Photon Factory Activity Report 2016 #34 (2017)

AR-NW10A/2014G059, 2010G020

XAFS Study of Molecularly-Imprinted Pd Catalysts for Suzuki Coupling Reaction
Satoshi MURATSUGU*1,3, Niladri MAITY3, Hiroshi BABA1, Masahiro TASAKI1,Mizuki TADA1,2,3
1

Department of Chemistry, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602, Japan.
2
RCMS, Nagoya University, Furo-Cho, Chikusa-ku, Nagoya, 464-8602, Japan.
3
Institute for Molecular Science, Myodaiji, Okazaki, Aichi 444-8585, Japan.

1 Introduction
Molecularly imprinted Pd-complex catalysts withdifferent Pd loadings were prepared on a SiO2 surface bymolecular imprinting of a SiO2-supported Pd complex
with SiO2-matrix overlayers.[1] The local coordination
structures of the prepared molecularly imprinted Pdcomplex catalysts were investigated by Pd K-edge XAFS.
The catalytic performances of the molecularly imprinted
Pd complex catalysts were very different for various
combinations of aryl iodides and arylboronic acids, andreactants with bulky substituent groups were hindered on
the imprinted Pd catalysts.[1]2 Experimental
A Pd precursor complex (1) with a template molecule
was attached on a SiO2 surface functionalized with pstyryl moiety to prepare a SiO2-supproted Pd complex(A). SiO2-matrix overlayers of two different heights werestacked on the surface of A to prepare a molecularlyimprinted Pd complex on the SiO2 surface (B, Pd: 0.35wt%, low height; C, Pd: 0.23 wt%, high height).
Pd K-edge XAFS was measured in a transmission
mode at 20 K at the NW10A station with a Si(311)double-crystal monochromator. Ionization chambers
filled with pure Ar and pure Kr were used to monitor
incident and transmitted X-rays, respectively. EXAFS
spectra were analysed 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), andcorrection-of-edge energy (∆E0). Phase shifts andbackscattering amplitudes were calculated by the FEFF8code.
3 Results and Discussion
The local coordination structures of the supported Pdcomplexes were analyzed by Pd K-edge EXAFS (Table1). 1 with the template ligand was curve-fitted by Pd-P
bond at 0.223 ± 0.001 nm and Pd-O bond at 0.205 ±0.001 nm, whose coordination numbers (CNs) were both
fixed to be 2.0. The bond distances of the Pd-P and Pd-O
coordination in A were curve-fitted as 0.223 ± 0.001 and0.206 ± 0.002 nm, respectively, and the CNs of the Pd-P
and Pd-O bonds were curve-fitted as 1.7 ± 0.1 and 2.0 ±0.4, respectively. These results suggest that the local
coordination structure of 1 was maintained after it wasattached to the SiO2 surface. This interpretation wassupported with the results of 13C SS NMR and UV/visspectra.
The bond distances of the Pd-P and Pd-O coordinationin B and C were both fitted as 0.225 ± 0.001 and 0.203 ±0.002 nm, respectively, together with similar CN values(Table 1). These results also indicated the maintenance ofthe local coordination structure of the Pd complex in B
and C after the stacking of SiO2-matrix overlayers. The
Pd K-edge XANES of 1, A, B, and C were quite similar,
supporting the similar structures and oxidation states.
The Suzuki cross-coupling performance of the SiO2supported Pd complex catalysts was investigated on theprepared molecularly-imprinted Pd catalysts, and thesensitivity of the cross-coupling activity was dependent
on the height of the SiO2-matrix overlayers. The crosscoupling reactions of bulky reactants were strongly
suppressed on B and C compared with A, and thesensitivity was also dependent on the position of thesubstituent groups on the reactants.
Table 1 Structural Parameters Determined by Curve-Fitting Analysis ofPd K-edge EXAFS Measured at 20 KShell

CNR /nm∆E0 /eVσ2 /×105 nm2aPd-P

2.01
0.223 ± 0.001

5.4 ± 0.9

2.4 ± 0.2

Pd-O

2.0

0.205 ± 0.001

6.2 ± 2.2

5.8 ± 0.8

Pd-P

1.7 ± 0.1

A (Pd: 0.6 wt%) b0.223 ± 0.001
5.4

Pd-O

2.0 ± 0.4

0.206 ± 0.002

6.2

5.8

B (Pd: 0.35 wt%) c
0.225 ± 0.001
5.4

2.4

Pd-P

1.6 ± 0.2

Pd-O

1.9 ± 0.4

Pd-P

1.5 ± 0.2

0.203 ± 0.002
6.2
C (Pd: 0.23 wt%) d
0.225 ± 0.001
5.4Pd-O 1.6 ± 0.4
0.203 ± 0.002
6.2ak = 30-160 nm-1, R = 0.12-0.22 nm, Rf = 0.47%.
bk = 30-160 nm-1, R = 0.12-0.22 nm, Rf = 1.0%.
ck = 30-140 nm-1, R = 0.12-0.22 nm, Rf = 1.0%.
dk = 30-140 nm-1, R = 0.12-0.22 nm, Rf = 1.3%.

2.4

5.8
2.4
5.8Reference[1] S. Muratsugu, N. Maity, H. Baba, M. Tasaki, M. Tada,
Dalton Trans. 2017, 46, 3125-3134. (Selected as InsideBack Cover)* smuratsugu@chem.nagoya-u.ac.jp