C O M M U N I C A T I O N S
the sulfoxide PhSOMe (ca. 5% of the sulfone is formed). The yield
of enantiopure (ee ) 100%) fraction of (S)-PhSOMe was estimated
ca. 35% (based on the starting PhSOMe). On the other hand, the
1.5-fold excess of H2O2 left some sulfide unreacted (conversion
91%) (Figure 2b). The sulfide does not display any significant
sorption in the pores of 1 and thus comes out from the column
before the (R)-PhSOMe. Hence, in this case, both (R)- and (S)-
sulfoxides could be isolated with relatively high yields (yields of
pure enantiomers were ca. 35% each based on the starting PhSOMe,
i.e., 70% isolated net yield of pure enantiomers (Figure 2b)).
Apparently, using 1.5-fold excess of the oxidant, one could obtain
both enantiomers of the chiral sulfoxide PhSOMe in optically and
chemically pure form, provided that the column used is long enough.
In conclusion, we present the first successful liquid chromato-
graphic resolution of enantiomers (sulfoxides) using 1 as the chiral
stationary phase and the combined selective oxidation of thioethers
and enantioselective separation of the resulting sulfoxides in a one-
pot process, MOF 1 acting as both the heterogeneous catalyst and
the chiral stationary phase.
Figure 2. Catalytic oxidation of PhSMe/enantiomeric separation of
PhSOMe over a column with 1‚DMF, using 5-fold (a) and 1.5-fold (b)
excess of the oxidant. Elution rate ) 2 cm3/h; eluent CH2Cl2/CH3CN )
85:15.
The search for the new applications of porous metal-organic
frameworks in catalytic processes is also highly important for this
branch of chemistry. Earlier, we announced the highly chemo- and
size-selective oxidation of alkyl aryl sulfides by H2O2 using 1 as
the heterogeneous catalyst4a (for more details see the Supporting
Information). The oxidation process was nonstereoselective, result-
ing in racemic mixtures of the corresponding sulfoxides. Now, we
present the use of the unique combination of catalytic and adsorption
properties of the porous structure 1 for the isolation of both (R)-
and (S)-enantiomers of PhSOMe in a one-pot procedure, starting
from the corresponding sulfides. Here, the microporous homochiral
Zn-organic coordination polymer 1 acts as both the catalyst and
at the same time the chiral stationary phase for column liquid
chromatography.
First, we examined the catalytic activity of Zn-containing
catalysts toward the oxidation of alkyl aryl sulfides with H2O2 in
more detail (see Supporting Information). Surprisingly, the simple
Zn(NO3)2 was found to act as an effective catalyst for the alkyl
aryl sulfides oxidation by H2O2 in polar solvents, featuring the
quantitative conversion and up to 100% selectivity in some cases.
It is worth noting that because of the obvious nonporous nature of
the Zn2+ aquacomplex, there is no size limit for the substrate in
the homogeneous oxidation process. In turn, the heterogeneous
nature of the porous framework 1 leads to very low oxidation
conversions for the bulky p-NO2PhSOMe and PhSCH2Ph. It has
also been found that the heterogeneous selective oxidation of alkyl
aryl sulfides by 1 could be carried out in CH3CN or CH2Cl2/CH3-
CN (Supporting Information). The observed selectivity toward the
size of the substrate corroborates the robust porous structure of 1
and supports the heterogeneous nature of the catalysis.
Acknowledgment. The authors thank the Russian Foundation
for Basic Research, Grants 06-03-32214 and RFBR-JSPS 07-03-
91208, for financial support.
Supporting Information Available: Experimental procedures for
the sorption constant measurements, oxidation, and chromatographic
separations procedures. This material is available free of charge via
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The combined oxidation/separation experiments were made on
the same column as mentioned above. For the reasons of better
enantioselective separation effectiveness, PhSMe was chosen as
substrate. The mixture of the sulfide and H2O2 in the corresponding
organic solvent was loaded directly onto the top of the column,
and the products were slowly eluted with CH2Cl2/CH3CN mixture.
The resulted chromatograms are shown in the Figure 2. The (R)-
isomer of PhSOMe comes out first during the elution, followed by
a peak of the (S)-isomer. Despite some peak overlap, the major
part of the sulfoxides could be collected separately as optically pure
(R)- or (S)-enantiomers. The use of 5-fold excess of H2O2 results
in slight overoxidation of PhSOMe, with preferable formation of
(5) The stereoselection is due to the interaction of the sorbate with the inner
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sulfoxide molecules (e.g., PhSOCH2Ph) cannot enter the pores and hence
display zero sorption.
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