An efficient and selective photocatalytic system for the oxidation of sulfides to sulfoxides

Article abstract of DOI:10.1002/anie.200390166

A heterogenous nation membrane containing lead ruthenate pyrochlore (Pyc) and [Ru(bpy)₃]²⁺ (designated as | NPyc^-Ru(bpy)|) photochemically catalyzes the selective oxidation of organic sulfide to sulfoxide in the presence o

Full text of DOI:10.1002/anie.200390166

Angewandte
Chemie
source, does not form a lanthanide-bonded hydride ligand and
isobutene by b-H-elimination: M. G. Klimpel, J. Eppinger, P.
Sirsch, W. Scherer, R. Anwander, Organometallics 2002, 21,
Photocatalytic Oxidation
An Efficient and Selective Photocatalytic System
for the Oxidation of Sulfides to Sulfoxides**
4
021.
23] E. B. Coughlin, L. M. Henling, J. E. Bercaw, Inorg. Chim. Acta
996, 242, 205.
24] D. Stern, M. Sabat, T. J. Marks, J. Am. Chem. Soc. 1990, 112,
558. Ansa-ligand rearrrangement and formation of hydride-
[
[
1
Jyh-Myng Zen,* Shiou-Ling Liou,
Annamalai Senthil Kumar, and Mung-Seng Hsia
9
bridged ™flyover∫dimers seems to have drastic consequences on
the catalytic activity in olefin polymerization. For example, the
reaction of [{Et Si(C H )(3,4-Me -C H )Lu(m-H)} ] (5) with
2
5
4
2
5
2
2
The selective oxidation of organic sulfides to sulfoxides
without any overoxidation to sulfones is a challenging
research interest in synthetic organic chemistry, partly
because of the importance of sulfoxides as intermediates in
ethylene, propylene, and 1-hexene gave quantitatively m-hy-
dride/m-alkyl mono-insertion products at ambient temperature.
However, similar complexes such as 6 were also shown to be
highly efficient in the block copolymerization of ethylene and
polar monomers.[
3]
[1]
biologically active compounds. Of the many classical
1
[
25] A comprehensive survey of the H NMR chemical shifts (d ¼
oxidants, H O -based systems are considered to be relatively
2
2
1
1
.85±8.31 ppm) and 89Y- H coupling constants (23.8±35.3 Hz) of
[2]
clean and free of pollution. Nevertheless, under catalytic
conditions, the choice of H O conditions and the stoichio-
metry with respect to the catalyst are critical to the selectivity
of the reaction. Herein, we report a novel heterogeneous
photochemical system for the selective transformation of
organic sulfides to sulfoxides in the presence of oxygen using
dimeric yttrium hydrido complexes is presented in: K. C.
Hultzsch, P. Voth, K. Beckerle, T. P. Spaniol, J. Okuda, Organo-
metallics 2000, 19, 228.
2
2
[
26] Compound 4a (C H O Si Y ¥2C D ) crystallizes from benzene
5
2
62
2
2
2
6
6
in the monoclinic space group P2 /c with a ¼ 11.7875(2), b ¼
1
1
2
4.0396(3),
701.31(10) ä , and 1
c ¼ 16.8378(4) ä,
b ¼ 104.2053(12)8,
V¼
3
À3
¼ 1.364 gcm for Z ¼ 2. Data were
calcd
a nafion membrane doped with a lead ruthenate pyrochlore
collected at 193 K on a Nonius Kappa-CCD system. The
structure was solved by Patterson methods, and least-square
refinement of the model based on 3682 reflections (I > 2.0s(I))
converged to a final R1 ¼ 4.0% (wR2 ¼ 8.1%). Except H(1), all
hydrogen atoms were placed in calculated positions. H(1) was
located in difference Fourier maps and refined with isotropic
thermal parameters. CCDC-188842 (4a) contains the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/conts/retrie-
ving.html (or from the Cambridge Crystallographic Data Centre,
2þ
(
Pyc) catalyst and a [Ru(bpy) ] photosensitizer (designated
3
xÀ
as j NPyc Ru(bpy) j ). Figure 1a illustrates the typical pro-
cedure for the incorporation of Pyc into a nafion membrane.[
The membrane (5 î 5 cm) was first soaked with a mixture of
3]
2
þ
3þ
Pb and Ru ions (1.5:1), which led to electrostatic ex-
change of ions into the hydrophilic sites of nafion. The
xÀ
precipitation of Pyc (designated as j NPyc j ) was done by
treating the ion-exchanged membrane in 1.1m KOH at 53 8C
[
3a]
for 24 h with continuous purging of O2. The formation of
1
0
2 Union Road, Cambridge CB21EZ, UK; fax: (þ 44)1223-336-
[
3a]
Pyc was confirmed by X-ray diffraction analysis.
The
33; or deposit@ccdc.cam.ac.uk).
xÀ
[
27] a) N. Hˆck, W. Oroschin, G. Paolucci, R. D. Fischer, Angew.
Chem. 1986, 98, 748; Angew. Chem. Int. Ed. Engl. 1986, 25, 738;
b) K. Qiao, R. D. Fischer, G. Paolucci, J. Organomet. Chem.
j NPyc j membrane was found to be highly stable in organic
[
4]
2þ
media. Finally, a suitable amount of [Ru(bpy) ] was doped
3
xÀ
into the j NPyc j membrane simply by an ion-exchange
1993, 456, 185.
2þ
process from a solution containing 1 mm [Ru(bpy) ] . This
3
[
[
[
28] W. J. Evans, D. K. Drummond, T. P. Hanusa, R. J. Doedens,
xÀ
membrane (designated as j NPyc Ru(bpy) j ) was then used
Organometallics 1987, 6, 2279.
29] W. P. Kretschmer, S. I. Troyanov, A. Meetsma, B. Hessen, J. H.
Teuben, Organometallics 1998, 17, 284.
in organic syntheses. Very few photochemical reactions have
so far been reported for the sulfide oxidation reaction (SOR),
and all the cases resulted in a mixture of products from C
bond breakage and overoxidation through radical combina-
ÀS
30] a) K. C. Hultzsch, T. P. Spaniol, J. Okuda, Angew. Chem. 1999,
111, 163; Angew. Chem. Int. Ed. 1999, 38, 227; b) S. Arndt, P.
Voth, T. P. Spaniol, J. Okuda, Organometallics 2000, 19, 4690.
31] R. Duchateau, C. T. van Wee, A. Meetsma, P. T. van Duijnen,
J. H. Teuben, Organometallics 1996, 15, 2279.
32] T. I. Gountchev, T. D. Tilley, Organometallics 1999, 18, 2896.
33] J. P. Mitchell, S. Hajela, S. K. Brookhart, K. I. Hardcastle, L. M.
Henling, J. E. Bercaw, J. Am. Chem. Soc. 1996, 118, 1045.
[5]
tion reactions. In the present study a clean reaction [Eq. (1)]
[
occurs, and the controlled catalytic oxygen reduction reaction
(
(
ORR) to H O at the Pyc active sites is essential to the SOR
2 2
[
[
see below).
[*] Prof. Dr. J.-M. Zen, S.-L. Liou, Dr. A. S. Kumar, M.-S. Hsia
Department of Chemistry
National Chung Hsing University
Taichung 402 (Taiwan)
Fax: (þ886)4-2286-2547
E-mail: jmzen@dragon.nchu.edu.tw
[**] The National Science Council of the Republic of China is gratefully
acknowledged for financial support of this work.
Angew. Chem. Int. Ed. 2003, 42, No. 5
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577

Communications
change in the ipa value was observed on using
NGCE and NGCE-Ru(bpy); while a net
increase of approximately 60 mA in the
xÀ
ipa value was observed at the NPyc CME-
xÀ
Ru(bpy) than that at the NPyc CME. In
other words, there is no intrinsic effect on the
SOR by using [Ru(bpy)3]2 without the
assistance of the active Pyc site in nafion.
These preliminary electrochemical results
can indeed help to explain the reaction
mechanism of the photochemical oxidation
þ
of RSCH3 (R ¼ Ph, PhCOCH3, and
xÀ
PhOCH ) at the j NPyc Ru(bpy) j mem-
3
brane (see below).
Controlled experiments were carried out
under various experimental conditions (Ta-
ble 1) to rationalize the reaction mechanism.
It is clear that the success of the system lies in
the proper combination of catalyst, photo-
sensitizer, solvent composition, pH value,
O , and light illumination. A possible reac-
2
tion mechanism based on these results is
shown in Scheme 1, where Pyc plays a dual
catalytic role both in the ORR (dark reac-
tion) and the SOR (light reaction). It is
noteworthy that, since the Pyc is opaque,
only [Ru(bpy)3]2 can be involved in light
xÀ
Figure 1. a) Conceptional representation for the preparation of jNPyc Ru(bpy)j. b) Cyclic voltam-
metric response of various chemically modified electrodes at pH 1 in a supporting electrolyte consist-
ing of a mixture of CH CNand H O (3:4) without and with 5 mm PhSCH at u¼50 mVs
À1
.
3
2
3
þ
Table 1: The influence of the reaction conditions on the selective photochemical oxidation of RPhSCH
to RPhSOCH3.
3
To electrochemically charac-
terize the multicomposite
[
a]
xÀ
Entry Membrane catalyst
Solution
j NPyc Ru(bpy) j membrane and
2þ
CH CN:H O pH[b] O2
hn[c] t [h] yield [%]
Pyc [Ru(bpy)3]
3
2
to study the photoconversion of
2
þ
3þ
[
[
Ru(bpy) ] ![Ru(bpy) ]
(via
1
2
3
4
5
6
7
8
9
þ
±
±
3:4
3:4
3:4
1:4
3:4
14:1
3:4
3:4
3:4
1
1
1
ca. 7
1
1
1
ca. 7
1
þ
þ
þ
±
þ
þ
þ
±
8
8
8
8
8
8
3
8
3
±
±
±
3
3
2
þ
Ru(bpy) ] *) in the presence of
þ
þ
þ
þ
þ
±
þ
3
þ
þ
þ
þ
±
þ
Pyc, a simulated chemically modi-
fied electrode (designated as
þ
±
±
23
37
47
49
>97
xÀ
NPyc CME-Ru(bpy)) was pre-
þ
pared. The only difference in pre-
1 mL of 30% H O added
2
2
xÀ
paring the NPyc CME was that a
þ
þ
þ
þ
nafion-coated glassy carbon elec-
trode (NGCE) was first prepared
þ
þ
þ
þ
[
a] þ: presence, ±: absence, [RPhSCH : R¼H, COCH , OCH ]¼17 mm, Entries 1±8 tested with
3
3
3
by dip coating with 5 mL of a 5 wt% PhSCH . [b] Adjusted with dilute HCl. [c] A 500-W halogen lamp was used as the light source. As for
3
solution of nafion. As shown in entry 9, the yields for the substituted organic sulfides are: R¼COCH : 96% and R¼OCH : 90%.
3
3
Figure 1b,
peak at approximately 1.1 V versus
Ag/AgCl corresponding to the [Ru(bpy) ] /[Ru(bpy) ]
a well-defined redox
3
þ
2þ
3
3
xÀ
[6]
couple was observed at the NPyc CME. The anodic peak
current (i ) was much higher than that observed at the
pa
2
þ
[
Ru(bpy) ] -doped NGCE (NGCE-Ru(bpy)). The increase
3
in the current response clearly has something to do with the
existence of active Pyc catalyst inside nafion. The catalyst can
2
þ
3þ
somehow assist the reaction of [Ru(bpy) ] ![Ru(bpy) ]
3
3
2
þ
via [Ru(bpy) ] *. The importance of the active Pyc site in
3
nafion was further demonstrated by the following two experi-
ments. First, an irreversible oxidation peak at the redox
3
þ
2þ
potential of the [Ru(bpy) ] /[Ru(bpy) ] couple with a much
3
3
xÀ
higher ipa value with NPyc CME than with NGCE was
Scheme 1. Reaction mechanism for the photochemical sulfide oxida-
observed on addition of 5 mm PhSCH . Secondly, virtually no
tion reaction.
3
5
78
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Angewandte
Chemie
absorption in the membrane. The active Pyc site was reported
to be an efficient catalyst for the ORR,[3b,7] and hence, the
471; c) J. M. Fraile, J. I. GarcÌa, B. Lµzaro, J. A. Mayoral, Chem.
Commun. 1998, 1807; d) R. S. Varma, K. P. Naicker, Org. Lett.
999, 1, 189; e) J. Brinksma, R. L. Crois, B. L. Feringa, M. I.
Donnoli, C. Rosini, Tetrahedron Lett. 2001, 42, 4049; f) K. Sato,
M. Hyodo, M. Aoki, X.-Q. Zheng, R. Noyori, Tetrahedron 2001,
1
purging O is essential for the formation of H O during the
2
2
2
reaction. The control experiment in pure H O gave only
2
2
about 47% conversion with poor selectivity (Table 1). How-
57, 2469; g) S. Choi, J.-D. Yang, M. Ji, H. Choi, M. Kee, K.-H.
2
þ
ever, the assistance of Pyc and [Ru(bpy)3] in the SOR was
supported by the indirect electrochemical studies mentioned
Ahn, S.-H. Byeon, W. Baik, S. Koo, J. Org. Chem. 2001, 66, 8192.
[3] a) J.-M. Zen, A. S. Kumar, Acc. Chem. Res. 2001, 34, 772; b) J.-M.
Zen, A. S. Kumar, C.-C. Chen, J. Mol. Cat. A 2001, 165, 177; c) J.-
M. Zen, C.-B. Wang, J. Electrochem. Soc. 1994, 141. L51; d) J.-M.
Zen, C.-B. Wang, J. Electroanal. Chem. 1994, 368, 251 ± 256; e) J.-
M. Zen, A. S. Kumar, C.-C. Chen, Anal. Chem. 2001, 73, 1169, and
references therein.
earlier. The efficiency of the SOR was then evaluated by
xÀ
putting a 4.5 î 2 cm j NPyc Ru(bpy) j in a mixture of CH CN
3
(
30 mL), H O (40 mL), and 17 mm RSCH3 (R ¼ Ph,
2
PhCOCH , and PhOCH ) at pH 1, with constant purging of
3
3
O under illumination (500 Whalogen lamp) for 3 h. The
2
[4] The stability experiment was checked by continuously stirring the
products were analyzed simply by evaporation of the solution
j NPycxÀ j membrane (ca. 0.1 cm
2
) in a solution of about 99%
of the separated reaction product in CHCl with a rotary-
ethanol for 90 days. The membrane did not show any change in
weight, which illustrates the Pyc-modified nafion membrane has a
relatively rigid structure.
3
vacuum system. All reactions gave a single product of
sulfoxide (that is, no sulfone was observed on the TLC plate
and was further confirmed by NMR and mass spectroscopic
studies) in > 90% yield. The high selectivity of the current
approach was clearly demonstrated. Finally, three repeated
[
5] a) W. Adam, J. E. Arg¸ello, A. B. PeÊÿÊory, J. Org. Chem. 1998,
63, 3905; b) N. Somasundaram, C. Srinivasan, J. Photochem.
Photobiol. 1998, 115, 169; c) K. Chiba, Y. Yamaguchi, M. Tada,
Tetrahedron Lett. 1998, 39, 9035; d) E. L. Clennan, A. Aebisher, J.
Org. Chem. 2002, 67, 1036.
experiments were performed with PhSCH to test the
3
xÀ
recyclability of the j NPyc Ru(bpy) j system, and almost
[6] K. C. Pillai, A. S. Kumar, J.-M. Zen, J. Mol. Catal. A 2000, 160,
77.
2
the same yield was observed.
[
7] a) J. B. Goodenough, R. Manoharan, M. Parandhaman, J. Am.
Chem. Soc. 1990, 112, 2076; b) J.-M. Zen, R. Manoharan, J. B.
Goodenough, J. Appl. Electrochem. 1992, 22, 140.
In conclusion, we have demonstrated a clean and highly
selective photochemical oxidation of sulfide to sulfoxide on a
novel heterogeonous multicomponent nafion membrane
containing a Pyc catalyst and a [Ru(bpy)3]2 photosensitizer.
The high sulfoxide selectivity, lack of pollution, ease of
product separation, and recyclable nature of the muticompo-
nent membrane has a clear advantage over classical ap-
proaches. Further investigations are currently underway to
expand the scope of this reaction to sulfide compounds
containing more complicated organic structures and to a
macroscale synthesis.
þ
Stereoselective Alkylation
Highly Stereoselective N-Terminal
Functionalization of Small Peptides by Chiral
Phase-Transfer Catalysis**
Experimental Section
Photochemical experiments were carried out at pH 1 (adjusted with
HCl) in a mixture of CH CN and H O (3:4, ca. 70 mL) in a closed
3
2
Takashi Ooi, Eiji Tayama, and Keiji Maruoka*
round-bottomed flask sealed with a gasket-septum under constant
purging of O2 gas. Cyclic voltammetric (CV) experiments were
performed using a CHI workstation with a three-electrode system of
2
Peptide modification is an essential yet flexible synthetic
concept for screening targets efficiently and optimizing lead
structures in the application of naturally occurring peptides as
working (0.071 cm ), reference (Ag/AgCl), and counter (Pt disc,
2
0
.071 cm ) electrodes between À0.4 to 1.4 V. A negative current in the
cyclovoltammograms denotes an anodic response, while a positive
current denotes a cathodic current. The oxidized product was
[
1,2]
pharmaceuticals. The introduction of side chains directly to
a peptide backbone is a powerful method for preparing
nonnatural peptides. The achiral glycine subunit has generally
separated into CHCl and then analyzed by NMR spectroscopic (in
3
CDCl ) and mass spectrometric techniques after rotary-vacuum
3
evaporation. The yield of the products was determined on the basis
of the ratio between the molar weight of the reactant and the product.
[
3]
[4±8]
been used for this purpose and glycine enolates,
cals,
radi-
[
9±11]
and glycine cation equivalents[12,13] have been ex-
Received: July 17, 2002
Revised: August 27, 2002 [Z19755]
[
*] Prof. K. Maruoka, Dr. T. Ooi, E. Tayama
Department of Chemistry, Graduate School of Science
Kyoto University, Sakyo, Kyoto, 606-8502 (Japan)
Fax: (þ81)75-753-4041
[
1] a) M. C. CarreÊo, Chem. Rev. 1995, 95, 1717; b) Sulfur Centered
Reactive Intermediates in Chemistry and Biology, (Eds.: C.
Chatgilialoglu, K. D. Asmus), Nato ASI series, Plenum, New
York, 1990; c) M. Hudlick y¬ , Oxidations in Organic Chemistry,
ACS Monograph 186, American Chemical Society, Washington,
DC, 1980.
E-mail: maruoka@kuchem.kyoto-u.ac.jp
[
**] This work was supported in part by a Grant-in-Aid for Scientific
Research from the Ministry of Education, Culture, Sports, Science
and Technology, Japan.
[
2] a) H. S. Schultz, H. B. Freyermuth, S. R. Bu, J. Org. Chem. 1963,
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
28, 1140; b) T. Indrasena, R. S. Varma, Chem. Commun. 1997,
Angew. Chem. Int. Ed. 2003, 42, No. 5
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