Epoxidation of olefins catalyzed by manganese(III) porphyrin in a room temperature ionic liquid

Article abstract of DOI:10.1016/S0040-4039(03)00190-4

The epoxidation of several alkenes catalyzed by (meso-tetrakis(pentafluorophenyl)porphinato) manganese(III) chloride (MnTFPPCl) was carried out in a 3:1 [bmim]PF₆ ionic liquid/CH₂Cl₂ mixed solvent. The conversion and the yield of epoxide are excellent. It was also found that [bis(acetoxy)iodo]benzene [PhI(OAc)₂] is a more efficient oxidant than PhIO. The catalyst in the ionic liquids can be recycled for several runs without substantial diminution in the catalytic activity.

Full text of DOI:10.1016/S0040-4039(03)00190-4

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 44 (2003) 2069–2071
Epoxidation of olefins catalyzed by manganese(III) porphyrin in
a room temperature ionic liquid
Zhen Li and Chun-Gu Xia*
State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics,
Chinese Academy of Sciences, Lanzhou 730000, China
Received 3 December 2002; revised 9 January 2003; accepted 17 January 2003
Abstract—The epoxidation of several alkenes catalyzed by (meso-tetrakis(pentafluorophenyl)porphinato) manganese(III) chloride
(MnTFPPCl) was carried out in a 3:1 [bmim]PF6 ionic liquid/CH2Cl2 mixed solvent. The conversion and the yield of epoxide are
excellent. It was also found that [bis(acetoxy)iodo]benzene [PhI(OAc)2] is a more efficient oxidant than PhIO. The catalyst in the
ionic liquids can be recycled for several runs without substantial diminution in the catalytic activity. © 2003 Elsevier Science Ltd.
All rights reserved.
The use of ionic liquids as solvents for a broad range of
chemical processes is potentially one of the most signifi-
cant developments in the last decade.1 In contrast to
molten salts that have very high melting points and are
highly corrosive, ionic liquids are organic salts that are
liquid under ambient conditions. Ionic liquids with
tetrafluoroborate or hexafluorophosphate ions, for
example, are considered as inert solvents in most reac-
tions. In these cases the role of the ionic liquid is mainly
to provide a polar, weakly coordinating medium for a
transition metal catalyst that additionally offers special
solubility for starting materials and products. More-
over, the use of an ionic liquid solvent allows an easy
catalyst recycle without the need of any catalyst modifi-
cation. Recently results published by Song and Roh
indicate that the use of ionic liquids is also of advan-
tage in selective oxidation reactions.2
catalyst turnovers.7 However, the difficulty in recovery
and the high cost of the catalysts outweigh these
appealing features and so far have made their applica-
tions to synthesis impractical.
This report describes the use of manganese(III) por-
phyrin 1, (meso-tetrakis(pentafluorophenyl) porphi-
nato)manganese(III) chloride, for the epoxidation of
alkenes with PhI(OAc)2 in a [bmim]PF6/CH2Cl2 mix-
ture at room temperature. We selected 1-butyl-3-
methylimidazolium hexafluorophoshate [bmim]PF6 for
our model system since this liquid is stable in the
presence of both oxygen and water. To dissolve fully
the reactants in [bmim]PF6, it was essential to add a
small volume of CH2Cl2 to the ionic liquid. The CH2Cl2
improves the solubility of the substrates and product.
The epoxidation of alkenes and hydroxylation of alke-
nes catalyzed by metalloporphyrin complexes is the
subject of many investigations. A variety of oxygen
donors such as iodosylarenes, hypochlorites, alkylhy-
droperoxides, hydrogen peroxide and periodates have
been used for these transformations.3 Homogeneous
sterically hindered metalloporphyrin catalysts, and
those containing sophisticated chiral auxiliaries, or
strongly electron-withdrawing groups can exhibit high
regio-,3b,4 stereo-,4b,c,5 and enantioselectivity,6 and high
Keywords: epoxidation; ionic liquid; manganese porphyrin.
* Corresponding author. Tel.: +86-931-8276531; fax: +86-931-
8277088; e-mail: cgxia@ns.lzb.ac.cn
0040-4039/03/$ - see front matter © 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4039(03)00190-4

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Z. Li, C.-G. Xia / Tetrahedron Letters 44 (2003) 2069–2071
Table 1. Catalytic epoxidation of different olefins with 1a
systems, it was found that the use of PhI(OAc)2 under
the same conditions led to the epoxides in higher yields
and substrate conversion.
The unchanged reactants and products were both easily
removed from the reaction mixture via extraction with
n-hexane, which is immiscible with the ionic liquid used
in this work. The brown–red oily ionic liquid phase
containing the catalyst was reused five times using
PhI(OAc)2 as oxidant. The results are shown in Table 2.
One can see from the results that the recovered catalyst
gave comparable catalytic activity. In the case of sty-
rene and cyclohexene epoxidation, both catalytic activ-
ity and selectivity fall slightly after five reuses. For
hept-1-ene, the reused catalyst shows the same
efficiency (activity and selectivity) with that of fresh
catalyst. After the catalytic reaction, the UV–vis spec-
trum of the remaining ionic liquid containing the cata-
lyst showed the presence of undecomposed MnTFPPCl
by the presence of an unchanged Soret band at 473 nm,
which indicated that the catalyst is stable during the
reaction.
Entry
1
Substrate
Styrene
Oxidant
Conversionb Yieldb (%)
(%)
PhIO
PhI(OAc)2
81
95
58
89
65c
74
57
79
74
88c
97
20c
95
66c
98
2
3
4
5
Cyclohexene PhI(OAc)2
Cyclooctene PhI(OAc)2
1-Undecene PhI(OAc)2
96
83
Hept-1-ene
PhI(OAc)2
96
97c
99
6
7
Indene
PhI(OAc)2
100c
95
1,2-Dihydro- PhI(OAc)2
naphthalene
95c
69c
a All reactions were performed in capped vials in 2 mL mixed solvent
using a 50:25:1 oxidant/substrate/catalyst ratio.
b Determined by capillary GC integration against an internal quanti-
tative standard.
In summary, we have shown that ionic liquids can be
used as solvents in the metalloporphyrin catalyzed
olefin epoxidation and that PhI(OAc)2 is an efficient
oxygen donor. The use of an ionic liquid provides for
simple recycling of the catalyst. Further research
including the determination of the epoxidation mecha-
nism involved in the [bmim]PF6 and characterization of
the kinetics is in progress. We also hope to expand the
use of this oxidation approach to amines, alcohols,
hydrocarbons, and aromatics.
c In CH2Cl2.
Epoxidations were carried out in the presence of 4
mol% of 1 with several alkenes as substrates in
[bmim]PF6/CH2Cl2 (3:1, v/v) using PhI(OAc)2 as the
oxidant at room temperature. The results obtained are
given in Table 1. It was found that when the reactions
were carried out in pure CH2Cl2, the yield of the
epoxide was lower than that in the mixed solvent
system (entries 1, 6 and 7). However, it seems that
CH2Cl2 was a better solvent for hept-1-ene epoxidation
(entry 5). Moreover, the catalyst seemed to be very
active in the epoxidation of aromatic olefins (entries 6
and 7). Although PhIO is a common oxidant, generally
used as the oxygen source in metalloporphyrin catalytic
Acknowledgements
We are grateful to the National Natural Sciences Foun-
dation of China (29773056, 29933050) for financial
support of this research.
Table 2. The recycling experiment for the epoxidation of three substrates using PhI(OAc)2 as oxidant catalyzed by MnTFP-
a
PCl in [bmim]PF6/CH2Cl2
Entry
Cycle
Yieldb (%)
Selectivity (%)
Yieldb (%)
Selectivity (%)
Yieldb (%)
Selectivity (%)
1
2
3
4
5
6
Fresh
89
94
92
90
87
84
94
97
97
92
89
88
74
75
74
72
57
56
75
76
70
84
66
65
74
78
82
82
88
86
77
79
94
90
89
88
1
2
3
4
5
a All reactions were carried out in 2 mL of [bmim]PF6/CH2Cl2 (3:1, v/v) at room temperature for 4 h with 4 mol% catalyst, 0.05 mmol substrate
and 0.1 mmol PhI(OAc)2.
b Determined by capillary GC integration against an internal quantitative standard.

Z. Li, C.-G. Xia / Tetrahedron Letters 44 (2003) 2069–2071
2071
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