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H. Sugie et al. / Journal of Organometallic Chemistry 751 (2014) 711e716
hydrophobicity. Poly(ethylene glycol)-supported chiral TsDPEN
developed by Xiao was effective in asymmetric transfer hydroge-
nation of simple ketones by sodium formate in water [4h]. Silica
supported chiral catalysts have been utilized in water and showed
activity in ketone reduction when SDS surfactant was used [13]. We
have also successfully prepared crosslinked polymer-immobilized
chiral TsDPENs containing hydrophilic functional groups such as
carboxylate and sulfonate. These polymeric catalysts were applied
to asymmetric transfer hydrogenation of ketones in water [14].
In this study we have introduced a novel type of amphiphilic
polymer support that consists of a polystyrene main chain and a
quaternary ammonium salt and quaternary phosphonium salt as its
side chain functionality and applied to asymmetric transfer hy-
drogenation of cyclic sulfonimine. We would like to show the cat-
alytic activity of amphiphilic polymer-immobilized chiral catalysts
both in organic solvent and in water. We also describe the detailed
results of asymmetric transfer hydrogenation of cyclic sulfonimine
in various conditions.
2. Experimental
2.1. General
(R,R)-1,2-Diphenylethylenediamine ((R,R)-DPEN) was pur-
chased from Fuji Molecular Planning Co., Ltd. p-Styrenesulfonyl
chloride was prepared according to the method reported in the
literature [15]. All other commercial reagents were purchased from
Aldrich, Wako or TCI. Styrene and divinylbenzene were washed
with aqueous sodium thiosulfate and aqueous sodium hydroxide
and distilled over calcium hydride under a reduced pressure just
before use. 2,20-Azobis(isobutyronitrile) (AIBN) was purified by
recrystallization three times from anhydrous methanol. Water was
purified by a Millipore Milli-Q purification system. DMF was puri-
fied by distillation over calcium hydride under a reduced pressure.
All other chemicals were used without purification.
Scheme 1. Preparation of polymer-immobilized chiral 1,2-diamine monosulfonamide
4.
collected on a glass filter and washed with THF, methanol and
water and dried under vacuum.
Reactions were monitored by TLC using Merck precoated silica
gel plates (Merck 5554, 60F254). Column chromatography was
2.3. General procedure for asymmetric transfer hydrogenation in
CH2Cl2
performed with
a silica gel column (Wakogel C-200, 100e
200 mesh). Melting points were taken on a Yanaco micro melting
apparatus and are uncorrected. Optical rotations were measured on
a JASCO DIP-140 digital polarimeter with a 10-cm thermostated
microcell. 1H NMR and 13C NMR spectra were recorded on Varian
Mercury 300 (300 MHz 1H, 75 MHz 13C) spectrometer, and the J
values were recorded in Hertz. IR spectra were recorded with a
JASCO FT/IR-230 Fourier transform infrared spectrometer and were
reported in reciprocal centimeters (cmꢀ1). Elemental analyses
(carbon, hydrogen and nitrogen) were performed by a Yanaco-CHN
coder MT-6 analyzer. High-performance liquid chromatography
(HPLC) analyses were performed with a Jasco HPLC system
composed of a DG-980-50 three-line degasser, a PU 980 HPLC
pump, and a CO-965 column oven equipped with a chiral column
(Chiralcell OD-H, AS-H or AD-H, Daicel) with hexane/2-propanol as
an eluent. A Jasco UV-975 UV detector was used for the peak
detection.
A 10 mL round-bottomed flask equipped with a magnetic stir-
ring bar was charged [RuCl2(p-cymene)]2 (1.5 mg, 0.0025 mmol)
and the polymer-immobilized chiral 1,2-diamine mono-
sulfonamide 4 (0.006 mmol) in CH2Cl2 (1 mL) under argon atmo-
sphere. After three cycles of freeze-thaw under liquid nitrogen, the
mixture was heated to 40 ꢁC. After 1 h, the mixture was cooled to
room temperature to give polymereruthenium (II) complex. Cyclic
sulfonimine 5a (0.50 mmol) and 5:2 HCO2HeEt3N azeotropic
mixture (HCO2H 2.5 mmol) were then added and stirred at room
temperature for 24 h. After the removal of the polymeric catalyst by
filtration, the organic compounds were extracted twice with ether.
The conversion and enantioselectivity were determined by GC and
HPLC analysis, respectively.
In case of the reuse of the polymeric catalyst, the recovered
polymeric catalyst by filtration was transferred with CH2Cl2 (1 mL)
into a 10 mL round-bottomed flask equipped with a magnetic
stirring bar. Cyclic sulfonimine 5a (0.50 mmol) and 5:2 HCO2He
Et3N azeotropic mixture (HCO2H 2.5 mmol) were then added and
stirred at room temperature for 24 h.
2.2. General procedure for the preparation of polymer-immobilized
chiral 1,2-diamine monosulfonamide ligands 4
A glass ampoule equipped with a magnetic stirring bar was
charged with DMF (0.78 g), (1R,2R)-1 (71.9 mg, 0.19 mmol),
divinylbenzene (25.0 mg, 0.19 mmol), vinyl monomer (1.52 mmol)
2.4. General procedure for asymmetric transfer hydrogenation in
water
and AIBN (6.5 mg, 40 mmol). The ampoule was sealed after three
freeze-thaw cycles under liquid nitrogen. Copolymerization was
carried out at 60 ꢁC for 24 h. The ampoule was opened and the
resulting mixture was poured into ether. The obtained polymer was
A 10 mL round-bottomed flask equipped with a magnetic stir-
ring bar was charged [RuCl2(p-cymene)]2 (1.5 mg, 0.0025 mmol)
and the polymer-immobilized chiral 1,2-diamine sulfonamide 4