44
SKRIPOV et al.
clusters (BE(Pd3d5/2) = 335.7 eV) responsible for
o-CNB hydrogenation under mild conditions (P/Pd =
0.7 for the Pd(acac)2 precursor, and P/Pd = 0.3 for the
PdCl2 precursor). An increase in selectivity in o-CNB
hydrogenation was also observed for a Pt/γ-Fe2O3 cat-
alyst containing “electron-deficient” platinum clus-
ters [49]. Elucidation of the causes of the higher selec-
tivity of “electron-deficient” metal clusters in the
hydrogenation of nitrohaloarenes needs further theo-
retical studies. On the one hand, these clusters must
form stronger bonds with nucleophilic molecules
(haloanilines). If this is the case, then, if only the ther-
modynamic factor were taken into account, the selec-
tivity would decrease, not increase. However, electron
donor groups (e.g., the amino group) are known to
activate the С–Hal bond, shifting electron density to
the halogen atom and thereby facilitating the hydrog-
enolysis of this bond [50]. It is due to this circum-
stance that haloanilines rather than nitrohaloarenes
mainly undergo hydrogenolysis. Therefore, it is logical
to suppose that it is the low capacity of the “electron-
deficient” clusters to reverse bonding with the aro-
matic ring of the haloaniline that hampers the hydrog-
enolysis of the С–Hal bond. On the other hand, the
following geometric factor cannot be disregarded: the
planar adsorption of o-CA molecules on small clusters
is sterically difficult.
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ACKNOWLEDGMENTS
This study was carried out in the framework of the
project part of state assignment no. 4.353.2014/K from
the Ministry of Education and Science of the Russian
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KINETICS AND CATALYSIS
Vol. 58
No. 1
2017