Chiral BINAP-based hierarchical porous polymers as platforms for efficient heterogeneous asymmetric catalysis

Article abstract of DOI:10.1016/S1872-2067(17)62826-2

Two vinyl-functionalized chiral 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (BINAP) ligands, (S)-4,4′-divinyl-BINAP and (S)-5,5′-divinyl-BINAP, were successfully synthesized. Chiral BINAP-based porous organic polymers (POPs), denoted as 4-BINAP@POPs and 5-BINAP@POPs, were efficiently prepared via the copolymerization of vinyl-functionalized BINAP with divinyl benzene under solvothermal conditions. Thorough characterization using nuclear magnetic resonance spectroscopy, thermogravimetric analysis, extended X-ray absorption fine structure analysis, and high-angle annular dark-field scanning transmission electron microscopy, we confirmed that chiral BINAP groups were successfully incorporated into the structure of the materials considered to contain hierarchical pores. Ru was introduced as a catalytic species into the POPs using different synthetic routes. Systematic investigation of the resultant chiral Ru/POP catalysts for heterogeneous asymmetric hydrogenation of β-keto esters revealed their excellent chiral inducibility as well as high activity and stability. Our work thereby paves a path towards the use of advanced hierarchical porous polymers as solid chiral platforms for heterogeneous asymmetric catalysis.

Full text of DOI:10.1016/S1872-2067(17)62826-2

Chinese Journal of Catalysis 38 (2017) 890–898
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
Chiral BINAP‐based hierarchical porous polymers as platforms for
efficient heterogeneous asymmetric catalysis
Tao Wang a,c, Yuan Lyu a,#, Kai Xiong d, Wenlong Wang a, Hao Zhang e, Zhuangping Zhan d,
Zheng Jiang e, Yunjie Ding a,b,
*
a Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning, China
b State Key Laboratory of catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning, China
c University of Chinese Academy of Sciences, Beijing 100049, China
d Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, Fujian, China
e Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Two vinyl‐functionalized chiral 2,2’‐bis(diphenylphosphino)‐1,1’‐binaphthyl (BINAP) ligands,
(S)‐4,4’‐divinyl‐BINAP and (S)‐5,5’‐divinyl‐BINAP, were successfully synthesized. Chiral
BINAP‐based porous organic polymers (POPs), denoted as 4‐BINAP@POPs and 5‐BINAP@POPs,
were efficiently prepared via the copolymerization of vinyl‐functionalized BINAP with divinyl ben‐
zene under solvothermal conditions. Thorough characterization using nuclear magnetic resonance
spectroscopy, thermogravimetric analysis, extended X‐ray absorption fine structure analysis, and
high‐angle annular dark‐field scanning transmission electron microscopy, we confirmed that chiral
BINAP groups were successfully incorporated into the structure of the materials considered to
contain hierarchical pores. Ru was introduced as a catalytic species into the POPs using different
synthetic routes. Systematic investigation of the resultant chiral Ru/POP catalysts for heterogene‐
ous asymmetric hydrogenation of β‐keto esters revealed their excellent chiral inducibility as well as
high activity and stability. Our work thereby paves a path towards the use of advanced hierarchical
porous polymers as solid chiral platforms for heterogeneous asymmetric catalysis.
Received 22 February 2017
Accepted 23 March 2017
Published 5 May 2017
Keywords:
(S)‐4,4’‐divinyl‐BINAP
(S)‐5,5’‐divinyl‐BINAP
Porous organic polymers supported
ruthenium
Heterogeneous asymmetric
hydrogenation
β‐keto esters
© 2017, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
coordination bonds in MOFs and the presence of imine or
boronate ester groups in COFs, which severely limits their ap‐
Recently, porous organic materials, including porous organ‐
ic polymers (POPs), metal‐organic frameworks (MOFs), and
covalent organic frameworks (COFs) have emerged as versatile
platforms for the deployment of catalysts because of their po‐
rous nature and high surface area [1–7]. However, MOFs and
COFs are unstable under many circumstances such as in acidic,
basic, and moist environments because of the connection of the
plications in catalysis [8,9]. In contrast, POPs are advantageous
compared with MOFs and COFs in terms of hydrothermal sta‐
bility and chemical robustness because of the stronger linkage
of their versatile covalent bonds apart from imines and boro‐
nate esters [10–14]. Thus, POPs can be designed as an ideal
platform for incorporating molecular catalytic modules into
highly stable and recyclable heterogeneous catalytic systems by
* Corresponding author. Tel/Fax: +86‐411‐84379143; E‐mail: dyj@dicp.ac.cn
# Corresponding author. Tel: +86‐411‐84379601; Fax: +86‐411‐84379143; E‐mail: luyuan@dicp.ac.cn
This work was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB17020400).
DOI: 10.1016/S1872‐2067(17)62826‐2 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 38, No. 5, May 2017

Tao Wang et al. / Chinese Journal of Catalysis 38 (2017) 890–898
891
taking advantage of their permanent porosity and the ability to
tune their compositions and properties at the molecular level
[15–17].
noted, all the manipulations were performed under an Ar at‐
mosphere either in a glove box or using standard Schlenk tech‐
niques. DVB (80%) was provided by J&K Chemical as a mixture
of 1,2‐, 1,3‐, and 1,4‐DVB.
Compared with the large number of reported POPs, chiral
POPs remain scarce. Lin et al. [18] developed the synthesis
process for binaphthol‐ligated, Ti‐incorporating porous
cross‐linked polymers for catalytic asymmetric diethylzinc
addition to aldehydes. Wang and co‐workers [19] described the
construction of a α,α,α′,α′‐tetraaryl‐1,3‐dioxolane‐4,5‐dimeth‐
anol (TADDOL)‐embedded chiral POP catalyst and its struc‐
ture‐activity relationship. In addition, to date, most research
has been focused on microporous chiral POPs [18,20–22];
studies aimed at the syntheses of advanced hierarchical (in
combination with micropores and mesopores) chiral POPs are
even more scarce [23,24]. Abundant micropores generally fa‐
vour a high density of catalytically active sites distributed in the
catalyst particles, whereas mesopores improve the mass trans‐
fer efficiency to enable free contact of the substrate with cata‐
lytically active sites in heterogeneous catalysis [25–28]. There‐
fore, the synthesis of hierarchical chiral POPs is of great inter‐
est. The C2‐symmetric BINAP (2,2’‐bis(diphenylphosphino)‐
1,1’‐binaphthyl) ligand, which was reported by Noyori et al.
[29] in 1980, represents one of the most efficient ligands.
BINAP and its derivatives have been widely used in asymmetric
catalysis and extensively investigated, especially in asymmetric
hydrogenation. The heterogenization of BINAP has been a
long‐term research area in heterogeneous asymmetric catalysis
[30–38]. Using the BINAP ligand, Xiao et al. [23] synthesized a
vinyl‐modified BINAP dioxide through the steps of oxidation,
nitration, reduction, and acylation, which was denoted as
5,5’‐diacryloylamino BINAP dioxide. After copolymerization
with divinyl benzene (DVB) and reduction with HSiCl3, porous
cross‐linked polymers (PCPs) with BINAP (PCP‐BINAP) were
obtained. The prepared heterogeneous catalyst Ru/PCP‐BINAP
exhibited high activity and recyclability in the asymmetric hy‐
drogenation of β‐keto esters. Inspired by this creative work, we
recently reported excellent asymmetric hydroformylation cat‐
alysts through radical polymerization of (S)‐5,5’‐divinyl‐BINAP
and a series of comonomers.
2.2. Ligand Synthesis
The synthesis routes of (S)‐5,5’‐divinyl‐BINAP have been
previously reported. Here, we describe the synthesis routes of
(S)‐4,4’‐divinyl‐BINAP in Scheme 1.
Compound 1, (S)‐BINAP dioxide: (S)‐BINAP (3 mmol, 1.87
g) was dissolved in dichloromethane (DCM, 60 mL) followed by
the dropwise addition of H2O2 (18.32 mmol, 6.06 mL). The re‐
action was monitored by thin‐layer chromatography (TLC).
After being stirred for 30 min at room temperature, the solu‐
tion was extracted with water (30 mL). The organic phase was
washed with 10% NaHSO3 aqueous solution (50 mL) and dried
over Na2SO4. The solvent was removed under vacuum, and 1.95
g of a white solid (99% yield) was obtained, which was denoted
as (S)‐BINAPO.
Compound 2, (S)‐4,4’‐diBr‐BINAPO: (S)‐BINAPO (10 mmol,
6.55 g) was dissolved in DCM (150 mL) followed by the addi‐
tion of liquid bromine (30 mmol, 4.8 g) and pyridine (10 mmol,
0.79 g). After being stirred for 24 h at room temperature, the
solution was washed with 10% NaHSO3 aqueous solution, sat‐
urated brines, and saturated sodium bicarbonate aqueous solu‐
tion, dried over Na2SO4, and evaporated under vacuum to re‐
move the solvent. After repeating the above steps twice, 6.10 g
of a white solid (75% yield) was obtained, which was denoted
as (S)‐4,4’‐diBr‐BINAPO.
Compound 3, (S)‐4,4’‐divinyl‐BINAPO: (S)‐4,4’‐diBr‐BINAPO
(1.0 mmol, 0.82 g), potassium vinyltrifluoroborate (2.4 mmol,
0.32 g) and PdCl2(dppf)CH2Cl2 (0.08 mmol, 0.058 g) were
placed in a three‐necked flask. N‐propanol (n‐PrOH, 10 mL) and
triethylamine (2.0 mmol, 0.20 g) were added to the flask. The
reaction was monitored by TLC. After being refluxed for 3 h, the
solvent was removed under vacuum. The precipitate was
passed through a silica gel column and dried under vacuum to
produce 0.565 g of a white solid (80% yield), which was de‐
noted as (S)‐4,4’‐divinyl‐BINAPO.
Herein, we report the construction of two advanced hierar‐
chical chiral POPs, which were based on two synthesized vi‐
nyl‐functionalized chiral BINAP ligands, (S)‐4,4’‐divinyl‐BINAP
and (S)‐5,5’‐divinyl‐BINAP. The chiral BINAP‐based POPs,
which were denoted as 4‐BINAP@POPs and 5‐BINAP@POPs,
were efficiently prepared via the copolymerization of vi‐
nyl‐functionalized BINAP with DVB under solvothermal condi‐
tions. After exploring different synthetic routes and impreg‐
nating the POPs with a series of Ru species, the resultant mate‐
rials were systematically studied for the heterogeneous asym‐
metric hydrogenation of β‐keto esters.
Compound 4, (S)‐4,4’‐divinyl‐BINAP: (S)‐4,4’‐divinyl‐
BINAPO (1.0 mmol, 0.70 g), trichlorosilane (3.0 mmol, 0.41 g)
2. Experimental
2.1. Materials
All the solvents were analytical grade and were purified by
distillation under Ar atmosphere before use. Unless otherwise
Scheme 1. Synthesis of (S)‐4,4’‐divinyl‐BINAP.

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Tao Wang et al. / Chinese Journal of Catalysis 38 (2017) 890–898
and phenylsilane (3.0 mmol, 0.32 g) were placed in a
three‐necked flask with the addition of toluene (10 mL). The
reaction was monitored by TLC. After being refluxed for 3 h, the
solvent was cooled to 0 °C, followed by the slow addition of
NaOH aqueous solution. Then, the solution was extracted with
water and dried over Na2SO4. The solvent was removed under
vacuum. The precipitate was passed through a silica gel column
and dried under vacuum to produce 0.15 g of a white solid
were obtained via the same synthesis method.
2.4. Preparation of polymer‐supported catalysts
First, 0.41 g 4‐BINAP@POPs and 0.0069 g [Ru(benzene)Cl2]2
(0.028 mmol Ru) were added to 6 mL of N,N‐ dimethylforma‐
mide (DMF). After being refluxed for 3 h at 100 °C, the solvent
was removed under vacuum at 65 °C, and a dark‐green solid
was obtained, which was denoted as Ru/4‐BINAP@POPs.
Using 0.41 g of 5‐BINAP@POPs instead of 4‐BINAP@POPs
in the solution above, Ru/5‐BINAP@POPs‐1 were obtained via
the same strategies.
1
(21% yield), which was denoted as (S)‐4,4’‐divinyl‐BINAP. H
NMR (400 MHz, CDCl3) δ 5.38 (d, 1H, J = 10.9 Hz), 5.52 (d, 1H, J
= 17.1 Hz), 6.85–6.96 (m, 2H), 7.00–7.20 (m, 10H), 7.34–7.41
(m, 1H), 7.42–7.49 (m, 1H), 7.55–7.63 (s, 1H), 8.09 (d, 1H, J =
8.5 Hz); 31P NMR (161 MHz, CDCl3) −14.9 Hz.
As shown in path
B
of Scheme 2, the ligand
(S)‐5,5’‐divinyl‐BINAP was coordinated with [Ru(benzene)Cl2]
and then copolymerized with DVB to obtain the catalyst
Ru/5‐BINAP@POPs‐2. First, 0.1 g (S)‐5,5’‐divinyl‐BINAP and
0.0186 g [Ru(benzene)Cl2]2 (0.074 mmol Ru) were dissolved in
4 mL of DMF, and the mixture was stirred for 3 h at room tem‐
perature. Then, 1.0 g DVB, 0.025 g AIBN, and 6 mL of DMF were
added to the mixture. The mixture was first stirred for 10 min
at room temperature and then heated at 100 °C for 24 h. The
solvent was removed, and a dark‐green solid was obtained,
which was denoted as Ru/5‐BINAP@POPs‐2.
First, 0.35 g 5‐BINAP@POPs and 0.0072 g [Ru(p‐cyme)Cl2]2
(0.024 mmol Ru) were added to 5 mL of DMF. After being re‐
fluxed for 3 h at 100 °C, the solvent was removed and a
dark‐green solid was obtained, which was denoted as
Ru/5‐BINAP@POPs‐3.
2.3. Synthesis of BINAP@POPs
The synthesis of the BINAP@POPs and catalysts is summa‐
rized in Scheme 2. In an autoclave, 0.1 g (S)‐4,4’‐divinyl‐BINAP
and 1.0 g DVB were dissolved in 10 mL of tetrahydrofuran
(THF), followed by the addition of 25 mg of
2,2'‐azoisobutyronitrile (AIBN). The mixture was first stirred
for 10 min at room temperature and then heated at 100 °C for
24 h. The solvent was removed under vacuum at 65 °C, and a
white solid was obtained, which was denoted as
4‐BINAP@POPs.
Using 0.1
g
of (S)‐5,5’‐divinyl‐BINAP instead of
(S)‐4,4’‐divinyl‐BINAP in the solution above, 5‐BINAP@POPs
First, 0.27 g 5‐BINAP@POPs and 0.0050 g RuCl3∙xH2O(0.018
mmol Ru) were added to 5 mL of DMF. After being refluxed for
3 h at 100 °C, the solvent was removed and a dark‐green solid
was obtained, which was denoted as Ru/5‐BINAP@POPs‐3.
Path A
*
H2C HC
H2C CH
m
m
DVB, AIBN
PPh2
PPh2
PPh2
PPh2
H2C CH
n
THF, 100 °C, 24 h
2.5. Characterization
H2C CH
n
The liquid‐state NMR spectra were recorded on a 400‐MHz
spectrometer. The chemical shifts are reported in ppm. The 1H
NMR spectra were referenced to CDCl3 (0 ppm), and the 13C
[RuCl2(benzene)]2
DMF, r.t., 3 h
Path B
[RuCl2(benzene)]2
DMF, 100 °C, 3 h
NMR spectra were referenced to CDCl3 (77.0 ppm). All the 13
C
*
H2C HC
H2C CH
m
m
NMR spectra were measured with complete proton decoupling.
The signal patterns were indicated as s, singlet; d, doublet; t,
triplet; q, quartet; m, multiplet; br, broad singlet; and J, coupling
constant in Hz. The solid‐state NMR spectra were obtained
using a Varian Infinity‐Plus 400 spectrometer. The 31P MAS
NMR spectra were recorded with a 5‐mm probe at a frequency
of 161.8 MHz under a magic angle spinning rate of 10 kHz and a
delay of 4 s. The chemical shifts were referenced to 85% H3PO4.
The 13C CP/MAS NMR spectra were recorded under a magic
angle spinning rate of 6 kHz. Nitrogen isotherms at 77.3 K were
measured using a Quantachrome Autosorb‐1. Thermogravi‐
metric analysis (TGA) was performed using a NETZSCH STA
449F3, and the samples were heated from 40 to 1000 °C at a
rate of 10 °C/min under air. Inductively coupled plasma atomic
emission spectroscopy (ICP‐AES) analysis of the liquid samples
was performed on a Perkin‐Elmer 7300DV. High‐angle annular
dark‐field scanning transmission electron microscopy (HAADF
STEM) images were obtained using a JEM‐ARM200F. The
Ph2
Cl
DVB, AIBN
P
dmf
dmf
Ph2
P
Ru
Cl
Cl
Ru
Cl
P
Ph2
dm
dm
H2C CH
DMF,100 °C, 24 h
n
P
Ph2
H2C CH
n
Ru/5-BINAP@POPs-1 and Ru/5-BINAP@POPs-2
*
HC H2C
HC CH2
*
m
m
HC H2C
HC CH2
m
m
Ph2
P
[RuCl2(benzene)]2
DMF, 100 °C, 3 h
Cl
Ru
Cl
PPh2
PPh2
dm
dm
H2C CH
n
H2C CH
n
P
Ph2
H2C CH
n
H2C CH
n
Scheme 2. Synthesis of 4‐BINAP@POPs, 5‐BINAP@POPs, and its sup‐
ported Ru complexes.

Tao Wang et al. / Chinese Journal of Catalysis 38 (2017) 890–898
893
K‐edge extended X‐ray absorption fine structure spectra
(EXAFS) of Ru were obtained at the BL14W1 beamline of SSRF,
SINAP (Shanghai, China) using a Si(311) crystal monochroma‐
tor. The storage ring was operated at 3.5 GeV with injection
currents of 200 mA. The data were recorded in the fluores‐
cence mode. The EXAFS data were analysed using the Demeter
software package. Fourier transformation of the EXAFS data
was applied to the k3‐weighted functions. The theoretical scat‐
tering amplitude and phase‐shift functions of all the paths for
fitting the EXAFS data were calculated using the FEFF6 code.
in a glove box), washed with ipro (3 × 2 mL); the catalyst was
then used directly for the next catalytic reaction.
3. Results and discussion
3.1. Characterization
The pore properties of the three catalysts were analysed
using N2 physisorption isotherms (Fig. 1(a)). The catalysts
were insoluble and porous with large surface areas of
1058–1070 m2/g (ABET) and pore volumes of 1.19–1.64 cm3/g.
The Ru/5‐BINAP@POPs‐2 contained larger mesopores than
the Ru/4‐BINAP@POPs and Ru/5‐BINAP@POPs‐1. Meanwhile,
the polymers of 4‐BINAP@POPs and 5‐BINAP@POPs had sur‐
face areas greater than 1600 m2/g. The high P/Ru molar ratio
(P/Ru = 2) can explain the different pore properties of the
polymers and catalysts. Notably, polyDVB, which is obtained by
the self‐polymerization of DVB, only gives a ABET of 816 m2/g.
These results demonstrate that the addition of the rigid and
sterically chiral divinyl‐BINAP ligand is beneficial for increasing
the surface areas and pore volumes of polymers. The three
catalysts all contained micropores and mesopores, as further
confirmed by the pore size distribution curves calculated using
density functional theory (DFT; Fig. 1(b)).
2.6. Catalytic process
As a typical run for asymmetric hydrogenation of β‐keto es‐
ters, 0.026 g Ru/5‐BINAP@POPs‐1 catalyst, 0.20 g methyl
acetoacetate, and 2 mL of isopropanol (ipro) were added to a
30‐mL autoclave in a glove box. After the reactor was purged
with H2 four times, its pressure was finally adjusted to the de‐
sired value, heated from room temperature to the reaction
temperature of 50 °C, and stirred for 10 h. The catalyst was
separated by centrifugation, and the product was analysed
using gas chromatography (GC; Agilent 7890B gas chromato‐
graph equipped with a flame ionization detector and a Cy‐
closil‐B capillary column).
For recycling the catalyst, 0.052 g Ru/5‐BINAP@POPs‐1
catalyst, 0.40 g methyl acetoacetate, and 4 mL of ipro were
used. The catalyst was separated by centrifugation (performed
The 13C MAS NMR spectra of 4‐BINAP@POPs and
5‐BINAP@POPs both contained clear resonance peaks at 145,
137, and 128 ppm, which were assigned to the carbon of naph‐
0.30
0.25
0.20
0.15
0.10
0.05
0.00
(a)
(b)
2500
2000
1500
1000
500
(c)
(1)
(2)
(1)
*
*
*
*
*
*
*
(4)
(2)
(3)
*
(3)
(5)
0
0
1
10
Pore width (nm)
200 150 100 50
Chemical shift (ppm)
0.0 0.2 0.4 0.6 0.8 1.0
Relative pressure (p/p0)
100
80
60
40
20
0
(d)
(f)
(e)
(1)
(2)
(3)
(4)
(5)
(3)
250 200 150 100 50
0
-50 -100
200 150 100 50
0
-50 -100
0
200 400 600 800 1000
Temperature (oC)
Chemical shift (ppm)
Chemical shift (ppm)
Fig. 1. N2 isotherms (a), pore size distribution calculated by DFT (b), 13C CP/MAS NMR spectra (c), 31P MAS NMR spectra (d), 31P MAS NMR spectra (e),
and TG curves (f) of Ru/4‐BINAP@POPs (1), Ru/5‐BINAP@POPs‐1 (2), Ru/5‐BINAP@POPs‐2 (3), 4‐BINAP@POPs (4), and 5‐BINAP@POPs (5).

894
Tao Wang et al. / Chinese Journal of Catalysis 38 (2017) 890–898
thalene and benzene rings of the BINAP ligand and DVB (Fig.
1(c)). The resonance peaks near 44.0 ppm with relatively large
peak areas are mainly attributed to the carbon in the alkyl
linker formed by the copolymerization of vinyl functional
groups. Notably, the spectra show small peaks at 114 ppm cor‐
responding to vinyl groups, indicating the high degree of the
copolymerization of the ligands and DVB. The 31P MAS NMR
spectrum of 4‐BINAP@POPs produced a signal at −14.0 ppm
and that of 5‐BINAP@POPs produced a signal at −14.6 ppm
(Fig. 1(d)). No other obvious signals are observed for either
polymer, which indicates that the phosphine in the polymer
backbone is not oxidized. The 31P MAS NMR spectrum of
Ru/5‐BINAP@POPs‐2, a representative catalyst, exhibited a
broad peak at 52.8 ppm, which could be assigned to the unpro‐
tected phosphine coordinated with Ru species (Fig. 1(e)). In
addition, the relatively less intensive peak at 24.9 ppm was
attributed to phosphorus of phosphine oxide.
Excellent thermal stability is a crucial requirement for pol‐
ymer‐supported catalysts. The TGA curves under air demon‐
strate that the catalysts exhibited excellent thermal stability
without any decomposition at 300 °C (Fig. 1(f)).
To confirm the state of the Ru species in our heterogeneous
catalyst, EXAFS and HAADF‐STEM characterization were em‐
ployed for the fresh and used Ru/5‐BINAP@POPs‐1 catalyst. As
observed in Fig. 2 and Table 1, no obvious Ru–Ru bonds were
detected regardless of whether the sample was fresh or used,
Fig. 3. HAADF‐STEM images of fresh (a) and used (b) (recycled 6 times)
Ru/5‐BINAP@POPs‐1 catalyst.
indicating that Ru species are dispersed as a single atom on the
5‐BINAP@POPs, which was further confirmed by the
HAADF‐STEM images (Fig. 3). In addition, P, Cl, and O were
coordinated with Ru, whose coordination numbers are all two
[40–42]. Moreover, considering the uncertainty of the fitting
results, we believe that the bond lengths of Ru–P and Ru–Cl in
the fresh and used samples were the same because they are all
from the same ligands. The Ru–O bond lengths of the fresh and
used Ru/5‐BINAP@POPs‐1 sample were 1.90 and 2.13 Å, re‐
spectively. The distinct bond length of Ru–O is due to the dif‐
ference between DMF and ipro. The Ru species in the fresh
sample was coordinated with the O atom of DMF. Ipro was se‐
lected as the reaction solvent for the asymmetric hydrogena‐
tion of the ‐keto ester. Therefore, the Ru species in the used
sample was coordinated with the O atom of ipro.
3.2. Catalytic tests
Experiment
Fitting
3.2.1. Reaction rate of Ru/4‐BINAP@POPs and
Ru/5‐BINAP@POPs‐1
The effect of the catalysts for the hydrogenation of methyl
acetoacetate on the reaction rate and enantioselectivity was
studied using Ru/4‐BINAP@POPs and Ru/5‐BINAP@POPs‐1
(Fig. 4). Ru/5‐BINAP@POPs‐1 produced a 74.3% yield and
(a)
89.1% enantiomeric excess (ee) within
1 h, whereas
Ru/4‐BINAP@POPs only produced a 29.1% yield and 84.6% ee.
(b)
100
90
0
1
2
3
4
5
6
80
R (Å)
yeild
ee
yeild
ee
}
Ru/4-BINAP@POPs
70
60
50
40
30
20
Fig. 2. Ru K‐edge k3‐weighted Fourier‐transform EXAFS spectra of fresh
(a) and used (b) (recycled 6 times) Ru/5‐BINAP@POPs‐1 catalyst.
}Ru/5-BINAP@POPs-1
Table 1
Curve‐fitting analysis of the EXAFS traces.
R
Sample
Shell
N
R (Å)
σ2103 (Å2)
2.5(1.0)
factor
Ru/5‐BINAP@
POPs‐1 (fresh)
Ru–P 2.0 2.26(0.04)
0.006
Ru–Cl 2.0 2.40(0.02)
Ru–O 2.0 1.90(0.02)
Ru–P 2.0 2.22(0.06)
Ru–Cl 2.0 2.34(0.02)
Ru–O 2.0 2.13(0.04)
3.0(1.0)
11.4(7.0)
0
2
4
6
8
10
Time (h)
Ru/5‐BINAP@
POPs‐1 (used)
14.7(10.0) 0.012
8.4(3.5)
Fig. 4. Effect of Ru/4‐BINAP@POPs and Ru/5‐BINAP@POPs‐1 on the
reaction rate and enantioselectivity. Reaction conditions: methyl aceto‐
acetate (1.72 mmol), catalyst (0.00172 mmol Ru), ipro (2 mL), initial H2
pressure (4 MPa), 50 °C, 10 h, and the yield and ee values were deter‐
mined by GC on a Cyclosil‐B capillary column.
1.3(2.0)
N, coordination number; R, distance between absorber and backscat‐
tered atom; σ2, Debye‐Waller factor.

Tao Wang et al. / Chinese Journal of Catalysis 38 (2017) 890–898
895
After 6 h, the yield was more than 98% for both catalytic sys‐
Table 3
tems. In particular, Ru/5‐BINAP@POPs‐1 produced a 99.5%
yield and 94.3% ee after 10 h. Ru/5‐BINAP@POPs‐1 exhibited
a higher reaction rate and similar enantioselectivity compared
with Ru/4‐BINAP@POPs. Considering the similarity in the pore
structures of the two catalysts, the divinyl derivatives of BINAP,
which were substituted in different positions, affected the chi‐
ral characters of the BINAP ligand in the polymer backbone and
may ultimately affect their catalytic performance. The bulky
building blocks formed in the 4,4’‐positions were closer to the
phosphorus atoms of BINAP than the 5,5’‐positions, which
made the catalyst of Ru/4‐BINAP@POPs not easily accessible
to the substrate.
Optimization of hydrogenation reaction parameters.
Entry
1
2
Solvent a
THF
PhH
PhMe
MeOH
ipro
ipro
ipro
ipro
ipro
Temp. (°C) pH2 (MPa) Yieldb (%) eeb (%)
50
50
50
50
50
40
60
70
80
50
50
50
50
50
4
4
4
4
4
4
4
4
4
1
2
3
5
6
>99.5
64.1
>99.5
>99.5
>99.5
89.1
>99.5
>99.5
>99.5
>99.5
>99.5
>99.5
>99.5
>99.5
84.1
72.9
68.9
91.9
94.3
93.6
94.6
91.4
92.6
91.3
92.7
93.4
94.6
95.0
3
4
5
6
7
8
9
10
11
12
13
ipro
ipro
ipro
ipro
3.2.2. Catalytic activities of different 5‐BINAP@POP‐supported
catalysts
14
ipro
The
catalytic
performance
of
different
a
Reaction conditions: methyl acetoacetate (1.72 mmol),
Ru/5‐BINAP@POPs‐1 (0.00172 mmol Ru), solvent (2 mL), 10 h.
b Determined by GC on a Cyclosil‐B capillary column.
5‐BINAP@POP‐supported catalysts was also studied (Table 2).
As previously mentioned, Ru/5‐BINAP@POPs‐1 and
Ru/5‐BINAP@POPs‐2 were synthesized via different strategies
(post‐synthesis and one‐pot, respectively), leading to distinct
effects on the catalytic activity. The catalyst prepared through
post‐synthesis (Table 2, entry 1) exhibited better activity and
enantioselectivity than the one‐pot sample (Table 2, entry 2).
This finding may be attributed to part of the Ru species being
embedded in the framework of the Ru/5‐BINAP@POPs‐2 cata‐
lyst, which therefore restricted the accessibility of the reagent
to the active sites of the catalyst [39]. Ru/5‐BINAP@POPs‐3
and Ru/5‐BINAP@POPs‐4 were obtained using the
post‐synthesis strategy using the Ru precursors of
[Ru(p‐cyme)Cl2]2 and RuCl3∙xH2O, respectively. The activity and
enantioselectivity of the catalysts decreased in the order
Ru/5‐BINAP@POPs‐1 > Ru/5‐BINAP@POPs‐3 > Ru/5‐BINAP@
OPs‐4. Therefore, the catalyst that was post‐synthesized by the
5‐BINAP@POPs polymer and [Ru(benzene)Cl2]2 precursor
were selected for further study.
Table 4
Asymmetric hydrogenation of β‐keto esters by Ru/5‐BINAP@POPs‐1a.
Entry
1
Substrate
Yieldb (%)
>99.5
eeb (%)
94.3
2
3
>99.5
>99.5
95.1
93.6
4
5
6
>99.5
>99.5
85.0
94.6
89.2
92.9
7
>99.5
>99.5
90.0
91.8
3.2.3. Optimization of reaction conditions
8c
The effects of various parameters (solvent, reaction tem‐
perature, and H2 pressure) on the product yield and enantiose‐
lectivity were investigated (Table 3). The insoluble catalyst was
well swollen by a wide range of organic solvents. Alcoholic sol‐
9d
92.6
91.9
a Reaction conditions: substrates (1.72 mmol), catalyst (0.00172 mmol
Ru), ipro (2 mL), initial H2 pressure (4 MPa), 50 °C, 10 h.
b Determined by GC on a Cyclosil‐B capillary column.
c Catalyst (0.00172 mmol Ru), S/C = 4000.
d Catalyst (0.0086 mmol Ru), substrates (43 mmol), reaction time = 20
h.
Table 2
Different 5‐BINAP@POP‐supported catalysts for hydrogenation reac‐
tion.
Entry
Catalyst a
Yieldb (%)
>99.5
79.9
97.3
87.2
eeb (%)
94.3
85.8
91.7
86.1
vents were better selections than the others, and the use of ipro
resulted in slightly higher enantioselectivity than the use of
methanol (Table 3, entries 1–5). The effect of temperature on
the reaction was investigated in the range of 40–80 °C (Table 3,
entries 5–9). The reaction rate slowed down with decreasing
temperature; however, the enantioselectivity was not signifi‐
cantly affected by this factor. In addition, the enantioselectivity
improved from 91.3% to 95.0% when the H2 pressure in‐
1
2
3
Ru/5‐BINAP@POPs‐1
Ru/5‐BINAP@POPs‐2
Ru/5‐BINAP@POPs‐3
Ru/5‐BINAP@POPs‐4
4
a
Reaction conditions: methyl acetoacetate (1.72 mmol), catalyst
(0.00172 mmol Ru), ipro (2 mL), initial H2 pressure (4 MPa), 50 °C, 10
h.
b Determined by GC on a Cyclosil‐B capillary column.

896
Tao Wang et al. / Chinese Journal of Catalysis 38 (2017) 890–898
creased from 1 to 6 MPa (Table 3, entries 10–14).
3.2.4. Expansion of substrate scope
20
10
0
Next, we examined the scope of asymmetric hydrogenation
of β‐keto esters by Ru/5‐BINAP@POPs‐1 (Table 4). Excellent
production yields were obtained with high enantioselectivities.
In the hydrogenation of tert‐butyl acetoacetate and isobutyl
acetoacetate, the catalyst exhibited lower performances than
the other substrates (Table 4, entries 5 and 6). Notably, the
catalyst demonstrated satisfactory activity at very high molar
ratios of the substrate and catalyst (S/C = 4000) for 10 h (Table
4, entry 8). When the amount of the reaction substrate was
increased to 43 mmol, a long reaction time of 20 h was needed
to obtain a satisfactory result (Table 4, entry 9), which was
most likely due to the effect of mass transfer. The uniform dis‐
tribution of the BINAP ligand in the polymer backbone and
abundant pore structures of the catalyst may afford a qua‐
si‐homogeneous flexible character to the ligands in the frame‐
work while the reaction proceeds [43].
0
1
2
3
4
5
Time (h)
Fig. 5. Hot filtration for the Ru/5‐BINAP@POPs‐1 catalyst in the asym‐
metric hydrogenation of methyl acetoacetate. Reaction conditions:
methyl acetoacetate (1.72 mmol), catalyst (0.00172 mmol Ru), ipro (2
mL), initial H2 pressure (4 MPa), 50 °C.
polymers. The chiral POPs supporting Ru catalysts prepared
using two different synthetic routes were systematically inves‐
tigated to demonstrate their excellent catalytic performance for
heterogeneous asymmetric hydrogenation of β‐keto esters.
Characterization by NMR and EXAFS confirmed that through
copolymerization with DVB, the chiral ligands were incorpo‐
rated into the polymer backbone by an alkyl linker. The alkyl
linker formed by the vinyl groups in the prepared polymers
could maintain the quasi‐homogeneous flexible character of the
BINAP ligand in the polymer backbone [43]. Ru species were
firmly coordinated by chiral BINAP ligands fixed on the poly‐
mer backbone to prevent leaching during recycling usage.
Meanwhile, abundant pore structures and uniformly implanted
chiral BINAP ligands in the polymer were favourable for highly
efficient chiral inducibility of β‐keto esters on coordinated Ru
sites.
3.2.5. Reusability of Ru/5‐BINAP@POPs‐1
The asymmetric hydrogenation of methyl acetoacetate was
selected to evaluate the reusability of Ru/5‐ BINAP@POPs‐1
(Table 5). The catalyst can be reused for at least 6 cycles with
complete conversion and high enantioselectivity. We further
confirmed the heterogeneous nature of the system using ICP
analysis. During the recycling, the amount of Ru species in the
filtrate was less than 0.06 ppm for each round of hydrogena‐
tion. The morphologies of fresh and used Ru/5‐BINAP@POPs‐1
were examined using HAADF STEM (Fig. 3). In addition, no
obvious Ru nanoparticles were formed after the sixth run, as
evidenced by the EXAFS results (Fig. 2 and Table 1). Note that
even with a high P/Ru ratio (P/Ru = 2), the catalyst exhibited
high stability during the recycling. The hot filtration test results
for the Ru/5‐BINAP@POPs‐1 in the asymmetric hydrogenation
of methyl acetoacetate are presented in Fig. 5. Because the sub‐
strate conversion was no more than 15%, the ee value is not
listed. The results indicate that when the insoluble catalyst was
removed from the hot reaction mixture by filtration, the reac‐
tion stopped and no additional products were generated. This
finding indicated that the reaction was indeed heterogeneous.
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Tao Wang et al. / Chinese Journal of Catalysis 38 (2017) 890–898
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Graphical Abstract
Chin. J. Catal., 2017, 38: 890–898 doi: 10.1016/S1872‐2067(17)62826‐2
Chiral BINAP‐based hierarchical porous polymers as platforms
for efficient heterogeneous asymmetric catalysis
Tao Wang, Yuan Lyu *, Kai Xiong, Wenlong Wang, Hao Zhang,
Zhuangping Zhan, Zheng Jiang, Yunjie Ding *
Dalian Institute of Chemical Physics, Chinese Academy of Sciences;
University of Chinese Academy of Sciences;
Xiamen University;
Shanghai Institute of Applied Physics, Chinese Academy of Sciences
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95%) and could be reused for 6 runs in the asymmetric hydrogena‐
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