RSC Advances
Paper
4. Conclusions
In summary, we report on an easy, highly efficient, and
continuously reversible phase transfer process directed towards
NMNPs (Pt, Ru, Ir, Pd, and Au) in an aqueous/1-pentanol
biphasic system. By comparing a series of organic solvents
(alcohols, toluene, and n-heptane), we reveal the essence of
thermoregulated phase transfer, namely a reversible hydrogen-
bond-selective process. Due to the special structure of thermo-
regulated ligand Ph P(CH CH O) CH , suitable gas atmo-
2
2
2
22
3
spheres (carbon monoxide, hydrogen, nitrogen) are found
decisive for the successful phase transfer of NMNPs. Aer six
cycles of reversible phase transfer, the NMNPs (Pt, Ru, Ir, and
Pd) size and distribution almost remain constant, while the size
of Au-NPs has an obvious increase. With the aid of ICP-AES, we
can know that the phase transfer efficiency of NMNPs from 1-
pentanol to aqueous or vice versa isn't less than 99.9%. In
Fig. 5 Recycling efficiency of the as-prepared Pt-NPs for the ster-
eoselective semihydrogenation of DPA.
29,30
bioactive molecules, avors, and natural products.
Seeing
36,37
contrast with other reversible phase transfer protocols,
that our protocol provided an easy, highly efficient, and
which needed supplementary phase transfer agents, ligands, or
reagents, our protocol has almost the best reversible phase
transfer ability. Moreover, we successfully demonstrate the
feasibility of separation and recycling of the as-prepared Pt-NPs
catalyst, which exhibits exceptionally high catalytic activity,
better stereoselectivity, and excellent reusability in the semi-
hydrogenation of DPA. Herein, we anticipate that our protocol
not only provides an innovative avenue for the development of
the NMNPs phase-transfer technology but also is found to be
very effective for the in situ separation and recycling of NMNPs
catalysts.
continuously reversible phase transfer ability for NMNPs, we
rstly employed the as-prepared Pt-NPs as catalysts for the
hydrogenation of DPA to evaluate the catalytic activity, selec-
tivity, and reusability.
Various reaction conditions for the hydrogenation of DPA were
studied and the results were summarized in Table 2. The effect of
ꢂ
reaction temperature was investigated in the range of 40–80 C at
1
MPa H for 20 min (Table 2, entry 1–5). With the increasing of
2
reaction temperature, the conversion of DPA increased from 19%
to approximately 100%, and the stereoselectivity to cis-stilbene
(cis-ST) had a slight decrease. In the range from 0.5 to 3 MPa
(Table 2, entry 4, 7, 8, 9), we can know that the stereoselectivity to
cis-stilbene also had a slight decrease. To our surprise, the
product of complete hydrogenation to diphenylethane (DPE) had
Acknowledgements
not been detected during the process of changing reaction We gratefully acknowledge the nancial support provided by
conditions. Therefore, the as-prepared Pt-NPs exhibited a very the National Natural Science Foundation of China (21173031,
high catalytic activity to the semihydrogenation of DPA and 21373039).
a better stereoselectivity to cis-stilbene.
Once the optimal reaction condition was selected, it was
employed for other metal nanoparticles in the hydrogenation of
DPA. The results (Table S1, ESI†) indicated that Au-NPs didn't
Notes and references
1
Y. Lin, H. Skaff, T. Emrick, A. D. Dinsmore and T. P. Russell,
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show any catalytic activity, while Ru-NPs and Ir-NPs exhibited
a very low catalytic activity. As for Pd-NPs, however, it produced
a very high stereoselectivity to cis-stilbene up to 99%, though
there was a relatively low catalytic activity compared with Pt-
NPs. To our satisfaction, all the catalysts were able to achieve
the separation from products, and successfully recycled.
Next, the reusability of the as-prepared Pt-NPs was examined.
Aer reaction, the upper 1-pentanol phase was separated from
the lower catalyst-containing phase by simple phase separation.
And the lower catalyst-containing phase was directly reused in
the next reaction run. Under the identical reaction conditions to
entry 4 in Table 2, the recovered Pt-NPs were reused for 13 times
without evident decrease in conversion and stereoselectivity
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(
Fig. 5). In general, the as-prepared Pt-NPs catalyst exhibited
a very high turnover number (TON) of 7400 for the semi-
hydrogenation of DPA, which was far superior to most of the
31,32
33
34
35
hitherto known catalysts, such as Pd,
Pt, Ru, and Rh.
462.
6334 | RSC Adv., 2016, 6, 6329–6335
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