Bis(trimethylsilyl) peroxide extends the range of oxorhenium catalysts for olefin epoxidation [2]

Full text of DOI:10.1021/ja973043x

11536
J. Am. Chem. Soc. 1997, 119, 11536-11537
exhibit high catalytic activity. Table 1 defines the scope of
this new process with representative substrates including fairly
unreactive olefins and/or progenitors of sensitive epoxides.9,10
With the present protocol, terminal olefins, problematic in the
original procedure,1a can be efficiently converted into the
corresponding epoxides. The work-up procedure simply in-
volves destruction of the traces of H2O2 with manganese dioxide
and evaporation of the hexamethyldisiloxane.10
We found that when water (1 equiv with respect to the olefin)
is intentionally added at the beginning of the MTO-catalyzed
epoxidation of cis-4-octene, BTSP is hydrolyzed within 10 min
(as determined by GC), and poor conversions are observed
presumably due to the sensitivity of the generated epoxidizing
species to excess water (Vide infra). In addition, a significant
amount of the diol, resulting from hydrolytic ring-opening of
the epoxide, is formed. At the other extreme, efforts to remove
all traces of water by running the process in the presence of 4
Å molecular sieves almost stopped the epoxidation catalysis.
Control experiments demonstrated that MTO is not absorbed
or inactivated by the molecular sieves under these conditions.
Similarly, very sluggish epoxidation is observed when Re2O7
Bis(trimethylsilyl) Peroxide Extends the Range of
Oxorhenium Catalysts for Olefin Epoxidation
Andrei K. Yudin and K. Barry Sharpless*
Department of Chemistry and Skaggs Institute
for Chemical Biology, The Scripps Research Institute
10550 North Torrey Pines Road
La Jolla, California 92037
ReceiVed August 29, 1997
The main goal of our research over the years has been the
development of catalytic reactions for the selective oxidation
of olefins. These endeavors led recently to a highly efficient
olefin epoxidation process.1 This new method is similar to the
earlier Herrmann epoxidation system2a-d in that both use
methyltrioxorhenium (MTO) as the catalyst source and hydrogen
peroxide as the oxidant. The crucial difference in the new
procedure is the requirement for pyridine ligands but the solvent
switch (from tert-butyl alcohol2b to methylene chloride1) also
greatly enhances the effectiveness of the pyridine-modified
rhenium catalyst. We report here on further improvements in
this epoxidation catalysis, the most significant being replacement
of the organometallic rhenium species (e.g., MTO) by cheaper
and more stable inorganic rhenium oxides (e.g., Re2O7, ReO3-
(OH), and ReO3).
Among the known organometallic oxorhenium (VII) species
(R-ReO3) capable of catalyzing olefin epoxidation, MTO ap-
pears to be the most stable with respect to oxidative and/or
hydrolytic removal of the alkyl group (Vide infra).3 Hence, cata-
lyst modification by variation of the R-substituent on the rhen-
ium center was not rewarding despite extensive efforts in the
Herrmann laboratory.2a-d,4 In addition, R-ReO3 compounds,
including MTO, are quite expensive.5 These factors provided
the incentive to seek water-free epoxidation conditions which
would hopefully extend the lifetime of the MTO catalyst. This
goal and much more was accomplished by simply replacing
aqueous H2O2 with bis(trimethylsilyl)peroxide (BTSP)6-8 as an
oxygen atom source (eq 1).
(6) (a) Cookson, P. G.; Davies, A.; Fazal, N. J. Organomet. Chem. 1975,
99, C31. (b) Taddei, M.; Ricci, A. Synthesis 1986, 633. (c) For a convenient,
large-scale (0.5 mol) preparation of BTSP from bis(trimethylsilyl)urea and
urea/H2O2 complex in dichloromethane, see: Jackson, W. P. Synlett 1990,
536. The product obtained according to this method is virtually free of
hexamethyldisiloxane, a common, albeit harmless, byproduct in cognate
BTSP preparations (see the Supporting Information for details of a 1 mol
preparation). (d) Babin, P.; Bennetau, B.; Dunogue`s, J. Synth. Commun.
1992, 22, 2849.
(7) Thermal stabilities of silylated organic peroxides have been studied:
Vesnovskii, B. P.; Thomadze, A. V.; Suchevskaya, N. P.; Aleksandrov,
Yu. A. Zh. Prikl. Khim. 1982, 55, 1005. Pure BTSP has an active oxygen
content of only 9% (cf. tert-butyl hydroperoxide, 17.8%; di-tert-butyl
peroxide, 10.9%; hydrogen peroxide, 47%).
(8) For applications of BTSP in organic synthesis, see: (a) Brandes, D.;
Blaschette, A. J. Organomet. Chem. 1973, 49, C6. (b) Brandes, D.;
Blaschette, A. ibid. 1974, 73, 217. (c) Tamao, K.; Kumada, M.; Takahashi,
T. Ibid. 1975, 94, 367. (d) Salomon, M. F.; Salomon, R. G. J. Am. Chem.
Soc. 1979, 101, 4290. (e) Adam, W.; Rodriguez, A. J. Org. Chem. 1979,
44, 4969. (f) Suzuki, M.; Takada, H.; Noyori, R. ibid. 1982, 47, 902. (g)
Weber, W. P. Silicon Reagents in Organic Synthesis; Springer-Verlag: New
York, 1983. (h) Kanemoto, S.; Oshima, K.; Matsubara, S.; Takai, K.; Nozaki,
H. Tetrahedron Lett. 1983, 24, 2185. (i) Matsubara, S.; Takai, K.; Nozaki,
H. Ibid. 1983, 24, 3741. (j) Matsubara, S.; Takai, K.; Nozaki, H. Bull. Chem.
Soc. Jpn. 1983, 56, 2029. (k) See ref 6b. (l) Hayakawa, Y.; Uchiyama, M.;
Noyori, R. Tetrahedron Lett. 1986, 27, 4195. (m) Curci, R.; Mello, R.;
Troisi, L. Tetrahedron 1986, 42, 877. (n) Kanemoto, S.; Matsubara, S.;
Takai, K.; Oshima, K.; Utimoto, K.; Nozaki, H. Bull. Chem. Soc. Jpn. 1988,
61, 3607. (o) Davis, F. A.; Lal, S. G.; Wei, J. Tetrahedron Lett. 1988, 29,
4269. (p) Olah, G. A.; Ernst, T. D. J. Org. Chem. 1989, 54, 1204. (q)
Camporeale, M.; Fiorani, T.; Troisi, L.; Adam, W.; Curci, R.; Edwards, J.
O. Ibid. 1990, 55, 93. (r) Shibata, K.; Itoh, Y.; Tokitoh, N.; Okazaki, R.;
Inamoto, N. Bull. Chem. Soc. Jpn. 1991, 64, 3749. (s) Chemla, F.; Julia,
M.; Uguen, D. Bull. Soc. Chim. Fr. 1993, 130, 547. (t) Irie, R.; Hosoya,
N.; Katsuki, T. Synlett 1994, 255. (u) Prouilhac-Cros, S.; Babin, P.;
Bennetau, B.; Dunogue`s, J. Bull. Soc. Chim. Fr. 1995, 132, 513. (v) Adam,
W.; Korb, M. N. Tetrahedron 1996, 52, 5487. (w) Adam, W.; Golsch, D.;
Sundermeyer, J.; Wahl, G. Chem. Ber. 1996, 129, 1177. (x) Barton, D. H.
R.; Chabot, B. M. Tetrahedron 1997, 53, 487. (y) Barton, D. H. R.; Chabot,
B. M. Ibid. 1997, 53, 511. (z) We recently became aware that Sundermeyer
and co-workers used BTSP for the oxidation of olefins and aromatic
hydrocarbons catalyzed by the d0-oxo- and -peroxo metal complexes:
Kleinhenz, D.; Jost, C.; Wahl, G.; Sundermeyer, J. Submitted for publication.
(9) The original MTO-based procedure (ref 1a) remains superior for the
preparation of highly acid-sensitive epoxides (e.g., indene oxide).
(10) Standard procedure for epoxidation on a 10 mmol scale in
dichloromethane exemplified for 1-decene (Table 1, entry 3). In a 25 mL
scintillation vial equipped with a magnetic stirring bar, 1-decene (1.41 g,
10 mmol) was placed followed by addition of 4 mL of dichloromethane.
To this solution was added BTSP (2.8 g, 15 mmol). The vial was immersed
into ice/water bath. After 5 min Re2O7 (24 mg, 0.05 mmol) was added
followed by 10 µL of water. The reaction turned bright yellow and was
allowed to warm to room temperature and stirred for 14 h. Disappearance
of BTSP in the course of the reaction was monitored by gas chromatography.
Upon completion, water (3 drops) was added followed by manganese dioxide
(ca. 5 mg) in order to decompose the remaining H2O2. The destruction of
H2O2 was evident by the disappearance of yellow color. The mixture was
then dried over Na2SO4. Concentration afforded 1-decene oxide (1.48 g,
94% yield) of a colorless oil. Analytically pure sample was obtained by
distillation.
In addition to MTO, readily available inorganic rhenium
oxides (e.g., Re2O7, ReO3(OH), and ReO3) were also found to
(1) (a) Rudolph, J.; Reddy, K. L.; Chiang, J. P.; Sharpless, K. B. J. Am.
Chem. Soc. 1997, 119, 6189. (b) Cope´ret, C.; Adolfsson, H.; Sharpless, K.
B. Chem. Commun. 1997, 16, 1565.
(2) For applications of MTO in organic synthesis, see: (a) Hoechst AG;
Herrmann, W. A.; Marz, D. W.; Kuchler, J. G.; Weichselbaumer, G.;
Fischer, R. W.; DE Pat. 3.902.357, 1989. (b) Herrmann, W. A.; Fischer, R.
W.; Marz, D. W. Angew. Chem., Int. Ed. Engl. 1991, 30, 1638. (c)
Herrmann, W. A.; Fischer, R. W.; Rauch, M. U.; Scherer, W. J. Mol. Catal.
1994, 86, 243. (d) Herrmann, W. A. J. Organomet. Chem. 1995, 500, 149.
(e) Al-Ajlouni, A. M.; Espenson, J. H. J. Am. Chem. Soc. 1995, 117, 9243.
(f) Pestovsky, O.; van Eldik, R.; Huston, P.; Espenson, J. H. J. Chem. Soc.,
Dalton Trans. 2 1995, 133. (g) Adam, W.; Mitchell, C. M. Angew. Chem.,
Int. Ed. Engl. 1996, 35, 533. (h) Boelow, T. R.; Spilling C. S. Tetrahedron
Lett. 1996, 37, 2717. (i) Al-Ajlouni, A. M.; Espenson, J. H. J. Org. Chem.
1996, 61, 3969. (j) Herrmann, W. A.; Correia, J. D. G.; Rauch, M. U.;
Artus, G. R. J.; Ku¨hn, F. E. J. Mol. Catal. 1997, 118, 33. (k) Espenson, J.
H.; Abu-Omar, M. M. AdV. Chem. Ser. 1997, 253, 99. (l) ARCO Chemical
Technology; Crocco, G. L.; Shum, W. P.; Zajacek, J. G.; Kesling, H. S.,
Jr.; US Pat 5.166.372, 1992.
(3) (a) For a comprehensive study on the base-induced decomposition
of MTO, see: Abu-Omar, M. M.; Hansen, P. J.; Espenson, J. H. J. Am.
Chem. Soc. 1996, 118, 4966. (b) In the presence of pyridine and H2O2,
MTO is slowly oxidized, producing pyridinium perrhenate and CH3OH:
Yudin, A. K.; Sharpless, K. B. Unpublished results.
(4) Herrmann, W. A.; Ku¨hn, F. E. Acc. Chem. Res. 1997, 30, 169.
(5) (a) Herrmann, W. A.; Ku¨hn, F. E; Fischer, R. W.; Thiel, W. R.;
Romao, C. C. Inorg. Chem. 1992, 31, 4431. (b) for the most recent, and
best, procedure, see: Herrmann, W. A. et al. In press.
S0002-7863(97)03043-6 CCC: $14.00 © 1997 American Chemical Society

Communications to the Editor
J. Am. Chem. Soc., Vol. 119, No. 47, 1997 11537
Table 1. Epoxidation of Olefins with Bis(trimethylsilyl) Peroxide
(BTSP) Catalyzed by High-Valent Oxorhenium Derivatives
Scheme 2
regenerable XOH species helps in ferrying the peroxogroup from
silicon to rhenium.11
In accord with the previous observations, additives such as
pyridines serve to prevent sensitive epoxide ring-opening by
buffering the highly acidic rhenium species.1 Notably, com-
pared to the original system, the amount of ligand necessary to
achieve the desired protection is now decreased from 12 to
0.5-1 mol % in both MTO and Re2O7-catalyzed epoxidations.13
In some instances MTO loadings can be lowered to 0.25 mol
% without affecting conversionssa manifestation of prolonged
catalyst lifetime under the present conditions.
The use of Re2O7, ReO3(OH), and ReO3 as catalyst precursors
is a particularly important feature of the present protocol.
Catalytic activities of these inorganic rhenium species for
epoxidation with H2O2 were known to be very poor.14 Gener-
ally, the high acidity of these systems does not allow epoxides
to be isolated except in special cases such as cis-cyclooctene
(which yields an epoxide which is particularly resistant to acid-
catalyzed ring opening).14e In the present system, Re oxides
are comparable and in some cases superior to MTO especially
for the epoxidation of terminal olefins and dienes. The cost of
the process can be significantly reduced by using these less-
expensive oxorhenium catalysts in combination with BTSP
which is now more available through improved preparations.6,15
We stress, however, that despite its great thermal stability BTSP
is subject to facile hydrolysis in the presence of water and acids
which results in formation of hazardous 100% H2O2.8
In summary, conditions were found under which simple
inorganic oxorhenium species act, for the first time, as efficient
olefin epoxidation catalysts. It appears that the hydrolytic
stability of MTO has been the sole reason for its superiority
over other rhenium oxides for epoxidation catalysis. In addition,
use of BTSP, which can be easily and economically prepared
on a large scale, leads to one of the simplest epoxidation
processes imaginable.
Scheme 1
is used as a catalyst for the epoxidation of 1-decene under anhy-
drous conditions (ca. 7% conversion after 2.5 h). The reaction
is dramatically accelerated upon addition of 5 mol % water.
On the basis of these observations, there appears to be a role
for a trace of water or similar protic species (e.g., CH3OH is
also effective) to enable rapid turnover of the catalytic cycle.11
The scenario shown in Scheme 1 indicates the hydrolytic
generation of free H2O2 from BTSP.
Thus, intrinsic “slow addition” of hydrogen peroxide to the
oxorhenium precursor is managed by the “proton dependent”
cycle (Scheme 1) which accomplishes transfer of the peroxo
group from Si to Re. In contrast, it is very difficult to exercise
such control in the H2O2 (aqueous or anhydrous) MTO-catalyzed
epoxidation processes; for example, slow addition of H2O2 does
not help in achieving higher conversions due to faster MTO
decomposition at lower H2O2 concentrations.12
Acknowledgment. We thank the National Institutes of General
Medical Sciences, National Institutes of Health (GM-28384), the
National Science Foundation (CHE-9531152), and the W. M. Keck
Foundation for providing financial support. Professor M. G. Finn of
the University of Virginia, Mr. J. P. Chiang, Drs. H. Adolfsson, C.
Cope´ret, P. T. Ho, and W. Pringle are thanked for many helpful
discussions.
Supporting Information Available: Experimental details (2 pages).
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JA973043X
Worthy of note, hydrolysis of BTSP to H2O2 (Scheme 1) is
the simplest of many scenarios which could explain the
requirement for protic species. In a more general way, the need
for a proton source is accommodated in Scheme 2. Here, a
(12) Ironically, MTO is stabilized at higher H2O2 concentrations:
Herrmann, W. A.; Fischer, R. W.; Scherer, W.; Rauch, M. U. Angew. Chem.,
Int. Ed. Engl. 1993, 32, 1157.
(13) The use of 12 mol % of pyridine completely arrested the reaction,
presumably due to base-mediated decomposition of MTO (see also ref 3).
(14) (a) For the epoxidation of C2-20 olefins with stoichiometric Re2O7
in the presence of pyridine, see: Union Oil Co. of California; Fenton, D.
M.; US Pat. 3,316, 279. (b) For early applications of Re2O7 in olefin/H2O2
oxidation catalysis see: duPont de Nemours and Co.; Parshall, G. W.; US
Pat. 3,657,292 and 3,646,130, 1972. (c) Warwel and co-workers found that
Re2O7 is a more effective epoxidation catalyst if the right solvent is chosen.
Their system employs 60% aqueous H2O2 in 1,4-dioxane at 90 °C and 1,2-
diols are isolated in good yields, the initially formed epoxides being unstable
in this system: Warwel, S.; Ru¨sch gen Klaas, M.; Sojka, M. Chem.
Commun. 1991, 1578. (d) Herrmann, W. A.; Correia, J. D. G.; Kuhn, F.
E.; Artus, G. R. J. Chem. Eur. J. 1996, 2, 168.
(11) In contrast to epoxidation with aqueous H2O2 where equilibrating
bis- and monoperoxo complexes are produced instantaneously upon exposure
of the catalyst to the oxidant, the reaction between equimolar amounts of
MTO and BTSP has a considerable induction period under anhydrous
conditions. We attribute this phenomenon to the necessity of “acidity build-
up” (the water molecule coordinated to the rhenium center of the bisperoxo
complex of MTO is highly acidic: Herrmann, W. A.; Fischer, R. W.; Marz,
D. W. Angew. Chem. Int. Ed. Engl. 1993, 103, 1991). Adventitious moisture
can trigger an autocatalytic decomposition of an acid-sensitive BTSP into
H2O2 and hexamethyldisiloxane. Alternatively, partial hydrolysis of BTSP
could afford Me3SiOOH which could act as an oxidant in the present system.
For the use of silyl hydroperoxides in epoxidation, see: (a) Dannley, R.
L.; Jalics, G. J. Org. Chem. 1965, 30, 2417. (b) Rebek, J.; McCready, R.
Tetrahedron Lett. 1979, 20, 4337.
(15) MTO and Re2O7 were purchased from Strem Chemicals, Inc. ReO3
and HOReO3 were purchased from Aldrich Chemical Co. For industrial
sources of rhenium, see: Peacock, R. D. The Chemistry of Technetium and
Rhenium; Elsevier: Amsterdam, 1966.