Synthesis, characterization and catalytic performance in enantioselective reactions by mesoporous silica materials functionalized with chiral thiourea-amine ligand

Article abstract of DOI:10.1007/s11164-020-04301-w

Chiral heterogeneous catalysts have been synthesized by grafting of silyl derivatives of (1R, 2R)- or (1S, 2S)-1,2-diphenylethane-1,2-diamine on SBA-15 mesoporous support. The mesoporous material SBA-15 and so-prepared chiral heterogeneous catalysts were characterized by a combination of different techniques such as X-ray diffractometry (XRD), Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM), and Brunauer–Emmett–Teller (BET) surface area. Results showed that (1R, 2R)- and (1S, 2S)-1,2-diphenylethane-1,2-diamine were successively immobilized on SBA-15 mesoporous support. Chiral heterogeneous catalysts and their homogenous counterparts were tested in enantioselective transfer hydrogenation of aromatic ketones and enantioselective Michael addition of acetylacetone to β-nitroolefin derivatives. The catalysts demonstrated notably high catalytic conversions (up to 99%) with moderate enantiomeric excess (up to 30% ee) for the heterogeneous enantioselective transfer hydrogenation. The catalytic performances for enantioselective Michael reaction showed excellent activities (up to 99%) with poor enantioselectivities. Particularly, the chiral heterogeneous catalysts could be readily recycled for Michael reaction and reused in three consecutive catalytic experiments with no loss of catalytic efficacies.

Full text of DOI:10.1007/s11164-020-04301-w

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-020-04301-w
Synthesis, characterization and catalytic performance
in enantioselective reactions by mesoporous silica
materials functionalized with chiral thiourea‑amine ligand
Yaşar Gök1 · Halil Zeki Gök1
Received: 31 August 2020 / Accepted: 10 October 2020
© Springer Nature B.V. 2020
Abstract
Chiral heterogeneous catalysts have been synthesized by grafting of silyl derivatives
of (1R, 2R)- or (1S, 2S)-1,2-diphenylethane-1,2-diamine on SBA-15 mesoporous
support. The mesoporous material SBA-15 and so-prepared chiral heterogene-
ous catalysts were characterized by a combination of diferent techniques such as
X-ray difractometry (XRD), Fourier transform infrared (FT-IR), thermogravimet-
ric analysis (TGA), feld emission scanning electron microscopy (FESEM), and
Brunauer–Emmett–Teller (BET) surface area. Results showed that (1R, 2R)- and
(1S, 2S)-1,2-diphenylethane-1,2-diamine were successively immobilized on SBA-15
mesoporous support. Chiral heterogeneous catalysts and their homogenous counter-
parts were tested in enantioselective transfer hydrogenation of aromatic ketones and
enantioselective Michael addition of acetylacetone to β-nitroolefn derivatives. The
catalysts demonstrated notably high catalytic conversions (up to 99%) with moder-
ate enantiomeric excess (up to 30% ee) for the heterogeneous enantioselective trans-
fer hydrogenation. The catalytic performances for enantioselective Michael reaction
showed excellent activities (up to 99%) with poor enantioselectivities. Particularly,
the chiral heterogeneous catalysts could be readily recycled for Michael reaction and
reused in three consecutive catalytic experiments with no loss of catalytic efcacies.
Keywords Chirality · Enantioselectivity · Heterogeneous catalysis · Mesoporous
materials
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s1116
4-020-04301-w) contains supplementary material, which is available to authorized users.
* Yaşar Gök
yasargok@mehmetakif.edu.tr
1
Department of Biomedical Engineering, Bucak Faculty of Technology, Burdur Mehmet Akif
Ersoy University, 15300 Bucak/Burdur, Turkey
Vol.:(0123456789)
1 3

Y. Gök, H. Z. Gök
Introduction
Catalysis is one of the most important key technologies for the preparation of
organic compounds that facilitate the life of human beings [1–3]. Many prod-
ucts such as modern drugs and agrochemicals can proceed under the cataly-
sis of organic reactions in the presence of homogenous or heterogeneous cata-
lysts [4–9]. After the thalidomide tragedy [10–12], the certain drugs have been
intended to contain single enantiomer in consistent with the regulations of FDA
[13]. Homogeneous enantioselective catalysis is one of the powerful methods
used for many years to meet the demand for enantiopure compounds in pharma-
ceutical feld [5–7]. In this method, prochiral starting compounds can be con-
verted into chiral products as a result of the reaction catalyzed by a small amount
of a chiral ligand in enantioselective catalysis. To date, a large number of chiral
catalysts with very high catalytic activity for enantioselective catalysis have been
published in the literature [14–19]. However, the industrial applications of these
privileged stereodirecting chiral catalysts are often hindered by their high costs,
the inability to recover them after their use, and the removal of toxic metals from
the organic product.
In recent years, immobilization of chiral ligands on solid support materials
such as SBA- and MCM-type silicas have attracted enormous attention because
the advantages of heterogeneous catalysts such as easy separation and recycling
can be combined with the advantages of homogeneous catalysts such as high
activity and selectivity [2, 4, 20–23]. Although there are many diferent types
of solid support materials [24], mesoporous silica materials stand out among
other materials due to their physicochemical parameters such as having controlla-
ble morphology, size, surface chemistry, pore size and porous structure [24–27].
Since the frst report of mesoporous silica materials [28], much research efort
has been devoted to synthesize silica-supported heterogeneous catalysts with
many diferent functional groups to be used in enantioselective catalysis [3, 4,
23, 29]. One of the most preferred way to prepare highly active and selective chi-
ral heterogeneous catalysts is the immobilization of privileged chiral ligands on
silica supports via covalent or non-covalent interaction [2, 30–32].
Chiral ligands with C2 symmetry are known as privileged chiral catalyst that
give very good results in homogeneous enantioselective catalysis [7, 14]. C2 sym-
metric chiral ligands have the rigid structure containing functional groups with
donor atoms such as oxygen, nitrogen and phosphorous which allow the chiral
ligand to coordinate to the metal atom. (1R, 2R)- and (1S, 2S)-1,2-diphenyle-
thane-1,2-diamine as a member of C2 symmetric ligands have been subject of
many studies in the feld of enantioselective catalysis [33–36]. However, the stud-
ies in enantioselective heterogeneous catalysis with the immobilized 1,2-dipheny-
lethane-1,2-diamine onto the mesoporous materials are still limited [37, 38].
In this study, our aim is to prepare readily accessible, robust and recyclable
chiral heterogeneous catalysts. To achieve this, mesoporous silica nanoparti-
cles functionalized with (1R, 2R)- and (1S, 2S)-1,2-diphenylethane-1,2-diamine
derivatives were synthesized by covalently grafting of silyl derivatives of (1R,
1 3

Synthesis, characterization and catalytic performance in…
2R)- and (1S, 2S)-1,2-diphenylethane-1,2-diamine on SBA-15 and then character-
ized. The catalytic efciencies of novel heterogeneous catalysts were investigated
and compared in enantioselective transfer hydrogenation reaction of a series of
aromatic ketones and in enantioselective Michael addition of acetylacetone to
β-nitroolefn derivatives.
Experimental
Materials and equipment
Triblock copolymer Pluronic P123 [(EO)20–(PO)70–(EO)20], triethoxy(3-aminopro-
pyl)silane (APTES), tetraethyl orthosilicate (TEOS), thiophosgene (CSCl2), (1R,
2R)-1,2-diphenylethane-1,2-diamine, (1S, 2S)-1,2-diphenylethane-1,2-diamine and
all other reagents were obtained from commercial suppliers (Merck or Fluka). All
the materials used during the experiments were of analytical grade. All solvents
were dried and purifed as described by Perrin and Armarego [39]. FTIR spectra
1
were measured on a PerkinElmer Spectrum 65 spectrometer using KBr pellets. H
and 13C NMR spectra were recorded on a Varian Mercury 400 MHz spectrometer
using CDCl3 (99.9%). Mass spectra were measured on a Micromass Quattro LC/
ULTIMA LC–MS/MS and a Bruker Daltonics MALDI-TOF spectrometer. The
XRD measurement was carried out on a PANalytical Empyrean X-ray difractome-
ter using Cu-Kα radiation (λ=0.154056 nm) within the scattering angle 2θ range of
1–10° and 10–80o, respectively. The FESEM images were recorded on a Jeol SEM-
7100-EDX instrument. The TGA measurements were carried out on a Seiko SII TG/
DTA 7200 instrument by heating from room temperature to 800 °C at a heating rate
of 10 °C/min under N2 atmosphere with a fow rate of 2 mL/min. N2 adsorption/
desorption isotherms were measured on a Micrometrics Surface Area and Porosity
TriStar II analyzer. The specifc surface area was calculated by BET method, and the
pore size distribution calculated by Barrett–Joyner–Halenda (BJH) method. Optical
rotations were measured with a Rudolph Autopol-I series polarimeter. Analytical
chiral HPLC separations were performed on a Shimadzu Prominence LC-20A with
DAD detection. GC separations were performed on Shimadzu GC-2010 Plus using
chiral columns.
Synthesis
Synthesis of SBA‑15
Mesoporous SBA-15 nanoparticle was synthesized according to the procedure
described by Zhao et al. using Pluronic P123 as template with a molar gel composi-
tion of 1.00 TEOS/0.02 Pluronic P123/5.58 HCl/182.55 H2O [40]. In a typical prep-
aration, 16.0 g of pluronic P123 was dissolved in 1.6 M HCl (600 mL) solution with
stirring at 41 °C. Then, 37 mL TEOS was added dropwise to the solution at 41 °C
and stirred for 20 h at room temperature. The mixture was aged at 80 °C for 15 h
1 3

Y. Gök, H. Z. Gök
under static condition. The solid product was fltered, washed with distilled water
and air-dried at room temperature overnight. To remove the template, the dried
SBA-15 was calcined from 150 °C to 550 °C for 4 h and 550 °C for 8 h, yielding the
fnal mesoporous SBA-15 nanoparticles.
Synthesis of triethoxy (3‑isothiocyanatopropyl)silane (1)
Triethoxy(3-aminopropyl)silane (APTES) (0.8 g; 3.61 mmol) was added to the fask
containing freshly distilled dry THF (15 mL) and dry NEt3 (1.1 g; 10.82 mmol) as
the base under nitrogen atmosphere at 0 °C. The reaction mixture was stirred for
15 min at this temperature. Then, thiophosgene (0.62 g; 5.42 mmol) was added drop-
wise through a dropping funnel to the stirring solution at 0 °C under nitrogen atmos-
phere. The resulting reaction mixture was stirred for further 3 h. At the end of this
period, the reaction was allowed to warm to room temperature and fltered of. The
fltrate was evaporated under reduced pressure to dryness. Then, the remaining crude
product was extracted with water and dichloromethane solvent system. The organic
layer was dried over anhydrous Na2SO4, and then the solvent was evaporated under
reduced pressure to give a crude product. The obtained crude product was purifed
by silica gel column chromatography. The elution was carried out successively with
hexane–ethyl acetate (5:95) solvent system, afording the product as pale-yellow oil.
Yield: 0.542 g (57%). FT-IR (disk) ν=2974, 2927, 2886, 2178, 2097, 1679, 1443,
1
1390, 1345, 1192, 1165, 1099, 1071, 954, 873, 779 cm−1. H-NMR (400 MHz,
CDCl3, ppm) δ: 0.71–0.75 (m, 2H), 1.26 (t, J=6.8 Hz, 9H), 1.81–1.89 (m, 2H), 3.54
(t, J=7.0 Hz, 2H), 3.86 (q, J=6.9 Hz, 6H). 13C-NMR (100 MHz, CDCl3, ppm) δ:
7.7 (CH2), 18.3 (CH3), 24.1 (CH2), 47.3 (CH2), 58.5 (CH2), 129.3 (C).
1‑((1R,2R)‑2‑amino‑1,2‑diphenylethyl)‑3‑(3‑(triethoxysilyl)propyl)thiourea (4)
(1R, 2R)-1,2-diphenylethane-1,2-diamine 2 (0.1 g, 0.47 mmol) and 4 mL of dry
CH2Cl2 were placed in a two-neck fask under nitrogen atmosphere at room tempera-
ture. Triethoxy(3-isothiocyanatopropyl)silane 1 (0.113 g, 0.43 mmol) in dry CH2Cl2
(6 mL) was added dropwise to this resulting mixture. The reaction was monitored
by thin-layer chromatography and completed in 24 h. The crude product was puri-
fed by fash chromatography over silica gel with CH2Cl2/CH3OH (97/3) resulting in
0.13 g (62%) of pure 4 as a transparent oil. 4; Found: C, 60.28; H, 7.99; N, 8.68%;
′molecular formula C24H37N3O3SSi′ requires C, 60.59; H, 7.84; N, 8.83; S, 6.74%.
[α]16 =+21 (c, 1.0, CHCl3). FT-IR (disk) ν=3292, 3053, 3034, 2926, 1733, 1540,
D
1494, 1454, 1390, 1264, 1165, 1100, 1074, 956 cm−1. 1H-NMR (400 MHz, CDCl3,
ppm) δ: 0.51–0.52 (m, 2H), 1.24 (t, J=7.0 Hz, 9H), 1.62–1.63 (m, 2H), 2.11 (br, s,
2H), 3.37–3.48 (m, 2H), 3.81 (q, J=7.0 Hz, 6H), 4.37 (s, br, 1H), 6.05 (s, br, 1H),
7.24–7.28 (m, 3H), 7.30–7.36 (m, 9H). 13C-NMR (100 MHz, CDCl3, ppm) δ: 7.5
(CH2), 18.3 (CH3), 22.3 (CH2), 46.7 (CH2), 58.4 (CH2), 60.3 (CH), 63.8 (CH), 126.5
(CH), 127.8 (CH), 127.9 (CH), 128.4 (CH), 128.6(CH), 128.9 (CH), 141.7 (C),
141.8 (C), 181.9 (C). MS (MALDI-TOF) MS calculated [M]− for C24H37N3O3SSi:
475.24; found: 475.01 [M]+.
1 3

Synthesis, characterization and catalytic performance in…
1‑((1S,2S)‑2‑amino‑1,2‑diphenylethyl)‑3‑(3‑(triethoxysilyl)propyl)thiourea (5)
The same procedure given for 4 was followed for the synthesis of 5 except that (1S,
2S)-1,2-diphenylethane-1,2-diamine 3 was used instead of (1R, 2R)-1,2-dipheny-
lethane-1,2-diamine 2. C24H37N3O3SSi 5. Yield: 0.12 (59%). Found: C, 60.51; H,
7.63; N, 8.97%; ′molecular formula C24H37N3O3SSi′ requires C, 60.59; H, 7.84;
N, 8.83; S, 6.74%. [α]16 = −21 (c, 1.0, CHCl3). FT-IR (disk) ν=3277, 3063, 3028,
D
2926, 2974, 1732, 1538, 1494, 1453, 1389, 1348, 1294, 1216, 1192, 1165, 1100,
1
1072, 1029, 954 cm−1. H-NMR (400 MHz, CDCl3, ppm) δ: 0.52 (m, 2H), 1.24
(t, J=7.0 Hz, 9H), 1.62 (m, 2H), 2.09 (br, s, 2H), 3.31–3.55 (m, 2H), 3.81 (q,
J=7.0 Hz, 6H), 4.37 (s, br, 1H), 6.07 (s, br, 1H), 7.24–7.28 (m, 3H), 7.31–7.38
(m, 9H). 13C-NMR (100 MHz, CDCl3, ppm) δ: 7.5 (CH2), 18.3 (CH3), 22.3 (CH2),
47.0 (CH2), 58.4 (CH2), 60.3 (CH), 63.8 (CH), 126.5 (CH), 127.8 (CH), 127.9 (CH),
128.6 (CH), 128.9 (CH), 129.4 (CH), 141.6 (C), 141.7 (C), 181.9 (C). MS (ESI+)
MS calculated [M+H]+ for C24H38N3O3SSi: 476.2; found: 476.2 [M+H]+
General procedure for the synthesis of SBA‑15 supported chiral thiourea‑amine
catalysts (6–7)
Before the functionalization, SBA-15 was activated under vacuum at 120 °C for 2 h.
Compound 4 or 5 (0.08 g) in 40 mL of dry toluene was added dropwise to SBA-15
(1 g) under nitrogen atmosphere at room temperature and then refuxed for 20 h.
Soxhlet extraction with dichloromethane for 20 h yielded mesoporous silica nano-
particles-supported chiral thiourea-amine catalysts 6–7.
Synthesis of mesoporous SBA‑15 nanoparticles‑supported 1‑((1R,2R)‑2‑amino‑1,2
‑diphenylethyl)‑3‑(3‑(triethoxysilyl)propyl)thiourea bifunctional catalyst (6) Syn-
thesis of 6 was performed by using SBA-15 (1 g) and 1-((1R,2R)-2-amino-1,2-
diphenylethyl)-3-(3-(triethoxysilyl)propyl)thiourea 4 (0.080 g) in 40 mL toluene. The
product was obtained as a white powder (~1.08 g).
Synthesis of mesoporous SBA‑15 nanoparticles‑supported 1‑((1S,2S)‑2‑amino‑1,2
‑diphenylethyl)‑3‑(3‑(triethoxysilyl)propyl)thiourea bifunctional catalyst (7) Syn-
thesis of 7 was performed by using SBA-15 (1 g) and 1-((1S,2S)-2-amino-1,2-
diphenylethyl)-3-(3-(triethoxysilyl)propyl)thiourea 5 (0.08 g) in 40 mL toluene. The
product was obtained as a white powder (~1.08 g).
General procedure for the enantioselective transfer hydrogenation of aromatic
ketones
A mixture of [Ru(p-cymene)Cl2]2 (0.002 mmol) and corresponding chiral ligands
(4 and 5) (0.004 mmol) or chiral heterogonous catalysts 6–7 (0.03 g,~0.004 mmol)
i
in PrOH (7 mL) were placed under a nitrogen atmosphere in a standard Schlenk
tube. The reaction mixture was heated and stirred under nitrogen at 82 °C for 2 h.
1 3

Y. Gök, H. Z. Gök
After cooling to room temperature, the aromatic ketone (1 mmol) was added to this
mixture and the solution was then heated to 82 °C. To initiate the reaction, the solu-
i
tion of NaOH (0.2 mmol) in PrOH was added to the stirring reaction mixture. To
monitor the conversions of ketones to corresponding secondary alcohols, a small
volume of reaction mixture was taken from Schlenk tube via micro-syringe and
diluted with iPrOH and then passed from microflter or short silica gel column. The
conversion and enantiomeric excess were monitored by GC using Agilent HP-Chiral
20B column.
General procedure for enantioselective Michael reaction of acetylacetone
to nitroolefns
A mixture of corresponding chiral ligands (4 and 5) (0.014 mmol) or chiral het-
erogonous catalysts 6–7 (0.083 g;~0.014 mmol) and a nitrostyrene derivative
(0.2 mmol) in water/dry solvent were placed in a fask under a nitrogen atmosphere.
The reaction mixture was stirred under nitrogen at room temperature for 10 min.
The acetylacetone (0.4 mmol) was added to this mixture, and the solution was
stirred at room temperature for further 48 h. At the end of period, chiral hetero-
gonous catalysts 6–7 were recovered by simple fltration. Crude product was puri-
fed by silica gel column chromatography. The enantiomeric excess was determined
by HPLC using YMC Chiral ART Amylose-C column. The absolute confguration
of the product was assigned by comparison of HPLC profle with the reported litera-
ture [41].
Results and discussion
Preparation and characterization
The stepwise synthesis of chiral heterogonous catalysts 6–7 is shown in Scheme 1.
The frst step was the synthesis of triethoxy(3-isothiocyanatopropyl)silane 1 as it
is not commercially available. The synthesis of triethoxy(3-isothiocyanatopropyl)
silane 1 in the presence of carbon disulfde has been reported in many studies so far
[42–44]. In the present study, the silyl precursor triethoxy(3-isothiocyanatopropyl)
silane 1 was synthesized with a moderate yield by using thiophosgene instead of
carbon disulfde and purifed by chromatographic separation instead of Kügelrohr
distillation. In our synthesis, APTES was reacted with thiophosgene in dry dichlo-
romethane at 0 °C. At the end of this reaction, the desired product was obtained
as pale-yellow oil with the yield of 65% after chromatographic separation. The
1
obtained spectral data of triethoxy(3-isothiocyanatopropyl)silane 1 from FT-IR, H
and 13C NMR were in consistent with previously obtained data [44].
The reaction of (1R, 2R)-1,2-diphenylethane-1,2-diamine 2 and (1S, 2S)-1,2-di-
phenylethane-1,2-diamine 3 with triethoxy(3-isothiocyanatopropyl)silane 1 aforded
the desired thiourea-amine bifunctional chiral ligands 4 and 5, respectively, in mod-
erate yield after purifcation of crude products over silica gel column chromatogra-
phy. The FT-IR measurements of 4–5 were performed by KBr disk technique on a
1 3

Synthesis, characterization and catalytic performance in…
Scheme 1 Synthesis of mesoporous silica nanoparticles-supported chiral thiourea-amine catalysts 6–7
PerkinElmer Spectrum 65 Spectrometer. The FT-IR spectra of 4–5 were very similar
since they were isomers. The observation of an intense C=S stretching vibration
band in a region around 1070 and 740 cm−1 is characteristic for thiourea compounds
[45]. In FT-IR spectra of 4–5, the band from –NH2 stretching was observed as super-
1
posed to the N–H stretching around 3300 cm−1. In addition to the H-NMR, 13C-
NMR and elemental analysis results of 4–5, the observation of expected molecular
ion peaks in their mass spectra confrmed that the chiral thiourea-amine catalysts
4–5 were synthesized successfully. (See Supporting information for the mass spectra
of 4 and 5.)
The SBA-15 was prepared by hydrolysis of TEOS in the presence of P123 as
a templating agent, according to the previously published method [40]. The
removal of P123 was performed by calcination at 550 °C for 8 h, yielding the fnal
mesoporous SBA-15 material. The last step was the functionalization of SBA-15
with chiral ligands 4 and 5. For this, the chiral thiourea-amine ligands 4 and 5 were
covalently grafted onto SBA-15 by the reaction of ethoxy groups of 4 and 5 with the
silanol groups on the surface of SBA-15, afording 6 and 7. Then, all synthesized
1 3

Y. Gök, H. Z. Gök
mesoporous silica materials (SBA-15, 6 and 7) were characterized by a combination
of several techniques such as FT-IR, TGA, BET, XRD and FESEM.
FT-IR spectroscopy was used as frst to characterize SBA-15 and chiral heter-
ogeneous catalysts (6–7). Figure 1 shows the FT-IR spectra of SBA-15 and 6–7.
The FT-IR spectra of SBA-15 showed the characteristic stretching, bending and
out of plane vibrations for Si–O bonds around 1085, 805 and 460 cm−1, respec-
tively. Silanol groups in the structure of this silica material are characterized by
the observed vibrational band around 970 cm−1. In addition to that, bare SBA-15
showed a band around 1660 cm−1 belonging to water adsorbed by SBA-15 and a
band around 3425 cm−1 due to stretching from silanol groups in the structure of
SBA-15. The compatibility of the values obtained in the FT-IR spectrum of the
SBA-15 with the values in the literature confrms that the synthesis of SBA-15 has
been successfully carried out [46–48].
Grafting of 4 and 5 on SBA-15 was confrmed by the appearance of new bands
in the FT-IR spectra of 6–7. The appearance of a weak band around 3080 cm−1
was attributed to the aromatic ring vibration. The new band around 2940 cm−1 was
assigned to stretching vibration of C–H from CH2. The vibrational band around
1100 cm−1 corresponding to the C=S group of 6–7 could not be observed due to
the overlaying of Si–O vibration of SBA-15 onto the vibrational band of C=S at the
same region. The band from N–H and –NH2 stretching (at 3420 cm−1) was super-
posed to the hydroxyl stretching from silanol groups and from physically absorbed
molecular water. All these FT-IR spectral data demonstrate that chiral silyl deriva-
tives 4 and 5 have been grafted successfully on the SBA-15 pores.
To check the morphology and texture of SBA-15 and 6–7, scanning electron
microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) measurements
were performed. The SEM images of SBA-15 and 6–7 are compared in Fig. 2.
These images demonstrate that SBA-15 and chiral heterogeneous catalysts 6–7 have
wormlike morphology. The EDX spectrum of SBA-15 showed that the structure of
mesoporous silica material contains only Si and O. Elemental scanning mapping
(b)
(a)
SBA-15
SBA-15
4
6
5
7
3400
2400
1400
400
3400
2400
1400
400
Wavenumber (cm-1)
Wavenumber (cm-1)
Fig. 1 FTIR spectra of 4, 6 and SBA-15 (a); FTIR spectra of 5, 7 and SBA-15 (b)
1 3

Synthesis, characterization and catalytic performance in…
Fig. 2 Scanning electron micrograph of SBA-15 (a), 6 (b) and 7 (c); EDX analysis of 6 (d) and EDX
elemental scanning maps of 6 (e-ı)
measurement also confrmed the presence of Si and O atoms in the structure of
SBA-15. (See SI for the images.) The presence of Si, O, C, N and S atoms in the tex-
ture of 6 and 7 was clearly exhibited by EDX measurements and elemental scanning
mappings. (See SI for 7.)
The purity, phase and crystallinity of SBA-15 and 6–7 were measured by X-ray
difraction technique. Low-angle XRD of SBA-15 is displayed in Fig. 3. The XRD
Fig. 3 Low-angle XRD patterns
of SBA-15, 6 and 7
SBA-15
6
7
0.5
1.5
2.5
3.5
4.5
2θ(degree)
1 3

Y. Gök, H. Z. Gök
(a)
(b)
SBA-15
6
7
SBA-15
6
7
0
0.2
0.4
0.6
0.8
1
0
10
20
30
40
50
Relative pressure (P/P0)
Pore diameter (nm)
Fig. 4 a N2 sorption isotherms and b pore size distribution for SBA-15, 6 and 7
Table 1 Structural parameters
Samples
SBET (m2/g)a
Dp (nm)b
Vp (cm3/g)c
of SBA-15, 6 and 7
SBA-15
(6)
(7)
459
327
347
5.68
5.50
5.51
0.51
0.38
0.39
aSBET surface area, calculated BET method. bDp =pore diameter, cal-
culated BJH method, cVp =pore volume
of SBA-15 showed strong difraction refection (100) at 2θ=0.90. The presence of
strong difraction refections in the low-angle XRD pattern of SBA-15 confrmed
that this mesoporous silica material has a well-defned hexagonal symmetry [28,
46, 49]. Observation of the same characteristic peak for 6–7 after grafting of chiral
ligands 4 and 5 on SBA-15 confrmed no loss of structural ordering (Fig. 3). N2
adsorption–desorption isotherms were performed in order to calculate the pore vol-
ume, pore size distribution and specifc surface area of SBA-15 and 6–7. Adsorp-
tion–desorption isotherms and pore size distribution curves for SBA-15 and 6–7 are
shown in Fig. 4. The values of Brunauer–Emmett–Teller (BET) surface area (SBET),
pore volume (Vp) and pore diameter (Dp) obtained from the measurement are given
in Table 1.
The adsorption–desorption isotherms obtained for bare SBA-15 corresponds
to the type IV isotherm with an H1 hysteresis cycle according to the IUPAC clas-
sifcation [50]. The adsorption isotherms show an increase in the amount of N2
adsorption at 0.6 < P/P0 < 0.7 for SBA-15. The N2 adsorption–desorption iso-
therms of chiral heterogeneous catalysts 6–7 showed the main characteristic of
mesoporous materials with a high surface area and a narrow pore size distribu-
tion as same as its bare analogue SBA-15. The observation of a decrease in the
surface area and pore volume of 6–7 can be taken as clear evidence for the graft-
ing of chiral ligands 4 and 5 on SBA-15 (Table 1). Thermogravimetric analyses
(TGA) of 6–7 were performed to calculate the amount of grafted chiral ligands
4 and 5 on SBA-15. The obtained TGA curves of SBA-15 and 6–7 are shown
1 3

Synthesis, characterization and catalytic performance in…
Fig. 5 TGA analysis of SBA-15,
6 and 7
100
98
96
94
92
90
88
86
84
SBA-15
6
7
0
200
400
600
800
Temperature (°C)
in Fig. 5. The calculated amounts of chiral ligands 4 and 5 on SBA-15 are pre-
sented in Table 2. TGA curve of bare SBA-15 has two distinct regions of weight
loss. The frst mass loss region was observed between 20 and 150 °C attributed
to the thermodesorption of physically adsorbed water from silica surface. In the
second region in the temperature range from 150 to 650 °C, the weight loss was
calculated as 1.4%. TGA curve in this region is nearly fat. The 1.4% of weight
loss can be attributed to the silanol condensation [51]. The TGA results proved
that SBA-15 showed thermal stability in the studied temperature range. In the
TGA curves of 6–7, the frst weight loss was observed below 200 °C which can
be attributed to the trapped solvents and physically adsorbed water [52, 53]. It
is very obvious from TGA curves that the weight loss of 6–7 in the frst region
shows a decreased value compared to the frst region of bare mesoporous materi-
als, indicating that 6–7 have higher hydrophobic character than bare mesoporous
material [54]. After that, the weight loss in the second region between 150 and
600 °C can be assigned to the decomposition of covalently bounded chiral ligands
4 and 5 within the pores. The amount of grafted chiral ligands 4 and 5 on SBA-15
for 6 and 7 was estimated to be 8.3 and 6.9% from the TGA curves, respectively.
Table 2 Percentage of weight
Samples
Weight loss (% w/w)
Residu-
loss of SBA-15, 6 and 7 versus
als>650 °C
(%w/w)
temperature
20–150 °C
150–750 °C
SBA-15
(6)
(7)
3.8
2.3
2.4
1.4
8.3
6.9
94.8
89.4
90.7
1 3

Y. Gök, H. Z. Gök
Catalytic studies
Catalytic activity for enantioselective transfer hydrogenation
The catalytic activities of the Ru (II) complexes of the synthesized chiral thiourea-
amine chiral homogenous catalysts 4 and 5, and their heterogeneous derivatives 6
and 7, respectively, were tested in enantioselective transfer hydrogenation (ATH)
of various aromatic ketones. During the performing of these reactions, the Ru (II)
complexes of 4–7 were prepared in situ. For this, 4–7 and [RuCl2(p-cymene)]2 were
mixed in isopropyl alcohol (iPrOH) for 2 h at 82 °C. Enantioselective transfer hydro-
genation reactions were carried out by adding ketone and base on those complexes
prepared in situ.
The acetophenone was chosen as the model substrate to optimize the reaction
conditions in the presence of homogenous chiral thiourea-amine catalyst 5. To deter-
mine the base ratio and the type of base, a series of test reactions were performed.
The obtained results are summarized in Table 3. The initial reaction condition for
i
the frst entry was determined as follows: PrOH as hydrogen donor, NaOH as the
base and substrate/catalyst (S/C) ratio as 250:1. The efect of base amount on the
conversion was investigated by using diferent moles of base in reaction. The con-
versions were calculated from the GC measurements by using the area under the
peak corresponding to the ketone and its alcohol product. As seen from Table 3, the
highest conversions of acetophenone to the corresponding alcohol were obtained in
the reaction containing the base in the range of 0.2–1 mmol (Table 3, entries 3–6).
But, increasing the base mmol above 0.2 mmol resulted in a decrease in enantiose-
lectivity. The highest enantioselectivity was obtained as 23% ee; in that case, the
amount of base mmol was 0.2 (Table 3, entry 3). Without base or catalyst 5 under
identical reaction conditions, 1-phenylethanol was obtained with the conversions of
4% and 60%, respectively. Moreover, no reaction occurred between acetophenone
and isopropyl alcohol in the absence of [RuCl2(p-cymene)]2 (Table 3, entries 8).
After fnding the ratio of base as 0.2 mmol, next study was planned to compare
the base activity in conversion of aromatic ketones to corresponding secondary alco-
t
hols. Various bases such as NEt3, KOH and BuOK have been explored under the
same reaction conditions. As seen from Table 3, all three bases have lower conver-
sion values than that of NaOH after 24 h reaction times (Table 3, entries 10–12).
The highest conversion (94%) and enantioselectivity (23% ee) were obtained in the
presence of NaOH as the base (Table 3, entry 3).
Under the optimized conditions (82 °C, s/c=250/1, NaOH as the base), the cata-
lytic activity of homogenous chiral ligands 4 and 5 was investigated in homogenous
ATH of a series of aromatic ketones to their corresponding alcohols. The results are
summarized in Table 4. In the case of 4 and 5, the highest catalytic activities (99%)
were obtained in the ATH reaction of 4′-chloroacetophenone and 4′-bromoaceto-
phenone with poor enantioselectivities (Table 4, entries 12, 16 for 4 and 13, 17 for
5). Changing the substituent at p-position of the aromatic ketones from chlorine or
bromine to methyl or methoxy, the reactions aforded the corresponding secondary
alcohols in lower conversion with better enantioselectivities (Table 4, entries 4, 8 for
4 and 5, 9 for 5). The highest enantioselectivity was obtained as 32% ee within 2 h
1 3

Synthesis, characterization and catalytic performance in…
Table 3 Reaction optimization for enantioselective transfer hydrogenation of acetophenonea
Entry
Time
(h)
Base
mmol
Conversion
(%)b
% eec
1
2
3
4
5
6
2 (24)
2 (24)
2 (24)
2 (24)
2 (24)
2 (24)
2(24)
24
NaOH
NaOH
NaOH
NaOH
NaOH
NaOH
–
NaOH
NaOH
KOH
0.05
0.1
0.2
0.4
0.8
1
15/49
20/70
49/94
52/95
21/94
40/97
1(4)
–
60
8/38
6/34
4/18
30/29(R)
31/21(R)
29/23(R)
26/18(R)
10/5(R)
15/9(R)
ras
–
ras
21/16(R)
16/9(R)
19/22(R)
7d
8e
9f
10
11
12
–
0.2
0.2
0.2
0.2
0.2
24
2(24)
2(24)
2(24)
t-BuOK
NEt3
aReactions were performed by using 1 mmol acetophenone in 7 mL of iPrOH with Ru/ligand=1:2. Sub-
strate/catalyst ratio was 250:1 for the entries 1–12
bDetermined by GC (HP-Chiral-20B)
cAbsolute confguration was confrmed by comparing the retention times of the enantiomers on the GC
traces with that reported in the literature
dIn the absence of NaOH
eIn the absence of [RuCl2(p-cymene)]2
fIn the absence of catalyst 5
in reaction of 4′-methylacetophenone and 4′-methoxyacetophenone catalyzed with 4
(Table 4, entries 4 and 8). From these results, it can be concluded that the introduc-
tion of electron withdrawing substituents such as chlorine or bromine atom to the
p-positions of related aromatic ketones resulted in higher conversion and poor enan-
tioselectivity, whereas the presence of an electro donating group such as methyl or
methoxy at the p- position of aromatic ketones tended to lower catalytic activity and
moderate enantioselectivity.
To compare the catalytic activity of chiral heterogeneous catalysts 6–7 with their
homogenous counterparts 4 and 5, they were also used as catalysts in enantiose-
lective transfer hydrogenation under identical reaction conditions. According to the
results from Table 4, it is obvious that the heterogenized chiral catalyst 6–7 pro-
moted the conversion of ketones to their corresponding alcohols enantioselectively,
which demonstrated the chiral recognition ability of 6–7. The heterogeneous cat-
alysts 6–7 showed the lower activity but comparable enantioselectivity with their
1 3

Y. Gök, H. Z. Gök
Table 4 Ru-catalyzed enantioselective transfer hydrogenation of ketones with chiral thiourea-amine cata-
lysts 4, 5 and their heterogeneous counterparts 6-7a
Entry
R
Catalyst
Time
(h)
Conversion
(%)b
% eec
1
H
H
H
4
6
7
4
5
6
7
4
5
6
7
4
5
6
7
4
5
6
7
2(24)
2(24)
2(24)
2(24)
2(24)
2(24)
2(24)
2(24)
2(24)
2(24)
2(24)
2(9)
69(96)
7(32)
5(9)
18(51)
27(62)
5(11)
11(33)
50(89)
37(75)
6(21)
19(59)
61(98)
68(99)
9(18)
25(40)
94(99)
89(99)
9(17)
35(31)(S)
29(28)(S)
11(8)(R)
32(25)(S)
18(13)(R)
34(30)(S)
13(11)(R)
32(29)(S)
22(19)(R)
30(26)(S)
5(3)(R)
17(14)(S)
11(10)(R)
16(14)(S)
4(3)(R)
18(16)(S)
10(9)(R)
14(12)(S)
1(ras)
2d
3d
4
OCH3
OCH3
OCH3
OCH3
CH3
CH3
CH3
CH3
Cl
Cl
Cl
Cl
Br
5
6d
7d
8d
9
10d
11d
12
13
14d
15d
16
17
18d
19d
2(9)
2(24)
2(24)
2(6)
2(6)
2(24)
Br
Br
Br
2(24)
9(14)
aReactions were performed by using 1 mmol acetophenone and 0.004 mmol catalysts 4–7 in 7 mL of
iPrOH with Ru/ligand=1:2
bDetermined by GC (HP-Chiral-20B)
cAbsolute confguration was confrmed by comparing the retention times of the enantiomers on the GC
traces
dReactions were performed by following the same reaction conditions using 30 mg of SBA-15-supported
catalyst 6 or 7 instead of catalysts 4 or 5 in 7 mL of iPrOH with Ru/ligand=1:2
homogeneous counterparts 4–5 under identical reaction conditions. The lower cat-
alytic activity of grafted mesoporous materials 6–7 can be explained due to their
inhomogeneous distribution onto SBA-15, which causes slower reaction rates and
slow difusion of guest molecules throughout the mesoporous matrix during the cat-
alytic process [55–58].
On the other hand, the highest enantioselectivity was obtained as 34% ee in the
reaction of 4′-methoxyacetophenone within 2 h in the presence of 6, which was a
1 3

Synthesis, characterization and catalytic performance in…
better result than the result of its homogeneous counterpart 4 (Table 4, entry 6). The
higher enantioselectivity of 6 than its homogenous counterpart 4 can also be attrib-
uted to the inhomogeneity of SBA-15-supported catalyst 6 which causes a regional
increase in the density of chiral ligand on the surface of SBA-15 or near the pore
mount of SBA-15. In comparison of catalytic activity of 6 with 7, the enantioselec-
tive transfer hydrogenation of aromatic ketones in the presence of 7 resulted in lower
conversions and enantioselectivities (Table 4, entries 2, 3, 6, 7, 10, 11, 14, 15, 18
and 19). As shown in Table 1, catalysts 6 and 7 have similar BET surface area, pore
volume and pore diameter. It was expected for both to show similar activity and
enantioselectivity. However, the amount of grafted organic groups onto SBA-15 in
6 was relatively higher than that of 7 according to the results of TGA presented in
Table 2. The lower catalytic activity and enantioselectivity of 7 can be attributed to
the low concentration of chiral ligand in the texture of 7.
In order to improve the catalytic activity of 6–7, the enantioselective transfer
hydrogenation of acetophenone was carried out with varying amounts of heteroge-
neous catalysts 6–7. The results are summarized in Table 5. A sharp increase in cat-
alytic activity but a slight infuence on enantioselectivity was observed by using the
increasing amount of 6–7 in ATH. The increasing S/C ratio of 6 from 250/1 to 62/1
resulted in 98% conversion with 30% ee for a 48-h reaction period (Table 5, entries
1, 3, 4 for 6 and 5, 8, 9 for 7). For 7, the conversion and enantioselectivity values in
the same reaction were 98% and 10% ee at the end of 24-h period (Table 5, entry 9).
These results demonstrate that adding a higher amount of heterogeneous catalyst to
the reaction medium provided similar catalytic activity and enantioselectivity com-
pared to the results of homogenous catalysts.
The recyclability of the heterogeneous catalysts 6 and 7 was also investigated as
shown in Table 5. After the reactions, the SBA-15-supported catalysts 6 and 7 were
separated from the reaction mixture by simple fltration. All were washed with a
plenty of water and dried under vacuum. The recovered catalysts 6–7 were then sub-
jected to the next run without any treatment. In the second run of the catalysts 6–7,
very sharp decreases were observed in the catalytic activity and enantioselectivity
values of the catalysts (Table 5, entries 2 and 7). The dramatical decrease in the
catalytic activity and enantioselectivity might be the result of leaching of Ru metal
from 6 to 7.
In order to test if ruthenium was leached out from the catalyst during the reac-
tion, two diferent tests were performed. In the frst test, [Ru(p-cymene)Cl2]2 was
further added to the third run of 7 (Table 5, entry 8). After the next 24 h, a conver-
sion of 60% has been obtained, but no enantioselective induction was observed. A
conversion of 60% was the same as the conversion obtained in the blind trial without
catalyst (Table 3, entry 9). No observation of enantioselectivity can be thought that
decomposition or deactivation of the active species on the surface and in the pores
of SBA-15 would occur irreversibly in the recycling route [37].
As a second test, a hot fltration test for the model enantioselective transfer
hydrogenation reaction under the optimal conditions was carried out. In this
study, catalyst 6 aforded 1-phenylethanol with the conversion of 17% and 72%
in the 2nd and 24th hours of the reaction (Table 5, entry 3). Then, this reaction
was repeated, and in the 2nd hour of the reaction, catalyst 6 was separated from
1 3

Y. Gök, H. Z. Gök
Table 5 The efect of catalyst amount on Ru-catalyzed ATH of acetophenone with 6–7 and recyclability
of 6-7a
Entry
Catalysts
Run
Catalyst
Conversion
(%)b,c
% eed
mg (mmol)
1e
2
60 mg (0.01)
–
1
2
1
1
1
1
2
3
1
1
6
6
6
6
6
7
7
7
7
7
8(23){27}
1(3)
17(23){23}(S)
13(8) (S)
3e
4
90 mg (0.015)
90 mg (0.015)
120 mg (0.02)
60 mg (0.009)
–
17(72){83}
20(24)f
24(90){98}
18(30)
1(3)
(60)
50(66)
82(98)
17(26){26}(S)
21(24)(S)
23(30){30}(S)
15(15) (R)
5(2) (R)
ras
12(12) (R)
12(10) (R)
5e
6
7
8g
9
–
90 mg (0.013)
120 mg (0.018)
10
aReactions were performed by using 1 mmol acetophenone in 7 mL of iPrOH with Ru/ligand=1:2
bDetermined by GC (HP-Chiral-20B)
cResults at 2nd hour of the reactions are shown outside of parentheses and those of 24th hour are in
parentheses
dAbsolute confguration was confrmed by comparing the retention times of the enantiomers on the GC
traces
eThe reaction was followed for 48 h and the conversion at 48th hour was given in {}
fCatalyst 6 was separated from the hot reaction mixture by simple fltration after 2 h and resultant super-
natant solution was then permitted to continue under the same condition for 24 h
g0.004 mmol of [Ru(p-cymene)Cl2]2 was added a second time at the third run of 7
the hot reaction mixture by simple fltration. The supernatant solution was then
allowed to continue under the same condition without catalyst 6 for a further
22 h. Afterward, the conversion of acetophenone to 1-phenylethanol in the 2nd
and 24th of the reaction was found as 21% and 24%, respectively, according to
the GC analyses (Supporting information, Figure S25 and S26) (Table 5, entry
4). These results showed that leaching of ruthenium did not occur during the
reaction.
To determine whether there was a change in the active site of catalysts, FT-IR
measurements of recovered catalysts 6–7 were taken. All the catalysts showed
the similar FT-IR spectra, but the FT-IR spectra recorded after the second run
of recovered catalysts 6–7 were diferent from the FT-IR spectra of 6–7 recorded
before their frst use in catalytic reaction. (See SI for the spectra.) The obser-
vation of diferent signals for the recovered catalysts 6–7 in their FTIR spectra
can be probably due to decomposition or deactivation of catalysts in mesoporous
1 3

Synthesis, characterization and catalytic performance in…
silica structures. Therefore, the decrease in the catalytic activity of recovered cat-
alysts 6–7 can be attributed to the instability of grafted 4 and 5 in channels of
SBA-15 [59].
Catalytic activity for enantioselective Michael reaction
The catalytic activity of chiral heterogeneous catalysts 6–7 and their homogeneous
counterparts 4–5 was investigated in enantioselective Michael addition of acetylac-
etone to trans-β-nitrostyrene. Initially, the blank experiments were performed in dif-
ferent reaction solvents such as water, toluene and dichloromethane by using the sup-
porting material SBA-15. As shown in Table 6, no product formation was observed
in the presence of those materials (entries 1–3). Then, homogeneous chiral thiourea-
amine catalysts 4 and 5 and their heterogeneous counterparts 6–7 were examined in
the same reactions. From Table 6, we can see that the solvent has clearly afected
the catalytic performance of catalysts. In all entries, the product formation in water
yielded higher than that in dichloromethane or toluene. The highest conversion was
obtained as 99% under the catalysis of 6 and 7 at room temperature (Table 6, entries
10 and 15). Their homogenous counterparts 4 and 5 gave also satisfactory results in
the Michael reaction with the conversion values of 87 and 97%, respectively. How-
ever, no enantioselectivity was observed in the presence of catalysts 4–7.
We next examined the efect of temperature and amount of catalysts so that enan-
tioselectivity can be achieved. An increase in the reaction temperature or the amount
of catalyst resulted in lower conversions, and no enantioselectivity was determined
(Table 6, entries 11, 12, 16, 17). After these results from the entries, the optimized
conditions were preferred as follows: using 7% mol catalyst and water as solvent
at room temperature. Silica-supported catalysts 6–7 gave moderate to high conver-
sions with poor enantioselectivities for various substrates (Table 7). In the case of
electron-donating substituents at p- or o-positions of benzene ring, high conversions
with low enantioselectivity were obtained in the presence of 6–7 (Table 7, entries
9–16). In contrast, electron-withdrawing substituents at p- or o-positions of benzene
ring resulted in lower conversions but still high enough (71–99%) (Table 7, entries
1–8).
The highly active organofunctionalized mesoporous silica catalysts 6 and 7 were
easily recovered by simple fltration. Then, the reusability of 6–7 was studied in
the Michael addition of acetylacetone to β-nitrostyrene under the optimized condi-
tion (Table 8). The recycling experiments of this substrate showed that the catalysts
6–7 could completely maintain the high conversion even for the third use (Table 8,
entries 3 and 6).
Conclusion
In conclusion, we have successfully synthesized chiral heterogeneous catalysts 6 and
7 through grafting of silyl derivatives of (1R, 2R) or (1S, 2S)-1,2-diphenylethane-
1,2-diamine (4 and 5) on SBA-15. The catalytic efciencies of catalysts 4–7 in enan-
tioselective transfer hydrogenation of aromatic ketones and enantioselective Michael
1 3

Y. Gök, H. Z. Gök
Table 6 Screening of the reaction conditions for enantioselective Michael addition of acetylacetone to
trans-β-nitrostyrene a
Entry
Catalyst
Solvent
Conversion
(%)b
ee
(%)c
1
SBA-15
H2O
–
–
2
3
4
5
6
7
8
9
10
11d
12e
13
14
15
16d
17e
18
19
SBA-15
SBA-15
CH2Cl2
Toluene
H2O
CH2Cl2
Toluene
H2O
CH2Cl2
Toluene
H2O
H2O
H2O
CH2Cl2
Toluene
H2O
–
–
–
–
4
4
4
5
5
5
6
6
6
6
6
7
7
7
7
7
87
22
31
97
37
43
99
98
92
80
88
99
98
94
65
99
rac
rac
rac
rac
rac
rac
5
rac
rac
5
rac
5
rac
rac
rac
rac
H2O
H2O
CH2Cl2
Toluene
aReactions were performed by using trans-β-nitrostyrene (0.2 mmol) and acetylacetone (0.4 mmol)
bDetermined by the area under the peaks corresponding to the components in HPLC chromatogram
cEnantiomeric excess was determined by HPLC analysis using YMC chiral ART Amylose-C column
[41]
dReactions were performed at 50 °C; ethe amount of catalyst was doubled
addition of acetylacetone to nitroolefns were investigated. Chiral thiourea-amine
catalysts 4 and 5 catalyzed the enantioselective transfer hydrogenation of acetophe-
none and aforded the corresponding alcohols in high conversion (94–96%) with
moderate enantioselectivity (23–31% ee). Under the optimized conditions, their sil-
ica-supported derivatives 6–7 exhibited comparable enantioselectivity and catalytic
activity. The catalysts 6–7 showed excellent activities (99%) and moderate enanti-
oselectivities (30% ee) for the enantioselective transfer hydrogenation of acetophe-
nones. In enantioselective Michael addition of acetylacetone to nitroolefns, 6–7
1 3

Synthesis, characterization and catalytic performance in…
Table 7 Enantioselective Michael addition of acetylacetone to representative trans-β-nitrostyrene
derivativesa
Entry
R
Catalyst
Conversion
(%)b
ee
(%)c
1
2
3
4
5
6
7
8
2-Br(10)
2-Br(10)
2-Br(10)
2-Br(10)
4-Br(11)
4-Br(11)
4-Br(11)
4-Br(11)
2-MeO(12)
2-MeO(12)
2-MeO(12)
2-MeO(12)
4-MeO(13)
4-MeO(13)
4-MeO(13)
4-MeO(13)
4
5
6
7
4
5
6
7
4
5
6
7
4
5
6
7
99
80
99
80
84
71
85
75
99
97
99
97
99
99
99
99
rac
rac
5
rac
10
9
10
9
9
rac
rac
rac
rac
rac
rac
5
10
11
12
13
14
15
16
5
aReactions were performed by using trans-β-nitrostyrene derivative (0.2 mmol) and acetylacetone
(0.4 mmol)
bDetermined by the area under the peaks corresponding to the components in HPLC chromatogram
cEnantiomeric excess was determined by HPLC analysis using YMC chiral ART Amylose-C column
[41]
showed remarkably high catalytic activity (up to 99%) but poor enantioselectivity.
The heterogeneous catalysts 6–7 did not lose their activities in multiple consecutive
catalytic runs, and they were recycled for at least three times in Michael addition of
acetylacetone to trans-β-nitrostyrene. Further investigation to improve the efciency
and recyclability of these kinds of catalysts is ongoing in our laboratory and will be
published in due course.
1 3

Y. Gök, H. Z. Gök
Table 8 Recycling studies of mesoporous silica-supported catalysts 6–7 in enantioselective Michael
addition of acetylacetone to trans-β-nitrostyrenea
Entry
Run
Catalyst
Conversion
(%)b,c
1
2
3
4
5
6
1
2
3
1
2
3
6
6
6
7
7
7
99
99
99
99
99
99
aReactions were performed by using trans-β-nitrostyrene derivative (0.2 mmol) and acetylacetone
(0.4 mmol)
bDetermined by the area under the peaks corresponding to the components in HPLC chromatogram
cEnantiomeric excess was determined by HPLC analysis using YMC chiral ART Amylose-C column. All
entries resulted in racemic mixture [41]
Acknowledgements Mert AKGÜN from Science and Technology Application and Research Centre,
Çanakkale Onsekiz Mart University, is gratefully acknowledged for his technical assistance. The authors
would like to thank İrem Tutkum Aykut for her assistance during GC measurements.
Author contributions YG is responsible for conceptualization, project administration, visualization,
investigation, writing—review & editing, funding acquisition, supervision. HZG is responsible for meth-
odology, investigation, writing—original Draft, conceptualization, resources and data curation.
Funding This work was supported by The Scientifc and Technological Research Council of Turkey
(TÜBİTAK, project no: KBAG-118Z523).
Availability of data and material The data that support the fndings of this study are available in the sup-
plementary material of this article.
Compliance with ethical standards
Conficts of interest The authors declare that they have no confict of interest.
References
1. H.U. Blaser, E. Schmidt, Asymmetric Catalysis on Industrial Scale (Wiley-VCH, Weinheim, 2004)
2. M. Heitbaum, F. Glorius, I. Escher, Angew. Chemie - Int. Ed. 45, 4732 (2006)
3. F. Meemken, A. Baiker, Chem. Rev. 117, 11522 (2017)
4. G. Szllsi, Catal. Sci. Technol. 8, 389 (2018)
1 3

Synthesis, characterization and catalytic performance in…
5. E.N. Jacobsen, A. Pfaltz, H. Yamamoto, Comprehensive Asymmetric Catalysis (Springer, Berlin,
1999)
6. I. Ojima, Catalytic Asymmetric Synthesis, 2nd edn. (Wiley, New York, 2000)
7. T.P. Yoon, E.N. Jacobsen, Science 299, 1691 (2003)
8. N. Amirmahani, N.O. Mahmoodi, M. Malakootian, A. Pardakhty, N. Seyedi, Res. Chem. Intermed.
46, 4595 (2020)
9. F. Mohajer, G.M. Ziarani, A. Badiei, Res. Chem. Intermed. (2020)
10. H. Sauer, J. Gunther, J. Hescheler, M. Wartenberg, Am. J. Pathol. 156, 151 (2000)
11. R.J. D’Amato, M.S. Loughnan, E. Flynn, J. Folkman, Proc. Natl. Acad. Sci. U. S. A. 91, 4082
(1994)
12. E. Tokunaga, T. Yamamoto, E. Ito, N. Shibata, Sci. Rep. 8, 6 (2018)
13. K.M. Rentsch, J. Biochem. Biophys. Methods. 54, 1 (2002)
14. S. Gladiali, E. Alberico, Chem. Soc. Rev. 35, 226 (2006)
15. R. Noyori, M. Yamakawa, S. Hashiguchi, J. Org. Chem. 66, 7931 (2001)
16. C. J. Wang, Z. H. Zhang, X. Q. Dong, X. J. Wu, Chem. Commun. 1431 (2008)
17. A. Matsunami, Y. Kayaki, Tetrahedron Lett. 59(6), 504 (2018)
18. F.E. Held, S.B. Tsogoeva, Catal. Sci. Technol. 6(3), 645 (2016)
19. C. Borie, L. Ackermann, M. Nechab, Chem. Soc. Rev. 45(5), 1368–1386 (2016)
20. W. Xie, H. Wang, Renew. Energy 145, 1709 (2020)
21. M. Nikoorazm, Z. Rezaei, B. Tahmasbi, J. Porous Mater. 27, 671 (2020)
22. E. Baráth, Synth. 52(04), 504 (2020)
23. S. Samadi, A. Ashouri, M. Samadi, ACS Omega 5, 22367 (2020)
24. P. Van Der Voort, K. Leus, E. De Canck, in Introduction to porous materials. ed. by D. Atwood, B.
Crabtree, G. Meyer, D. Woollins, H.V. Huynh (Wiley, New York, 2019)
25. F. Hofmann, M. Cornelius, J. Morell, M. Fröba, Angew. Chemie - Int. Ed. 45, 3216 (2006)
26. Z. Teng, W. Li, Y. Tang, A. Elzatahry, G. Lu, D. Zhao, Adv. Mater. 31, 1707612 (2019)
27. J.G. Croissant, Y. Fatieiev, A. Almalik, N.M. Khashab, Adv. Healthc. Mater. 7, 1700831 (2018)
28. J.S. Beck, J.C. Vartuli, W.J. Roth, M.E. Leonowicz, C.T. Kresge, K.D. Schmitt, C.T.W. Chu, D.H.
Olson, E.W. Sheppard, S.B. McCullen, J.B. Higgins, J.L. Schlenker, J. Am. Chem. Soc. 114, 10834
(1992)
29. Y. Cao, S. Che, in Chiral nanomaterials: preparation, properties and applications. ed. by Z.T. Tang
(Wiley, USA, 2018), pp. 121–177
30. H. Albuquerque, L. Carneiro, A.P. Carvalho, J. Pires, A.R. Silva, Polyhedron 79, 315 (2014)
31. A.R. Silva, Curr. Org. Chem. 18(10), 1226 (2014)
32. J. Chen, N.A. Butt, W. Zhang, Res. Chem. Intermed. 45, 5959 (2019)
33. J. Cossy, F. Eustache, P.I. Dalko, Tetrahedron Lett. 42, 5005 (2001)
34. J. Takehara, S. Hashiguchi, A. Fujii, S.I. Inoue, T. Ikariya, R. Noyori, Chem. Commun. 12, 233
(1996)
35. P.G. Echeverria, C. Férard, P. Phansavath, V. Ratovelomanana-Vidal, Catal. Commun. 62, 95 (2015)
36. F. Foubelo, C. Nájera, M. Yus, Tetrahedron Asymmetry 26, 769 (2015)
37. P.N. Liu, P.M. Gu, F. Wang, Y.Q. Tu, Org. Lett. 6(2), 169 (2004)
38. S. Hashiguchi, A. Fujii, J. Takehara, T. Ikariya, R. Noyori, J. Am. Chem. Soc. 117, 7562 (1995)
39. D.D. Perrin, W.F.L. Armarego, Purifcation of Laboratory Chemicals, 2nd edn. (Pergamon, UK,
1989)
40. D. Zhao, Q. Huo, J. Feng, B.F. Chmelka, G.D. Stucky, J. Am. Chem. Soc. 120, 6024 (1998)
41. W. Yao, J. Zhu, X. Zhou, R. Jiang, P. Wang, W. Chen, Tetrahedron 74, 4205 (2018)
42. S.F. Lu, D.M. Du, J. Xu, S.W. Zhang, J. Am. Chem. Soc. 128, 7418 (2006)
43. Z. Fu, W. Yuan, N. Chen, Green Chem. 20, 4484 (2018)
44. B.A. Ondrusek, H. Chung, ACS Omega 2(7), 3951 (2017)
45. D.M. Wiles, B.A. Gingras, T. Suprunchuk, Can. J. Chem. 45, 469 (1967)
46. W. Xie, L. Zhao, Energy Convers. Manag. 79, 34 (2014)
47. L.B.O. de Freitas, I.J.G. Bravo, W.A.A. de Macedo, E.M.B. de Sousa, J. Sol-Gel Sci. Technol. 77,
186 (2016)
48. A.A. Shahrnoy, A.R. Mahjoub, S. Shokrollahi, N. Ezzati, K. Elsner, C.T. Koch, Appl. Organomet.
Chem. 34(7), e5645 (2020)
49. J.C. Doadrio, E.M.B. Sousa, I. Izquierdo-Barba, A.L. Doadrio, J. Perez-Pariente, M. Vallet-Regí, J.
Mater. Chem. 15, 462 (2006)
50. K.S.W. Sing, Pure Appl. Chem. 57, 603 (1985)
1 3

Y. Gök, H. Z. Gök
51. J.M. Kim, S.M. Chang, S.M. Kong, K.S. Kim, J. Kim, W.S. Kim, Ceram. Int. 35, 1015 (2009)
52. S. Rohani, G.M. Ziarani, A. Badiei, A. Ziarati, M. Jafari, A. Shayesteh, Appl. Organomet. Chem.
32, e4397 (2018)
53. L. Zhang, J. Liu, J. Yang, Q. Yang, C. Li, Chem. - An Asian J. 3, 1842 (2008)
54. C.P. Jaroniec, R.K. Gilpin, M. Jaroniec, J. Phys. Chem. B 101, 6861 (1997)
55. D. Jiang, Q. Yang, J. Yang, L. Zhang, G. Zhu, W. Su, C. Li, Chem. Mater. 17, 6154 (2005)
56. X. Liu, P. Wang, Y. Yang, P. Wang, Q. Yang, Chem. - An Asian J. 5, 1232 (2010)
57. X. Liu, P. Wang, L. Zhang, J. Yang, C. Li, Q. Yang, Chem. - A Eur. J. 16, 12727 (2010)
58. D. Jiang, Q. Yang, H. Wang, G. Zhu, J. Yang, C. Li, J. Catal. 239, 65 (2006)
59. Z. Tang, J. Sun, H. Zhao, S. Bai, X. Wu, H. Panezai, Microporous Mesoporous Mater. 260, 245
(2018)
Publisher’s Note Springer Nature remains neutral with regard to jurisdictional claims in published
maps and institutional afliations.
1 3