Photon Factory Activity Report 2005 #23Part B (2006)
Surface and Interface

10B/2003G250

XAFS study on phenoxyethoxymethyl-polystyrene (PEM)-based novel
microencapsulated osmium oxide catalyst
Tomoko YOSHIDA1, Hisao YOSHIDA*1, Tasuku ISHIDA2, Sh KOBAYASHI2
1
Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
2
The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.

Experimental
The Os LIII-edge XAFS measurement was performed atroom temperature in transmission mode at the BL-10B
station [2] of KEK-PF, Tsukuba, Japan, with a Si(311)channel-cut monochromator. The sample was sealed witha polyethylene film in a dry atmosphere. Normalizationof XANES and data reduction on EXAFS were carriedout as described elsewhere [3].
Results and discussion
For the Os LIII-edge XANES of PEM-MC Os catalyst,
the position of white line was close to that for OsO2 andK2OsO4 (Fig. 1), indicating that the starting material,
OsO4, was reduced to Os6+ or Os4+ ions during thepreparation procedure. The figure of the XANES for thecatalyst was similar to that for OsO2 except for the intensewhite line.
To clarify the local structure around the Os atoms in
the catalyst, we performed nonlinear curve-fitting
analyses of the Fourier-filtered EXAFS of the first andthe second shells around Os atoms by a least-squares
method. The Os-O (or Os-C) shell was empiricallyextracted from the EXAFS of OsO4. The results are listed
in Table 1. The coordination numbers (CN) andinteratomic distances (R) for short and long Os-O bondsin the catalyst were estimated as ca. 2 and 1.85 Å, and ca.
4 and 2.01 Å, respectively, similar to those in the OsO2reference sample. This suggests that Os ions in thecatalyst have similar local structure to that in OsO2. The
higher white line intensity mentioned above suggest that
the OsO2 species in polymer are more cationic or more

symmetric than that in the bulk OsO2 as they are highly
dispersed in polymer.

4

Normalized absorbanceIntroduction
Osmium-catalyzed dihydroxylation of olefins is one of
the most efficient methods for the preparation of vicinal
diols. Recently, a new catalyst, phenoxyethoxymethylpolystyrene (PEM)-based polymer-supported osmiumoxide catalyst (PEM-MC Os catalyst) [1], was developed
based on a microencapsulation (MC) technique. Thecatalyst
successfully
proceeds
asymmetricdihydroxylation of olefins using biscinchona alkaloids asa chiral legand and K3Fe(CN)6 as a cooxidant in
H2O/acetone, and easily recovered by filtration and reused
without loss of activity several times. In order toelucidate the active site structure of the catalyst, in thepresent study, we applied X-ray absorption technique toinvestigate the electronic state and local structure of Os
species in the catalyst.

(a)3(d)(c)2(b)

1010840

10860

10880

10900

10920

10940

X-ray energy / eV
Fig. 1: Os LIII-edge XANES of (a) PEM-MC Os catalyst,(b) OsO4, (c) OsO2 and (d) K2OsO4·2H2O.

Table 1: Results of curve-fitting analyses
2sampleshellCN
R / nm∆σOs-O(C)
2.5
0.185-0.00460
PEM-MC
Os-O(C)
4.2
0.201-0.00244
Os catalyst
Os-O(C)
2.0
0.349-0.00098
Os-O(C)
2.1
0.186-0.00292
OsO2Os-O(C)
4.1
0.200
-0.00070
Os-O(C)
2.00.344-0.00007OsO4Os-O(C)40.17002∆σ : difference of Debye-Waller factor from that for
OsO4.

References[1] S. Kobayashi et al., Org. Lett. 3, 2649 (2001).
[2] M. Nomura, A. Koyama, KEK Report 89-16, 1 (1989).
[3] T. Tanaka, et al., J. Chem. Soc., Faraday Trans. 1 84,2987 (1988).
* h-yoshida@esi.nagoya-u.ac.jp

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