Efficient heterogeneous catalytic systems for enantioselective hydrogenation of prochiral carbonyl compounds

Article abstract of DOI:10.1016/j.jcat.2004.08.040

A proficient heterogeneous catalyst system for stereoselective hydrogenation of carbonyl compounds was synthesized, involving anchoring of Ru^II-phosphine-diamine complexes on the inner surfaces of organo-functionalized mesoporous MCM-41 and MCM-48 materials. Powder XRD and TEM experiments reveal highly ordered hexagonal and cubic patterns of the organically modified MCM-41 and MCM-48 materials, respectively, even after incorporation of Ru complexes. Moreover, the integrity of the Ru complexes was retained after anchoring into the mesoporous hosts, which was supported from FTIR, ³¹P CP MAS NMR, and XPS analyses. This new heterogeneous catalyst shows promising activity and selectivity in the enantioselective hydrogenation of prochiral ketones. The effects of reaction time, temperature, and hydrogen pressure on the catalytic activity and enantioselectivity were studied in detail. As high as 95-99% ee could be obtained using these solid catalysts under heterogeneous reaction conditions. The anchored solid catalysts can be recycled effectively and reused several times without any loss in activity and selectivity.

Full text of DOI:10.1016/j.jcat.2004.08.040

Journal of Catalysis 228 (2004) 386–396
www.elsevier.com/locate/jcat
Efficient heterogeneous catalytic systems for enantioselective
hydrogenation of prochiral carbonyl compounds
Anirban Ghosh, Rajiv Kumar ∗
Catalysis Division, National Chemical Laboratory, Pune 411 008, India
Received 6 May 2004; revised 25 August 2004; accepted 31 August 2004
Available online 27 October 2004
Abstract
A proficient heterogeneous catalyst system for stereoselective hydrogenation of carbonyl compounds was synthesized, involving anchoring
II
of Ru –phosphine–diamine complexes on the inner surfaces of organo-functionalized mesoporous MCM-41 and MCM-48 materials. Powder
XRD and TEM experiments reveal highly ordered hexagonal and cubic patterns of the organically modified MCM-41 and MCM-48 materials,
respectively, even after incorporation of Ru complexes. Moreover, the integrity of the Ru complexes was retained after anchoring into
31
the mesoporous hosts, which was supported from FTIR, P CP MAS NMR, and XPS analyses. This new heterogeneous catalyst shows
promising activity and selectivity in the enantioselective hydrogenation of prochiral ketones. The effects of reaction time, temperature, and
hydrogen pressure on the catalytic activity and enantioselectivity were studied in detail. As high as 95–99% ee could be obtained using these
solid catalysts under heterogeneous reaction conditions. The anchored solid catalysts can be recycled effectively and reused several times
without any loss in activity and selectivity.
2004 Elsevier Inc. All rights reserved.
Keywords: Heterogeneous catalysis; Organo-functionalization; Mesoporous materials; Ru–phosphine–diamine complex; Heterogenization;
Enantioselectivity; Hydrogenation
1. Introduction
drogenation of olefins, such catalysts are normally not very
active for hydrogenation of carbonyl groups. However, the
activity can be remarkably enhanced with the addition of
stoichiometric amounts of ethylenediamine [8,9], which de-
celerates hydrogenation of C=C bonds and in turn accel-
erates C=O hydrogenation by a “metal–ligand bifunctional
catalysis” (MLBC) mechanism [10,11]. This concept, es-
tablished by Noyori et al., was successfully applied toward
hydrogenation of prochiral ketones by using RuII–chiral-
diphosphine–chiral-diamine species as a soluble catalyst in
the organic phase [4,10–12]. Appropriate enantiomers of
2,2ꢀ-bis(diphenylphosphino)-1,1ꢀ-binaphthyl (BINAP) and
1,2-diphenylethylenediamine (DPEN) as the above-noted
chiral ligands (coordinated to RuII) are widely used nowa-
days in the production of various specialty chemicals [4].
While several attempts have been made to heterogenize
the soluble transition metal complex catalysts for a vari-
ety of reactions to overcome the disadvantages inherent to
homogeneous catalytic systems [13–15], there has been lim-
The synthesis of enantiomerically pure chiral compounds
has fascinated researchers because of its immense impor-
tance in the synthesis of fine chemicals, pharmaceuticals,
agrochemicals, and fragrance chemicals [1]. An explosive
research in this area has been inspired by the fact that the
undesired enantiomer of a chiral compound could be a toxin
in some biological processes, whose detrimental effects can
outdo the vitalities of the desired enantiomer [2,3].
Enantioselective reduction of prochiral ketones to cor-
responding chiral alcohols, involving molecular dihydro-
gen and catalytic amounts of transition metal complexes,
is quite important from both fundamental and industrial
application viewpoints [4–7]. Although, Wilkinson’s RuII–
phosphine complexes are well recognized to catalyze hy-
*
Corresponding author. Fax: +91 20 2589 3761.
E-mail address: rajiv@cata.ncl.res.in (R. Kumar).
0021-9517/$ – see front matter
doi:10.1016/j.jcat.2004.08.040
2004 Elsevier Inc. All rights reserved.

A. Ghosh, R. Kumar / Journal of Catalysis 228 (2004) 386–396
387
ited success in the case of asymmetric heterogeneous catal-
ysis [16]. Moreover, homogeneous catalysts are character-
ized by high activity and selectivity, which are not gener-
ally achieved by the corresponding heterogeneous catalysts
[17–19]. However, recent studies have revealed that some
heterogenized catalysts indeed can give equivalent or higher
selectivity and yields compared to their homogeneous coun-
terparts [20–22].
Surface modification of M41S-type mesoporous materi-
als, having high surface areas (> 1000 m2 g−1) and easily
accessible pores (diameter 20–100 Å), by organic functional
groups [23,24] has fascinated researchers owing to its im-
mense importance in developing newer strategies for im-
mobilization of catalytically reactive species [15,25], and
hence, can be one of the appropriate choices for immobi-
lization of RuII–phosphine complexes.
Here we report the synthesis, characterization, and cat-
alytic applications of new heterogeneous catalytic systems
for enantioselective hydrogenation of carbonyl compounds.
We have used a postsynthetic grafting method (followed by
covalent tethering) for organo-functionalization of the in-
ner surfaces of MCM-41 and MCM-48, and thereafter het-
erogenized RuII–phosphine or RuII–diphosphine complexes
on those surface-modified MCM-41 and MCM-48 materi-
als. These new heterogeneous catalyst systems were char-
acterized by powder XRD, FTIR spectroscopy, ICP-AES
analyses, N2 adsorption measurements, 31P CP MAS NMR
spectroscopy, XPS, and TEM experiments, which reveal that
the integrity of the mesoporous supports and the RuII com-
plexes was retained after the immobilization process. Ap-
plying these heterogeneous catalysts, we have obtained ex-
cellent enantioselectivity in the hydrogenation of prochiral
ketones. Acting as a true heterogeneous catalyst, it shows
comparable activity and selectivity even after four recycles
without any leaching of the Ru complex from the support.
The Ru complexes were also grafted onto the organically
modified surfaces of amorphous (fumed) silica for compar-
ison of activity and selectivity in hydrogenation reactions,
where considerable leaching of ruthenium from fumed silica
supports was observed after the reactions.
potassium tert-butoxide (tBuOK), and 2-propanol were pur-
chased from Loba Chemie, India, and were used as received
without further purification.
2.2. Syntheses of parent and organo-functionalized
MCM-41 and MCM-48
Initial molar gel compositions of the syntheses mix-
ture of MCM-41 and MCM-48 were SiO2–0.32 NaOH–
0.2 CTABr–125 H2O and SiO2–0.4 NaOH–0.21 CTABr–
120 H2O, respectively. In a typical synthesis, fumed silica
(3 g) was added to a solution of x g of NaOH [x = 0.64
(MCM-41), 0.8 (MCM-48)] in 25 mL H2O and stirred for
1 h. To this mixture, a solution of y g of CTABr [y = 3.64
(MCM-41), 3.82 (MCM-48)] in 50 mL H2O was added
dropwise and stirred for another 1 h. Finally z mL of H2O
[z = 37 (MCM-41), 33 (MCM-48)] was added to the synthe-
sis gel, stirred further for 30 min, and autoclaved at 100 ◦C
for 16 h (MCM-41), and at 150 ◦C for 36 h (MCM-48). All
the as-synthesized mesoporous samples were air-calcined at
540 ◦C for 10 h.
Surface modification of MCM-41 and MCM-48 materi-
als was achieved by a postsynthesis grafting method [23].
One gram of the calcined MCM-41 or MCM-48 materials
was suspended in 30 mL of dry dichloromethane (DCM),
and first treated with 0.03 mL of dichlorodiphenylsilane
(Ph2SiCl2) for 1 h under inert conditions to passivate the
silanol groups on the external surface by silylation [26].
By this method the tethering of desired organic functional
groups is expected to occur predominantly inside the chan-
nels [26]. The contents were then cooled to liquid N2 tem-
perature and 1 mL of the desired trialkoxyorganosilane
(TPEN or CPTS) was added dropwise to this slurry. The
temperature was gradually increased to 40 ◦C and the re-
action mixture was further stirred for 24 h under inert at-
mosphere, filtered, washed several times with dry DCM,
and dried under vacuum. The resultant ethylenediamine- and
chloro-functionalized mesoporous materials thus obtained
were designated as EN-MCM-41/48 and Cl-MCM-41/48,
respectively.
2.3. Anchoring of RuCl2(PPh3)3 and Ru–(S)-BINAP
complexes inside ethylenediamine-functionalized MCM-41
and MCM-48
2. Experimental
2.1. Materials
The RuCl2(PPh3)3 complex was synthesized applying a
published procedure [27]. One gram of EN-MCM-41 or
EN-MCM-48 was added to a solution containing 38 mg
(0.04 mmol) of the RuCl2(PPh3)3 complex dissolved in
30 mL of dry DCM, and the mixture was stirred at room tem-
perature for 12 h under inert atmosphere, filtered, washed
with dry DCM, and dried under vacuum. The resultant ma-
terial was designated as RuP-EN-MCM-41/48 (Scheme 1A).
The [Ru(benzene)Cl2]2 complex was synthesized apply-
ing a published procedure [28]. One gram of the EN-MCM-
41/48 sample was treated with 30 mg (0.06 mmol) of the
RuCl3 · xH2O,
(SDPEN), (S)-2,2ꢀ-bis(diphenylphosphino)-1,1ꢀ-binaphthyl
[(S)-BINAP], N-[3-(trimethoxysilyl)propyl]-ethylenedi-
amine (TPEN), 3-chloropropyltrimethoxy silane (CPTS),
fumed silica (surface area = 384 m2 g−1), dichlorodiphenyl-
silane (Ph2SiCl2), acetophenone, p-methylacetophenone,
p-chloroacetophenone,p-methoxyacetophenone,propiophe-
none, cyclohexylmethylketone, and cyclobutylphenylketone
were purchased from Aldrich. Cetyltrimethylammonium
bromide (CTABr), triethylamine (NEt3), ethylmethylketone,
(S,S)-1,2-diphenylethylenediamine

388
A. Ghosh, R. Kumar / Journal of Catalysis 228 (2004) 386–396
Scheme 1. (A) Immobilization of RuCl (PPh ) complex onto ethylenediamine-functionalized MCM-41 and MCM-48. (B) Immobilization of Ru–(S)-BINAP
2
3 3
complex inside ethylenediamine-functionalized MCM-41 and MCM-48. (C) Covalent tethering of SDPEN on chloro-functionalized MCM-41 and MCM-48,
and immobilization of Ru–(S)-BINAP complex on the resultant SDPEN-MCM-41 and SDPEN-MCM-48 materials.
[Ru(benzene)Cl2]2 complex and 75 mg (0.12 mmol) of (S)-
2,2ꢀ-bis(diphenylphosphino)-1,1ꢀ-binaphthyl [(S)-BINAP or
SB] dissolved in 30 mL of dry DCM and refluxed for 12 h
under N2 atmosphere, filtered, washed with dry DCM, and
dried under vacuum. The resultant material was designated
as Ru–SB-EN-MCM-41/48 (Scheme 1B).
plex and 75 mg (0.12 mmol) of (S)-BINAP (SB) dissolved
in 30 mL of dry DCM and refluxed for 12 h under N2 at-
mosphere, filtered, washed with dry DCM, and dried under
vacuum. The resultant material was designated as Ru–SB–
SDPEN-MCM-41/48 (Scheme 1C).
2.5. Grafting of different Ru complexes on surfaces of
amorphous silica
2.4. Grafting of (S,S)-1,2-diphenylethylenediamine
(SDPEN) inside chloro-functionalized MCM-41 and
MCM-48, and anchoring of Ru–(S)-BINAP complex
The surfaces of amorphous silica were also organically
modified according to the following procedure. One gram of
fumed silica was suspended in 30 mL of dry DCM, and to
this either 1 mL of TPEN or 1 mL of CPTS was added drop-
wise. The reaction mixture was stirred for 24 h under inert
atmosphere and reflux conditions, filtered, washed several
times with dry DCM, and dried under vacuum to obtain the
respective organo-functionalized silica materials designated
as EN–SiO2 or Cl–SiO2, respectively.
Further, 1 g of the Cl–SiO2 material was added to a solu-
tion containing 106 mg (0.5 mmol) of SDPEN and 0.14 mL
of triethylamine (NEt3) in 30 mL of dry methanol, refluxed
for 24 h under inert conditions, filtered, washed with a
methanol–water mixture and then with methanol, and dried
A chiral diamine moiety was introduced into the inner
surfaces of MCM-41 and MCM-48 via a nucleophilic sub-
stitution mechanism (Scheme 1C). The chiral diamine com-
pound chosen here was (S,S)-1,2-diphenylethylenediamine.
One gram of chloro-functionalized MCM-41 or MCM-48
(Cl-MCM-41/48) was added to a solution containing 106 mg
(0.5 mmol) of SDPEN and 0.14 mL of triethylamine (NEt3)
in 30 mL of dry methanol, refluxed for 24 h under inert con-
ditions, filtered, washed with a methanol–water mixture and
then with methanol, and dried under vacuum. The resultant
material was designated as SDPEN-MCM-41/48.
One gram of the SDPEN-MCM-41/48 material was
treated with 30 mg (0.06 mmol) of [Ru(benzene)Cl2]2 com-

A. Ghosh, R. Kumar / Journal of Catalysis 228 (2004) 386–396
389
under vacuum. The resultant material was designated as
SDPEN–SiO2.
The RuCl2(PPh3)3 and Ru–(S)-BINAP complexes were
anchored on EN–SiO2 and SDPEN–SiO2 materials by
similar methods as in the case of MCM-41 or MCM-48
(Scheme 1). The resultant materials were designated as
RuP–EN–SiO2, Ru–SB–EN–SiO2, and Ru–SB–SDPEN–
SiO2, respectively.
2.6. Catalytic hydrogenation reactions
The catalytic hydrogenation reactions of different prochi-
ral aliphatic, alicyclic, and aromatic ketones were performed
in a 100 mL high-pressure autoclave at temperatures rang-
ing from 80 to 120 ◦C, H2 pressure ranging from 0.34 to
2.76 MPa, stirring speed 500 rpm, and for different dura-
tions ranging from 1 to 6 h. One hundred milligrams of
the solid catalyst, potassium tert-butoxide as the base, and
2-propanol as solvent were used in each reaction. Thereafter,
the catalysts were recovered from the hot reaction mixtures
by filtration and recycled four times for hydrogenation of the
same substrates under identical conditions.
Fig. 1. Powder XRD patterns of the (A) (a) EN-MCM-41, (b) SDPEN-
MCM-41, (c) RuP–EN-MCM-41, (d) Ru–SB–EN-MCM-41, and (e) Ru–
SB–SDPEN-MCM-41 materials; and (B) (a) EN-MCM-48, (b) SDPEN-
MCM-48, (c) RuP–EN-MCM-48, (d) Ru–SB–EN-MCM-48, and (e) Ru–
SB–SDPEN-MCM-48 materials.
by measuring the optical rotation of the individual enan-
tiomers on a JASCO DIP-1020 digital polarimeter and com-
paring with the literature [29,30]. Further, the separated
enantiomers were also analyzed by GC to confirm their re-
spective retention time and quantification.
Inductively coupled plasma–atomic emission spectro-
scopic (ICP-AES) analyses of the catalysts before and after
reactions and the reaction mixtures after filtration of the cat-
alysts were performed on a Perkin–Elmer 1200 inductively
coupled plasma spectrophotometer.
2.7. Characterization techniques
Powder XRD patterns were recorded at room tempera-
ture on a Rigaku D Max III VC instrument with Ni-filtered
Cu-Kα radiation (λ = 1.5404 Å), in the 2θ range 1.5–10◦
at a scan rate of 1◦ min−1. The specific surface areas of the
samples were determined by the BET method from N2 ad-
sorption isotherms at 77 K using an Omnisorb CX-100 Coul-
ter instrument. Prior to the adsorption experiments, the sam-
ples were activated at 150 ◦C for 6 h at 1.333 ×10−2 Pa. The
FTIR spectra were recorded at diffuse reflectance mode on a
Perkin–Elmer Spectrum One spectrophotometer operated at
a resolution of 4 cm−1. The 31P CP MAS NMR spectra were
recorded at 11.7 T and 202.64 MHz in a Bruker DRX-500
FT NMR spectrophotometer. XPS analyses of the catalysts
before and after hydrogenation reactions were recorded on
a VG Microtech ESCA 3000 spectrometer using unmono-
chromatized Mg-Kα radiation (photon energy = 1253.6 eV)
at a pressure better than 0.133 µPa, pass energy of 50 eV, and
electron take-off angle of 60◦. TEM images of the samples
were recorded on a Jeol Model 1200 EX instrument operated
at an accelerating voltage of 100 kV.
The reaction mixtures were analyzed by an Agilent 6890
series gas chromatograph (GC) containing a chiral capil-
lary column (10% permethylated β-cyclodextrin, 30 m ×
0.32 mm × 0.25 µm film thickness) and flame ionization de-
tector. The enantiomeric excess (ee) values were determined
quantitatively from integration of peak areas in the chro-
matogram. The products were also confirmed by GC–mass
spectroscopy (GCMS) on a Shimadzu GCMS-QP 2000A in-
strument. The absolute configuration of the products was
determined after chemical separation of the enantiomers,
3. Results and discussion
3.1. Powder X-ray diffraction
Fig. 1A shows the powder X-ray diffraction (XRD) pat-
terns recorded from (a) EN-MCM-41, (b) SDPEN-MCM-
41, (c) RuP-EN-MCM-41, (d) Ru–SB-EN-MCM-41, and
(e) Ru–SB–SDPEN-MCM-41 materials. The typical hexag-
onal phase (p6mm) of MCM-41 [main (100) peak with weak
(110), (200), and (210) reflections] is clearly visible in all
the samples. Fig. 1B shows the XRD patterns of the (a) EN-
MCM-48, (b) SDPEN–MCM-48, (c) RuP–EN-MCM-48,
(d) Ru–SB-EN-MCM-48, and (e) Ru–SB–SDPEN-MCM-
48 materials, in which the strong (211) and (220) reflections
along with the weak (321), (400), (420), (322), (422), and
(431) reflections are observed in all the materials, charac-
teristic of the cubic phase (Ia3d) of MCM-48. These re-
sults indicate ordered mesoporosity even after incorporation
of organic functional groups and Ru complexes. However,
a slight decrease in the peak intensities was observed in the
case of the Ru complex loaded samples, which might be due

390
A. Ghosh, R. Kumar / Journal of Catalysis 228 (2004) 386–396
Table 1
Physical characteristics of the organo-functionalized MCM-41 and MCM-48 materials before and after anchoring of RuCl (PPh ) and Ru–(S)-BINAP
2
3 3
complexes
a
b
c
a
Materials
% Ru
d
Pore
diameter
(Å)
Pore
Surface
area
(m g
hkl
0
(w/w)
(Å)
(Å)
volume
3
−1
2
−1
)
(cm g
)
EN-MCM-41
–
41.05 (100)
41.15 (100)
41.79 (100)
40.11 (100)
40.49 (100)
40.83 (100)
47.40
47.52
48.25
46.31
46.75
47.15
28.43
28.39
28.42
29.79
29.82
29.75
1.06
0.90
0.83
1.08
0.93
0.84
993
864
824
1031
877
828
RuP–EN-MCM-41
Ru–SB–EN-MCM-41
Cl-MCM-41
SDPEN-MCM-41
Ru–SB–SDPEN-MCM-41
0.309
0.329
–
–
0.348
EN-MCM-48
–
38.12 (211)
38.67 (211)
38.77 (211)
38.92 (211)
39.05 (211)
39.09 (211)
93.37
94.72
94.97
95.33
95.65
95.75
25.40
25.31
25.36
26.93
26.91
27.01
1.19
1.07
0.98
1.23
1.06
0.95
1336
1176
1122
1510
1268
1141
RuP–EN-MCM-48
Ru–SB–EN-MCM-48
Cl-MCM-48
SDPEN-MCM-48
Ru–SB–SDPEN-MCM-48
0.319
0.351
–
–
0.335
d
RuP–EN–SiO
Ru–SB–EN–SiO
Ru–SB–SDPEN–SiO
0.327
0.345
0.329
–
–
–
–
–
–
–
–
–
–
–
–
n.d.
n.d.
n.d.
2
2
2
a
Analyzed from ICP-AES.
b
c
d
Calculated from XRD patterns (nλ = 2d sinθ, where n = 1 and λ = 1.5404 Å). Values in parentheses are respective principal Miller indices.
√
√
a
0
= d
× 2/ 3 (for MCM-41); a = d
×
6 (for MCM-48).
100
0
211
n.d., not determined.
to partial filling of the void space due to the presence of Ru
complexes inside the mesopores.
3.3. FTIR spectra
Fig. 2 shows the FTIR spectra of the (A) (a) RuP–
EN-MCM-41 and (b) Ru–SB–SDPEN-MCM-41 materials;
and (B) (a) RuP–EN-MCM-48 and (b) Ru–SB–SDPEN-
MCM-48 materials. Insets show the FTIR spectra of the
(A) SDPEN-MCM-41 and (B) SDPEN-MCM-48 materials.
The characteristic P–Ph band at ca. 1086 cm−1 [31] were
observed in the spectra of the RuP–EN-MCM-41/48 and
Ru–SB–SDPEN-MCM-41/48 materials, clearly indicating
the incorporation of Ru–phosphine complexes. In the case
of SDPEN-MCM-41 (inset of Fig. 2A) and SDPEN-MCM-
48 (inset of Fig. 2B) materials, the characteristic bands of
–NH2 at 3303 and 3365 cm−1 and another two bands at 2935
and 2872 cm−1 corresponding to asymmetric and symmet-
ric vibrations, respectively, of the –CH2 groups of the propyl
chain of the silylating agent were observed, indicative of an-
choring of amine moieties in the mesopores.
A comparison of d spacings and unit cell parameter (a0)
values (calculated from XRD patterns) of the functionalized
MCM-41 and MCM-48 materials, and those with anchored
Ru complexes, is presented in Table 1. The Ru contents
in each material (including the Ru complex–SiO2 compos-
ite materials), analyzed by ICP-AES, are also included in
Table 1.
3.2. Specific surface area
The specific surface area, pore volume, and pore diameter
values (estimated from N2 adsorption–desorptionisotherms)
of the functionalized MCM-41 and MCM-48 materials, and
those with anchored Ru complexes, are presented in Table 1.
In the case of EN-MCM-41 material, ca. 13 and 17% de-
creases in surface area values were observed after incorpo-
ration of RuCl2(PPh3)3 and Ru–(S)-BINAP complexes, re-
spectively. Similar decreases were observed after anchoring
of SDPEN and Ru–(S)-BINAP (ca. 15 and 20%, respec-
tively) inside Cl-MCM-41 material. Analogous trends were
also observed in the surface area values of the MCM-48
materials, and in the pore volumes of the MCM-41 and
MCM-48 materials after anchoring of the Ru complexes.
The pore diameter values of these materials, however, did
not change considerably after anchoring of the Ru com-
plexes. All these results indicate that partial filling of the
mesopores had occurred by the aforesaid complexes, which
are anchored inside of the pore structure.
3.4. 31P CP MAS NMR spectra
The 1H–31P coupled CP MAS NMR spectra of the
(a) RuP–EN-MCM-41, (b) Ru–SB–EN-MCM-41, and (c)
Ru–SB–SDPEN-MCM-41 materials are given in Fig. 3. The
spectrum of the RuP–EN-MCM-41 material reveals two ma-
jor 31P signals at δ = 36 and 69 ppm, each split by J coupling
to other 31P nuclei (Fig. 3, curve a). The integrated intensity
for these major signals is in the ratio 1:1. The RuCl2(PPh3)3
molecule has a distorted square pyramidal structure, with the
equatorial positions occupied by two PPh3 groups trans to
each other, and two –Cl ligands trans to each other. Another
PPh3 group occupies the axial position (Scheme 1A). This

A. Ghosh, R. Kumar / Journal of Catalysis 228 (2004) 386–396
391
Fig. 2. FTIR spectra of the (A) (a) RuP–EN-MCM-41 and (b) Ru–SB–SDPEN-MCM-41 materials; and (B) (a) RuP–EN-MCM-48 and (b) Ru–SB–
SDPEN-MCM-48 materials. Insets represent the FTIR spectra of the (A) SDPEN-MCM-41 and (B) SDPEN-MCM-48 materials.
rial, in which two distinct peaks of almost equal intensity
were observed (Fig. 3, curve a), signifying the existence of
two nonequivalent phosphorus atoms in the material.
The 31P NMR spectra of the Ru–SB–EN-MCM-41 and
Ru–SB–SDPEN-MCM-41 materials (Fig. 3, curves b and c)
also show two distinct peaks of approximately equal inten-
sity at δ ∼ 40 and 71 ppm, which can also be attributed to
the presence of two nonequivalent phosphorus atoms of the
BINAP ligand inside the material. The inclusion of the EN
and SDPEN moieties on the mesoporous silica surface leads
to two nonequivalent phosphorus environments inside the
Ru–SB–EN-MCM-41 (Scheme 1B) and Ru–SB–SDPEN-
MCM-41 (Scheme 1C) materials, respectively, which ac-
1
31
counts for the two strong 31P signals.
Fig. 3. The H– P coupled CP MAS NMR spectra of the (a) RuP–EN-
MCM-41, (b) Ru–SB–EN-MCM-41, and (c) Ru–SB–SDPEN-MCM-41
materials.
3.5. X-ray photoelectron spectra
makes the central Ru nuclei coordinatively unsaturated. The
three phosphorus atoms in RuCl2(PPh3)3 may be grouped
into (i) one distinct (one PPh3 group in axial position) and
(ii) two equivalent (two PPh3 groups in equatorial position
trans to each other) phosphorus environments (Scheme 1A).
On interaction of RuCl2(PPh3)3 with the chelating ethyl-
enediamine ligand of the EN-MCM-41 material, one PPh3
group in the equatorial position leaves the system due to a
strong trans effect of another PPh3 group. Thus, the biden-
tate ethylenediamine ligand coordinates with the Ru nuclei
through (i) the vacant equatorial position created by the PPh3
group, and (ii) through the already vacant axial position,
thus creating two nonequivalent phosphorus environments
(Scheme 1A). This mechanism depicted in Scheme 1A is
supported by the spectrum of the RuP–EN-MCM-41 mate-
Additional support for the anchoring of the RuII com-
plexes onto the solid mesoporous materials was obtained by
XPS analyses. Table 2 represents the Ru 3d5/2, Ru 3p3/2
,
N 1s, Si 2p, and P 2p core-level binding energies (BE)
obtained from XPS analyses of the EN-MCM-41/48 and
SDPEN-MCM-41/48 materials before and after anchoring
of RuCl2(PPh3)3 and Ru–(S)-BINAP complexes, and of the
Ru complex–fumed silica composite materials. From the Ru
3d5/2 and 3p3/2 BE values at ca. 280 eV and ca. 465 eV, re-
spectively, it is evident that all ruthenium in the catalysts are
present as RuII species [32]. The P 2p BE values are also
consistent with those obtained from RuII–phosphine com-
plexes [32]. This further showed that the integrity of the
RuCl2(PPh3)3 and Ru–(S)-BINAP complexes was retained

392
A. Ghosh, R. Kumar / Journal of Catalysis 228 (2004) 386–396
Table 2
a
Core-level binding energies (in eV) of various elements present in the catalyst precursors and the anchored catalysts
Materials
Ru 3d
Ru 3p
N 1s
Si 2p
P 2p
5/2
3/2
EN-MCM-41
–
–
399.4
400.1
400.2
400.1
400.7
103.4
103.4
103.4
103.4
103.4
–
RuP–EN-MCM-41
Ru–SB–EN-MCM-41
SDPEN-MCM-41
Ru–SB–SDPEN-MCM-41
280.5
280.8
–
464.8
465.0
–
131.3
131.5
–
280.8
465.0
131.6
EN-MCM-48
–
–
399.5
400.2
400.3
400.0
400.6
103.4
103.4
103.4
103.4
103.4
–
RuP–EN-MCM-48
Ru–SB–EN-MCM-48
SDPEN-MCM-48
Ru–SB–SDPEN-MCM-48
280.5
280.7
–
464.9
465.0
–
131.3
131.4
–
280.7
465.0
131.5
RuP–EN–SiO
Ru–SB–EN–SiO
Ru–SB–SDPEN–SiO
280.6
280.8
280.8
464.8
464.9
464.9
400.3
400.3
400.5
103.3
103.3
103.3
131.4
131.5
131.6
2
2
2
a
The core-level binding energies were aligned with respect to the C 1s binding energy of 285 eV using adventitious carbon.
when anchored into the supports, with no beam damage suf-
fered by the supports.
area electron diffraction (SAED) patterns of the samples
shown in Figs. 4B and 4D are given in Figs. 4E and 4F, re-
spectively. The TEM images and SAED patterns are well
consistent with the regular hexagonal and cubic mesophases
of MCM-41 and MCM-48, respectively, with homogeneity
in patterns throughout, which indicates the retention of or-
dered patterns of MCM-41 and MCM-48 even after anchor-
ing of the above-noted RuII–phosphine complexes, further
corroborating the XRD results (Fig. 1).
The N 1s BE values in the EN-MCM-41/48 and SDPEN-
MCM-41/48 materials indeed confirm successful grafting of
amine moieties inside the mesopores, previously inferred
from FTIR spectra (insets of Fig. 2). However, an increase
in N 1s BE values by ca. 0.6–0.7 eV was observed after
loading of the Ru complexes in each material, which can
be attributed to coordination of N atoms with the RuII nu-
clei. All these results strongly support the stable anchoring
and immobilization of RuCl2(PPh3)3 and Ru–(S)-BINAP
complexes onto the surface of MCM-41 and MCM-48 meso-
porous materials.
3.7. Enantioselective hydrogenation of prochiral ketones
All the heterogeneous catalysts prepared in this study
were exploited in the enantioselective hydrogenation of
prochiral aliphatic, alicyclic, and aromatic ketones, and the
results are summarized in Table 3 (for aliphatic and alicyclic
ketones) and Table 4 (for aromatic ketones). Similar reac-
tions were also performed with the pure Ru–SB–SDPEN
3.6. Transmission electron microscopy
Fig. 4 represents TEM images recorded from (A) RuP–
EN-MCM-41, (B) Ru–SB–SDPEN-MCM-41, (C) RuP–EN-
MCM-48, and (D) Ru–SB–SDPEN-MCM-48. The selected
Fig. 4. TEM images of the (A) RuP–EN-MCM-41, (B) Ru–SB–SDPEN-MCM-41, (C) RuP–EN-MCM-48, and (D) Ru–SB–SDPEN-MCM-48. (E) and (F)
show the SAED patterns of the samples shown in (B) and (D), respectively.

A. Ghosh, R. Kumar / Journal of Catalysis 228 (2004) 386–396
393
Table 3
Enantioselective hydrogenation of prochiral aliphatic and alicyclic ketones
a
Ru–SB–SDPEN-MCM-41/48
+ H −−−−−−−−−−−−−−−−−−−−−→
2
t
BuOK, 2-Propanol
b
c
Entry
Catalyst
Substrate
Conversion
(mol%)
TOF
(h
ee
(%)
−1
)
1
1
1
1
1
1
1
1
1
1
2
1
2
3
4
5
6
7
8
9
RuP–EN-MCM-41
R
R
R
R
R
R
R
R
R
R
= C H , R = CH
91
93
96
90
94
97
91
> 99
72
79
515
495
483
494
469
507
455
940
362
394
16
28
99
14
29
99
90
> 99
91
94
2
5
3
3
3
3
3
3
3
3
2
Ru–SB–EN-MCM-41
Ru–SB–SDPEN-MCM-41
RuP–EN-MCM-48
Ru–SB–EN-MCM-48
Ru–SB–SDPEN-MCM-48
= C H , R = CH
2
5
2
= C H , R = CH
2
5
2
= C H , R = CH
2
5
2
= C H , R = CH
2
5
2
= C H , R = CH
2
5
2
Ru–SB–SDPEN–SiO
2
= C H , R = CH
2
5
d
2
Ru–SB–SDPEN
= C H , R = CH
2
5
2
Ru–SB–SDPEN-MCM-41
Ru–SB–SDPEN-MCM-48
= Cyclohexyl, R = CH
3
3
2
10
a
= Cyclohexyl, R = CH
Reaction conditions: catalyst = 100 mg; substrate = 7 mmol; substrate:base = 100:1; Ru:substrate = 1:2265 (RuP–EN-MCM-41), 1:2194 (RuP–EN-
MCM-48), 1:2128 (Ru–SB–EN-MCM-41), 1:1994 (Ru–SB–EN-MCM-48), 1:2011 (Ru–SB–SDPEN-MCM-41), 1:2089 (Ru–SB–SDPEN-MCM-48), 1:2000
◦
(Ru–SB–SDPEN); temperature = 100 C; H pressure = 1.38 MPa; stirring speed = 500 rpm; duration = 4 h (heterogeneous), 2 h (homogeneous).
2
b
Absolute configuration of all the reaction products is (S).
c
−1
−1
.
TOF = (mmol of ketone converted to alcohol) × (mmol of Ru) × h
d
Reaction under homogeneous conditions.
Table 4
Enantioselective hydrogenation of prochiral aromatic ketones
a
Ru–SB–SDPEN-MCM-41/48
+ H −−−−−−−−−−−−−−−−−−−−−→
2
t
BuOK, 2-Propanol
b
c
Entry
Catalyst
Substrate
Conversion
(mol%)
TOF
(h
ee
(%)
−1
)
1
2
3
4
5
6
7
RuP–EN-MCM-41
Ar = Ph, R = Me
Ar = Ph, R = Me
Ar = Ph, R = Me
Ar = Ph, R = Me
Ar = Ph, R = Me
Ar = Ph, R = Me
Ar = Ph, R = Me
89
92
94
86
91
96
92
> 99
95
97
98
99
95
96
88
91
75
79
504
489
472
472
454
501
460
990
478
507
493
517
478
501
442
475
377
413
18
Ru–SB–EN-MCM-41
Ru–SB–SDPEN-MCM-41
RuP–EN-MCM-48
Ru–SB–EN-MCM-48
Ru–SB–SDPEN-MCM-48
31
93
22
39
95
94
> 99
94
96
96
98
91
93
95
96
91
93
Ru–SB–SDPEN–SiO
2
d
8
9
Ru–SB–SDPEN
Ar = Ph, R = Me
ꢀ
Ru–SB–SDPEN-MCM-41
Ru–SB–SDPEN-MCM-48
Ru–SB–SDPEN-MCM-41
Ru–SB–SDPEN-MCM-48
Ru–SB–SDPEN-MCM-41
Ru–SB–SDPEN-MCM-48
Ru–SB–SDPEN-MCM-41
Ru–SB–SDPEN-MCM-48
Ru–SB–SDPEN-MCM-41
Ru–SB–SDPEN-MCM-48
Ar = 4 -Me-Ph, R = Me
ꢀ
10
11
12
13
14
15
16
17
18
Ar = 4 -Me-Ph, R = Me
ꢀ
Ar = 4 -Cl-Ph, R = Me
ꢀ
Ar = 4 -Cl-Ph, R = Me
Ar = Ph, R = Et
Ar = Ph, R = Et
ꢀ
Ar = 4 -MeO-Ph, R = Me
ꢀ
Ar = 4 -MeO-Ph, R = Me
Ar = Ph, R = Cyclobutyl
Ar = Ph, R = Cyclobutyl
a
Reaction conditions: catalyst = 100 mg; substrate = 7 mmol; substrate:base = 100:1; Ru:substrate = 1:2265 (RuP–EN-MCM-41), 1:2194 (RuP–EN-
MCM-48), 1:2128 (Ru–SB–EN-MCM-41), 1:1994 (Ru–SB–EN-MCM-48), 1:2011 (Ru–SB–SDPEN-MCM-41), 1:2089 (Ru–SB–SDPEN-MCM-48), 1:2000
◦
(Ru–SB–SDPEN); temperature = 100 C; H pressure = 1.38 MPa; stirring speed = 500 rpm; duration = 4 h (heterogeneous), 2 h (homogeneous).
2
b
Absolute configuration of all the reaction products is (S).
c
−1
−1
.
TOF = (mmol of ketone converted to alcohol) × (mmol of Ru) × h
d
Reaction under homogeneous conditions.
complex [9] under homogeneous conditions for comparative
purposes.
ilar catalytic activity, they exhibit poor enantioselectivity
[ee < 25% (for RuP–EN-MCM-41/48), and < 40% (for Ru–
SB–EN-MCM-41/48)]. From these results it is clear that
both the biphosphine and the diamine ligands around the
central RuII ion necessarily have to be chiral for maxi-
mum enantioselection in agreement with the observations
of Noyori et al. [10,11]. Almost comparable activity and
enantioselectivity of MCM-41- and MCM-48-based cata-
From the tables, it is evident that all the substrates were
hydrogenated with very high conversion (upto 99%) and
excellent enantiomeric excess (upto 99%) by the Ru–SB–
SDPEN-containing catalysts (Table 3, entries 3, 6–10, and
Table 4, entries 3, 6–18). Although, the RuP–EN-MCM-41/
48 and Ru–SB–EN-MCM-41/48 catalysts also show sim-

394
A. Ghosh, R. Kumar / Journal of Catalysis 228 (2004) 386–396
lysts show that the reaction rate does not essentially depend
upon whether the support is MCM-41 or MCM-48, possibly
due to a similar rate of interaction between substrate mole-
cules and catalyst active site. Control experiments with the
homogeneous Ru–SB–SDPEN complex (entry 8 in Tables 3
and 4) show that reaction is ca. twice faster in homogeneous
system vis-à-vis the same complex anchored in MCM-41
and MCM-48. However, the ee was almost comparable. This
could be due to a slower rate of interaction between the sub-
strate and the catalyst in the heterogeneous solid–liquid sys-
tem compared to that in the homogeneous liquid system. In
the case of acyclic ethylmethylketone, while the conversion
is higher vis-à-vis cyclohexylmethylketone (Table 3, entries
3 and 6 versus 9 and 10), as expected due to relative bulki-
ness of the substituent group in the vicinity of the carbonyl
group, the ee in the case of both the substrates was com-
parable. A similar trend was also observed in the case of
acetophenone and cyclobutylphenylketone (Table 4, entries
3 and 6 versus 17 and 18). However, there was insignificant
effect of substitution in the aromatic ring of acetophenone
on the conversion as well as ee (Table 4, entries 3, 6, 9–16)
in agreement with the results obtained by Hu et al. [18]. The
detailed catalytic studies, discussed below, were performed
using acetophenone as substrate.
beginning of the reactions. For the reaction involving the ho-
mogeneous catalyst, the substrate was almost quantitatively
hydrogenated at ca. 2 h time. This accounts for the high TOF
values in the case of the homogeneous catalyst compared to
its heterogeneous counterparts (Tables 3 and 4), expectedly
due to restricted interaction between substrate and catalyst
under heterogeneous conditions compared to that under ho-
mogeneous conditions, as noted above.
3.7.2. Influence of temperature
A critical temperature of 100 ◦C is required to acquire
the activation energy for hydrogenation by the chosen cata-
lyst system, both homogeneous and heterogeneous (Fig. 6).
At this temperature the maximum conversion of acetophe-
none by the Ru–SB–SDPEN-MCM-41/48 catalyst system
was achieved. By increasing the temperature to 120 ◦C, no
further change in reaction rate was observed. However, the
best ee was obtained at 100 ◦C; below and above this tem-
perature the ee decreases slightly.
3.7.3. Influence of H2 pressure
The pressure of molecular hydrogen inside the reaction
vessel has a pronounced effect over the conversion. But
the enantioselectivity of the heterogeneous catalyst does not
significantly depend on the H2 pressure. As represented in
Fig. 7, the conversion of acetophenone markedly increases
with H2 pressure. It was envisaged that maximum conver-
sion of the substrate and ee were achieved at ca. 1.4 MPa
pressure, beyond which no further enhancement in reaction
rate as well as in ee was experienced.
3.7.1. Influence of reaction time
The influence of reaction time over the conversion and
enantioselectivity in the hydrogenation of acetophenone is
presented in Fig. 5. It was found that for MCM-41- and
MCM-48-based heterogeneous catalysts, the conversion in-
creases as the reaction proceeds, as expected, and reaches an
optimum value (> 90%) before 4 h time. The enantiomeric
excess values, however, attain a maximum from the very
Fig. 5. Influence of reaction time over (A) conversion and (B) enan-
tioselectivity in the hydrogenation of acetophenone by the Ru–SB–SDPEN-
MCM-41, Ru–SB–SDPEN-MCM-48, and homogeneous Ru–SB–SDPEN
catalysts.
Fig. 6. Influence of temperature over (A) conversion and (B) enan-
tioselectivity in the hydrogenation of acetophenone by the Ru–SB–SDPEN-
MCM-41, Ru–SB–SDPEN-MCM-48, and homogeneous Ru–SB–SDPEN
catalysts.

A. Ghosh, R. Kumar / Journal of Catalysis 228 (2004) 386–396
395
cant leaching of the metal and therefore metal complex. Be-
sides, both of these catalysts were effectively recycled four
times for hydrogenation of acetophenone without any sig-
nificant decline in activity and enantioselectivity (Table 5).
In contrast to these, the catalyst prepared by anchoring the
Ru–(S)-BINAP complex onto SDPEN-functionalized fumed
silica (Ru–SB–SDPEN–SiO2 material) showed a substantial
amount of leaching of Ru metal (ca. 26.5% of the total Ru
content present in the catalyst used) during reaction in the
first cycle, which also leads to a major decrease in catalytic
activity and selectivity after four recycles (Table 5).
The stability of the heterogeneous catalysts after hydro-
genation reactions was also supported from XPS analyses
of the filtered catalysts. The core-level BE of the elements
in the recycled MCM-41- and MCM-48-based catalysts (Ta-
ble 6) match exactly with those in the parent materials be-
fore reaction (Table 2), indicating that neither the metal nor
the ligands changed their chemical environment during re-
actions. However, in the case of the Ru–SB–SDPEN–SiO2
sample, the Ru 3d5/2 BE could not be evaluated since the
core-level spectra merged with the C 1s spectra (Table 6).
Moreover, the characteristic Ru 3p3/2 peak at ca. 465 eV
was not observed at all (Table 6) due to insufficient concen-
tration of RuII species mainly because of significant leaching
of the Ru complex from the silica matrix.
Fig. 7. Influence of H pressure over (A) conversion and (B) enan-
2
tioselectivity in the hydrogenation of acetophenone by the Ru–SB–SDPEN-
MCM-41, Ru–SB–SDPEN-MCM-48, and homogeneous Ru–SB–SDPEN
catalysts.
3.7.4. Recycle studies
The stability of the heterogeneous catalysts was evaluated
by recovering them from the hot reaction mixtures by filtra-
tion, and analyzing the filtrates for Ru content by ICP-AES.
In the case of Ru–SB–SDPEN-MCM-41/48 catalysts, the Ru
4. Summary and conclusions
In conclusion, the synthesis of efficient heterogeneous
catalyst systems, by anchoring of RuCl2(PPh3)3 and Ru–
(S)-BINAP complexes inside ethylenediamine- and (S,S)-
contents in the total filtrate were found to be ca. 1 × 10−3
%
of the total Ru present in the catalyst, indicating insignifi-
Table 5
Recycle studies of the heterogeneous catalysts for hydrogenation of acetophenone
Ru–SB–SDPEN–SiO
Ru–SB–SDPEN-MCM-41
Ru–SB–SDPEN-MCM-48
No. of
2
recycles
Conversion
(mol%)
ee
(%)
Conversion
(mol%)
ee
(%)
Conversion
(mol%)
ee
(%)
0
1
2
3
4
92.0
78.3
58.9
42.3
20.6
94
84
72
71
70
94.0
93.7
93.8
93.5
93.3
93
93
93
93
93
96.0
95.9
95.7
95.8
95.4
95
95
95
95
95
Table 6
a
Core-level binding energies (in eV) of various elements in the recycled heterogeneous catalysts after hydrogenation of acetophenone
b
Catalysts
Ru
3d
Ru
3p
N
1s
Si
2p
P
2p
No. of
recycles
5/2
3/2
Ru–SB–SDPEN-MCM-41
1
2
280.8
280.8
465.0
465.0
400.7
400.7
103.4
103.4
131.6
131.6
Ru–SB–SDPEN-MCM-48
1
2
280.7
280.7
465.0
465.0
400.6
400.6
103.4
103.4
131.5
131.5
c
d
Ru–SB–SDPEN–SiO
a
1
m
n.d.
400.5
103.3
131.6
2
The core-level binding energies were aligned with respect to the C 1s binding energy of 285 eV using adventitious carbon.
b
c
d
The catalysts were filtered from hot reaction mixtures, washed thoroughly with 2-propanol and DCM, and thereafter analyzed by XPS.
m, merged with the C 1s core-level spectra, could not be identified separately.
n.d., not detected.

396
A. Ghosh, R. Kumar / Journal of Catalysis 228 (2004) 386–396
1,2-diphenylethylenediamine-functionalized MCM-41 and
MCM-48, for enantioselective hydrogenation of prochiral
carbonyl compounds, has been demonstrated. In depth char-
acterization of these new catalyst systems by powder XRD,
FTIR, ICP-AES, N2 adsorption, 31P CP MAS NMR, XPS,
and TEM analyses strongly point toward stable immobi-
lization of the RuII complexes inside the mesoporous ma-
trices. The Ru–(S)-BINAP complex anchored on SDPEN-
functionalized MCM-41/48 (Ru–SB–SDPEN-MCM-41/48)
reveals excellent activity and enantioselectivity. The enan-
tioselectivity of the catalysts does not essentially depend
upon the duration of reaction, temperature, and pressure of
hydrogen. Both the biphosphine and diamine ligands neces-
sarily have to be chiral to achieve maximum enantioselectiv-
ity in the hydrogenation of prochiral ketones. This catalyst
system can be recycled effectively and reused several times
without any leaching of the metal complex from the support
and without any decline in activity and selectivity.
[5] J. Halpern, Science 217 (1982) 401.
[6] R. Noyori, Asymmetric Catalysis in Organic Synthesis, Wiley, New
York, 1994, Chap. 2, pp. 17–94.
[7] T. Ohkuma, R. Noyori, in: E.N. Jacobsen, A. Pfaltz, H. Yamamoto
(Eds.), Comprehensive Asymmetric Catalysis, vol. 1, Springer, Berlin,
1999, pp. 199–246.
[8] T. Ohkuma, H. Ooka, S. Hashiguchi, T. Ikariya, R. Noyori, J. Am.
Chem. Soc. 117 (1995) 2675.
[9] T. Ohkuma, H. Ooka, T. Ikariya, R. Noyori, J. Am. Chem. Soc. 117
(1995) 10417.
[10] R. Noyori, T. Ohkuma, Angew. Chem. Int. Ed. 40 (2001) 40.
[11] R. Noyori, M. Yamakawa, S. Hashiguchi, J. Org. Chem. 66 (2001)
7931.
[12] R. Noyori, S. Hashiguchi, Acc. Chem. Res. 30 (1997) 97.
[13] P.N. Liu, P.M. Gu, F. Wang, Y.Q. Tu, Org. Lett. 6 (2004) 169.
[14] T. Ohkuma, H. Takeno, Y. Honda, R. Noyori, Adv. Synth. Catal. 343
(2001) 369.
[15] D.E. De Vos, M. Dams, B.F. Sels, P.A. Jacobs, Chem. Rev. 102 (2002)
3615.
[16] C.E. Song, S. Lee, Chem. Rev. 102 (2002) 3495.
[17] A. Hu, H.L. Ngo, W. Lin, Angew. Chem. Int. Ed. 42 (2003) 6000.
[18] A. Hu, H.L. Ngo, W. Lin, J. Am. Chem. Soc. 125 (2003) 11490.
[19] A. Zsigmond, K. Bogar, F. Nothiesz, J. Catal. 213 (2003) 103.
[20] P. McMorn, G.J. Hutchings, Chem. Soc. Rev. 33 (2004) 108.
[21] R. Raja, J.M. Thomas, M.D. Jones, B.F.G. Johnson, D.E.W. Vaughan,
Acknowledgments
J. Am. Chem. Soc. 125 (2003) 14982.
[22] M.D. Jones, R. Raja, J.M. Thomas, B.F.G. Johnson, D.W. Lewis,
J. Rouzaud, K.D.M. Harris, Angew. Chem. Int. Ed. 42 (2003) 4326.
[23] A. Stein, B.J. Melde, R.C. Schroden, Adv. Mater. 12 (2000) 1403.
[24] P. Mukherjee, S. Laha, D. Mandal, R. Kumar, Stud. Surf. Sci.
Catal. 129 (2000) 283.
[25] J.M. Thomas, Angew. Chem. Int. Ed. 38 (1999) 3588.
[26] D.S. Shephard, W. Zhou, T. Maschmeyer, J.M. Matters, C.L. Roper,
S. Parsons, B.F.G. Johnson, M.J. Duer, Angew. Chem. Int. Ed. 37
(1998) 2719.
A.G. acknowledges Council of Scientific and Industrial
research (CSIR), Government of India for a research fellow-
ship. The authors thank a research grant from CSIR network-
ing project CMM0005 on “Catalysis and Catalysts”.
References
[27] F.H. Jardine, Prog. Inorg. Chem. 31 (1984) 265.
[28] M.A. Bennett, A.K. Smith, J. Chem. Soc., Dalton Trans. (1974) 233.
[29] H.C. Brown, B.T. Cho, W.S. Park, J. Org. Chem. 53 (1988) 1231.
[30] K. Nakamura, T. Matsuda, J. Org. Chem. 63 (1998) 8957.
[31] D. Venegas-Yazigi, M. Campos-Vallette, A.B.P. Lever, J. Costamagna,
R.O. Latorre, W. Hernandez G., J. Chil. Chem. Soc. 48 (2003) 79.
[32] J.W. Robinson (Ed.), Practical Handbook of Spectroscopy, CRC Press,
Boca Raton, FL, 1991, pp. 183–418.
[1] A.N. Collins, G.N. Sheldrake, J. Crosby (Eds.), Chirality in Industry:
The Commercial Manufacture and Applications of Optically Active
Compounds, Wiley, New York, 1997.
[2] R.A. Sheldon, Chirotechnology, Dekker, New York, 1993.
[3] I. Ojima (Ed.), Catalytic Asymmetric Synthesis, second ed., Wiley,
New York, 2000.
[4] R. Noyori, (Nobel Lecture 2001) Adv. Synth. Catal. 345 (2003) 15.