10.1002/ejic.201700931
European Journal of Inorganic Chemistry
COMMUNICATION
dilute O2 conditions. It is also worth pointing out that
although the experiments are conducted at 40 bar gas
being hydrolysed to the ketone.18, 27 , 28 , Although the
29
mechanism of Pd(II) catalyzed synthesis of acetals and ketals
pressure, the catalyst does not need high pressures to has been studied, the full mechanism has yet to be
operate. We carried out tests which showed that the catalyst elucidated.27,28,29 We are therefore commencing studies
could operate at much lower pressures and not affect the which will help us better understand this catalyst system.
initial rate. Nevertheless, the substrate tests in Table 2 were
In conclusion, the Wacker oxidation of styrenes to
run over 24 hours in small reactors; under such conditions ketones is a difficult reaction and utilzing O2 for direct
the reaction would become limited in O2 as the reaction catalyst turnover is a real challenge. To date there have not
progressed. Therefore, lower pressures could be used if an
been studies exploring a range of ligands. We have shown
open system was employed (with an O2 ballast vessel), or if a that a number of factors are important and greatly effect
larger reactor with a larger head space was used. Although aerobic catalyst performance. Such studies are important if
the use of a continuous flow system would be the most we are to design the next generation of catalysts with
suitable approach to safely use of O2 on a larger scale.24
performance suitable for industrial application. Future work
will involve kinetic and mechanistic studies in order to gain a
better understanding of the key steps, assisting us to design
better catalysts in the future.
Table 2. Oxidation of styrenes by [(PNO)Pd(NCMe)2][OTf]2
Acknowledgements For financial support, we thank the China
Scholarship Council (No. 201506030041) (H. Chai), the Department for
Employment and Learning, Northern Ireland (L. M. Dornan) and the
EPSRC (N.L. Hughes). For HR ESI-MS analysis of ligands and palladium
complexes we thank Conor McGrann.
Keywords: oxidation • palladium • ketone • styrene• ketal
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