Highly enantioselective epoxidation of unfunctionalized olefins catalyzed by chiral jacobsen's catalyst immobilized on phenoxy-modified zirconium poly(syrene-phenylvinylphosphonate)phosphate

Article abstract of DOI:10.1002/adsc.200900424

Chiral Jacobsen's catalyst was axially immobilized onto phenoxy-modified zirconium poly(styrene-phenylvinylphosphonate)phosphate (ZPS-PVPA). The immobilized catalysts show comparable ee values for asymmetric epoxidation of styrene and much higher ee value

Full text of DOI:10.1002/adsc.200900424

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DOI: 10.1002/adsc.200900424
Highly Enantioselective Epoxidation of Unfunctionalized
Olefins Catalyzed by Chiral Jacobsenꢀs Catalyst Immobilized on
Phenoxy-Modified Zirconium Poly(syrene-phenylvinylphos-
phonate)phosphate
Xiaochuan Zou,a Xiangkai Fu,a,* Yuedong Li,a Xiaobo Tu,a Shaodong Fu,a
Yunfei Luo,a and Xiaoju Wua
a
College of Chemistry and Chemical Engineering, Research Institute of Applied Chemistry Southwest University, Key
Laboratory of Applied Chemistry of Chongqing Municipality, Key Laboratory of Eco-environments in Three Gorges
Reservoir Region, Ministry of Education, Chongqing, Peopleꢀs Republic of China
Fax : (+86)-23-6825-4000; phone: (+86)-23-6825-3704; e-mail: fxk@swu.edu.cn
Received: June 20, 2009; Revised: November 17, 2009; Published online: December 30, 2009
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.200900424.
Abstract: Chiral Jacobsenꢀs catalyst was axially im- the absence of expensive O-coordinating axial bases
mobilized onto phenoxy-modified zirconium poly- for the asymmetric epoxidation of olefins, especially
ACHTUNGTRENNUNG(styrene-phenylvinylphosphonate)phosphate (ZPS- for the epoxidation of a-methylstyrene (conversion:
PVPA). The immobilized catalysts show comparable from 24.3% to 99.9%; ee: from 29.4% to 73.7%),
ee values for asymmetric epoxidation of styrene and which may overcome the last obstacle for the poten-
much higher ee values for a-methylstyrene (73.7% tial industry application of chiral Jacobsenꢀs catalyst.
vs. 54.0%) and indene (99.9% vs. 65.0%) than the
homogeneous Jacobsenꢀs catalyst. Moreover, the as-
synthesized catalysts are relatively stable and can be Keywords: asymmetric epoxidation of unfunctional-
recycled at least five times without significant loss of ized olefins; axially coordinated immobilization;
activity and enantioselectivity. A point worth empha- chiral Jacobsenꢀs catalyst; phenoxy-modified support;
sizing is that the heterogeneous catalysts afforded re- zirconium
poly(styrene-phenylvinylphosphonate)-
markable increases of conversion and ee values in phosphate
Introduction
tive centers[3] as well as poor performance in recycles.
Besides, almost all the asymmetric epoxidation reac-
The importance of chiral building blocks, such as opti- tions[4] catalyzed by heterogeneous Mn
ACTHUNRTGNE(GNU III) salen
cally active epoxides, for pharmaceutics and agro- complexes were in need of excess and expensive addi-
chemical synthesis accounts for the impressive titives as axial bases that made them insignificant for
amount of papers published on homogeneous Jacob- industry applications.
sen-type complexes in recent years.[1] However, such
Inorganic-organic hybrid materials have been a top-
catalysts are not easily recovered for reuse or recycle. ical object of a lot of studies because of their combin-
Consequently, the last decades have witnessed an in- ing properties of the inorganic and organic compo-
tense research effort to heterogenize chiral Jacobsen- nents.[5] These kinds of materials have the advantage
type salen MnACHTUNGTRENNUNG
(III) complexes on supports[2] in an at- of possessing a uniform distribution of functional or-
tempt to make them recyclable and to enhance their ganic groups within their framework, which allows us
stability, activity, and selectivity. Unfortunately, de- to tailor their density, chemical reactivity, and thermal
spite their excellent performance in easy separation, stability. A large number of hybrid materials with var-
the heterogeneous catalysts often suffer from de- ious chemical compositions and organic groups have
creased catalytic efficiency, which is likely due to the been well-documented, showing interesting proper-
leaching of salen Mn
and/or the inaccessibility of the reagents to the reac- are emerging, especially in the application of catalyst
(III) complexes during reaction, ties,[6] and their applications as catalysts and supports
ACHTUNGTRENNUNG
Adv. Synth. Catal. 2010, 352, 163 – 170
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Xiaochuan Zou et al.
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support for heterogenizing salen MnACTHNUTRGENUG(N III) complexes. ganic/organic molar ratio and the framework of the
Our research has, for many years, been concerned organic-inorganic hybrid ZPS-PVPA can be easily de-
with metal phosphonate chemistry for catalysts and signed and assembled to generate caves, holes, pores,
catalyst supports.[7] Recently, we have reported the micropores, channels and secondary channels with
chiral salen MnACHTUNGTRENNUNG(III) complex axially immobilized on various sizes and shapes by appropriate modification
diamine- or sulfonic groups-modified ZSPP and their process of the polystyrene part. In addition to these
catalytic epoxidation of styrene, which performed merits, the surface of the supports and the caves,
high conversion, enantioselectivity and reusability. We holes, pores, micropores, channels in the supports may
have also reported the chiral salen MnACTHNUGRTNEUNG(III) complex provide microenvironment effects different from
axially immobilized on diamine- or polyamine-modi- either pure polystyrene or inorganic supports on cata-
fied ZPS-PVPA and their use in catalytic epoxidation, lytic performance for heterogeneous asymmetric ep-
which exhibited great activity and enantioselectivity oxidation.
in the asymmetric epoxidation of unfunctionalized
olefins. Especially, in the epoxidation of a-methylstyr-
ene, both the conversion and enantiometric excess Results and Discussion
could exceed 99%. Furthermore, the immobilized cat-
alyst could be reused at least ten times without signifi- In conjunction with ongoing work in our laboratory
cant loss of activity and enantioselectivity, but excess on the heterogenization of salen Mn
and expensive addititives as axial bases are still re- in this work, chiral salen Mn(III) was axially immobi-
quired to improve the catalytic activity of immobi- lized onto phenoxy-modified zirconium poly(styrene-
lized catalysts. phenylvinylphosphonate)phosphate by the phenoxy
Herein, we extend our attempts to heterogenize groups[7b,8,9]. As illustrated in Scheme 1 and Scheme 2,
ACHTUNGTREN(NGNU III) complexes,
AHCTUNGTRENNUNG
chiral Jacobsenꢀs catalyst which was axially immobi- the chiral homogeneous catalyst salen Mn
lized on phenoxy-modified ZPS-PVPA in which inor-
ACHTUNGTRENN(UNG III) was
Scheme 1. Synthetic route for the support.
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Highly Enantioselective Epoxidation of Unfunctionalized Olefins
Scheme 2. Synthetic route for the supported catalyst.
synthesized according to the standard literature pro- micro-crystals of amorphous zirconium phosphonate,
cedures.[1]
its layer structure followed the arrangement of “order
The immobilized catalysts were characterized by in short range, but disorder in long distance”, thus the
FT-IR, DR UV-Vis, AAS, XPS, SEM, and TEM, possible structure of the heterogeneous catalysts was
which evidenced the effective salen ligand and salen deduced as shown in Figure 1.
Mn heterogenization (see Supporting Information).
The catalytic activity and selectivity of catalysts 1a–
FT-IR spectra and the DR UV-Vis spectra of catalysts 1d were explored for the asymmetric epoxidation of
of 1a–1d matched well with the expected chemical unfunctionalzed olefins using m-CPBA as an oxidant
structure of the salen MnACTHNUGTRNEUNG(III) complex. The presence system. Jacobsenꢀs catalyst and corresponding homo-
of the characteristic imine band at 1630 cmÀ1 in the geneous chiral Mn
FT-IR spectra and the broad bands at near 250, 320
and 420 nm in the diffusion reflection UV-Vis spectra
confirmed the successful anchoring of the chiral Ja-
cobsen catalyst axially coordinated onto ZPS-PVPA
ACHTUNGTNER(NUNG salen)OPh (1e) were also exam-
by phenoxy groups. The amount of salen MnACTHNUGRTNEUNG(III)
complex was 0.36–0.60 mmolgÀ1 as determined by
AAS based on the element Mn. XPS of 1d gave fur-
ther evidence for the successful immobilization based
on the fact that the characteristic peak at 642.3 eV of
Mn 2p3/2 was clear. The SEM and TEM indicated that
the diameter of the particles of the heterogeneous
catalysts 1a–1d was in the submicron range. It also
showed that the catalysts were loose and different
shapes and sizes of caves, holes, pores and channels
existed in every particle. Generally, one of the advan-
tages of the layered zirconium phosphonate is that all
the organic groups are located on the surfaces, inter-
lamellar regions and interlayer surfaces no matter
whether they are crystalline semi-crystalline or amor-
phous, which results from their self-assembled layered
structure on the nanometer scale.[7a] Actually for the Figure 1. Possible structure of the immobilized catalyst.
Adv. Synth. Catal. 2010, 352, 163 – 170
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Table 1. Asymmetric epoxidation of alkenes catalyzed by 1a–1d with m-CPBA as oxidant.[a]
Entry Substrate Catalyst
Oxidant
Temperature [8C] Conversion [% (h)][b] Selectivity [%][c] ee [%][c]
1
2
3
4
5
6
7
8
Jacobsen m-CPBA/NMO
0
0
0
0
0
0
0
99.9 (1)
98.0 (1)
98.8 (1)
99.9 (1)
92.8 (1)
99.9 (1)
24.3 (1)
74.3 (6)
99.9 (1)
98.9 (1)
87.3 (1)
99.3 (1)
95.4 (1)
99.9 (1)
25.9 (1)
76.9 (6)
99.9 (1)
99.2 (1)
98.9 (1)
98.5 (1)
96.0 (1)
99.9 (1)
32.6 (1)
99.1
99.5
56.6
58.8
54.3
60.9
57.8
62.1
98.7
99.1
91.7
94.3
92.7
96.0
95.5
96.6
99.8
98.1
98.8
99.2
97.6
>99.9
98.4
52.0[d]
49.5[d]
67.3[d]
69.9[d]
45.8[d]
73.7[d]
29.4[d]
81.4[d]
47.0[e]
45.8[e]
12.9[e]
25.8[e]
21.5[e]
31.6[e]
9.25[e]
43.4[e]
65.0[f]
63.5[f]
56.6[f]
95.5[f]
82.3[f]
99.5[f]
78.8[f]
1e
1a
1b
1c
1d
1d
1d
m-CPBA/NMO
m-CPBA
m-CPBA
m-CPBA
m-CPBA
m-CPBA/NMO
m-CPBA
À78
9
Jacobsen m-CPBA/NMO
0
10
11
12
13
14
15
16
17
18
19
20
21
22
23
1e
1a
1b
1c
1d
1d
1d
m-CPBA/NMO
m-CPBA
m-CPBA
m-CPBA
m-CPBA
0
0
0
0
0
0
m-CPBA/NMO
m-CPBA
À78
Jacobsen m-CPBA/NMO
0
1e
1a
1b
1c
1d
1d
m-CPBA/NMO
m-CPBA
m-CPBA
m-CPBA
m-CPBA
0
0
0
0
0
0
m-CPBA/NMO
[a]
Reactions were carried out at the desired temperature in CH2Cl2 (3.00 mL) with alkene (0.500 mmol), NMO (338 mg,
2.50 mmol, if necessary), nonane (internal standard, 56.0 mL, 0.500 mmol) and immobilized Mn
(0.0250 mmol, 5.00 mol%).
Conversions were determined by GC, by integration of product peaks against an internal quantitative standard (nonane),
ACHTUNGTREN(NUNG III)salen complexes
[b]
correcting for response factors.
[c]
[d]
[e]
[f]
Determined by GC with a chiral capillary column (HP19091G-B233, 30 mꢂ25 mmꢂ0.25 mm).
Expoxide configuration S.[2j]
Epoxide configuration S.[4e]
Epoxide configuration 1S,2R.[4e]
ined for comparison purposes. The results are sum- 52.0%). And the increase in ee values was mainly at-
marized in Table 1. The racemic samples of the epox- tributed to the unique spatial environment constituted
ides were independently prepared by the epoxidation by the axially rigid bulky group and the special struc-
of the corresponding alkenes with m-CPBA in CHC13 ture of ZPS-PVPA that is constituted by a large varie-
at 273 K[2j] and detected by gas chromatography ty of polystyrene segments which are hydrophobic
(GC). The conversions (with nonane as internal stan- and easily modified, as well as the zirconium phos-
dard) and ee values of epoxidation reaction were de- phate-phosphonate which is hydrophilic and has a
termined by GC with a chiral capillary column self-assembled layered structure on the nanometer
(HP19091G-B233, 30 mꢂ25 mmꢂ0.25 m). All reac- scale. Similar results were reported by Li,[10] where
tions proceeded smoothly, and the heterogeneous cat- salen MnACTHNUTRGNE(NUG III) axially immobilized on MCM-41 via
alysts showed higher ee values at the same conversion rigid phenoxy groups presented a 72.0% ee value in
level compared to the corresponding homogeneous the NaClO aqueous/organic biphasic system. The het-
Jacobsenꢀs catalyst and 1e under the same conditions erogenized catalysts also showed good catalytic activi-
with m-CPBA as oxidant system. Actually, when it ty and enantioselectivity for relatively bulkier olefins,
comes to the MnACHTNUGTRNEUNG(salen)OPh, the classic Jacobsenꢀs like indene (conversion: 99.9%; ee: 99.5%). This indi-
catalyst afforded somewhat higher ee values at equal cated that the active sites in the caves, holes, pores,
conversions; this proved that the linker OPh plays a microporous, and channels of ZPS-PVPA also could
minor role to the same degree as in the homogeneous be accessed readily by the bulkier reactant. However,
system.
in the case of styrene, the enantiomeric excess values
When a-methylstyrene was used as substrate with (9.25–43.4%) were not encouraging.
immobilized catalysts 1a–1d, there was a significant
It was also found that the conversions and the
improvement in enantioselectivity (67.3–81.4% vs. enantioselectivity increased with increasing linkage
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Highly Enantioselective Epoxidation of Unfunctionalized Olefins
lengths. Similar results were obtained by Li[11] so the amine-modified organic-inorganic hybrid support
results might be due to the active intermediates of ZPS-PVPA by our group.[7b] Actually, the axial coor-
salen Mn(V) immobilized salen MnACTHNUTRGNE(NUG III) complexes dinating group for the immobilized catalysts 1a–1d in
which may attack the substrate more expediently with this paper is the phenoxy linker group which has simi-
increasing linkage lengths. Whereas, in the case of 1c, lar properties in electronic structure and coordination
there was a slightly decrease in conversion and ee performance with O-coordinating axial bases such as
values (entries 5, 13, 21), The proper reason could be NMO (N-methylmorpholine N-oxide). Therefore, it is
that the location between support and salen MnACTHUNRTGNEUNG(III) deduced that these observations are caused by both
was so close that it led to a twist against each other, organic-inorganic hybrid support ZPS-PVPA and the
shielding and interfering with their active catalytic phenoxide axial coordinating group, for which, not a
centers and lowering their catalytic performance. For single one can be dispensed with. The O-coordinating
all the substrates, enantiomeric excess values in- axial bases additive may interfere with the well-de-
creased and conversions slightly decreased with de- fined molecular geometry and conformation of the
creasing temperature (entries 8, and 16). The reason chiral MnACTHNUGRTENUNG(III) salen complex of the immobilized cata-
should be attributed to both an increase in enantiofa- lysts 1d, when it is added to the heterogeneous
À
cial selectivity in the initial C O bond-forming step system, thus decreasing the conversion and chirality
and suppression of the trans-pathway in the second recognization. Further studies concerning the mecha-
step at low temperature.[11]
nism of this novel behaviour for these immobilized
In addition, it is interesting to find out here that re- catalysts are currently in progress.
markably increases of conversion and ee values were
To study the recyclability of the heterogeneous cat-
obtained in the absence of expensive O-coordinating alyst and the leaching of the metal complex from the
axial bases for the asymmetric epoxidation with the immobilized catalyst during the epoxidation of ole-
heterogeneous catalyst 1d, especially for the epoxida- fins, we applied catalyst 1d in repeated epoxidation
tion of a-methylstyene (conversion: from 24.3% to reactions with a-methylstyrene as a model substrate.
99.9%; ee: from 29.4% to73.7%; entries 6 and 7), sim- At the end of each cycle, the catalyst was precipitated
ilar results were also obtained for styrene (entries 14 from the reaction system by adding hexane and subse-
and 15) and indene (entries 22 and 23). These obser- quently used in the next runs without further purifica-
vations are not in agreement with other literature re- tion. The filtrate showed no trace of the metal com-
ported earlier for both homogeneous and heterogene- plex on UV-Vis and by AAS after the first run, which
ous systems, where O-coordinating axial bases are indicated that the salen MnACTHUNRTGNEUNG(III) complex was strongly
rather essential for catalyst stability and enantioselec- bonded on the phenoxy-modified ZPS-PVPA sup-
tivity.[12] These observations are also not in accord- ports. The data in Table 2 showed only a slightly de-
ance with heterogeneous salen MnACTHNUGRTENUNG(III) catalysts axial- crease in activity and enantioselectivity for the first
ly coordinatively immobilized on diamine- or poly- five runs (conversion: from 99.9% to 93.8%; ee: from
Table 2. The recycling of immobilized catalyst in the asymmetric epoxidation of a-methylstyrene with m-CPBA as oxidant.[a]
Entry
Cycle
Catalyst
Oxidant
Temperature [8C]
Conversion [% (h)][b]
Selectivity [%][c]
ee [%][c,]
1
2
3
4
5
6
7
8
Fresh
2
3
4
5
6
7
8
1d
1d
1d
1d
1d
1d
1d
1d
1d
1d
1d
m-CPBA
m-CPBA
m-CPBA
m-CPBA
m-CPBA
m-CPBA
m-CPBA
m-CPBA
m-CPBA
m-CPBA
m-CPBA
0
0
0
0
0
0
0
0
0
0
0
99.9 (2)
99.9 (2)
98.5 (2)
95.5 (2)
93.8 (2)
88.8 (2)
85.8 (3)
77.8 (3)
70.1 (4)
67.8 (4)
43.6 (5)
60.9
61.2
59.5
57.6
57.3
53.2
52.8
50.2
50.0
43.7
39.9
73.7[d]
72.1[d]
73.1[d]
69.5[d]
67.5[d]
65.2[d]
63.7[d]
60.5[d]
55.8[d]
54.2[d]
53.4[d]
9
10
11
9
10
11
[a]
Reactions were carried out at the desired temperature in CH2Cl2 (3.00 mL) with alkene (0.500 mmol), NMO (338 mg,
2.50 mmol, if necessary), nonane (internal standard, 56.0 mL, 0.500 mmol) and immobilized Mn
(0.0250 mmol, 5.00 mol%).
Conversions were determined by GC, by integration of product peaks against an internal quantitative standard (nonane),
correcting for response factors.
ACHTUNGTREN(NUNG III)salen complexes
[b]
[c]
[d]
Determined by GC with a chiral capillary column (HP19091G-B233, 30 mꢂ25 mmꢂ0.25 mm).
Expoxide configuration S.[2j]
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73.7% to 67.5%). Further recycles of the heterogene- metric epoxidation of olefins, especially for the epoxi-
ous catalyst resulted in poor conversions; however, dation of a-methylstyrene (conversion: from 24.3% to
still a higher enantioselectivity than that of the homo- 99.9%; ee: from 29.4% to 73.7%). To the best of our
geneous counterpart was obtained even after eleven knowledge, there are no other reports on the asym-
runs. The good performance of these heterogeneous metric epoxidation generating the products in very
catalysts with regard to ees maybe mainly due to their good conversions and excellent enantioselectivities
novel support, combining properties of the inorganic under mild conditions without using any additives in
and organic components. The microenvironment[13] of the salen Mn
ACTHNUTRGNEU(GN III) system, which may overcome the
ZPS-PVPA for asymmetric epoxidation consisted of last obstacle for wide application in organic synthesis
polystyrene parts which are hydrophobic and the as well as in industry of chiral Jacobsenꢀs catalyst.
hybrid zirconium phosphonate parts which are hydro-
philic and their self-assembled layered structure on
the nanometer scale. A large number of polystyrene Experimental Section
segments exist in ZPS-PVPA, which are folding, have
a curl assignment, parallel, crossing, coinciding, or Preparation of Homogeneous Chiral Jacobsenꢀs
even twining, combined with the layered zirconium Catalyst
phosphonate-phosphate all lead eventually to form
Chiral Jacobsenꢀs catalyst were synthesized according to the
different caves, holes, pores, micropores, channels and
secondary channels with various sizes and shapes, and
their threshold effect giving rise to their excellent cat-
alytic properties. Generally, layered zirconium phos-
phonate is relatively stable, while the layered struc-
ture maybe destroyed under some extreme conditions
such as base solutions. However, the virgin layered
structure and channels, holes and caves could be
roughly recovered in standing under aqueous phase
conditions which is helpful to carry out self-assembly
for layered zirconium phosphonate. Hence, these
kinds of heterogeneous catalysts have the singular ad-
vantage of recyclability. The decrease in the activity
for more cycles might be caused by a physical loss
standard literature procedures.[1]
Preparation of Homogeneous Chiral Mn
Complex (1e)[2j]
ACHTUNGTRENUN(NG salen)OPh
MnACTHNUGRTENUNG(III) salenC1 (1.56 g, 2.56 mmol) and PhONa (0.359 g,
3.09 mmol, 1.2 equiv-) were added in ethanol (60.0 mL), and
the mixture was refluxed for 5 h at 808C (Scheme 2). After
cooling to room temperature, ethanol was removed, CH2Cl2
was added, and the organic phase was washed with distilled
water. Then it was washed with saturated NaCl solution and
dried over anhydrous Na2SO4. Removal of the CH2Cl2 gives
the brown-dark solid Mn
80.0%.
ACHTUNGTNER(NUNG III)salenOPh complex; yield:
during the recovery process and/or by a gradual Preparation of ZPS-PVPA
degradation of the catalysts under the epoxidation
conditions and continuous stirring.
The synthesis and characterization of ZPS-PVPA have been
reported early by our group.[7b]
Preparation of ZHPS-PVPA (4a)
Conclusions
ZPS-PVPA (6.00 g, 8.55 mmol) was added to ethanol
(80.0 mL) containing concentrated sulfuric acid (3.44 g,
35.0 mmol) and catalyst FeCl3·6H2O (132 mg, 0.488 mmol)
and this suspension was stirred for 30 min at 508C. Then
H2O2 (13.2 mL) was added to the mixture and the mixture
was stirred for an additional 20 h. The solid was filtered and
washed with ethanol and deionized water until neutrality to
give ZHPS-PVPA; yield: 86.0%.
In summary, phenoxy-modified organic-inorganic
hybrid support-zirconium poly(styrene-phenylvinyl-
phosphonate)-phosphate has been synthesized and
characterized for the first time, which was used for
immobilization of chiral Jacobsenꢀs homogeneous cat-
alyst. Comparing the heterogeneous catalysts with the
corresponding homogeneous catalyst and other heter-
ogeneous catalysts known from the relevant literature,
the as-synthesized heterogeneous catalysts showed
comparable or even higher conversions and enantio-
selectivities, which was mainly attributed to the spe-
cial structure of ZPS-PVPA. Moreover, the heteroge-
neous catalyst could be conveniently separated from
the reaction system by simple precipitation in hexane
and be recycled at least five times with insignificant
loss of ee and activity. Especially, it was found here
that the heterogeneous catalysts afforded remarkably
increases of conversion and ee values in the absence
of expensive O-coordinating axial bases for the asym-
Preparation of ZCMPS-PVPA (3)
Chloromethyl methyl ether (9.30 mL), anhydrous zinc chlo-
ride (1.92 g, 14.2 mmol) and ZSP-PVPA (6.00 g, 8.55 mmol)
were mixed and stirred at 458C for 8 h. After cooling, a
small amount of water and methanol was added into the
mixture, which was filtered, washed with methanol and ace-
tone and dried under vacuum to afford ZCMPS-PVPA;
yield: 90.0.%.
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Highly Enantioselective Epoxidation of Unfunctionalized Olefins
References
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(4b–4d)
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(20.0 mL) (the molar ratio of diphenol to chlorine element
in ZCMPS-PVPA is 5:1), and the mixture was kept at 808C
for 24 h under N2. After the reaction, the resin-like product
was filtered and washed with substantive amounts of deion-
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Preparation of ZHPS-PVPA-[Mn
(1a)
ACHTUNGTREN(NUNG III)salen Complex]
A mixture of MnACHTUNGTRENNUNG(salen)Cl (2.73 g, 4.30 mmol), ZHPS-PVPA
(0.50 g) and sodium hydroxide (0.150 g, 3.75 mmol) was
added to tetrahydrofuran (80.0 mL) and this suspension was
stirred for 20 h under reflux. The mixture was then filtered,
washed thoroughly with ethanol, CH2Cl2 and deionized
water, respectively, to produce 1a as a dark brown powder
that was dried under vacuum. The CH2Cl2 filtrate was exam-
ined by UV-Vis until no peaks could be detected (with
CH2Cl2 as reference). Yield: 90.0%.
Preparation of Phenoxy-Modified ZCMPS-PVPA-
[MnACHTUNGTRENNUNG(III)salen Complex] (1b–1d)
A solution of chiral salen MnACHTNUTRGNE(UNG III) (2.73 g, 4.30 mmol), phen-
oxy-modified ZCMPS-PVPA (4b–4d) (0.50 g) and an adequate
amount of sodium hydroxide in tetrahydrofuran (50.0 mL) was
vigorously stirred for 24 h under reflux. The dark brown
powder was collected by filtration and washed thoroughly with
ethanol, CH2Cl2 and deionized water, respectively, and dried
under vacuum. The CH2Cl2 filtrate was examined by UV-Vis
until no peaks could be detected (with CH2Cl2 as reference).
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A
solution of alkene (0.500 mmol), NMO (338 mg,
2.50 mmol, if necessary), nonane (internal standard,
56.0 mL, 0.500 mmol) and immobilized Mn(III)salen com-
AHCTUNGTRENNUNG
plexes (0.0250 mmol, 5%, based on the Mn amount in the
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Acknowledgements
The financial support from the Committee for Economics of
Chongqing Municipality (grant 2008-65) is gratefully ac-
knowledged.
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