Photon Factory Activity Report 2022 #40 (2023)

BL-9C, BL-12C, AR-NW10A/2019G105, 2021G110, 2021G113

XAFS Characterization of N-Heterocyclic Carbene-attached Cr and Rhincorporated Ceria (NHC-r-Cr0.19Rh0.06CeOz)
Satoshi MURATSUGU*1, Satoru IKEMOTO1, Mizuki TADA1,2

Department of Chemistry, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602,Japan.
2
Research Center for Materials Science (RCMS) & Integrated Research Consortium on
Chemical Science (IRCCS), Nagoya University, Furo-cho, Chikusa, Aichi 464-8602, Japan.
1

1 Introduction
ICy-r-Cr0.19Rh0.06CeOz was newly prepared by theattachment of 1,3-dicyclohexylimidazol-2-ylidene
Cr0.19Rh0.06CeOz(r(ICy)on
H2-reduced
Cr0.19Rh0.06CeOz),[1] and it showed catalytic activity for
the1,4-arylationofcyclohexenone
withphenylboronic acid, whereas r-Cr0.19Rh0.06CeOz
without ICy was inactive.[2] We investigated the local
coordination structures of ICy-r-Cr0.19Rh0.06CeOz andr-Cr0.19Rh0.06CeOz before and after the attachment ofICy.[2]2 Experimental
Rh K-edge XAFS of ICy-r-Cr0.19Rh0.06CeOz and rCr0.19Rh0.06CeOz were measured in a transmission
mode at room temperature at the NW10A station witha Si(311) double-crystal monochromator. Samples
were grounded and packed into a cell, and the cell wassealed with Kapton films under an Ar atmosphere so as
not to be exposed to the air. EXAFS spectra wereanalyzed using ATHENA and ARTEMIS programs.
k3-Weighted EXAFS oscillations were Fouriertransformed 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 calculatedby the FEFF8.
3 Results and Discussion
Figure 1 shows Rh K-edge EXAFS Fourierandrtransforms
ICy-r-Cr0.19Rh0.06CeOz
andcurve-fitted
structural
Cr0.19Rh0.06CeOz,
parameters are summarized in Table 1. The curvefitted CN and R for Rh-Rh bond of ICy-rCr0.19Rh0.06CeOz were 1.3 ± 0.2 and 0.207 ± 0.001 nm,
respectively, and those of r-Cr0.19Rh0.06CeOz without
ICy modification were also 1.3 ± 0.2 and 0.207 ±0.001 nm, respectively. The curve-fitted CN and R for
Rh-O bond (the interaction between Rh nanocluster
and the surface of r-Cr0.19Rh0.06CeOz) ofICy-r-Cr 0.19 Rh 0.06 CeO z were 2.8 ± 0.3 and 0.262 ±0.001 nm, respectively, and those of rCr0.19Rh0.06CeOz without ICy modification were also
2.8 ± 0.4 and 0.261 ± 0.001 nm, respectively. The
similar values indicated the maintenance of Rh
nanocluster structure on the surface.
FT-IR, XPS, and photoluminescence spectroscopy
showed that the ICy was existed as carbene specieson the surface of r-Cr0.19Rh0.06CeOz, and ICy-rCr0.19Rh0.06CeOz exhibited catalytic performances for
1,4-arylation of cyclohexenone (yield: >99%). On theother hand, Cr0.19Rh0.06CeOz (without ICy) did notshow any catalytic activity for the 1,4-arylation,suggesting that the interaction of the ICy carbene
ligand with the Rh nanocluster played a key role toinduce the catalytic activity. DFT calculations
suggested that ICy carbene ligand controlled theadsorption sites of the phenyl group on the Rh
nanocluster to promote the C-C bond formation of thephenyl group and cyclohexenone.

Figure 1. Rh K-edge EXAFS FTs of (a) ICy-rCr0.19Rh0.06CeOz and (b) r-Cr0.19Rh0.06CeOz.

Photon Factory Activity Report 2022 #40 (2023)

Table 1. Curve-fitting Results of Rh K-edge EXAFS
Fourier Transforms of ICy-r-Cr0.19Rh0.06CeOz and rCr0.19Rh0.06CeOz aShellCN

R /nm∆E0/eVσ2 /×10-5nm2

ICy-r-Cr0.19Rh0.06CeOz
1.3 ± 0.2
0.207
± 10 ± 2 5 ± 1
Rh–O
0.001
2.8 ± 0.3
0.262
± -2 ± 1 10 ± 1
Rh–Rh
0.001
r-Cr0.19Rh0.06CeOz
Rh–O
1.3 ± 0.20.207± 9±25±10.001
Rh–Rh
2.8 ± 0.40.261± -2 ± 1 10 ± 10.001
a k range and R range were 30-140 nm-1 and 0.12-0.27
nm, respectively.

References[1] S. Ikemoto et al., Phys. Chem. Chem. Phys. 21,20868-20877 (2019).
[2] S. Ikemoto et al., J. Am. Chem. Soc. 145, 14971504 (2023).
* smuratsugu@chem.nagoya-u.ac.jp