Full Papers
doi.org/10.1002/cctc.202001553
ChemCatChem
Catalyst’s recyclability
Experimental Section
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An important consideration for the design of this magnetic
catalyst expects efficient recovery and recycling due to its
magnetic nature. In this case, it was found that catalyst 5 was
easily recovered via an outer magnet near the bottle. As shown
in Figure 6, in a consecutive aerobic oxysulfonylation/ATH one-
pot process of phenylacetylene and sodium benzenesulfinate
by setting the reaction time to be within 26 h to test catalyst
recyclability,[15] we found that the recycled catalyst 5 could be
reused for six times. In the sixth run, the dual catalysis could
still produce the chiral final 9a in 86% yield with 98% ee value,
where the Ru-loss in catalyst 5 after the sixth run was 7.3%
detected by an inductively coupled plasma optical emission
spectrometer (ICPÀ OES) analysis (see Table S2 and Figure S6 in
the ESI).
Preparation of catalysts 4–5
In a typical synthesis, (Coating with 1,2-bis(triethoxysilyl)ethane and
ArDPEN-siloxane) the obtained solids Fe3O4@SiO2 (1) (0.40 g) were
suspended in an alkaline solution (0.70 mL of NaOH (2.0 M) in
mixed 250.0 mL of water and 50.0 mL of ethanol with ultra-
sonication for 20 minutes. After that, an aqueous solution (0.08 g
(0.088 mmol) of FC-4, 0.16 g (0.44 mmol) of CTAB and 0.40 mL
(25 wt%) of NH3·H2O in 3.0 mL of water) was added, and the
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mixture was stirred at 38 C for another 30 minutes. Next, 0.89 g
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(2.50 mmol) of 1,2-bis(triethoxysilyl)ethane and 0.15 g (0.27 mmol)
of ArDPEN-siloxane in 2.0 mL of ethanol (2 minutes later) was
added at room temperature, and the mixture was stirred under
vigorous stirring for a further 1.5 h. Finally, the temperature was
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raised to 80 C and the mixture was stirred at 80 C for another 3 h.
After cooling the above mixture down to room temperature, the
solid was collected by filtration to afford the Fe3O4@SiO2@[Si] (2) as
a black powder. (Selective etching of SiO2) To remove the surfactant,
the collected 2 were dispersed in 120 mL of solution (80 mg
(1.0 mmol) of ammonium nitrate in 120 mL (95%) of ethanol), and
Conclusion
°
the mixture was stirred at 60 C for 10 h. After cooling the above
mixture down to room temperature, the solids were filtered and
washed with excess water and ethanol, and dried at 60 C under
vacuum overnight to afford the Fe3O4@[Si] (3) (0.68 g) as a dark-
gray powder. (Encapsulation with FeCl3) An aqueous solution (0.30 g
(1.85 mmol) of FeCl3 in 3.0 mL of water) was added to 3 at room
temperature under vacuum, and the resulting mixture was filtered
In conclusion, by utilizing a yolk-shell-structured magnetically
mesoporous silica as a support, we immobilize chiral Ru/
diamine species into the nanochannels of the outer mesopo-
rous silica shell and the FeCl3 species on the inner magnet core,
constructing a bifunctional magnetic catalyst. As presented in
this study, the bifunctional catalyst enables an efficient aerobic
oxysulfonylation/ATH one-pot cascade process. The supported
FeCl3/diamine species proceeds an aerobic oxysulfonylation
between aryl-substituted alkynes and sodium sulfinates to
produce β-keto sulfones intermediate, whereas the supported
Ru/diamine- species could sequentially reduce the in-situ
generated intermediate, affording various chiral β-hydroxysul-
fones products with enhanced yields and enantioselectivities.
Furthermore, the catalyst can be easily recovered via an outer
magnet and repeatedly recycled, presenting a practical advant-
age in the application. The study here also highlights a
compartmentalization-type immobilization method to over-
come the negative cross-interactions between FeCl3 and chiral
Ru/diamine-complexes for the realization of feasible sequential
enantioselective organic transformation.
°
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and dried at 60 C at room temperature. (Coordination with
(MesRuCl2)2 ) 50.0 mg (0.086 mmol) of (MesRuCl2)2 was added to a
suspension of 4 (0.50 g) in 20.0 mL of dry CH2Cl2 at room temper-
°
ature, and the resulting mixture was stirred at 25 C for 12 h. The
solids were filtered and rinsed with excess dry CH2Cl2. After Soxhlet
extraction for 4.0 h in CH2Cl2, the solids were collected and dried at
°
60 C under vacuum overnight to afford the magnetic catalyst 4 as
a brownish red powder. The TG analysis showed the FeCl3-loading
was 128.64 mg (0.7941 mmol) per gram of catalyst. An inductively
coupled plasma optical emission spectrometer (ICPÀ OES) analysis
showed that the Ru loadings were 50.39 mg (0.4989 mmol of Ru)
per gram of catalyst.
General procedure for tandem reaction
In a typical procedure, catalyst 5 (50.37 mg, 20.0 mol% of FeCl3,
based on TG analysis and 2.51 mol% of Ru, based on ICP analysis),
alkynes (0.20 mmol), and sodium sulfinates (0.30 mmol), and 4.0 mL
of EtOH/H2O (v/v=3:1) were added sequentially to a 10.0 mL
round-bottom flask. The resulting mixture was then stirred at 50 C
for the first 10–16 h. After completion of the aerobic oxysulfonyla-
tion, the HCO2Na (2.0 mmol) was added to this solution and the
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resulting mixture was then stirred at 50 C for the second 14–24 h.
During this period, the reaction was monitored by TLC. After
completion of the reaction, the catalysts were separated by an
external magnet for the recycling experiment. The aqueous solution
was extracted with ethyl ether (3×3.0 mL). The combined ethyl
ether extracts were washed with aqueous Na2CO3 and then
dehydrated with Na2SO4. After evaporation of the solvent, the
resulting residue was purified by silica gel flash column chromatog-
raphy to afford the desired product. The ee values were determined
using HPLC analysis using a UV-Vis detector and Daicel chiral-cel
column (Φ 0.46×25 cm).
Figure 6. Reusability of the aerobic oxysulfonylation/ATH one-pot process of
phenylacetylene and sodium benzenesulfinate (the error bars represent the
standard deviation).
ChemCatChem 2020, 12, 1–8
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