Communication
Dalton Transactions
the catalytic mechanism, as well as to explore its potentiality
in the isomerization of the allylic alcohol moiety in the natural
opioids.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
We acknowledge the Project CTQ2015-67384-R (MINECO)
funded by the FEDER program, the PAI group FQM-317 and
the COST Action CM1302 (WG1, WG2).
Notes and references
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Scheme 2 Proposed mechanism for the isomerization of 2-cyclohexe-
nol to cyclohexanone mediated by catalyts 1 and 2.
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1
the H NMR spectrum at 2.82 (H2) and 3.22 ppm (H3) (see the
ESI†) as observed for the allyl alcohol complex [RuCp(η2-
CH2vCH–CH2–OH)(PTA)2](CF3SO3), which was studied theor-
etically and by neutron scattering.13 The disposition adopted
in solution by the ligands in complex 3 has been investigated
by means of a 1H–1H ROESY experiment, revealing that the
2-cyclohexenol is placed almost parallel to the Cp ring, resem-
bling the exo geometry adopted by the allyl alcohol in the
complex [RuCp(η2-CH2vCH–CH2–OH)(PTA)2](CF3SO3), as indi-
cated by the ROE cross peaks between the hydrogens of the Cp
and sp3 carbons H1, H4a, H5a and H6a of the alkene bond of
2-cyclohexenol (Fig. 3). This coordination mode, which is
recurrent in the catalytic isomerization reactions mediated by
1 and 2, helps to determine the conversion and the kinetics.
Nevertheless, and in contrast with the isomerization of linear
allylic alcohols, the possible catalytic isomerization process
(Scheme 2) of 2-cyclohexenol does not depend on the presence
of water in the reaction medium and needs further study by
theoretical simulations and scattering techniques to character-
ize whether the water molecules act as spectators.
13 F. Scalambra, N. Holzmann, L. Bernasconi, S. Imberti and
A. Romerosa, ACS Catal., 2018, 8, 3812–3819.
14 M. Serrano-Ruiz, P. Lorenzo-Luis, A. Romerosa and
A. Mena-Cruz, Dalton Trans., 2013, 42, 7622.
15 B. González, P. Lorenzo-Luis, M. Serrano-Ruiz,
É. Papp, M. Fekete, K. Csépke, K. Osz, Á. Kathó,
F. Joó and A. Romerosa, J. Mol. Catal. A: Chem., 2010, 326,
15–20.
Conclusions
In conclusion, we found that complexes 1 and 2 can catalyse
the difficult isomerization of 2-cyclohexenol to cyclohexanone
under mild conditions with outstanding conversion rates, both 16 F. Scalambra, M. Serrano-Ruiz and A. Romerosa, Dalton
in water and in a water/cyclohexane biphasic system. For the Trans., 2017, 46, 5864–5871.
latter medium, it is possible to recycle the catalyst up to 7 17 D. J. Nelson, J. A. Fernández-Salas, B. J. Truscott and
times. The reaction is currently under investigation to unravel
S. P. Nolan, Org. Biomol. Chem., 2014, 12, 6672–6676.
Dalton Trans.
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