M Caryl bond, a relevant step of the Heck reaction[8] and of the
SHOP process.[9] Herein we report on the conversion of a
Received: May 17, 2001 [Z17132]
[1] R. A. Sheldon, J. K. Kochi, Metal-Catalyzed Oxidations of Organic
Compounds, Academic Press, New York, 1981.
[2] Chlorohydrins: W. F. Richey, Kirk ± Othmer Encyclopedia of Chem-
ical Technology, Vol. 6, Wiley, New York, 1993, pp. 140.
[3] The Activation of Dioxygen and Homogeneous Catalytic Oxidation
(Eds.: D. H. R. Barton, A. E. Martell, D. T. Sawyer), Plenum, New
York, 1993.
[4] B. J. Wallar, J. D. Lipscomb, Chem. Rev. 1996, 96, 2625.
[5] B. Meunier, Chem. Rev. 1992, 92, 1411.
[6] J. T. Groves, R. Quinn, J. Am. Chem. Soc. 1985, 107, 5790.
[7] A. S. Goldstein, R. H. Beer, R. S. Drago, J. Am. Chem. Soc. 1994, 116,
2424.
[8] R. Neumann, M. A. Dahan, Nature 1997, 388, 353.
[9] C. L. Hill, I. A. Weinstock, Nature 1997, 388, 332.
[10] J. M. Thomas, R. Raja, G. Sanker, R. G. Bell, Nature 1999, 398, 227.
[11] R. G. Finke, H. Weiner, J. Am. Chem. Soc. 1999, 121, 9831.
[12] R. A. Sheldon, Top. Curr. Chem. 1993, 164, 22.
[13] C. L. Hill, C. M. Prosser-McCartha, Coord. Chem. Rev. 1995, 143, 407.
[14] T. Okuhara, N. Mizuno, M. Misono, Adv. Catal. 1996, 41, 113.
[15] I. V. Kozhevnikov, Chem. Rev. 1998, 98, 171.
‡
[Pd CH2CMe2Ph] moiety into the corresponding phenyl
‡
derivative, [Pd Ph] , and the subsequent functionalization of
the latter by conventional C2H4 migratory insertion chemistry
ˆ
to produce C6H5CH CH2.
‡
The cationic complex [Pd(CH2CMe2Ph)(dmpe)(PMe3)]
(1) (dmpe ˆ Me2PCH2CH2PMe2) can be generated by react-
ing the palladacycle [PdCH2CMe2-o-C6H4)(dmpe)] (2)[10] with
‡
[HPMe3] BAr4 (Arˆ 3,5-C6H3(CF3)2). At 608 C it under-
+
CH2CMe2Ph
PMe3
P
P
P
P
[HPMe3]+BAr4
BAr4
Pd
Pd
[16] N. Mizuno, M. Misono, Chem. Rev. 1998, 98, 199.
[17] C. L. Hill, Activation and Functionalization of Alkanes, Wiley, New
York, 1989, p. 243.
[18] M. T. Pope, A. Müller, Angew. Chem. 1991, 103, 56; Angew. Chem. Int.
Ed. Engl. 1991, 30, 34.
2
1-BAr4
(1)
+
P
[19] R. Neumann, Prog. Inorg. Chem. 1998, 47, 317.
[20] The TON of 26 reported in ref. [6] is still one of the highest for the
epoxidation of cis-cyclooctene with 1 atm of molecular oxygen alone.
[21] N. Mizuno, C. Nozaki, I. Kiyoto, M. Misono, J. Am. Chem. Soc. 1998,
120, 9267.
60 °C
Pd
BAr4
P
PMe3
3-BAr4
[22] B. Meunier, A. Robert, G. Pratviel, J. Bernadou, The Porphyrin
Handbook, Academic Press, New York, 2000, p. 119.
[23] The oxygenation of adamantane was carried out under the following
conditions: 1, 11 mmol; solvent, 1,2-dichloroethane/benzene ˆ 8 mL/
Â
Â
[*] Dr. J. Campora, Dr. P. Palma, Prof. Dr. E. Carmona, Dr. J. A. Lopez,
D. del Río
2 mL; adamantane, 12.4 mmol; pO , 1 atm; reaction temperature,
2
Â
Departamento de Química Inorganica-Instituto
356 K; reaction time, 118 h. The conversion was 4% and the
selectivities for 1-adamantanol, 2-adamantanol, and 2-adamantanone
were 79, 11, and 10%, respectively.
de Investigaciones Químicas
Universidad de Sevilla-Consejo Superior de Investigaciones
Científicas
C/Americo Vespucio s/n, Isla de la Cartuja
41092 Sevilla (Spain)
[24] R. A. Sheldon, J. K. Kochi, Oxidation and Combustion Reviews,
Vol. 5, 1973, p. 135; R. Neumann, M. Dahan, J. Am. Chem. Soc. 1998,
120, 11969.
[25] The amount of oxygen consumed was 1.5 mmol when the amount of
cyclooctene oxide produced was 2.9 mmol. The corresponding con-
version was 16%.
Fax : (‡34)95-4460565
E-mail: campora@cica.es
ppalma@cica.es
guzman@cica.es
[26] C. Nozaki, I. Kiyoto, Y. Minai, M. Misono, N. Mizuno, Inorg. Chem.
1999, 38, 5724.
Â
Dr. E. Gutierrez-Puebla, Dr. A. Monge
Instituto de Ciencia de Materiales
Consejo Superior de Investigaciones Científicas
Campus de Cantoblanco, 28049 Madrid (Spain)
Â
Ä
[**] This work was supported by the Direccion General de Ensenanza
Â
Superior e Investigacion Científica (Project 1FD97-0919), the Minis-
Â
terio de Educacion y Ciencia (PFPI grant to D. del Rio), and the Junta
de Andalucia. J. A. L. thanks the CONACYT and the University of
Guanajuato (Mexico) for a fellowship.
Supporting information (kinetic data and reaction rates for the
transformation 1 !3 calyzed by 4) for this article is available on the
WWW under http://www.angewandte.com or from the author.
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