Photon Factory Activity Report 2017 #35 (2018)

AR-NW10A/2016G078, 2014G060, 2014G059

XAFS Characterization of Molecularly-Imprinted Ru Porphyrin Complex
Catalysts for Cholesterol Epoxidation

Satoshi MURATSUGU*1, Hiroshi BABA1, Tatsuya TANIMOTO1, Masahiro TASAKI1,Yosuke TERAO1, Mizuki TADA1,2
1
Department of Chemistry, Graduate School of Science, Nagoya University, Furo, Chikusa, Aichi
464-8602, Japan.
2
Research Center for Materials Science (RCMS) & Integrated Research Consortium on Chemical
Science (IRCCS), Nagoya University, Furo, Chikusa, Aichi 464-8602, Japan.
1 Introduction
A molecularly imprinted Ru porphyrin complex
catalysts was prepared on a SiO2 surface from a SiO2supported Ru porphyrin complex with SiO2-matrix
overlayers.[1] The local coordination structures of theprepared molecularly imprinted Ru porphyrin complex
catalysts were investigated by Ru K-edge XAFS. The
chemoselective epoxidation of cholesterol derivatives wasachieved on the molecularly imprinted Ru complex
catalyst.[1]2 Experiment
The molecularly imprinted Ru catalyst was prepared ina step-by-step manner: (A) The attachment of a Ru
porphyrin complex (1) on a SiO2 surface to produce (2),(B) the removal of CO ligand to produce (3), (C) thecoordination of a template to produce (4), (D) thestacking of SiO2-matrix overlayers to produce (5), and (E)the removal of the template to produce the molecularly
imprinted Ru catalyst (6).
Ru K-edge XAFS of 1, 2, 3, and 4 were measured in atransmission mode, and that of 5 and 6 were measured ina fluorescence mode at 20 K at the NW10A station with aSi(311) double-crystal monochromator and MSSD.
EXAFS spectra were analyzed using ATHENA andARTEMIS programs. k3-Weighted EXAFS oscillations
were Fourier transformed into R-space, and curve-fitting
analysis was performed in R-space with coordination
number (CN), interatomic distance (R), Debye-Waller
factor (σ2), and correction-of-edge energy (∆E0). Phase
shifts and backscattering amplitudes were calculated by
the FEFF8.
3 Results and Discussion
The local coordination structures of the molecularly
imprinted Ru porphyrin complexes were analyzed by Ru
K-edge XANES and EXAFS (Figure 1). The shape of Ru
K-edge XANES of 1, 2, 3, 4, 5, and 6 were almost similar,indicating that the oxidation state of Ru in Ru porphyrin
was almost identical. The Ru K-edge XANES of The
curve-fitted CN and R for Ru-N (porphyrin) bond of 1, 2,3, 4, 5, and 6 were 0.205 ± 0.001 nm (CN = 4.3 ± 0.9),
0.205 ± 0.001 nm (CN = 3.7 ± 1.1), 0.206 ± 0.001 nm(CN = 3.2 ± 0.6), 0.204 ± 0.001 nm (CN = 4.2 ± 0.8),
0.206 ± 0.001 nm (CN = 3.8 ± 1.0), and 0.207 ± 0.001nm (CN = 3.2 ± 0.4), respectively, indicating themaintenance of Ru porphyrin structure. This was also
supported with the results of 13C SS NMR and UV/visspectra. The existence of Ru-N (template) bond was also
observed on 4 and 5, whose CN and R were 0.184 ± 0.003
nm (CN = 0.9 ± 0.7), 0.186 ± 0.006 nm (CN = 0.4 ± 0.6),
respectively.
High chemoselectivity for the C5=C6 epoxidation ofcholesterol derivatives without protecting 3-position OH
group was achieved on the molecularly imprinted Ru
porphyrin complex catalyst (6). The yield of C5=C6epoxide for cholesterol epoxidation was increased to be
95% on 6 compared to that on 1 (30%) and on 2 (23%).

Figure. 1: k3-Weighted Ru K-edge EXAFS Fouriertransforms of 1, 2, 3, 4, 5, and 6 (k = 30–160 nm-1).
References[1] S. Muratsugu, H. Baba, T. Tanimoto, K. Sawaguchi, S.
Ikemoto, M. Tasaki, Y. Terao, M. Tada, Chem.
Commun. 2018, 54, 5114 - 5117.
* smuratsugu@chem.nagoya-u.ac.jp