Magnetically recoverable nanoparticles: Highly efficient catalysts for asymmetric transfer hydrogenation of aromatic ketones in aqueous medium

Article abstract of DOI:10.1002/adsc.201100017

Two magnetic chiral iridium and rhodium catalysts were prepared via directly postgrafting 1,2-diphenylethylenediamine-derived organic silica or 1,2-cyclohexanediamine-derived organic silica onto the silica-coated iron oxide nanoparticles followed by complexation with iridium(III) or rhodium(III) complexes. During the asymmetric transfer hydrogenation of aromatic ketones in aqueous medium, the magnetic chiral catalysts exhibited high catalytic activities (up to 99% conversion) and enantioselectivities (up to 92% ee). Both catalysts could be recovered easily by magnetic separation and be reused ten times without significantly affecting their catalytic activities and enantioselectivities.

Full text of DOI:10.1002/adsc.201100017

FULL PAPERS
DOI: 10.1002/adsc.201100017
Magnetically Recoverable Nanoparticles: Highly Efficient
Catalysts for Asymmetric Transfer Hydrogenation of Aromatic
Ketones in Aqueous Medium
a,
a
a
a
a
Guohua Liu, * Hongyuan Gu, Yunqiang Sun, Jie Long, Yulong Xu,
a,
and Hexing Li *
a
The Key Laboratory of Resource Chemistry of Ministry of Education, College of Life and Environmental Science,
Shanghai Normal University, Shanghai 200234, Peopleꢀs Republic of China
Fax : (+86)-21-6432-2511; phone: (+86)-21-6432-1819; e-mail: ghliu@shnu.edu.cn or HeXing-Li@shnu.edu.cn
Received: January 9, 2011; Published online: May 17, 2011
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.201100017.
Abstract: Two magnetic chiral iridium and rhodium tivities (up to 99% conversion) and enantioselectivi-
catalysts were prepared via directly postgrafting 1,2- ties (up to 92% ee). Both catalysts could be recov-
diphenylethylenediamine-derived organic silica or ered easily by magnetic separation and be reused ten
1
,2-cyclohexanediamine-derived organic silica onto times without significantly affecting their catalytic
the silica-coated iron oxide nanoparticles followed activities and enantioselectivities.
by complexation with iridium(III) or rhodium(III)
A
H
U
G
E
N
N
ACHTUNGTRENNUNG
complexes. During the asymmetric transfer hydroge- Keywords: asymmetric transfer hydrogenation; cata-
nation of aromatic ketones in aqueous medium, the lyst recycling; enantioselectivity; magnetic nanoparti-
magnetic chiral catalysts exhibited high catalytic ac- cles; magnetic separation
Introduction
Fe O nanoparticles as a support and directly post-
3 4
modified chiral ruthenium complexes onto magnetic
Heterogeneous catalysts for asymmetric catalysis nanoparticles, which exhibited excellent enantioselec-
have attracted a great deal of interest due to their tivity and remarkable reusability in the asymmetric
general advantages of easy separation and efficient hydrogenation of aromatic ketones. Recently, a simi-
[1]
recycling. Among these heterogeneous catalysts ex- lar strategy for enantioselective acylation has also ap-
[
4b]
plored so far, magnetic catalysts show some salient peared in the literature.
Additionally, a practical
[2]
features. Their intrinsically superparamagnetic prop- strategy employing magnetic mesocellular materials
erties provide a more convenient strategy to remove as magnetic supports for asymmetric catalysis also re-
the magnetic catalyst by an appropriate external mag- vealed high catalytic efficiency and reusability. The
netic field, which make recovery and recycling of cat- group of Hyeon and Kim reported that a chiral Cin-
alyst much easily. Furthermore, magnetic nanoparti- chona alkaloid ligand trapped in magnetic mesocellu-
cles can be functionalized easily through appropriate lar materials exhibited a high enantioselectivity in Os-
[
5a]
surface coatings/modification, which are able to load catalyzed asymmetric dihydroxylation,
various functionalities. In particular, magnetic cata- the magnetic mesocellular foam materials developed
Similarly,
[
5b]
lysts show remarkable chemical and mechanical sta- by the groups of Li and Yang has been applied in
bility, which can enhance the durability of recycling the Ru-catalyzed asymmetric transfer hydrogenation
catalysts. Due to these advantages, exploitation of the of imines and aromatic ketones. Although these suc-
functionality of homogeneous catalysts on magnetic cessful samples employing magnetic materials as sup-
nanoparticles represents a rapidly growing field that ports have been explored, however, these researches
mainly focused on bare magnetic nanoparticles and
Recently, some magnetic nanoparticles have been magnetic mesocellular materials. Their intrinsic dis-
The pio- advantages, such as magnetic aggregation of bare
neering work reported by Linꢀs group utilized bare magnetic nanoparticles and magnetic loss of magnetic
[4]
is on the verge of being applied in industry.
[
5]
[
3–7]
used successfully in asymmetric catalysis.
[
4a]
Adv. Synth. Catal. 2011, 353, 1317 – 1324
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Guohua Liu et al.
FULL PAPERS
mesocellular materials, do still hinder their applica- [Cp*IrCl ] with (S,S)-TsDPEN modified SiO -coated
2
2
2
tion in industry. Thus, searching for more suitable Fe O nanoparticles or of [Cp*RhCl ] with (R,R)-
3
4
2 2
magnetic materials to overcome these restrictions is TsDACH modified SiO -coated Fe O nanoparticles,
2
3
4
still a challenge for realizing practical applications. and apply them to the asymmetric transfer hydroge-
Recently, the development of other magnetic materi- nation of aromatic ketones in aqueous medium. Our
[
6]
als has obtained great achievements. In particular, attentions focus on construction of a uniform shape of
the use of SiO -coated Fe O as a support shows an the magnetic catalysts, investigation of the tailored
2
3
4
[
7]
obvious superiority in catalysis fields. This strategy structure and surface chemistry of SiO -coated mag-
2
of outside surface coatings does not only reduce netic catalysts, and exploration of catalystꢀs reusabili-
greatly magnetic aggregation of bare magnetic nano- ty.
particles, but also does avoid the magnetic losses of
magnetic mesocellular materials. More importantly,
the functionality of chiral catalysts on the outside sur- Results and Discussion
face of magnetic nanoparticles can remain in the
same chiral microenvironment as the homogeneous Syntheses and Characterization of the Catalysts
catalyst, showing highly catalytic efficiency in stereo-
control performance.
The magnetic chiral iridium and rhodium catalysts,
5
Chiral h -Cp*-M (M=Ru, Rh and Ir) complexes abbreviated as Cp*IrTsDPEN-MNPs (5) and
bearing N-sulfonylated 1,2-diamines are a type of Cp*RhTsDACH-MNPs (6), were prepared by a post-
highly effective catalyst for the asymmetric hydroge- grafting method. As shown in Scheme 1, the SiO2-
[
8]
nation of ketones as well as cyclic imines. In particu- coated Fe O magnetic nanoparticles denoted as
3
4
lar, some of catalysts can accelerate significantly the SiO @Fe O (4) were synthesized readily via a similar
2
3
4
[
13]
asymmetric transfer hydrogenation of ketones in solvothermal method to that reported, followed by
[
9–11]
[14]
aqueous medium,
which is economic and environ- an SiO -coated procedure. The silica source, (S,S)-
2
mentally friendly. Thus, the immobilization of chiral TsDPEN-derived chiral ligand 2 or (R,R)-TsDACH-
5
[10]
[15]
h -Cp*-Rh-TsDACH
[DACH=1,2-cyclohexanedi- derived chiral ligand 3, was then grafted onto the
5
[11]
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
amine] or h -Cp*-Ir-TsDEPN catalysts
[DPEN= magnetic nanoparticles through refluxing in toluene
1
,2-diphenylethylenediamine] onto magnetic nanopar- for 24 h. Finally, the crude products 5 and 6 were suc-
ticle materials for asymmetric transfer hydrogenation cessfully obtained via direct complexation of (S,S)-
of ketones in water-medium does not only solve the TsDPEN-modified magnetic nanoparticles [(denoted
problem of expensive transition metal catalyst recy- as (S,S)-TsDPEN-MNPs)] with [Cp*IrCl ] or (R,R)-
2
2
cling but also does match the needs of green chemis- TsDACH-modified magnetic nanoparticles [(denoted
try. as (R,R)-TsDACH-MNPs)] with [Cp*RhCl2]2 using
Recently, we report a series of heterogeneous cata- NEt as a basic reagent. In order to remove unreacted
3
[
12]
lysts for green catalysis, some of them have exhibit- starting materials, the crude products were Soxlet ex-
ed excellent catalytic activity and enantioselectivity in tracted thoroughly in toluene to afford the pure cata-
[
12a–c]
asymmetric hydrogenation reactions.
As part of lysts 5 and 6 as red powders. Elemental analyses of 5
our ongoing research aimed at the development of re- and 6 calculated from the mass % of N (0.40 and
usable catalysts for asymmetric hydrogenation, we 0.34%) showed that the loading amounts of nitrogen
herein report the development of a convenient atoms were 0.286 and 0.243 mmol per gram catalyst.
method for the preparation of two magnetic, N-sul- As compared with the data [27.6 mg (0.144 mmol) of
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
fonylated diamine-based chiral iridium and rhodium Ir and 12.5 mg (0.121 mmol) of Rh per gram catalyst]
catalysts 5 and 6 through direct complexation of of the inductively coupled plasma (ICP) optical emis-
Scheme 1. Preparation of the magnetic catalysts 5 and 6.
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Magnetically Recoverable Nanoparticles: Highly Efficient Catalysts for Asymmetric Transfer Hydrogenation
sion spectrometer analyses, a 1:2 mole ratio of M AHCUTNGRNENUG( Ir
or Rh)/nitrogen indicated that one equivalent of N-
sulfonylated 1,2-diamine moieties coordinated with
one metal atom. Such a structural arrangement was
consistent with the structure reported in the litera-
[8]
ture. In addition, as compared with the metal load-
ing amounts of 5 and 6 with the theoretically initial
values in synthetic experiments, it was found that
about 10% of the organometallic complexes could be
incorporated onto the magnetic nanoparticles, which
was further confirmed by the data of the thermogravi-
metric analyses (TGA) that 11.11% of the mass loss
in 5 and 9.48% of the mass loss in 6 were obtained
(
see Figure S2 in Supporting Information).
FT-IR spectra of 4–6 (Figure 1) displayed strong
À1
bands around 3400, 1096 and 464 cm , which are as-
cribed to the characteristic bands of n
and d
(SiÀO) in magnetic nanoparticles. Weak bands
of 5 and 6 at 3100–2800 cm were assigned to asym-
A
T
N
T
N
U
G
A
H
N
T
E
N
G
Figure 2. The wide-angle powder XRD patterns of 4–6.
ACHTUNGTRENNUNG
À1
metric and symmetric stretching vibrations of CÀH electron microscopy (SEM) images exhibited clearly
À1
bonds while the bands at 1557–1451 cm were attrib- that the average sizes of 5 and 6 were about 380 and
uted to breathing vibrations of C=C bo nds in aromat- 430 nm, forming a stable dispersed state and showing
[
16]
ic ring. Furthermore, the bands indicative of n
A
H
U
G
R
N
U
G
À1
C) around 1145 cm were overlapped partly by the silica coating as shown in Figure 3 (a). The transmis-
absorbance from nACHTUNGTRENNUNG
[16a,b]
cles.
the organometallic complexes demonstrated their suc- capsulated by thin silica layer of 35 nm thickness
cessful incorporation onto the magnetic nanoparticles. [Figure 3 (b)]. Such a kind of silica coatings did not
Figure 2 show the wide-angle X-ray powder diffrac- only prevent the exposure of magnetite nanoparticles
tion (XRD) patterns of 4-6. Obviously, several typical on the surface and avoid the anisotropic magnetic di-
peaks of SiO @Fe O (4) were observed in 5 and 6, polar attraction among nanoparticles but also did
2
3
4
suggesting that there were no obvious changes after retain enough superparamagnetic property to sepa-
the subsequent surface modifications. The scanning rate the magnetic catalysts. As shown in Figure 4 (a),
the magnetization curves measured at 300 K showed
that 4 and 6 were superparamagnetic and had mag-
netization saturation values of 132.8, 56.3 and
À1
3
7.7 emug, respectively. As could be seen from
Figure 4 (b), the catalysts 5 and 6 were readily disper-
sible in reactive system and could be easily separated
with a small magnet near the bottle.
Catalytic Properties of the Magnetic Nanoparticles-
Supported Chiral Catalysts
With the magnetic catalysts in hand, we examined
their catalytic activity and enantioselectivity in the
asymmetric transfer hydrogenation of aromatic ke-
tones in aqueous medium according to the reported
[
11]
literature, in which the catalytic reaction was car-
ried out using HCO Na as a hydrogen source and
2
1.0 mol% amount of 5 or 6 as catalyst. Because a cer-
taibn reaction time was required to render efficiently
catalytic reaction in a heterogeneous catalytic system,
the reaction time was prolonged to 8 h. When aceto-
phenone was chosen as a substrate, the catalyst 5
gave (S)-1-phenyl-1-ethanol with 98.6% conversion
Figure 1. The FT-IR spectra of 4–6.
Adv. Synth. Catal. 2011, 353, 1317 – 1324
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Guohua Liu et al.
FULL PAPERS
Figure 3. The SEM images (a) and the TEM images (b) of 5 and 6.
6
gave the (R)-configuration product, in which the ab-
solute configuration did not affect their ee values. In a
comparison of the enantioselectivities of 5 and 6 with
those of the homogeneous Cp*IrTsDPEN and
Cp*RhTsDACH, the nearly identical enantioselectivi-
ties indicate that the modified homogeneous catalysts
on the magnetic nanoparticles could not result in a
change of the chiral microenvironment, which could
be further proved by the XPS spectra. As shown in
Figure 5, the same binding energy of 5 as Cp*IrTsDP-
EN or of 6 as Cp*RhTsDACH was observed, where-
by these values obviously deviated from the values of
[
Cp*IrCl ] or [Cp*RhCl ] (see Figure S3 in Support-
2 2 2 2
ing Information). On the basis of these results, the
catalysts 5 and 6 were further investigated using a
series of aromatic ketones as substrates (entries 6–10,
6–20). In general, high conversions and no side prod-
ucts, and high enantioselectivities were obtained
under similar conditions.
To investigate the nature of 5 and 6 prepared by a
chemical-bonding method and those via an in situ
post-modification method, and to eliminate the effect
1
Figure 4. (a) The magnetization curves of 4–6 at 300 K. (b)
The separation-redispersion process of the catalyst 5.
and an 89.6% ee value (Table 1, entry 2). Such an of non-covalent adsorption on the catalytic process,
enantioselectivity was comparable to that of two control experiments were carried out using (S,S)-
[
11]
Cp*IrTsDPEN (entry 2 versus 1 ) and obviously TsDPEN-MNPs plus [Cp*IrCl2]2 and
higher than that of the parent catalyst (entry 2 versus Cp*IrTsDPEN as catalysts under similar reaction
). Similarly, the catalyst 6 did also show the nearly conditions. It was found that the former afforded the
4
plus
3
same enantioselectivity as Cp*RhTsDACH (entry 12 corresponding alcohol with 78.9% conversion and
versus 11) and gave obviously a higher enantioselec- 77.2% ee value (entry 4), while the latter gave the cor-
tivity than the parent catalyst (entry 12 versus 13). A responding alcohol with 84.3% conversion and 88.1%
low enantioselectivity in both parent catalysts should ee value (entry 5). The former result suggested that
be due to the hydrolysis of organic silicas 2 and 3 the catalyst synthesized by an in situ post-modifica-
during the catalysis process, in which the change of tion method could also result in a catalytic perfor-
the chiral microenvironment derived from hydrolysis mance. However, the lower catalytic activity and
was responsible for a low enantioselectivity. Such a enantioselectivity than 5 should be due to the fact
phenomenon had been observed in our previous re- that a small part of the post-modified [Cp*IrCl ] had
2
2
[12e]
[12a–c]
port.
configuration of catalyst 5 offered the (S)-configura- similar result was also obtained using (R,R)-
tion product while the (R,R)-configuration of catalyst TsDACH-MNPs plus [Cp*RhCl2]2 as catalyst
In contrast, it was found easily that the (S,S)- not been coordinated on the catalytic process.
A
a
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Magnetically Recoverable Nanoparticles: Highly Efficient Catalysts for Asymmetric Transfer Hydrogenation
Figure 5. The XPS spectra: (left) Cp*IrTsDPEN and 5; (right) Cp*RhTsDACH and 6.
[a]
Table 1. Asymmetric transfer hydrogenation of aromatic ketones.
[b]
[b]
Entry
Catalyst
Substrate
Conversion [%]
ee [%]
1
2
3
4
5
6
7
8
9
Cp*IrTsDPEN
7
7
7
7
7
8
9
10
11
12
7
7
7
7
7
8
9
99.2
98.6
91.5
78.9
84.3
99.6
98.4
96.7
96.4
99.5
>99.9
99.9
96.8
77.7
96.5
98.2
99.5
99.4
>99.9
99.1
90.0
89.6
76.2
77.2
88.1
88.7
92.5
87.2
81.6
79.0
87.9
87.6
74.2
77.2
86.6
84.0
86.7
85.9
85.0
85.6
5
2+
A
H
U
G
R
N
U
G
2
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(S,S)-TsDPEN-MNPs+
A
H
U
G
R
N
U
G
2
2
4+Cp*IrTsDPEN
5
5
5
5
5
10
11
12
13
14
15
16
17
18
19
20
Cp*RhTsDACH
6
3+
A
H
U
G
R
N
U
G
2
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(R,R)-TsDACH-MNPs+
2
2
4+Cp*RhTsDACH
6
6
6
6
6
10
11
12
[
a]
Reactions were carried out in water. Reaction conditions: catalysts (4.0 mmol of Ir or Rh, based on the ICP analysis),
HCO Na (0.68 g, 10.0 mmol), Bu NBr (0.29 g, 0.80 mmol), ketone (2.0 mmol) and 2.0 mL water, reaction temperature
2
4
(
408C), reaction time (8.0 h).
[
b]
Determined by chiral GC or HPLC analysis (see Figure S4 in Supporting Information).
(
entry 14). The latter showed that the catalyst pre- plus Cp*RhTsDACH as a catalyst (entry 15). Howev-
pared via non-covalent adsorption on the catalytic er, both catalytic activity and enantioselectivity disap-
process gave nearly the same enantioselectivity as peared completely when the catalysts that had under-
Cp*IrTsDPEN, which was further confirmed using 4 gone a Soxlet extraction process were employed
Adv. Synth. Catal. 2011, 353, 1317 – 1324
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Guohua Liu et al.
FULL PAPERS
[a]
Table 2. Reusabilities of 5 and 6 for asymmetric transfer hydrogenation of acetophenone.
Catalyst
Recycle
1
2
3
4
5
6
7
8
9
10
5
Conv. [%]
ee [%]
Conv. [%]
ee [%]
98.6
89.6
99.9
87.6
99.0
89.0
99.3
86.5
99.2
88.9
99.4
85.7
99.1
88.8
99.7
85.2
98.1
87.4
99.2
85.2
97.6
87.2
97.8
85.7
96.3
86.6
98.0
85.4
98.0
86.3
96.9
84.8
98.5
86.1
98.6
84.2
95.9
86.0
98.6
83.8
6
[
a]
Reactions were carried out in water. Reaction conditions: catalysts (4.0 mmol of Ir or Rh, based on the ICP analysis),
HCO Na (0.68 g, 10.0 mmol), Bu NBr (0.29 g, 0.80 mmol), ketone (2.0 mmol) and 2.0 mL water, reaction temperature
2
4
(408C), reaction time (8.0 h).
(
Soxlet extracting 4 plus Cp*IrTsDPEN or 4 plus Experimental Section
Cp*RhTsDACH in toluene), indicating that the non-
covalent adsorption on the catalytic process could be General Remarks
eliminated completely through the Soxlet extraction.
All experiments, which were sensitive to moisture or air,
This was also further proved by ICP analyses (nearly
same loading amounts of Rh or Ir were detected in
solution after Soxlet extraction). In other words, cata-
were carried out under an Ar atmosphere using standard
Schlenk techniques. 2-(4-Chlorosulfonylphenyl)ethyltrime-
thoxysilane, (1S,2S)-1,2-diphenylethylenediamine, (1R,1R)-
lysts 5 and 6 prepared via a chemical-bonding method 1,2-cyclohexanediamine, [Cp*IrCl ] and [Cp*RhCl ] were
2
2
2 2
did not only give a higher catalytic efficiency than purchased from Sigma–Aldrich Company Ltd. and used as
those made via an in situ post-modification method, received. Compound 2 was synthesized according to the re-
[
15]
ported procedure.
The products were analyzed by GC
but also could overcome the loss of catalyst from
non-covalent adsorption, resulting in a high catalyst
reusability.
using a Supelco b-Dex 120 chiral column (30 mꢂ0.25 mm
i.d., 0.25 mm film) or HPLC with a UV-Vis detector using a
Daicel OJ-H chiralcel columns(1 0.46ꢂ25 cm).
An important feature of the design of the catalysts
5
and 6 was the easy and reliable separation via an
Characterization
appropriate magnetic field. For example, upon com-
pletion of the reaction, the heterogeneous catalysts 5 Rh and Ir loading amounts in the catalysts were analyzed
and 6 were quantitatively recovered via a small using an inductively coupled plasma optical emission spec-
trometer (ICP, Varian VISTA-MPX). Fourier transform in-
magnet held near the bottle [Figure 4 (b)]. As shown
frared (FT-IR) spectra were collected on a Nicolet Magna
in Table 2, when acetophenone was used as a sub-
5
50 spectrometer using the KBr method. X-ray powder dif-
strate, in ten consecutive reactions, the recycled cata-
lyst 5 still afforded 95.9% conversion and 86.0% ee
while the recycled catalyst 6 gave 98.6% conversion
and 83.8% ee. The slight decrease of catalytic activity
and tiny change of enantioselectivity should be due to
fraction (XRD) studies were carried out on a Rigaku D/
Max-RB diffractometer with Cu-Ka radiation. Scanning
electron microscopy (SEM) images were obtained using a
JEOL JSM-6380LV microscope operating at 20 kV. Trans-
mission electron microscopy (TEM) images were performed
the normal loss of the catalysts during the work-up on a JEOL JEM2010 electron microscope at an acceleration
stage.
voltage of 220 kV. X-ray photoelectron spectroscopy (XPS)
measurements were performed on a Perkin–Elmer PHI
5
000C ESCA system. All the binding energies were calibrat-
ed by using the contaminant carbon (C =284.6 eV) as a
1s
Conclusions
reference. The magnetic measurements were performed
with a Lake Shore VSM 736 at room temperature. Liquid
In conclusion, we have supplied a facile approach to
prepare two magnetic nanoparticles-supported chiral
iridium and rhodium catalysts 5 and 6. Both catalysts
exhibited highly catalytic activities (up to 99%) and
high enantioselectivities (up to 92% ee) in the asym-
metric transfer hydrogenation of aromatic ketones in
aqueous medium. In particular, both heterogeneous
catalysts could be recovered easily by using a magnet.
Neither filtration nor extraction was necessary. The
recycled catalysts 5 and 6 were reused 10 times and
still showed high catalytic efficiency without affecting
obviously their enantioselectivities, showing their
good potential for industry applications.
1
13
H NMR, C NMR spectra were recorded using a Bruker
AV-400 spectrometer. Elemental analyses were performed
with a Carlo Erba 1106 Elemental Analyzer.
Catalyst Preparation
Synthesis of 3: Under an argon atmosphere, to a stirred so-
lution of (R,R)-DACH (1.00 g, 8.77 mmol) and triethylamine
(
1.06 mL, 17.54 mmol) in 20 mL dry dichloromethane was
added a solution of 2-(4-chlorosulfonylphenyl)ethyltrime-
thoxysilane 1 (0.71 g, 2.19 mmol) in 2 mL dry dichlorome-
thane at 08C. The resulting mixture was then allowed to
warm to room temperature slowly and was stirred for anoth-
er 3 h. After the solvent had been removed under vacuum,
the residue was rapidly passed through a short column
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Adv. Synth. Catal. 2011, 353, 1317 – 1324

Magnetically Recoverable Nanoparticles: Highly Efficient Catalysts for Asymmetric Transfer Hydrogenation
(
silica gel, eluent: Et N:CH OH:CH Cl =1:10:100) and
was allowed to react at 408C for 8 h. During that time, the
reaction was monitored constantly by TLC. After comple-
tion of the reaction, the magnetic catalyst was separated by
a small magnet near the bottle for the recycle experiment.
3
3
2
2
concentrated under vacuum to afford 3 as a beige glass;
yield: 0.67 g (1.67 mmol, 76.3%). For NMR and IR spectra
2
0
see Figure S2 in Supporting Information. [a] : À243.7 (c
D
1
0
.002, CH OH); H NMR (400 MHz, CDCl ): d=7.84–7.82
The aqueous solution was extracted by Et O (3ꢂ3.0 mL).
3
3
2
(
d, J=8.40 Hz, 2H), 7.33–7.31 (d, J=8.40 Hz, 2H), 4.46 (s,
The combined Et O extract was washed with brine twice
2
NH, 3H), 3.56 (s, 9H), 2.80- 2.76 (t, J=8.40 Hz, 2H), 2.76-
and dehydrated with Na SO . After the evaporation of
2
4
2
1
2
3
3
1
.73 (m, 1H), 2.58–2.54 (m, 1H), 1.99–1.96 (m, 1H), 1.68–
Et O, the residue was purified by silica gel flash column
2
.54(m, 3H), 1.06–1.28 (m, 4H), 1.01–0.96 (t, J=8.40 Hz,
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
chromatography to afford the desired product. The conver-
sion and the ee value could be determined by chiral GC
using a Supelco b-Dex 120 chiral column (30 mꢂ0.25 mm
i.d., 0.25 mm film) or HPLC analysis with a UV-Vis detector
using a Daicel OJ-H chiralcel columns (F 0.46ꢂ25 cm).
13
H); C NMR (126 MHz, CDCl ): d=11.1, 24.8, 28.9, 32.5,
3
4.9, 50.8, 54.9, 59.9, 127.4, 128.7, 138.7, 149.6; IR (KBr): n=
424 (s), 2981 (m), 2943 (m), 1640 (m), 1565 (s), 1473 (m),
445 (m), 1400 (m), 1149 (s), 1067 (s), 1039 (s), 945 (m), 853
À1
(
m), 548 cm (m); HPLC-MS (100 eV): m/z (%)=402.16
+
+
[M] , 403.20 [M+H] ; elemental analysis (%) calcd. for
Supporting Information
C H N O SSi: C 50.72, H 7.51, N 6.96; S, 7.96; found: C
17
30
2
5
Experimental procedures and analytical data for the ob-
tained chiral aromatic alcohols are available as Supporting
Information.
50.68, H 7.63, N 6.91, S 7.89.
Preparation of Cp*IrTsDPEN-MNPs (5): To a stirred sus-
pension of SiO @Fe O (4) (1.0 g) in 15 mL dry toluene was
2
3
4
added a solution of 2 (0.15 g, 0.30 mmol) in 5 mL dry tolu-
ene. The resulting mixture was refluxed for 24 h under an
argon atmosphere. After magnetic separation, the red crude
solid (S,S)-TsDPEN-MNPs was suspended in 20 mL dry
CH Cl again and [Cp*IrCl ] (0.12 g, 0.15 mmol) was added
Acknowledgements
2
2
2 2
at room temperature. The resulting mixture was stirred at
room temperature for 2 h. After magnetic separation, the
red crude product was extracted thoroughly in toluene sol-
vent using a Soxlet apparatus to remove homogeneous and
unreacted start materials. The solid was dried at 608C under
vacuum for 24 h to afford Cp*IrTsDPEN-MNPs (5) as a red
powder; yield: 1.12 g (48.1% relative to 4). IR (KBr): n=
We are grateful to China National Natural Science Founda-
tion (20673072), Shanghai Sciences and Technologies Devel-
opment Fund (10J1400103, 10JC1412300) and Shanghai Mu-
nicipal Education Commission (S30406) for financial sup-
port.
3
1
4
448 (s), 3066 (w), 2923 (w), 2821 (w), 1618 (m), 1451 (m),
354 (m), 1154 (s), 1093 (s), 810 (w), 694 (w), 572 (m),
À1
References
69 cm (m); elemental analysis (%) found: C 5.56, H 0.78,
N 0.40, S 0.46.
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