Novel chiral sulphonato-salen-manganese(III)-pillared hydrotalcite catalysts for the asymmetric epoxidation of styrenes and cyclic alkenes

Article abstract of DOI:10.1002/adsc.200505244

A novel chiral sulphonato-salen-manganese (III) complex has been prepared and intercalated into a Zn-Al layered-double hydroxide (LDH) structure. The resulting catalyst was found to be highly active and enantioselective in the epoxidation of various styre

Full text of DOI:10.1002/adsc.200505244

FULL PAPERS
DOI: 10.1002/adsc.200505244
Novel Chiral Sulphonato-Salen-Manganese(III)-Pillared
Hydrotalcite Catalysts for the Asymmetric Epoxidation of
Styrenes and Cyclic Alkenes
Samiran Bhattacharjee, James A. Anderson*
Surface Chemistry and Catalysis Group, Department of Chemistry, Meston Walk, Aberdeen, AB 24 3UE, Scotland, UK
Fax: (þ44)-1224-272-921, e-mail: j.anderson@abdn.ac.uk
Received: June 13, 2005; Accepted: October 7, 2005
Abstract: A novel chiral sulphonato-salen-manganese styrene was converted with 62% ee and 70% selectiv-
À1
(
III) complex has been prepared and intercalated into ity with a TOF of 327 h . In the case of styrenes and
a Zn-Al layered-double hydroxide (LDH) structure. cyclic alkenes, TOF decreased as follows: a-methyl-
The resulting catalyst was found to be highly active styrene>4-methylstyrene>styrene and 1-methyl-1-
and enantioselective in the epoxidation of various cyclohexene>1-phenyl-1-cyclohexene>cyclohexene.
styrenes and cyclic alkenes when using a combination The catalyst could be recycled without detectable loss
of pivalaldehyde and molecular oxygen at atmospher- of efficiency.
ic pressure and room temperature. At 94% conver-
sion, 1-methyl-1-cyclohexene could be converted to Keywords: asymmetric epoxidation; chiral salen-man-
epoxide with 68% ee and 90% selectivity with a turn- ganese(III); heterogeneous catalysis; immobilization;
À1
over frequency (TOF) of 234 h , whereas 4-methyl- LDH host catalyst
Introduction
by simple phase separation techniques at room tempera-
ture. Ease of separation of the catalyst when it is in a
[
6,7]
Epoxides are importantintermediates for the synthesis of different phase from the reactants/products is also a driv-
complex molecules which find use in fine chemical syn- er for the heterogenisation of such a system. Various de-
thesis. Asymmetric epoxidation of prochiral alkenes grees of success have been achieved by attaching the ac-
[
8]
presents a powerful strategy for the synthesis of enantio- tive chiral salen system to zeolites, to polystyrene and
[
9]
merically enriched epoxides. In the past two decades polymethacrylate resin (polymer supported), to silica
[
10]
there has been great progress in catalytic asymmetric al- via chloropropyl spacers, metallated with manganese[
11]
kene epoxidation. Important contributions have been andusingorgano-functionalisedmesoporousmaterials
[
1]
[2–4]
made using Sharpless and Jacobsen/Katsuki
sys- as well as in the subsequent testing of the anchored sys-
[12]
tems. Chiral salen-Mn(III) complexes (Jacobsenꢀs cata- tems in the epoxidation of alkenes. Kureshy et al. re-
lyst) show high enantioselectivities in the epoxidation ported on dicationic chiral Mn (III) complexes immobi-
of unfunctionalised alkenes under homogenous condi- lised between the layers of montmorillonite clay. Subse-
[5]
tions. Despite high activity, selectivity and chiral induc- quent testing of their catalyst in the epoxidation of non-
tion, this system has several disadvantages including the functionalised alkenes using NaOCl as oxidant gave a
use of sodium hypochlorite as oxidant, use of chlorinated highereeforcertainalkenesthanthatfoundunderhomo-
[
13,14]
solvents and the difficulty in recovering the catalyst after geneous conditions. Recently, Li and co-workers
[
6,7]
use. Cavazzini et al. reported that sterically hindered demonstrated that chiral salen-Mn(III) catalyst when ax-
chiral salen-Mn(III) complexes containing long perfluoro- ially immobilised into MCM-41 through complexation of
alkyl substituents showed similar ee and yield using cer- the manganese via the oxygen atoms of the phenoxy
[
13]
tain alkenes (indene, 1-methylindene, 1-methylcyclohex- groups produced epoxide with 72% ee, whereas the
ene, triphenylethylene, benzosuberene and 1,2-dihydro- same complex immobilised via a phenylsulphonic
[
14]
naphthalene) employing fluorousbiphasic conditions un- group gave a slightly higher ee value for the epoxida-
der equivalent oxidizing conditions using PhIO/pyridine tion of a-methylstyrene. These phenoxy or phenylsul-
N-oxide when compared with standard homogeneous phonic group-anchored catalysts showed significantly
Mn-salen complexes. The advantage was that the cata- higher % ee than the homogenous analogues (56% ee)
[
13,14]
lysts could be readily recovered from the fluorous layer for a-methylstyrene epoxidation.
Adv. Synth. Catal. 2006, 348, 151 – 158
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151

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Samiran Bhattacharjee, James A. Anderson
Hydrotalcites, due to their high surface area, homoge- ideal methodologies would be based upon the direct use
neous cation site distribution, basicity and anion ex- of oxygen or air as oxidant. The present paper deals with
change capacity, find use in many catalytic applications. the synthesis of a new LDH, [Zn2.15Al0.86(OH)6.02
Examples of these include catalysed reactions such as [Mn(Cl)salen]0.19[C H COO] ·2 H O as well as a
]
6
5
0.48
2
[
15]
[16]
[17]
Knovenagel, Micheal, Claisen–Schmidt, aldoli- study of its performance as a heterogeneous catalyst in
sations, and in hydrogenation of aromatics as well as the epoxidation of a-methylstyrene, 4-methylstyrene,
in selective oxidation reactions and in the Baeyer– styrene, 1-methyl-1-cyclohexene, 1-phenyl-1-cyclohex-
[18]
[
19]
[
20]
Villiger oxidation of ketones.
Recent advances in ene and cyclohexene using a combination of pivalalde-
the pillaring of hydrotalcite by polyoxometallate anions hyde/molecular oxygen at atmospheric pressure as oxi-
have demonstrated that these materials may exhibit suf- dant. Intercalated systems containing chiral salen-man-
ficiently large gallery heights toallow catalytic oxidation ganese(III) complexes for the epoxidation of these mol-
[
21]
of relatively large organic compounds including the ecules have not been previously reported.
shape-selective epoxidation of alkenes by changing the
[
22]
size of intercalating species. A tungstate-exchanged,
layered double hydroxide was found to show excellent Results and Discussion
catalytic activity in oxidative bromination and bro-
mide-assisted epoxidation reactions and displayed The preparation of chiral (sulphonato)-manganese(III)
over 100 times greater activity than its homogeneous an- and its LDH compound LDH-[Mn(Cl)salen], is out-
[23]
alogue. LDH-OsO catalysts have been shown to dis- lined in Scheme 1. The chiral Schiff base ligand (abbre-
4
play good performance in the asymmetric dihydroxyla- viated as 1; Scheme 1) was prepared by refluxing two
[24]
[25]
tion of olefins. It was recently reported that the equivalents of sodium salicylaldehyde-5-sulphonate
chiral sulphonato-salen-manganese(III) complex, and (R,R)-1,2-diammoniumcyclohexane mono-(þ)-tar-
II
III
Na [Mn(Cl)salen], intercalated into a Zn -Al layered trate in a water-ethanol medium. In aqueous solution,
2
double hydroxide showed high conversion, selectivity the chiral salen ligand, 1, instantly reacts with mangane-
and de in the oxidation of R-(þ)-limonene using 75– se(II) acetate tetrahydrate to produce the dianionic
1
50 psi of molecular oxygen and pivalaldehyde as sacri- compound, Na [Mn(OAc)salen] (2) in 95% yield. The
2
ficial aldehyde. Later it was shown that this LDH- acetyl ligand in 2 was readily replaced by chloride at
[
26,27]
[
Mn(Cl)salen] catalyst
showed higher conversion, room temperature by reaction with NaCl solution to
2
À
selectivity and de % for R-(þ)-limonene and (À)-a- give 3 with good yield (97%). The [Mn(Cl)salen] ion
pinene epoxidation under atmospheric pressure of air was intercalated into the zinc(II)-aluminium(III) lay-
[
28]
or dioxygen, compared with published data for other ered double hydroxide at room temperature by reaction
heterogenised Mn-salen catalysts. The catalytic activi- in aqueous medium between LDH-[C H COO] and
ties and mechanism of the epoxidation of alkenes by [Mn(Cl)salen] , by ion exchange of the benzoate ion.
LDH-[Mn(Cl)salen] catalyst along with the preparation The apparent equilibrium constant for the exchange
of other new layered double hydroxide containing salen- process was calculated as 0.0461 at 298 K. The
6
5
2
À
2
À
metal complexes are currently being pursued to develop [Mn(Cl)salen]
and LDH-[Mn(Cl)salen] (4) were
a better understanding of the parameters influencing the characterised by FTIR, TGA, UV-visible, X-ray powder
[
29]
[30]
selectivity of the oxidation products. Although the diffraction and elemental analysis. The X-ray powder
system described in the present work makes effective diffraction patterns of LDH-[C H COO] and LDH-
6
5
use of the sacrificial aldehyde (2:1 molar ratio with sub- [Mn(Cl)salen] showed that the basal spacing of the
strate) and in situ preparation of the peracid is a distinct LDH was increased from 15.22 to 18.78 Š following
advantage over the use of externally produced oxidant, the exchange process. The gallery height of the catalyst
Scheme 1. Preparation of chiral sulphonato-manganese (III) and the LDH-hosted catalyst.
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Chiral Sulphonato-Salen-Manganese(III)-Pillared Hydrotalcite Catalysts
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[
Mn(Cl)salen] also provide supporting evidence for
the successful incorporation of the complex into the
[
27]
LDH-host. The UV-visible (nujol mull) spectrum of
the catalyst showed similar features as the free complex,
indicating that during intercalation, no change in the lo-
cal environment of the manganese(III) coordination
centre took place.
The epoxidation of a-methylstyrene, 4-methylstyr-
ene, styrene, 1-methyl-1-cyclohexene, 1-phenyl-1-cyclo-
hexene and cyclohexene were studied over the LDH-
[
Mn(Cl)salen catalyst] at room temperature in the pres-
ence of dioxygen and pivalaldehyde using toluene as sol-
vent. The reactions are expressed by Eqs. (1) and (2)
(
Scheme 2) and the results summarised in Tables 1–3.
Scheme 2. LDH-hosted Mn-salen-catalysed epoxidation of
cyclic alkenes and styrenes in the presence of pivalaldehyde. An example of the reaction profile is shown in Figure 1
which shows the conversion of 4-methylstyrene and se-
lectivity to epoxide. Results indicate that the selectivity
to epoxide remained fairly constant at ca. 70% even as
is 14.1 Š when the thickness of the brucite layers (4.7 Š) the substrate underwent conversion in the range of 70
was subtracted. Similarity between the FTIR bands and to 90% conversion. During this period, the ee remained
2
À
intensities in the free [Mn(Cl)salen]
and LDH- constant also at 62% (not shown).
[
Mn(Cl)salen] compounds, and in particular, the pres-
Blank tests under identical reaction conditions re-
À1
ence of bands at 1116 and 1032 cm due to vibrations vealed that no epoxide was formed using a-methylstyr-
À1
of the sulphonato group and at 573 cm for n(MnÀO) ene, 4-methylstyrene, styrene, 1-methyl-1-cyclohexene
of the intercalated catalyst 4, qualitatively confirm the and 1-phenyl-1-cyclohexene either when catalyst was
2
À
presence of the [Mn(Cl)salen] compound in the lay- absent or when LDH-[C H COO] alone was added. Cy-
6
5
ered double hydroxide. Elemental analysis of LDH- clohexene was the one exception, being oxidized very
[
Mn(Cl)salen] is consistent with the unit formula slowly (5.5% conversion) after 6 h by dioxygenin the ab-
[
2
Zn2.15Al0.86(OH)6.02][Mn(Cl)salen]0.19[C H COO]
H O. TGA profiles for [Mn(Cl)salen] and LDH- conditions.
2
·
sence of catalysts but under otherwise identical reaction
6
2
5
0.48
À
[a]
Table 1. Epoxidation of a-methylstyrene, 4-methylstyrene, styrene, 1-methyl-1- cyclohexene, 1-phenyl-1-cyclohexene and cy-
clohexene.
[
c]
Alkene
Time [h]
Conversion [%]
91
Epoxide selectivity [%]
70
ee [%]
TOF
[d]
2.5
28
360.2
[
[
[
d]
e]
d]
3
6
4
.0
.0
.0
94
71
94
70
88
90
62
18
68
327.1
121.8
234.2
[
b]
6
6
.0
.0
93
86
74
27
165.0
121.2
[
f]
84.0
NC
[
[
[
[
[
[
a]
b]
c]
d]
e]
f]
Reaction conditions: ca. 1 mmol, 2 mmol pivalaldehyde, 10 mL toluene, 0.05 g catalyst, 14.5 psi molecular oxygen at 298 K.
Also performed at 358 K, 2 h reaction time and 100 psi dioxygen: conversion, 100%; selectivity, 81%; ee, 67%.
À1
Turnover frequency calculated by the expression [mol product/h ]/[mol metal catalyst].
Not determined.
Epoxide configuration S.
NC, achiral.
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Samiran Bhattacharjee, James A. Anderson
[a]
Table 2. Performance of reused catalyst in the epoxidation of a-methylstyrene, 4-methylstyrene and styrene.
Run
Alkene
Time [h]
Conversion [%]
Epoxide selectivity [%]
ee [%]
1
2
3
1
2
3
1
2
3
a-Methylstyrene
a-Methylstyrene
a-Methylstyrene
4-Methylstyrene
4-Methylstyrene
4-Methylstyrene
Styrene
2.5
2.5
2.5
6.0
6.0
6.0
3.0
3.0
3.0
91
91
90
94
95
93
71
70
70
70
69
69
70
71
70
88
88
87
28
27
27
62
61
62
18
18
18
Styrene
Styrene
[
a]
Reaction conditions: ca. 1 mmol, 2 mmol pivalaldehyde, 10 mL toluene, 0.05 g catalyst, 14.5 psi molecular oxygen at 298 K.
[a]
Table 3. Performance of reused catalyst in the epoxidation of 1-methyl-1-cyclohexene, 1-phenyl-1-cyclohexene and cyclohex-
ene.
Run
Alkene
Time [h]
Conversion [%]
Epoxide selectivity [%]
ee [%]
1
2
3
1
2
1
2
3
1-Methyl-1-cyclohexene
1-Methyl-1-cyclohexene
1-Methyl-1-cyclohexene
1-Phenyl-1-cyclohexene
1-Phenyl-1-cyclohexene
Cyclohexene
4.0
4.0
4.0
6.0
6.0
6.0
6.0
6.0
94
93
93
93
93
84
83
83
90
89
90
86
86
74
74
73
68
67
67
27
26
–
Cyclohexene
Cyclohexene
–
–
[
a]
Reaction conditions: ca. 1 mmol, 2 mmol pivalaldehyde, 10 mL toluene, 0.05 g catalyst, 14.5 psi molecular oxygen at 298 K.
oxide was only slightly affected as a result of the reduced
selectivity whereas the ee was effectively the same under
both sets of conditions. The reaction profile for 1-meth-
yl-1-cyclohexene as a function of time is shown in Fig-
ure 2. Between 60 and 95% conversion, the selectivity
to epoxide remained fairly constant dropping from 92
to 90%. The ee was also only marginally affected with
a drop from 70 to 68% over this same conversion range
(
not shown). The presence of the methyl group in 1-
methyl-1-cyclohexene was significant in terms of influ-
encing both activity and selectivity as shown by compar-
ing results with those for cyclohexene. Under identical
reaction conditions (298 K and 14.5 psi of molecular
oxygen), epoxidation of cyclohexene gave a TOF that
was almost half the magnitude while epoxide selectivity
was reduced from 90 to 74% (Table 1). However, when
compared in the asymmetric epoxidation of 1-methyl-1-
cyclohexene and 1-phenyl-1-cyclohexene at atmospher-
ic pressure of dioxygen and at 298 K, the former afford-
ed much higher enantiomeric excess and TOF than the
latter (Table 1) although no significant loss in epoxide
selectivity was found. The reason for this unexpected
Figure 1. Conversion of 4-methylstyrene and selectivity to
epoxide as a function of time at 298 K, 14.5 psi oxygen pres-
sure.
The asymmetric epoxidation of 1-methyl-1-cyclohex- negative effect on ee in case of 1-phenyl-1-cyclohexene
ene was tested using LDH-[Mn(Cl)salen] catalyst, at at- is unclear at present. The fact that the TOF for the bulky,
mospheric pressure of dioxygen and at 298 K as well as phenyl-substituted cyclohexene was greater that the cy-
at a higher pressure (100 psi) and temperature clohexene itself, suggests that mass transport did not dic-
(
358 K). Although at higher temperature and pressure tate the relative rates of reaction shown in Table 1 and
the reaction rate was increased, the overall yield of ep- Figure 1.
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Chiral Sulphonato-Salen-Manganese(III)-Pillared Hydrotalcite Catalysts
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À1
Figure 3. Comparison of TOF (h ) of: (a) cyclohexene, (b)
styrene, (c) 1-phenyl-1-cyclohexene, (d) 1-methyl-1-cyclohex-
ene, (e) R-(þ)-limonene, (f) (À)-a-pinene, (g) 4-methylstyr-
ene, and (h) a-methylstyrene, over LDH hosted Mn-salen
catalyst.
Figure 2. Conversion of 1-methyl-1-cyclohexene and selectiv-
ity to epoxide as a function of time at 298 K and 14.5 psi oxy-
gen pressure.
The epoxidation of styrenes was carried out under the styrenes than for methyl-substituted cyclic alkenes. It
identical conditions as for the cyclic alkenes. Among the was recently shown that a-pinene showed a slightly
[
27]
three substituted styrenes, and in terms of the enantio- higher TOF than R-(þ)-limonene under identical re-
meric excess, 4-methylstyrene produced the best results action conditions as used for styrenes and cyclic alkenes
giving epoxide with 62% ee compared to 28 and 18% for (Figure 3). The TOF followed the order: cyclohexene¼
a-methylstyrene and styrene, respectively. In terms of styrene<1-phenyl-1-cyclohexene<1-methyl-1-cyclo-
double bond activation, methyl substitution either in hexene<R-(þ)-limonene<a-pinene<4-methyl-
the para (4) or a-positions both led to greater reaction styrene<a-methylstyrene. The results indicate that the
rates. The turnover frequency (TOF) was increased as electron-donating methyl group when directly bonded
follows: styrene<4-methylstyrene<a-methylstyrene.
to the alkene functionality, or located in a position which
A comparison of TOFis shown in Figure 3 for the styr- would lead to ring activation, significantly enhances the
enes and cyclic alkenes. For the cyclic alkenes, reaction nucleophilicity of the double bond, thereby increasing
rate could also be increased by methyl substitution as in- the rate of epoxidation.
dicated in Figure 3 where the TOF was increased in the
While using relatively simple, methyl-substituted styr-
order cyclohexene<1-phenyl-1-cyclohexene<1-meth- enes and cyclic alkenes, it is possible to assume that ster-
yl-1-cyclohexene. The relative TOFof the LDH catalyst ic factors, or rather differences in steric factors as a con-
in the epoxidation of styrenes and cyclic alkenes showed sequence of major structural dissimilarities, are not re-
that the catalytic activity was clearly dependent on the sponsible for the range of substrate activities and that
nature of the substrate. It is interesting to note that the electronic effects are largely responsible for the range
styrene (external double bond) and cyclohexene (inter- of TOFs observed. However, in terms of ee, it is expect-
nal double bond) showed almost the same TOF under ed that the structure of the substrate molecule in the vi-
identical conditions (Table 1). However, when both cinity of the alkene double bond will be largely respon-
functional groups were present such as in R-(þ)-limo- sible for dictating the chirality of the resulting product.
nene, the internal double bond was selectively epoxi- The nature of the bulky ligand groups surrounding the
[
26,27]
dised,
bond epoxidation was increased by the phenyl group role as summarised in literature findings as follows.
with respect to a cyclohexene ring. The catalytic activity The analogue of Jacobsenꢀs catalyst lacking the bulky
of styrene (external double bond) and nitrochromene tert-butyl ligands in the 3 and 5 positions on the phenyl
internal double bond) using an analogue of Jacobsenꢀs unit, under homogeneous and heterogeneous (encapsu-
indicating that the rate of external double catalyst active centre is also expected to play a major
(
[
31]
catalyst under homogeneous conditions showed that lated in zeolite Y) forms, using NaOCl as oxidant at low
styrene found much lower TOF than nitrochromene, temperature (at 58C), and using 1-methyl-1-cyclohex-
À1
giving TOFs of 3 and 198 h for styrene and nitrochro- ene and styrene, as substrates gave very poor enantio-
mene, respectively. Again, this illustrates the impor- meric excess and a very low conversion in the case of
[
8]
tance of the substituent groups in activating the alkene 1-methyl-1-cyclohexene. The sterically hindered long
function. perfluoroalkyl-substituted salen-Mn(III) catalyst gave
Despite the similar reactivity of styrene and cyclohex- 58% ee at 100% conversion at 1008C using PhIO/pyri-
ene, higher TOFs were obtained for methyl-substituted dine N-oxide in the epoxidation of 1-methyl-1-cyclohex-
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FULL PAPERS
Samiran Bhattacharjee, James A. Anderson
[
6,7]
ene in the homogeneous phase. Another report found
that the salen-Mn(III) complexes supported on amor-
phous silica or MCM-41, using 1-phenylcyclohex-1-ene
gave epoxide with 84% ee, when the 3,5-positions of
the salicyl phenyl ring of the salen ligand were substitut-
[
32]
ed by tert-butyl groups, whereas the enantioselectivity
was reduced from 84% to 34%, when the tert-butyl
group at the 3-position was absent from the phenyl
ring of the salen ligand, although electronic modifica-
[
32]
tion may play a role in addition to any steric effects.
Salen-Mn(III) complexes supported on amorphous sili-
ca or MCM-41 catalysts were less effective in the case of
styrene, with an ee and epoxide yield of 30% and 70%,
[32]
respectively. Chiral salen-Mn(III) catalyst when ax-
[
13]
ially immobilised into MCM-41 via either phenoxy
[
14]
or phenylsulphonic group showed higher ee % than
the homogeneous counterparts for the epoxidation of
a-methylstyrene.
Figure 4. Comparison of ee (light shading) and yield (dark
shading) of epoxide (%) of styrene over (a) zeolite-immobi-
In most cases, the enantioselectivity of immobilized
salen-Mn(III) catalysts is lower than their homogeneous
[8]
[32]
lized, (b) MCM-41-supported, (c) LDH-hosted, and a-
methylstyrene over (d) MCM-41 via phenylsulphonic
counterparts. Some of these immobilized catalysts ex- group,[14] (e) LDH-hosted, and for 4-methylstyrene (f)
hibit higher ee values than in the case of their homoge- LDH-hosted, and 1-methyl-1-cyclohexene over (g) zeolite-
[
12–14,33]
[8]
[6]
neous counterparts.
The spatial effect including immobilized, (h) perfluoroalkyl-substituted, (i) LDH-
hosted and for 1-phenyl-1-cyclohexene over (j) MCM-41-sup-
the surface effect originating from the supports as well
as the immobilisation modes are considered to be the
[32]
ported, (k) LDH-hosted and cyclohexene over (l) cationic
[35]
[
13,14,34]
salen-Mn(III) and (m) LDH-hosted forms.
main reason for the increase in ee values.
have shown
We
that the sulphonato-chiral Mn(III)
complex in Zn(II)/Al(III) LDH gave higher de % in Mn(III). However, the yield of epoxide was much
[25–27]
[
32]
[
32]
the stereoselective epoxidation of R-(þ)-limonene and higher here than previously reported.
The LDH-
a-pinene than the results previously reported for [Mn(Cl)salen] catalystgave amuch higheryield of epox-
salen-Mn(III). The origin of the high ee of some styrenes ide but with a similar ee for styrene epoxidation as re-
[
8]
and cyclic alkenes using the present LDH hosted cata- ported for zeolite-entrapped Mn-salen. In the case of
lyst may be associated with the attachment of the a-methylstyrene, salen-Mn(III) when axially immobi-
[14]
salen-Mn(III) complex within the layered double hy- lised into MCM-41 via a phenylsulphonic group
droxide via the sulphonato group and also potentially, gave a much higher ee and yield of epoxide than
on the presence of positive charges in the layered host LDH-hosted catalyst. While the % ee values obtained
along with an appropriate gallery height.
are very respectable, further modifications to the system
A comparison of some of the better published data for are being made which will hopefully yield further im-
epoxidation of a-methylstyrene, 4-methylstyrene, styr- provements.
[
36]
ene, 1-methyl-1-cyclohexene, 1-phenyl-1-cyclohexene
Very recently, Linker et al. showed experimental
and cyclohexene compared with that obtained using evidence for radical pathways during the epoxidation
LDH-[Mn(Cl)salen], is shown in Figure 4. The compar- of 1,4-cyclohexadienes using the Jacobsenꢀs catalyst un-
ison shows that the modified Jacobsenꢀs catalyst within der homogeneous conditions. At this stage, the mecha-
the LDH host is highly active in non-chlorinated solvent nism of the oxidation of alkenes over LDH-hosted
(
toluene) and using dioxygen in combination with piva- Mn-salen catalyst is not known. Mechanistic studies as
laldehyde as oxidant in the asymmetric epoxidation of 1- well as comparative studies with the use of the other
methyl-1-cyclohexene, and found to produce the epox- transition metal-salen complexes into the LDH in the
ide with slightly lower yield but higher ee % than that re- epoxidation of different alkenes as well as the use of oth-
ported for perfluoroalkyl-substituted salen-Mn(III) un- er oxidants are in progress to help determine the role of
[
6]
der fluorous biphasic conditions. For the same reac- the LDH host on the enantio- and diastereoselectivities.
tion, the present LDH-based catalyst gave much higher The stability of the catalyst was studied by performing
conversion, selectivity and ee than reported for zeolite repeatedepoxidationreactionsusingthesameconditions
[
8]
entrapped Mn-salen where dichloromethane was as described above. At the end of each reaction cycle, the
used as solvent and NaOCl as oxidant. The phenyl-sub- catalyst was recovered by filtration and washed with tol-
stituted cyclic alkene, 1-phenyl-1-cyclohexene, is a rela- uene, dried and reused. The results are shown in Tables 2
tively poor substrate (in ee %), and gave much lower ee and3forcatalystreuseduptothreetimes. Theconversion
than previously reported for MCM-41-supported salen- [%], selectivity[%]andee[%] werealmost identicalirre-
156
asc.wiley-vch.de
ꢁ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2006, 348, 151 – 158

Chiral Sulphonato-Salen-Manganese(III)-Pillared Hydrotalcite Catalysts
FULL PAPERS
spectiveofthenumberofcycles. Noevidenceforleaching solution through an addition funnel with constant stirring and
gentle heating (at 708C). The resulting mixture was heated at
of Mn or decomposition of the catalyst complex was ob-
reflux for 1 h with stirring and cooled to room temperature.
servedduringthecatalysisreaction. NotracesofMnwere
The volume was reduced by 50% by rotary-evaporation until
detectedintheliquid reactionmixturebyAAspectrosco-
a yellow solid separated, which was filtered off and washed
py. The FTIR spectrum of the solid catalyst after reuse
was identical to the fresh catalyst.
with ethanol (200 mL). The yellow solid was then recrystallised
from water-diethyl ether mixture and dried over silica gel;
Yield: 98%.
Conclusions
Preparation of Na [Mn(Cl)salen]·2 H O (3)
LDH-[Mn(Cl)salen] was an excellent catalyst system
for the asymmetric epoxidation of styrenes and cyclic al-
kenes. The LDH-[Mn(Cl)salen] gave good product se-
2
2
To an aqueous solution (30 mL) of Mn(O CMe) ·4 H O
2
2
2
(
1.72 g, 7.0 mmol), an aqueous solution (20 mL) of the ligand
lectivity and yield of the asymmetric epoxidation of styr- 1 (1.75 g, 6.5 mmol) was added dropwise with stirring. Saturat-
enes and cyclic alkenes using molecular oxygen at at- ed aqueous sodium chloride solution (3 mL) was added to the
mixture after the complete addition of ligand, stirring was con-
tinued for 1 h and the mixture allowed to stand for 2 h. The
green solid was separated, filtered and washed with cold water
mospheric pressure with mild solvents. The fact that
the LDH-hosted catalyst was active for these reactions
under low molecular oxygen pressure (14.5 psi) using
toluene as solvent is of significance in view of the current
literature for asymmetric epoxidation catalysts for this
reaction. The nature of the support environment is
thought to play a significant role. The asymmetric induc-
tion was good, being higher or comparable with results
obtained with salen-Mn(III) complex supported on zeo-
lite or MCM-41 or using homogeneous perfluoroalkyl-
(
9
100 mL) and ethanol (100 mL) and dried over silica gel; yield:
7%.
Preparation of LDH-[Mn(Cl)salen] (4)
The LDH-[Mn(Cl)salen] was obtained by the partial substitu-
2
À
[6,8,32]
tion of intercalated C H COO ions by the [Mn(Cl)salen]
substituted salen.
The advantages of the present catalyst for the asym-
metric epoxidation of styrenes and cyclic alkenes are:
6
5
ions. The LDH-[C H COO] was prepared by mixing a solution
6
5
of zinc(II) nitrate tetrahydrate (29.75 g, 100 mmol), and alumi-
nium(III) nitrate (12.50 g, 33.3 mmol) in de-carbonated water
1) The sulphonato-salen-manganese(III) complexes and
(
100 mL), together with a further separate solution prepared
by dissolving benzoic acid (21.96 g, 180 mmol) and NaOH
15.60 g, 390 mmol) in de-carbonated water (100 mL) under
hydrotalcite-based catalyst are readily prepared from
aqueous medium without using organic solvents, unlike a
large number of catalysts based on salen-metal complexes
which are synthesised using chlorinated solvents.
(
a nitrogen atmosphere. The gel-like mixture was digested at
348 K for 62 h. Upon cooling, the product was isolated by filtra-
2
) Salt formation and the need to use low (below am- tion, washed with water (700 mL) and ethanol (200 mL) and
dried overnight at 333 K; yield: 90%.
bient) temperatures is avoided by the use of molecular
oxygen/pivalaldehyde instead of NaOCl as used in Jacob-
Na [Mn(Cl)salen] (1.71 g, 2.51 mmol) was dissolved in de-
2
[5]
carbonated water (50 mL) and LDH-[C H COO] (5.0 g) was
6
5
senꢀs system.
) LDH-[Mn(Cl)salen] catalyst is highly active at room
added to the solution and stirred for 10 h at room temperature
under a nitrogen atmosphere. The pale green product was fil-
tered off and washed with water (300 mL) and dried at over-
night at 333 K.
3
temperature in molecular oxygen as oxidant and toluene
as solvent, instead of the chlorinated solvent used by oth-
[8]
ers to achieve maximum activity and selectivity.
Catalytic Reaction
Experimental Section
Catalytic epoxidation of styrenes and cyclic alkenes with mo-
lecular oxygen was carried out in a two-neck, round-bottom
flask equipped with a condenser. In a typical run, 1 mmol of al-
kene, 2 mmol of pivalaldehyde, 10 mL of toluene and 0.050 g of
catalyst were stirred at room temperature (298 K) while bub-
bling molecular oxygen at atmospheric pressure. Catalytic ep-
oxidation of 1-methyl-1-cyclohexene with molecular oxygen at
100 psi was carried out in a stainless steel autoclave fitted with
pressure sensor and stirrer and held at constant temperature
using an external oil bath.
Preparation of Chiral Sulfonato-Salen Ligand, H L (1)
2
[
37]
(
R,R)-1,2-Diammoniumcyclohexane
mono-(þ)-tartrate
[38]
and sodium salicylaldehyde-5-sulfonate were prepared us-
ing a literature method. A mixture of 2.97 g (11.2 mmol) of
(
3
R,R)-1,2-diammoniumcyclohexane mono-(þ)-tartrate and
.12 g (22.5 mmol) of potassium carbonate were combined
with 20 mL of water-ethanol (1:4) into a two-necked round-
bottomed flask with reflux condenser and an addition funnel.
The mixture was heated and stirred with a magnetic stirrer.
A solution of sodium salicylaldehyde-5-sulfonate (5.54 g,
The reaction products and enantiomeric excess were deter-
mined using a Hewlett-Packard GC/MS fitted with CYDEX-B
fused silica chiral column using both FID and MS detectors.
22 mmol) in 20 mL of water was added dropwise to the above
Adv. Synth. Catal. 2006, 348, 151 – 158
ꢁ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
157

FULL PAPERS
Samiran Bhattacharjee, James A. Anderson
Acknowledgements
[22] T.Tatsumi, K.Yamamoto, H. Tajuma, H. Tominaga,
Chem.Lett. 1992, 815–818.
We thank the EPSRC for a Research award. (GR/S67371/01)
and Dr. John M. D. Storey (University of Aberdeen) for useful
comments on the manuscript.
[23] B. Sels, V. D. De, M. Buntinx, F. Pierard, A. Kirsch-De
Mesmaeken, P. A. Jacobs, Nature 1999, 400, 855–857.
[24] B. M. Choudary, N. S. Chowdari, K. Jyothi, M. L. Kant-
am, J. Am. Chem. Soc. 2002, 124, 5341–5349.
[
25] S. Bhattacharjee, J. A. Anderson, Chem. Commun. 2004,
References and Notes
554–555.
[
26] S. Bhattacharjee, J. A. Anderson, Catal. Lett. 2004, 95,
[1] a) T. Katsuki, K. B. Sharpless, J. Am. Chem. Soc. 1980,
119–125.
1
02, 5974–5976; b) R. A. Johnson, K. B. Sharpless, Cata-
[27] S. Bhattacharjee, T. J. Dines, J. A. Anderson, J. Catal.
2004, 225, 398–407.
[28] C. Scuster, W. F. Holderich, Catal. Today 2000, 60, 193–
207.
nd
lytic Asymmetric Synthesis, (Ed.: I. Ojima), 2 edn, Wi-
ley-VCH, New York, 2000, pp. 231–280.
2] T. Katsuki, Catalytic Asymmetric Synthesis, (Ed: I. Oji-
ma), 2 edn, Wiley-VCH, New York, 2000, chapter 6B,
pp. 287–325.
3] E. N. Jacobsen, M. H. Wu, in: Comprehensive Asymmet-
ric Catalysis, (Eds.: E. N. Jacobsen, A. Pfaltz, H. Yama-
moto), Springer, New York, 1999, chapter 18.2,
pp. 649–677.
4] T. Katsuki, J. Mol, Catal, A. Chem., 1996, 113, 87–107
and references cited therein.
[
[
nd
[29] S. Bhattacharjee, J. A. Anderson, unpublished work.
[30] Data: For ligand (1): IR (KBr): n(OH),3210;n(CH¼N),
À1
1634; n(CÀO), 1522, n(SO ), 1110 and 1035 cm ; anal.
3
found (%): C 45.72, H 3.79, N 5.36; calcd. (%) for Na2
C H N S O : C 45.61, H 3.84, N, 5.32. For ligand (2):
2
0
20
2
2
8
IR:n(C¼N), 1623, n(CÀO), 1540, n(SO ), 1029 and 1117,
3
À1
[
n(MnÀO), 573, n(MnÀN), 430 cm ; UV-vis: l¼798,
576, 466, 365, 295, 250; anal. found (%): C 38.93, H
3.76, N 4.10, Mn 8.23; calcd. (%) for Na MnC H N S
2 2
[
5] a) E. N. Jacobsen, W. Zhang, J. Org. Chem. 1991, 56, 2296–
2
22 25
2
298; c) E. N. Jacobsen, W. Zhang, A. R. Muci, J. R. Ecker,
O : C 39.17, H 3.74, N 4.15, Mn 8.15. For ligand (3):
12
L. Deng, J. Am. Chem. Soc. 1991, 113, 7063–7064.
6] M. Cavazzini, A. Manfredi, F. Montanari, S. Quici, G.
Pozzi, Chem. Commun. 2000, 2171–2172.
7] M. Cavazzini, A. Manfredi, F. Montanari, S. Quici, G.
Pozzi, Chem. Commun. 2001, 4639–4649.
8] M. J. Sabater, A. Corma, A. Domenech, V. Fornes, H.
Garcia, Chem. Commun. 1997, 1285–1286.
9] L. Canali, E. Cowan, H. Deleuze, C. L. Gibson, D. C. Sher-
rington, J. Chem. Soc. Perkin Trans. 1. 2000, 2055–2066.
IR: n(C¼N), 1626, n(CÀO), 1545, n(SO ), 1026 and
3
À1
[
[
[
[
1118, n(MnÀO), 575, n(MnÀN), 430 cm ; UV-vis (nujol
mull): l¼800, 574, 465, 363, 295, 250; anal. found: C
35.25, H 3.27, N 3.98, Mn 8.20; calcd. for Na MnC H
2
20 22
N S O Cl: C 35.16, H 3.22, N 4.11, Mn 8.05. For LDH-
2
2
12
o
[C H COO]: XRD: 2q/ (d-spacing, Š): 5.8(15.22),
6 5
11.3(7.82), 17.0(5.21), 22.7(3.91); anal. found: Zn 34.61,
Al 5.58, H O 8.83; calcd for LDH-[C H COO]: Zn
2
6
5
o
34.75, Al 5.67, H O 8.91. For 4: XRD: 2q/ (d-spacing,Š):
2
[
[
[
[
[
[
[
10] B. M. Choudary, N. S. Chowdari, M. L. Kantam, P. L.
Santhi, Catal. Lett. 2001, 76, 213–218.
11] D.-W. Park, S.-D. Choi, S.-J. Choi, C.-Y. Lee, G.-J. Kim,
Catal. Lett. 2002, 78, 145–151.
12] R. I. Kureshy, N. H. Khan, S. H. R. Abdi, I. Ahmad, S.
Singh, R. V. Jasra, J. Catal. 2004, 221, 234–240.
13] S. Xiang, Y. Zhang, Q. Xin, C. Li, Chem. Commun. 2002,
4.7(18.78), 8.6(10.27), 13.8(6.41), 19.7(4.50); anal. found
(%): Zn 29.03, Al 4.69; [Mn(Cl)salen] 24.88, H O 7.53;
2
calcd (%) for 4: Zn 29.14, Al 4.81, [Mn(Cl)salen] 25.06,
H O 7.47; UV-Vis (nujol mull): l¼799, 552, 446, 350,
2
270, 226.
[31] R. I. Kureshy, N. H. Khan, S. H. R. Abdi, S. Singh, I.
Ahmed, R. S. Shukla, R. V. Jasra, J. Catal. 2003, 219,
1–7.
[32] F. Bigi, L. Moroni, R. Maggi, G. Sartori, Chem. Com-
mun. 2002, 716–717.
[33] G.-J. Kim, J.-H. Shin, Tetrahedron Lett. 1999, 40, 6827–
6830; X. Yu, J. Huang, S. Li, L. Li, C. Che, Chem. Com-
mun. 1999, 1789–1790; G.-J. Kim, S.-H. Kim, Catal. Lett.
1999, 57, 139–143.
2
696–2697.
14] H. Zhang, S. Xiang, C. Li, Chem. Commun. 2005, 1209–
211.
1
15] M. L. Kantan, B. M. Choudary, Ch. V. Reddy, K. K. Rao,
F. Figueras, Chem. Commun. 1998, 1033–1034.
16] B. M. Choudary, M. L. Kantam, Ch. V. Reddy, K. K.
Rao, F. Figueras, J. Mol. Catal. Part A: Chem. 1999,
1
46, 279–284.
17] E. Suzuki, Y. Ono, Bull. Chem. Soc. Jpn. 1998, 61, 1008–
012.
[34] A. Cornejo, J. M. Fraile, J. I. Garcia, M. J. Gil, C. I. Her-
rerias, G. Legarreta, V. Martinez-Merino, J. A. Mayoral,
J. Mol. Catal. A: Chem. 2003, 196, 101–108.
[35] K. Srinivasan, P. Michaud, J. K. Kochi, J. Am. Chem. Soc.
1986, 108, 2309–2320.
[
[
[
1
18] K. Yamaguchi, K. Mori, T. Mizugaki, K. Ebitani, K. Ka-
nada, J. Org. Chem. 2000, 65, 6897–6903.
19] a) S. Narayanan, K. Krishna, Chem. Commun. 1997,
[36] U. Engelhardt, T. Linker, Chem. Commun. 2005, 1152–
1154.
1
991–1992; R. Unnikrishnan, S. Narayanan, J. Mol. Cat-
al. Part A: Chem. 1999, 144, 173–179.
[37] J. F. Larrow, E. N. Jacobsen, Organic Synth. 1997, 75, 1–10.
[38] M. Botsivali, D. F. Evans, P. H. Missen, M. W. Upton, J.
Chem. Soc. , Dalton Trans. 1985, 1147–1149; K. J. Berry,
F. Moya, K. S. Murray, A. B. van der Bergen, B. O. West,
J. Chem. Soc. Dalton Trans. 1982, 109–116.
[
20] G.-J. ten Brink, I. W. C. E. Arends, R. A. Sheldon, Chem.
Rev. 2004, 104, 4105–4123 and references cited therein.
21] F. Cavani, F. Trifiro and A. Vaccari, Catal. Today 1991,
[
1
1, 173–301.
158
asc.wiley-vch.de
ꢁ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2006, 348, 151 – 158