Encapsulation of a chiral MnIII(salen) complex in ordered mesoporous silicas: An approach towards heterogenizing asymmetric epoxidation catalysts for non-functionalized alkenes

Article abstract of DOI:10.1016/j.tetasy.2005.09.022

Two immobilized chiral Mn^III(salen) complexes covalently anchored on modified MCM-41 (50 A) and SBA-15 (75 A) were prepared using 3-aminopropyltriethoxysilane as a reactive surface modifier to afford comparable or even higher enantioselectivity

Full text of DOI:10.1016/j.tetasy.2005.09.022

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 16 (2005) 3562–3569
Encapsulation of a chiral MnIII(salen) complex in ordered
mesoporous silicas: an approach towards heterogenizing
asymmetric epoxidation catalysts for non-functionalized alkenes
Rukhsana I. Kureshy,* Irshad Ahmad, Noor-ul H. Khan, Sayed H. R. Abdi,
Kavita Pathak and Raksh V. Jasra
Silicates and Catalysis Discipline, Central Salt and Marine Chemicals Research Institute (CSMCRI), Bhavnagar 364 002,
Gujarat, India
Received 29 July 2005; accepted 12 September 2005
Available online 14 November 2005
Abstract—Two immobilized chiral MnIII(salen) complexes covalently anchored on modified MCM-41 (50 A) and SBA-15 (75 A)
were prepared using 3-aminopropyltriethoxysilane as a reactive surface modifier to afford comparable or even higher enantioselec-
tivity than homogeneous catalysts for the enantioselective epoxidation of a series of smaller to bulkier alkenes. The catalyst immo-
bilized in silica with larger pore diameters was found to be more active. Compared to homogeneous catalysts, the heterogenized
catalysts are more stable and can be recycled four times with retention of enantioselectivity.
˚
˚
ꢀ 2005 Elsevier Ltd. All rights reserved.
1. Introduction
for epoxidation of non-functionalized alkenes. The solid
chiral catalysts accommodated in the pores or cavities
of the porous materials show differences in reactivity
and enantioselectivity of the epoxidation reaction.2b,8,10
It is, therefore, intuitive to graft the active metal com-
plex onto solid supports of varied pore sizes to examine
the influence of surface and pores on catalytic activ-
ity and enantioselectivity (confinement effect) of the
MnIII (salen) complex without loosing its merits. Meso-
porous materials have received extensive attention due
to their ordered pore structure, good thermal stability,
large surface area and ease of modification by utiliz-
ing the available surface silanol groups for the anchor-
ing of a homogeneous catalyst.13 Herein, we have
synthesized the siliceous MCM-41 and SBA-15 to
immobilize the chiral MnIII(salen) complex 1 using
3-aminopropyltriethoxysilane (APTES) as a reactive
surface modifier. The immobilized catalysts 1a (complex
1 supported on MCM-41) and 1b (complex 1 supported
on SBA-15) lead to markedly higher ee for 4-chlorosty-
rene (69–71%) than the homogeneous complex 1 and
other reported immobilized MnIII(salen) complexes8,14
anchored on MCM-41. Furthermore, catalysts 1a and
1b epoxidized bulkier alkenes with high chiral induction
(up to 96%) and the catalysts are reusable for up to four
cycles.
Homogeneous catalysts usually display higher activities
and enantioselectivities than heterogeneous catalysts for
enantioselective catalytic reactions. However, the prod-
uct separation and catalyst recovery is difficult for
homogeneous systems.1 An immobilized enantioselec-
tive catalytic system is one of the most promising strat-
egies to produce single optically active enantiomers due
to easy separation and recycling of the catalyst.2 One
general way to transform a homogeneous catalytic reac-
tion into heterogeneous process involves anchoring of
active catalytic sites on a solid support by a linker
group. Such immobilization of MnIII(salen) comp-
lexes also effectively prevents the formation of inactive
dimericor polymeric
l-oxo intermediate species
through isolation of the active metal sites.3 Several
papers have recently appeared on the immobilization
of chiral MnIII(salen) complexes onto solid supports
such as organic polymers4–6 and inorganicsolids of
various porosity2b,7–12 with moderate to excellent results
*
Corresponding author. Fax: +91 278 2566970; e-mail: rkureshy@
csmcri.org
0957-4166/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2005.09.022

R. I. Kureshy et al. / Tetrahedron: Asymmetry 16 (2005) 3562–3569
3563
2. Results and discussion
adsorption–desorption isotherm, X-ray powder diffrac-
tion, SEM and TEM, which evidenced the effective com-
plex immobilization with a catalyst loading in the range
23–25 mg/100 mg (data are given in the Experimental).
2.1. Synthesis and characterization of catalysts
The preparation of immobilized catalysts, 1a and 1b,
was carried out by covalent grafting of preformed, well
characterized MnIII(salen) complex 1 onto APTES mod-
FTIR spectra of complexes 1a and 1b were in good
agreement with the expected chemical structure of the
organicmoieties. In partiuclar, the formation of the
immobilized complexes 1a and 1b was confirmed by
the presence of bands near 2954 and 1536 cmÀ1 due to
m(CH2) of the propyl arm of the silylating agent and
m(HAC@N) of the azomethine group, respectively.
These bands were absent in IR spectra of MCM-41 5
and SBA-15 50 (Fig. 1).
˚
ified MCM-41 (pore diameter 50 A) and SBA-15 (pore
˚
diameter 75 A), respectively (Scheme 1). To make the
catalytic environment of immobilized complexes 1a
and 1b analogous to that of homogeneous system, the
grafting of complex 1 was done through the 5th position
of salen ligand 4. The functionalization of calcined
MCM-41 5 and SBA-15 50 was performed by their inter-
action with APTES 6 in toluene under reflux condition.
Functionalized MCM-41 7 and SBA-15 70, which were
thus obtained, interacted with 1 to give the immobilized
complexes 1a and 1b, respectively. The immobilized
complexes were repeatedly extracted with CH2Cl2 in
order to ensure the elimination of any physically
bounded MnIII(salen) complex from the silica matrix.
Solid reflectance UV–vis spectra also supported the suc-
cessful immobilization of the complexes as the charac-
8
teristiccharge transfer and d–d transition bands
near
425 and 520 nm of homogeneous MnIII(salen) complex
1 are present as broad bands for immobilized complexes
1a and 1b (Fig. 2). The virgin silica materials do not
show any band in these regions.
The immobilized catalysts 1a and 1b were characterized
by FTIR, solid reflectance spectroscopy, microanalysis,
inductive coupled plasma atomic emission (ICP), N2
To further confirm that salen complex 1 was grafted on
modified MCM-41 and SBA-15, complexes 1a and 1b
Scheme 1. The synthesis of immobilized catalyst on MCM-41 and SBA-15 (a) resolved (1R,2R)-diamino cyclohexane, CHCl3, 0 ꢁC; (b)
5-chloromethyl tert-butyl-salicylaldehyde, dry MeOH, reflux, 24 h; (c) Mn (OAc)2Æ4H2O, LiCl, dry EtOH, reflux, 12 h; (d) and (e) toluene, reflux,
24 h.

3564
R. I. Kureshy et al. / Tetrahedron: Asymmetry 16 (2005) 3562–3569
A
3400
1029
569
2865
1252
1536
2954
1613
B
1539
1629
797
2955
3433
C
D
462
461
1083
2929
1636
795
797
3442
3446
1085
1636
464
1088
3000
2000
1500
1000
400
4000
cm-1
Figure 1. Representative IR spectra of calcined SBA-15 (D), aminopropyl modified SBA-15 (C), immobilized MnIII(salen) complex 1b on surface
modified SBA-15 (B), MnIII(salen) complex 1 (A).
D
(100)
C
B
(110) (200)
a
b
A
200
300
400
500 600 700
Wavelength (nm)
c
Figure 2. Solid reflectance UV–vis spectra of calcined MCM-41
(A), aminopropyl modified MCM-41 (B), immobilized MnIII(salen)
complex 1a (C), MnIII(salen) complex 1 (D).
2
3
4
5
6
Angle (2 theta)
Figure 3. (a) Representative XRPD patterns of calcined MCM-41, (b)
aminopropyl modified MCM-41, (c) immobilized complex 1a.
were dissolved in HF solution and the resulting mass
extracted with CH2Cl2. After complete removal of the
solvent, the resulting brown mass was analyzed by
UV–vis and IR spectroscopy, which showed the pre-
sence of MnIII(salen) complex 1. These observations
are consistent with that reported for the immobilization
of salen on siliceous material.14
thus confirming the retention of the physical structure
of the siliceous material (Fig. 4).
The BET surface area, pore diameter, pore volume and
microanalysis of calcined MCM-41, SBA-15 and immo-
bilized complexes are given in Table 1 suggesting that
complex 1 is present inside the pores of the support
material.
X-ray powdered diffraction patterns of MCM-41 and
SBA-15 show three well-resolved peaks indexed to 100,
110 and 200 reflections (a) of hexagonal space group
p6mm. The mesoporous structure of these supports
remain undisrupted as the immobilized complexes 1a
and 1b are bonded on their surface. This was confirmed
by monitoring the X-ray diffraction at each step of
immobilization (Fig. 3).
2.2. Asymmetric catalytic epoxidation
Six representative non-functionalized alkenes 4-chloro-
styrene, indene, 2,2-dimethylchromene, 6-cyano-2,2-
dimethylchromene, spiro[cyclohexane-1,20-[2H][1]chro-
mene] and 6-methoxy-2,2-dimethylchromene were stud-
ied with these immobilized catalysts for asymmetric
epoxidation. To compare the epoxidation capability of
TEM images for calcined MCM-41 and SBA-15 showed
two-dimensional hexagonal structures (p6mm)15 that
remained unaffected on immobilization of complex 1

R. I. Kureshy et al. / Tetrahedron: Asymmetry 16 (2005) 3562–3569
3565
Figure 4. Representative TEM images of calcined SBA-15 (A) and complex 1b (B).
Table 1. Physico-chemical characterization data of MCM-41, SBA-15, aminopropyl modified MCM-41 (7) and SBA-15 (70) and immobilized
complexes 1a, 1b
Total pore volume (cm3/g)
BET surface area (m2/g)
C/N ratio
˚
Compound
Mn loading/mg/100 mg
BJH pore diameter (A)
1
—
—
—
23
—
—
25
—
—
—
14.13
—
4.03
10.2
—
MCM-41
7
1a
50.0
35.0
19.0
75.0
65.0
52.0
1.041
0.416
0.129
1.229
0.651
0.401
825
477
332
743
342
245
SBA-15
70
1b
4.08
10.10
the heterogeneous catalyst, complex 1 was used as a ref-
erence catalyst for the epoxidation of all the alkenes
under homogeneous conditions. The asymmetric
epoxidation of the alkenes were carried out with com-
plexes 1, 1a and 1b (5 mol % with respect to substrate)
in dichloromethane at 0 ꢁC using NaOCl as oxidant
and the data summarized in Table 2. The immobilized
catalysts 1a and 1b are active (yields; 90–99%) and enan-
tioselective (ee, 69–96%). Complex 1 under homoge-
neous conditions also showed similar activity (yields;
94–100%) and enantioselectivity (ee; 46–98%) with these
substrates, suggesting that the local environment around
the active catalytic site is not unchanged on immobiliza-
tion. Furthermore, compared to the homogeneous sys-
tem (8 h), the time taken for the completion of the
epoxidation reaction increases only marginally under
the heterogeneous system (10 h), predictably due to
slower diffusion2b of the reactant and the oxidant mole-
cules into the mesopores of MCM-41 and SBA-15.
Remarkably, when 4-chlorostyrene was used as a sub-
strate with immobilized catalysts 1a and 1b, there was
a significant improvement in enantioselectivity (ee, 69–
71%; entries 2 and 3) over the homogeneous system
(ee, 46%; entry 1). Similar results were obtained with
MCM-41 supported chiral MnIII and CrIII(salen) com-
plexes for the epoxidation of chlorostyrene,16 a-methyl-
styrene2b and cis-b-methylstyrene.10b The increase in ee
is mainly attributed to the unique spatial environment
constituted by the chiral catalyst and mesopores of
MCM-41 and SBA-15. MCM-41 and SBA-15 alone
showed negligible catalytic activity towards the epoxida-
tion of 4-chlorostyrene as the representative substrate
(2%, entries 4 and 5) suggesting that the supported mate-
rials are not responsible for epoxidation reaction. In
general, SBA-15 supported catalyst 1b, where the pore
size is larger, performed better than MCM-41 supported
catalyst 1a, as evident from their TOF values.
The solid catalysts were filtered, washed thoroughly with
distilled water, methanol and CH2Cl2 and then used for
the next cycle. The aqueous and organic layers of the fil-
trate were tested for the presence of manganese by ICP.
As there was no trace of manganese in the filtrate, it was
concluded that MnIII(salen) is intact on the solid sup-
port and that no leaching took place during the epoxida-
tion reaction.
Recycling experiments were conducted with recovered
immobilized MnIII(salen) complexes 1a and 1b for
the epoxidation of 2,2-dimethylchromene, as a repre-
sentative substrate. The data are summarized in Table
3 and show only a marginal decrease in activity in
subsequent epoxidation runs, however, the enantio-
selectivity remains unchanged. The characterization of
the recycled catalyst (by FTIR spectra, XRPD and
CHN analysis) also suggests partial degradation of
the catalyst along with entrapment of some of the
reactants within the mesopores that cause a gradual
slow down of the epoxidation reaction in the successive
recycle runs. These observations are in agreement with
earlier reports based on immobilized MnIII(salen)
system.8
3. Conclusion
Chiral MnIII(salen) complexes were immobilized onto
mesoporous solids namely, MCM-41 and SBA-15, and
used for the enantioselective epoxidation of various alk-
enes. The immobilized complexes are stable, recyclable
and give comparable or even higher ees (e.g., 4-chloro-
styrene) than homogeneous catalysts. The SBA-15 based
catalyst, which had a larger pore diameter, was found to
be more active than the MCM-41 based MnIII(salen)
catalyst.

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R. I. Kureshy et al. / Tetrahedron: Asymmetry 16 (2005) 3562–3569
Table 2. Product yields, ee and TOF for enantioselective epoxidationa of non-functionalized alkenes catalyzed by 1, 1a and 1b
Entry
Catalyst
Product
Yield (%)b
ee (%)c
TOFd · 10À4
Config.
1
2
3
4
5
1f
1a
100
98
99
2e
46
69
71
—
—
6.94
5.44
5.50
—
R
O
R
1b
MCM-41
SBA-15
R
—
—
Cl
2e
—
O
6
7
8
1f
96
96
99
86
82
84
6.66
5.33
5.50
1R,2S
1R,2S
1R,2S
1a
1b
O
9
10
11
1f
99
98
99
98
94
96
6.87
6.80
5.50
3R,4R
3R,4R
3R,4R
1a
1b
O
O
NC
12
13
14
1f
98
93
97
92
89
88
6.80
5.16
5.38
3R,4R
3R,4R
3R,4R
1a
1b
O
O
15
16
17
1f
94
90
92
82
78
77
6.52
5.00
5.11
3R,4R
3R,4R
3R,4R
1a
1b
O
O
MeO
18
19
20
1f
97
92
96
85
81
82
6.73
5.11
5.33
3R,4R
3R,4R
3R,4R
1a
1b
O
a Reactions were performed in CH2Cl2 (4 ml) with catalyst 0.05 mmol, substrate 1.00 mmol, NaOCl 2.75 mmol.
b Isolated yield.
c By 1H NMR using chiral shift reagent (+)-Eu(hfc)3/chiral capillary column GTA type/chiral HPLC column OB, OD, OJ.
d Turn over frequency is calculated by the expression [product]/[catalyst] · time, sÀ1
.
e Conversion, not isolated yield.
f Reaction time was 8 h under homogeneous reaction condition while it was 10 h with catalyst 1a and 1b.
Table 3. Recycling data for enantioselective epoxidationa of 2,2-
dimethyl chromene as a representative substrate using immobilized
sis, amphiphillic triblock copolymer P123 was used in
the reported procedure.11 Gas chromatography (Shima-
dzu GC 14B) was used for the determination of purity,
time and conversions. Enantiomeric excesses of the
catalysts 1a and 1b
Run
Catalyst
Yield (%)
eeb
TOF · 10À4
1
resultant epoxides were determined by H NMR using
1
2
3
4
1a (1b)
1a (1b)
1a (1b)
1a (1b)
98 (99)
95 (97)
91 (93)
91 (92)
94 (96)
94 (96)
94 (96)
94 (95)
5.44 (5.50)
5.27 (5.38)
5.06 (5.17)
5.06 (5.11)
chiral shift reagent (+)-Eu(hfc)3, which were further
confirmed by HPLC (Shimadzu SCL-10AVP) using a
DAICEL Chiralcel columns OJ/OB for IND, OD for
CR, CNCR, MCR, CYCR, 4CSTR and by GC using
a Reactions were performed in CH2Cl2 (4 ml) with the recovered cat-
alyst, substrate 1.00 mmol, NaOCl 2.75 mmol for 10 h.
b By chiral HPLC column, Chiralcel OD.
1
Astec GTA chiral column (30 m) for 4CSTR. H and
13C{1H} NMR spectra were recorded on a 200 and
50 MHz spectrometer (Bruker, F113V). The IR spectra
were recorded on a Perkin–Elmer Spectrum GX spectro-
photometer in KBr/Nujol mull. Electronic spectra were
recorded on a Varian UV–vis–NIR CARY 500 SCAN
Spectrophotometer. Diffuse reflectance spectra were
obtained from a UV–vis–NIR Scanning Spectrophoto-
meter UV-3101 PC. Microanalysis was done on a
Perkin–Elmer model 2400 CHNS analyzer. Inductive
coupled plasma spectrometer (Perkin–Elmer Instru-
ment, Optical Emission spectrometer, Optima 2000
DV) was used for Mn estimation. X-ray powder diffrac-
tion patterns of the samples were recorded on a Philips
XꢀPert MPD diffractometer. BET surface area was
determined using N2 sorption data measured at 77 K
using volumetricadsorption set-up (Mriocmeritsic
ASAP-2010, USA). The pore diameter of the samples
was determined from the Barret, Joyner and Halenda
(BJH) method. TEM analysis was accomplished by
4. Experimental
4.1. General
(1R,2R)-Diaminocyclohexane was resolved from the
technical grade cis–trans mixture (Aldrich). Indene
(IND) and 4-chlorostyrene (4CSTR) were passed
through a pad of neutral alumina before use. 2,2-
Dimethylchromene (CR), 6-cyano-2,2-dimethylchromene
(CNCR), 6-methoxy-2,2-dimethylchromene (MCR)
and spiro[cyclohexane-1,20-[2H][1]chromene] (CYCR)
were synthesized by reported procedures.17 All the sol-
vents used were purified by known methods.18 MCM-
41 was synthesized by using cetyl pyridinium chloride
as a structure directing agent while for SBA-15 synthe-

R. I. Kureshy et al. / Tetrahedron: Asymmetry 16 (2005) 3562–3569
3567
transmission electron microscope (TEM) Philips Tecnai
20. SEM analysis of the sample was done by scanning
electron microscope model LEO 1430 VP.
878, 827, 712, 644, 590 cmÀ1
;
1H NMR (CDCl3,
200 MHz): d ppm 1.23 (18H, s), 1.42 (9H, s), 1.47–2.10
(m, 8H), 3.30–3.48 (2H, m), 4.56 (s, 2H), 6.85 (d, 1H,
J = 1.9 Hz), 7.05 (d, J = 2.0 Hz), 7.43 (d, 1H,
J = 2.2 Hz), 7.52 (d, 1H, J = 2.2 Hz), 8.32 (1H, s), 8.44
(1H, s), 13.50 (br s, 1H), 14.48 (1H, br s); 13C{1H}, d
ppm 24.2, 24.8, 26.2, 29.3, 29.6, 29.8, 33.9, 34.1, 35.2,
45.8, 72.3, 78.1, 116.8, 118.2, 122.4, 126.4, 127.4,
127.6, 136.2, 139.8, 157.9, 161.5, 164.8, 165.7; Complex
1 yield 90%; IR (KBr): 3400, 2954, 2865, 1613, 1536,
4.2. Preparation of 3-aminopropylsilyl-functionalized
MCM-41 7 and SBA-15 70
A suspension of APTES (4.56 g, 20.63 mmol) and 10 g
of calcined MCM-41/SBA-15 in 90 ml of toluene was
heated at reflux with stirring under an inert atmosphere
for 24 h. The resulting masses were cooled to 25–30 ꢁC
and filtered. The solids were filtered, washed successively
with dry toluene, diethyl ether and dried under vacuum
at ambient temperature. The dried material was sub-
jected to Soxhlet extraction with dry dichloromethane
for 24 h. Finally, solids 7 and 70 were dried at 50–
55 ꢁC under vacuum for 8 h. The characterization was
accomplished by microanalysis (Table 1), IR-, diffuse
reflectance UV–vis. Spectroscopy, XRPD, nitrogen
sorption studies. IR (KBr) for 7: 461, 795, 1085, 1636,
2929, 3442 cmÀ1. Diffuse reflectance UV–vis: 240,
335 nm; IR (KBr) for 70 460, 795, 1080, 1636, 2922,
1252, 1029, 569 cmÀ1: UV–vis (CH2Cl2) 284, 416, 422,
30
399, 320, 284 nm; ½aŠ ¼ þ663 (c 0.04 g, 0.064 mmol/
D
100 ml, CH2Cl2).
4.4. Immobilization of unsymmetrical MnIII(salen)
complex 1 on aminopropyl-functionalized MCM-41 7
and SBA-15 70
The unsymmetrical MnIII(salen) complex 1 ( 352.4 mg,
0.562 mmol) in dry toluene (10 ml) was refluxed with
surface modified MCM-41/SBA-15 7/70 (1 g) for 48 h
under an inert atmosphere. The immobilized catalyst
1a/1b was filtered, washed thoroughly with dry toluene,
diethyl ether and extracted repeatedly with methanol
and dichloromethane on a Soxhlet extractor until the
washings become colourless. All the washings were com-
bined, the solvent evaporated and the residue dissolved
in toluene (10 ml). The difference of the initial and final
concentration was measured by UV–vis spectroscopy
and gave the amount of complex covalently bonded on
modified MCM-41 7 and SBA-15 70. The characteriza-
tion of chiral MnIII(salen) catalysts 1a and 1b immobi-
lized on MCM-41/SBA-15 was accomplished by
microanalysis (Table 1). Complex 1a yield 90%; IR
3446 cmÀ1
375 nm.
. Diffuse reflectance UV–vis: 270, 340,
4.3. Synthesis of unsymmetrical MnIII(salen) complex 1
Chiral catalyst 1 was obtained through the synthetic
sequence given in Scheme 1 as follows: (1R,2R)-(À)-N-(2-
hydroxy-3,5-di-tert-butylbenzaldehyde)-1-amino-2-cyclo-
hexaneimine 319 was condensed with 5-chloromethyl-3-
tert-butylsalicyaldehyde20 in dry methanol to form an
unsymmetrical chiral salen based ligand 4, which on
complexation with Mn(OAc)2Æ4H2O/LiCl gave complex
1. Yield (80–82%), Anal. Calcd for C33H47ClN2O2: C,
73.54; H, 8.73; N, 5.20. Found: C, 73.48; H, 8.73; N,
5.17; IR (KBr) 3411, 2957, 2863, 1629, 1597, 1470,
1441, 1390, 1361, 1272, 1251, 1204, 1172, 1095, 1044,
(KBr): 3433, 2955, 1629, 1539, 1083, 797, 462 cmÀ1
Solid reflectance UV–vis 240, 335, 425, 520 nm.
Complex 1b yield 89%; IR (KBr) 3426, 2957, 1614,
1540, 1082, 801, 462 cmÀ1. Solid reflectance UV–vis
.
Figure 5. SEM micrograph of MCM-41 and SBA-15 samples (A) calcined MCM-41, (B) complex 1a, (C) calcined SBA-15, (D) complex 1b.

3568
R. I. Kureshy et al. / Tetrahedron: Asymmetry 16 (2005) 3562–3569
0.06
0.05
0.04
0.03
0.02
0.01
0.00
270, 340, 435, 510 nm. Solid reflectance spectroscopy
(DRS), IR-, XRPD, ICP, SEM, TEM and N2 sorption
studies and data are shown in Figures 5–8.
4.4.1. Enantioselective epoxidation of non-functionalized
alkenes. Enantioselective epoxidation reactions were
carried out using the catalysts 1, 1a and 1b (0.05 mmol)
with 4-chlorostyrene, indene, 2,2-dimethylchromene, 6-
cyano-2,2-dimethylchromene, 6-methoxy-2,2-dimethyl-
chromene and spiro[cyclohexane-1,20-[2H][1]chromene]
(1 mmol) as substrates in 1/4 ml of dichloromethane
with buffered NaOCl (2.75 mmol) (pH 11.5) as an oxi-
dant under homogeneous/heterogeneous reaction condi-
tion. The addition of NaOCl was carried out in five
equal portions at 0 ꢁC. The epoxidation reaction was
monitored by GC with n-tridecane (0.1 mmol) as the
20 40
60 80 100 120 140 160
Pore Diameter (A)
Figure 8. N2 adsorption pore diameter and relative pore volume of
calcined SBA-15 (a), aminopropyl modified SBA-15 (b), immobilized
complex 1b (c).
800
0.12
GLC internal standard for product quantification. After
completion of the reaction, the immobilized catalysts 1a
and 1b were separated by centrifugation, washed thor-
oughly with water, methanol, dichloromethane and
dried for re-use experiments.
0.10
700
600
500
400
300
200
100
0.08
0.06
0.04
0.02
0.00
0
10 20 30 40 50 60 70 80
Pore Diameter (A)
Acknowledgements
R.I.K. is grateful to DST, CSIR Network Project on
Catalysis, Irshad Ahmad to CSIR (SRF) for financial
support and also to P. K. Ghosh, the Director of the
Institute, for providing access to the instrumentation
facility.
0
0.2
0.4
0.6
0.8
1
1.2
References
Relative Pressure (P/P0)
1. Yao, X.; Chen, H.; Lu, W.; Pan, G.; Hu, X.; Zhen, Z.
¨
Figure 6. N2 adsorption–desorption isotherms and BJH pore size
distribution curves of calcined MCM-41.
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