Immobilization of chiral Rh catalyst on glass and application to asymmetric transfer hydrogenation of aryl ketones in aqueous media

Article abstract of DOI:10.1016/j.cclet.2014.01.007

A chiral catalyst, Cp*RhTsDPEN (Cp* = pentamethyl cyclopentadiene, TsDPEN = substitutive phenylsulfonyl-1,2- diphenylethylenediamine), was synthesized and immobilized at the surface of glass. The immobilized catalyst exhibited good catalytic efficiency for asymmetric transfer hydrogenation of aromatic ketones in water with HCOONa as hydrogen source.

Full text of DOI:10.1016/j.cclet.2014.01.007

Chinese Chemical Letters 25 (2014) 613–616
Contents lists available at ScienceDirect
Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
Original article
Immobilization of chiral Rh catalyst on glass and application to
asymmetric transfer hydrogenation of aryl ketones in aqueous media
*
*
Tan-Yu Cheng , Jing-Lan Zhuang, Hui Yao, Huai-Sheng Zhang, Guo-Hua Liu
Key Laboratory of Resource Chemistry of Ministry of Education, College of Life and Environmental Science, Shanghai Normal University, Shanghai 200234,
China
A R T I C L E I N F O
A B S T R A C T
Article history:
A chiral catalyst, Cp*RhTsDPEN (Cp* = pentamethyl cyclopentadiene, TsDPEN = substitutive phenylsul-
fonyl-1,2-diphenylethylenediamine), was synthesized and immobilized at the surface of glass. The
immobilized catalyst exhibited good catalytic efficiency for asymmetric transfer hydrogenation of
aromatic ketones in water with HCOONa as hydrogen source.
Received 7 October 2013
Received in revised form 10 December 2013
Accepted 24 December 2013
Available online 10 January 2014
ß 2014 Tan-Yu Cheng and Guo-Hua Liu. Published by Elsevier B.V. on behalf of Chinese Chemical
Society. All rights reserved.
Keywords:
Heterogeneous Rh catalyst
Asymmetric transfer hydrogenation
Aromatic ketones
Glass substrate
1. Introduction
asymmetric catalysis. Asymmetric transfer hydrogenation (ATH) is
one of the most important asymmetric catalytic reactions, and it is
Self-assembled monolayers (SAMs) are an excellent tool to
change surface properties of materials. The method has attracted a
lot of interest and has developed rapidly in the past years.
Nanotechnology has developed rapidly in recent decades, and it is
widely used in several areas. SAMs are often used to prepare
nanoparticles [1–3], because most nanoparticles need to be
functionalized and have their biological toxicity reduced. Glass
plates are also good supports for functional molecules. Fluorescent
sensors were assembled on glass, which were used for the
detection of nitroaromatic compounds in the vapor phase [4–6].
Fluorescent proteins were immobilized on glass surfaces, and they
were very important for potential applications in bionanotechnol-
ogy [7]. Some metal catalysts were supported on glass surfaces,
which were used to catalyze oxidation reactions [8,9].
normally promoted by transition metal catalysts [10–17]. Noyori
et al. found that chiral TsDPEN exhibited excellent catalytic activity
and enantioselectivity in the asymmetric transfer hydrogenation
of aromatic ketones [18], and they have made outstanding
contributions in this area [19,20]. Compared with homogeneous
catalysts, heterogeneous immobilization molecular catalysts at the
surfaces of materials have several outstanding advantages,
including facile product purification, easy catalyst recovery from
reaction mixtures and reusability. Normally, the materials used for
immobilizing molecular catalysts are mesoporous silica [21,22],
magnetic materials [23], zeolites [24], organic polymers [25], or
high surface area carbon [26]. However, to the best of our
knowledge there is no chiral catalyst that is immobilized on a glass
surface.
Chiral compounds are very important in our daily life, especially
in medicinal chemistry, because different configurations have
different drug activities. As such, enantioselective synthesis has
attracted increasing interest from chemists during the past few
decades. There are three main approaches to asymmetric
synthesis, which are chiral pool synthesis, chiral auxiliaries, and
What we are interested in is material supported catalysts in an
effort to achieve highly active and recyclable heterogeneous
catalysts [27–31]. Herein, the ligand of TsDPEN (substitutive
phenylsulfonyl-1, 2-diphenylethylenediamine) with ethynyl
group was synthesized, and the ligand was conjuncted with a
silica source via click chemistry. Then, the homogeneous catalyst
was prepared through stirring the solution of the ligand and
[Cp*RhCl2]2 in dichloromethane at room temperature. At last, the
obtained catalyst was immobilized at the surface of glass plates to
form the heterogeneous catalyst, which showed good catalytic
efficiency and enantioselectivity.
*
Corresponding authors.
E-mail addresses: tycheng@shnu.edu.cn (T.-Y. Cheng), ghliu@shnu.edu.cn
(G.-H. Liu).
1001-8417/$ – see front matter ß 2014 Tan-Yu Cheng and Guo-Hua Liu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2014.01.007

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T.-Y. Cheng et al. / Chinese Chemical Letters 25 (2014) 613–616
3700
Cl
Rh
O
Cl
H
N
H
2
2
Ph
Ph
Ph
N
308.8 eV (Rh 3d)
3600
3500
3400
3300
3200
3100
Rh
O
N
S
N
S
Ph
O
O
OH
OH
N
N
Postgrafting
N N
N N
Si
O
OH
Si
O
O
O
O
302
304
306
308
310
312
314
316
Homogeneous catalyst
GH-catalyst
Binding energy (eV)
Scheme 1. Preparation of heterogeneous catalyst supported on glass.
Fig. 1. XPS spectrum of the Rh active site within GH-catalyst.
2. Experimental
with UV–vis detector using Daicel OJ-H chiral column (1
0.46 cm  25 cm).
2.1. Preparation of the glass containing hydroxyl group
3. Results and discussion
Microscope glass slides were used for monolayer preparation.
The substrates were oxidized with piranha solution for 15 min
(concentrated H2SO4 and 33% aqueous H2O2 in 3:1 ratio; caution:
piranha should be handled carefully) and rinsed with MilliQ water
(MQ). After drying with nitrogen stream, the substrates were used
immediately to provide a freshly hydroxyl terminated surface on
which to form the silanized monolayer.
3.1. XPS analysis of GH-catalyst
The click reaction was used for the synthesis of the TsDPEN
ligand with the trimethoxysilane group, which combined with Rh
to form the homogeneous catalyst (see Supporting information).
The heterogeneous catalyst was synthesized by grafting the
homogeneous catalyst onto the oxidized glass with excess
hydroxy groups. According to the XPS data, the O/Si ratio of
normal glass was 1.53, and that of oxidized glass was 2.11. That
indicated that excess hydroxy groups were obtained after the
glass was oxidized. The content of sulfur increased from 0 to
0.61%. This was because a few sulfonic groups were produced
when the glass was oxidized by sulfuric acid. The glass we used
were normal slides, so there was plentiful carbon according to the
XPS data. After grafting the homogeneous catalyst onto the slides,
the XPS N1s and Rh3d signals indicated that the catalyst was
immobilized successfully. As shown in Fig. 1, the binding energy
of Rh3d was 308.8 eV, which was nearly the same with
Cp*RhTsDPEN (309.3 eV).
2.2. Preparation of glass-supported heterogeneous catalyst (GH-
catalyst)
As shown in Scheme 1, processed glass were immersed in the
solution of silanizing homogeneous catalyst in CH2Cl2 until the
solvent evaporated completely. To remove the unreacted homo-
geneous catalyst, the prepared glass were treated with ultrasound
in CH2Cl2 and EtOH. The glass-supported heterogeneous catalyst
(GH-catalyst) was obtained after the glass dried.
2.3. Typical catalytic procedure
A
typical procedure was as follows [32]: GH-catalyst,
HCOONa (20 mg, 0.3 mmol), ketones (2.0 mmol), and 2.0 mL
water were added in a 10 mL round bottom flask. The mixture
was allowed to react at 40 8C for 4 h. During the reaction, it was
monitored constantly by TLC. The conversion and ee value could
3.2. AFM analysis of GH-catalyst
The resulting AFM images are shown in Fig. 2. The surface
roughness exhibited by the root-mean-square (RMS) height value
for glass was 2.60 nm. After grafting, the RMS value for the catalyst
6 decreased to 2.19 nm. This decrease in roughness can be
be determined by chiral GC using a Supelco
b-Dex 120 chiral
column (30 m  0.25 mm (i.d.), 0.25 m film) or HPLC analysis
m
Fig. 2. AFM images of the glass (A) and GH-catalyst (B).

T.-Y. Cheng et al. / Chinese Chemical Letters 25 (2014) 613–616
615
Table 1
Shanghai Municipal Education Commission (Nos. 14YZ074,
12ZZ135), Shanghai Normal University (Nos. DXL122,
SK201329) for financial support.
Asymmetric transfer hydrogenation of aromatic ketones.a
OH
Cat.
O
Appendix A. Supplementary data
Ar
HCOONa, H O
Ar
2
o
40 C
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.cclet.2014.01.007.
Entry
Ar
Conv.b (%)
ee (%)b
1
2
Ph
95
98
93
97
86
87
99
99
84
94
99
85
94
87
91
93
90
93
84
84
85
93
94
80
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3
4-ClPh
4-BrPh
4-MePh
4-MeOPh
4-NO2Ph
4-CF3Ph
4-CNPh
3-MeOPh
3-Br
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