Communication
Catalysis Science & Technology
and mild temperature). This protocol is both simple and
clean, and so constitutes an important contribution to green
sustainable chemistry, with the potential for application on a
larger scale.
Acknowledgements
Scheme 4 The Ru species present on magadiite during the one-pot
synthesis of biphenols from phenols.
Financial support was provided by JSPS KAKENHI grant num-
bers 17H03456 and 16K14480. We thank Dr. Uruga, Dr. Kato,
and Dr. Ina (SPring-8) for XAFS measurements. TEM experi-
ments were carried out at the Research Center for Ultrahigh
Voltage Electron Microscopy, Osaka University.
lower energies, which was attributed to the formation of
Ru(0) species (Fig. 1(b)). This change indicates that the Ru3+
species is reduced under an H2 atmosphere to form the active
Ru(0) species for diphenoquinone hydrogenation. Further-
more, upon exposure of the H2-treated Ru/magadiite to air,
the obtained XANES spectrum was comparable to that of the
fresh Ru/magadiite (Fig. 1(c)). These results suggest that the
active Ru3+ species for the oxidative coupling stage is regene-
rated by re-oxidation of the Ru(0) species with O2.
These phenomena were also supported by the extended
X-ray absorption fine structure (EXAFS) spectra (Fig. S3†). As
shown, the Fourier transform (FT) of the k3-weighted EXAFS
spectrum of the fresh Ru/magadiite (Fig. S3(a)†) was similar
to that of RuIJOH)3 (Fig. S3(h)†), exhibiting two scattering
peaks at 1.7 and 2.8 Å. Following treatment with H2, these
two peaks disappeared and a new peak arose at 2.4 Å, which
was assigned to the Ru–Ru metal shell (Fig. S3(b)†). Again,
upon exposure of the H2-treated Ru/magadiite to air, the
resulting EXAFS spectrum was comparable to that of the
fresh Ru/magadiite (Fig. S3(c)†). These results therefore con-
firm reduction of the active Ru3+ NPs for the oxidative cou-
pling of phenols on magadiite under an H2 atmosphere to
form the active Ru(0) NP species for successive dipheno-
quinone hydrogenation, while the active Ru3+ species was
regenerated once again by oxidation of the Ru(0) species un-
der air (Scheme 4). The same redox property was observed in
situ XAFS measurement of the Ru/magadiite after the one-pot
reaction.† This reversibility therefore renders the prepared
Ru/magadiite species a reusable dual-function catalyst for the
green one-pot transformation of phenols to biphenols.
Notes and references
‡ The other supported Ru catalysts and magadiite-supported Pd, Rh, Pt, and Ni
catalysts were prepared by deposition methods.†
1
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Conclusions
In conclusion, we successfully developed a green one-pot syn-
thesis of biphenols using Ru/magadiite, which acts as dual-
functional catalyst for the regioselective oxidative coupling of
phenols in the presence of O2 followed by the successive
hydrogenation of the obtained diphenoquinones using H2.
This novel method exhibits a number of key advantages over
existing routes to biphenols, including removal of the neces-
sity to isolate intermediate products, the use of O2 and H2
as green oxidant and reductant, respectively, and the produc-
tion of only water as a by-product. In addition, the Ru/
magadiite catalyst is easily handled in the context of recover-
ability and reusability, and only mild reaction conditions are
required for the transformation (i.e., atmospheric pressure
4
Catal. Sci. Technol.
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